| 摘要 |
PURPOSE:To form an optically transmittable plastic fiber having good optical transmittability at a high temp. by consisting a protective layer of an ester thermoplastic elastomer and specifying the shrinkage rate when said layer is subjected to a dry heat treatment. CONSTITUTION:The ester thermoplastic elastomer is used as the protective layer and the shrinkage rate by the dry heat treatment for 240hr at 120 deg.C is <=5%. The dry heat treatment for 240hr at 120 deg.C refers to the heat treatment to be executed for 240hr at 120 deg.C by using a suitable heating means under the atmosphere having no moisture. The shrinkage rate is the quantity of the shrinkage by the heat treatment, expressed by per cent, relative to the unit length before the heat treatment in the fiber direction of the optically transmittable fiber. The shrinkage rate in the dry heat treatment for 240hr at 120 deg.C is required to be <=5%, preferably <=3%, more preferably <=1%. |
