BIURET DIISOCYANATES

1,235,213. Polyurethane coating. FARBENFABRIKEN BAYER A.G. 13 Sept., 1968 [18 Sept., 1967], No. 43593/68. Heading B2E. [Also in Division C3] Substrates eg. wood, metal (e.g. steel) or glass may be coated with lacquer solutions of polyurethanes prepared by reacting a polyhydroxy compound, optionally a chain lengthening agent, and a polyisocyanate which is aliphatic, cycloaliphatic or araliphatic or an isocyanurate containing copolymer of one of these polyisocyanates with an aromatic polyisocyanate, the polyisocyanate containing an N:N-dialkyl substituted semicarbazide, carbazic ester or carboxylic acid hydrazide group, and a biuret, urethane, acylated urea or isocyanurate group at least once in the molecule. The polyisocyanates are suitably used in the form of 5 to 50% mixtures with other polyisocyanates which do not contain the semicarbazide, carbazic ester or acid hydrazide groups. Suitable polyhydroxy compounds are those polyesters and polyethers used conventionally in the art, whilst glycols and diamines may be used as chain lengthening agents. In typical Examples, wood, steel and glass is coated with solutions in organic solvents of a reaction product of a polyester derived from phthalic acid (or its anhydride) and trimethylolpropane and polyisocyanates, typical of which are those of the formula: