Patent GB-1017060-A (GB)
Title: Reflex reflecting sheet material
IPC: B44F1/04
Filed: 1962-06-29
Abstract: 1,017,060. Laminates. MINNESOTA MINING & MANUFACTURING CO. June 29, 1962 [June 29, 1961], No. 25067/62. Heading B5N. [Also in Division G2] To avoid " blacking out " of a beaded highbrilliancy reflex reflector due to a covering film of water, e.g. rain, the reflector is constructed with reflex-reflecting sheeting which comprises a continuous layer of glass beads 13, each provided with an underlying reflecting layer, e.g. metal layer 14 as of silver or aluminium, a transparent cover film 12 overlying but unattached to most of the beads and a binder 15 in which the beads unattached to the cover layer are partially embedded, the continuous layer of beads being divided into discrete hermetically sealed pockets having a maximum lateral dimension of 0À75 inch by the beads between the pockets being flooded over and optically obscured by a pressure-formed heat-sealed cross grid pattern connection as at 18 between the cover film and the binder layer formed by material displaced from the binder layer. Typically the grid pattern seal lines are <SP>1</SP>/ 64  inch wide, the pockets are <SP>1</SP>/ 8  inch square, the glass beads are of refractive index 1À7 to 2À0 and have a diameter of 10 to 200Á, and the combined thickness of the binder layer 15 and cushion layer 16 is 1 to 3 times this diameter. Preferably, the binder layer is formed of polymethyl methacrylate which may contain a pigment, e.g. rutile TiO 2  or a coloured material, and the cushion layer 16 may be of a similar pigmented polymeric material but preferably has some flexibility as by mixing with the methacrylate polymer an ethyleacrylate polymer and epoxidized soya bean oil plasticizer. The sheeting may be formed by applying the tacky face of a heat-softened polythene layer on a paper sheet to a mass of glass beads, heating the polythene coating so that the beads are about half submerged, in the coating, and then cooling the sheet with its adherent layer of beads. The beaded surface is then rollcoated with a solution of the pigmented methacrylate polymer and the coating removed by buffing with felt to expose the tops of the beads, followed by vapour deposition of aluminium and then application of the cushion coating of the flexible plasticized polymer. Reference is also made to the use of beads coated hemispherically with metal. A stretch resistant layer 17 of a material which does not become tacky at temperature at which the cushion layer becomes thermoplastic is then applied. Suitable materials are cellulose acetate butyrate, polyvinyl butyrate, polycarbonate resins but polyethylene terephthalate is preferred. Alternatively, the die elements used in the heat-sealing step may be coated with a silicone release agent. The paper sheet and polythene layer support is then stripped away from the glass beads which are then covered with a cover film of polyethylene terephthalate, cellulose acetate or cellulose acetate butyrate but preferably of biaxially oriented polymethyl methacrylate. The resulting assembly is then placed in a laminating press having heated platens, one of which at least is a grid pattern die. Preferably, the die platen engages the rear of the assembly so that the cover film has a smooth surface on which silk-screen printing may be effected, but alternatively the die platen may engage the cover film with either a smooth or a similar registered back-up die platen against the layer 17.