Patent GB-661940-A (GB)
Title: Improvements in and relating to the production of viscose rayon threads
IPC: D01F2/06
Filed: 1949-05-27
Abstract: <PICT:0661940/IV (a)/1> Viscose rayon threads are manufactured by extruding viscose through a jet into a coagulating bath, withdrawing the thread as formed from the bath while it is in an incompletely regenerated state, passing the still incompletely regenerated thread to a thread-advancing, thread-storage device on which the thread advances successively in a number of consecutive turns through an oxidizing zone where an aqueous oxidizing agent is applied to the turns of the thread still in the acid condition, and heating the turns of thread in both the acid and the oxidizing zones so that regeneration of the thread is substantially completed when the thread leaves the oxidizing zone.  In a modification of the invention, the thread advances through a single aqueous liquid zone which contains both an acid and an oxidizing agent.  The temperature in the treating zone may be 60-100 DEG  C. and preferably above 70 DEG  C.  An aqueous solution of sulphuric, phosphoric, nitric or hydrochloric acid may be applied to the thread as it advances on the thread-advancing, thread storage device, aqueous sulphuric acid solutions containing about 0.05-15 per cent by weight of sulphuric acid being preferred. Alternatively aqueous sulphuric acid solution having a pH value below 4.5 and containing about 0.01-5 per cent by weight of the acid may be carried by the thread from the coagulant bath or may be applied to the thread on a godet or a thread-advancing device before passing to the heating device.  The aqueous oxidizing agent used in the oxidizing zone may be oxy-halogen compounds, such as the hypohalites, e.g. hypochlorous, hypobromous, or hypoiodous acid or the corresponding alkali metal or alkaline-earth metal salts; halites such as chlorous, bromous, or iodous acids and their alkali metal and alkaline-earth metal salts; and the soluble salts of the per compounds, such as the peroxides (e.g. hydrogen peroxide and compounds liberating hydrogen peroxide such as the alkali and alkaline-earth metal peroxides), permanganates, perborates, persilicates, percarbonates and persulphates. Preferred oxidizing solutions are sodium hypochlorite solutions, sodium chlorite solutions or chlorine water containing about 0.05 to 0.3 per cent of available chlorine and having a pH value of 5-10.  The completely regenerated thread leaving the oxidizing zone may be washed free from acid and oxidizing agent in a washing zone immediately succeeding the oxidizing zone and the turns of thread may be heated in the washing zone.  A list of types of suitable washing liquids is given.  An aqueous desulphurizing zone may be provided between the oxidizing and washing zones.  In an example viscose is extruded through a jet 11 (Fig. 1), into a conventional sulphuric acid coagulating bath to form a thread 14 which is drawn through the bath by means of a godet 15 round which the thread 14 is lapped once.  The thread is withdrawn from the godet while still in an incompletely regenerated state and while wet with the acid bath liquid and then transferred to a thread-storage thread-advancing reel 19 of the type described in Specification 413,414, [Group IX].  The reel is tilted downwards towards the take-up end and is heated internally by introducing steam through a hollow shaft 20 and exhausting it through a concentric shaft 21.  The heat from the steam is conducted to the thread-bearing metal bar member 26 of the reel 19 to heat the thread 14.  The reel 19 is driven at a higher peripheral speed than the godet 15 to stretch the thread which is temporarily stored on the reel in a helical package.  A 0.4 per cent aqueous sulphuric acid solution is delivered on the thread helix from tube 22 and an aqueous sodium chlorite solution (pH about 8, available chlorine about 0.05 per cent) is delivered on the thread helix from tube 23, both solutions being at room temperature.  An oil-in water emulsion containing about 0.93 per cent of ammonia and 0.4 per cent of a mixture of oils and sulphonated fatty acid esters is delivered on to the thread helix from a tube 24.  The three solutions intermingle on the reel to form a continuous film 25 which envelopes most of the thread helix, flows toward the thread take-up end of the reel 19 and discharges excess liquid into a tray 28.  The thread emerging from the film 25 is a substantially completely regenerated and lubricated thread substantially free from treating agents and by-products.  A number of turns of the thread helix at the discharge end of the reel are free from liquid film 25 and are dried by heating and temporary storage on the reel, after which they leave the reel and are collected as a package 32 of twisted lubricated thread.  The tube 22 may be omitted and a combined acid and oxidizing solution may be delivered by the single tube 23.  In other examples in which the apparatus shown in Fig. 1 is used the treatment conditions differ from those described above in the following essential respects.  Example 2: the sodium chlorite solution is replaced by a dilute aqueous sodium hypochlorite solution.  Example 3: no solution is delivered from tube 22 and an increased supply of aqueous sodium chlorite solution is delivered from tube 23. Example 4: no solution is delivered from tube 22, aqueous sodium hypochlorite solution is delivered from tube 23 and a 2 per cent aqueous sulphuric acid solution free from dissolved salts is delivered at room temperature through tube 16 on to the thread on godet 15.  In example 5 the godet 15 is substituted by a preliminary thread-advancing reel and in example 6 the treatment and apparatus are as in example 4 but the godet 15 is heated by steam introduced into its interior through a hollow shaft 17 and exhausted through a concentric hollow shaft 18.  In a second series of illustrated examples the thread is treated by very similar processes but in this case the godet 15 is replaced by two preliminary thread-advancing reels in series and dilute aqueous sulphuric acid solution is applied to the second reel or to both reels in addition to the solutions applied to the main thread advancing reel 19.  An illustrated description is given of a modified apparatus by means of which the processes described in any of the preceding examples may be carried out and in which the reel 19 is replaced by a pair of thread-advancing drums internally heated with steam, between which drum is a stationary steam-heated heater to heat the turns of thread between the drums.  In a further modification this heater may be replaced by two banks of infra-red ray lamps fitted with reflectors. Specifications 378,467, 385,477, 413,413, 423,152, 661,939 and U.S.A. Specification 2,294,866 are referred to.