Patent ID: 8378026

Claim:
A transparent rubber-modified styrenic resin composition produced by the process of: (1) polymerizing a reactant mixture comprising about 5 to about 30 parts by weight of a styrene-butadiene rubbery copolymer, about 20 to about 40 parts by weight of styrenic monomer, about 30 to about 60 parts by weight of unsaturated carboxylic acid alkyl ester monomer and about 0 to about 15 parts by weight of vinyl cyanide monomer, wherein the amount of styrene-butadiene rubbery copolymer, styrenic monomer, unsaturated carboxylic acid alkyl ester monomer, and vinyl cyanide monomer is based on 100 parts by weight of the total monomers, to a point of phase inversion in a first reactor at a temperature ranging from about 80 to about 130° C. for about 0.5 to about 2 hours to prepare a first polymerization product comprising the rubbery polymer and a matrix resin comprising the styrenic monomer, the unsaturated carboxylic acid alkyl ester monomer and the vinyl cyanide monomer; (2) continuously introducing the first polymerization product into a second reactor and polymerizing the first product therein at a temperature ranging from about 100 to about 150° C. for about 1.5 to about 3 hours, while supplying about 0 to about 5 parts by weight of additional styrenic monomer or unsaturated carboxylic acid alkyl ester monomer per 100 parts by weight of the reactant mixture to prepare a second polymerization product comprising the rubbery polymer and a matrix resin comprising the styrenic monomer, the unsaturated carboxylic acid alkyl ester monomer and the vinyl cyanide monomer; and (3) continuously introducing the second polymerization product into a third reactor and polymerizing the second product therein at a temperature ranging from about 110 to about 160° for about 1.5 to about 3 hours, while supplying about 0 to about 5 parts by weight of additional styrenic monomer or unsaturated carboxylic acid alkyl ester monomer per 100 parts by weight of the reactant mixture to prepare a third polymerization product comprising the rubbery polymer and a matrix resin comprising the styrenic monomer, the unsaturated carboxylic acid alkyl ester monomer and the vinyl cyanide monomer, wherein the difference between the refractive index of the rubbery copolymer and the refractive index of the matrix resin of the third polymerization product is about 0.005 or less and the transparent rubber-modified styrenic resin composition has a haze of about 5% or less as measured by a Nippon Denshoku Haze meter using a 3 mm thick test sample, and wherein the process includes adding a combined amount of at least 3 parts by weight additional styrenic monomer, unsaturated carboxylic acid alkyl ester monomer, or both, in the second reactor and the third reactor so that the difference between the refractive index of the rubbery copolymer and the refractive index of the matrix resin of the third polymerization product is about 0.005.