Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/14—Treatment of polymer emulsions
  • C08F6/22—Coagulation

Definitions

• EP-B-O 591 888 discloses a process for working up aqueous dispersions of fluorinated thermoplastics, which comprises using hydrogen ions for substantive replacement of the cations in the aqueous dispersion resulting from the polymerization, compressing the dispersion, if necessary after diluting with water, releasing the compressed dispersion through one or more small aperture(s) so that it coagulates, applying the coagulated phase, if necessary after diluting with water and/or heating, to a filter where it is washed, mechanically dewatering the product, comminuting the same to give a free-flowing product and, if necessary, drying to the desired residual moisture.
• the work-up preferably takes place continuously.
• the compression here may take place in commercially available high-pressure homogenizers.
• the compressive pressure depends on the apparatus available, and pressures are usually from 200 to 400 bar, appropriately about 300 bar.
• the invention therefore provides a process for the coagulation of fluoropolymer dispersions, in which the dispersion is compressed by gas pressure and the compressed dispersion is released through one or more small apertures, and so coagulates.
• Preferred embodiments of this invention are described in more detail below.
• Fluoropolymers which may be used are any of the usual highly fluorinated polymers, in particular fluorinated thermoplastics prepared by the known emulsion polymerization process, and especially fluoroelastomers, or else mixtures of these with fluorinated thermoplastics.
• the crude dispersions may therefore be used directly with polymer contents of from 10 to 45% by weight.
• Use may be made of any gas which does not react with the fluoropolymer or with the water, and these include carbon dioxide.
• Advantageous gases are those whose capability for dissolution in the dispersion under the conditions used is relatively good, since the result is a relatively porous coagulate, and therefore undesirable ancillary substances are relatively easy to remove during the washing which follows.
• the dissolution of the gas in the dispersion may take place at low pressure, followed by setting of the desired final pressure.
• the amount of a gas which enters into the dispersion by way of dissolution under the desired pressure can be influenced by agitation, the mode of feed - for example by bubbling - and the duration of contact. If necessary, one skilled in the art may carry out routine experiments in this regard.
• the dissolution of the gases and the application of pressure may take place at from 0 to 100°C, preferably at from about 20 to 40°C.
• the compressive pressure depends on the gas used and may readily be determined by simple exploratory experiments. Pressures are usually from 50 to 400 bar (5 • 10 "6 to 4 • 10 7 Pa).
• the gas may be compressed using the usual compressors, that is to say the apparatus costs for producing the pressure required are substantially lower than for the process of EP-B-O 591 888.
• Gases which may be used are inert gases, such as helium or argon, nitrogen, carbon dioxide, air and fluorinated hydrocarbons, where these do not liquefy under the conditions used. Preference is given to nitrogen, air and carbon dioxide.
• the process of the invention can achieve high precipitation rates, and this is important not only with regard to the final yield of polymer but also for the recovery of the fluorinated emulsifier usually used from the wastewater formed in this process and composed of the aqueous filtrate, the treatment of which is made easier at the low resultant polymer concentrations in the filtrate (WO-A-99/62830 and WO-A-99/62858).
• the polymer content in the wastewater here should be well below 1% by weight.
• a great advantage of the process of the invention is that the resultant coagulated polymer can be washed in a manner similar to that of the process of EP-B-O 591 888 on a filter belt, and can be dewatered on a belt press, advantageously at slightly subatmospheric pressure, whereas elastomers usually require complicated apparatus, such as screw systems (US-A-4 132 845).
• coagulation, washing and dewatering may preferably take place continuously.
• the process is particularly advantageous for preparing high-purity polymers, e.g. when coagulating fluoropolymer latices prepared by emulsion polymerization with addition of little or no buffer and/or whose exchangeable ions have been removed, since the "mechanical" coagulation of the invention requires no addition of mineral acids or of salts, another factor advantageous for the recovery of the emulsifier (WO-A-99/62830).
• An aqueous dispersion having a content of 33% of a fluoroelastomer containing 60% of vinylidene fluoride units and 40% of hexafluoropropene units, as obtained from the polymerization, is brought to 250 bar using nitrogen, in a pressure vessel at room temperature, and released via the annular gap of a homogenizer (high-pressure homogenizer from APN Gaulin GmbH, L ⁇ beck).
• the resultant coagulate is dewatered in a filter press, and washed.
• the aqueous filtrate (the undiluted aqueous phase separated from the coagulate) comprises 0.8% of polymeric material.
• Example 1 is repeated, except that when the pressure is applied nitrogen is bubbled through the dispersion.
• the aqueous filtrate comprises 0.3% of polymeric materials.
• Example 1 is repeated, except that an aqueous dispersion is used which has a content of 26% of a fluoroelastomer containing 31% of vinylidene fluoride units, 37% of hexafluoropropene units and 32% of tetrafluoroethylene units, and whose exchangeable ions have been removed.
• the aqueous filtrate comprises 0.5% of polymeric materials.
• Example 3 is repeated, except that when the pressure is applied nitrogen is bubbled through the dispersion.
• the aqueous filtrate comprises 0.3% of polymeric materials.
• An aqueous dispersion which has a content of 20% of a perfluoroelastomer containing bromotrifluoroethylene units and having a Mooney viscosity ML 1+10/121°C of 85 (determined to ASTM D1646), and whose exchangeable ions have been removed, is brought to 180 bar using nitrogen in a pressure vessel at room temperature, and released via the annular gap of a homogenizer (high-pressure homogenizer from APN Gaulin GmbH, L ⁇ beck). The resultant coagulate is dewatered in a filter press, and washed. The aqueous filtrate comprises 0.5% of solids.
• Example 5 is repeated with the following modifications: carbon dioxide is used instead of nitrogen, the temperature is 40°C and the pressure 100 bar.
• the aqueous filtrate comprises 0.3% of solids.
• Example 5 is repeated with the dispersion whose exchangeable anions had not been removed.
• the solids content in the aqueous filtrate is 1%.
• Example 1 is repeated, except that the following mixture was used:
• the aqueous filtrate comprises 0.5% of polymeric materials.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)

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• 2000
  • 2000-02-01 DE DE2000104229 patent/DE10004229A1/de not_active Withdrawn
• 2001
  • 2001-01-31 EP EP01908761A patent/EP1268573A1/en not_active Withdrawn
  • 2001-01-31 AU AU2001236598A patent/AU2001236598A1/en not_active Abandoned
  • 2001-01-31 CA CA002396630A patent/CA2396630A1/en not_active Abandoned
  • 2001-01-31 WO PCT/US2001/003152 patent/WO2001057096A1/en active Application Filing
  • 2001-01-31 JP JP2001557927A patent/JP2003522230A/ja not_active Withdrawn

Non-Patent Citations (1)

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