Patent ID: 6861488

Claim:
A process for producing a vinyl chloride-based polymer comprising conducting a suspension polymerization of either vinyl chloride monomer or a mixture of vinyl chloride monomer and a monomer capable of copolymerization with the vinyl chloride monomer, in an aqueous medium and using an oil soluble polymerization initiator in an aqueous medium and using an oil soluble polymerization initiator in a polymerization vessel, wherein the oil soluble polymerization initiator comprises: (A) t-amyl peroxyneodecanoate, and (B) an organic peroxide that is different from the component (A) and has a 10 hour half-life temperature in a solution with a concentration of 0.1 mol/liter in trichloroethylene within a range from 30° C. to 55° C., and when the polymerization conversion rate reaches a value within a range from 65% to 90%, the reaction temperature of a polymerization mixture inside the polymerization vessel is raised by a temperature increase of between 5 and 30° C., followed by addition of an antioxidant to said polymerization mixture, wherein a ratio of quantities of said component (A) and said component (B), in terms of a weight ratio (A)/(B), is within a range from 1/5 to 5/1; a combined quantity of said component (A) and said component (B) is within a range from 0.02 to 0.15 carts by weight per 100 carts by weight of said vinyl chloride monomer or said mixture of vinyl chloride monomer and a monomer capable of copolymerization with vinyl chloride monomer; and said vinyl chloride-based polymer has an improved anti-initial discoloration property.