| 摘要 |
PURPOSE: To obtain a sheet board which has extremely low double refraction even if resin having optical anisotropy is extrusion molded by heating both ends of the lip of a die to higher temperature than a central part, thereby reducing the neck-in of the resin, and improving the transferability. CONSTITUTION: Thermoplastic resin 8 of melted state extruded from a die 2 is locally heated to a higher temperature than a central part at both ends of a sheet by a heater 7 for heating both ends of the sheet provided at both ends of a lip opening 6. As a result the resin viscosities of both the ends of the sheet are reduced from that of the central part, and the flows of the resins at both the ends of the sheet are accelerated. The heating temperatures of both the ends of the lip of the die are preferably higher at least by 10 deg.C preferably by 20 deg.C than the central part of the lip. |
