Process for making high solids acrylic dispersion lacquer

Claim 1

A process for preparing a high solids acrylic dispersion lacquer coating composition having an acrylic polymer binder content of about 25-45% by weight in a nonaqueous medium; wherein the acrylic polymer binder consists essentially of (1) 25-45% by weight, based on the weight of the binder, of Polymer A comprising about 90-99.5% by weight, based on the weight of Polymer A, of polymerized methyl methacrylate and about 0.1-5% by weight, based on the weight of Polymer A, of polymerized allyl methacrylate and 0.4-5% by weight, based the weight of Polymer A, of polymerized alkyl amino alkyl methacrylate and having a weight average molecular weight, measured by gel permeation chromatography, of about 90,000-130,000; (2) 5-25% by weight, based on the weight of the binder, of Copolymer B comprising about 40-60% by weight, based on the weight of Copolymer B, of polymerized methyl methacrylate and 40-60% by weight, based on the weight of Copolymer B, of polymerized alkyl acrylate having 6-12 carbon atoms in the alkyl group and having a weight average molecular weight, measured as above, of about 20,000-40,000; and (3) 40-60% by weight, based on the weight of the binder, of a graft copolymer of Polymer A which forms a backbone of the graft copolymer and Copolymer B attached to the backbone which forms side chains of the graft copolymer; and wherein the nonaqueous medium comprises (a) an aliphatic solvent which is at 25° C. a nonsolvent for Copolymer B; and (b) a coalescing solvent which at 50° C. and above is a solvent for the binder and at 25° C. is a nonsolvent for the binder; wherein the process comprises the following steps: Step (1) adding about 50-70% by weight of the monomers for Polymer A and the backbone of the graft copolymer to a polymerization vessel with coalescing solvent, bridging solvent and low boiling solvent selected from the group of methanol or a blend of acetone and petroleum ether and maintaining a reflux temperature; Step (2) adding about 0.1-2% by weight, based on the weight of Polymer A and the backbone of the graft copolymer, of an azo polymerization catalyst with coalescing solvent to the reaction mixture of step (1) and polymerizing said monomers; Step (3) adding at a substantially uniform rate the remaining 30-50% by weight of the monomers for Polymer A and the backbone of the graft copolymer and a coalescing solvent and about 0.1-2% by weight, based on the total weight of the monomers for Polymer A and the backbone of the graft copolymer, of an azo polymerization catalyst while maintaining the reflux temperature and polymerizing said monomers; Step (4) adding about 40-60% by weight of monomers of Copolymer B and the side chains of the graft copolymer and about 0.5-2% by weight, based on the weight of the above monomers, of a peroxy polymerization catalyst while maintaining the reflux temperature and polymerizing said monomers; Step (5) adding at a substantially uniform rate the remaining 40-60% by weight of the monomers of Step (4) with the above same amount of peroxy polymerization catalyst while maintaining the reflux temperature and polymerization said monomers; Step (6) adding at a substantially uniform rate, about 2-10% by weight, based on the weight of the monomers for Polymer A, Copolymer B and the graft copolymers, of methyl methacrylate monomer with about 0.1-1% by weight of azo polymerization catalyst and the above peroxy polymerization catalyst while maintaining the refux temperature and polymerizing said monomers; Step (7) adding at a substantially uniform rate about 15-25% by weight, based on the weight of the resulting reaction mixture of the above steps, of an aliphatic hydrocarbon solvent which is a nonsolvent for Polymer A and the backbone of the graft copolymer; and Step (8) adding about 5-10% by weight, based on the weight of the reaction mixture, of the aliphatic hydrocarbon solvent of Step (7) containing about 0.1-10% by weight, based on the weight of the solvent, of the peroxy polymerization catalyst and polymerizing any residual monomers and cooling the resulting composition to an ambient temperature.