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A correlation between the peak cavity pressure and filling time was found empirically during the injection molding process.Based on this correlation, a holding pressure control method to improve the stability of peak cavity pressure was proposed.Fluctuations in peak cavity pressure were compared among with the typical holding pressure control, cavity pressure feedback control, and the control proposed in this study for GPPSS, PMMA, PP, and POM.In the case of GPPS and PMMA, the fluctuations in peak cavity pressure for the control proposed in this study were smaller than those for control holding pressure control, and almost equal to those for cavity pressure feedback control.Under stable mold temperature and melt temperature conditions, negative correlations between peak cavity pressure and filling time were found for GPPS and PMMA which have meet viscosities with relatively large temperature dependences. When mold temperature and melt temperature were varied widely, correlations were found for all the materials used in this study.In conclusion, it was confirmed that the control proposed in this study can be effective to control even small fluctuation of peak cavity pressure when using materials with relatively large temperature dependent melt viscosities such as GPPS and PMMA. Further more simple control systems to improve reproducibility in product quality can be developed by the approach developed in this study without using cavity pressure feedback control.

In this study, we developed a novel transcription-molding process and experimentally discussed its validity for fabricating polymer products having the precise microstructure on the surface. The process was named “Melt-Transcription Process” which consists of two characteristic stages; coating and compression. In the coating stage, a molten polymer is coated on the surface of a metal mold having the precise microstructure by a coating device specially designed in this study. The thickness of the coated polymer melt is typically 100 μm or more. Immediately after coating, the coated polymer is compressed against the mold surface so as to make the polymer flow into the microstructure cavities engraved on the mold, and to fabricate the 3-dimensional structure of polymer products. The pressure required for compression is quite lower than that in conventional nano-imprinting process, because the molten polymer of high temperature is distributed in advance over the mold surface in the coating stage. The “Melt-Transcription Process” was applied to fabricate polymer products with the size of 150 mm in length, 150 mm in width and 1 mm in thickness, having the microstructure of tens micrometers on their surface. Cyclo-olefin polymer (COP) and Polymethyl methacrylate (PMMA) were used as the polymer materials, and the dimensions and transcription ratios (the ratio of the height of the transcribed microstructure to the depth of the microstructure on the mold) of the molded microstructure were experimentally evaluated. As a result, by the Melt-Transcription Process, the microstructure was sufficiently transcribed on a very thin substrate of large surface area with high transcription ratios, typically 95% or more, under relatively low compression pressure of less than 10 MPa. The process was also applied for fabricating products with a range of thicknesses and we could experimentally verify that products composed of a membrane of 80 μm thickness and a surrounding frame with 1.95 mm thickness were successfully molded. Furthermore, we fabricated a micro-lens array product by using film grade PMMA with relatively higher viscosity in a product having 125 μm in thickness and a size of 102 mm × 102 mm.