| 摘要 |
PURPOSE:To obtain a film, which has high Young's modulus and is excellent in high-speed slitting, by a method wherein polyester containing specified components is biaxially oriented and heat-treated so as to set the density, the change of thickness and the friction coefficient of a resultant film at specified values respectively. CONSTITUTION:In a film consisting of polyester, the major component of which is carboxylic acid residue and ethylene glycol residue represented by a structural unit I, which contains at least one kind out of carboxylic acid residues represented by structural units II and III and the molar ratio of said residues of which satisfies the formula represented at the lowermost line, its density lies within the range of 1.44-1.50g/cm<3>, the change of its thicknesses in width direction is 15% or less and its friction coefficient lies within the range of 0.5-4.0. Because the film, which has high Young's modulus and is excellent in slitting at high speed, the film can be thinned and consequently the miniaturization of magnetic tape and capacitor can be contrived. |
