| 摘要 |
PURPOSE:To obtain a biaxially oriented polyethylene terephthalate film excellent in slitting properties, scratch resistance and dimensional stability at high temp. and having high strength in its longitudinal direction by setting the F5 value and thermal shrinkage factor of the film in the longitudinal direction thereof to predetermined values and setting the double refraction and density thereof to predetermined values. CONSTITUTION:A biaxially stretched polyethylene terephthalate film is characterized by that the F5 value in the longitudinal direction thereof at room temp. is 12-25kg/mm<2>, the thermal shrinkage factor in the longitudinal direction thereof at 150 deg.C is 6% or less and double refraction contributing to the amorphous part thereof represented by formula (wherein nax, nay and naz are respectively refractive indexes dna to which the amorphous part thereof in the longitudinal, lateral and thickness directions of the film contributes) is 0.06-0.13 and the density thereof is 1.383-1.394. The orientation of the crystallite of the film is mainly determined by the combination of the temp. and stretching magnification at a time of stretching in lateral and longitudinal directions but, since a tendency is different by the heating or stretching system of a film forming machine, a proper condition is selected by a film forming machine to be used. |
