GB1067585A - Process and apparatus for the production of films - Google Patents

Abstract

1,067,585. Coatings. ING. A. MAURER S. A. April 10, 1964 [April 11, 1963], No. 14948/ 64. Heading B2E. [Also in Divisions B5 and D1] A process for the production of a smooth uniform thermoplastic coating on a carrier web comprises the steps of casting an incompletely homogeneous coating from a heterogeneous mixture, as hereinafter defined, on the surface of a heated roller, and subjecting said coating to pressure over an area defined by the surface of a heated homogenisation carrier web which the coating is in contact to complete homogenisation of the coating, By the term hetergeneous mixture as applied to the starting materials is meant for example, an only slightly stirred mixture of granulate or powder of a thermoplastic material and plasticiser, if desired, together with fillers and/or colourants or the like, in which the solid particles are only partly wetted, or a granulate or powder of thermoplastic synthetic resins of the same or different kind without additives, the heterogeneity of these pure granulates or powders only consisting of the physical continuity of the mass. The pressure on the coating may be exerted by the carrier web, forming a concave surfacce moving in the same direction against the surface of the roller as is the roller thereby effectirig complete homogenisation of the coating. Said web is urged toward the heated roller by two auxiliary rollers which are mounted against the circumference of the heated roller. The concave surface may move at a speed greater than the circumferential speed of the heated roller, and the difference in speed between the surface of the roller and the concave surface may be such as to produce a frictional force corresponding to 2 to 20 times the layer strength of the molten coating. Suitably, the coating is of a thermoplastic synthetic resin e.g. polyethylene, polypropylene, polyvinyl chloride, polystyrene and co-polymers thereof. In Fig. 2. molten coating S is pressed by carrier web 10 which is to be coated, over sector # on calender roll 3. The carrier web must here be subjected to tension and withstand certain tensile stresses so that is it possible to exert pressure over the whole peripheral area of roller 3, defined by angle #, as a result of which the homogenisation can be effected in a manner according to the invention. A modification can be made in the apparatus shown in Fig. 3, so that coating of a web and homogenisation can be effected at the same time by running a carrier web between the elastic roller 13 and the melt S. In Fig. 4, an apparatus is shown in which the coating is effected of a roller 11 at the point 1' by means of a doctor blade 12 which may be heated. Coating S is pressed by auxiliary rollers 5, 6 and 7 against the peripheral area of roller 11 defined by angle 8 by means of a tensioned metal band 9. In this embodiment of the invention, which has only one roller, an elastic roller, as shown in Fig. 3, can also be used to replace rollers 5 and 6 when it is desired to exert pressure by a carrier web to be coated, as shown in Fig. 2.