JP5392188B2 - Method for producing fluoropolymer aqueous dispersion - Google Patents

Description

The present invention relates to a method for producing a content less fluoropolymer aqueous dispersion of the fluorinated emulsifier.

  When producing fluoropolymers such as polytetrafluoroethylene (hereinafter referred to as “PTFE”), melt moldable fluororesins, fluoroelastomers by emulsion polymerization, the polymerization reaction is not hindered by chain transfer in an aqueous medium. A fluorine emulsifier is generally used.

  A fluoropolymer powder is obtained by agglomerating and drying an aqueous emulsion polymerization liquid of a fluoropolymer obtained by emulsion polymerization (hereinafter referred to as “fluorinated polymer aqueous emulsion polymerization liquid”). The PTFE powder is used for various purposes after being molded by a method such as paste extrusion molding. In addition, a non-ionic surfactant or the like is added to the fluorine-containing polymer aqueous emulsion polymerization solution as necessary, followed by a stabilization treatment, followed by a concentration treatment to obtain a fluorine-containing polymer containing a high concentration of the fluorine-containing polymer. An aqueous polymer dispersion (hereinafter referred to as “high concentration fluorine-containing polymer aqueous dispersion”) is obtained. This aqueous dispersion of high-concentration fluorine-containing polymer is used for various coating applications, impregnation applications, etc. by adding various compounding agents as required.

  By the way, the fluorine-containing emulsifier is expensive, and the amount of the fluorine-containing emulsifier greatly affects the production cost of the fluorine-containing polymer powder and the fluorine-containing polymer aqueous dispersion. Therefore, it is desired to recover the fluorine-containing emulsifier and reuse it. . Fluorine-containing emulsifiers are substances that are not easily decomposed in nature. For this reason, in recent years, it has been desired to reduce the content of the fluorine-containing emulsifier contained in not only industrial wastewater but also the fluorine-containing polymer aqueous dispersion.

  As a method for reducing the content of the fluorinated emulsifier contained in the aqueous fluorinated polymer dispersion, as shown in Patent Documents 1 to 3, a basic anion exchange resin (hereinafter referred to as “IER”) is included. There is a method in which the fluorine-containing emulsifier in the aqueous fluoropolymer dispersion is brought into contact with the aqueous fluoropolymer dispersion and adsorbed on the IER to remove it.

  Strongly basic IER is said to be capable of efficiently adsorbing and removing the fluorine-containing emulsifier from the fluorine-containing polymer aqueous dispersion compared to weakly basic IER. Yes.

Japanese translation of PCT publication No. 2002-532583 (see paragraph 0021) Japanese translation of PCT publication No. 2005-501956 (see paragraph number 0032) JP-T-2006-515375 (see paragraph 0032)

  The fluorinated emulsifier adsorbed with the strongly basic IER was difficult to elute from the strongly basic IER when a water-soluble organic solvent was added and elution was not promoted, and the recovery efficiency of the fluorinated emulsifier was extremely low.

  On the other hand, the fluorinated emulsifier adsorbed with weakly basic IER can be eluted and recovered relatively easily without adding a water-soluble organic solvent. However, the fluoropolymer aqueous dispersion treated with weakly basic IER has poor stability, and the fluoropolymer particles easily settled with time. In addition, the fluoropolymer aqueous dispersion treated with weakly basic IER has a low concentration rate, and moreover, agglomerates of the fluoropolymer are easily generated during the concentration, and the production efficiency of the high concentration fluoropolymer aqueous dispersion is improved. It was bad.

  The present inventors examined the cause of insufficient stability and concentration efficiency of the fluoropolymer aqueous dispersion treated with weakly basic IER, and found that it was due to the influence of the organic carboxylic acid contained. I found it.

  The aqueous fluoropolymer dispersion may contain an organic carboxylic acid produced by the decomposition of a polymerization initiator or the like used during the emulsion polymerization of the fluoromonomer. In addition, an organic carboxylic acid may be added to the fluoropolymer aqueous dispersion in order to lower the pH of the fluoropolymer aqueous dispersion and improve the adsorption efficiency of the fluorinated emulsifier by IER.

  With strong basic IER, the organic carboxylic acid contained in the fluoropolymer aqueous dispersion can be adsorbed and removed, but with weakly basic IER, the organic carboxylic acid contained in the fluoropolymer aqueous dispersion can be almost adsorbed and removed. There wasn't. For this reason, the fluorine-containing polymer aqueous dispersion treated with weakly basic IER often contains an organic carboxylic acid, and the above-described problems have occurred.

Therefore, the object of the present invention is to produce a fluorine-containing polymer aqueous dispersion having a low content of fluorine-containing emulsifier, which is easy to elute and recovering the fluorine-containing emulsifier, and having excellent storage stability and concentration efficiency. It is to provide a method.

The present invention provides the following.
[1] A fluorine-containing polymer aqueous dispersion containing a fluorine-containing polymer, a fluorine-containing emulsifier, and an organic carboxylic acid represented by the following general formula (1) is contacted with a weakly basic IER to form the fluorine-containing polymer. A method for producing a fluorine-containing polymer aqueous dispersion, wherein the emulsifier is adsorbed and removed, and then the organic carboxylic acid is adsorbed and removed by contacting with a strongly basic IER.
Q (CH ₂ ) _m (CH (OH)) _n COOH (1)
(In formula (1), Q is H, CH ₃ or COOH, m and n are each independently 0 or an integer of 1 to 4, and 4 ≧ n + m ≧ 1.)
[2] The method for producing an aqueous fluoropolymer dispersion according to [1], wherein the fluoropolymer is PTFE.
[3] The method for producing an aqueous fluoropolymer dispersion according to [2], wherein the standard specific gravity of the PTFE is 2.15 to 2.35.
[4] Any of [1] to [3], wherein the content of the fluorine-containing emulsifier in the aqueous dispersion of the fluorine-containing polymer before being brought into contact with the weakly basic IER is 750 ppm to 10,000 ppm with respect to the mass of the fluorine-containing polymer. A process for producing an aqueous dispersion of a fluorine-containing polymer according to claim 1.
[5] Any of [1] to [4], wherein the content of the fluorinated emulsifier in the aqueous fluoropolymer dispersion after contact with the weakly basic IER is 200 ppm or less with respect to the mass of the fluoropolymer. A process for producing an aqueous dispersion of a fluorine-containing polymer according to claim 1.
[6] The method for producing an aqueous fluoropolymer dispersion according to any one of [1] to [5], wherein the organic carboxylic acid is a compound represented by the following general formula (2).
HOCO (CH ₂ ) _m COOH (2)
(In the formula (2), m is 0 or an integer of 1 to 4.)
[7] Any of [1] to [6], wherein the content of the organic carboxylic acid in the aqueous fluoropolymer dispersion before contacting with the weakly basic IER is 100 ppm to 2000 ppm with respect to the mass of the fluoropolymer. A process for producing an aqueous dispersion of a fluorine-containing polymer according to claim 1.
[8] Any of [1] to [7], wherein the content of the organic carboxylic acid in the aqueous fluoropolymer dispersion after contact with the strongly basic IER is 100 ppm or less with respect to the mass of the fluoropolymer. A process for producing an aqueous dispersion of a fluorine-containing polymer according to claim 1.

According to the present invention, a fluorine-containing polymer aqueous dispersion containing a fluorine-containing polymer, a fluorine-containing emulsifier, and the organic carboxylic acid represented by the general formula (1) is first contacted with a weakly basic IER. Thus, the fluorine-containing emulsifier is adsorbed on the weakly basic IER. Subsequently, it is made to contact with strong basic IER, and organic carboxylic acid etc. which could not be adsorbed by weak basic IER are adsorbed to strong basic IER.
For this reason, there can be obtained a fluorine-containing polymer aqueous dispersion having a small content of the fluorine-containing emulsifier and the organic carboxylic acid and excellent in storage stability and concentration efficiency.
Further, since the fluorinated emulsifier is adsorbed on the weakly basic IER, the fluorinated emulsifier can be easily eluted and recovered and reused.

  First, the fluoropolymer aqueous emulsion polymerization liquid used in the method for producing the fluoropolymer aqueous dispersion of the present invention will be described.

  The fluorine-containing polymer aqueous emulsion polymerization liquid used in the present invention contains a fluorine-containing polymer, a fluorine-containing emulsifier, and a specific organic carboxylic acid. Such a fluorine-containing polymer aqueous emulsion polymerization solution is obtained by emulsion polymerization of a fluorine-containing monomer in an aqueous medium in the presence of a fluorine-containing emulsifier.

  The fluorine-containing monomer used in the emulsion polymerization is not particularly limited, and tetrafluoroethylene (hereinafter referred to as “TFE”), hexafluoropropylene, perfluoro (alkyl vinyl) ether (wherein the alkyl group has 1 to 1 carbon atoms). 5)), trifluorochlorethylene, (perfluorobutyl) ethylene, vinylidene fluoride, and the like.

  A preferred example of the fluorine-containing polymer aqueous emulsion polymerization liquid is a PTEF aqueous emulsion polymerization liquid obtained by emulsion polymerization of TFE in an aqueous medium. In the present invention, PTFE refers to a small amount of halogenated ethylene such as chlorotrifluoroethylene, propylene halide such as hexafluoropropylene, perfluorocarbon, and the like, in addition to a TFE homopolymer. It is intended to include so-called modified PTFE, which is PTFE containing polymerized units based on monomers that can be copolymerized with TFE, such as fluorovinyl ethers such as fluoro (alkyl vinyl ether).

  The standard specific gravity of PTFE in the PTEF aqueous emulsion polymerization liquid is preferably 2.15 to 2.35, more preferably 2.15 to 2.30. In addition, in this invention, the standard specific gravity of PTFE means the value measured by the method described in the Example mentioned later.

  The average particle diameter of the PTFE fine particles in the PTEF aqueous emulsion polymerization liquid is 0.10 to 0.50 μm, preferably 0.12 to 0.40 μm, particularly preferably 0.15 to 0.30 μm. If the average particle size of the PTFE fine particles is less than 0.10 μm, mechanical properties as PTFE tend to be impaired. On the other hand, if the average particle size of the PTFE fine particles exceeds 0.50 μm, the PTFE fine particles are liable to settle, and the storage stability tends to be impaired. In the present invention, the average particle diameter of the PTFE fine particles means a value measured by the method described in Examples described later.

  The number average molecular weight of PTFE can be arbitrarily selected. Among these, 100,000 to 30 million is preferable, 200,000 to 25 million is more preferable, and 300,000 to 20 million is particularly preferable. When the number average molecular weight of PTFE is less than 100,000, mechanical properties as PTFE tend to be lowered. Moreover, when the number average molecular weight of PTFE exceeds 30 million, it is difficult to produce industrially.

  The fluorine-containing emulsifier contained in the fluorine-containing polymer aqueous emulsion polymerization solution is not particularly limited as long as it is used for emulsion polymerization of a fluorine-containing monomer. Examples thereof include a fluorinated carboxylic acid and a salt thereof which may have an etheric oxygen atom, a fluorinated sulfonic acid and a salt thereof, and the like. Examples of the salt include ammonium salts and alkali metal salts (Li, Na, K, etc.), and ammonium salts are preferable. Especially, the fluorine-containing carboxylic acid which may have an etheric oxygen atom, and its salt are preferable.

  Specific examples of the fluorine-containing carboxylic acid include perfluorocarboxylic acid, perfluorocarboxylic acid having an etheric oxygen atom, and fluorine-containing carboxylic acid having a hydrogen atom.

  Examples of perfluorocarboxylic acid include perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, and perfluorononanoic acid.

As perfluorocarboxylic acid having an etheric oxygen atom, C ₃ F ₇ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COOH, C ₄ F ₉ OC ₂ F ₄ OCF ₂ COOH, C ₃ F ₇ OC ₂ F _{4 OCF 2 COOH, C 2 F} 5 OC 2 F 4 OCF 2 COOH, C 2 F 5 OCF 2 CF 2 OCF 2 CF 2 OCF 2 COOH, C 2 F 5 O (CF 2) 5 COOH, CF 3 OC 2 F ₄ OCF ₂ COOH, CF ₃ OCF ₂ OCF ₂ OCF ₂ COOH, CF ₃ OCF ₂ OCF ₂ OCF ₂ OCF ₂ COOH, CF ₃ O (CF ₂ CF ₂ O) ₂ CF ₂ COOH, CF ₃ OCF ₂ CF ₂ CF _{2 OCF 2 COOH, C 4 F 9} OCF 2 COOH, C 4 F 9 OCF 2 CF 2 COOH, CF 3 O CF (CF ₃ ) CF ₂ OCF (CF ₃ ) COOH, C ₄ F ₉ OCF (CF ₃ ) COOH, and the like can be given.

Examples of the fluorinated carboxylic acid having a hydrogen atom include ω-hydroperfluorooctanoic acid, C ₃ F ₇ OCF (CF ₃ ) CF ₂ OCHFCOOH, CF ₃ CFHO (CF ₂ ) ₅ COOH, CF ₃ O (CF ₂ ) ₃ OCFCCF ₂ COOH, CF ₃ O (CF ₂ ) ₃ OCHFCOOH, C ₃ F ₇ OCHFCF ₂ COOH, CF ₃ CFHO (CF ₂ ) ₃ COOH, and the like can be given.

Examples of the fluorine-containing sulfonic acid include perfluorooctane sulfonic acid and C ₆ F ₁₃ CH ₂ CH ₂ SO ₃ H.

  The content of the fluorine-containing emulsifier in the fluorine-containing polymer aqueous emulsion polymerization solution is preferably 750 ppm to 10000 ppm, more preferably 1000 ppm to 8000 ppm, and particularly preferably 1500 ppm to 6000 ppm with respect to the mass of the finally obtained fluorine-containing polymer. When the content of the fluorinated emulsifier is less than 750 ppm, the fluorinated polymer aggregates during polymerization, and the yield tends to decrease. When the content of the fluorine-containing emulsifier exceeds 10,000 ppm, it becomes difficult to obtain the fluorine-containing polymer as fine particles.

The fluorine-containing polymer aqueous emulsion polymerization liquid used in the present invention contains an organic carboxylic acid represented by the following general formula (1). Preferably, it is organic carboxylic acid represented by the following general formula (2). Hereinafter, even when described as an organic carboxylic acid, the organic carboxylic acid represented by the general formula (1) is meant.
Q (CH ₂ ) _m (CH (OH)) _n COOH (1)
(In formula (1), Q is H, CH ₃ or COOH, m and n are each independently 0 or an integer of 1 to 4, and 4 ≧ n + m ≧ 1.)
HOCO (CH ₂ ) _m COOH (2)
(In the formula (2), m is 0 or an integer of 1 to 4.)

Specific examples of the organic carboxylic acid include HOCOCH ₂ COOH (malonic acid), HOCO (CH ₂ ) ₂ COOH (succinic acid), HOCO (CH ₂ ) ₃ COOH (glutaric acid), HOCO (CH ₂ ) ₄ COOH (adipine) Acid), HOCOCH ₂ CH (OH) COOH (malic acid), CH ₃ CH (OH) COOH (lactic acid), HOCO (CH (OH)) ₂ COOH (tartaric acid), HOCO (CH (OH)) ₄ COOH (D - galactaric acid and D- glucaric _{acid), HOCOCH 2 CH (OH)} COOH, CH 3 CH (OH) COOH, CH 3 COOH ( acetic _{acid), CH} 3 _CH 2 COOH (propionic _{acid), CH 3 (CH 2)} 2 COOH (butyric acid), CH ₃ (CH ₂ ) ₃ COOH (valeric acid) may be mentioned. Preferably, it is a kind selected from HOCOCH ₂ COOH, HOCO (CH ₂ ) ₂ COOH, HOCO (CH ₂ ) ₃ COOH and HOCO (CH ₂ ) ₄ COOH.

  The content of the organic carboxylic acid in the fluoropolymer aqueous emulsion polymerization liquid is preferably 100 ppm to 2000 ppm, more preferably 200 ppm to 2000 ppm, and particularly preferably 300 ppm to 2000 ppm with respect to the mass of the finally obtained fluoropolymer.

  If the content of the organic carboxylic acid is in the above range, the pH of the aqueous fluoropolymer emulsion solution becomes acidic, and the adsorption efficiency of the fluoroemulsifier by the weakly basic IER described later is good.

  In addition, the said organic carboxylic acid may be produced | generated by decomposition | disassembly of the polymerization initiator etc. which were used at the time of emulsion polymerization of a fluorine-containing monomer. For example, when a fluorine-containing monomer is emulsion-polymerized using disuccinic acid peroxide as a polymerization initiator, the disuccinic acid peroxide is decomposed during or after the emulsion polymerization process to produce two molecules of succinic acid. For this reason, even if it does not add organic carboxylic acid, organic carboxylic acid is contained in the fluorine-containing monomer aqueous | water-based emulsion polymerization liquid, and pH may be acidic.

  The fluorine-containing polymer aqueous emulsion polymerization solution used in the present invention is preferably stabilized with a nonionic surfactant before removing the fluorine-containing emulsifier from the fluorine-containing polymer aqueous emulsion polymerization solution (hereinafter referred to as nonionic surfactant). A fluoropolymer aqueous emulsion polymerization liquid stabilized with a surfactant is referred to as "low-concentration fluoropolymer aqueous dispersion").

Examples of the nonionic surfactant include surfactants represented by the following general formula (A) and / or general formula (B).
^{R 1 -O-A-H ···} (A)
(In formula (A), R ¹ is an alkyl group having 8 to 18 carbon atoms, and A is a polyoxyalkylene chain composed of 5 to 20 oxyethylene groups and 0 to 2 oxypropylene groups.)
R ² —C ₆ H ₄ —O—B—H (B)
(In the formula (B), R ² is an alkyl group having 4 to 12 carbon atoms, and B is a polyoxyethylene chain composed of 5 to 20 oxyethylene groups.)

Specific examples of the nonionic surfactant in the general formula (A), for _{example, C 13 H 27 - (OC} 2 H 4) 10 -OH, C 12 H 25 - (OC 2 H 4) 10 -OH, _{C 10 H 21 CH (CH 3} ) CH 2 - (OC 2 H 4) 9 -OH, C 13 H 27 - (OC 2 H 4) 8 -OCH (CH 3) CH 2 -OH, C 16 H 33 - _{(OC 2 H 4) 10 -OH} , HC (C 5 H 11) (C 7 H 15) - (OC 2 H 4) 9 non-ionic surfactant having a molecular structure such as -OH and the like. Examples of commercially available products include Dow Taditol (registered trademark) 15S series, Nippon Emulsifier New Coal (registered trademark) series, Lion Corporation Lionol (registered trademark) TD series, and the like.

Specific examples of the nonionic surfactant of the general formula _{(B), C 8 H 17} -C 6 H 4 - (OC 2 H 4) 10 -OH, C 9 H 19 -C 6 H 4 - (OC Non-ionic surfactants having a molecular structure such as ₂ H ₄ ) ₁₀ —OH can be mentioned. Examples of commercially available products include Dow Triton (registered trademark) X series, Nikko Chemical Nikkor (registered trademark) OP series, and NP series.

  The low-concentration fluoropolymer aqueous dispersion preferably contains the nonionic surfactant in an amount of 1 to 20 mass%, more preferably 1 to 10 mass%, based on the mass of the fluoropolymer. It is especially preferable to contain 2-8 mass%. When the content of the nonionic surfactant is within the above range, the fluoropolymer aqueous dispersion has good mechanical stability and wettability.

  Next, the manufacturing method of the fluorine-containing polymer aqueous dispersion of this invention is demonstrated.

  The low-concentration fluoropolymer aqueous dispersion is first brought into contact with a weakly basic IER to adsorb the fluoroemulsifier in the low-concentration fluoropolymer aqueous dispersion to the weakly basic IER (hereinafter referred to as weakly basic IER). The aqueous fluoropolymer dispersion after the contact is referred to as “weakly basic IER-treated fluoropolymer aqueous dispersion”).

  In the present invention, the weakly basic IER is an ion exchange resin having an amino group as an ion exchange group. The ion exchange group of weakly basic IER is preferably a primary to tertiary amino group, more preferably a secondary to tertiary amino group, and particularly preferably a tertiary amino group.

  Examples of weakly basic IERs include styrene-divinylbenzene crosslinked resins having amino groups as ion exchange groups, acrylic-divinylbenzene crosslinked resins having amino groups as ion exchange groups, and cellulose resins having amino groups as ion exchange groups. And a granular resin. Among these, a styrene-divinylbenzene crosslinked resin having an amino group as an ion exchange group is preferable.

  The average particle diameter of the weak basic IER is preferably 0.1 to 2 mm, more preferably 0.2 to 1 mm, and particularly preferably 0.3 to 0.8 mm. It is preferable that the particle diameter of the weakly basic IER is uniform because it is difficult to block the flow path when the low concentration fluoropolymer aqueous dispersion is passed. If the average particle diameter of the weak basic IER is within the above range, for example, the flow path is blocked when a low concentration fluoropolymer aqueous dispersion is passed through a column or cylinder filled with the weak basic IER. It is hard to do.

  Examples of commercially available products of weakly basic IER include Diaion (registered trademark) WA-30 manufactured by Mitsubishi Chemical Corporation, Lewatit (registered trademark) MP-62WS manufactured by LANXESS, Dowex Marathon (registered trademark) WBA manufactured by Dow. It is done.

  The method for contacting the low-concentration fluoropolymer aqueous dispersion with the weakly basic IER is not particularly limited. 1) A method in which weakly basic IER is put into an aqueous dispersion of low-concentration fluorine-containing polymer and stirred or shaken. 2) A low-concentration fluorine-containing column or cylinder filled with weakly basic IER is separated by gravity or by a pump. Examples thereof include a method of passing an aqueous polymer dispersion. The method 2) is preferable. By placing the column or cylinder filled with the strong basic IER downstream of the column or cylinder filled with the weak basic IER, the contact with the weak basic IER and the contact with the strong basic IER are continuously performed. Can be done. In addition, by passing an aqueous solution of a nonionic surfactant through a column or cylinder filled with basic IER to adsorb the nonionic surfactant on the particle surface of the basic IER, low concentration fluorine-containing The passage of the polymer aqueous dispersion is stable.

  In addition, when adsorbing the fluorine-containing emulsifier to the weakly basic IER, the lower the pH of the low-concentration fluorine-containing polymer aqueous dispersion, the better the adsorption efficiency of the fluorine-containing emulsifier by the weakly basic IER. The pH of the aqueous polymer dispersion is preferably 7 or less. The pH of the low-concentration fluoropolymer aqueous dispersion can be lowered by increasing the content of the organic carboxylic acid represented by the general formula (1).

  The aqueous fluoropolymer dispersion after contact with the weakly basic IER (weakly basic IER-treated fluoropolymer aqueous dispersion) has a fluorine-containing emulsifier content of 200 ppm or less based on the mass of the fluoropolymer. Preferably, it is 100 ppm or less, more preferably 50 ppm or less, and most preferably 5 ppm or less. Moreover, considering the influence on the environment, the lower the lower limit value is not particularly limited, the smaller the content of the fluorine-containing emulsifier, the better. The lower limit is preferably 1 ppm, more preferably 0.1 ppm, and most preferably 0.01 ppm.

  Next, the weakly basic IER-treated fluoropolymer aqueous dispersion is brought into contact with the strongly basic IER, and the organic carboxylic acid in the weakly basic IER-treated fluoropolymer aqueous dispersion is adsorbed to the strongly basic IER (hereinafter referred to as “low basic IER”). The aqueous fluoropolymer dispersion after contact with the strongly basic IER is referred to as “strongly basic IER-treated fluoropolymer aqueous dispersion”).

  In the present invention, the strongly basic IER is an ion exchange resin having a quaternary ammonium base as an ion exchange group. Examples of strongly basic IER include styrene-divinylbenzene crosslinked resin having quaternary ammonium base as ion exchange group, acrylic-divinylbenzene crosslinked resin having quaternary ammonium base as ion exchange group, quaternary ammonium base And a granular resin made of a cellulose resin having an ion exchange group. Among these, a granular resin made of a styrene-divinylbenzene crosslinked resin having a quaternary ammonium base as an ion exchange group is preferable.

  The average particle size of the strongly basic IER is preferably 0.1 to 2 mm, more preferably 0.2 to 1 mm, and particularly preferably 0.3 to 0.8 mm. The particle size of the strongly basic IER is preferably within the above-mentioned range, and it is preferable that the particle size is uniform because the channel is less likely to be blocked when the weakly basic IER-treated fluoropolymer aqueous dispersion is passed.

  Examples of commercially available strong base type IERs include Lewatit (registered trademark) MP800OH manufactured by LANXESS, Lewatit (registered trademark) M800KR manufactured by LANXESS, Lewatit (registered trademark) MP600 manufactured by LANXESS, PUROLITE (registered trademark) A200MBOH manufactured by Purolite, and the like. Is mentioned.

  The contact method between the weakly basic IER-treated fluoropolymer aqueous dispersion and the strongly basic IER can be the same method as mentioned in the contact method between the low-concentration fluoropolymer aqueous dispersion and the weakly basic IER. .

  The aqueous fluoropolymer dispersion after contact with the strongly basic anion exchange resin (strongly basic IER-treated fluoropolymer aqueous dispersion) has an organic carboxylic acid content of 100 ppm or less based on the fluoropolymer. More preferably, it is 70 ppm or less, More preferably, it is 50 ppm or less, Most preferably, it is 5 ppm or less. As the content of the organic carboxylic acid is smaller, the stability and concentration efficiency of the fluoropolymer aqueous dispersion are improved, so the lower limit is not particularly limited. The lower limit is preferably 1 ppm, more preferably 0.1 ppm, and most preferably 0.01 ppm.

  The strongly basic IER-treated fluoropolymer aqueous dispersion thus obtained has a reduced content of the fluorinated emulsifier and the organic carboxylic acid.

  The content of the fluorine-containing emulsifier in the strongly basic IER-treated fluorine-containing polymer aqueous dispersion is 200 ppm or less, preferably 100 ppm or less, more preferably 50 ppm or less, based on the mass of the fluorine-containing polymer. Preferably it is 5 ppm or less.

  Further, the content of the organic carboxylic acid is 100 ppm or less, preferably 70 ppm or less, more preferably 50 ppm or less, and most preferably 5 ppm or less with respect to the mass of the fluoropolymer.

  In the present invention, since the fluorinated emulsifier is adsorbed on the weakly basic IER, the fluorinated emulsifier can be easily eluted from the weakly basic IER, and the fluorinated emulsifier contained in the eluent is purified by a known method. Can be recycled.

  As a means for eluting the fluorine-containing emulsifier from the weakly basic IER that has absorbed the fluorine-containing emulsifier, known methods can be used in addition to the method using a heated alkaline aqueous solution described in WO2007 / 043278.

  In addition, organic carboxylic acid is adsorbed to strong basic IER, but organic carboxylic acid can be eluted from strong basic IER by using a known eluent such as alkaline aqueous solution or saline. Can be reused.

  The strongly basic IER-treated fluoropolymer aqueous dispersion can be used as it is. Further, the fluorine-containing polymer concentration may be concentrated to about 60 to 75% by mass by a known concentration process. As the concentration process, known methods such as centrifugal sedimentation, electrophoresis, and phase separation can be used as described on page 32 of the fluororesin handbook (Takaomi Satokawa, edited by Nikkan Kogyo Shimbun, 1990). .

  In addition, since the content of the fluorine-containing emulsifier is reduced in the strongly basic IER-treated fluorine-containing polymer aqueous dispersion, stability and concentration rate may be lowered. In such a case, an anionic surfactant other than the fluorine-containing emulsifier may be added before or after concentration in order to improve the stability and concentration rate. Specific examples include ammonium laurate, ethanolamine laurate, ammonium cinnamate, ammonium lauryl sulfate, sodium lauryl sulfate, triethanolamine lauryl sulfate, ammonium pt-butylbenzoate, and the like. The content of the anionic surfactant other than the fluorine-containing emulsifier is preferably 0.01 to 0.3% by mass and more preferably 0.02 to 0.25% by mass with respect to the mass of the fluorine-containing polymer.

  The high-concentration fluoropolymer aqueous dispersion obtained by the concentration process can be used as it is or diluted with water. In addition, to improve stability and wettability, or to optimize viscosity, viscosity adjustment of additional nonionic surfactants, anionic surfactants other than fluorine-containing emulsifiers, polyethylene oxide and polyurethane systems Agents, various leveling agents, preservatives, colorants, fillers, organic solvents, alkaline substances such as ammonia, and other known components are added as necessary. You may use as a fluorine-containing polymer aqueous dispersion whose fluoropolymer concentration is 55-70 mass%, and surfactant concentration is 2-12 mass% with respect to the fluorine-containing polymer mass. This aqueous fluoropolymer dispersion can be used for various applications that have been used in the past, such as coating glass fiber cloths for use on printed circuit boards and roofing materials for membrane structures, and coating the surface of cooking utensils. Use to improve releasability, Use after baking to stretch and make fluoropolymer fibers, Use with dusting powder to prevent dusting, Mix with battery active material to make binder It can be used for many purposes, such as for use and for preventing dripping when melted by adding to plastic.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, these do not limit this invention at all. The measuring method of the physical property values described in the examples is as follows.

(A) Number average molecular weight of PTFE: In accordance with the method of Suwa (Journal of Applied Polymer Science, 17, 3253 (1973)), the number average molecular weight M is obtained from the latent heat ΔHc (cal / g) in differential thermal analysis by the following formula. It was.
M = 2.1 × 10 ¹⁰ × ΔHc− ^5.16

  (B) Average particle diameter of PTFE fine particles: After drying the PTFE aqueous emulsion polymerization solution, a photograph was taken at a magnification of 10,000 using a scanning electron microscope, 100 PTFE fine particles were arbitrarily selected from the taken images, and each PTFE fine particle was selected. The major axis and the minor axis were measured and obtained from the average value.

(C) PTFE concentration, surfactant concentration: About 10 g of PTFE aqueous dispersion was put in an aluminum dish (mass W ₀ ), weighed (mass W ₁ ), and dried at 120 ° C. for 1 hour (mass W ₂ ). and from 380 ° C. 35 minutes after drying the mass (weight _{W 3),} it was determined by the following equation. The surfactant concentration in the present invention is a numerical value including a fluorine-containing emulsifier and other thermal decomposition components.
PTFE concentration (% by mass) = [(W ₃ −W ₀ ) / (W ₁ −W ₀ )] × 100
Surfactant concentration (mass% / PTFE) = [(W ₂ −W ₃ ) / (W ₃ −W ₀ )] × 100

  (D) Concentration of fluorine-containing emulsifier: Methylene blue solution (12 g of sulfuric acid is gradually added to about 500 mL of water in a glass bottle, and after cooling, 0.03 g of methylene blue and 50 g of anhydrous sodium sulfate are dissolved therein, and water is added to add 1 L 4 mL) and 5 mL of chloroform were added, and 0.1 g of a 1000 to 3000-fold diluted solution of the measurement sample was added and shaken vigorously. After standing, the lower chloroform phase was collected. The collected chloroform phase was filtered with a filter having a pore size of 0.2 μm, and the absorbance at 630 nm was measured with a spectrophotometer. The chloroform phase exhibits a blue color depending on the amount of the fluorine-containing emulsifier. Using 0.1 g of a fluorine-containing emulsifier solution having a known concentration in advance, the absorbance was measured in the same manner to prepare a calibration curve, and the calibration curve was used to determine the concentration of the fluorine-containing emulsifier in the measurement sample.

  (E) Succinic acid concentration: Measured by a calibration curve method using LC-MS (liquid chromatography with a mass spectrometer).

  (F) pH: measured by the glass electrode method.

  (G) Viscosity: No. in Brookfield viscometer. Measurement was performed at 60 revolutions using one spindle.

  (H) Conductivity: Measured with a conductivity tester manufactured by Lacom.

  (I) Standard specific gravity: Measured according to ASTM D1457-91a and D4895-91a. 12.0 g of PTFE was weighed and held at 34.5 MPa for 2 minutes in a cylindrical mold having an inner diameter of 28.6 mm. The molded piece was put in an oven at 290 ° C., heated at 120 ° C./hr, held at 380 ° C. for 30 minutes, cooled at 60 ° C./hr, held at 294 ° C. for 24 minutes, and then cooled. After holding this test piece for 12 hours in a desiccator at 23 ° C., the specific gravity ratio between the molded product and water was measured by a water immersion method at 23 ° C., and this was used as the standard specific gravity.

  (J) Storage stability: The fluoropolymer aqueous dispersion was placed in a 100 ml graduated cylinder (liquid depth of about 140 mm), allowed to stand at room temperature for 1 month, and the thickness (mm) of the resulting supernatant was visually measured. . Next, the measuring cylinder was turned upside down for 30 seconds to erect again after draining, and the thickness (mm) of the deposit adhered to the lower part was measured. In this evaluation, it means that the smaller the supernatant and lower part deposits, the better the storage stability.

[Recovery test of fluorine-containing emulsifier]
(Test Example 1)
In a 2 L beaker, 50 g of weakly basic IER (trade name “Lewatit (registered trademark) MP-62WS” manufactured by LANXESS) and a fluorine-containing emulsifier (structural formula: CF ₃ CF ₂ OCF ₂ CF ₂ OCF ₂ COO ⁻ (NH ₄ ) ⁺ ) 1000 g of a 10,000 ppm aqueous solution was added and stirred for 24 hours. After stirring, the concentration of the fluorinated emulsifier in the aqueous solution was 1639 ppm, so that 8.4 g of the fluorinated emulsifier was adsorbed on the weakly basic IER. Moreover, since the weight after collect | recovering weakly basic IER and making it dry at 60 degreeC for 4 hours was 33.9g, 0.24g of fluorine-containing emulsifier will adsorb | suck per 1g.
In a 9 cc glass bottle containing a stirrer, 0.5 g of weakly basic IER adsorbing the fluorine-containing emulsifier and 5 g of a 2% aqueous solution of sodium hydroxide were added and stirred at 60 ° C. for 1 hour.
When the concentration in the aqueous solution was measured, it contained 121 ppm of the fluorine-containing emulsifier, and the recovery rate of the fluorine-containing emulsifier from the weakly basic IER was 46%.

(Test Example 2)
10000 ppm aqueous solution of 50 g of strongly basic IER (Purolite (registered trademark) A200MBOH manufactured by Purolite) and a fluorine-containing emulsifier (structural formula: CF ₃ CF ₂ OCF ₂ CF ₂ OCF ₂ COO ⁻ (NH ₄ ) ⁺ ) in a ₂ L beaker. Was added and stirred for 24 hours. After stirring, the concentration of the fluorinated emulsifier in the aqueous solution was 5 ppm, and thus 10 g of the fluorinated emulsifier was adsorbed on the strongly basic IER. Further, since the weight after collecting strongly basic IER and drying at 60 ° C. for 4 hours was 35 g, 0.28 g of the fluorinated emulsifier per 1 g was adsorbed.
A 9 cc glass bottle containing a stirrer was charged with 0.5 g of strongly basic IER adsorbing the fluorine-containing emulsifier and 5 g of a 2% aqueous solution of sodium hydroxide, and stirred at 60 ° C. for 1 hour.
When the concentration in the aqueous solution was measured, the fluorine-containing emulsifier was not contained, and the recovery rate was 0%.

  The results of Test Example 1 and Test Example 2 are shown in Table 1. This compares the recovery rate of the fluorinated emulsifier adsorbed on each IER, and it can be seen that the fluorinated emulsifier adsorbed on the weakly basic IER has better recovery efficiency than the strong basic IER.

Example 1
As fluorinated _{emulsifier, CF 3 CF 2 OCF 2 CF} 2 OCF 2 COO - using _(NH ^{4) +,} stainless steel autoclave of 100L was charged with 61L of deionized water, paraffin wax 0.6 kg, the polymerization catalyst 26.3 g of disuccinic acid peroxide was added, the interior of the autoclave was purged with nitrogen, and after reducing the pressure, the TFE monomer was introduced while stirring at 65 ° C., and emulsion polymerization was performed at a pressure of 1.8 MPa. After the polymerization, the autoclave was cooled, and the paraffin wax solidified on the top was removed to obtain 80 kg of a PTFE aqueous emulsion polymerization liquid (a). This PTFE aqueous emulsion polymerization liquid (a) has a PTFE concentration of 25% by mass, the content of the fluorinated emulsifier is 3000 ppm with respect to the PTFE mass, and the average primary particle diameter of the PTFE fine particles is 0.26 μm. The number average molecular weight was 1.3 million, the standard specific gravity of PTFE was 2.20, and the content of succinic acid was 544 ppm with respect to the mass of PTFE. Moreover, it is estimated that organic carboxylic acids other than succinic acid are not contained.
A nonionic surfactant (manufactured by Nippon Emulsifier Co., Ltd., trade name “Newcol (registered trademark) 1308FA”) and water are added to this PTFE aqueous emulsion polymerization liquid (a), and the PTFE concentration is 23% by mass. A low concentration PTFE aqueous dispersion (b) having an agent concentration of 3% based on the PTFE mass was obtained.
Nonionic surface activity by a tube pump on a column of 80 cm length and 0.9 cm inner diameter (internal volume 51 cc) packed with weak basic IER (trade name “Lewatit (registered trademark) MP62WS” manufactured by LANXESS) 100 mL of a 1.5 mass% aqueous solution of the agent (Newcol (registered trademark) 1308FA) was passed at 50 cc / hour. Subsequently, 32 L of the low concentration PTFE aqueous dispersion (b) was passed at 120 cc / hour for about 275 hours to obtain a weakly basic IER-treated PTFE aqueous dispersion (c). This weakly basic IER-treated PTFE aqueous dispersion (c) had a fluorine-containing emulsifier content of 10 ppm relative to the PTFE mass and a succinic acid content of 204 ppm relative to the PTFE mass.
Next, a non-ionized tube with a tube-type pump was filled with a strongly basic IER (manufactured by Purolite, trade name “PUROLITE (registered trademark) A200MBOH”) with a length of 80 cm and an inner diameter of 0.9 cm (internal volume 51 cc). 100 mL of a 1.5% by mass aqueous solution of a system surfactant (Newcol (registered trademark) 1308FA) was passed at 50 cc / hour. Then, 16 L of the weakly basic IER-treated PTFE aqueous dispersion (c) was passed through this column at 120 cc / hour to obtain a strongly basic IER-treated PTFE aqueous dispersion (d1). This strongly basic IER-treated PTFE aqueous dispersion (d1) had a fluorine-containing emulsifier content of 3 ppm with respect to the PTFE mass and a succinic acid content of 1 ppm or less with respect to the PTFE mass.
Next, the strongly basic IER-treated PTFE aqueous dispersion (d1) was concentrated by electrophoresis for 30 hours, and 3.6 L of a high concentration PTFE aqueous dispersion (e1) (PTFE content 67.67). 9 mass% and specific gravity 1.622) were obtained. The dry mass of the aggregate generated in the concentration operation was 40 g, and the yield in the concentration step was 84%.
Next, the obtained high-concentration PTFE aqueous dispersion (e1) was diluted with water and added with a nonionic surfactant to prepare a PTFE content of 60.7% by mass, a surfactant content. An aqueous PTFE dispersion (f1) having a content of 5.0% by mass with respect to PTFE mass was obtained. After the PTFE aqueous dispersion (f1) was allowed to stand for 1 month, the resulting supernatant was 2.3 mm, and the sediment was 4.2 mm.

(Comparative Example 1)
16 L of the weakly basic IER-treated PTFE aqueous dispersion (c) obtained in Example 1 was concentrated by electrophoresis for 44 hours, and 2.4 L of a high concentration PTFE aqueous dispersion (e2) ( The PTFE concentration was 68.1% by mass and the specific gravity was 1.625). The dry mass of the aggregate generated in the concentration operation was 106 g, and the yield in the concentration step was 57%.
Next, this high-concentration PTFE aqueous dispersion (e2) is diluted with water, and a nonionic surfactant is added to prepare a PTFE fine particle content of 60.4% by mass. An aqueous PTFE dispersion (f2) that was 5.0% by mass with respect to the mass of the PTFE fine particles was obtained. After this PTFE aqueous dispersion (f2) was allowed to stand for 1 month, the resulting supernatant was 3.8 mm, and the sediment was 5.6 mm.

  The results of Example 1 and Comparative Example 1 are shown in Table 1. The high-concentration PTFE aqueous dispersion of Example 1 had a succinic acid content of 1 ppm or less, had a short concentration time during electric concentration, and had a good concentration rate. Moreover, the amount of aggregates generated was small and the yield was high. Furthermore, it was excellent in storage stability.

  The fluorine-containing polymer aqueous dispersion of the present invention is used for coating on a glass fiber cloth and used for a roofing material of a printed circuit board or a membrane structure building, for use on a surface of a cooking utensil to improve releasability, Use after baking and stretching to make fluorine-containing polymer fibers, Use with dusting powder to prevent dusting, Use with battery active material to make binder, Add to plastic and melt It can be used for many purposes, such as for preventing dripping.

Claims (8)

A fluorine-containing polymer aqueous dispersion containing a fluorine-containing polymer, a fluorine-containing emulsifier, and an organic carboxylic acid represented by the following general formula (1) is contacted with a weakly basic anion exchange resin to form the fluorine-containing polymer. A method for producing a fluorine-containing polymer aqueous dispersion, wherein the emulsifier is adsorbed and removed, and then the organic carboxylic acid is adsorbed and removed by contact with a strongly basic anion exchange resin.
Q (CH ₂ ) _m (CH (OH)) _n COOH (1)
(In formula (1), Q is H, CH ₃ or COOH, m and n are each independently 0 or an integer of 1 to 4, and 4 ≧ n + m ≧ 1.)   The method for producing an aqueous fluoropolymer dispersion according to claim 1, wherein the fluoropolymer is polytetrafluoroethylene.   The method for producing an aqueous fluoropolymer dispersion according to claim 2, wherein the standard specific gravity of the polytetrafluoroethylene is 2.15 to 2.35.   The content of the fluorine-containing emulsifier in the fluorine-containing polymer aqueous dispersion before contacting with the weakly basic anion exchange resin is 750 ppm to 10,000 ppm with respect to the mass of the fluorine-containing polymer. A process for producing the aqueous fluoropolymer dispersion as described.   The content of the fluorine-containing emulsifier in the fluorine-containing polymer aqueous dispersion after contacting with the weakly basic anion exchange resin is 200 ppm or less with respect to the mass of the fluorine-containing polymer. A process for producing the aqueous fluoropolymer dispersion as described. The said organic carboxylic acid is a compound represented by following General formula (2), The manufacturing method of the fluorine-containing polymer aqueous dispersion in any one of Claims 1-5.
HOCO (CH ₂ ) _m COOH (2)
(In the formula (2), m is 0 or an integer of 1 to 4.)   The content of the organic carboxylic acid in the fluoropolymer aqueous dispersion before contacting with the weakly basic anion exchange resin is 100 ppm to 2000 ppm with respect to the mass of the fluoropolymer. A process for producing the aqueous fluoropolymer dispersion as described.   The content of the organic carboxylic acid in the fluoropolymer aqueous dispersion after being brought into contact with the strongly basic anion exchange resin is 100 ppm or less based on the mass of the fluoropolymer. A process for producing the aqueous fluoropolymer dispersion as described.