THERMOSETTING COATING COMPOSITION

摘要

A thermosetting coating composition which may have nonvolatile solids content as high as 60% or greater and which may be employed as an automotive topcoat. The composition, exclusive of pigments, solvent, reactive and non-reactive diluents and other non-reactive components, consists essentially of: (A) A binder composition consisting essentially of: (1) Between about 30 and about 75 weight percent of one or more low viscosity resins selected from hydroxy functional acrylic polymers, hydroxy functional polyethers and hydroxy functional polyesters, each of which (i) is substantially soluble in the solvent of the composition and (ii) has a number average molecular weight of between about 1000 and about 2500; and (2) Between about 70 and about 25 weight percent of one or more crosslinked dispersion polymers each of which is substantially insoluble in the solvent of the composition; and (B) An aminoplast crosslinking agent in an amount of between about 5 and about 40 parts per 100 parts of said binder composition. The crosslinked dispersion polymer is prepared by free radical polymerization of 0.5 to 3.5 weight percent of di-,tri- or tetravinyl monomers and 99.5 to 96.5 weight percent of at least one other copolymerizable monoethylenically unsaturated monomer, in the presence of (i) hydrocarbon dispersing liquid which is a solvent for the polymerizable monomer, but a non-solvent for the resulting crosslinked polymer, and (ii) polymeric dispersion stabilizer which is solvated by said dispersing liquid and associated with said crosslinked polymer so as to maintain a separation between particles thereof, thereby inhibiting coagulation of said particles, wherein polymerization is carried out at elevated temperature such that the dispersion polymer first forms and then is crosslinked.