Patent ID: 7491357

Claim:
A solution casting process, in which dope containing a polymer and a solvent is cast on to a support to form a cast film, said cast film is stripped from said support to obtain a polymer film, and said polymer film is stretched, said solution casting process comprising a step of: while said polymer film is stretched, applying tension of 80 N/m or more thereto in a stretching direction, wherein polymer film surface temperature thereof is set equal to or more than a glass transition temperature Tg thereof, wherein said polymer is constituted by a cellulose ester, and satisfies conditions of: 2.5 ≦A+B≦ 3.0 I 1.25≦B≦3.0 II where A and B are each a degree of substitution of an acyl group formed by substituting a hydrogen atom in hydroxy groups in cellulose, and A is a degree of substitution of an acetyl group formed by substituting a hydrogen atom in said hydroxy groups in said cellulose, and B is a total degree of substitution of at least one of a propionyl group, a butyryl group, a pentanoyl group, and a hexanoyl group formed by substituting a hydrogen atom in said hydroxy groups in said cellulose.