Note: Descriptions are shown in the official language in which they were submitted.
l~S5~;1
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PHOTOTHERMOGRAPHIC COMPOSITION AND PROC~SS
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to photothermographic
silver halide materials as well as a method of preparing
such materials. In one of its aspects it relates to a
photothermographic silver halide composition capable of
being coated comprising photosensitive silver halide and
other components with a specified combination of solvents.
DESCRIPTION OF THE STATE OF THE ART
Photothermographic materials are well known in the
photographic art. Photothermographic materials are also
known as heat developable photographic materials. The
photothermographic materials after imagewise exposure are
heated to moderately elevated temperatures to produce a
developed image in the absence of separate processing
solutions or baths. The heat development can provide a
developed silver image in the photothermographic material.
The term "material" as used herein, such as in
photothermographic material, is intended to include elements
and compositions. For instance, the use of "photothermo-
graphic material" is intended to refer to photothermographic
element and photothermographic composition.
An example of a known photothermographic silver
halide material comprises (a) a hydrophilic photosensitive
silver halide emulsion containing a gelatino peptizer with
(b) an organic solvent mixture, (c) a hydrophobic binder and
(d) an oxidation-reduction image-forming composition com-
prising (i) a silver salt of a long-chain fatty acid, such
as silver behenate or silver stearate, with (ii) an organic
reducing agent, such as a phenolic reducing agent. It has
been desirable to have hydrophilic photosensitive silver
halide emulsion containing a gelatino peptizer in such a
photothermographic material because of the higher photo-
sensitivity of the silver halide emulsion and the ease ofcontrol in preparation of the emulsion based on conventional
S56~L
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aqueous silver halide gelatino emulsion technology. A
problem has been encountered in preparing such photothermo-
graphic silver halide materials. This problem involves the
mixing of a hydrophilic photosensitive silver halide emulsion
containing a gelatino peptizer with a composition, as
described, containing hydrophobic components including a
hydrophobic binder, such as poly(vinyl butyral), and
a silver salt of a long-chain fatty acid, such as a silver
salt of behenic acid. Typically, when a hydrophilic photo-
sensitive silver halide emulsion containing a gelatinopeptizer is mixed with such hydrophobic materials and then
coated on a suitable support to produce a photothermographic
element, the resulting photothermographic element produces
a less than desired degree of photosensitivity, contrast
and maximum density upon exposure and heat processing.
This problem has been encountered in photo-
thermographic silver halide materials, as described in, for
example, U.S. Patent 3,666,477 of Goffe, issued May 30, 1972.
Goffe proposed addition of alkylene oxide polymers and
a mercaptotetrazole derivative to the photothermographic
material to help provide increased photosensitivity.
In addition, a variety of organic solvents have
been proposed in order to help prepare a photothermographic
silver halide composition containing the described com-
ponents. Such organic solvents that have been proposedinclude isopropanol, acetone, toluene, methanol, 2-methoxy-
ethanol, chlorinated solvents, acetone-toluene mixtures and
certain non-aqueous polar organic solvents. These solvents
in photothermographic materials are described in, for example,
U.K. Specifications 1,422,145; 1,460,868; and 1,354,186.
The described individual solvents, such as isopropanol, have
not provided the desired improved described properties.
There has been a continuing need to provide improved relative
speed and contrast with desired maximum image density.
S~l
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SUI~MARY OF T~E INVENTION
It has been found according to the invention that
the described advantages are provided in a photothermo-
graphic silver halide composition capable of being coated on
a support comprising a hydrophilic photosensitive sllver
halide emulsion containing a gelatino peptizer with an
organic solvent mixture, a hydrophobic binder and an
oxidation-reduction image-forming composition comprising (i)
a silver salt of a long-chain fatty acid with (ii) an
organic reducing agent for said silver salt of a long-
chain fatty acid, wherein the solvent mixture comprises
a combination of (A) an alcohol photographic speed-increasing
solvent which is a compound selected from the group con-
sisting of benzyl alcohol photographic speed-increasing
solvents and 2-phenoxyethanol speed-increasing solvents, (B)
an aromatic hydrocarbon solvent that is compatible with the
benzyl alcohol solvent. An especially useful organic solvent
mixture as described comprises (C) a minor portion, that is
up to 10% by weight of the mixture, of the hydrophobic
binder, such as poly(vinyl butyral).
A photothermographic composition according to the
invention can be prepared by very thoroughly mixing, such as
by ultrasonic wave mixing, (I) a hydrophilic photosensitive
silver halide emulsion with (II) an organic solvent mixture
comprising (A) an alcohol photographic speed-increasing
solvent with (B) an aromatlc hydrocarbon solvent that ls
compatible with the alcohol solvent and (C) O to 10~ by
weight of said organlc solvent mixture of a hydrophobic
binder, such as poly(vinyl butyral) and then very thoroughly
mlxing the resultlng product with (III) comprising (a) a
hydrophobic binder and (b) an oxidation-reduction image-
formlng composition comprlsing (i) a silver salt of a long-
chain fatty acld with (ii) an organic reducing agent,
typically ln an organic solvent. A photothermographic
element according to the invention can be prepared by
coatlng the resultlng photothermographic composition on a
suitable support.
~55~1
-4
An image can be developed ln the photothermographic
element after exposure by merely heatlng the photothermo-
! graphic element to moderately elevated temperatures.
DETAILED DESCRIPTION 0~ THE INVENTION
A variety of descrlbed alcohol photographlc
speed-increasing solvents are useful in the described solvent
mlxture. It ls necessary that the described alcohol solvent
be compatible with the described aromatlc hydrocarbon solvent
and other components of the photothermographlc sllver hallde
composition. Some alcohol solvents can be lnsufflclently
soluble in the described composltion to be useful, such as
chloro, hydroxy and nltro substltuted benzyl alcohols.
Selection of an optimum alcohol solvent will depend upon
such factors as the particular components of the photo-
thermographic composltion, the desired image, coatlng
, condltlons, the partlcular aromatic hydrocarbon solvent, the
particular photographic silver halide emulsion, and the
concentration of the various components of the photothermo-
,~ graphic composition. Combinatlons of alcohol solvents
' 20 can be useful if desired. Selection of an optlmum alcohol
solvent can be carried out by a simple test in which the
alcohol solvent is used in Example 1 ln place of benzyl
alcohol. If the results of the alcohol solvent selected are
slmilar to those of Example 1, the alcohol solvent is con-
sidered to be at least satisfactory. The descrlbed alcohol
photographlc speed-increaslng solvents can be selected from,
for example, phenalkylols and phenoxyalkylols, ln which
the alkylol contains 1 to 4 carbon atoms, and in which the
phenyl group ls unsubstltuted or substltuted with lower
alkyl, such as alkyl containing 1 to 4 carbon atoms, lower
alkoxy, such as alkoxy containlng 1 to 4 carbon atoms,
fluorosubstltuted lower alkyl or phenoxy.
The term "speed-increaslng" as used hereln with
regard to the speed-lncreaslng solvent is intended to mean
that the alcohol solvent provldes a hlgher relatlve speed
-- . .
~1255~1
-4a-
compared to a similar photothermographic composition containing
no alcohol solvent.
The described benzyl alcohol solvent can be sub-
stituted benzyl alcohol or can be benzyl alcohol which is
substituted with a group which does not adversely affect the
desired solvent or sensitometric properties produced by the
benzyl alcohol derivative. Examples of substituents which
do not adversely affect the desired properties include
methyl, phenoxy, trifluoromethyl, methoxy and ethoxy.
Unsubstituted benzyl alcohol is preferred.
5 5
--5--
A variety of aromatic hydrocarbon solvents are
userul ln the described solvent mlxture wlth the descrlbed
alcohol speed-lncreaslng solvent. The aromatlc hydrocarbon
solvent must be compatible wlth the alcohol solvent and
other components of the photothermographic composltion
wlthout adversely affecting the deslred solvent and sen-
sltometric properties produced by the solvent mixture. The
optimum aromatic hydrocarbon solvent can be selected based
on such factors as the particular components of the photo-
thermographic compositlon, the particular alcohol solvent,
coating conditions for the photothermographic composition,
the particular photosensitive silver halide emulsion and the
llke. Combinations of aromatic hydrocarbon solvents can
be useful if desired.
Examples of useful aromatic hydrocarbon solvents
include toluene, xylene and benzene. Toluene ls preferred
as a solvent with benzyl alcohol.
Other solvents that are useful in place of or in
combination with the described aromatic hydrocarbon solvents
include butyl acetate, dlmethyl acetamide and dimethyl-
formamide. These solvents can be useful in combination if
- desired. However, an aromatic hydrocarbon solvent, such as
toluene, is preferred with the described alcohol solvent,
such as benzyl alcohol.
A range of concentration Or described alcohol
- solvent is useful in the described photothermographic silver
halide composition. Typlcally, the alcohol solvent is
useful at a concentration which produces a photothermographic
element as coated containing the alcohol within the range of
30 about 0.50 grams/m2 to about 2.80 grams/m2. An especially
useful concentration of alcohol solvent, such as benzyl
alcohol, is within the range of about 0.8 grams to about
1.35 grams of alcohol solvent/m2 of support of the described
photothermographic element. ~he optimum concentration of
alcohol solvent will depend upon the particular components
of the photothermographic material, coating conditlons,
deslred image, the partlcular aromatic hydrocarbon solvent,
the partlcular alcohol solvent and the like.
a~
55~1
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A range of concentratlon of aromatic hydrocarbon
solvent is useful in the described photothermographic
silver halide composition also. The concentration of
aromatic hydrocarbon solvent is typically within the
range of 30% to about 80% by weight of total photothermo-
graphic composition. A preferred concentration of aromatic
hydrocarbon solvent, such as toluene, is within the range
of about 70% to about 80% by weight of total photothermo-
graphic composition. The optimum concentration of aromatic
hydrocarbon solvent will depend upon the described factors
that relate to selection of the optimum concentration of
described alcohol solvent.
A range of ratios of described alcohol solvent to
aromatic hydrocarbon solvent is useful in the described
solvent mixture at the time of mixing the solvent mixture
with the silver halide. Typically, the ratio of alcohol
solvent to aromatic hydrocarbon solvent at this point is
within the range of about 1:10 to about 1:30. A preferred
ratio of described alcohol solvent to aromatic hydrocarbon
solvent is within the range of about 1:15 to about 1:25.
An optimum ratio of alcohol solvent to aromatic hydrocarbon
solvent will depend upon such factors as the particular
solvents, the specific components of the photothermographic
silver halide composition, coating conditions, the desired
image, the particular silver halide emulsion and the like.
Typically, in the described photothermographic
composition, that is prior to coating onto a suitable
support, the ratio of alcohol solvent to hydrocarbon solvent
is within the range of about 1:50 to 1:200 with a preferred
range of 1:75 to 1:150.
The photothermographic materials according to the
invention comprise a photosensitive component which consists
essentially of photosensitive silver halide. The photo-
sensitive silver halide is in the form of a hydrophilic
photosensitive silver halide emulsion containing a gelatino
S5~i1
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peptizer. The photosensitive silver halide is especially
useful due to its high degree of photosensitivity compared
to other photosensitive components. A typical concentration
of hydrophilic photosensitive silver halide emulsion con-
taining a gelatino peptizer in a photothermographic com-
position according to the invention is within the range of
about 0.2 to about l.O mole of photosensitive silver halide
per mole of the described silver salt of a long-chain fatty
acid in the photothermographic material. Other photo-
sensitive materials can be useful in combination with thedescribed photosensitive silver halide if desired. Preferred
photosensitive silver halides are silver chloride, silver
bromoiodide, silver bromide, silver chlorobromoiodlde or
mixtures thereof. For purposes of the invention, silver
iodide is also considered to be a photosensitive silver
halide. A range of grain size of photosensitive silver
halide from very coarse grain to very fine grain silver
halide is useful. Very fine grain silver halide is typically
preferred.
The hydrophilic photosensitive silver halide
emulsion containing a gelatino peptizer can be prepared by
any of the procedures known in the photographic art which
involve the preparation of photographic silver hallde
gelatino emulsion. Useful procedures and forms of photo-
sensitive silver halide gelatino emulsions for purposes of
the invention are described in, for example, the Product
Licensing Index, ~olume 92, December 1971, Publication 9232
on page 107, published by Industrial Opportunities Limited,
Homewell, Havant Hampshire, PO9 lEF, UK. The photographic
silver halide, as described, can be washed or unwashed, can
be chemically sensitized using chemical sensitization
procedures and materials known in the photographic art, can be
protected against the production of fog and stabilized
against loss of sensitiVity during keeping as described in
the mentioned Product Licensing Index publication.
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A hydrophilic photosensitive silver halide emulsion
containing a gelatino peptizer which contains a low concen-
tration of gelatin is often very useful. The concentration
of gelatin which is very useful is typically within the range
of about 9 to about 15 grams per mole of silver.
The term "hydrophilic" is intended herein to
mean that the photosensitive silver halide emulsion con-
taining a gelatino peptizer is compatible with an aqueous
solvent.
The gelatino peptizer that is useful with the
photosensitive silver halide emulsion can comprise a variety
of gelatino peptizers known in the photographic art. The
gelatino peptizer can be, for example, phthalated gelatin
or non-phthalated gelatin. Other gelatino peptizers that
are useful include acid or base hydrolyzed gelatins. A non-
phthalated gelatin peptizer is especially useful with the
described photosensitive silver halide emulsion.
The photosensitive silver halide emulsion can con-
tain a range of concentration of the gelatino peptizer.
Typically, the concentration of the gelatino peptizer is
within the range of about 5 grams to about 20 grams of
gelatino peptizer, such as gelatin, per mole of silver in the
silver halide emulsion. This is described herein as a low-
gel silver halide emulsion. An especially useful concentration
of gelatino peptizer is within the range of about 9 to
about 15 grams of gelatino peptizer per mole of silver in
the silver halide emulsion. The optimum concentration of
the gelatino peptizer will depend upon such factors as the
particular photosensitive silver halide, the desired image,
the particular components of the photothermographic com-
position, coating conditions, the particular benzyl alcohol
solvent and the particular aromatic hydrocarbon solvent.
The silver halide emulsion pH can be maintained
within a range of pH. Typically, the silver halide emulsion
pH is maintained within the range of about 5.0 to about 6.2
during the emulsion precipitation step. Lower pH values may
cause undesired coagulation and higher pH values may cause
undesirable grain growth.
l~S~l
g
The temperature of the reactlon vessel within
whlch the silver hallde emulslon ls prepared ls typlcally
malntalned wlthln a temperature range of~about 35C to about
75C durlng the composltlon preparatlon. The temperature
range and duratlon of the preparatlon can be altered to
produce the deslred emulslon graln slze and deslred com-
position properties. The silver hallde emulslon can be
prepared by means of emulsion preparatlon technlques and
apparatus known in the photographlc art.
An especlally useful method for preparatlon of the
photothermographlc composltlon ls by a slmultaneous double-
~et emulslon additlon of the components (I) and (II) lnto a
Jacket enclosing an ultrasonic means for exposlng the
composition to hlgh frequency waves. After combinatlon ln
the ~acket and thorough mlxlng due to the ultrasonlc waves,
? ~ the mlxture can be wlthdrawn and recirculated through the
~acket encloslng the ultrasonlc m~ans for addltional mixlng
or wlthdrawn lmmedlately and comblned readlly wlth other
rl addenda to produce the deslred photothermographlc composltlon.
~'. 20 A variety of hydrophobic binders are useful in the
described photothermographlc materials. The blnders that
are useful include various colloids alone or in comblnatlon
as vehicles and/or binding agents. The hydrophobic binders
which are suitable include transparent or translucent
materials. Useful binders lnclude polymers of alkylacrylates
and methacrylates, acryllc acld, sulfoalkylacrylates or
methacrylates, and those whlch have crosslinking sites that
facllltate hardenlng or curlng. Other useful hydrophoblc
blnders lnclude hlgh molecular welght materlals and reslns,
such as poly(vlnyl butyral), cellulose acetate butyrate,
poly(methyl methacrylate~, poly(styrene), poly(vlnyl chlorlde),
chlorinated rubber, poly(lsobutylene), butadlene-styrene
copolymers, vinyl chlorlde-vinyl acetate copolymers,
copolymers of vinyl acetate, vinyl chloride and maleic
anhydride and the like. It ls lmportant that the hydrophoblc
blnder not adversely a~fect the sensitometric or other
~.
~.
55ti1
--10--
desired properties of the described photothermographic
material. Poly(vinyl butyral) is especially useful.
This is available under the trade~e "BUTVAR" from
The Monsanto Company, U.S.A.
A range of concentration of hydrophobic binder can
be useful in the photothermographic silver halide materials
according to the invention. Typically, the concentration of
hydrophobic binder in a photothermographic silver halide com-
position according to the invention is within the range of
about 20 to about 65 mg/dm2. An optimum concentration of
the described binder can vary depending upon such factors as
the particular binder, other components of the photothermo-
graphic material, coating conditions, desired image, processing
temperature and conditions and the like.
If desired, a portion of the photographic
silver halide in the photothermographic composition
according to the invention can be prepared in situ in the
photothermographic material. The photothermographic com-
position, for example, can contain a portion of the photo-
graphic silver halide that is prepared in or on one or more
of the other components of the described photothermographic
material rather than prepared separate from the described
components and then admixed with them. Such a method of
preparing silver halide in situ is described in, for example,
U.S. Patent 3,457,075 of Morgan et al, issued July 22, 1969.
The described photothermographic composition com-
prises an oxidation-reduction image-forming combination con-
taining a long-chain fatty acid silver salt with a suitable
reducing agent. The oxidation-reduction reaction resulting
from this combination upon heating is believed to be
catalyzed by the latent image silver from the photosensitive
silver halide produced upon imagewise exposure of the photo-
thermographic material followed by overall heating of the
photothermographic material. The exact mechanism of image
formation is not fully understood.
~!255~1
A variety of silver salts of long-chain fatty
acids are useful in the photothermographic materials according
to the lnvention. The term "lon~-chaln" as used hereln ls
lntended to refer to a ratty acid containlng 12 to 30 carbon
atoms and which is typically resistant to darkenlng upon
exposure to light. Use~ul long-chain fatty acld sllver salts
lnclude, for example, silver stearate, sllver behenate,
sllver caprate, silver hydroxystearate, silver myrlstate and
silver palmltate. A minor proportlon of another sllver salt
oxidizing agent which is not a long-chain fatty acld sllver
salt can be useful in comblnatlon wlth the sllver salt Or
the long-chain fatty acld lf desired. Such silver salts
which can be useful in combination with the descrlbed sllver
salts of a long-chain fatty acid include, for example,
; 15 silver benzotriazole, silver imidazole, silver benzoate and
~ the like. Combinations of silver salts of long-chain fatty
; acids can be useful in the described photothermographlc
materials if desired.
~, A variety of organic reducing agents are useful in
the described photothermographic sllver hallde materlals
accordlng to the lnvention. These are typically silver
halide developing agents which produce the desired
oxidation-reduction image-forming reactlon upon exposure and
heating of the descrlbed photothermographic silver hallde
material. Examples of useful reduclng agents lnclude
polyhydroxybenzenes, such as hydroquinone and alkyl sub-
stltuted hydroquinones; catechols and pyrogallol; phenylene-
dlamlne developing agents; amlnophenol developlng agents;
ascorblc acld developlng agents, such as ascorblc acid and
ascorbic acld ketals and other ascorblc acld derlvatives;
hydroxylamlne developlng agents; 3-pyrazolidone developlng
agents such as l-phenyl-3-pyrazolldone and 4-methyl-4-
hydroxymethyl-l-phenyl-3-pyrazolldone; hydroxytetronlc acld
and hydroxytetronamide developlng agents; reductone
developlng agents; bls-B-naphthol reducing agents; sulfon-
amldophenol reduclng agents and the llke. Comblnatlons Or
, ~".....
55t~1
-12-
organlc reduclng agents can be useful ln the described
photothermographlc sllver hallde materlals. Sulfonamldo-
phenol developlng agents, such as descrlbed ln Belglan
Patent 802,519 lssued January 18, 1974, can be especlally
useful ln the photothermographlc sllver hallde composltlon.
A range of concentratlon Or the organlc reduclng
agent can be useful ln the descrlbed photothermographlc
sllver hallde materlals. The concentratlon of organlc
reduclng agent ls typically withln the range of about
5 mg/dm2 to about 20 mg/dm2, such as wlthln the range of
about 10 to about 17 mg/dm2. The optlmum concentration of
organlc reduclng agent wlll depend upon such factors as the
particular long-chaln fatty acld, the deslred lmage, processin~
condltlons, the partlcular solvent mlxture, coating condltlons
and the llke.
The order of addltion of the descrlbed components
for preparlng the photothermographic compositlon before
coating the composition onto a sultable support ls lmportant
to obtain optimum photographic speed, contrast and maxlmum
density. In an especlally useful method accordlng to the
invention the low-gel silver halide emulsion ls added to an
ultrasonlc mixing means through one lnlet and a solvent
mixture containing toluene, up to about 10% by weight
poly(vlnyl butyral) and benzyl alcohol ls added through
another lnlet. The low-gel silver hallde ls dlspersed
thoroughly ln thls environment by ultrasonlc waves. The
resultlng product is then combined with the remainlng
components of the deslred photothermographlc composition.
If the low-gel silver halide is not dispersed as described
before addlng the other components, the sllver hallde gralns
ln the composltlon have a tendency to clump together and
preclpltate to the bottom of the contalner ln whlch the
composltion is mlxed.
~,
l~St~l
~13-
A variety of mixing means are useful for preparing
the descrlbed composltlons. However, the mlxlng means
should be one whlch provldes very thorough mixing, such as
an ultrasonlc mlxlng means. Other mlxlng means than ultrasonlc
mixing means that can be useful are commerclally avallable
- colloid mlll mixing means and dlspersator mixing means known
in the photographlc art. A blender, such as a blender known
under the trade name of "Waring" blender, does not produce
the very thorough mixlng that ls desired in most cases.
It is desirable, ln some cases, to have what ls
descrlbed as a tonlng agent, also known as an actlvator-
; toning agent, in the photothermographlc materlal accordlng
to the invention. Combinations of toning agents can often
be useful. Typical toning agents lnclude, for e~ample,
phthalimide, succlnlmlde, N-hydroxyphthallmide, N-hydroxy-
1,8-naphthalimide, N-hydroxysuccinimide, 1-(2H)-
phthalazinone and phthalazinone derivatlves.
Photothermographlc materials according to the
invention can contain other addenda that are userul ln
imaging. Suitable addenda in the descrlbed photothermo-
graphlc materials include development modl~lers that
functlon as speed-lncreasing compounds, hardeners, anti-
static layers, plasticizers and lubricants, coating alds,
brighteners, spectral sensitlzing dyes, absorbing and fllter
dyes, matting agents and the like.
It is useful in certain cases to include a
stabilizer in the described photothermographic material.
This can help in stabilizatlon of a developed lmage. Com-
binations of stabillzers can be useful lf deslred. Typlcal
stabillzers or stabilizer precursors include certaln
halogen compounds, such as tetrabromobutane and 2-(tribromo-
methylsulfonyl), benzothiazole, which provide improved post-
processing stabllity and azothioethers and blocked azollne
thlone stabllizer precursors.
The photothermographlc elements accordlng to the
inventlon can comprlse a varlety Or supports which can
1~2S5~1
--14--
tolerate the processing temperatures useful in developing
an image. Typical supports include cellulose ester,
poly(vinyl acetal), poly(ethylene terephthalate), poly-
carbonate and polyester film supports. Related film and
resinous support materials, as well as paper, glass, metal
and the like supports which can withstand the described
processing temperatures are also useful. Typically a
flexible support is most useful.
The photothermographic compositions can be coated
on a suitable support by coating procedures known in the
photographic art including dip coating, airknife coating,
curtain coating or extrusion coating using hoppers. If
desired, two or more layers can be coated simultaneously.
The described silver halide and oxidation-reduction
image-forming combination can be in any suitable location in
the photothermographic element according to the invention
which produces the desired image. In some cases it can be
desirable to include certain percentages of the described
reducing agent, the silver salt oxidizing agent and/or other
addenda in a protective layer or overcoat layer over the
layer containing the other components of the element as
described. The components, however, must be in a location
which enables their desired interaction upon processing.
It is necessary that the photosensitive silver
halide, as described, and other components of the imaging
combination be "in reactive association" with each other in
order to produce the desired image. The term "in reactive
association", as employed herein, is intended to mean that
the photosensitive silver halide and the image-forming
combination are in a location with respect to each other
which enables the desired processing and produces a useful
image.
A useful embodiment of the invention is a photo-
thermographic silver halide composition capable of being
coated on a support comprising ~a~ an aqueous photosensitive
- ~2S~til
-15--
silver hallde emulsion contalnlng a gelatlno peptlzer wlth
(b) an organic solvent mixture comprlslng a comblnatlon Or a
benzyl alcohol photographlc speed-lncreasing solven~, such
as benzyl alcohol, with toluene and up to 4~ by welght
5 poly(vinyl butyral), (c) a hydrophobic polymeric blnder
conslsting essentially of poly(vinyl butyral) and (d) an
oxidation-reduction image-rorming combination comprlslng
(i) a silver salt or a long-chain fatty acld conslstlng
essentially of silver behenate wlth (11) an organlc reducing
10 agent consisting essentially of a sulfonamldophenol. This
composition can be coated on a suitable support to produce
a photothermographic element according to the lnventlon.
Another embodiment of the inventlon is a method of preparing
a photothermographlc element comprising coating the resulting
15 composition onto a suitable support to produce a photothermo-
graphic element as desired.
A variety of imagewise exposure means are useful
; wlth the photothermographic materials according to the
invention. The imaging means according to the lnvention
20 can be any suitable source of radiation to which the photo-
thermographic material is sensitive. The imaging materials
according to the invention are typically sensitive to the
t ultraviolet and blue regions of the spectrum and exposure
means which provide this radiation are preferred. Typically,
25 however, if a spectral sensitizing dye or combination of
spectral sensitizing dyes are present in the photothermo-
graphic material, exposure means using other ranges of the
electromagnetic spectrum can be useful. Typically, a photo-
thermographic material according to the invention is exposed
30 imagewise with a visible light source, such as a tungsten
lamp. Other sources of radiation can be useful and include,
for instance, lasers, electron beams, X-ray sources and the
like. The photothermographic materials are typlcally
exposed imagewise to produce a developable latent image.
:
llZ55til
--16--
A visible image can be developed in the photo-
thermographic material according to the invention withln a
short time, such as within several seconds, merely by
heating the photothermographic material to moderately
elevated temperatures. For example, the exposed photothermo-
graphic material can be heated to a temperature within the
range of about 100C to about 200C, such as a temperature
within the range of about 110C to about 140C. Heating is
carried out until a desired image is developed, typically
within about 2 to about 30 seconds, such as about 2 to
about 10 seconds. Selection of an optimum processing time
and temperature will depend upon such factors as the desired
image, particular components of the photothermographic
element, the particular latent image and the like.
A variety of means can be useful to produce the
necessary heating of the described photothermographic
material to develop the desired image. The heating means
can be a simple hot plate, iron, roller, infrared heating
means, hot air heating means or the like.
Processing according to the invention is typically
carried out under ambient conditions of pressure and
humidity. Pressures and humidity outside normal atmospheric
conditions can be useful if desired; however, normal
atmospheric conditions are preferred.
The following examples are included for a further
understanding of the invention.
Example 1
This illustrates the invention.
A silver behenate/behenic acid dispersion (C) was
prepared by blending the following components:
acetone 250 ml
toluene 250 ml
poly(vinyl butyral~ 30.3 g
behenic acid 16.0 g
35 silver behenate 42.0 g
~55~jl
-17-
A silver hallde gelatlno photosensltlve
dispersion (Z) was prepared as follows: An aqueous solution
of 10 3 molar lithium bromide was added to 0.02 mole of a
400 A silver bromoiodlde (6 mole % lodlde) gelatino emulsion
(40 grams non-phthalated gelatin per silver mole) to produce
a total weight of 200 grams. The resulting mixture was
stlrred for 15 minutes at 40C and a pH of 6.1 with a pAg
of 8.4. The emulsion was centrifuged for 20 minutes at 3000
rpm. The resulting supernatant was discarded and a 100 mg
sample of the wet centrifuged silver halide emulsion was
treated with ultrasonic waves for 30 seconds in the presence
of 3 ml of a solvent mixture containing toluene (87 grams)
and 4~ by weight poly(vinyl butyral) with 4 grams of
benzyl alcohol.
Thls resultlng sllver hallde dlsperslon (Z) was
combined with the following components:
acetone/toluene (1:9 parts 0.15 ml
by volume) solution con-
~ taining 0.01% by weight
- 20 3-ethyl-2-thio-2,4-
oxazolidinedione
(speed-increasing addenda)
acetone/toluene (1:9 parts 0.50 ml
by volume) solution con-
taining 0.01% by weight
3-ethyl-5-(3-ethyl-2-
benzoxazolylideneethylidene)-
- l-phenyl-2-thiohydantoin
(sensitizing dye)
silver behenate dispersion C 3.6 ml
(described above)
(oxidizing agent)
The resulting composition was mixed by shaking for several
mlnutes. The dispersion was combined with the following
solutions and coated on an unsubbed poly(ethylene
terephthalate) film support at a o.oo8 inch (8 mils)
wet coatlng thlckness:
~'~
l~Z55~1
--18--
acetone~toluene (1:1 parts Q.50 ml
by volume) solution con-
taining 25% by weight 2,6-
dichloro-4-benzenesulfon-
amidophenol (reducing agent)
toluene solution containing 2 drops
siloxane surfactant (containing
2% by weight silicone AF-70,
trademark of the General Electric
Company)
acetone solution containing 5% 0.30 ml
by weight 2-(tribromomethyl-
sulfonyl)benzothiazole
(stabilizer)
The resulting coating was dried at 48.9C for
5 minutes. This produced a photothermographic element
according to the invention. The element was imagewise
exposed to light through a 1.0 neutral density and a
graduated density step wedge to produce a developable
latent image in the photothermographic element. The
resulting image was developed by heating the photothermo-
graphic element for 5 seconds at 140C. A high contrast
developed image was produced. The image had a maximum
density above 3.8 and a minimum density of 0.12.
The resulting photothermographic element was free from
mottle and exhibited a smooth surface.
The resulting photothermographic element and
its sensitometric properties compared favorably with a
similarly prepared photothermographic element that con-
tained silver halide having a similar grain size but which,
in the absence of gelatin, had been formed in a poly(vinyl
butyral) composition with an acetone solvent in place of the
combination of benzyl alcohol and toluene.
Example 2
This illustrates use of a phthalated gelatin
peptized silver halide emulsion containing less than 9 grams
of phthalated gelatin per mole of silver in a non-aqueous
photothermographic material according to the invention.
55Sà~
--19--
A gelatino silver halide emulsion was prepared by
adding following Solutions B and C simultaneously to following
Solution A at the rate of 6.3 milllliters per minute.
Solution A
Phthalated gelatin 9 g
Distilled water 783 ml
Temperature 35C
pH 5.0
VAg + 60 mv
Solution B
NaBr 133.9 g
KI 4.6 g
Distilled water 152 ml
Room temperature (about 20C)
Total Vol. 186 ml
Solution C
AgN03 170 g
Distilled water 109 ml
Room temperature (about 20C)
Total Vol. 143 ml
After 50 seconds, Solution A was adjusted to a
VAg + 110 mv with a bromide ion solution. The total
precipitation time was approximately 22 minutes, i.e.
until Solution C was completely added. Then Solution B
25 addition was stopped. The final composition had a pH of
5.50 and a pAg of 8.41. The temperature of the reaction
vessel was increased to 40C and the pH was adjusted to
3.5 with 1.5 N nitric acid. The supernatant was decanted
and the coagulum was redispersed by adding 10 3 M lithium
3 bromide solution to make a final weight of 1300 grams
(pAg 7.70) and ad~usting the composition to a pH of 6.50
with 2.0 M lithium hydroxide. This procedure was repeated
twice and after removal of the final supernatant the con-
centrated coagulum (about 500 grams per silver mole) was
1~ ~SS~I
-20-
adjusted to pH 6.5 and a pAg of 8.3 with vigorous stirring
at 40C ~or 30 minutes to insure complete dispersal and
ionic equilibrium before chill setting for storage. The
resulting silver halide emulsion at 40C was mixed with 3 ml
of a solvent mixture containing toluene (87 grams), 4~ by
weight poly(vinyl butyral) and benzyl alcohol (4 grams)
using an ultrasonic mixing means. The resulting composition
was then combined with other components as described in
Example 1 to provide a photothermographic element according
to the invention.
The resultlng photothermographlc element was
imagewise exposed to light to provlde a developable latent
image in the element. The image was developed by heating
the element at 125C for 5 seconds. The developed image
had a maximum density of 1.64 and a minimum density of 0.26.
Example 3
The procedure described in Example 2 was repeated
; with the exception that one of the compounds designated as
A - G was used as the solvent at 0.90 mole per mole of
silver halide in place of the described concentration of
benzyl alcohol.
Compound Name
A benzyl alcohol
B DL-~-methylbenzyl alcohol
25 C o-phenoxybenzyl alcohol
D m-(trifluoromethyl)benzyl alcohol
E p-bromobenzyl alcohol
F o-iodobenzyl alcohol
G Sucrose
The photothermographic element containing the
described compounds was prepared with the silver halide
as described in Example 2. The resulting photothermographic
elements were each imagewise exposed for one-eighth second
to a mercury light source through a graduated density step
wedge to produce a developable latent image in the element.
The image was developed by heating the element at 125C
for 5 seconds in each instance. The sensitometric results
~or each of the compounds noted is glven ln following
Table I:
,w. ,
l~Z55C~1
--21--
X 3 r-- O ~L:) O ~1 ~D 3
3 O~ 3 0 r-l
.. . . . ,~ .
E~
~D O t-- 0 3 ~I r I O
~3 O O O O O O O
o
C)
O ~ ~D O O CO
3 ~ ~D ~ ~:
.
O ~ ~ ~ O ~ O O
H t~
a) ~ O
Q~ ~1 .
~a) o
E~ a~ u
Q
a~ o ~ ~ ~ 3 0 Il~
~ o a~ co O ~1 ~I
,1 ~ ~ ~ ~
td
a~
~:
a
:~
o 2;
o c> a) c) ~
~ ~ ~ *
5~1
-22-
The data in Table I illustrates that Compounds
B, C and D produce results similar to Compound A (benzyl
alcohol). That is, the compounds produce increased
relative speed and maximum density compared to the photo-
thermographic element containing no benzyl alcohol.
Compounds E, F and G produced detrimental relative speed
results. Enhanced contrast was observed in photographic
elements containing Compounds B and C.
Example 4
The procedure described in Example 2 was repeated
with the exception that one of the compounds designated 4A,
4H, 4I and 4J was used as the solvent at 0.90 mole per mole
of silver halide in place of the described concentration of
benzyl alcohol.
15Compound Name
4A benzyl alcohol
4H _-methylbenzyl alcohol
4I _-methoxybenzyl alcohol
4J 2-phenoxyethanol
The resulting coatings were imagewise exposed
for 10 3 seconds to a tungsten light source through a
graduated density step wedge to produce a developable latent
image in the exposed photothermographic element. The
imagewise exposed photothermographic element was processed
by heating the element at 125C for 5 seconds. A
developed image was produced in each element. The
sensitometric results were as follows:
1~255~ 1
-23--
~C O O
~D
H ~J N
~ ~ a~
rl
~ OOOOO
t~ O O O O
~_ O ~1 ~I r-l (~
H ~1
H
a
D
E~ ~ a)
~n o
a)o o~ ~ ~ o
O ~ ~ U~ ~
r~ J O
td
~ J~
P;
*
~ a~ ~
O ~: C X H 1~ ~)
E~ ~z; a)
O ~;
V *
,.
-24-
Improvement in photographic speed, contrast, and maximum
density with reduced minimum density was observed when
comparing the results for Compounds 4A, 4H, 4I and 4J with
the control. The use of benzyl alcohol and its derivatives
in the described photothermographic material also provldes
a reduction in haze in the photothermographic layer of the
element. The photothermographic element in each instance
after processing is free of haze.
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
invention.
