Patent GB-932211-A (GB)
Title: Improved decorative sheet material
IPC: B44C5/00
Filed: 1959-10-09
Abstract: 932,211. Laminates. MINNESOTA MINING & MANUFACTURING CO. Oct. 9, 1959 [Oct. 15, 1958], No. 34356/59. Class 140. [Also n Groups XV and XX] A decorative sheet comprises a dimensionally stable weather-resistant transparent front layer having a smooth front face, an underlying flexible and stretchable opaque light-reflecting layer, and a pattern of design elements of discrete groupings of small glass or synthetic resin beads between the two layers with the opaque layer stretched about the rear and side portions of the design elements and secured to the transparent layer in areas between the elements, the elements being encapsulated between the layers with the beads in contact with the rear surface of the transparent layer and with an adjacent field of air about the points of contact. The beads may have a refractive index of from 1.7 to about 2.0 or even higher, and may have a diameter of from 20 to 100 microns or even up to 0.01 inch. The beads may be of varying diameter, may be opaque or transparent and coloured or colourless, and may be coated or uncoated. Heavy calendered paper may be coated with a mixture of rubber-grade styrene monomer, benzoyl peroxide, di-tert.-butyl peroxide, and xylene, cured at 220‹ F. for 5 minutes, coated with polyvinyl butyral in " Cellosolve " (Registered Trade Mark) acetate, dried at 180‹ F. and then heated to 280‹ F., vacuumcoated with aluminium, and given a pressuresensitive adhesive coating with a heptane solution of methyl iso-amyl acrylate. Silvered transparent glass beads of diameter 35 to 70 microns are distributed patternwise over the adhesive coating. The application of the beads may be effected by applying a specified tacky coating to the wires of a woven wire screen and passing the screen through a hopper of loose beads. The screen is pressed into contact with the pressure-sensitive adhesive layer by passage between rubber rollers, whereupon the beads transfer in the pattern of the screen to the adhesive layer, the beads being half embedded in the adhesive coating. The silver from the projecting hemispherical parts of the beads is dissolved off with acidified potassium dichromate solution and, after washing and drying, the assembly is removed from the paper base and united by pressure on the bead-carrying face with a biaxially oriented methyl methacrylate sheet, the portions of the assembly between the bead groups being pressed by the rubber rollers towards the front sheet. The material may be rolled up, and may be coated on the rear side with a pressure-sensitive or heat- or solventactivatable adhesive. The material may be used to form borders, letters, or emblems on calendars, desk pads, and pictures. The surface may be polished or waxed. The vacuum coating may be of copper or silver, or a thin aluminium foil or a metal flake pigment layer may be used. The metal layer and the protective layer therefor may be replaced by an opaque pigmented resinous reflective layer, e.g. of polyvinyl butyral containing an oil-modified sebacic ester plasticizing resin, titanium dioxide, and silica aerogel. As shown, the front layer 30 of glass or of polymethyl methacrylate, polystyrene, cellulose acetate butyrate or polyethylene terephthalate, which may contain a phthalocyanine pigment or finely-divided yellow ferric hydroxide or which may be associated with a separate coloured layer 31 above or below layer 30, overlies groups 33 of small spherical glass beads 34, encapsulated by the adhesive layer 36, the specular reflecting layer 37, and the protective resinous layer 38. A thin flexible transparent coloured layer may be interposed between layers 37 and 36.