Toshiharu Hatakeyama

Development of ultraprecise injection molding method for thermoplasticlenses

We have developed a new method of injection molding (GATESEALTN injection molding method) for ultra-precise plastic lenses. Our method is summarized as follows: 1) The filling pressure is selected to make the pressure of the polymer the same as the atmospheric pressure at opening the mold, and the mold temperature at injection is higher than the glass transition temperature (Tg); 2) After injection filling and sealing the gate, the pressure and temperature of the polymer in the cavity are homogenized by keeping the temperature of the mold constant at above Tg; 3) The mold is gradually cooled down below the heat distortion temperature without any change in specific volume. The surface figure accuracy is a peak—to-valley roughness better than 0.3 im and a root mean square roughness better than 0.04 pm. The unique feature of our method is to control the temperature of the mold after injecting a constant weight of polymer into the cavity of constant volume. We are now mass—producing a wide range of thermoplastic lenses for optical systems by this new injection molding method.