| 摘要 |
Non-fibrous polytetrafluoroethylene granular powder characterized by a wet-sieve size of less than 40 microns, a shape factor of less than 15, an anisotropic expansion factor in the range 1.02 to 1.26 and a surface smoothness of more than 15 seconds may be prepared by pulverizing coarse polytetrafluoroethylene particles at temperature below 330 DEG C. chiefly by collision force. The polymer may be prepared by polymerizing tetrafluoroethylene in the gas phase at 3 to 10 kg./cm.2 at a temperature of 0 DEG to 40 DEG C. in the presence of water containing a polymerization initiator, e.g. ammonium persulphate, sodium bisulphite and ferrous sulphate. The powders may be moulded and sintered to form dense, non-porous articles. |
