| 摘要 |
Particles of aluminium, copper, nickel, iron, glass, comminuted asbestos, silica, graphite, talc, crystalline and synthetic amorphous mica, and carbon black are individually coated with particles of polytetrafluoroethylene and heated above the transition point thereof to sinter the coating. The product, in loose uncompacted form, may be used as a filler in polytetrafluoroethylene compositions (see Groups IV(a) and V). Specifications 837,199 and 894,707 are referred to. Reference has been directed by the Comptroller to Specification 787,359.ALSO:A filler, for incorporation in filled polytetrafluoroethylene (PTFE) shapes (see Group V) comprises loose uncompacted particles of a solid material having a softening point higher than the transition temperature of PTFE, said particles having been individually coated with particles of PTFE and heated above the transition temperature to sinter the PTFE. Solid materials specified are metals such as aluminium, copper, nickel and iron, glass, comminuted asbestos, silica, graphite, talc crystalline or amorphous synthetic mica and carbon black. Specifications 837,199 and 894,707 are referred to. Reference has been directed by the Comptroller to Specification 787,359.ALSO:A process for moulding polytetrafluoroethylene (PTFE) incorporating a filler comprises first sintering the filler particles individually coated with PTFE to obtain filler particles coated with sintered PTFE and then mixing the product in loose uncompacted form with more PTFE and moulding to the desired shape. In the first stage the PTFE preferably amounts to 1 to 35% by volume of the filler and in the final product 10 to 60%. The moulding operation may be effected by paste extrusion, rolling, or calendering. The shape required may be moulded under pressure alone and subsequently sintered without application of pressure. The unsintered PTFE added in each or either stage may be in the form of a colloidal dispersion or in particle form. The filler material should have a higher softening point than PTFE, be available in fine particle form, and be inert to PTFE, examples being aluminium; copper; nickel and iron; glass; asbestos; silica; graphite; talc; mica; and carbon black. The particle size of the filler is preferably greater than that of the PTFE. The sintering temperature is preferably above 627 DEG F. e.g. 700 to 750 DEG F. Specifications 837,119 and 894,707 are referred to. Reference has been directed by the Comptroller to Specification 787,359. |
