| 摘要 |
<p>1476272 Sintered particles of tetrafluoroethylene polymer MITSUI FLUOROCHEMICALS CO Ltd 24 Feb 1975 [26 Feb 1974] 7642/75 Heading C3C Sintered particles of a non-melt-fabricable tetrafluoroethylene polymer (i.e. having a melt viscosity at 380‹ C. of at least 1 x 10<SP>9</SP> poises) prepared by aq. dispersion polymerization and having an average particle size of 5-500 microns, a sphere factor (as defined) of 1À0-1À2 and containing at least one enclosed void which causes the particles to have a precipitation rate in trichloroethylene (as defined) of no greater than 20% are claimed. The sintered particles are made by (a) atomizing an aq. dispersion obtained from the aq. dispersion polymerization of tetrafluoroethylene and containing (i) 5-80% by wt. of unsintered non- melt-fabricable particles of the polymer, of average particle size 0À05-0À5 micron, (ii) 0À2-20% by wt. of the particles of a non- ionic or anionic surfactant having a b.p. less than the polymer sintering temperature and (iii) 0À2-20% by wt. of either a liquid foaming agent having a b.p. below the polymer sintering temperature and a water solubility of 15 gm./100 ml. or less at 25‹ C., or a solid foaming agent which decomposes at a temperature below the polymer sintering temperature, (b) heating the atomized dispersion at above the polymer sintering temperature in an inert atmosphere, (c) cooling the sintered particles below the polymer sintering temperature, and (d) recovering the sintered particles. In the examples mixtures of a non-ionic surfactant or dodecyl benzene sulphonate, water and trichloro-trifluoro-ethane, propyl ether, ammonium carbonate or petroleum ether were emulsified, optionally with an ultrasonic wave generator and added to an aqueous dispersion of polytetrafluoroethylene or a copolymer of tetrafluoroethylene and hexafluoropropylene, and the mixture was placed in tank 1 of Fig. 1 from which it was fed to a binary fluid nozzle 5 where it was atomized at outlet 6 with air from compressor 3 and sent via pipe 4 to nozzle 5. The atomized dispersion emerges into sintering chamber 9 where heated air from 7 enters via pipe 8 and foams the drops of the dispersion and sinters the polymer particles which are then cooled in 10 by cool air from pipe 11. The sintered particles are then sent to cyclone 12 and recovered in receiver 20.</p> |
