CA1079109A - Electrophoretic imaging process in which an electrically photosensitive colorant is subjected to an applied field - Google Patents

Abstract

ELECTROPHORETIC MIGRATION IMAGING PROCESS, CASE A

Abstract of the Disclosure An improved electrophoretic migration imaging process is disclosed wherein the improvement comprises the use of elec-trically photosensitive particles containing a colorant having an absorption maximum greater than about 410 nm. and having the formula:

Description

1079~0~
t Field of the Invention This invention relates to electrophoretic migration imaging processes and, in particular, to the use of certain pho-tosensitive pigment materials in such processes.
Background of the Invention In the past, there has been extensive description in the patent and other technical literature of electrophoretic m~gration 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 con-ventional photoelectrophoretic migration imaging processes, another type o~ electrophoretic migration imaging process which advantageously provides for image reversal is described in U.S~
Patent 3,976,485 by Groner.

Certain important differences exist between the spe-cific electrophoretic migration imaging processes described, for example, in the above-noted patents to Sugarman, Kaprelian, Tulagin et al, Clark and Yeh, all of which deal with conven-tional electrophoretic migration imaging processes, and the above-noted Groner U.S. patent. The Groner Patent describes a novel method and apparatus for obtaining image reversal as a consequence of the electrical interaction between unexposed photosensitive particles and a "dark charge exchange"
electrode quite different from that which occurs in conventional electrophoretic migration imaging processes. However, there are certain general points of similarity existing in each of the electrophoretic migration imaging processes described in the foregoing patents.

-2-In general, each of the foregoing electrophoretic migration imaging processes typically employs a layer of elec-trostatic charge-bearing photoconductive particles, i.e., elec-trically photosensitive particles, positioned between two spaced electrodes, one of which may be transparent. To achieve image formation in these processes, the charge-bearing photosensitive particles positioned between the two spaced electrodes, as described above, are sub~ected to the influence of 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 of one or the 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 surface is composed ideally of electrically photosensitive par-ticles of one charge polarity, either negative or positive polarity, and the image formed on the opposite polarity elec-trode surface is composed ideally of electrically photosensitive particles having the opposite charge polarity, either positive or negative.
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 pho-tosensitive particles. And, of course, to obtain an easy-to-read, visible image it is important that these electrically pho-tosensitive particles be colored, as well as electrically photo-sensitive. Accordingly, as is apparent from the technical lit-erature 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 photo-sensitivity and which exhibit good colorant properties. Thus, for example, various types of electrically photosensitive mate-rials 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.
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 element, e.g., photoconductive plates, drums, or webs used in electrophotographic office-copier devices. For example, both Sugarman and Kaprelian in the above-20 referenced patents state that electrically photosensitive mate-rials useful in electrophoretic migration imaging processes may be selected from known classes of photoconductive materials.
And, the phthalocyanine pigments described as a useful electri-cally photosensitive material for electrophoretic imaging pro-cesses in U.S. Patent 3,615,558 by Tulagin et al have long been known to exhibit useful photoconductive properties.
It is recognized, as set forth above, that many useful electrically photosensitive materials which are employed in electrophoretic migration imaging processes can be and have been 30 selected from known photoconductive materials. However, in accord with the present invention it has unexpectedly been found after extensive investigation of one particular class of known iO79 10 9 photoconductive materials including, but not limited to, those materials described in U.~. Patents 3,246,983 issued April 19, 1966, 3,567,450 issued March 2, 1971, 3,653,887 issued April 43 1972, and 3,873,312 issued March 25, 1975, that a particular subclass of these materials within the larger class of organic photoconductive materials exemplified by the above-noted patents exhibits highly useful properties in electrophoretic migration imaging process, whereas many closely related materials within this same class of known organic photoconductive materials show little or no utility in electrophoretic migration imaging pro-cesses.
Su~mary of the Invention In accord with the present invention, it has been dis-covered that electrostatic charge-bearing particles comprising an electrically photosensitive colorant material having an absorption maximum to visible light greater than about 410 nm.
and having the following formula are particularly suitable for use in electrophoretic migration imaging processes:

R~ _~R2 ~ Rl_ R2 I. z ~ ~ C =C-Ar ) I C =C-~C Z
`-t' R4 R5 ~R4 R5 "t ' 1 wherein:
n represents O or 1, m represents the integer 1 or 2;
Ar represents a substituted or unsubstituted, carbocyclic or heterocyclic aromatic ring group, preferably having 6 to about 20 ring atoms in the aromatic ring, e.g., phenyl, naph-thyl, anthryl, etc., Z represents the nonmetallic atoms necess~ry to complete a carbocyclic or heterocyclic aromatic ring group, preferably hav-~07910~

ing 5 to about 14 ring atoms in the aromatic ring, e.g., phenyl,anthryl, carbazole, pyrrole, etc.;
each of Rl, R2, R3, R4 and R5, which may be the same or different, when taken alone, represents hydrogen, nitro, cyano, a halogen such as fluorine, chlorine, bromine or iodine, an alkoxy preferably having 1 to about 8 carbon atoms, a substi-tuted or unsubstituted alkyl having 1 to about 8 carbon atoms in the alkyl group, a substituted or unsubstituted, carbocyclic or heterocyclic aromatic ring group having 5 to about 14 carbon atoms in the aromatic ring, e.g., benzisoxazole, a carboxy ester having 1 to about 4 carbon atoms, an amide having the formula:

wherein R6 represents hydrogen or a substituted or unsubstituted aromatic ring group or a substituted or unsubstituted alkyl as defined immediately hereinabove, an amino, preferably saturated heterocyclic amino groups containing 5 to about 8 ring atoms such as pyrrolidinyl, piperidino, morpholino, etc., dialkylamino, diarylamino, dialkarylamino such as ditolylamino, or diaralkyl-amino such as dibenzylamino wherein the alkyl group contained in such amino is preferably a lower alkyl having 1 to about 8 carbon atoms and the aryl group contained in such amino is, for example, phenyl, naphthyl, etc.;
each of Rl, R2 and R3, when taken together,is free from any saturated N-heterocyclic ring group fused to the aromatic ring group formed by Z; and with the provisos that (i) when m represents 1 and n repre-sents 0, Ar represents phenylene, and more than one of R4, R5 and the substituents on Ar represent either nitro or cyano, then at least one of Rl, R2 or R3 represents diarylamino or dialk-arylamino and (ii) when both m and n represent 1, Ar representsphenylene, any two of Rl, R2 and R3 represent hydrogen and the remaining one of Rl, R2 and R3 represents a dialkylamino group, 1~79~09 then such dialkylamino group contains 2 to about 8 carbon atoms in the alkyl group.
A variety of different substituents may be present in the above-defined formula in the case where Ar represents a sub-stituted aromatic group. In general, the substituents on Ar may be selected from the same class of substituent groups defined above for R1, R2, R3, R4 and R5.
When used in an electrophoretic migration imaging process, the charge-bearing, electrically photosensitive parti-cles of the present invention are positioned between two spacedelectrodes; preferably these particles are contained in an elec-trically insulating carrier such as an electrically insulating liquid or an electrically insulating, liquefiable matrix mate-rial, e.g., a thixotropic or a heat- and/or solvent-softenable material, which is positioned between the spaced electrodes.
While so positioned between the spaced electrodes, the photosen-sitive particles used in the invention are subjected to an elec-tric 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 migrate to one or the other of the electrode sur-faces to form on at least one of these electrodes an image pat-tern 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 As noted hereinabove, many of the photosensitive mate-rials which have been found useful in the electrically photosen-sitive particles used in the electrophoretic migration imaging 10'79109 processes of the present invention have previously been found to possess useful levels of photoconductivity. For example, U.S.
Patents 3,246,983, 3,567,450, 3,653,887 and 3,873,312 teach that certain of the specific m~terials, which are described herein as useful in the preparation of electrically photosensitive parti-cles for electrophoretic migration imaging processes, have pre-viously been identified as useful photoconductors. However, it has unexpectedly been found that, while certain of the materials described as photoconductors in U.S. Patents 3,246,983~
o 3,567,450, 3,653,887 and 3,873,312 do provide useful electri-cally photosensitive material for use in electrophoretic migra-tion imaging processes, many other quite similar photoconductive materials described in these same patents have little or no utility in electrophoretic migration imaging processes.
Accordingly, as will be apparent upon comparing struc-tural formula I above with the materials disclosed in U.S. Pat-ents 3,246,983, 3,567,450, 3,653,887 and 3,873,312, it can beseen that structural formula I includes certain materials as useful materials in electrophoretic migration imaging processes which are not disclosed in either of the two aforementioned pat-ents, and also that structural formula I excludes many materials which are disclosed as useful photoconductors in these same pat-ents. In brief, for reasons not fully understood by applicants, it has been found that materials having structural formula I
hereinabove provide a highly useful electrically photosensitive material for electrophoretic migration imaging processes, whereas materials which may have structural formulas quite simi-lar to that shown in formula I and which are known to possess useful photoconductive properties do not serve as a useful mate~
rial for electrophoretic migration imaging processes.
In addition to the unexpectedly useful levels of elec-trical photosensitivity exhibited by the materials of formula I

above in electrophoretic migration imaging processes, in com-parison with that exhibited by similar organic photoconductive materials, the materials of formula I generally exhibit certain other properties which make these materials quite useful in electrophoretic migration imaging processes. Among other such useful properties, the materials of formula I are typically highly colored materials, generally exhibiting an absorption maxima to visible light at a wavelength greater than 410 nm, preferably in the 420 to 600 nm region of the visible spectrum.
Thus, these materials, in general, tend to have a yellow, orange, or magenta hue. In contrast, many, although not all, of the organic photoconductive materials described in U.S. Patents

3,246,983 and 3,567,450 are colorless materials. Also, whereas many of the organic photoconductive materials described in U.S.
Patents 3,246,983, 3,567,450, 3,653,887 and 3,873,312 are soluble in conventional organic solvents, e.g., aliphatic hydrocarbon solvents such as Isopar G ~ or alkylated aromatic solvents such as Solvesso ~ 100, and therefore can readily be coated or cast, together with a binder, from conventional organic solvents onto a conductive support to form photoconductive plates, webs, drums and the like useful in conventional electrophotographic applica-tions, the materials of formula I tend to be highly insoluble or only slightly soluble in such conventional organic solvents.
This latter property of substantial insolubility in conventional organic solvents is advantageous in electrophoretic migration imaging processes, particularly in those embodiments of such processes wherein the electrically photosensitive material is dispersed in particulate form in an electrically insulating carrier such as a conventional aliphatic hydrocarbon liquid to form an electrophoretic migration imaging suspension.

Typical electrically photosensitive colorant materials which may be used in the present invention have the formula I
illustrated hereinabove.
The terms "substituted alkyl group" and "substituted aromatic ring group" as used in the present application are defined to means those substituents which do not interfere with the electrical photosensitivity of the colorants used in the invention and which are conventionally recogniæed in the art as typical substituents for alkyl and aromatic groups, lG respectively. A partial listing of representative such substi-tuted alkyl groups includes the following materials. Typically, these materials contain 1 to about 8 carbon atoms in the alkyl group thereof.
a. alkoxyalkyl having a total of 2 to about 8 carbon atoms, e.g., ethoxypropyl, methoxybutyl, propoxymethyl, etc.
b. aryloxyalkyl, e.g., phenoxyethyl, naphthoxymethyl, phenoxy-pentyl, etc., c. aminoalkyl, e.g., aminobutyl, aminoethyl, aminopropyl, etc.
d. hydroxyalkyl, e.g., hydroxypropyl, hydroxyoctyl, hydroxy-methyl, etc., e. aralkyl, e.g., benzyl, phenethyl, ~ diphenylalkyl, etc., f. alkylaminoalkyl, e g., methylaminopropyl, methylaminoethyl, etc., and also including dialkylaminoalkyl, e.g., diethyl-aminoethyl, dimethylaminopropyl, propylaminooctyl, etc., g. arylaminoalkyl, e.g., phenylaminoalkyl, diphenylaminoalkyl, N-phenyl-N-ethylaminopentyl, N-phenyl-N-ethylaminohexyl, naphthylaminomethyl, etc., h. nitroalkyl, e.g., nitrobutyl, nitroethyl, nitropentyl, etc., i. cyanoalkyl, e.g., cyanopropyl, cyanobutyl, cyanoethyl, etc., 3 j. haloalkyl, e.g., chloromethyl, bromopentyl, chlorooctyl, etc., and k alkyl substituted with an acyl group having the formula:

-C-R

wherein R is hydroxy, hydrogen, aryl, e.g., phenyl, naph-thyl, etc., lower alkyl having 1 to about 4 carbon atoms, e g., methyl, ethyl, propyl, etc., amino including substi-tuted amino, e.g., diloweralkylamino, lower alkoxy having 1 to about 8 carbon atoms, e.g., butoxy, methoxy, etc., aryl-oxy, e.g., phenoxy, naphthoxy, etc.
A partial listing of representative substituted aro-matic ring groups includes the following materials. Typically, the substituent groups on these aromatic materials contain from 1 to about 8 carbon atoms.
a. alkoxyaryl, e.g., ethoxyphenyl, methoxyphenyl, propoxynaph-thyl, etc., b. aryloxyaryl, e.g., phenoxyphenyl, naphthoxyphenyl, phenoxy-naphthyl, etc., c. aminoaryl, e.g., aminophenyl, aminonaphthyl, aminoanthryl, etc., d. hydroxyaryl, e.g., hydroxyphenyl, hydroxynaphthyl, hydroxy-anthryl, etc., e. biphenylyl, f. alkylaminoaryl, e.g., methylaminophenyl, methylaminonaphthyl, etc., and also including dialkylaminoaryl, e.g., diethyl-aminophenyl, dipropylaminophenyl, etc., g. arylaminoaryl, e.g., phenylaminophenyl, diphenylaminophenyl, N-phenyl-N-ethylaminophenyl, naphthylaminophenyl, etc., h. nitroaryl, e.g., nitrophenyl, nitronaphthyl, nitroanthryl, etc., i. cyanoaryl, e.g., cyanophenyl, cyanonaphthyl, cyanoanthryl, etc., 1~79109 j. haloaryl, e.g., chlorophenyl, bromophenyl, chloronaphthyl, etc., k. alkaryl, e.g., tolyl, ethylphenyl, propylnaphthyl, etc., and 1. aryl substituted with an acyl group having the formula:

-C-R

wherein R is hydroxy, hydrogen, lower alkyl having 1 to about

4 carbon atoms, e.g., methyl, ethyl, propyl, butyl, etc., aryl, e.g., phenyl, naphthyl, etc., amino including substi-tuted amino, e.g., diloweralkylamino, lower alkoxy having 1 to about 8 carbon atoms, e.g., butoxy, methoxy, etc., aryl-oxy, e.g., phenoxy, naphthoxy, etc.
Within the class of materials having formula I above, three individual subclasses of materials have been found to exhibit particularly useful properties for electrophoretic migration imaging processes. These three subclasses of materi-als may be represented by the following structural formulas:

Ar (C = C ~ R7 III. Ar ~ C = C ~ 9 ~ 2 / ~ N-R
IV. ~r t C = C ~ ) 2 wherein Ar ls as defined hereinabove; each of R4 and R5, which may be the same or different, represents hydrogen or a cyano group; and each of R7, R8, R9, R10 and Rll, when taken alone, represents a substituted or unsubstituted, acyclic lower alkyl having 2 to about 8 carbon atoms or a substituted or unsubstituted, carbocyclic aromatic ring group preferably having 6 to about 14 ring atoms in the aromatic ring, such as an aryl group, e.g., phenyl, or an alkaryl, e.g., tolyl, ethyiphenyl, etc., and R7 and R8, when taken together, represent a pyrrolidinyl or a piperidino group.
In general, the photosensitive materials of formula I
above which have, to date, been found most useful in the present invention because of their high degree of photosensitivity and other desirable properties, for example, color separation in multicolor electrophoretic migration imaging processes and the like, tend to exhibit a yellow or orange coloration and a maxi-mum absorption w~velength, Amax, within the range of from about 420 to about 600 nm. Although photosensitive materials repre-sented by formulas II-IV above have generally been found most useful among the various materials described within the general class having formula I, a variety of different materials within the class defined by formula I have been tested and found to exhlbit useful levels of electrical photosensitivity in elec-trophoretic migration imaging processes. A partial listing of representative such materials is included herein in Table 1.

, ~, CU
Lr C\J

o ~ s~
O ~ ~1 N t`~
o _~ V

~ ~ V

Pl 8 Ilv~

V V

~cs o., ~ CO

~079~09 N
~p~J~y P

~ ~ -- IV
[~

0,1~ ~I N (r) ~ :~
r _ 1 6-~h ~ V- V ~ ~J
0~ ~

_, 0~ ~ O

V

~ _, v h co (~

N

O ~ N ~) J IS~
O ~ Cl N N N
C~

~079~09 N

V

~3 ~'~ ~
C~

E~ l v l ~ v ~ 5~
O,t' ~D ~ o~
O ~ C~ N C\J N

~079109 C~

~ ~ P

$ p _I

~;

~ ~ o o ~i 10791()5~

As indicated hereinabove, the electrically photosensi-tive colorant material described herein is used in the prepara-tion of electrically photosensitive imaging particles of elec-trophoretic migration imaging processes. In general, electri- .
cally photosensitive particles useful in such 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. Typically, these particles are composed of one or more colorant materials such as those described in the present inven-tion. However, these electrically photosensitive particles may also contain various nonphotosensitive materials such as elec-trically 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 may con-tain other photosensitive materials such as various sensitizing dyes and/or chemical sensitizers to alter or enhance their re-sponse characteristics to activating radiation.
When used in an electrophoretic migration imaging pro-cess in accord with the present invention, the electrically pho-tosensitive material described herein as shown in formulas I-V
hereinabove is typically positioned, in particulate form, between two or more spaced electrodes, one or both of which typically being transparent to radiation to which the electri-cally photosensitive material is light-sensitive, i.e., activa-ting radiation. Although the electrically photosensitive mate-rial, in particulate form, may be dispersed simply as a dry pow-der between two spaced electrodes and then subjected to a typi-cal electrophoretic migration imaging operation such as that described in U.S. Patent 2,758~939 by Sugarman referenced here-inabove, it is more typical to disperse the electrically photo-1~)791~)9 fiensitive partlculate materlal ln n electrlcally lnBUlat~nB
carrier, fiuch as an electrically lnsulating l~quld, or an elec-trlcally insulating, lique n able matrlx material, such as a heat- and/or solvent-softenable polymeric material or 8 thlxo-troplc polymerlc material. Typlcally, when one emp~oys such a dispersion of electrically photofiensitive particulate material and electr~cally 1nsulating carrier materlal between the spaced electrodes of an electrophoretic mlgration imaglng system, lt is con~ent~onal to employ from about 0.05 part to about 2.0 parts of electrically photosensltlve particulate materlal for each 10 parts by weight of electrically insulating carrier material.
As indicated above, when the electrically photo6ensltlve partlcles used ln the present ln~ention are dlspersed in an electrically lnsulatlng carrier material, such carrier material may assume a ~ariety of physical forms and may be selected rrom a variety of different materials. For example, the carrier material may be a matrix of an electrically insulating, normally ~olid polymeric material capable of being softened or lique~led upon application of heat, sol~ent, and/or pressure BO that the electrically photosensitive particulate material dlspersed therein can migrate through the matrix. In another, more typlcal embodiment of the in~ention, the carrier material can comprise ~n electrically insulsting liquld ~uch as decane, paraffin, s~hi~
odorless solvent 3440 (a kero~ene fraction marketed by the Standard 011 Comp~ny, Ohio)~ ~arious isoparaffinic hydrocarbon liqu~ds such 8S those sold under the trademark Isopar G by Exxon Corporation and ha~ing a boiling point in the range Or 145C. to 186C., various halogen~ted hydrocarbons fiuch as carbon tetra-chloride~ trichloromonofluoromethane, and the like, various alkylated aromat$c hydrocarbon liquid~ such as the aIkylated benzenes, for example, xyleneR, and other alkylated aromatlc hydrocarbons such as are deficribed ln U.S. Patent 2,899,335.

iO79109 An example of one such useful alkylated aromatic hydrocarbonliquid which is co~mercially available is Solvesso 100 made by lxxon Corp. Solvesso 100 has a boiling point in the range of about 157C. to about 177C. 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 22C, the electrically insulating carrier material used in the present invention is a material having a resistivity greater than about 109 ohm-cms, preferably greater than about ohm-cm. When the electrically photosensitive particles used in the present invention are incorporated in a carrier material, such as one of the above-described electrically insulating liquids, various other addenda may also be incor-porated 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 o~ liquid electrographic developer compositions where they are employed for purposes substantially similar to that described herein. Thus, extensive discussion of these materials herein is deemed unnecessary~ These materials are typically polymeric materials incorporated by admixture thereo~ into the liquid carrier vehicle of the suspension. In addition to, and possible 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 photosensitive particles In addition to the foregoing charge control agent materials, various polymeric binder materials such as various natural, ~eml-~ynthetlc or ~ynthetlc resins, ~ay be dl~peraed or dissolved ln the electrlcally ln6ulatlng carrier to ~erve a6 a fixing material for the flnal photo~ensitive partlcle lmage ~ormed on one of the spaced electrode~ u~ed ln electrophoretic mlgration imaging systems. Here again, the use Or ~uch fixlng addenda 16 conventional and well known ln the closely related art of liquld electrographic developer composltions so that extended dl~cus~ion thereof is unnecessary herein.
The proce~s of the present lnvention will be descrlbed in more detail wlth reference to the accompanying dr~wing, FIG. 1, which illustrates a typical apparatus which employs the electrophoretic migration ~maging process of the lnvention.
FIG. 1 shows a transparent electrode 1 supported by two rubber drive roller6 10 capable Or lmparting a translatlng motion to electrode 1 in the direction of the arrow. Electrode 1 may be composed of a layer of optically transparent material, ~uch as glass or an electrically insulating, tran6parent polymeric support such as polyethylene terephthalate, covered wlth a thln, optically transparent, conductlve layer such a8 tln oxide, indium oxide, nlckel, and the llke.

Spaced opposlte electrode 1 and ln pressure contsct there-with ls a second electrode 5, an ldler roller whlch 6erves a6 a counter electrode to electrode 1 ~or produclng the electrlc field used ln the electrophoretlC mlgratlon lmaglng process.
Typically, electrode 5 hss on the 6urface thereo~ a thln, electrlcally insulatlng layer 6. Electrode 5 ls connected 107910~

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 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 10 may be positioned between electrodes 1 and 5 by applying material 4 to either or both of the surfaces of electrodes 1 and 5 prior to the imaging process or by injecting electrically photo-sensitive ima~ing 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 transparency, a lens system 12, and any necessary or desirable radiation filters 13, such as color filters, whereby electrically photosensitive material 4 is i.rradiated 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 particulate material 4 in the nip 21 between electrodes 1 and 5 without 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.
~ s sho~.n in Fig. 1, electrode 5 is a roller electrode having a conductive core 14 connected to power source 15. The 10'7glO5~

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.
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 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 material 4 is 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 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 elec~
trodes 1 and 5 during the electrophoretic mi~ration ima~in~ ~rocess of t`~e present invention may vary considerably; however, it has 3 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 iO'79109 medium in the electrode gap. For example, when electricallyinsulating liquids such as isoparaf~inic hydrocarbons 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.
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 10 ~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, incor-poration of suitable light sensitive addenda in or together with the electrically photosensitive material of formula I
used in the present invention, 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 concurrent 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 in which they are dispersed, for example, an electrically insulating liquid, such as occurs in convcntion~ 3ui~ electro~ra~hic developing compositions composed of toner particles which acquire a charge upon being dispersed in an electrically insulating carrier liquid.

~28-lmB~e dlBCrlminatl~n ~CCUr8 ln the lectrophor-tlc migratlon lmaglng process Or the pre~ent lnvention aB a re6u~t of the combined application of electrlc ~ield ana actl~atlng radiatlon on the electrically photo6ensltive partlcula~te material dl6persed between electrodes 1 and 5 of the apparatug shown ln FIG. l. That i8, in a typlcal lmaging operatlon, upon appllcatlon of sn electrlc fleld between e~ectrodes l and 5, the particleQ 4 of charge-bearing, electrically photoEensltlve materlal are attracted ln the dark to elther electrodes l or 5, depending upon which of these electrodes has a polarlty opposlte to that of the original charge polarlty acqulred by the electri-cally photosensitive particles. And, upon exposing partlcle~ 4 to actlvating electromagnetic radlation, lt ls theorized that there occurs neutralizatlon or reversal of the charge polarlty associated with either the exposed or unexposed partlcleg. In typlcal electrophoretlc mlgratlon lmaglng systems wherein elec-trode l bears a conductlve surface, the exposed, electrlcally photosensitive particles 4, upon coming lnto electrical contact with such conductive gurface, undergo an alteration (usually a reversal) of thelr origlnal charge polarity as a regult of the comblned appllcatlon of electrlc ~ield and actlvating radiatlon.
In any case, upon the application of electric field and activat-ing radiation to electrically photosensitlve particulate material 4 disposed between electrodes 1 and 5 of the apparatus shown ~n FIG. l, ,~

10791~)9 one can effectively obtain image discrimination so that an image pattern is formed by the electrically photosensitive particles which corresponds to the original pattern of activating radiation.
Typically, using the apparatus shown in FIG. 1, one obtalns a visible image on the surface of electrode 1 and a complementary image pattern on the surface of electrode 5.
Subsequent to the application o~ 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 FIG. 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 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/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 charge 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/or 5 upon evaporation of the li~uid carrier.
The electrically photosensitive colorant material used in the imaging process of the present invention may be used to form monochrome images, or the material may be admixed with other electrically photosensitive material of proper color and photo-sensitivity and used to form polychrome images. As indicated, many of the electrically photosensitive colorant materials having -3o-~ormula I described herein have an especially useful yellow or orange hue and therefore are particularly suited for use in polychrome imaging processes which employ a mixture of two or more differently colored electrically photosensitive particles, e.g., a mixture of cyan particles which are principally sensitive to red light, magenta particles which are principally sensitive to green light, and yellow or orange particles containing the electrically photosensitive colorant materials described in the present invention ~hich are principally sensitive to blue light.
10 When such a mixture of multicolored electrically photosensitive particles is formed, for example, in an electrically insulating carrier liquid, this liquid mixture of particulate material exhibits a black coloration. Preferably, the specific cyan, magenta, and yellow particles selected for use in such a poly-chrome 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 invention, the parts and percentages being by weight unless otherwise stated.

Examples Image Evaluation Apparatus An image evaluation apparatus was used in each of the sllcceeding examples to carry out the electrophoretic migrat~on ;maging process described herein. This apparatus was a device of the type illustrated in FIG. 1. In this apparatus, a trans-l~ting NESA or NESATRON (trademarks of PPG for a conduct-ive tin oxide treated glass or a conductive indium oxide sputtered glass, respectively) glass plate served as electrode 1 and was in pressure contact with a 10 centimeter diameter aluminum roller 14 covered with a thin insulating layer of poly(vinyl butyral)-TiO2 coated paper 6 which served as electrode 5. NES~
pl~te 1 was supported by two 2.8 cm. diameter rubber drive rollers 10 positioned beneath NESA plate 1 such that a 2.5 cm.
opening, symmetric with the axis of the aluminum roller 14, exi-ted 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 NESA plate 1.
The exposing activating radiation was supplied from a light ~O source 8 consisting of a Kodak Carousel projector and had a maximum intensity of 3500 footcandles at the NESA glass plate exposure plane. The voltage between the electrode 5 and NESA
plate 1 was variable up to 10 kilovolts. However, most tests were made in the 0.5 to 2 kv range NESA plate 1 was negative polarity in the case where electrically photosensitive particulate material 4 carried a positive electrostatic charge, and NESA
plate 1 was positive in the case where electrically photosensitive electrostatically charged particles were negatively charged.
The translational speed of NESA plate 1 was variable between about 1.25 cm. and about 30 cm. per second. In the following examples, image formation occurs on the surfaces of NESA glass plate 1 and electrode 5 after simultaneous application of light exposure and electric field to electrically photosensitive iO79109 particulate material 4. In this image evaluation apparatus, each diflerent type of material to be evaluated for use as electrically photosensitive particulate material 4 was admixed with a liquid carrier as described below to form a liquid imaging dispersion which was placed in nip 21 between the electrodes l and 5.
If the material being evaluated for use as material 4 possessed a useful level of electrical photosensitivity, one obtained a negative-appearing image reproduction of original ll on electrode 5 and a complementary image on electrode l.
Imaging Dispersion Preparation In the following examples a series of 46 different imaging dispersions were prepared to evaluate various types of materials for electrical photosensitivity. These dispersions were prepared by ball-milling the various materials to be tested for electrical photosensitivity at high concentration with a polymeric charge control agent and then diluting the resultant mixture with another polymer solution, such as by ultrasonic agitation. The exact ratios of the various materials used in the initial high concentration ball-mill concentrate ~ and subsequent polymer solution are outlined below: ;
Ball-Mill Concentrate 1. 1 gram of material to be tested for electrical photosensitive properties, 2. 1 gram of polymeric charge control agent consisting of a copolymer of vinyl toluene, lauryl methacrylate, lithium methacrylate, and methacrylic acid, the monomeric weight percent ratio of vinyl toluene to lauryl methacrylate to lithium methacrylate to methacrylic acid being as follows:56:40:3.~:.4, 30respectively.

3. llO grams of stainless steelballs having a diameter of about 3 mm., and ~079109 4. 12.2 grams Or carrler llquld con~l~tlng o~ ~ol~e--o lO0 (purchased ~rom t~e Exxon Corporat~on) or, lternatively, 10.7 grams Or Isopa ~ G (purcha~ed ~rom thc Exxon Corporstion ) .

Each of the ball-mlll concentrates ha~i~g the abo~e-noted composltlon were ball-mllled ~n a 125 mllllllter gla~s Jar at 115 revolutlons per mlnute ~or at least one week. m e ball-mlll concentrates were then d~luted by addlng 35.0 grams of a 40% by welght ~olutlon of Piccotex lO0 (a styrene-toluene copolymer purchased ~rom the Pennfiyl~ani~ rndustrlalChemlcsl Corporstlon) in Isopa ~ G at a rate o~ 15 ~illllltcr~
per minute through a hollow ultrasonic probe. Durlng thls dilution operatlon the temperature of the imaglng dlsper~ion thus being formed was maintalned Rt approxlmately 20C.
Examples l-32 $able 2 herelnarter contatn6 the result6 ~or 46 difrerent materials evaluated for electrical photo-6ensltlvlty propertles for use in electrophoretlc migrat~on imaglng. The fir6t 32 materlals e-~aluated ln Table 2 correspond to the 32 materials set forth ~erelnbefore ln Table l. Each of these 32 dlfferent materials had a ~ormula withln structural formula I set forth hereinbefore and exhibited electrlcal photosensltlvlty when tested ln a mlgratlon ~maging process using the image evaluatlon apparatus a6 outllned above. However, the last 14 materlsls, l.e., materlals 33-46 dlsplayed no electrical photoresponse under the~e same evaluation condltlons.
Each of these last 14 materlals tested had a ~tructural formula outside the scope of formula I snd therefore outslde the scope of the pre~ent lnven~lon. However, the 6tructural formula o~
the materials labelled 33-46 ls qulte ~lmllar to structural formula I, thereby lndicatlng the surprlslng ~pect of the present lnventlon whereln lt has been ~ound that, ~or the particular clas~ o~ known organlc photoconducti~e materials tested herein, certain Or these materlals display use~ul le~elæ
of clectr~c~l photo~en~ltlvity uitable ror electrophoretic migration imaging processes (i.e., see materials 1-32 of Table 2), whereas other closely related materials within this same general class of known organic photoconductors do not possess useful levels of electrical photosensitivity in electrophoretic migration imaging (i.e., see materials 33-46 of Table 2). In Table 2, the speed of the NESA plate electrode 1 used in the above-described image evaluation apparatus is noted as well as various other evaluation parameters. Since materials 1-32 are identical to compounds 1-32 of Table 1, their structure is not presented in Table 2. Useful images are obtained with each of compounds 1-32 under the test condltions noted in Table 2.

107910g L~ ~ o o o X ~ ~ ~ ~ ~ L~ C~l ~ ~ ~ Lr~ C\J 0 ~ J ~t ~ J
-c tn '`
3 ~ a~
~ ~ ~ ~ ~ ~ `J N N

a) ,, o ~i~ OOOOOOOOOOOO

a) ~
~ ~l ~
E-l rl h ~t~ +++++++++++I++
O
P~

~P~
rJ
H ~ U2 U~ H ~ H U~ U~ H U~
rl rl ~i O ~ ~ ~ ~ Lr~ ~ O ~ ~ ~ U~

V

~079109 o o o o o L~ o o oo o o o o o o D~
D~C>
. . . ,~, CUC~l N C~ l N (~J C\J
~ ~ ~1 N~`J C~l N
D~ _~

h ¦
D~
$ ~ ~ ~ ~ ~:5 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~1 ~ ~ U~D~ CQ tQ U~ D~ D~D~D~ D~ D~ D~ D~ D~ D~

~za) ooooooooooooooooo ~ :z :zz z; z z; æ z z æz æ z æ z z z o o ~I
~~I ~
h + + + + + I + + + + + + + + + + +
td O

rl rl ~l ~ U~ U2 U~ U~ H H H H H U2 U~ H H U~ u~
.rl rl z ~ '~) ~ C~ (~ O ~ N ~ ~ ~ O ~ co (~ O ~I N
O ~ ~1 ~ ~1 N N N N N N N N N N (`f ) (~ (~
0~
C~

i~79109 , I

U~
U~ C) a~ ~ a) a~ u, ~ a)~
U~ _, a o U~
~ td a) s~
rl ~n rl a) s:
a) :4 ~; a .,-i o ~\Ia~ "~
+~
~I) C) ~r~
o ~
~, ~ ~ ~ , E~~ ~ ~ , rl O
~ ~ , ::~ ~Q a) ~ o~

~ ~ ~ o ~
~ .~
q~

o ,~ ~ o _, V
v E~

iO79109 ~1 ~xl ~c U~ _ C~ C) ~ ~ a ,1 a~ CQ
U~ _ h o ~Q~
~d~
a ~ ~ rl a) ~ ~
o C) C~l a~
C~
~1 ~rl h +~ ~
~ h rl E~ ~ O
~ P~
*

b~
O
rl ~;
~ N
~ 1 0~

O ~ N

r -x u~
a a) u~
a cq ~
a o 'Q ~ -h t~ ~
rl ~1 a) .~
~, o C~
C~l a a) ~ ~
C~ rl rl S~
~ 1 ~ O
P~ ~
*

bD
~ rl ~1 ~ C`J
~ 1~ N ~;

O æN

¢) 7 r~

iO79109 r , ~
x a) ~1 a) u, a)\.

a) a~ ~;
h o X
~n ~^
S~
a) s~
,~
~1 ~ tR
rl a~ ~
r( o c (~l a~ ~>
a C) rl ~ ~ t~
E~ S~ ~
~13 0 1 1 ~

o 10'~9109 e ~c 0~
~n c a a) CQ
c~ a td U~ ~rl 1~;

r~l ~
a) 5 ~rl a _,~
a~
~rl o a +~
C) ~rl ~I s~ ~
~ a3 0 E~ P~ ~

bO

o : A r~ p V ~ N N

~: ~ ~ V

1079~09 Example 49:
In this example, the use of the materials described by structural formula I herein in a polychrome electropho-retic migration imaging process was de~lonstrated. In this exarn-ple, three separate cyan, magenta and yellow monochrome disper-sions were prepared. Each such monochrome dispersion was pre-pared using the dispersion preparation technique outlined above.
The electrically photosensitive material used as the photosensi-tive and colorant material in the cyan dispersion was Cyan Blue GTNF,Colour Index No. 74160, a beta form of copper phthalocya-nine available from American Cyanamid. The electrically photo-sensitive material used as the photosensitive and colorant mate-rial in the magenta dispersion was Sandorin Brilliant Red 5BL~
a quinacridine pigment similar or identical to Pigment Red 192 of the Colour Index and available from the Sandoz Corporation.
The electrically photosensitive material used as the photosensi-tive and colorant material of the yellow dispersion was material 9 of Tables 1 and 2, i.e., 9,10-bis[4-(tolylamino)styryl]anthra~
cene. After preparing each of the above~escribed ,pmpcJrp,e dispersions, these three dispersions were admixed together in a volume ratio of cyan to magenta to yellow of 1:1:1. The resul-tant "trimix" dispersion was used to form multicolor electropho-retic migration images using the above-describedimage evaluation apparatus. In this multicolor imaging example, the intensity of the imagewise exposure on the plane of the NESA plate was 2000 footcandles and the translational speed of the NESA plate during the multicolor imaging operation was about 30 cm./sec. A
Kodak Wratten 2B filter was included in the exposure beam of light. The voltage between electrode 5 and NESA plate 1 was maintained at 1 kilovolt during the imaging operation. As a result, it was found that a good quality three-color negative-to-positive print was formed on blocking layer 6 of electrode 5 and, also, a good positive-to-positive multicolor print was formed on the surface of NESA plate 1.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims (9)

claim:

1. In 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 material to an image pattern of radiation to which the material is photo-sensitive, thereby obtaining image formation on at least one of said electrodes, the improvement which comprises using as at least a portion of said material an electrically photo-sensitive colorant having an absorption maximum greater than 410 nm. and having the formula:

wherein n represents 0 or 1;
m represents 1 or 2;
Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
Z represents the nonmetallic atoms necessary to complete a carbocyclic or heterocyclic aromatic ring group having 5 to 14 ring atoms in the aromatic ring;
each of R1 R2 R3 R4 and R5 which are the same or different, when taken alone, represent hydrogen, nitro, cyano, halogen, an alkoxy having 1 to 8 carbon atoms, a saturated heterocyclic amino having 5 to 8 ring atoms; a dialkylamino, diarylamino, dialkarylamino, or diaralkylamino wherein the alkyl group contained in such amino is a substituted or unsubstituted alkyl having 1 to 8 carbon atoms in the alkyl; a substituted or unsubstituted alkyl having 1 to 8 carbon atoms in the alkyl; a substituted or unsubstituted, carbocyclic or heterocyclic aromatic ring group having 5 to 14 carbon atoms in the aromatic ring, a carboxy ester having 1 to 4 carbon atoms, or an amide having the formula wherein R6 represents hydrogen or a substituted or unsubstituted aromatic group or a substituted or unsubstituted alkyl as defined above each of R1, R2 and R3, when taken together, are free from any saturated N-heterocyclic ring group fused to the aromatic ring formed by Z;
with the provisos that (i) when m represents 1 and n represents 0, Ar represents phenylene, and more than one of R4, R5, and the substituents on Ar represent either nitro or cyano, then at least one of R1, R2 or R3 represents diarylamino or dialkarylamino and (ii) when both m and n represent 1, Ar represents phenylene, any two of R1, R2 and R3 represent hydrogen and the remaining one thereof represents a dialkylamino group, then such dialkylamino group has 2 to 8 carbon atoms in the alkyl group.

2. In an electrophoretic migration imaging process which comprises subjecting an electrically insulating carrier material positioned between at least two electrodes to an applied electric field and exposing said carrier material to an image pattern of radiation, said carrier material containing electrically photosensitive particles which comprise at least one colorant component photosensitive to said radiation, thereby obtaining image formation on at least one of said electrodes, the improvement which comprises using in at least a portion of said particles an electrically photosensitive colorant component having an absorption maximum greater than about 410 nm, and having the following formula:

wherein n represents 0 or 1;
m represents 1 or 2;
Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
Z represents the nonmetallic atoms necessary to complete a carbocyclic or heterocyclic aromatic ring group having 5 to 14 ring atoms in the aromatic ring;
each of R1, R2, R3, R4 and R5, which are the same or different, when taken alone, represent hydrogen, nitro, cyano, halogen, an alkoxy having 1 to 8 carbon atoms, a saturated heterocyclic amino having 5 to 8 ring atoms; a dialkylamino, diarylamino, dialkarylamino, or diaralkylamino wherein the alkyl group contained in such amino is a substituted or unsubstituted alkyl having 1 to 8 carbon atoms in the alkyl; a substituted or unsubstituted alkyl having 1 to 8 carbon atoms in the alkyl; a substituted or unsubstituted, carbocyclic or heterocyclic aromatic ring group having 5 to 14 carbon atoms in the aromatic ring, carboxy ester having 1 to 4 carbon atoms, or an amide having the formula wherein R6 represents hydrogen or a substituted or unsubstituted aro-matic group or a substituted or unsubstituted alkyl as defined above;
each of R1, R2 and R3, when taken together, are free from any saturated N-heterocyclic ring group fused to the aromatic ring formed by Z;

with the provisos that (i) when m represents 1 and n represents 0, Ar represents phenylene, and more than one of R4, R5, and the substituents on Ar represent either nitro or cyano, then at least one of R1, R2 or R3 represents diarylamino or dialkarylamino and (ii) when both m and n represent 1, Ar represents phenylene, any two of R1, R2 and R3 represent hydrogen and the remaining one thereof represents a dialkylamino group, then such dialkylamino group has 2 to 8 carbon atoms in the alkyl group.

3. In an electrophoretic migration imaging process which comprises subjecting an electrically insulating carrier material positioned between at least two electrodes to an applied electric field and exposing said carrier material to an image pattern of radiation, said carrier material containing electrically photosensitive particles which comprise at least one colorant component photosensitive to said radiation, thereby obtaining image formation on at least one of said electrodes, the improvement which comprises using in at least a portion of said particles an electrically photosensitive colorant component having an absorption maximum greater than about 410 nm and having the following formula:

2 wherein Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
each of R4 and R5, which are the same or different, represents hydrogen or a cyano group; and each of R7 and R8, which may be the same or different, when taken alone, represents a substituted or unsubstituted 3 acyclic lower alkyl having 2 to about 8 carbon atoms or a substituted or unsubstituted, carbocyclic aromatic ring group having 6 to about 14 ring atoms in the aromatic ring and R7 and R8, when taken together, represent a pyrrolidinyl or a piperidino group.

4. In an electrophoretic migration imaging process which comprises subjecting an electrically insulating carrier material positioned between at least two electrodes to an applied electric field and exposing said carrier material to an image pattern of radiation, said carrier material containing electrically photosensitive particles which comprise at least one colorant component photosensitive to said radiation, thereby obtaining image formation on at least one of said electrodes, the improvement which comprises using in at least a portion of said particles an electrically photosensitive colorant component having an absorption maximum greater than about 410 nm. and having the following formula:

2 wherein Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
each of R4 and R5, which are the same or different, represents hydrogen or a cyano group; and R9 represents a substituted or unsubstituted, acyclic lower alkyl having 2 to about 8 carbon atoms or a substituted or unsubstituted, carbocyclic aromatic ring group having 6 to about 14 ring atoms in the aromatic ring.

5. In an electrophoretic migration imaging process which comprises subjecting an electrically insulating carrier material positioned between at least two electrodes to an applied electric field and exposing said carrier material to an image pattern of radiation, said carrier material containing electrically photosensitive particles which comprise at least one colorant component photosensitive to said radiation, thereby obtaining image formation on at least one of said electrodes, the improvement which comprises using in at least a portion of said particles an electrically photosensitive colorant component having an absorption maximum greater than about 410 nm. and having the following formula:

2 wherein Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
each of R4 and R5, which are the same or different, represents hydrogen or a cyano group; and each of R9, R10 and R11, which may be the same or different, represents a substituted or unsubstituted, acyclic lower alkyl having 2 to about 8 carbon atoms, or a substituted or unsubstituted, carbocyclic aromatic ring group having 6 to about 14 ring atoms in the aromatic ring.

6. In an electrophoretic migration imaging process which comprises subjecting an imaging suspension positioned between at least two electrodes to an applied electric field and exposing said suspension to an image pattern of radiation, said suspension containing an electrically insulating carrier liquid and finely-divided, electrically photosensitive particles which comprise at least one colorant component photosensitive to said radiation, thereby obtaining image formation on at least one of said electrodes, the improvement which comprises using in at least a portion of said particles an electrically photosensitive colorant component having an absorption maximum greater than about 410 nm. and having the following formula:

wherein n represents 0 or 1;
m represents 1 or 2;
Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
Z represents the nonmetallic atoms necessary to complete a carbocyclic or heterocyclic aromatic ring group having 5 to 14 ring atoms in the aromatic ring;
each of R1, R2, R3, R4 and R5, which are the same or different, when taken alone, represent hydrogen, nitro, cyano, halogen, an alkoxy having 1 to 8 carbon atoms, a saturated heterocyclic amino having 5 to 8 ring atoms; a dialkylamino, diarylamino, dialkarylamino, or diaralkylamino wherein the alkyl group contained in such amino is a substituted or unsubstituted alkyl having 1 to 8 carbon atoms in the alkyl; a substituted or unsubstituted alkyl having 1 to 8 carbon atoms in the alkyl; a substituted or unsubstituted, carbocyclic or heterocyclic aromatic ? group having 5 to 14 carbon atoms in the aromatic ring, a carboxy ester having 1 to 4 carbon atoms, or an amide having the formula wherein R6 represents hydrogen or d substituted or unsubstituted aro-matic group or a substituted or unsubstituted alkyl as defined above;
each of R1, R2 and R3, when taken together, are free from any saturated N-heterocyclic ring group fused to the aromatic ring formed by Z;
with the provisos that (i) when m represents 1 and n represents 0, Ar represents phenylene, and more than one of R4, R5, and the substituents on Ar represent either nitro or cyano, then at least one of R1, R2 or R3 represents diarylamino or dialkarylamino and (ii) when both m and n represent 1, Ar represents phenylene, any two of R1, R2 and R3 represent hydrogen and the remaining one thereof represents a dialkylamino group, then such dialkylamino group has 2 to 8 carbon atoms in the alkyl group.

7. In an electrophoretic migration imaging process as defined in claim 6, the improvement which comprises using in at least a portion of said particles an electrically photosensitive colorant component having any one of the following formulas:

2 2 2 wherein Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
each of R4 and R5, which are the same or different, represents hydrogen or a cyano group; and each of R7, R8, R9, R10 and R11, when taken alone, represents a substituted or unsubstituted, acyclic lower alkyl having 2 to about 8 carbon atoms or a substituted or unsubstituted, carbocyclic aromatic ring group having 6 to 14 ring atoms in the aromatic ring group and, R7 and R8, when taken together, represent a pyrrolidinyl or piperidino group.

8. In an electrophoretic migration imaging process as defined in claim 6, the improvement which comprises using in at least a portion of said particles an electrically photo-sensitive colorant component having the formula:

2 wherein Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
each of R4 and R5, which are the same or different, represents hydrogen or a cyano group; and each of R7 and R8, when taken alone, represents a substituted or unsubstituted, acyclic lower alkyl having 2 to about 8 carbon atoms or a substituted or unsubstituted, carbocyclic aromatic ring group having 6 to about 14 ring atoms in the aromatic ring and R7 and R8, when taken together, represent a pyrrolidinyl or a piperidino group.

9. In a multicolor electrophoretic migration imaging process which comprises subjecting an imaging suspension positioned between at least two electrodes to an applied electric field and exposing said suspension to an image pattern of activating radiation, said suspension containing an electrically insulating carrier liquid and a mixture of at least two differently colored, finely-divided, electrically photosensitive particles, particles of one color being photo-sensitive to a different spectral range of said radiation than particles of a different color, at least some of said particles comprising at least one colorant component photosensitive to some portion of said radiation, thereby obtaining formation of A multicolor image on at least one of said electrodes, the improvement which comprises using in at least a portion of said particles an electrically photosensitive colorant component having an absorption maximum greater than about 410 nm. and having the following formula:

wherein n represents 0 or 1;
m represents 1 or 2;
Ar represents a substituted or unsubstituted, carbo-cyclic or heterocyclic aromatic ring group having 6 to 20 ring atoms in the aromatic ring;
Z represents the nonmetallic atoms necessary to com-plete a carbocyclic or heterocyclic aromatic ring group having 5 to 14 ring atoms in the aromatic ring;
each of R1, R2, R3, R4 and R5, which are the same or different, when taken alone, represent hydrogen, nitro, cyano, halogen, an alkoxy having 1 to 8 carbon atoms, a saturated hetero-cyclic amino having 5 to 8 ring atoms; a dialkylamino, diaryl-amino, dialkarylamino, or diaralkylamino wherein the alkyl group contained in such amino is a substituted or unsubstituted alkyl having 1 to 8 carbon atoms in the alkyl; a substituted or unsub-stituted alkyl having 1 to 8 carbon atoms in the alkyl; a sub-stituted or unsubstituted, carbocyclic or heterocyclic aromatic ring group having 5 to 14 carbon atoms in the aromatic ring, a carboxy ester having 1 to 4 carbon atoms, or an amide having the formula wherein R6 represents hydrogen or a substituted or unsubstituted aromatic group or a substituted or unsubstituted alkyl as defined above;
each of R1, R2 and R3, when taken together, are free from any saturated N-heterocyclic ring group fused to the aro-matic ring formed by Z;
with the provisos that (i) when m represents 1 and n represents 0, Ar represents phenylene, and more than one of R4, R5, and the substituents on Ar represent either nitro or cyano, then at least one of R1, R2 or R3 represents diarylamino or di-alkarylamino and (ii) when both m and n represent 1, Ar repre-sents phenylene, any two of R1, R2 and R3 represent hydrogen and the remaining one thereof represents a dialkylamino group, then such dialkylamino group has 2 to 8 carbon atoms in the alkyl group.