PURPOSE: To obtain an optically non-anisotropic thermoplastic resin sheet by arranging a thermoplastic resin sheet extrusion molded to have a specified double refraction.
CONSTITUTION: Three layers of thermoplastic resins non-adherent to each other are extruded together to obtain a core layer as a thermoplastic resin sheet with the double refraction of under 8×10-5 in the final form. The resin A for the core layer herein used is preferably a vinyl chloride resin composition as a transparent resin. The thermoplastic resin B for the surface layer (protective layer) sandwitching the core layer herein used is preferably a low-density polyethylene. The use of the vinyl chloride resin component as the thermoplastic resin A facilitates the simultaneous extrusion in the combination with the low-density polyethylene because the extrusion temperature of both the resins are close to each other. As the sheet as the core layer is characterized by being optically non-anisotropic, addition to the non-adherent resins used in both the surface layers, there is no possibility of developing optical anisotropy due to peeling. Or as both the surface layers function as a protective film, this can prevent the attaching of dirts or the like thereby making it advantageous for the use in the field extremely vulnerable to dirts, for example, optical recording material.
FUKUDA YOSHIAKI
USAMI KATSUYUKI
KANEZAKI KAZUHARU
