Patent ID: 7101925

Claim:
A process to substantially remove the fluorinated anionic surfactants comprising the following steps: a) addition to a fluoropolymer dispersion comprising polymers chosen from the following groups: tetrafluoroethylene (TFE) homopolymer; homopolymers and copolymers based on CTFE; VDF/HFP fluoroelastomers, containing TFE and/or vinylethers selected between perfluoroalkyl vinylethers and/or perfluoroalkoxyalkyl vinylethers; optionally containing hydrogenated olefins; TFE and/or VDF amorphous and/or crystalline fluoropolymers containing dioxole rings having 5–7 atoms; or copolymers of tetrafluoroethylene (TFE) with comonomers having at least one unsaturation of ethylene type, said copolymers comprising hydrogenated and/or fluorinated comonomers, the comonomer amount being lower than 3% by weight; of a nonionic surfactant, in an amount in the range 1.5%–25% by weight referred to the fluoropolymer weight; b) addition to the dispersion of a salt, soluble in water and not giving precipitates in the dispersion under the use conditions; c) contact of the dispersion with a basic anionic exchanger; d) separation of the dispersion from the basic anionic exchanger; before step d) the dispersion is filtered on a 180 micrometer net and successively on a 10 micrometer net according to the following: a dispersion aliquot of about 250 ml, obtained after the treatment with the anionic exchanger, is transferred into a cylindrical vessel equipped on the bottom with a circular section filter having a diameter of 3 cm with 180 micron mesh; the time necessary to filter the dispersion volume from the resins is measured; the dispersion after filtration is transferred into cylindrical vessel equipped on the bottom with a circular section filter having a diameter of 3 cm, with 10 micron mesh; the time necessary to allow the whole dispersion amount to cross the filter, is measured; the time necessary to let pass the dispersion volume through the filter with 180 micron mesh is lower than 10 seconds; the time necessary to let pass the dispersion volume through the 10 micron mesh filter is lower than 90 seconds.