GB830841A - A process for dyeing and impregnating animal leather - Google Patents

Abstract

A solution in an organic solvent containing both a di-isocyanate modified polyhydroxy compound having free hydroxyl groups, and also a polyisocyanate, is applied to leather during or after its dyeing or colouring with a soluble or insoluble dye or insoluble pigment. Preferably, the solution also contains an accelerator for the reaction between the modified polyhydroxy compound and the polyisocyanate and the dye or other colouring matter may be dissolved or dispersed in this solution. Insoluble inorganic or organic pigments, or dyestuffs soluble in the solvents used for the solution, as for example cellulose acetate disperse dyes, or chromium-containing metallized dyes may be used. The diisocyanate-modified polyhydroxy compound is prepared by reacting polyhydroxy compounds of relatively high molecular weight, e.g. polyesters of dicarboxylic acids and dihydric and polyhydric alcohols, with diisocyanates, e.g. toluylene-, hexamethylene-, p-phenylene-, or 4,4-diphenyl-methane-diisocyanates. The diisocyanate is used in a proportion such that the diisocyanate-modified polyhydroxy compound obtained still has free hydroxyl groups, so that, when applied to the leather, it cross-links with the polyisocyanate added to form a product impervious to water and organic solvents used in dry cleaning. Suitable polyisocyanates include known monomeric polyisocyanates, and reaction products of polyhydric alcohols and diisocyanates which still contain isocyanate groups as, e.g., those of 1 mol. of hexanetriol with 3 mols. of toluylene- or hexamethylene, diisocyanate. Suitable solvents include ethyl acetate, acetone, the methyl ether of glycol acetate, trichlorethylene, methylene choride, benzene and mixtures of these. The solution may be applied by spraying or dipping, and drying and cross-linking may be accelerated by gently heating the leather. Accelerators which may be added to the solution include organo metallic compounds, e.g. of the titanic acidstearyl alcohol ester type, in conjunction with reaction products of phenyl isocyanate with tertiary amines. Leather treated as described above exhibits an improved "handle," resistance to rubbing, and water-repelling properties, and the dyeing is fast to washing and dry-cleaning.