GB449955A - Improvements in electric insulating materials - Google Patents

Abstract

The electric insulation resistance of animal textile fibres, particularly wool or silk or their mixtures, is improved by treatment with a tannic acid or with other agent capable of tanning leather, or with naphthol sulphonic acid, or with an acid chloride of an organic acid, or with an anhydride of an aliphatic carboxylic acid containing from 2--5 carbon atoms, or with a salt or oxide of a metal giving acid or amphoteric oxides, or with formaldehyde or paraformaldehyde. The material to be treated may be in the loose or in the form of hanks or cops or as fabrics or tape. In examples, wool in hanks is wetted out with hot water and treated with either formaldehyde solution at 80 DEG C. or tannic acid solution at the boil or a boiling solution of aluminium sulphate; alternatively the wool is dried and treated with a bath of acetic anhydride, acetic acid and zinc chloride at 40 DEG C., or with acetic anhydride alone at 80 DEG C., or with a bath of benzoyl chloride containing powdered chalk at 60 DEG C.; as a further alternative, the treatment with tannic acid may be followed by treatment with acetic anhydride; and in each case, after removal of the reagents by washing, the materials are dried for at least 3 hours at 110 DEG C. In other examples, silk in hanks is similarly treated with tannic acid, aluminium sulphate, acetic anhydride, or with tannic acid followed by acetic anhydride. Specification 271,948, [Class 36], is referred to.