| abstract |
Free-flowing sintering powders based on polymers containing at least 98.5% by weight of tetrafluoroethylene units can be prepared from colloidal polymer dispersions obtained in a customary manner by emulsion polymerization, stirring being carried out initially, optionally with the addition of an inorganic salt, until thickening, indicated by optical inhomogeneities, is achieved, an organic liquid which wets the polymer particles and is soluble in water to the extent of not more than 15% by weight then being added and stirring then being continued until granules are produced. The polymers preferably contain up to 1.5% by weight of polymerized units of at least one modifying, perfluorinated monomer. The free-flowing sintering powders have a high bulk density, an excellent flow time and further advantageous properties. They can be provided with customary fillers and are suitable for ram extrusion and for press-sintering processing to give sintered blocks and subsequently veneer-cut films. |