Melt coating composition and coating process

摘要

A process for the low solvent or solvent free coating of heat resistant substrates by using a coating substance which has a melting point or range below about 200 DEG C and which is heat crosslinkable. The substrate is coated at temperatures between about 20 DEG and 250 DEG C and the coating is subsequently heated to more elevated temperatures to effect crosslinking. The coating substance contains active hydrogen, preferably hydroxyl bearing compounds and blocked polyisocyanates which become reactive when the coating substance is heated to effect cross-linking. In a preferred embodiment, the blocked polyisocyanates consist of at least 40 equivalent percent alkanol or cycloalkanol blocked polyisocyanates. Also a coating substance containing at least 50 wt.% of a combination of active hydrogen, preferably hydroxyl bearing compounds and blocked isocyanates. The combination has a melting point of less than 200 DEG C and a blocked isocyanate group to active hydrogen ratio of about 1:2 to 1:9. At least 40 equivalent percent of the blocked polyisocyanates are alkanol or cycloalkanol blocked and the remainder are blocked such that they are reactive at temperatures at least 30 DEG C lower than the alkanol or cycloalkanol blocked polyisocyanates. The coating substance has a viscosity of less than about 40,000 cP at or below about 250 DEG C.