GB862157A - Electrically insulating sheathing of metals and metallic parts and products obtainedthereby - Google Patents

Abstract

Metals are sheathed with thin, continuous, electrically insulating layers by moulding with an epoxy resin moulding composition which hardens when heated. The moulding composition contains an aromatic polyamine as hardener, the formaldehyde condensates of aniline or m-toluidine, containing more than 50% of their nitrogen content in the form of primary amino groups, and also diaminodiaryl alkanes, e.g. 4 : 41-diaminodiphenyl ethane, 4 : 41 - diamino - 3 : 31 - dimethyldiphenyl methane, 4 : 41 - diaminodiphenyldimethyl methane, and 4 : 41-diaminodiphenyl methane being particularly suitable. Fillers, e.g. ground rock, wood flour, cellulose, asbestos fibres, glass fibres, mica, kaolin, quartz, metallic oxides or metallic powders, are added, either immediately after solution of the hardener in the epoxy resin or by grinding in a ball mill with the ripened and solidified solution. In the example quoted, 103 parts of p : p1-diaminodiphenyl methane are dissolved in 400 parts of an epoxy resin which is liquid at room temperature and has been prepared from 4 : 41-dihydroxydiphenyl-dimethyl methane and epichlorhydrin, the solvation taking place at 60-62 DEG C. in the course of 1 hour. The solution, at 50 DEG C., is poured on to a flat plate and kept for 4 hours in an oven at 50 DEG C., after which it is cooled to room temperature and the resultant brittle resin ground in a cross-heater mill. For the production of the moulding composition, 350 parts of the resin thus ground are further ground together with 650 parts talc, 15 parts glycerol monostearate, and 20 parts nigrosin for 32 hours in a ball mill and the resultant composition is compressed into annular tablets.