US2919985A - Antifoggants and stabilizers for photographic silver halide emulsions - Google Patents

Description

United. States Patent Fritz Del-sch and Millet R. De Angelus, Binghamton,

N.Y., assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Application August 15, 1958 Serial No. 755,149

6 Claims. (CI. 96-66) The present invention relates to the use of antifogging and stabilizing agents for photographic silver halide emulsions and, more particularly, to the use of bis(carboxy lower alkyl-2,3-)quinoxalinyl dithio ethers, their salts and esters for such purpose.

Iti s known that light-sensitive emulsions such as gelatin silver halide emulsions have a tendency to fog. Such fog may be caused in a number of ways as, for example, by excessive ripening of the emulsion, during storage of the film particularly at elevated temperatures and humidity or by prolonged development of the exposed emulsion.

A great numberof substances have been described in the literature as being effective in preventing an increase in fog through stabilizing or controlling the keeping qualities of light-sensitive silver halide emulsions. Although many of these compounds have the ability to reduce fog tendencies and to improve stability, they are deficient in that they lower the sensitivity of the emulsions and in many cases reduce optical and dye sensitivity.

We have now found that bis(carboxy lower alkyl-2,3-) quinoxalinyl dithio ethers, their salts and esters are not only excellent stabilizers or antifogging agents for lightsensitive silver halide emulsions but, in addition, they have the ability of performing this function without lowering the sensitivity of the emulsion with which they are associated or without reducing the sensitivity of the emulsion to light of longer wave length attributable to the presence of sensitizing dyes.

The use of such compounds to inhibit fog and to stabilize silver halide emulsions, either by locating the same in the emulsion, in layers adjacent thereto or in processing baths for the emulsions, constitutes the purposes and objects of the present invention.

The stabilizers the use of which is contemplated herein may be represented by the following formula:

wherein R is hydrogen; an aliphatic radical such as alkyl, i.e., methyl, ethyl, propyl, butyl, amyl or the like; hydroxyalkyl, i.e., hydroxymethyl, hydroxyethyl and the like; carboxyalkyl, i.e., carboxymethyl, carboxyethyl and the like; aryl such as phenyl, toluyl, naphthyl, carboxyphenyl, sulfophenyl and the like; aralkyl such as benzyl or a monovalent cation such as sodium, potassium, silver, ammonium or the like and n is a whole number of from 1 to 3. Examples of compounds within the ambit of such formula which we have found to be effective are:

(l) 2,3-quinoxaline dithio acetic acid (2) The methyl, phenyl or ethyl ester of 2,3-quinoxaline dithio acetic acid (3) 2,3-quinoxaline dithio propionic acid and its sodium and silver salts The above compounds are prepared by refluxing 2,3- quinoxaline dithiol with a bromo aliphatic acid such as bromoacetic acid, fi-bromop-ropionic acid or gammabromobutyric acid in the presence of an acid binding agent such as sodium hydroxide, pyridine or the like. After cooling, the reaction mixture is acidified with a dilute acid and the solid which is precipitated is recrystallized from ethanol.

The free acid thus produced may be converted to its salt by reaction with a water soluble compound containing the desired cation such as potassium carbonate, sodium carbonate, silver nitrate, ammonium carbonate or the like.

If the esters-are desired, they are produced in the conventional manner by refluxing the free acid with the desired alcohol or phenol in the presence of hydrochloric acid.

Beneficial effects and fog reduction are obtained when solutions of the aforementioned compounds are incorporated in the silver halide emulsions as ripening finals or as coating finals. Ripening finals" are added dur ing the ripening or the sensitivity increasing stage of the emulsion making process. Suchradditions may be made before,'during or after the decomposition of the soluble silver salt such as silver nitrate by means of soluble halides such as potassium bromide in the presence of a colloidal carrier such as gelatine, .PVA, solubilized casein or albumin. 9

Coating finals are added to the emulsion just prior to coating on a suitable support such as glass, paper or film at a time when the emulsion has nearly obtained its maximum sensitivity. 7

When used as ripening finals, our antifoggants or stabilizers are best employed in a concentration of 1 to 25 mgs. per .6 mol of silver halide and when used as coating finals in a concentration of 10 to 300 mgs. per .6 mol of silver halide. The concentration used depends on the type of emulsion involved and it is recommended that the optimum concentration be determined from case to case. In some instances, it is advantageous to apply the antifoggant in a layer adjacent to the silver. halide emulsion layer, i.e., in an undercoating or in an antiabrasion gelatinsurface coating. In other cases, they may be applied in one or all processing baths. I

The antifoggants may be used in various photographic emulsions, e.g., non-sensitized, orthochromatic, panchromatic, X-ray emulsions, paper emulsions and color emulsions. They may be used alone or in combination with other antifoggants and stabilizers or in combination with sulfur, -reduction, -metal, and noble metal sensitizers or in combination with hydroxypolyethenoxy derivatives, i.e., those obtained by reacting ethylene oxide with an alcohol, phenyl, amine or the like. (See U.S.P. 1,970,578.)

The invention is further illustrated by the following examples but it is to be understood that the invention is not to be restricted thereto.

Example I exposed in a Type IIB Sensitometer and developed in a developer of the following composition:

The results of this procedure are tabulated as follows:

Relative Fog at 12 Oven Fog Quantity of Compound Used Speed Developat 6' Dement velopment 100 15 .30 400 mgs 100 15 17 The stabilizer used in this example was prepared as follows: To a solution containing 9 grams of sodium hydroxide in 175 milliliters of water were added 9.7 grams of 2,3-quinoxaline dithiol. To this solution in a small volume of water were added 13.9 grams of bromoacetic acid. The reactants were allowed to reflux for 3 hours. The reaction mixture was then cooled and acidified with concentrated hydrochloric acid to pH 2 and chilled in ice. The precipitate was collected, dissolved in ethanol, treated with charcoal and allowed to crystallize slowly overnight in a cooler. Recrystallization from ethanol gave 8 grams of a pure yellowishorange product.

Example II The procedure was the same as in Example I excepting that there was used as the stabilizer 2,3-quinoxaline dithio propionic acid. The results were similar to those obtained in Example I.

The stabilizer was prepared in the same manner as that of Example I while substituting p-bromopropionic acid for bromoacetic acid.

Example III Exposed samples of a photographic film were developed for 12 minutes at 65 F. in a standard metol-hydroquinone developer. Two tests were made, one with a normal developing solution and one with a developer containing 500 mgs. of the stabilizer of Example I per one liter of developer. Sensitometric strips developed in the normal developer (control) for 12 minutes showed a fog of .30, whereas those strips which were developed in a developer containing the stabilizer had a fog of .20.

Example IV The procedure was the same as in Example III excepting that there was used as the stabilizer 2,3-quinoxaline dithio butyric acid.

The results were substantially the same as those of Example III.

The stabilizer of Example IV was prepared in the same way as that of Example I while replacing the bromoacetic acid by gamma-bromobutyric acid.

Modifications of the invention will occur to persons skilled in the art. Thus, it is evident that in lieu of using the compounds of the examples, any of the compounds mentioned above may be employed with equally good results. We, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. A light-sensitive photographic material comprising a base and a light sensitive silver halide emulsion layer thereon, said light-sensitive material containing as an antifoggant and stabilizer a compound of the following formula:

wherein R is selected from the class consisting of hydrogen, an aliphatic radical, aryl, aralkyl and a moncwalent cation, and n is a whole number from 1 to 3.

2. The article as defined in claim 1 wherein said antifoggant is located in the silver halide emulsion.

3. The article as defined in claim 1 wherein said antifoggant is located in a layer adjacent to said silver halide emulsion.

4. A light-sensitive photographic material comprising a base with a light-sensitive silver halide emulsion thereon, said emulsion containing as an antifoggant 2,3-quinoxaline dithio acetic acid.

5. The process of minimizing and preventing fog in light-sensitive silver halide materials comprising a base having a light-sensitive silver halide emulsion thereon which comprises exposing said emulsion and developing the same in a silver halide developer in the presence of an antifoggant and stabilizer of the following formula:

References Cited in the file of this patent UNITED STATES PATENTS Allen et al. Apr. 24, 1956 Murray et al. Jan. 14, 1958

Claims (1)

1. 5. THE PROCESS OF MINIMIZING AND PREVENTING FOR IN LIGHT-SENSITIVE SILVER HALIDE MATERIALS COMPRISING A BASE HAVING A LIGHT-SENSITIVE SILVER HALIDE EMULSION THEREON WHICH COMPRISES EXPOSING SAID EMULSION AND DEVELOPMENT THE SAME IN SILVER HALIDE DEVELOPER IN THE PRESENCE OF AN ANTIFOGGANT AND STABILIZER OF THE FOLLOWING FORMULA: