Mold for molding the substrate of an optical disk

#The present invention relates to an optical disc such as the digital versatile disc (DVD), to a mold used in an injection molding machine for manufacturing the optical disc, and to an injection molding machine for manufacturing the optical disc.

#FIG. 6 is a sectional view of a part of a conventional compact disc (hereinafter called CD). The CD has a substrate 30 having a thickness of about 1.2 mm, made of transparent polycarbonate. On one of surfaces of the substrate, an information recording surface 31 is formed. The recording surface 31 comprises pits which are spirally formed. The other surface is finished to a mirror surface to form an information reading surface 30a.

#A reflection layer 31 is formed on the recording surface 31 by vacuum deposition of aluminum. On the reflection layer 32, a protection layer 33 consisting of resin is formed. Formed on the protection layer 33 is a coating 34 of print for a label.

#FIG. 1 is a sectional view showing a part of an optical disc according to the present invention;

#FIG. 2 is a sectional view showing an injection molding machine for molding a substrate of the optical disc;

#FIG. 3 is an enlarged sectional view of a central portion of the injection molding machine of FIG. 1;

#FIG. 1 is a sectional view showing a part of an optical disc according to the present invention. The disc has a substrate 21 having a thickness of about 1.2 mm and made of transparent polycarbonate. On one of the surfaces of the substrate 21, an information recording surface 25 having a plurality of spirally arranged information pits 21a is formed. On the other surface of the substrate 21, an information reading embossed surface 26 is formed.

#The information reading surface 26 has a plurality of dummy pits 21b each having the same depth H as the depth H of the information pit 21a. The pit 21b does not carry information, and hence is physically formed.

#A reflection layer 22 is formed on the recording surface 25 by vacuum deposition of aluminum, so that the information by the pits 21a is transferred to the reflection layer. On the reflection layer 25, a protection layer 23 consisting of resin is formed. Formed on the protection layer 23 is a coating 24 of print for a label.