Method of preparing thermoplastic resin having superior gloss, impact strength and whiteness

A method for preparing an acrylonitrile-butadiene-styrene (ABS) based thermoplastic resin comprising:

• (A) emulsion-polymerizing butadiene monomer to prepare a rubber latex having an average particle diameter of 1,800 Å to 5,000 Å, a polymerization conversion ratio of at least 90%, a swelling index of 12 to 40, and an average gel content of 70 to 95%;
• (B) emulsion-polymerizing 45 to 75 parts by weight of the rubber latex with 17 to 40 parts by weight of styrene and 4 to 20 parts by weight of acrylonitrile to prepare an acrylonitrile-butadiene-styrene (ABS) graft copolymer latex;
• and
• (C) coagulating the acrylonitrile-butadiene-styrene (ABS) graft copolymer latex with a coagulant at 60 to 80° C., followed by aging at 80 to 99° C., to obtain an acrylonitrile-butadiene-styrene (ABS) graft copolymer powder,
• wherein the step of preparing the rubber latex comprises:
• (i) introducing 50 to 95 parts by weight of the butadiene monomer, out of a total of 100 parts by weight thereof, together with 0.1 to 0.5 parts by weight of a molecular weight controlling agent to perform a primary reaction;
• and
• (ii) introducing 0.1 to 0.3 parts by weight of the molecular weight controlling agent together with 5 to 50 parts by weight of the remaining content of butadiene monomer to perform a secondary reaction,
• wherein a ratio of the molecular weight controlling agent to butadiene monomer to the molecular weight controlling agent used in the secondary reaction is higher than that used in the primary reaction, and a reaction time of the secondary reaction is longer than that of the primary reaction.