Patent GB-796561-A (GB)
Title: Improvements in or relating to electrical insulating materials
IPC: H01B3/46
Filed: 1956-06-15
Abstract: 796,561. Elastomeric siloxane coated glass fabrics. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 15, 1956 [June 23, 1955], No. 18567/56. Class 140. - A resilient elastomeric electrical insulating material having an organopolysiloxane coating on one or both sides of a bias woven glass fabric is produced by coating the fabric 10 which consists of interwoven threads formed of glass fibres coated with a size, e.g. starch, gelatine, amine, resins such as silicone varnish, and vegetable oil in any admixture, in tank 18 with a liquid binder 20, e.g. starch, vegetable oils, polyvinyl acetate, oil-modified phenolic resins, and phenyl methyl siloxanes, which may be present in amount from 3 to 15 per cent by weight of the fabric, which is then cured in oven 26 having heating elements 28 to retain the predetermined bias weave configuration, prior to coating with an organopolysiloxane gel 36 in one or more organic solvents, e.g. toluene, xylene, or naphtha, in vat 34 which may result in a coating of 0.5 to 40 ml. thickness. The organopolysiloxane gel is cured to a solid elastomer by passage through tower 38 containing heating elements 39, in which the temperature progressively increases from room temperature at its lower end to 290‹ C. at its upper end, and the fabric is then placed under a tension of from 5 to 60 pounds per inch width, imposed by a series of rollers 52 to break the binder coating 64 but not the organopolysiloxane coating 68 whereby the individual threads 70 are released from the predetermined set bias weave configuration, prior to cutting into tapes at rollers 56 and winding on take-up rollers 60. The organopolysiloxane gel may be applied to one side of the fabric and a layer of pressuresensitive adhesive, e.g. dimethyl silicone, Dow XC-269, 270 and 271, may be applied to the other side. Suitable organopolysiloxane gels or gums have from 1.75 to 2.25 monovalent organic radicals R and R<SP>1</SP>, e.g. methyl, ethyl, propyl, amyl, phenyl, per silicon atom and at least 60 per cent of the units present as RR<SP>1</SP>SiO units are prepared from oils derived from dialkyl silane or a mixture thereof with diaryl silane, both having approximately two hydrolysable groups, e.g. halogen, alkoxide, or amino groups. The oils are converted to gels by treatment with ferric chloride, concentrated sulphuric acid, sulphuryl chloride, bromide, or fluoride, phenyl phosphoryl dichloride, alkoxy phosphoryl dihalides, or acyl peroxide which may contain at least one aromatic acyl radical and may contain an inorganic substituent such as a halogen or nitro group, e.g. benzoyl peroxide, benzoyl acetyl peroxide, dinaphthoyl peroxide, benzoyl lauryl peroxide. A filler, e.g. asbestos, clay, barium titanate, iron oxide, bentonite, zinc oxide, lithopone, titania, magnesia, graphite, slate, mica, diatomaceous earth, calcium carbonate, lead oxide, alumina, calcium silicate, may be present up to 200 per cent by weight of the gel. The gel may be cured to a solid elastomer by the action of an acyl peroxide and heat. The gel also may be cured by exposure to electron irradiation in which case peroxide converters are not used.