Patent GB-573081-A (GB)
Title: Process for improving the tensile strength and other properties of synthetic linear polyamide articles
IPC: D06M13/152
Filed: 1942-10-12
Abstract: <PICT:0573081/IV/1> The tensile strength and other properties of synthetic linear polyamide filaments, bristles, yarns, films and other articles is improved by heating them above 120 DEG  C., but below the melting point of the polyamide while they are in an essentially dry condition and under tension sufficient, at least, to prevent contraction in length.  The dry condition of the polyamide articles is such that the moisture content if any is below 0.7 per cent based on the weight of of polyamide; it is below that present through equilibrium with an atmosphere of 15 per cent relative humidity.  As shown, an undrawn filament 1, after extrusion from the molten polymer, quenching and drying, is led to feed rolls comprising brass roll 2 and rubber rolls 3, 4, whence it is fed over adjustable hook 14 into an electrically heated bath of molten Wood's metal in the heat-insulated vessel 6.  The temperature of the bath is maintained at about 30 DEG  to 150 DEG  C. below the melting point of the polymer.  The filament passes round immersed roll 9 and is stretched by the pull of rolls 10-12.  In an example, a filament of polyhexamethylene sebacamide is dried over calcium chloride to a moisture content below 0.7 per cent.  It is then passed through molten Wood's metal and stretched.  The filament has improved tensile strength, modulus of elasticity and resilience, a reduced thermo-extensibility factor, and an increased elongation at break. The tendency to absorb moisture from the air is reduced.  In another example, polyhexamethylene adipamide film is dried to 0.5 per cent moisture content and then stretched while passing through hot mineral oil.  The linear polyamide may be a simple condensation polymer or it may be a polyester-amide, e.g. one formed by condensation between a glycol, a dibasic acid and a diamine.  Amide-forming derivatives of amino acids which may be used in forming the polymer include esters, anhydrides, amides, lactams, acid halides, N-formyl derivatives, carbamates, and nitriles in presence of water.  Amide-forming derivatives of dibasic carboxylic acids include esters, anhydrides, amides, acid halides, and, in the presence of water, nitriles, cyanocarboxylic acids, cyanoamides, and cyclic imides. Amide-forming derivatives of the diamines include carbamates, N-formyl derivatives and N,N1-diformyl derivatives.  The polyamides may be mixed with synthetic resins such as phenol-formaldehyde, p - t - butylphenol - formaldehyde and o - cyclohexylphenol-formaldehyde resins.  They may be mixed with delustrants such as titanium dioxide, zinc oxide, carbon black and barium sulphate, or with plasticizers such as phenols and sulphonamides.  The polyamide articles may be heated with kerosene, molten salts, nitrogen, hydrogen, or carbon dioxide, or by passing the articles over hot metal surfaces, or by subjecting them to infra-red radiation or placing them in a high-frequency electrical field.  The treated filaments, films or like materials may be used for making parachute cords or fabrics, aeroplane fabrics, balloon cloth, tyre cords, bristles, fishing leaders, sewing thread, photographic films, shower curtains, umbrellas, wrapping-films and moisture-proof containers.  Specifications 461,236 and 552,097 are referred to.