Method of preparing thermoplastic resin, thermoplastic resin composition including the same, and method of manufacturing injection-molded article using thermoplastic resin composition
The present invention relates to a method of preparing a thermoplastic resin, a method of preparing a thermoplastic resin composition including the same, and a method of manufacturing an injection-molded article using the thermoplastic resin composition. By using a mixture of molecular weight modifiers having different reactivities according to the present invention, coagulation may be performed using a small amount of coagulant, productivity may be increased, and a molded article, which is manufactured using a thermoplastic resin, having excellent appearance characteristics along with superior mechanical strength, processability, or the like may be provided.
1. A method of preparing a thermoplastic resin, the method comprising emulsion-polymerizing an aromatic vinyl compound and a vinyl cyan compound, wherein a mixture of 20 to 54% by weight of mercaptan and 46 to 80% by weight of an alpha-alkyl styrene multimer is used as a molecular weight modifier,
wherein the emulsion polymerizing comprises:
i) a polymerization step of polymerizing 100 parts by weight of a monomer mixture comprising 50 to 80% by weight of the aromatic vinyl compound and 20 to 50% by weight of the vinyl cyan compound, 0.05 to 1 part by weight of the molecular weight modifier, 0.01 to 1 part by weight of an initiator, and 0.1 to 3 parts by weight of an emulsifier;
ii) a termination step of terminating the polymerization step when a conversion rate in the polymerization step is 90% or more; and
iii) a coagulation step of adding a 0.1 to 3 parts by weight of an acid coagulant to 100 parts by weight of a latex that is obtained after the termination step, followed by coagulation, and
iv) a dehydration and drying step of the coagulated slurry,
wherein the wet powder obtained after the dehydration has a water content of 45% by weight or less,
wherein the thermoplastic resin has a weight average molecular weight of 350,000 to 750,000 g/mol.
2. The method according to claim 1 , wherein the mixture has 20 to 30% by weight of mercaptan 70 to 80% by weight of the alpha-alkyl styrene multimer.
3. The method according to claim 1 , wherein the mercaptan is one or more selected from a C1 to C20 chain alkyl mercaptan and a C1 to C20 branched alkyl mercaptan.
4. The method according to claim 1 , wherein the alpha-alkyl styrene multimer is one or more selected from an alpha-methyl styrene multimer and an alpha-ethyl styrene multimer.
5. The method according to claim 4 , wherein the multimer is one or more selected from a dimer, a trimer, and a tetramer.
6. The method according to claim 1 , wherein the polymerization step i) is carried out at 60 to 95° C.
7. The method according to claim 1 , wherein the coagulant of the coagulation step iii) is sulfuric acid.
8. The method according to claim 1 , wherein the coagulation step iii) is carried out at 80 to 110° C.
9. The method according to claim 1 , wherein the wet powder has a water content of 40% or less.