Biaxially stretched film and production method thereof, polarizer protective film, decorative film, and laminated film

摘要

The present invention provides a method for producing a biaxially stretched film that has low thermal shrinkage and excellent dimensional stability. A biaxially stretched film is produced by biaxially stretching an unstretched thermoplastic resin film composed of at least one thermoplastic resin layer in the longitudinal direction and the width direction. The method for producing a biaxially stretched film of the present invention includes a step (I) of preheating a thermoplastic resin film to a temperature in a rubber-like flat region in a storage modulus curve, and a thermoplastic resin film in the rubber-like flat region. Step (II) of biaxial stretching at a stretching speed of 500% / min or more while heating to temperature, and the thermoplastic resin film after step (II) in the glass-rubber transition region or glass in the storage elastic modulus curve Step (III) in which the temperature is lowered to the temperature in the region, and Step (IV) in which the thermoplastic resin film after Step (III) is relaxed at the temperature in the glass-rubber transition region.