GB1378974A - Pulverulent heat-hardenable coating amterial - Google Patents

Abstract

1378974 Pulverulent coating materials CASSELLA FARBWERKE MAINKUR AG 19 Sept 1972 [20 Sept 1971] 43354/72 Heading C3R Pulverulent heat-hardenable coating materials comprise (A) 30 to 45% by weight of a polyester having an average M.W. of 500 to 6000, an acid number below 20, an hydroxyl number of 400 to 800 and a softening temperature of 80‹ to 150‹ C., the polyester being the reaction product of a mixture of (1) 90 to 10 mol per cent of isophthalic acid a lower alkanol ester thereof or an equivalent, based on isophthalic acid, of poly-lower alkylene diol ester thereof and 10 to 90 mol per cent of terephthalic acid, a lower alkanol ester thereof or an equivalent, based on terephthalic acid of poly-lower alkylene diol ester thereof and (2) a mixture of 70 to 100 mol per cent of at least one saturated aliphatic polyol having 4 to 6 hydroxyl groups and 30 to 0 mol per cent of at least one saturated aliphatic glycol whose hydroxyl groups are separated from each other by at least 3 carbon atoms, (B) 55 to 70% by weight of a polyisocyanate having at least 50% of its isocyanate groups masked with a heat-cleavable lactam moiety and (C) up to 2% by weight of a catalyst which promotes heat cleavage of the lactam moiety and hardening of the coating. In a typical example, a polyester derived from pentaerythritol, hexane diol, isophthalic acid and terephthalic acid is mixed with a 3-isocyanatomethyl-3,5,5- trimethylcyclohexylisocyanate / # - caprolactam reaction product, dibutyl tin dilaurate and titanium dioxide. The mixture is milled, sieved applied to a metal plate and baked at 180‹ C. to cleave the masking groups and allow the free isocyanate groups to react with the polyester. Other polyester-forming compounds, polyisocyanates and catalysts are listed.