Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates generally to migration imaging
systems and more specifically to migration imaging members
utilizing electrically conductive substrates comprising poly-
styrene sulfonic acid. The invention also relates to the
process of imaging these members and to the imaged migration
members.
Migration imaging systems capable of producing high
quality images of high density, continuous tone and high
resolutio~ have been developed. In a typical embodiment of
these migration imaging systems, an imaging member comprising
a substrate, a layer of softenable material containing
electrically photosensitive migration material is latently
imaged, e.g., by electrically charging the member and exposing
the charged member to a pattern of activating electromagnetic
radiation, such as light. When the photosensitive material is
originally in the form of a fracturable layer located at the
upper surface of the softenable material, particles of the
migration material and exposed areas of the migration member
migrate towards the substrate when the member is developed by
decreasing the resistance of the softenable layer sufficient
to allow migration of the migration material in depth in the
softenable material.
Various methods for developing, i.e., reducing the
resistance of the softenable material to migration of the
migration material, the latent image in the migration imaging
systems are known. These various development modes include
solvent wash-away and softening the softenable material, e.g.,
by solvent vapor softening, heat softening and combinations
thereof, as well as other
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methods of reducing the resistance of the softenable material
to allow migration of the migration material in depth in the
softenable material.
In the solvent wash-away development method, migra-
tion material migrates in imagewise configuration in depth in
the softenable layer as the softenable layer is dissolved,
leaving an image of migrated particles corresponding to desired
image pattern on the substrate, with the softenable layer and
unmigrated migration material substantially completely washed
away.
The imaging system disclosed in U.S. Patent No.
3,520,687, issued July 14, 1970, generally comprises a
combination of process steps which include forming a latent
image on a migration imaging member and developing with
solvent liquid or vapor or heat or combinations thereof to
render the latent image visible. In certain methods of
- forming the latent image, non-photosensitive or photosensit-
ively inert, fracturable layers and particulate material may
be used to form images, as described in U.S. Patent No.
3,656,990, issued April 18, 1972, wherein a latent image is
( formed by a wide variety of methods including charging in
imagewise configuration by the use of a mask or stencil; first
forming such a charged pattern on a separate photoconductive
insulating layer according to conventional xerographic repro-
duction techniques and then transferring this charaed pattern
to the imaging member by bringing the two layers into very
close proximity and utilizing breakdown techniques as described,
for example, in Carlson, U.S. Patent 2,982,647 and Walkup, U.S.
Patents 2,825,814 and 2,937,943. In addition, charged patterns
conforming to selective shaped electrodes, or combinations of
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electrodes, may be formed by the "TESI" dlscharge technique as more
fully disclosed in Schwartz, U.S. Patents 3,023,731 and 2,919,967
or by the techniques described in Walkup, U.S. Patents 3,001,848
and 3,001,849 as well as the electron beam recording techniques,
for example, as disclosed in Glenn, U.S. Patent 3,113,179.
Preferred migration imaging members comprise a layer of
softenable material containing migration material. This softenable
~layer overlies an aluminized Mylar substrate in the preferred
embodiments. However, unexpected results are obtained by using
conductive polymers as a replacement for the metallic layers, e.g.,
aluminum, normally used as substrate overcoatings in migration
imaging members.
The unexpected results obtained from using electrically
conductive substrates comprising polystyrene sulfonic acid is that
the white light density increased by 50% as compared to the original
density of the unprocessed members. Furthermore, the image obtained
is neutral in color as compared to a reddish color obtained in
normal migration imaging members using selenium as the migration
material and an aluminized Mylar substrate.
Futhermore, when using meniscus development as disclosed
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in ~po~din~ application Serial Number ~00,~40, filed
uqus~ J9~l
,r ~OOO, the speed at which the migration imaging member
may be processed through the meniscus developer is not critical
when using the member of the instant invention, since objectional
interference colors do not form on the imaged members of the instant
invention as is quite prevalent when using normal migration imaging
members containing partially reflecting conductive layers such as
aluminized Mylar substrates.
SUMMhRY OF THE I~ENTION
In accordance with one aspect of this invention there
is provided a migration imaging method comprising:
providing an imaging me~ber comprising an electrically
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conductive substrate co~prising polystyrene sulfonic acid;
a layer of substantially electrically insulating
softenable material overlying said substrate, said softenable
material capable of having its resistance to migration of
photosensitive migration material decreased sufficiently to
allow migration of migration material in depth in said
softenable layer;
a layer of photosensitive migration material
contiguous the surface of the softenable material opposite the
substrate and contacting the softenable material;
applying an electrical latent image to said migration
material; and
developing said imaging me~ber by decreasing the
resistance to migration of migration material in depth in the
softenable layer at least sufficient to allow imagewise
migration of migration material at least in depth in said
softenable layer whereby no color interference patterns are
present on the image and the image is neutral in color.
In accordance with another aspect of this invention
there is provided a migration imaging member comprising:
( an electrically conductive substrate comprising poly-
styrene sulfonic acid;
a layer of substantially electrically insulating
softenable material overlying said substrate, said softenable
material capable of having its resistance to migration of
photosensitive migration material decreased sufficiently to
allow migration of migration material in depth in said soften-
able layer, and a layer of photosensitive migration material
contiguous the surface of the softenable material opposite the
substrate and contacting the softenable material.
In accordance with another aspect of this ;nvention
there is provided a migration imaged member comprising:
a layer of substantjally electrically insulating
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softenable material and a layer of neutral colored photo-
sensitive migration material selectively distributed
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in depth in~ softenable material in first image
pattern and a complementary image pattern
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of photosensitive migra~ion material in said softenable material
spaced apart from said first image pattern where said complementary
image pattern is contiguous to the surface of and ~contacting
said softenable layer and said softenable layer overlying an
electrically conductive substrate comprising polystyrene sulfonic
acid.
In accordance with another aspect of this invention
there is provided a migration imaged member with no color inter-
ference patterns on its surface comprising an imagewise pattern
of neutral colored photosensitive migration material contacting
an electrically conductive substrate comprising polystyrene
sulfonic acid.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention as well as
other objects and further features thereof, reference is now made
to the following detailed disclosure of this inventlon taken in t
conjunction with the accompanying drawings wherein:
Fig. 1 is a partially schematic drawing representing a
layer configuration migration imaging member. -
Fig. 2 is a partially schematic drawing representing the
charging step of a layer configuration migration imaging member
with a corotron charging device.
Fig. 3 is a partially schematic drawing of the process of
imagewise exposing to activating electromagnetic radiation a
- uniform charged migration imaging member.
Fig. 4 is a partially schematic drawing of a wash-away
developed migration imaqing member where the unmigrated migration
material and softenable material has been washed away and the
imagewise migrated migration material is contained on the
electrically conductive substrate. The substrate comprises
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polystyrene sulfonic acid.
DESCRIPTION OF THE PREFERRED EMBODIMEMTS
Referring now to Fig. 1 which shows a schematic of a
layer configuration migration imaging member which contains a layer
of migration material 1 overlying a layer of softenable material 2
which overlies an electrically conductive substrate comprising
polystyrene sulfonic acid 3.
Substrate 3 is a polystyrene sulfonate, i.e., polystyrene
sulfonic acid, which is available from ~ational Starch and Chemical
Co., under the trade name Versal-TL. The molecular weight of the
preferred polystyrene sulfonic acid should be from about 70,000 to
100,000. Other suitable electrically conductive substrates comprise
polyvinyl benzyl trimethyl ammonium chloride, poly ~-N-dimethyl-
3,5, methylene piperdinium chloride, poly-4-vinyl pyridine and
mixtures thereof. Especially preferred as substrate 3 is a mixture
of polystyrene sulfonic acid and Cabosil, a colloidal pyrogenic
silica pigment available from Cabot Corp. The preferred amount by
weight of Cabosil based on the weight of polystyrene sulfonic acid
is from about 1 to about 15 percent. Especially preferred amounts
of Cabosil is from about 5 to about 10 percent by weight. The
Cabosil, it is believed, improves the adhesion of the polystyrene
sulfonic acid to the Mylar substrate in addition to reducing the
surface tackiness of the polystyrene sulfonic acid.
Softenable layer 2 may be any suitable material, typically
a plastic or thermoplastic which is capable of having its resistance
to migration reduced sufficiently to allow migration of migration
material in depth in the softenable material. Furthermore, as a
specific preferred embodiment of development, the softenable
material should be capable of being soluble in a solvent or soften-
able, for example, in a solvent liquid, solvent vapor, heat or
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combinations thereof. Preferably, the softenable material
should have a softening range of at least about 10C. and an
initial softening point of about 90Co and a surface melt
viscosity in the range between about 104 to lO9 poise.
"Softenable" as used herein to depict softenable
layer 2 is intended to mean any material which can be rendered
by the development step thereof, or the softening step hereof,
more permeable to particles migrating through its bulk.
Typically preferred substantially electrically in-
sulating softenable material includes a host of plastic andthermoplastic materials; paraffins and waxes and other materials
which are typically substantially electrically insulating, and
capable of having their resistance to migration reduced to
allow migration of the migration material, may be used in the
advantageous system of the present invention. Such substantially
electrically insulating softenable material will typically
have resistivities not less than about 101 ohms-cm, and pre-
ferably have resistivities not less than about 1012 ohms-cm.
Specifically preferred substantially electrically insulating
softenable material includes copolymers of styrene and hexyl-
methacrylate; copolymers of styrene and n-butyl-methacrylate;
copolymers of styrene and octyl-acrylate; copolymers of
styrene and t-decylate-styrene and copolymers of methyl/meth-
acrylate and t-decylate-styrene.
Softenable layer 3 may be of any suitable thickness.
However, softenable layer thicknesses from about 1/2 to about
16 microns are found to be preferred.
Migration layer 1 has portions which migrate towards
or to substrate 3 during normal migration imaging under the
influence of a migration imaging force. Layer 1 may be a
fracturable layer of a particulate layer. Layer 1 may be
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continuous or a semi-continuous layer, such as a fracturable
layer in a SWhSS cheese pattern which is capable of breaking
up into discrete particles of the size of an image element
or less during the development step permitting portions to
migrate towards the substrate in image configuration. The
thickness of layer 1 is preferably from about 0.01 to about 2.0
microns thick although 5 micron layers have been found to give
good results for some material.
When layer 1 comprises particles, a preferred average
particle size is from about 0.01 to about 2.0 microns. Layers
of particle migration material preferably should have a thick-
ness range from about the thickness of the smallest element
of migration material in the layer to about twice the thickness
of the largest element in that layer. It should be recognized
that the particles may not be all packed tightly together
laterally or vertically so that some of the thickness of layer
1 may constitute softenable material.
Migration material 1, preferably, should be sub-
stantially insoluble in the softenable material and otherwise
not adversely reactive therewith, and in any solvent liquid
or vapor which may be used in the development step hereof.
Photosensitive material for layer 1 permits the imaging member
hereof to be imaged by the optimum electrical-optical mode
hereof, to be further described, which is a simple, direct,
optically sensitive method of producing high quality images.
Typically, such photosensitive material includes inorganic
or organic insulating materials.
While photoconductive particles (and "photoconductive")
is used in its broadest sense to means particles with increased
electrical conductivity when aluminated with electromagnetic
radiation and not necessarily those which have been found to
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be useful in xerography in xerographic pigment-binder plate
configurations have been found to be a class of particles use-
ful in the instant invention. These particles are referred to
as "electrically photoconductive" particles in this invention
and while the photoconductive effect is sufficient in the
present invention to provide an "electrically photosensitive"
material, it does not appear to be a necessary effect. Apparent-
ly, the necessary effect, according to the invention, is the
selective relocation of the charge into, within or on the
material or particles, said relocation being effective by
light reacting on the bulk or surface of the "electrically
photosensitive" material, by exposing said material or particles
to activating radiation which may specifically include photo-
conductive effects, photoinjection, photoemission, photo-
chemical effects and others which cause said selective re-
location of charge.
Referring now to the unexpected results which are
obtained by using layer configuration migration imaging members
of the lnstant invention which contain electrically conductive
substrates comprising polystyrene sulfonic acid. The conduct-
ive polymer, when used as a substrate, unexpectedly enhances
optical density along with the conversion of the image from
normally a reddish image to a neutral image, i.e., black. The
unprocessed film has specular densities of 1.0 in white light
and 1.5 in blue light. After meniscus development, of the
type disclosed in aforementioned Canadian Application 121,788,
the images have specular densities of 1.5 in white light and
1.5 in blue light. The image is neutral, i.e., black, and
the white light density is increased by 50% compared to the
original unprocess
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density. It has been found that the density increase is not
accompanied by any loss of resolution. It is speculated that
the density enhancement is due to a slight flatening of the
completely migrated particles. This flatening effect of the
migration particles may be responsible for the less critical
meniscus solvent contact times required during meniscus
development, since the contact times can be increased beyond
the optimum range known prior to this invention for normal
layer configuration migration imaging member utilizing
aluminized Mylar* substrates without obtaining objectionable
interference colors on the imaged member.
The modes of imaging migration imaging members as
illustrated in Figures 1 - 4 include (1) applying to the
migration layer 1 an imagewise migration force as illustrated
in Figs. 1, 2 and 3, which typically are associated with a
latent imagewise charge on the imaging member, which causes
directly or indirectly a force on the migration layer towards
the bulk of the softenable layer and towards the electrically
conductive substrate which in the instant invention comprises
polystyrene sulfonic acid. The imagewise migration force
applying step may occur before, during or after the development
step, i.e., reducing the resistance of the softenable material
to migration of the migration material sufficiently to allow
migration of the migration material in depth in the softenable
material. As illustrated in Fig. 4, the member may be wash-
away developed resulting in softenable layer 2 along with
unmigrated migration material 1 being washed away leaving
imagewise migrated migration material 1 on electrically
conductive substrate 3, as illustrated in Fig. 4.
Referring now to Fig. 2, a latent image is formed by the
* trade mark
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optimum electrical-optical mode hereof, on the member, where
layer 1 comprises photosensitive material, by the preferred
method which comprises the steps of uniformly charging with a
corona device 4, as illustrated in Fig. 2 and imagewise expos-
ing 5, as illustrated in Fig. 3. As mentioned, in Fig. 2 the
imaging member is uniformly electrostatically charged, illustrat-
ively by means of corona discharge device 4 which is shown to
be transversing the member from left to right depositing a
uniform, illustratively positive charge on the surface of layer
1. For example, excellent sources of corona discharging devices
useful in discharge of the member are disclosed in Vyverberg
. Patent 2,836,725 and Walkup Patent 2,777,957.
Referring now to Fig. 3, a second step, in the embodi-
ment of the optimum electrically-optical mode of forming the
latent image after charging the member, is exposed the member
to an imagewise pattern of activating radiation 5. For purpose
of illustration, the surface electrical charges are depicted
as having moved into particulate layer 1 in the illuminated
areas.
The member having the electrically latent image
thereon, as illustrated by Fig. 3, is developed by reducing the
resistance of the softenable material to migration of the
migration material in depth in the softenable material, as
illustrated here, wash-away developed, forming an imaged
migration imaging member, as illustrated in Fig. 4.
The member may be developed by merely softening the
softenable material 2 by the application of heat, solvent
vapors, or combinations thereof, or any other means for soft-
ening the softenable material of softenable layer 2 to allow
migration of the migration material 1. The softening of the
softenable material also allows the development of the latently
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imaged member, whereby migration material 1 is allowed to
migrate in depth in softenable layer 2 in image configuration.
The following examples further specifically define
the present invention of providing an electrically conductive
substrate comprising polystyrene sulfonic acid in migration
imaging members. The parts and percentages are by weight unless
otherwise indicated. All exposures are from a tungsten filament
light source unless otherwise specified. The examples below
are intended to illustrate various preferred embodiments of
using and fabricating a migration imaging member containing an
electrically conductive substrate comprising polystyrene
sulfonic acid. The examples are directed, primarily, to wash-
away development which is amply described in Goffe, U.S. Patent
3,520,681.
EXAMPLE I
A layer configuration migration imaging member is
fabricated by mixing polystyrene sulfonic acid, available from
National Starch and Chemical Co., under the trade name of
Versal-TL #70, with 5% by weight of Cabosil, a colloidal
pyrogenic silica pigment available from Cabot Corp., in order
to improve the wetting properties of the polystyrene sulfonic
acid to the Mylar substrate. The transparent conductive coat-
ing is then applied with a gravure roller at 11 feet per
minute. The resultant film is approximately 2.6 microns thick.
A layer of softenable material comprising about a 12 weight
percent solution of a custom synthesized of about 80/20 mole
percent copolymer of styrene and hexylmethacrylate having a
molecular weight of about 41,300, intrinsic viscosity in
toluene of about 0.16 at about 25C. is coated onto the
electrically conductive substrate comprising polystyrene
sulfonic acid with a gravure roller and then allowed to dry.
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The softenable material has a thickness of approximately 2
microns. The surface of the softenable material is then coated
with amorphous selenium by a vacuum deposition process as fully
; described in Canadian Patent No. 913,474 issued October 31,
1972. Vacuum evaporation of selenium onto the softenable layer
results in a layer of particulate selenium being formed, having
an average particle size of about 0.4 micron.
This imaging member is uniformly electrostatically
charged using a corona device to a surface potential of positive
200 volts, imagewise exposed to activating electromagnetic
radiation, here light, of approximately 5 ergs/cm2 of 4,000
angstroms light through a photographic transparency in contact
with the member. The member is then developed by immersing
for a few seconds in l,l,l-trichloroethane. The unmigrated
particles and substantially all of the softenable material
are washed away, thereby leaving an image on the transparent
conductive substrate. A high quality migration imaged member
is obtained with contrast densities of 1.5 specular, and con-
trast exposed resolution of greater than 400 line pairs/mm.
There is no color interference patterns observed on the film
and the white light density has increased 50% compared to the
original unprocessed density. The unprocess film specular
density is 1.0 in white light and 1.5 in blue light. After
meniscus development, the specular density is 1.5 in white
and 1.5 in blue light. It is observed that the image is
neutral in color, i.e., black.
EXAMPLE II
An imaging member is prepared as in Example I. The
specular density is 1.0 in white light and 1.5 in blue light.
This film is then meniscus developed in accordance with afore-
mentioned Canadian Application 121,788.
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The process speed through the meniscus developer is
2.5 inches per second with Freon TMC*, available from DuPont
as the developing solvent. Excellent images are obtained with
the meniscus development and the specular density is 1.5 in
white light and 1.5 in blue light. Therefore, the image is
neutral and the white light density is increased by 50%
compared to the original unprocessed density. The density is
not accompanied by a loss of resolution compared to conventional
migration imaging films as it is still possible to achieve
contact exposure resolution in excess of 400 line pairs/mm.
Also, there is no interference color observed when the trans-
parent conductive layer is used with meniscus developed
migration imaging members.
EXAMPLE III
A layer configuration migration imaging member is
fabricated by mixing polystyrene sulfonic acid, available
from National Starch and Chemical Co., under the trade name of
Versal-TL #70, with 5~ by weight of Cabosil, a colloidal
pyrogenlc silica pigment available from Cabot Corp., in order
to improve the wetting properties of the polystyrene sulfonic
acid to the Mylar substrate. The transparent conductive
coating is then applied with a Dilt's* coater using a 72Q
gravure roller at 40 feet per minute. The resultant film is
approximately 2.0 microns thick. A layer of softenable material
comprising about a 12 weight percent solution of a custom
synthesized polymer of about 80/20 mole percent copolymer of
styrene and hexylmethacrylate having a molecular weight of
about 41,300, intrinsic viscosity in toluene of about 0.16
at about 25~C. is coated onto the electrically conductive sub-
strate comprising polystyrene sulfonic acid with a gravure
* trade marks
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roller and then allowed to dry. The softenable material has
a thickness of approximately 2 microns. The surface of the
softenable material is then coated with amorphous selenium by
a vacuum deposition process as fully described in aforementioned
Canadian Patent 913,474. Vacuum evaporation of selenium onto
the softenable layer results in a layer of particulate selenium
being formed, having an average particle size of about 0.4
micron.
This imaging member is uniformly electrostatically
charged using a corona device to a surface potential of positive
20Q volts, imagewise exposed to activating electromagnetic
radiation, here light, of approximately 5 ergs/cm2 of 4,000
angstroms light through a photographic transparency in contact
with the member. The member is then developed by immersing
for a few seconds in l,l,l-trichloroethane. The unmigrated
particles and substantially all of the softenable material
are washed away, thereby leaving an image on the transparent
conductive substrate. A high quality migration imaged member
is obtained with contrast densities of 1.5 specular, and
contrast exposed resolution of greater than 400 line pairs/mm.
There is no color interference patterns observed on the film
and the white light density has increased 50~ compared to the
original unprocessed density. The unprocess film specular
density is 1.0 in white light and 1.5 in blue light. After
meniscus development, the specular density is 1.5 in white
and 1.5 in blue light. It is observed that the image is
neutral in color, i.e., black.
EXAMPLE IV
An imaging member is prepared as in Example III.
The specular density is 1.0 in white light and 1.5 in blue
light. This film is then meniscus developed in accordance
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with aforementioned Canadian patent application Serial Number
121,788.
The process speed through the meniscus developer is
2.5 inches per second with Freon TMC, available from DuPont as
the developing solvent. Excellent images are obtained with
the meniscus development and the specular density is 1.5 in
white light and 1.5 in blue light. Therefore, the image is
neutral and the white light density is increased by 50~ compared
to the original unprocessed density. The density is not
accompanied by a loss of resolution compared to conventional
migration imaging films as it is still possible to achieve
contact exposure resolution in excess of 400 line pairs/mm.
Also, there is no interference color observed when the trans-
parent conductive layer is used with meniscus developed
migration imaging members.
It will be understood that various other changes in
the details, material, steps and arrangement of parts, which
have been herein described and illustrated in order to explain
the nature of the invention, will occur to and may be made by
those skilled in the art upon a reading of this disclosure,
and such changes are intended to be included within the
principle and scope of this invention.
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