PURPOSE: To improve the twist of a film and to reduce fraction defective of a product by controlling the nonuniformity in thickness in longitudinal and width directions and a heat shrinkage stress difference and by reducing the moisture content of a surface layer of a composition roll to be in a prescribed range.
CONSTITUTION: A polyester film is constituted of a polymer containing, for instance, polyethylene terephthalate, polyethylene-2,6-naphthalate, polyethylene- bis-α,β-(2-chlorophenoxy)-ethane-4,4'-dicarbochelate or the like of about 70wt.% or above. The film constituted of polyethylene terephthalate is desirable. A composition roll is prepared by rolling up the film of which the nonuniformity in thickness in longitudinal and width directions is 8% or less and a heat shrinkage stress difference between both ends in the longitudinal direction is 0 to 100g/mm2. The moisture content of the surface of the roll is controlled to be 0.05 to 0.20wt.% and the thickness of a biaxially orientated film prepared by sequential biaxial orientation or biaxial orientation is made 25 to 150μm preferably.
YAMAGISHI HIDEKI
TOKUHARA TETSUJI
