Precursor film for retardation films, retardation film, and liquid crystal display device

Abstract

Provided is a film that is made of a propylene-based copolymer selected from among propylene-based random copolymers and propylene-based block copolymers, the film being useful as a precursor film for the production of a retardation film by stretching. The propylene-based copolymer forming the film contains crystals containing smectic crystals, wherein the percentage of smectic crystals to all the crystals of the propylene-based copolymer. The film has an in-plane retardation of 50 nm or less and a thickness falling within the range of 30 to 200 μm. The propylene-based copolymer is a copolymer that has a parameter (A) falling within the range of from 0.0007 to 0.1, the parameter (A) being calculated from Formula (1) defined for a stress-strain curve produced as a result of stretching a film made of the polymer at a tensile rate of 100 mm/minute at a temperature at which a stress of 0.8±0.1 MPa is produced at a strain of 200%: (A)=(B600−B200)/400  Formula (1) wherein B600 and B200 represent a stress (MPa) at a strain of 600% and a stress (MPa) at a strain of 200%, respectively.

Dependencies are inferred from the claim text.