| 摘要 |
1,216,888. Electrical insulation. MINNESOTA MINING & MFG. CO. 16 April, 1968 [17 April, 1967], No. 17967/68., Heading D1P. Insulation for a cable, transformer or capacitor comprises synthetic paper saturated with oil, e.g. mineral, polypropylene or polybutene oil. The material of the paper may be polypropylene, poly-4-methylpentene, polybutene- 1, propylene/ethylene copolymer, or a polycarbonate, having a softening point above 110‹C. The paper is formed from at least 50% of fine fibres having a diameter of less than 10 microns and up to 50% of coarse fibres having a diameter of less than 30 microns. The fine fibres are formed by extruding a fine stream of the molten polymer into a stream of hot gas. The fibres are formed into paper by a wet or dry process. The fibres in the paper may be bonded together by heat optionally in the presence of a solvent. The formed paper is washed to remove polar impurities and dried. The dried paper has a Gurley porosity of less than 20,000 seconds per 100 cc or air. The oil-saturated paper has a dielectric strength of at least 1,400 volts per mil at a thickness of 5 mils; a dissipation factor less than 0.001 at 500 volts, 60 cps and 160‹C; and a dielectric constant at 60 cycles AC of less than 3 at 80 ‹C. |
