Process for producing a styrenic resin composition

A process for producing a styrenic resin composition comprising the steps of:

• compounding 100 parts by weight of a styrenic resin having a water content greater than 2% by weight, and 0.01-5.0 parts by weight of an organic phosphorus-containing antioxidant in an extruder to form said styrenic resin composition;
• wherein said phosphorous-containing antioxidant is formed by mixing (a) 20 to 99.9 wt % of organic phosphite or phosphonite with (b) 0.1 to 80 wt % of acid-binding metal salt treated with a surface conditioning agent, prior to mixing or compounding with said styrenic resin;
• wherein the weight ratio of said surface conditioning agent to said acid-binding metal salt is 0.1 to 50 wt %:99.9 to 50 wt %;
• wherein said surface conditioning agent is selected from the group consisting of silane coupling agents, titanate coupling agents, zirconate coupling agents, aluminate coupling agents, zirco-aluminate coupling agents, non-ionic surfactants, and anionic surfactants;
• wherein said styrenic resin having a water content greater than 2% by weight comprises 5-100 wt % of a rubbery graft copolymer (A) and 95-0 wt % of a styrenic copolymer (B) based on the dry weight of said styrenic resin;
• wherein said rubbery graft copolymer(A) is prepared by graft polymerization of 50-90 wt % of styrenic monomer, 10-50 wt % of vinyl cyanide monomer, and 0-40 wt % of copolymerizable monomer in the presence of a rubbery polymer latex, followed by coagulation and recovery to have a water content of 5-50 wt %;
• and
• wherein said styrenic copolymer(B) is prepared by coploymerization of 50-90 wt % of styrenic monomer, 10-50 wt % of vinyl cyanide monomer, and 0-40 wt % of copolymerizable monomer.