GB952703A - Paper-making process - Google Patents

Abstract

Water-laid webs are made from fibres prepared from wet-spun filaments of an acrylonitrile polymer containing at least 80% acrylonitrile in the polymer by beating the fibres in aqueous suspension to fibrillate them, contacting them with a dilute aqueous solution of a strong mineral acid before or during the beating step and then depositing them to form a web. The polymer may be polyacrylonitrile or a binary or ternary copolymer containing at least 80% of acrylonitrile, the balance being another olefinic monomer or monomers e.g. vinyl acetate. The specification includes a list of emitable monomers. Alternatively, the polymer may be a blend of polyacrylonitrile or a copolymer with another copolymer which may contain less than 80% acrylonitrile or with cellulose acetate, so proportioned that the blend contains at least 80% of acrylonitrile. The acid may be sulphuric, phosphonic, hydrochloric or nitric acid. The fibres may be treated with the acid and then rinsed substantially free of acid before beating. They may then be dried and stored before being beaten. Alternatively, the acid may be added to the beater. The water-laid web may also contain other fibres, e.g. of cellulose, asbestos, glass or silk, which may be beaten separately from the acrylonitrile polymer fibres. The polymer fibres may be collapsed by stretching or uncollapsed. The strength of the product is improved by drying at higher temperatures, e.g. on a heated drum. If necessary, anti-foaming agents such as octyl alcohol may be employed.