Note: Descriptions are shown in the official language in which they were submitted.
lO~(J188
This invention relates to dry, activator sheets
for use in bleaching photographic elements containing a
silver image and a bleachable dye and to photographic elements
and processes for bleaching silver images and dyes.
Many methods to produce positive color images with
photographic silver halide materials have been described in the
art. m ose which are successfully employed in today's color
photographic art include the silver dye bleach process, as
described, for example, in J. S. Friedman, History of Color
Photo~raPhy~ (1944) pp. 405-429 and A. Meyer, The Journal of
Photographic Science, Vol. 13, 90-97 (1965); the color imaging
process, as described in U.S. Patent 2,252,718; and reversal
processes which utilize the color development of photographic
silver halide elements containing incorporated color-forming
couplers, as described, for example, in U.S. Patents 2,944,900;
2,984,567 and 3,189,452. In each of these processes~ however,
lengthy solution processing techniques are required which rely
heavily on precision control and sophisticated techniques in
order to produce color photographic images of high quali~y.
The silver dye bleach process involves developing a
silver image in an exposed silver halide emulsion containing
bleachable dye, and subsequently bleaching the dye in those areas
where the silver has been developed. ~11 the silver ion is
removed or rendered transparent and insensitive to light by
the bleach action, leaving a positive dye image in the areas
where no metallic silver was present.
In most color photographic processes utilizing
the above silver dye bleach system, it has been necessary to
subject the exposed film to a large number of processing
baths to achieve the discernable image. The exposed element
is first developed with a black-and-white developer solution
to produce a metallic silver image containing overall dye and
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A ~
~ 090188
then subjected to a strongly acidic dye bleach bath which
decolorizes the dye in just those areas where the developed
silver is present. The residual silver and silver halide are
then removed in a subsequent bleach and fix bath and a direct-
positive color image is obtained.
Photothermographic elements, i.e., photographic
elements which produce a silver image upon imagewise exposure and
then heat development, are described, for example, in Evans and
McLaen U.S Patent 3,801,321 issued April 2, 1974; Sullivan,
Cole and Humphlett U.S. Patent 3,785,830 issued January 15, 1974;
and Haist et al. U.S. Patents 3,301,678 and 3,531,285. These
elements are particularly desirable in that an image can be
produced by a dry process.
Michel et al., U.S. Patent 3,414,411, issued December
3, 1968, discloses an "in-camera" type system employing a photo-
graphic element comprising a support having thereon a silver
halide emulsion containing the salt of an acid and a developed
silver image having in association therewith a bleachable dye, or
dye precursor. The exposed emulsion is contacted with a viscous
alkaline processing solution and with a web having an acidic substi-
- tuent which is capable of exchanging hydrogen ion with the cation
of the salt of an acid which is present in the emulsion to lower
the pH of the emulsion to a level at which imagewise bleaching
of the dye in areas of metallic silver and in the presence of a
silver complexing agent proceeds. The dye bleaching is described
as being conducted in the presence of a catalyst and the web is
delaminated to uncover the image.
The processing solution of Michel et al., U.S. Patent
3,414,411, however, requires the use of salts which upon drying render
the coating translucent or substantially opaque due to crystallization
and the web must be delaminated from the element for viewing pur-
poses. The acid used in the processing web is non-diffusible and
immobile. Thus, in order to bleach the silver metal, ion
1~018t~
exchange must take place and the web must be peeled apart from
the element.
The use of conventional dye bleach solutions is in some
ways undesirable in that it is difficult to control the composi-
tion of the solution and the process is time consuming.
It has thus been desirable to provide a photographic and
preferably photothermographic dye bleach process which is dry,
stable and does not require removing the bleaching web to prod-
uce a positive color image.
Summary of the Invention
It has been discovered according to the present invention
that an element comprising a silver image and at least one over-
all bleachable dye, that is a dye that is capable of being
bleached in a silver dye-bleach process, can provide a positive
dye image, in the absence of solutions, by contacting the element
at moderately elevated temperatures, e.g. about 50C to about
150C, with a dye activator sheet comprising a support having
thereon a layer or layers comprising a nonvolatile, diffusible
acid and a non-hydrolyzable polymeric vehicle wherein the layer
has a pH of up to 6.0, especially up to 4.0, and a melting point
lower than 200C.
Thus, in accordance with the present teachings, a dry,
activator sheet for a dry, thermal silver dye-bleach process is
provided comprising a support having thereon a layer or layers
comprising
a) a nonvolatile, diffusible acid selected from the group
consisting of nonvolatile, diffusible mineral acids and
organic acids containing up to 10 carbon atoms, the acid
being nonvolatile at processing t~mperatures of 50 to
150C in the activator sheet,
lQ90188
b) a silver halide complexing agent, and
c) a non-hydrolyzable polymeric vehicle.
The layer or layers have a pH of up to 4.0 and a melting point
lower than 200C.
In accordance with a further teaching, a silver dye-bleach
process of thermally dye bleaching a photographic element is
provided which comprises a silver image in reactive association
with a dye that is bleached in a silver dye-bleach process com-
prising contacting the image with a dry, activator sheet compris-
ing a support having thereon a layer or layers comprising
a) a nonvolatile diffusible acid selected from the group
consisting of nonvolatile, diffusible mineral acids and
organic acids containing up to 10 carbon atoms, the acid
being nonvolatile at processing temperatures of 50 to
150C in the activator sheet,
b) a silver halide complexing agent, and
c) a non-hydrolyzable polymeric vehicle.
The layer or layers have a pH of up to 6.4 and a melting point
lower than 200C and heating to a temperature of from about 50
to about 150C to laminate the sheet to the element and produce
a dye image.
In accordance with yet a further teaching, a photographic
element is provided comprising a support having thereon a first
layer containing a silver metal image in reactive association with
a dye that is bleached in a silver dye-bl~ach process and laminated
to the first layer a transparent second layer which comprises
a) a nonvolatile, diffusible acid selected from the group
consisting of mineral acids and organic acids containing up
10 carbon atoms, the acid being nonvolatile at processing
temperatures of 50 to 150C in the activator sheet,
b) a silver halid complexing agent, and
c) a non-hydrolyzable polymeric vehicle.
-5-
~ 0~8l~
The second layer has a pH of up to 4.0 and melting point lower
than 200C.
Detailed Description of the Invention
The term "dry" as used herein is intended to refer to
materials that are dry to the touch.
The support for the dry, activator sheet or web can be any
material which retains dimensional stability at bleaching tempera-
tures. Examples of suitable supports are paper, poly-olefins such
as polyethylene or polypropylene, polycarbonate, high temperature-
resistant film supports such as supports from 1,1,3-trimethyl-5-
carboxy-3-(p-carboxyphenyl)indan polymers, cellulose acetate
butyrate, polyethylene terephthalate, and the like. The preferred
support materials are those which are transparent so that the
positive color image can be viewed through the activator sheet.
The support has thereon, either in a layer or layers, the
nonvolatile, diffusible acid and the polymeric vehicle. The
support and layer or layers containing the above substituents
can also be separated by an intermediate layer such as a timing
layer, such as a Tio2 layer, which allows the silver image to be
heat developed and bleached in a single heating step, and wherein
the timing layer allows the development of the silver image prior
to the bleaching by the activator sheet.
The acid used must be nonvolatile to avoid release of un-
desired materials and must be mobile and diffusible in the
photographic laminate comprising the described activator sheet
and the photographic element so that the silver image can be
effectively bleached in a short period of time. The acid can
be selected from the group consisting of nonvolatile, diffusible
~j~ -6-
lQ~0188
mineral acids and organic acids containing up to 10 carbon
atoms.
Nonvolatile mineral acids useful herein include
sulfuric acid, sulfamic acid, phosphoric acid, and the like.
Examples of nonvolatile, diffusible organic acids
useful herein are those acids containing up to 10 carbon atoms
including carboxylic acids such as citric acid, acetic acid,
and other acids such as p-toluenesulfonic acid, phenylphosphonic
acid, phenylphosphoric acid, phenylphosphinic acid, benzene-
sulfonic acid, p-toluene sulfinic acid, and the like.
me term "nonvolatile" as used herein is intended to
mean that no significant concentration of the acid, as described,
is releasable from the activator sheet or element according
to the invention at processing temperature.
It is critical that the acid be diffusible. By
the term "diffusible acids" it is meant that the acids in
themselves are mobile within the photographic laminant at
the processing temperatures employed or they can be rendered
mobile by the use of a suitable thermal solvent.
m e acid incorporated in the activator sheet is
generally strongly acidic and/or present in sufficient
proportions to provide a pH of 6.o or lower, especially up to 4.0,
in the layer or layers on the support. Acids which are unable
even at large proportions to reduce t~e pH in the layer or layers
to a value below 6.o would not be suitable for use according
to the invention.
me polymeric vehicle useful in this invention is a
film-forming polymeric material containing organic residues
which are non-hydrolyzable or slow to hydrolyze such as
poly(vinyl alcohol), poly(acrylic acid), poly(styrene sulfonic
acid), poly(vinyl pyrrolidone), poly(ethylene oxide), and
-- 7 --
1(~30188
the like. It is critical that the vehicle be non-hydrolyzable
or slow to hydrolyze because hydrolyzable vehicles such as
gelatin compete for hydrogen ions and become hydrolyzed and
denatured by the presence of the acid in the layer. The
resulting layers then would be effective for only a short
period of time after coating.
By the term "non-hydrolyzable vehicle'r it is meant
that a coating containing said vehicle and said diffusible acid,
when kept at room temperature, i.e. about 19C, 50~ relative
humidity for about 4 weeks, shows no appreciable loss in
activity due to pH changes caused by, for example, trans
esterification or transamidation reactions.
Examples of non-hydrolyzable vehicles useful herein
are sulfonated polystyrene, poly(acrylic acid), poly(acrylamide),
poly(vinyl alcohol), poly(vinylpyrrolidone), poly(ethylene oxide),
and active methylene containing polymers such as copolymers of
acrylamide and ethyl 5-(m- and p-vinylphenyl)-3-oxo-pentanoate,
copolymers of acrylamide and 6-(m- and p-vinylbenzyl)-2,4-
hexanedione and the like.
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~'
1(~9018~
A silver halide complexing agent generally known
in the art as a ~ixing agent must be present in either the
activator sheet o~ the invention or it must be incorporated
in the photographic element employed. As used herein, the
term "complexing agent" refers to compounds which either (1)
dissolve and remove silver ion from the emulsion layer or
(2) are stabilizing compounds which react with the silver
ion to render it insensitive to light and transparent.
The complexing agent employed herein in one form can
be that of a conventional silver halide solvent. Silver halide
solvents are defined as compounds which, when employed in an
aqueous solution (60C), are capable of dissolving more than ten
times the amount (by weight) of silver halide which can be
dissolved in water at 60C.
Typical useful silver halide solvents include
water-soluble thiosulfates (e.g., sodium thiosulfate, potassium
thiosulfate, ammonium thiosulfate~ and the like), thiourea, ethylene-
thiourea, a water-soluble thiocyanate (e.g., sodium thio-
cyanate, potassium thiocyanate and ammonium thiocyanate), and
a water-soluble sulfur-containing dibasic acid. ~ater-soluble
diols used to advantage include those having the formula:
- HO(CH2CH2Z)pCH2CH20H, wherein p is an integer of from 2 to 13,
and Z represents oxygen or sulfur atoms such that at least
one third of the Z atoms are sulfur and there are at least
two consecutive Z~s in the structure of the compound which
are sulfur atoms. The diols advantageously used are also
included in compounds having the formula: H0(-CH2CH2X)c_l-
2CH2X )d-l(-cH2cH2x)e-l(cH2cH2xl)f l~CH2CH2X)g l-CH2CH20H,
wherein X and X represent oxygen or sulfur, such that when
X represents oxygen, Xl represents sulfur, and when X
represents sulfur, X represents oxygen; and each of c, d, e,
f and g represents an integer of from 1 to 15, such that the
~(~g~
sum of c+d~e~f~g represents an integer of from 6 to 19,
and such that at least one third of the total of all the
X's plus all the Xl's represents sulfur atoms and at least
two consecutive X's and/or X 's in the structure of the
compound are sulfur atoms.
Typical diols include the following:
1) 3,6-dithia-1,8-octanediol
HOCH2CH2SCH2CH2SCH2CH20H
2) 3,6,9-trithia-1,11-undecanediol
HocH2cH2scH2cH2scH2cH2scH2cH2oH
3) 3,6,9,12-tetrathia-1,14-tetradecanediol
H(CH2CH2S)4CH2CH2H
4) 9-oxo-3,6,9,12,15-tetrathia-1,17-heptadecane-
diol
HO(cH2cH2s)2cH2cH2o(cH2cH2s)2cH2cH2oH
5) 9,12-dioxa-3,6,15,18-tetrathia-1,20-
eicosanediol
H0(CH2CH2S)2(CH2CH20)2(CH2CH2S)2( 2
6) 3,6-dioxa-9,12-dithia-1,14-tetradecanediol
Ho(cH2cH2o)2(cH2cH2s)2cH2cH2oH
7) 3,12-dioxa-6,9-dithia-1,14-tetradecanediol
2cH2o(cH2cH2s)2cH2cH2ocH2cH2oH
8) 3,18-dioxa-6,9,12,15-tetrathia-1,20-eicosanediol
HocH2cH2o( cH2cH2s)4cH2cH2ocH2cH2oH
: 9) 12,18-dioxa-3,6,9,15,21,24,27-heptathia-1,29-
nonacosanediol
(CH2CH2S)3CH2CH2CH2CH2SCH2CH2(CH2 2 )3
CH2 CH20H
10) 6,9,15,18-tetrathia-3,12,21-trioxo-1,23-
tricosanediol
HocH2cH2o(cH2cH2s)2cH2cH2o(cH2cH2s)2
CH2CH20CH2CH20H
: Water-soluble sulfur-containing dibasic acids which
can be used include those having the formula: HOOCCH2-
(SCH2CH2)qSCH2COOH~ in which q represents an integer of from
10~01~
1 to 3, and the alkali metal and ammonium
salts of said acids. Typical illustrative examples include:
1) ethylene-bis-thioglycolic acid
OccH2scH2cH2scH2cooH
2) 3,6,9-trithiahendecane dioic acid
HOOCCH2 ( SCH2CH2 )2SCH2COOH
3) 3,6,9,12-tetrathiatetradecanedioic acid
HOOCCH2 ( SCH2C~2 ) 3SCH2COOH
4) ethylene-bis-thioglycolic acid disodium salt
105) ethylene-bis-thioglycolic acid dipotassium salt
6) ethylene-bis-thioglycolic acid diammonium salt
7) 3,6,9-trithiahendecane dioic acid disodium salt
8) 3,6,9,12-tetrathiatetradecanedioic acid
disodium salt
The complexing agent, if included in the emulsion,
must not desensitize the emulsion. Various complexing agents
which can be incorporated in the emulsion layers of the
` photographic element without adversely affecting the element
include thiouronium and isothiouronium salts, such as 2,2'-
methylsulfonylimino bls(ethyl isothiouronium para toluene
sulfonate), 3,5-thiouronium-1-methyl-1-propane sulfonate, 3,5-
thiouronium-l-propane sulfonate~ and the like as described in
U.S. Patents 3,531,285 and 3,301,678; aminothiazolines such as
2-amino-2-thiazolium trichloroacetate and the like, azo thio-
ethers and blocked azolinethiones such as those described,
for example, in U.S. Patent 3,824,103 and complexing agents
such as those described in U.S. Patent 3,785,830.
If the complexing agent is incorporated in the
activator sheet, any of the above complexing agents can be
used in addition to other complexing agents such as thiourea
and the like.
The activator sheet can also contain a thermal
solvent, if desired, to aid the acid in diffusing to the
-- 10 _
emulsion layer. The thermal solvent should be added if the
depressed melting point of the mixture of the diffusible acid
and the complexing agent, if any, is 200C or higher. The
thermal solvents can, at any rate, accelerate the rate of
bleaching by depressing the melting point of the mixture.
By the term 'rthermal solvent" it is meant a non-
hydrolyzable organic material which is a solid at ambient
temperatures, but which has a mixed melting point with the other
ingredients at or below the temperature of the thermal process
employed. Preferred thermal solvents for this invention include a
variety of ethers, sugars and alcohols which act as solvents for
the incorporated materials functioning in the process.
Examples of useful thermal solvents can be found
in U.S. Patent 3,667,959 issued June 6, 1972; U.S. Patent
3,347,675 issued October 17, 1967 and U.S. Patent 3,438,776
issued April 15, 1969 and include non-hydrolyzable polar
solvents containing up to 10 carbon atoms such as ethylene
glycol, and low molecular weight polyethylene glycol and poly-
ethylene oxide, l,10-decanediol, 1,6-hexanediol, sorbitol and
the like.
In accordance with the invention, a catalyst may be
incorporated in the photographic emulsion, the acidic processing
web, or in both of these materials to aid in obtaining an
optimum dye image. The presence of a catalyst is needed in the
activator sheet if the pH is above 4Ø Advantageously, the
bleaching of the image dye is conducted in the presence of a
suitable catalyst, such as a phenazine, a quinoxaline, an anthra-
quinone, or a pyrazine. A number of catalysts useful herein
- are described in U.S. Patent 2,183,395 and 2,270,118. These
compounds oxidize the metallic silver to silver ion, and in
1()~01~
so doing are reduced. m e reduced catalyst then cross-oxidizes
with the image dye. mis cross-oxidation decolorizes, i.e.
bleaches, the image dye and oxidizes the catalyst back to its
original state.
If the activator sheet is at a pH of about 4.0 to
about 6.o, a catalyst must be included in the activator sheet.
If the pH of the activator sheet is 4.0 or lower, the use of
a catalyst is optional.
Other addenda such as bleaching compounds, dye bleach
competers and fixing compounds known in the art can be
incorporated into the activator sheet of this invention.
In order to satisfactorily bleach out the silver
image with a brief heating step, the activator sheet must have
a pH not greater than 6.0, especially not greater than 4.0, and
must have a melting point sufficiently low to enable the
acid at processing temperatures to diffuse to the emulsion layer,
i.e. a melting point below about 200C, such as within the range
of about 50C to about 150C. mus, the strength and proportion
of the acid can be adjusted to achieve the low pH values and the
use of-the thermal solvent can lower the melting point of acids
having higher melting points in order to achieve these properties.
It is pointed ou~ that if gelatin is used as a binder
in the emulsion layers, since it is a buffer, more acid should
be used~ Binders which are not buffers may require the use of
less acid.
m e acid component as described can be present in a
range of concentration in the activator sheet so long as the pH
of the layer or layers in the sheet is 6.o or less, especially not
greater than 4Ø Preferably the acid is present from about
3 1.0 g/m2 to about 50.0 g/m2 in the activator sheet. m e polymeric
vehicle preferably is present from about 1.0 g/m2 to about
50.0 g~m2 in the activator sheet. Typical concentrations for
complexing agents are from about 1.0 g/m2 to about 50.0 g/m2 or
(about 1 mole to about 5 mole/mole of silver halide). mermal
solvents can be present from about 1.0 g/m2 to about 50.0 g/m2
- 12 -
1()~3()18~
while catalysts such as phenazine are preferably pre~ent
from about 0 to about 100 mg/ft2 in the activator sheet,
depending upon the pH of the activator sheet.
The activator sheet can be prepared by coatlng onto
a suitable support a coating solution comprising the acid,
the vehicle, optionally the complexing agent, the thermal solvent,
and catalyst if the pH is above 4.0, and then drying. m e
various components are coated from a solvent such as methanol,
ethanol, acetone, water or the like. me various components
can be coated ln one layer or in different ad~acent layers.
A typlcal activator sheet or web comprises the
following components
thiourea 5.4 g/m
1,6-hexanediol 5.4 g/m
p-toluenesulfonic acid 5.4 g/m
poly(vinylpyrrolidone) 2.7 g/m
Triton TX-100 (m is is a 1.25 ml (10% ~olution)
surfactant which is a
sodium salt of an alkyl
aryl polyether sulfonate
and is a trademark of Rohm
and Haas Co., U.S.A.).
in methanol/distilled water (50:50 parts by volume)
This activator sheet or web has an effective p~ of 4.0 or less.
m e s~lver and dye images are bleached by merely
placing the activator sheet over the image and laminating by
applying heat at the melting point of the components in the
activator sheet and lightly pressing the two sheets together,
such as with a roller or other suitable means. A positive dye
lmage is produced in the element by bleaching upon briefly
heating the laminate, preferably to a temperature of about
50C to about 150C and more preferably from about 90C to about
120C over a time period ranging from about 2 to about 300
seconds, preferably from about 15 to 30 seconds. The temperature
and length of heating can be varied widely depending on the
thickness of the emulsion, activator chemistry layers, desired
- 13 -
B
. . .. ,., . . . . . . . . , . _ . . ... . . ~ .
`` 10~0~
lmage, and the llke.
Any sultable means can be useful to provide thedeslred processing temperature. The heating means can be a
slmple hot plate, lron, roller, oven or the like.
Processing is usually carried out under atmospheric
condltions of pressure and humidity. Conditions outside
normal atmospherlc pressures and humidlty can be employed if
desired.
In a preferred embodiment, the support for the
actlvator sheet is transparent so that the image is vislble
through the activator sheet. It ls a partlcular advantsge of
thls lnvention that the activator sheet need not be del~mlnated
from the image. The resultlng photographic element comprises a
support having thereon a first layer containing a silver metal
image and overall bleachable dye and laminated to the dye image
a transparent second layer comprising
a) a nonvolatile, diffusible acld selected from
the group consisting of nonvolatile, diffusible
mineral acids and organic acids containlng up to
10 carbon atoms and
b) a nonhydrolyzable polymeric vehicle
whereln said second layer or layers have a pH of up to 6.o,
especlally up to 4.0, and a melting point lower than 200C.
Alternatlvely, the resultlng photographic element
can comprise a support havlng thereon a first layer containing
a sllver metal image and overall bleachable dye and laminated
thereon a transparent second layer or layers comprising
- a) a nonvolatile diffusible acid selected from the
group consisting of nonvolatile, diffusible
mineral acids and organic acids containing up to
10 carbon atoms
b) a silver halide complexing agent and
c) a nonhydrolyzable polymeric vehicle wherein said
second layer or layers have a pH of up to 6.o,
especially up to 4.0, and a melting point lower
:~ than 200C.
- 14 -
~Q~
me photographic element can be prepared using
any source for the silver image. For example, the silver
image can be provided by imagewise exposing a photographic
emulsion containing a silver salt such as silver behenate, silver
laurate, silver trifluoroacetate and silver halide such as
silver chloride, silver chlorobromide, or the like to provide a
latent image and chemically developing or physically developing
the latent image in a conventional developer bath or by heat
if using a photothermographic element.
In yet another embodiment, a silver image with an
overall dye covering can be obtained by simply depositing
silver through a mask and overall depositing the bleachable
dye.
The bleachable dyes used herein are well known in
the art. m e term "bleachable dyes" as used herein includes
compounds which are dye precursors, i.e., colorless compounds
which become colored during processing of the photographic
materials and shifted dyes which shift hypsochromically or
bathochromically to the desired image hues when sub~ected
to a different environment such as a change in pH, reaction
with a material to form a complex, etc. The term "non-
diffusible" as used herein refers to bleachable dyes which in
themselves are non-diffusible in the emulsion, or dyes which
are rendered non-diffusible by the use of a suitable mordant,
such as those described in U.S. Patent 2,882,156. The elements
of this invention can have a single emulsion coating for monochrome
dye images formed from either one or a mixture of bleachable dyes,
which dye images are either colored or neutral (e.g., black and
white) images. Primarily, azo dyes are used in silver dye-bleach
systems because the bleaching process cleaves the -N=N- double bond
to give two aromatic fragments. Typical azo dyes which can be used
in the practice of this invention are listed in numerous patents,
- 15 -
~j
l~Y0~8
some of which are U.S. Patent Nos. 923,265; 999,996; 1,042,300;1,077,628; and U.S. Patent Nos. 3,178,290; 3,178,291; 3,183,225
and 3, 211, 556.
Bleachable dyes include those known in the art and
dyes such as disclosed in the Color Index (third edition)
published by the Society of Dyers and Colourists, copyright 1971,
printed by Lund Humphreys, Bradford and London, provided they
are bleachable as herein described. m is includes bleachable
dyes such as azo dyes, formazan dyes, azoxy dyes, xanthene dyes,
azine dyes, phenylmethane dyes, nitroso dyes, indigo dyes,
quinones, nitro-substituted dyes, phthalocyanines, and others
known to one skilled in the art. Precursors to these dyes as
known in the art, such as, hydrazo or diazonium compounds to
yield azo dyes, tetrazolium salts to yield formazan dyes, etc.,
are also useful herein.
me bleachable dyes are defined as those dyes which
in the presence of a photographic image comprised of silver metal
and an aqueous solution of a silver complexing agent such as thio-
urea and an electron transport agent such as phenazine at pH
20 values up to 4.0 suffer discharge of their color proportionate
to the amount of silver metal present. Further examples of these
dyes may be found in U.S. Patent 3,202,511; 3,493,372 and
U.K. Patents 1,146,118 and 1,255,857.
The elements of this invention may have a plurality
of coatings each containing a different bleachable dye for
providing multicolor images. Especially useful arrangements
are those in which at least three light-sensitive emulsion
layers are provided which are respectively sensitized to blue,
green and red radiation, and contain, respectively, non-
30 diffusible yellow, magenta and cyan dyes. me emulsions usedin this invention can contain the bleachable dyes. However,
it is also possible, and sometimes preferabl~, to incorporate
- 16
~,
10~0188
the bleachable dye in an alkaline-permeable layer contiguous
to the emulsion layer. This arrangement provides increased
speed, especially when the bleachable dye containing layer is
coated adjacent to the emulsion layer. mus, in one useful
arrangement, a support has coated thereon, in the following
order, layers containing, respectively, blue-sensitive
silver halide, bleachable yellow dye; green-sensitive silver
halidej bleachable magenta dye; red-sensitive silver halide
and bleachable cyan dye.
m e dyes can be added by any of the conventional
methods known in the art, for example, as dispersions in
which ballasted dyes are rendered partially soluble
by use of a sulfonic acid or carboxylic acid substituentj
or as dispersions wherein an oil soluble dye is dispersed
alone or in the presence of a high boiling solvent in the
photographic binder.
In the silver dye-bleach system, photographically
developed silver is used to reduce a dye from a colored to
a colorless form. m is dye bleaching step is usually carried
out in an acidic solution in the presence of a silver ion
complexing agent and a dye bleach catalyst. In this
invention, a dry sheet is provided to carry out the bleach
step. This step can be carried out at a pH up to 4.0 without
the need of a silver dye-bleach catalyst.
me bleachable dyes are preferably used at a
concentration ranging from about 0.1 g/m2 to about 3.oo g/m2
to achieve a discernible image, depending on the molar
extinction coefficient of the dye, and whether a reflection
-- 1~ --
.
~(~90188
print or transparency ls deslred.
In the preferred embodlment the photographlc element
ls completely dry processed. The sllver lmage ls produced by
a photothermographlc process uslng a photothermographlc element.
Typlcal photothermographlc elements to which the
bleachable dyes are added are descrlbed ln U.S. Patent 3,785,830
of Sulllvan, Cole and Humphlett, U.S. Patent No. 3,301,678 and
U.S. Patent 3,531,285 both by Halst, Humphlett and Johnson
and U.S. Patent 3,801,321 of Evans and McLaen.
Other photothermographlc elements which are processed
by heat lnclude those containing a silver salt and a base
precursor such as the salt of trlfluoroacetic acid, and an
amine, or bis-isothiuronlum compound such as those described
in U.S. Patents3,669,670; 3,301,678 and 3,531,285.
The photothermographic element can comprise a
support havlng thereon a reduclng agent, a silver salt oxldlzlng
agent, and a photosensltlve sllver hallde composltlon. Typlcally,
preferred photothermographic elements are described in U.S.
Patents 3,785,830 and 3,801,321.
Various reducing agents useful in photothermographic
compositions containing bleachable dyes and optlonally sllver
complexlng agents are for example, polyhydroxybenzenes such as
hydroqulnone developing agents lncludlng, for lnstance, hydro-
quinone, alkyl substituted hydroqulnones, exempllfied by
- tertiarybutylhydroquinone, methylhydroquinone, 2,5-dlmethyl-
hydroquinone and 2,6-dimethylhydroqulnone; catechols and
pyrogallol; halo-substltuted hydroqulnones such as chlorohydro-
qulnone or dlchlorohydroquinone; alkoxy substituted hydroquinones
such as methoxyhydroquinone or ethoxyhydroquinone and the
like. Other reducing agents which can be employed include
reductone developing agents such as anhydro dihydro piperidino
hexose reductone; hydroxytetronic acid reducing agents and
- 18 _
1~0~
hydroxy~etronimide developlng agents; 3-pyrazolidinone developing ag-
ents such as l-phenyl-3-pyrazolidinone and 4-methyl-4-hydroxymethyl-
l-phenyl-3-pyrazolidlnone and those described in British Patent
930,572 published July 3, 1963; certain hydroxylamine developlng
agents; ascorbic acid developing agents such as ascorbic acid,
ascorbic acid ketals, and other ascorbic acid derivatives,
phenylenediamine developing agents; certain aminophenol developing
agents and the like. Combinations of reducing agents can also
be employed. Preferred reducing agents are sulfonamido-
phenols such as 2,6-dichloro and 2,6-dibromo-4-benzenesulfon-
; amidophenols as described in U.S. Patent 3,801,321 and bis-
Deta-naphthols such as described in U.S. Patent 3,751,249.
The silver salt oxidizing agent can be a silver salt
of a long chain fatty acid such as silver behenate, silver
stearate, silver oleate, silver laurate, silver hydroxystearate,
silver caprate, silver myristate and silver palmitate as well
as silver benzoate, silver phthalate, silver acetate, silver
phthalazinone, silver benzotriazole and silver saccharin.
A particularly useful silver salt herein is a silver salt of
a thione. The silver salt of the thione can be prepared in
situ in the photothermographic materials by combining a source
of silver, such as silver trifluoroacetate, with the thione
compound in the compositlon. The thione compound is a compound
represented by the formula:
Rl__ __~
N - C=S
ZCOOH
-- 19 --
~ 01~8
wherein Rl represents atoms completing a 5 member hetero-
cyclic nucleus, such as a thiazoline nucleus, and Z is
alkylene, such as alkylene containing 1 to 3O carbon atoms,
typically 1 to lO carbon atoms. Examples of suitable 5
member heterocyclic nuclei are thiazoline-2-thione, benzo-
thiazoline-2_thione, imidazoline-2-thione or similar hetero-
cyclic thione nucleus. The heterocyclic nucleus can contain
substitutent groups which do not adversely affect the described
photothermographic nlaterials such as alkyl containing 1 to 3
carbon atoms, or phenyl. Alkylene as employed herein includes
so called branched chain alkylene such as -CH-
-
An especially suitable silver salt formin~ thione com--
pound is a thiazoline-2-thione represented by the formula:
R21C > =S
Z COOH
wherein zl is alkylene containing 1 to 4 carbon atoms, typically
methylene, R2 and R3 are each selected from the group consist-
ing of hydrogen, alkyl containing 1 to 4 carbon atoms, and
aryl containing 6 to lO carbon atoms, or taken together are
atoms completing a benzo group. The alkyl, aryl and benzo
groups can be substituted with groups which do not adversely
affect the described photothermographic materials.
Another suitable silver salt formlng thione compound is
an imldazoline-2-thione represented by the formula:
' 411 ~ =S
Z2COOH
- 20 -
)18~
wherein z2 is alkylene containing 1 to 4 carbon atoms~
typically ethylene; R6 is alkyl, typically alkyl contain-
ing 1 to 3 carbon atoms, such as methyl, ethyl or
propyl, aryl containing 6 to 10 carbon atoms, such as phenyl,
or carboxyalkyl, such as carboxyethyl and carboxymethyl;
R4 and R are each selected from the group consisting of
hydrogen, alkyl containing 1 to 4 carbon atoms, such as
methyl, ethyl and propyl, aryl containing 6 to 10 carbon
atoms, such as phenyl or tolyl, or R4 and R5 taken together
are atoms completing a benzo group.
A further suitable silver salt forming thione compound
is an oxazoline-2-thione represented by the formula:
R7ll _ o
811 ~>
Z2COOH
wherein z2 is as described; R7 and R8 are each selected from
the group consisting of hydrogen~ alkyl containing 1 to 4
carbon atoms, such as methyl, ethyl, and propyl, aryl contain-
: ing 6 to lO carbon atoms, such as phenyl or tolyl, or R7 and
R taken together are atoms completing a benzo group.
Examples of suitable thione compounds within the
deecribed formulas include:
3-(2-carboxyethyl)-4-methyl-4-thiazoline-2-thione,
3-(2-carboxyethyl)benzothiazoline-2-thione,
3-(2-carboxyethyl)-5-phenyl-1,3,4-oxadiazoline-2-thione,
3-(2-carboxyethyl)-5-phenyl-1,3,4-thiadiazoline-2-thione,
3-(carboxymethyl)_4_methyl-4-thiazoline-2-thione~
3-(2-carboxyethyl)-1-phenyl-1,3,4-triazoline-2-thione,
1,3-bis(2-carboxyethyl)imidazoline-2-thione,
1,3-bis(2-carboxyethyl)benzimidazoline-2-thione,
3-(2-carboxyethyl)-1-methylimidazoline-2-thione,
3-(2-carboxyethyl)benzoxazoline-2-thione, and
3-(1-carboxyethyl)-4-methyl-4-thiazoline-2-thione.
- 21 -
1(~90188
The described thione compounds can be prepared
employing processes known in the art. The described silver
complexes of the thione compounds can be prepared in situ,
as described, or the silver complexes can be isolated.
The photosensitive silver halide useful herein can
include, for example, silver chloride, silver bromide, silver
bromoiodide, silver chlorobromoiodide, or mixtures thereof.
For the purposes of the invention, silver iodide is also
included as a photosensitive silver halide. While the photo-
sensitive silver halide can be prepared in situ in thephotothermographic material, this is not necessary according to
the invention. The photosensitive silver halide can be coarse
or fine-grain, very fine-grain photosensitive silver halide being
especially useful. The photosensitive silver halide can be
prepared by any of the well-known procedures employed in the
photographic art. The silver halide can be prepared, for
example, employing single-~et preparation techniques, double-
~et preparation techniques, such as techniques employed in
preparing Lippmann emulsions and the like. Surface image or
internal image ~ilver halide materials can be used. If desired,
mixtures of surface and internal image silver halide materials
can be used. Negative type silver halide is typically employed.
The silver halide materials can be regular grain such as described
in Klein and Moisar, Journal of Photographic Science, Volume 12,
No. 5, September-October (1964), pages 242-251.
The photosensitive silver halide can be chemically
sensitized employing techniques known in the photographic arts.
Although a binder is not essential with the photo-
thermographic materials described, a binder is typically em-
ployed. The binders which are useful with the describedphotothermographic materials include various colloids
- 22 -
90188
employed alone or in combination as vehicles and/or bindlng
agents which do not adversely affect the desired photothermo-
graphic propertles of the described compositions and in varlous
layers of a photothermographic element. Suitable materials
can be hydrophilic or hydrophoblc. The binders whlch are
suitable are transparent or translucent and include both
naturally-occurring substances such as protelns, for example,
gelatln, gelatin derlvatlves, cellulose derlvatlves, poly-
saccharldes such as dextran, gum arabic and the like; and
synthetic polymeric substances such as water soluble polyvinyl
compounds llke poly(vinylpyrrolidone), acrylamide polymers and
the llke. Other synthetic polymeric compounds which can be
employed include dispersed vinyl compounds such as in latex
form and particularly those which increase dimensional stability
of photothermographic materials. Suitable binders include
polymers such as water insoluble polymers of alkyl acrylates or
methacrylates and those whlch have cross-linking sites which
facilltate hardenlng or curing as well as those having recurring
sulfobetaine unlts. Especlally sultable bindlng agents include
high molecular weight materials and reslns such as poly(vinyl
butyral), cellulose acetate butyrate, poly(methyl methacrylate),
poly(vinylpyrrolldone), ethyl cellulose, poly(styrene), poly-
(vinyl chloride), chlorinated rubber, poly(isobutylene), butadiene-
styrene copolymers, vinyl chlorlde-vinyl acetate copolymers,
copolymers of vlnyl acetate, vinyl chloride and maleic acid,
poly(vinyl alcohol), high molecular weight ethylene oxide polymers
and active methylene polymers such as those described in U.S. Patent
3,904,418 by Ponticello and Mowrey.
The photothermographic compositio~ can be coated on
a wide varlety of supports. Useful supports include those which
can withstand the processing temperatures employed such as
cellulose ester film, poly(vinyl acetal) film, polystyrene film,
` -`` 1(~90~8~il
poly(ethylene terephthalate) film, polycarbonate film and re-
lated fllms or resinous materials, as well as glass, paper,
metal and the like. Typically a flexible support is employed.
Hardenable layers of a photothermographic element,
as described, can be hardened by various organic or inorganic
hardeners alone or in combination, such as aldehydes, ketones,
vinyl sulfones, aziridines, mucrochloric acid and the like which
do not adversely affect the sensitometric properties of the
photothermographic materials. Hardeners which cause adverse
reduction of the described compositlon should be avoided.
The photothermographic elements and materials
according to the invention can contain addenda and layers commonly
employed in photo~hermographic elements, such as antistatic
and/or conducting layers, plasticizers and/or lubricants,
surfactants, matting agents, brightening agents, light-
absorbing materials, filter dyes, antihalation dyes and
absorbing dyes, and the like.
The various components of the photothermographic
materials of the invention can be added from water solutions,
or suitable organic solvent solutions can be used. The
components can be added using various procedures known in
the photographic art.
If desired, an agent, sometimes referred to as a toning
agent or activator-toning agent, can be employed with the photother-
mographic materials according to the invention to provide an
increase in density at certain processing temperatures. Suitable
toning agents, also known as activator-toning agents, include cyclic
imide toning agents such as phthalimide, N-hydroxyphthalimide,
- 24 -
succinimide, and N-hydroxysuccinimide, and the like. These
are described, for instance, in Belgian Patent 766,590, issued
June 15, 1971. Sulfolane in some instances can provide
improved results in the described photothermographic compositions.
Some photothermographic elements and compositions described
according to the invention do not need a toning agent.
Spectral sensitizing dyes can be used conveniently
to confer additional sensitivity to the light sensitive
silver halide employed according to the invention. For
instance, additional spectral sensitization can be obtained
by treating the silver halide with a solution of a sensitizing
dye in an organic solvent or the dye can be added in the form
of a dispersion. Spectral sensitizers which can be used include
the cyanines, merocyanines, complex(trinuclear or tetranuclear)
merocyanines, complex(trinuclear or tetranuclear) cyanines,
holopolar cyanines, styryls, hemicyanines, such as enamines,
oxonols, and hemioxonols.
A range of concentrations of each component in the
photothermographic material can be employed. Typically, each
light sensitive layer of a photothermographic element according
to the invention can comprise a) from about 0 to about l.0 x lO l
moles of silver as the described complex and b) about l.0 x lO 3
to about l.0 x lO 2 moles of the described photosensitive
silver halide per square meter of support and c) a reducing
agent in at least molar equivalency to conduct development based
on reducible silver ions and up to lO times equivalent in excess.
An optimum concentration of each component will depend upon the
particular components, the desired image, processing temperature
and the like.
The bleachable dye can be added directly to the
photothermographic composition prior to coating or can be added
after the composition is applied to the support.
- 25 -
A
0188
The photothermographic layer and/or other layers
of a photothermographic element according to the invention
can be coated by various coating procedures including dip
coating, airkni~e coating, curtain coating or extrusion
coating using hoppers of the type described in U.S. Patent
2,681,294 of Beguin, issued June 15, 1954. If desired, two
or more layers can be coated simultaneously by procedures
known in the art.
The silver image on the photothermographic element
can be produced after imagewise exposure within a short time by
merely moderately overall heating the photothermographic element.
For instance, a visible image on a photothermographic element
according to the invention can typically be produced within a
few seconds, e.g. about 1 to about 60 seconds after exposure by
heating the element to about a temperature within the range of
100C to about 250C, typically about 130C to about 180C.
Usually, the time of heating is less than about 20 seconds,
such as about 2 to 5 seconds at a temperature of about 180C.
Optimum time of heating and optimum temperature of heating can
be determined employing test procedures well known in the art.
One embodiment of the invention accordingly is a
method of developing and stabilizing an image in an exposed
photothermographic element comprising a support having thereon
(a) a reducing agent, as described, (b) a silver salt of a
thione compound, also as described, (c) a photosensitive
component consisting essentially of photosensitive silver
halide, (d) a bleachable dye and, if desired, (e) a binder,
comprising heating the photothermographic element to a temperature
within the range of about 100C to about 250C.
In developing an image in a photothermographic
element according to the invention, increasing or decreasing
the length of time of heating can enable use of a higher or
lower temperature within the described range.
- 26 -
.
lQ30188
In some cases it may be convenient to produce the
positive dye image using only a single heating step. This can
be accomplished by placing a timing layer between the photo-
thermographic element and the activating sheet and exposing
and heat processing whereby the bleaching is delayed until
the silver image is developed.
If moisture is present in the activator sheet, the
sheet should be preheated to a molten state prior to laminating
to release excess moisture and prevent gas bubbles when the dry
~activator sheet is laminated to the silver dye image.
The activator sheet described herein is stable
in the dry condition and can be kept on a shelf for long
periods of time prior to use.
; m e invention is further illustrated by the
following examples.
Example 1
A heat-developable photographic element was
prepared by combining the following components and coating on a
suitable paper support:
A. A sulfur and gold sensitized, cubic-grained
silver bromide emulsion (0.4 gAg/m2)
B. l-Phenyl-3-pyrazolidone ~1.08 g/m2)
C. 1,8-(3,6-Dioxaoctane)-bis-isothiuronium-p-toluene-
sulfonate (3.24 g/m2)
D. a,a-bis[4-(3',6'-disulfo-8'-heptoyl~mino-1'-
naphthol-2'-yl)azo-2,5'-dimethylphenyl]toluene,
tetrasodium salt (0.2 g/m2)
E. Gelatin (6.75 g/m2)
A sample of the above prepared element was imagewise
exposed to tungsten light through a graduated-density test object
to provide a latent image which was then thermally developed
by contacting the sample for 5 seconds with a heated metal block
- 27 -
,~
l~g~188
having a temperature of 200C. A negative silver scale was
produced. Two samples were then laminated in contact with
the following activator sheet for 15 seconds at 100C both
freshly coated and after one hour. The activator sheet comprised
a film support having coated thereon
Sulfonated polystyrene 1.8 g/m2
Thiourea 10.8 g/m
p-Toluenesulfonic acid 10.8 g/m2
l,10-Decanediol 10.8 g~m
Positive magenta dye images were observed which gave
excellent uniform bleaching and good minimum densities. The
equivalent results indicated fresh activity of the activator
sheet and activity after 1 hour were equal~
In a similar manner, 1,6-hexanediol and ethyleneglycol
were used as replacements for l,10-decanediol and similar
results were obtained.
Effective silver halide solvents which replaced
thiourea were also shown, including:
A.
H
~N> =S
3 H
B. HO-CH2-CH2-S-CH2-CH2 S CH2 2
3 \ " / CH3
C N - C - N
CH3 / \ CH4
2 2 2 2 2 CH2 COOH
- 28 -
105~0188
Example 2 - comParative Exam~le
A photographic element containing a cellulose acetate
support having coated thereon 2.90 g of AgBr/m2 and the azo
dye having the structure
CH3 OH NH-C-(CH2)5cH3
~N - N~OS03Na
H-C
\
O
\ CH3 OH NH-C-(CH2)5cH3
CH3 S~3 ~ S03Na
was imagewise exposed and processed for 3 minutes in Kodak
Developer Dl9, fixed and dried. m e dried negative silver
image was bleached by laminating it to an activator web coated
on a polyethylene terephthalate support for 20 seconds at 90C.
The preparation contained the following compounds coated thereon
(per square meter~:
Thiourea 5.4 g
Distilled water 54 ml
Sulfonated polystyrene 10.8 ml
(18.3% solution ln water)
Polyacrylic acid (Acrysol10.8 ml
A-3 which is a trademark of
Rohm and Haas Co., U.S.A.)
(25% solution)
Hydrochloric acid 10.8 ml
Distilled water containing5.4 ml
6% saponin
A positive dye image was formed. However, the acid
was too volatile.
Example 3
A sample of photothermographic element was prepared
B by combining the following components and coating on a suitable
paper support: 29 - _ ~ _
18l~
A. A sulfur and gold sensitized cubic grained silver
bromide emulsion (0.43 gAg/m2).
B. l-phenyl-3-pyrazolidone (1.08 g/m2)
C. Dimethyldodecylammonium hydrogen malonate (3.24 g/m2)
D. a,a-bis[4-(3',6'-disulfo-8'-heptoylamino-1'-
naphthol-2'-yl) azo-2,5'-dimethylphenyl]toluene, tetrasodium
salt (0.21 g/m2)
E. Gelatin (6.75 g/m2)
F. 2,2'-methyl sulfonyl imino bis(ethyl isothiouronium
para-toluene sulfonate) (3.24 g/m2)
A sample was exposed with tungsten light through a
graduated density test object to provide a latent image which
was thermally developed as in Example 1 for 30 seconds at
150C. The element was then laminated with an activator
she~t comprising a polyester film support having coated thereon
a layer containing polyacrylic acid at 2.7 g/m2 and
p-toluenesulfonic acid at 5.4 g/m2. The complexing agent
was the isothiouronium salt in the emulsion layer. The
laminated structure was then heated to 100C and after
1 minute a well-defined positive magenta dye image was obtained.
Example 4
A sample of the photothermographic element described
in Example 3, but with a poly(ethylene terephthalate) film support,
was exposed through a graduated-density test object
and directly laminated with an acid activator sheet
comprising a polyester film support comprising (a) a first
layer containing titanium dioxide at 21.6 g/m2 and
gelatin at 2.16 g/m2 and overcoated with (b) a second
layer containing polyacrylic acid at 2.7 g/m2,
p-toluene sulfonic acid at 5.4 g/m2 and thiourea at
5.4 g/m . m e laminated structure was then thermally
- 30 -
1()301~
processed by contact for one minute with a metal block heatedto 150C. A reflectlon prlnt comprlslng a well-deflned,
posltlve magenta dye lmage resulted whlch lndlcated that sllver
development and bleachlng were carrled out ln a slngle heatlng
: step, presumably due to the volumlnous T102 layer acting as
a timing layer for the silver-dye bleach reaction.
Example 5
This example illustrates the use of a photothermo-
graphlc materlal, such as described in Evans and McLaen U.S.
Patent 3,801,321, to produce a dye image according to the practice
of thls lnventlon:
A sllver behenate/behenlc acld dlsperslon was pre-
pared by ball-mllllng the followlng components for 72 hours:
Sllver behenate 33.6 g
Behenlc acid 25.4 g
Poly(vinyl butyral)12.0 g
Acetone/toluene (1:1 by
volume) 675 ml
Photothermographic elements were then prepared by
comblning the followlng addenda and coating the compositlon at
o.oo6 lnch on a polyethylene terephthalate film support both
-with and wlthout a titanium dloxide reflectlve layer:
Sllver behenate dlsperslon
(as prepared above) 2.0 ml
Silver bromoiodide emulslon peptized
in poly(vinyl butyral)
(3.0 l/mole Ag, 100 g polymer/mole
Ag, 6 mole % iodlde) 2.0 ml
Poly(vlnyl butyral) (2-1/2 wt. %
of an acetone/toluene solution) 2.0 ml
Azo dye havlng the structure 40 mg
1(?5~0188
OH
~,CO~ tC~ > 4Q~C5Hl l-t
2~N~N~CH3
CH2CH2S02NH2
2,6-Dichloro-4-benzenesulfonamido- 60 mg
1,8-(3,~-Dioxaoctane)bis-iso-
thiuronium-p-toluene sulfonate 100 mg
Samples of the coatings were exposed through a
graduated-density test ob~ect and thermally developed for 30
: seconds at 150C. The developed samples, which contained a
negatlve silver lmage and a uniform distribution of dye, were
10 then laminated with an acid activator sheet prepared by
coating the following composition on a polyethylene
terephthalate film support at a wet thickness of 0.006 inch:
Polyacrylic acid (Acrysol A-3) 10 ml
(25 wt. % aqueous solution)
Thiourea 5 g
p-Toluene sulfonic acid 5 g
Ethanol/water (1:1 by volume to
: total volume of 81 ml
The laminated structures were heated to 120C for
30 seconds and well-defined, positive dye images were obtained.
Example 6
A photothermographic material was prepared by the
following steps:
(l) A silver thiazoline thione complex was prepared
by combining the following addenda and blending for 45 minutes
~t 48.9C:
1()90188
3-(2-carboxyethyl)benzo-
thiazoline-2-thione 14.8 g
Silver trifluoroacetate 5.25 g
Isopropyl alcohol 27 ml
Distilled water
(2) A developer toner solution was prepared as
follows:
` Methanol 30 ml
t-Butylhydroquinone 3 g
3-Mercapto-l-H-1,2-4-triazole 20 ml
Methanol to a total volume 35 ml
(3) A final coating composition was prepared by
combining the above-identi~ied mixtures in the following
proportlons:
S,ilve,r com~lex disper,sion 105 ml
~as aescrl~ed unde~ ~1) above)
Developer-toner mixture 35 ml
Solution containing 10~ by weight 1 ml
saponin
Gelatin peptized silver iodide
emulsion 6 ml
Azo dye 380 ml
' The final composition was coated at 0.94 milliliters
per square decimeter on a polyethylene coated paper support. The
photothermographic material was exposed imagewise for 4
seconds and then thermally developed by contact for 15
seconds with a metal block heated to 140C. A negative
silver image and a uniform distribution of magenta dye was
observed. The sample was then laminated in contact with a
sample of an activator sheet and heated to 70C for 60
seconds. The activator sheet consisted of a polyethylene
terephthalate film support having coated thereon a layer
comprising 10.8 grams per square meter thiourea,
5.4 grams per square meter ethylene glycol~ 1.9 grams
lQ5~0188
per square meter sulfonated polystyrene, and 0.001 llter
per square meter sulfuric acld.
After heating, the elements were left lamlnated
and a well-defined positive magenta dye image was observed.
The invention has been described in detail with
particular reference to preferred embodiments thereof, but
it will be understood that variations and modifications can
be effected within the spirit and scope of the inventlon.
- 34 -
