Patent GB-283481-A (GB)
Title: Process for fining freshly spun artificial silk threads
IPC: D01F2/00
Filed: 1928-01-05
Abstract: 283,481. Norddeutsche Verwaltungs Ges. Jan. 10, 1927, [Convention date]. Grant of Patent opposed. Cellulose ester solutions and other cellulose solutions, processes for making filaments from; apparatus for making filaments.-To reduce the denier number of freshly-prepared completelycoagulated artificial threads, the latter in the swollen state as produced by treatment with agents that swell cellulose hydrate either by suitably modifying the coagulating process or by a separate treatment to which the freshly-spun threads are subjected, are stretched positively, without being subjected to sliding friction, by contact with surfaces moving with increasing speeds, for example, by passage over or around two or more rollers, the later rollers of the series moving at peripheral speeds greater than those of the rollers that precede them. The relative speeds are usually so chosen that the threads are stretched so as to give an increase of length at least 25 per cent, for example, an increase of 30, 40, or 60 per cent. After stretching, the swelling-agent is removed, and the threads are preferably dried under tension. By the stretching, the quality of the threads, particularly their strength, is improved; and this effect is most marked if the filaments are initially of 6 deniers or less. To secure the necessary grip on the threads, the stretching rollers may be resiliently mounted and their surfaces may be covered with soft rubber, but rollers of glass, porcelain, hard rubber &c. may be employed; and the extent to which the threads are lapped round the rollers is determined according to the diameter of the latter, rollers of large diameter requiring only a partial lap, while with small diameter rollers the threads should be passed one or more times round the rollers. In the latter cases, in order to avoid chafing of the threads there must be a relative lateral displacement of the threads or the rollers either by suitably located guides for the thread arriving at and leaving the roller in conjunction with longitudinal grooving of the surface of the roller which is preferably of slightly conical form, or automatically by employing the construction of reel described in Specification 3831/11, which by itself gives the necessary lateral displacement. The threads are finally collected in centrifuges or on reels, spools or rollers, and the latter may be used as the stretching-means. As swelling-agents there may be used concentrated solutions of zinc chloride, and of calcium thiocyanate, ammoniacal-copper solutions, and strong mineral acids especially sulphuric acid of 50 per cent or higher concentration, for example, of 70 per cent strength and preferably cooled to below room temperature; and to the sulphuric acid bath may be added glucose, alkali sulphates, compounds, synthetic tanning materials, and pyridine and other organic bases, and it is advisable to employ the bath for as long a time as possible since bye-products having a desirable effect tend to accumulate during the swelling operation. It is preferred to use a combined coagulating and swelling bath; thus employing the process of Specification 166,931 in which the acid concentration is inversely proportional to the titre of the thread to be spun, it becomes possible so to employ the single bath method in the case of the lower counts. The action of the swelling- agent should be stopped after the completion of the stretching-process, and at the latest while the threads are passing on to the reeling device as by sprinkling the spool or one or more of the later stretching rollers with water or dilute acid or alkali solution and by rotating it in such liquid, and if necessary by sprinkling the material while in the centrifuge. To the washing-liquids may be made additions similar to those made to the swelling-bath. In examples, a crude viscose prepared according to Specification 135,205. is spun into 70 per cent sulphuric acid maintained at 90‹ C., and the coagulated and swollen threads are passed over two rollers the second running at a peripheral speed 60 per cent greater than the first, drenched with water in the second roller, and finally collected in a centrifuge and at the same time again sprinkled with water; a viscose prepared according to Specification 135,205, is extended into 20 per cent sulphuric acid under the conditions set out in Specification 166,931 for producing filaments of 3.5 deniers, and the threads are next passed through a swelling-bath of 68 per cent sulphuric acid, then over a stretching-roller and finally on to a glass roller running in a dilute acid bath and at a speed to give a 30 per cent increase in length to the threads; a cuprammonia-cellulose solution, after ripening, is spun into 70 per cent sulphuric acid at 8‹ C., and the threads passed once round a ribbed roller, then through a gutter supplied with dilute acid and on to a reel rotating at 40 per cent higher speed and sprinkled also with dilute acid; a crude viscose prepared according to Specification 135,205, is extended into concentrated zinc chloride solution acidified with hydrochloric acid, and the threads are then passed over a first roller and finally on to a stretching and winding roller sprinkled with dilute sulphuric acid. Specifications 264,161, 274,521 and 274,690 also are referred to. The Specification as open to inspection under Sect. 91 (3) (a) refers to a process in which a solution in ether-alcohol of moist nitrocellulose is extended through glass nozzles into 55‹ BÚ sulphuric acid, and the threads are passed one or more times round a reel of the automaticdisplacement type and then on to a winding-reel running at a higher peripheral speed in a bath of sulphuric acid, ether and alcohol. This subjectmatter does not appear in the Specification as accepted.