| 摘要 |
1,264,696. Film thickness control apparatus. E. I. DU PONT DE NEMOURS & CO. 19 Sept., 1969 [20 Sept., 1968], No. 46241/69. Heading B5B. The thickness uniformity of uniaxially or biaxially stretched thermoplastic polymer films, is controlled by measuring the thickness of each of a plurality of lanes across the film before and after stretching, comparing with a desired standard thickness and adjusting the thickness of pre-stretch lanes accordingly. It is preferred to produce a polyethylene terephthalate film by casting from an extrusion die 11, which has a plurality of adjustment devices 13a, 13b ... (13n), (not shown), on to a quench drum 12 which is internally cooled. The film 10 passes through a heating device 14, which consists of many heating elements arranged parallel to the longitudinal axis of the film, and the film is then heated to its orientation temperature and stretched at 15 and thereafter wound up into roll form 16. A first thickness measuring device 17 is situated between the quench drum 12, and the heater 14, and a second thickness measuring device 21 between the stretching device 15 and the roll 16; each consists of a radiation source 19, 19<SP>1</SP> emitting beta rays, and a detector 20, 21, and powered by motors 18, 22, traverse the width of the film. They each generate electrical signals which are a function of the film thickness, and hence of its mass, at each of a number of preselected points across the width of the film as determined by the action of rotary switches 28, 29. Hence as the film travels through the apparatus, the thickness of a number of hypothetical lanes is monitored. The signals are sent to the computer 26, where the cumulative masses of the film before and after stretching are compared. Adjustments to the pre-stretch thickness are made either by altering the orifice opening 13 to any lane, or by varying the power input to one of the heating elements in 14.
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