GB647059A - Stretching and laminating film - Google Patents

Abstract

A continuous film or sheet of plastic material is stretched by continuously passing the sheet through a heating zone of limited width bordered on each side by a zone of lower temperature, and progressively stretching the sheet laterally as it passes therethrough, thereby bringing the side portions of the stretched sheet into the zones of lower temperature so that they become cooler and their tendency to stretch further is diminished. The films or sheets may be composed of rubber hydrochloride, cellulose esters, or polyvinyl compounds. Plasticizers, dyes, or pigments, may be included in the composition of the film. The process results in uniformly stretched films and sheets. The film may be passed through an oven by means of travelling devices which grip it at the edges and stretch it laterally while it is in a heat-softened state. Heated air may be passed through the oven and baffles may be provided to regulate the air currents and control the temperature. Alternatively, the film may be stretched laterally while passing through a heated liquid. The stretched film may be laminated with other film layers while it is still hot from the stretching operation. For carrying out the process, apparatus is described which is substantially the same as that described in Specification 647,054.ALSO:A continuous film or sheet of rubber hydrochloride or other thermostretchable material is stretched laterally by continuously passing the sheet through a heating zone of limited width bordered on each side by a zone of lower temperature, and progressively stretching the sheet laterally as it passes therethrough, thereby bringing the side portions of the stretched sheet into the zones of lower temperature so that they become cooler and their tendency to stretch further is retarded. Plasticizers, dyes or pigments may be included in the composition. The process gives a more uniformly stretched sheet. The sheet may be passed through an oven by means of travelling gripping devices which diverge so as to stretch the sheet laterally while it is in a heat-softened state. Heated air may be passed through the oven and baffles may be provided to regulate the air currents and control the temperature. Alternatively, the film may be stretched laterally while passing through a heated liquid. The stretched film or sheet may be laminated with other films or sheets, while it is still hot from the stretching operation. The temperature used for stretching may be 75-110 DEG C. The sheet may be stretched to as much as 800 per cent of its original width. For carrying out the process, apparatus is described which is substantially the same as that described in Specification 647,054.