GB1409786A - Quenching of polymeric film - Google Patents

Abstract

1409786 Electrostatic pinning of films IMPERIAL CHEMICAL INDUSTRIES Ltd 17 April 1973 [12 May 1972] 22341/72 Heading B5B In apparatus for electrostatically pinning a molten polymeric film 1 to an electrically earthed casting surface 2 comprising a pinning wire electrode 8 extending transversely across the casting surface in the proximity of or prior to the region of first contact of the film thereon, the dielectric insulators 12, 13 located beyond the film edges are movable along the wire electrode by an amount corresponding to any transverse fluctuations that may occur in the film edges by means activated by a sensor of the transverse fluctuations of the film edges so that sparking between the wire electrode and the margins of the casting surface is impeded. In Fig. 2, the pinning wire is held under slight tension between fixed points 15, 16, and the tubular insulators 12, 13 which may be of polytetrafluoroethylene are gripped by clamps 18, 19, suitably of reinforced urea-formaldehyde or phenol-formaldehyde resin mounted on carriers 20 and 21, located in a guide channel not shown. The rack and pinion mechanisms 22, 24 and 23, 25 are driven by electric motors controlled by a relay circuit connected to edge sensors downstream of the casting drum which bear against the edges of the film and monitor the edge fluctuations. Actuation of the motors by the relay circuit moves cameras 20, 21 along the guide channels so that insulators 12, 13 are moved by a distance corresponding to the movement of the film edges and in the direction of the film edge movement, ensuring that the insulators remain slightly overlapping the film edges. In a modification the movement of the insulators is controlled by the comparison of output signals derived from potentiometers coupled to the drive for the casting drum 2 and that for the cameras 20, 21 as it has been found that the film edge fluctuations are proportional to changes in the linear speed of the films. Contamination of the wire by condensation of volatile matter may be avoided by electrically heating it or by impinging a hot gaseous blast thereon. In Fig. 3, a wire electrode 8 is drawn from a supply reel 28, traversed across drum 2 and wound up on reel 29 driven by motor 30, its movement and tension being governed by torque limiter 31. The wire is energized at terminal 32. This avoids wire contamination otherwise caused by condensation of volatile matter on a static electrode. In order to position the electrode accurately in relation to the film it is passed around guide pulleys 33 and 34 made of dielectric material, e.g. urea-formaldehyde or phenolformaldehyde resin together with the tubular insulators 12 and 13 through which it is threaded. Film-forming materials with which the apparatus may be used include polycarbonates, polyamides, polyimides, polysulphones, polyolefins, polyvinyl chloride, linear polyesters and polyesterethers, but it is said to be particularly useful in the production of polyethylene terephthalate film.