GB569385A - Improvements in or relating to methods of preparing leather and to leather prepared thereby - Google Patents

Abstract

569,385. Making leather. AMERICAN CYANAMID CO. May 13, 1943, No. 7654. Convention date, July 25, 1942. [Class 76] Hides and skins are tanned by impregnation with an aqueous solution or dispersion of a water-soluble methylol melamine and with another tanning agent which may be a vegetable or metal salt tanning agent or formaldehyde. Preferably, the methylol melamine treatment precedes that with the known tanning agent. In examples : (1) pickled calf skins are drummed with salt solution, then with a solution of trimethylol melamine added in stages, the pH adjusted to 3.5 by sulphuric acid, and tanning completed with basic chromic sulphate, or with a chromic acid liquor followed by treatment with thiosulphate ; (2) a pickled goatskin or calfskin aftor drumming in salt solution was drummed with trimethylol melamine, the pH adjusted to 3.8, and tanning completed with a basic solution of aluminium sulphate. The pH was adjusted to 6 by soda ash and disodium phosphate, and the skin drained, washed and fat liquored with a sulphonated vegetable oil; (3) a bated or bated and pickled skin was drummed with salt solution and then with trimethylol inelamine and its pH adjusted to about 4. Tanning was completed with sulphited quabracho added in stages ; (4) a pickled skin was drummed with salt solution, then with trimethylol melamine, and tanning completed with a solution of ferric sulphate containing sodium citrate, the pH being brought to 4.1 by adding sodium bicarbonate ; (5) pickled sheepskins were treated with trimethylol melamine in stages, and tanning completed with formaldehyde, borax being added towards the end. The tanned product was fat liquored with a sulphated sperm coconut oil mixture, with interim additions of (a) acetic acid, (b) potash alum, (c) a sulphonated higher alcohol. Methylol melamine for use in the process may be prepared by boiling 1 mol. melamine with 3.5 mols. aqueous 30 per cent formaldehyde at pH 9.0 for 20 mins., cooling, and separating and drying the crystals obtained.