| 摘要 |
796,610. Chemically resistant proofed or agglutinated fibrous sheet materials; impregnated bearing surfaces; coated fabrics; felt. DU PONT DE NEMOURS & CO., E. I. Sept. 22, 1955 [Sept. 24, 1954], No. 27123/55. Classes 42 (2) and 140. [Also in Group IX] Chemically-resistant proofed or agglutinated fibrous materials, and impregnated bearing surfaces suitable for use as sealing materials such as gaskets and packings comprise in intimate association a tetrafluoroethylene polymer in fibrous form and a tetrafluoroethylene polymer in non-fibrous, coagulated form. The polymers employed are derived from 85-100 per cent of tetrafluoroethylene and 0-15 per cent of ethylene, trifluorochloroethylene, difluorodichloroethylene, vinyl fluoride, hexafluoropropylene, or vinylidene chloride. The fibrous material may be in the form of continuous filament or staple fibre fabricated into woven fabrics, braids, batts or felts which may be needle-punched and may have received a shrinkage treatment. The braids may be made from a yarn of tetrafluoroethylene polymer filaments or monofils slit from a sheet or film of the polymer. Ribbons or tape of the polymer may be braided. The fibrous material is impregnated with a dispersion of the polymer in an organic liquid or in water, all or part of which may be replaced by a compatible liquid such as ethylene glycol. The dispersion may contain silicon carbide, aluminium oxide, graphite, or zirconium oxide. The vehicle for the dispersion may be removed by evaporation, using heat or reduced pressure, or the dispersion may be broken by freezing followed by warming, by heating to a temperature at which the dispersion is no longer stable, or by addition of electrolytes or coagulating agents such as acetone. The impregnated material is generally heated after setting or breaking the dispersion, to remove water and to decompose or remove dispersing agents. The packing may seal moving parts, e.g. valve stems, pump shafts, and motor shafts. Coated fabrics are made by smearing or doctoring on to one of the above dried, impregnated materials a thin coating of a tetrafluoroethylene polymer paste, prepared by breaking an aqueous dispersion of the polymer. Felt is made from 6-10 denier, 5 inch, drawn, polytetrafluoroethylene filament staple blended with 3 per cent by weight of 3 denier, 2.5 inch viscose rayon staple. The blend is carded and cross-lapped into a web which is passed through a needle loom ten times (Example 1) or twenty times (Example 2) the web being turned over between successive passes. The loom is equipped with the etched needles described in Example 1 of Specification 765,153. Specifications 631,504, 631,570, 686,438 and 689,801, [all in Group IV (a)], also are referred to. |
