| 摘要 |
PURPOSE: To prevent fusing of a preform to the surface of a mold by removing a surface altered layer of the preform and press molding the preform in a softened state. CONSTITUTION: A preform prepared from a glass material such as print glass is treated by chemical etching in which the preform is immersed in an acidic aqueous solution such as acetic acid, etc., washed with water, immersed in an aqueous solution of an alkali such as NaOH, etc., in a warm bath, washed with water and dried to remove a surface altered layer in thickness of about 10-200Åfrom the surface of the preform. Then the preform is placed in an upper and a lower molds having spherical mold surfaces subjected to precise planishing processing, is heated to a softened state together with the upper and the lower molds in an N2 or Ar gas atmosphere by a heating source at the outer peripheral part and press molded by applying a load to the upper mold. Then the pressure is removed, the molding is cooled to give an optical lens having a uniform composition in the surface layer part and in the inner layer. When using the material from which the altered layer is removed, the material can be molded in <= about 300 shots under the same conditions without fusing.
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