US3640719A

US3640719A - Silver halide emulsions containing bis-heterocyclic n-containing compounds as antifoggants

Info

Publication number: US3640719A
Application number: US843742A
Authority: US
Inventors: Anita Von Konig; Franz Moll; Wolfgang Muller-Bardorff; Wilhelm Saleck
Original assignee: Agfa Gevaert AG
Current assignee: Agfa Gevaert AG
Priority date: 1968-08-06
Filing date: 1969-07-22
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08
Also published as: GB1274071A; BE737119A; DE1797027B2; CH516177A; DE1797027A1; DE1797027C3; FR2015184A1

Abstract

The stability of photographic silver halide emulsions against the formation of fog is improved by the addition of bisheterocyclic triazole, oxazole, thiazole, imidazole, thiadiazole or thiadiazolidine type compounds.

Description

United States Patent Von K'tinig et. al.

Koeln-Stammhein; Wolfgang Miller-Bardorff, Koeln; Wilhelm Saleck, Schilclgen,

all of Germany Assignee: Agfa-Gevaert Aktiengesellschaft, Leverkusen,Germany Filed: July 22, 1969 App1.No.: 843,742

Foreign Application Priority Data Aug. 6, 1968 Germany ..P 17 97 027.3

us. Cl. ..96/l09, 260/306.6, 260/302 s,

260/307 F, 260/308 Int. Cl ..G03c 1/34 Field 6: Search ..96/l09; 260/3066, 302 s, 307 F,

[ Feb. 8, 1972 [56] References Cited UNITED STATES PATENTS 3,256,294 6/ 1966 DAmico ..260/ 306.6 X 3,364,028 1/1968 Von Konig ..96/109 X FOREIGN PATENTS OR APPLICATIONS 220,166 3/1962 Austria ..96/109 616,822 1/1949 Great Britain ..96/l09 Primary Examiner-Norman G. Torchin Assistant Examiner-Won H. Louie, Jr. Attorney-Connolly and Hutz [57] ABSTRACT The stability of photographic silver halide emulsions against the formation of fog is improved by the addition of bis-heterocyclic triazole, oxazole, thiazole, imidazole, thiadiazole or thiadiazolidine type compounds.

2 Claims, No Drawings SILVER HALIDE EMULSIONS CONTAINING BIS- IIETEROCYCLIC N-CONTAINING COMPOUNDS AS ANTIFOGGANTS PHOTOGRAPHIC MATERIAL WITH IMPROVED PROPERTIES This invention relates to a photographic silver halide emulsion the stability of which is improved by addition of substituted bis-heterocyclic compounds.

It is well known that photographic emulsions on storage become spontaneouslydevelopable without exposure to light. There is normally a detectable amount of the silver salt reduced during development at unexposed areas. This phenomenon is commonly called fog or chemical fog. Fog depends both upon the nature of the emulsion and the conditions of development. For a given emulsion it increases with the degree of development. It is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is desirable to have emulsionsas stable as possible under the condition of high temperature, which may occur in tropical climates. Fog usually appears over the whole area of the. lightsensitive layer, but when severe is quite frequently nonuniform.

It is known that certain compounds particularly hetero cyclic mercapto or imino compounds have an antifoggant and stabilizing effect when incorporated into photographic silver halide emulsions and so improve greatly the keeping qualities of the emulsions. Mostly the so-called fog inhibitors or stabilizers form difficulty soluble or insoluble silver compounds with the silver ions of the photographic emulsion. It is also known that inorganic or organic mercury compounds can be used. Many of these stabilizers however, are of limited utility since they have a desensitizing effect or alter the gradation;

It is among the objects of the invention to provide stabilizers which cause no reduction inthe sensitivity at concentrations at which they achieve sufficient stabilization. Another object is to provide a photographic silver halide emulsion that is stable against the production of fog upon storageand stable with respect to the speed and contrast of the emulsion. Other objects and advantages will become apparent from a consideration of the following description and examples.

We now have found that photographic silver halide emulsions can be stabilized with respect to the formation of fog even under extreme storage conditions and with respect to speed and contrast of the emulsion very effectively by the addition of a bis-heterocyclic compound of the following formulas:

in which:

2 or Z represents the ring members necessary for completing a triazole, oxazole, thiazole, imidazole, thiadiazole or thiadiazolidine type ring. These heterocyclic rings may also carry other substituents, e.g., alkyl or alkylthio, preferably containing up to eight carbon atoms, such as methyl, ethyl, propyl, butyl, hexyl, heptyl or octyl groups, or substituents of the aryl series, in particular phenyl groups, which may be substituted, e.g., with short chain alkoxy or alkyl groups having up to three carbon atoms or with halogen or the like; furthermore, they may also be substituted with alkylamino or arylamino groups, e.g., phenylamino.

Compounds of the thiazole series include thiazoles or benzothiazoles and substitution products thereof, compounds of the oxazole series include oxazole, benzoxazole, naphthoxazole or substituted derivatives thereof, compounds of the triamle series include triazole or bcnzotriazole or (Jul e rri1? tin-int The bis-heterocyclic compounds are prepared in known manner. The preparation of compound I is described in detail below. Other heterocyclic compounds which may be used according to the invention are obtained by analogous reactions. Compounds of Formula I or of Formula II are obtained, depending on the tautomeric form in which the heterocyclic compounds react. In the list of formulas, all the compounds are given as S,S'-diesters of dithiocarbonic acid but this does not exclude the possibility of the compounds being present in the form of Formula II.

COMPOUND I 35.4 g. of l-phenyl-3-mercapto-l,2,4-triazole and 8 g. of sodium hydroxide dissolved in 6.5 ml. of water are suspended in 300 ml. of carbon tetrachloride. A solution of 47 g. of phosgene in 200 ml. of carbon tetrachloride which has been freshly prepared at -5 C. is added to this suspension with stirring at 20 to 30 C. in the course of minutes. After the reaction mixture has been stirred for a further l8 hours, the excess phosgene is blown off with dry nitrogen and the precipitated product is separated by vacuumfiltration. The crude product is purified by washing it several times with water, methanol and ether. Yield: 22 3., mp. 192 C.

COMPOUND 2 41.8 g. of Zmercapto-S-anilino-l,3,4-thiadiazole and 8 g. of sodium hydroxide dissolved in 6.5 ml. of water are suspended in 300 ml. of carbon tetrachloride. A solution of 47 g. of phosgene in 200 ml. of absolute carbon tetrachloride is added to this suspension dropwise at room temperature while the mixture is stirred at 20 to 30 C. After the smeary mass has been left to stand for several hours, the excess phosgene is blown off with dry nitrogen and the precipitated product is removed by vacuum filtration. The crude product is purified by washing it several times with water, methanol and ether. Yield: 26.5 g. mp. 181C.

COMPOUND 3 A solution of 12 g. of phosgene in 200 ml. of dry carbon tetrachloride is added dropwise with stirring to a suspension of 37.8 g. of the sodium salt of 2-mercaptobenzo-thiazole in 300 ml. of carbontetrachloride at to C. in 2 hours. After the reaction mixture has been stirred for another 20 hours at 0 to 5 C., the excess phosgene is blown off with dry nitrogen and the precipitated product is removed by vacuum filtration. The product is purified by washing it several times with water and methanol. Yield: g., m.p. 135 C.

COMPOUND 4 A solution of 37 g. of phosgene in 200 ml. of dry carbon tetrachloride is added dropwise to a suspension of 34.6 g. of the sodium salt of Z-mercaptobenzoxazole in 5 ml. of water and 300 ml. of carbon tetrachloride with stirring at room temperature in the course of 2 hours, and the reaction mixture is then stirred for another half hour. The excess phosgene is blown off with carbon dioxide and the product is separated by vacuum filtration. The crude product is purified with washing several times with water, methanol and ether. Yield: 4 g., m.p. 143 C. Another 4.5 g. of compound 4 can be obtained by concentrating the reaction liquid by evaporation at C.

COMPOUND 5 COMPOUND 6 A solution of 11 g. of phosgene in 200 ml. of dry carbon tetrachloride is added dropwise in the course of 1 hour at room temperature with stirring to a suspension of 52.8 g. of the potassium salt of 2-mercapto-5-thioxo-4-phenyl-l,3,4- thiadiazoline in 300 ml. of dry carbon tetrachloride, the reaction mixture is then stirred for another 18 hours and the excess phosgene is blown off with dry nitrogen and the product is separated by vacuum filtration. The crude product is purified by washing several times with water, methanol and ether.

1 Yield: 33 g. decomposition point 175 C.

COMPOUND 7 41.3 g. of 2-mercapto-5-butylmercapto-1,3,4-thiadiazole and 8 g. of sodium hydroxide dissolved in 6.5 ml. of water are suspended in 300 ml. of carbon tetrachloride. A solution of 47 g. of phosgene in 200 ml. of dry carbon tetrachloride is added dropwise to this suspension at room temperature with stirring in the course of 2 hours. After stirring the reaction mixture for another 18 hours, the excess phosgene is blown off with dry nitrogen and the precipitated sodium chloride is removed by vacuum filtration. The reaction mixture is concentrated by evaporation in vacuo at 10 to 20 C. The oily residue becomes crystalline when cooled below 0 C. The crude product is dissolved in methylene chloride after it has been washed several times with water and methanol. The solution in methylene chloride is treated with active charcoal and carefully concentrated by evaporation in vacuo. Yield: 25 g., m.p. 5 1 C.

COMPOUND 8 26.6 g, of 2-amino-5-mercapto-l,3,4-thiadiazole and 8 g. of sodium hydroxide dissolved in 6.5 ml. of water are suspended in 300 ml. of carbon tetrachlorideuA solution of 57 g. of phosgene in 200 ml. of dry carbon tetrachloride are added dropwise to the suspension in 2 hours with stirring at room temperature. After another l8 hours stirring, the excess phosgene is blown off with dry nitrogen and the product is separated by vacuum filtration. The crude product is purified by washing it several times with water, methanol and ether. Yield: 28 g., m.p. 167 C.

The heterocyclic compounds for use according to the invention can be hydrolyzed relatively easily, in particular in alkaline media. Apart from being added to the silver halide emulsion layers, they may also be added to separate layers since in any case they diffuse into the silver halide emulsion layers during development. The separate layer may be a water-permeable intermediate layer or a protective layer or, as in the silver salts diffusion process, it may, of course, be an image receiving layer.

Since the mercapto group is protected, the sensitivity obtainable in the photographic emulsion is generally greater than when using stabilizers with free SH-groups. The sensitivity is not deleteriously etfected during storage.

A further advantage of the inventive emulsion is that images of particular fine grains are obtained. This effect is caused by the hydrolysis of the compounds in the alkaline developer to produce free mercapto groups, and which gradually slows down the development. At the same time, the maximum sensitivity is not reduced by the delayed release of the SH-group. The bis-heterocyclic compounds can be added to the silver halide emulsion at any stage during the preparation of the emulsion. It is preferred to incorporate these compounds before the afterripening.

The photographic silver halide emulsions are prepared in accordance with common practice including the steps of:

l. Precipitation of the silver halide in the presence of a protective colloid and physical ripening;

2. Removal as by washing from the resulting emulsion, the

excess water-soluble salts that have fonned as a result of the precipitation; and

3. Chemical ripening (afterripening) the washed product to impart the desired sensitivity to the emulsion.

The bis-heterocyclic compounds can be used in any silver halide emulsion. Suitable silver halides for the emulsion are silver chloride, silver bromide or mixtures thereof, if desired containing up to 10 mols percent of silver iodide. The silver halides may be dispersed in the usual hydrophilic compounds such as carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, alginic acid and its salts, esters or amides or, preferably, gelatin.

The methods of incorporating the compounds in emulsions are relatively simple and well known to those skilled in the art of emulsion making. It is convenient to add the stabilizers from solutions in appropriate solvents whereby the solvent should be completely free from any deleterious effect on the ultimate light-sensitive material. Suitable are in particular solvents miscible with water such as methanol, ethanol alone or in admixtures.

The concentration of the stabilizers in the emulsion can vary widely, for instance from about 1 mg. to 5 g. per kg. of flowable emulsion. Preferred are amounts of l to 50 mg. per kg. of emulsion. The specific concentration depends on the type of the emulsion and on the effects desired. The optimum concentration for any given emulsion will be apparent to those skilled in the art upon making the tests and observations customarily employed in the art of emulsion making.

The emulsions can also be optically sensitized with cyanine rhodacyanine or merocyanine dyes such as described by F. M. l-iamer, The Cyanine Dyes and Related Compounds, Interscience Publishers, (1964).

The emulsions may also contain chemical sensitizers, e.g., reducing agents such as stannous salts, polyarnines such as diethyltriamine or sulfur compounds as described in US. Pat. No. 1,574,944. For chemical sensitization, one may further add to the given emulsions salts of noble metals such as ruthenium, rhodium, palladium, iridium, platinum or gold, as described in the article by R. Koslowsky, Z.Wiss.phot. 46, 65-72 (1959). The emulsions may also contain polyalkylene oxides, especially polyethylene oxide, and derivatives thereof, as chemical sensitizers.

The emulsions according to the invention may additionally contain the usual stabilizers, e.g., homopolar or salt-type compounds of mercury with aromatic or heterocyclic n'ngs, such as mercaptotriazoles, simple mercury salts, sulfonium mercury double salts, and other mercury compounds. Other stabilizers which may be used include azaindenes, especially tetraor pentaazaindcnes, in particular those substituted with hydroxyl percent aqueous formaldehyde solution as hardener. The emulsion prepared in this way is divided into five parts: Part A is used as a blank without further additives.

Part B in addition contains 5 mg. of stabilizer No. 1.

Part C in addition contains 10 mg. of stabilizer No. 1.

Part D in addition contains 5 mg. of stabilizer No. 5.

Part E in addition contains 10 mg. of stabilizer No. 6.

The samples are then applied onto a cellulose acetate support, exposed in a sensitometer behind a grey step wedge, and developed at 20 C. for 6 and 16 minutes, respectively, in a developer of the following composition:

Sodium suifite, anhydrous 70.0 g. Borax 7.0 g. Hydroquinone 3.5 g. p-Monomethylaminophenol 3.5 g. Sodium citrate 7.0 g. Potassium bromide 04 g.

Make up to 1 liter with water.

The results of the sensitometric determination are shown in the following Table 1.

TABLE 1 After 3 days storage in heating cupboard, developmenttime Development time 6 min. Development time 16 min. 16 min.

Sensitiv- Sensitiv- Sensitivity in ity in ity in degrees, degrees, degrees. Sample DI 'y Fog DIN 7 Fog DIN y Fog A 40. 5 1. 05 0.25 40. 9 1. 70 0.33 41. 0 1. 65 0.37 B 40. 5 0. 85 0.20 41. 0 1. 0. 28 40.9 1.35 0.30 C 40. 4 0.85 0. 18 40. 7 1. 30 0. 26 10.8 1. 20 0. 24 D 40. 6 0.85 0. 20 40. 8 1. 30 0. 29 41. 1 1. 30 0. 27 E 40. 4 0.85 0. 20 40. 9 1. 30 0. 28 40. 7 1. 30 0. 27

3=one shutter stop or double sensitivity.

or amino groups. Compounds of this type have been described in the article by Birr, Z.Wiss.phot. 47, 2-58, (1952). Other suitable stabilizers include heterocyclic mercapto compounds, e.g., l-phenyl-5-mercaptotctrazole, quaternary benzthiazole derivatives and benztriazoles.

The emulsions may be hardened in the usual manner, for example, with formaldehyde or halogen-substituted aldehydes that contain a carboxyl group, e.g., mucobromic acid, diketones, methanesulfonic acid esters and dialdehydes.

The stabilizers which we have described may be used in various kinds of photographic emulsions. in addition to being useful in X-ray and other nonoptically sensitized emulsions they may also be used in orthochromatic, panchromatic and infrared-sensitive emulsion. They may also be used for emulsions suitable for use in the silver salt diffusion process for color-photographic emulsions and for photographic materials for the silver dye bleach process.

EXAMPLE 1 A completely ripened silver iodobromide gelatine emulsion of maximum sensitivity which contains 5 mols percent of Agl is prepared for casting by adding, per kg. of emulsion, 200 mg. of 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene as basic stabilizers, 600 mg. of saponin as wetting agent and 10 ml. of a 10 Development time 6 min.

The effect on the fog is observed both after 6 minutes and after 16 minutes development, and there is hardly any reduction in sensitivity. The stabilizing effect is maintained even after 3 days storage in the heating cupboard at 60 C.

EXAMPLE 2 A completely ripened highly sensitive silver iodobromide gelatine emulsion containing 5 mols percent of Agl is prepared for casting by adding 200 mg. of 4-hydroxy-6- methyl-1,3,3a,7-tetraazaindene as basic stabilizer, 600 mg. of saponin as wetting agent and 10 ml. of a 10 percent formaldehyde solution as hardener per kg. of emulsion. The emulsion prepared in this way is divided into three parts:

Part A is used as a blank without additive.

Part B contains 20 mg. of compound No. 2.

Part C contains 10 mg. of compound No. 4.

The samples are then applied onto a cellulose acetate support, exposed in a sensitometer behind a grey step wedge and developed at 20 C. for 6 and 16 minutes, respectively, in a developer indicated in Example 1. The results of the sensitometric test are shown in the following Table 2.

taste? Sensitiv- Sensitivity in ity in ity in degrees, degrees, degrees, Sample DIN 'Y Fog DIN 7 Fe; l )l N '1 1' 0g A. ll). 0 0. Hi) 0. 26 40. 5 l. 25 1.36 40, 3 l. H 12 IL 40.0 i). (l. 22 40. 2 l. 20 U, 31) 40. 5 1.10 (1.62 U 40. 2 0. ill) U. 18 40. 5 l. 10 l). 2U 40, 5 1.00 l). 32

3 =0no shutter stop or double sensitivity.

EXAMPLE 3 A completely ripened, high-sensitive iodobromide gelatine emulsion containing 8 mols percent of Agl is prepared for casting by adding 200 mg. of 4-hydroxy-6-methyl-l,3,3a,7- tetraazaindene as basic stabilizer, 600 mg. of saponin as wetting agent and ml. of a 10 percent formaldehyde solution as hardener per kg. of emulsion. The emulsion prepared in this way is divided into five parts:

Part A is used without additive.

Part B contains in addition 5 mg. of compound No. 3. Part C contains in addition 20 mg. of compound No. 3. Part D contains in addition l mg. of compound No. 7. Part E contains in addition 5 mg. of compound No. 7.

The samples are then applied onto a cellulose acetate support, exposed in a sensitometer behind a grey step wedge and developed at 20 C. for 6 and 16 minutes, respectively, in a developer given in Example 1. The results of the sensitometn'c test are summarized in the following Table 3.

TABLE 3 0 mediately and after 2 days storage in a heating cupboard at 60 C. and 40 percent atmospheric moisture. Development was carried out for 6 minutes at 39 C. in a pmethylarninophenol developer of the following composition:

p-Methylaminophenol l g.

Sodium sulflte, anhydrous l3 g. Hydroquinone 3 g. Soda, anhydrous 26 g.

Potassium bromide Dissolve in water and make up to '1 liter.

The samples were then fixed and washed and the fog was measured with a direct view densitometer. The gamma and sensitivity were not altered by the additives.

After 3 days storage in heating cupboard, development time Development time 6 min. Development time 16 min. 16 min.

Sensitiv Sensitivity in ity in degrees, degrees, 7 Fog DIN 'Y Fog DIN 'y Fog 0.85 0. 1s 40. 1 1. 35 0. 40. 0 1.30 0. 28 0.80 0. 16 40. 2 1. 30 0. 26 40. 5 1. 20 0. 22 0.75 0. 14 40. 3 1. 25 0. 23 40. 2 1. 20 0. 20 0. 00 0. 16 40. 2 1. 0. 23 40. 2 1. 30 0. 24 0. 90 0. 16 40. 4 1. 0. 2A 40. s 1. 20 0. 23

3=mlo shutter stop or double sensitivity.

A completely ripened, high-sensitive iodobromide gelatine After heating b d emulsion containing 3.5 mols percent of Agl is prepared for Fr fiii fi i l 0 ti b a in 2 f 4-h x -6- eth l-l 3a 7- Develop time in minutes as ng y dd g mg ydro y m y Compound Mg./kg.0[ tetraazaindene as basic stabilizer, 600 mg. of saponin as number emulsion 2 6 2 6 wetting agent and 10 ml. of a 10 percent formaldehyde solu- Control Sample N (L 02 25 021 4o tron as hardener per kg. of emulsion. The emulsion prepared 1 0 0.09 0.12 0.06 0. (1)8 60 0.00 0.10 0.10 0. 5 in this way is divided into three parts. 6 60 0. 09 19 0. 07 19 Part A blank which is used without additive. Part B EXAMPLE 6 3:: ofcompound 4 The stabilizers according to the invention can also be used very advantageously in the afterripening. f comptgund 5 n l A silver iodobromide gelatine emulsion containing 6 mols e Samp es are en app onto a C6 u ose acetate percent of silver iodide is prepared in the usual manner. For

port, exposed in a sensitometer behind a grey step wedge and developed at 20 C. for 6 and 16 minutes, respectively, in a developer given in Example 1. The results of the sensitometric test are shown in the following Table 4.

TAB LE 4 the afterripening, the pAg value is adjusted to 8.9, the pH to 6.9 and the viscosity to about 20 cp. Aurous thiocyanate is then added and the emulsion is divided into eight parts (based on 600 g. of AgBr).

Sensltiv- Sensltiv- Sensitivity in ity in tty in degrees, degrees, degrees, Sample DIN 'y Fog DIN 'y Fog DIN 7 Dog A. 80. H (i. 40 (l. 22 43. H 0. (ill 0. 29 42. (i 0. ()5 (1, 48 it. 40. 3 (1.40 0. i2 44. 7 0. till 0. i4 44. 2 0.60 (l. 18 40. l) i). 40 0. 14 44. l) 0. (ll) 0. 14 44. 2 0. (i0 0. 31

3 =01) shutter stop or double sensitivity.

Part A EXAM] LE 5 blank without additive.

A silver chlorobromide emulsion (20 mol percent of AgBr), Part B which has not been washed in water and which contains 0.18

with 8 mg. of compound No. i added.

9 10 Part C ple which had been stored in the heating cupboard is substanwith 10 mg. of compound No. 2 added. tially improved. Part D We claim: 6 mg. of compound No. 3. 1. A light-sensitive photographic material having at least Part E 5 one silver halide emulsion layer, which contains a stabilizer of 12 mg. of compound No. 4. the following formula: Part F 16 mg. of compound No. 5.

l 10mg. ofcompound No. 6. 10 b g r Part H V 8 mg. of compound No. 8.

Afterripening is continued to obtain maximum sensitivity 0:8 0 8:0 and the samples are prepared for casting by adding 600 mg. of l P saponin as wetting agent, 10 ml. of a 10 percent aqueous forp maldehyde solution as hardener and 200 mg. of 4-hydroxymethyl-1,3,3a,7-tetraazaindene as basic stabilizer per kg.

The samples are then applied onto a cellulose acetate support, exposed in a sensitometer behind a grey step wedge, and in which Z or Z represent the ring members necessary for developed at C. for 6 and 16 minutes, respectively, in a completing a ring of the triazole series, the oxazole series, the developer as given in Example 1. The results of the senthiazole series, the imidazole series, or a benzoxazole, sitometric determination are shown in Table 6. benzothiazole, thiadiazole or thiadiazoline ring.

TABLE 6 After 3 days storage in heating cupboard, development time Development time 6 min. Development time 16 min. 16 min. Sensitiv- Sensitlv- Sensitivity in ity in ity in degrees, degrees, degrees, Sample DI Y Fog DIN 'y Fog DIN 'y Fog Type 0. 65 0. 17 Type 1. 05 0. +0 0.85 0. 48 +0 0. 67 0. 10 5:0 1. 10 0. 15 +0.5 1. 00 0.26 +0. 5 0. 68 0.11 +0. 2 1.15 0.17 :l:0 1. 10 0. 29 0. 5 0. 60 0.09 0. 5 1. 00 0.12 0. 5 0. 95 0.18 +0 0.70 0. 12 +0.5 1. 20 0.19 i0 1. 10 0. 31 0. 2 0. 63 0.10 +0 1. 00 0.13 0. 5 0. 95 0. 27 +0. 3 0. 65 0. 13 +0.5 1. 00 0. 18 if] 0. 95 0. 32 +0.5 0. 70 0.14 +0. 3 1.15 0. 20 +0.5 1.15 0.

3=one shutter stop or double sensitivity. Mm The table also gives the result of a stability test. The samples 2. A light-sensitive photographic material according to were stored for 3 days at 60 C. It will be seen from this that claim 1, characterized in that Z and Z represent a 1,3,4- not only the fog in the fresh sample but also the fog in the samthladiazole ring.

Claims

2. A light-sensitive photographic material according to claim 1, characterized in that Z and Z'' represent a 1,3,4-thiadiazole ring.