Method for producing resin composition and method for producing molded article

A method for producing a resin composition, the method comprising:

• obtaining a resin composition by heating and melt-kneading a mixture containing a particulate nucleating agent in which a cumulative 50% particle size (D50) in a volume-based particle size distribution is equal to or more than 0.1 μm and equal to or less than 300 μm and a thermoplastic resin using a twin screw extruder including, inside a cylinder, a screw having kneading discs,
• wherein the obtaining a resin composition includes extruding the mixture supplied into the twin screw extruder in an ejection direction under kneading conditions in which X and Y satisfy 4.0≤X in a range of 6.0×103≤Y≤7.0×104 when a volume-based ejection amount represented by Equation (I) is denoted by X (10−6·kg·h−1·mm−3), and a strain rate represented by Equation (II) is denoted by Y (min−1),
• volume-based ejection amount=ejection amount (kg/h) of twin screw extruder/internal capacity (106·mm3) of cylinder, and [Equation (I)]
• strain rate=rotation rate (min−1) of screw×radius (mm) of screw/width (mm) of narrow part inside cylinder. [Equation (II)]