| 摘要 |
PURPOSE:To obtain a metrial for optical instruments having superior heat resistance, coefft. of photoelasticity, superior moldability, small residual strain in the molded product, and small birefringence by using a specified copolymer. CONSTITUTION:A copolymer having recurrent units expressed by the formulas I and II are used as monomers, and the molar fraction of the monomer (I) is regulated to 5-20% and the reduced viscosity [etaSP/C] in 0.5g/dl concn. methylene chloride soln. at 20 deg.C is 0.3-0.8dl/g. Such copolymer has good fluidity in the molding stage, and the birefringence is small because of small molding strain due to small residual strain after molding. The birefringence is made smaller because of the small coefft. of photoelasticity, thus resulting superior optical characteristics. Accordingly, when such copolymer is used in several optical instruments, advantageous results are realized. For example, sensitivity for reading information recorded in a disc is improved, and occurrence of error is inhibited, further, stable operation of an optical storage disc is attained because of the superior thermal and mechanical characteristics of the material. |
