Process for hardening gelatin

A process for hardening gelatin or a hydrophilic non-gelatin high molecular weight material containing primary and/or secondary amino groups selected from polyethyleneamine, poly(ethylene-4-amino-1,2,4-triazole, .beta.-aminoacrylic acid-ethylene-maleic acid copolymers and vinylamine-acrylic acid copolymers which comprises adding to the gelatin or the high molecular weight material a compound represented by the following general formula (I):

• ##STR14## wherein R.sub.1 and R.sub.2, which may be the same or different, each represents a monovalent residue which is bended through a carbon atom or a sulfur atom thereof to the nitrogen atom forming the carboxylic acid ester, and R.sub.1 and R.sub.2 may combine to form a ring structure;
• R is a divalent or trivalent residue which is bonded through a carbon atom or a nitrogen atom thereof to the carbon atom of the carboxyl group in the carboxylic acid ester;
• and n is 2 when R is a divalent residue and n is 3 when R is a trivalent residue, wherein the amount of said compound of general formula (I) is from about 0.1% to 10% be weight based on the weight of dry gelatin or the hydrophilic non-gelatin high molecular weight material.