GB935290A - Preparing carboxalkylated gelatin useful in photography - Google Patents

Abstract

The invention comprises carboxymethylated pigskin gelatin The carboxymethyl gelatin may be prepared by liming raw pork rinds in the presence of an a -halogeno aliphatic acid and then extracting the gelatin derivative by known methods. The acid may be bromoacetic or chloroacetic acid and the liming mixture may contain calcium hypochlorite. The rinds, after liming, may be treated with dilute acid and washed before the gelatin derivative is extracted. The derivative may be extracted with water and the extraction may take place at a pH of 4 to 5. Alternatively, pigskin gelatin may be subjected to the following treatments in any order: (i) treatment with an aqueous solution to a pH from 8,5 to 10,5 containing at least 2% by weight of ammonium sulphate or ammonium acetate, and (ii) treatment with an a -halogeno aliphatic acid and a solution at a pH from 8,5 to 10,5 and at from 40 to 60 DEG F. whereby -CH2,COOH groups are introduced into the gelatin. Treatment (i) may be applied for at least 2 days. The gelatin may be in suspension in said solutions. The concentration of the ammonium salt in treatment (i) is 5%. The acid may be bromoacetic acid and may be in a concentration from 2 to 20% by weight of the gelatin. After either or both of said treatments the gelatin may be treated with activated carbon and may be given an additional treatment with a saturated solution of magnesium oxide containing excess solid magnesium oxide, before treatment (ii). The gelatin derivative is useful in the production of photographic emulsions, e.g. silver halide emulsions or emulsions optically sensitised with a cyanine dye. Specification 649,545 is referred to.