U.S. patent number 3,894,512 [Application Number 05/227,025] was granted by the patent office on 1975-07-15 for electrostatic developing apparatus.
This patent grant is currently assigned to Research & Development Laboratories of Ohno Co., Ltd.. Invention is credited to Genji Ohno.
United States Patent |
3,894,512 |
Ohno |
July 15, 1975 |
Electrostatic developing apparatus
Abstract
Apparatus is disclosed for developing electrostatic latent
images, comprising a developer supply unit formed of a liquid
repellent layer having a thickness in the range of 3.mu. to 400.mu.
(preferably 5.mu. to 330.mu.), and a substrate, and having
uniformly distributed pores disposed therethrough. A liquid
developer is supplied to the back surface of this unit, and an
exposing unit is disposed to form electrostatic latent images onto
the front surface of the developer supply unit. As a result, the
liquid developer applied to the back surface of the liquid
repellent layer is distributed on the front surface by the action
of the electric field established by the latent image.
Inventors: |
Ohno; Genji (Yokohama,
JA) |
Assignee: |
Research & Development
Laboratories of Ohno Co., Ltd. (JA)
|
Family
ID: |
11655976 |
Appl.
No.: |
05/227,025 |
Filed: |
February 17, 1972 |
Foreign Application Priority Data
|
|
|
|
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Feb 18, 1971 [JA] |
|
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46-7076 |
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Current U.S.
Class: |
399/238 |
Current CPC
Class: |
G03G
9/18 (20130101); G03G 15/102 (20130101) |
Current International
Class: |
G03G
15/10 (20060101); G03G 9/00 (20060101); G03G
9/18 (20060101); G03g 013/00 () |
Field of
Search: |
;118/266,DIG.23,637
;117/17.5,37LE,93.4A ;355/10 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rimrodt; Louis K.
Assistant Examiner: Millstein; Leo
Attorney, Agent or Firm: Staas & Halsey
Claims
What is claimed is:
1. Apparatus for electrostatically reproducing an original image
onto an image bearing medium, said apparatus comprising:
supply means for supplying a liquid developer;
transfer means including a first layer having a first exposed
surface, and a second layer disposed upon said first layer to form
a composite assembly, said second layer having a liquid repellent,
second surface, said composite assembly having a plurality of
openings disposed therethrough, each of said openings through said
first layer presenting a surface wettable whereby the flow of
liquid developer from said supply means is facilitated;
means for receiving an electrostatic latent image theron
corresponding to the original image and disposed with respect to
said transfer means;
means for forming a surface tension contact angle being more than
90.degree. with said second surface in said openings; and
means for effecting liquid developer flow through selected openings
of said composite assembly in response to an electric field
emanating from said electrostatic latent image.
2. Apparatus as claimed in claim 1, wherein at least one of said
transfer means and said receiving means is moved so that successive
portions of said transfer means are exposed to the electric field
emanating from the electrostatic latent image.
3. Apparatus as claimed in claim 1, wherein said transfer means
comprises a cylindrical member including said first and second
layers.
4. Apparatus as claimed in claim 1, wherein said transfer means
comprises a continuous, flexible belt including said first and
second layers.
5. Apparatus as claimed in claim 1, wherein said second layer has a
thickness in the range of 3.mu. to 400.mu. .
6. Apparatus as claimed in claim 5, wherein said second layer has a
preferred thickness in the range of 5.mu. to 330.mu..
7. Electrostatic printing apparatus for developing electrostatic
images on a photoconductive plate with a liquid developer
containing fine colored particles suspended in an aqueous liquid
carrier which comprises:
a developer supply unit having a back surface and a repellent
surface layer 3-400.mu. thick over the back surface forming a front
surface, said developer supply unit having uniformly closely spaced
10-100.mu. pores in said back surface and said repellent layer
penetrating from the front surface through the back surface;
means for providing liquid developer to the back surface of the
developer supply unit;
means for contacting a photoconductive plate having an
electrostatic pattern thereon with liquid developer closely spaced
to the front surface of the developer supply unit; and
means for forming a surface tension contact angle at said surface
layer adjacent said substrate in said pores with said liquid
developer, said contact angle being more than 90.degree.; and means
for exposing said liquid developer to an electrostatic pattern in
said photoconductive plate to provide electrostatic induction
influencing said surface tension angle at said repellent surface
layer for attracting said liquid developer through said pores
toward said electrostatic pattern for developing said electrostatic
pattern.
8. The apparatus of claim 7 wherein the repellent layer comprises
polyethylene, polystyrene, poly-4-fluoroethylene,
poly-3-fluoroethylene chloride, silicone varnish or alkyd
resin.
9. The apparatus of claim 7, wherein the developer supply unit
comprises a cylindrical member including said substrate and said
repellent layer forming an outer surface of said cylindrical
member.
10. The apparatus of claim 7 wherein the developer supply unit
comprises a flexible endless belt substrate.
11. Electrostatic apparatus for developing latent images on a
photoconductive member with a liquid developer containing particles
suspended in a water-containing carrier which comprises:
a developer supply unit having a substrate with a liquid-repellent
layer disposed on the substrate, said developer supply unit having
a plurality of pores through the substrate and repellent layer,
said substrate exhibiting affinity for the liquid developer;
means for providing the liquid developer to the developer supply
unit; and
means for contacting a photoconductive member having an
electrostatic latent image preformed thereon with liquid
developer;
said developer supply unit having means comprising said liquid
repellent material forming a contact angle in said pores greater
than 90.degree. with water-containing liquid developer in the
absence of an electrostatic field and less than 90.degree. under
the influence of said electrostatic latent image, thereby
permitting flow of the liquid developer through said pores adjacent
said latent image.
12. The apparatus of claim 11 wherein said repellent layer is about
3-400.mu. thick and said pores have openings of about 10-100.mu..
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for developing
electrostatic, latent images.
2. Description of the Prior Art
Known methods have been used to develop electrostatic latent images
formed on the surface of a photoconductive insulating plate of an
insulating film. Typically, an electrostatic image is formed on the
insulating member, and the image is developed by charged, colored
particles adhering to the electrostatic latent images. Such methods
employing dry developers have such defects as the scattering of the
colored particles and the use of complex and expensive apparatus.
In such methods the use of liquid developers incurs the risk of
fire, and the liquid developer may be poisonous and have an
objectionable odor. Typically, liquid developers require the use of
an organic solvent which has a high resistance and low dielectric
constant. The liquid development method is satisfactory in
providing copies of high resolution compared with dry development
methods, but those portions where no image appears on the latent
image forming unit may be contaminated because the whole surface of
this unit receives the liquid developer. Further, a liquid
developer requires a hot drying process after developing or the use
of a low boiling point solvent.
SUMMARY OF THE INVENTION
It is a further object of this invention to provide a new liquid,
electrostatic, latent image developing apparatus which reduces the
risk of fire and does not require the use of a liquid developer
having poisonous character of an objectionable odor.
It is a still further object of this invention to eliminate the
drying processes and to apply liquid developer only to the latent
image without damping the whole surface of the latent image forming
unit.
These and other objects of this invention are accomplished by
providing an apparatus for developing images in which the developer
adheres only to those portions where the latent images have been
formed without damping the other portions of the latent image
forming unit. In particular, the liquid developer is applied to the
back of a developer supply unit and is prevented from exuding onto
the unit surface due to a liquid repellent surface provided by a
layer of this unit. Thus, the liquid developer does not adhere to
those portions of the surface of the electrostatic latent image
forming unit, comprised illustratively of a photoconductive
sensitive plate or an insulating film where no electrostatic latent
image exists. Conversely, the developer exudes from the surface of
the developer supply unit, and adheres to those portions of the
plate surface where the latent image has been established. The
liquid developer is absorbed and developes these portions of the
surface, because of the electrostatic polarization or induction of
the developer by the electric charges of the latent images. The
electrostatic, latent image lowers the contact angle between the
developer and the liquid repellent layer, upon those portions where
the electrostatic latent image has been established.
Illustratively, a developer supply unit has a liquid repellent
layer of 3.mu. to 400.mu. thickness (5.mu. to 330.mu. thickness is
preferable) disposed on a surface of a porous substrate except for
the portions of the minute pores. The porous substrate is disposed
to confront a photoconductive, sensitive plate or an insulating
film upon which the electrostatic latent images are established.
The sensitive plate has a plurality of pores distributed uniformly
a close spacings, over the entire surface thereof; the openings are
penetrated from the back to the front surface openings.
As a result of this invention, it is not required to have such high
resistance and low dielectric constant as the carrier liquid of the
charged, fine particles used in the conventional methods.
Therefore, the developer of this invention could be water, or other
incombustible, odorless and innoxious solutions containing
water.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing
out and distinctly claiming the subject matter which is regarded as
the invention, a preferred embodiment is disclosed in the following
detailed description taken in conjunction with the accompanying
drawings, in which:
FIG. 1 is a cross-sectional view of the contact angle of a liquid
drop on the surface of a liquid repellent film;
FIG. 2 is a cross-sectional view of the change of the said contact
angle, when the liquid repellent film is charged;
FIG. 3 is a perspective, enlarged view of a fine porous developer
supply unit in accordance with the teachings of this invention;
FIG. 4 is a cross-sectional view of the developer supply unit shown
in FIG. 3;
FIG. 5 is a cross-sectional view of an embodiment of the
invention;
FIG. 6 is a further cross-sectional view of the embodiment shown in
FIG. 5; and
FIG. 7 is a side view of another embodiment of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown a liquid drop 2 of water
disposed on an uncharged liquid repellent film 1. The contact angle
.theta. between the film surface uncharged and the drop is greater
than 90.degree. and the film surface is not wetted. Referring to
FIG. 2, however, the liquid repellent insulating film is charged;
as a result the contact angle .theta. decreases to less than
90.degree., and the liquid drop is able to wet the film surface.
The wetting effect is dependent upon the liquid repellent intensity
of the film surface, the kind of liquid, and the applied voltages.
When a water drop is placed on a film of 3-fluoro ethylene chloride
resin, for example, the contact angle .theta. of an uncharged film
is 108.degree.. When a film of this material is charged to -500V,
the angle .theta. decreases to 56.degree. and the film surface is
wetted.
FIG. 3 is a perspective view of a photosensitive plate used in
accordance with the teachings of this invention. A layer 5 having a
liquid repellent surface and a specified thickness is formed on a
substrate 4 to form a composite assembly. A plurality of minute
pore openings 6 extend through the composite assembly and are
distributed uniformly at close spacings over the entire surface
thereof. The composite assembly shown in FIG. 3 forms unit 7.
FIG. 4 shows the arrangement of the liquid developer supply unit 7
indicated in FIG. 3 in relation to an electrostatic-latent image
forming unit 8. The electrostatic latent image forming unit 8 is a
sensitive plate composed basically of a conductive supporting
substrate 9, a photoconductive layer 10, and an insulating layer
11, as illustratively described in U.S. Pat. application Ser. No.
528,624. The photosensitive plate 8 may be charged with
electrostatic latent images 3 (indicated by dotted lines), and
disposed in the front of the developer supply unit 7.
Now, the substrate 4 of the unit 7 is selected properly so that the
contact angle of the developing liquid therewith is less than
90.degree. to thereby wet the substrate surface. Also, the
characteristics of the liquid repellent layer 5 is selectively
chosen that the contact angle of the developing liquid exceeds
90.degree. in the absence of a charge, but becomes less than
90.degree. in the presence of a weak electric field to permit the
surface of the liquid repellent layer to be wetted.
In the image developing process, the liquid developer is supplied
from the back surface of the developing supply unit 7, whereby the
developer enters the minute pores 6 of the substrate 4 to be
selectively directed to the liquid repellent surface of layer 5. In
particular, the flow of the developer through the pores 6 is
retarder to a greater extent at those portions of the unit 7 where
no electrostatic latent image has been established. Conversely, the
liquid developer is drawn through the minute pores 6 of the
substrate 4 under the influence of the charges of the latent
images, which generate an electrostatic induction or an
electrostatic polarization to attract the liquid developer. At the
same time, the contact angle .theta. of the liquid developer with
respect to the liquid repellent layer is decreased at those
portions of the unit 7 adjacent to the electrostatic images formed
on the unit 8. The developer, therefore, wets the inside of the
minute pores 6 of the liquid repellent layer 5 to exude onto the
surface of this layer 5. As mentioned above, the liquid repellent
layer 5 of the developer supply unit 7 entirely restricts developer
flow at the portions disposed adjacent to those portions of unit 8
where no latent image is formed, and causes the developer to exude
onto those portions adjacent to the latent image.
The thickness of the liquid repellent layer is selected in the
range of 3.mu. to 400.mu. , and is preferably determined to be from
5.mu. to 330.mu.. When the thickness of the liquid repellent layer
is less than 3.mu., the surface portions without a latent image are
often contaminated by fine dust and other particles adhering to the
minute pores, to effect thereby the uniformity of liquid flow
through the minute pores and/or to interrupt the smooth surface of
the latent image forming unit. When this thickness exceeds 400.mu.,
the effect of the charge of the latent image is weakened and
sufficient developer flow does not readily occur. The optimum
thickness of the liquid repellent layer varies with the quantity of
the charges of the latent images, the velocity of the developer
flow, the viscosity of the developer, the dielectric constant and
electric resistance of the developer, the surface tension of the
developer and the distance between the developer supply unit and
the surface of the latent image, etc. According to results of
conducted experiments, good results may be obtained when the
thickness of the liquid repellent layer is selected in the range of
5.mu. to 330.mu..
When the liquid developer supply unit 7 is contaced with or closely
spaced from the electrostatic latent image forming unit 8, the
developer exuded onto the surface of the liquid repellent layer 5
is attracted to those surface portions adjacent to the latent image
to thereby develop the latent images. As mentioned above, the
developer does not come into contact with the surface of the latent
image forming unit, where no latent image appears so that the
latent image forming unit does not necessarily require a surface
having a liquid repelling property; therefore, various types of
latent image forming units may be used in this invention.
The size of the minute pores or openings of the substrate of the
liquid developer supply unit varies with the resolution of the
copied image required and is selected in the range of 10.mu. to
100.mu. and is preferably chosen to be in the range of 10.mu. to
50.mu. for business copy. The spacing between pores is selected in
the range of 10.mu. to 100.mu. . When the size of a minute pore
becomes less than 10.mu., the pores are blocked with accumulations
of developers when the developer supply unit is used repeatedly.
When the pore diameter is greater than 100.mu., the liquid
repelling force of the layer becomes weak and the portions of the
surface of this layer where no latent image exists become
contaminated and the printed image becomes visually rough.
The substrate with minute pores, may be easily made by wellknown
methods of manufacturing a metallic porous filter by perforating
the minute pores of the desired sizes on the entire surface, or by
photoetching on a copper (or other suitable metallic) plate;
alternatively a metallic mesh with interstices of the desired size
may also be used as the substrate of the invention.
The substrate 4 may be made liquid repellent: 1) by spraying to
form the coating; 2) by connecting the substrate to one polarity of
a DC power source, and 3) by applying electric charges of opposite
polarity to the sprayed liquid particles at the time when the
solution such as polyethylene, polystyrene, alkyd resin or silicone
varnish, etc., is being sprayed thereon. When the composing liquid
of the developer is water or contains water, the coating may be
formed by applying a thin film of oil and fat such as mineral oil,
wax, etc., onto the surface of the substrate.
In addition to the materials metnioned above, those materials
having a contact angle with respect to the liquid component of the
developer, is over 90.degree. with no charge and is less than
90.degree. under the effect of the electric charges of the latent
image, and can be used to form the liquid repellent layer of this
invention.
The developer of this invention is composed of a liquid as main
agent and of such agents to adjust coloring, surface tension, and
viscosity, etc. The composing liquid of the developer must have an
affinity with the substrate, to achieve a contact angle not less
than 90.degree. to the liquid repellent surface of the developer
supply unit, and less than 90.degree. when exposed to the effects
of the electric charges of the latent image to permit wetting of
the liquid repellent layer on the surface portions adjacent to the
latent images of the latent image forming unit. Water, glycerine,
ethylene, glycol, etc. are suitable for use as the composing liquid
of the developer, when the materials of the liquid repellent layer
are polyethylene, polysylene, 4-fluoro ethylene, 3-fluoro ethylene
chloride, silicone varnish, and alkyd resin.
The coloring agent may be disposed in either a liquid state or in a
suspension state, or may be the mixture of both states. If the
developer liquid is water or includes water as a component such
water-soluble dyes as malachite green, methyl violet, victoria
blue, persian orange, etc., may be used. If the developer liquid
includes alcohol, such alcohol-soluble dyes as pigment green,
carmine FB, etc., may be used.
The surface tension adjusting agent is employed to adjust the
optimum contact angle according to the properties of the liquid
repellent layer and the developing velocity, and is adjusted by
mixing two kinds of liquid having different surface tension, or by
utilizing a very small amount of a well known surface active
agent.
The viscosity adjusting agent is added to adjust the liquidity of
the developer according to the developing velocity. However, if the
developer liquid is water or includes water as a component, a
liquid soluble resin such as polyvinyl alcohol, dextrin, gelatin,
methyl melamin, etc., may be added with the solution state. The
viscosity adjusting agent can also serve to fix the coloring agent
when the developer drys after being transferred to the
electrostatic latent image forming unit or to a piece of blank
print paper (medium).
The electrostatic latent image, which is developed in accordance
with the method of this invention, may be applied to many different
electrostatic reproducing processes such as the method wherein
images are formed by an electric discharge on the surface of an
insulating film, etc., or the method wherein a latent image is
formed by electric charge or light irradiation onto a
photoconductive sensitive plate composed of zinc oxide, cadmium
sulfide, selenium, organic semiconductor, etc. The latent images
however, must be maintained at least until the development is
performed. For this reason, the methods of forming an electrostatic
latent image by distributing internal electric charges or space
electric charges, as described in Japanese Patent Publications No.
23,910/1967, No. 1552/1968, and No. 6385/1969, or by the PIP method
may be preferred.
FIG. 5 shows an embodiment of the developing apparatus of the
invention, having a developer supply unit of cylindrical
configuration. FIG. 6 is a cross-section view of the embodiment
shown in FIG. 5. FIG. 7 shows an embodiment of the developer supply
unit including an endless belt member.
In FIGS. 5, 6 and 7, like mumbers will be used to designate
corresponding elements. Unit 13 supplies the developer to the
inside surface of a cylindrical unit 12 or endless belt developer
supply unit 12a. In turn the units 12 and 12a supply the liquid
developer through the pores to selected portions of the surface of
the repellent layer 5. As noted above, the repellent layer 5 is
disposed over the entire surface of the porous substrate 4 except
for those portions of the fine pores.
As shown in FIGS. 5 and 6, the unit 13 causes the developer to
drain from a small hole 16 located at the tip of a pipe 15 which is
disposed along the axis of the unit 12. In FIG. 7 the developer is
supplied to the back surface of a flexible belt 12a by a roller 17
which is employed to draw developer from a reservoir thereof and
apply it to the back surface of the flexible belt 12a. It is noted
that both units 12 and 12a include the porous substrate 4 and the
repellent layer 5.
When the developer supply unit 12 is rotated in the direction of
the arrow by a driving device (not shown), the unit 12 applies the
developer from its back surface to those portions of its front
surface opposite the electrostatic latent images formed on the
image forming unit 8. As the unit 8 is moved in the direction shown
by the arrow and the units 12 and 12a rotate, successive portions
of the latent image are brought in close relation to the developer
supply unit 12 to thereby transfer the developer onto those surface
portions of the unit 8 charged with the latent image.
EXAMPLE 1
The porous substrate of 3-mm thickness was made by pressing and
sintering brass powder having grain diameters in the order of
50.mu.. The surface of the substrate was ground smoothly, and
openings or pores disposed therethrough having a mean diameter in
the order of 14.mu.. The substrate was connected to an electrode of
1 KV D.C. source while the other source electrode is connected to a
spray nozzle. A silicone varnish (with 5 percent parts of resin) is
sprayed by the nozzle to be electrodeposited on the substrate; the
dried varnish forms the liquid repellent layer of about 60.mu.
thickness. This substrate was used as a developer supply unit.
______________________________________ Next, a liquid developer,
composed of Methylene blue 6g Polyvinyl alcohol (3% solution) 50cc
Water 50cc ______________________________________
was supplied uniformly to the back of the supply unit. Next, the
surface of the liquid repellent layer of this unit was
press-contacted with a zinc oxide sensitized paper, upon which the
electrostatic latent image was formed. The parts of the latent
images were developed onto the sensitized paper as clear blue
images corresponding to the original picture image.
EXAMPLE 2
A liquid repellent layer of 8.mu. thickness was made by the same
method as the Example 1 on one surface of a brass screen of 30 cm
width and 250 meshes; the covering screen was used as the endless
developer supply unit 12a of the FIG. 7. A developer composed
of:
Carbon black 7g Victoria blue 0.15g Gelatin 2g Glycerine 15g Water
100cc was supplied to the inside surface of the thus covered
screen.
The latent image forming unit 8 was formed in the following manner.
A coating material composed of:
Cadmium sulfide activated by copper 90g Vinyl chloride 20g Xylene
50cc Dichlrol ethane 10cc
was coated and dried to a thickness of about 100.mu. on an
aluminium plate of about 2 mm thickness. Further, a polyester layer
of about 8.mu. thickness was formed on this plate, to provide a
space charge type of photoconductive sensitive plate. The
electrostatic latent image formed on the above sensitive plate by
well-known methods, was developed with the developer supply unit
12a at a speed of 5 cm per second; a clear, blue-black image was
obtained.
EXAMPLE 3
As in Example 2, a benzol solution of low molecular weight
polyethylene was electrodeposited by the method set out in Example
1, on the surface of a substrate perforated by minute pores having
a diameter of about 50.mu.. The pores were formed by photoetching
to a density of 100 pores per mm.sup.2 through a copper plate of
50.mu. thickness. Next, the substrate was heated sufficiently,
fused, and adhered to provide the developer supply unit 12. Using
this supply unit 12, electrostatic latent images formed on a zinc
oxide sensitized paper were developed at the speed of 7 cm per
second by a developer composed of,
Victoria blue 3g Persian orange 5g Methylol melamine 5g Water
100cc
A clear image was obtained on the zinc oxide print medium.
Numerous modifications and adaptations of the system of the
invention will be apparent to those skilled in the art and thus it
is intended by the dependent claims to cover all such modifications
and adaptations as fall within the true spirit and scope of the
invention.
* * * * *