CA1115578A - Electrophotosensitive materials for migration imaging processes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Electrophotosensitive materials having the structure I. or II. wherein:
m and n represent zero, one or two;
L3 through L7, represent hydrogen, alkyl, aralkyl, aryl, or, in addition, any two of L1, L2 and L3 or any two of L4, L5, L6 and L7 together represent the elements needed to complete a carbocyclic ring;
R represents alkyl, aryl or hydrogen;
A1 represents a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic nucleus and said substituents may be a heterocyclic secondary amino, alkoxy, amino, arylamino, dialkyl-amino, diarylamino, alkyl, aryl and halogen;
A2 represents a basic substituted or unsubstituted nucleus selected from the group consisting of imidazole, 3H-indole, thiazole, benzothiazole, naphtho-thiazole, thianaphtheno-7?,6?,4,5-thiazole, oxazole, naphthoxazole, selenazole, benzoselanazole, naphthoselen-azole, thiazoline, 2-quinoline, 4-quinoline, 1-isoquino-line, benzimidazole, 2-pyridine, 4-pyridine, and thia-zolene are disclosed.

-1a-

Description

S5~8 Field of the Invention This invention relates to electrophoretic migration imaging processes and, in particular, to the use of certain novel photosensitive pigment materials in such processes.

Background of the Invention In the past, there has been extensive description in the patent and other technical literature o~ electrophoretic migration imaging processes. ~or example, a description o~ 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 photoelectrophoretic migration imaging processes, another type o~ electrophoretic migration imaging process which advantageously provides ~or image reversal is described in Groner, ~.S. Patent 3,976,485 issued August 24, 1976. This latter process has been termed photoimmobilized electrophoretic recording or PIER.
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 Or which may be transparent. To achieve image formation in these processes, the charge-bearing photo-sensitive particles positioned between the two spaced electrodes, as described above, are subjected to the in~luence Or an electric field and exposed to activating radiation. As a result, the charge-bearing electrically photosensitive particles are caused to migrate electrophoretically to the surface o~ one or the ~k .

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other of the spaced electrodes, and one obtains an image pattern 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 elec-trically 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 application) so that the image formed on one electrode s~lrface is composed ideally Or 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.
In any case, regardless of the particular electropho retic migration imaging process employed~ it is apparent that an essential component of any such process is 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 migratlon 557~3 imaging processes, for example, in U.S. Patents 2~753,939 by Sugarman, 2,940,847 by Kaprelian, and 3,384,488 and 3,615,558 by Tulagin et al., noted hereinabove.
In large part, the art, to date, has generally selected useful electrically photosensitive or photoconductive pigment materials 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 electrophoto-graphic office-copier devices. For example, both Sugarman and Kaprelian in the above-re~erenced patents state that electrically photosensitive materials useful in electrophoretic migration imaging processes may be selected from known classes of photoconductive materials. Also, the phthalocyanine pigments described as a useful electrically photosensitive material for electrophoretic imaging processes in U.S. Patent 3,615,558 by Tulagin et al. have long been known to exhibit useful photo-conductive properties.

Summary of the Invention -~~~
In accord with the present invention, a group of materials has been discovered which are useful in electrophoretic migration imaging processes. To the best of our knowledge, none of said materials have been previously identified as photoconductors.
The generalized structures for pigments of this invention are as follows:

S~7~51 o A

I. ~ A1-cL~(=cL2-CL3)=~-\ / and II. A2=CL~ CL5~=CL6 CL7)--~ ~ o wherein:
M and N represent zero, one or two;
Ll through L7, represents hydrogen, alkyl, aralkyl, aryl, and in addition any two of Ll, L2, and L3 and any two o~ L~, L5, L6, and L7 may together represent the elements needed to complete a carbocyclic ring;
R represents alkyl, aryl, hydrogen, etc.
Al may be the same as A2 and in addition represents an aryl group (e.g., phenyl, naphthyl, anthryl) or a substituted ; or unsubstituted heterocyclic nucleus such as thiophene, benzo[b]thiophene, naphtho[2,3-b]thiophene, furan, isobenzo-furan, chromene, pyran, xanthene, pyrrole, 2H-pyrrole, pyrazole, indolizine, 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;]quinoline; 192,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinoline; lH,5H-benzo[ij]quinolizinej

2,3-dihydro-lH,5H-benzo[ij]quinolizine; 2,3-dihydro-lH,5H-benzo[ij]quinolizine and 2,3,6,7-tetrahydro-lH,5H-benzo[ij]-quinolizine, 10,11-dihydro-9H-benzo[a]xanthen-8-yl; 6,7-dihydro-5H-benzo[b]pyran-7-yl, and said substi~uents may be a heterocyclic secondary amino, alkoxy, amino~ arylamino, dialkylamino, diarylamino, alkyl, aryl and halogen;

i7~

A2 represents a basic subst~tuted or unsubstituted heterocyclic nucleus of the type used in cyanine dyes.
Representative examples of SUC}l nuclei include:
a) an imidazole nucleus such as imidazole and 4-phenylimidazole;
b) 3H-indole nucleus such as 3H-indole, 3,3-dimethyl-3H-indole, 3,3,5-trimethyl-3H-indole;
c) a thiazole nucleus such as thiazole, 4-methyl-thiazole, 4-phenylthiazole, 5-methylthiazole, 5-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 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, tetrahydrobenzothiazole, 5,6-dimethoxybenzothiazole, 5,6-dioxymethylenebenzothiazole, 5-hydroxybenzo-thiazole and 6-hydroxybenzothiazole;
e) a naphthothiazole nucleus such as naphtho[l,2-d]-thiazole,naphtho[2,1-d]thiazole, naphtho[2,3-d]-thiazole, 5-methoxynaphtho[2,1-d]thiazole, 5-ethoxynaphtho[2,1-d]thiazole, 8-methoxynaphtho-[1,2-d]thiazole and 7~methoxynaphtho[1,2-d]-thiazole;

~5S7~

f) a thianaphtheno-7',6',4,5 thiazole nucleus such as 4'-methoxythlanaphtheno-7',6',4,5-thiazole;
g) an oxazole nucleus such as 4-methyloxazole, 5-methyloxazole, 4-phenyloxazole, 4,5-diphenyl-oxazole, 4-ethyloxazole, 4,5-dimethyloxazole : and 5-phenyloxazole;
h) a naphthoxazole nucleus such as naphtho[l,2]oxazole and naphtho[2,1]oxazole;
i) a selenazole nucleus such as 4-methylselenazole and 4-phenylselenazole;
j) a benzoselenazole nucleus such as benzoselenazole, 5-chlorobenzoselenazole, 5-methoxybenzoselenazole, 5-hydroxybenzoselenazole and tetrahydrobenzo-selenazole;
k) a naphthoselenazole nucleus such as naphtho-[1,2-d]selenazole, naphtho[2,1-d]selenazole;
1) a thiazoline nucleus such as thiazoline and 4-methylthiazoline;
m) a 2-quinoline nucleus such as quinoline, 3-methylquinoline, 5-methylquinoline, 7-methyl-quinoline, 8-methylquinoline, 6-chloroquinoline, : 8-chloroquinoline, 6-methoxyquinoline, 6-ethoxyquinoline, 6-hydroxyquinoline and 8 .~ hydroxyquinoline;
n) a 4-quinoline nucleus such as quinoline, 6-methoxyquinoline, 7-methylquinoline and ~ 8-methylquinoline;
: o) a l-isoquinoline nucleus such as isoquinoline and 3,4-dihydroisoquinoline;

~:~LlS~

p) a benzimidazole nucleus such as 1,3-diethyl-benzimidazole and l-ethyl-3-phenylbenzimid-azole;
q) a 2-pyridine nucleus such as pyridine and 5-methylpyridine;
r) a 4-pyridine nucleus;
s) a thiazoline nucleus;
t) an acenaphthothiazole nucleus; and u) benzoxazole.

Unless stated otherwise, 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 carbons such as phenyl, naphthyl, anthryl or to alkyl or aryl substituted aryl groups such as tolyl, ethylphenyl, biphenylyl, etc.; aralkyl refers to aryl substituted alkyl groups such as benzyl, phenethyl, etc.;
cycloalkyl refers to saturated carbocyclic ring groups which may have alkyl, aryl or aralkyl substituents such as cyclopropyl, cyclopentyl, cyclohexyl, 5,5-dimethylcyclohexyl, etc.; alkoxy refers to alkyloxy groups where alkyl is as defined above, such as methoxy, ethoxy, isopropoxy, butoxy, etc.
When used in an electrophoretic migration imaging process, charge-bearing, electrically photosensitive particles formulated from the materials of the present invention are positioned between two spaced electrodes; preferably these particles are contained in an electrically insulating carrier such as an electrically insulating liquid or an electrically insulating, liquefiable matrix material, e.g., a thixotropic or a heat- and/or solvent-softenable material, which is .

` -~lSS78 positioned between the spaced electrodes. While so positioned between the spaced electrodes, the photosensitive particles are sub~ected to an electric field and exposed to a pattern of activating radiation. As a consequence, the charge-bearing, electrically photosensitive particles undergo a radiation-induced variation in their charge polarity and mi~rate to one or the other of the electrode surfaces to form on at least one of these electrodes an image pattern representing a positive-sense or negative-sense image of the original radiation exposure pattern.

Brief Description of the Drawings Fig. 1 represents diagrammatically a typical imaging apparatus for carrying out the electrophoretic migration imaging process of the invention.

Description of the Preferred Embodiments In accordance with the preferred embodiment of the present invention there is provided a group of materials which are useful in electrophoretic migration imaging processes.
Said materials have the structure according to general Formulas I and II wherein:
Ll through L7, M and N, are as previously definedg Al represents 2,3,6,7-tetrahydro-lH,5H-benzo[ij]-quinolizine or a substituted or unsubstituted phenyl group wherein the substituents are selected from the group consisting of alkoxy, diarylamino, dialkylamino, morphilino di-p-tolylamino and pyrrolidino;

A2 represents a substituted and unsubstituted nucleus such as thiazole, thiazoline, benzothiazole, naphthothiazole, benzoxazole, benzoselenazole, 2-quinoline, 4-quinoline and 3H-indole.

~ S57~

In general the materials of ~ormula I which have been found to be electrophotosensltive tend to exhiblt a maximum absorption wavelength, Amax, within the range of from about 420 to about 750 nm. A variety of difrerent materials within the class defined by Formula I have been tested and found to exhibit useful levels of electrical photosensitivity in electrophoretic migration imaging processes.
A partial listing of representative such materials is included herein in Table I. In Table I Et represents C2H5.
Methods for making the materials disclosed and claimed herein include 30urnal of American Chemical Society, 35, 959 (1913), Journal of American Chemical Society, 73, 5326-5363 (1951), and U.S. Patents 2,165,339 and 2,956,881.

. ~ ff~ ~
~J.~57~3 T A B L E

Number Material Color ~ ~7~ Magenta ~!:tii i 2 t~ Yellow Ettl\ ~i

3 ,~ Purple Et.~ ~

0,~

4 ~ -a~ Purple CzHs o ~ ~P3~ ~ Cyan o 6 Et~ Purple lt ~.~Io 7 c~ ~ ~ Purple Et 11~
Cn3~ ~t:H3 ~, 8 t ~ Blue / CH~
~:t ~-~

.

.

~557~3 T A B L E

Number Material Color -,CH3 9 t~ "~ \o Green ~ ~
~t " ~ , , .~ ~9~ a\ ~ Purple ,C~2 .;~I

~ a~\."~ Orange Et ./ ~.
~ O.
12 t~ Orange ~ ~ .

13 ~ Purple C2~s ' ~t o ;.
14 ' ¦ ~ ~{~/ ~ Orange C2~5 3 .;~"`i\ ~-.~ D Orange ;-; O
16 ~ ~ =,c{~s~\ ~ Purple .,i i ' ~ i T A B L E

Number Material Color 17 ~ _ ~ ~ Purple c2aS

18 ,~ =Q~ Orange C~3 ,~

19 ,i~ Purple ~ ;

,~ Blue 21 1~ 5 Orange t~ i 22 ~ > ~a~\ ~ Pink Et 23 i~i Purple ~,~

T A B L E

Number Material Color , 24 ~5~=~d~ ~ Blue I~ Green C2~6 , ~
~ "

t'~
26 ~ ~{~ Purple 2 5 /o/

O
27 C~3~~0~-~H~==_~=cH~a ~ Purple o : 28 czH5~ .=3_OE- ? Orange ,,~

29 ( ~ ~ ~ ~ Orange O
C 3~ Purple ~T

~,~/ lllSS78 T A B L E

Number Materlal Color 31 ~ Plnk ,.

(Q ~ C - \ ~ Plnk ~r~ 7 33 (' ~ Orange '' i 3~ ~CH 3 ~ c~x~/ ~ Reddish Brown ~2~ Orange 36 (C2Hs)~ ~ ~,{~q~J~ Purple , .

~ i;57~3 T A B L E

Number Material Color 37 ,l ~ ,; / ~ Blue ~3 t;~;

38 ~ Orange Ql ~

~3 1' 39 '~ ~Q~'\ ~ Orange T

As indicated hereinabove, the electrically photo-sensitive material described herein is useful in the preparation of the electrically pllotosensitive imaging particles used in electrophoretic migration imaging processes. In general, electrically photosensitive particles use~ul in such processes have an average particle size wlthin the range of from about .01 micron +o about 20 microns, preferably from about .01 to about 5 microns. Typically, these particles are composed o~

one or more colorant materials such as the colorant materials described in the present invention. However, these electrically photosensitive particles may also contain various nonphotosensitive materials such as electrically insulating polymers, charge control agents, various organic and inorganic fillers, as well as various additional dyes or pigment materials to change or enhance various colorant and physical properties of the electrically photosensitive ; particle. In addition, such electrically photosensitive particles ;S7~

may contain other photosensitive materials such as various sensitizing dyes and/or chemical sensitizers to alter or enhance their response characteristics to activating radiation.
When used in an electrophoretic migration imaging process in accord with the present inventiong the electrically photosensitive material described in Table I are typically positioned in particulate form, between two or more spaced electrodes, one or both of which typically being transparent to radiation to which the electrically photosensitive material is light-sensitive, i.e., activating radiation. Although the electrically photosensitive material, in particulate form, 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 particulate material in an electrically insulating carrier, such as an electrically insulating liquid, or an electrically insulating, liquefiable matrix material, such as a heat- and/or solvent-softenable polymeric material or a thixotropic polymeric material.
Typically, when one employs such a dispersion of electrically photosensitive particulate material and electrically insulating carrier material 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 particulate material for each lO parts by weight of electrically insulating carrier material.
As indicated above, when the electrically photosensitive particles used in the present invention are dispersed in an electrically insulating carrier material, such carrier material ~ ~ ~ S S7 ~

may assume a variety of physical forms and may be selected from a variety of different materials. For example, the carrier material may be a matrix of an electrically insulating, normally solid polymeric material capable of being softened or liquefied upon application of heat, solvent, andtor pressure so that the electrically photosensitive particulate material dispersed therein can migrate thro~gh the matrix. In another, more typical embodiment of the invention, the carrier material can comprise an electrically insulating liquid such as decane, paraffin, Sohio Oderless Solvent 3440 (a kerosene fraction marketed by the Standard Oil Company, Ohio), various iso-paraffinic hydrocarbon liquids such as those sold under the trademark Isopar G by Exxon Corporation and having a boiling point in the range of 145C to 186C, various halogenated hydrocarbons such as carbon tetrachloride, trichloromonofluoro-methane, 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 No. 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 157C
to about 177~ and is composed of 9 percent dialkyl benzenes, 37 percent trialkyl benzenes, and 4 percent aliphatics.
Typically, whether solid or liquid at normal room temperatures, i.e., about 22C, the electrically insulating carrier material used in the present invention is a material having a resis-tivity greater than about 109 ohm-cm, preferably greater than about 1012 ohm-cm. When the electrically photosensitive particles ~ormed from the materials of the present invention are incorporated in a carrier material such as one ~ - ~
~557B

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 developer compositions where they are employed for purposes substantially similar to that described herein. Thus, extensive discussion of the materials herein is deemed unnecessary. These materials are typically polymeric materials incorporated by admixture thereof into the liquid carrier vehicle of the suspension. In addition to, and possibly related to, the aforementioned enhance-ment 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 photosensitive particles.
In addition to the foregoing charge control agent materials, various polymeric binder materials such as various natural, semi-synthetic or synthetic resins, may be dispersed or dissolved in the electrically insulating carrier to serve as a fixing material for 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 developer compositions so that extended discussion thereof is unnecessary herein.
The process of the present invention will be described in more detail with reference to the accompanying drawing, Fig.
3 1, which illustrates a typical apparatus which employs the electrophoretic migration imaging process of the invention.

l~ S~7~

Fig. 1 shows a transparent electrode 1 supported by two rubber drive rollers 10 capa~le of imparting a translating motion to electrode 1 in the direction of the arrow. Electrode 1 may be composed of a layer of optically transparent material, such as glass or an electrically insulating, transparent poly-meric support such as polyethylene terephthalate, covered with a thin, optically transparent, conductive layer such as tin oxide, indium oxide, nickel, and the like. Optionally, depend-ing upon the particular type of electrophoretic migration imaging process desired, the surface o~ 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 by Groner in U.S. Patent 3,976,485 issued August 24, 1976.
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, elec-trically insulating layer 6. Electrode 5 is connected to oneside 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 particulate material 4 which is positioned between electrodes 1 and 5.
Typically electrically photosensitive particulate material 4 is dispersed in an electrically insulating carrier material such as described hereinabove.
The electrically photosensitive particulate material 4 may be positioned between electrodes 1 and 5 by applying ~20-" ~1557~

material 4 to either or both of the surfaces of electrodes 1 and 5 prior to the imaging process or by inject~ng electrically photosensitive imaging material 4 between electrodes 1 and 5 during the electrophoretic migration imaging process.
As shown in Fig. 1, exposure of electrically photo~
sensitive particulate material 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 transparency9 a lens system 12, and any necessary or desirable radiation filters 13, such as color filters, whereby electrically photosensitive material 4 is irradiated with a pattern of activating radiation corresponding to original image 11. Although the electrophoretic migration imaging system represented in Fig. 1 shows electrode 1 to be transparent to activating radiation from light source 8, it is possible to irradiate electrically photosensitive particu-late material 4 in the nip 21 between electrodes 1 and 5 with-out either of electrodes 1 or 5 being transparent. In such a - system, although not shown in Fig. 1, the exposure source 8 and lens system 12 is arranged so that image material 4 is exposed in the nip or gap 21 between electrodes 1 and 5.
As shown in Fig. 1, 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 electrically photosensitive particulate material 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.

~21-i57~

Although electrode 5 is shown as a roller electrode and electrode 1 is shown as essentially a translatable, flat plate electrode in Fig. 1, either or both of these electrodes ~ay 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 material 4 is dis-persed 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 particulate material 4 is 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.
The strength of the electric field imposed 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 medium in the electrode gap. For example, when ` electrically insulating liquids such as isoparaffinic hydro-carbons are used as the carrier in the imaging apparatus of Fig. 1, the applied voltage across electrodes 1 and 5 typically is within the range of from about 100 volts to about 4 kilovolts or higher.

~ S57~3 As explained hereinabove, image formation occurs in electrophoretic migration imaging processes as the result of the combined action of activating radiation and electric field on the electrically photosensitive particulate material 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 para-meters such as field strength, activating radiation intensity, incorporation of suitable light sensitive addenda in or together with the electrically photosensitive particles formed from the material of Formula I, e.g., by incorporation of a persistent photoconductive material, and the like, it is possible to alter the timing of the exposure and field application events so that one may use sequential exposure and field application events rather than convurrent field application and exposure events.
When disposed between imaging electrodes 1 and 5 of Fig. 1, electrically photosensitive particulate material 4 exhibits 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 material ln which they are dispersed, for example, an electrically insulating liquid, such as occurs in conventional liquid electrographic developing compositions composed of toner particles which acquire a charge upon being dispersed in an electrically insulating carrier liquid.
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 particulate material ~l~SS7 51 dispersed between electrodes 1 and 5 of the apparatus shown in Fig. 1. That is, in a typical imaging operation, upon application of an electric field between electrodes 1 and 5, the particles 4 of charge-bearing, electrically photosensitive material 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 electromagnetic 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 systems wherein elec-trode 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 ~0 dark charge exchange material as described by Groner in afore-mentioned 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 photo-sensitive particles, as these partlcles 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 particulate material 4 disposed between electrodes 1 and 5 of the apparatus shown in Fig. 1, one can effectively obtain image discrimination so that an image pattern is formed by the electrically photosensitive -24_ SS7~3 particles which corresponds to the original pattern of activating radiation. Typically, using the apparatus shown in Fig. 1, one obtains a visible image on the surface of electrode 1 and a compleMentary image pattern on the surface of electrode 5.
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/or 5 of the apparatus shown in ~ig. 1 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 coat-ing 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/or 5 by incorporating a polymeric binder material 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. Alternatively3 a coating of a resinous binder (which has been admixed in the carrier liquid), may be formed on the surfaces of electrodes 1 and/or 5 upon evaporation of the liquid carrier.
The electrically photosensitive colorant material of Formula I may be used to form monochrome images, or the material ma~ be admixed with other electrically photosensitive material of proper color and photosensitivity and used to form polychrome images. Said electrically photosensitive colorant material of th~
present invention also may be used as a sensitizer for other electrophotosensitive material in the formation of monochrome -25~

``~ 5~7~

images. When admixed with other electrically photosensitive materials, selectively the photosensitive material of the present invention may act as a sensitizer and/or as an elec-trically photosensitive particle. ~any of the electrically photosensitive colorant materials having Formula I have especially useful hues which make them particularly suited for use in polychrome imaging processes which employ a mixture of two or more differently colored electrically photosensitive particles. When such a mixture of multicolored electrically photosensitive particles is formed~ for example, in an electri-cally insulating carrier liquid, this liquid mixture of particulate rnaterial exhibits a black coloration. Preferably, the specific cyan, magenta~ and yellow particles selected for use in such a polychrome 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.
The following examples illustrate the utility of the Formula I ma~erials in electrophoretic migration imaging processes.

Examples 1-39:
Imaging Apparatus 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 Fig. 1. In this apparatus, a translating 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) S57~

resin which served as electrode 5. Plate 1 was supported by two 2.8 cm. diameter rubber drive rollers 10 positioned beneath film plate 1 such that a 2.5 cm. opening, symmetric with the axis of the aluminum roller 14g 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 film plate 1.
The original transparency to be reproduced consisted of adjacent strips of clear (W0), red (W29), green (W61) and blue (W47B) filters. The light source consisted of a Kodak Ektagraphic AV434A Carousel Projector with a 1000 watt Xenon Lamp. The light was modulated with a Kodak No. 5 flexible M-carbon eleven step 0.3 neutral density step tablet. The residence time in the action or exposure zone was 10 milliseconds.
The log of the light intensity (Log I) was as follows:

_Log I
erg/cm2/sec .
_ Filters W0 Clear 5.34 W29 Red 4.18 W61 Green 4.17 W47B Blue 4.15 The voltage between the electrode 5 and film plate 1 was about 2 kv. Film plate 1 was negative polarity in the case where electrically photosensitive particulate material 4 carried a positive electrostatic charge, and film plate 1 was positive in the case where electrically photosensitive electrostatically charged particles were negatively charged. The trans]ational SS7~

speed of film plate 1 was about 25 cm. per second. In the following examples, image formation occurs on the surfaces of film plate 1 and electrode 5 after simultaneous application of light exposure and electric field to electrically photosen-sitive material evaluated for use as electrically photosen-sitive particulate material 4 was admixed with a liquid carrier as described belo~ to form a liquid imaging dispersion which was paced in nip 21 between the electrodes 1 and 5. If the material being evaluated for use as material 4 possessed a useful leel of electrical photosensitivity, one obtained a negative-appearing image reproduction of original 11 on elec-trode 5 and a complementarty image on electrode 1.

Imaging Dispersion Preparation Imaging dispersions were prepared to evaluate each of the materials in Tables I through XI. The dispersions were ' prepared by first making a stock solution of the Eollowing components. The stock solution was prepared simply by combin-in& the components.

Isopar G 2.2 g Solvesso~ 1.3 g Piccotex~100 1.4 g PVT~ O.l g *Poly(vinyltoluene-co-lauryl methacrylate-co-lithium methacrylate-co-methacrylic acid) 56/4Q/3.6tO.4 A 5 g aliquot of the stock solution was combined in a closed container with 0.045 g of the Table I material to be tested and 12 g of Hamber 440 stainless steel balls. The prepara-tion was then milled for three hours on a paint shaker.

Each Or the 39 materials described in Table I were tested according to the just outlined procedures. Each of such materials were found to be electrophotosensitlve as evidenced by obtaining a negative appearing image of the original on one electrode and a complementary image on the other electrode.
Materials 1, 2, 4, 5, 7, 9, 11, 12, 13, 14, 15, 16, 17, 18, 21, 22, 24, 26, 28, 31, 33, 35, 37 and 39 provide images having good to excellent quality. Image quality was determined visually having regard to minimum and maximum densities, speed and color saturation.
The invention has been described in detail with particular reference to certain preferred embodiments thereor, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

.

Claims (4)

WE CLAIM:

1. An electrophoretic migration imaging process which comprises subjecting an electrically photosensitive colorant material positioned between at least two electrodes to an applied electric field and exposing said materials to an image pattern of radiation to which the material is photo-sensitive, thereby obtaining image formulation on at least one of said electrodes, the improvement which comprises using as at least a portion of said material, an electrically photosensitive material having a structure selected from the group consisting of:

I. and II. wherein:
m and n represent zero, one or two;
L1 through L7, represent hydrogen, alkyl, aralkyl, aryl, or, in addition, any two of L1, L2 and L3 or any two of L4, L5, L6 and L7 together represent the elements needed to complete a carbocyclic ring;
R represents alkyl, aryl or hydrogen;

A1 represents a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic nucleus and said substituents may be a heterocyclic secondary amino, alkoxy, amino, arylamino, dialkylamino, diarylamino, alkyl, aryl and halogen;
A2 represents a basic substituted or unsubstituted nucleus selected from the group consisting of imidazole, 3H-indole, thiazole, benzothiazole, naphthothiazole, thianaphtheno-7?,6?,4,5-thiazole, oxazole, naphthoxazole, selenazole, benzoselenazole, naphthoselenazole, thiazo-line, 2-quinoline, 4-quinoline, 1-isoquinoline, benzimid-azole, 2-pyridine, 4-pyridine, and thiazolene.

2. A process according to Claim 1 wherein A2 represents a substituted or unsubstituted nucleus selected from the group consisting of thiazole, thiazoline, benzothia-zole, naphthothiazole, benzoxazole, benzoselenazole, 2-quino-line 4-quinoline and 3H-indole.

3. A process according to Claim 2 wherein A1 represents 2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizine or a substituted or unsubstituted phenyl group wherein said sub-stituents are selected from the group consisting of alkoxy, diarylamino, dialkylamino, morphilino, di-p-tolylamine and pyrrolidino.

4. A process according to Claim 3 wherein said material is selected from the group consisting of and