Resin composition comprising polymer particles and manufacturing method thereof

A resin composition comprises mixed particles and a thermoplastic resin, the mixed particles comprising polymer particles I and polymer particles II in a mass ratio of the polymer particles I relative to the polymer particles II of 55/45 to 75/25, each of the polymer particles I having a three-layered structure composed of an innermost layer made of a rigid polymer c comprising 80 to 100% by mass of a methacrylic acid ester unit, an intermediate layer made of a soft polymer i comprising 40 to 99.9% by mass of an acrylic acid ester unit and 0.1 to 5% by mass of a poly-functional monomer unit wherein the soft polymer i has a glass transition temperature of less than 25°C, and an outermost layer made of a rigid polymer o comprising 80 to 100% by mass of a methacrylic acid ester unit, the polymer particles I having a weight-average molecular weight of an acetone soluble-matter of 70,000 to 100,000 and a volume average particle diameter determined by a light-scattering method of 150 to 300 nm, and each of the poly