JP2008013669A - Method for producing aqueous fluoropolymer dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a fluoropolymer aqueous dispersion excellent in dispersion stability and mechanical stability in a high yield even when contacted with an anion exchange resin.
A method for producing an aqueous fluoropolymer dispersion comprising a step of bringing a crude fluoropolymer aqueous dispersion into contact with an anion exchange resin, wherein the crude fluoropolymer aqueous dispersion is preliminarily contacted with a nonionic interface before the above step is performed. A method for producing an aqueous fluoropolymer dispersion, comprising adding an activator and a nonionic water-soluble polymer.
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Description

The present invention relates to a method for producing an aqueous fluoropolymer dispersion.

Since the fluoropolymer aqueous dispersion can form a film having excellent chemical stability, non-adhesiveness, weather resistance, etc. by a method such as coating or impregnation, cooking utensils, piping linings, glass Widely used in applications such as cloth-impregnated membranes. In these applications, the fluoropolymer aqueous dispersion preferably has a high fluoropolymer concentration. Therefore, a fluoropolymer aqueous dispersion obtained by polymerizing a fluoromonomer in the presence of a fluorinated surfactant in an aqueous medium is used. Has been. However, in recent years, it has been desired to reduce the fluorine-containing surfactant contained in the product.

As a method of removing the fluorine-containing surfactant from the aqueous fluoropolymer dispersion, a method of removing the fluorine-containing surfactant by contacting with an anion exchange resin in the presence of a nonionic surfactant has been proposed (for example, , See Patent Document 1).
However, even if a nonionic surfactant is added, polymer aggregates are generated in the process of contact with the ion exchange resin, and problems such as a reduction in processing speed and a decrease in yield may occur.
Japanese translation of PCT publication No. 2002-532583

An object of the present invention is to provide a method for producing an aqueous fluoropolymer dispersion excellent in dispersion stability and mechanical stability in a high yield even when contact is made with an anion exchange resin.

The present invention is a method for producing an aqueous fluoropolymer dispersion comprising the step of bringing the aqueous crude fluoropolymer dispersion into contact with an anion exchange resin, wherein the crude fluoropolymer aqueous dispersion is preliminarily contacted with the nonionic interface before performing the above steps. A method for producing an aqueous fluoropolymer dispersion comprising adding an activator and a nonionic water-soluble polymer.
The present invention is a fluoropolymer composition obtained from the above method for producing an aqueous fluoropolymer dispersion.
The present invention is described in detail below.

The method for producing an aqueous fluoropolymer dispersion according to the present invention includes a nonionic surfactant and a nonionic water-soluble aqueous solution previously added to a crude fluoropolymer aqueous dispersion before the step of bringing the crude fluoropolymer aqueous dispersion into contact with an anion exchange resin. It is characterized by adding a functional polymer.
In the production method of the present invention, since the nonionic surfactant and the nonionic aqueous polymer are added in advance before the contact step, the fluorine-containing surfactant concentration is low, and the mechanical stability and the dispersion stability are improved. An excellent aqueous fluoropolymer dispersion can be obtained with good yield.

In the present invention, the crude fluoropolymer aqueous dispersion is obtained by dispersing particles comprising a fluoropolymer in an aqueous medium in the presence of a fluorine-containing surfactant.

The fluoropolymer is not particularly limited. For example, polytetrafluoroethylene [PTFE], tetrafluoroethylene [TFE] / hexafluoropropylene [HFP] copolymer [FEP], TFE / perfluoro (alkyl vinyl ether) [ PAVE] copolymer [PFA], ethylene / TFE copolymer [ETFE], polyvinylidene fluoride [PVDF], polychlorotrifluoroethylene [PCTFE] and the like.
The PTFE may be a tetrafluoroethylene [TFE] homopolymer or a modified polytetrafluoroethylene [modified PTFE]. In the present specification, the modified PTFE means a non-melt processable fluoropolymer obtained by polymerizing TFE and a small amount of monomer. Examples of the trace monomer include fluoroolefins such as HFP and chlorotrifluoroethylene [CTFE], fluoro (alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms; Fluorodioxole; perfluoroalkylethylene; ω-hydroperfluoroolefin and the like.
The fluoropolymer is preferably a perfluoropolymer, and more preferably PTFE.

The crude fluoropolymer aqueous dispersion generally has a fluoropolymer content of 5 to 70% by mass, a preferable lower limit of 20% by mass, and a preferable upper limit of 60% by mass.
The concentration of the fluoropolymer is based on the heating residue (Z) obtained by taking about 1 g (X) of the aqueous dispersion in an aluminum cup having a diameter of 5 cm, drying at 100 ° C. for 1 hour, and further drying at 300 ° C. for 1 hour. P = Z / X × 100 (%).

The particles made of the above fluoropolymer generally have an average primary particle diameter of 100 to 500 nm, preferably 200 to 400 nm.
The average primary particle size is determined by measurement using a dynamic light scattering method.

Examples of the fluorine-containing surfactant include fluorine-containing anionic surfactants.
Examples of the fluorine-containing anionic surfactant include perfluorooctanoic acid and / or a salt thereof (hereinafter, “perfluorooctanoic acid and / or a salt thereof” may be collectively referred to as “PFOA”). Perfluorooctylsulfonic acid and / or a salt thereof (hereinafter, “perfluorooctylsulfonic acid and / or a salt thereof” may be collectively abbreviated as “PFOS”).

In the present specification, the fluorinated surfactant is preferably perfluorocarboxylic acid and / or a salt thereof. When the fluorine-containing anion compound is a salt, examples of the counter ion forming the salt include an alkali metal ion or NH ₄ ⁺ , and examples of the alkali metal ion include Na ⁺ and Ka ^+. . Examples of the counter ion include NH ₄ ⁺ . When the PFOA and PFOS are salts, they are not particularly limited, and examples thereof include ammonium salts.

The fluorine-containing surfactant preferably has an average molecular weight of 1,000 or less, more preferably an average molecular weight of 500 or less, and a carbon number of 5 to 12 in terms of easy removal. preferable.

In the present invention, the aqueous crude fluoropolymer dispersion generally contains a fluorine-containing surfactant in an amount corresponding to 500 to 20000 ppm of the fluoropolymer.
In the present specification, the fluorine-containing surfactant concentration was determined by adding an equal amount of methanol to an aqueous dispersion and performing Soxhlet extraction or centrifugation, followed by high performance liquid chromatography [HPLC] described later. Is.

In the present specification, the aqueous medium is not particularly limited as long as it is a liquid containing water, and in addition to water, for example, a fluorine-free organic solvent such as alcohol, ether, ketone, paraffin wax, and / or a fluorine-containing organic solvent. May also be included.

The crude fluoropolymer aqueous dispersion can be prepared, for example, by polymerizing in the presence of the above-mentioned fluorine-containing surfactant.
The fluoromonomer used in the polymerization is not particularly limited, and examples thereof include TFE, HFP, PAVE, vinylidene fluoride [VDF], chlorotrifluoroethylene [CTFE] and the like.
The polymerization may use a fluorine-free monomer such as ethylene in addition to the fluoromonomer.
In the present invention, in the polymerization, reaction conditions such as temperature, pressure, surfactant concentration and the like can be appropriately set according to the kind and amount of the target fluoropolymer.

The aqueous dispersion of the crude fluoropolymer may be an aqueous dispersion after polymerization obtained by carrying out the polymerization, or an aqueous solution obtained through post-treatment such as concentration and dilution of the aqueous dispersion after polymerization. It may be a dispersion.
The post-treatment can be performed by a conventionally known method such as a phase separation concentration method, an ultrafiltration method, or an electric concentration method.
Examples of the phase separation method include, for example, the method described in US Pat. No. 3,037,953, and examples of the ultrafiltration method include, for example, the method described in JP-B-2-34971. Can include, for example, the method described in British Patent No. 642025.

In the method for producing a fluoropolymer of the present invention, the step of bringing the crude fluoropolymer aqueous dispersion into contact with the anion exchange resin is aimed at reducing the fluorine-containing surfactant such as PFOA.
Although the said contact process is not specifically limited, Preferably it can carry out similarly to the method of Japanese translations of PCT publication No. 2002-532583 gazette.
The contact step can be performed by contacting an anion exchanger made of a strongly basic resin that has been previously adjusted to OH type. For example, a crude fluoropolymer aqueous dispersion whose pH is adjusted to 7 to 9 is made basic. It is preferable to make contact in the environment.

In the fluoropolymer production method of the present invention, a nonionic surfactant and a nonionic water-soluble polymer are added to the crude fluoropolymer aqueous dispersion in advance before the contact step.

The nonionic surfactant in the present invention is a compound having a hydrophobic group and a hydrophilic group in the molecule, and those having an average molecular weight of less than 1000 are preferably used.
The nonionic surfactant is not particularly limited, and examples thereof include ether-type nonionic surfactants such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkylene alkyl ether, and ethylene oxide / propylene oxide blocks. Polyoxyethylene derivatives such as copolymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters and other ester-type nonionic surfactants, polyoxyethylene Examples include amine-based nonionic surfactants such as alkylamines and alkylalkanolamides.
Moreover, the nonionic surfactant which does not have an alkylphenol in a structure can be used preferably.

In the production method of the present invention, the nonionic surfactant is preferably added in an amount of 1 to 30 parts by mass with respect to 100 parts by mass of the fluoropolymer.
As for the addition amount of the said nonionic surfactant, a more preferable minimum is 5 mass parts with respect to 100 mass parts of fluoropolymers, and a more preferable upper limit is 20 mass parts.

The production method of the present invention only suppresses a decrease in dispersion stability caused by contact with a nonionic surfactant and an anion exchange resin by adding a nonionic water-soluble polymer before the above-described contact step. In addition, the yield can be improved, and an aqueous fluoropolymer dispersion having good storage stability can also be obtained. The mechanism by which each of the above effects is obtained by adding a nonionic water-soluble polymer is not clear, but the nonionic water-soluble polymer suppresses aggregation caused by contact between the ion exchange resin and the fluororesin particles. it is conceivable that.

The nonionic water-soluble polymer is a compound having a solubility in water of 0.1 mg / 100 ml or more and an average molecular weight of 10,000 to 2,000,000.
The nonionic water-soluble polymer is different from the nonionic surfactant described above in that the average molecular weight is within the above range.
The nonionic water-soluble polymer improves the mechanical stability of the aqueous dispersion obtained as the average molecular weight is higher, but if the average molecular weight is too high, the viscosity of the aqueous dispersion becomes high and handling is difficult. May be.
The solubility in water is preferably 1 mg / 100 ml or more.
The average molecular weight is preferably 10,000 to 1,000,000.

The nonionic water-soluble polymer is preferably at least one selected from the group consisting of polyoxyalkylenes such as polyvinyl pyrrolidone, polyvinyl methyl ether, polyvinyl alcohol, polyoxyethylene, and polyoxyalkylene copolymers. More preferably, at least one selected from the group consisting of polyvinyl pyrrolidone, polyvinyl methyl ether, polyoxyalkylene and polyvinyl alcohol, and at least one selected from the group consisting of polyoxyalkylene, polyvinyl pyrrolidone and polyvinyl alcohol More preferably, it is polyvinyl pyrrolidone or polyethylene oxide.
Only 1 type may be used for the said exemplary compound, respectively, and 2 or more types may be used for it.

Each average molecular weight of the polyvinyl pyrrolidone and the polyvinyl methyl ether has a more preferable lower limit of 20,000 and a more preferable upper limit of 1,000,000.

The polymerization degree of the polyvinyl alcohol is preferably 300 to 6000. The higher the degree of polymerization, the higher the average molecular weight and the mechanical stability. However, when the degree of polymerization is too high, the viscosity of the aqueous dispersion becomes high and handling may be difficult. The polymerization degree has a more preferable lower limit of 500 and a more preferable upper limit of 5000.

The saponification degree of the polyvinyl alcohol is preferably 70 to 99 mol%. Within this range, the higher the degree of saponification, the lower the water solubility, and the lower the degree of saponification, the higher the water solubility. However, the above range is suitable for preparing a stable aqueous dispersion. A more preferred lower limit is 75 mol%, and a more preferred upper limit is 98 mol%, still more preferably 95 mol%.

Examples of the polyoxyalkylene include polyethylene oxide and polypropylene oxide.
The average molecular weight of the polyethylene oxide has a more preferable lower limit of 100,000 and a more preferable upper limit of 1,000,000.
The polyoxyalkylene copolymer may be a block copolymer.

In the method for producing an aqueous fluoropolymer dispersion of the present invention, the nonionic water-soluble polymer is preferably added in an amount of 0.00001 to 5 parts by mass with respect to 100 parts by mass of the fluoropolymer.
When it is less than 0.00001 parts by mass with respect to 100 parts by mass of the fluoropolymer, dispersion stability and polymer yield may be insufficient. When it exceeds 5 parts by mass with respect to 100 parts by mass of the fluoropolymer, The viscosity of the aqueous dispersion may increase, making handling difficult.
The amount of the nonionic water-soluble polymer added is preferably 0.0001 parts by mass, more preferably 0.0005 parts by mass, and more preferably 1 part by mass with respect to 100 parts by mass of the fluoropolymer. A more preferred upper limit is 0.1 part by mass.

If the manufacturing method of the fluoropolymer aqueous dispersion of this invention includes the above-mentioned contact process, it will contain conventionally well-known processes, such as a phase-separation concentration method, an ultrafiltration method, an electric concentration method, etc. Also good.

The aqueous fluoropolymer dispersion obtained from the method for producing an aqueous fluoropolymer dispersion of the present invention is excellent in mechanical stability, dispersion stability and storage stability. Furthermore, since this aqueous dispersion has a low concentration of the fluorine-containing surfactant, it can be made into a composition or molded article in which the physical properties are not deteriorated due to the mixing of the fluorine-containing surfactant.
The fluoropolymer composition obtained from the method for producing an aqueous fluoropolymer dispersion of the present invention is also one aspect of the present invention.

The aqueous fluoropolymer dispersion obtained from the method for producing an aqueous fluoropolymer dispersion of the present invention is excellent in mechanical stability, dispersion stability and storage stability.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Each amount in each Example and Comparative Example is based on mass unless otherwise specified.

(1) Average primary particle diameter It was determined by measurement using a dynamic light scattering method.

(2) Fluoropolymer concentration (P)
About 1 g (X) of the aqueous dispersion was put in an aluminum cup having a diameter of 5 cm, dried at 100 ° C. for 1 hour, and further dried at 300 ° C. for 1 hour, based on the heating residue (Z), the formula: P = Z / XX It is determined at 100 (%).

(3) Nonionic surfactant content (N)
About 1 g (Xg) of the aqueous dispersion was placed in an aluminum cup having a diameter of 5 cm, and heated residue (Yg) heated at 100 ° C. for 1 hour. Further, the obtained heated residue (Yg) was heated at 300 ° C. for 1 hour. It is calculated from the heated residue (Zg) by the formula: N = [(Y−Z) / Z] × 100 (%).

(4) Concentration of fluorine-containing surfactant in aqueous dispersion After adding an equal amount of methanol to the aqueous dispersion for coagulation and Soxhlet extraction, high performance liquid chromatography [HPLC] is performed under the following conditions. Was determined by In calculating the fluorine-containing surfactant concentration, a calibration curve obtained by HPLC measurement with a known concentration of the fluorine-containing surfactant at the above eluate and conditions was used.
(Measurement condition)
Column: ODS-120T (4.6φ × 250 mm, manufactured by Tosoh Corporation)
Developing solution: acetonitrile / 0.6% perchloric acid aqueous solution = 1/1 (vol / vol%)
Sample volume: 20 μL
Flow rate: 1.0 ml / min Detection wavelength: UV 210 nm
Column temperature: 40 ° C

(5) Mechanical stability Using a tube pump equipped with a Tygon tube having an outer diameter of 7.9 mm and an inner diameter of 4.8 mm, 100 ml of an aqueous dispersion was circulated at a rate of 200 ml / min at 35 ° C. for 1 hour. Then, the aggregate was collected with a 200 mesh stainless steel net, washed with water, measured for mass after drying at 120 ° C. for 1 hour, and the mass ratio with respect to the polymer initially contained in the aqueous dispersion used in the test was determined. Asked.

(6) Standing stability 500 g of an aqueous dispersion was placed in a 500 ml capacity polybin, placed in a constant temperature bath at 40 ° C., and allowed to stand for 1 month. The aqueous dispersion after standing was stirred for 30 minutes at room temperature with a desktop ball mill, and then aggregates were collected with a 200 mesh stainless steel net, washed with water, measured for mass after drying at 120 ° C. for 1 hour, and tested. The mass ratio with respect to the polymer initially contained in the aqueous dispersion used in was determined.

Example 1
(1) Nonionic surfactant Leocol TD90D (Lion Corporation) was added to a PTFE aqueous dispersion having a polytetrafluoroethylene [PTFE] concentration of 30%, an average primary particle size of 250 nm, and an ammonium perfluorooctanoate [PFOA] concentration of 2000 ppm (vs. PTFE). Polyoxyethylene alkyl ether manufactured by Eisai) is added in an amount corresponding to 15% of PTFE, and Alcox E-30 (Polyoxyethylene manufactured by Meisei Chemical Co., Ltd., molecular weight of about 300,000) is added to 0.3% of PTFE. Was added in the form of a 5% aqueous solution so as to achieve an amount, and mixed uniformly to prepare an aqueous PTFE dispersion.
The PTFE concentration of the obtained aqueous dispersion was 28.5%.

(2) 250 ml of OH type anion exchange resin Amberjet AMJ4002 (trade name, manufactured by Rohm and Haas) was charged, and 250 mL of 5% aqueous solution of Leocol TD90D was placed on a 20 mm diameter column adjusted to 40 ° C. After passing through the solution, 7500 ml (8932 g) of the PTFE aqueous dispersion obtained in (1) was passed at a rate of 500 ml / hr. Furthermore, the fluoropolymer aqueous dispersion was recovered to the point where 250 mL of a 5% aqueous solution of Leocol TD90D was passed.
The obtained aqueous fluoropolymer dispersion was 9185 g, and the fluoropolymer concentration was 27.6%. That is, the amount of polymer after passing through (the amount of recovered aqueous dispersion × polymer concentration) was 2544 g with respect to 2549 g of polymer before passing through (amount of aqueous dispersion × polymer concentration), and the yield was 99.8%. Met.
The PFOA concentration was below the detection limit (10 ppm of the fluoropolymer mass).

To the fluoropolymer aqueous dispersion, 127 g of Leocol TD90D was added, stirred uniformly, and allowed to stand at 70 ° C. Since the aqueous dispersion separated into two phases after 12 hours, the lower phase was recovered to obtain 3632 g of an aqueous dispersion having a fluoropolymer concentration of 70%.
Furthermore, water and a nonionic surfactant (Leocor TD90D) were added to adjust the fluoropolymer concentration to 60% and the Leocol TD90D concentration to 5% (with respect to the fluoropolymer), and the mechanical stability test and the stationary stability were performed. As a result, the polymer aggregate by the mechanical stability test was 0.6%, and the polymer aggregate by the stationary stability test was 2%.

Comparative Example 1
(1) A PTFE aqueous dispersion was prepared in the same manner as in Preparation Example 1 except that an equal amount of water was added instead of the aqueous solution of Alcox in Example 1. The PTFE concentration of the obtained aqueous dispersion was 28.5%.

(2) Using the aqueous dispersion obtained in Comparative Example (1), contact with an anion exchange resin was performed in the same manner as in Example 1 (2).
The obtained fluoropolymer aqueous dispersion was 8907 g, and the fluoropolymer concentration was 26.9%. That is, the yield after the ion exchange treatment was 94%.
Each test was performed on a dispersion having a fluoropolymer concentration of 60% and a nonionic surfactant concentration of 5% (vs. fluoropolymer) obtained by adding water and a nonionic surfactant (Leocor TD90D) after the contact. As a result, the polymer agglomerate by the mechanical stability test was 2.4%, and the polymer agglomerate by the storage stability test was 5%.

Comparative Example 2
In the dispersion obtained from the contact step and concentration in Comparative Example 1 (2), Alcox E-30 (polyoxyethylene manufactured by Meisei Chemical Co., Ltd., molecular weight of about 300,000) was 0.3% with respect to the fluoropolymer. Each test was performed on a dispersion obtained by adding a 5% aqueous solution so that the amount of the dispersion was uniform and mixing them uniformly. The polymer agglomerate by mechanical stability test was 1.2% and the polymer agglomerate by storage stability test was 5%.

The difference in the aggregation rate of each test shown by the above-mentioned Examples and Comparative Examples appears as a large difference in mass processing (continuous production), so it was considered an industrially useful method.

The aqueous fluoropolymer dispersion obtained from the method for producing an aqueous fluoropolymer dispersion of the present invention is excellent in mechanical stability, dispersion stability and storage stability. Furthermore, since this aqueous dispersion has a low concentration of the fluorine-containing surfactant, it can be made into a composition or molded article in which the physical properties are not deteriorated due to the mixing of the fluorine-containing surfactant.

Claims (8)

A method for producing an aqueous fluoropolymer dispersion comprising a step of contacting a crude fluoropolymer aqueous dispersion with an anion exchange resin, comprising:
A non-ionic surfactant and a nonionic water-soluble polymer are added to the crude fluoropolymer aqueous dispersion in advance before the step is performed. The method for producing an aqueous fluoropolymer dispersion according to claim 1, wherein the nonionic surfactant does not contain a benzene ring in the hydrophobic group. The method for producing an aqueous fluoropolymer dispersion according to claim 1 or 2, wherein the nonionic water-soluble polymer has an average molecular weight of 10,000 to 2,000,000. The method for producing an aqueous fluoropolymer dispersion according to any one of claims 1 to 3, wherein the nonionic water-soluble polymer is at least one selected from the group consisting of polyoxyalkylene, polyvinyl pyrrolidone and polyvinyl alcohol. . The production of the aqueous fluoropolymer dispersion according to any one of claims 1 to 4, wherein 0.0001 to 5 parts by mass of a nonionic water-soluble polymer is added to 100 parts by mass of the aqueous crude fluoropolymer dispersion. Method. The method for producing an aqueous fluoropolymer dispersion according to any one of claims 1 to 5, wherein the fluoropolymer constituting the crude fluoropolymer aqueous dispersion is polytetrafluoroethylene [PTFE]. The method for producing an aqueous fluoropolymer dispersion according to any one of claims 1 to 6, wherein the fluoropolymer constituting the crude fluoropolymer aqueous dispersion has an average primary particle diameter of 100 to 500 nm. A fluoropolymer composition obtained from the method for producing an aqueous fluoropolymer dispersion according to any one of claims 1 to 7.