GB1593564A - Heatdevelopable photographic silver halide material - Google Patents

Description

(54) HEAT-DEVELOPABLE PHOTOGRAPHIC SILVER HALIDE MATERIAL (71) We, EASTMAN KODAK COMPANY, a Company organized under the Laws of the State of New Jersey, United States of America of 343 State Street, Rochester, New York 14650, United States of America do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a heat-developable photographic silver halide material.

It is well known to produce a silver image in a heat developable material, also known as a photothermographic material, by imagewise exposure, and overall heating. The exposure produces a latent image which is developed and, in some cases, stabilized by the heating.

Heat developable materials and processes are described, for example in U.S. Patents 3,301,678, 3,152,904 and 3,392,020 and British Patent 1,161,777.

According to the present invention there is provided by a heat developable photographic material which comprises a support bearing (A) a layer which contains, or adjacent layers which together contain, (i) a photosensitive silver halide, (ii) a silver halide developing agent (or a precursor thereof), (iii) a development activator precursor and (iv) a polymeric binder, and (B) adjacent to the layer or layers (A) a layer which contains (v) an azoaniline dye, the developing agent (ii) being capable at an elevated temperature of bleaching the dye (v) so that on imagewise exposure and overall heating of the material, silver halide (i) is reduced to silver in exposed areas and dye (v) is bleached in unexposed areas, and the azoaniline dye (v) being a compound of the formula given below.

A material of the invention gives, on exposure and processing, coincident negative silver and dye images. The silver image is produced by development of silver halide which occurs in exposed areas upon release of development activator from the precursor. The dye image is produced by bleaching of azoaniline dye in unexposed areas by unoxidized developing agent which diffuses from the heat-developable layer or layers.

The azoaniline dyes (v) present in heat-processable materials of the invention bear electron withdrawing groups and are believed to undergo nucleophilic displacement of the azo function when reacted with suitable nucleophiles such as developer moieties. These azoaniline dyes are represented by the formula:

wherein X is a benzene, thiophene, pyrrole, thiazole or furan ring having at least one electron withdrawing group that it is a nitro, halo, such as chloro or bromo, trifluoromethyl, acetyl, cyano or methylsulphonyl group) selected to provide a sum of ortho, meta and para Hammett substituent constants that is greater than +0.7; R', R2, R3 and R4 are individually selected from hydrogen, alkyl containing 1 to 12 carbon atoms, such as methyl, ethyl, propyl, butyl and pentyl, alkoxy containing 1 to 12 carbon atoms, such as methoxy or ethoxy, acyl containing 1 to 12 carbon atoms, such as propionyl, butyryl and pentanoyl, and amido containing 1 to 12 carbon atoms, such as acetamido, propionamido and butyramido; R1 and R2 may complete a fused-on ring which may be substituted; Y and Z are individually selected from hydrogen, alkyl containing 1 to 12 carbon atoms (which may be substituted) and cycloalkyl containing 5 to 7 carbon atoms. The described Hammett substituent constants can be determined by methods known in the art, such as by the method described by D.H. McDaniels and H.C. Brown, Journal of Organic Chemistry, pages 420-426 (1958).

The concentration of azoaniline dye in layer B can vary depending upon such factors as the desired image, the processing conditions, and the particular components of the heat-developable layer or layers. An optimum azoaniline dye concentration is typically within the range 10- to 10 mole per mole of silver in the heat-developable layer or layers.

A heat-developable photographic material of the invention contains a photosensitive silver halide, for example silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide, or a mixture thereof. The photographic silver halide can be coarse or fine grain. The composition containing the photographic silver halide can be prepared by any of the well-known procedures in the photographic art, such as a single-jet method, or a double-jet method, such as is used in making Lippmann emulsions, ammoniacal emulsions and thiocyanate or thioether ripened emulsions as described in the Product Licensing Index, Volume 92, December 1971, publication 9232. Surface image or internal image silver halide grains, or their mixtures can be useful, also as described in the above Product Licensing Index publication. The silver halide composition can be a regular grain emulsion, such as the type referred to in the above Product Licensing Index publication. Negative type silver halide compositions are especially useful; however, direct positive compositions can also be used. Those heat-developable photographic materials according to the invention are particularly useful which contain silver bromide or silver bromoidide gelatino emulsions.

Typically, a concentration of photographic silver halide is used which provides from 2 to 20 milligrams of silver per square decimeter of support.

At least one silver halide developing agent has to be present in the layer or layers (A), either as such or in the form of a precursor, which is sufficiently active to provide the necessary bleaching of the azoaniline dye. Useful active silver halide developing agents include polyhydroxybenzenes, such as hydroquinone developing agents, including hydroquinone itself, alkyl-substituted hydroqunones (such as tertiary-butylhydroquinone, methylhydroquinone, 2,5-dimethylhydroqunone and 2,6-dimethylhydroquinone); chlorohydroquinone, dichlorohydroquinone; alkoxy-substituted hydroquinones (such as methoxyhydroquinone and ethoxyhydroquinone); catechols and pyrogallol; methyl hydroxy naphthalene; and methyl gallate. A combination of an ascorbic acid developing agent (such as ascorbic acid or an ascorbic acid ketal) with a polyhydroxybenzene developing agent is often suitable, for instance a mixture of hydroquinone with ascorbic acid. Examples of other developing agents which can be used alone or in combination are aminophenol developing agents, such as p-aminophenol; reductone developing agents, such as anhydrodihydropiperidino hexose reductone; and 3-pyrazolidone developing agents, which are especially useful, including, for example, 1-phenyl-3-pyrazolidone, 4-methyl-4hydroxymethyl-1-phenyl-3-pyrazolidone, and other such developing agents described in British Patent 930,572.

A range of concentration of the silver halide developing agent or developing agent combination, can be used in a heat-developable photographic material of the invention.

Typically, a concentration of from 0.1 to 1 mole of total developing agent per mole of silver halide in the material is suitable.

The reaction between the exposed silver halide and the silver halide developing agent is carried out with the aid of an activating concentration of the development activator precursor (iii). Such a compound is typically a base-release agent or base precursor which upon heating increases the pH of the reaction medium containing the silver halide developing agent and the exposed photosensitive silver halide to a sufficient extent to bring about the desired development reaction. Examples of useful development activator precursors are guanidinium compounds, quaternary ammonium malonates, certain amino acids, such as 6-aminocaproic acid, heat cleavable hydrazides and oxazolidones as described in U.S. Patent 3,531,285. Especially useful activator precursors are compounds which are also stabilizer precursors and may thus be described as activator-stabilizer precursors. Such compounds include ionic compounds formed by the reaction of an acid and a base or by ionic exchange using known ionic compounds. Preferred activator-stabilizer precursor compounds, are represented by the formula: (I) QmA'w wherein Q is a base portion, especially a protonated basic nitrogen containing moiety, and A' is an acid anion that is an alpha-sulphonylacetate or a 2-carboxycarboxamide; and wherein m and w are integers such that the compound is neutral. Typically, m is 1 to 4 and w is 1 to 2. For example, when Q is a bivalent cation and A' is a univalent anion, m is 1 and w is 2. Particularly useful alpha-sulphonylacetates include, ethylenebis(sulphonylacetate), methylenebis(sulphonylacetate) and phenylsulphonylacetate. Q can be a variety of protonated basic nitrogen-containing moieties as described in "Research Disclosure", November 1976, Item 15109 and described and claimed in United Kingdom Patent Application No. 32794/77 (Serial No. 1579260) for example. Compounds in which A' is of Formula I and Q is one of the Formulae II to V of that Application are very suitable.

Examples of useful activator-stabilizer precursors within this class of compounds are bis(2-amino-2-thiazolinium)methylene bis(sulphonylacetate), and 1 1,3-bis[2S-(N,N'- ethyleneisothioure a)ethyl] lurea ethylenebis(sulphonylacetic acid) represented by the formula:

Another class of useful activator precursors includes 2-carboxycarboxamides as described in "Research Disclosure", March 1977, item 15567 and described and claimed in United Kingdom Patent Application No. 53525/77 (Serial No. 1590190). Especially useful 2-carboxycarboxamide salts are 1 ,3-bis(2-amino-2-thiazolinyl)propane. N,N'ethylenebis(phthalamic acid) and 1,3-bis[2S-(N,N'-ethyleneisothiourea)ethyl]urea. ethylenebis(sulphonylacetate). Some of the activator and activator-stabilizer precursor compounds have limited solubility in aqueous formulations and may have to be incorporated in a coating composition with the aid of an organic solvent.

The concentration of development activator precursor needed in a sensitive material of the invention is typically within the range, and preferably 1.0 to 1.5, 0.5 to 2.0 moles per mole of silver in the material, these ranges applying both to the concentration of a single compound and to the total concentration of a mixture of two or more compounds.

The heat-developable photographic materials of the invention can contain a variety of polymeric binders, alone or in combination. Certain of the described components can either be preformed or be formed in situ merely by mixing the constituents in the presence of a solvent and the binder. For instance, an activator-stabilizer precursor containing an acid and base moiety can be formed in situ by mixing the acid and base portions in the presence of a solvent and binder. Suitably polymeric binders include both-naturally occurring substances and their derivatives, such as gelatin, gelatin derivatives, cellulose derivatives, and polysaccharides such as dextran and gum arabic; and synthetic polymeric materials, such as water-soluble polyvinyl compounds like poly(vinyl pyrrolidone) and acrylamide polymers. The layers A and B of the heat developable materials can also contain, alone or in combination with the described binders, other synthetic polymeric binders such as dispersed vinyl compounds, for instance in latex form, particularly those known to increase the dimensional stability of photographic materials. If desired, heat-developable photographic materials of the invention can contain an overcoat layer, and /or an interlayer and/or a subbing layer. An overcoat layer, for example, can increase resistance to abrasion and other marking of the material. An overcoat layer, interlayer or subbing layer can contain alone or in combination the described binders. Useful synthetic polymers which can be used as binders include those described in the above referred to Product Licensing Index publication. Effective polymers include, for instance, water insoluble polymers of alkylacrylates and methacrylates, acrylic acid, sulphoalkylacrylates, methacrylates and polymers that have crosslinking sites which facilitate hardening or curing, and polymers having recurring sulphobetaine units as described in Canadian Patent No. 774,054.

An optimum vehicle for layer B can also be within those vehicles described for the layer or layers A. It is necessary that the vehicles for layers A and B be compatible to provide the desired imaging. Typically, the vehicle for layer A is a gelatino binder.

The photosensitive layer (or layers) A and the layer B can be coated on a variety of supports, a support being chosen which is not harmed unduly by the elevated temperatures to be used for development and which does not adversely affect the sensitometric properties at such temperatures. Typical supports include cellulose ester film, poly(vinyl acetal) film, poly(ethylene terephthalate) film, polycarbonate film, glass, paper and metal. Preferably the support is a flexible support such as a paper support.

A preferred material of the invention comprises a support having thereon (A) at least one heat-developable photographic layer comprising (i) photosensitive silver halide, (ii), a 3-pyrazolidone silver halide developing agent, (iii) an activating concentration of the activator precursor 1 ,3-bis(2-amino-2-thiazolinyl)propane. N ,N ' -ethylenebis(phthalamic acid), and (iv) a polymeric binder and (B) at least one layer comprising an azoaniline dye that is bleached in the non-image areas of the material upon development of a latent image in the layer A by uniformly heating the material.

The heat-developable material, especially the layer or layers A, can contain a spectral sensitizing dye or combination of dyes to confer additional sensitivity on the light-sensitive silver halide. Useful spectral sensitizing dyes are described, for example, in the above referred to Product Licensing Index publication. In addition, supersensitizing addenda which do not absorb visible light may be used. The sensitizing dyes and other addenda can be incorporated into the material from water solutions or suitable organic solvent solutions by procedures, such as described in the above referred to Product Licensing Index publication and known in the photographic art.

The layers A and B, and any other layers of a photographic material according to the invention can be coated by various coating procedures. If desired, two or more layers can be coated simultaneously in known manner.

The preferred coverage ranges of the essential components of a material of the invention are for the layer or layers A (i) 105 to 104 mole of photosensitive silver halide, (ii) 106 to 104 mole of total silver halide developing agent and (iii) 2 x 10-5 to 5 x 10-4 mole of total activator precursor per dm2 and for layer B 10-6 to 10 5 mole of the azoaniline dye/dm2.

The term "bleached" is used herein with regard to the azoaniline dye to refer to the dye being either rendered colourless or changed in colour, to an extent sufficient for the developed silver image in layer or layers A to be enhanced.

After imagewise exposure of a heat-developable photographic material of the invention, an image can be developed therein by heating to a temperature within the approximate range 115 to 1800C, usually within the range of 135 to 165"C. Where the activator precursor is an activator-stabilizer precursor, the developed image will be stabilized.

A variety of energy sources can be useful in making an imagewise exposure, including for example, a light source, a laser, an electron beam or an X-ray source.

An image is typically developed by heating the photographic material to a temperature within the described range for from 1 to 60 seconds, such as about 1 to about 30 seconds. By increasing or decreasing the temperature, the processing time may be decreased or increased respectively.

Various means are useful for heating the material after exposure; the material can be brought into contact with a simple hot plate, iron or rollers or dielectric heating means can be employed.

Small concentrations of moisture can be present during processing such as those present in conventional photographic paper supports at atmospheric conditions, such as at about 25"C and 40% relative humidity.

The silver halide photosensitive dispersion or emulsion can be washed or unwashed to remove soluble salts formed during precipitation; can be chemically sensitized; can contain development modifiers that function as speed-increasing compounds; and can contain antifoggants and emulsion stabilizers as described in the Product Licensing Index, Volume 92, December 1971, Item 9232. The sensitive layer or layers can contain hardeners, antistatic agents, plasticizers, lubricants, coating aids, matting agents, brighteners, absorbing and filter dyes which do not adversely affect the desired properties of the heat developable material and other addenda as described, for example, in the above referred to Product Licensing Index publication.

Whilst in a useful arrangement of layers in a photographic material according to the invention, the sensitive layer group or layers A is above the dye-containing layer B, it can be in some cases desirable to have the layer or layers A between the support and the layer B. In this instance, the support can be transparent to permit the imagewise exposure being made through it. If a layer is used between the layer or layers A and the layer B, it must permit the unoxidized developing agent to transfer by diffusion from A to B.

In selecting useful dyes for layer B, a combination of tests can be employed. Suitable tests are the solution test described in Example 8 and the film test described in Example 9 below.

The following examples are included for a further understanding of the invention. Those examples which relate to dyes which are not azoaniline dyes are comparative examples. Example I - Photothermographic material and process containing layers A and B containing an azoaniline dye A solution of the dye:

(30 milligrams) in 10 ml of a 4% dichlormethane solution of cellulose acetate was coated at a 4-mil wet coating thickness on a poly(ethylene terephthalate) film support. The resulting coating (layer B) was permitted to dry and then overcoated with a mixture of the following: 4-methyl-4-hydroxymethyl- 1 - 75 mg phenyl-3-pyrazolidone referred to herein as MOP) 2-amino-2-thiazolinium tri- 500 mg chloroacetate (referred to herein as TAT) 2% photographic gelatin 10 ml in water silver bromoiodide gelatino 1 ml emulsion (0.09 micron grain size, 6 % iodide) Surfactant (5% by weight surfactant 0.2 ml 10G) (a nonylphenoxypolyglycidol available from the Olin Corp., USA, known as Surfactant 10G) The resulting composition was overcoated on the layer B at a wet coating thickness of 4 mils. This provided a silver coverage of 130 milligrams of silver per ft2 (13 mg of silver per square decimeter). The resulting layer A was permitted to dry to provide a photothermographic material according to the invention. This material was imagewise exposed to roomlight to provide a developable latent image and then heated for the time and temperature described in following Table E I to provide a difference in dye density between the unexposed areas of the material as shown in that table.

Table E I Visual Density (Dmax) Process Ag + Dye Dye* Time (secs.) Temp ( C) Exposed Unexposed Exposed Unexposed (a) 10 138 2.5 1.6 1.3 1.3 (b) 20 175 2.2 0.6 0.9 0.5 10 at 138 followed # (c) by 20 at 175 2.7 0.3 1.0 0.4 *Layer A was removed with warm water to reveal the dye only image.

A control coating like that described above but from which layer B containing the dye was missing provided the following results given in Table E II.

Table E II (Control) Visual Density (Dmax) Process (Ag only) Time (secs.) Temp eC) Exposed Unexposed 10 140 1.43 0.09

10 at 140 followed ) by 20 at 175 1.61 0.11 Example 2 - Variation of concentration Photothermographic materials were made and tested as described in Example 1 but using different concentrations of certain constituents which gave coverages over the following ranges: MOP 2.25 - 6.4 mg/dm2 TAT 11.0 - 37.5 mg/dm2 AgBrI emulsion 3.5 - 10.0 mg/dm2 The materials made were E tested using both single step and two-step heat processing, as described in Table E I.

In each case the heating was stopped when the minimum density areas was transparent, that is, when the Dmin area cleared. The results of this processing are given in following Table E III. For these examples, it is to be noted that regardless of the coating composition and processing conditions, essentially the same dye density (Dmax 0.5 - 0.6 and Dmin 0.25) was obtained in each case.

Table E III Examples of Process of Invention with Concentration Ranges Quantity Processing Time Dmax Dmin Compound (mg/dm) (Sec/ C) Ag + Dye Ag Dye Ag + Dye Ag Dye MOP 3.4 TAT 11.0 120"/160 1.4 1.0 0.6 0.24 0.04 0.22 AgXa 5.7 Dye c 2.25 20"/130 1.75 1.25 0.5 0.2 0.05 0.27 followed by 20"/180 MOP 6.4 TAT 37.5 20"/160 1.75 1.25 0.5 0.34 0.13 0.27 AgXb 10.0 Dye c 2.25 MOP 2.25 TAT 34.0 60"/115 0.9 0.4 0.5 0.25 0.04 0.21 followed by 60"/160 AgXb 3.5 Dyec 2.25 a AgBrI emulsion A - This is a silver bromoiodide gelatino emulsion containing 2.5 mole - iodide and having a 0.09 micron grain size. b AgBrI emulsion B - This is a silver bromoiodide gelatino emulsion containing 2.5 mole % iodide and having a 0.09 micron grain size. cDye 22 described in Table E IX.

Example 3 - Different binder Photothermographic materials were made and tested as described in Example 1 with the exception that poly(vinyl butyral) (commercially available as 'Butvar' B-76: 'Butvar' is a trade mark) was used as a binder for the dye instead of cellulose acetate.

The destruction of the dye by MOP is very rapid in poly(vinyl butyral), and competitive in rate with the silver halide development process in the layer containing silver halide.

However, a low density dye image can be obtained at short processing times, that is 2 to 5 seconds.

The results obtained are given in Table E IV.

Table E IV Amount Dmax Dmin Compound (mgldm2) Process* Ag + Dye Dye Ag + Dye Dye MOP 4.5 2"/160 1.2 0.55 0.46 0.35 TAT 37.5 Dye 22 2.25 5"/160 1.05 0.42 0.32 0.26 Butvar B-76 15.0 on unsubbed poly(ethylene terephthalate) film support *Time in seconds/temperature in "C.

Example 4 - Combination of developing agents In some cases ascorbic acid may develop a layer containing silver halide without satisfactorily bleaching the dye in the adjacent dye-containing layer, this effect apparently being due to insufficient penetration of the ascorbic acid into that layer. This effect is illustrated by the present Example for which cellulose acetate was used as the binder for the dye-containing layer. It has been found that when hydroquinone is used as the sole developing agent, this will completely bleach the dye in the dye-containing layer but will not satisfactorily develop the latent image in the silver halide-containing layer. However, useful results may be obtained using a mixture of suitable concentrations of ascorbic acid and hydroquinone in the layer containing the silver halide. This is demonstrated by the results of Table E V below which were obtained by making sensitive materials analogous to those described in Example 1, containing constituents at the coverages indicated in that table, which also gives the processing considions used. These results show that a coverage of 0.19 milligrams of hydroquinone per square decimeter gave useful effects with the ascorbic acid.

Table E V Effect of Hydroquinone on Ascorbic Acid Performance/Dye in Cellulose Acetate Amount Processing Time Dmax Dmin Compound (mg/dm) (Sec/ C) Ag + Dye Dye Ag + Dye Dye Ascorbic 1.5 Acid TAT 22.5 60"/180 1.90 1.22 1.20 1.17 AgXa 5.7 Dye 22 2.25 T-1** 30.0 above + 0.19 60"/160 1.52 0.74 0.6 0.55 hydroquinone above + 0.28 30"/135 1.84 1.2 0.8 0.8 hydroquinone followed by 30"/160 aAgBrI emulsion A **T-1 as used in this table and in other tables herein means cellulose acetate.

Example 5 - Dispersion of coupler solvent with developing agent and dye The procedures described in the above examples were repeated with ascorbic acid as the developing agent but with the described dye dispersed in the phenolic coupler solvent 2,4-di-tertiary-amylphenol (Coupler Solvent A) in the silver halide-containing layer rather than in an undercoat. It was found that upon heating the photothermographic material so made after imagewise exposure that the dye was bleached uniformly rather than preferentially in the non-image areas. In addition, it was observed that the photothermographic coatings on gel subbed poly(ethylene terephthalate) film support or on cellulose acetate film support were free of undesired pinholes or blisters in the coatings. This result was believed not due to the surfactant used in the preparation of the dispersion.

Accordingly, by using a dispersion of coupler solvent A, ascorbic acid can be overcoated upon a layer containing a dye in cellulose acetate and the desired properties of the coating maintained upon heating the photothermographic material.

Typical results of this heat processing are given in following Table E VI. The maximum density-minimum density ratios in dyes are similar to those obtained with the use of a silver halide containing layer containing MOP with cellulose acetate. Two differences, however, are to be noted: Xa) the concentration of ascorbic acid required is significantly less than that for MOP and (b) the maintenance of a high concentration of aminothiazoline in the silver halide-containing layer was significant. It was observed that improved results were obtained in processing by contacting the side of the film opposite the support with the heating means.

Table E VI Use of Dispersion of Coupler Solvent A With Ascorbic Acid/Dye in Cellulose Acetate Amount Processing Time Dmax Dmin Ingredients (mg/dm) (Sec/ C) Ag Ag + Dye Dye Ag Ag + DyeDye AA* 1.2 TAT 22.5 20"/160 0.62 - - 0.13 AgXa 5 face down** Coupler Solvent A 18 above + Dye 21 2.25 30"/160 - 0.93 0.54 - 0.24 0.22 T-1 30 face down** AA* 0.57 TATa 22.5 AgXa 2.5 90"/160 0.32*** 0.86 - 0.1*** 0.4 Coupler Solvent A 18 Dye 21 1.5 T-1 15 AA* 0.94 0.42 0.35 0.65 1.05 MOP 0.18 15"/160 AgXa 2.5 face down** Coupler Solvent A 18 Dye 21 1.5 T-1 15 aAgBrI emulsion A * AA as described herein is ascorbic acid.

** face down means that the side of the heat developable photographic element containing the silver halide was contacted with the heating means.

*** Layer A was removed with warm water to reveal the silver only image.

Example 6 - Processing temperature latitude The procedures of Example 1 were repeated with the following components in layers A and B: layer A: ascorbic acid 0.6 mg/dm2 TAT 22.5 mg/dm2 photographic gelatin 15 mg/dm2 silver bromoiodide emulsion A 2.5 mg/dm2 layer B: dye 21 specified below 1.5 mg/dm2 poly(vinyl butyral) 15 mg/dm2 The layers were coated on a poly(ethylene terephthalate) film support.

Dye 21 used in layer B has the following structure:

The processing temperatures used for heating the imagewise exposed photothermographic material and the results obtained upon heating are given in following Table E VII.

The results indicate that ascorbic acid has no difficulty bleaching dye 21 in a poly(vinyl butyral) binder. The sensitometric characteristics of the photothermographic material are not significantly changed over a processing temperature range of 115"C to 1600C.

Table E VII The Process of the Invention with Ascorbic AcidlDye in poly(vinyl butyral) The Effect of Temperature at a Constant Heating Time of 30 Sec.

Temp. ("C) 100 115 125 135 150 160 Dmax 1.08 0.96 0.85 0.85 0.89 0.87 Ag + Dye Dmin 1.08 0.35 0.35 0.38 0.52 0.44 Dmax 0.88 0.62 0.62 0.60 0.71 0.63 Dye Dmin 0.88 0.35 0.35 0.38 0.50 0.44 Example 7 - Developer concentration range The procedures described in Example 1 were repeated with the following components in layers A and B: layer A: ascorbic acid concentration as indicated in following Table E VIII TAT 22.5 mg/dm2 silver bromoiodide emulsion A 2.5 mg/dm2 photographic gelatin 15 mg/dm2 layer B: dye 21 as described in Example 6 1.5 mg/dm2 (density = 0.90) poly(vinyl butyral) 15.0 mg/dm2 The layers were coated on a poly(ethylene terephthalate) film support. The photothermographic material so prepared was imagewise exposed to light and then uniformly heated as described in Example 1. The results obtained are given in following Table E VIII.

Table E

Table E IX Solution Test Results on Azoaniline Dyes Dye Number Dye Structure Test Result*

1 O2N N=N < NH2 N 2 /C2N5 N 02N N=N C2H4CN /C2H5O O2NN-N N 3 cH-N Y 24 (Yellow 0 Y 4 O2N t N=N NEt2 (Yellow) NHCOCH3 CH3 5 < N=N (C3)2 Y 02N N=N NHc?'C;i3)2 (Orange) N8COCH3 6 02N iN=N 02N-NeN-)" sCzH5 0 J \e2H4- (Yellow) NHCOCH3 N=N C2N4cN < O2 N\/QHN$j N CN3 Table E IX (cont'd) Solution Test Results on Azoaniline Dyes Dye Number Dye Structure Test Result*

r 8 02H/ N=N (Colourless) Cl NHCOCH3 9 O2N 02N < N=H (yellow) (Yellow) Cl NHCOCH3 \ ?(CzCN(CN3)2 10 N=N -N=N-Y (Orange) Ct NHCOCH3 11 o2NN=NN(C2fl5 d Y Cl NH=H3 C2H4-89 (Yellow) o N02 12 F3c 49=N < NEt2 (Colourless) NHCoc1(3 N02 C2HS 13 13 N=N N\' Y C?'2 (Yellow) NHCOCH3 14 02N ?J=NNft2 (Yellow) COCH3 NHCOCH3 Cl 15 N < S502 N MW Cl Table E IX (cont'd) Solution Test Results on Azoaniline Dyes Dye Number Dye Structure Test Result*

Cl 16 02N < /CIHg N Cl 17 ozH-NrN- /CZHg 17 02H < HXN /C2H5 N C2HqCN CL CH3 N02 SOCH3 18 02N 4= N X z (Brown) Cl NHCOCH3 8r OÇH3 19 O2N N"NN(C2H4OcOC?'3)2 (Yellow) I NHCOCN3 NO2 20 02N4N=NXNs (Yellow) Ci C?'3 notC2?'5 21 (Brown) \ < 9 CH2 4 (Brown) CN NHCOCH3 H02 CHs 22 Q?' N=N 02N4N=NXNHCHCH2CH(CH3)2 (Orange) CN HHCOCHI OH 23 Ils 0zN Y (Brown) NHso2M e Table E IX (cont'd) Solution Test Results on Azoaniline Dyes Dye Number Dye Structure Test Result*

24 HZNSOz-/fY ld SOZF 802F OH 25 CONH(CH2)4-0 < t C5 Y Y NHSOZ Ii i=N SN NO2 ( Y=N-$j N(C?'3)2 N(CH3)2 26 0 Y Ozi S N=N N\C2H4Ct (Colourless) NO2 27 (CHJ)Z c3 Y (CIIJ)ZCCI H 0 NHCOC?'3 28 )CS NE t2 Y 02N 29 H3COZS-(0N=N-(P)-" Y C L HHCOCH3 Table E IX (cont'd) Solution Test Results on A zoaniline Dyes Dye Number Dye Structure Test Result*

Not tested solution - see Table E XII

Not tested * None of these dyes reacted with ascorbic acid alone or with aminothiazoline alone.

'N' indicates that a particular dye was not faded by the combination and 'Y' indicates that the dye was faded by the combination. t Color of dye solution after reaction.

Example 9 - Screening test for suitable dyes A screening test for useful dyes was also carried out with a photothermographic material, as described in Example 1, in which a dye was present in a cellulose acetate layer overcoated with a photothermographic layer containing the pyrazolidone developing agent.

This was Film Test I. Details and results of this test are given in following Table E X and Table E XI comparing the described dyes.

A further film screening test for useful dyes was carried out in which the dye was present in a cellulose acetate layer overcoated with a photothermographic layer containing ascorbic acid with the 3-pyrazolidone developing agent plus a coupler solvent dispersion in the photothermographic element. This was Film Test II. The details and results of this second screening test are given in following Table E XII with comparison to other results in Table E X.

Table E X A Comparison of Test Results Dye Number Solution Test* Film Test I* Film Test II* 1 N N 2 N 3 Y 4 Y Y 5 Y 6 Y 7 N 8 Y Y 9 Y 10 Y N 11 Y 12 Y Y Y 13 Y Y 14 Y Y 15 N 16 N - 17 N - faint 18 Y Y 19 Y Y 20 Y Y 21 Y 22 Y 23 Y 24 25 Y Y 26 Y Y 27 Y Y Y 28 Y 29 Y A dash means the dye was not tested. "N" means that the dye was not faded and "Y" means the dye was faded in the non-image areas.

Table E XII Dye Screening: Dye in T-lIMOP* Processing Conditions Dye Number Colour (Sec/ C) Image 13 orange 45/160 Yes Dye Screening : Dye in T-lIMOP** 1 yellow 60/180 No 27 blue 60/180 Yes 28 blue 60/180 Yes 12 red 60/180 Yes 13 red-orange 60/180 Yes 18 blue 60/180 Yes 10 red 60/180 No 20 violet 60/180 Yes * 30 mg of the dye in 10 ml of 5% by weight cellulose acetate was coated at a 3 mil wet coating thickness on a poly(ethylene terephthalate) film support and overcoated with a mixture of MOP (100 mg/dm2 of support), TAT (500 mg/dm2of support), silver bromoiodide emulsion A (1 ml), 4 drops of 10% by weight Surfactant 10G in water and 2% by weight gelatin (10 ml) at 3 mil wet coating thickness.

** 20 mg of each dye in 10 ml of 4% by weight cellulose acetate in dichloromethane was coated at 3 mil wet coating thickness on a poly(ethylene terephthalate) film support and then overcoated with a mixture of MOP (50 mg), TAT (250 mg), silver bromoiodide emulsion A (0.5 ml), 0.15 ml of 10% by weight Surfactant 10G in water, 2% by weight photographic gelatin (3 ml) and water (7 ml) at a wet coating thickness of 3 mils.

Table E XII Film Test II Dye Screening: Dye in T-1 cellulose acetatel ascorbic acid plus MOP with coupler solvent dispersion * Conditions Dye Number Colour (Sec/ C) Image 25 cyan 30/115 Yes 30 yellowy cyanS 30/160 Yes 31 blue 30/160 No 27 blue 30/160 Yes 14 magenta 15/180 Yes 12 orange 120/180 Yes 8 magenta 180/160 Yes 26 magenta 180/160 Yes 4 red 180/160 Yes Table E XII (cont'd) Film Test II Dye Screening: Dye in T-1 cellulose acetate/ ascorbic acid plus MOP with coupler solvent dispersion * Dye Number Colour Conditions Image 30 yellow 120/180 No 19 blue 10/160 Yes 17 orange 120/180 faint * Coating consisted of layer A on layer B on gel-subbed poly(ethylene terephthalate.

Coupler solvent A was used.

Layer B: A mixture of 2,4-di-t-amylphenol (2 ml), 5% by weight Alkanol B (3 ml), 2% gel (72 ml) and 10% Surfactant 10G dispersed together for 5 minutes with a polytron. This dispersion (50 ml) was then mixed with a mixture consisting of TAT (3.6 g), ascorbic acid (90 mg), MOP (30 mg), 10% Surfactant 10G (30 drops), 2% gel (60 ml) and AgBrI emulsion A 3 ml) and coated at 3 mil.

Layer B: Dye in amount indicated dissolved in a 2% solution of T-1 cellulose acetate (10 ml) in dichloromethane and coated at 3 mil. t Colour shift upon release of base.

Example 10 - Halation protection It was observed in those photothermographic materials described in the preceding examples that halation protection was provided. Accordingly, the dye layer of a the photothermographic material of the invention provides both halation protection and image enhancement. I1: halation protection is the main requirement desired, then the concentration of dye used need not be as high as when dye image enhancement is also desired. Thus halation protection can be provided when sufficient dye is present to provide a density of about 0.3. A photothermographic material providing halation protection and dye bleaching may use, for example, dyes which absorb in the red and in the red-green spectral regions, such as Dye 32* and 21 respectively, the material also comprising, for instance, a poly(vinyl butyral) binder for the dye-containing layer, and, coated thereover, a photothermographic layer containing a photosensitive composition containing MOP. TAT and photosensitive silver halide as described in Example 1.

* Dye 32 is an indoaniline dye of the structure

Claims (10)

WHAT WE CLAIM IS:

1. A heat-developable photographic material which comprises a support bearing (A) a layer which contains, or adjacent layers which together contain, (i) a photosensitive silver halide, (ii) a silver halide developing agent (or a precursor thereof), (iii) a development activator precursor and (iv) a polymeric binder, and (B) adjacent to the layer or layers (A) a layer which contains (v) an azoaniline dye, the developing agent (ii) being capable at an elevated temperature of bleaching the dye (v) so that on imagewise exposure and overall heating of the material, silver halide (i) is reduced to silver in exposed areas and dye (v) is bleached in unexposed areas, and the azoaniline dye (v) being a compound of the formula:

wherein X is a benzene, thiophene, pyrrole, thiazole or furan ring having at least one electron-withdrawing substituent which is a halogen atom or a nitro, trifluoromethyl, acetyl, cyano or methylsulphonyl group, the substituent or substituents being selected to provide a Hammett substituent constant or sum of ortho, meta and para Hammett substituent constants which is greater than 0.7, and each of R1, R2, R3, and R4 is a hydrogen atom, an alkyl, alkoxy, acyl or amido group having up to 12 carbon atoms, and each of Y and Z is a hydrogen atom, an alkyl group having up to 12 carbon atoms which may be substituted, or a cycloalkyl group having from 5 to 7 carbon atoms.

2. A material according to claim 1 wherein the azoaniline dye is one of the Dyes 21 and 22 specified herein.

3. A material according to either of the preceding dlaims wherein the silver halide developing agent (ii) is a 3-pyrazolidone developing agent, or is a polyhydroxybenzene developing agent used in conjunction with an ascorbic acid developing agent.

4. A material according to any of the preceding claims wherein the development activator precursor is an activator-stabilizer precursor of the formula I specified herein.

5. A material according to claim 4 wherein the activator-stabilizer precursor is bis(2-amino-2-thiazolinium) methylene bis(sulphonylacetate), 1 ,3-bis[2S-(N ,N ' - ethyleneisothiourea)ethyl] . ethylenebis(sulphonylacetic acid), 1, 3-bis 2-amino-2- thiazolinyl)propane.N,N'-ethylenebis(phthalamic acid), 1,3-bis-[2S-(N,N'ethyleneisothiourea)ethyl] urea.ethylenebis(sulphonylacetate) or N-(2-thiazolino-N' - (imidazolino)ethylenediamine ethylene bis(sulphonylacetate).

6. A material according to any of the preceding claims wherein the layer (B) contains a binder.

7. A material according to claim 6 wherein the layer (B) is coated between the support and the layer or layers (A).

8. A material according to claim 1 substantially as described in any of Examples 1 to 7, 9 and 10 herein.

9. A method of forming a photographic record which comprises imagewise exposing to actinic radiation a heatdevelopable material according to any of the preceding claims and heating the material overall to form an image of dye and silver in the exposed areas.

10. A photographic record formed by a method according to claim 9.