Biaxially stretched film and method of manufacturing the same, polarizer protective film, decorative film, and layered film

A method of manufacturing a biaxially stretched film in which an unstretched thermoplastic resin film comprising at least one thermoplastic resin layer is biaxially stretched in a longitudinal direction and a width direction to manufacture the biaxially stretched film, the method comprising:

• (I) preheating the thermoplastic resin film to a temperature in a rubbery plateau region in a storage elastic modulus curve;
• (II) biaxially stretching the thermoplastic resin film under a condition that a stretching speed is 500%/min or higher while heating the thermoplastic resin film to the temperature in the rubbery plateau region;
• (III) subsequently cooling the thermoplastic resin film to a temperature in a glass-to-rubber transition region or a glass region in the storage elastic modulus curve;
• and
• (IV) subsequently relaxing the thermoplastic resin film at a temperature in the glass-to-rubber transition region,
• wherein both a relaxation speed in the longitudinal direction and a relaxation speed in the width direction in said relaxing (IV) are 80%/min or higher, and
• wherein both a stretching magnification of the thermoplastic resin film in the longitudinal direction and a stretching magnification of the thermoplastic resin film in the width direction after (II) to (IV) with respect to the thermoplastic resin film before said biaxially stretching (II) are 1.5 to 3 times,
• wherein the at least one thermoplastic resin layer comprises a methacryl resin in which a triad syndiotacticity (rr) is 50% or larger.