Patent GB-567379-A (GB)
Title: Sheet materials of improved resistance to shattering
Filed: 1943-04-17
Abstract: 567,379. Compound sheet material. BRITISH CELANESE, Ltd. April 17, 1943, No. 6180. Convention date, March 20, 1942. [Class 140] Compound sheet material adapted to be shaped under the influence of heat, comprises a soft layer of transparent thermoplastic material having embedded in it an open-mesh wire fabric adapted to minimise shattering of the material by bullets and at least one hard layer of transparent thermoplastic material bonded to the soft layer, the soft layer being adapted to allow movement of the wire-mesh at temperatures suitable for bending the materialwithout permanently impairing the optical homogeneity of that layer. A hard layer may be bonded on each side of the soft layer. An anti-fogging layer, which may comprise cellulose acetate treated with a saponifying agent either before or after bonding, may be applied to one or both sides of the material. As shown, a soft layer A of thermoplastic material has ernbedded in it an open-mesh wire fabric W, two hard layers B and C of thermoplastic material bonded to opposite faces of A, and an anti-fogging layer D bonded to the outer face of B. A layer D may also be bonded to the outer face of C, or C may be dispensed with and the second layer D bonded directly to A. The individual wire of the fabric may be crimped at intervals as shown at 3. Layer A may comprise highly plasticized cellulose derivative sheets, e.g. cellulose acetate, acetatepropionate, acetate-butyrate, nitrate, or other (e.g. ethyl or benzyl cellulose), or highly plasticized sheets of polyvinyl acetate, copolymers of vinyl acetate and chloride, polymerized vinylidene chloride, poly methyl and/or ethyl acrylate, poly methyl methacrylate, polystyrene, or polyvinyl acetal. Plasticizers specified are dimethoxyethyl phthalate, dimethyl phthalate, diethyl phthalate, triacetin, dibutyl tartrate, methyl phthalyl ethyl glycollate, ethyl p-toluene-sulphonamide, triphenyl phosphate, isobutylene glycol, glycol derivatives (e.g. tri- or tetra-ethylene polyglycol esters and ethers), butyl phthalyl butyl glycollate, a mixture of ethyl o- and p-toluenesulphonamide, ethyl phthalyl ethyl glycollate, chlorinated diphenyls, dibutyl phthalate, and tricresyl phosphate. The soft layer may contain 70-85 parts by weight of plasticizer, and the hard layers less than 50 parts, e.g. 23-45 parts. The hard layer or layers may be of plasticized cellulose acetate and the soft layer of plasticized polyvinyl acetate, the layers being united by the use of mutual solvents. The wire mesh may be formed of fine gauge high-tensile strength steel or alloy and of square or hexagonal mesh. The material may be moulded at about 325‹ F. if of cellulose acetate. The wire mesh may be embedded in the layer as it is formed by casting or extrusion, or two preformed sheets may be bonded together with the wire mesh between. The wire may be precoated with a soft plastic composition. A wire fabric may be placed on a soft preformed sheet and a layer of plastic flowed, brushed, or sprayed thereover. The hard layer may be of the same chemical material as the soft layer, or may be of inherently harder and/or tougher material. It may be built up of two or more layers, the outer being harder and/or tougher than the inner. The two hard layers may be of different composition or thickness. The compound material may have from two to seven layers. One or more layers may contain dyes and/or ultra-violet light absorbers. The material may be made opaque or translucent by addition of fillers and pigments. In example 1, a cellulose acetate sheet highly plasticized with dimethoxyethyl phthalate and having a wire-mesh fabric embedded therein, is bonded between cellulose acetate sheets lightly plasticized with dimethoxyethyl phthalate. In example 2, a polyvinyl acetate sheet highly plasticized with methylphthalyl, ethylglycollate and having wire-mesh fabric embedded therein, is bonded between polyvinyl acetate sheets lightly plasticized with methylphthalyl ethyl glycollate. In example 4, plasticized polyvinyl acetal resin having open-mesh wire fabrio embedded therein, is bonded to a sheet of cellulose acetate plasticized with dimethyl phthalate. In example 3, plasticized polyvinyl acetal resin having wire-mesh fabric embedded therein is bonded between polymerized methyl methacrylate sheets or (in example 15) between polystyrene sheets. The Specification as open to inspection under Sect. 91 refers also to an ethyl cellulose sheet plasticized with methylphthalyl ethylglycollate, together with a stabilizer, and having wiremesh fabric embedded therein bonded between cellulose acetate sheets plasticized with dimethyl phthalate. This subject-matter does not appear in the Specification as accepted.