| 摘要 |
PURPOSE:To obtain a biaxially stretched polyester film excellent in winding characteristics and surface smoothness and suitable for base film of magnetic recording mediums by adding a specific amount of practically spherical particles of colloidal silica having a specific average grain size to the polyester film. CONSTITUTION:A polyester (preferably polyethylene terephthalate), containing 0.01-5wt% (preferably 0.1-1wt%) practically spherical particles of colloidal silica having an average grain size of 0.1-1mum, preferably 0.15-0.5mum, is molded into a sheet form and stretched in two stages to form a biaxially stretched film. |
