| 摘要 |
PURPOSE:To obtain the subject film excellent in the balance between strength in the longitudinal direction and that in the transverse direction, having a resistance to casting and useful as a PCP paper, etc., by heat treating a film having a specified pore content in a specified condition. CONSTITUTION:A polybutylene terephthalate film containing 10-65wt.% inorganic fine powder is monoaxially stretched by 1.5-4 times at a temperature of >=glass transition temperature of the above-mentioned terephthalate and within a range of <=100 deg.C. Heat treatment is subsequently carried out at a temperature of >= the above-mentioned stretching temperature and within a range of [the melting point (Tm) of the above-mentioned terephthalate -70 deg.C]-[Tm -5 deg.C], thus obtaining the objective film having >=5% pore content and >=1.5 of ratio (R) of tensile modulus (Ym) in the stretching direction to tensile modulus (Yc) in the direction perpendicular to that, i.e., (R)=(Ym)/(Yc). |
