Development of Injection Molding of an High Density Optical Disk by Rapid Heating Stamper

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In injection molding of an optical disk, precise minute pit pattern is transcripted from that on a nickel stamper of 0.3mm thickness. However various defects, i.e.miss-transcription, multiple transcription, flow-mark, etc.are sometimes generated. These defects reduce with increasing die temperature, but cooling efficiency of a product decreases and molding cycle time become long. In this paper a model stamper, on which thin nickel film is plated and heated by direct current, is developed. Then, transcription behavior is examined. A rapid heating stamper model is made. Its size is 100mm in length, 10mm in width, and 5mm in thickness. A thin nickel layr of 10mum thickness is plated on AIN (aluminum nitride) ceramic plate and annealed at 400ﾟC temperature in 15 minutes. Then the surface is finished by buffing. Then Electrodes was put on its both ends and electric power of 10V and 12A is applied to the nikkel layr. Surface temperature is measured by thermo-couple. Temperature rise of 65ﾟC is obtained in 1.5 seconds after power-on and 50ﾟC temperature drop in 5 seconds after power-off. In injection molding with the model stamper, heat-starting time (t_0) and heat-holding tiem (DELTAt) are changed. "t_0=0" is defined as injection-starting time. On the surface of a stamper many fine scratches are observed. In injection molding without heating. transcription of scratch is not clear. It means that the transcription is incomplete. When appropriate heating is applied (t_0=-ls, DELTAt=2s), scratches are transcripted clearly. In the case of long heating (t_0=0s, DELTAt=3s), voids are generated because of high temperature.