To provide an optical disk having transparency, high degree of transferability and mass productivity by using plant origin resin such as polylactic acid based resin and to provide materials of its substrate.
A substrate 12 of the optical disk 10 is formed by compounding polymethylmethacrylate with the polylactic acid based resin composite. A polylactic acid based resin composite contains polylactic acid based resin whose content of lactide is reduced to 1,000 ppm or less and mold release agent of addition 0.16-0.32 phr, and weight ratios of the polylactic acid based resin and the polymethylmethacrylate are 70:30-50:50. If proper quantity of the polymethylmethacrylate is blended, thermal resistance will be improved, while maintaining the advantage of the plant origin resin of the substrate 12. Also, if the lactide in the polylactic acid based resin is reduced, transfer accuracy and transparency of the substrate 12 will be excellent. Further, mass productivity is assured without spoiling transferability and transparency of the substrate 12 by optimizing the addition of the mold release agent.
MIYAZAKI MASAHIRO
HIGUCHI MASAHIRO
MAENO YOSHIAKI
ARAI TAKASHI
SUGI MASAHIRO
SANYO MAVIC MEDIA CO LTD
MITSUI CHEMICALS INC