Patent ID: 8022139

Claim:
A polylactic acid composition comprising (A) a polylactic acid-series resin and (B) an acrylic triblock copolymer, which fulfills the following requirements (1) to (6): (1)(P) a parameter represented by the following formula (1) is in the range of 0.05 to 10: P =(η A /η B )×(φ B /φ A ) (1) wherein η A is a melt viscosity (Pa·s) of the polylactic acid-series resin (A) at a temperature of 200° C. and a shear rate of 100 sec −1 , η B is a melt viscosity (Pa·s) of the acrylic triblock copolymer (B) at a temperature of 200° C. and a shear rate of 100 sec −1 , φ A is a volume fraction (%) (25° C.) of the polylactic acid-series resin (A) relative to the total volume of the polylactic acid-series resin (A) and the acrylic triblock copolymer (B), and φ B is a volume fraction (%) (25° C.) of the acrylic triblock copolymer (B) relative to the total volume of the polylactic acid-series resin (A) and the acrylic triblock copolymer (B); (2) the acrylic triblock copolymer (B) comprises (B1) a polymer block having a glass-transition temperature of not higher than 25° C., (B2a) a polymer block which has a glass-transition temperature of not lower than 60° C. and is bound to a terminal of the polymer block (B1), and (B2b) a polymer block which has a glass-transition temperature of not lower than 60° C. and is bound to another terminal of the polymer block (B1); (3) the polymer block (B1) contains a unit derived from an acrylic ester as a main structural unit, and the polymer block (B2a) and the polymer block (B2b) independently contain a unit derived from an methacrylic ester unit as a main structural unit; (4) both of the weight-average molecular weights of the polymer block (B2a) and the polymer block (B2b) are smaller than the weight-average molecular weight of the polymer block (B1), (5) the acrylic triblock copolymer (B) is a polymer obtained by an anionic polymerization in the presence of an organoaluminum compound, and is free from a halogen atom, and (6) the weight average molecular weight of the polymer block (B2a) is larger than the weight average molecular weight of polymer block (B2b), and the proportion (molecular weight ratio) of the weight average molecular weight of the polymer block (B2a) relative to the polymer block (B2b) is 1.2 to 8.