| 摘要 |
PURPOSE:To prepare a film with good slit properties by satisfying simultaneously values of respectively given range of birefringence rate and degree of surface orientation. CONSTITUTION:Birefringence rate DELTAn of a biaxially oriented polyester film should be in the range of -0.035--0.015 and also degree of surface orientation DELTAP should be in the range of 0.166-0.171. A film with birefringence DELTAn of -0.035 or less is extremely weak in the vertical direction strength, while particles are peeled off the surrounding polymer easily for a film with degree of surface orientation DELTAP of 0.171 or more and dropouts are increased when used for a magnetic tape. Further, the surface properties of a film with good balance for the magnetic tape is achieved in case the number of pieces Nn (Pc./mm<2>) of (n) degree interference fringe measured by the multi-interference method satisfies 50<=N<=250, 10<=N2<=250, 0.5<=N1/N2<=15 simultaneously. |
