Note: Descriptions are shown in the official language in which they were submitted.
~397Z
BACKGROU~D OF THE I~VENTIOl~
Field of the Invention - This invention relates to
compositions and methods of use of such compositions. More
specifically, this invention is directed to vanadyl phthalo-
cyanine/dye compositions and fluid dispersionsthereof. 'rhese fluid dispersions are useful in photoelectro-
phoretic imaging processes.
Description o the Prior Art - As is generally
recognized in the artt a photoelectrophoreti* imaging system
is on~ wherein electrically photosansitive particles dispersed
( in a carrier liquid are initially subtjected to an electric
field and either simultaneously or thereafter exposed to
aetivating eleetromagn,atic radiation conforming to an image
pattern. Photoelectrophoretie imaging techniques may be
adapted for the preparation of both monochrDmatic and poly-
chromatic reproductions. A detailed disclosure of both the
monatchromatic and polyehromatie photoelectrophoretic imaging
systems ean be ound in U.S. Patents 3,383,993; 3,384,488;
3,384,565 and 3,384,566. In one of the preferred
embodiments of the photoelectrophoretic imaging method deseribed
in the above patents, a layer of an imaging suspension eomprising
eleetrically photosensitive pigment partieles in an insulating
earrier liquid is confined between an injeetin~ eleetrode
~; and a blockint~ electrode (at least one of the eleetrodes being
; 2~ ~at least partially transparent); the photosensitive dispersion
s~bjected to an applied eleetrie field; and thereafter exposed
; to aetivating~elqctromagnetic radiation conforming to an image
pattern. Typically,~ eomplementary images are formed on the
opposing surf'aces of the electrodes whieh are in eontaet with
the dispersion of pigment particles. In a monochromatic
system, pigment partieles of only one color are required,
, : :
X
~,:, . ~ :
11~339~7z
however, particles o~ more than one shade of the same color
may be utilized if it is desired to provide the capability
to produce a range of monochromatic colors. In a polychror,~atic
system, images of more than one cGlor, and preferably full
color, may be formed by utilizing a plurality of differently
colored pigment particles which ideally have spectral response
curves which do not substantially overlap each other, thereby
providing the necessary color separation. In the preferrecl
photoelectrophoretic imaging system re~erred to hereinabove,
the pigment particles correspond to the subtractive colors
yellow, c~an and magenta, The yellow pigment particles are
primaril~ responsive to light with~n the blue region of the
electromagnetic spectrum; the cyan particles are primarily
photoresponsive to light within the red portion of the electro-
magnetic spectrum; and the magenta particles are primarilyresponsive to light within the green portion o~ the electro-
magnetic spectrum. Therefore, when a full color reproduction
is projected upon a suspension containing these three pigments,
the cyan particles will respond to those portions of the ~lage
input corresponding to the color red, and upon being photo-
activated will migrate from the electrode surface on which
the image i5 to he formed thereby leaving beh.~nd the yellow
and magenta pigment particles which togethex appear as red~
Similarly, image input corresponding to green light will
cause magenta parti~les to migrate and image input corresponding
to blue light will cause the yellow particles to migrate.
Where white light imringes upon tre suspension containing
, .
~ -4-
.. . ...
. ' - .` `
11~39~z
the above three pigment particles, all such particles should
migrate thereby leaving the surfa~e of the image substantially
devoid of pigment. ~le resulting image can thereafter be
transferr ~ to a receiving sheet such as white paper and
thus the portions of the image which are deficient of pigment
will appear as white in the finished copy. In order to obtain
good colcr separation, it would be preferable that each
pigment migrate only in response t:o activating electromagnetic
radiation within its principal region of absorption.
Due to electrical interactic-~s between the pigments
and other unknown factors, photosl:imulated particle migration
is often incomplete resulting in t~aces of the "subtracted"
pigment remaining at the injectiny electrode thereby imparting
undesired color to the image residing on this electrode.
lS As is discussed in the patents previously incorporated
by reference, the pigment particles used in photoelectrophoretic
imaging systems are initially charged and ca~sed to migrate
to the surface of one of two opposing electrodes in response
to an electric field established ~etween these electrodes.
Upon absorption of light within i~s principal region of
photores~onse, these pigments, it is theorized, generate hole-
electron pairs, and depending upon the relative mobility of
these charge carriers in the pigment, either one or both of
; ; these charge carriers are injecte~ into the liquid carrier
medium. Upon the injection of only one species of carrier
~!:
' `
t in~o the medium, the particle will thereby acquire a net
, ~
;~ -5-
, , :
~1~39~2
charge wllicll preferably will be identical in sign to the
polarity of charge of the electrode to which it had
previously migrated. This similarity in charge will cause
the pigment particle to be repelled by this formerly
attractive electrode resulting in its migration to the surface
of the opposing electrode where it forms a complementary
image. It will be appreciated thct if the above theoretical
explanation is correct, the injection of both species of
charge carrier into the liquid caYrier medium will result
in a failure to generate the desired ir.lage. Moreover, in
the event of indiscriminate injection of charge carriers from
the photoactivated pigment into th~ liquid carrier medium
and the subseguent transfer of such carriers to a nonphoto-
~ activated particle, the non~hotoactivated pigment particle
1 15 will migrate just as if it had absorbed the imaging energy.
This migration of nonphotoactivated particles will seriously
impair color separation in the desired reproduction.
It thus appears that in order for good colorseparation to be maintained and faithful reproduction of
an original to be achieved, it is necessary to maintain
selective electrophotographic response of the pigments to
their colors of primary absorption. It is also apparent
, .
that this can only be achieved by preventing indiscriminate
injection of charge carriers from photoactivated pigments
into the liquid carrier medium,
The prior art contains frequent reference to
various treatment of photoelectrophoretic pigments with
i
'' `~
:
, ~ :
~lQ39q2
diverse material.s in order to modify or enhance the electro-
photographic response of such pigments For example, th~ literature
discloses: (a) the adsorption of ~onor and acceptor molecules on pic~
ments utilized in photoelectrophoretic imaging (b) thè inc:'usion
of such electrically active materials in the insulating
liquid carrier containing such pigment parti~les, or (c)
the application of these e lectrically active materials to
one of the electrodes used in confii-ing the pigment dispersion.
All of tha above treatments are said to result in charge
transfer complex :Eormation between the pigments and these
electrically active materials, thereby facilitating injection
of electrons from photoactivated p gment particles into the
surrounding medium, U,S, Application Serial No, 566, 846, filed
July 21, 1966, now abandoned; pub]ished in Japan on March
30, 1970, Application Serial No, 4636667, filed July 20, 1967
Photoactive polymeric materials have also been
disclosed as effective in modification of the electrophoretic
response of pigment particles used in photoelectrophoretic
~: imaging systems, U,S Application Serial No. 863, 507, file~October 3, 1969, published in Holland on P~pril 6, 1971 as
Application Serial No, 70.14614. Poly(N-vinylcarbazole) i5
diselosed in this Dutch patent as useful in the agglomeration
- ~ ,
and/or eneapsulation of ph~tomigratory pigment particles thereby
enhancing the electrophotographic response of these particles
25 to imaging energies,
Although the prior art systems described above
~ ~ :
~ enable substantia1 enhancement in the photoresponse eharaeter-
:~ isties of photomigratory pigment particles used in ph~toe lectro-
:: phoretic lmaging, further improvement is still required
::
-7-
:~' ,, , . ~ -
~.~V3g7Z
especially with regard to the problems associated with color
separation and reduction in D
mln
It is, therefore, an object of an aspect of this
invention to remedy the above, as well as-related deficiencies
in the prior art.
More specifically, it is an object of an aspect of
this invention to modulate the photoelectric response of
certain photomigratory pigments so as to control the indis-
criminate injection of charge carriers generated within such
pigments from influencing the movement of nonphotoactivated
pigments.
An object of an aspect of this invention is to
provide a photomigratory pigment composition having improved
selective response to activating electromagnetic radiation.
Additional objects of this invention include the
use of the above compositions in photoelectrophoretic and
photo-immobilization electrophoretic recording systems and
methods.
SUM~RY OF THE INVENTION
In accordance with one aspect of this invention
there is provided a photosensitive composition comprising
an insulating carrier liquid having dispersed therein from
about 0.1 to about 10 weight percent vanadyl phthalocyanine
pigment and, based upon vanadyl phthalocyanine pigment
concentration, about .1 to about 10 weight percent of at
least one desensitizing dye of the formula
(X)m Y (2) n
~-
--8--
-.
. . .
. .
~1~397Z
wherein X and Z are independently selected
from the group consisting of -NH2
and -NHR;
R is phenyl or phenylsulfonate;
Y is phenyl; and
m and n can range from 0 to 2, with
the proviso that either m or n is
at least l
At least a portion of the pigment and desensitizing dye (also
hereinafter referred to as "substituted phenazinP compounds")
are intimately physically associated with one another, how-
ever, the degree of association will vary depending upon the
method used in combining these materials. In a prefexred
embodiment of this invention the vanadyl phthalocyanine
pigment is also "treated" with one or more polymeric
materials of the type disclosed in U.S. Patent No. 4,032,339,
issued June 28, 1977, either prior or subsequent to "desensit-
',: ization" with one or more of the above substituted phenazine
compounds.
I 20 In accordance with another aspect of this invention
!~ there is provided a photosensitive composition comprising
an insulating carrier liquid having dispersed therein from
about 0.1 to about lO weight percent vanadyl phthalocyanine
, ~ ~ and, a desensitizing effective amount of at least one compound . : :
25~of the~formula: -
~N~
(X)m Y (Z)n
wherein~X and Z are independently selected
: : from the group consisting of -NH2
; I and -NHR
30 : ; R is phenyl or phenylsulfonate
Y is phenyl
. m and n can range 0 to 2,,with the
: ~proviso that either m or n is at
Ieast l
',: ~ , ~
_g_
., ; .
~ ' .:
~3~7Z
at least a portion of the desensitizing compound present
in the composition being intimately associated with at
least some of the phthalocyanine pigment present therein.
Substituted phenazine compounds which are preferred
in the compositions of the invention include the indulins,
pheno-safranine, nigrosine and aniline black. The intimate
association of vanadyl phthalocyanine pigments with one or
more of the above compounds apparently influences the extent
to which photoactivated charge carriers are injected into the
medium within which the photoactivated particles are routinely
suspended. The precise nature of the physical and/or
electrical influence exerted by the compounds on the pigment
particle is not known at this time. However, it is hypothesized
. ,
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: ` ,,' ' ~. , ,. ~ ' " , ' ' ,
1.11039'~z
that the intimate association of such compounds with the pigmen'
particle serves to provide recombination centers in which
photoinjected holes and electrons are trapped and thus
neutralize one another. ~his trapping olf both species
of charge carrier has the effect of reducing th~ speed of
phc~toe]ectrophoretic response of the vanadyl phthalocyanine
pigments and in addition reduces t:he influence that such
photoinjected charge can potentially have upon the movement
of nonphotoactivated pigment particles also disp~rsed in the
same medium as the phthalocyanine pignents. The vanadyl
phthalocyanine pi~ments which are desensitized in the manner
described above can also be optiondlly treated with other
materials such as polymers and/or electron donors or acceptors
to further modify the photoelectrophoretic response of the
pigment particles.
BRIEF DESCRIPTION OF r'HE DR~WINGS
Fig. l~is a graphical illustration of the photoelectro-
phoretic response of the desensitized vanadyl phthalocyanine
pigments which are prepared according to the method of this
inventio~.
~'
DESCRIPTION OF THE INVENTION
INCLUDING PREFERRED EMBODIMENTS
The pho~osensitiv compositions of this invention
can be prepared by dispersing vanadyl phthalocyanine in a solvent
within which a substituted phenazine compound of the above'formula
has been previously dissolved, followed by ball-milling the
resultant disperslon for an interval sufficient to promote
~ ' .
_10-
i~39'~Z
intimate association of the substit~ted ph~nazine compound
with the suspended pigment particlec. The solvent can then
he driven off, or preferably, an insulating carrier fluid,
such as mineral oil, added to the dispersion and then the
resulting dispersion heated in such a manner so as to
facilitate the selective evaporation of the polymer solvent.
The above procedure results in the intimate association of
at least some of the substituted phena~ine compounds with
at least some of the pigment partic'es.
The photosensitive pigment:s of this composition
can comprise vanadyl phthalocyanine in any one of its stable
forms. The vanadyl phthalocyanine pigment of thi~ composition
can be prepared ~y any one of the techniques disclosed in the
technical and patent literature, see for example, Moser and
Thomas, Phthaloc~anine Compounds, Chapter 3, ACS Monograph
Series, Reinhold Publishing Corp., ~ew York (1963).
U.S. Patent No. 3,825,422 (to Gruber and Grushkin)
specifically describes the preparation of vanady~ phthalo-
cyanine pigments for use in photoelectrophoretic imaging
systems. Once having prepared a vanadyl phthalocyanine
pigment, the pigment is further refined hy "acid pasting"
in concentrated sul~uric acid or other appropriate acidic
medium. Acid pasting generally merely involves dissolving
the unrefined vanadyl phthalocyanine pigment in the acidic
medium and agitating the resulting solution. The temperature
of the acid pasting medium is not allowed to rise to a level
which could result in decomposition of the pigment. Subse~uent
.
to this acid pasting procedure the pigment is separated from
the acidic solution by quenching in water or pouring over i~e
- ~11-
.
.. . . . ..
~397~
Ma-terials not dissolved during the acid pasting procedure
are separated from the acidic solution by filtration prior
to quenching with water. The terms "photosensiti~e",
"photomigratory", "photoactive" and "photoelectrically active"
are used interchangeably throughout this disclosure to
describe the photoelectric properties of the above pigments
of the compositions of this invention.
The substituted phenazine compounds of the
photosensitive composikions of this invention are preferably
soluble in a liquid within which the vanadyl phthalocya~ine
is soluble. Most, if not all of the compounds within the
scope of the formula previously set forth herein are
commercially available or can be prepared by techniques disclosed
in the technical literature from readily available starting
materials.
In the preferred compositions of this invention,
the substituted phenazine compound used in the "treatment"
of vanadyl phthalocyanine pigments are sulfonated indulins.
The preferred composi~ions of this invention contains either
one of a combination of the matPrials whose structural formulae
are set forth hereinbelow:
.
~0 Nilo38~N ~XM ~ ..
J ~ ~ u_~&~ 503NIl N20
0 . ~aO35--~ ~
n~o ~ ols~ ~ H~503N~ N20
IS~'5~53~ o
'
--12--
~r
~:
.
.
.. . . . .
.
~1~3~
As indicated previously most, if not all o~ the pigments and
dyes referred to hereinabove are readily commercially available
or can be prepared by any one of numerous techniques disclosed
in the literature. The preferred dyes whose formulae are
set forth hereinabove can be readily prepared by the
procedures described by F. Kehrmann et al; his synthesis
appearing in Ber., 56, 2394 (1923); Helv. Chim. Acta, 8, 61
(1925); Ber., 46, 3009 (1913~; and Helv. Chim, Acta, 8, 63
(1925). The Kehrmann synthesis is directive for the compounds
whose formulae are set forth hereinabove and is, thus, the
preferred route for their preparation.
The relative concentration of desensiti~ing dye to
pigment particles is a function of the relative efficiency
with which such dye is capable of sorption on the pigment
and the extent of intended modification of the photoelectric
response of the pigment. Generally, the relative concentration
of desensitizing dye to pigment can range from about 0.1 to
about 10 weight percent. In a preferred embodiment of this
invention, the desensitizing dye to pigment concentration
is in tke range of from about 1 to about 5 weight percent.
It will be appreciated that certain desensitizing dyes can
interact more efficiently with vanadyl phthalocyanine
than do others and thus the preferred concentration
o desensitizing dye to pigment may vary from one composition
to another.
In the oreferred embodiments of this invention, the
desensitized pigment is further modified by sorption of polymeric
material thereon and/or therein. As indicated previously
polymeric material which have been found especially compatible
-13-
,
39~2
with such desensitized pigments are disclosed in
aforementioned U. S. Patent No. 4,Q32,339. Such furtller
modification with these polymeric materials can be achieved by
simply dispersing the desensitized pigment in a solution
of the polymeric materials followed by removal of ~he polymer solvent.
One class of olymeric materials which is especially
preferred for use in com~ination with the desensitized pigment
is represented by the following formula
H H
C - C ~n
H Z
wherein Z is a pendant group of the formula
~ or ~
X is a substituent substantially incapable
of withdrawing electrons from the electron
rich pyridinyl moiety;
m is a whole number from 0 to 3;
and
n is a whole number in excess of 25.
The polymeric materials which are associated with
25~ the desensitized plgment can comprise any one or combination of
polymer segments having structural units of the formula set forth
~ hereinabove. The vinyl pyridine and substituted vinyl pyridine
: monomers embraced by the above formula are generally commercially
available, and where unavailable from commercial sources can
be rountinely prepared by methbds disclosed in the literature
from readily available materials. See, for example, Vinyl and
Diene Monomers, Vol. XXIV, part 3, page 1376, Edited by E.C. Leonard,
~ '
-14-
ilC~39~
Wiley-Interscicnce Publica~ion, N.Y.~. (].~71). These monomeKs
can be l~olymerized by standard free radical ~nd anionic
polymerization techni.ques. In the preferred embodi.ments of this
invention, the polymeric material comprises poly(2-vinylpyri-
dine). The method of association Or the desensitized piqment
with the polymer will to some extent li.mit the type of polymers
suitable for use in this composition. For example, where the
composition is prepared as described previously (solvent sorption
of polymer on pigment), the polymer cannot, as a practical matter,
be extensively cross-linked without adversely affecting its
solubility alld thus its abili.ty to be associated with the
pigment. The relative molecular weig~.t of the polymers
suitable for use in compositi.ons of this invention does not
otherwise appear to be critical. Polymers of 2-vinylpyridine
having a number average molecular weight in the range of from
about 103 to 106 are suitable for preparation of the compositions
of this invention by the above procedures; with polymers of
2-vinylpyridine havi.ng a molecular weight in the range of 7000
to 10,000 being preferred. There is, however, an increasing
tendency for polymers of 4-vinylpyridine to cross-link as their
number average molecular weight exceeds 4000, and thus alternative
methods of preparation of the photosensitive composition with
this polymer are preferable to that described above. It is
understood that any reference herein to the molecular weights
of the polymers of this composition is based upon results obtained
by gel permeation chromatogxaphy techni~ues using the Q values
for polystyrene as a reference. The vinyl pyridine monomers and
substituted vinyl pyri.dine monomers corresponding to the above
formula can a.lso be randomly copolymerized with a numbex of vinyl
-15-
llQ397Z
monomers and acrylatc monomers. l~l1e ,tructural units contri-
buted to the copolymex by these vinyl and acrylate monomers
must of course ~c el~ctrically compatible with the contemplated
envi.ronment of use of the resultant materials. That is, the
strllCtUral U~litS contribut~d to the resultant copolymers hy
thcse monomers must ke substantially incapable of modifi.cation
of the electronic i.nteraction of the vinyl pyridine units
and substi1~uted vinyl pyridine units of the copolymer with
the desensitized vanadyl phthalocyanine pigment. Vinyl monomers
which satisfy the above requirements include styrene, alpha methyl
styrene, para methyl styrene and 4-isopropyl styrene. Acrylate
monomers which satisfy the above requ~rements include n-butyl-
methacrylate, methyl methacrylate and ethyl me-thacrylate.
Generally, any one or more of these materials can be copoly-
merized with the vinyl pyridine monomers and/or substituted
vinyl pyridine described hereinabove in accord with standard
free radical and anionic initiated,polymerization techniques.
If desired t:hese same materials can be formed.into block
copolymers by standard anionic polymerization techniques. For
: ,
example, one of the monomers of the block copolymer can be
initia~ly polymerized under conditions designed to produce an
unterminated radical on the polymer segment formed from the
flrst monomer. The second monomer can then be added to the
charge, whereupon the radical of the,previously polymerized
'material will serve to initiate polymerization of the newly
, .
added monom~r and result ln its propagation on the prepoly-
merized poly~er segment.
Irrespectivc:of which type of copolymer is formed
from the above materials, the mole concentration of struc-
: tural units contributed by the vinyl pyridine and/or substituted
, -16-
.. . - , . .. . . . ...
~103~
vinyl pyridine monomers relative to the structural units con-
tributed by the other monomers should generally exceed about
20 and preferably 50 mole percent.
Another class of polymeric materials which is
especially preferred for use in combination with the desensi-
tized pigment is represented by the formula
~ C - C tm
O O - (CH2)n - N~
wherein R is methyl or hydrogen
R' and R'' are independently selected
from the group consisting of hydrogen,
alkyl of 1-10 carbon atoms, phenyl
and substituted phenyl, said phenyl
substituent being incapable of with-
drawing electrons from the electron
rich phenyl group;
m is in excess of about 25, and
n is in the range of from 1 to 5.
The polymer component of the desensitized pigment
dispersion can comprise any one or combination of polymer
segments having structural units of the formula as set forth
hereinabove. A number of the monomers used in preparation
o the polymers having structural units satisfying the above
truatural formula are readily commercially available or can
be prepared by technigues disclosed in the literature from
materials which are readily commercially available. See,
for example, Functional Monomers, Vol. II, page 651 et seq.
Edited by R. H. Yokum and E. B. Nyquist, Marcel Depker, Inc.
tl974). In the preferred embodiments of this invention, the
polymeric component comprises poly(N,N-dimethylaminoethyl-
methacrylate). The monomer used in preparation of this polymer
is available from the Rohm and Hass Corporation of Philadelphia.
-17-
X
.
}39'72
Such MOnomers can hc polymcrized by frec radical or anionic
polymerization tcchniqucs. It is prefcrable in the pr~paration
of such polymers to control the~ degree of polymerization so
that the number average molecular we~ght (Mn) does no-t exceed
about 100,0~0. It is und~rstood that any reference hercin to
thc molecular weights of polymers of this composi-tion is based
upon results obtained by gel permeation chromatography tech-
niques using the Q values for polystyrene as a reference. The
molecular weight of such polymers can be readilv controlled
by simply ccntrollin~ the relative concen~ration of monomer
in the polymerization medium and/or hy the addition of a chain
transfer agent to the polymerization medium. In certain
instances, the growing radical will behave as a chain transfer
agent thereby restricting polymer chain growth to within the
preferred range. Benzene is capable of both serving as a
solvent for the polymerization of such monomers and effectively
controls the molecular weight by acting as a chain transfer
agent. The amino alkyl acrylate monomers and substituted amino
alkyl acrylate monomers corresponcling to the above formula
can also be randomly copolymerized with a number of vinyl
monomers and acrylate monomers. The structural units contri-
buted to~the copolymer by these vinyl and acrylate monomers
must of course be electrically compatible with the contemplated
environmen-t of use of the resultant materials. That is, the
structural units contributed to the resultant copolymers by
these monomers must be substantially incapable of mo~ificatio
'
of the electronic relationship of the amino al~yl acrylates
;~ units and substituted amino~alky1 ac~ylate units of the copoly-
mer relative to the desensitized pigment. Vinyl monomers
which satisfy the above requirements includc styrene,
alpha methyl styrene, para methyl styrene and 4-isopropyl styrene.
:
,
11(3397;~
Acryla-te mollomcrs which satisfy the ~bove rcquirements .include
n-butylmethacrylatc, methyl methacrylate and ethyl metllacrylate.
Generally, any one or more of these materials can be copoly-
merized with the amino a]kyl acrylate monomers and/or substituted
amino alkyl acrylate described hereinabovc in accord ~ith
standard free radical and anionic ini.tiated polymerization
techniques. If desired these same materials can be formed
into block copolymers by standard anionic polymerization tech-
niques. For example, one of the monomers of the block copolymer
can be intilly polymerized under conditions designed to
produce an unterminated radical on the polymer segment formed
from the fiLst monomer. The second m~nomer can then be added
to the charge, whereupon the radi.cal of the previously poly- -
merized material will serve to initiate polymerization of the
newly added monomer and result in its propagation on the
prepolymerized polymer segment.
Irrespective of which type of copolymer is formed
from the above materials, the mole concentratlon of structural
units~contributed by the amino alkyl acrylate and/or substituted
amino alkyl;acrylate monomers relative to the structural units
contributed by the other monomers should generally exceed
about 20 and preferably 50 mole percent.
: The effective relative concentration of polymer to
desensitized pigment particle is a function of the relative
eff~icieney with which such polymer is capable of sorption on
the desensitized .pigment and the desi.red modification of the
photoelectric response of the desensitization pigment. Generally,
the re~lative concentration of polymer to desen5itized pigmcnt
can range from about 1 to about 20 weight percent. In a pr~ferred
-19-
~, :
:~ ~
11~39'72
embodiment of this invontion, the pol~-mer to pigmcnt concentra-tion
is in the r~ngc of from about 5 to abc~ut 10 weigl~t percen-t.
It will be appreciated that certain polymers interac-t more
efficiently with desensitized vanadyl phthalocyanine than~ do
others and t}lus the preferred concentration of polymer to pigment
may vary from one composition to another.
The desensitized pigment particles prepared in the
manner and from the mat~rials described hereinabove can be
dispersed in an insulating carrier liquid and the resulting
dispersion used in both photoelectrophore~.ic and photoimmobilization
electrophoretic recording systems and methods.
The insulating carrier liquid of this dispersion
preferably possesses a resistance of at least 107 ohm-cm or greater.
Materials which satisfy these requirements and which are
chemically compatible with the photomigratory pigment
composition of this invention include saturated hydrocarbons
such as decane, dodecane, N-tetradecane, molten paraffin,
molten~beeswax, and other molten thermoplastic materials,
Sohio~Odorless Solvent (a kerosene fractlon available from
Standàrd Oil~of~Ohlo); Isopar G~(a long chain aliphatic
h ~ roo~arbon~avai~lable~from~ Humble Oil Company of ~ew ~e'rsay)
and:Klearol~ta~mineral oil product available xom Witco
Ch~mical Company of:~ew~York City) are generally pre~erred
as~insulating llquid~carrlers;- ~
The photomigratory c~omposi~tion preparad from
the~above mater~ials may also be~dispersed in the insulating
carr:ier liquid~tQ~ether with at least~ one other Figment having
its~pr~lnclpal region:of light absorption substantially outsi.de
the~region~of th~ principal region of light absorption of the
photomig~ratory~plgment~prepared acc.ording to this invention.
tradc ~ ~
20-
- -., ~ .. .. . . . ... . . . . .
Z
In a preferred embodiment of this invention, the photomigratory
composition is dispersed in the insulating carrier liquid
together with a magenta colored pigment and a yellow colored
pigment. ~he combined pigment concentration in the insulating
carrier liquid should preferably be in the range of Erom about
2 ~o about 10 weight percent. In the event that the photomigratory
pigment dispersion is to be used in a photoimmobilization
electrophoretic recording process of the type described in
U.S. ~atent 3,976,485 (to ~roner), the useful range
of pigment concentration can be as low as about 0.1 weight
percent and preferably range from about ~.1 up to about 0.5
weight percent.
rrhe photomigratory materials of this invention
can have a particle size within the range of rrom about 0.1
up to about 3 microns. T7ne relative particle size of such
materials in the insulating carrier liquid need not be uniform
and in f~ct, a particle size distribution within the previously
stated range may provide certain enhanced imaging capabilities.
In a typical photoèlectrophoretic or photoimmobilization
electrophoretic recording system, the photomigratory composition/
insulating liquid carrier dispersion is passed through an
imaging zone defined by two electrodes; one of which is
;;nominally designated as "the injecting electrode" and che
othe~r of which is nominally designated as "the blocking
e;lectr~ode." In the cont`ext of this invention, the blocking
ele~trode is regarded as an electrode ~hich is substantially
incapable of effecting~charge eschange with the photomigratory
pigments; whereas, the~iniecting electrode freely exchanges
charge with photoactivated photomigratory pigments. In a photo-
immobilization e}ectrophoretic recording system, the injecting
electrode will be typically coated w~th a dark injecting substance,
such as a Lewis acid. The gap hetween the electrades which defines
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the imaging zone can range from about 10 to about 250 microns.
In order to achieve satisfactory image resolution and density
with minimal background, the dielectric strength of the pigment
dispersion at the imaging zone r~ust be sufficient to support
a field of at least 12 volts/micron; however, in order to
achieve imaging capabilities of superior quality, the liquid
~dispersion should be preferably capable of supporting a field
of about ~0 volts/micron.
As indicated previously, the intimate association
- of desensitizin~ dye with vanadyl phthalocyanine can in some
instances affect the efficiency of photoresponse of this
pigment. In order to compensate for any loss in electro-
photo,graphic speed, such pigments may be optionally doped
with s~all quantities (0.05 to about 5 mole percent based
on vanadyl phthalocyanin,e concentration) of electron acceptor
compounds. Electron acceptor compounds which are suitable
for use in compensating for any loss in photosensitivity
of vanadyl phthalocyanine pigments include 2,4,7-trinitro-
9-fluore~none and~maLo~onitrile der~ivatbves~thereQf. These
p;igments may also~be treated with certain polymers ln order
to further modify their photoelectrophoretic response.
Typical of such polymers which can be used include poly-
ethylene~, poly(utyrene~ and poly(2-vinylpyridine~.
The E'xamp~les which~ol~10~further define, describe
and~i}lustrate the;~preparation and use of the desensitized photo-
mlgratory pigments prepared acc~ording to the method of this
invention.~ Apparatus and techniques used in the preparation
and~evaluation of~`such materials are standard as hereinbefore
desc;ribed.~ Parts and~percentages appearing in such ExampLes
~` ~ ; are~by~welght unless~stipulated otherwlse.
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EXAMPLE I
Synthesis of Vanadyl Phthalocyanine - Into a 12
liter flask equipped with a magnetic stirrer and an air
condenser are added 247 grams of phthalic anhydride, 247
~rams of urea, 3 liters of chloronaphthalene and 100 grams
of vanadium trichloride. The mixture is heated to boiling
under reflux conditions for approximately 45 minutes, cooled
to 25C and thereafter filtered. The solids which are re-
covered are washed with 300 mls of ethanol, t~en slurried
in lOO mls of ethanol for two hours and substantially filtered.
The recovered pigment is thereafter subjected to a series of
washes which are carried out at 70C, each ~lash lasting
approximately 2 hours: first wash, 2 liters of ~O% sodium
hydroxide solution; second wash, 2 liters of 20% hydrochloric
acid; and third wash, 2~liters of deionized water. The
~pigment is recovered by filtration, the filter cake allowed
to air dry for 24 hours and then dried in a vacuum oven at
65~C. The material produced in the manner which is described
above is further~refined by an acid pasting technique which
s~described as follows~: ~
About 7.5 grams of unrefined vanadyl phthalocyanlne
9 ~dissolved in 40 mls of concentrated~sulfuric acid and
stirrèd for about~50 mlnutes (the temperature of the system
being carefully~monitored so as not to permit the solution
temperature~to exoeed 3~5~C).~ The~solution i9 then poured
hro ~ ~;a~ooars~e fri~ttQd funnel and~soraYed into one liter
of ~ ex~which is~mai;tàinedl~at~a tem~erature in the ranae
of~ about 18~;to 25C.~ The spray injection o~ the filtrate
is~a~ccomplished by~means~of~two concentric glass tubes, so
poaltioned~as to~create a~vacuum at the orific~e of the center
tube when alr lS forced bet~een the inner and outer walls of
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11039~2
the tube. Liquid passing through the center tube is atomized
at the orifice by the passage of air between the two walls.
EXAMPL~ II
Preparation of poly(N,N-dimethylaminoethylmeth-
acrylate) - About 25 milliliters of N,N-dimethylaminoethylmeth-
acrylate (available from Rohm and Haas, Philadelphia, Pa.)
and 0.125 grams azobisisobutyronitrile are introduced into a
glass lined resin kettle containing 50 milliliters benzene.
The contents of the kettle are then heated to about 65C and
maintained at that temperature for about ~6 hours.~ The contents
of the kettle are allowed to cool to room temperature,
diluted with additional benzene to a total volume of 100 milliliters
and freeze dried overn1ght. Yield 20.6 grams white powder,
Mw = 113,000; Mn = 32,000; MWD = 3.53 (value obtained by standard
GPC echniques based upon an estimated Q value of 41).
E ~ PLE III
Preparation of Poly(2-vinylpyridine) by free
radlGa~1 solution;polymerizat1on - Commercia11y available
2-vinylpy~rldine~ obtained~from Reilly Tar and Chemical Co.,
Indiannapo1is, Indiana) is initially purified by vacuum
distillation at 5~Torr and 38C. Azobisisobutyronitrile
was~`selected~as~the~free radical inltiator for use in this
synth~sis~(available'from Eastman Kodak Co. of Rochester,
New~York~
Into~a~3~;neck~10~0~mi~1 round bottom flask equipped
with~a~mèchaniGa1 stirre~r;, a~sparging tube and a reflux
co~dénser~is~pouréd~45 mls of benzene. The temperature of
the~flask~and its~contents~are;~elevated to about 50C and
maintained~;~at~this~1eve1 from approximately 2 110urs while the
henzene~`Ls~sparged wlth~argon.~ Abou~ 150 mgs (0.75 wei~ht
11~3~72
percent) of azobic.isobutyronitrile are introduced into the
flask followed by 20 grams of 2-vinylpyridine. The solution
is maintained at 50C for 12 hours under argon and then at
55C for an additional 24 hours. The solution i5 cooled to
35C and diluted with lS0 Mls tetrahydrofuran. The benzene/
tetrahydrofuran/polymer solution is added dropwise to ~ mixture
containing approximately 6 pints petroleum ether and 4 pints
hexane. The solvent mixture is maintained in a constant
state of agitation ~uring the dropwice addition of the polymer
solution. The addition of the polymer solution to this solvent
quenches the polymerization and resu],ts in Frecipitation of
the polymer. The polymer solids are recovered by filtratlon
washed with petroleum ether and dried at 70C in an air
circulating oven overnight. Yield: 80~ (16 grams) of cream
colored polymer are obtained-, Mn = 36K; ~w = 63.8K; MWD = 1.77.
Number average molecular weight and weight average molecular
weight analysis by gel permeation chromatography based upon
a Q factor of 41.
EXAMPLE IV
Indulin 6B tetrasulfonate (CI 50405) is prepared
according,to the procedure described by Solodar and Monahan in
Can. J. Chem,, 54, 2902-2914 (1976).~
The procedu~re~ of Example I is repeated, except for
the add1tion of about 0.75 grams of Indulin 6B tetrasulfonate
to~an~a~queous~dispersl~on of the acid pasted vanadyl phthalocyanine
pigment, ~acid paste pigment being disper9ed directly without
;prior~drying). After briefly slurrying these materials together,
the solids are separated from the fluid by filtration and
dried.
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The c1esensitized vanadyl p~-thalocyanille ~igment
thus produced can be further modifieci by polymer trea~ment
with the material prepared according to ~xample II.
The procedure of part ~ is repeated except that the
desensitized vanadyl phthalocyanine pigmen1 is modiEied by
polymer treatment wi-th the material prepared according to
Example III.
--C--
Alternatively, the vanadyl phthalocyanine pigment
can be associated with Indulin 6B tetrasulfonate by initially
milling dri~d acid pasting vanadyl phthalocyanine pigment
in alcohol t~5% absolute alcohol) fo~lowed by dispersal of
the pigment in aqueous solutions. The Indulin 6B tetrasulfonate
is added to this aqueous pigment dispersion, the materials
allowed to interact briefly and the solids separated
from the liquid by filtration. The filtrate can be collected
and analyzed colometrically to determine the extent of
adsorption of dye by -the igment.
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I~ yet another alternative procedure, the acid past~dvanadyl phthalocyanine is milled in benzene and benzene/
ethanol solution of the dye added thereto. Milling continues
for a relative]y brief interval after wl~ich sufficient
mineral oil ~learol, Witco Chemical Co., New York City) is
added to the dispersion. The benzene/ethanol fraation is
removed ~y selectiv~ evaporation (flash evapora-tion techni~ues
and additional mineral oil added to produce a desensitized
pigment dispersion in which the pigment concentration is in
the range of from ~-lOQ~ by weight.
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11C1 397Z
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In yet another alternative treatment method, the
dye can be added directly to the acid solution of pigment
during the acid pasting process.
EXAMPLE V
The polymer treated desensitized pigment pre~ared
in the manner described in Example IV, Part B, is combined
with a mineral oil dispersion of photoelectrically active
magenta pigment and a mineral oil dispersion of photoelectrically
active yellow pigment. The relative pigment concentrations
in the dispersion are approximately l:l:l. The combined
pigment concentration in the mineral oi} is in the range
o~ from about 8-lO percent by weight.
The imaging qualities of resultant dispersion are
evaluated in a photoelectrophoretic imaging mode of the
~ype described in U.S. Patent 3,384,488.
:~ :
The above procedure is repeated with similarly
polymer treated vanadyl phthalocyanine pigment which has not
u~der~one desensitization. Comparison of images produced by
the~respeotives "trimixes" indicates improved green rendition
a~d speed conformity within the trimix containing the desen-
aipizçd vanadyl phthalocyanine pigment.
Figure~1~i11ustrates the characteristic response
aurves~f~desensitized~and non-desensitized (polymer modified)
vanadyl~phthalocyanine pigments to red light. The data shows
the~desensitized sample to be slower by~a factor of two
(20.3 10g~exposure)~at a spe~edpoint of 0.5~DmaX. Under the
appropriate~circumstances 1t may prove advantageoUS to mix
the s10wer pigment~with~the~faster pigment to arrive at a cyan
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whose photoresponse would thus be pre-isely balanced to other -~
pigments used in conjunction therewith.
It should be apparent from the foregoing disclosure
that the substituted phenazene compounds described herein
can also be used in conjunction with other pigments in
photoelectrophoretic imaging processes and that similar
desensitization of the treated pigment will also result.
The above specified embodiments of this invention
are merely illustrative of the subject matter described
herein and not he interpreted as delineat ng the scope
of this invention which is set forth hereinafter in the claims.
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