| 摘要 |
PURPOSE:To obtain a sheet with a preset optical distorsion by placing a birefringence measuring device and a thickness meter between a glazing unit and a take-up unit and connecting an arithmetic unit to a speed rate setting device. CONSTITUTION:A molten resin 5 extruded from a die 1 is fed between a lower roll 2a and a middle roll 2b and is forwarded around the upper roll 2c approximately half round to transfer a sheet surface during this period. It is then cooled and solidified and the glazing is finished and the thickness of the sheet is determined. It is finally taken up on take-up rolls 10a and 10b. During this procedure, the thickness of the sheet is successively measured by means of a thickness measuring sensor 6 and a thickness meter 7 and the birefringence of the sheet is also successively measured by means of birefringence measuring sensors 8a and 8b and a birefringence measuring device 9. The values of the thickness and the birefringence of the sheet is put in an arithmetic unit 15 to operate a birefringence. Comparing the operated birefringence with the aimed birefringence set by means of a birefringence setting device 17, a signal is sent to a speed rate setting device so as to make these values equal and the rotating speed of the take-up rolls 10a and 10b to the glazing rolls 2a, 2b and 2c is controlled. E.g. if a sheet with little optical distorsion is required, the set value is made zero. |
