Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~L~68~56 FN 401 29CAN5A
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FOG SUPPRESSANT FOR PHOTOTHERMOGRAPHIC
IMAGI NG COMPOS ITIONS
Background_of the Invent_on
The present invention relates to a thermally
developable, photosensitive material, and particularly to a
thermally developable, photosensitive material which does
not require the presence of mercury to suppress fogging.
A variety of methods which comprise subjecting
photographic materials containing photosensitive components
such as silver halide or the like to a so-called dry
processing by heating to thereby obtain an image are known.
Of these photosensitive materials which can form
photographic images using dry processing, the most common
one is a thermally developable, photosensitive material as
described in U.S. Patent Nos. 3,152,904, 3,457,075,
3,707,377 and 3,909,271, in which an oxidation-reduction
image forming composition comprising, as essential
components, organic silver salt oxidizing agents (for
example, silver behenate), photocatalysts such as
photosensitive silver halide, and reducing agents (for
example, 2,2'~methylenebis [4-methyl-6-t-butyl] phenol), is
utilized. While the thermally developable, photosensitive
material is stable at ambient temperature, after exposure
to light, the organic silver salt oxidizing agent and
reducing agent present in the photosensitive layer undergo,
when heated generally at temperatures of higher than about
80C, preferably greater than about 100C, an oxidation-
reduction reaction due to the catalytic action of the
photocatalyst which is present in proximity to the organic
silver salt oxidizing agent and reducing agent to thereby
form silver. The exposed areas of the photosensitive layer
are~rapidly darkened so that a contrast is formed between
the unexposed areas (background) to form an image.
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Mercury, in the form of mercuric salts such as mercuric
bromide or mercuric acetate, is generally included in the thermal-
ly developable, photosensitive material to suppress background
darkening or fog upon processing. Birkeland, U.S. Patent No.
3,589,903 discloses that by incorporating mercuric ion in a light-
sensitive heat-developable imaging sheet containing catalytic
amounts of light-sensitlve silver halide in catalytic association
with organic silver salt oxidation-reduction image-forming means,
the sheet is given increased speed, stability and contrast.
Ulbing, U.S. Patent 3,692,526 discloses that a combination of a
mercury salt, such as a mercury halide with thiourea dioxide in a
heat-processable photosensitive element, composition and/or
process provides reduced background print-out. When -the mercury
salt, e.g., mercuric chloride, or thiourea dioxide is used alone
in the absence of the combination, no satisfactory image is
produced.
It is well known that excessive exposure to mercury can
result in corrosive effects on skin and mucous membranes, nausea,
vomiting, abdominal paln, and kidney damage. Elimination of at
least a portion of the mercury from paper and Eilm would be
beneficial to those involved in the manufacturing process and to
the environment after disposal. Accordingly, it would be highly
desirable to provide an additive to photothermographic elements
which would prevent fog formation but not be toxic to humans or to
the environmentO
Summary of the_Invention
This invention provides a heat-developable, photo-
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sensitive sheet material containing an image-forming system
including at least one photosensitive silver halide catalyst or
photosensitive silver halide catalyst-forming component and as a
heat image -forming means, at least one organic silver compound and
at least one reducing agent therefor, the oxidation-reduction
reaction of which to produce a visible image is accelerated by
said catalyst, said image-forming system further containing at
least one indan or tetralin derivative, said derivative having at
least two carboxyl groups, e.g. 1,1,3-trimethyl-5-carboxyl-3-(p-
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carboxyphenyl)indan. The indan or tetralin derivative
makes it possible to significantly reduce, or even
completely eliminate, the level of mercury in the thermally
developable, photosensitive material, while greatly
reducing thermal fog resulting from heat development of the
exposed photosensitive material. In addition, environ-
mental re~uirements can be satisfied and workers will not
come in contact with excessive levels of mercury.
Detailed Description
The indan and tetralin derivatives suitabl~ for
the compositions of this invention must have at least two
carboxyl groups.
The class of indan de~ivatives can be represented
by the structural formula
R6
X--~ RS
R2
and the class of tetralin derivatives can be represented by
the structural formula
X f~ 4
.
.
wherein Rl, R2,~ R3, R4, R5, R6, R7, R8 independently
represent hydrogen, alkyl group having 1 to 4
carbon atoms,~-COOH or -RCOOH where R
represents an alkyl group or an aryl group,
said alkyl group having from 1 -~o 4 carbon
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atomsl said aryl group having 1 or ~ rings, and
X represents -COOH.
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The compound preferred for use in the present invention is
1,1,3-trimethyl-5-c~rboxyl-3-(p-carboxyphenyl)indan. This
compound can be represented by the formula:
~IOOCC ~ COOll
CH3 CH3
This compound can be prepared by the method described by
Alfred Steitz, Jr~ and James O. Knobloch in Journal of
Paint Technology, Vol. 40, No. 524, September 1968, pp.
384-388. A sufficient amount of indan or tetralin
derivative should be added to the composition so that
thermal fog will be suppressed but so that sensitivity and
gamma will not be reduced. The amount of indan or tetralin
derivative should range from 0.5 to 20 percent by weight,
preferably 1 to 15 percent~ by weight, more preferably 5 to
10 percent by weight, based on the weight of oxidizing
agent in the photosensitive material.
The fog suppressant o~ the present invention is
; useful with photothermographic systems that comprise the
followlng ingredients applied to a suitable support:
~ ~a) photosensitive silver halide prepared in
; ~ situ or ex situ,
(b) an oxidation-reduction image-forming
combination comprising:
i) a silver salt or complex of an organic
compound as an ~oxidizing agent, and
; (ii) an organic reducing agent or developing
agent, and
; (c) a vehicle or binder.
Photothermographic emulsions are usually
constructed as one or~two layers on~a substrate, Single
layer constructions must contain the oxidizing agent, the
photosensitive silver halide, the organic reducing or
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developing agent, and binder, as well as optional additional
materials such as toners, coating aids and other adjuvants. Two-
layer construc-tions must contain the oxidizing agent and silver
halide in one emulsion layer (usually the layer adjacent the subs-
trate) and the other ingredi.ents in the second layer or both
layers.
Photosensitive silver halide can be generated in situ
throughout the surface of the coating of the organic silver salt
or complex, or it can be added as a preformed material. U.S.
Patent No. 3,457,075 describes formation of photosensitive silver
halide by an in situ process. U.S. Patent No. 3,871,887, incor-
porated herein by reference, describes addition of preformed
photosensitive silver halide to a photothermographic imaging
composition.
The silver halide may be any photosensitive silver
halide such as silver bromide, silver iodide, silver chloride,
silver bromoiodide, silver chlorobromoiodide, silver chloro-
bromide, etc., and may be added to the emulsion layer in any
fashion which places it in catalytic proximity to the silver
source. The silver halide is generally present as 0.75 to 15
percent by weight of the imaging layer, although larger amounts up
to 20 or 25 percent are useful. It is preferred to use from 1 to
10 percent by weight silver halide in the imaging layer and most
preferred to use from 1.5 to 7.0 percent.
Oxidizing agents (b)(i) suitable for the practice of the
present invention include silver salts of long chain fatty
carboxylic acids having 10 to 30 carbon atoms, silver salts of
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organic compounds having 6 to 24 carbon atoms and containing an
imlno group, and silver salts of organic compounds having 4 to 10
carbon atoms and containing a mercapto group or a -thione group.
Specific examples of such oxidizing agents include silver
behenate, silver arachidate, silver nonadecanoate, silver stear-
ate, silver heptadecanoate, silver palmitate, silver laurate,
silver saccharinate, 5-substituted salicyladoxime silver salt,
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benzotriazole silver salt, phthalazinone silver salt,
3-mercapto-4-phenyl-1,2,4-triazols silver salt, and the
like. Silver behenate and silver arachidate are the most
suitable. The above-men~ioned oxidizing agents may be used
alone or in mixture.
The oxidizing agent should constitute from about
20 to 70 percent by weight of the imaging layer.
Preferably it is present as 30 to 55 percent by weight.
The second layer in a two-layer construction would not
affect the percentage of the oxidizing agent desired in the
single imaging layer.
The reducing agent for silver ion may be any
material, preferably organic material, which will reduce
silver ion to metallic silver, Organic reducing agents
(b)(ii) suitable for the practice of the present invention
include substituted or unsubstituted bisphenols,
substituted or unsubstituted naphthols, di- or
polyhydroxybenzenes, hydroguinone ethers, ascorbic acids or
its derivatives, 3-pyrazolidones, pyrazoline-5-ones,
reducing sugars and the like. Specific examples of such
reducing agents include hydroquinone, methylhydroquinone,
chlorohydroquinone, bromohydroquinone, phenylhydroquinone,
t-octylhydroquinone, t-butylhydroquinone, 2,5-dimethylhydro-
quinone, 2,6-dimethylhydroquinone, methoxyhydroquinone,
methoxyphenol, hydroquinone monobenzyl ether, catechol,
pyrogallol, resorcin, p-aminophenol, 2,4,4-trimethylpentyl-
bis(2~hydroxy-3,5-dimethylphenyl)methane,
bis(2-hydro~y-3-t-butyl-5-methylphenyl)methane,
bis(2-hydroxy-3,5-di-t-butylphenyl)methane,
4,4'-methylenebist2-methyl-6-t-butylphenol),
4,4' methylenebis( 2t 6-di-t-butylphenol),
2,2'-methylenebist6-t-butyl 4-ethoxyphenol),
methylhydronaphthalene, phenidone, methyl gallate, lactose,
ascorbic acid and the like. The above-mentioned reducing
agents may be alone or in mixture. A suitable reducing
agent may be chosen depending on the organic silver salt
oxidizin~ agent employed in combination therewith. For
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example, when there is employed as the oxidizing agent a
long chain fatty acid silver salt such as silver behenate
which is relatively hard to reduce, relatively strong
reducing agents, e.g. a bisphenol such as
2,2'-methylenebis(4-methyl-6-t-butyl)phenol, are preferably
employed. On the other hand, with organic silver salt
oxidizing agents such as silver laurate which are
relatively easy to reduce, relatively weak reducing agents,
e.g. substituted phenols such as p-phenylphenol, are
preferably employed. With organic silver salt oxidizing
agents such as benzotriazole silver salt which is very hard
to reduce, stronger reducing agents such as ascorbic acids
are preferably employed. The reducing agent should be
present as 1 to 10 percent by weight of the imaging layer.
In a two-layer construction, if the reducing agent is in
the second layer, slightly higher proportions, of from
about 2 to 15 percent tend to be more desirable.
Binders (c) suitable for the practice of the
present invention may be selected from any of the well-
known natural and synthetic resins such as gelatin,
polyvinyl acetals, polyvinyl chloride, polyvinyl acetate,
cellulose acetate, polyolefins, polyesters, polystyrene,
polyacrylonitrilel polycarbonates, and the like.
Copolymers and terpolymers are of course included in these
definitions. The polyvinyl acetals, such as polyvinyl
butyral and polyvinyl formal, and vinyl copolymersJ such as
polyvinyl acetate/chloride are particularly desirable. The
binders are generally used in a range of from 20 to 75
percent by weight of each layer, and preferably about 30 to
55 percent by weight,
The support has to be stable at processing
temperatures between 60 and 150C. Suitable supports
include sheets or foils of a paper, cellulose acetate,
polyethylene terephthalate, fabric, metal foils, and glass
In the case of a paper support, the paper may carry the
usual auxiliary layers such as baryta coatings,
polyethylene coatings, and the like.
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The system can also comprise other conventional
photographic addenda, for example, tone~s, spectral
sensitizing dyes, development modifiers, auxi]iary reducing
agents, coating aids, image stabilizers, activators, image
stabiliæer precursors, and the like. Toners such as
phthala~inone, phthalazine and phthalic acid are not
essential to the construction, but are highly desirable.
These materials may be present, for example, in amounts of
from 0.2 to 5 percent by weight. Compounds containing
mercury can also be added to the system. Generally, as
more of the indan or ~etralin derivative is added to
photothermographic composition, a higher level of
mercury-containing compound can be removed.
The following non-limiting examples will further
illustrate this invention.
EXAMPLE I
A photosensitive composition was prepared by the
following procedure:
Homogenate of silver behenate (half soap) (120 9)
was mixed with 54 g toluene for 15 minutes. Polyvinyl
butyral solution (3 ml of solution of 6.25 g/100 ml
methanol) were added to the mixture, and the resulting
mixture was stirred for 15 minutes. Polyvinyl butyral
(20 g) was then added to ~he mixture. The resulting
mixture was ~tlrred for an additional 15 minute~. A dye
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solution (6 ml) consisting of 0.25 g Dye Il and 0.25 g Dye
II2 in 500 ml me~hanol was added to the mixture. The
resulting mixture was stirred for 50 minutes. The mixture
was denoted as Solution A.
The following ingredients in the amounts
indicated were introduced into a breaker with sti~ring.
Amount
In~redient ~
Acetone 66.0
Methyl ethyl ketone 13.6
Methanol 9.4
Silica 0.6
Cellulose acetate 6.7
Phthalazine 0-34
Phthalic acid 0.3
Tetrachlorophthalic acid anhydride 0.25
1 r 1 Bis(2-hydroxy-3-t-butyl- 4.50
5-methyl phenyl~ methane
1,1,3-Trimethyl-5-carboxyl-3- as indicated
(p-carboxyphenyl)indan in Table I
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1 Dye I is represented by the formula
N / \ 5 ~ ~S
C2115
2 Dye II is represented by the formula
:
2H5COONa
C=CH-CH=C\ C
C2H5
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This mixture was denoted as Solution B.
TABL,E I
Amount of
1,1,3-trimethyl-5-carboxyl-3-
(p-carboxyphenyl)indan
Run No.~ of Solution B)
. _ . . . .
0
2 0.05
3 0.10
4 0.20
Solution A was coated on a paper substrate at an
orifice opening of 2 mil. The coating was dried for 5 min.
at 175F (80C).
Solution B was coated over the dried coating
prepared from Solution A at an oriice opening of 2.25 mil.
The coating prepared from Solution B was dried for 5 min.
a~ 175F (80C).
Each sample was exposed with a tungsten light
source through a continuous wedge at a level of 10,000
meter candle seconds~ The exposed sample~ were developed
for 3 seconds at 263F (131C). The results are shown in
Table II.
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TABLE II
: Run No. Dmin Dmax Speed Roint* Gamma
1 0.26 1.50 2.21 64.9
2 0.13 1.56 2.~3 62.9
: 3 0.11 1.57 2.42 61.5
; 4 Or O6 1.55 2.91 50.1
* Speed point represents the logarithm of the amount of
exposure necessary to obta.in an optical density of fog
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The data in Iable II show that addition of
1,1,3-trimethyl-5~carboxyl-3~(p-carboxyphenyl)indan reduces
Dmin. This result indicates that thermal fog is
efectively suppressed.
Although the indan derivative was introduced in
the topcoat in the foregoing example, it can also be
introduced in the coatin~ containing the organic silver
salt.
EXAMPLE II
Example I can be repeated with the sole
difference being that an equivalent amount of 1,2,3,4-
tetrahydro-1,8-naphthalenedicarboxylic acid is used in lieu
of 1,1,3-trimethyl-5-carboxyl-3-(p-carboxyphenyl)indan.
Various modifications and alterations of this
invention will become apparent to those skilled in the art
without departing from the scope and spirit of this
invention, and it should be understood that this invention
is not to be unduly limited to the illustrative embodiments
set forth herein.
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