Melt coating composition and coating process

A coating composition which can be cross-linked by heat and has a melting point or range below 200.degree. C comprising blocked polyisocyanates and polyhydroxyl compounds, wherein at least 40 equivalent percent of the blocked polyisocyanates consist of alkanol- or cycloalkanol-blocked polyisocyanates, said composition having a substantially constant viscosity of not more than 40,000 cP at a temperature between about 20.degree. C and 250.degree. C, and the polyisocyanates being selected from the group consisting of 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, mixtures of 2,4- and 2,6-diisocyanatotoluene, 4,4'-diisocyanatodiphenylmethane, 4,4'-diisocyanatodiphenyl - dimethylmethane, 1,5-diisocyanatonaphthalene, mixtures of homologues or isomers obtained by phosgenation of aniline/formaldehyde condensates, the triisocyanate containing urethane groups obtained by reacting 3 mols of 2,4-diisocyanatotoluene with 1 mol of trimethylolpropane and the isocyanato-isocyanurate obtained by trimerizing 2,4-diisocyanatotoluene.

A coating composition which can be cross-linked by heating comprising

• i. at least 50% by weight of a combination of blocked polyisocyanates and polyhydroxyl compounds having a melting point or melting range below about 200.degree. C and having an equivalent ratio of blocked isocyanate groups to hydroxyl groups of about 1:2 to about 9:1, about 40 to 99 equivalent percent of said blocked polyisocyanates being alkanol or cycloalkanol blocked and about 60 to 1 equivalent percent of said blocked polyisocyanates having a deblocking temperature at least about 30.degree. C below the deblocking temperature of the alkanol or cycloalkanol blocked polyisocyanate, and
• ii. up to 50% by weight of polymeric substances not substantially reactive with said hydroxyl groups.

A coating composition which can be cross-linked by heating to a sufficient temperature comprising

• i. at least 50% by weight of a combination of blocked polyisocyanates and polyhydroxyl compounds having a melting point or melting range below about 200.degree. C and having an equivalent ratio of blocked isocyanate groups to hydroxyl groups of about 1:2 to about 9:1, about 40 to 99 equivalent percent of said blocked polyisocyanates being alkanol or cycloalkanol blocked and about 60 to 1 equivalent percent of said blocked polyisocyanates having a deblocking temperature at least about 30.degree. C below the deblocking temperature of the alkanol or cycloalkanol blocked polyisocyanates, and
• ii. up to 50% by weight of polymeric substances not substantially reactive with hydroxyl groups
• in which constituents (i) and (ii) together having a substantially constant viscosity of not more than 40,000 cP at a temperature between about 20.degree. C and 250.degree. C.