| 摘要 |
PURPOSE:To obtain a disc with little tracking miss and drop out by a structure wherein the title film consists of polyethylene terephthalate film, the content of COOK terminal group of which is the specified value or less and the refractive index in the direction of the thickness, the index of resistance to surface damage and the coefficient of humidity expansion in arbitrary direction within the plane of which are specified. CONSTITUTION:The content of COOH terminal group of polyethylene terephthalate in filmy state must be 30 equivalent per ton or less. The tracking miss of a magnetic disc made of a base material, the content of COOH terminal group of which must exceed 30 equivalent per ton, increases. The refractive index in the thickness of the film must be 1.492 or less. If said index is larger than 1.492, the number of drop outs tends to increase and also tracking misses increases. Next, the index of resistance to surface damage of the film must be 2% or less. The coefficient of humidity expansion of the film must mentioned above is larger than said range, tracking miss tends to occur during the reproduction of record in a magnetic disc having high recording density and consequently the correct reproduction of signals becomes difficult. |
