GB1169692A - Improvements in or relating to Electrical Insulation - Google Patents

Abstract

1,169,692. Mica coatings. ENGLISH ELECTRIC CO. Ltd. 20 Oct., 1966 [22 July, 1965; 24 Aug., 1965], Nos. 31336/65 and 36407/65. Heading B2E. [Also in Divisions B5 and H1] Mica tape or sheet for use in electrical insulation is prepared by coating a tape or sheet of backing material with a resin bonding agent comprising an epoxy phenolic resin which is applied in solution in a mixture of two solvents which have different boiling points from each other, the phenolic resin component of the epoxy phenolic resin having been precondensed to such an extent that only very small amounts of volatile material will be released during gellation and virtually none during curing of the epoxy phenolic resin, placing at least one layer of mica flakes or mica paper on the resin coated backing material, and heating the resin bonding agent at least to the stage of gellation. The precondensed resin may be applied to the backing material in solution in a mixture of methyl ethyl ketone and methyl isobutyl ketone which may contain between 40 and 60% by wt. methyl ethyl ketone. The backing material may be impregnated with the solution of epoxy phenolic resin in a mixture of methyl ethyl ketone and methyl isobutyl ketone, heated to the stage of gellation of the resin, a layer of mica paper placed on the impregnated backing material and attached thereto by application of heat and pressure. The phenolic resin content of the epoxy phenolic resin may be between 25 and 35% by wt. Suitable backing materials are glass cloth, silk, synthetic fabrics, or mixtures of such materials. Thes olution of the epoxy phenolic resin may be applied to the backing material by spraying, brushing, or by means of a roller. One or more layers of mica flakes or paper may be applied with intermediate coatings of the resin-bonding agent. A final coating of the resin-bonding agent may be applied followed by a final layer of glass cloth. An intermediate layer or layers of glass cloth may be used. A single conductor or a stack of conductors may be wrapped with the mica tape or sheet e.g. a copper conductor may be wrapped with a layer of the tape or sheet half lap wound, stocked with similar conductors, the stack wrapped with twelve layers of the tape or sheet, half lap wound, placed in an autoclave which is evacuated, the tape then impregnated with a suitable resin e.g. an epoxy or polyester resin, or the tape or sheet may have been impregnated with a suitable resin e.g. a mixture of bisphenol A epoxy resin and one or more cycloaliphatic resins as disclosed in Specification 1,169,691, the vacuum replaced by positive pressure, formed to the desired size in a jig, and finally heated in an oven to cure the resin bonding agent and the impregnating resin. Alternatively, the wrapped conductor may be removed from the autoclave, compressed in a suitable press to the desired size, and then heated in an oven.