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In injection molding of an optical disk, mis-transcription of pits sometimes occurs, especially when pit density is low and smooth surface part is dominant. Deformation of a mold and injection molding machine may possibly make influence on transcription property in such situation. In this paper, direct measurement of mold cavity gap has been carried out, together with microscopic observation of transcription state, and the relationship between them was discussed. Finally, the following conclusions were obtained. (1) Low stiffness of mold closing system is suitable for precise transcription of a fine pattern, because cavity pressure decrease in cooling state is retarded. (2) Mold closing force should be applied to the mold itself, settled on the fixed platen, both in usual injection and injection compression molding, for preventing detachment of the mold from the platen due to nozzle contacting force.

In the injection molding of an optical disk, a precise minute pit pattern is transcribed from a nickel sheet stamper in 0.3mm thickness. Various defects or mis-transcriptions are sometimes generated, but the causes of these defects have not yet been completely clarified. Thus ideal molding conditions and optimum mold designs can not be precisely determined.In this paper, the injection molding of an optical disk for a sample-servo-type application is performed by using an injection-compression molding system and the generation mechanism of transcription defects was studied. The following conclusions were obtained.: (1) Mis-transcriptions are classified into three types; multiple transcription errors, scratches in radial directions and scratches in other direction. Their occurrence is affected by the compression pressure holding time and mold temperature. (2) In the case of rather low mold temperatures, multiple transcription errors occur when the compression time is short, but scratches occur when the compression holding time is long. (3) A relative displacement of the polymer molding from the stamper cccurs when a cooling time is longer than 10s, which results in multiple transcription error.

Capillary flow experiments were performed to evaluate the slip property of injection moldable ceramic compounds of Al2O3, and the following results were obtained. Firstly, slip velocity us was obtained by applying the Mooney method, and the effects of material temperature, particle size and binder composition on the slip velocity were evaluated. Secondly, it was found that the slip velocity changed significantly, when counter pressure was applied at the exit of the capillary. Then, the slip velocity was expressed by an empirical equation considering the pressure effect. Thirdly, an accurate viscosity equation was obtained, based on the pressure dependent slip behavior. Lastly, the flow behavior in a capillary was discussed in consideration of the slip behavior, and the application of counter pressure was found to be effective for realizing high strain rate flow.

Generation of molding defects in ceramic injection molding, e. g. melt front asperity or surface roughness of an injected part, has been examined by using radial flow in a circular mold cavity. The following results were obtained. Firstly, it was found that an injected part is separated into 2 regions: region I with rough surface and region II with smooth and fine surface. The rough surface of region I results from a rough melt front, which moves to the mold surface and forms the surface of an injected part in the early filling stage. Secondly, front asperity is generated by the blowout of voids at the front surface, which are mixed into the material and by jetting flow. Voids in the sprue can be prevented by applying counter pressure. An injection molding method using a film gate with proper gap and a side gate is proposed. In this method, high pressure is applied to the filling material in the sprue to reduce voids, and it becomes possible to mold parts with smooth surfaces by removing voids in the sprue and jetting flow in the mold cavity.