Optical Digital Disk Duplication by a Photopolymer Process
For the production of optical discs we have developed a new disc duplication process and apparatus using a liquid photopolymer (2P) resin curable by ultraviolet rays, different from the conventional method using thermoplastic resins. One of the most important problems in the 2P process using liquid molding resins is the generation of tiny bubbles during molding. To solve this problem, we have developed a 2P resin injection molding system. Information transfer can be attained by injecting 2P resin from the center of a mold into a clearance between the mold and a base board and pressing the latter, whereby the resin uniformly spreads. During this operation, the base board is firmly clamped to the central injection shaft, preventing the 2P resin from penetrating into the central hole of the base board. Compact Disc duplication tests were conducted using the present process to check the block error rate and thickness unevenness. It was found that the block eror rate averaged 20 counts/sec or less and that the thickness unevenness was sufficiently low to meet the requirements for the Compact Disc Standard. Further, it was ascertained that even if the mold was initially contaminated, it was cleaned by the self-cleaning efect of the 2P resin. Productivity comparable to that of the injection method was attained using four molds. In the evaluation of Compact Disc duplication, no increase in the error rate was observed in the production of about several thousand replicas.
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