Patent GB-568044-A (GB)
Title: Improvements in or relating to the production of transparent polyamide articles
IPC: C08L77/00
Filed: 1943-04-23
Abstract: Transparent articles, e.g. films, yarns or fibres, are produced by dissolving a film or fibre-forming synthetic linear polyamide having a quench index above 125 mils. in a solution consisting of a water-soluble metal salt and methanol or ethanol, shaping the solution, evaporating substantially all the alcohol from the formed article at a rate slow enough to prevent bubble formation and, before the article comes into contact with water or an atmosphere with a relative humidity in excess of 50 per cent, washing the metal salt from the article with water having a temperature not exceeding 40 DEG C., and drying the article. Interpolyamides are preferably used, e.g. one from hexamethylene diammonium adipate and sebacate; the proportion of the former ingredient ranging from 15 to 45 per cent. If the article is heated to above about 50 DEG  C. prior to the washing step, it should preferably be cooled to 25-35 DEG  C. before washing in water at 25 DEG  C. or less.  If slight traces of alcohol are present in the article at the time of washing, the film is initially washed with water having a temperature below 10 DEG  C., and then may be washed at a higher temperature, e.g. as high as 40 DEG  C.  Suitable metal salts which may be used in the solvent composition are zinc, magnesium, lithium, strontium, aluminium, titanium, bismuth, cobalt or iron, chloride, bromides, iodides, nitrates or thiocyanates. Preferably, calcium chloride is employed. Films formed from the solution should be dried under tension to prevent wrinkling.  They may be used as wrapping materials, decoration, sheeting, for photographic films, for drawing into articles such as cups, for making tubes by rolling and scanning sheet material, either between hot rolls followed by cold rolls, or on a mandrel first under a hot roller and then a cold roller.  The tubes may be drawn, if desired, while filled with liquid, to prevent collapse, or for artificial lace by cutting a design in the film or films. The cutter may be heated to free the edges of the sheets as it cuts.  Examples describe: (1) solution of 500 parts of polymer from 30 per cent hexamethylene diammonium adipate and 70 per cent hexamethylene diammonium adipate (quench index 180 mils.) in 500 parts of fused calcium chloride and 1500 parts dehydrated methanol, and formation of a film on a glass plate at 50 DEG  C. in air at the same temperature and with a relative humidity of 5 per cent.  After 10 minutes, the temperature is varied to 100 DEG  C. and maintained for 30 minutes.  The glass-clear film is washed in water at 18 DEG C. and dried under slight tension.  Example (2) is similar, but employs commercial methanol and washes at 0 DEG  C. Example (3) describes film formation by casting on a belt. Example (3) employs a polymer from 40 per cent of hexamethylene diammonium adipate, 30 per cent of hexamethylene diammonium sebacate and 30 per cent of caprolactam.  The solvent consisted of 5 per cent calcium chloride and 95 per cent methanol.  Directions are given in the Specification for determining the quench index of a polyamide.  Specifications 461,236, 542,509, 563,078 and U.S.A. Specifications 2,071,250 and 2,130,948 are referred to.ALSO:Transparent articles, e.g. films, yarns or fibres, are produced by dissolving a film-forming or fibre-forming synthetic linear polyamide having a quench index above 125 mils in a solution consisting of a water-soluble metal salt and methanol or ethanol, shaping the solution, evaporating substantially all the alcohol from the formed article at a rate slow enough to prevent bubble formation and, before the article comes into contact with water or an atmosphere with a relative humidity above 50 per cent, washing the metal salt from the article with water having a temperature not exceeding 40 DEG  C. and drying the article. Interpolyamides are preferably used.  If the article is heated to above about 50 DEG  C. prior to the washing step it should preferably be cooled to 25-35 DEG  C. before washing in water at 25 DEG  C. or less.  If slight traces of alcohol are present in the article at the time of washing, the film is initially washed with water having a temperature below 10 DEG  C. and then may be washed at a higher temperature, e.g. as high as 40 DEG  C.  Suitable metal salts which may be used in the solvent composition are zinc, magnesium, lithium, strontium, aluminium, titanium, bismuth, cobalt or iron chloride, bromides, iodides, nitrates or thiocyanates. Preferably, calcium chloride is employed.  Films formed from the solutions should be dried under tension to prevent wrinkling. They may be used as wrapping materials, decorative sheeting, for photographic films, for drawing into articles such as cups, for making tubes by rolling and seaming sheet material either between hot rolls, followed by cold rolls, or on a mandrel first under a hot roller and then a cold roller.  The tubes may be drawn, if desired, while filled with liquid to prevent collapse, or for artificial lace by cutting a design in the film or films.  The cutter may be heated to fuse the edges of the sheets as it cuts.