Field of the Invention
[0001] This invention relates to electrography and, in particular, to certain electrically
photosensitive pigment particles for use in electrophoretic migration imaging processes.
Background of the Invention
[0002] In the past, there has been extensive description in the patent and other technical
literature of electrophoretic migration imaging processes. For example, a description
of such processes may be found in U.S. Patents 2,758,939 by Sugarman issued August
14, 1956 ; 2,940,847, 3,100,426, 3,140,175 and 3,143,508, all by Kaprelian ; 3,384,565,
3,384,488 and 3,615,558, all by Tulagin et al ; 3,384,566 by Clark ; and 3,383,993
by Yeh. In addition to the foregoing patent literature directed to conventional electrophoretic
migration imaging processes, another type of electrophoretic migration imaging process
which advantageously provides for image reversal is described in Groner, U.S. Patent
3,976,485, issued August 24, 1976. This latter process has been termed "photoimmobilized
electrophoretic recording" or sometimes abbreviated as PIER.
[0003] In general, each of the foregoing electrophoretic migration imaging processes typically
employs a layer of electrostatic charge- bearing photoconductive particles, i.e.,
electrically photosensitive particles, positioned between two spaced electrodes, one
of which may be transparent. To achieve image. formation in these processes, the electrically
photosensitive particles positioned between the two spaced electrodes are subjected
to an applied electric field and exposed to radiation to which the particles are light-sensitive.
As a result, the electrically photosensitive particles are caused to migrate electrophoretically
to the surface of one or the other of the spaced electrodes, and an image pattern
is formed on the surface of these electrodes. Typically, a negative image is formed
on one electrode, and a positive image is formed on the opposite electrode. Image
discrimination occurs in the various electrophoretic migration imaging processes as
a result of a net change in charge polarity of either the exposed electrically photosensitive
particles (in the case of conventional electrophoretic migration imaging), or the
unexposed electrically photosensitive particles (in the case of the electrophoretic
migration imaging process described in the above-noted Groner patent), so that the
image formed on one electrode surface is composed ideally of electrically photosensitive
particles of one charge polarity, either negative or positive polarity, and the image
formed on the opposite polarity electrode surface is composed ideally of electrically
photosensitive particles having the opposite charge polarity, either positive or negative
respectively.
[0004] In any case, regardless of the particular electrophoretic migration imaging process
employed, it is apparent that an essential component to practice such process i3 the
electrically photosensitive particles. And, of course, to obtain an easy-to-read,
visible image it is important that these electrically photosensitive particles be
colored, as well as electrically photosensitive. Accordingly, as is apparent from
the technical literature regarding electrophoretic migration imaging processes, work
has been carried on in the past and is continuing to find particles which possess
both useful levels of electrical photosensitivity and which exhibit good colorant
properties. Thus, for example, various types of electrically photosensitive materials
are disclosed for use in electrophoretic migration imaging processes, for example,
in U.S. Patents 2,758,939 by Sugarman, 2,940,847 by Kaprelian, and 3,384,488 and 3,615,558
by Tulagin et al., noted hereinabove.
[0005] In large part, the art, to date, has generally selected useful electrically photosensitive
and/or photoconductive particles for electrophoretic migration imaging from known
classes of photoconductive materials which may be employed in conventional photoconductive
elements e.g., photoconductive plates, drums, or webs used in electrophotographic
office-copier devices, as taught for example, in US patents 2,758,939 and 2,940,847.Also,
the phthalocyanine pigments described as useful electrically photosensitive particles
for electrophoretic imaging processes in U.S. Patent 3,615,558 by Tulagin et al have
long been known to exhibit useful photoconductive properties.
Summary of the Invention
[0006] The object of the invention is to extend the diversity of particles available as
electrically photosensitive particles for use in electrophoretic migration imaging
processes by resorting to materials which, to the applicant's knowledge, have not
been previously identified as photoconductors.
[0007] In accordance with the invention, electrically photosensitive particles for electrophoretic
migration imaging processes comprise a compound having one of the following formulas
:

or

wherein
m and n are zero, one or two ;
R1 and R2 are the same or different and each represents hydrogen, alkyl or aryl ;
Y represents 0 or S ;
L1, L2, L , L4 and L5 represent hydrogen, alkyl or aryl, or in addition, either L and L2 or any two of L3, L4 and L together represent the atoms needed to complete a carbocyclic ring ;
A represents a basic heterocyclic nucleus selected from the group consisting of an
imidazole ; a 3H-indole ; a thiazole ; a benzothiazole ; a naphthothiazole ; a thianaphtheno-7',6',4,5-thiazole
; an oxazole ; a benzoxazole ; a naphthoxazole ; a selenazole, a benzoselenazole ;
a naphthoselenazole ; a thiazoline ; a 2-quinoline ; a 4-quinoline; a 1-isoquinoline
; a benzimidazole ; a 2-pyridine ; a 4-pyridine, and a thiazoline ;
A2 represents the A nuclei, an aryl group or a heterocyclic nucleus selected from the
group consisting of thiophene ;benzo [b]-thiophene ; naphtho/2,3-b/thiophene ; furan
; isobenzofuran ; chromene ; pyran ; xanthene ; pyrrole ; 2H-pyrrole ; pyrazole ;
indoline ; indole ; 3H-indole ; indazole ; carbazole ; pyrimidine ; isothiazole; isoxazole
; furazan ; chroman, isochroman ; 1,2,3,4-tetrahydroquinoline ; 4H-pyrrolo-[3,2,1-ij]quinoline
; 1,2-dihydro-4H-pyrrolo[3,2,1-i,j]quinoline ; 1,2,5, 6-tétrahydro-4H-pyrrolo[3,2,1-ij]quinoline
; 1H,5H-benzo[ij]quinolizine; 2,3-dihydro-1H,5H-benzo[ij]quinolizine ; 2,3,6,7-tetrahydro-lH,5H-benzo-[ij]quinolizine
; 10,11-dihydro-9H-benzo[a]xanthen-8-yl ; and 6,7-dihydro-5H-benzo[b]pyran-7-yl ;
indolizine.
[0008] In the above mentioned formulae, representatives of substituent A
1 include basic heterocyclic nuclei selected from the group consisting of :
a) an imidazole nucleus, such as 4-phenylimidazole ;
b) a 3H-indole nucleus such as 3H-indole; 3,3-dimethyl-3H-indole ; and 3,3,5-trimethyl-3H-indole;
c) a thiazole nucleus such as thiazole, 4-methylthiazole, 4-phenylthiazole, 5-methylthiazole,
5-phenylthiazole; 4,5-dimethylthiazole ; 4,5-diphenylthiazole ; and 4-(2-thienyl)-thiazole
;
d) a benzothiazole nucleus such as benzothiazole, 4-chlorobenzothiazole, 5-chlorobenzothiazole,
6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, 5-methylbenzothiazole,
6-methylbenzothiazole, 5-bromobenzothiazole, 6-bromobenzothiazole, 4-phenylbenzothiazole,
5-phenylbenzothiazole, 4-methoxybenzothiazole, 5-methoxybenzothiazole, 6-methoxybenzothiazole,
5-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole, 5-ethoxybenzothiazole,
tétrahydrobenzothiazole ; 5,6-dimethoxybenzothiazole; 5,6-methylenedioxybenzo- thiazole
; 5-hydroxybenzothiazole, and 6-hydroxybenzothiazole ;
e) a naphthothiazole nucleus such as naphtho/1,2-d/thiazole, naphtho/2,1-d/thiazole,
naphtho[2,3-b]thiazole, 5-methoxy- naphtho/2,1-d/thiazole, 5-ethoxynaphtho/2,1-d/thiazole,
8-methoxynaphtho/1,2-d/thiazole, and 7-methoxynaphtho/1,2-d/ thiazole ;
f) a thianaphtheno-7',6',4,5-thiazole nucleus such as 4-methoxy- thianaphtheno-7',6',4,4-thiazole
;
g) an oxazole nucleus such as 4-methyloxazole, 5-methyloxazole, 4-phenyloxazole; 4,5-diphenyloxazole;
4-ethyloxazole, 4,5-dimethyloxazole, and 5-phenyloxazole ;
h) a benzoxazole nucleus such as benzoxazole, 5-chlorobenzoxazo- le, 5-methylbenzoxazole,
5-phenylbenzoxazole, 6-methylbenzoxazole; 5,6-dimethylbenzoxazole ; 4,6-dimethylbenzoxazole
; 5-methoxybenzoxazole; 5-ethoxybenzoxazole, 5-chlorobenzoxa- zole, 6-methoxybenzoxazole,
5-hydroxybenzoxazole and 6-hydroxybenzoxazole ;
i) a naphthoxazole nucleus such as naphtho/1,2-d/oxazole and naphtho[2,1-d]oxazole
;
j) a selenazole nucleus such as 4-methylselenazole and 4-phenyl- selenazole ;
k) a benzoselenazole nucleus such as benzoselenazole, 5-chloro- benzoselenazole, 5-methoxybenzoselenazole,
5-hydroxybenzo- selenazole and tetrahydrobenzoselenazole ;
1) a naphthoselenazole nucleus such as naphtho/1,2-d/selenazole, or naphtho[2,1-d]selenazole
;
m) a thiazoline nucleus such as thiazoline and 4-methylthiazo- line ;
n) a 2-quinoline nucleus such as quinoline, 3-methylquinoline, 5-methylquinoline,
7-methylquinoline, 8-methylquinoline, 6-chloroquinoline, 8-chloroquinoline, 6-methoxyquinoline,
6-ethoxyquinoline, 6-hydroxyquinoline and 8-hydroxyquinoline;
o) a 4-quinoline nucleus such as quinoline, 6-methoxyquinoline, 7-methylquinoline,
and 8-methylquinoline ;
p) a 1-isoquinoline nucleus such as isoquinoline and 3,4-dihydro isoquinoline ;
q) a benzimidazole nucleus such as 1,3-diethyl-benzimidazole and 1-ethyl-3-phenylbenzimidazole
;
r) a 2-pyridine nucleus such as pyridine and 5-methylpyridine ;
s) a 4-pyridine nucleus ; and
t) a thiazoline nucleus.
[0009] When A 2 is an aryl group, it may represent phenyl, naphthyl, anthryl group etc.
[0010] Alkyl refers to aliphatic hydrocarbon groups of generally 1-20 carbon atoms such
as methyl, ethyl, propyl, isopropyl, butyl, heptyl, dodecyl, octadecyl, etc. Aryl
refers to aromatic ring groups of generally 6-20 carbon atoms such as phenyl, naphthyl,
anthryl or to alkyl or aryl substituted aryl groups such as tolyl, ethylphenyl, biphenylyl,
etc.
Description of the Preferred Embodiments
[0011] In accordance with the preferred embodiments of the present invention, the electrically
photosensitive particles which are useful in electrophoretic migration imaging processes
comprise compounds which have the structure according to Formulas I and II wherein
:
R1, R2, L1, L2, L3, L4, L5, m and n are the same as previously defined ;
A1 is a nucleus selected from the group consisting of benzothiazole, naphthothiazole
and thiazoline ; and
A2 is 2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizine.
[0012] In general the particles which comprise compounds of Formulas I and II and which
have been found to be electrically photosensitive tend to exhibit a maximum absorption
wavelength, A max, within the range of from about 420 nm to about 750 nm. A variety
of different particles which comprise the compounds defined by Formulas I and II have
been tested and found to exhibit useful levels of electrical photosensitivity in electrophoretic
migration imaging processes.
[0013] A partial listing of representative compounds is included herein in Tables I through
III. In these tables Et represents C
2H
5. Compounds disclosed herein and methods for making them are disclosed in U.S. Patents
2,036,546 ; 2,089,729 ; 2 165,338 ; 2,170,803 ; 2,170,807 ; 2,263,757 and 2,519,001.

[0014] In general, electrically photosensitive particles useful in electrophoretic migration
imaging processes. have an average particle size within the range of from about .01
micron to about 20 microns, preferably from about .01 to about 5 microns. These particles
are colorants. These electrically photosensitive particles may also contain various
non- photosensitive materials such as electrically, insulating polymers, charge control
agents, various organic and inorganic fillers, as well as various additional dyes
or pigments to change or enhance various colorant and physical properties of the electrically
photosensitive particles. In addition, such electrically photosensitive particles
may contain other photosensitive materials such as various sensitizing dyes and/or
chemical sensitizers to alter or enhance their response characteristics to radiation
to which they are light-sensitive.
[0015] When used in an electrophoretic migration imaging process in accord with the present
invention, the electrically photosensitive
.particles which comprise compounds described in Tables I through III, hereinabove,
are typically positioned between two or more spaced electrodes, one or both typically
being transparent to radiation to which the electrically photosensitive particles
are light-sensitive, i.e., activating radiation The electrically photosensitive particles
may be dispersed simply as a dry powder between two spaced electrodes and then subjected
to a typical electrophoretic migration imaging operation such as that described in
U.S. Patent 2,758,939 by Sugarman. It is more typical to disperse the electrically
photosensitive particles in an electrically insulating carrier, such as an electrically
insulating liquid, or an electrically insulating, liquefiable matrix, such as a heat-
and/or solvent-softenable polymer or a thixotropic polymer. Typically, when one employs
such a dispersion of electrical-ly photosensitive particles and electrical- ly insulating
carrier between the spaced electrodes of an electrophoretic migration imaging system,
it is conventional to employ from about 0.05 part to about 2.0 parts of electrically
photosensitive particles for each 10 parts by weight of electrically insulating carrier
material.
[0016] The carrier can comprise an electrically insulating liquid such as decane, paraffin,
Sohic
Oder- less Solvent 3440 (a kerosene-fraction marketed by the Standard Oil Company,
Ohio), various isoparaffinic hydrocarbon liquids such as those sold under the trademark
Isopar G by Exxon Corporation and having a boiling point in the range of 145°C to
186°C, various halogenated hydrocarbons such as carbon tetrachloride, trichloromonofluoromethane,
and the like, various alkylated aromatic hydrocarbon liquids such as the alkylated
benzenes, for example, xylenes, and other alkylated aromatic hydrocarbons such as
are described in U.S. Patent 2,899,335. An example of one such useful alkylated aromatic
hydrocarbon liquid which is commercially available is Solvesso 100 made by Exxon Corporation.
Solvesso 100 has a boiling point in the range of about 157°C to about 177
0C and is composed of 9 percent xylene, 16 percent of other monoalkyl benzenes, 34
percent dialkyl benzenes, 37 percent trialkyl benzenes, and 4 percent aliphatics.
Typically, whether solid or liquid at normal room temperatures, i.e., about 22°C,
the electrically insulating carrier used in the present invention has a resistivity
greater than about 10
9 ohm-cm, preferably greater than about 10
12 ohm-cm. When the electrically photosensitive particles of the present invention are
incorporated in a carrier, such as one of the above-described electrically insulating
liquids, various other addenda may also be incorporated in the resultant imaging suspension.
For example, various charge control agents may be incorporated in such a suspension
to improve the uniformity of charge polarity of the electrically photosensitive particles'dispersed
in the liquid suspension. Such charge control agents are well known in the field of
liquid electrographic developers where they are employed for purposes substantially
similar to that described herein. These charge control agents are typically polymers
incorporated by admixture thereof into the liquid carrier of the suspension. In addition
to, and possibly related to, the aforementioned enhancement of uniform charge polarity,
it has been found that the charge control agents often provide more stable suspensions,
i.e., suspensions which exhibit substantially less settling out of the dispersed electrical-
ly photosensitive particles.
[0017] In addition to the foregoing charge control agents, various polymeric binders such
as various natural, semi-synthetic or synthetic resins, may be dispersed or dissolved
in the electrically insulating carrier to fix the final photosensitive particle image
formed on one of the spaced electrodes used in electrophoretic migration imaging systems.
Here again, the use of such fixing addenda is conventional and well known in the closely
related art of liquid electrographic developers.
[0018] The present invention will be described in more detail with reference to the accompanying
drawing which illustrates a typical apparatus which employs electrophoretic migration
imaging process using the electrically photosensitive particles of the invention.
[0019] The drawing shows a transparent electrode 1 supported by two rubber drive rollers
10 capable of imparting a translating motion to electrode 1 in the direction of the
arrows. Electrode 1 may be composed of a layer of optically transparent material,
such as glass or an electrically insulating, transparent polymeric support such as
polyethylene terephthalate, covered with a thin, optically transparent, conductive
layer such as tin oxide, indium oxide, nickel, and the like. Optionally, depending
upon the particular type of electrophoretic migration imaging process desired, the
surface of electrode 1 may bear a "dark charge exchange" material, such as a solid
solution of an electrically insulating polymer and 2,4,7,trinitro-9-fluorenone as
described in the above-described Groner U.S. Patent 3,976,485 issued August 24, 1976.
[0020] Spaced opposite electrode 1 and in pressure contact therewith is a second electrode
5, an idler roller which serves as a counter electrode to electrode 1 for producing
the electric field used in the electrophoretic migration imaging process. Typically,
electrode 5 has on the surface thereof a thin, electrically insulating layer 6. -Electrode
5 is connected to one side of the power source 15 by switch 7. The opposite side of
the power source 15 is connected to electrode 1 so that as an exposure takes place,
switch 7 is closed and an electric field is applied to the electrically photosensitive
particles 4 which are positioned between electrodes 1 and 5. Typically electrically
photosensitive particles 4 are dispersed in an electrically insulating carrier such
as described hereinabove.
[0021] The electrically photosensitive particles 4 may be positioned between electrodes
1 and 5 by applying the particles 4 to either or both of the surfaces of electrodes
1 and 5 prior to the imaging process or by injecting the electrically photosensitive
particles 4 between electrodes 1 and 5 during the electrophoretic migration imaging
process.
[0022] As shown in the drawing, exposure of electrically photosensitive particles 4 takes
place by use of an exposure system consisting of light source 8, an original image
11 to be reproduced, such as a photographic transparency, a lens system 12, and any
necessary or desirable radiation filters 13, such as color filters, whereby electrically
photosensitive particles 4 are irradiated with a pattern of activating radiation corresponding
to original image 11. Although the electrophoretic migration imaging system represented
in the drawing shows electrode 1 to be transparent to activating radiation from light
source 8, it is possible to irradiate electrically photosensitive particles 4 in the
nip 21 between electrodes 1 and 5 without either of electrodes 1 or5 being transparent.
In such a system, although not shown in the drawing, the exposure source 8 and lens
system 12 is arranged so that particles 4 are exposed in the nip or gap 21 between
electrodes 1 and 5.
[0023] As shown in the drawing, electrode 5 is a roller electrode having a conductive core
14 connected to power source 15. The core is in turn covered with a layer of insulating
material 6, for example, baryta paper. Insulating material 6 serves to prevent or
at least substantially reduce the capability of electrical- ly photosensitive particles
4 to undergo a radiation induced charge alteration upon interaction with electrode
5. Hence, the term "blocking electrode" may be used, as is conventional in the art
of electrophoretic migration imaging, to refer to electrode 5.
[0024] Although electrode 5 is shown as a roller electrode and electrode 1 is shown as essentially
a flat plate electrode in the drawing, either or both of these electrodes may assume
a variety of different shapes such as a web electrode, rotating drum electrode, plate
electrode, and the like as is well known in the field of electrophoretic migration
imaging. In general, during a typical electrophoretic migration imaging process wherein
electrically photosensitive particles 4 are dispersed in an electrically insulating,
liquid carrier, electrodes 1 and 5 are spaced such that they are in pressure contact
or very close to one another during the electrophoretic migration imaging process,
e.g., less than 50 microns apart. However, where electrically photosensitive particles
4 are dispersed simply in an air gap between electrodes 1 and 5 or in a carrier such
as a layer of heat-softenable or other liquefiable material coated as a separate layer
on electrode 1 and/or 5, these electrodes may be spaced more than 50 microns apart
during the imaging process.
[0025] The strength of the electric field applied between electrodes 1 and 5 during the
electrophoretic migration imaging process of the present invention may vary considerably;
however, it has generally been found that optimum image density and resolution are
obtained by increasing the field strength to as high a level as possible without causing
electrical breakdown of the carrier in the gap between the electrodes. For example,
when electrically insulating liquids such as isoparaffinic hydrocarbons are used as
the carrier in the imaging apparatus of the drawing, the applied voltage across electrodes
1 and 5 typically is within the range of from about 100 volts to about 4 kilovolts
or higher.
[0026] As explained hereinabove, an image is formed in electrophoretic migration imaging
processes as the result of the combined action of activating radiation and electric
field on the electrically photosensitive particles 4 disposed between electrodes 1
and 5 in the attached drawing. Typically, for best results, field application and
exposure to activating radiation occur concurrently. However, as would be expected,
by appropriate selection of various process parameters such as field strength, activating
radiation intensity, incorporation of suitable light sensitive addenda in or together
with the electrically photosensitive particles by incorporation of a persistent photoconductive
material, and the like, it is possible to alter the timing of the exposure and field
application so that one may use sequential exposure and field application rather than
concurrent field application and exposure.
[0027] When disposed between electrodes 1 and 5 of the drawing, electrically photosensitive
particles 4 exhibit an electrostatic charge polarity, either as a result of triboelectric
interaction of the particles or as a result of the particles interacting with the
carrier in which they are dispersed, for example, an electrically insulating liquid,
such as occurs in conventional liquid electrographic developers composed of toner
particles which acquire a charge upon being dispersed in an electrically insulating
carrier liquid.
[0028] Image discrimination occurs in the electrophoretic migration imaging process of the
present invention as a result of the combined application of electric field and activating
radiation on the electrically photosensitive particles dispersed between electrodes
1 and 5 of the apparatus shown in the drawing. That is, in a typical imaging operation,
upon application of an electric field between electrodes 1 and 5, the electrically
photosensitive particles 4 are attracted in the dark to either electrodes 1 or 5,
depending upon which of these electrodes has a polarity opposite to that of the original
charge polarity acquired by the electrically photosensitive particles. And, upon exposing
particles 4 to activating radiation, it is theorized that there occurs neutralization
or reversal of the charge polarity associated with either the exposed or unexposed
particles. In typical electrophoretic migration imaging processes wherein electrode
1 bears a conductive surface, the exposed, electrically photosensitive particles 4,
upon coming into electrical contact with such conductive surface, undergo an alteration
(usually a reversal) of their original charge polarity as a result of the combined
application of electric field and activating radiation. Alternatively, in the case
of photoimmobilized electrophoretic recording (PIER), wherein the surface of electrode
1 bears a dark charge exchange material as described by Groner in aforementioned U.S.
Patent 3,976,485, one obtains reversal of the charge polarity of the unexposed particles,
while maintaining the original charge polarity of the exposed electrically photosensitive
particles, as these particles come into electrical contact with the dark charge exchange
surface of electrode 1. In any case, upon the application of electric field and activating
radiation to electrically photosensitive particles 4 disposed between electrodes 1
and 5 of the apparatus shown in the drawing, one can effectively obtain image discrimination
so that an image is formed by the electrical- ly photosensitive particles which corresponds
to the original pattern of activating radiation. Typically, using the apparatus shown
in the drawing, one obtains a visible image on the surface of electrode 1 and a complementary
image on the surface of electrode 5.
[0029] Subsequent to the application of the electric field and exposure to activating radiation,
the images which are formed on the surface of electrodes 1 and 5 of the apparatus
shown in the drawing may be temporarily or permanently fixed to these electrodes or
may be transferred to a final image receiving element. Fixing of the final particle
image can be effected by various techniques, for example, by applying a resinous coating
over the surface of the image bearing substrate. For example, if electrically photosensitive
particles 4 are dispersed in a liquid carrier between electrodes 1 and 5, one may
fix the image or images formed on the surface of electrodes 1 and 5 by incorporating
a polymeric binder in the carrier liquid. Many such binders (which are well known
for use in liquid electrophotographic liquid developers) are known to acquire a change
polarity upon being admixed in a carrier liquid and therefore will, themselves, electrophoretically
migrate to the surface of one or the other of the electrodes. Alternatively, a coating
of a resinous binder (which has been admixed in the carrier liquid), may be formed
on the surfaces of electrodes 1 and 5 upon evaporation of the liquid carrier.
[0030] The electrically photosensitive particles comprising compounds of Formulas I &
II may be used to form monochrome images, or the particles may be admixed with other
electrically photosensitive particles of proper color and photosensitivity and used
to form polychrome images. Said electrically photosensitive particles of the present
invention also may be used as a sensitizer for other electrically photosensitive materials
in the formation of monochrome images. When admixed with other electrically photosensitive
particles, selectively the electrically photosensitive particles of the present invention
may act as a sensitizer and/or as an electrically photosensitive particle. Many of
the electrically photosensitive particles comprising compounds having Formulas I or
II have especially useful hues which make them particularly suited for use in polychrome
electrophoretic migration imaging processes which employ a mixture of two or more
differently colored electrically photosensitive particles. When such a mixture of
multicolored electrically photosensitve particles is formed, for example, in an electrically
insulating carrier liquid, this liquid mixture of particles exhibits a black coloration.
Preferably, the specific cyan, magenta, and yellow particles selected for use in such
a polychrome electrophoretic migration imaging process are chosen so that their spectral
response curves do not appreciably overlap whereby color separation and subtractive
multicolor image reproduction can be achieved.
[0031] The following examples illustrate the utility of electrically photosensitive particles
comprising the compounds of Formulas I and II in electrophoretic migration imaging
processes.
Examples 1-28:
Imaging Apparatus
[0032] An imaging apparatus was used in each of the following examples to carry out the
electrophoretic migration imaging process described herein. This apparatus was a device
of the type illustrated in the drawing. In this apparatus, a film base having a conductive
coating of 0.1 optical density cermet (cr SiO) served as electrode 1 and was in pressure
contact with a 10 centimeter diameter aluminum roller 14 covered with dielectric paper
coated with poly(vinyl butyral) resin which served as electrode 5. Electrode 1 was
supported by two 2.8 cm. diameter rubber drive rollers 10 positioned beneath electrode
1 such that a 2.5 cm. opening, symmetric with the axis of the aluminum roller 14,
existed to allow exposure of electrically photosensitive particles 4 to activating
radiation. The original transparency 11 to be reproduced was taped to the back side
of electrode 1.
[0033] The original transparency to be reproduced consisted of adjacent strips of clear
(WO), red (W29), green (W61) and blue (W47B) Wratten filters. The light source consisted
of a projector with a 1000 watt Xenon Lamp. The light was modulated with an eleven
step 0.3 neutral density step tablet. The residence time in exposure zone was 10 milliseconds.
The log of the light intensity (Log I) was as follows:

The voltage between the electrodes 1 and 5 was about 2 kV. Electrode 1 was negative
polarity in the case where electrically photosensitive particles 4 carried a positive
electrostatic charge, and electrode 1 was positive in the case where electrically
photosensitive particles 4 were negatively charged. The translational speed of electrode
1 was about 25 cm. per second. In the following examples, an image was formed on the
surfaces of electrodes
1 and 5 after simultaneous appli-, cation of light exposure and electric field to electrically
photosensitive
`particles 4 admixed with a liquid carrier as described below to form a liquid imaging
dispersion and which dispersion had been placed in nip 21 between the electrodes 1
and 5. If the compounds being evaluated for use as particles 4 possessed a useful
level of electrical photosensitivity, one obtained a negative-appearing image reproduction
of original 11 on electrode 5 and a complementary image on electrode 1.
Imaging Dispersion Preparation
[0034] Imaging dispersions were prepared to evaluate each of the compounds in Tables I through
III as electrically photosensitive particles. The dispersions were prepared by first
making a stock solution of the following components. The stock solution was prepared
simply by combining the components.

A 5 g. aliquot of the stock solution was combined in a closed container with 0.045
g. of the Table I compound to be tested and 12 g. of Hamber 440 stainless steel balls.
The dispersion was then milled for three hours on a paint shaker.
[0035] Each of the 28 compounds described in Tables I through III were tested according
to the just outlined procedures. Each of the compounds were found to be electrically
photosensitive as evidenced by obtaining a negative appearing image of the original
on one electrode and a complementary image on the other electrode.