FILM STRUCTURE HAVING UNDULATING SURFACE

摘要

1,273,617. Film with undulating surface. E. I. DU PONT DE NEMOURS & CO. 9 Dec., 1969 [10 Dec., 1968], No. 60063/69. Heading B5B. A biaxially oriented thermoplastics film is disclosed, characterized by one undulating surface, the wavelength and amplitude of the undulations being such that the ratio of wavelength to amplitude is less than 2000/1, and preferably between 500/1 and 1500/1. The film is made by the extrusion of molten thermoplastics material through an orifice having one serrated lip on to a cooled quench drum and biaxially orienting the film 2.5 to 5 times in each of two mutually perpendicular directions in the plane of the film. Preferably the serrated extrusion lip has from 50 to 500 serrations per inch and each serration has a depth of from 1 to 10 mils. The amplitude of the undulations may be less than 10% of the total thickness of the film. In a preferred method, the depth and number of serrations on the extrusion lip and the degree of orientation are adjusted to produce a film having the desired ratio of wavelength to amplitude on the surface thereof. Up to 1200 parts per million of particulate filler preferably calcium carbonate, but alternatively silica or lithium hydride, may be added. Pigments may also be added. Examples illustrate the production of such films from polyethylene terephthalate using hopper lip serration dimensions of radius 1 mil, height 4 to 9 mils, width 4 to 14 mils and number per inch 56 to 112. The films are stretched from 2.6 to 3.2 times in each direction, giving surface undulations with a height of 0.015 to 0.040 mils, a wavelength of 32to 65 mils, and a wavelength to amplitude ratio of 750 to 2670. A control film with no undulations is also made. The winding slopes of the examples vary from 135 to 237.