Long stretched film and production method therefor

A method for manufacturing a stretched film for producing a long-length stretched film having a slow axis in an angle of 5° or more and 85° or less on average with respect to a width direction thereof by stretching a long-length resin film while being conveyed so as to pass through an oven in a state in which each of both end portions of the resin film are held by first grippers and second grippers that are capable of holding the end portions of the resin film, wherein:

• the oven has a preliminary heating zone, a stretching zone, a thermal fixing zone, and a reheating zone in this order from an upstream side;
• the stretching zone includes a specific zone having a temperature gradient capable of setting a temperature of an intermediate area such that a temperature of an end portion on a second gripper side therein is higher than a temperature of an end portion on a first gripper side therein by 5° C. or higher and 15° C. or lower, the intermediate area being an area of the resin film in the width direction excluding the both end portions thereof;
• and
• the reheating zone has a temperature capable of heating the resin film to a temperature of Tg+5° C. or higher and Tg+20° C. or lower (Tg representing a glass transition temperature of a resin forming the resin film),
• the manufacturing method comprising:
• a step of holding the both end portions of the resin film by the first grippers and the second grippers;
• a step of passing the resin film through the preliminary heating zone;
• a step of passing the resin film through the stretching zone such that a moving distance of the first grippers is longer than a moving distance of the second grippers;
• a step of passing the resin film through the thermal fixing zone;
• and
• a step of passing the resin film through the reheating zone.