US2668113A - Photographic antibronzing agents - Google Patents

Description

Patented Feb. 2, 1954 PHOTOGRAPHIG AN TIBRONZIN G AGENTS Henry J. Schwalenstocker, Rochester, N. Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 26, 1951, Serial No. 208,058

This invention pertains to photographic materials and more particularly to light-sensitive silver halide emulsions. Still more particularly it pertains to photographic silver halide emulsions which produce photographic silver images which do not degrade in color upon drying at elevated temperatures.

The practice of hot-drying or hot-ferrotyping of photographic prints causes a degradation of the silver image characterized by an undesirable change in color. In the case of certain emulsions a loss in density also occurs. For instance, developed blue-black silver images usually degrade to a purplish or plum color and warm-tone images of basically brown color degrade to a green or black image upon hot-drying. Many compounds have been proposed for addition to photographic silver halide emulsions to prevent or reduce the color degradation described above. While some of the known materials reduce color degradation they have a tageous. In addition, such compounds cause a degradation in the basic image color of warmtone emulsions.

An object of the present invention is to provide photographic emulsions that yield developed silver images which do not undergo serious color degradation upon hot-drying. Another object is to provide such emulsions which are not desensitized by the adjuvants which prevent color degradation. A further object is to provide a simple and yet effective way of reducing color degradation by the addition of available chemical compounds. Still further objects will be apparent from the following description of the invention.

It has been found that the incorporation of saltsof mercaptoazoles with N-hydrocarbonsubstituted biguanides and especially N-arylsubstituted biguanides with photographic silver halide emulsions provide a high degree of color stabilization of the emulsions without any undesirable effect on the light-sensitive properties of the emulsions.

' The salts referred to above may be represented by the general formula:

NHR

wherein R. is hydrogen, or an alkyl or aryl group 9 Claims. (01. 95-7) strong desensitizing action which is disadvan- 2 I and R is an alkyl or aryl group Z constitutes the residue of a mercaptoazole. Thus, R and R may be methyl, ethyl, propyl, isopropyl, isobutyl, phenyl, tolyl, naphthyl, etc., and I-IS--Z may be a mercaptoazole. Among the useful mercaptoazoles are Z-mercaptdbenzthiazole, 2- mercaptobenzoxazole, and 5-mercaptotetrazole and their alkyl and aryl substituted derivatives, e. g., l-phenyl-S-mercaptotetrazole, l-a-naphthyl 5 mercaptotetrazole, 1 5 naphthyl 5- mercaptotetrazole, 1 p diethylamino phenyl- 5 mercaptotetrazole, 1 o methoxy phenyl- 5 mercaptotetrazole, 1 p chlor phenyl 5- mercaptotetrazole, 2,5 dimercapto 1,3,4 thiadiazole. 1 benzyl 5 mercaptotetrazole, 1- cyclohexyl 5 mercaptotetrazole, 1 methyl- 5 mercaptotetrazole and 1 ethyl 5 mercaptotetrazole. r

The mercaptoazole salts of the N-hydrocarhon-substituted biguanides can be prepared by reacting the merca'ptoazole and the N-arylbiguanide in substantially equimolecular proportions in water or a methanol or ethanol solution and allowing the addition salts to crystallize.

Photographic silver images can be improved by the use of the novel salts described above by introducing them from an aqueous solution or an ethanol or methanol solution into the lightsensitive emulsion at some stage in its preparation prior to coating or into a subcoating or overcoating colloid composition, e. g., gelatin. Alternatively, the compounds may be incorporated in the photographic emulsion layer before or during development, e. g., by including them in the developing solution. They are preferably added to the photographic emulsion prior to coating.

In general, the salts are used in an amount of 0.1 to 1.0% by weight of the silver in the emulsion. When used in a gelatin overcoating or a developer solution or an ethanol or aqueous treating solution for the developed and fixed layer a similar or equivalent amount should be used.

The invention will be further illustrated but is not intended to be limited by the following examples.

EXAMPLE I One gram of phenylbiguanide mercaptobenzothiazole salt (A) was dissolved in 40.0 ml. of ethanol and this solution was added to a silver halide photographic emulsion composed of approximately AgBr and 40% AgCl. The solution was added to the fluid emulsion immediately i r to c n -in. u n ii s eryi betw e made from these coatings shows that while com.-

pound (A) causes an increase. warmth. of. basic image color, compound (13) causes a decrease in warmth of color. Gomparison of coatings employing equal quantities of the two ma: terials indicates that compound (A): is more effective than compound (B) in stabilizing image color on hot drying. The effect on sensitivity of. the emulsion is noted in Table I.

Table I Print Ex-- tity. Ad uvant posure Re- Added 1 quired 2 8O 70 200 75 400 S 80 75 200 130 400 140 G5 1 Expressed in milliliters of solution per unit of emulsion.

l Expressed as relative time of exposure required to produce matched prints from a. given negative. (Larger numbers indicate slower emulsion speed.)

EXA V P H A gelatin solution to be used as a protective coating which-results-in a final gelatin concentration of approximately 1 by weight was prepared in the usual manner. Quantities oi? phenylbiguanide 1-phenyl-5 mercaptotetrazole salt (A) were added tothe gelatin solution such that the final concentration of (A) in the gelatin solution ranged from 0650 13001200 gram per liter. The resulting solutions were applied as a protective layer to a coating ofphotographic emulsion such as-that described in Example I. Controlcoatings were made in which lsphenyl-o-mercaptotetrazole (B) was present in comparable quantities and in which noadjuvant was present.

Examination of normallyand hot-dried prints made from exposed photographic papers using these coatings in: this case showed that coinpound B in all cases caused an undesirable loss in warmthof basic image color while compound A on the other hand increased warmth. of basic imagecolor. Further it was demonstratedthat, while only 0050 gram of compound A per liter of gelatin solution provided satisfactory color stability on hot drying, compound B did not provide this degree of stability when used in concentrations as high as 0.200 grams per liter of gelatin solution. The effect of these, materialson emulsion sensitivity is noted in Table II.

l Expressed. in grams of material per liter of overcoating 531R 11.

4 EXAMPLE III When photographic prints made from an exposed and developed printing paper made from an emulsion of the type described in Example I were immersed in a water solution of phenylbiguanide mereaptobenzothiazole salt of 0.0005M concentration for one minute after normal processing it was found that color loss on hot drying was markedly decreased as compared to prints which didnot receive such treatment.

EXAMPLE IV fine gram of o-tolylbiguanide l-phenyl-S-mercaptotetrazo'le salt was dissolved in 400 ml. of ethanol and this solution was added to a silver halide photographic emulsion composed of approximately AgBr and 40% AgCl. The solution was added to the emulsion immediately prior to coating in quantitiesvarying between 200 and 800 ml, of solution per unit of emulsion.

Comparison of prints made from coatings of these emulsions with prints made on coatings of similar emulsion containing no adjuvant shows that this material provides a distinct improvement in image color of hot-dried prints.

EXAMPLE V Following the procedure of Example IV the following aryl biguanide salts were evaluated in the emulsion described in Example IV;

1. orTolylbiguanide mercaptobenzothiazole salt.

2. o-Tol'ylbiguanide mercaptobenzoxazole salt.

3. Phenylbiguanide 1 phenyl-5-mercaptotetrazole salt.

4. Phenylbiguanide mercaptobenzoxazole salt.

These compounds were all found to be effective in preventing loss of color on hot-drying of prints and gave results comparable with those described in Example IV with the o-tolylguanide l-phenyl- SemercaptQtetraZole salt.

EXAMPLE VI I enumerated under Example V. Examination of the-above prints after hot-drying as compared to untreated-prints shows that color loss is reduced in each case where prints were treated in a solution of arylbiguanide salt.

EXAMPLE VII The following salts were prepared in ethanol such that the final concentration of solid salt in ethanol solution was of the order of 1 gram per 40o ml; of solution:

(A) Phenyl biguanide 2,5 dimercapto 1,3,4-

thiadiazole (B)-Biphenyl biguanide 2,5 dimercapto 1,3,4-

thiadiazole (C) Biplrenyl biguanide-l-phenyl-5-mercaptotetrazole.

' thesesalts were found to yieldhot-dried prints with image color superior to similar prints made from light-sensitive coatings made from similar emulsions free from such respective adjuvants.

In place of the specific hydrocarbon-substituted biguanide mercaptoazole salts described in the foregoing examples there may be substituted equivalent amounts of other such salts which fall within the scope of the above general formula. Among the additional salts which give similar results are: methyl, ethyl, phenyl and diphenyl biguanide 1-e-naphthyl- 5-mercapto tetrazole or other substituted 5-mercaptotetrazole salts, 5-mercapto 1,3,4-triazole salts, thio barbituric acid salts, salts of mercapto thiodiazoles and mercapto pyrimidines. Orthotolylbiguanide salts of the above mercapto compounds can also be used.

The compounds may be used in various types of emulsions which contain sensitizing dyes and other agents, e. g., anti-fogging agents, colloidhardening agents, wetting and surface active agents, delusterants, etc. which modify the characteristics of an emulsion.

The invention is, of course, not limited to emulsions having gelatin as the water-permeable colloid for the silver halide binding agent or the overcoating or subcoating. Suitable additional colloids include agar-agar, polyglycuronic acids, zein, collodion, water-soluble cellulose derivatives, such as substantially hydrolyzed cellulose acetate, cellulose esters of hydroxy monocarboxylic acids, e. g., lactic or glycolio acids, alkali metal salts of cellulose esters of dicarboxylic acids, such as phthalic acid, polyvinyl alcohol, partially hydrolyzed polyvinyl acetate and interpolymers thereof with unsaturated materials, such as styrene, maleic acid, etc., water-soluble polyvinyl acetals and other hydrophilic synthetic or natural resins and polymeric compounds. Suitable hydrophilic colloids of the above types are described in United States Patents 2,110,491, 2,276,322, 2,276,323, 2,286,215 and 2,211,323.

An advantage of this invention is that it provides an effective way of reducing the color degradation of photographic images when subjected to hot-drying. Another advantage is that the adjuvants do not have any significant desensitizing effect on the light-sensitivity of the photographic emulsions. The use of phenylbiguanide 2-mercaptobenzothiazole salt is especially advantageous in photographic warm-tone paper emulsions. A further advantage is that the salts have a high degree of solubility in methanol, ethanol and water which means that they can readily be associated with emulsions and photographic layers without the necessity of using expensive solvents and special procedures for their introduction into the photographic element. A still further advantage is that the adjuvants can be readily prepared from available chemicals.

As many widely different embodiments of this invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not to be limited except as defined by the claims.

What is claimed is:

1. A photographic element comprising a support bearing a light-sensitive silver halide emulsion layer which contains a salt of a mercaptoazole with an N-hydrocarbon-substituted biguanide in an amount constituting 0.1% to 1.0% by weight of the silver in said emulsion.

2. A photographic element comprising a support bearing a light-sensitive silver halide emulsion layer which contains a salt of a mercaptoazole with an N-aryl-substituted biguanide in an. amount constituting 0.1% to 1.0% by weight of the silver in said emulsion.

3. A photographic element comprising a paper base having a gelatino-silver-halide emulsion layer containing a salt of a mercaptoazole with an N-hydrocarbon-substituted biguanide in an amount-constituting 0.1% to 1.0% by weight of the silver in said emulsion.

4. A photographic element comprising a paper base having a gelatino-silver-halide emulsion layer containing a salt of a mercaptoazole with an N-aryl-substituted biguanide in an amount constituting 0.1% to 1.0% by weight of the silver in said emulsion.

5. A photographic element comprising a paper base bearing a gelatino silver halide emulsion layer which contains a mercaptobenzothiazole salt of phenylbiguanide in an amount constituting 0.1% to 1.0% by weight of the silver in said emulsion.

6. The process of improving the color of a photographic silver image which comprises incorporating with the silver halide emulsion layer of a photographic paper prior to the completion of hot-drying a salt of a mercaptoazole with an N-hydrocarbon-substituted biguanide in an amount constituting 0.1% to 1.0% by weight of the silver in said emulsion.

7. The process of improving the color of a photographic silver image which comprises incorporating with the silver halide emulsion layer of a photographic paper prior to the completion of hot-drying a salt of a mercaptoazole with an N-aryl-substituted biguanide in an amount constituting 0.1% to 1.0% by weightof the silver in said emulsion.

8. A photographic silver halide emulsion containing a salt of a mercaptoazole with an N- hydrocarbon-substituted biguanide, in an amount constituting 0.1% to 1.0% by weight of the silver in said emulsion.

9. A photographic silver halide emulsion containing a salt of a mercaptoazole with an N- aryl-substituted biguanide, in an amount constituting 0.1% to 1.0% by weight of the silver in said emulsion.

HENRY J. SCHWALENSTOCKER.

References Cited in the tile of this patent UNITED STATES PATENTS Number Name Date 1,725,934 Reitstotter Aug. 27, 1929 1,763,989 Sheppard et al 'June 17, 1930 2,317,184 Dreyfuss Apr. 20, 1943 2,368,647 Dreyfuss Feb. 6, 1945 FOREIGN PATENTS Number Country Date 524,556 Great Britain Aug. 8, 1940 573,745 Great Britain Dec. 4, 1945

Claims (1)

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT BEARING A LIGHT-SENSITIVE SILVER HALIDE EMULSION LAYER WHICH CONTAINS A SALT OF A MERCAPTOAZOLE WITH AN N-HYDROCARBON-SUBSTITUTED BIGUANIDE IN AN AMOUNT CONSTITUTING 0.1% TO 1.0% BY WEIGHT OF THE SILVER IN SAID EMULSION.