Note: Descriptions are shown in the official language in which they were submitted.
7~
--1--
P~OTOS ENS I T I VE MATERIALS
CONTA}NING IONIC DYE COMPOUNDS AS INITIATORS
Back~round of ~he Invention
The present invention relates to noYel
photohardenable compositions and to photosensitive
materials employing them. More particularly, it relates
to free radical ad~ition polymerizable compositions
containing an ionic dye-counter ion complex such as a
ca~ionic dye-borate anion complex or an anionic
dye-iodonium ion complex as a photoinitiator.
~.S. Patents 4,399,20g and 4,440,84S to The Mead
Corporation desctibe imaging materials and imaging
processes in which amages are formed through exposure
controlled release of an image-~orming agent from a
microcapsule containing a photohardenable composition.
The imaging ~aterial is exposed image-wise to actinic
radiation and ~ubjected ~o a uniform rupturing force.
Typically the image-forming agent i~ a color precursor
which is released image-wise from the microcapsules
whereupon it reacts wi~h a developer to form a visible
i~age.
One of ~the problems which has ~een encoun~ered in
designing commercially accep~able panchromatic, ~ull color
imaging materials employing these ~echniques has been the
relatively short wavelengths band to which most
~' .
~L28~
--2--
photohardenable compositions ~re 6ensitive to actinic
radiation. In most cases, the compositions are only
sensitive to ultraviolet radiation or blue light, e.g.,
350 to ~80 n~.
Full color pho~osensi~ive materials ~re described
in U.S. Patent No. a,842,976, issued June 27, 1989,
an~ ~I,S. Paten~ Mo. a,57~,8~1, issued March 1~,
1~86. ~)ese imaging materials include a
photosens~tive laye~ which contains three sets of
microcapsules. Each set of microcapsules is sensitive to
a different band ~f radiation in the ultraviolet or blue
spectrum and contains a cyan, ~agenta or yellow
image-forming agen~. The absorption spectra o~ the
initiators employed in t~ese microcapsules are never
perfectly distinct. ~here is always some degree of
overlap in the absorption curves and sometimes it is
~ubstantial. Exposure conditions therefore must be
controlled carefully to avoid cross-exposure.
It would be desirable to extend the sensitivi~y
of the photohardenable compositions used in these imaging
materials to longer wav21engths. By extending the
sensitivity o~ the photohardenable compositions to longer
wavelengths, the amount of overlap in ~he absorption
spectra of ~he initiators and the concommitant incidence
of cross-ex~osure can be reduced~ It would be
particularly desirable if compositions could be designed
with sensitivities to selected wavelength bands throughout
the visible ~pectrum (~00 to 700 nm) since thi~ would
provide a visible light-sensitive material which could be
exposed by direct re~lection or transmission imaging and
withou~ i~age processing.
MDX 188 P2 -3-
Summary of the Invention
It has been found that ionic dye-counter ion
compounds, such as cationic dye-borate anion compounds,
~re useful photoinitiators of free radical addition
reactions. Such compounds consist of a visible light
absorber (the ionic dye) ionically bonded to a reac~ive
counter ion. The coun~er ion is reactive in the sense
that upon excitation of ~he dye the counter ion donates an
electron to or accepts an electron from the excited dye.
This electron transfer process generates radicals capable
of initiating polymerization of a monomer.
The mechanism whereby the compounds absorb energy
- and generate free radicals is not entirely clear. It is
believed that upon exposure to actinic radiation, the dye
ion is excited to a singlet state in which it accepts an
electron from or donates an electron to the counter ion.
For a cationic dye borate anion compound, this can be
illustrated by the following equation:
BR4 D+ ~ D + BR4.
The lifetime of the dye singlet state is
extremely short by comparison to the lifetime of the
triplet state. The quenching rate constants which have
been observed suggest that the ionic compounds experience
a very efficient electron transfer via the singlet state.
In solution in the polymerizable compound, tight ionic
pairing of the counter ion and the dye is believed to
provide favorable spacial dis~ribution promoting electron
transfer to ~uch an extent that the transfer occur~ even
~8~
MDX l88 P2 -4-
though the lifetime of the singlet sta~e is very short.
Of course, t~is does not mean that electron transfer is
restricted to the singlet state. Ionic dyes which have
siynificant populations of triple~ state may undergo
electron transfer ~hrough the singlet state, triplet
state, or both singlet and triplet states.
Upon transfer of the electron, a radical is
formed. The ionic compounds used as initiators in the
present invention do not appear to exhibit back electron
transfer. It is believed ~hat following electron
transfer, the dye and counter ion become disassociated
such that back electron transfer does not occur.
The ionic compounds used in the present inven~ion
are different than the collision generated species
encountered in other photosensitive systems such as
collision complexes which yield encounter complexes,
exciplexes and/or contact ion pairs. See for example,
Ravarnos, George J. and Turrol Nicholas J.,
~Photosensitization by Reversible Electzon Transfer~,
Chem. Rev. 1986, 40l-449.
In accordance with the present invention the
ionic dye and the counter ion are present in the
photo~olymerizable composition as a stable, non-transient
compound, and not as a dissociated ion pair. Formation of
the compound is not dependent upon diffusion and
collision. As distinguished from photographic materials
and compositions containing collision dependent complexes
essentially all of the sensitizing dye present in the
photosensitive materials of the present invention prior to
exposure is ionically bonded to the the counter ion.
The ionic compounds used as initiators in the
present invention can also be characterized in that they
MDX 18B P2 -5
are soluble in nonpolar solvents such as TMPTA and the
like. They are soluble in an amount of at least about
0.1% and perferably at least about 0.3%. While these
amounts are not large, they are substantial considering
the normally lower solublity of ionic materials in polar
solvents. While the compounds are soluble, the dye and
the counter ion do not dissociate in solution. They
remain ionically bonded to each other.
In dye-sensitized photopolymerizable
compositions, visible light is absorbed by a dye having a
comparable absorption band, the dye is raised to its
excited electronic state, the lifetime of which may be
10 9 to 10-3 second, depending upon the nature
(singlet or triplet) of the excited state. During this
time, absorbed energy in the form of an electron must be
transferred to or from the dye molecule to produce the
free radical. In prior initiator systems, this ~ransfer
is diffusion controlled. The excited dye must interact
(collide) with another molecule in the composition which
quenches the dye and generates a free radical. In ~he
present invention, the transfer is not diffusion
(collision~ controlled. Electron transfer occurs a~
greater than diffusion controlled rates. In terms of
Stern-Volmer kinetics, this means the quenching constant
(Kq) of the excited dye is greater than 101 and, more
particularly, greater than 1012 have been observed for
the ionic compounds. A~ these rates, electron transfer
can occur through the singlet state.
Thus, the present invention provides a means for
generating free radicals from the excited state of an
ionic dye and insodoing provides photohardenable
compositions which are sensitive at longer wavelengths~
MDX 188 P2 -6-
One of the particular advantages of using ionic
dye-counter ion compounds as initiators of free radical
addition reactions is the ability to select from a wide
variety of dyes which absorb at substantially different
wavelengths. The absorption characteristics of the
compound are principally determined by the dye. Thus, by
selecting a dye which absorbs at 400 nm or greater, the
sensitivity of the photosensitive material can be extended
well into the visible range. Furthermore, compounds can
be selected which are respectively sensitive to red, green
and blue light without substantial cross-talk.
The ionic dye-counter ion compounds are
particularly useful in providing $ull color photosensitive
materials. In these materials, a layer including three
sets of microcapsules having distinct sensitivity
charac~eristics is provided on a support. Each set of
microcapsules respectively contains a cyan, magenta, and
yellow color-forming agent.
The absorption characteristics of the three sets
of microcapsules in a full color photosensitive material
must be sufficiently different that the cyan-forming
capsules can be differentially hardened at a predetermined
wavelength or over a predetermined wavelength
range without hardening the magenta or yellow-forming
capsules and, likewise~ the magenta~forming and
yellow-forming capsules can be selectively hardened upon
exposure respectively to second and third wavelengths
without hardening the cyan-forming capsules or hardening
the other of the yellow-forming or magenta-forming
-
~;~8~
MDX l8~ P2 -7-
capsules. Microcapsules ~aving ~his characteristic (i.e.,
cyan-, magenta- and yellow-~orming capsules which can be
selectively hardened by exposure at distinct wavelengths
without cross-exposure) are referred to herein as having
~distinctly different sensitivities. a
As indicated above, because most photohardenable
compositions are sensitive to ultraviolet radiation or
blue light and they tend not to be sensitive to
wavelengths greater than about 480 nm, it has been
difficult to achieve microcapsules having distinct
sensitivities at three wavelengtbs. Often it can only be
achieved by carefully adjusting the exposure amounts so as
not to cross-expose the capsules.
The present invention facilitates the achievement
of distinct sensitivities by shi~ting the peak absorption
of at least one of the initiators to higher wavelengths,
such as wavelengths greater ~han about 400 nm. In this
manner~ instead of attempting to establish distinct
- sensi~ivities at three wavelengths within the narrow
wavelength range of, for example, 350 nm to 480 nm,
sensitivity can be established over a broader range of,
for example, 350 to 550 nm or higher. In accordance with
the invention, the sensitivity of the microcapsules can be
extended well into the visible spectrum to 600 nm and in
some cases to about 700 nm. In the preferred case
compounds are provided which are respectively sensitive to
red, green and blue light.
A principal object of the present invention is to
provide photohardenable compositions which are sensitive
to visible light, e.g., wavelengths greater than about 400
nm.
~8~
MDX 188 P2 -8-
A further object of ~he present invention i~ to
provide visible light-sensitive photohardenable
compositions which are useful in the imaging materials
described in U.S. Patents ~,399,209 and 4,~40,846.
Another object of the present invention is to
provide photohardenable compositions which are sensitive
at greater than about 400 nm and which are useful as
photoresists or in forming polymer images.
These and other objects are accomplished in
accordance with the present invention which, in one
embodiment, provides:
A photohardenable composition comprising a free
radical addition polymerizable or crosslinkable compound
and a ionic dye-counter ion compound, said ionic
dye-counter ion compound being capable of absorbing
actinic radiation and producing free radicals which
initiate free radical addition polymerization or
crosslinking of said addition polymerizable or
crosslinkable compound.
Another embodiment of the present invention
resides in a photosensitive material comprising a support
having a layer of photosensitive microcapsules on the
surface thereof, said microcapsules containing an internal
phase including a photohardenable composition comprising a
free radical addition polymerizable or crosslinkable
compound and a an ionic dye-counter ion compound.
Still another embodiment of the present invention
resides in a photosensitive material useful in forming
full color images comprising a support having a layer of
photosensitive microcapsules on the surface thereof, said
. .~
8~
MDX 188 P2 -9-
photosensitive microcapsules comprising a first set of
microcapsules having a cyan image-forming agent associa~ed
therewith, a second set of microcapsules having a magenta
image-forming agent associa~ed therewith, and a third set
of microcapsules having a yellow image-forming ayent
associated therewith, at least one of said first, second,
and third sets of microcapsules containing an internal
phase which includes a photohardenable composition
including a free radical addition polymerizable or
crosslinkable compound and an ionic dye-counter ion
compound~
A further embodimen~ of the present invention
resides in a photosensitive material comprising a support
having a layer of a photohardenable composition on the
surface thereof, said photohardenable composition
comprising a free radical addition polymeriæable or
crosslinkable compound and an ionic dye-counter ion
compound which provides a quenching constant (~q) which is
greater than lolO and preferably greater than 10~
In accordance with more particular embodiments of
the invention, the ionic compound is a cationic dye-borate
anion compound and still more particularly a cyanine
dye-borate anion compound or an anionic dye compound such
as ionic compounds of xanthene dyes with iodonium or
pyryllium ions.
~2~
--10--
Det~iled Description of the Invention
Cati~nic dye-borate anion compounds ~re known in
the art. Their preparation and use in imaging systems is
described .in U.S. Patents 3,567,453; 4,307,1B2; 4,343,8gl;
S 4,447,521; and 4,45~,227. The ~ompounds used in the
present invention can be represented by ~he general
formula !I)~
~ ~R4 ~I)
R2~ ~ R3
where D~ is a ca~ionic dye; and Rl, R2, R3, and
R4 are indepen~ently selected from the group consisting
of alkyl, aryl, alkaryl, allyl, aralkyl, alkenyl, alkynyl,
alicyclic ~nd saturated or unsaturated heterocyclic groups.
Useful dyes form photoreducible but dark stable
complexes with borate anions and can be cationic methine,
polymethine, ~riarylmethane, indoline, thiazine, ~anthene,
oxazine and acridine dyes. ~ore specifically, ~he dyes
may be cationic cyanine, carbocyanine, hemicyanine/
rhodamine and azomethine dyes. In addition to being
cationic, the dyes should not contain ~roups which would
neutlalize or desensitize the complex or render the
complex poorly ~ark stable. Examples of groups which
generally ~hould not be present in the dye are acid groups
such as free carboxylic or ~ulphonic acid groups.
MDX 18B P2
Specific examples of useful cationic dyes are
Methylene Blue, Safranine 0, Malachite Green, cyanine dyes
of the general for~ula (II) and rhodamine dyes of the
formula (III):
5 ~ ~/ ~ ' ~
1 ~ (II)
n = O, 1, 2, 3,
R = alkyl
Y = CH=C~, N-CH3, C(CH3)2, O, ~, Se
co,R'
(III)
~0 R', R = alkyl, aryl, and any combination thereof
While they have not been tested, the cationic
cyanine dyes disclosed in U.S. Pa~ent 3,495,9~7 should be
useful in the present invention.
The borate anion is designed such that the borate
radical generated upon exposure to light and after elec-
tron transfer ~o the dye (Eq. 1) readily dissociates with
the formation of a radical as follows:
BR4 _~ BR3 ~ R- (Eq. 2)
~'~8~7~
MDX 188 P2 -12-
For example particularly preferred anions are
triphenylbutylborate and trianisylbutylborate anions
because they readily dissociate to triphenylborane or
trianisylborane and a butyl radical. On the other hand
tetrabutylborate anion does not work well presumably
because the tetrabutylborate radical is not stable and it
readily accepts an electron back from the dye in a back
electron transfer and does not dissociate efficiently.
Likewise, tetraphenylborate anion is very poor because the
phenyl radical is not easily formed.
Preferably, at least one but not more than three
of Rl, R2, R3, and R4 is an alkyl group. Each of
Rl, R2, R3, and R4 can contain up tc 20 carbon
atoms, and they typically contain 1 to 7 carbon atoms.
More preferably Rl-R4 are a combination of alkyl
group(s~ and aryl group(s) or aralkyl group(s~ and still
more preferably a combination of three aryl groups and one
alkyl group.
Representative examples of alkyl groups repre-
sented by Rl-R4 are methyl, ethyl, propyl, butyl,
pentyl, hexyl, octyl, stearyl, etc. The alkyl group~ may
be substituted, for example, by one or more halogen,
cyano, acyloxy, acyl, alkoxy or hydroxy groups.
Representative examples of aryl groups repre-
sented by Rl-R4 include phenyl, naphthyl and substi-
tuted aryl groups such as anisyl. Alkaryl groups include
methylphenyl, dimethylphenyl, etc. Representative
examples of aralkyl groups represented by Rl-R4 groups
include benzyl. Representative alicyclic groups include
cyclobutyl~ cyclopentyl, and cyclohexyl groups~ Examples
-
~Z~7~
MDX 188 R2 -13-
of an alkynyl group are propynyl and ethynyl, and examples
of alkenyl groups include a vinyl group.
As a general rule, useful ionic dye compounds
must be identified empirically, however, potentially
useful dye and counter ion combinations can be identified
by reference to the Weller equa- tion (Rehm, D. and
Weller, A., Isr. J Chem. ~1970), 8, 259-271), which can be
simplified as follows.
~G = EOx-Ered E~' ~Eq. 3)
where G is the change in the Gibbs free energy, EoX is
the oxidation potential of the borate anion B~4,
Ered is the reduction potential of the cationic dye, and
Eh ~ is the energy of light used to excite the dye.
Useful compounds will have a negative free energy change.
Similarly, the difference between the reduction potential
of the dye and the oxidation potential of the borate must
be negative for the compounds to be dark stable, i.e., Eox
- Ered > O.
As indicated, E~. 2 is a simplification and it
does not absolutely predict whether a compound will be
useful in the present invention or not. There are a
number of othex factors which will influence this
determination. One such factor is the effect of the
monomer on the complex. Another factor is the radial
distance between the ions. It is also known that if the
Weller equation produces too negative a value, deviations
from the equation are possible. Furthermore~ the Weller
equation only predicts electron transfer, it does not
~'Z8~
MDX 188 P2 -14-
predict whether a particulae dye complex is an efficient
initiator of polymerization. The equation is a useful
first approximation.
Specific examples of cationic dye-borate anion
compounds useful in the present invention are shown in the
following table with their ~ max.
~2~
hl)X 188 P2 14A--
- Table
Compound No. Structure ~\ ma~ (TMPTA)
1. ~ 5 5 2 nm
C ~ ~2~3
Ph3~ H~
2. 0~5 5~0 568 nm
4~15 ~ 4N15
Ph3~ 4H~
3 0~0 ~ 4 92 nm
~C6H13 1l-S6Hl3
3 4 9
4 C~ sx~ 428 nm
3 a 3
Ph3~ R-C,~Hg
,o~ N ~ 658 nm
(CH~ )~ 5, 11(Q'3)2
. ~.
Ph38 V ~-~C4Hg
6. a~3 X~ N ~,CN 528 rlm
~H2 N~112
~h3~ 6~C~Hg
~ Z 8 ~
MDX 18B P2 -15-
s
NO ~ I ~ ~50nm
H3CN2~ U12C~3
Ar3B-R '
No. R' Ar
7A n-butyl phenyl
7~ n~hs%yl phenyl
7C n butyl anlsyl
B. 55Onm
R . R
Ar3_B_R~
No. ' R ~r
8A methyl n-~utyl phenyl
8B methyl n-hexyl phenyl
8C n-butyl n-~utyl phenyl
8~ n ~utyl n-~xyl ph~nyl
8E n-heptyl n-butyl phenyl
8~ n-hep~yl n-hexyl phenyl
8G ethyl n-butyl phenyl
~28~7~
MDX lB8 P2 -16-
9- ~ ~ ~ 570 nm Sys~em
~1* C~
( 3 ~ 4 9
10. ~ ~ ~ 590 nm System
(~ ~ C
11. ~ 640nm
R A~ 3~!- ~ ' ~
. No~ R R'` Ar
llA methyl n-butyl phenyl
llB methyl n-hexyl phenyl
llC n-butyl n-butyl phenyl
llD n-butyl n-hexyl phenyl
llE n-pentyl n-butyl phenyl
llF n-pentyl n-hexyl phenyl
llG n-heptyl n-butyl phenyl
llH n-heptyl n-hexyl phenyl
11I methyl n-butyl anisyl
~3
~3 a33 740 nm System
(~3~3 C4~9
.. . . .
~q~8~7~Ln
MDX 188 P2 -17-
The cationic dye-borate anion compounds can be
prepared by reacting a borate salt with a dye in a coun-
terion exchange in a known manner. See Hishiki, Y.,
Repts. Scio Research Inst. (1953), 29, pp 72-79. Useful
bora~e sal~s are sodium salts sucb as sodium tetraphenyl-
borate, sodium triphenylbutylborate, sodium trianisyl-
butylborate and ammonium salts such as tetra0thylammonium
tetraphenylborate.
Anionic dye compounds are also useful in the
present invention. Anionic dye-iodonium ion compounds of
the formula ¦IV):
IR5-I-R~]n D~n (IV)
where D- is an anionic dye and R5 and R6 are
independently selected from the group consisting of
aromatic nucleii such as phenyl or naphthyl and n is 1 or
2; and anionic dye~pyryllium compounds of the formula (V):
D-n L~ n (V)
where D- and n are as defined above are typical examples
of anionic dye complexes.
Representative examples of anionic dyes include
xanthene and oxonols. In addition to iodonium and
pyryllium ions) other compounds of anionic dyes and
sulfonium cations are potentially useful.
~8~
MDX 188 P2 -18-
As in the case of the cationic dye compounds,
usef ul dye-cation combinations can be identif ied through
the Weller equation as having a negative free energy.
Selected examples o~ anionic dye rompounds are
shown in Table 2 ~ max. ca. 570 nm in TMPTA).
~2~
~DX 1~8 P2 -lg-
Tabl e 2
~a
~6,
` o~ ,~.
(~I
C ~0~ 0
~Z8~74~
MD% 188 P2 -20-
The most typical exa~ples of a free radical
addition polymerizable or crosslinkable compound useful in
the present invention is an ethylenically unsaturated com-
pound and, more specifically/ a polyethylenically unsatu-
rated compound. These compounds include bo~h monomers
having one or more ethylenically unsaturated groups, such
as vinyl or allyl groups, and polymers having terminal or
pendant ethylenic unsaturation. Such compounds are well
known in the art and include acrylic and methacrylic
tO esters of polyhydric alcohols such as trimethylolpropane,
pentaerythri~ol, and the like; and acrylate or methacry-
late terminated epoxy resins, acrylate or methacrylate
terminated polyesters, etc. RepresentatiVe examples
include ethylene glycol diacrylate, ethylene glycol
dimethacrylate, trimethylolpropane triacrylate (TMPTA),
pentaerythritol tetraacrylate, pentaerythritol tetra-
methacrylate, dipentaerythritol hydroxypentacrylate
(DPHPA), hexanediol-1,6-dimethacrylate, and diethyl-
eneglycol dimethacrylate.
The ionic dye compound is usually used in an
amount up to about 1% by weight based on the weight of the
photopolymerizable or crosslinkable species in the
photohardenable composition. More typically, the compound
is used in an amount of about 0.2~ to O.S~ by weight.
While the compound can be used alone as the
initiator, film speeds tend to be quite low and oxygen
inhibition is observed. It has been found that it is
preferable to use the compound in combination with an
autoxidizer. ~n autoxidizer is a compound which is
capable of consuming oxygen in a free radical chain
process.
~z~
MDX 188 P2 -21-
Examples of useful autoxidizers are
N,~-dialkylanilines. Examples of preferred
N,N-dialkylanilines are dialkylanilines substituted in one
or more of the ortho-, meta-, or ~ - position by the
following group~: methyl, ethyl, isopropyl~ t-butyl~
3,4-tetramethylene, phenyl, trifluoromethyll acetyl,
ethoxycarbonyl, carboxy, carboxylate, trimethylsilymethyl,
trimethylsilyl, triethylsilyl, trimethylgermanyl,
triethylgermanyl, trimethylstannyl, triethylstannyl,
n-butoxy, n-pentyloxy, phenoxy, hydroxy, acetyl-oxy,
methylthio, ethylthio, isopropylthio, thio-(mercapto-),
acetylthio, fluoro, chloro, bromo and iodo.
Representative examples of N,N-dialkylanilines
useful in the present invention are 4-cyano-Nr N-dimethyl-
aniline, 4-acetyl-N,N-dimethylaniline, 4-bromo-N,
N-dimethylaniline, ethyl 4-(N,N-dimethylamino) benzoate,
3-chloro-N,N-dimethylaniline, 4-chloro-N,N-dimethylaniline,
3-ethoxy-N,N-dimethylaniline, 4-fluoro-N,N-dimethylaniline,
4-methyl-N,N-dimethylaniline, 4-ethoxy-N,N-dimethylaniline,
N,N-dimethylthioanicidine, 4-amino- N,N-dimethylaniline,
3-hydroxy-N,N-dimethylaniline, N,N,N',N'-tetramethyl-1,4-
dianiline, 4-acetamido-N, N-dimethylaniline, etc.
Preferred N,N-dialkylanilines are substituted with
an alkyl group in the ortho-position and include 2,6-
diisopropyl-N,N-dimethylaniline, 2,6-diethyl-N,N-dimethyl-
aniline, ~,N,2,4,6-pentamethylaniline (PMA) and
p~t-butyl-N,N-dimethylaniline.
The autoxidizers are preferably used in the
present invention in concentrations of about 4-5% by weight.
:, .:. ,
8 ~7
-22-
The photohardenable composi~ions o~ the present
invention c~n be coated upon a ~upport in a conYentional
manner and used as a photoresist ~r in ph~tolithography to
form a polymer image or they can be encapsulated as
~escribed in U.S. Paten~s 4,399,209 and ~,~40,846 and used
to control the release of ~n image-forming agent. The
latter processes typically involve image-wise exposing the
photosensitive ma~erial to actinic radia~ion and subjecting
the layer of ~icrocapsules to a uniform rupturing force
such as pressure, abrasion, or ultrasonic energy whereupon
the image-forming agent is released from ~he microcapsules
for reaction with a developer.
Several processes can be used to form color images
as explained in U.~. Patent ~,842,~76, issued July 27, 1989. If
the microcapsules contain photosensitive compositions which
lS are sensitive to red, green and blue light, images can be
formed by direct transmission or reflection imaging or by
image processing. Image processing may involve forming
color ~eparations (color-seps) corresponding to the red,
green and blue component images and sequen~ially exposing
the photosensitive ~aterial ~o three distinct bands of
radiation hereinaf~er designated ~ -2, and ~ -3
through each color separation. ~therwise, it may involve
electronic processing in which the image or subject to be
recorded i~ view~d through a Dunn or matrix camera and ~he
output ~rom the camera electronically ~rives three exposure
~ources corresponding to ~ -2, And ~-3.
Alternatively, the image may be produced synthetically,
e.g., a computer-generated image.
~.~
~LZ~
MDX 188 P2 -23-
While the discussion herein relates to forming
3-color full color images, 4-color images are also
possible. For example, microcapsules containing cyan,
mayneta, yellow, an~ black image-forming agen~s can be
provided which have distinct sensitivities at four
wavelengths, e.g., A -1, /\-~ 3, and A-4.
In accordance with the invention, at least one set
of the microcapsules in a full color system contains an
ionic dye compound. The other sets also may contain an
ionic dye compound, or they may contain a different type of
photoinitiator.
In accordance with the preferred embodiments of
the invention, a full color imaging system is provided in
which the microcapsules are sensitive to red, green, and
blue light respectively. The photosensitive composition in
at least one and possibly all three microcapsules are
sensitized by an ionic dye compound. For optimum color
balance, the microcapsules are sensitive (~ max) at about
450 nm, 550 nm, and 650 mn, respectively. Such a system is
useful with visible ligbt sources in direct transmission or
reflection imaging. Such a material is useful in making
contact prints or projected prints of color photographic
slides. They are also useful in electronic imaging using
lasers or pencil light sources of appropriate wavelengths.
Because the ionic dye compounds absorb at
wavelengths greater than 400 nm, they are colored.
Typically, the unexposed dye compound is present with the
image-forming agent in the image areas and, thus~ the color
of the compound must be considered in determining the color
of the image. However, the compound is used in very small
~28~74L~
MDX 188 P2 -24-
amoun~s compared to the image-forming agent and exposure
sometimes bleaches the compound.
The photohardenable compositions of the present
invention can be encapsulated in various wall formers using
techniques known in the area o~ carbonless paper including
coacervation, interfacial polymerization, polymerization of
one or more monomers in an oil, as well as various melting/
dispersing, and cooling methods. To achieve maximum sensi-
tivities, it is important that an encapsulation technique
be used which provides high quality capsules which are
responsive to changes in the internal phase viscosity in
terms of their ability to rupture. Because the borate
tends to be acid sensitive, encapsulation procedures
conducted at hiyher pH ~e.~.~ greater than about 67 are
lS preferred.
Oil soluble materials have been encapsulated in
hydrophilic wall-forming materials such as gelatin-type
materials (see U.S. Patent Nos. 2,730,456 and 2,800,457 to
Green et al) including gum arabic, polyvinyl alcohol,
carboxy-me~hylcellulose; resorcinol-formaldehyde wall
formers (see U.S. Patent No. 3,755,190 to ~art, et al):
isocyanate wall-formers (see U.S. Patent ~o. 3,914,511 to
Vassiliades) isocyanate-polyol wall-formers (see U.S.
Patent No. 3,796,669 to Ririntani et al), urea-formaldehyde
wall-formers, particularly urea-resorcinol-formaldehyde in
which oleophilicity is enhanced by the addition of resorci-
nol tsee U.S. Patent Nos. 4~001,140; 4,087,376 and
4,089!802 to Foris et al) and melamine-formaldehyde resin
and hydroxypropyl cellulose (see commonly assigned U.S.
Patent No. 4,025,455 to Shackle).
MDX 188 P2 -25-
Urea-resorcinol-formaldehyde and melamine-
~ormaldehyde capsules with low oxygen permeability are
preferred. In some cases to reduce oxygen permeability it
is desirable to ~orm a double walled capsule by conducting
encapsulation in two stages.
A capsule size sbould be selected which minimizes
light attenuation. The mean diameter of the capsules used
in this invention typically ranges from approx}mately 1 to
25 microns. As a general rule, image resolution improves
as the capsule size decreases. If the capsules become too
small, they may become inaccessible in ~he pores or the
fiber of the substrate. These very small capsules may
therefore be screened from exposure by the substrate~ They
may also fail to rupture when exposed to pressure or other
rupturing means. In view of these problems, it has been
determined that a preferred mean capsule diameter range is
from approximately 10 microns. Technically, however, the
capsules can range in size up to the point where they
become visible to the human eye.
An open phase system may also be used in
accordance with the invention instead of an encapsulated
one. This can be done by dispersing what would otherwise
be the capsule contents throughout the coating on the
substrate as discrete droplets. Suitable coatings for this
embodiment include polymer binders whose viscosity has been
adjusted to match the dispersion required in the coating.
Suitable binders are gelatin, polyvinyl alcohol,
polyacrylamide, and acrylic lattices. Whenever reference
is made to ~capsules" and ~encapsulation~ without reference
to a discrete capsule wall in this specification or the
~28~
MDX 188 P2 -26-
appended claims, those terms are intended to include the
alternative of an open phase system.
The photosensitive material of the present inven-
tion can be used to control the interaction of various
image-forming agents.
In one embodiment of the present invention the
capsules may contain a benign visible dye in the internal
phase in which case images are formed by contacting the
exposed imaging material under pressure with a plain paper
or a paper treated to enhance its affinity for the visible
dye. A benign dye is a colored dye which does not
interfere with the imaging photochemistry, for example, by
relaxing the excited state of the initiator or
detrimen~ally absorbing or attenuating the exposure
radiation.
In a preferred embodiment of the invention, images
are formed through the reaction of a pair of chromogenic
materials such as a color precursor and a color developer,
either of which may be encapsulated with the
photohardenable compos.ition and function as the image
forming agen~. In general, these materials include
colorless electron dona~ing type compounds and are well
known in the art. Representative examples of such color
formers include substantially colorless compounds having in
their partial skeleton a lactone~ a lactam, a sultone, a
spiropyran, an ester or an amido structure such as
triarylmethane compounds, bisphenylmethane co~pounds,
xanthene compounds, fluorans, thiazine compounds,
spiropyran compounds and the like. Crystal Violet Lactone
and Copikem X, IV and XI are often used. The color formers
can be used alone or in combination.
MDX 188 P2 -27-
' The developer materials conventionally employed in carbonless paper technology are also useul in the present
invention. Illustrative examples are clay minerals such as
acid clay, active clay, attapulgite, etc~ organic acids
such as tannic acid, gallic acid, propyl gallate, etc.;
acid polymers such as phenol-formaldehyde resins, phenol
acetylene condensation resins, condensates between an
organic carboxylic acid having at least one hydroxy group
and formaldehyde, etc.; metal salts or aromatic carboxylic
acids such as zinc salicylate, tin salicylate, zinc
2-hydroxy naphthoate, zinc 3,5 di-tert butyl salicylate~
zinc 3,5-di~ methylbenzyl)salicylate, oil soluble metal
salts or phenol-formaldehyde novolak resins (e.g., see U.S.
Patent Nos. 3,672,935; 3,732,120 and 3,737,410) such as
zinc modified oil soluble phenol-formaldehyde resin as
disclosed in ~.S. Patent No. 3,732,12n, zinc carbonate etc.
and mixtures thereof.
As indicated in U.S. Patents 4,3g9,209 and
4,440,846, the developer may be present on the photo-
sensitive sheet (providing a so-called self-contained
system) or on a separate developer sheet.
In self-contained systems, the developer may be
provided in a single layer underlying the microcapsules as
disclosed in ~.S. Patent No. 4,440,846. Alternatively, the
color former and the color developer may be individually
encapsulated in photosensitive capsules and upon exposure
both capsule sets image-wise rupture releasing color former
and developer which mix to form the image. Alternatively,
the developer can be encapsulated in non-photosensitive
capsules such that upon processing all developer capsules
MDX 188 P2 -28-
rupture and release developer but ~he color former
containing capsules rupture in only the unexposed or
under-exposed area which are the only areas where the color
former and developer mix. Still another alternative is to
encapsulate the developer in photosensitive capsules and
the color former in non-photosensitive capsules.
The present invention is not necessarily limited
to embodiments where the image-formlng agent is present in
the internal phase. Rather, this agent may be present in
the capsule wall of a discrete capsule or in the binder of
an open phase system or in a binder or coating used in
combination with discrete capsules or an open phase system
designed such that the image-wise ruptured capsules release
a solvent for the image-forming agent. Embodiments are
also envisioned in which a dye or chromogenic material is
fixed in a capsule wall or binder and is released by
interaction with the internal phase upon rupturing the
capsules.
The most common substrate or this invention is a
transparent film since it assist in obtaining uniform
development characteristics, however, paper may also be
used. The paper may be a comrnercial impact raw stock, or
special grade paper such as cast-coated paper or chrome-
rolled paper. Transparent films such as polyethylene
terephthalate can be used. Translucent substrates can also
be used in this invention.
Synthesis Examples 1 and 2 respectively illustrate
the preparation of borates and dye-borate compounds.
MDX 188 P2 -29-
SY~THESIS ~XAMPLE 1
Dissolve triphenylborane in 150 ml dry benzene
(lM) under nitrogen atmosphere. Place flask in a cool
water bath and, while stirring, add n-BuLi, ~1~1 eg.) via
syringe. A white precipitat~ soon formed after addition
was s~arted. Stirring is continued about 45-60 min.
Dilute with 100 ml hexane ancl filter, washing with hexane.
Thi~ resultant Li salt is slightly air unstable. Dissolve
the white powder in about 200 ml distilled water and, with
vigorous stirring, add aqueous solu~ion of tetramethyl
ammonium chloride ~1.2 eg. of theoretical in 200 ml). A
thick white precipitate forms. Stir this aqueous mixture
about 30 min. at room temperature, then filter. Wash
collected white solid with distilled water.
As an alternative synthesis, to a l.OM solution of
2.0 equivalents of l-butene in dry, oxygen-free
dichlor~methane, under inert atomosphere, was added slowly
dropwise with stirring, 1.0 equivalents of a lnOM solution
of dibromethane-methylsulfide complex in dichloromethane.
The reaction mixture stirred at reflux for 36 hours and the
dichloromethane and excess l-butene were removed by simple
distillation. Vacuum distillation of the residue afforded
0.95 equivalents of a colorless mobile oil (Bp 66-7 0~35 mm
Hg, ~BNMR;bs (4.83PPM~. ~nder inert atmosphere, ~his oil
was dissolved in dry, oxygen-free tetrahydrofuran to give a
l.OM solution and 3.0 equivalents of a 2.0M solution of
phenylmagnesium chloride in tetrahydrofuran were added
dropwise with stirring. After stirring 16 hours, ~he
resultant solution was added slowly with vigorous stirriny
to 2 equivalents of tetramethylammonium chloride, as a 0.2
~2~3~7~
MDX 188 P2 -30-
M solution, in water. The resulting white floccula~e solid
was filtered and dried to afford a near quantitative amounk
of t~e desired product Mp 250-2C, ~BNMR:bs ~-3.70PPM)~
SYNTHESIS EXAMPLE 2
Sonicate a suspension of a borate salt (1 g/10 ml)
in MeO~, to make a very fine suspension. Protect flask
from light by wrapping with aluminum foil then add 1
equivalent of dye. Stir this solution with low heat on a
hot plate for about 30 min. Let cool to room temperature
then dilute with 5-10 volumes of ice waterO Filter the
resultant solid and wash with water un~il washings are
colorless. Suction filter to dryness. Completely dry
initiator compound by low heat (about 50C) in a vacuum
drying oven. Initiator is usually formed quantitatively.
Analysis by H-NMR indicates 1:1 compound formation
typically greater than 90%.
The present invention is illustrated in more
detail by the following non-limiting Exampl~s.
Exam~le 1
Capsule Preparation
1. Into a 600 ml stainless steel beaker, 104 g
water and 24.8 g isobutylene maleic anhydride copolymer
(18%) are weighed.
2. The beaker is clamped in place on a hot plate
under an overhead mixer. A six-bladed, 45 pi~ch~ turbine
impeller is used on the mixer.
~Z~3~L7~0
MDX 188 P2 -31-
3. After thoroughly mixing, 3.1 g pectin
(polygalacturonic acid methyl ester) is slowly sif~ed into
the beaker. This mixture is stirred for 20 minutes.
4. The pH is adjusted to 4.0 using a 20~ solution
of H2SO4, and 0.1 g Quadrol (2-hydroxypropyl
ethylenediamine with propylene oxide from BASF) is added.
5. The mixer is turned up to 3000 rpm and the
internal phase is added over a period of 10-15 seconds.
Emulsification is continued for 10 minutes.
6. At the start of emulsification, the hot plate
is turned up so heating continues during emulsification.
7. After 10 minutes, the mixing speed is reduced
to 2000 rpm and 14.1 9 urea solution (50% w/w), 3~2 g
resorcinol in 5 g water, 21.4 9 formaldehyde (37~), and 0.6
9 ammonium sulfate in 10 ml water are added at two-minute
intervals.
8. The beaker is covered with foil and a heat gun
is use~ to help bring the temperature of the preparation to
65C. When 65C is reached, the hot plate is adjusted to
maintain this temperature for a two to three hour cure time
during which ~he capsule walls are formed.
9. After curing~ the heat is turned off and the
pH is adjusted to 9.0 using a 20~ NaO~ solution.
10. Dry sodium bisulfite (2.8 g) is added and the
capsule preparation is cooled to room temperature.
Three batches of microcapsules were prepared for
use in a full color imaging sheet using the three internal
phase compositions set forth below. Internal Phase A
provides a yellow image-forming agent and is sensitive at
420 nm, Phase B provides a magenta image-forming agent and
. . .
~2~3~7~)
--32--
is 6ensitive at 480 nml and Phase C contains d cyan
image-forming Agen~ and ~ cati~nic dye-bo~ate anion complex
which is ~ensitive ~t 570 nm. ~he three bat~hes of
microcapsules were mixed, coated on a support, and dried to
provide a full color imaging ~heet.
Internal Phase A (420 nm)
TMPTA 35 9
DPHPA 15 9
3-Thenoyl-7-diethylamino coumarin15 g
2-Mercaptobenzoxazole ~BO) 2.0 g
Pentamethylaniline (PM~) 1.0 9
Reakt Yellow (BAS~) 5.0 9
SF-5~ (Union Carbide Isocyanate)1.67 g
N-10~ Desmodur Polyi~ocyanate Resin) 3.33 9
Internal Phase B (480 nm)
... . . .
TMPTA 35 9
DP~PA 15 9
9-(4'-Isopropylcinnamoyl)-
1,2,4-te~rahydro-3~, 6~, lOH[l]-
- benzopyrano[9, 9A,l-yllquinolazine-
10-one 0.15 9
MBO 1.0 9
PMA 2.0 9
~agenta Çolor Former
~D-5100~ilton Davis Chemical Co) 8.0 g
SF-50 1.67 g
N-100 3;33 9
Internal Phase C (570 nm)
. .
TMPTA 50 9
Cationic Dye Compound No. 20.15 9
PMA 2.0 g
Cyan Colo~ Pormer
(S-29663~Hilton Davis Chemical Co.) 4.0 9
~_50 1.67 g
N-100 3.33 9
* Tx~de~ark
~.,
~' ~
~Z8~
MDX 188 P~ -33~
Example 2
Capsule Preparation
1. Into a 600 ml stainless steel beakee, 110 g
water and 4.6 9 isobutylene maleic anhydride copolymer
(dry) are weighed.
2. The beaker is clamped in place on a hot plate
under an overhead mixer. A six-bladed, 45 pitch~ turbine
impeller is used on the mixer.
3. After thoroughly mixing, 490 9 pectin
}0 (polygalacturonic acid methyl ester) is slowly sifted into
the beaker. This mixture is stirred for 2 hours at room
temperature (800-1200 rpm).
4. The pH is adjusted to 7.0 with 20~ sulfuric
acid.
5. The mixer is turned up to 3000 rpm and the
internal phase is added over a period of 10-15 seconds.
Emulsification is continued for 10 minutes. Magenta and
yellow precursor phases are emulsified at 25-30C Cyan
phase is emulsified at 45-50C (oil), 25-30~C (water).
6. At the start of emulsification, the hot plate
is turned up so heating continues during emulsification.
7. After 10 minutes, the pH is adjusted to 8.25
with 20~ sodium carbo~ate, the mixing speed is reduced to
2000 rpm, and a solution of melamine-formaldehyde
prepolymer is slowly added which is prepared by dispersing
3.9 g ~elamine in 44 g water, adding 605 g formaldehyde
solution (37~) and heating at 60C until the solution
clears plus 30 minutes.
.. . . .
~z~
MDX 18B P2 -34~
8. The pH is adjusted to 6.0, ~he beaker is
covered with foil and placed in a water bath to bring the
temperature of the preparation to 65C. When 65C is
reached, the hot plate i5 adjuste~ ~o maintain this
temperature for a two hour cure time during which the
capsule walls are formed.
9. After curing, mixing speed is reduced to 600
rpm, formaldehyude scanvenger solution (7.7 g urea and 7.0
g water) is added and the solution was cured another 40
minutes.
10. The pH is adjusted to 9.5 using a 20~ NaOH
solution and stirred overnight at room temperature.
Three batches of microcapsules were prepared as
above for use ~n a full color imaging sheet using the
three internal phase compositions set forth below.
Yellow Forming Capsules (420 nm)
TMPTA 35 9
DPHPA 15 g
3-Thenoyl-7-diethylamino coumarin15 9
2-Mercaptobenzoxazole (MBO) 2.0 9
2,6-Diisopropylaniline 1.0 g
Reakt Yellow (BASF) 5.0 g
N-lOO(Desmodur Polyisocyanate Resin) 3.33 9
Magenta Forming Capsules (550 nm)_
TMPTA 9
Compound 8A 0.2 9
2,6-Diisopropylaniline 2.0 9
HD51~0 (Magenta color
precursor from ~ilton-Davis
Chemical Co.) 12.0 9
8~
-35-
~yan ~ormin~ C~psules (S50 nm)
TMPTA 50 g
Compound 11 ~ 0.31 9
2,6-dii~opropylaniline~ 7.0 9
Cyan Precursor (CP-177
of ~ilton-Davis Chemical Co.)6 g
The three batches of microcapsules were blended
together and coated on a support to provide an imaging
material in accordance with the present invention.
~aving described the invention in detail and by
reference to preferred embodiments thereo, it will be
apparent that ~odi~ications and variations are possible
without departing from the ~cope of the invention defined
in the appended claims.
* ~rade~mark
~''
