GB1042376A - Polyurethane lacquers - Google Patents

Abstract

A heat hardenable polyurethane lacquer which contains no free -NCO groups and which is stable on storage at room temperature, is prepared by reacting (1) an alkyd resin having more than 2 free -OH groups and containing inert, saturated or unsaturated, straight or branched chain aliphatic residues having at least 8 C atoms in an amount of at least 40% of the weight of the resin, said resin having a viscosity when dissolved in 50% by weight of xylene of less than 200 seconds, measured in accordance with German Standard Specification DIN 53211 in a 4 mm. cup at 20 DEG C., with (2) a diisocyanate in an amount of more than 1 mol. per mol. of alkyd resin, but not more than the stoichiometric amount, in an inert solvent, the solvent forming more than 40% by weight of the reaction mixture, until no free isocyanate groups can be detected in the reaction product. The alkyd resin may contain natural or synthetic higher fatty acid residues, e.g. alkyd resins modified with linseed oil, soya bean oil, coconut oil or the corresponding fatty acids or the fatty acids of cotton seed oil, corn oil, sunflower oil or tall oil. The fatty acids may be replaced by fatty alcohols. Polycarboxylic acids which may be used to prepare the alkyd resin are: succinic, adipic, maleic and phthalic acids or their anhydrides. In Example (1) an alkyd resin prepared from soya bean oil fatty acid, pentaerythritol (containing 12% dipentaerythritol), glycerine and isophthalic acid, having a viscosity of 60 seconds (M.W. about 1600) was dissolved in white spirit and reacted with tolylene diisocyanate. A lacquer was obtained after heating for several hours at 80-100 DEG C.