GB824433A - Continuous production surfacing of thermoplastic sheet and film - Google Patents

Abstract

<PICT:0824433/IV (a)/1> A continuous web of organic thermoplastic material is produced by forming a web of film or sheet from a mass of the material by means of a calender of heated rolls, of which the last is a heated rotating hard, rigid back-up roll, heating the web to a desired working temperature on the heated rotating back-up roll by causing the web to pass over and in contact with a substantial portion of the peripheral surface of the roll, passing the resulting heated web through a nip formed between the back-up roll and a hard, rigid counter-rotating surfacing roll maintained at a lower temperature than the back-up roll and having a peripheral surface for applying a desired finish to the web, subjecting the web in the nip to a pressure sufficient to obtain complete mating of the web to the peripheral surface of the back-up roll, continuously adjusting the distance between the rolls to provide the needed clearance for the web to pass through the nip under such pressure but without forming a bank of the material therein, the speed of the surfacing roll being so regulated as to cause the web to leave the back-up roll after passing through the nip and follow the surfacing roll in contact with a substantial portion of its peripheral surface, and stripping the web from the surfacing roll after it has been cooled on the surfacing roll to a temperature at which it is form-stable. As shown, a mass of thermoplastic organic material 10 is introduced into a calender comprising hard, rigid heated rolls 12, 14, 16 and 18 which are rotatable on fixed parallel axes, adjacent rolls being oppositely rotatable. Roll 18 is a back-up roll. The material is formed into a web 10a which passes through the nip between roll 18 and a hard, rigid surfacing roll 20 having a desired peripheral finish. The roll 20 is rotatable oppositely to roll 18 about an axis which is laterally displaceable with respect to the axis of roll 18, and is urged towards roll 18 by a yieldable pressure loading system. This may comprise a fluid-pressure cylinder 22 having a plunger 23 acting on the shaft 24 of the roll 20. The roll 20 is maintained at a lower temperature than the roll 18 and is preferably driven at the same or a slightly faster peripheral speed than the roll 18. The web 10a is made to follow the surfacing roll 20 after its passage through the nip between rolls 18 and 20 and thereafter passes over stripping roll 25, which is preferably driven at a peripheral speed about 3% above that of roll 20. The web then passes over idler rolls 26 and cooling rolls 27 to a wind-up roll 28.