U.S. patent number 3,707,138 [Application Number 05/097,649] was granted by the patent office on 1972-12-26 for apparatus for transferring a developed image from a photosensitive member to a receiver.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to Randle Velore Cartwright.
United States Patent |
3,707,138 |
Cartwright |
December 26, 1972 |
APPARATUS FOR TRANSFERRING A DEVELOPED IMAGE FROM A PHOTOSENSITIVE
MEMBER TO A RECEIVER
Abstract
Apparatus is provided for transferring a developed toner image
from a photoconductor to a receiver by a method which includes
applying to the receiver a bias voltage opposite in polarity to the
charge on the developed toner image. The toned photoconductor is
precharged to the same polarity as the developed toner image to
assure a maximum charge on the toner particles forming the image
prior to their contact with the receiver and then flooded with
light prior to and/or during the transfer to reduce the forces of
attraction between the toner particles and the photoconductor.
Inventors: |
Cartwright; Randle Velore
(Honeoye Falls, NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
22264471 |
Appl.
No.: |
05/097,649 |
Filed: |
December 14, 1970 |
Current U.S.
Class: |
118/638; 399/315;
430/125.5 |
Current CPC
Class: |
G03G
15/169 (20130101) |
Current International
Class: |
G03G
15/16 (20060101); G03g 013/00 () |
Field of
Search: |
;118/637 ;117/17.5,93.4
;96/1.4,1.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
T869004 (Def. Pub.), Culhane, U.S. published in Dec. 69.
|
Primary Examiner: Stein; Mervin
Assistant Examiner: Millstein; Leo
Claims
I claim:
1. Apparatus for transferring a toner image from an element,
comprising a photoconductive insulating layer overlying a
translucent conductive base, to a receiver, the toner image being
formed of toner particles having a charge of a first polarity
thereon which create forces of attraction between the toner
particles and the photoconductive insulating layer, said apparatus
comprising:
a. a corona discharge electrode for applying an electrostatic
charge of said first polarity to the toner image on said
photoconductive insulating layer;
b. means, including a rotatable cylinder and an opposed backing
roller forming a nip there between, for bringing the toner image on
said photoconductive insulating layer into face to face
relationship with the receiver along at least a line of contact,
said line of contact and the respective central axes of said
cylinder and said roller lying in a common plane;
c. a source of direct current potential for applying an electrical
potential of a second and opposite polarity to the receiver at said
line of contact to attract the toner image to the receiver;
d. a source of illumination for exposing said photoconductive
insulating layer to actinic radiation through said translucent
conductive base to reduce the forces of attraction between the
toner particles and said element ; and
e. means for separating said element from the receiver as the
receiver passes from said nip along an exit plane, wherein the
included angle between said common plane and said exit plane is
less than 90.degree..
2. Apparatus for transferring a toner image as claimed in claim 1
wherein said cylinder is translucent and said source of
illumination comprises a tubular light source mounted inside said
cylinder.
3. In an electrophotographic machine, apparatus for transferring a
toner image from a flexible element, comprising a photoconductive
insulating layer overlying a transparent conductive base, to a
receiver, the toner image being formed of toner particles having a
charge of a first polarity thereon which create forces of
attraction between the toner particles and the photoconductive
insulating layer, said apparatus comprising:
a. a transparent rotatable roller;
b. an electrically conductive roller mounted in opposed
relationship with said transparent roller to form a nip there
between;
c. means for moving the receiver through said nip , in face to face
contact with the toner image on said photoconductive insulating
layer;
d. a corona discharge electrode for applying an electrostatic
charge of said first polarity to the toner image on said
photoconductive insulating layer prior to the entry of the toner
image into said nip;
e. a source of direct current potential connected to said
electrically conductive roller for applying an electrical potential
of a second and opposite polarity to said receiver as said receiver
passes through said nip to attract the toner image to said
receiver; and
f. a lamp mounted inside said transparent roller for uniformly
illuminating said photoconductive insulating layer through said
conductive base as said element carrying the toner image thereon
passes through said nip to reduce the forces of attraction between
the toner particles and said element.
4. Apparatus for transferring a toner image from a photoconductive
element to a receiver, the toner image being formed of toner
particles having an electrostatic charge of a first polarity
thereon which create forces of attraction between the toner
particles and the photoconductive element, said apparatus
comprising:
a. charging means for applying an electrostatic charge of said
first polarity to the toner image on said photoconductive
element;
b. means for bringing the charged toner image on said
photoconductive element into face to face relationship with the
receiver along at least a line of contact, said means
comprising:
1. a rotatable cylinder, and
2. a translucent backing roller disposed in opposed relationship to
said cylinder, said backing roller being formed of an electrically
conductive material, said cylinder and said backing roller forming
a nip between which said photoconductive element and the receiver
pass;
c. potential applying means connected to said backing roller for
applying an electrical potential of a second and opposite polarity
to the receiver to attract the toner image to the receiver; and
d. a source of radiation mounted within said backing roller for
exposing said photoconductive element to actinic radiation during
contact between the toner image and the receiver to reduce the
forces of attraction between the toner particles and said
photoconductive element.
5. Apparatus for transferring a toner image from a photoconductive
element of the type having a photoconductive insulating layer
overlying a substantially transparent conductive layer to a
receiver, the toner image being formed of toner particles having an
electrostatic charge of a first polarity thereon which create
forces of attraction between the toner particles and the
photoconductive element, said apparatus comprising:
a. charging means for applying an electrostatic charge of said
first polarity to the toner image on said photoconductive
element;
b. means for bringing the charged toner image on said
photoconductive element into face to face relationship with the
receiver along at least a line of contact, said means
comprising:
1. a substantially transparent rotatable cylinder located to
contact the side of said photoconductive element opposite the toner
image, and
2. at least one electrically conductive backing roller disposed in
opposed relationship to said cylinder for contacting the receiver
and said cylinder, said cylinder and said backing roller forming a
nip between which said photoconductive element and the receiver
pass;
c. potential applying means connected to said backing roller for
applying an electrical potential of a second and opposite polarity
to the receiver during contact with the toner image to attract the
toner image to the receiver; and
d. means for exposing said photoconductive element to actinic
radiation during contact between the toner image and said receiver
to reduce the forces of attraction between the toner particles and
said photoconductive element, said means for exposing being located
inside said cylinder.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a method and apparatus for transferring a
toned electrostatic image from a photoconductive member to a
receiver and, more particularly, to an improved transfer method and
apparatus utilizing electrical bias means and illuminating
means.
2. Description of the Prior Art
In a conventional electrophotographic process, an electrostatic
image is formed on a photoconductive surface as by placing a
uniform electrostatic charge on the photoconductive surface which
surface is subsequently exposed to a radiation pattern to dissipate
the charge in the exposed areas. This electrostatic image is then
toned by a suitable developer having toner particles which are
attracted by the charged areas of the image. The toner particles
comprising the developed image are then transferred to a suitable
receiver by contacting the receiver to the image bearing
photoconductive surface and applying a potential to the receiver of
opposite polarity to the charge on the toner particles to bring
about image transfer. To reproduce copies of excellent quality and
with a high contrast image, it is desirable to transfer to the
receiver as much of the developed image as possible. Any residual
toner particles which remain on the photoconductive surface after
transfer must be removed therefrom prior to the forming and
transfer of subsequent images to prevent ghost images from being
formed during subsequent transfers. It is difficult to clean off
excess toner particles without scratching or otherwise injuring the
delicate photoconductive surface. As a result, the life of the
photoconductive surface tends to be limited by mechanical and
electrical failure resulting from toner abrasion.
To improve the quality of the copies reproduced and/or to reduce
the deleterious effects of cleaning, various attempts have been
made to increase the efficiency of the transfer process. U.S. Pat.
No. 3,414,409 to Gallo discloses a transfer method in which image
transfer is accomplished without charging the receiver. In
accordance with the teachings of this patent the image bearing
photoconductive layer is contacted with the receiver and the
photoconductive layer is uniformly illuminated at the point of
transfer. U.S. Pat. No. 3,520,604 to Shelffo discloses a transfer
roller which is charged by a DC voltage supply having a polarity
which is the same as the polarity of the electrostatic charges in
the latent image portions. U.S. Pat. No. 3,444,369 to Malinaric
discloses subjecting a developed toner image on a photoconductor to
a low level corona discharge of a polarity opposite the charge on
the toner particles overlying the image area. In some environments,
such transfer devices have not been found entirely satisfactory.
Incomplete transfer produces a poor quality print of low image
contrast and the residual toner particles remaining on the
photoconductive surface have resulted in scumming and scratching of
the photoconductive surface during the cleaning operation.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved
apparatus for transferring toner particles from a photoconductive
surface to a receiver.
Another object of the invention is to provide an improved method
for transferring toner particles from a photoconductive surface to
a receiver.
Still another object of the invention is to provide a more complete
transfer of a toned image from a photoconductive surface to a
receiver.
Yet another object of the invention is to reduce the scumming and
scratching of a photoconductive surface resulting from toner
particle abrasion.
These and other objects are accomplished, in accordance with the
present invention, by applying an electrical charge to a previously
charged, exposed and developed photoconductor of the same polarity
as the charge on the toner particles forming the developed image.
The photoconductor is then brought into face to face relationship
with the receiver along a line or area of contact. A bias potential
opposite in polarity to the charge on the toned image is applied to
the receiver to attract the toner particles forming the image to
the receiver and the photoconductor is exposed to radiation along
the line or area across which transfer occurs to reduce the forces
of attraction between the photoconductor and the toner
particles.
In a preferred embodiment of the invention, a transfer apparatus is
provided with a corona charger which applies to the photoconductor
an electrostatic charge of the same polarity as the charge on the
toner particles forming the toner image. The photoconductor and the
receiver are subsequently brought into a face to face relationship
along at least a line of contact. Along the line of contact, an
electrical potential opposite in polarity to the charge on the
toned image is applied to the receiver by a source of potential and
a source of radiation illuminates the photoconductor. The
precharging of the photoconductor increases the attraction between
the toner image and the receiver and its illumination at the time
of transfer reduces the attraction between the photoconductor and
the toner image thereby achieving a more complete transfer of the
toner particles forming the image.
More specifically, the preferred embodiment of the invention is
adapted for use with a flexible photoconductor comprising a
photoconductive insulating layer overlying a transparent base. The
photoconductor carrying a developed toner image thereon is moved
past a corona which applies an electrostatic charge to the
photoconductive surface of the photoconductor of the same polarity
as the charge on the toner particles forming the image. The toner
image and the receiver are then brought into face to face contact
by movement of the photoconductor and the receiver through the nip
formed by a transparent cylinder and an opposed electrically
conductive backing roller. As the receiver and the photoconductor
pass together through the nip, a source of direct current potential
connected to the backing roller applies to the receiver a bias
voltage opposite in polarity to the charge on the toned image and a
lamp mounted inside the transparent roller uniformly illuminates
the photoconductive surface of the photoconductor through the
transparent conductive base.
BRIEF DESCRIPTION OF THE DRAWING
In the detailed description of the preferred embodiment of the
invention presented below, reference is made to the accompanying
drawing wherein corresponding parts are identified by like numerals
and in which:
FIG. 1 is a diagrammatic side elevational view of a conventional
electrophotographic mechanism embodying the transfer station of the
present invention.
FIG. 2 is an enlarged, fragmentary view of a portion of FIG. 1,
showing the transfer station in greater detail.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now the the drawing there is shown an electrophotographic
mechanism M, which includes an endless, flexible photoconductive
element such as a web or belt 1 comprising a photoconductive
insulating surface 2 overlying a conductive base 3 and extending
around spaced rollers 4 and 6. The belt 1 is moved through an
endless path and is illustrated as being driven by motor 8 through
a drive belt 10 connected to roller 6. The roller 4 is mounted as
shown so that it is freely rotatable. The belt 1 is driven in the
direction of arrows 11 past a charging station 12 which places a
uniform electrical charge (either positive or negative) over its
photoconductive surface; an exposure station 14 whereat the belt is
exposed to a radiation pattern, such as a light image from an
original, to discharge the photoconductive surface in accordance
with the radiation pattern to form an electrostatic latent image; a
developing station 16 whereat the latent image is developed by
depositing toner thereon; a novel transfer station T, described in
detail below, whereat the developed image is transferred to a
receiver 18; and finally a cleaning station 20 whereat the
photoconductive surface of the belt 2 is cleaned of residual toner
particles. The charging, exposure, developing and cleaning stations
are mentioned herein without detailed description and may be
understood to be selectable as required by one skilled in the art
from any suitable form known in the prior art.
At the transfer station T, the developed toner image on the
photoconductive surface 2 of the belt 1 is brought into contact
with the receiver 18 which is fed from a supply (not shown) by a
pair of opposed feed rollers 21 through a nip 22 formed between
rollers 4 and 24. The roller 24 has a soft, compliant, electrically
conductive surface and can be set to apply a controlled pressure at
the nip 22 to provide firm contact between the receiver 18 and the
toned image as they pass together between the rollers 4 and 24. The
roller 24 is insulated from ground so that an electrical potential
from a DC source 26 opposite in polarity to the charge on the toner
particles forming the image, may be applied to it to effect image
transfer as the receiver passes through the nip. To assure
immediate separation of the receiver from the photoconductive
surface after transfer, it is furthermore desirable that the guide
path for the exiting receiver 18 formed by the opposed rollers 23
is arranged so that the clockwise angle A from the plane passing
through the axes of the rollers 4 and 24 to the plane of the
exiting receiver be 90.degree. or less. In some embodiments of the
invention, the single conductive pressure or backing roller 24
shown in FIG. 2 can be replaced by two or more such rollers to
increase contact time between the receiver 18 and photoconductive
belt 1 to enhance image transfer. In this case, the angle A would
be the clockwise angle from the planes passing through the axis of
the exit roller and the axis of the roller 4 to the plane of the
exiting receiver 18. After separation, the receiver 18, in
accordance with known practice, can be fed to a fusing station 25
whereat the toner image is permanently fixed to the receiver, as by
opposed feed rollers 23.
To increase the charge on the toner particles forming the image and
therefore their attraction to the receiver 18, which is
oppositively biased by the source 26, means are provided, such as a
corona discharge device 28 upstream of nip 22. The corona 28
applies a uniform electrostatic charge to the photoconductive
surface 2 of the belt 1 and the developed image of a polarity
opposite to the potential applied to the roller 24 by the source
26.
To reduce the charge on the photoconductive surface 2 of the belt 1
in the toned areas and thereby decrease the attraction between the
photoconductive belt and the developed toner image, the
photoconductive surface of the belt is exposed along the line or
area of image transfer to radiation, such as actinic radiation, by
means of, for example, an incandescent lamp 30. The lamp 30 also
prevents charge buildup on the photoconductive surface in the
untoned areas as a result of charging with the corona 28. As best
seen in FIG. 2, the tubular light source 30 is mounted inside of
roller 4. Accordingly, both the roller 4 and the conductive base 3
of the belt 1 must be translucent, and preferably transparent.
Alternatively, the illumination source 30 can be mounted inside
roller 24 so that it can directly illuminate the photoconductive
surface 2 of the belt 1. In this instance, of course, roller 24 and
the receiver 18 must be formed from a properly selected translucent
or transparent material. If desired, a reflector 32, such as an
eliptical reflector, may be provided around a portion of the light
source 30 as shown in FIG. 2, to direct the radiation to the area
of transfer. The use of reflector 32 is optional and illumination
of the photoconductive surface may occur before and/or during
transfer. Illumination of the image bearing photoconductive surface
2 of the belt may be by means of a very brief flash of high
intensity light or by a relatively longer exposure to comparatively
low level illumination. The former has the advantage of high speed
and is, therefore, more suitable for a continuous process
apparatus.
Exposure of the photoconductive surface to radiation, such as
actinic radiation, substantially neutralizes the electrostatic
charge pattern. The toner particles forming the image are attracted
toward the oppositively biased receiver 18 with which they are in
contact.
From the foregoing, the advantages of the present invention are
readily apparent. Novel transfer apparatus has been disclosed which
achieves a more complete transfer of the toned image than
previously known apparatus. This is accomplished by precharging the
toned image and by flooding the photoconductor with light and
applying a bias voltage to the receiver at the time of transfer to
facilitate the transfer.
The invention has been described in detail with reference to a
preferred embodiment thereof, but it will be understood that
variations and modifications can be effected within the spirit and
scope of the invention.
* * * * *