U.S. patent number 3,850,627 [Application Number 05/290,618] was granted by the patent office on 1974-11-26 for electrophoretic imaging method.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Edward Forest, Paul C. Swanton, John W. Weigl, John B. Wells.
United States Patent |
3,850,627 |
Wells , et al. |
November 26, 1974 |
ELECTROPHORETIC IMAGING METHOD
Abstract
An electrophoretic imaging process wherein a suspension of
particles in a carrier liquid are placed between a photoconductive
electrode and a second electrode. With an electrical field applied
between the photoconductive electrode and the second electrode the
photoconductor is exposed to imagewise radiation which causes
particles on the surface of the photoconductive electrode to be
driven away in image configuration by charge exchange with the
photoconductive electrode. The migrating particles form a negative
image on the second electrode leaving a positive image behind on
the photoconductive electrode.
Inventors: |
Wells; John B. (Rochester,
NY), Swanton; Paul C. (Webster, NY), Weigl; John W.
(West Webster, NY), Forest; Edward (Rochester, NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
26801488 |
Appl.
No.: |
05/290,618 |
Filed: |
September 20, 1972 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
104389 |
Jan 6, 1971 |
|
|
|
|
Current U.S.
Class: |
430/34;
430/35 |
Current CPC
Class: |
G03G
17/04 (20130101) |
Current International
Class: |
G03G
17/00 (20060101); G03G 17/04 (20060101); G03g
013/22 () |
Field of
Search: |
;96/1PE,1R,1.3
;117/17.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Klein; David
Assistant Examiner: Goodrow; John L.
Attorney, Agent or Firm: Ralabate; James J. Petre; David C.
Tomlin; Richard A.
Parent Case Text
This is a continuation, of application Ser. No. 104,389, filed Jan.
6, 1971 now abandoned.
Claims
What is claimed is:
1. A method of imaging which comprises the steps of:
a. providing a layer of a suspension of finely divided particles in
an insulating carrier liquid on the surface of a first electrode
said first electrode comprising a photoconductive layer having a
thickness of up to about 5 microns;
b. applying an electrical field across said suspension until at
least a portion of said particles in said suspension migrate to
said first electrode to form a relatively uniform particulate layer
thereon;
c. exposing said photoconductive layer to a pattern of
electromagnetic radiation to which said photoconductive layer is
sensitive, and simultaneously;
d. applying an electrical field between said first electrode and a
second electrode having an electrically insulating surface in
contact with said suspension until at least a portion of said
particles on said first electrode exchange charge with said first
electrode in areas corresponding to illuminated areas of said
photoconductive layer and migrate away from said first electrode to
form an image on said second electrode.
2. The method of claim 1 wherein said suspension is provided in the
form of a solid layer of particles in a solid binder and said
binder is made a liquid prior to particle migration.
3. The method of claim 1 wherein said photoconductive layer is
provided on the surface of a transparent conductive member and said
photoconductive layer is exposed to radiation through said
transparent conductive substrate.
4. The method of claim 1 wherein said photoconductive layer is
provided on a substrate.
5. The method of claim 1 wherein said photoconductive layer is
overcoated.
6. The method of claim 1 wherein said photoconductive layer is
overcoated with an active transport material.
7. The method of claim 1 wherein said particles comprise dyed
thermoplastic materials.
8. The method of claim 1 wherein said particles comprise metallic
materials overcoated with a resin material.
9. The method of claim 1 wherein said particles comprise magnetic
particles overcoated with a resin material.
10. The method of claim 1 wherein said particles comprise spirit
soluble dye materials.
11. The method of claim 1 wherein said photoconductive layer
comprises selenium.
12. The method of claim 1 wherein said photoconductive layer
comprises metal-free phthalocyanine.
13. The method of claim 1 wherein said photoconductive layer is
overcoated with poly (N-vinyl carbazole).
14. The method as defined in claim 1 wherein said particles have a
diameter of up to about 5 microns.
15. The method as defined in claim 1 wherein said particles have a
diameter of up to about 2 microns.
16. The method as defined in claim 15 wherein said particles have a
surface having a bulk resistivity of about 10.sup.5 ohm-cm or
more.
17. The method as defined in claim 1 wherein said particles have a
surface having a bulk resistivity of about 10.sup.5 ohm-cm or
more.
18. The method as defined in claim 1 wherein said photoconductive
layer is provided on the surface of a transparent conductive
substrate and said photoconductive layer is exposed to radiation
through said transparent conductive substrate, and said particles
have a diameter of up to about 2 microns and have a surface having
a bulk resistivity of about 10.sup.5 ohm-cm or more.
Description
BACKGROUND OF THE INVENTION
This invention relates to imaging systems. More specifically this
invention concerns an electrophoretic imaging system.
The use of photoconductors to form images is well known. For
example, in xerography such as described in U.S. Pat. No. 2,297,691
to C. F. Carlson photoconductors are widely used. In this process a
layer of a photoconductor on a conductive substrate is first
provided with a uniform electrostatic charge on its surface in the
dark and is then exposed to a light image which causes the
photoconductor to allow charge to dissipate through it to the
conductor in light struck areas leaving a pattern of electrostatic
charge on the surface of the photoconductor. This electrostatic
image is then made visible by any number of methods. In one process
finely divided particles of colorant called toner which is
attracted by the electrostatic charge is cascaded across the
photoconductor. Normally a carrier material for the toner is used
to ensure that all areas of the photoconductor are contacted with
toner. The toner material may also be dispersed in an insulating
carrier liquid; the combination is called a liquid developer. As
liquid developer is brought into contact with the photoconductor
the toner material is drawn out of the liquid and is held to the
photoconductor by electrostatic attraction. Many variations of the
above processes exist. In one variation shown in U.S. Pat. No.
2,892,709 to E. F. Mayer the surface of the photoconductor is
charged through a liquid developer layer while the photoconductor
is exposed to a light image. The photoconductor will not accept a
charge in illuminated areas thus forming an electrostatic image on
dark areas. The toner material in the liquid developer is drawn to
or precipitates on the surface of the photoconductor in the charged
areas forming a visible image.
The above processes have a number of deficiencies. A major problem
is that the photoconductors must be charged to an initial potential
and then discharged in image configuration to provide an
electrostatic image of sufficient strength to attract toner
particles. These two process steps take a certain amount of time to
complete which slows process speed. The process of U.S. Pat. No.
2,892,709 requires that the charging of the photoconductor be
accomplished through an insulating liquid having particles
dispersed therein which is relatively inefficient. Also the above
processes are subject to background formed by particles adhering to
areas of the photoconductor which are not charged. These particles
of toner in background areas interfere with final image
quality.
Another disadvantage of prior art systems is that the
photoconductive layer must be insulating enough to hold a high
charge for the time necessary to develop an image. Further, the
prior art processes require that the toner material be carefully
selected to have the proper triboelectric relationships to the
carrier material and to the charge on the surface of the
photoconductor. Also the prior art processes are not capable of
producing positive and negative images at the same time and can
change image sense only by the addition of complicated process
steps.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a method of imaging
using a photoconductive layer which overcomes the above noted
disadvantages.
It is another object of this invention to provide a novel
electrophoretic imaging system.
It is another object of this invention to provide an
electrophoretic imaging system which can utilize a relatively wide
range of photoconductive layers.
It is another object of this invention to provide an
electrophoretic imaging system which is capable of forming images
out of a relatively wide range of materials.
It is another object of this invention to provide an
electrophoretic imaging system capable of producing full color
images.
It is another object of this invention to provide an
electrophoretic imaging system capable of producing positive images
directly from negative input.
It is another object of this invention to provide an
electrophoretic imaging system which can simultaneously form
positive and negative images.
It is another object of this invention to provide an
electrophoretic imaging system capable of producing magnetically
readable images from optical input.
The above objects and others are accomplished in accordance with
this invention by providing an electrophoretic imaging system
wherein finely-divided particles dispsersed in an insulating liquid
are placed between a photoconductive injecting electrode and a
second electrode. The photoconductive injecting electrode is
exposed to a pattern of radiation to which it responds while a
field is applied across the suspension between the photoconductive
injecting electrode and the second electrode.
The photoconductive injecting electrode causes those particles
which are within interaction range of the illuminated parts of the
electrode to take on the same sign of charge as the photoconductive
electrode and be repelled by it. These repelled particles migrate
to the surface of the second electrode in image configuration
forming a negative image on the surface of the second electrode and
leaving a positive image behind. To obtain the greatest advantages
of this invention where a uniform dispersion of particles in a
liquid is used the dispersed particles are initially forced to the
surface of the photoconductive electrode by application of field.
For example, where the photoconductive electrode is held at a
positive potential with respect to the second electrode during
imaging the suspension is first charged negatively by, for example,
a negative corona discharge which causes the particles to take on a
negative charge. When the suspension is placed on the positive
photoconductive electrode the particles are drawn to the surface of
the photoconductive electrode leaving a relatively thick layer of
particle-free liquid between the particles and the second
electrode. When the photoconductor is exposed to radiation to which
it is sensitive, particles which are adjacent to illuminated areas
of the photoconductive electrode exchange charge with the
photoconductive electrode and migrate through the liquid to the
second electrode. The improvement in the process which arises from
pre-charging may now be appreciated: when pre-charging is used
initially only liquid contacts the second electrode and, therefore,
background is measurably improved. In other words, the only
particles which contact the second electrode are those which have
migrated there as a result of charge exchange with the
photoconductive electrode.
It is this change in charge polarity which distinguishes the
present concept from prior art processes such as that shown in U.S.
Pat. No. 2,892,709. The prior art processes do not involve change
in polarity of toner particles upon contact with illuminated or
unilluminated areas of photoconductive members. The present process
is, therefore, clearly distinguishable from conventional
xerographic processes wherein insulating particles are merely drawn
to an area of high electrostatic potential.
Preferably the photoconductive layer is applied to a transparent
conductive substrate through which exposure is made while field is
applied. This structure is preferred since it makes the most
efficient use of the imagewise radiation. The photoconductive layer
may be overcoated or a layer may be used between the
photoconductive layer and the conductive substrate.
The particles which may be dispersed in the insulating liquid may
be insulating, semi-conductive or conductive and may comprise two
or more components. Since it is essential that the particles be
capable of accepting and retaining charge injected from the
photoconductive electrode, it has been found desirably that the
surface of the particles be made of a material which has a bulk
resistivity of at least 10.sup.5 ohm cm and preferably 10.sup.7 ohm
cm or greater. There is no known upper limit of operability in that
particulate dyed plastics having resistivities of greater than
10.sup.13 ohm cm have been found to work very well.
In accordance with this invention images may be rapidly formed of
virtually any particulate material. The particles may be, as stated
above, insulating, semi-conductive or conductive. For the
production of colored images, the particles may advantageously be
dyed thermoplastic materials which are especially suitable for full
color transparency or opaque image formation. The advantage of
using dyed thermoplastic materials instead of opaque colored
pigments is that brightly colored materials may be made which can
be readily fused to form a fixed, final image. To produce a
polychrome image two or more monochrome images are made which are
transferred in register to a single substrate and fused thereon.
For other applications the particles may be chosen to be reflective
glass beads, luminescent, phosphors, ferromagnetic pigments,
reflective resin coated metal particles, microcapsules containing
liquids or other materials, catalytic particles or particles
otherwise specially formulated for specific end uses when in the
form of shaped patterns. For example the images can be used as
masks for graphic art purposes or as resists for etching.
The carrier liquid may comprise any suitable insulating material.
Typical insulating liquids include decane, dodecane, tetradecane,
kerosene, molten paraffin, molten beeswax or other molten
thermoplastic material, mineral oil, silicone oils such as dimethyl
polysiloxane, fluorinated hydrocarbons and mixtures thereof.
Mineral oil and kerosene are preferred because of their low cost
and excellent insulating qualities. Alternatively, the colorant
particles may be pre-coated on the photoconductive electrode in a
solid binder such as Piccotex polystyrene resin available from
Pennsylvania Industrial Chemical Co. or eicosane wax for ease of
handling and storage. The binder is melted or dissolved by a
dielectric solvent such as those listed above prior to imaging so
that the particles are free to migrate from one electrode to
another independently of one another. Other Typical solvent-soluble
dielectric binder materials include hydrogenated rosin esters such
as Staybelite Esters 5 and 10 available from Hercules Powder Co.,
phenolformaldehyde resins such as Amberol ST-137-x available from
Rohm and Haas, and Piccotex 75 and 100 and Piccopale 70 SF
available from Pennsylvania Industrial Chemical Co.
It is desirable to use particles of a relatively small size because
small particles provide more stable suspensions and provide images
of higher resolution than would be possible with larger particles.
It is thus preferred that the particles be less than 1 or 2 microns
in average cross section although particles up to about 5 microns
may readily be used. No lower limit on particle size is presently
known.
The concentration of particles dispersed in the liquid depends on
the density of the final image desired, the use to which the image
is to be put and the size of the particles, the solubility of added
dispersants, and other factors generally known to those skilled in
the art of ink or plastic coating formulation. For example, when
finely-divided dyed resinous materials are dispersed in mineral oil
or kerosene from about one part by weight to about 50 parts by
weight resinous material dispersed in 100 parts liquid provide
satisfactory images.
The transparent conductive substrate for the photoconductive layer
may comprise any suitable material. Typical transparent conductive
materials include conductively coated glass, such as aluminum, or
tin oxide coated glass or transparent plastic materials such as
polyester films overcoated with similar materials and cellophane.
Alternatively, a layer such as a resinous film or sheet may be
placed between the photoconductive layer and its backing electrode.
This is particularly desirable for applications wherein the
photoconductive layer is to be used only for a single exposure.
Also the photoconductive layer may be self supporting.
The photoconductive layer may comprise any suitable photoconductive
material. Typical photoconductive materials include inorganic
materials such as cadmium sulfide, cadmium sulfoselenide, selenium,
mercuric sulfide, lead oxide, lead sulfide, cadmium selenide, and
mixtures thereof dispersed in binders or as homogeneous layers.
Typical organic photoconductive materials include pigments such as
quinacridones, carboxanilides such as,
8,13-dioxodinaphtho-(2,1-b;2'
,3'-d)-furan-6-carbox-p-methoxy-anilide;
8,13-dioxodinaphtho-(2,1-b; 2',3'-d)-furan-6carbox-m-chloroanilide;
carboxamides such as,
N-2"-pyridyl-8,13,dioxdinaphtho-(2,1-b;2',3'-d)-furan-6-carboxamide;
N-2"-(1",3"-diazyl)-8,13-dioxodinaphtho-(2,1-b;2',3'-d)-furan-6-carboxamid
e; triazines, benzopyrrocolines, anthraquinones, azo compounds
particularly those having aromatic substituents with a hydroxyl
group in a position ortho to the azo linkage, dioxazines,
substituted pyrenes, phthalocyanines, dispersed in binders, and
organic materials such as poly (N-vinyl carbazole); poly (9-vinyl
anthracene); poly (3-vinyl pyrenes); which are homogeneous
photoconductors whose sensitivity may be augmented by complexing
suitable Lewis acids as described by H. Hoegl in the Journal of
Physical Chemistry 69, 755 (1965); poly (triphenylamine) as
described in U.S. Pat. No. 3,265,496; poly (N-propenyl carbazole)
as described in U.S. Pat. No. 3,341,472 and mixtures thereof. The
photoconductor may comprise one or more components and may comprise
photoconductive pigments dispersed in photoconductive or inert
binders and may be overcoated with, for example, a protective layer
of an active transport layer which is capable of transporting the
type of charge carrier which is desired to be imparted to the
particles. An active transport layer for holes, for example, poly
vinyl carbazole may be coated over an evaporated amorphous selenium
layer or over a binder structure comprising the "x"-form of
phthalocyanine or trigonal selenium or a mixture of both in an
inert dielectric binder, or contained in a polyvinyl carbazole
binder as long as the backing electrode is made positive relative
to the opposing electrode. The speed at which images can be made
can become dependent on the rate of carrier transport through the
overcoating. It is, therefore, desirable to use materials capable
of fast carrier transport.
A preferred photoconductive layer comprises selenium overcoated
with a layer of poly (N-vinyl carbazole). The poly (N-vinyl
carbazole) permits passage of photogenerated and injected holes but
yet protects the selenium from abrasion and solvent attack.
Other overcoating materials which will protect photoconductors but
allow passage either of holes or electrons or both include, poly
(methylene pyrene), poly-1-vinyl pyrene, and binder dispersions of
triphenylamine or 2,4,7 trinitro-9-fluorenone comprising more than
about 30 weight percent of the above compounds.
The second electrode may comprise any suitable conductive material.
Typical conductive materials include tin oxide coated glass,
metals, conductive rubber carbon black binder dispersions and
conductive paper.
The second electrode preferably has an insulating web or layer over
its outer surface to help support the relatively high fields used
in this invention. Typical insulating materials include, paper,
polyethylene coated paper, cellulose acetate, nitro cellulose,
polystyrene, polytetrafluoroethylene, and related fluorinated
polyolefins, polyvinyl fluoride, polyurethane and polyethylene
terephthalate.
BRIEF DESCRIPTION OF THE DRAWING
The advantages of this improved method of electrophoretic imaging
will become apparent upon consideration of the detailed disclosure
of this invention, especially when taken in conjunction with the
accompanying drawing wherein:
FIG. 1 is a side sectional view of a simple exemplary
electrophoretic imaging system in accordance with this
invention.
FIG. 2A-D are diagrammatic representations of the process steps and
particle migration responses which are believed to occur in the
system.
FIGS. 3A-E show alternative embodiments of the photoconductive
layer.
The sizes and shapes of the drawings should not be considered as
actual sizes or even proportional to actual sizes because many of
the elements have been purposely distorted in size or shape in
order to more fully and clearly describe the invention.
Referring now to FIG. 1, there is seen a transparent conductive
layer 1 on transparent substrate 2 which are in this exemplary
instance made up of a transparent conductive layer of tin oxide on
a glass substrate. Such electrodes are available commercially under
the name Nesa Glass and are available from the Pittsburgh Plate
Glass Co. There is no requirement that this electrode be
transparent or conductive. For example an insulating film of
polyethylene terephthalate may be placed over the electrode and the
system will still operate. This electrode may be a plate, drum,
roller, web or other configuration.
On the surface of layer 1, there is provided photoconductive layer
3 which may be for example, one micron selenium overcoated with a 3
micron layer of polyvinyl carbazole. On layer 3 there is provided a
layer 4 of finely-divided particles in an insulating carrier
liquid. The layer may be, for example, finely-divided particles of
a dyed thermoplastic material in mineral oil. The particles may be
fluorescent, glass beads or magnetic. The use of magnetic particles
provides a method for converting a light image directly into a
computer readable image. Further, the system can be used for
preparing masters for printing. The images can be used as masks for
graphic arts processes. Many variations are possible, for example,
the unfused or unfixed image can be used as a mask for ink roll up
to reverse the image sense of the image formed. The substrate
behind an unfused image could be bleached to form a permanent
image. The unfused image can be formed on a diazo substrate for
forming a diazo image. The image can be used as a heat receptor for
thermographic images. The particles can be selected to be inert to
acids or solvents, the image serving as a resist when transferred
to glass or metal for selective etching. The images can be foamed
or built up for Braille use. By using methyl violet particles,
hectograph masters may be formed.
since the inert particles may comprise for example, brilliantly
colored thermoplastic materials, high quality full color images may
be produced by transferring three or more monochrome images formed
in this process to a substrate in register and fused thereon by a
single heating step. Electrode 5 is held at a high potential, the
naturally occurring corona generated at the nip between roller 5
and liquid 4 forces the particles to the surface of layer 3. After
the particles have been driven to the surface of layer 3, an
electrode generally designated 5 which is a conductive roller 11
covered by paper 12 is used to apply a field across suspension 4.
Electrode 5 may be a drum, web, plate or other configuration. As
roller 5 traverses suspension 4, switch 7 is closed which connects
in this exemplary instance the negative terminal of source of high
dc potential 6 to electrode 5. The opposite terminal of source 6 is
connected to layer 1 and ground. It is not necessary that surface
12 be insulating but an insulating layer is preferred to help
support the relatively high fields used in this process. For
example, in an apparatus as shown in FIG. 1, 2,500 volts and more
are conventionally used.
Alternatively, corona source 8 may be used to traverse the
suspension driving particles to layer 3. A roller held at a high
potential may be substituted for corona source 8. The use of a
separate charging member such as source of corona 8 is preferred
since it is more efficient for depositing particles. After the
particles have been driven to surface 3, electrode 5 traverses the
suspension with field applied as shown. As roller 5 traverses layer
4, photoconductive layer 3 is exposed to imagewise radiation 10
which causes particles adjacent layer 3 in illuminated areas to
migrate through the liquid and adhere to the surface of layer 12 in
image configuration. This image may be fixed on surface 12, for
example, by heat or transferred to another member as desired
providing a negative image. The remaining particles on the
photoconductor may also be transferred to paper or film providing a
positive image.
Referring now to FIG. 2A there is shown transparent conductive
layer 11 on transparent support 12. On layer 11 is coated
photoconductive layer 13. Suspension 14 which comprises negatively
charged finely-divided particles 17 dispersed in liquid 15 is
provided on photoconductor 13. Electrode 21 having insulating
surface 19 is placed in contact with the suspension 14. With no
field applied the particles are uniformly dispersed throughout the
suspension.
Referring now to FIG. 2B field is applied by closing switch 23
which connects source of dc potential 25 with conductive electrodes
21 and 11. Field application causes the negatively charged
particles 17 to move toward electrode 11.
Referring now to FIG. 2C photoconductor 13 is exposed to imagewise
radiation 27 which causes charge carriers generated in the
photoconductor to be injected into particles adjacent illuminated
areas of photoconductor 13 and be repelled by it.
Referring now to FIG. 2D particles 17 have migrated through the
suspension and adhere to the surface of layer 19, forming a
negative particulate image on surface 19 and leaving a positive
particulate image behind on surface 13. Either image may be fixed
in place or transferred to another member. Transfer may be assisted
by application of field between the transfer member and the
electrode to which the particles are adhering. The particles
remaining on the photoconductor may be transferred using uniform
illumination and electrical field to improve transfer
efficiency.
Referring now to FIG. 3(A), there is seen an embodiment for use in
this invention wherein photoconductive layer 112 is placed on
conductive transparent layer 113. The suspension of particles is
placed directly on layer 112.
FIG. 3(B) shows an alternative embodiment in that photoconductive
layer 112 on transparent conductive substrate 113 is overcoated to
protect layer 112 from the action of solvents of abrasion. A
preferred coating material 117 is a material which can transport
carriers generated by layer 112 to the particles in the suspension
which is coated on the surface of layer 117.
FIG. 3(C) shows an embodiment wherein photoconductive layer 118
comprises photoconductive particles dispersed in a binder forming a
self-supporting film of photoconductor which during operation is
placed on transparent conductive layer 119 and has the suspension
coated on its free surface.
FIG. 3(D) shows an injecting electrode where a dielectric film 120
such as a polyethylene terephthalate is placed between the
photoconductive layer 112 and transparent conductor 113. Layer 120
acts to support layer 113.
FIG. 3(E) shows an embodiment wherein photoconductive layer 112
supported by dielectric film 120 is overcoated with a transport
material 117. This embodiment provides a protected photoconductive
layer which may be readily recycled in the system and yet is
flexible.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following Examples further specifically illustrate the improved
electrophoretic imaging system provided by this invention.
Parts and percentages are by weight unless otherwise indicated. The
following Examples are intended to illustrate various preferred
embodiments of the present invention. All of the Examples are
carried out in an apparatus of the general type illustrated in FIG.
1. A 500 watt quartz iodine light source is used to illuminate a
black and white negative transparency, the image being projected by
a lens through the tin oxide coated glass on which the particular
photoconductor is coated. The suspension is formed by dispersing
finely divided particles of the specific material in an insulating
liquid. The suspension is milled until the particles are less than
about 2 microns in cross section and are uniformly dispersed.
EXAMPLE I
A source of high potential is connected to a roller electrode which
has a one inch diameter steel core and a 3/4 inch layer of
polyurethane having a resistivity of 5 .times. 10.sup.8 ohm cm
forming a 2.5 inch diameter roller. A paper sheet is placed over
the polyurethane surface to receive the images. The other lead of
the source of high potential is connected to the conductive surface
of a NESA glass plate.
A 1 micron layer of selenium is vacuum evaporated onto the
conductive surface of the NESA glass plate to form the
photoconductive electrode. Approximately two parts of magenta dyed
resin type R103-6 available from the Radiant Color Co. Richmond,
California is suspended in about 5 parts of Sohio Odorless Solvent
3454, a mixture of kerosene fractions available from Standard Oil
Co. of Ohio. This suspension is coated onto the selenium surface
using a No. 4 Mayer coating rod. The roller electrode is rolled
across the suspension at a rate of about 2 inches per second with a
potential of about 3,500 volts applied. The roller is held at a
negative potential with respect to the photoconductive electrode.
As the roller traverses the suspension, the photoconductor is
exposed to light projected through a negative transparency. On
completion of roller traverse a positive image is found adhering to
the paper on the roller electrode and a negative image is found on
the photoconductor surface.
EXAMPLE II
The experiment of Example I is repeated except that prior to roller
traverse and imagewise illumination the suspension is subjected to
a source of corona from a corona generating electrode held at a
negative 7,000 volts with respect to ground. The image formed on
the paper is compared to the image formed in Example I. The image
formed in this Example is found to have a decreased background.
EXAMPLE III
The experiment of Example II is completed except that the selenium
is coated with a 0.5 micron protective layer of poly (N-vinyl
carbazole) (PVK). The coating is applied by dissolving about 2
parts by weight PVK in 60 parts dioxane and 40 parts cyclohexanone
and coating the solution on the selenium using a No. 4 Mayer rod.
The coating is allowed to dry. The suspension is placed on this
coating. PVK is an example of an active transport dielectric. On
completion of roller traverse, a positive image of excellent
quality is found adhering to the paper.
In the following Examples IV-VI, the particles are dispersed in a
solid binder which is dissolved just prior to imaging by
application of a solvent. These layers have an advantage in that
colored liquids need not be handled.
EXAMPLE IV
A photoconductive layer is formed by dispersing about one part by
weight of the X-form of metal-free phthalocyanine made as shown in
U.S. Pat. No. 3,357,989 in a mixture containing 3 parts of PE-200
(a polyesster resin available from Goodyear Tire and Rubber Co.),
about 15 parts of methyl ethyl ketone, and about 10 parts of
toluene. The slurry is coated on a 2.0 mil Mylar film, a polyester
available from duPont using a No. 6 wire wound rod producing a
photoconductive layer of about 4-5 microns dry thickness. This
mylar backed photoconductive layer is then overcoated with an ink
suspension of about 2 parts by weight Lawter Cyan Blue (B-2858
HI-VIZ pigment available from the Lawter Chemicals Inc. Chicago,
Ill.) and about 1 part eicosane, and 15 parts Sohio 3454, a mixture
of kerosene fractions available from Standard Oil of Ohio using a
No. 8 wire wound rod providing a 5-6 micron layer dry. This
combination of photoconductor, substrate and particle-binder layers
is placed on a NESA glass plate the photoconductive layer in
contact with the conductive Nesa glass coating. the photoconductor
is exposed and traversed by the roller as in Example i except that
the paper on the roller is wetted with Sohio 3454 which dissolves
the binder for the Lawter Cyan Blue pigment. On completion of
roller traverse, a positive image is formed on the paper on the
roller electrode. In this embodiment the photoconductive layer can
be varied from about 1 to 50 microns and the particle-binder layer
can be varied from about 3 to about 20 microns with satisfactory
results.
EXAMPLE V
The experiment of Example IV is repeated except that the
photoconductive layer is replaced with a photoconductive layer made
by coating about one part by weight Monastral Red B, a quinacridone
pigment available from dupont, one part by weight PE-200, about 6
parts by weight methyl ethyl ketone and about 4 parts by weight
toluene on 2.0 mil Mylar as in Example IV. An image is formed as in
Example IV.
EXAMPLE VI
The experiment of Example IV is repeated except that the
photoconductive layer is made by coating a slurry of about 2 parts
Indofast Yellow Lake Y-5713, available from Harmon Color, Division
of Allied Chemical and Dye Company about 1 part PE-200, about 15
parts by weight methyl ethyl ketone and about 10 parts by weight
toluene on 2 mil Mylar as in Example IV. A cyan image is formed as
in Example IV with the exception that the roller is held at a
positive about 3,500 volts with respect to the Nesa glass.
EXAMPLE VII
The experiment of Example III is repeated except that the magenta
dyed resin particles are replaced by particles of iron oxide,
Mapico EG3, available from Columbia Carbon Co., New York, New York,
overcoated with melamine-formaldehyde resin. The paper receiver
sheet is also replaced by a Mylar sheet available from duPont. The
image formed may then be magnetized and used as a ferromagnetic
master as shown, for example, in Ferrography by Atkinson and Ellis,
Journal of the Franklin Institute, Volume 252, No. 5 November,
1951. It may also be used as a record in machines equipped for the
automatic reading of magnetic patterns, for example, printed on a
bank check and read in an automatic magnetic check sorter.
EXAMPLE VIII
The experiment of Example III is repeated except that the magenta
dyed resin particles are replaced with particles of Luxol Fast
Black L, a spirit soluble dye available from duPont. The image
formed on the paper reciever sheet may then be used as a spirit
master.
EXAMPLES IX-XI
Spirit masters are made in these Examples as in Example VIII except
that in Example IX the particles are Grasol Fast Brilliant Red BL,
available from Geigy Chemical Co., in Example X the particles are
Luxol Fast Scarlet C and in Example XI the particles are gentian
violet available from Hartman-Leddon Co.
EXAMPLE XII
In this Example a full color image is prepared by combining yellow,
cyan and magenta monochrome images. Frist, red, yellow and blue
separation images are prepared using conventional techniques to
provide negative transparencies. a magenta image is made as in
Example III using the proper separation image. A cyan image is
formed as in Example III using Lawter Cyan Blue B2, as the
particles, exposure being made through the proper separation image.
A yellow image is formed as in Example III using Strong Lemon
Yellow B2141, available from Lawter Chemical Inc. in place of the
magenta particle. The three images are transferred in register to a
receiver sheet. Since the particles are all resinous fusible
materials fixing is accomplished by radiant or contact heating
providing a full color positive image.
EXAMPLE XIII
The experiment of Example XII is repeated except that Sunset Yellow
P6000 G, Blue R103-G-119 and Magenta P1700 available from Radiant
Color Co., Richmond, Cal. are used as the particles. The image is
fixed as in Example XII.
Although specific components and proportions have been described in
the above Examples, other materials as listed above, where suitable
may be used with similar results. In addition, other materials may
be added to the various layers to synergize, enhance or otherwise
modify their properties. For example, the photoconductive layer may
be dye-sensitized to alter its photoresponse.
Other modifications and ramifications of the present invention will
occur to those skilled in the art upon a reading of the present
disclosure. These are intended to be included within the scope of
this invention.
* * * * *