| 摘要 |
PURPOSE: To avoid generation of residual stress caused by difference of inner temp. attributed to sudden cooling by performing mold release when the inside and outside of a lens blank formed in a predetermined vol. become a specified temp. condition and keeping it for a predetermined time in a set atmosphere at the heat distortion temp. or to the specified temp. or lower. CONSTITUTION: At first, a specified amt. of material pellets are melted in an injection molding machine 21 and it is injected into a mold 27 for molding a lens blank. Then, when the max. temp. in the lens blank formed into a predetermined vol. is at least the glass transition temp. and the temp. in the neighborhood of the surface is cooled to the heat distortion temp. or lower, mold release is performed from the mold 27 for molding. Then, the gate of the lens blank is cut and after it is carried into a preliminary room of a stress relaxation room and the room is made vacuum, it is carried into the stress relaxation room 22 in which the inner pressure is kept at 76cmHg and is kept for a predetermined time in an atmosphere set in a range from the heat distortion temp. to 40 deg.C below the heat distortion temp. to perform stress relaxation. It is possible thereby to relax the inner stress, to prevent moisture absorption and oxidative deterioration from being generated. |
