Patent GB-535932-A (GB)
Title: Process for the manufacture of laminated strips of cellulose ester fibres
IPC: D21H11/20
Filed: 1939-08-23
Abstract: 535,932. Esterifying cellulose fibres for making paper &c. MAY, P. (Sandoz, Ltd.). Aug. 23, 1939, No. 24280. [Class 2 (ii)] Strips, sheets and layers consisting of fibrous cellulose esters possessing high electrical insulation power, good mechanical strength, and good resistance to water, are obtained by subjecting fibrous cellulosic material to the action of an esterifying agent, derived from a lower carboxylic acid, i.e. one containing not more than 4 carbon atoms, grinding the material before the esterification has reached the desired degree, completing the esterification process without further grinding, and transforming the esterified material into sheets, layers, and strips by applying it on to appropriate apparatus suitable for the formation of paper and cardboard, further mechanical disintegration of the fibres being avoided. Lamination of the sheets may take place directly from the esterification mixture, if desired after neutralizing the catalyst and diluting the mixture with lower fatty acids, or organic non-solvents of the esterified fibres. Lamination may be effected after washing to remove the esterifying liquid, but preferably before drying. For the esterification there may be used hydrogen halide acid, perchloric acid, a halogenated carboxylic acid, an organic sulphonic acid, sulphuric or phosphoric acid, zinc chloride, tin chloride, ferric chloride, copper sulphate or perchlorate, or a halogen, as catalyst. Sieves or , filters including drum filters are used in forming layers of the fibrous cellulose esters. The tensile strength of the products is increased by treating them with an aliphatic carboxylic acid in vapour or liquid form. The sheets of paper or cardboard may be passed through a bath of glacial or diluted acetic acid. The cellulose ester strips may also be subjected to a treatment with steam under pressure. Thin tissue paper, parchment paper, or thick cardboard may be produced. The material may be used for electrical insulation, for packing foodstuffs, for damp-proof wall paper, or for building material. In an example, dried bleached linters are ground in a closed hollander at a raised temperature in an acetylation mixture comprising acetic anhydride, acetic acid, and zinc chloride until a cellulose monoacetate is obtained. The mixture is diluted with acetic acid and the loose fibres are formed into a strip by means of a perforated roller. The strip is washed and dried. In another example, purified cotton waste is ground in acetic acid in a pin mill, centrifuged, and then treated with acetic anhydride, acetic acid, and benzine, naphtha, benzene, toluene, carbon tetrachloride, or chlorobenzene, and perchloric acid. Esterification is continued up to the triacetate stage. Sodium acetate is added to neutralise the catalyst, and the mixture is moulded on a closed round or long sieve machine. The strip so formed is washed and calendered. Soda cellulose obtained from wood is esterified to the monoacetate stage using 1-5-naphthalene disulphonic acid as catalyst. The mixture is cooled and the fibres are ground in a ball-mill. The catalyst is neutralized and the mixture is then moulded in a closed round sieve machine to form a paper strip. The cellulosic material may be wood shavings, bast fibres, .linen, hemp, ramie, old paper, rags, regenerated cellulose. The cellulose ester formed may be a propionate, butyrate, or aceto-butyrate.