| 摘要 |
PURPOSE:To provide excellent heat resistance, moisture resistance and mechanical properties and a good optical transmission characteristic even at a high temp. by using a core material layer consisting of a transparent methacrylic polymer which contains specific weight % or above of a methyl methacrylate unit and of which the intrinsic-viscosity number is in a specific range. CONSTITUTION:The basic constituting unit of the fiber consists of the core material layer 11 and a sleeve material layer 12 from the inside or the basic constituting unit consists of the core material layer 21, the sleeve material layer 22 and a protective layer 23 form the inside. The transparent polymer of which at least 70% in terms of the weight % of the monomer consists of methyl methacrylate and of which the intrinsic-viscosity number eta (in chloroform, 25 deg.C) is 0.55-0.9dl/g is used for the methacrylic polymer to be used as the layers 11 and 21. The satisfactory characteristics in terms of the mechanical properties, thermal shrinkage rate, heat resistance and moisture resistance are not obtainable if the methacrylic polymer having <=0.55dl/g eta is used. The formability is poor and the fiber is not practicably usable if said number exceeds 0.9dl/g. |
