Rubbery polymer, graft copolymer, and thermoplastic resin composition

1. A graft copolymer (B-I) produced by grafting at least one vinyl monomer (b-I) selected from the group consisting of aromatic vinyl, alkyl (meth)acrylate, and vinyl cyanide to a rubbery polymer mixture including a rubbery polymer (A-I) and a hydrophobic substance, the rubbery polymer (A-I) including an alkyl (meth)acrylate unit and a multifunctional monomer unit copolymerizable with alkyl (meth)acrylate, the hydrophobic substance having a kinematic viscosity of 5 mm 2 /s or more at 40° C. or a kinematic viscosity of 2 to 4 mm 2 /s at 100° C., the hydrophobic substance comprising a hydrocarbon.

2. The graft copolymer (B-I) according to claim 1 , wherein an amount of the multifunctional monomer unit is 0.1 to 5.0 parts by mass relative to 100 parts by mass of a total amount of the alkyl (meth)acrylate unit and the multifunctional monomer unit.

3. The graft copolymer (B-I) according to claim 1 , wherein a ratio between the rubbery polymer (A-I) and the vinyl monomer (b-I) is such that a proportion of the rubbery polymer (A-I) is 10% to 90% by mass and a proportion of the vinyl monomer (b-I) is 90% to 10% by mass (with the total proportion of the rubbery polymer (A-I) and the vinyl monomer (b-I) being 100% by mass).

4. The graft copolymer (B-I) according to claim 1 , wherein the rubbery polymer mixture is a polymerization product produced by polymerizing a miniemulsion containing alkyl (meth)acrylate, the multifunctional monomer, the hydrophobic substance, an emulsifier, and water.

5. The graft copolymer (B-I) according to claim 4 , wherein an amount of the hydrophobic substance is 0.1 to 10 parts by mass relative to 100 parts by mass of alkyl (meth)acrylate.

6. The graft copolymer (B-I) according to claim 4 , wherein the rubbery polymer (A-I) included in the polymerization product has a volume-average particle size of less than 1000 nm.

7. A thermoplastic resin composition comprising the graft copolymer (B-I) according to claim 1 .

8. A molded article produced using the thermoplastic resin composition according to claim 7 .

9. A method for producing a rubbery polymer (A-I), the method comprising a miniemulsion formation step in which a mixture (a-I) containing alkyl (meth)acrylate, a multifunctional monomer copolymerizable with alkyl (meth)acrylate, a hydrophobic substance, an emulsifier, and water is formed into a miniemulsion, the hydrophobic substance having a kinematic viscosity of 5 mm 2 /s or more at 40° C. or a kinematic viscosity of 2 to 4 mm 2 /s at 100° C., the hydrophobic substance comprising a hydrocarbon, and a polymerization step in which the miniemulsion is polymerized.

10. A method for producing a graft copolymer (B-I), the method comprising grafting at least one vinyl monomer (b-I) selected from the group consisting of aromatic vinyl, alkyl (meth)acrylate, and vinyl cyanide to the rubbery polymer (A-I) produced by the method for producing the rubbery polymer (A-I) according to claim 9 .

11. A method for producing a thermoplastic resin composition, the method comprising using the graft copolymer (B-I) produced by the method for producing the graft copolymer (B-I) according to claim 10 .

12. A method for producing a molded article, the method comprising using the thermoplastic resin composition produced by the method for producing the thermoplastic resin composition according to claim 11 .

13. The graft copolymer (B-I) according to claim 1 , wherein the hydrophobic substance has a kinematic viscosity of 5 mm 2 /s or more and 67.7 mm 2 /s or less at 40° C. or a kinematic viscosity of 2 to 4 mm 2 /s at 100° C.