Patent GB-356327-A (GB)
Title: Manufacture of hollow artificial silk
IPC: D01F2/30
Filed: 1930-06-16
Abstract: Hollow threads of artificial silk are obtained by dissolving an acidyl cellulose in a mixture of one or more solvents with one or more non-solvents other than alcohol which have a higher boiling-point than the solvents and which constitute at least 20 per cent of the solvent mixture; preheating the solution before it leaves the spinning nozzle, preferably to a temperature as high as possible, and spinning into an atmosphere having a temperature below the boiling point of the non-solvent or non-solvents.  Thus, acetyl cellulose soluble in acetone is dissolved in a mixture of 75-80 parts acetone and 25-20 parts toluene to form a 20-24 per cent solution; the solution is heated to 50-85 DEG  C. and spun from a nozzle having orifices 0,07-0,10 mm. into an atmosphere of about 20-70 DEG  C. to give a thread having a single titre of about 4 deniers.  The thread produced is in the form of a crumpled tube having a multilobate, roundish section of great bulk.  Instead of acetone other solvents such as methylene chloride and ethyl chloride may be used; toluene may be replaced by benzene, xylene, hydroaromatic or aliphatic hydrocarbons, ether, or a mixture of such.  The spinning conditions are adjusted so that a hard surface is formed on the filaments by the rapid evaporation of the solvent and the consequential increase in proportion of non-solvent.  For threads of finer titre, the proportion of non-solvent is increased.  The spinning solution, should be free from water and the drying air should be sufficiently dry to avoid condensation of moisture on the thread; it is advisable to arrange the collecting or winding device in an atmosphere of raised temperature and low moisture content.  The threads are generally spun in a closed shaft-like cell, the drying air being introduced either in countercurrent or parallel.  Air currents may also flow in both directions, leaving the cell by a common outlet advantageously situated near the zone at which the hollow space is formed; in this case the countercurrent is at a higher temperature to counteract any tendency of the hollow thread to collapse.  Eddies may be produced by constrictions &c. to promote evaporation at particular zones; similar effects may be obtained by devices adapted to radiate heat, e.g. a heating lamp furnished with a concave mirror.  A number of examples are given relating to solutions of acetone-soluble cellulose acetate, containing 54 per cent acetic acid, dissolved in a 80/20 mixture of acetone-toluene and including counter and parallel currents and also a cell with a constriction.  The Specification as open to inspection under Sect. 91 (3) (a) describes also the following:-An acetone-soluble cellulose acetate dissolved in a mixture of 60 parts acetone, 30-35 parts benzene and 10-5 parts methyl alcohol, to produce a 24 per cent solution, is heated to 60-65 DEG  C. and spun at a draught speed of 100 metres per minute into a countercurrent of air heated to 35 DEG  C., to produce a thread of 4 1/2 to 6 deniers which is of multilobate cross section with an internal hollow space.  With similar conditions a solvent mixture composed of acetone, benzene, alcohol in the ratios 60 : 20 : 20 gives solid threads.  This subject-matter does not appear in the Specification as accepted.