GB1364089A - Tensioning of foils films and other thin sheets - Google Patents

Abstract

1364089 Trays; mirror frames and mounts INITIAL PLASTICS Ltd 13 Dec 1972 [30 Dec 1971] 60770/71 Headings A4A and A4X [Also in Divisions B7 and G2] A tray or a mirror comprising a flexible sheet held in tension by a supporting frame is made by fixing the sheet around its edge to the frame with the frame at a temperature substantially below ambient temperature and the sheet at a temperature substantially above that of the frame and subsequently bringing the frame to ambient temperature. The tray may be similar to that described in Specification 1325894 having a sheet tensioned over a lattice structure frame; in this case the sheet may be fixed to the cross-member of the lattice structure frame. As shown a mirror is made by heat sealing a film 4 to the rim 3 of a circular disc 1 cooled to a temperature of -20‹C. The disc gradually warms up and tensions the film in a uniform manner. As the disc warms up air trapped between the film and the concave upper surface 2 of the disc increases in temperature and pressure so that the upper surface of the film becomes slightly convex. Holes may be formed in the disc if the surface of the mirror is required to be flat. The sheet may be made of metal or of a metallized thermoplastic material; the frame may be made of a thermoplastic material or metal. In another embodiment a rear-viewing mirror for a motor vehicle comprises a film fixed to an outer surrounding rim and an inner circular rim of a rectangular plate. Air may be injected into the space between the plate and the part of the film bounded by the circular rim to form a mirror which is part plane and part convex.