Patent GB-426397-A (GB)
Title: Improvements in optical projection screens
IPC: G03B21/62
Filed: 1933-09-01
Abstract: 426,397. Projection screens. BRITISH CELANESE, Ltd., and MOSS, W. H., 22, Hanover Square, London. Sept. 1, 1933, No. 24287. [Class 97 (i)] [See also Group VIII] Projection screens comprise a textile fabric, made from an organic cellulose derivative, having its interstices filled with a film-forming substance ; the screen may be coloured or patterned, and may be more opaque at the centre than at the margin. The fabric may be made from yarns of cellulose acetate, formate, propionate, or butyrate, ethyl, methyl, or benzyl cellulose, or ether-esters such as oxyethyl cellulose acetate, which may be stretched or partially saponified during manufacture, and may be treated to reduce the opacity with oil, fat, or a resin such as polyvinyl acetate before or after making into fabric, or opacity-modifying agents may be introduced into the spinning solution. The film-forming composition may comprise an organic cellulose derivative or cellulose nitrate or nitroacetate, a polymerized vinyl compound, e.g. polyvinyl acetate, polyacrylic esters, a polymerized ester of an unsaturated acid, or an alkyd resin preferably modified by heating with higher fatty acids or glycerides thereof, together with, if desired, plasticisers, synthetic resins, inflammabilityreducing agents, dyes, or finely divided insoluble material to give a matt surface. Alternatively, cellulose may be deposited from viscose or cuprammonium cellulose solutions. A cellulose acetate fabric may be coated with cellulose acetate having different solubility characteristics, e.g. a fabric made of acetone-soluble cellulose acetate may be coated with a different cellulose acetate dissolved in ethyl acetate, or a fabric made from cellulose acetate of low acetyl value insoluble in ethylene-methylene-ether, with a cellulose acetate of high acetyl value dissolved in ethylene-methylene-ether. A solution of material identical with the fabric material may be sprayed on in such a way that the solvent evaporates rapidly. Plasticisers specified are :-sulphonamides such as toluene ethyl sulphonamide, and xylene monomethyl sulphonamides, tartrates, such as dibutyl or dibenzyl tartrate, phthalates such as diethyl or dibutyl phthalate, esters of polyhydric alcohols such as triacetin, phosphates of phenols and substituted (e.g. halogenated) phenols or naphthols, e.g. triresorcinol phosphate, condensation products of phenols or naphthols or homologues or substitution products, e.g. chlorphenols, with ketones such as acetone, cyclohexanone, methyl cyclohexanone, cyclopentanone, &c., diphenylol propane or other diphenylol or substituted diphenylol substitution products of methane hydrocarbons or of substituted methane hydrocarbons, such as di - para - oxy - phenyl - diphenyl - methane obtainable by condensation of benzophenone dichloride with phenol, the solid intermediate condensation products of furfural, benzaldehyde or other aldehyde with acetone or other ketones (including cyclic ketones), alkyl derivatives of phenol, e.g. tertiary butyl phenol. Synthetic resins specified are :-the condensation products of furfural, formaldehyde, or other aldehyde with diphenylol propane or other condensation products of phenols and ketones including cyclohexanone, cyclopentanone, &c., the condensation products of aldehyde such as furfural or phenolic bodies, with aliphatic or cycloparaffm ketones, e.g. acetone, cyclohexanone &c., urea-formaldehyde resins, sulphonamide-aldehyde resins, or the reaction products of polyhydric alcohols such as glycols, glycerine &c., with phthalic acid or anhydride or other polybasic acid or anhydride. The inflammability reducing substance may be a halogenated organic compound, an ammonium salt or other substance which evolves a non- inflammable gas, or may be also a plasticiser, e.g. trichlor- and tribrom-acetanilide. A composition specified consists of vinyl acetate, diphenylol-propane-formaldehyde resin, and tricresyl phosphate. The coated fabric may be given a matt surface on one or both sides by subjecting the sheet to pressure and, if desired, heat, for example between plain or engraved rolls, by subjecting to the action of moist steam, by abrasion, by treating with a liquid comprising a solvent which pits the material, by applying a discontinuous coating, e.g. by applying an aqueous dispersion of cellulose acetate, or by applying a coating composition containing, e.g. cellulose acetate and a finely-divided white or colourless substance, e.g. silica, barium hydroxide, zinc oxide, titanium dioxide, talc, and other white or colourless heavy metal oxides, hydroxides, and silicates, or insoluble high-melting organic compounds such as are referred to in Specification 346,678, and, if desired, distributing this further coating more evenly by pressure and, if desired, heat. Dyes may be applied to the sheet material to give a coloured or patterned effect, and may be included in the film-forming composition or a finishing composition. The centre portion of the screen may be made more opaque than the margin by applying to the centre a heavier coating of matt surfacing material or a clear coat containing a dye. The fabric may be coated while held under tension, which may be obtained by applying a shrinking agent to the fabric when clamped in a frame, or the fabric may be stretched after coating. In an example, a cellulose acetate woven fabric is stretched in a wooden frame, sprayed with a vinyl acetate dope, dried, and then sprayed with a dope containing cellulose acetate, dibutyl tartrate, and finely divided silica. The fabric may be woven so as to withstand the necessary tension, as by providing a strong selvedge, or strong wefts at the ends. Each edge of the fabric may be turned over as a hem into which a rod, lath &c. for the application of the tension may be inserted, or cords or wires having loops or eyes at intervals may be worked into the edges of the fabric. Heat and pressure may be applied to coalesce the edges of the fabric and embed the laths, rods, &c. Specifications 340,324, 340,325, 340,326, 340,436, 340,437, 343,062, and 378,858 are referred to. According to the Provisional Specification, any textile fabric may be coated, including fabrics made from nitrocellulose, cellulose nitroacetate, polymerized vinyl compound, e.g. acetate yarns, regenerated cellulose yarns such as viscose or cuprammonium artificial silk, or yarns obtained by the complete saponification of organic cellulose esters, and cotton, linen, &c. fabrics, which may be mercerized &c. Specifications 323,790, [Class 2 (ii)], and 389,823 also are referred to.