Patent GB-943946-A (GB)
Title: Staple fibre production
IPC: D01F11/02
Filed: 1962-10-04
Abstract: 943,946. Cross-linked regenerated cellulose staple fibres. LIPACO S.A. Oct. 4, 1962 [Oct. 5, 1961], No. 37496/62. Drawings to Specification. Heading B5B. Cross-linked regenerated cellulose fibres are produced by impregnating regenerated cellulose (particularly that obtained from viscose) in the form of a filamentary bundle or tow having a total denier of 3000 to 1,500,000 and while still in the gel or never-dried state after spinning with an aqueous solution of formaldehyde, an aldehyde containing two or more -CHO groups or a hydroxyaldehyde, drying and curing the impregnated bundle of filaments and then cutting the latter into staple fibres. The tow is preferably saturated with the solution of the aldehyde and its liquid content then reduced, as by squeezing, until its liquid content (based on the weight of oven-dried impregnated filaments) is less than the water imhibition of the filaments in the gel state. The aldehyde solution may contain a curing catalyst which when formaldehyde (the preferred aldehyde) is used, is preferably a metal salt which is soluble to the extent of at least 0.03 gram mols. per litre of water at 20 C. and pH5 and which is zinc sulphate or a salt of a group II metal with a monobasic acid which would be at least 50% ionized in its normal aqueous solution at 18 C. Magnesium chloride is a suitable catalyst. The formaldehyde concentration may be such as to provide from 0.1 to 3% of formaldehyde bound to the cellulose. Such concentrations may be within the range of 0.5 to 6%, although higher concentrations may be used. The proportion of catalyst used is preferably 0.003 to 0.09 mols. per 100 grams of cellulose. This is normally equivalent to a concentration of about 0.03 to 0.9 mols./litre. The temperature of the aldehyde solution is normally 15 to 50 C., preferably 20  to 40 C. and it may contain a wetting agent and 0.2 to 4% of a finishing agent. The time of contact between the tow and the aldehyde solution may be 2 to 20 minutes. The tow may be treated with the aldehyde solution in two or more stages, the tow being removed from the initial impregnation bath and squeezed to remove excess aldehyde solution, immersed in a second aldehyde solution, removed, again squeezed and so on. Multi-stage treatment of the filaments is particularly desirable when treating high tenacity filaments such as are produced using spinning baths having relatively high zinc sulphate contents followed by a fixation stretch in hot dilute acid. In such cases it is desirable to use relatively concentrated aldehyde solutions, e.g. concentrations of around 15%. In passing through the aldehyde solution the tow is in all cases preferably plaited or looped on a foraminous endless belt type conveyer and upon emerging from the impregnation zone is preferably removed from the belt as a straight tow and in this form passed through squeeze rolls to remove excess liquid. Drying is preferably, carried out at 80 to 120 C. for, e.g. 10 to 45 minutes, while the tow is under a tension of about 0.1 to 0.3 gram/denier and the tow may be allowed to contract 4 to 7% of its length during drying, but it may also be dried in a relaxed plaited state. After drying the tow may be further heated to cure (or to complete the curing of) the impregnated filaments usually at 110 to 180 C., preferably 125 to 180 C. in a relaxed plaited or looped form. The tow emerging from the spinning bath is processed to complete its regeneration and to remove salts and other impurities before being impregnated with the aldehyde solution. The impregnation may be effected by spraying the tow with the aldehyde solution while it is being conveyed in plaited form on the belt conveyer, e.g. at two or more impregnating stations alternating with pairs of co-operating squeeze rollers. Specification 930,132 is referred to.