| 摘要 |
PURPOSE:To manufacture a sheet which is inexpensive and possesses few optical distorsions, by heating and pressing the thermoplastic resin sheet obtained through fusion and extrusion. CONSTITUTION:As for a resin sheet, after both sides of the same have been sandwiched by either ferrous plates or steel plates by putting the sheet into a frame whose thickness accuracy is favorable by cutting down along an inner edge of the frame, the same is preheated for several minutes by placing the same between a top and bottom plates of a pressing machine without applying pressure to the plates. Deaeration is performed by repeating decompression actions about three times upon application of appropriate pressure to the sheet after preheating. Then the sheet is heated for several minutes by applying appropriate pressure to the sheet after that. The sheet is unloaded by removing the pressure after cooling has been performed sufficiently after heating. As for the appropriate pressure which is expressed hereupon, low pressure is favorable so long as air does not remain within the sheet and when the pressure is high, optical distortion is generated. The pressure falls normally within a range of 30-60/cm<2> which is desirably 35-50/cm<2>. In addition to the above, a heating or preheating temperature is the molding temperature of said resin and is more than the fusion temperature of said resin and than the decomposition temperature of that. |
