| 摘要 |
<p>Free-flowing polytetraethylene powders comprising a major proportion by weight of aggregated particles which have a relatively smooth exterior with substantially no fluffy projections, which powders have an angle of repose of not more than 45 degrees and an average particle diameter of 100 to 5000 microns, may be prepared by agitating a mixture of polytetrafluoroethylene particles having an average diameter of less than 300 microns and an organic liquid capable of wetting polytetrafluoroethylene, having at atmospheric pressure a boiling-point between 0 DEG and 200 DEG C. and simultaneously heating the mixture to a temperature of at least 30 DEG C. until a free-flowing powder is obtained. The polytetrafluoroethylene may be mixed with filler particles, e.g. of glass, molybdenum disulphide or graphite, and mixing may be effected by tumbling. Specified liquids are hydrocarbons, alcohols, acyclic and heterocyclic ethers, ketones, aldehydes and halogen compounds. Water may also be present. In examples polytetrafluoroethylene powders are agitated in the presence of carbon tetrachloride, trichloroethylene, trichlorotrifluoroethane and acetone, with and without water, and glass, fibrous glass, graphite and molybdenum disulphide powders, to give free-flowing powders suitable for moulding.</p> |
