Note: Descriptions are shown in the official language in which they were submitted.
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
.
s~
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
--3-
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
.
--8-
` -
~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.
--10--
. ~ ff~ ~
~J.~57~3
T A B L E
Number Material Color
~ ~7~ Magenta
~!:tii i
0
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 ~-~
.
-11--
.
~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
-12-
5S78
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
~,~
SS78
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
--14--
~,~/ 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
Q3
36 (C2Hs)~ ~ ~,{~q~J~ Purple
, .
--15--
~ 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
-16-
;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
-17-
~ ~ ~ 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
-18-
~ - ~
~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.
19-
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
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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)
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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
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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.
5578
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.
.
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