Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~04587ti
Background of the Invention
Field of the Invention
This invention relates to certain photolytically
active polybrominated stabilizer precursors and photothermographic
elements, compositions and processes using said precursors to
provide improved stable images. In one of its aspects it
relates to a photothermographic element comprising (a)
photographic silver halide in association with (b) an oxidation-
reduction image-forming combination comprising (i) a heavy metal
10 salt oxidizing agent with (ii) an organic reducing agent,
(c) a polymeric binder and (d) a photolytically active
polybrominated organic compound stabilizer precursor as described.
In another of its aspects it relates to a photothermographic
composition comprising photographic silver halide, a polymeric
binder and a photolyticall~r active polybrominated organic
compound stabilizer precursor as described. A further aspect
relates to such photographic compositions which are photothermo-
graphic materials. A further aspect relates to a method of
developing a stable image in a photothermographic element com-
20 prising the described photographic silver halide in associationwith the oxidation-reduction image-forming combination and
the described stabilizer precursors.
Description of the State of the Art
It is known to obtain an image in a photosensitive
element by so-called dry processing with heat. The photo-
thermographic element employed for providing such an image can
contain a reducing agent, a light-insensitive silver salt of an
organic acid, such as silver behenate, as an oxidizing agent
and a low concentration of photographic silver halide. Such
30 photothermographic materials are described, for example, in
U.S. Patent 3,457,075 of Morgan et al, issued July 22, 1969,
U.S. Patent 3,152,904 of Sorensen et al, issued October 13, 1964,
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1~4587~;
British Speci~ication 1,161,777 published August 20, 1969;
U.S. Patent 3,392,020 of Yutzy et al, issued July 9, 1968;
U S Patent 3,707,377 of Tiers et al, issued December 26, 1972
and in Research Disclosure, January, 1973, pages 16-21.
In a photothermographic material one of the main
difficulties involves post-processing stability. Because
heat developable photographic elements are suitable for
so-called dry processing with heat and are designed to
eliminate a fixing step which normally would remove undeveloped
10 silver, it is necessary that a means be provided for post-
processing stabilization to enable room-light handling.
Several means have been proposed to answer the
need for post-processing stability of photothermographic
elements. These include, for example, (1) washing the
element with water to remove undeveloped silver salts, (2)
heating the element to release Bronstead or Lewis acid such as
HCl, borontrifluoride or HF from compounds such as m-nitrobenzene-
sulfonyl chloride, para-toluenesulfonic acid urea addition
complex or ;E~-acetamidobenzenediazonium fluoroborate and (3)
20 chelation of the oxidizing agent with, for example,
salicylaldoxime or benzotriazole as described in U.S. Patent
3~152,904 of Sorensen et al, issued October 13, 1964. Another
method proposed for solving the problem of post~processing
instability is to provide a photothermographic combination in
which the oxidation-reduction image-forming combination is on
one sheet of material and the latent image-forming photographic
silver halide on a separate sheet. The sheets are separated
after imagewise exposure such as described in U.S. Patent 3,152,904.
A further means proposed for stabilization involves swabbing
30 a 1~ solution of phenylmercaptotetrazole onto the surface of
the overall heated photothermographic material or rubbing
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1~4587~;
benzotriazole into the surface of the photothermographic element.
These proposed means for stabilization are not useful for
large volume handling of heat developable photographic materials.
It has also been proposed to provide stabilized
images in heat developable, photographic materials by treating
the developed image with a solution containing certain thiol
or thione compound stabilizers. This is described, for example,
in U.S. Patent 3,617,289 of Ohkubo et al, issued November 2, 1971.
One of the compounds proposed for this solution stabilization
10 is 1-phenyl-5-mercaptotetrazole. Unfortunately, the addition
of this compound to unexposed photographic silver halide
compositions provides undesired desensitization at concentrations
which produce stabilization and toning of a developed image.
Another means of stabilization of an image in a
photothermographic material is described in Belgian Patent 768,071
published July 30, 1971. Certain stabilizer precursors which
. are azole thioethers or blocked azoline thiones are employed
in photothermographic materials according to the description
in this reference. An example of a stabi}izer precursor
20 proposed in photothermographic materials is 5-methoxycarbonyl-
thio-l-phenyltetrazole. Unfortunately, this compound does not
always provide the desired increased stability in the developed
image.
Another means for post-processing stabilization of
certain photothermographic materials is described in U.S.
Patent 3,707,377 of Tiers et al, issued December 26, 1972.
Certain polyhalogenated organic oxidizing agents such as
tetrabromobutane and tribromoquinaldine are described in
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1045876
certain heat developable photographic materials to provide
post-processing stabilization. Unfortunately, tetrabromobutane
and tribromoquinaldine do not provide the desired stabilization
in certain photothermographic materials. For instance, photo-
thermographic elements containing tribromoquinaldine cannot be
expected to be processable above about 50C without undesired
decomposition of the tribromoquinaldine. As illustrated in
the following comparative examples, the photolytically active
polybrominated organic compound stabilizer precursors
according to the invention provide surprisingly improved
stabilization without significantly adversely affecting maximum
density and without undesired decomposition.
Halogenated organic compounds have been employed
in photographic materials for various purposes, such as
.. .... .
antifoggants. Halogenated organic antifoggants for photographic
emulsions are described, for example, in U.S. Patent 3,128,187
of Segal et al, issued April 7, 1964; U.S. Patent 3,232,762
of Ford et al, issued February 1, 1966; u.s. Patent 2,732,303
of Morgan et al, issued January 24, 1956; U.S. Patent 2,835,581
20 of Tinker et al, issued May 20, 1958 and U.S. Patent 3,271,154
of Dersch, issued September 6, 1966. None of these patents,
however, indicate that the photolytically active polybrominated
organic compound stabilizer precursors according to the invention
can be employed in photothermographic materials to provide
- improved post-processing stability.
Photographic materials which do not contain photographic
silver halide and comprising tribromomethylsulfonyl derivatives
of certain heterocyclic compounds such as benzothiazole compounds
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1~4S876
and benzimidazole compounds are described in Canadian Patent
831,465 issued January 6, 1970. ~his patent, however, does not
described photothermographic materials containing photographic
silver halide.
There has been a continuing need for photothermographic
materials comprising an image-forming combination containing
photographic silver halide which have improved post-processing
image stability, tha-t is reduced background density and no
significant decrease in desired maximum density when employing
a halogen-containing stabilizer precursor.
Summary of the Invention
It has been found according to the invention that
the described improvements are provided in a photothermographic
element or composition as described by employing as a bromine
containing organic stabilizer precursor a polybromo compound
represented by the formula:
R
or R3 - S02 - C - Br
Br3C N CBr3 R2
wherein
R is alkyl containing 1 to 6 carbon atoms,
Rl is hydrogen or a bromine atom,
R is a bromine atom or a carbamoyl group, and
R3 is an aromatic chromophore group which has the
property of imparting to said bromine compound
stabili~er precursor the ability to absorb electro-
magnetic radiation having a wavelength between about
250 and 385 nm, and at least one of Rl, R2 and R3 is
or contains a bromine atom.
The described improvements are provided, for example,
in a photothermographic element comprising a support having
thereon a layer comprising (a) photographic silver halide in
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association with (b) an oxidation-reduction image-~orming
combination comprising (i) a heavy metal salt oxidizing agent,
pre~erably a silver salt oxidizing agent, with (ii) an organic
reducing agent, (c) a polymeric binder for the layer and (d)
a bromine compound stabilizer precur~or as described.
; A latent image in the described photothermographic ~ -
element or composition can be developed by overall heating
; the element or composition to moderatel~ elevated temperatures.
Detailed Description of the Invention
A variety of bromine compound stabilizer precursors,
- ~ as described within the above formulas, can be employed
according to the invention to provide improved post-processing
stability without significantly adversely affecting desired
properties of the photothermographic material.
Different tests can be emplo~ed to determine whether
compounds or materials are useful as stabilizer precursors
as described depending upon the particular photothermographic
element, composition, desired image, processing conditions
and the like. One test which can be employed for certain
photothermographic elements is as follows:
A silver behenate-behenic acid dispersion (A) is
; prepared by ball-milling the following components for 72 hours:
silver behenate 168.0 g
behenic acid 64.o g
poly(vinyl but~ral) 120.0 g
lithium stearate 16.4 g
acetone-toluene (1:1 parts by volume) 2.0 1
A photothermographic element is prepared by combining
141 ml of the described dispersion (A) with the following ~ -
; 30 addenda, mixing thoroughly and coating at o.63 g of composition ~ ~ ~-
per square decimeter on a suitable paper support:
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1~45876
acetone solution containing 0.01~ 18.0 ml
by weight 3-ethyl-5~(3-ethyl-2-
benzothiazolinylidene)-l-methyl-
ethylidene]-2-thio-2,4-oxazolidinedione
acetone solution containing 10% by 24.o ml
weight 2,6-dichloro-4-benzenesul~on-
amidophenol
poly(vinyl butyral)-silver 22.0 ml
bromoiodide emulsion (6 l./mole Ag.,
6 mole ~ I, 100 g. polymer/mole Ag)
acetone-toluene (1:1 by volume) 4~.0 ml
organic solvent solution, typically 11.0 ml
acetone, containing polybromo stabilizer
precursor according to the invention
(typically organic solvent solution
containing about 3~ by weight of
stabilizer precursor according to
the invention)
.. . ... .
The resulting photothermographic element is permitted to dry.
20 It is then imagewise exposed to tungsten light for 1 second.
and then overall heated by contacting the exposed photothermo-
graphic element for about 2 to 4 seconds with a metal block
heated to 150C. Preferred stabilizer precursors according
to the invention should prevent buildup of background density
or minimum density above 0.10 density unit more than the
original minimum density of a developed image without
significantly adversely affecting maximum density~
It is believed that the described brominated organic
compounds according to the invention are precursors to the
moiety which upon combination with silver ions or atoms
prevents instability due to roomlight exposure. The exact
mechanism of stabilization is not fully understood. It is
believed, however, that upon imagewise exposure of a photo-
thermographic material containing photographic silver halide
to-actinic radiation, latent image spe~s of metallic silver
are formed in the photographic silver halide remaining in the
background areas of the photothermographic element to produce
unwanted background printup, especially after subsequent
overall heating. It is believed that the bromine from the
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described stabilizer precursors of the invention is at least
in part released photolytically and attacks and destroys
the latent image metallic silver sites before they produce
printup, that is before background fog is produced, without
attacking the developed silver image to any significant
degree. It is believed that the photolytically released
bromine comprises free radicals which reoxidize the latent
image silver atoms in the photographic silver halide to
silver ions.
An advantage of the bromine containing stabilizer
precursors according to the invention is that they have
sufficient thermal stability for use in the described photo-
thermographic materials. This is illustrated in the
following comparative examples.
One useful class of stabilizer precursors according
to the invention within the described formulas comprises a
compound wherein described Rl and R2 are each bromine atoms
and R3 is phenyl, naphthyl or benzothiazole.
The term "aromatic chromophore group'r as employed
herein is intended to mean a group which imparts to the bromine
compound stabilizer precursor containing the group the ability
to release at least one bromine atom when exposed to electro-
magnetic radiation having a wavelength between about 250 and
385 nm. A variety of aromatic chromophore groups can provide j~
this desired property. Especially useful aromatic chromophore r ~:
groups include phenyl, naphthyl or benzothiazole. These gro~ups
can contain substituent groups which do not adversely affect
the stabilizing action of the stabilizer precursors according
to the invention, such as methyl, ethyl and the like.
The term "polybromo" or "polybrominated" compound as
employed herein is intended to mean a compound as described
containing two or more bromine atoms.
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1~J4S876
Useful stabilizer precursors as described include,
for example, the following compounds: --
2-tribromomethylsulfonylbenzothiazole
2,4-bis(tribromometh~ 6-methyltriazine
2,2-di~romo-2-phenylsulfonylacetamide
The described polybrominated organic compounds can
be prepared by methods known in the art. For example, the
parent organic compound can be brominated employing conventional
bromination processes. An example preparation is the preparation
of 2-tribromomethylsul~onylbenzothiazole which comprises adding
dropwise at 5 to 10C. 150 milliliters of bromine to a stirred
solution o~ 240 grams of sodium hydroxide in 2.5 liters of water.
Upon completion o~ the addition, a solution of 110 grams o~ 2-
carboxymethylmercaptobenzothiazole and 50 grams of sodium
bicarbonate in 1.25 liters o~ water is added dropwise. Stirring
is continued ~or 3 hours and the resulting white mixture is
allowed to stand overnight at room temperature. The resulting
white solid can be collected by filtration and recrystallized
from acetic acid to provide the desired 2-tribromomethylsulfonyl-
benzotriazole having a melting point of 168-170C.
Another example of a useful preparation is the
preparation o~ 2,4-bis(tribromomethyl)-6-methyltriazine in
which a mixture o~ 140 grams of 2,4,6-trimethyltriazine and 520
grams of sodium acetate dispersed in 2,300 milliliters of acetic
acid is heated to 70C. while adding 520 milliliters o~ bromine ;~
slowly with stirring over a 2-hour period. me temperature is
raised to 90C. for one hour and the mixture is allowed to stand
about 16 hours. After standing, 2 liters of water is added and
the so~id mixture resulting is collected by-filtration and
30 recrystallized ~rom acetonitrile. The desired 2,4-bis(tribromo- ;~;
methyl)-6-methyltriazine has a melting point of 153-155C. ~-
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Some halogenated organic compound impurities can be
present in the resulting compositions. These impurities can be
separated, i~ desired, before mixing the desired brominated
compound stabilizer precursor with the described photothermo-
graphic materials.
Ihe described ~olybrominated stabilize~ precursors
according to the invention are use~ul in a variety o~ silver
halide photothermographic materials.
The useful concentration o~ stabilizer precursor
according to the invention will depend upon different factors
such as the particular photothermographic element,
particular components of the photothermographic material,
desired image, desired image stability and the like. A use~ul
concentration o~ stabilizer precursor according to the invention
is about 0.002 mole to about 0.75 mole of the described stabilizer
precursor per mole of total silver in the photothermographic
material. An especially use~ul concentration is about 0.01
; mole to about 0.5 mole o~ the described stabilizer precursor
per mole o~ total silver in the photothermographic material.
When combinations of stabilizer precursors are employed according
to the invention, the total concentration o~ stabilizer precursors
is within the described concentration range. The optimum
concentration useful can be determined based on the described `~
~actors.
Typical photothermographic materials in which the
stabilizer precursors of the invention are use~ul are described,
for example, in U.S. Patent 3,457,075 of Morgan et al, issued `
July 22, 1969; u.s. Patent 3,152,904 of Sorensen et al, issued
October 13, 1964; u.s. Patent 3,429,706 of Shepard et al, issued
February 25, 1969; u.s. Patent 3,672,904 of deMauriac, issued ~-
June 27, 1972 and Research Disclosure, January, 1973, pages 16-21.- -,
The stabilizer precursors o~ the invention are especially useful
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1~458716
in photothermographic materials comprising (a) photographic
silver halide in association with (b) an oxidation-reduction
image-forming combination comprising (i) a silver salt of a
long-chain fatty acid, such as silver behenate, with (ii) a
phenolic reducing agent, (c) a pol~(vinyl butyral) binder,
(d) a toner, also known as an activator-toning agent
or known as a toner-accelerator, comprising l-(2H)-
phthalazinone, succinimide or N-hydroxy-1,8-naphthalimide,
and (e) a spectral sensitizing dye.
An especially use~ul embodiment of the invention is
a photothermographic element comprising a support having thereon
a layer comprising (a) photographic silver halide in association
with (b) an oxidation-reduction image-forming combination
comprising (i) silver behenate, with (ii) a sulfonamidophenol
reducing agent, (c) a poly(vinyl butyral) binder for the layer,
(d) a toner comprising 1-(2H)-phthalazinone, succinimide or
N-hydroxy-1,8-naphthalimide, and (e~ a stabilizing concentration
of 2-tribromomethylsulfonylbenzothiazole, 2,4-bis(tribromomethyl)-
6-methyltriazine or 2,2-dibromo-2-phenylsulfonylacetamide.
me described photothermographic materials according
to the invention comprise a photosensitive component which is
photographic silver halide. In the photothermographic materials
it is believed that the latent image silver resulting from the
photosensitive salt acts as a catalyst for the described oxidation- ;
reduction image-forming combination. A typical concentration
range of photographic silver halide is from about 0.01 mole to
about 20.0 moles of photographic silver halide per mole of
silver salt oxidizing agent, for example, per mole of silver
behenate. Other photosensitive silver salts can be used in
combination with the photographic silver halide if desired.
Useful photosensitive silver salts include silver-dye complexes.
Preferred photographic silver halides are silver chloride,
silver bromide, silver bromoiodide, silver chlorobromoiodide
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1C~45876
or mixtures thereof. Very fine-grain photographic silver
halide is especially use~ul although coarse or ~ine-grain
photosensitive sllver halide can be employed ii desired. The
photographic silver halide can be prepared by any of the
procedures known in the photographic art. Such procedures
and iorms of photosensitive silver halide are described,
for example, in the Product Licensing Index, Volume 92,
Decembe~, 1971, publication 9232 on page 107, paragraph I.
The photographic silver halide according to the invention can
be unwashed or washed, can be chemically sensitized, can be
protected against the production of fog and stabilized against --
loss of sensitivity during keeping, as described in the
above Product Licensing Index publication
The photothermographic elements and compositions
: .
according to the invention comprise an oxidation-reduction
image-forming combination which contains a heavy metal salt
oxidizing agent, prererably a silver salt oxidizing
agent, especially a silver salt oi a long-chain iatty acid.
Such silver salt oxidizing agents are resistant to darkening upon
illumination. Typically useful silver salts oi long-chain
fatty acids are those containing about 17 to 30 carbon atoms.
Compounds which are useiul silver salt oxidizing agents include: -
silver behenate, silver stearate, silver oleate, silver laurate,
silver hydroxystearate, silver caprate, silver myristate and silver
palmitate. Silver salts which are not silver salts of long-chain
iatty acids can be employed in combination with the silver
sa~ts oi lon~-chain iatty acids. Such silver salt oxidizing
agents which are ~seiul include, for example, silver benzoate,
silver ~enzotriazole, silver terephthalate, silver phthalate and -~
the like. Examples of other heavy metal salt oxidizing agents are~
gold stearate, mercury behenate and gold behenate. Combinations
oi oxidizing agents are also use~ul.
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1~45876
~ he described photothermographic elements and com-
positions can comprise various organic reducing a~ents.
Use~ul reducing agents which can be employed with the described
stabilizer precursors include substituted phenols and naphthols,
~or example, bis-beta naphthols. ~uitable bis-beta-naphthols
include, for example, 2,2'-dihydroxy-1,1'-binaphthyl, 6,6'-
dibromo-2,2'-dihydroxy-1,1'-binaphthyl or 6,6'-dinitro-2,2'-
dihydroxy-l,l'-binaphthyl. Other reducing agents which can be
employed in photothermographic elements, according to the
invention, include polyhydroxybenzenes such as hydroquinone,
alkyl-substituted hydroquinones such as tertiary butyl-
hydroquinone, methylhydroquinone, 2,5-dimethylhydroquinone ~ -
and 2,6-dimethylhydroquinone; catechols and pyrogallols,
chloro-substituted hydroquinones such as chlorohydroquinone
or dichlorohydroquinone, alkoxy-substituted hydroquinone
such as methoxyhydroquinone or ethoxyhydroquinone; aminophenol
reducing agents, such as 2,4-diaminophenols and methylamino~
phenols; ascorbic acid reducing agents such as ascorbic acid,
ascorbic acid ketals and ascorbic acid derivatives, hydroxylamine
reducing agents; 3-pyrazolidone reducing agents such as l-phenyl-
3-pyrazolidone and 4-methyl-4-hydroxymethyl-1-phenyl-3-
pyrazolidone and the like. Combinations of reducing agents can
be employed i~ desired.
Especially use~ul reducing agents which can be
employed in the photothermographic materials according to the
invention are sulfonamidophenol reducing agents as described in
Research Disclosure, January, 1973, pages 16-21. One especially
ùse~ul class o~ sulfonamidophenol reducing agents is represented ~- -
by the ~ormula: R5 ~ 4
NHS02-R6 '
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:
,
1~4S876
wherein R is phenyl, naphth~l, methylphenyl, thienyl, q~linolinyl,
thiazyl, or alk~l containing 1 to 4 carbon atoms, such as methyl,
- ethyl, propyl or butyl; R is hydrogen, R S02NH-, alkoxy - -
containing 1 to 4 carbon atoms, such as methoxy, ethoxy, propoxy
and butoxy, bromine or chlorine, R5 is hydrogen, bromine,
chlorine, alkyl containing 1 to 4 carbon atoms, as described,
or alkoxy containing 1 to 4 carbon atoms, such as methoxy,
ethoxy and propoxy. R4, R5 and/or R6 can contain substituent
groups which do not adversely a~ect the reducing properties
of the described sulfonamidophenol reducing agents or the
desired sensitometric properties of the photothermographic
elements and materials of the invention. Examples of substituent l-
~
groups which can be present are alkyl containing 1 to 3 carbon !:
atoms such as methyl, ethyl and propyl, chlorine, bromine and
phenyl. In some cases, it is desirable to avoid an amino
group as a substituent. The amino group, in some cases, provides
an overly active reducing agent.
It is desirable, in some cases, to employ a so-called
toning agent, also known as an activator-toning agent or a
toner-accelerator, in the photothermographic materials o~ the
invention. Useful toning agents are described, for example, in
Belgian Patent 766,5~o issued June 15, 1971 and in Research
Disclosure, January, 1973, pages 16-21. Combinations of toning
agents can be employed in the photothermographic materials
according to the invention if desired. Typical toning agents
; include, for example, phthalimide, N-hydroxyphthalimide,
N-potassium phthalimide, succinimide, N-hydroxy-1,8-naphthalimide
and N-hydroxysuccinimide. In some cases other toning agents can
be employed such as 1-(2H)-phthalazinone, 2-acetylphthalazinone
and the like.
It is desirable, in some cases, to employ a combination ~
of stabilizer precursors in the photothermographic materials of -
the invention.
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l~S876
In addition to combinations of stabilizers within the
described ~ormula according to the invention, other image
stabilizers or stabilizer precursors can in some cases be
employed with the stabilizer precursors of the invention.
Typical stabilizer precursors which can be employed in com-
bination with the stabilizer precursors of the invention
include, for example, azole thioethers and blocked azoline
thione stabilizer precursors as described in Belgian Patent
768,071 issued July 30, 1971.
A photothermographic element or composition as
described according to the invention can contain various colloids
and polymers alone or in combination as vehicles, binding agents
and in various layers. Suitable materials can be hydrophobic
or hydrophilic. They are transparent or translucent and include
both naturally-occurring substances such as proteins, for
example, gelatin, gelatin derivatives, cellulose derivatives,
polysaccharides such as dextran, gum arabic and the like; and
synthetic polymeric substances such as water soluble polyvinyl
compounds like poly(vinyl pyrrolidone), acrylamide polymers and
the like. 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 photographic materials. Effective polymers include water-
insoluble polymers of alkyl acrylates and methacrylates, ~ ;
acrylic acid, sulfoalkyl acrylates, methacrylates and those
which have crosslinking sites which facilitate hardening or
curing as well as those having recurring sulfobetaine units ;
as described in Canadian ~atent 774,054. Especially useful high
molecular weight materials and resins include poly(vinyl
butyral), cellulose acetate butyrate, poly(methyl methacrylate),poly(vinyl pyrrolidone), ethylcellulose, polystyrene, poly(vinyl
chloride), chlorinated rubber, polyisobutylene, -;
- 16 _
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104~76
butadiene-styrene copolymers, vinyl chloride-vinyl acetate
copolymers, copolymers of vinyl acetate, vinyl chloride
and maleic acid and poly(vinyl alcohol). - -- --
The useful concentration of reducing agent accordingto the invention will vary depending upon the particular
photothermographic element, desired image, processing
conditions, particular stabilizer precursor employed and
the like. A useful concentration of reducing agent is typically
from about 0. 2 mole to about 2.0 moles of reducing agent per
mole of photographic silver halide. A useful concentration
of reducing agent in relationship -to oxidizing-agent, such as
silver behenate or silver stearate, is typically from about
0.01 mole to about 20 moles of reducing agent per molé of
silver salt of a long-chain fatty acid, such as per mole of
silver behenate, in the photothermographic material. Reducing
agents can be employed in combination. ~hen combinations
are employed, the total concentration of reducing agent is
typically within the described concentration range.
Photothermographic materials according to the invention
20 can contain development modifiers that function as speed-
increasing compounds, hardeners, antistatic layers, plasticizers
and lubricants, coating aids, brighteners, spectral sensitizing
dyes, absorbing and filter dyes, also as described in the
Product Licensing Index, Volume 92, December, 1971, publication
9232, pages 107-lI0. :
me photothermographic elements according to the
invention can comprise a wide variety of supports. Typical
supports include cellulose nitrate film, cellulose ester film,
poly(vinyl acetal) ~ilm, polystyrene film, poly(ethylene
3 terephthalate) film, polycarbonate film, film supports as -~
described in U.S. Patent 3,634,o89 of Hamb, issued January 11, - -
: 1972 and U.S. Patent 3,725,070 of Hamb et al, issued April 3, :-:
1973 and related films or resinous materials, as well as glass,
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1~45876
paper, metal and the like supports which can withstand the
processing temperatures employed according to the invention.
Typically a flexible support is employed.
The photothermographic compositions and other
compositions according to the invention can be coated on a
suitable support by various coating procedures including dip
coating, air knife coating, curtain coating or extrusion
coating using hoppers such as described in U.S. Patent 2,681,294
of Beguin issued June 15, 1954. I~ desired, two or more layers
can be coated simultaneously such as described in U.S. Patent
2,761,791 of Russell, issued September 4, 1956 and British
Patent 837,og5.
Spectral sensitizing dyes can be used in the described
photothermographic elements and compositions of the invention
to confer additional sensitivity to the elements and compositions
of the invention. Usefiul sensitizing dyes are described, for
example, in the Product Licensing Index, Volume 92, December,
1971, publication 9232, pages 107-110, paragraph XV.
After imagewise exposure of a photothermographic
element according to the invention, typically a visibIe light, -~
the resulting latent image can be developed merely by overall
heating the element to moderately elevated temperatures.
This overall heating merely involves heating the described
element overall to a temperature within the range of from
about 80C. to about250C. such as for about 0.5 to about
60 seconds. By increasing or decreasing the length of time
of heating, a higher or lower temperature within the described ~-
range can be employed depending upon the desired image,
particular reducing agent, and the like. Typically, a lower
processing temperature is desired. A preferred processing
temperature range is from about 115C. to about 175C. A
developed and stabilized image is typically produced within
- 18 -
~)45876
several seconds, such as from about o.5 seconds to about
60 seconds.
Any suitable means can be used for providing the
desired processing temperature range. The heating means can
- be a simple hot plate, iron, roller or the like.
Processing is usually carried out under ambient
conditions of pressure and humidity. Conditions outside `
normal atmospheric pressure and humidity can be employed if
desired.
The described stabilizer precursor according to the
invention can be in any suitable location in the photothermo-
graphic material according to the invention which provides the
desired stabilized image. If desired, one or more of the `
~ .
components of the photothermographic element according to
- the invention can be in one or more layers of the element.
For example, in some cases, it can be desirable to include
certain percentages of the reducing agent, toner, image
stabilizer precursor and/or other addenda in a protective layer
over the photothermographic element. This in some cases can
20 reduce migration of certain addenda in the layers of the
photothermographic element.
The described stabilizer precursors according to the
invention can be used in, for example, photothermographic
materials comprising photographic silver halide as described
in U.S. Patent 3,679,426 of Youngquist, issued July 25, 1972;
U.S. Patent 3,667,958 of Evans, issued June 6, 1972; U.S.
Patent 3,667,959 of Bo~ara and deMauriac, issued June 6, 1972;
Belgian Patent 766,590 issued June 15, 1971; U.S. Patent
- 3,672,904 of deMauriac, issued June 27, 1972; Belgian
: 3 Patent 772,371 issued October 15, 1971 and Research Disclosure,
January 1973, Item 10513, pages 16-21.
..
- 19 _ ..
1~4S876
A variety of methods of incorporating a stabilizer
precursor according to the invention into photothermographic
materials as described can be employed. A typical method of
preparing a photothermographic material according to the
invention is described in U.S. Patent 3,839,o49 issued
October 1, 1974. The described stabilizer precursor can be
incorporated in the described photothermographic materials
at various stages in preparation.
The following examples are included for a further
10 understanding of the invention.
Example
This is a comparative example.
A silver behenate-behenic acid dispersion A is - ~
prepared by ball-milling the following components for 72 hours: -
silver behenate 168.0 g
behenic acid 64.o g
~- poly(vinyl butyral) 120.0 g
lithium stearate 16.4 g
acetone-toluene (1:1 parts by volume) 2.0 1.
A photothermographic element is prepared by combining
141 ml. of the above-described dispersion (A) with the
following addenda, mixing thoroughly and coating at 0.63 g of
composition/dm2 on a suitable paper support:
Acetone solution containing 0.01%18.0 ml
by weight 3-ethyl-5-[(3-ethyl-2-
benzothiazolinylidene)-l-methyl-
ethylidene]-2-thio-2,4-oxazolidinedione - -
Acetone solution containing 10% by 24.0 ml
weight 2,6-dichloro-4-benzenesulfon-
amidophenol
Poly(vinyl butyral)-silver bromoiodide 22.0 ml
emulsion, (6 l./mole Ag, 6 mole % I, ; -
100 g polymer/mole Ag) -~
Acetone-toluene (1:1 by volume) 44.0 ml
- 20
1~145876
The following composition is coated over the element
at a coverage o~ 0.43 g/dm , thereby providing a protective
layer containing approximately 10.76 mg cellulose acetate/dm2
o~ support.
cellulose acetate 5,0 g
acetone-dichloromethane (1:1 parts by volume) 200.0 ml
The resulting photothermographic element is imagewise
exposed for 1 second to tungsten light and then overall heated
by contacting the photothermographic element ~or 2 seconds
on a metal block heated to 150C. The sensitometric results
for the resulting developed image are given in following
Table I. The processed element is then subjected to 1500 ~t.
candles of light for 72 hours. The sensitometric data resulting
~rom this stability test are also given in following Table I.
,,
Example 2
e procedure described in Example 1 is repeated with
the exception that the described composition contained 11 milliliters
, of an acetone solution containing 3~ by weight of 2-tribromo-
methylsul~onylbenzothiazole, and, the acetone-toluene solvent
mixture was reduced to 33 milliliters.
e resulting photothermographic element was imagewise
exposed and then overall heated as described in Example 1.
It was then exposed to 1500 ~t. candles of light ~or 72 hours
also as described in Example 1. me resulting sensitometric
data are given in following Table I.
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1~45876
' Example 3
A silver behenate dispersion is prepared by ball- -
milling the ~ollowing components ~or 100 hours:
silver behenate 50.0 g
poly(vinyl butyral) 15.0 g
methyl isobutyl ketone 500 ml
A photothermographic element is prepared by
combining the following addenda in the order indicated,
mixing thoroughly and coating the resulting composition on
an unsubbed poly(ethylene terephthalate) film support at
0.74 milliliters per square decimeter:
poly(vinyl butyral)-silver bromide 200.0 ml
' emulsion (6 liters of emulsion
per mole of silver~ 100 g. of
,~.; ' polymer per mole of silver)
b' acetone solution containing o.66 60.0 ml
milligrams of 2-(5,5-dicyano-
' ' 4-phenyl-2,4-pentadienylidene)-
: 1-ethylnaphtho[1,2-d]-thiazoline
~old one hour at room temperature)
. ~ . ' ' '
;, silver behenate dispersion as 500.0 ml~ -' described above
. . ~
acetone solution containing 50.0 ml
10% by weight succinimide thold
one hour at room temperature)
acëtone'~~so'lut'ion'~containing~ ~' . 180.0 ml
14% by weight poly(vinyl butyral)
acetone solution containing ' 180.0 ml '
6.3~ by weight 4-benzenesulfon-
amidophenol
acetone solution containing 50.0 ml :~
5% by weight 2,4-dihydroxy-
benzophenone
acetone-toluene solution 3000 ml
(1:1 by volume~ containing
2% by volume silicone
surfactant (Silicone AF-70
which is a trade name of
the General Electric Co.,
U.S.A.)
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acetone solution containing 20.0 ml
2.28~ by weight anhydrous
lithium iodide (hold one hour
at room temperature)
The resulting photothermographic element is also
overcoated with the following composition at 0.25 milliliters
- per square decimeter:
poly[4,4'-(hexahydro-4,7-methano- 5.0 g
indan-5-ylidene)diphenylene carbonate]
dichloroethane 95.0 ml
acetone 4.0 ml
silicone surfactant (L-522 which0.5 ml
is a trade name of and sold by
the Union Carbide Co., U.S.A.)
After drying, the photothermographic element is -
separated into several equal parts. One part is maintained
as a control and the remaining parts are dipped quickly into
a solution of 30 grams per liter of tribromoquinaldine,
referred to herein as TBQ, in 2-butanone and air dried.
Control and comparative examples of the described photothermo-
graphic element are also prepared in the same manner by dipping
film strips into the solvents alone or into a solution of
2~tribromomethylsulfonylbenzothiazole, also referred to herein
as TSB, respectively. Each film sample is exposed imagewise for
5 minutes to red light from the zero order light of a calibrated
monochromator when protected with a filter combination that
permits only radiation of wavelengths longer than 590 nanometers
to pass. me respective samples are then overall heated as
indicated in the following Table II employing the listed time -
30 and temperature conditions. In Table II the term "con" is used ~;
to identify untreated f~lm samples used as controls and the
term "S-C" is used to identify solvent treated control
samples.
- 24 -
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1~45876
The described polylerominated organic compounds
according to the invention are useful in the photothermo~
graphic element.according to Example 3 as an incubation anti-
foggant, An incubation antifoggant is intended to mean a
compound according to the invention which increases stability
in the photothsr oerQphic rstsrial prlor to imagswise sxposurs.
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5~76
The data in Table II indicates that the TBQ
treated coatings do not provide useful images with the
described element, processing time and temperature listed.
It is believed that the undesired results with TBQ are
due at least in part to undesired decomposition of TBQ
at temperatures above 50C. This is demonstrated in
the following examples. Photolytic ef~iciency o~
stabilizer precursors according to the invention can also
be tested employing the procedure in the ~ollowing examples~ -
Example
The thermal stability of proposed stabilizer precursors
can be determined by dissolving about 5 milligrams o~ the
proposed stabilizer precursor and about 5 milligrams o~
cadmium iodide in 5 milliliters of 2-butanone and immersing
the sample in a thermostaticall~ controlled water bath
while raising the temperature o~ the water bath slowly ~rom
room temperature to 75C. over a period o~ 6 hours of continuous
observation. The temperature at which each sample produces
color is recorded. Those proposed stabilizer precursors
which provide a color below about 60C. are considered
insu~ficiently stable for purposes of the invention. The
results are recorded in the ~ollowing Table III.
The proposed stabilizer precursors can also be
qualitively evaluated for relative photolytic efficiency by
preparing solutions in the manner described for the thermal
stability test in Example 4. The solution is exposed to
actinic light from an unfiltered xenon arc lamp ~or 5 seconds
at a distance o~ 10 centimeters. The density of the color
produced in the solution is observed and an arbitrary reading
of the density qualitatively is given to each solution o~
_ 27 _
1~458'^~6
excellent, good, ~air or poor. The relative photolytic
efficiency ratings are given in the following Table III.
The following compounds are tested:
Compound A - 2-tribromomethylsulfonylbenzothiazole
(TSB)
: Compound B - l-methyl-2-(2-hydroxy-3,3-tri-
chloropropyl)quinolinium ~-
toluenesulfonate
Compound C - 2,4-bis(tribromomethyl)-6-methyl-
s-triazine (re~erred to herein
as BMT)
Compound D - bis(tribromomethyl)sulfoxide
Compound E - bis(tribromomethyl)sulfone
. . Compound F - a(lph)a,alpha,alpha-tribromoquinaldine -
Table III
Decomposition Photolytic
; CompoundTemperature (C) Efriciency : :
. A ' Above 75 Good
- 20 B 50 Poor ~.
C Above 75 Excellent
D . 73 Excellent
. E 60 Excellent
F 50 Good
; m e tests reported in the above table indicate that
compounds A and C are especially useful because their :
decomposition temperature is above 75C.
Example 5
.
me procedure described in Example 2 is repeated
30 with the exception that the compound 2,4-bis(tribromomethyl)- -
6-methyl-s-triazine (BMT) is employed in place of 2-
tribromomethylsul~onylbenzothiazole (TSB). Results.similar
to those in Example 2 are obtained. ~ :
.
~ - 28 _
1~4S876
Examp1e 6
Five strips of a photothermographic paper, i.e.
3M Compan~ Dry Silver Paper Type 7743, which is a trade name
of 3M Company, U.S.A., are treated as follows:
- Sample No.
1 Untreated Original (Control 1)
2 Solvent treated (Control 2)
3 TBQ treated
4 BMT treated
TSB treated
The solvent treated sample is prepared by stroking
the front surface of the 3M Company Dry Silver Paper Type 7743
once with a camel's hair brush which has been dipped into
2-butanone.
m e TBQ and BMT treated samples are prepared in
the same manner as the solvent treated sample except, in
place of the solvent, a solution is used comprising 20 grams ;
- per liter of the stabilizer precursor in the solvent.
The TSB treated sample is prepared as described
20 above except that the concentration o~ the solution was
only 9 grams of TSB per liter.
The samples are dried overnight in the dark and
treated in a fadeometer the next day. The fadeometer is a
standard testing apparatus which provides exposure to intense
light. The total reflected densities were measured for each
sample at 550 nanometers after 4 hours and after 28 hours
fading in the high intensity xenon arc fadeometer. The measured
densities are recorded in the following Table IV.
Table IV
Reflection density after
Sample No. Fading Time (Moursl Compound ~ -
4 28
1 0.10 0.26 1.04Control
2 0.10 0.43 1.19Solvent
3 0.09 0.17 0.16 TBQ
4 0.09 0.10 0.13 BMT
0.07 0.11 0.22 TSB*
*It is believed that these densities would be lower if the
treating solution were as concentrated as the treating
solutions of the other samples.
~jj",. g_ . .' ~
1~4S876
3M Company Dry Silver Paper Type 77~3, which is a
trade name of 3M Company, U.S.A., comprises a paper support
having thereon a photothermographic layer comprising a toner
which is 1-(2H)-phthalazinone with 2,2'-methylenebis(4-
methyl-6-tertiarybutylphenol), silver behenate, silver bromide,
aluminum oxide, and tetrabromobutane. The photothermographic
layer is overcoated with a vinylacetate and vinylacetate-
vinyl chloride copolymer layer. Tetrabromobutane is employed
as a stabilizer.
The invention has been described in detail with
particular reference to preferred embodiments thereo~, but it
will be understood that variations and modifications can be
effected within the spirit and scope of the invention.
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