EP1268573A1 - Process for working up aqueous dispersions of fluoropolymers - Google Patents

Process for working up aqueous dispersions of fluoropolymers

Info

Publication number
EP1268573A1
EP1268573A1 EP01908761A EP01908761A EP1268573A1 EP 1268573 A1 EP1268573 A1 EP 1268573A1 EP 01908761 A EP01908761 A EP 01908761A EP 01908761 A EP01908761 A EP 01908761A EP 1268573 A1 EP1268573 A1 EP 1268573A1
Authority
EP
European Patent Office
Prior art keywords
dispersion
gas
pressure
fluoropolymers
aqueous
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01908761A
Other languages
German (de)
French (fr)
Inventor
Klaus Hintzer
Albert Killich
Bernhard Hirsch
Rudolf Erber
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
3M Innovative Properties Co
Original Assignee
3M Innovative Properties Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 3M Innovative Properties Co filed Critical 3M Innovative Properties Co
Publication of EP1268573A1 publication Critical patent/EP1268573A1/en
Withdrawn legal-status Critical Current

Links

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.

Landscapes

  • 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)

Abstract

Process for working up aqueous dispersions of fluoropolymers. Fluoropolymer dispersions, in particular of fluoroelastomers, can be coagulated without adding chemicals, by compression with the aid of a gas and release through one or more small apertures.

Description

Process For Working Up Aqueous Dispersions Of Fluoropolymers
Description
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.
In particular for semicrystalline fluorinated thermoplastics, this coagulation process gives excellent results with respect to degree of precipitation and purity of the precipitated product, and for process operating times. However, it is not transferable to fluoroelastomers, since some of the dispersion coagulates during the pumping required for compression, forming a coating on the apparatus, because the coagulate is tacky.
This makes continuous operation of the coagulation apparatus impossible.
Another disadvantage of the known process is that the apparatus required for the compression of dispersions is not everywhere available.
It has now been found that the process mentioned can be transferred to fluoroelastomers if the dispersion is compressed with the aid of a gas and the resultant compressed dispersion is released in a manner known per se through one or more small apertures, and so coagulates.
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 • 107 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).
According to the invention, as in the process of EP-B-O 591 888, 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).
The examples below describe the invention in more detail. Percentages are based on weight. Example 1
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, Lϋbeck). 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 2
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 3
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 4
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.
Example 5
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, Lϋbeck). The resultant coagulate is dewatered in a filter press, and washed. The aqueous filtrate comprises 0.5% of solids.
Example 6
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 7
Example 5 is repeated with the dispersion whose exchangeable anions had not been removed. The solids content in the aqueous filtrate is 1%.
Example 8
Example 1 is repeated, except that the following mixture was used:
80% of a terpolymer containing 31% of vinylidene fluoride units, 37% of hexafluoropropene units, 31% of tetrafluoroethylene units and 1% of bromotrifluoroethylene units, and having a Mooney viscosity ML 1+10/121°C of 70 (determined to ASTM D 1646), and
20% of a copolymer having 96% of tetrafluoroethylene units and 4% of perfluoro n-propyl vinyl ether units, MFI 372°C, 5 kg = 2.2 g/10 min, determined to ISO 12086. The aqueous filtrate comprises 0.5% of polymeric materials.

Claims

Patent claims
1. A process for coagulating fluoropolymer dispersions, which comprises compressing the aqueous dispersion with the aid of a gas and releasing the dispersion through one or more small apertures so that it coagulates.
2. The process as claimed in claim 1, wherein the fluoropolymer is a fluoroelastomer or a mixture of a semicrystalline fluorinated thermoplastic with a fluoroelastomer.
3. The process as claimed in claim 1 or 2, wherein the gas pressure is from 50 to 400 bar.
4. The process as claimed in one or more of the preceding claims, wherein the gas is nitrogen, carbon dioxide or air.
5. The process as claimed in one or more of the preceding claims, wherein a dispersion is used from which the exchangeable ions have been removed.
6. The process as claimed in one or more of the preceding claims, wherein coagulation, washing and dewatering take place continuously.
7. The process as claimed in claim 6, wherein washing and dewatering take place on a filter belt.
EP01908761A 2000-02-01 2001-01-31 Process for working up aqueous dispersions of fluoropolymers Withdrawn EP1268573A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE2000104229 DE10004229A1 (en) 2000-02-01 2000-02-01 Coagulation of aqueous fluoropolymer, especially fluoro-elastomer, dispersions comprises pressurizing the dispersion with a gas and expanding it through one or more small orifices
DE10004229 2000-02-01
PCT/US2001/003152 WO2001057096A1 (en) 2000-02-01 2001-01-31 Process for working up aqueous dispersions of fluoropolymers

Publications (1)

Publication Number Publication Date
EP1268573A1 true EP1268573A1 (en) 2003-01-02

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Family Applications (1)

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EP01908761A Withdrawn EP1268573A1 (en) 2000-02-01 2001-01-31 Process for working up aqueous dispersions of fluoropolymers

Country Status (6)

Country Link
EP (1) EP1268573A1 (en)
JP (1) JP2003522230A (en)
AU (1) AU2001236598A1 (en)
CA (1) CA2396630A1 (en)
DE (1) DE10004229A1 (en)
WO (1) WO2001057096A1 (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6593416B2 (en) 2000-02-01 2003-07-15 3M Innovative Properties Company Fluoropolymers
US6720360B1 (en) * 2000-02-01 2004-04-13 3M Innovative Properties Company Ultra-clean fluoropolymers
US8105515B2 (en) 2005-05-12 2012-01-31 Nitto Denko Corporation Method of manufacturing polytetrafluoroethylene particle aggregate and method of manufacturing polytetrafluoroethylene product
US20080015304A1 (en) 2006-07-13 2008-01-17 Klaus Hintzer Aqueous emulsion polymerization process for producing fluoropolymers
CN101437877B (en) 2006-05-01 2011-12-07 日东电工株式会社 Process for production of polytetrafluoroethylene sheet, and process for production of polytetrafluoroethylene seal tape
US20080264864A1 (en) 2007-04-27 2008-10-30 3M Innovative Properties Company PROCESS FOR REMOVING FLUORINATED EMULSIFIER FROM FLUOROPOLMER DISPERSIONS USING AN ANION-EXCHANGE RESIN AND A pH-DEPENDENT SURFACTANT AND FLUOROPOLYMER DISPERSIONS CONTAINING A pH-DEPENDENT SURFACTANT

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3464964A (en) * 1966-06-13 1969-09-02 Pennsalt Chemicals Corp Coagulation of polytetrafluoroethylene latex
US4623678A (en) * 1985-04-26 1986-11-18 The Dow Chemical Company Method for shear coagulation of latex resins
DE4233824A1 (en) * 1992-10-08 1994-04-14 Hoechst Ag Process for working up aqueous dispersions of fluorothermoplastics

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0157096A1 *

Also Published As

Publication number Publication date
CA2396630A1 (en) 2001-08-09
DE10004229A1 (en) 2001-08-02
WO2001057096A1 (en) 2001-08-09
AU2001236598A1 (en) 2001-08-14
JP2003522230A (en) 2003-07-22

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