US2158204A - Fog inhibitor for photographic emulsions - Google Patents

Description

Patented May 16, 1939 UNITED STATES TE NT QFF [C E FOG INHIBITOR FOR; PHOTOGRAPHIC EMULSIONS i New Jersey No- Drawing. Original application.,May. 7, 1936, Serial No. 78,464; Divided and this application January 22, 1937, Serial No. 121,863

6' Claims.

This invention relates to fog inhibitors for photographic emulsions and to photographic emulsions containing them.

This application is a division of application Serial No. 78,464, filed May 7, 1936.

It is known that photographic emulsions particularly ultra-sensitive emulsions, or those con taining color sensitizers exhibit a tendency to forma deposit of silver in the emulsion. This deposit extends more or less uniformly over the entire emulsion and is known as fog. Photographic fog is of two types, local and general. Local. fog is'formed by exposure of the film or plate: at undesired points, as by a light leakv in the-.came'ra. General fog or; as it is sometimes known, chemical fog, is formed in. a number of ways. It may be caused by the conditions under which the film or plate is stored, such as conditions of high temperature or unusually long time of storage. The nature of the emulsion, as where emulsions are highly sensitive may also produce chemical fog, as 'well as the conditions of development of the emulsion, as by development'for protracted periods of time or at temperatures above normal. Highly sensitive emulsions are more likely tofog than those of lower sensitivity, owing to the small amount of energy required to make a silver halide grain developable. We are concerned primarily with general or chemical fog.

The primary object of the present invention is to provide anti-fogging or fog inhibiting agents for ultra-sensitive photographic emulsions and to thereby increase the stability of the emulsions. A further object is to provide anti-fogging agents which do not markedly lower the sensitivity of the emulsion.

These objects are accomplished by incorporating in the emulsion an alicyclic amine having at least two nuclei, each containing at least one NH2 group. Either or both nuclei may be further substituted. The nuclei may be of the benzene or naphthalene type and the NI-Iz group may be in either or in both of these nuclei. The nuclei may-be further substituted, for example, with an alkyl group, or with two alkyl groups, or they may be unsubstituted except for the NHz groups.

These compounds are incorporated in a fast negative emulsion, particularly a silver halide emulsion. The emulsion used may be one which is intended to be used directly after 'emulsification or one which is subjected to ripening by treatment at a high temperature or by treatment with ammonia.

The first class of compounds which we may use includes benzidine and its derivatives. These include benzidine, amino substituted derivatives. of benzidine, such as tetra-methyl benzidine; ring substituted derivatives of benzidine, such as-ortho-tolidine and dianisidine. of compounds which we contemplate using are the amino derivatives of diphenyl methane. These. include p:p'-diamino diphenyl methane; derivatives in which the amino group is substituted, such as tetra-methyl diamino diphenyl methane and p:p'-tetra-ethyl diamino diphenyl methane; ring substituted derivatives, such as 2 :2 -4 z 4 -tetra-amino-5 -dimethyl diphenyl methane (sulfate).

In the diphenyl methane type of compound, which hasthe following structural. formula:

the CI-Iagroup between the rings may be replaced by other groups, such as --(CH2)n-, S'-, -Q--.

In these compounds the benzene nucleus may be substituted by a naphthalene nucleus which may contain substituent groups in the ring, as described above'for the benzene ring compounds. The compounds'described above do not all function equally well as fog inhibitors and difierent amounts are required to secure the maximum fog inhibiting effect. This effect will depend to some extent on the type of emulsion used. In general, the amount of fog inhibiting agent used in the emulsion will vary from .01 gram to 5 grams per 1000 cos. of wet emulsion. The following table will serve to illustrate amounts which we have found to be satisfactory. In each case the amount specified is used with 1000 cc. of a gelatino-silver halide emulsion.

Grams Benzidine 1 Tetra-methylbenzidine 1 o-Tolidine less than 1 Dianisidine 1 p:p-Diaminodiphenylmethane 1 Tetra-methyldiaminodiphenylmethane 1-5 p:p-Tetra-ethyldiaminodiphenylmethane l-5 2 2'-4 4' -tetra-amino-5 5'-dimethyldiphenylmethane (sulfate) less than 1-5 The second class ing them with any suitable solvent which is inert with respect to the sensitive emulsion, such as water, methyl alcohol, ethyl alcohol, acetone and others. The following example, which is by way of illustration only, indicates methods of incorporating the anti-fogging agents in emulsions according to our invention.

Example I A gelatino-silver halide negative emulsion which contained sensitizing agent and which had been made in the usual way and had a pH of 7.4 was heated on a water bath sufficiently to melt it. To a 1000 cc. portion of this emulsion there were added 100 cos. of an ethyl alcohol solution containing 1 gram of benzidine. The resulting solution was thoroughly mixed and was coated on 'glass plates, dried and incubated for 7 days at 60 C. to obtain a fog test. The fogging produced at the end of this time was very much less than that produced on a plate coated with the emulsion to which no fog inhibiting agent had been added.

The fog inhibiting agents which we have described may be used in various kinds of photographic emulsions. In addition to being useful in ordinary non-color sensitized emulsions they may also be used in orthochromatic, panchromatic and X-ray emulsions. They may be used with or without color sensitizing dyes and if used with the sensitizing dyes they may be added to the emulsion before or after the dyes are added. Various silver salts may be used as the sensitive salt, such as silver bromide, silver iodide, silver chloride or mixtures of these. The dispersing agent may be gelatin or other colloids, such as collodion, albumin, or suitable cellulose organic derivatives or artificial resins.

It is to be understood that we contemplate as included within our invention all modifications and equivalents coming within the scope of the appended claims.

What we claim and desire to secure by Letters Patent of the United States is:

1. A photographic emulsion comprising gelatin having a sensitive silver salt dispersed therein and containing as an antifoggant benzidine.

2. A photographic emulsion comprising gelatin having a sensitive silver salt dispersed therein and containing as an antifoggant ortho-tolidine.

3. A photographic emulsion comprising gelatin having a sensitive silver salt dispersed therein and containing as an antifoggant 2:2'-4:4'-tetraamino-5:5-dimethyl diphenyl methane sulfate.

4. A photographic emulsion comprising gelatin having a sensitive silver salt dispersed therein and containing as an anti-foggant a compound having the general formula wherein Y is selected from the group consisting of amino and alkylamino groups, and Z is selected from the group consisting of alkyl, oxalkyl, and hydrogen.

6. A photographic emulsion comprising gelatin having a. sensitive silver salt dispersed therein and containing as an anti-foggant a compound having the general formula I Z Z wherein X is selected from the group consisting of sulfur, oxygen,'and (CI-I2)" where n is any whole number, T is selected from the group consisting of amino and alkylamino', Y is selected from the group consisting of amino, alkylamino, and hydrogen, and Z is selected from the group consisting of alkyl and hydrogen.

SAMUEL E. SHEPPARD.

WALDEMAR VANSELOW.