U.S. patent number RE36,935 [Application Number 08/523,757] was granted by the patent office on 2000-10-31 for multiplex image reproducing apparatus.
This patent grant is currently assigned to Konica Corporation. Invention is credited to Satoshi Haneda, Seiichiro Hiratsuka, Hisashi Shoji.
United States Patent |
RE36,935 |
Haneda , et al. |
October 31, 2000 |
Multiplex image reproducing apparatus
Abstract
A method of reproducing multiplex images wherein an
electrostatic image is formed on an image retainer by using a
common electrostatic image forming device, the electrostatic image
formed on the image retainer is developed, the steps of the above
are repeated to superpose a plurality of toner images on the image
retainer, and the toner images is transferred on a recording paper
by one step. The developings other than the first time developing
are carried out in such a manner that the surface of a developer
layer on a developer feeding carrier does not contact with the
surface of the toner image on the image retainer.
Inventors: |
Haneda; Satoshi (Hachioji,
JP), Shoji; Hisashi (Hachioji, JP),
Hiratsuka; Seiichiro (Tokyo, JP) |
Assignee: |
Konica Corporation
(JP)
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Family
ID: |
27563641 |
Appl.
No.: |
08/523,757 |
Filed: |
September 5, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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697540 |
May 2, 1991 |
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380299 |
Jul 12, 1989 |
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656582 |
Oct 1, 1984 |
4599285 |
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Reissue of: |
868020 |
May 29, 1986 |
04679929 |
Jul 14, 1987 |
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Foreign Application Priority Data
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Oct 3, 1983 [JP] |
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58-183152 |
Oct 4, 1983 [JP] |
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58-184381 |
Oct 7, 1983 [JP] |
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58-187000 |
Oct 7, 1983 [JP] |
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58-187001 |
Dec 17, 1983 [JP] |
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58-238295 |
Dec 17, 1983 [JP] |
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58-238296 |
Jan 26, 1984 [JP] |
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59-13167 |
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Current U.S.
Class: |
399/302; 399/298;
399/303; 430/54 |
Current CPC
Class: |
G03G
13/0133 (20210101); G03G 13/01 (20130101) |
Current International
Class: |
G03G
13/01 (20060101); G03G 015/01 () |
Field of
Search: |
;430/52,54
;355/244,245,246,265,326R ;399/298,302,303 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2944986 |
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Jun 1980 |
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DE |
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3524159 |
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Jan 1986 |
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DE |
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3531098 |
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Mar 1986 |
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DE |
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5031824 |
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Jul 1973 |
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JP |
|
85827 |
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Jul 1977 |
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JP |
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2111868 |
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Jul 1983 |
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GB |
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Other References
Patent Abstracts of Japan, vol. 6, No. 22 (P-101) [900], Feb. 9,
1982; JPA-56-144,452; Nov. 10, 1981..
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Primary Examiner: Codd; Bernard
Attorney, Agent or Firm: Bierman; Jordan B. Bierman,
Muserlian and Lucas
Parent Case Text
.[.This is a division of Ser. No. 656,582 Filed: Oct. 1, 1984, now
U.S. Pat. No. 4,599,285..]. .Iadd.This application is a
continuation of application Ser. No. 07/697,540, filed May 2, 1991,
now abandoned, which is a continuation of application Ser. No.
07/380,299, filed Jul. 12, 1989, now abandoned, which is a Reissue
application of U.S. Pat. No. 4,679,929 issued Jul. 14, 1987, which
was a division of Ser. No. 656,582, filed Oct. 1, 1984 and issued
as U.S. Pat. No. 4,599,285, and claims the priority of Japanese
183152/83 filed Oct. 3, 1983, 184381/83 filed Oct. 4, 1983,
187000/83 filed Oct. 7, 1983, 187001/83 filed Oct. 7, 1983,
238295/83 filed Dec. 17, 1983, 238296/83 filed Dec. 17, 1983, and
13167/84 filed Jan. 26, 1984, as claimed in U.S. application
868,020, filed May 29, 1986, now issued as U.S. Pat. No.
4,679,929..Iaddend.
Claims
What is claimed is: .[.
1. An apparatus for reproducing multiplex images comprising an
image retainer having thereon an electrostatic image retaining
layer, means for forming an electrostatic image on said image
retainer, means for developing the electrostatic image formed on
the image retainer to form a toner image, an oscillating electric
field applied between the image retainer and a developer feeding
carrier to develop said electrostatic images, means for superposing
a plurality of toner images on the image retainer, and means for
transferring the toner images onto a recording paper in one
step..]..[.2. The apparatus for reproducing multiplex images
according to claim 1 wherein the surface of a developer layer on a
developer feeding carrier does not contact with the surface of the
toner image on the image retainer..]..[.3. The apparatus for
reproducing multiplex images according to claim 2 comprising means
for superposing at least one portion of a spot distribution
exposure of the preceding image exposure and at least one portion
of a spot distribution exposure of the following image
exposure..]..[.4. The apparatus for reproducing multiplex images
according to claim 3 wherein the spots of the preceding image
exposure and the following image exposure are varied in
size..]..[.5. In an apparatus for reproducing multiplex images
comprising an electrostatic image formed on an image retainer,
means for developing the electrostatic image formed on the image
retainer by using a developer consisting of a plurality of
components, means for superposing a plurality of toner images on
the image retainer, the improvement characterized in that said
developing means operates under a condition mentioned below:
where V.sub.AC is an amplitude (V) of AC component of developed
bias, f is a frequency (Hz), and d is a gap (mm) between the image
retainer and a developer feeding carrier for a feeding
developer..]..[.6. The apparatus for reproducing multiplex images
according to claim 5 wherein the gap between the image retainer and
the developer feeding carrier is larger than the thickness of the
developer layer formed on the developer feeding carrier during
developing..]..[.7. The apparatus for reproducing multiplex images
according to claim 5 comprising multiplex images formed by using
developers in order from the developer having a smaller absolute
value of mean charge quantity..]..[.8. The apparatus for
reproducing multiplex images according to claim 3 comprising
multiplex images formed by reducing successively the amplitude of
the AC component of electrical field applied between the image
retainer and the developer feeding carrier during
development..]..[.9. The apparatus for reproducing multiplex images
according to claim 5 comprising multiplex images formed by
increasing successively the frequency of the AC component of
electric field applied between the image retainer and the developer
feeding carrier during development..]..[.10. In an apparatus for
reproducing multiplex images comprising an electrostatic image
formed on an image retainer, means for developing the electrostatic
image formed on the image retainer by using a one-component
developer, and means for superposing a plurality of toner images on
the image retainer, the improvement characterized in that said
developing means operates under the following condition:
where V.sub.AC is an amplitude (V) of AC component of developing
bias, f is a frequency (Hz), and d is a gap (mm) between the image
retainer and a developer feeding carrier for a feeding
developer..]..[.11. The apparatus for reproducing multiplex images
according to claim 10 wherein the gap between the image retainer
and the developer feeding carrier is larger than the thickness of a
developer layer formed on the developer feeding carrier during
development..]..[.12. The apparatus for reproducing multiplex
images according to claim 10 comprising multiplex images formed by
using developers in order from the developer having a smaller
absolute value of mean charge quantity..]..[.13. The apparatus for
reproducing multiplex images according to claim 10 comprising
multiplex images formed by reducing successively the amplitude of
the AC component of electric field applied between the image
retainer and the developer feeding carrier during
development..]..[.14. The apparatus for reproducing multiplex
images according to claim 10 comprising multiplex images formed by
increasing successively the frequency of the AC component of
electric field applied between the image retainer and the developer
feeding carrier during development..]..[.15. The apparatus for
reproducing multiplex images according to claim 10 wherein the
electrostatic image retaining member of the image retainer consists
of a photosensitive member..]..[.16. The apparatus for reproducing
multiplex images according to claim 2 wherein the electrostatic
image retaining member of the image retainer consists of a
dielectric member..]..[.17. An apparatus for reproducing multiplex
images comprising an image retainer having thereon an electrostatic
image retaining layer, means for forming an electrostatic image on
said image retainer, means for superposing a plurality of toner
images on the image retainer, transfer means for transferring the
toner images on a recording paper by one step, and means for
developing the electrostatic image formed on the image retainer to
form a toner image wherein the surface of a developer layer on a
developer feeding carrier does no contact with the surface of the
toner image on the toner retainer other than during the first time
development..]..[.18. In an apparatus for
reproducing multiplex images comprising an electrostatic image
formed on an image retainer, means for developing the electrostatic
image formed on the image retainer by using a developer consisting
of a plurality of components, and means for superposing a plurality
of toner images on the image retainer, the improvement
characterized in that said developing means operates under a
condition mentioned below:
where V.sub.AC is an amplitude (V) of AC component of developing
bias, f is a frequency (Hz), and d is a gap (mm) between the image
retainer and a developer feeding carrier for feeding developer; the
gap between the image retainer and the developer feeding carrier is
larger than the thickness of a developer layer formed on the
developer feeding carrier during development; multiplex images
formed by reducing successively the amplitude of AC component of
electric field applied between the image retainer and the developer
feeding carrier during development, and multiplex images formed by
increasing successively the frequency of AC component of electric
field applied between the image retainer and the developer feeding
carrier during development..]..[.19. In an apparatus for
reproducing multiplex images comprising an electrostatic image
formed on an image retainer, means for developing the electrostatic
image formed on the image retainer by using a one-component
developer, and means for superposing a plurality of toner images on
the image retainer, the improvement characterized in that said
developing means operates under a condition mentioned below:
where V.sub.AC is an amplitude (V) of AC component of developing
bias, f is a frequency (Hz), and d is a gap (mm) between the image
retainer and a developer feeding carrier for feeding developer; the
gap between the image retainer and the developer feeding carrier is
larger than the thickness of a developer layer formed on the
developer feeding carrier during development; multiplex images
formed by reducing successively the amplitude of AC component of
electric field applied between the image retainer and the developer
feeding carrier during development; and multiplex images formed by
increasing successively the frequency of AC component of electric
field applied between the image retainer and the developer feeding
carrier during development..]..[.20. An apparatus for reproducing
multiplex images comprising an image retainer having thereon an
electrostatic image retaining layer, means for forming an
electrostatic image on said image retainer, means for developing
the electrostatic image formed on the image retainer to form a
toner image, means for eliminating residual electric charges, means
for superposing a plurality of toner images on the image retainer,
and transfer means for transferring the toner images on a recording
paper by one step..]..[.21. The apparatus for reproducing multiplex
images according to claim 2 comprising a two-component developer
having a toner and an insulating carrier..]..[.22. The apparatus
for reproducing multiplex images according to claim 2 comprising a
one-component developer consisting of an insulating toner..]..[.23.
The apparatus for reproducing multiplex images according to claim 2
wherein the image retainer consists of a photosensitive image
retainer having a photoconductive photosensitive layer and a
transparent insulating layer, in that order, laminated on an
electroconductive supporting member, and means for forming an
electrostatic image by primary charging, secondary charging, image
exposure simultaneous with the secondary charging and sequential
uniform exposure, said primary charging dropping a potential of the
electrostatic images substantially to zero..]..[.24. The apparatus
for reproducing multiplex images according to claim 2 wherein the
image retainer consists of a photosensitive image retainer having a
photoconductive photosensitive layer and a transparent insulating
layer laminated on an electroconductive supporting member, in that
order, means for forming the electrostatic image of a first toner
image by primary charging, secondary charging and sequential image
exposure, said primary charging dropping a potential of the
electrostatic images substantially to zero, and means for forming
the electrostatic image of a second toner image by primary
charging, secondary charging, and sequential image exposure, said
primary charging dropping a potential of the electrostatic images
substantially to zero..]..[.25. The method of reproducing multiplex
images according to claim 2 wherein the image retainer consists of
a photosensitive image retainer having a photoconductive
photosensitive layer and a transparent insulating layer laminated
on an electroconductive supporting member, in that order, means for
forming the electrostatic image of a first toner image by primary
charging, secondary charging, image exposure simultaneous with the
secondary charging and sequential uniform exposure, said primary
charging dropping a potential of the electrostatic images
substantially to zero, and means for forming the electrostatic
image of a second toner image by primary charging, secondary
charging, image exposure simultaneous with the secondary charging
and sequential uniform exposure, said primary charging dropping a
potential of the electrostatic images substantially to
zero..]..[.26. The apparatus for reproducing multiplex images
according to claim 2 wherein the image retainer consists of a
photosensitive image retainer having a photoconductive
photosensitive layer and a transparent insulating layer, in that
order, laminated on an electroconductive supporting member, and
means for forming the electrostatic image of a toner image by
uniform primary charging on said photosensitive image retainer in
the first developing, uniform secondary charging in a plurality
reversed to said primary charging and sequential image exposure,
said primary charging dropping a potential of the electrostatic
images substantially to zero..]..[.27. In a color image forming
apparatus comprising an image retainer, means for forming a color
image on said image retainer, transfer means for transferring on a
transfer member the color image formed on said image retainer by
said color image forming means, and fixing means for fixing on said
transfer member the color image transferred on said transfer member
by said transfer means, the improvement characterized in that said
color image forming means comprises only one latent image forming
means, and a plurality of developing means for visualizing a latent
image formed on said image retainer by said latent image forming
means, said one latent image forming means being used repeatedly in
one cycle of a reproduced image forming step..]..[.28. The color
image forming apparatus according to claim 27, wherein said latent
image forming means comprises means for applying an electric
charge, a light source, a deflector for deflecting a light
irradiated from the light source, and a scanning optical system
arranged between said light source and said image
retainer..]..[.29. The color image forming apparatus according to
claim 28 wherein said electric charge applying means
comprises a primary charger and a secondary charger..]..[.30. The
color image forming apparatus according to claim 28 wherein said
light source in said scanning optical system is a laser light
source..]..[.31. The color image forming apparatus according to
claim 30 wherein said deflector in said scanning optical system is
a rotary polygon mirror..]..[.32. The color image forming apparatus
according to claim 27, wherein said developing means is arranged in
the vicinity of said image retainer in non-contact
fashion..]..[.33. The color image forming apparatus according to
claim 27 wherein an alternating electric field is applied between
said image retainer and said developing means..]..[.34. The color
image forming apparatus according to claim 27 comprising electrical
charge eliminating means for eliminating a residual electric charge
on said image retainer each time at which said latent image forming
means is used, said charge eliminating means being arranged in the
vicinity of said transfer means..]..[.35. The apparatus for
reproducing multiplex images according to claim 17 consisting of a
single means for forming an electrostatic image on said image
retainer, and at least two of said means for
developing said electrostatic image formed on the
image..]..Iadd.36. An apparatus for reproducing multiplex images
comprising an image retainer having thereon an electrostatic image
retaining layer, means for charging said image retainer, means for
forming an electrostatic image on said image retainer, means for
developing the electrostatic image formed on the image retainer to
form a toner image, an oscillating electric field applied between
the image retainer and a developer feeding carrier to develop said
electrostatic images, means for superposing a plurality of toner
images on the image retainer, means for transferring the toner
image onto a recording paper in one step, and
means for superposing at least one portion of a dot exposure of the
preceding image exposure and at least one portion of a dot exposure
of the following image exposure wherein the surface of a developer
layer on a developer feeding carrier does not contact the surface
of the toner image
on the image retainer..Iaddend..Iadd.37. The apparatus for
reproducing multiplex images according to claim 36 wherein each
multiplex image is developed by repeated use of said means for
developing in which an amplitude of an AC component of electric
field applied between said image retainer and a developer feeding
carrier for feeding developer is reduced with each of said repeated
use of said means for
developing..Iaddend..Iadd.8. The apparatus of claim 36 wherein the
electrostatic image retaining member of the image retainer consists
of a dielectric member..Iaddend..Iadd.39. The apparatus of claim 36
wherein said developer layer comprises a one-component developer
consisting of an insulating toner..Iaddend..Iadd.40. The apparatus
for reproducing multiplex images according to claim 36 wherein the
image retainer consists of a photosensitive image retainer having a
photoconductive photosensitive layer and a transparent insulating
layer, in that order, laminated on an electroconductive supporting
member, and means for forming an electrostatic image by primary
charging, secondary charging, image exposure simultaneous with the
secondary charging and sequential uniform exposure, said primary
charging dropping a potential of the electrostatic
images substantially to zero. .Iadd.41. The apparatus for
reproducing multiplex images according to claim 36 wherein the
image retainer consists of a photosensitive image retainer having a
photoconductive photosensitive layer and a transparent insulating
layer laminated on an electroconductive supporting member, in that
order, means for forming the electrostatic image of a first toner
image by primary charging, secondary charging and sequential image
exposure, said primary charging dropping a potential of the
electrostatic images substantially to zero, and means for forming
the electrostatic image of a second toner image by primary
charging, secondary charging, and sequential image exposure, said
primary charging dropping a potential of the electrostatic image
substantially to zero..Iaddend..Iadd.42. The apparatus for
reproducing multiplex images according to claim 36 wherein the
image retainer consists of a photosensitive image retainer having a
photoconductive photosensitive layer and a transparent insulating
layer laminated on an electroconductive supporting member, in that
order, means for forming the electrostatic image of a first toner
image by primary charging, secondary charging, image exposure
simultaneous with the secondary charging and sequential uniform
exposure, said primary charging dropping a potential of the
electrostatic images substantially to zero, and means for forming
the electrostatic image of a second toner image by primary
charging, secondary charging, image exposure simultaneous with the
secondary charging and sequential uniform exposure, said primary
charging dropping a potential of
the electrostatic images substantially to zero..Iaddend..Iadd.43.
The apparatus for reproducing multiplex images according to claim
36 wherein the image retainer consists of a photosensitive image
retainer having a photoconductive photosensitive layer and a
transparent insulating layer, in that order, laminated on an
electroconductive supporting member, and means for forming the
electrostatic image of a toner image by uniform primary charging on
said photosensitive image retainer in the first developing, uniform
secondary charging in a plurality reversed to said primary charging
and sequential image exposure, said primary charging dropping a
potential of the electrostatic images substantially to
zero..Iaddend..Iadd.44. The apparatus of claim 36 wherein said dot
exposure of the preceding image exposure and said dot exposure of
the following image exposure are varied in size..Iaddend..Iadd.45.
The apparatus of claim 36 wherein said developer layer comprises a
two-component developer having a toner and an insulating carrier,
said insulating carrier having a resistivity of at least 10.sup.8
.OMEGA.-cm when a voltage for generating an electric field of 1,000
V/cm is
applied..Iaddend..Iadd.46. An apparatus for reproducing multiplex
images comprising an image retainer having thereon an electrostatic
image retaining layer, means for forming an electrostatic image on
said image retainer, means for superposing a plurality of toner
images on the image retainer, transfer means for transferring the
toner images to a recording paper in one step, and means for
developing the electrostatic image formed on the image retainer to
form a toner image wherein, in the formation of each multiplex
image, the surface of a developer layer on a developer feeding
carrier does not contact the surface of the toner image on the
image retainer other than during the development of the first toner
image, wherein the image retainer consists of a photosensitive
image retainer having a photoconductive photosensitive layer and a
transparent insulating layer, in that order, laminated on an
electroconductive supporting member, and said electrostatic image
forming means comprises a primary charging means, a secondary
charging means which exposes said image retainer to an image light
simultaneously with the secondary charging and sequential uniform
exposure means, said primary charging means dropping a potential of
the electrostatic images substantially to zero..Iaddend..Iadd.47.
An apparatus for reproducing multiplex images comprising an image
retainer having thereon an electrostatic image retaining layer,
means for forming an electrostatic image on said image retainer,
means for superposing a plurality of toner images on the image
retainer, transfer means for transferring the toner images to a
recording paper in one step, and means for developing the
electrostatic image formed on the image retainer to form a toner
image wherein the surface of a developer layer on a developer
feeding carrier does not contact the surface of the toner image on
the image retainer other than during the first development wherein
the image retainer consists of a photosensitive image retainer
having a photoconductive photosensitive layer and a transparent
insulating layer laminated on an electroconductive supporting
member, in that order, and said electrostatic image forming means
comprises a primary charging means, a secondary charging means and
sequential image exposure means, said primary charging means
dropping a potential of the electrostatic images
substantially to zero..Iaddend..Iadd.48. An apparatus for
reproducing multiplex images comprising an image retainer having
thereon an electrostatic image retaining layer, means for forming
an electrostatic image on said image retainer, means for
superposing a plurality of toner images on the image retainer,
transfer means for transferring the toner images to a recording
paper in one step, and means for developing the electrostatic image
formed on the image retainer to form a toner image wherein the
surface of a developer layer on a developer feeding carrier does
not contact the surface of the toner image on the image retainer
other than during the first development wherein the image retainer
consists of a photosensitive image retainer having a
photoconductive photosensitive layer and a transparent insulating
layer laminated on an electroconductive supporting member, in that
order, means for forming the electrostatic image of a first toner
image by primary charging, secondary charging, and image exposure
simultaneous with the secondary charging and sequential uniform
exposure, said primary charging dropping a potential of the
electrostatic images substantially to zero, and means for forming
the electrostatic image of a second toner image by primary
charging, secondary charging, and image exposure simultaneous with
the secondary charging and sequential uniform exposure, said
primary charging dropping a potential of
the electrostatic images substantially to zero..Iaddend..Iadd.49.
An apparatus for reproducing multiplex images comprising an image
retainer having thereon an electrostatic image retaining layer,
means for forming an electrostatic image on said image retainer,
means for superposing a
plurality of toner images on the image retainer, transfer means for
transferring the toner images onto a recording paper in one step,
and means for developing the electrostatic image formed on the
image retainer to form a toner image wherein, in the formation of
each multiplex image the surface of a developer layer on a
developer feeding carrier does not contact the surface of the toner
image on the image retainer other than during the development of
the first toner image, wherein said developer comprises a
two-component developer having a toner and an insulating carrier,
said insulating carrier having a resistivity of at least 10.sup.8
.OMEGA.-cm when a voltage for generating an electric field of 1,000
V/cm is applied, means for generating an oscillating field between
said image retainer and said developer feeding carrier..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reproducing method and,
more particularly, to a multiplex image reproducing method of
superposing toner images on an image retainer having a
photoconductive photosensitive member by repeatedly retaining and
developing electrostatic images on the image retainer.
2. Description of the Prior Art
As the above-specified image reproducing method, there are known in
the art the methods which are disclosed in Japanese Patent
Laid-Open Nos. 144452/81, 116553/83 and 116554/83.
In any of these methods, the image retainer has on its surface a
layer of a photoconductive photosensitive material such as Se, and
the development resorts to a reversal method in which there is
applied to an electrostatic image having a lower potential than
that of the background a toner for frictionally charging it with
the same polarity. According to this method, there arises a problem
that the photoconductive photosensitive surface layer is generally
and relatively liable to have its electrostatic image retaining
performance changed by the charging step and to be subjected to the
"toner filming" or have its photosensitivity degraded. As compared
with such a positive developing methods as in the ordinary
electrophotographic reproducing machine, i.e., the developing
method in which the electrostatic image has a higher potential than
the background so that a toner charged with an opposite polarity is
applied to that electrostatic image, moreover, the development by
the reversal developing method has a problem that control of the
toner application is so difficult that a sufficient development
density cannot be attained or that a reproducing apparatus is
liable to have its inside blotted by the toner scattered.
As the method in which an image retainer having a dielectric
surface layer is used to retain an electrostatic image on the
dielectric surface layer, on the other hand, there is known in the
art a method using an electrostatic recording head, a method using
a screen photosensitive member (as is disclosed in Japanese Patent
Publication No. 34616/79) or a method using a screen control
electrode (as in disclosed in Japanese Patent Laid-Open No.
137363/81). The electrostatic image retaining methods thus
disclosed are superior in that the electrostatic image
retainability and the toner image retainability required of the
photosensitive member are separated of each other. In these
methods, more specifically, it is deemed that the share of
retaining the electrostatic image is borne by the electrostatic
recording head, the screen photosensitive member or the screen
control electrode, whereas the share of retaining the toner image
is borne by the dielectric surface layer. Those methods are
featured by that color data are retained consecutively and
independently as the electrostatic image on the dielectric surface
layer. However, the toner image formed on the dielectric layer
cannot be other than a monochromatic one at all times.
This is because the developing method is conducted by the contact
development so that a previous toner image is disturbed or color
mixing occurs upon the development even if another electrostatic
image could be recorded on the previously formed toner image.
As the method in which an image retainer having a magnetic surface
layer is used to form a magnetic image on the magnetic layer, on
the other hand, there is known in the art methods, which are
disclosed in Japanese Patent Laid-Open Nos. 90342/75, 100732/76 and
106253/81. These reproducing methods resorting to that magnetic
image is excellent in that the retainability of an electrostatic
image by the corona discharge or the like and the retainability of
a toner image required of the photosensitive member can be
separated from each other. In the reproducing methods using the
magnetic image, more specifically, it is deemed that retention of
the magnetic image makes whole use of the inside of the magnetic
layer while not having its surface state changed as is different
from the photosensitive member, and that the share of the toner
image retainability is borne by the surface of the magnetic layer.
Those methods are featured by that the color data can be newly
retained as the magnetic image independently of the toner image
formed on the magnetic surface layer. However, the toner image
retained on the magnetic layer cannot be other than a monochromatic
one at all times.
The method disclosed in Japanese Patent Laid-Open No. 144452/81
retains a color image on an image retainer: by forming an
electrostatic image on the surface of an image retainer, which has
been charged by a charger, by first exposure means and developing
it by first developing means; by forming an electrostatic image on
the same charged surface by second exposure means and developing it
by second developing means; and by forming an electrostatic image
on the same charged surface by third exposure means and developing
it by third developing means. The method thus specified has
problems that the separate exposure means are required for the
respective ones of the repeated formations of the electrostatic
images to enlarge the size of the reproducing apparatus and to
raise the cost of the same and that synchronizations of the
exposure of the respective exposure means with the image retainer
have relationships with the respective positions of the exposure
means so that the synchronous control is troublesome to make it
liable to invite color shift. Moreover, each of the development of
that method is conducted by the forced method in which the
electrostatic image having a lower potential at its exposed portion
than that of the background has such toner applied thereto as is
charged with the same polarity. In that forced developing method,
the toner for effecting the charge at the same polarity as that of
the charge of the image retainer is so used in the developer that
it may not be applied to the background. As a result, the reversal
developing method has a problem that although the toner is repulsed
by the background potential so that it is reluctant to invite any
fog, it is also reluctant to be applied to the electrostatic images
so that a sufficient developed density can hardly be obtained.
Since the reversed image is obtained, according to this reversal
developing method, color reproduction of a positive image cannot be
effected so that the coloring is limited to the technique using the
dot exposure of a printer or the like. In case it is intended to
obtain a positive image when an ordinary original is to be
reproduced, it is reversed, and the counter-measure for this
reversal is difficult. Since the potential at the photosensitive
layer of the exposed portion is at the same polarity as that of the
developer although it is low, moreover, the reversal developing
method has a problem that the developer is reluctant to be applied
to the electrostatic images so that it is liable to be scattered to
blot the inside of the reproducing apparatus.
On the other hand, the disclosed in Japanese Patent Laid-Open No.
144452/81 is one conducted under a non-contact jumping developing
condition in which the second and later developments by the
reversal developing method are conducted such that the layers of
the developers formed by the developing means are not in contact
with the surface of the image retainer. This method has problems
that the development is reluctant to have a sufficient density and
is liable to be blotted with the toner scattered unless a strong
bias voltage is applied to the developing means to strongly apply
the toner to the electrostatic images, and that, the strong bias
voltage is applied to the developing means, it is liable to leak to
the image retainer or the like, or toner of another color is liable
to stick to the toner image developed before or the background.
The methods disclosed in Japanese Patent Laid-Open Nos. 116553/83
and 116554/83 are substantially the same as that in Japanese Patent
Laid-Open No. 144452/81 in that the formations and developments of
the electrostatic images are conducted by different means for the
respective repetitions. As a result, those methods also have
problems that the reproducing apparatus has its size enlarged to
raise the cost, and that the synchronous control of the exposures
of the respectie exposing means is so difficult as to invite the
color shift. Here, the method disclosed in Japanese Patent
Laid-Open No. 116554/83 is different from the method disclosed in
Japanese Patent Laid-Open No. 144452 in that the respective
developments by the reversal developing method are conducted under
the contact developing condition, in which the developer layers
formed by the developing means brush the surface of the image
retainer, thereby to solve the problems of the reversal developing
method that the sufficient developing density can hardly be
obtained and that the toner is liable to be scattered. Moreover,
the method disclosed in Japanese Patent Laid-Open No. 116553/83 is
different from the same Japanese Patent Laid-Open No. 144452/81 in
that, in the second and later retentions of the electrostatic
images, too, the surface of the image retainer is recharged before
exposure by the chargers, which are placed in front of the
respective exposing means, so that toner in another color may not
be applied during a later development to the portions having the
toner adhered thereto after the previous development. Since the
second and latter developments are conducted under the contact
developing condition, however, those methods have a serious problem
that the toner adhered after the previous development is liable to
be shifted during the subsequent development or to be mixed into
the developer of the subsequent developing means.
A prototype in which an electrostatic latent image is expressed in
a multi-color image is concerned with a color image using an
electrophotographic system. This system of the prior art separates
the colors of an original through an optical filter and repeats the
charging, exposing, developing and transferring steps by using the
separated colors. In order that respective images of color
particles such as yellow, magenta, cyan and black colors may be
retained, more specifically, those steps are repeated four times by
that system. There also exists the so-called "dichromatic
developing method", in which electrostatic latent images of
different polarities are formed on a common photosensitive member
(or an image carrier) and are developed by particles of black and
red colors. These multi-color image retaining methods are
desirable, because they can add color data as compared with the
data obtained from the dichromatic images, but have the following
problems:
(1) Transfer to a transfer member is required at each development
of each color to enlarge the size of the machine and to elongate
the time period necessary for the image retention; and
(2) It is necessary to ensure the accuracy of positional shifts
resulting from the repetitions.
In view of these problems, there has been conducted a trial in
which a plurality of toner images are developed in a superposed
manner on a common photosensitive member so that the transfer step
may be finished by one time to reduce the size of the machine.
As the developer to be used in this machine, on the other hand,
there exists a two-component developer, which is composed of a
toner and a carrier, and a one-component developer which is
composed only of a toner. The one-component developer has some
problems in the charge control of the toner but has advantages that
no consideration is necessary into the concentration and agitation
of the toner and the carrier, and that the size of the machine can
be reduced.
The two-component developer requires control of the ratio of the
toner to the carrier but has an advantage that it is easy to
control the frictional charges of the toner particles. Since a
magnetic material of black color need not be much contained in the
toner particles, on the other hand, the two-component developer
composed of a magnetic carrier and a non-magnetic toner can use a
color toner having no color turbidity by the magnetic material so
that a clean color image can be formed.
In the multiplex development, incidentally, it is sufficient to
repeat several times the developments of the photosensitive member
which has already been formed with the toner image. However, the
multiplex development has problems that the toner image retained at
a previous step on the photosensitive member is disturbed upon
development of a subsequent step, and that the toner having already
been applied to the photosensitive member is returned to a
developing sleeve acting as a developer carrier until it steals
into the developing means at a subsequent step, in which a
developer in a color different from that of the developer of the
previous step, thereby to cause color mixing. In order to obviate
those problems, there is disclosed in Japanese Patent Laid-Open No.
144452/81, for example, means for superposing an a.c. component
upon a developing bias while the photosensitive member being out of
contact with the developer layer on the developing sleeve acting as
the developer carrier for developing an electrostatic latent image,
except the developing means for first forming the toner image on
the photosensitive member. However, there arises a problem that the
image can neither have a sufficient density nor be freed from the
disturbance or color mixing.
SUMMARY OF THE INVENTION
The present invention has been conceived so as to solve the above
problems which are concomitant with the image reproducing method of
the prior art. A first object of the present invention is to a
multiplex image reproducing method which is enabled to reduce the
size of and the cost for a recording apparatus and to make easy and
accurate the synchronous control of image exposures by using a
common apparatus for repeatedly retaining electrostatic images. A
second object of the present invention is to provide a multiplex
image reproducing method which can facilitate control of the
adhesion of toners to electrostatic images so that a sufficient
developing density can be attained under a non-contact jumping
developing condition to prevent any fog and the mixture and
application of the toners in different colors not only in the case
by the ordinary developing method for application the toners
charged with an opposite polarity to the electrostatic images but
also in the case by the forced developing method.
The present invention resides in a multiplex image reproducing
method of the type, in which toner images are superposed on an
image retainer having
a photoconductive photosensitive surface layer by repeating the
retentions and developments of electrostatic images on the image
retainer, characterized in that the retentions of said
electrostatic images are repeated by means of a common apparatus.
The above-identified first object is achieved by the
above-specified construction, and the above-identified second
object is achieved by using in the developing means the
two-component developer which contains a mixture of a toner and an
insulating carrier.
Another object of the present invention is to provide a novel
multiplex image reproducing method in which the retentions of
electrostatic images are stabilized by using means for retaining
the electrostatic images on a dielectric layer and in which a
method of superposing developed images on the dielectric layer is
devised.
The above-specified object of the present invention can be achieved
by a multiplex image reproducing method of the type, in which a
plurality of color toner images are superposed on an image retainer
by repeating the retentions and developments of the electrostatic
images on the image retainer, characterized in that the retentions
of said electrostatic images are conducted on the dielectric
surface layer.
Still another object of the present invention is to provide a
multiplex image reproducing method of the type, in which a number
of magnetic recording heads are juxtaposed to an image retainer
formed of a magnetic layer and an insulating layer, if necessary,
so that a number of magnetized regions may be formed on the
magnetic layer of the image retainer thereby to write an image by
sending an image signal current synchronized with the movement of
the image retainer to the respective ones of said magnetic
recording heads, while the image retainer being moved at a constant
speed, whereby a toner image is obtained by applying a magnetic
toner to the written image to develop it, characterized in that a
plurality of toner images are formed in a superposed manner on the
image retainer by repeating the image writing and developing
operations. The developments are conducted under the condition in
which the developer layers formed by the developing means are out
of direct contact with the surface of the image retainer. Thus,
there is no fear that the toner images once formed are damaged upon
the subsequent development so that the plural toner images can be
superposed.
Moreover, the color images can be recorded by using the plural
toner images in combination with toners of different colors such as
yellow, cyan, magenta and black colors.
A further object of the present invention is to provide a multiplex
image reproducing method which can not only obtain positive images
and negative images but also resort to the developing method, in
which a developer charged with a polarity opposite to that of an
electrostatic image is applied to the electrostatic image by the
coulomb force, so that the application of the developer to the
electrostatic image can be made sufficient while reducing
scattering of the developer.
The above-specified object of the present invention can be achieved
by a multiplex image reproducing method of the type, in which toner
images are superposed on an image retainer by repeating the
retentions and developments of electrostatic images upon the image
retainer, characterized in that said electrostatic images are
formed either by conducting image exposures after an image retainer
formed with a transparent insulating surface layer on a
photoconductive photosensitive layer has been charged primarily and
secondarily or by uniformly exposing that image retainer after the
image retainer has been subjected to an image exposure
simultaneously with the secondary charge.
More specifically, the multiplex image reproducing method of the
present invention is different especially in the retentions of the
electrostatic images from those methods which are disclosed in
Japanese Patent Laid-Open Nos. 144452/81, 116553/83 and 116554/83.
In other words, the method of the present invention is
characterized in that the image retainer is constructed to have the
transparent insulating surface layer formed on the photoconductive
photosensitive layer, and in that the electrostatic images are
formed either by primarily and secondarily charging the image
retainer and by subjecting the charged surface of the same to the
image exposure or by conducting the image exposure simultaneously
with the secondary charging treatment and by subsequently effecting
the uniform exposure. The above problems invited in the multiplex
image reproducing method by the reversal developing method of the
prior art can be eliminated by using the above-specified method of
retaining the electrostatic images.
A further object of the present invention is to provide a multiplex
image reproducing method which can densely and finely reproduce a
color image such as a landscape image, construct a reproducing
apparatus in a small size and at a low cost, and facilitate the
synchronous control of image exposures.
The above-specified object of the present invention can be achieved
by a multiplex image reproducing method of the type, in which a
plurality of color toner images are superposed on an image retainer
by charging the surface of the image retainer, by conducting the
image exposures at least repeatedly, and by conducting a
development each time of the image exposure by developing means,
characterized: in that said image exposures are conducted such that
the spot position of a previous image exposure and the spot
position of a subsequent image exposure are superposed as the spot
distribution exposure; and in that the image exposures thus
repeated are performed by means of a common apparatus.
A further object of the present invention is to provide a multiplex
image reproducing method of reproducing images having a desirable
density but neither disturbance nor color mixing by the use of a
developer containing a plurality of components.
The above-specified object of the present invention can be achieved
by a multiplex image reproducing method of the type, in which an
image is retained on an image carrier by repeating a plurality of
times both the step of forming a latent image on said image carrier
and the step of developing said latent image by the use of a
developer having a plurality components, characterized in that the
following relationships are satisfied:
wherein, at each developing step: the amplitude of the a.c.
component of a developing bias is designated by V.sub.AC (V); the
frequency of the same by f (Hz); and the gap between said image
carrier and a developer carrier for carrying said developer by d
(mm).
More specifically, we, the Inventors, have researched the method of
retaining an image by conducting the development of the same while
the a.c. component being superposed on the developing bias, and
have discovered that there is a region in which an image of high
quality can be obtained without incurring any disturbance and color
mixing of the image in accordance with the manner of selecting the
developing conditions such as the a.c. bias or the frequency.
The present invention contemplates to provide a novel method which
is based upon the above-specified discovery.
Moreover, the above-specified object of the present invention can
be achieved by the multiplex image reproducing method of the type,
in which an image is retained on an image carrier by repeating a
plurality of times both the step of forming a latent image on said
image carrier and the step of developing said latent image,
characterized in that the following relationship is satisfied:
wherein, at each developing step: the amplitude of the a.c.
component of a developing bias is designated by V.sub.AC (V); the
frequency of the same by f (Hz); and the gap between said image
carrier and a developer carrier for carrying said developer by d
(mm).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing the construction of one
embodiment of the reproducing apparatus for practising the method
of the present invention:
FIG. 2 is a schematic view showing the construction of a laser beam
scanner for image exposure;
FIG. 3 is a partially sectional view showing one example of
developing means;
FIGS. 4 to 7 are flow charts for practising the methods of the
present invention, respectively;
FIG. 8 is a partially sectional view showing the construction of an
image retainer in another reproducing apparatus for practising the
method of the present invention;
FIG. 9 is a schematic view showing the construction of the
reproducing apparatus;
FIG. 10 is a diagram schematically showing changes in the charged
states of one example of the process of electrostatic images;
FIG. 11 is a chart showing changes in the potential at the surface
portion of the image retainer in a manner to correspond to FIG.
10;
FIGS. 12 to 17 are flow charts of practising the method of the
present invention, respectively;
FIGS. 18 to 21 are flow charts showing another embodiment of the
method of the present invention to be practised by the reproducing
apparatus of FIG. 1, respectively;
FIGS. 22 to 25 are flow charts showing flow charts of an embodiment
of the method of the present invention to be practised by the
recording apparatus of FIG. 9, respectively;
FIGS. 26 and 27 are schematic views showing an example of the
recording apparatus to be used for practising another embodiment of
the method of the present invention, respectively; and
FIGS. 28 to 30 are flow charts for practising the method of the
present invention, respectively.
In FIGS. 31 to 38 showing a further embodiment of the present
invention:
FIG. 31 is a sectional view showing developing means and a
photosensitive drum;
FIGS. 32 and 33 are diagrams showing changes in the image density
when an a.c. current is changed;
FIG. 34 is a diagram showing the density characteristics when a
field intensity and a frequency are changed;
FIGS. 35 and 37 are schematic views showing the essential portions
of the multiplex image reproducing apparatus which are equipped
with a plurality of developing means;
FIG. 36 is a chart showing changes in the surface potential of the
photosensitive drum which is used in the multiplex image
reproducing apparatus of FIG. 35; and
FIG. 38 is a chart showing changes in the surface potential of the
photosensitive drum which is used in the multiplex image
reproducing apparatus of FIG. 37.
FIGS. 39 and 40 are diagrams showing changes in an image density
when an a.c. voltage applied to the developing means is changed in
a further embodiment of the present invention;
FIG. 41 is a diagram showing the density characteristics when a
field intensity and a frequency are changed;
FIGS. 42 and 43 are schematic views showing other examples of the
recording means which are used for practising the method of the
present invention, respectively; and
FIGS. 44 to 46 are flow charts for practising the method of the
present invention, respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in detail in the following
in connection with the embodiments thereof with reference to the
accompanying drawings.
FIG. 1 is a schematic view showing the construction of one example
of recording apparatus for practising the method of the present
invention; FIG. 2 is a schematic view showing a laser beam scanner
for image exposure; FIG. 3 is a partially sectional view showing
one example of developing means; and FIGS. 4 to 7 are flow charts
for practising the method of the present invention,
respectively.
In the recording apparatus of FIG. 1: reference numeral 1 is a
drum-shaped image retainer which is formed with a photoconductive
photosensitive material such as Se and which is made rotatable in
the direction of arrow; numeral 2 is a charger for uniformly
charging the surface of the image retainer 1; numeral 3 is an
exposing lamp for uniformly exposing to a weak optical ray the
surface of the image retainer which is used in the example of the
flow chart of FIG. 7; numeral 4 is an image exposing ray of color
images of different colors; numerals 5 to 8 are developing means
using as their developers toners of different colors such as
yellow, magenta, cyan or black; numerals 9 and 10 are a
pre-transfer charger and a pre-transfer exposing lamp which are
provided, if necessary, respectively, so that a color image
retained on the image retainer 1 with its plural color toner images
being superposed may be easily transferred to a recording member P;
numeral 11 is transfer means; numeral 12 is fixing means for fixing
the toner images transferred to the recording member P; numeral 13
is charge eliminating means which is composed of a charge
eliminator and/or a charge eliminating corona discharger; and
numeral 14 is cleaning means having a cleaning blade or a fur brush
which is adapted to come into contact with the surface of the image
retainer 1 after transfer of the color images for eliminating the
residual toners left on the surface and to leave the surface of the
image retainer 1 by the time the surface having been subjected to a
first development arrives.
Here, it is preferable to use as the charger 2 a corona discharger,
as shown, which can apply such a stable charge as is hardly
affected by a previous charge, especially in case the surface of
the image retainer having already been charged is to be
additionally charged. In case the drum-shaped image retainer 1 is
used as in that reproducing apparatus, moreover, the image exposing
ray 4 may be such an optical ray as has been prepared by filtering
a slit ray separately for colors, for example, the optical ray of
an ordinary monochromatic electrophotographic reproducing machine.
In order to reproduce a clear color image, however, an optical ray
prepared by the laser beam scanner, as shown in FIG. 2, is
preferable.
The laser beam scanner of FIG. 2 is formed into the image exposing
ray 1 for scanning the surface of the image retainer 4 at a
constant speed by turning on or off the laser beam, which has
emanated from a laser 21 such as a He--Ne laser, by means of an
acoustic-optical modulator 22 to deflect by means of a mirror
scanner 23 composed of a rotating polygonal or optagonal mirror
thereby to guide it through a focusing f-0 lens 24. Incidentally,
reference numerals 25 and 26 indicate mirrors, and numeral 27
indicates a lens for enlarging the diameter of a beam incident upon
the focusing f-e lens 24 so as to reduce the diameter of the beam
on the image retainer 1. If such a laser beam scanner as is shown
in FIG. 2 is used for forming the image exposing ray 4, the
electrostatic images can be easily retained with a shift for
different colors, as will be described hereinafter, so that a clear
color image can be reproduced. Despite of this fact, the image
exposing ray 4 is not limited to the slit exposing ray or a dot
exposing ray by the laser beam but may be one which is prepared by
using an LED, a CRT, a liquid crystal or an optical fiber
transmitter, for example. In the reproducing apparatus in which the
image retainer can take a planar state such as a belt shape,
moreover, the image exposing ray may be a flash light.
As the developing means 5 to 8, on the other hand, there can be
preferably used those which have such a construction as is shown in
FIG. 3.
In FIG. 3: reference numeral 31 indicates a developing sleeve which
is made of a non-magnetic material such as aluminum or stainless
steel; numeral 32 is a magnet which is equipped in the
circumferential direction with a plurality of magnetic poles
disposed inside of the developing sleeve 31; numeral 33 is a layer
thickness regulating blade for regulating the thickness of a
developer layer formed on the developing sleeve 31; numeral
34 is a scraper blade for scraping the developer layer after
development from the surface of the developing sleeve 31; numeral
35 is an agitating rotor for agitating the developer in a developer
reservoir 36; numeral 37 is a toner hopper; numeral 38 is a toner
supply roller which is formed in its surface with a recess for
receiving the toner to supply the toner from the toner hopper 37 to
the developer reservoir 36; and numeral 39 is a power supply for
applying a bias voltage containing a vibratory voltage component,
as the case may be, to the developing sleeve 31 through a
protecting resistor 40 to generate an electric field for
controlling the movements of the toner between the developing
sleeve 31 and the image retainer 1. FIG. 3 shows that the
developing sleeve 31 and the magnet 32 are rotatable in the
directions of arrows, respectively. It is, however, sufficient that
the developing sleeve 31 and the magnet 32 be fixed, or that the
developing sleeve 31 and the magnet 32 be rotatable in a common
direction. In case the magnet 32 is fixed, it is customary to
strengthen the magnetization or to dispose two magnetic poles of
identical or different polarities adjacent to each other so that
the density of the magnetic flux of the magnetic pole facing the
image retainer 1 may be stronger than that of another magnetic
pole.
In these developing means, the magnetic poles of the magnet 32 are
usually magnetized to a density of magnetic flux of 500 to 5,000
gausses to attract the developer in the developer reservoir 36 to
the surface of the developing sleeve 31 by that magnetic force so
that the attracted developer is formed, while having its thickness
regulated by the layer thickness regulating blade 33, into a
developer layer. This developer layer is moved in the same
direction as or in the opposite direction (although FIG. 3 shows
the same direction) to the rotating direction of the image retainer
1, as indicated by the arrow, to develop the electrostatic image of
the image retainer 1 in the developing region, in which the surface
of the developing sleeve 31 faces the surface of the image retainer
1, whereas the residual is scraped away from the surface of the
developing sleeve 31 by the scraper blade 34, until it is returned
to the developer reservoir 36. Moreover, the development, e.g., at
least the second or subsequent developments, which are repeated for
superposing the color toner images, is preferred to be conducted
under the non-contact jumping developing condition so that the
toner caught by the image retainer 1 during the previous
development may not be shifted by the later development. FIG. 3
shows the state in which the development is executed under the
non-contact jumping developing condition.
Moreover, it is preferable to use in the developing means 5 to 8
the so-called "two-component developer" which is composed of a
non-magnetic toner and a magnetic carrier and which is enabled to
obtain a toner image of clear color without any necessity for
containing a black or brown magnetic material in the toner and to
easily effect the control of charging the toner. Specifically, the
magnetic carrier may preferably be an insulating carrier which has
a resistivity of 10.sup.8 .OMEGA. cm or more or, preferably,
10.sup.13 or more and which is prepared either by dispersing and
containing fine particles of a ferromagnetic or paramagnetic
material such as tri-ion tetroxide .gamma.-ferric oxide, chromium
dioxide, manganese oxide, ferrite or manganese-copper alloy in a
resin such as a styrene resin, a vinyl resin, an ethyl resin, a
denaturated rosin resin, an acrylic resin, a polyamide resin, an
epoxy resin or polyester resin, or by covering the surfaces of the
particles of those magnetic materials with the above-specified
resins. If that resistivity is low, there arises such a problem, in
case the bias voltage is applied to the developing sleeve 31, that
the charges are caused to migrate into the carrier particles so
that they become liable to be trapped by the surface of the image
retainer 1 and so that the bias voltage is not sufficiently
applied. Especially, if the carriers are trapped by the image
retainer 1, the color image has its tone adversely affected.
Incidentally, the resistivity is a vlaue which is obtained by
tapping the particles in a container having an effective sectional
area of 0.50 cm.sup.2, by subsequently loading the tapped particles
with a load of 1 Kg/cm.sup.2, and by reading out a current value
when a voltage for generating an electric field of .[.1.000.].
.Iadd.1,000 .Iaddend.V/cm is applied across the load and the bottom
electrode.
If the carriers have an average particle diameter less than 5
.mu.m, on the other hand, the magnetization obtainable becomes too
weak. If the average particle diameter of the carriers exceeds 50
.mu.m, there arise tendencies that the image is not improved, and
that a breakdown and a discharge become liable to occur so that a
high voltage cannot be applied. Therefore, the average particle
diameter preferably has a value more than 5 .mu.m and less than 50
.mu.m, and a fluidizer such as hydrophobic silica is suitable added
as an additive, if necessary.
The toner may preferably be prepared by adding a variety of
pigments and, if necessary, a charge controlling agent to a resin
to have an average particle diameter of 1 to 20 .mu.m and may
preferably have an average charge of 3 to 300 .mu.c/g or,
especially, 10 to 100 .mu.c/g. If the toner has an average particle
diameter smaller than 1 .mu.m, it becomes reluctant to leave the
carrier. If the average particle diameter exceeds 20 .mu.m, on the
other hand, the image has its resolution degraded.
As the toner in the method of the present invention, there is used
a magnetic or non-magnetic one which is used as an ordinary toner
and which is prepared by dispersing a coloring agent if necessary
and a suitable amount of magnetic material in a known resin. As the
resin, there can be enumerated a synthetic resin such as: phenol,
polystyrene, alkyd, polyacryl or polyethylene; polycarbonate,
polyester, polyamide, polyether, polyolefin, polystyrene, a
styrene-acrylate copolymer, a styrene-methacrylate copolymer, an
unsaturated styrene-ethylene monoolefin copolymer,
styrene-vinylester copolymer, a styrene-vinylester copolymer, a
styrene-vinylether copolymer, a styrene-acrylonitrile copolymer, a
stryene-methacrylonitrile copolymer, a styrene-acrylamide
copolymer, a styrene-halogated vinylidene copolymer or polyvinyl
acetate; a binary, ternary or more copolymer of those; or a mixture
of those copolymers.
As the coloring agent, in the other hand, there are enumerated a
variety of inorganic pigments, an organic pigment, a direct dye, an
acid dye, a basic dye, a mordant, an acid mordant dye, a dispersed
dye, an oil-soluble dye and so on. As a black pigment, more
specifically, there can be enumerated carbon black, acetylene
black, lamp black, graphite, mineral black, anyline black, cyanine
black and so on. As a yellow pigment, there can be enumerated
chrome yellow, zinc yellow, barium chromate, cadmium yellow, lead
cyanamide, calcium plumbate, Naphthol Yellow S, Hansa Yellow 10G,
Hansa Yellow 5G, Hansa Yellow 3G, Hansa Yellow G, Hansa Yellow GR,
Hansa Yellow A, Hansa Yellow RN, Hansa Yellow R, Pigment Yellow L,
Benzine Yellow, Benzine Yellow G, Benzine Yellow GR, Permanent
Yellow NCG, Vulcan Fast Yellow 5G, Vulcan Fast Yellow R, Tartrazine
Yellow Lake, Quinoline Yellow Lake, Anthragen Yellow 6GL, Permanent
Yellow FGL, Permanent Yellow H10G, Permanent Yellow HR,
Anthrapyrimidine Yellow, and so on. As a red pigment, there can be
enumerated a red iron oxide, red lead, silver vermilion, Cadmium
Red, Permanent Red 4R, Para Red, polytungustophosphoriclacid, Fire
Red, vermilion, Parachlor Orthonitroaniline Red, Lithol Fast
Scarlet G. Brilliant Fast Scarlet, Brilliant Carmine BS, Permanent
Red F2R, Permanent Red F4R, Permanent Red FRL, Permanent Red FRLL,
Permanent Red F4RH, Fast Scarlet VD, Vulcan Fast Rubin B, eosine
lake, Rhodamine Lake, Rhodamine Lake Y, Alyzarin lake, Thioindigo
Red B, Thioindigo maroon, Permanent Red FGR, PV Carmine HR, and so
on. As a blue pigment, there can be enumerated ultramarine,
prussian blue, cobalt blue, Alkali Blue Lake, Peacock Blue Lake,
Victoria Blue Lake, Metalless Phthalocyanine Blue, copper
phthalocyanine, Fast Sky Blue, Indanthrene Blue RS, Indanthrene
Blue BS, Indigo, and so on. As a yellow dye, there can be
enumerated C.I. (i.e., Color Index) Direct Yellow 98, C.I. Direct
Yellow 89 and C.I. Direct Yellow 88 (all of which are of direct
type), C.I. Acid Yellow 1, C.I. Acid Yellow 3 and C.I. Acid Yellow
7 (all of which are of acid type), C.I. Basic Yellow 1, C.I. Basic
Yellow 2 and C.I. Basic Yellow 11 (all of which are of basic type),
C.I. Modern Yellow 26 (which is of mordant or acid mordant type),
C.I. Disperse Yellow 1, C.I. Disperse Yellow 3 and C.I. Disperse
Yellow 4 (all of which are of disperse type), C.I. Solvent Yellow
2, C.I. Solvent Yellow 6 and C.I. Solvent Yellow 14 (all of which
are of oil soluble type), and so on. As a red dye, there can be
enumerated C.I. Direct Red 1, C.I. Direct Red 2 and C.I. Direct Red
4 (all of which are of direct type), C.I. Acid Red 8, C.I. Acid Red
13 and C.I. Acid Red 14 (all of which are of acid type), C.I. Basic
Red 2, C.I. Basic Red 14 and C.I. Basic Red 27 (all of which are of
basic type), C.I. Modern Red 21 (which is of mordant or axid
mordant type), C.I. Disperse Red 1, C.I. Disperse Red 4 and C.I.
Disperse Red 5 (all of which are of disperse type), C.I. Solvent
Red 1, C.I. Solvent Red 3 and C.I. Solvent Red 8 (all of which are
of oil-soluble type), and so on. As a blue dye, there can be
enumerated C.I. Direct Blue 1, C.I. Direct Blue 6 and C.I. Direct
blue 22 (all of which are of direct type), C.I. Acid Blue 1, C.I.
Acid Blue 7 and C.I. Acid Blue 22 (all of which are acid type),
C.I. Basic Blue 7, C.I. Basic Blue 9 and C.I. Basic Blue 19 (all of
which are of basic type), C.I. Modern Blue 48 (which is of mordant
or acid mordant type), C.I. Disperse Blue 1, C.I. Disperse Blue 3
and C.I. Disperse Blue 5 (all of which are of disperse type), C.I.
Solvent Blue 2, C.I. Solvent Blue 11 and C.I. Solvent Blue 12 (all
of which are oil-soluble type), and so on. However, the coloring
agent should not be limited to those thus far enumerated. Moreover,
the colors of the toners should not be limited to the
above-specified four but can be freely selected in accordance with
the object of use.
As the magnetizing material for magnetizing the toner, there can be
used a material which is similar to that used in the carrier. The
amount of addition of the magnetic material is preferred to be
smaller than 60 wt. % of the toner and especially preferred to be
up to 30 wt. % so that the clearness of the color of the toner may
not be deteriorated.
In order to improve the clearness of the color of the toner,
moreover, it is possible to use a coloring magnetic material or a
transparent magnetic material using a rare earth element. As a
suitable one for the coloring magnetic material, there can be
enumerated: for a red color, an iron oxide (e.g., a red oxide), a
material prepared by covering the surface of Ni with a copper
oxide, or a material prepared by causing Ni to absorb Cadmium Red;
for a blue color, cobalt or its compound; and for a yellow color,
aniron oxide or a material prepared by causing Ni to absorb Cadmium
Yellow.
Moreover, it is quite natural that there can be applied to the
above-specified toner a variety of known additives, which are
usually used in the toner, such as a charge control agent.
On the other hand, the toner to be used in the present invention is
preferred to have an average particle diameter of 1 to 20 .mu.m and
an average charge of 1 to 300 .mu.c/g or, especially preferably, 3
to 30 .mu.c/g. If the toner has an average particle diameter
smaller than 1 .mu.m, it becomes reluctant to leave the carrier. If
the average particle diameter exceeds 20 .mu.m, on the other hand,
the resolution of the image is degraded.
If the developer composed of a mixture of the insulating carrier
and the toner thus for described, it is possible to easily set the
bias voltage, which is to be applied to the developing sleeve 31 of
FIG. 3, without any fear of leakage such that the toner is
sufficiently applied to the electrostatic image but without any
fog. Incidentally, in order to make more effective the control of
development and movement of the toner by the application of such
bias voltage, the magnetic material to be used in the magnetic
carrier may be contained in the toner within such a range as will
not deteriorate the color clearness.
The descriptions made hereinbefore are directed the constructions
of to the developing means and the developer which are preferably
used in the method of the present invention. However, the present
invention is not limited to them but may use such developing means
and developer as are disclosed in Japanese Patent Laid-Open Nos.
30537/75, 18656 to 18659,80, 144452/81, 116553/83, and 116554/83.
More preferably, there may be resorted to such a non-contact
jumping developing condition by a two-component developer as is
disclosed in Japanese Patent Laid-Open Nos. 57446/83, 96900 to
96903/83 and 97973/83.
By the use of the recording apparatus thus far described, the
method of the present invention, as shown in FIGS. 4 to 7, can be
put to practice. Incidentally, all of FIGS. 4 to 7 show the step at
which the .[.development of FIG. 2.]. .Iadd.latent image formation
with the apparatus .Iaddend.has been conducted.
FIG. 4 shows an embodiment of the present invention, in which an
exposed portion PH provides a background whereas an unexposed
portion DA is formed with an electrostatic image by an
electrostatic image retaining method and in which the development
is conducted by applying to the electrostatic image a toner charged
with an opposite polarity. This is the embodiment having one color
image reproducing cycle comprising, according to the reproducing
apparatus of FIG. 1, the steps of: uniformly conducting a first
charge of the surface of the image retainer 1 in its initial state,
in which the image retainer 1 is cleared of a charge by the charge
eliminating means 13 and cleaned by the cleaning means 14 to a
potential 0, at its one rotation by means of the charger 2;
executing a first image exposure of the charged surface by means of
the image exposing ray 4 of each of different colors so that the
potential other than the electrostatic image portion may be
substantially 0; conducting a first development of the
electrostatic image, the resultant potential of which is
substantially equal to that of the first charge, by means of such
one of the developing means 5 to 8 as uses a developer having a
color toner corresponding to the image exposing ray 4; uniformly
eliminating the charge to return again the surface potential of the
image retainer 1 to zero by means of the charge eliminating means
13 (or only its charge eliminating lamp) because the potential of
the electrostatic image, which is dropped as a result that it traps
the toner T charged with the opposite polarity, is still higher
than that of the background; uniformly conducting a second charge
again at a second rotation by means of the charger 2; conducting
such a second image exposure of the secondly charged surface by
means of the image exposing ray 4 having a color different from the
previous one as will drop the potential at other than the
electrostatic image portion substantially to zero; conducting a
second development of the electrostatic image obtained with a toner
T' by means of another developing means using a developer
containing a color toner corresponding thereto; subsequently
repeating third and fourth retentions and developments of the
electrostatic image in a similar manner; operating the pre-transfer
charger 9 and the pre-transfer exposing lamp 10 until the color
image, which has been subjected to the fourth development so that
the color toner images are superposed, moves therethrough after
that color image has been retained; next transferring the color
image to the member P, which is being fed in synchronism with the
rotations of the image retainer 1, by means of the transfer means
11; fixing the color image transferred to the recording member P by
means of the fixing means 12; eliminating the charge from the
surface of the image retainer 1 having the transferred color image
by means of charge eliminating means 13; and cleaning the
charge-removed surface of the image retainer 1 by means of the
cleaning means 14 until the initial state is restored to complete
the one color image reproducing cycle. More specifically, the
charging operation for each retention of the electrostatic image is
performed by the charger 2, and the image exposure is performed by
means of the common slit exposing means, which is equipped with
filter switching means, or the common exposing means which is
constructed of the laser beam scanner of FIG. 2, for example. This
makes it unnecessary to use another image exposing means for
retaining the electrostatic image at each time so that the
reproducing apparatus can be constructed in a small size and at a
low cost and so that the synchronous control of the retention of
the electrostatic image at each time can be conducted with ease.
Incidentally, the charge elimination by the charge eliminating
means 13, which is
interposed between a previous development and a subsequent charging
operation, can be omitted.
Since the development is effected by the method of developing the
electrostatic image with the toner charged with the opposite
polarity, the embodiment of FIG. 4 being described can easily
enhance the developed densities of the respective colors so that a
clear color image can be easily reproduced. Incidentally, in order
to avoid the color mixing, the d.c. biases at the developments may
be set a consecutively higher levels at the later steps. In a
matter to correspond to this setting, moreover, the charged
potentials may be set at consecutively higher levels.
FIGS. 5 to 7 show other embodiments of the present invention, in
which electrostatic images are retained by an electrostatic
retaining method of forming the image exposed portion PH into an
electrostatic image at a lower potential than the background
portion and in which the developments are conducted by applying to
the electrostatic images the toners for charging the same with the
same polarity as that of the background potential.
The embodiment of FIG. 5 by the reproducing apparatus of FIG. 1 has
one color image reproducing cycle comprising the steps of:
uniformly charging the surface of the image 1 in the same initial
state as that of FIG. 4 at its one rotation by means of the charger
2; projecting the image exposing rays 4 of different colors by the
laser beam scanner of FIG. 2 onto the charged surface to conduct a
first image exposure thereby to drop the potential of the
electrostatic image portion substantially to zero; conducting a
first development of the obtained electrostatic image by such any
one of the developing means 5 to 8 as uses the developer (of which
the toner charges the image retainer 1 with the same polarity, as
is different from the embodiment of FIG. 4) having the color toner
corresponding to the image exposing ray 4; conducting a second
image exposure projecting the image exposing ray 4 of a different
color onto a position, which is shifted from the projected position
of the previous developing ray 4, at a second rotation by means of
the same laser beam scanner without any use of the charger 2;
developing the electrostatic image thus obtained to have a
substantially zero potential with a developer having a toner of
corresponding color; and subsequently repeating the third and
fourth retentions and developments of the electrostatic image in
like manners thereby to subsequently complete the one color image
reproducing cycle similarly to FIG. 4. In this embodiment,
incidentally, even if the electrostatic image having the
substantially zero potential is developed so that it traps the
toner T for effecting the charge with the same polarity as that of
the charge of the image retainer 1, the potential is not
substantially equal to that of the background portion, as shown. As
a result, upon the development for applying the toner T' of
different color to the electrostatic latent image retained later,
the toner T' is frequently applied in a superposed manner to the
electrostatic image portion having previously trapped the toner T,
although the portion is neither exposed nor written in yet. Since
the laser beam scanner is used for preparing the image exposing ray
4, however, the projection position of the image exposing ray 4 at
each time is so remarkably simple that the charging operation can
be finished at one time. Moreover, it can be prevented by setting
the d.c. biases of the respective developments at consecutively
lower levels that the electrostatic images of different colors are
liable to be superposed, whereby an excellently clear color image
can be obtained.
The embodiment of FIG. 6 is one which is improved in such defects
of the embodiment of FIG. 5 that the electrostatic image cannot be
positively retained in the superposed manner at the position where
the electrostatic image has been previously formed, and that there
is a fear, to the contrary, that a toner of different color may be
applied, even if a little, by the subsequent development to the
electrostatic image portion which has been previously developed.
More specifically, the embodiment of FIG. 6 is identical, at the
steps from the initial time to the first development, to the steps
up to the first development of FIG. 5 but is different from the
same in the steps of: subsequently conducting or not the charge
elimination by means of the charge eliminating means 13 (or only
the charge eliminating lamp); uniformly conducting the second
charge again at the second rotation by means of the charger 2;
conducting the second image exposure and the second development of
the charged surface; and subsequently repeating the third and
fourth retentions and developments of the electrostatic image in a
similar manner. Thus, in the embodiment of FIG. 6, in which the
surface of the image retainer 1 is uniformly charged again after
the previous development and is then subjected to the subsequent
electrostatic image retentions and developments, there can be
attained the effects that the electrostatic image can be retained
in the superposed manner on the position where the electrostatic
image has been previously retained, like the embodiment of FIG. 4,
and that, in case the position of the subsequent electrostatic
image is shifted from that of the previous one, the subsequent
toner of different color is hardly applied to the image position to
which the previous toner is applied.
The embodiment of FIG. 7 is one which is especially devised to
prevent a subsequent toner of different color from being applied to
an image position to which a previous toner has been applied. This
example is identical in the steps before a first development to the
embodiments of FIGS. 6 and 7 but is different from the same in the
steps of: either previously uniformly exposing, after the first
development, the surface of the image retainer 1 by the user of the
pretransfer exposing lamp 10 or the charge-eliminating lamp of the
charge-eliminating means 13, and subsequently conducting a second
charge by means of the charger 2, or previously uniformly
conducting a second charge by means of the charger 2, and
subsequently uniformly conducting a weak exposure by means of the
exposing lamp 3; then conducting a second image exposure and a
second development; and repeating third and fourth retentions and
developments of electrostatic images in a similar manner. Here, if
the uniform exposure is previously conducted after the development,
the portion which has been developed to trap the toner has its
charge uneliminated so that it is held at a high potential, whereas
the remaining portion is dropped substantially to a zero potential,
whereupon the potential at the portion having the toner can be
raised by conducting the second charge to a level slightly higher
than that at the other portion, where the electrostatic image is to
be retained, thereby to charge the surface of the image retainer 1.
On the other hand, even if the second charge is previously
conducted after the development to uniformly charge the surface of
the image retainer 1 whereupon the weak exposure is uniformly
conducted, the charged state of the surface of the image retainer 1
becomes similar to that obtainable in case the uniform exposure has
been previously conducted. As a result, when the subsequent
electrostatic image retained with a shift of position is to be
developed, the previous portion having the toner is at a higher
potential so that it can be effectively prevented from trapping the
toner of different color.
In any of the foregoing embodiments, it is preferred that the
developing means 5 to 8 use the developer which is composed of a
mixture of the toner and the insulating carrier, and that the
development is conducted under the non-contact jumping developing
condition. As a result, as has also been described, it becomes
possible to prevent the mixing of the toner of different color and
to easily apply the bias voltage suitable for the toner control,
whereby a color image having a high developed density and an
excellent clearness can be reproduced even in the case of the
electrostatic image retaining method and the developing method, as
in the embodiments of FIGS. 5 to 7, in which the image exposing
means such as the laser beam scanner can be advantageously
used.
Next, the embodiments of FIGS. 4 to 7 will be described more
specifically in the following in connection with Examples 1 to 4,
respectively.
EXAMPLE 1 (I.E., EMBODIMENT OF FIG. 4)
The reproducing apparatus, as shown in FIG. 1, was used. However,
the exposing lamp 3 was not used, but the image retainer 1 had a
surface layer of a photosensitive material such as CdS and a
circumferential speed of 180 mm/sec. The surface of the
above-specified image retainer 1 was charged with a voltage of -500
V by means of the charger 2 using the corona discharger, and its
charged surface was subjected to the slit exposure through a blue
filter. As a result, there was retained in the image retainer 1 the
electrostatic image in which the exposed portion PH had the
background potential of -50 V whereas the unexposed portion DA had
the potential of -500 V. The electrostatic image thus retained was
firstly developed by the developing means 5, as shown in FIG.
3.
The developing means 5 used the developer, which was composed of: a
carrier prepared by dispersing and containing 50 wt. % of magnetite
in a resin to have an average particle diameter of 20 .mu.m, a
magnetization of 30 emu/g and a resistivity of 10.sup.14 .OMEGA. cm
or higher; and a non-magnetic toner prepared by adding 10 wt. parts
of a benzine derivative as the yellow pigment and another charge
controlling agent to the styreneacryl resin to have an average
particle diameter of 10 .mu.m, under a condition that the ratio of
the toner to the carrier was 25 wt. %. Moreover, the non-contact
jumping developing conditions was resorted to, under which the
developing sleeve 31 had an external diameter of 30 mm and a number
of revolutions of 100 r.p.m., under which the magnet 32 has its N
and S magnetic poles of a magnetic flux density of 1,000 gausses
and a number of revolutions of 1,000 r.p.m., under the layer of the
developer in the developed region had a thickness of 0.7 mm, under
which the gap between the developing sleeve 31 and the image
retainer 1 was 0.8 mm, and under which a superposed voltage
containing a d.c. voltage of -100 V and an a.c. voltage of 3 kHz
and .[.1.000.]. .Iadd.1,000 .Iaddend.V was applied to the
developing sleeve 31.
While the developing image was being developed by the developing
means 5, the remaining developing means 6 to 8, as shown in FIG. 3,
were held in their undeveloping state. This was achieved by
disconnecting the developing sleeve 31 from the power supply 39
into its floating state, by grounding the same to the earth, or by
positively applying the d.c. bias voltage, which had the same
polarity as the charge of the image retainer 1 but the opposite
polarity to the charge of the toner, to the developing sleeve 31.
Of these, it is preferred to apply the d.c. bias voltage. Since the
developing means 6 to 8 were made to conduct their developments
under the non-contact jumping developing condition like the
developing means 5, it was not necessary to especially eliminate
the layer of the developer from the developing sleeve 31. Of those
developing means 6 to 8: the developing means 6 used a developer
which was prepared by replacing the toner of the developer of the
developing means 5 by a toner containing polytungstate as the
Magenta pigment in place of the yellow pigment; the developer 7
used a developer which was prepared by replacing the same toner by
a toner containing copper phthalocyanine as the cyan pigment; and
the developing means 8 used a developer which was prepared by
replacing the same toner by a toner containing carbon black as the
black pigment. It is quite natural that a toner containing other
pigment and dye could be used as the color toner, and that the
order of the colors to be developed and the order of the developing
means could be suitably selected.
The surface of the image retainer 1, which had been subjected to
the first development, was recharged to -600 V by operating the
charge eliminating means 13 and the charger 2 (although the former
may be left inoperative). The charged surface was subjected to the
second exposure by the slit exposure through a green filter, and
the developing sleeve 31 was then subjected to the second
development with the Magenta toner by the developing means under
the non-contact jumping developing condition for applying the
superposed voltage of a d.c. voltage of -200 V and an a.c. voltage
of 3 kHz and 1,000 V. Likewise, the following steps were repeated:
the charge, the slit exposure through a red filter, and the third
development of the cyan toner by the developing means 7; and the
charge, the slit exposure without any filtration, and the fourth
development of a black toner by the developing means 8. In the
second and later developments, incidentally, the amplitudes and
frequencies of the d.c. bias component and a.c. component of the
voltage to be applied to the developing sleeve 31, the selecting
time of a time selecting conversion, and so on were suitably
changed in accordance with the changes in the surface potential,
the developing characteristics and the color reproductivity of the
image retainer 1. Especially, it was effective for preventing the
color mixing of the toner that the charge potentials were made
consecutively higher whereas the d.c. biases were made
consecutively higher.
The color images of four colors were made liable, when they were
retained on the image retainer 1 as a result of the fourth
development, to be transferred by the pre-transfer charger 9 and
the pre-transfer exposing lamp 10, and were than transferred to the
recording member P by the transfer means 11 until they were fixed
by the fixing means 12. The image retainer 1 having the color
images transferred thereto had its charge eliminated by the charge
eliminator 13 and its residual toner scraped off from its surface
by the contacts of the cleaning blade or fur brush of the cleaning
means 14. At the instant when the surface having the color images
retained therein passed through the cleaning means 13, the one
color image reproducing cycle was completely ended.
The color image thus reproduced was so clear that the respective
colors exhibited sufficient densities, but a slight color mixing of
the toners was found at the portion in which the respective color
toners are densely trapped.
EXAMPLE 2 (I.E., EXAMPLE OF FIG. 5)
The reproducing apparatus, as shown in FIG. 1, was used. However,
the exposing lamp 3 was not used, but the image retainer 1 had a
surface layer of a photosensitive materail such as CdS and a
circumferential speed of 180 mm/sec. The surface of the
above-specified image retainer 1 was charged with a voltage of +500
V by means of the charger 2 using the corona discharger, and its
charged surface was subjected to the first image exposure in a
density of 16 dots/mm by the laser beam scanner of FIG. 2 using a
He--Ne laser. As a result, there was retained in the image retainer
1 the electrostatic image in which the exposed portion PH had a
potential of +50 V contrary to the background potential of +500 V.
The electrostatic image thus retained was firstly developed by the
developing means 5, as shown in FIG. 3.
Incidentally, the developing conditions by the developing means 5
were made identical to those of Example 1 except that the carrier
of the developer had an average particle dize of 30 .mu.m, that the
ratio of the toner to the carrier was 20 wt. %, and that the
superposed voltage of a d.c. voltage of +400 V and an a.c. voltage
of 1.5 kHz and 1,000 V was applied to the developing sleeve 31.
Moreover, the conditions of the remaining developing means 6 to 8
were identical to those of the Example 1 except the bias voltages.
In this case, however, the bias voltages for holding the developing
means taking no part in the development in the state other than the
development had a polarity opposite to both those of the charge of
the toner and the charge of the image retainer 1.
The surface of the image retainer 1 having been subjected to the
first development was subjected again to the second image exposure
without any change in the density but with a shift of the dot
position by means of the same laser beam scanner without operating
one of the pre-transfer charger 9, the pre-transfer exposing lamp
10, the charge eliminating means 13, the cleaning means 14 and the
charger 2, and was then subjected to the second development with
the Magenta toner by the developing means 6. Likewise, the third
development with the cyanic toner by the developer means 7 and the
fourth development with the black toner by the developing means 8
were repeated. In the second and later developments, incidentally,
the amplitudes and frequencies of the d.c. bias component and a.c.
component of the voltage to be applied to the developing sleeve 31,
the selecting time of a time selecting conversion, and so on were
suitably changed in accordance with the changes in the surface
potential, the developing characteristics and the color
reproductivity of the image retainer 1.
Especially, in this case it was effective for preventing the color
mixing of the toner that the d.c. biases were made consecutively
lower at the respective steps.
After the fourth development had been conducted to retain the color
image of four colors on the image retainer 1, it was transferred
and fixed to the recording member P like the Example 1, and the
image retainer 1 had its charge eliminated and was cleaned, thus
ending the one color image reproducing cycle.
The color image thus reproduced was clear like that of the
Embodiment 1.
EXAMPLE 3 (I.E., EMBODIMENT OF FIG. 6)
By using the same apparatus as that of the Example 2, the color
image reproduction was performed under the same conditions as those
of the Example 2 except that the voltage to be applied to the
developing sleeve 31 of the developing means was a superposed
voltage of a d.c. voltage of +400 V and an a.c. voltage of 500 Hz
and 250 V, that the charge elimination was conducted by means of
the pre-transfer exposing lamp 10 before each image exposure on and
after the second image exposing step, and that the surface
potential of the image retainer 1 was then recharged with +500 V by
the charger 2.
The color image reproduced was more clear than that obtained by the
Example 2, because the color mixture of the toners was reduced at
the portion where the respective color toners were densely
trapped.
According to this Example, incidentally, the previous image exposed
position and the subsequent image exposed position can be
superposed, as has been described hereinbefore, and, in this case,
the order of the colors to be developed imparts considerable
influences upon the clearness of the color image. It is, therefore,
necessary to determine especially carefully the order of the colors
to be developed.
EXAMPLE 4 (I.E., EMBODIMENT OF FIG. 7)
By using the same apparatus as that of the Example 2 except the
provision of the exposing lamp 3, the color image reproduction was
conducted under the same conditions as those of the Example 2
except that the voltage to be applied to the developing sleeve 31
of the developing means was a superposed one of a d.c. voltage of
+450 V and an a.c. voltage of 2 kHz and 500 V, and that both the
charge by the charger 2 for raising the surface potential of the
image retainer 1 to +600 V and the uniform, weak exposure by the
exposing lamp 3 for dropping the surface potential to +500 V were
conducted before each image exposure on and after the second image
exposure.
The color image thus reproduced has no color mixing of the
respective color toners even at a portion, where the toners were
densely trapped, so that it was remarkably clear.
Even in this Example, like the Example 3, the previous image
exposed position and the subsequent image exposed position can be
superposed.
According to the present invention, the common apparatus can be
used for the repeated electrostatic image retentions to provide
excellent effects that the reproducing apparatus can be constructed
in a small size and at a low cost, and that the synchronous control
of each image exposure can be conducted easily and accurately.
Moreover, each development can be conducted either by the
developing method, in which there is applied to an electrostatic
image relatively easy to have its developed density controlled to a
toner for charging it with the opposite polarity, or by the
developing method in which the laser beam scanner can be used as
the image exposing means and in which there is applied to the
electrostatic image a toner for charging it with the common
polarity. According to either of the developing methods, still
moreover, there can be attained an excellent effect that the
development can be conducted under the non-contact jumping
developing condition to reproduce the color image having a
sufficient developed density and an excellent clearness.
As has been described hereinbefore, incidentally, the present
invention should naturally be limited neither to the method, in
which the image retained uses the drum-shaped recording apparatus,
but also to the method in which the color image is transferred to
the recording member. In other words, the present invention can be
applied to the method, in which the image retainer is mounted on a
base such as that for electrofax paper and in which the color image
retained thereon is not transferred but fixed. In this application,
there can be dispensed with the pre-transfer charger, the
pre-transfer exposing lamp, the transfer means and the cleaning
means. It is true, but the pre-transfer charger, the pre-transfer
exposing lamp or the charge eliminating means can be omitted in the
transfer case, too, and the transfer may be a direct pressure one
or one using an intermediate transfer member whereas the fixing
operation should not be limited to one using a heat roller.
In other embodiments of the present invention, the image retainer 1
is constructed, as shown in FIG. 8, of: a conductive base 1a made
of aluminum or nickel; a photoconductive photosensitive layer 1b
made of Se, CdS, Si or the like and formed on the conductive base
1a; and a transparent insulating surface layer 1c made of a
transparent resin and formed on the photoconductive photosensitive
layer 1b, and said conductive substrate 1a being grounded to the
earth. Indicated at reference numeral 2 in FIG. 9 is a primary
charger which is composed, in combination, of a lamp 2a for
irradiating the surface of the image retainer 1 and a corona
discharger 2b. Numeral 3' indicates a secondary charger which is
composed of a corona discharger. Here, the primary charger 2 need
not necessarily be equipped with the lamp 2a in case the
photoconductive photosensitive layer 1b of the image retainer 1 has
such semiconductor characteristics as exhibit a rectifying action
that charges can be implanted from the base 1a. Indicated at
numeral 15 is a corona discharger for charging toners prior to
transfers.
In the reproducing apparatus thus constructed, when the primary
charger 2 conducts the corona discharge by its corona discharger 2b
while irradiating the surface of the image retainer 1 by its lamp
2a (which may not be required as the case may be, as has been
described hereinbefore), the image retainer 1 is charged, as shown
in FIG. 10A, in its photoconductive photosensitive layer 1b and on
the surface of its transparent insulating surface layer 1d. When
the secondary charger 3' conducts the corona discharge of the
charged surface of the image retainer 1, the charges on the surface
of the transparent insulating surface layer 1c are reduced because
the photoconductive photosensitive layer 1b has an insulating
property in this case, so that the charged state of the image
retainer 1 charges as shown in FIG. 10B. When the image exposing
ray 4 is incident upon that surface of the image retainer 1 thus
secondarily charged, the surface charges of the photoconductive
photosensitive layer 1b at the exposed portion PH are reduced while
being left as they are at the unexposed portion DA so that the
charges of the image retainer 1 change, as shown in FIG. 10C. The
changes of the surface potential of the image retainer 1 in this
meanwhile are shown in FIG. 11, in which the potentials in states
A, B and C correspond to the changed states of FIGS. 10A, B and C,
respectively. More specifically, the potential of the exposed
portion PH exposed to the image exposing ray 4 takes such surface
one as is indicated at C(PH) in FIG. 11, whereas the potential of
the unexposed portion having received none of the image exposing
ray 4 is at C (DA) which is substantially the same as the surface
potential indicated at B in FIG. 11. This results in that an
electrostatic image having a surface potential at C(PH) with
respect to that background is retained by the image exposing ray 4.
The electrostatic image thus retained can be developed like the
ordinary electrophotographic reproducing machine with such a
developer as will charge the exposed portion PH with a polarity
opposite to that of the latent image, and this development is
conducted by any one of such a color of the developing means 5 to 8
as corresponds to the image exposing ray 4 having formed the
electrostatic image. When the development is conducted to apply the
toner, the potential of the electrostatic image is dropped in
accordance with the trapped amount of the toner having been charged
in the opposite polarity. However, the charge of the unexposed
portion DA of the image retainer 1, which has received none of the
image exposing ray 4, remains in such a state DA of FIG. 10C as is
identical to that of FIG. 10B, and the surface potential of the
same portion is at the same potential C(DA) as that of B of FIG. 11
even with a dark attenuation. As a result, if the image exposing
ray 4 of another color is incident with a shift from the position
of the previous image exposing ray 4 at the second rotation of the
image retainer 1, an electrostatic image can be retained like the
previous exposure with neither of the primary and secondary
charging operations. Thus, the second and later retentions of the
electrostatic images by making use of the first primary and
secondary charging operations are easily effected in case the
previous development or developments are conducted by the
developing method, in which a developer for charging in an opposite
polarity is applied, and under the noncontact jumping condition.
This is partly because the application of the toners to the
electrostatic images can be more easily conducted than the
developing method, in which the developing agent for charging in
the same polarity to make it unnecessary to apply such a high
voltage to the developing sleeve 16 as to apply the toners to the
electrostatic images so that the charged state of the image
retainer 1 is held stable, and partly because the developer layer
of the developing means is kept away from the surface of the image
retainer 1 by resorting to the non-contact jumping developing
condition so that the charged state of the image retainer 1 is held
stable. Incidentally, the shift of the position of the subsequent
image exposing ray 4 with respect to the previous image forming ray
4 so as to retain the electrostatic images of different colors can
be easily conducted by using the laser beam scanner of FIG. 3 for
producing the image exposing ray 4.
The present invention should not be limited to the embodiment in
which the second and later retentions of the electrostatic images
are conducted by making use of the first primary and secondary
charging operations. Generally speaking, however, the primary and
secondary charging operations may be conducted each time of the
second and later retentions of the electrostatic images, or
therefore the previous charges may be eliminated by the charge
eliminating means 13 or only the secondary charging operation may
be so executed as to compensate the dark attenuation. Especially
either in case the primary and secondary charging operations are
executed again without eliminating the previous charges or in case
only the secondary charging operation is executed, the scorotron
corona discharger may preferably for allowing stable charging
operations even in the presence of the previous charges may
preferably be used as the corona dischargers of the primary charger
2 and the secondary charger 3'. It is especially desired when a
graded reproductivity is stressed or in case the image exposing ray
4 is of slit or flash exposure type that the primary and secondary
charging operations are conducted again each retention of the
electrostatic images. Moreover, it is possible to adopt the NP or
KIP method by which the electrostatic images are retained by
conducting the image exposure simultaneously with secondary
charging operation after the primary charging operation and by
conducting the exposure of the whole surface. In the several
methods thus far described, the electrostatic image potential can
be so controlled in dependence upon the relative strengths of the
primary and secondary charges that the exposed portion and the
unexposed portion may be in an identical or opposite polarity.
Considering the feasibility of the development, however, it is
preferable that the exposed and unexposed portions take opposite
polarities.
The electrostatic image at the second rotation thus retained is
developed by such one of a color different from the previous one of
the developing means 5 to 8 as corresponds the image exposing ray 4
having retained that electrostatic image. Likewise, at the third
and fourth rotations of the image retainer 1, too, both the
retentions of the electrostatic images and the developments by the
different developing means corresponding to those electrostatic
images are conducted to form a color image which has toner images
of different colors superposed on the image retainer 1. Moreover,
the surface of the image retainer 1 having been subjected to the
last development has, if necessary, charges applied to its toner
image by means of the corona discharger 15 and is then irradiated
by the pre-transfer lamp 10 so that the color image can be easily
transferred to the recording member P by the transfer means 11. The
color image thus transferred to the recording member P is fixed to
the recording member P by the fixing means 12. The surface of the
image retainer 1 having the color image transferred thereto has its
charges eliminated by the charge eliminating means 13 so that the
residual toners after the transfer are eliminated as a result that
the cleaning blade of the cleaning means 14 having been kept away
until the time comes into abutment against the surface of the image
retainer 1. At the time the surface portion of the image retainer 1
having retained the color image moves over the cleaning means 14,
the cleaning blade leaves the surface of the image retainer 1, thus
completing the one color image reproducing cycle.
FIG. 12 is a flow chart showing the changes of the surface
potential of the image retainer of the embodiment of the present
invention, in which an electrostatic image is retained each time
with an image exposing ray by making use of the first primary and
secondary charging operations. FIG. 13 is a flow chart showing the
changes of the surface potential of the image retainer of the
embodiment of the present invention, in which only the secondary
charging operations is conducted prior to the second and later
electrostatic image retentions. FIG. 14 is a flow chart showing the
changes of the surface potential of the image retainer of the
embodiment of the present invention, in which the primary and
secondary charging operations are conducted after charges are
eliminated from the second and later retained electrostatic images
like the first one. All of these Figures show, like FIGS. 10 and
11, the embodiments of the present inventions for retaining the
electrostatic images by the negative exposure, where the image
exposed portion retains the electrostatic images, to which the
toners are applied. On the contrary, FIG. 15 is a flow chart
showing the changes of the surface potential of the image retainer
of the embodiment of the present invention for retaining the
electrostatic images by the positive exposure, where the exposed
portion is formed into the background portion whereas the unexposed
portion is formed into the electrostatic image, to which the toners
are applied, by changing the conditions for the primary and
secondary charging operations in the embodiment of FIG. 14. On the
other hand, FIGS. 16 and 17 are flow charts showing the changes of
the surface potentials of the image retainers of the embodiments of
the present invention using the electrostatic image retaining
process called the "NP or KIP process". FIG. 16 corresponds to the
case of the positive exposure like FIG. 15, whereas FIG. 17
corresponds to the case of the negative exposure like FIGS. 12 to
14. The embodiments of FIGS. 16 and 17 will be briefly described in
the following. FIG. 16 shows the embodiment comprising the steps
of: imparting charges to the photoconductive photosensitive layer
1b by the primary exposing operation to charge the image retainer 1
positive; subsequently conducting an image exposure in a secondary
charging operation to form an ion image on the transparent
insulating surface layer 1c thereby to charge the image retainer 1
negative; subjecting the whole surface to an exposure to retain
such an electrostatic image that the potential of the unexposed
portion not having been subjected to the image exposure during the
secondary charging operation exhibits a positive value; applying a
toner charged in an opposite polarity to that electrostatic image
by a development; and subsequently repeating a charge elimination
(which may be omitted) and an electrostatic image retention and
development similar to the aforementioned ones. On the other hand,
FIG. 17 shows the embodiment comprising the steps of: charging the
image retainer 1 negative by a primary charging operation contrary
to the fact that the image retainer 1 is charged positive in the
embodiment of FIG. 16; charging the image retainer 1 positive by a
subsequent second charging operation and a simultaneous image
exposure; subjecting the whole charged surface to an exposure so
that the potential of the unexposed portion other than the portion
having been subjected the image exposure during the secondary
charging operation is negative like the primary charging
operation;
applying a toner in an opposite polarity by a development to the
electrostatic image at a portion which has been charged positive by
the image exposure during the secondary charging operation;
.[.nad.]. .Iadd.and .Iaddend.subsequently repeating a charge
elimination (which may be omitted), and an electrostatic image
retention and a development like the aforementioned ones.
Incidentally, all FIGS. 12 to 17 show the step, at which the second
development has been conducted, and the embodiments in which the
second image exposure is shifted from the first one. However, not
only in the embodiments of FIGS. 14 to 17, in which the charge
elimination and the primary and the secondary charging operations
are repeated at each time, but also in the embodiments of FIGS. 12
and 13, the subsequent image exposing ray is incident upon the
previous image exposed position, in which the electrostatic image
is formed, by means for increasing the quantity of light of the
image exposing ray the more for a later time so that the toner of a
color different from the previous one can be applied in a
superposed manner by the developments. Indicated at reference
letters T and T' in FIGS. 12 to 17 are toners in different colors,
which are applied to the surface of the image retainer.
In any of the embodiments of FIGS. 12 to 17, moreover, each
development is conducted with the developer in a polarity opposite
to that of the electrostatic image thereby to provide an excellent
effect that a remarkably clear color image can be reproduced with
little scattering of the developer, and the reproducing apparatus
is so constructed as is shown in FIG. 9 thereby to provide an
advantage that the primary and secondary chargers and the image
exposing ray producing apparatus taking part in the respective
retentions of the electrostatic images can be commonly used. These
embodiments of FIGS. 12 to 17 will be described more specifically
in the following in connection with Examples 5 to 10.
EXAMPLE 5 (I.E., EMBODIMENT OF FIG. 12)
The reproducing apparatus shown in FIG. 9 was used. Despite of this
fact, the image retainer 1 was prepared by forming a transparent
insulating film having a thickness of 20 .mu.m on a CdS
photosensitive layer having a thickness of 30 .mu.m and had a
circumferential speed of 180 mm/sec. The image retainer 12 thus
prepared was so charged by means of a d.c. scorotron corona
discharger 2b, while being subjected to a uniform exposure by the
lamp 2a of the primary charger 2, that its surface potential took a
level of +1,000 V. Next, the image retainer 1 was charged to have a
surface potential of -100 V by means of the secondary charger 3
composed of the scorotron corona discharger having an a.c.
component. This charged surface was subjected to a writing exposure
with a density of 16 dots/mm by means of the laser beam scanner
using the He-Ne laser, as shown in FIG. 2, to retain an
electrostatic image having a background potential of -100 V and an
exposed portion potential of +50 V. This electrostatic image was
developed by the developing means 5 shown in FIG. 3.
The developing means 5 used the developer, which was composed of: a
carrier prepared by dispersing and containing 50 wt. % of magnetite
in a resin to have an average particle diameter of 20 .mu.m, a
magnetization of 30 emu/g and a resistivity of 10.sup.14 .OMEGA. cm
or higher; and a non-magnetic toner prepared by adding 10 wt. parts
of a benzine derivative as the yellow pigment and another charge
controlling agent to the styrene-acryl resin to have an average
particle diameter of 10 .mu.m, under a condition that the ratio of
the toner to the carrier was 20 wt. %. Moreover, the non-contact
jumping developing condition was resorted to, under which the
developing sleeve 31 had an external diameter of 30 mm and a number
of revolutions of 100 r.p.m., under which the magnet 32 has its N
and S magnetic poles of a magnetic flux density of 900 gausses and
a number of revolutions of 1,000 r.p.m., under which the layer of
the developer in the developed region had a thickness of 0.7 mm,
under which the gap between the developing sleeve 31 and the image
retainer 1 was 0.8 mm, and under which a superposed voltage
containing a d.c. voltage of -50 V and an a.c. voltage of 2.5 kHz
and 2,000 V was applied to the developing sleeve 31.
While the developing image was being developed by the developing
means 5, the remaining developing means 6 to 8, as shown in FIG. 3,
were held in their undeveloping state. This was achieved by
disconnecting the developing sleeve 31 from the power supply 39
into its floating state, by grounding the same to the earth, or by
positively applying the d.c. bias voltage, which had the same
polarity as the charge of the image retainer 1 but the opposite
polarity to the charge of the toner, to the developing sleeve 31.
Of these, it is preferred to apply the d.c. bias voltage. Since the
developing means 6 to 8 were made to conduct their developments
under the non-contact jumping developing condition like the
developing means 5, it was not necessary to eliminate the layer of
the developer layer from the developing sleeve 31. Of those
developing means 6 to 8: the developing means 6 used a developer
which was prepared by replacing the toner of the developer of the
developing means 5 by a toner containing polytungstate as the
.[.Magenta.]. .Iadd.magenta .Iaddend.pigment in place of the yellow
pigment; the developer 7 used a developer which was prepared by
replacing the same toner by a toner containing copper
phthalocyanine as the cyan pigment; and the developing means 8 used
a developer which was prepared by replacing the same tone by a
toner containing carbon black as the black pigment. It is quite
natural that the toner containing other pigment and dye could be
used as the color toner, and that the order of the colors to be
developed and the order of the developing means could be suitably
selected. Especially in case the positions of the image exposing
rays were superposed, the order of the colors to be developed had
to be carefully determined because it had a serial relationship
with the clearness of the color image.
When the surface of the image retainer 1 developed by the
developing means 5 arrived again at the position, where it was to
be exposed to the image exposing ray 4, after it had passed through
the positions of the corona discharger 15 and the pre-transfer lamp
10, both of which were not necessary until the final transfer was
conducted, the charge eliminating means 13 and the cleaning means
14, both of which are held in their inoperative states, and the
primary charger 2 and the secondary charger 3' which came into
their paused states after having conducted the primary and
secondary charging operations, a second writing operation was
conducted with a shift of the dot positions, in a doubled light
quantity and in the same dot density by means of the same laser
beam scanner as the previous one. The electrostatic image thus
obtained had a potential of +200 V for the background portion
potential of -100 V. The resultant electrostatic image was
developed by the developing means 6 under the same conditions as
those of the developing means 5 except that a voltage having a d.c.
component of 100 V and an a.c. component of 2.5 kHz and 2,000 V was
applied to the developing sleeve 31.
Likewise, at the third rotation of the image retainer 1, a writing
operation was conducted in a tripled light quantity by means of the
laser beam scanner to retain an electrostatic image having a
potential of +350 V for a background portion potential of -100 V.
This electrostatic iamge was developed by the developing means 7
under the same conditions as those of the developing means 5 except
that a voltage having a d.c. component of 250 V and an a.c.
component of 2.5 kHz and 2,000 V was applied to the developing
sleeve 31. Likewise, moreover, a writing operation was conducted at
the fourth rotation of the image retainer 1 in a quadrupled light
quantity by means of the laser beam scanner to retain an
electrostatic iamge of +500 V for a background potential of -100 V.
This electrostatic image was developed by the developing means 8
under the same conditions as those of the developing means 5 except
that a voltage having a d.c. component of 400 V and an a.c.
component of 2.5 kHz and 2,000 V was applied to be developing
sleeve 31.
At the stage when that fourth development was conducted so that the
color image of four colors was retained on the image retainer 1,
the corona discharger 15 and the pre-transfer lamp 10 were operated
to make the color image liable to be transferred, and this color
image was transferred to the recording member P by the transfer
means 11 and fixed by the fixing means 12.
The image retainer 1 having the color image thus transferred
thereto had its charges eliminated by the charge eliminating means
13 and its surface cleared of the residual toners by the abutment
against the cleaning blade of the cleaning means 14. As a result,
the one color image reproducing cycle was completely finished at
the time the surface having the color image retained therein passed
over the cleaning means 14.
The color image thus reproduced was freed from any color mixing not
only at the portion, to which the respective color toners were
coarsely applied, but also as the portion, to which the same were
densely applied, so that it was remarkably clear.
EXAMPLE 6 (I.E., EMBODIMENT OF FIG. 13)
The same reproducing apparatus as that of the Example 5 was used,
and primary and secondary charging operations were conducted under
the same conditions as those of the Example 5 by means of the
primary charger 2 and the secondary charger 3'. After that, the
writing operations was conducted by the same laser beam scanner as
that of the Example 5 but in a light quantity four times as large
as that of the first writing operation of the Example 5 and with
the same dot density as that of the Example 5 to retain an
electrostatic image having an exposed portion potential of +500 V
for a background portion potential of -100 V in the image retainer
1 under the same conditions as those of the Example 5.
This electrostatic image was developed by the developing means 5
under the same conditions as those of the Embodiment 5 except that
a superposed voltage composed of a d.c. voltage of 50 V and an a.c.
voltage of 1.5 kHz and 1,000 V was applied to the developing sleeve
31.
Moreover, when the surface of the image retainer 1 thus developed
by the developing means 5 arrived again at the position of the
secondary charger 3', the image retainer 1 is so charged again by
the secondary charger 3' that its surface potential took a level of
-100 V. That surface was subjected to second writing and exposing
operations under the same conditions as the previous ones except
the shift of the dot positions by means of the same laser beam
scanner to retain again an electrostatic image. This electrostatic
image was developed by the developing means 6 using the same
developer as that of the Example 5 and under basically the same
conditions as the developing conditions of the developing means
5.
Like the second operation, moreover, the charging and exposing
operations were repeated to develop a third electrostatic image by
the developing means 7 and to develop a fourth electrostatic image
by the developing means 8 in a similar manner. In this case, each
development was conducted by suitably changing the d.c. bias
component and the amplitude, frequency, duty ratio and so on of the
a.c. component of the voltage, which was to be applied to the
developing sleeve 31, in accordance with the changes, developing
characteristics and color reproducing state of the surface
potential of the image retainer 1.
After the fourth development has been conducted to retain a color
image of four colors on the image retainer 1, the operations of
reproducing the color image was completed like the Example 5.
The reproduced image thus obtained was remarkably clear like that
of the Example 5.
EXAMPLE 7 (I.E., EMBODIMENT OF FIG. 14)
The reproducing apparatus shown in FIG. 9 was used. Despite of this
fact, the image retainer 1 was prepared by forming a transparent
insulating film having a thickness of 10 .mu.m on an .alpha.-Si
photosensitive layer having a thickness of 10 .mu.m and had a
circumferential speed of 180 mm/sec. The image retainer 1 thus
prepared was charged with a voltage of +700 V by the primary
charger 2, while being uniformly exposed to the lamp 2a like the
Example 5, and was then charged with a voltage of 0 V by the
secondary charger 3'. This charged surface was subjected to a
writing operation by the laser beam scanner like the Example 5. The
electrostatic image thus obtained had a potential of +300 V with
respect to the background portion potential of 0 V. The resultant
electrostatic image was developed by the developing means 5 under
the same conditions as those of the Example 5 except that a voltage
composed of a d.c. component of 100 V and an a.c. component of 500
Hz and 400 V was applied to the developing sleeve. A second
development was conducted by the developing means 6 using the same
developer as that of the Example 5 and under the same conditions as
those of the developing means 5 by executing the primary and
secondary charging operations and the image exposure under the same
conditions as those of the first development after the charge
eliminating means 13 had been operated to eliminate the charges
(although this charge eliminating step might be omitted). Third and
fourth developments were repeated in the same manner as that of the
second one by means of the developing means 7 and 8, respectively.
The developers of the developing means 7 and 8 were the same as
those of the Example 5, respectively. Although substantially
unnecessary for practical purposes, however, the change of the
conditions of the voltage to be applied to the developing sleeve
was conducted like the Example 6 in accordance with the potential
change, the developing characteristics and the color reproductivity
of the image retainer 1. Thus, the color image reproducing
operations were completed like the Example 5.
The reproducing image thus obtained was remarkably clear like the
Example 5.
EXAMPLE 8 (I.E., EMBODIMENT OF FIG. 15)
The reproducing apparatus shown in FIG. 9 was used. Despite of this
fact, the image retainer 1 was prepared by forming a transparent
insulating film having a thickness of 10 .mu.m on an .alpha.-Si
photosensitive layer having a thickness of 10 .mu.m and had a
circumferential speed of 180 mm/sec. The image retainer 1 thus
prepared was charged with a voltage of -700 V by the primary
charger 2, while being uniformly exposed to the lamp 2a like the
Example 5, and was then charged with a voltage of +300 V by the
secondary charger 3'. This charged surface was subjected to a slit
exposure through the blue filter of an ordinary color reproducing
machine. As a result, there was obtained at a potential of +300 V
an electrostatic image which corresponds to the unexposed portion
with respect to the background portion of 50 V corresponding to the
exposed portion. The resultant electrostatic image was developed by
the developing means 5 under the same conditions as those of the
Example 5 except that a voltage composed of a d.c. component of 50
V and an a.c. component of 500 Hz and 400 V was applied to the
developing sleeve. A second development was conducted by the
developing means 6 using the same developer as that of the Example
5 and under the same conditions as those of the developing means 5
by executing the primary and secondary charging operations and the
image exposure through a green filter under the same conditions as
those of the first development after the charge eliminating means
13 had been operated to eliminate the charges (although this charge
eliminating step might be omitted). Third and fourth developments
were repeated in the same manner as that of the second one but by
changing the exposing filters into a red filter and an neutral
filter, respectively, to form an electrostatic image, and this
electrostatic image was developed by means of the developing means
7 and 8, respectively. The developers of the developing means 7 and
8 were the same as those of the Example 5, respectively. Although
substantially unnecessary for practical purposes, however, the
change of the conditions of the voltage to be applied to the
developing sleeve was conducted like the Example 6 in accordance
with the potential change, the developing characteristics and the
color reproductivity of the image retainer 1. Thus, the color image
reproducing operations were completed like the Example 5.
The reproduced image thus obtained was remarkably clear like the
Example 5.
EXAMPLE 9 (I.E., EMBODIMENT OF FIG. 16)
The reproducing apparatus shown in FIG. 9 was used. Despite of this
fact, the image retainer 1 was prepared by forming a transparent
insulating film having a thickness of 10 .mu.m on an .alpha.-Si
photosensitive layer having a thickness of 10 .mu.m and had a
circumferential speed of 180 mm/sec. The image retainer 1 thus
prepared was charged with a voltage of +700 V by the primary
charger 2, while being uniformly exposed to the lamp
2a like the Example 5, and was then charged with a voltage of -100
V by the secondary charger 3'. This charged surface was
simultaneously subjected to a slit exposure through the blue filter
of an ordinary color reproducing machine, and then to a uniform
exposure. As a result, there was retained at a potential of +300 V
an electrostatic image which corresponds to the unexposed portion
with respect to the background portion of -100 V corresponding to
the exposed portion. The resultant electrostatic image was
developed by the developing means 5 under the same conditions as
those of the Example 5 except that a voltage composed of a d.c.
component of 0 V and an a.c. component of 500 Hz and 400 V was
applied to the developing sleeve. A second development was
conducted by the developing means 6 using the same developer as
that of the Example 5 and under the same conditions as those of the
developing means 5 by executing the primary and secondary charging
operations, the image exposure through a green filter, and the
uniform exposure under the same conditions as those of the first
development after the charge eliminating means 13 has been operated
to eliminate the charges (although this charge eliminating step
might be omitted). Third and fourth developments were repeated in
the same manner as that of the second one but by changing the
exposing filters into a red filter and an neutral filter,
respectively, to form an electrostatic image, and this
electrostatic image was developed by means of the developing means
7 and 8, respectively. The developers in the developing means 7 and
8 were the same as those of the Example 5, respectively. Although
substantially unnecessary for practical purposes, however, the
change of the conditions of the voltage to be applied to the
developing sleeve was conducted like the Example 6 in accordance
with the potential change, the developing characteristics and the
color reproductivity of the image retainer 1. Thus, the color image
reproducing operations were completed like the Example 5.
The reproduced image thus obtained was remarkably clear like the
Example 5.
EXAMPLE 10 (I.E., EMBODIMENT OF FIG. 17)
The reproducing apparatus shown in FIG. 9 was used. Despite of this
fact, the image retainer 1 was prepared by forming a transparent
insulating film having a thickness of 10 .mu.m on an .alpha.-Si
photosensitive layer having a thickness of 10 .mu.m and had a
circumferential speed of 180 mm/sec. The image retainer 1 thus
prepared was charged with a voltage of -700 V by the primary
charger 2, while being uniformly exposed to the lamp 2a like the
Example 5, and was then charged with a voltage of +300 V by the
secondary charger 3'. Simultaneously with this secondary charging
operation, the charged surface was subjected to a writing operation
by means of the laser beam scanner and then to a uniform exposure.
As a result, there was retained at a potential of +300 V an
electrostatic image which corresponds to the exposed portion with
respect to the background portion of -100 V corresponding to the
unexposed portion. The resultant electrostatic image was developed
by the developing means 5 under the same conditions as those of the
Example 5 except that a voltage composed of a d.c. component of 50
V and an a.c. component of 500 Hz and 400 V was applied to the
developing sleeve. A second development was conducted by the
developing means 6 using the same developer as that of the Example
5 and under the same conditions as those of the developing means 5
by executing the primary and secondary charging operations, the
image exposure, and the uniform exposure under the same conditions
as those of the first development after the charge eliminating
means 13 had been operated to eliminate the charges. Third and
fourth developments were repeated in the same manner as that of the
second one, and this electrostatic image was developed by means of
the developing means 7 and 8, respectively. The developers in the
developing means 7 and 8 were the same as those of the Example 6,
respectively. Although substantially unnecessary for practical
purposes, however, the change of the conditions of the voltage to
be applied to the developing sleeve was conducted like the Example
6 in accordance with the potential change, the developing
characteristics and the color reproductivity of the image retainer
1. Thus, the color image reproducing operations were completed like
the Example 5.
The reproduced image thus obtained was remarkably clear like the
Example 5.
According to the Examples of the present invention thus far
described, it is possible to change the potentials and polarities
of the electrostatic images in dependence upon the relative
strengths of the primary and secondary charging operations and to
easily conduct the positive or negative exposure. It is also
possible to superpose the developers under the non-contact jumping
developing conditions and especially to make the electrostatic
images and the developers have opposite polarities. As a result,
the developers are easily applied to the electrostatic images so
that the adjustment of the developing conditions of the image
retainer for the changes in the potential can be facilitated to
reproduce a color image having a sufficient density and an
excellent clearness while having little scattering of the
developers. Since the common charger and image exposing ray
producing means are used for each retention of the electrostatic
images, moreover, there can be attained an effect that the
recording apparatus can be reduced in size and cost without being
troubled by registration.
Incidentally, the present invention can be applied to such an image
retainer as is applied to a base, as in electrofax paper, and that
the color image retained thereon is not transferred but fixed. In
this case, the pre-transfer lamp, the transfer means, the cleaning
means and so on can be dispensed with. It is true but the
pre-transfer lamp 10 and the charge eliminating means 15 can be
omitted in the case of the transfer, and this transfer may be
conducted not only the corona transfer one but also a bias roller
one, an adhesion transfer, a direct pressure one or on using an
intermediate transfer member, whereas the fixture should not be
limited to the heat roller.
On the other hand, it is a great advantage that the polarities of
the potentials of the latent images of the image portion and the
non-image portion can be reversed by the balance in the strength
between the primary and secondary charging operations. Even if the
polarities are common, however, the development can naturally be
conducted by changing the developing bias conditions. As to the
potentials at this time, the relationship, in which the zero
potential in FIGS. 12 to 17 is shifted up or down, holds as it is.
A similar development can be conducted if the developing bias is
accordingly changed.
FIGS. 18 to 21 show other embodiments of the method of the present
invention. Incidentally, FIGS. 18 to 21 all show the steps after
the second development has already been conducted.
FIG. 18 shows the embodiment of the reproducing method of the
present invention, comprising the steps of: uniformly subjecting
the surface of the image retainer 1 in the initial state, which has
had its charges eliminated by the charge eliminating means 13 of
the reproducing apparatus of FIG. 1 and has been cleaned by the
cleaning means 14 to have a zero potential, to a first charging
operation by means of the charger 2; subjecting the charged surface
to a first image exposure of different color by the image exposing
means 4, as shown in FIG. 2, to retain an electrostatic image in
which the potential of the exposed portion PH is dropped with
respect to the background potential of the unexposed portion DA;
firstly developing the electrostatic image by any one of the
developing means 5 to 8, which uses as its developer the color
toner corresponding to the first image exposure, so that the
potential of the electrostatic image by the first image exposure is
elevated up to the background potential as a result that the color
toner having been frictionally charged with the same polarity as
that of the charges of the image retainer 1 is applied; secondly
charging the image retainer 1 uniformly again at the second
rotation by means of the charger 2 with or without the charge
elimination by the charge eliminating means 13, because that
portion cannot retain the electrostatic image even if it is
subjected again to the image exposure; conducting a second image
exposure by the same image exposing means 4 as the previous one
with the same spot density as that of the previous image exposure
and in a manner that the positions are superposed at least
partially; subsequently conducting a second development by another
development means using as its developer the color toner
corresponding to the second image exposure; subsequently repeating
in a like manner third and fourth charging operations and image
exposures to retain a color image having a plurality of color toner
images superposed on the image retainer 1; operating one or both of
the pre-transfer charger 9 and the pre-transfer exposing lamp 10,
if necessary, from the step at which the fourth development is
conducted to the step as which the color image finishes its
passage; transferring the color image by the transfer means 11 to
the recording member P being fed in synchronism with the rotations
of the image retainer 1; fixing the color image transferred to the
recording member P by the fixing means 12; eliminating the charges
from the surface of the image retainer 1, from which the color
image has been transferred, by the charge eliminating means 13; and
cleaning the image retainer 1 by the cleaning means 14 until the
initial state is restored, thus completing the one cycle of the
color image reproduction. Thus, by conducting the image exposure of
each time such that the spot positions are superposed at least
partially, it is possible to prevent the color image retained from
having its picture element density dropped so that the color image
can be reproduced densely and finely in its colors. Incidentally,
the retention of such an electrostatic image by the second image
exposure at a position different from that having previously
trapped the toner T as has a lower potential at its exposed portion
PH that the background potential at its unexposed portion DA is
intended to shown the case in which the color image has in that
particular position none of the picture elements of the color of
the toner T. Indicated at reference letter T' is the toner which
has been applied at the second development. Although FIG. 18 shows
the case in which the spot positions of the image exposures of the
respective times are completely superposed, the spot positions may
be partially superposed. In the method of the present invention,
moreover, since the retentions of the electrostatic images at the
respective times can be conducted by the common apparatus, as has
been described hereinbefore, the reproducing apparatus can be
conducted in a small size and at a low cost, and the synchronous
control of the image exposure can be easily conducted.
FIG. 19 shows the embodiment of the present invention, which is the
same as the embodiment of FIG. 18 until the first development but
different therefrom in that, after the first development, the
surface of the image retainer 1 is either secondly charged by the
charger, after it has been uniformly exposed by the pre-transfer
exposing lamp 10 or the charge eliminating lamp of the charge
eliminating means 13, or uniformly but weakly exposed by means of
the exposing lamp 3 after it has been secondly charged by the
charger 2, so that the electrostatic image retainer portion having
trapped the previous toner T is made to have such a slightly higher
potential than that of the background portion that it is liable to
retain the electrostatic image, whereupon, like the embodiment of
FIG. 18, the second image exposure and the second development are
executed, followed by repeating the third and fourth image
exposures and developments in a similar manner to retain the color
image. The embodiment of FIG. 19 is suitable in case it is
undesirable to apply the subsequent toner T' to the previous toner
T. Generally speaking, more specifically, most of the images are
required to have a reproductivity of black letters. According to
the method being described, the light is not passed fully at the
subsequent writing and the color toner to be subsequently applied
in a superposed manner can be prevented from being applied by
firstly conducting the writing operation of a black letter portion
so that the vagueness of colors and the shift of positions can be
prevented. Thus, it is possible to obtain an image in which a
preferential color is stressed. In combination with the embodiment
of FIG. 18, on the other hand, an image of the selected color can
be stressed or weakened. It is quite natural that the charge
eliminating step and the charging step can be introduced after the
first development and after the subsequent process is entered.
FIGS. 20 and 21 show the embodiments of the present invention,
which are improved in the problem of mixing by applying the
subsequent toner T' in a manner to surround the previous toner T,
because the mixing state of a color toner is changed in dependence
upon the fixing method or the color superposing order to change the
color balance if the subsequent toner T' is superposed upon the
previous toner T. The embodiments of FIGS. 20 and 21 correspond to
those of FIGS. 18 and 19, respectively, but are different therefrom
in that the spot of the second image exposing ray, i.e, the
subsequent image exposing ray is made so large by the image
exposing means 4, i.e., by means of the lens 27 of the laser beam
scanner of FIG. 2 as to enclose the spot of the first image
exposing ray, i.e., the previous image exposing ray. Incidentally,
the boundaries between the unexposed portion DA and the exposed
portion pH in the second image exposure are shown in two ways,
i.e., the upper portion shows the spot of the second image exposing
ray, and the lower portion shows the exposing area shield by the
center toner image. In the embodiments of FIGS. 20 and 21, too, the
color image retained can be prevented from having its picture
element density dropped so that it can have its colors retained
densely and finely, and the problem of toner mixing is eliminated
so that a color image having clearer colors can be retained in the
embodiments of FIGS. 20 and 21. Especially in the embodiment of
FIG. 21, as compared with the embodiment of FIG. 20, the portion,
in which the previous spot and the subsequent spot are superposed,
does not trap or is reluctant to trap the subsequent toner T' on
the previous toner T thereby to prevent the toners T and T' from
being mixed to exhibit a mixed color at the portion having the
spots superposed because the subsequent toner T' is applied only
around the previous spot, so that a beautiful blended color can be
attained.
Incidentally, in the embodiments of FIGS. 18 and 19, the toners are
mixed so that the color developing sequence exerts great influence
upon the clearness of the color image. It is, therefore, important
to determine the sequence of the developments. In the embodiments
of FIGS. 20 and 21, however, the importance of the developing order
is not so high as that of the embodiments of FIGS. 18 and 19.
Despite of this fact, how the colors are arranged from the central
portion to the outer side still influences upon the tone of the
color image.
The foregoing are the embodiments in which all the developments by
the developing means 5 to 8 are conducted by the developing method
of applying the toner charged with the same polarity as that of the
background potential to the electrostatic image corresponding to
the exposed portion having a lower potential than that of the
background potential. According to the reproducing apparatus shown
in FIG. 9, however, the developments of the method of the present
invention can be conducted by the developing method of applying the
toner charged with the polarity opposite to that of the
electrostatic image to the electrostatic image.
FIG. 22 shows the embodiment of the reproducing method of the
present invention, comprising the steps of: subjecting like the
above embodiment the surface of the image retainer 1, which has had
its charges eliminated by the charge eliminating means 13 of the
reproducing apparatus of FIG. 9 and has been cleaned by the
cleaning means 14 to have a zero potential, to a primary charging
operation by means of the charger 2; subjecting the surface to a
secondary charging operation by means of the secondary charger 3';
subsequently subjecting the charged surface to a first image
exposure by the image exposing means 4 like that of FIG. 2; firstly
developing the electrostatic image, in which the absolute value of
the potential of the exposed portion pH retained is higher than the
background potential of the unexposed portion DA, by that one of
the developing means 5 to 8, which uses as its developer the toner
for effecting the changing operation with a polarity opposite to
that of the electrostatic image of the color corresponding to the
first image exposure, so that the surface potential of the
electrostatic image retaining portion is dropped by the toner
having the opposite polarity applied; discharging again the surface
of the image retainer 1 before the image exposure at the second
rotation by means of the second charger 3' to retain the
electrostatic image in the
previously developed electrostatic image retaining portion, too;
conducting again a second image exposure by the same image exposing
means 4 as the previous one with the same spot density as that of
the previous image exposure and in a manner that the positions are
superposed at least partially; subsequently conducting a
development by another developing means using as its developer the
color toner corresponding to the second image exposure having the
same charging characteristics as those of the first development;
subsequently repeating in a like manner third and fourth
electrostatic image retentions and developments, thus completing
the one cycle of the color image reproduction like the embodiments
of FIGS. 18 to 21 after the color image has been retained.
According to this embodiment, all the developments are conducted by
applying the toners for charging the electrostatic images with an
opposite polarity so that the control of the developing densities
of the respective colors is easier than the embodiments of FIGS. 18
to 21.
FIG. 23 shows an embodiment of the present invention, which is
different from the embodiment of FIG. 22 in that not only the
secondary charging operation by the secondary charger 3' is
conducted but also the primary charging operation is conducted
beforehand by the primary charger 2 during the time period between
the first development and the second image exposure, and in that
the charge elimination is also conducted by the charge eliminating
means 13 prior to the primary charging operation. According to the
embodiment of FIG. 23, it becomes possible to apply the toner T' in
the same density to the toner T having been previously applied.
FIGS. 24 and 25 show embodiments of the method of the present
invention, which are different from the embodiments of FIGS. 22 and
23 in that the second image exposure is conducted in a manner to
change the spot diameter like the embodiments of FIGS. 20 and 21.
According to the embodiments of FIGS. 24 and 25, there can be
attained a result that the vagueness due to the color mixing can be
eliminated like the embodiments of FIGS. 10 and 21.
Next, the embodiments of FIGS. 18 to 21 and FIGS. 22 to 25 thus far
described will be described in more detail in the following as
Examples 11 to 18, respectively.
EXAMPLE 11
The reproducing apparatus of FIG. 1 was used. However, the exposing
lamp 3 was not used, but the image retainer 1 had a photosensitive
surface layer of Se and a circumferential speed of 180 mm/sec. This
image retainer 1 has its surface charged to +500 V by means of the
charger 2 using the scorotron corona discharger, and the charged
surface was subjected to a first image exposure in a density of 16
spots/mm by means of the laser beam scanner of FIG. 2 using the
He-Ne laser.
As a result, there was retained in the image retainer 1 an
electrostatic image which had a background potential of +500 V but
an exposed portion potential of +30 V. The resultant electrostatic
image was subjected to a first development by the developing means
5 shown in FIG. 3.
The developing means 5 used the developer, which was composed of: a
carrier prepared by dispersing and containing 50 wt. % of magnetite
in a resin to have an average particle diameter of 30 .mu.m, a
magnetization of 30 emu/g and a resistivity of 10.sup.14 .OMEGA. cm
or higher; and a non-magnetic toner prepared by adding 10 wt. parts
of a benzine derivative as the yellow pigment and another charge
controlling agent to the styrene-acryl resin to have an average
particle diameter of 10 .mu.m, under a condition that the ratio of
the toner to the carrier was 20 wt. %. Moreover, the non-contact
jumping developing condition was resorted to, under which the
developing sleeve 31 had an external diameter of 30 mm and a number
of revolutions of 100 r.p.m., under which the magnet 32 has its N
and S magnetic poles of a magnetic flux density of 1,000 gausses
and a number of revolutions of 1,000 r.p.m., under which the layer
of the developer in the developed region had a thickness of 0.7 mm,
under which the gap between the developing sleeve 31 and the image
retainer 1 was 0.8 mm, and under which a superposed voltage
containing a d.c. voltage of +400 V and an a.c. voltage of 1.5 kHz
and 1,000 V was applied to the developing sleeve 31.
While the developing image was being developed by the developing
means 5, the remaining developing means 6 to 8, as shown in FIG. 3,
were held in their undeveloping state. This was achieved by
disconnecting the developing sleeve 31 from the power supply 39
into its floating state, by grounding the same to the earth, or by
positively applying the d.c. bias voltage, which had the polarity
opposite to that of the charge of the image retainer 1 i.e., the
opposite polarity to the charge of the toner, to the developing
sleeve 31. Of these, it is preferred to apply the d.c. bias
voltage. Since the developing means 6 to 8 were made to conduct
their developments under the non-contact jumping developing
condition like the developing means 5 it was not necessary to
especially eliminate the layer of the developer from the developing
sleeve 31. Of those developing means 6 to 8: the developing means 6
used a developer which was prepared by replacing the toner of the
developer of the developing means 5 by a toner containing
polytungstate as the .[.Magenta.]. .Iadd.magenta .Iaddend.pigment
in place of the yellow pigment; the developer 7 used a developer
which was prepared by replacing the same toner by a toner
containing copper phthalocyanine as the cyan pigment; and the
developing means 8 used a developer which was prepared by replacing
the same toner by a toner containing carbon black as the black
pigment. It is quite natural that a toner containing other pigment
and dye could be used as the color toner, and that, as has been
touched hereinbefore, the sequence of the colors to be developed
and accordingly the sequence of the developing means could be
suitably selected.
The surface of the image retainer 1 thus having been subjected to
the first development was subjected, after it had been secondly
charged with +500 V at the second rotation by means of the charger
2 while the pre-transfer exposing lamp 10 being operated but the
charge eliminating means 13 and the cleaning means 14 being left
inoperative, to a second image exposure again in the superposed
spot positions and in the same spot density by means of the same
laser beam scanner and then to a second development using the
.[.Magenta.]. .Iadd.magenta .Iaddend.toner by the developing means
6. Likewise, a third development using the cyan toner by the
developing means 7 and a fourth development using the black toner
by the development means 8 were repeated. In each of the
developments, incidentally, the developing density of each color
can be adjusted in accordance with the changes of the surface
potential of the image retainer 1, the developing characteristics,
the color reproductivity and so on by changing the d.c. bias
components and the amplitude and frequency of the voltage to be
applied to the developing sleeve 31, and the selecting time of the
time selecting conversion.
After the fourth development was conducted so that the four-color
image was retained on the image retainer 1, it was made liable to
be transferred by the pre-transfer charger 9 and the pre-transfer
exposing lamp 10 so that it was transferred to the recording member
P by the transfer means 11 until it was fixed by the fixing means
12. The image retainer 1 having the color image transferred thereto
had its charges eliminated by the charge eliminating means 13 and
its surface cleared of the residual toners by its abutment against
the cleaning blade or fur brush of the cleaning means 14. The one
cycle of the color image reproduction was completely ended at the
time when the surface having retained the color image therein
passes over the cleaning means 14.
The color image thus reproduced had the vagueness in color due to
the color mixing but had a high density of spot picture elements
and a finely expressed pattern.
EXAMPLE 12
The same reproducing apparatus of FIG. 1 as that of the Example 11
was used. In this case, however, the apparatus is equipped with the
exposing lamp 3. And, a first development was conducted under
absolutely the same conditions as those of the Example 11 except
that a superposed voltage of a d.c. voltage of +40 V and an a.c.
voltage of 2 kHz and 1,000 V was applied in the development to the
developing sleeve 31. Next, at the second rotation, the surface of
the image retainer 1 having been subjected to the first development
was secondly charged with +600 V by means of the charging means 2
and was then subjected to a uniformly and weak exposure by the
exposing means 3 to take a surface potential of +500 V. As a
result, the surface potential of the portion having trapped the
toner T by the first development came into a slightly higher state
than +500 V. Therefore, this image retainer 1 had its surface
subjected to a second image exposure and a second development like
the Example 11. The exposure, uniform and weak exposure and
development described above were repeated thirdly and fourthly
thereby to conduct the color image reproduction like the Example
11.
The color image thus reproduced was finely expressed not
differently of that of the Example 11 except that the tone of the
mixed-color portion is stressed slightly better in its previously
color than that of the Example 11.
Incidentally, in this Example, too, similar effects can be attained
even if the charging operation is conducted by means of the charger
2 after a uniform exposure using the pre-transfer exposing lamp 10
or the exposing lamp of the charge eliminating means 13 in place of
the charging operation and the uniform and weak exposure.
EXAMPLE 13
The same reproducing apparatus as that of the Example 11 was used.
The reproduction of a color image was conducted absolutely similar
to the Example 11 except that a first image exposure using a spot
having a diameter of 20 .mu.m, a second image exposure using a spot
having a diameter of 30 .mu.m, a third image exposure using a spot
having a diameter of 40 .mu.m, and a fourth image exposure using a
spot having a diameter of 50 .mu.m in the same spot position and in
the same density of 16 spots/mm were conducted by the switching
operation of the lens 27 of the laser beam scanner thereby to
retain an electrostatic image having a potential of +50 V with
respect to the background potential of +600 V, that a superposed
voltage of a d.c. voltage of +450 V and an a.c. voltage of 1.5 kHz
and 1,000 V was applied for the development to the developing
sleeve 31, and that the colors were superposed in the order of the
black, cyan, red and yellow toners.
The color image thus reproduced was substantially cleared of any
vagueness by the color mixing so that it has a fine and clear
tone.
Incidentally, in this Example, an identical color image could be
attained even if the charging operation between the first
development and the second image exposure, i.e., the charging
operation between the previous development and the subsequent image
exposure was omitted.
EXAMPLE 14
The same reproducing apparatus as that of the Example 12 was used.
The reproduction of a color image was conducted under absolutely
the same conditions as those of the Example 12 except that the
image exposures were conducted in the same manner as the Example 13
to retain the same electrostatic image, and that a superposed
voltage of a d.c. voltage of 30 .[.450.]. V and an a.c. voltage of
2 kHz and 500 V was applied for the development to the developing
sleeve 31.
The color image thus reproduced had a fine and clear color tone
which was hardly different from that of the Example 13.
EXAMPLE 15
The reproducing apparatus of FIG. 9 was used. The image retainer 1
was prepared by laying a transparent insulating surface layer
having a thickness of 20 .mu.m on a photosensitive layer of CdS
having a thickness of 30 .mu.m, and had a circumferential speed of
180 m/sec. The image retainer 1 thus prepared was primarily charged
to have a surface potential of +1,000 V by means of the d.c.
scorotron corona discharger while being uniformly exposed by the
exposing lamp of the primary charger 2. Next, the image retainer 1
was charged to have a surface potential of -100 V by means of the
secondary charger 3' which is constructed of the scorotron corona
discharger having an a.c. component. The resultant charged surface
was subjected to a first image exposure in a density of 16 spots/mm
by means of the laser beam scanner of FIG. 2 using the He-Ne laser
to retain an electrostatic image exhibiting a potential of +200 V
with respect to the background potential of -100 V. The resultant
electrostatic image was firstly developed by the developing means 5
under the same conditions as those of the Example 11 except that
only an a.c. voltage component of 1.5 kHz and .[.1.000.].
.Iadd.1,000 .Iaddend.V was applied to the developing sleeve 31, and
that the charging polarity of the toner was opposite to that of the
electrostatic image. In this Example, moreover, a second image
exposure and a second development were conducted like the Example
11 after a secondary charging operation by the secondary charger 3'
was conducted again at the second rotation of the image retainer 1.
Likewise, a secondary charging operation, an image exposure and a
development were subsequently repeated thirdly and fourthly, and
reproduction of the color image was then conducted like the Example
11.
Since, in this Example, the developments were effected by the
coulomb attractive force, the density adjustment of the color image
reproduced could be conducted more easily than the cases of the
Examples 11 to 14, by which the toners for charging in the same
polarity were applied to the electrostatic image, so that the color
image obtained had the same color tone as that by the Example
11.
EXAMPLE 16
The reproduction of a color image was conducted under the same
conditions as those of the Example 15 except that the image
retainer 1 was prepared by placing a transparent insulating surface
layer having a thickness of 10 .mu.m on an .alpha.-Si
photosensitive layer having a thickness of 10 .mu.m, that a primary
charging operation was effected to +700 V by means of the primary
charger 2, that a secondary charging operation was effected to 0 V
by the secondary charger 3' to retain electrostatic images, the
first one of which had a potential of +300 V and the second and
later of which had a similar potential with respect to the
background potential of 0 V, in the image exposures by the laser
beam scanner, that the voltage to be applied to the developing
sleeve 31 for the development was a superposed one composed of a
d.c. voltage of +100 V and an a.c. one of 500 Hz and 400 V, and
that a charge elimination by the charge eliminating means 13, the
primary charging operation by the primary charger 2, and the
secondary charging operation by the secondary charger 3' were
conducted prior to the second and later image exposures.
In this Example, the color tone of the color image reproduced wire
similar to that of the Example 11, and the densities of the
respective colors could be better adjusted.
EXAMPLE 17
The reproduction of the color image was conducted under absolutely
the same conditions as those of the Example 15 except that the
image exposure by the laser beam scanner was conducted, like the
Example 13, firstly with a spot having a diameter of 20 .mu.m,
secondly with a spot having a diameter of 30 .mu.m, thirdly with a
spot having a diameter of 40 .mu.m, and fourthly with a spot having
a diameter of 50 .mu.m, in the same spot position and in the same
density of 16 spots/mm to retain an electrostatic image having a
potential of +400 V with respect to the background potential of
-100 V, and that the colors were superposed in the order of the
black, cyan, red and yellow toners.
The color image thus reproduced had a color tone similar to that by
the Example 13 but had a clearer tone.
In this Example, too, the density adjustments of the respective
colors could naturally be easily effected.
EXAMPLE 18
The reproduction of the color image was conducted under absolutely
the same conditions of those of the Example 16 except that the
image exposure by the laser beam scanner used the same spot and
spot density as those of the Example 17 to retain an electrostatic
image having a potential of +300 V at each time with respect to the
background potential of 0 V.
The color image thus reproduced was substantially the same as that
by the
Example 17.
In this Example, too, the density adjustments of the respective
colors could naturally be easily effected.
According to the Examples of the present invention thus far
described, it is possible to make the spot densities fine thereby
to reproduce a fine color image and to prevent any color mixing
thereby to reproduce a color image having a clear color tone. Since
the retentions of the electrostatic images are conducted by the
common apparatus, moreover, there can be attained excellent effects
that the reproducing apparatus can be constructed in a small size
and at a low cost, and that the synchronous control of the image
exposure as to the image retainer is facilitated.
Incidentally, the present invention can be applied to the case, in
which the image retainer has a belt or sheet shape, or to such an
image retainer, e.g., electrofax paper as is placed on a base as
can fix without any transfer the color image retained thereon by
the toners. In this case, it is highly necessary to consider the
superposing sequence of the color toners, but there arises an
advantage that the pre-transfer lamp, the transfer means and the
cleaning means can be dispensed with. Despite of this fact, the
pre-transfer lamp and the charge eliminating means can be omitted
in case the toners have predetermined polarities and quantities of
charges so that they can be transferred. On the other hand, the
transfer may be not only the corona type but also a bias roller
type, an adhesion type and a pressure type through an intermediate
transfer member. It is quite natural that the fixing operation
should not be limited to a heat roller type.
The methods of the Examples 15 to 18 according to the present
invention are highly advantageous in that the polarities of the
potentials at the image portion and the non-image portion can be
reversed by the balance between the strengths of the primary and
secondary charging operations. However, the development can be
effected even by using the same polarities and by changing the
developing bias conditions. As to the potentials at this time,
there holds as it is the relationship in which the zero potential
of FIGS. 21 to 23 is shifted up and down. If the developing bias is
accordingly changed, a like development can be made. Moreover,
those methods can naturally be applied even to the NP- or
KIP-method.
FIGS. 26 and 27 are schematic views showing the constructions of
the embodiments of the reproducing apparatus which are used for the
method of the present invention, respectively. FIGS. 28 to 30 are
flow charts for the method of the present invention,
respectively.
In FIG. 26, reference numeral 41 indicates a drum-shaped image
retainer which is constructed by laying a dielectric layer such as
a resin on a metal base and which is made rotatable in the
direction of arrow, and numeral 43 indicates an electrostatic
recording head which is equipped with needle discharge poles. The
remaining portions are identical to those of the example of FIG.
1.
The pre-transfer charger 9 may be omitted in case the transfer can
be sufficiently effected merely by the transfer means 11. The
electrostatic recording head 43 is used to form an electrostatic
image having a charged spot distribution on the dielectric layer of
the image retainer 41 by means of the needle discharge poles which
are arrayed in one or plural rows.
Of the toners: the black toner is similar to that of the
two-component developer of the prior art; the cyan toner is
prepared by adding copper phthalocyanine in place of carbon black
having a black color; the Magenta is prepared by similarly adding
polytungstophosphate; and the yellow toner is prepared by similarly
adding a benzidine derivative. However, those toners should not be
limited to those color toners made of such pigments, but it is
naturally possible to use color toners made of dyes and to add an
electrification controlling agent or the like, if necessary. On the
other hand, the sequence of the colors to be developed by the
developing means 5 to 8 using the developers of different color
toners has to be carefully determined because it exerts influences
upon the tone of the color image.
The method of the present invention can be practised by the
reproducing apparatus of FIG. 26 described above but can also be
carried out by the reproducing apparatus shown in FIG. 27.
The reproducing apparatus of FIG. 27 is one in which a series of
recording members are formed with dielectric layers on their
surfaces to provide an image retainer 41'. The retentions and
developments of electrostatic images are repeated while the image
retainer 31' is being linearly conveyed. Along the conveyor passage
of the image retainer 41', the prewriting charger 2, the
electrostatic recording head 43 and the developing means 5 to 8 are
repeatedly arranged side by side, and the fixing means 12 for
fixing the color image to the image retainer 41' is disposed at the
last position. The reproducing apparatus under consideration does
not require the pretransfer charger, the transfer means, the charge
eliminating means and the cleaning means but can reproduce a series
of color images. In order that the image retainer 41' may not
depend, however, it is necessary to strengthen the tension or to
provide such a supporting roller midway as to prevent the toners
applied to the image retainer 41' from being offset, although not
shown.
In the reproducing apparatus shown in FIG. 26, too, the
pre-transfer charger 9, the transfer means 11, the charge
eliminating means 13 and the cleaning means 14 can be dispensed
with if the image retainer 41 is prepared by rolling an image
retainer similar to the image retainer 41', which is used in the
reproducing apparatus of FIG. 27, on a drum.
The method of the present invention, as is exemplified by the
embodiments of FIGS. 28 to 30, can be practised by the reproducing
apparatus thus far described. Incidentally, FIGS. 28 to 30 all show
the steps after a second development has been finished.
The embodiment of FIG. 28 shows the method of the present
invention, comprising the steps of: subjecting the surface of the
image retainer 41 to a first writing operation by means of the
electrostatic recording head 43, either from the initial state
(which is shown to be a charged state), in which the surface of the
image retainer 41 has its charges eliminated by one or both of the
charge eliminating means 13 and 13, cleaned by the cleaning means
14 and charged to be positive or negative by the pre-writing
charger 2, if necessary, according to the reproducing apparatus of
FIG. 26 or from the initial state, in which the image retainer 41'
is conveyed from the left and charged to be negative or positive by
the first pre-writing charger 2, if necessary, according to the
reproducing apparatus of FIG. 27, thereby to retain an
electrostatic image at a potential having a polarity different from
that of the background potential; firstly developing that
electrostatic image by the developing means 5; conducting a second
writing operation by the electrostatic recording head 43 after the
uniform charging operation by the charger 2, if necessary, either
when the image retainer 41 comes into its second rotation,
according to the reproducing apparatus of FIG. 26, or when the
image retainer 41' advances to the position of the next charger,
according to the reproducing apparatus of FIG. 27; secondly
developing the electrostatic image thus retained by the developing
means 6; .[.subsequtnely.]. .Iadd.subsequently .Iaddend.repeating
third and fourth writing and developing operations in a similar
manner so that a color image having superposed color images is
retained on the image retainer 41 or 41'; and either fixing the
resultant color image to the recording member P by means of the
fixing means 12, after the color image has been made reluctant to
be transferred by the pretransfer charger 9 so that it is
transferred to the recording member P by the transfer means 11,
according to the reproducing apparatus of FIG. 26, or directly
fixing the same color image to the image retainer 41' by the fixing
means 12 according to the reproducing apparatus of FIG. 27.
According to the reproducing apparatus of FIG. 26, moreover, the
surface of the image retainer 41 thus having the color image
transferred thereto has its charges eliminated by the charge
eliminating means 13, and cleared of the residual toners by the
cleaning means 14, and further has its charge eliminated, if
necessary, by the charge eliminating means 13, thus ending one
cycle of the color image reproduction. According to the reproducing
apparatus of FIG. 27, on the other hand, the portion of the image
retainer 41', which has been formed with the color image, ends its
steps of reproducing the color image when it completely passes the
fixing means 12.
Moreover, the embodiment of FIG. 29 uses the reproducing apparatus
of FIG. 26 and is similar to that of FIG. 28 except that the image
retainer 41 having the toner images retained thereon has its
charges eliminated by the charge eliminating means 13 before a
subsequent image retaining stage is entered after each
development.
The embodiment of FIG. 30 resorts to the reproducing apparatus of
FIG. 26 and is different from that of FIG. 28 in that the
pre-writing charger 2 is operated before each writing
operation.
Incidentally, reference letters T and T' appearing in FIGS. 28 to
30 indicate toners of different colors, which are applied to the
image retainer 41 or 41'.
In the method of the present invention, the developing means other
than that conducting each development under the non-contact jumping
developing conditions can be easily held in an inoperative state,
even if the developer layer is not removed from the developing
sleeve 31, by disconnection of the developing sleeve 31 from the
power supply 39 into a floating state, by grounding the developing
sleeve 31 to the earth, or positively applying such a d.c. bias
voltage to the developing sleeve 31 as has a polarity identical to
that of the electrostatic image, i.e., opposite to that of the
charges of the toners. Of these, the application of the bias
voltage having the opposite polarity to that of the toners may be
preferably used to hold the developing means in the inoperative
state.
Next, the embodiment of FIGS. 28 to 30, which are practised by the
reproducing apparatus of FIG. 26, will be described in more detail
as the following Examples 19 to 21, respectively.
EXAMPLE 19
The reproducing apparatus shown in FIG. 26 was used. The image
retainer 41 was prepared by laying an insulating layer having a
thickness of 20 .mu.m on an aluminum base and had a circumferential
speed of 180 mm/sec. The image retainer 41 thus prepared had its
surface charged to -100 V by means of the pre-writing charger 2
using the scorotron corona discharger and then subjected to writing
operation in a distribution density of 10 spots/mm by means of the
electrostatic recording head 43 the needle electrodes of which had
their tips spaced by about 30 .mu.m from the surface of the image
retainer 41. As a result, there was retained on the image retainer
41 an electrostatic image which had a written portion potential of
+200 V with respect to the background portion potential of -100 V.
The resultant electrostatic image was firstly developed by the
developing means 6 shown in FIG. 3. This developing means 6 used
the developer, which was composed of: a carrier having 50 wt. % of
magnetite dispersed and contained in a resin and having an average
particle diameter of 20 .mu.m, a magnetization of 30 emu/g and a
resistivity of 10.sup.14 .OMEGA. or higher; and a nonmagnetic toner
prepared by adding 10 wt. % of copper phthalocyanine and another
electrification control agent as the cyan pigment to the
styrene-acryl resin and which had an average particle diameter of
10 .mu.m, under the condition of the ratio of 10 wt. % of the toner
to the carrier. Moreover, the non-contact jumping developing
conditions were resorted to under which the developing sleeve 31
had an external diameter of 30 mm and a number of revolutions of
100 r.p.m., under which the magnet 32 had a magnetic flux density
of its N and S magnetic poles of 1,000 gausses and a number of
revolutions of 1,000 r.p.m., under which the developer layer had a
thickness of 0.7 mm at its developed portion, under which the gap
between the developing sleeve 31 and the image retainer 1 was 0.8
mm, and under which a bias voltage having a d.c. voltage component
of 0 V and an a.c. voltage component of 1.5 kHz and 1,000 V was
applied to the developing sleeve.
The surface of the image retainer 41 having been firstly developed
was subjected to such a second writing operation with a spot
position shift from the first writing operation but in the same
spot density again by the same electrostatic recording head 43 but
without operating the pre-transfer charger 9, the charge
eliminating means 13 and 13, the cleaning means 14 and the
pre-writing charger 2 that the written portion took a potential of
+300 V. Next, a second development was conducted by the developing
means 6 under the same conditions as those of the developing means
5 except that the toner of the developer used one which was
prepared by adding polytungstophosphate as the Magenta pigment in
place of the cyan pigment, and that a bias voltage having a d.c.
voltage component of 100 V and an a.c. voltage component of 1.5 kHz
and 1,000 V was applied. Likewise, a third writing operation for
elevating the potential of the written portion to +400 V and a
third development were conducted by the developing means 7 under
the same conditions as those of the developing means 5 except that
the toner of the developer used one which was prepared by adding a
benzidine derivative as the yellow pigment, and that the developing
bias was composed of a d.c. component of 200 V and an a.c.
component of 1.5 kHz and 1,000 V. Moreover, a fourth writing
operation for raising the potential of the written portion to +500
V and a fourth development were conducted by the developing means 8
under the same conditions as those of the developing means 5 except
that the toner of the developer used one which was prepared by
adding carbon black as the black pigment, and that the developing
bias had a d.c. component of 300 V and an a.c. component of 1.5 kHz
and 600 V. The color image thus retained on the image retainer 41
was transferred to and fixed on the recording member P. Moreover,
the surface of the image retainer 41 thus having the color image
transferred thereto had its charges eliminated by the charge
eliminating means 13 and cleared of the residual toners by the
cleaning means 14.
The reproduced image thus obtained had little mixing of the color
toners and was a remarkably clear color image.
Incidentally, in this Example, the spot position of the subsequent
writing operation may be superposed of that of the previous writing
operation, or, the discharge voltage of the electrostatic recording
head 43, and the voltage value, frequency and selected time of the
d.c. or a.c. component of the volatage to be applied to the
developing sleeve may be so changed in the writing and/or
developing operations as to adjust the developed densities of the
respective colors. If the spot positions of the writing operations
are superposed, the color mixing occurs to make the colors liable
to be vague. However, the tone can be enhanced by increasing the
spot density. In this case, moreover, especially the sequence of
colors to be developed plays an important role. By adjusting the
developed densities of the respective colors in the manner thus far
described, moreover, it is possible to obtain a color image which
has a changed tone.
EXAMPLE 20
The color image reproduction was conducted by the use of the same
reproducing apparatus as that of the Example 19 and under the same
conditions as those of the Example 19 except that the charging
operation of the Example 19 by the pre-writing charger 2 prior to
the first writing operation was not conducted to form an
electrostatic image having a potential of +150 V with respect to
the background potential of 0 V by a first writing operation, that
a superposed voltage having a d.c. voltage of +50 V and an a.c.
voltage of 3 kHz and 2,000 V was applied as the bias voltage upon
the development to the developing sleeve 31, and that charge
elimination was conducted before second and later writing
operations by the charge eliminating means 13 to retain an
electrostatic image having a potential of +150 V with respect to
the background potential of 0 V even in the second and later
writing operations. The reproduced image thus obtained was a color
image having an excellent clearness like that of the Example
19.
EXAMPLE 21
The color image reproduction was conducted by the use of the same
reproducing apparatus as that of the Example 19 under the same
conditions of those of the Example 19 except that the charge of
-300 V was conducted by the pre-writing charger 2 so that an
electrostatic image having a
potential of +50 V with respect to the background potential of -300
V was retained by a first writing operation, that a superposed
voltage composed of a d.c. voltage of -200 V and an a.c. voltage of
2 kHz and 1 kV was applied as a bias for the development to the
developing sleeve 31, and that the pre-writing charger 2 was used
before second and later writing operations. The reproduced image
obtained was a color image having an excellent clearness like that
of the Example 19.
By using the image retaining means having its electrostatic
retainability and toner image retainability separated, according to
the foregoing Examples of the present invention, there can be
attained excellent effects that the color tone and so on of the
color image can be easily changed, and that the color image having
the excellent clearness and a high tone can be reproduced so that
the reproduction can be stably effected.
Incidentally, the present invention can be applied to the case, in
which the image retainer has a belt or sheet shape, or to such an
image retainer, e.g., electrofax paper as is placed on a base as
can fix without any transfer the color image retained thereon by
the toners. In this case, it is highly necessary to consider the
superposed order of the color toners, but there arises an advantage
that the pre-transfer lamp, the transfer means and the cleaning
means can be dispensed with. Despite of this fact, the pre-transfer
lamp and the charge eliminating means can be omitted in case the
toners have predetermined polarities and quantities of charges so
that they can be transferred. On the other hand, the transfer may
be not only the corona type but also a bias roller type, an
adhesion type and a pressure type through an intermediate transfer
member. It is quite natural that the fixing operation should not be
limited to a heat roller type.
Although the Examples of the present invention thus far described
used the electrostatic recording head as the writing means,
moreover, other means can be similarly used if it can retain the
electrostatic charge image on the dielectric layer. More
specifically, there can be likewise applied either a method in
which the passage rate of a corona ion flow is controlled by
control electrodes so that an electrostatic image may be retained
on the dielectric layer, or a method in which a screen
photosensitive member is used so that the electrostatic charge
pattern retained thereon may be used for controlling the passage
rate of the corona ion flow to retain the electrostatic image on
the dielectric layer.
Other Examples of the present invention will be described in the
following. In the method of consecutively superposing toner images
by repeating the step of retaining a latent image on an image
carrier and the step of developing the retained latent image, as
has been described as the prior art, a development in a suitable
density has to be conducted without disturbing the toner image
which was retained in the image carrier at the previous step. Here,
the term "superposition" means not only that the toner images are
formed plural times in an identical position of the developing
regions of the image carrier but also that the toner images are
retained in plural times in another portion of the image region.
The result of our investigations has revealed that an excellent
image cannot be obtained even if the values such as the gap d (mm)
(which may be simply called the "gap" in the following) between the
image carrier and a developer carrier and the voltage V.sub.AC and
frequency f of the a.c. component of the developing bias are
satisfied so as to satisfy the above-specified conditions, and that
those parameters have close relationships to each other. Therefore,
experiments have been conducted by the developing means 16, as
shown in FIG. 31, with the parameters such as the voltage and
frequency of the a.c. component of the developing bias being
changed, so that the results, as shown in FIGS. 32 and 33, have
been obtained. Incidentally, the toner image is previously formed
on the photosensitive drum 1 acting as the image carrier drum. The
developing means 16 carries a developer D in the direction of arrow
B on the circumference of the sleeve 31 to supply the developer D
to a developing region E as a result that the sleeve 31 acting as
the developer carrier and the magnetic roll 32 are rotated.
Incidentally, the developer D is a two-component developer composed
of a magnetic carrier and a non-magnetic toner. Said carrier is
composed of ball-shaped particles which have an average particle
diameter of 30 .mu.m (which is a weight-averaged value measured by
means of the Omnicon Alpha (manufactured by Bausch & Lomb Inc.)
or the .[.Caulter.]. .Iadd.Coulter .Iaddend.Counter (manufactured
by .[.Caulter.]. .Iadd.Coulter .Iaddend.Inc.), a magnetization of
50 emu/g and a resistivity of 10.sup.14 .OMEGA. or more and which
are coated with a resin. Incidentally, the resistivity is a value
which is obtained by reading out a current value when a load of 1
kg/cm.sup.2 is applied to the tapped particles so that the carrier
particles have a thickness of 1 mm after the particles have been
tapped in a container having an effective sectional area of 0.50
cm.sup.2 and when a voltage for establishing an electric field of
1,000 V/cm is applied between the load and the bottom electrodes.
Said toner is prepared by adding a small quantity of an
electrification controlling agent to 90 wt. % of a thermoplastic
resin and 10 wt. % of a pigment (e.g., Carbon Black) and by
blending and pulverizing the mixture so that the particles may have
an average particle diameter of 10 .mu.m. The developer D is
carried in the direction of arrow B by rotating the magnetic roll
32 in the direction of arrow A and the sleeve 31 in the direction
of the arrow B. The developer D has its thickness regulated in its
carrying course by means of the head regulating blade 33. A
developer reservoir 47 is equipped therein with an agitating screw
35 so that the developer D may be sufficiently agitated. When the
developer D in the developer reservoir 47 is consumed, its supply
is made from the toner hopper 37 by rotating the toner supply
roller 38.
Between the sleeve 31 and the photosensitive drum 1, moreover,
there is connected a d.c. power supply 45 for applying the
developing bias. In order that the developer D may be vibrated in
the developing region E to be sufficiently supplied to the
photosensitive drum 1, an a.c. power supply 46 is connected in
series with the d.c. power supply 45. Reference numeral 40 is the
protecting resistor.
FIG. 32 shows the relationship between the amplitude of the a.c.
component, when the gap d between the photosensitive drum 1 and the
sleeve 31 is set at 1.0 mm; the thickness of the developer at 0.5
mm; when the charged potential of the photosensitive drum at 600 V;
and the developing bias has its d.c. component at 500 V and its
a.c. component at a frequency of 1 kHz, and the image density of a
toner image which is formed by the reverse phenomenon on the
exposed portion (at a potential of 0 V) of the photosensitive drum
1. The amplitude E.sub.AC of the intensity of the a.c. electric
field takes a value which is made by dividing the a.c. voltage of
the developing bias by the gap d. Curves A, B and C appearing in
FIG. 32 are the results obtained in case the toners used are
controlled to have average charges of 30 .mu.c/g, 20 .mu.c/g and 15
.mu.c/g, respectively. It is observed from the three curves A, B
and C that the effect of the a.c. component appears for the
amplitude of the a.c. component of the electric field of 200 V/mm
or larger, and that the toner image retained in advance on the
photosensitive drum is partially broken for the amplitudes of 2,500
V/mm or larger.
FIG. 33 shows the changes in the image density when the frequency
of the a.c. component of the developing bias is set at 2.5 kHz and
when the a.c. field intensity E.sub.AC is changed under the same
conditions of those of the experiments of FIG. 32.
According to these experiments, the image density is high when the
amplitude E.sub.AC of the a.c. field intensity exceeds 500 V/mm,
and the toner image retained in advance on the photosensitive drum
1 is partially broken when that amplitude exceeds 4 KV/mm, although
not shown.
Incidentally, as being seen from the results of FIGS. 32 and 33,
the image density highly changes across a certain amplitude, which
has a value obtainable hardly in dependence upon the average
charges of the toners, as seen from the curves A, B and C. The
reason therefor can be thought, as follows. In the two-component
developer, specifically, it is predicted that the toners are
charged by the friction with the carrier or by the mutual frictions
with one another, and that the charges of the toners distribute
over a wide range, and it is thought that toners having a large
quantity of charges are preferably developed. Even if the average
charges are controlled by the electrification controlling agent,
the ratio occupied by those toners having the large quantity of
charges does not change so much. As a result, it is thought that
the changes in the developing characteristics are found more or
less but not highly observed.
Now, experiments similar to those of FIGS. 32 and 33 were conducted
under changing conditions to pigeon-hole the relationship between
the amplitude E.sub.AC and frequency f of the a.c. field intentisy
so that the results shown in FIG. 34 could be obtained.
In FIG. 34: indicated at A is a region where a developing
unevenness is liable to occur; indicated at B is a region where the
effect of the a.c. component does not appear; indicated at C is a
region where the toners are liable to return, i.e., where the color
mixing is liable to occur; and indicated at D and E are regions
where the effect of the a.c. component appears so that no color
mixing occurs.
These results indicate that a proper region for the amplitude and
frequency of the intensity of the a.c. electric field exists so
that a next (or subsequent) toner image may be developed in a
proper density without breaking the toner image which was retained
at the previous step on the photosensitive drum 1. This is thought
to be explained by the following reasons.
In the region where the image density has a tendency to increase
for the amplitude E.sub.AC of the a.c. field intensity, e.g., for
the density curve of FIG. 32, i.e., where the amplitude of E.sub.AC
of the a.c. field intensity ranges from 0.2 to 1.2 KV/mm, the a.c.
component of the developing bias acts to make it liable to jump a
threshold value at which the toners fly from the sleeve. As a
result, even the toner having a small quantity of charges is
trapped by the photosensitive drum 1 so that it can be used for
.[.rhe.]. .Iadd.the .Iaddend.development. As a result, the image
density is increased to the higher level as the amplitude of the
a.c. field intensity becomes the larger.
For the region where the image density is saturated for the
amplitude E.sub.AC, i.e., where the amplitude E.sub.AC exceeds 1.2
KV/mm in the curve A of FIG. 32, this phenomena can be explained as
follows. In this region, more specifically, the toners are the more
intensely vibrated as the amplitude of the a.c. field intensity
becomes the larger, and the cluster formed as a result of the
aggregation of the toners becomes liable to be broken so that only
the toners having high charges are selectively applied to the
photosensitive drum 1 whereas the toner particles having low
charges become reluctant to be developed. Moreover, the toners
having low charges are liable to be returned to the sleeve 31 by
the a.c. bias because they have a weak image forming force even if
they are once trapped by the photosensitive drum 1. Since the
charges on the surface of the photosensitive drum 1 leak because
the amplitude of the field intensity of the a.c. component, still
moreover, the phenomenon that the toners become reluctant to be
developed become liable to occur. As a matter of fact that, it is
thought that those causes are overlapped to make the image density
constant for the increase in the a.c. component.
If the a.c. field intensity is raised to have an amplitude
exceeding 2.5 KV/mm under the condition of obtaining the curve A of
FIG. 32, for example, it is found that the toner image retained in
advance on the photosensitive drum 1 is broken, and that the degree
of this breakage is the higher for the higher a.c. component. This
is thought to be caused by the fact that such a force is applied on
the toners trapped by the photosensitive drum 1 as to return to the
sleeve 31 by the a.c. component.
In case the development is conducted by consecutively superposing
toner images on the photosensitive drum 1, it is a fatal problem
that the toner image or images having already been retained are
broken at a subsequent developing step.
As is seen by comparing the results of FIGS. 32 and 33, on the
other hand, the experiments conducted by changing the frequency of
the a.c. component have revealed that the image density becomes the
lower for the higher frequency. This is caused by the fact that the
toner particles have their vibrating range narrowed, because they
cannot follow the changes in the electric field, so that they
become reluctant to be trapped by the photosensitive drum 1.
On the basis of the experimental results thus far described, the
Inventors have attained a conclusion that a later development can
be conducted in a proper density without disturbing the toner image
already having been retained on the photosensitive drum 1, if each
development is conducted under the conditions satisfying the
following relationship when the amplitude of the a.c. component of
the developing bias is designated at V.sub.AC (V); the frequency of
the same at f (Hz); and the gap between the photosensitive sleeve 1
and the sleeve at d (mm).
In order to ensure a sufficient image density and not to disturb
the toner image having been retained by the previous step, it is
preferable that the relationships of the above-specified conditions
be satisfied:
If especially the following relationships of the above are
satisfied, it is possible to obtain a multi-color image having a
better clearness but no color vagueness and to prevent the toner of
another color from being mixed into the developing apparatus even
with a number of operations:
Moreover, it is further preferable to set the frequency of the a.c.
component at 200 Hz or higher so as to prevent the developing
unevenness due to the a.c. component and to set the frequency of
the a.c. component at 500 Hz or higher so as to eliminate the
influences from the beats, which are caused by the a.c. component
and by the rotations of the magnetic roll in case the rotating
magnetic roll is used as the means for supplying the developer to
the photosensitive drum 1.
According to the construction of the present invention thus far
described, in order to consecutively develop the subsequent toner
images in predetermined densities on the photosensitive drum
without breaking the toner images retained on the photosensitive
drum 1, it is further preferable to use either solely or in
suitable combination the following methods in accordance with the
repetitions of the developments:
(1) toners having consecutively higher charges are used;
(2) the amplitude of the field intensities of the a.c., component
of the developing bias are made consecutively smaller; and
(3) the frequencies of the a.c. component of the developing bias
are made consecutively higher.
In other words, the toner particles having the higher charges are
the more susceptible to the influences of the electric field. As a
result, the toner particles having high charges may return to the
sleeve at the step of the subsequent development if they are
trapped by the photosensitive drum 1 at an early development.
Therefore, the method (1) is intended to prevent the toners having
low charges from returning to the sleeve at a later development by
using those toner particles at the early development. The method
(2) is intended to prevent the toner particles, which have already
been trapped by the photosensitive drum 1, from returning by making
the field intensities consecutively the smaller in accordance with
the repetitions of the development (i.e., at the later steps of
developments). As the specific method of consecutively weakening
the electric field intensity, there is either a method of
consecutively dropping the voltage of the a.c. component or a
method of making the larger the gap d between the photosensitive
drum 1 and the sleeve 31 at the later steps of developments. On the
other hand, the method (3) is intended to prevent the toner
particles, which have already been trapped by the photosensitive
drum 1 from returning by raising the frequency of the a.c.
component consecutively to a higher level as the developments
are
repeated. Some effect can be obtained if those methods (1), (2) and
(3) are solely used, but a better effect can be attained, if they
are used in combination, for example by consecutively increasing
the toner charges in accordance with the repetitions of the
developments with the a.c. bias being consecutively dropped. In
case those three methods are adopted, moreover, proper image
density and color balance can be held by adjusting the d.c. biases,
respectively.
Other specific Examples practised by the use of the construction
thus far described will be explained in the following with
reference to FIGS. 35 and 37.
EXAMPLE 22
FIG. 35 is a schematic view showing an essential portion of a color
image reproducing apparatus. The photosensitive drum 1 having been
uniformly charged by means of the scorotron charger was exposed to
the ray, which had been guided from the He-Ne laser light source
(although not shown) through a rotary polygonal mirror 51 and a
focusing lens 52, to retain an electrostatic latent image. This
electrostatic latent image was developed by the first developing
means 5 so that a first toner image was retained on the
photosensitive drum 1. And, this first toner image was charged
again by the scorotron charger 2 and exposed without being
transferred to the recording paper so that a second toner image was
then retained by the second developing means 6. This is repeated
until a fourth toner image is retained. In other words, the steps
of the charging operation (the second and later ones of which are
not always required).fwdarw.the exposure.fwdarw.the development
were repeated four times in the form containing no transfer step.
After the toner images had been wholly retained on the
photosensitive drum 1, the pre-transfer exposing lamp 10 irradiated
the region, in which the toner image had been retained on the
photosensitive drum 1, to transfer the toner image to the recording
paper (the path of which is indicated by a broken line), which was
fed from the paper feeder (although not shown) by the transfer
means 11. The recording paper was heated and fixed by the fixing
means 12, which was composed of at lest one heated roller, until it
was discharged to the outside of the machine.
On the other hand, the photosensitive drum 1 having ended its
transferring operation had its charges eliminated by the charge
eliminating means 13, which had not been used during the toner
image retention, and was then cleared of the spare toners, which
had been left on the surface thereof, by the cleaning means 14
which had been left inoperative during the toner image
retention.
The color image reproducing apparatus thus far described were
caused to repeat the above operations each time its operation
button was depressed. Incidentally, in the present Example, the
photosensitive material used was selenium, and the photosensitive
drum 1 had a diameter of 120 mm, a circumferential speed of 120
mm/sec and a charged potential of 600 V. To the developing means 5
and 6 used, there was applied at each developing time a developing
bias which was composed of a d.c. component of 500 V and an a.c.
component having an amplitude of 1 KV and a frequency of 1 kHz. The
gap d between the photosensitive drum 1 and the sleeve of each of
the developing means was set at 0.8 mm. Moreover, the developer
used was a two-component developer which is composed of a magnetic
carrier and a non-magnetic toner. As this carrier, there was used a
ball-shaped one which had an average particle size of 30 .mu.m, a
magnetization of 50 emu/g and a resistivity of 10.sup.14 .OMEGA. or
more and which was coated with a resin. The toner was prepared by
adding a small quantity of an electrification controlling agent to
90 wt. % of a thermoplastic resin and 10 wt. 5 of a pigment. In the
developing means 5, 6, 7 and 8, respectively, there were used the
yellow, Magenta, cyan and black pigments, all of which had an
average quantity of charges of 20 .mu.c/g and an average particle
diameter of 10 .mu.m. The developer used was a mixture which was
composed of 80 wt. % and 20 wt. % of the above-specified carrier
and toner, respectively. Moreover, at each developing time the
sleeve 31 and the magnetic roll 32 were rotated in each of the
developing means in directions opposite to each other and had their
heads regulated by the magnetic blade so that the developer layer
had a thickness of 0.4 mm.
With the construction thus far described, as has been described
above, the toner images were consecutively superposed to form a
multi-color image. As a result, a visible image having a sufficient
density was obtained with neither breaking the toner images, which
had already been retained on the photosensitive drum 1 at the
subsequent development, nor any toner of another color being mixed
into each of the developing means.
The resultant superposed toner images were transferred to and fixed
to the recording paper so that a clearly reproduced image could
also be attained. Even after the toner images had been reproduced
on a number of sheets of the transfer paper, moreover, none of
other colors were not mixed into each of the developing means.
Incidentally, a small quantity of magnetic material was contained
in the toner of each developing means so that the fog of the image
could be further prevented by the magnetic force.
EXAMPLE 23
This example was practised by the color image reproducing apparatus
shown in FIG. 35, too. The difference from the Example 22 was that
both the gap d between the photosensitive drum 1 and the sleeve and
the d.c. component of the developing bias to be applied at the
developing time were different among the developing means. The gaps
and the d.c. components were set at 0.5 mm and 450 V, at 0.7 mm and
500 V, at 0.8 mm and 500 V, and at 1.0 mm and 550 V in the
developing means 5, 6, 7 and 8, respectively. The average
quantities of the charges of the toners and the amplitude and
frequency of the a.c. biases were common among the developing means
like the Example 22 and were set at 20 .mu.c/g, 1 KV and 1 kHz,
respectively.
In the present Example, the return of the toners on the
photosensitive drum 1 was prevented by constructing the
photosensitive drum 1 and the sleeves of the respective developing
means such that the gaps d inbetween were widened the more of the
developing sequence, and the balance of the densities of the
respective color toner images was held by raising the d.c. biases
in the developing order.
According to this Example, a clearer image was obtained, and
another color was not mixed into each of the developing means even
after the reproduction of the multiple sheets.
EXAMPLE 24
This Example was practised by the color image reproducing apparatus
shown in FIG. 35, too. The difference from the Example 22 was that
the a.c. component and d.c. component of the developing bias to be
applied at the developing time were different among the developing
means. The amplitudes of the a.c. components and the d.c.
components were set at 1.5 KV and 450 V, at 1.2 KV and 500 V, at
1.0 KV and 520 V, and at 0.8 KV and 550 V in the developing means
5, 6, 7 and 8, respectively. The average quantities of the toners,
the frequencies of the a.c. biases, and the gaps between the
photosensitive drum 1 and the sleeve were common among the
developing means like the Example 22 and were set at 20 .mu.c/g, 1
kHz and 0.8 mm, respectively.
In the present Example, the return of the toners on the
photosensitive drum 1 was prevented by setting the a.c. components
at lower levels in the developing order, and the balance of the
densities of the respective color toner images was held by
consecutively raising the d.c. biases.
According to the present Example, a clear multicolored image could
be obtained without any mixing of another color into each
developing means even after the reproducing operations of the
multiple sheets.
EXAMPLE 25
This Example was also practised by the color image reproducing
apparatus shown in FIG. 35.
The developing conditions were such that the amplitudes of the a.c.
components of the developing bias applied at the developing time
were all 1 KV for the respective developing means, and such that
the frequencies and the d.c. components of the same were set at 800
Hz and 450 V, at 1 kHz and 500 V, at 1.5 kHz and 550 V, and at 2
kHz and 600 V in the developing means 5, 6, 7 and 8,
respectively.
In each developing means, moreover, at the developing time only the
sleeve was rotated to supply the developer whereas the internal
magnets were fixed. The head height regulations were conducted by
the magnetic blade to provide a gap of 0.5 mm so that the developer
had a thickness of 0.2 mm.
The average quantities of the charges of the toners and the gaps
between the photosensitive drum 1 and the sleeve were common among
the respective developing means and were set at 20 .mu.c/g and 0.8
mm, and the remaining developing conditions and developers were the
same as those of the Example 22.
In the present Example, the return of the toners on the
photosensitive drum 1 was prevented by increasing the frequencies
of the a.c. components in the developing sequence, and the balance
of the densities of the respective color toner images was held by
consecutively raising the d.c. biases.
A clear multi-colored image could also be obtained by the present
Example, and another color was not mixed into each developing means
even after the reproductions of multiple sheets.
FIG. 36 is a flow chart showing the changes in the potential on the
photosensitive drum 1 when the developments are conducted by the
color image reproducing apparatus of FIG. 35. Reference letters PH
and DA indicate the exposed portion and the unexposed portion,
respectively.
The photosensitive drum 1 holds a predetermined potential when it
is charged by the scorotron charger 2, and the portion having been
optically irradiated has its potential dropped when the image
exposure is conducted. Next, by applying a bias, which has its d.c.
component substantially equal to the potential of that of the
unexposed portion, to the developing means, the toner charged
positively in the developing means is trapped by the exposed
portion having a lower potential so that a development is conducted
to retain a first visible image. The potential at that particular
portion rises a little (as indicated at DUP in the drawing) as a
result it traps the positive toners. Next, the potential on the
photosensitive drum 1 is so uniformly charged again by the charger
2 that it is raised to a predetermined potential (as indicated at
CUP in the same drawing). Next, if a second image exposure is
conducted and if a development is similarly conducted, the toners
are applied to the exposed portion to retain a second visible
image. By repeating these steps four times, four color visible
images are retained in a superposed manner on the photosensitive
drum 1.
In the methods thus far described, the second and later charging
operations can be omitted. In case these charging operations are
not omitted, on the other hand, a charge eliminating step may be
inserted before each of the charging operations.
All of the three Examples described hereinbefore conduct the
reversal developing methods but can be practised by the normal
developing method, i.e., the method in which the toners are applied
to the unexposed portion to retain toner images. In case the
superposed developments are conducted by the normal method,
however, it is necessary to introduce the charging step at each
time.
EXAMPLE 26
Next, the description to be made in the following is directed to
the case in which the developments were conducted by means of the
color image reproducing apparatus shown in FIG. 37.
The photosensitive drum 1 was made of a CdS photosensitive member
which had its surface covered with an insulating layer and had a
diameter of 120 mm, a circumferential speed of 120 mm/sec, an
insulating layer thickness of 20 .mu.m and a photosensitive layer
thickness of 30 .mu.m.
First of all, the photosensitive drum 1 had its surface charged to
+1,000 V by means of the primary charger 2 while being exposed all
over its surface by the action of a lamp L mounted in that charger
2. This exposure was conducted so as to facilitate injection of
charges into the photosensitive layer of the photosensitive drum 1.
Next, the surface of the photosensitive drum 1 was charged to -100
V to reduce the positive charges on the surface of its insulating
lay by means of the secondary charger 3' having an a.c. component.
The photosensitive drum 1 thus charged to -100 V was subjected to
an image exposure with a ray which was reflected from the rotary
polygonal mirror 51. The portion thus exposed took a plus potential
and was developed by the first developing means 5 so that a first
visible image was retained. Next, the photosensitive drum 1 was
uniformly charged again to -100 V by the secondary charger 3' and
was then subjected to an image exposure so that a second visible
image was retained by the second developing means 6. These
operations were repeated four times to retain all the visible
images on the photosensitive drum 1. After that, the pre-transfer
exposing lamp 10 irradiated the region, in which the visible images
of the photosensitive drum had been retained, and these visible
images were transferred by the transfer means 11 to the recording
paper (the path of which is shown by the broken line), which was
fed from the paper feeder (although not shown). The recording paper
was heated and fixed by the fixing means 12, which was composed at
least one heated roller, until it was discharged to the outside of
the machine.
On the other hand, the photosensitive drum 1 having its
transferring operation completed had its charges eliminated by the
charge eliminating means 10 which had not been used during the
toner image retention. After that, the photosensitive drum 1 was
cleared of the spare toners, which were left on its surface, by the
action of the cleaning means 14 which had been left inoperative
during the toner image retention.
The color image reproducing apparatus thus far described repeated
the foregoing operations each time its operating button was
depressed. The developing conditions of each developing step were
such that the developing bias to be applied at the developing time
had its a.c. component set at 1.5 KV and having a frequency of 2
kHz and its d.c. component set at 0 V, and such the gap d between
the photosensitive drum 1 and the sleeve of each developing means
was 0.5 mm. In each developing means, at the developing time the
sleeve and the magnetic roll were rotated in the same common
direction to carry the developer, and this developer had its layer
thickness regulated to 0.3 mm by the action of the magnetic
blade.
Each of the developers had the same composition as that of the
Example 22 except that its charge was controlled to -20
.mu.c/g.
With the construction thus far described, the multi-color images
were retained to form a visible image having a sufficient density
with neither breakage of the tone images, which had already been
retained on the photosensitive drum 1, nor any mixing of the toner
of another color into each developing means.
EXAMPLE 27
This example was likewise practised by the color image reproducing
apparatus shown in FIG. 37. The difference from the Example 26 is
located in that the average quantities of the developers used and
the d.c. component of the developing bias applied at the developing
time were different among the developing means and were set at -10
.mu.c/g and 0 V, at -15 .mu.c/g and 0 V, at -20 .mu.c/g and 20 V,
and at -40 .mu.c/g and 50 V in the developing means 5, 6, 7 and 8
respectively. On the contrary, the amplitudes and frequencies of
the a.c. bias and the gaps between the photosensitive drum 1 and
the sleeve were common among the respective developing means like
the Example 26 and were set at 1.5 KV, 2 kHz and 0.5 mm,
respectively.
In the present Example, the return of the toners on the
photosensitive drum 1 was prevented by controlling the
electrifications such that the average quantities of the charges of
the developers had their absolute values increased in the
developing sequence, and the balance of the densities among the
respective color toner images was held by consecutively increasing
the values of the d.c. biases.
According to the present Example, too, a clear multi-color image
was obtained, and another color was not mixed into each developing
means.
EXAMPLE 28
This Example was likewise practised by the color image reproducing
apparatus shown in FIG. 37. The difference from the Example 26 was
found in that the average quantities of the developers used and the
amplitudes of the a.c. components of the developing biases applied
at the developing time were different among the developing means
and were set at -10 .mu.c/g and 1.6 KV, at -15 .mu.c/g and 1.4 KV,
at -20 .mu.c/g and 1.2 KV, and at -40 .mu.c/g and 1.0 KV in the
developing means 5, 6, 7 and 8, respectively. The frequencies of
the a.c. biases, the potentials of the d.c. biases, and the gaps d
between the photosensitive drum 1 and the sleeve were shared among
the respective developing means and were set at 2 kHz, 0 V and 0.5
mm, respectively.
In the present Example, the return of the toners on the
photosensitive drum 1 was prevented, and at the same time the
balance among the densities of the respective color toner images
was held partly by controlling the electrifications such that the
average quantities of the charges of the developers had their
absolute values increased and partly by consecutively setting the
a.c. biases.
According to the present Example, a clearer multi-color image was
obtained, and no color was mixed into each developing means even
after reproductions of multiple sheets.
FIG. 38 shows the changes in the potentials on the photosensitive
drum when the developments are conducted by the color image
reproducing apparatus of FIG. 37.
After has been charged positive by the primary charger 2, the
photosensitive drum 1 is charged negative so that its surface
potential is dropped substantially to 0 V. Next by conducting the
image exposure, the portion optically irradiated has its potential
raised to trap the toners, which have been charged negative in the
developing means, so that the portion having trapped the toners has
its potential dropped (as indicated at DDW in the drawing). Next, a
uniform charging operation is so conducted by the secondary charger
that the surface potential is dropped substantially to 0 V, and the
image exposure and the development are repeated. After the visible
images of all the colors have been formed on the photosensitive
drum 1, the resultant toner images are transferred to the recording
paper, and the photosensitive drum 1 has its charged eliminated and
is then cleaned until the step advances to a subsequent image
reproduction.
In the methods described hereinabove, the second and later
secondary charging operations can be omitted. On the other hand,
the primary and secondary charging operations may be conducted each
time, and in this case the charge eliminating step may be
introduced prior to the charging step.
In the respective Examples thus far described, the corona transfer
is used as the toner image transfer, but another type may be used.
If the adhesion transfer disclosed in Japanese Patent Publication
Nos. 41679/71, 22763/73 or the like, for example, is used, the
transfer can be conducted without considering the polarities of the
toners. Moreover, it is possible to adopt the method of effecting
direct fixture to the photosensitive member as in the electrofax
method.
The two-component developer used in the present invention may
especially preferably be composed of a magnetic carrier as its
carrier and a non-magnetic toner as its toner.
The compositions of the toners are generally, as follows:
(1) Thermoplastic Resin: 80 to 90 wt. % of binder
Examples: polystyrene, styrene-acryl polymer, polyester, polyvinyl
butyral, epoxy resin, polyamide resin, polyethrene, and
ethylene-vinyl acetate copolymer, which are frequently used in a
mixed form;
(2) Pigment: 0 to 15 wt. % of coloring agent
Examples:
Black: Carbon Black;
Blue: copper phthalocyanine, derivative dye of sulfonamide;
Yellow: benzine derivative; and
Magenta: polytungstophosphate, Rhodamine Lake, Carmine 6B;
(3) Electrification Controlling Agent: 0 to 5 wt. %
Examples:
Plus: Nigrosine (i.e., electron donor); and
Minus: organic complex (i.e., electron acceptor);
(4) Fluidizer:
Examples: coloidal silica or hydrophobic silica as representative,
silocone varnish, metallic soap, nonionic active agent;
(5) Cleaning Agent: intended to prevent the filming of the toners
of photosensitive member
Examples:
fatty acid metal salt, oxidized silicate having a surface radical,
surface active agent containing fluorine; and
(6) Filler: intended to improve the surface gloss of images and to
reduce the cost for raw materials
Examples:
Calcium carbonate, clay, talc, pigment.
In addition to the above-enumerated materials, a magnetic material
may be contained so as to prevent a fog and a toner dispersion.
As the magnetic powders, there are proposed such powders of
tri-iron tetraoxide, .gamma.-ferric oxide, chromium dioxide, nickel
ferrite or iron alloy as have a diameter of 0.1 to 1 .mu.m. At
present, however, the tri-iron tetraoxide is frequently used and is
contained in 5 to 7 wt. % with respect to the toners. The
resistances of the toners are variable in dependence upon the kinds
and quantities of the magnetic powders. In order to provide a
sufficient resistance, however, it is preferred to contain 55 wt. %
or less of the magnetic material. Moreover, the quantity of the
magnetic material is desired to be contained in 30 wt. % or less so
that it may hold a clear color as the color toner.
In addition, as the resin suitable for the pressure fixing toner,
an adhesive resin such as wax, polyorefines, ethylene-vinyl acetate
copolymer, polyurethane or rubber is selected so that it may be
plastically deformed and adhered to paper by a force of about 20
kg/cm. A capsule toner may also be used.
The toners can be made of the above-enumerated materials and
prepared by the method known in the prior art.
In order to obtain a more preferable image in the construction of
the present invention, the particle diameters of those toners are
desired to be no more than 50 microns in their ordinary average
values in relation to the resolution. In the present invention, the
toner diameters of about 1 to 30 microns may preferably be used in
relation to the resolution, the toner scattering and the carriage,
although they are not restricted on principle.
In order to reproduce fine points and lines and to enhance the
gradation, moreover, the magnetic carrier particles may preferably
be particles composed of magnetic particles and a resin, for
example, a resin-dispersed system of magnetic powders and a resin
or resin-coated magnetic particles and may more preferably be
rounded to have an average particle diameter of 50 .mu.m or
smaller, especially preferably, a particle diameter no more than 30
.mu.m and no less than 5 .mu.m.
Moreover, in order to prevent the problems that the carrier
particles for providing an obstruction against the satisfactory
image reproduction are made liable to receive the charges by the
bias voltage so that they become liable to be trapped by the
surface of the image carrier and that the bias voltage is not
applied to a sifficient level, the carrier may have such an
insulating property of a resistivity no less than 10.sup.8 .OMEGA.,
preferably, 10.sup.13 .OMEGA., more preferably, 10.sup.14 .OMEGA..
Moreover, the carrier particles may have this resistivity and the
above-mentioned diameter.
The carrier particles described above can be prepared either by
coating the surface of the magnetic materials described as to the
toners with the thermoplastic resin or by making the particles of a
resin having fine magnetic particles dispersed and contained
therein and by selecting the resultant particles by the well-known
average diameter selecting means. Moreover, in order to improve the
agitating characteristics of the toners and the carriers and the
carrying characteristics of the developers and to improve the
electrification controlling characteristics of the toners thereby
to make the toner particles reluctant to aggregate or the toner
particles and the carrier particles to aggregate, it is desirable
to round the carriers. Of these rounded magnetic carrier particles,
the resin-coated ones are prepared by selecting magnetic particles
as round as possible and by coating the particles selected with a
resin, and the carriers having fine magnetic powders dispersed
therein are prepared either by rounding fine particles of a
magnetic material, if possible, by hot wind or water after making
the dispersed resin particles or by directly forming the rounded
dispersed resin particles by the spray dry method.
Incidentally, the present invention can be further modified on the
basis of the technical concept thereof. In the Examples, the
description has been made as to the case in which the two-component
developer composed of the toner and the carrier was used as the
developer having a plurality of components. However, the developer
may additionally contain a third component.
In the Examples, the description is limited to the development of
the color image. However, the present invention can be applied to
the case in which toners of the same color are developed in plural
times. In this case, a toner having an excellent gradation can be
retained on the photosensitive drum.
Still moreover, the present invention can be applied not only to
the reproducing apparatus by electrophotography but also to the
non-impact printer making use of the electrostatic reproducing
method or the magnetic reproducing method.
According to the Examples of the present invention, an image at a
subsequent step can be retained on an image carrier without
disturbing an image retained at a previous step even if the step of
retaining a latent image on the image carrier and the step of
developing the latent image with a developer having a plurality of
component are repeated a plurality of times.
In other words, a clear image can be retained on the image carrier
if the amplitude V.sub.AC and the frequency f of the a.c. component
and the gap d between the developer carrier and the image carrier
are so set as to satisfy the following relathinships:
In the other Examples, the developer D used was a one-component
magnetic developer which was prepared by blending and pulverizing
70 wt. % of a thermoplastic resin, 10 wt. % of a pigment (e.g.,
Carbon Black), 20 wt. % of a magnetic material and an
electrification controlling agent to have an average particle
diameter of 10 .mu.m. The quantity of the charges is controlled by
the electrification controlling agent.
In case the development is conducted with a one-component developer
using only the magnetic or non-magnetic toner, there can be used
developing means which is disclosed in U.S. Pat. Nos. 3,866,574 and
3,893,418. On the other hand, developing means having two or more
magnetic rollers may be used. The electric bias containing
vibratory components and applied upon the development has to be set
under such a condition that the toner image retained already on the
image retainer may neither be disturbed nor have a color mixing.
Under the bias condition used in the non-contact jumping
development, e.g., the condition as is disclosed in Japanese Patent
Laid-Open Nos. 18656 to 18659/80 and 106253/81, the toner images
having already been retained may be damaged by the vibrations of
the toners, which are caused by the intense a.c. electric field. In
case the developments according to the present invention are
repeated to superpose the toner images, the intensity of the a.c.
component of the bias has to be set within such a proper range
without deteriorating the retained toner images that a subsequent
toner image can be completely retained.
FIG. 39 shows the relationship between the amplitude of the a.c.
component, when the gap d between the photosensitive drum 1 and the
sleeve 31 is set at 0.7 mm; the thickness of the developer at 0.3
mm; the developing bias to be applied to the sleeve 31 has its d.c.
component at 500 V and its a.c. component at a frequency of 1 kHz;
and the charged potential of the photosensitive drum at 600 V, and
the image density of a toner image which is formed by the reverse
phenomenon on the exposed portion (at a potential of 0 V) of the
photosensitive drum 1. The amplitude E.sub.AC of the intensity of
the a.c. electric field takes a value which is made by dividing the
a.c. voltage of the developing bias by the gap d. Curves A, B and C
appearing in FIG. 39 are the results obtained in case the magnetic
toners used are controlled to have average charges of 5 .mu.c/g, 3
.mu.c/g and 2 .mu.c/g, respectively. It is observed from the three
curves A, B and C that the effect of the a.c. component appears for
the amplitude of the a.c. component of the electric field of 200
V/m or higher and 1.5 KV/mm or lower, and that the toner image
retained in advance on the photosensitive drum is partially broken
for the amplitude of 2,500 V/mm or larger.
FIG. 40 depicts the changes in the image density when the frequency
of the a.c. component of the developing bias is set at 2.5 kHz and
when the a.c. field intensity is changed under the same conditions
of those of the experiments of FIG. 32.
According to these experiments, the image density is high when the
amplitude E.sub.AC of the a.c. field intensity is 500 V/mm or
higher and 3.8 KV/mm or lower (although not shown in FIG. 39), and
the toner image retained in advance on the photosensitive drum 1 is
partially broken when that amplitude exceeds 3.2 KV/mm (although
not shown in FIG. 39).
Incidentally, as being seen from the results of FIGS. 39 and 40,
the image density highly changes across a certain amplitude, which
has a value obtainable hardly in dependence upon the average
charges of the toners, as seen from the curves A, B and C. The
reason therefor can be thought, as follows. Specifically, it is
predicted that the one-component developer has its charge
quantities distributed widely across the positive and negative
ranges because of the mutual frictions of the toner particles. As a
result, the average quantities of the charges take a small value,
but in fact toners having a large quantity of charges, e.g., 20
.mu.c/g or larger exist at a predetermined ratio and are thought to
be mainly developed. Even if the average charge quantity is
controlled by the electrification controlling agent, the ratio
occupied by the toners having that large charge quantity is not
varied so much, so that it is thought that the change in the
developing characteristics is not substantially observed.
Now, experiments similar to those of FIGS. 39 and 40 were conducted
under changing conditions to pigeon-hole the relationship between
the amplitude E.sub.AC and frequency f of the a.c. field intensity
so that the results shown in FIG. 41 could be obtained.
In FIG. 41: indicated at A is a region where a developing
unevenness is liable to occur; indicated at B is a region where the
effect of the a.c. component does not appear; indicated at C is a
region where the toners are liable to return; and indicated at D
and E are regions where the effect of the a.c. component appears so
that no toner return occurs.
These results indicate that a proper region for the amplitude and
frequency of the intensity of the a.c. electric field exists so
that a next (or subsequent) toner image may be developed in a
proper density without breaking the toner image which was retained
previously (at the previous step) on the photosensitive drum 1.
This is thought to be explained by the following reasons.
In the region where the image density has a tendency to increase
for the amplitude E.sub.AC of the a.c. field intensity, e.g., for
the density curve of FIG. 39, i.e., where the amplitude of E.sub.AC
of the a.c. field intensity ranges from 0.2 to 1.0 KV/mm, the a.c.
component of the developing bias acts to make it liable to jump a
threshold value at which the toners fly from the sleeve. As a
result, even the toner having a small quantity of charges is
trapped by the photosensitive drum 1 so that it can be used for the
development. As a result, the image density is increased to the
higher level as the amplitude of the a.c. field intensity
becomes
the larger.
On the other hand, the reason, for which the image density is
dropped in accordance with the increase in the amplitude of the
a.c. electric field (e.g., the region in which the amplitude
E.sub.AC of the a.c. field intensity is no less than 1 KV for the
density curve A of FIG. 29), can be thought in several ways. The
toners are the more intensely vibrated as the amplitude E.sub.AC of
the a.c. field intensity becomes the larger, and the cluster formed
as a result of the aggregation of the toners becomes liable to be
broken so that only the toners having high charges are selectively
applied to the photosensitive drum 1 whereas the toner particles
having low charges become reluctant to be developed. Moreover, the
toners having low charges are liable to be returned to the sleeve
31 by the a.c. bias because they have a weak image forming force
even if they are once trapped by the photosensitive drum 1. Since
the charges on the surface of the photosensitive drum 1 leak if the
amplitude of the field intensity of the a.c. component is too
large, still moreover, the phonomenon that the toners become
reluctant to be developed become liable to occur. As a matter of
fact that, it is thought that those causes are overlapped to make
the image density constant for the increase in the a.c.
component.
If the amplitude E.sub.AC of the a.c. field intensity is enlarged,
as has been described hereinbefore, on the other hand, the toner
image retained in advance on the photosensitive drum 1 is broken,
and the degree of this breakage is the higher for the higher a.c.
component. This is thought to be caused by the fact that the toners
trapped by the photosensitive drum 1 are acted by a force for
returning it to the sleeve 31 by the a.c. component. In case the
development is conducted by consecutively superposing toner images
on the photosensitive drum 1, it is a fatal problem that the toner
image or images having already been retained are broken at a
subsequent developing step.
As seen by comparing the results of FIGS. 39 and 40, on the other
hand, the experiments conducted by changing the frequency of the
a.c. component have revealed that the image density becomes the
lower for the higher frequency. This is caused by the fact that the
toner particles have their vibrating range narrowed, because they
cannot follow the changes in the electric field, so that they
become reluctant to be trapped by the photosensitive drum 1.
On the basis of the experimental results thus far described, the
Inventors have attained a conclusion that a later development can
be conducted in a proper density without disturbing the toner image
already having been retained on the photosensitive drum 1, if each
development is conducted under the conditions satisfying the
following relationships when the amplitude of the a.c. component of
the developing bias is designated at V.sub.AC (V); the frequency of
the same at f (Hz); and the gap between the photosensitive drum 1
and the sleeve at d (mm):
In order to obtain a sufficient image density but not to disturb
the toner images having been retained until the previous step, the
following condition, i.e., the region of FIGS. 29 and 30, in which
the image density has a tendency to increase for the a.c. electric
field, is desirably satisfied:
Of this region, it is preferable to satisfy the following region
corresponding to a slightly lower electric field in which the image
density takes its maximum:
Moreover, it is further preferable to set the frequency f of the
a.c. component at 200 Hz or higher so as to prevent the developing
unevenness due to the a.c. component and to set the frequency of
the a.c. component at 500 Hz or higher so as to eliminate the
influences from the beats, which are caused by the a.c. component
and by the rotations of the magnetic roll in case the rotating
magnetic roll is used as the means for supplying the developer to
the photosensitive drum 1.
On the other hand, not only the magnetic toner but also a
non-magnetic toner can be used. As the developing method using the
non-magnetic toner, there is known a method which is disclosed in
Japanese Patent Laid-Open No. 30537/75 or 22926/77, for example. In
order to easily transfer the visible image on the photosensitive
drum 1 to the recording paper, moreover, the specific resistance of
the toner is desired to be no less than 10.sup.13 .OMEGA. cm.
Incidentally, the resistivity is a value which can be obtained by
reading out a current value when a load of 1 Kg/cm.sup.2 is applied
to the particles tapped in a container having an effective area of
0.5 cm.sup.2 and when a voltage for establishing an electric field
of 1,000 V/cm is applied between the load and the bottom
electrodes.
Moreover, the materials composing the developer except the magnetic
material are similar to those of the foregoing Examples.
These materials may be simply blended and pulverized, but the
following additional devices are made, as the case may be:
1. An insulating material is added to the inside or surface of the
toner.
2. The toner is prepared either by coating in advance the surfaces
of magnetic powders with a surface active agent, an organic dye or
a specified resin or by activating in advance the same surfaces to
form cover films by polymerizations and by mixing the magnetic
powders with a resin or the like. This device is intended to
facilitate uniform dispersion into the resin and to improve the
image quality in a high humidity.
3. The developing quality is improved to prevent the toner scatter,
as the case may be, by selecting the magnetic characteristics of
the magnetic powders such as the shape, the axial ratio or the
retaining force of the same.
4. The fluidity is enhanced to improve the developing property by
mixing magnetic toners which have different particle diameters,
quantities of magnetic powders contained, magnetic characteristics
and electric resistances.
On the other hand, most of the magnetic powders are black so that
they can be used in place of the black pigment.
In addition, as the resin suitable for the pressure-sensitive
toner, wax, polyorefines, ethylenevinyl acetate copolymer,
polyurethan, rubber and so on are selected such that they are
elastically deformed and adhered to the paper by a force of about
20 Kg/cm.sup.2. Capsulated toners may also be used.
The particle diameters of those toners may preferably be no more
than 50 microns on an average value in relation to the resolution.
In the present invention, the toner particle diameters are not
limited on principle but may be ordinally about 1 to 30 microns in
relation to the resolution and the scattering and carriage of the
toners.
Incidentally, the present invention can be further modified on the
basis of the technical concept thereof. In the foregoing Examples,
the description is restricted to the development of the color
image. The present invention can also be applied to the case in
which toners of the same color are developed in plural times. In
this case, a toner image having an excellent gradation can be
retained on the photosensitive drum.
Moreover, the present invention can be applied not only to the
recording method for electrophotography but also the non-impact
printer which makes use of the electrostatic reproducing method or
the magnetic producing method.
Even both the step of retaining the latent image on the same image
carrier and the step of developing the latent image with the
one-component developer are repeated plural times, according to the
Examples of the present invention, an image at a subsequent step
can be retained on the image carrier without disturbing the image
which has been retained at a previous step.
In other words, a clear image can be retained on the image carrier
if the amplitude V.sub.AC and the frequency f of the a.c. component
and the gap d between the developer carrier and the image carrier
are so set as to satisfy the following relationship:
FIG. 42 shows a reproducing apparatus according to another
embodiment of the present invention, in which: reference numeral 61
indicates an image retainer which is constructed of such a magnetic
layer and an insulating layer as is prepared by evaporating or
sputtering a magnetic material on a metal base or by applying a
magnetic material dispersed in a binder to the metal base and which
is placed on a drum rotating in the direction of arrow; numeral 63'
indicates a magnetic erasing head; and numeral 63 indicates a
magnetic recording head. The remaining portions are identical to
the embodiment of FIG. 1.
The recording head 63 composed of one or more rows of recording
heads for retaining a magnetic image on the magnetic layer of the
image retainer 61. Magnetic force of the magnet 32 is arranged so
as not to disturb a magnetic image on the retainer 61.
The bias conditions for practising the method of the present
invention are preferred to satisfy the following inequalities:
For the two-component developer used:
For the one-component developer used:
In the above inequalities: V.sub.AC indicates the amplitude (V)
(although not an effective value) of the a.c. component of the
developing bias; f indicates the frequency (Hz); and d indicates
the gap (mm) between the image retainer, e.g., the sleeve and the
developer carrier.
Moreover, the order of the colored toners for image superpositions
has to be determined to be the most proper for the object because
it exerts influences upon the tone of the color image.
Although the foregoing description is directed to the reproducing
apparatus of FIG. 42, the method of the present invention can also
be practised by the reproducing apparatus shown in FIG. 43. In FIG.
43, parts having the same functions as those of FIG. 42 are
indicated by the same reference numerals as those of FIG. 42.
Shown in FIG. 43 is the reproducing apparatus in which a series of
recording members are prepared by placing a magnetic layer and a
colorless insulating layer on the surface of a conductive base to
provide an image retainer 61'. While this image retainer 61' is
being fed straight, the retentions and developments of the magnetic
images are repeated. Along the passage for the image retainer 61',
more specifically, the pre-writing charger 2, the magnetic erasing
head 63', the magnetic recording head 63 and developing means 5 to
8 are juxtaposed in a repeated manner, and the fixer 12 for fixing
the color image on the image retainer 61' is disposed at the last
position. This reproducing apparatus can reproduce a series of
color images without any provision of the pre-transfer charger, the
transfer means, the charge eliminating means and the cleaning
means. In order that the image retainer 61' may not depend, it is
necessary to increase the tension or to provide such a supporting
roller midway, although not shown, as providing the toners trapped
by the image retainer 61' from being offset.
In the recording apparatus shown in FIG. 42, too, the pre-transfer
charger 9, the transfer means 11, the charge eliminating means 13
and the cleaning means 14 can be omitted if the image retainer 61
is constructed by winding on the drum an image retainer which is
similar to the image retainer 61' used in the reproducing apparatus
of FIG. 43. In order to hide the color of the magnetic layer,
moreover, it is desired to provide a conductive layer or an
insulating layer having a white or desirable color.
In order to .[.practise.]. .Iadd.practice .Iaddend.the method of
the present invention, it is preferable to use the image retainer
having a highly insulating layer as the image retainer. Once the
developer is trapped by the image retainer, generally speaking, it
is remarkably difficult to remove, because not only the van der
Waals' force but also the image forming force acts, to cause
troubles such as the fog and the reduction in the transfer ratio.
These phenomena can be prevented by suitably charging the image
retainer in the same polarity as that of the charges of the toners.
However, the ordinary magnetic image retainer constructed of a
conductive base and a magnetic layer has such a low insulating
property that it is difficult to charge. Despite of this fact, this
ordinary image retainer can be charged by forming an insulating
layer on the surface of the magnetic layer. By using the image
retainer having the insulating layer on the surface of the magnetic
member, the unnecessary trap of the toners can be prevented to
enhance the transfer efficiency, and a charger is placed in front
of the magnetic image writing operation to effect the charging
operation so that the fog can be prevented. Moreover, the
insulating layer is also effective for protecting the magnetic
layer and for preventing the toner filming. If this toner filming
occurs, there arises no practical problem if it takes place on the
insulating layer. Moreover, the magnetic layer may also act as the
conductive base if it is conductive. In case the thickness of the
insulating layer is excessive, it drops the density and
magnetization of the magnetic image recorded. Therefore, that
thickness is preferred to be no more than 50 .mu.m or, preferably,
no more than 10 .mu.m.
Incidentally, FIG. 42 shows an embodiment of the reproducing
apparatus which uses an image retainer having the insulating layer,
but the pre-writing charger 2 and the charge eliminating means 13
can be omitted in case an image retainer having no insulating layer
is used.
In the embodiment of FIG. 42, the writing operation of the magnetic
image is conducted by the reproducing method of parallel
magnetization type using a ring head. However, a perpendicular
magnetization type method can be likewise used as the magnetically
writing means. In this case, the magnet 32 is fixed, and its
opposed magnetic poles are made different from the magnetizing
direction by the writing operation so that the toners may be
reluctant to jump to the non-image portion but liable to jump to
the image portion. In this case, it is needless to say that the
magnetizing direction and the magnetization facilitating direction
of the magnetic layer should be aligned.
On the other hand, the magnetic erasing head 63' and the magnetic
recording head 63 may be disposed in front of, in front of and at
the back of, or at the back of the pre-writing charger as shown in
FIGS. 42 and 43.
The image reproducing process using the reproducing apparatus
according to the method of the present invention will be described
in the following with reference to FIGS. 44 to 46.
In the embodiment of FIG. 44, by the reproducing apparatus of FIG.
42: (1) the surface of the image retainer 61 has its charges
eliminated by the image eliminating means 13 and cleaned by the
cleaning means 14; and the initial state, in which the surface of
the image retainer 61' is charged to a suitable potential e (in
which the broken lines indicate the presence of the charges) in the
same polarity as that of the toners, is established by the
pre-writing charger 2 so as to prevent the fog.
Next, after the residual magneticism m has been demagnetized by the
demagnetizing head 63' (shown at (3)), that surface is subjected to
a first writing operation by the recording head 63 to retain a
magnetic image M.sub.1 (shown at 4)) which is firstly developed by
the developing means 5 to obtain a first image T.sub.1 (shown at
(5)). Moreover, the image retainer 1 enters its second rotation in
the reproducing apparatus of FIG. 42 so that it is demagnetized by
the erasing head 63' (shown at (6)) and is subjected to a second
writing operation by the recording head 63 (shown at (7)). The
magnetic image M.sub.2 thus formed is secondly developed by the
developing means 6 to provide a second image T.sub.2 (shown at
(8)). Then, third and fourth demagnetizing, writing operations and
developments are likewise repeated so that a color image having its
color toner images superposed is retained on the image retainer 61.
The resultant color image is made liable to be transferred by the
pre-transfer charger 9 in the reproducing apparatus of FIG. 42 so
that it is fixed on the recording member P by the fixing means 12
after it has been transferred to the recording member P by the
transfer means 11. In the
reproducing apparatus of FIG. 43, on the other hand, that color
image is fixed directly on the image retainer 61' by the fixing
means 12. In the reproducing apparatus of FIG. 42, moreover, the
surface of the image retainer 61 having the color image transferred
thereto has its charges eliminated by the charge eliminating means
13 and is cleared of the residual toners by the cleaning means 14
until the one cycle of the color image reproduction is ended by
further eliminating the charges, if necessary. In case the
reproducing apparatus of FIG. 43 is used, too, the image retaining
process is not changed except for the shape of the image retainer
61'.
FIG. 45 shows a process which is simplified by omitting the
uniformly charging step from the process of FIG. 44. FIG. 46 shows
a process which is difference from that of FIG. 44 in that the
charger 2 is operated to effect the uniform charging operation
before each writing step. However, their basic operations are all
common.
Incidentally, reference letters T.sub.1 and T.sub.2 indicate the
toners of different colors, which are trapped by the image retainer
61 or 61'.
By conducting the developments under the non-contact jumping
developing conditions, according to the method of the present
invention, the developing means other than that conducting the
development of each time can be easily held in an inoperative
state, even if the developer layer is not removed from the
developing sleeve 31, by disconnecting the developing sleeve 31
from the power supply 39 into a floating state, by grounding the
same to the earth, or by positively applying a d.c. bias voltage
having a polarity opposite to that of the charges of the toners to
the developing sleeve 31. Of these means, it is preferable that the
developing means are held inoperative by applying the bias voltage
having a polarity opposite to that of the toners.
Next, the embodiments of FIGS. 44 to 46, which are practised by the
reproducing apparatus of FIG. 42, will be described in more detail
in the following in connection with Examples 29 to 31.
The reproducing apparatus shown in FIG. 42 was used. The image
retainer 61 was prepared by forming a Co alloy having a thickness
of 10 .mu.m on an aluminum base by the electron beam heating
operation and by forming the insulating layer having a thickness of
5 .mu.m on the surface of the Co alloy and which had a
circumference speed of 180 mm/sec. The surface of the image
retainer 61 thus prepared was charged to +50 V by the pre-writing
charger 2 using the scorotron corona discharger and was
demagnetized by means of the magnetic erasing head which had its
leading end spaced at a distance of about 30 .mu.m from the surface
of the image retainer 61. Next, a first image writing operation was
conducted in a distribution density of 10 spots/mm by means of the
recording head 63 which had a similar spacing. As a result, a first
magnetic image was retained on the image retainer 61. This magnetic
image was firstly developed by the developing means 6 shown in FIG.
3. This developing means 6 uses the developer, which was composed
of: a carrier having 50 wt. % of magnetite dispersed contained in a
resin and having an average particle diameter of 30 .mu.m, a
magnetization of 30 emu/g and a resistivity of 10.sup.14 .OMEGA. cm
or more; and a positive magnetic toner prepared by adding 25 wt. %
of magnetite, 10 wt. % of copper phthalocyanine as the cyan pigment
and an electrification controlling agent to a styreneacryl resin
and having an average particle diameter of 10 .mu.m, under the
condition that the ratio of the toner to the carrier was 10 wt. %.
Moreover, there were resorted to the non-contact jumping developing
conditions under which: the developing sleeve 31 had an external
diameter of 30 mm and a number of revolutions of 100 r.p.m.; the
magnet 32 and its N and S magnetic poles having a magnetic flux
density of 500 gausses and had a number of revolutions of 1,000
r.p.m.; the developer layer in the developing region had a
thickness of 0.7 mm; the gap between the developing sleeve 31 and
the image retainer 1 was 0.8 mm; and a bias voltage having a d.c.
voltage component of -50 V and an a.c. voltage component of 1.5 kHz
and 1,000 V was applied to the developing sleeve 31. In the
following Examples, the a.c. component has a sine wave, and its
exemplified values are effective ones.
The surface of the image retainer 61 having been subjected to the
first development was subjected again to an erasure by the same
magnetic erasing head 63' without operating the pre-transfer
charger 9, the charge eliminating means 13 and 13, the cleaning
means 14 and the pre-writing charger 2, and a second writing
operation was conducted in the same spot density but with the spot
position being shifted from that of the first writing operation by
means of the recording head 63. Next, a second development was
conducted by the developing means 6 which was under the same
conditions as those of the developing means 5 except that it used
as its toner a toner prepared by adding polytungstophosphate as the
.[.Magenta.]. .Iadd.magenta .Iaddend.pigment in place of the cyan
pigment. Likewise, a demagnetization and a third writing operation
were conducted. A third development was then conducted by the
developing means 7 which was under the same conditions as those of
the developing means 5 except that it used as its toner a toner
prepared by adding a bendizine derivative as the yellow pigment.
Moreover, demagnetization and a fourth writing operation were
conducted. A fourth development was conducted by the developing
means 8 which was under the same conditions as those of the
developing 5 except that it used a toner prepared by adding
.[.Carbon Black.]. .Iadd.carbon black .Iaddend.as the black
pigment. The color image thus retained on the image retainer 61 was
transferred to and fixed on the recording member P, as has been
described with reference to FIG. 42. Moreover, the surface of the
image retainer 61 having the color image transferred thereto had
its charged eliminated by the charge eliminating means 13 and was
cleared of the residual toners by the cleaning means 14.
The reproduced image thus obtained had little color toner mixing
and was a remarkably clear color image.
Incidentally, in the present Example, the spot position of a
subsequent writing operation may be overlapped upon that of a
previous writing operation. In the writing and developing
operations, moreover, the recording current of the recording head
3, and the voltage value, frequency and time selecting period of
the d.c. or a.c. component of the voltage to be applied to the
developing sleeve may be so changed as to adjust the developed
densities of the respective colors. If the writing spot positions
are superposed, the color mixing becomes liable to occur to invite
color vagueness but not to drop the resolution. In this case,
moreover, especially the sequence of the colors to be developed is
important. By adjusting the developing densities of the respective
colors in the aforementioned manner, on the other hand, it is
possible to attain a color image which has its tones changed.
EXAMPLE 30
The same reproducing apparatus as that of the Example 29 was used.
The color image reproduction was conducted under the same
conditions as those of the Example 29 except: that a magnetic image
was for a background potential of 0 V by a first writing operation
without any of the charging operation of the Example 29 by the
pre-writing charger 2 before the first writing operation, after the
charge elimination for demagnetization by the charge eliminating
means 13; that a superposed voltage composed of a d.c. voltage of
-50 V and an a.c. voltage of 3 kHz and 2,000 V was applied as the
bias voltage before development to the developing sleeve 31; and
that charge elimination and demagnetization were effected by the
charge eliminating means 13 before second and later writing
operations so that a magnetic image was retained for the background
potential of 0 V even during the second and later writing
operations.
The reproduced image which is excellent in clearness like that of
the Example 29 was thus obtained.
EXAMPLE 31
The color image reproduction was conducted by the use of the same
reproducing apparatus as that of the Example 29 and under the same
conditions as those of the Example 29 except: that a charging
operation is conducted to +300 V before a first writing operation
by the pre-writing charger 2 so that a magnetic image was retained
for the background potential of +300 V by the first writing
operation after it had been demagnetized; that a superposed voltage
composed of a d.c. voltage of +300 V and an a.c. voltage of 2 kHz
and 1 KV was applied as the bias before the development to the
developing sleeve 31; and that the pre-writing charger 2 was used
before the demagnetization and the second and later writing
operations. The reproduced image obtained was a color image which
was excellent in cleaness like that of the Example 29.
According to the Examples of the present invention, there can be
attained an excellent effect that the tone or the like of the color
image can be easily changed thanks to the use of the image
retaining means having its image retainability and toner image
formability separated so that a color image having excellent
clearness and a high tone can be reproduced while stabilizing the
reproduction.
Incidentally, the present invention can be applied not only to an
image retainer having a belt or sheet shape, but also to an image
retainer such as electrofax paper, which is placed on a base so
that the color image formed thereon by the toners is fixed without
being transferred. In this case, the sequence of superposing the
color toner images has to be taken into consideration, but the
transfer means, the cleaning means and so on can be omitted. It is
true, but the the charge eliminating means can be omitted, too, in
case the toners are transferred with a predetermined polarity and a
charge quantity. On the other hand, the transfer should not be
limited to the corona type but may be exemplified by the bias
roller type, the adhesion type, the direct pressure type or other
means using an intermediate transfer member, and the fixture is not
limited to the heat roller type.
In the foregoing embodiments of the present invention, moreover,
the magnetic recording head is used as the writing means, but
another means may be likewise used if the magnetic image is to be
retained on the magnetic layer. More specifically, the present
invention can be applied to the method, in which the magnetic image
is retained by heating imagewise a demagnetized magnetic layer,
while passing through a unidorm magnetic field, by the heating
means such as a laser and by cooling the heated magnetic layer in a
magnetic field.
Although the foregoing description has been directed only to the
reproduction of the color image, furthermore, the method of the
present invention can also be applied to the superposition of an
image of identical colors. In addition, the electrophotographic
image and the magnetic image can be reproduced in combination if an
electrophotogtaphic photosensitive layer is provided on the
magnetic layer.
* * * * *