| 摘要 |
PROBLEM TO BE SOLVED: To eliminate shrinkage caused in a secondary mold lens by forming an arcuate large thickness part within a specific range of the thickness of dark color lens on the second mold side in a part of a light color lens on the first molded primary mold side of an overlay type lens in which shrinkage has been caused after the lens molding. SOLUTION: A large thickness part 2a is previously formed at a position of a primary mold lens 2 where the occurrence of shrinkage is anticipated, a recess is formed in the corresponding part of a primary molding metal mold and then, molding is executed. However, since a shrinkage-caused position and the degree of shrinkage is hard to estimate, the position and amount of shrinkage are confirmed by first forming the metal mold without forming the recess and by performing a trial or the like, and the recess is formed in the metal mold for the primary molding according to its result so that the large thickness part 2a is formed on a part of the primary mold lens 2 where the occurrence of shrinkage is anticipated. The protruding amount of the large thickness part 2a is set to 10-30% of the thickness of a secondary mold lens 3. It is shaped into a cross-sectionally arcuate form, an when the shrinkage caused in the primary mold lens 2 is round, the large thickness part 2a to be formed is supposed to have a convex spherical surface and formed with the recess of the metal mold.
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