| 摘要 |
A novel tetrahydroxy oligomer crosslinkable with polyisocyanates to form a coating composition adapted for use as an automative topcoat and which upon curing forms a hard, glossy, coating with outstanding durability and excellent resistance to solvents and water. The coating composition comprises: (A) a tetrahydroxy oligomer having a number average (Mn) molecular weight of between about 600-2000 and being the reaction product of: (i) an ester containing pendant hydroxyl and carboxyl functionality and being made by reaction of reactants consisting essentially of: (a) a C3-C10 aliphatic diol, and (b) an alkyl hexahydrophthalic anhydride, wherein (a) and (b) are combined in the reaction mixture in an amount sufficient to allow reaction in about a 1:1 molar ratio; and (ii) a diepoxide having a number average molecular weight between about 130-1500, wherein (i) and (ii) are combined in the reaction mixture in an amount sufficient to allow reaction in about a 2:1 molar ratio, (B) a polyisocyanate crosslinking agent; (C) optionally a hydroxyl functional additive; and (D) solvent. The polyisocyanate crosslinking agent having two or more reactive isocyanate groups per molecule is included in the composition in an amount sufficient to provide between about 0.50 and about 1.6 reactive isocyanate groups per hydroxyl group present in the composition either on the tetrahydroxy oligomer or as a hydroxyl group of the hydroxy functional additive.
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