| 摘要 |
PURPOSE:To provide a manufacturing method for a substrate for a photoelectromagnetic disk wherein double refraction of the photoelectromagnetic disk prepared by laminating by vapor deposition of a protective film and a magnetic material on a substrate is low, i.e., which is preferably within a specific range by doubly passing when measured by nominal incidence by using parallel rays of He-Ne laser. CONSTITUTION:When a substrate for a photoelectromagnetic disk of at most 90mm diameter made of polycarbonate is molded by injection, a mold is filled with polycarbonate at 110-125 deg.C mold temperature at 60-120ml/sec speed to 50% of a mold cavity volume and thereafter at 70-110ml/sec from 50% to 90%. Lastly its pressure is kept (under 200-500kg/cm<2> for 0.2-0.7sec) for a last sink content (a volumetrically contracted content as cooling proceeds.). Therefor, a gate part is mechanically interrupted, the substrate is compressed under 550-750kg/cm<2> facial pressure, and cooling time (t sec) satisfies the formula 0.13Tm-9<= t<=0.13Tm-5 (Tm : mold temperature ( deg.C)). |
