WO2007074901A1 - Aqueous fluoropolymer dispersion - Google Patents

Abstract

The invention aims at providing an aqueous fluoropolymer dispersion which is suppressed in the viscosity increase due to liquid temperature rise and is therefore excellent in storage stability in spite of its low contents of a fluorinated surfactant and a fluorine-free surfactant. An aqueous fluoropolymer dispersion comprising an aqueous medium containing a fluorine-free surfactant and fluoropolymer particles dispersed therein, characterized in that the amount of the fluoropolymer particles is 35 to 70% by mass based on the dispersion, that the fluorinated surfactant content of the dispersion is 50ppm or below based on the amount of the fluoropolymer in terms of solid matter, that the content of the fluorinine-free surfactant is 1 to 5% by mass based on the amount of the fluoropolymer in terms of solid matter, and that the fluoropolymer is a modified polytetrafluoroethylene.

Description

 Specification

 Fluoropolymer aqueous dispersion

 Technical field

 [0001] The present invention relates to an aqueous fluoropolymer dispersion.

 Background art

 In aqueous fluoropolymer dispersions, various surfactants have heretofore been used for the purpose of maintaining the dispersion stability and storage stability of the fluoropolymer.

For example, Patent Document 1 uses an ethoxylated aliphatic alcohol type nonionic surfactant as a dispersant in a dispersion having an average particle size of 0.25 _i um polytetrafluoroethylene [PTFE] particles. By doing so, it is described that the generation of sludge near room temperature can be suppressed.

 [0003] In Patent Document 2, (1) an aqueous dispersion of PTFE is concentrated by an ultrafiltration method, a fluorine-containing surfactant is added in an amount of 0 to 0.1% by weight, and a stabilizing emulsifier is added. Concentrated aqueous dispersion containing 0.5 to 5% by weight of solids, (2) Alkylphenol in aqueous dispersion containing 20% by weight of PTFE and ammonium perfluorooctanoate 0.88] It describes a method for obtaining an aqueous dispersion having a PFOA amount of 60 ppm and a PTFE concentration of 59% by removing 98% of the PFOA by concentrating by ultrafiltration in the presence of a stable emulsifier having a structure. . However, this document does not describe the stability of the aqueous fluoropolymer dispersion when the PFOA in the aqueous fluoropolymer dispersion is further reduced.

 [0004] Patent Document 3 and Patent Document 4 disclose aqueous fluoropolymer dispersions with reduced PFOA. These references point out the problem of increasing the viscosity of the resulting fluoropolymer aqueous dispersion when PFOA is reduced. To overcome this problem, non-fluorine-based surfactants are added to fluoropolymers 1 to 1. A method of adding in the range of 12% has been proposed.

[0005] Patent Document 5 describes an aqueous PTFE dispersion in which the amount of a non-ionic surfactant is 1.5 to 4% by weight of PTFE particles. However, there is no specific description regarding the content of the fluorine-containing surfactant in this PTFE aqueous dispersion. [0006] Patent Document 6 describes a method of obtaining a fluoropolymer aqueous dispersion by adding a nonionic emulsifier and removing the fluorine-containing emulsifier by contacting with an anion exchanger. However, this method has a problem that the fluoropolymer in the obtained aqueous fluoropolymer dispersion is not highly concentrated and is not practical.

 Patent Document 1: Japanese Patent Application Laid-Open No. 47-6539

 Patent Document 2: JP-A-55-120630

 Patent Document 3: US Patent Application Publication No. 2004Z171736

 Patent Document 4: US Patent Application Publication No. 2004Z186219

 Patent Document 5: JP 2000-160118 A

 Patent Document 6: Special Table 2002-532583 ([Claims], [0025]) Disclosure of Invention

 Problems to be solved by the invention

[0007] In view of the above situation, the object of the present invention is to suppress the increase in viscosity due to an increase in the liquid temperature despite the low fluorine-containing surfactant concentration and the fluorine-free surfactant concentration, and is excellent in storage stability. It is to provide an aqueous fluoropolymer dispersion.

 Means for solving the problem

 [0008] The present invention relates to a fluoropolymer aqueous dispersion in which particles comprising a fluoropolymer are dispersed in an aqueous medium in the presence of a fluorine-free surfactant, and the particles comprising the fluoropolymer are composed of the fluoropolymer aqueous solution. 35 to 70% by mass of the dispersion, and the fluorine-containing surfactant in the aqueous fluoropolymer dispersion is below the amount corresponding to 50 ppm of the solid content of the fluoropolymer, and the fluorine-free surfactant is The fluoropolymer is an aqueous fluoropolymer dispersion characterized in that the amount corresponds to 1% by mass or more and 5% by mass or less of the solid content of the fluoropolymer, and the fluoropolymer is modified polytetrafluoroethylene.

 The present invention is described in detail below.

 [0009] The aqueous fluoropolymer dispersion of the present invention is one in which particles having a fluoropolymer force are dispersed in an aqueous medium in the presence of a fluorine-free nonionic surfactant.

In the aqueous fluoropolymer dispersion, the fluoropolymer is a modified polytetra Fluoroethylene [modified PTFE].

 The modified PTFE means a copolymer of TFE and a small amount of monomer other than TFE, which is non-melt processable.

 Examples of the trace monomer include fluoroolefins such as HFP and CTFE, fluoro having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms (alkyl butyl etherol); Rosioxol; perfluoroalkylethylene; ω-hydroperfluoroolefin.

In the modified PTFE, the very small proportion monomer content ί the total monomer units of the very small proportion monomer units derived from or, usually 0.001 to 1 Monore _^0/0, preferably ί or 0.005 to 0. 5 Monore _^0/0, the more favorable Mashiku in the range of 0.01 to 0.1 Monore ^_0/0.

 In the present specification, “the content (mol%) of a trace monomer unit in all monomer units” means the monomer from which the above “all monomer units” is derived, that is, a fluoropolymer. This means the mole fraction (mol%) of the trace monomer from which the trace monomer unit is derived, based on the total amount of the monomer that constitutes.

[0010] The average particle size of the fluoropolymer particles is 50 to 400 nm, preferably 100 to 350 nm.

 The average particle size is determined by measuring the transmittance of the 550 nm projection light with respect to the unit length of the aqueous dispersion with the fluoropolymer particle concentration adjusted to 0.22 mass%, and the directional direction diameter in the transmission electron micrograph. The permeability power is determined based on a calibration curve with the average particle diameter determined in the above.

The aqueous fluoropolymer dispersion of the present invention has a fluoropolymer particle strength of 35 to 70% by mass of the aqueous fluoropolymer dispersion.

 The preferred lower limit of the content of the fluoropolymer particles in the aqueous fluoropolymer dispersion is 40% by mass, a more preferred lower limit is 50% by mass, and a preferred upper limit is 65% by mass.

The content of the fluoropolymer particles is based on the heating residue (Z) obtained by taking about 1 lg (X) of a sample in an aluminum cup with a diameter of 5 cm, drying at 100 ° C for 1 hour, and further drying at 300 ° C for 1 hour. Formula: P = ZZXX 100 (%) [0012] The aqueous medium in the present invention 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 Z or fluorine-containing organic It may also contain a solvent.

[0013] The aqueous fluoropolymer dispersion of the present invention may have a fluorine-free surfactant as a surfactant within the range described below.

 The aqueous fluoropolymer dispersion may contain only one kind of the above non-fluorine-containing surfactant, or may contain two or more kinds! /.

[0014] The fluorine-free surfactant may be either a non-one surfactant or a char-on surfactant as long as it has a compound power not containing fluorine. It is preferably a non-ionic surfactant.

[0015] The non-ionic surfactant is not particularly limited as long as it is a non-ionic compound containing no fluorine (non-fluorine-containing non-ionic surfactant), and a known one is used. Can be used.

 Examples of the nonionic surfactant include ether type nonionic surfactants such as polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkylene alkyl ether, and the like; ethylene oxide Z propylene Polyoxyethylene derivatives such as oxide block copolymers; sorbitan fatty acid esters

Ester-type surfactants such as polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester; polyoxyethylene alkylamine, alkyl alkanolamide, etc. Amine noion surfactants; and the like.

 [0016] In the compound constituting the above-described surfactant, the hydrophobic group may be any of an alkylphenol group, a linear alkyl group, and a branched alkyl group, but the alkylphenol group is present in the structure. However, it is preferable that the compound does not have a benzene ring.

 [0017] Among the above-mentioned nonionic surfactants, polyoxyethylene alkyl ether type nonionic surfactants are preferred.

The polyoxyethylene alkyl ether type non-ionic surfactant has 1 carbon atom. Those having a polyoxyethylene alkyl ether structure having an alkyl group of 0 to 20 are preferred, and those having a polyoxyethylene alkyl ether structure having an alkyl group having 10 to 15 carbon atoms are more preferred. The alkyl group in the polyoxyethylene alkyl ether structure preferably has a branched structure.

 Examples of the polyoxyethylene alkyl ether type non-ionic surfactant include Genapol X080 (product name, manufactured by Clariant), Taditol 9—S-15 (product name, manufactured by Clariant), Neugen TDS-80 ( Product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). Examples of the non-ionic surfactant include those having an ethylene oxide propylene oxide [EO-PO] block copolymer structure, which is known as a pull nick type surfactant.

The EO-PO Roh having a block copolymer structure - The on-surfactants, EO content is preferably 30 to 90 wt%, more preferably 35 to 85 wt%, more preferably 40-60 weight ⁰ / It is ₀ , and the average molecular weight force multiplier <is 1000 to 10000, more preferably <is 2000 to 9 000, and more preferably 4000 to 8000. Examples of the pull-mouth nick type surfactant include Pluronic PE6800, Pluronic PE6400 (product name, manufactured by BASF), Genapol PF40, Genapol PF80 (product name, manufactured by Clariant), and the like.

 [0018] Among the fluorine-free surfactants in the present invention, as a surfactant, for example, alkylsulfonic acid and its salt, alkylsulfuric acid ester and its salt, alkylsulfosuccinic acid ester and its salt, oxyalkyl Sulfonated acids and their salts. As a non-fluorine-containing surfactant, a combination of a nonionic surfactant and a cation surfactant improves the storage stability and improves the liquid temperature in the resulting aqueous dispersion. Can suppress the increase in viscosity.

 [0019] In the aqueous fluoropolymer dispersion of the present invention, the fluorine-free surfactant is an amount corresponding to 1% by mass or more and 5% by mass or less of the fluoropolymer.

The above-mentioned aqueous fluoropolymer dispersion has a fluorine-free surfactant amount within the above-mentioned range, and is stored without significantly impairing crack resistance and mechanical stability, although it is lower than conventional aqueous fluoropolymer dispersions. Good stability and increased liquid temperature Accordingly, the increase in viscosity can be suppressed.

 The fluorine-free surfactant is preferably in an amount corresponding to 1 to 3.5% by mass of the particles having a fluoropolymer force.

 The more preferable lower limit of the content of the fluorine-free surfactant in the aqueous fluoropolymer dispersion is an amount corresponding to 2% by mass of the particles made of the fluoropolymer. In this specification, the content (N) of the non-fluorine-containing surfactant is the residue of heating (Yg) obtained by taking about 1 lg (Xg) of a sample in an aluminum cup with a diameter of 5 cm and heating at 100 ° C for 1 hour. Furthermore, the heating residue (Yg) obtained was calculated from the heating residue (Zg) heated at 300 ° C for 1 hour from the formula: N = [(YZ) / Z] X 100 (%) It is.

[0020] The aqueous fluoropolymer dispersion of the present invention may contain a fluorine-containing surfactant.

 The fluorine-containing surfactant is not particularly limited as long as it has the ability to contain a fluorine-containing compound and exhibits an emulsifying action. However, as the fluorine-containing compound to be constituted, those having an average molecular weight of 1000 or less are preferably removed. In terms of ease, those having an average molecular weight of 500 or less are more preferred, and those having 5 to 12 carbon atoms are preferred.

[0021] The above-mentioned fluorine-containing surfactants include those containing fluorine-containing compounds such as fluorine-containing carboxylic acid compounds and fluorine-containing sulfonic acid compounds (hereinafter referred to as "fluorine-containing surfactant activities"). Fluorine-containing carboxylic acid compounds and cocoons or their salts are more preferred.

 As the fluorine-containing compound, for example, perfluorooctanoic acid and Ζ or a salt thereof (hereinafter, “perfluorooctanoic acid and Ζ or a salt thereof” are collectively abbreviated as “PFOA”. Perfluorooctylsulfonic acid and Z or a salt thereof (hereinafter, “perfluorooctylsulfonic acid and Z or a salt thereof” may be abbreviated as “PFOS”). Etc.

 In the present invention, the fluorosurfactant is preferably perfluorocarboxylic acid and Z or a salt thereof.

When the fluorine-containing compound is a salt, examples of the counter ion forming the salt include alkali metal ions or NH +, and examples of the alkali metal ion include Na +, Ka +, etc. As the counter ion, NH + is preferable. PFOA and above

 Four

 When PFOS is a salt, it is not particularly limited, and examples thereof include an ammonium salt.

[0022] In the aqueous fluoropolymer dispersion of the present invention, the amount of the fluorine-containing surfactant is not more than the amount corresponding to 50 ppm of the fluoropolymer.

 The concentration of the fluorine-containing surfactant is preferably not more than an amount corresponding to 20 ppm, more preferably not more than an amount corresponding to 10 ppm.

 In the present specification, the content of the fluorine-containing surfactant is determined by performing high-performance liquid chromatography [HPLC] under the conditions described below after adding Soxhlet extraction with the same amount of methanol as the aqueous fluoropolymer dispersion. It is measured by.

[0023] The aqueous fluoropolymer dispersion of the present invention is obtained by (1) polymerizing a fluoropolymer and (2) adjusting the respective contents of the fluoropolymer, the fluorine-containing surfactant and the fluorine-free surfactant. Can do.

[0024] The step (1) can be performed by a known method such as suspension polymerization or emulsion polymerization.

 As the fluorine-containing monomer, non-fluorine-containing monomer, and additives such as a polymerization initiator and a chain transfer agent used in each of the above polymerizations, known ones can be used as appropriate. In the above-mentioned surfactants can be used.

 From the viewpoint of polymerization efficiency, each of the above polymerizations is preferably carried out in the presence of the above-mentioned fluorine-containing surfactant in an amount of from 0.0001 to LO mass% of the aqueous medium. The amount of the fluorine-containing surfactant is preferably 0.001% by mass or more of the aqueous medium, more preferably 1% by mass or more.

 [0025] In the step (2), depending on the amount of the fluorine-containing surfactant used in the step (1), the content of the fluoropolymer in the fluoropolymer dispersion obtained from the step (1), etc. The means, conditions, etc. can be selected as appropriate.

In the step (2), the contents of the fluoropolymer and the fluorine-containing surfactant are the phase separation method described in the pamphlet of International Publication No. 2004Z050719, the ion exchange resin method described in JP 2002-532583 A, It can be adjusted by performing a conventionally known operation such as a membrane treatment method described in 55-120630, an electrophoresis method described in UK Patent No. 642025, an evaporation method described in JP 2003-531232, etc. Aqueous, but can be obtained The amount of non-fluorine containing surfactant used in each operation must be limited so that the amount of non-fluorine containing surfactant in the dispersion does not exceed the scope of this application.

 In the above step (2), each operation may be performed once or may be performed twice or more. When each operation is performed twice or more, the same operation may be repeated, You can combine different operations.

 [0026] In the step (2), the content of the non-fluorine-containing surfactant is, for example, after the above-described operation, which limits the amount of the non-fluorine-containing surfactant used in each of the above-mentioned operations. It can be prepared by adding a fluorine-free surfactant.

 [0027] The aqueous fluoropolymer dispersion of the present invention has a mechanical stability with a good dispersion stability despite the extremely low content of fluorine-containing surfactants and fluorine-free surfactants and high fluoropolymer concentration. Excellent in stability and storage stability. Although the above fluoropolymer mono-aqueous dispersion has an extremely low content of each of the above-mentioned surfactants, the crack resistance and mechanical stability are not greatly impaired, it has excellent storage stability, and the liquid temperature. The increase in viscosity associated with the increase can be suppressed.

 When the above fluoropolymer aqueous dispersion contains the above-mentioned surfactant as a fluorine-free surfactant, it is particularly excellent in storage stability and can easily suppress an increase in viscosity accompanying an increase in liquid temperature.

[0028] The aqueous fluoropolymer dispersion of the present invention can be processed into, for example, a fluoropolymer powder, a molded article and the like.

 The fluoropolymer powder has a very low content of the fluorine-containing surfactant, and thus is useful as an excellent molded material. The fluoropolymer powder can be prepared by a conventional method according to the desired use.

[0029] The aqueous fluoropolymer dispersion of the present invention can be coated on a coating, cast film, impregnated body or the like as it is or with various additives.

The above fluoropolymer aqueous dispersion is, for example, an oven lining, cooking utensils such as ice trays, electric wires, pipes, ship bottoms, high-frequency printed circuit boards, conveyor belts, coating materials on iron bottom plates; fiber base materials, woven fabrics / nonwoven fabrics, etc. Can be processed into an impregnated material, etc. The fiber substrate is not particularly limited. For example, glass fiber, carbon fiber, And aramid fibers (Kepler (registered trademark) fibers, etc.).

 Processing of the aqueous fluoropolymer dispersion can be performed by a conventionally known method. The invention's effect

 [0030] Since the aqueous fluoropolymer dispersion of the present invention has the above-described configuration, the content of the fluorine-containing surfactant and the fluorine-free surfactant is extremely low, and the fluoropolymer mono has a high concentration. Furthermore, it is excellent in dispersion stability and storage stability, and can suppress an increase in viscosity accompanying an increase in liquid temperature.

 BEST MODE FOR CARRYING OUT THE INVENTION

[0031] The present invention will be described in more detail with reference to synthesis examples and test examples, but the present invention is not limited to these synthesis examples and test examples.

 In each synthesis example and test example, “part” represents “part by mass” unless otherwise specified.

[0032] The measurement performed in each test example was performed by the following method.

 (1) Average particle size

 Average particle size determined by measuring the transmittance of 550 nm projection light with respect to the unit length of an aqueous fluoropolymer dispersion adjusted to 0.22% by weight of the solid content of rosin and the directional direction diameter in a transmission electron micrograph Based on the calibration curve with the diameter, it was determined from the transmittance.

(2) Fluoropolymer concentration (P)

 About lg (X) sample is placed in an aluminum cup with a diameter of 5 cm, dried at 100 ° C for 1 hour, and further 300

. C, based on the residue (z) dried for 1 hour, and determined by the formula: p = zzxx 100 (%).

 [0033] (3) Fluorine-containing surfactant concentration

 The obtained aqueous dispersion was added with an equal amount of methanol and subjected to Soxhlet extraction, and then subjected to high performance liquid chromatography [HPLC] under the following conditions. In calculating the fluorine-containing surfactant concentration, a calibration curve obtained by HPLC measurement with the above-mentioned eluate and conditions was used for a known concentration of the fluorine-containing surfactant.

 (Measurement condition)

 Column; ODS—120 mm (4.6 x 250 mm, manufactured by Toso Co., Ltd.)

 Developing solution: acetonitrile ZO. 6 mass% perchloric acid aqueous solution = 1Z1 (vol / vol%)

Sample volume: 20 / z L Detection wavelength: UV210nm

 Column temperature; 40 ° C

[0034] (4) Content of non-fluorine-containing surfactant (N)

 About 1 lg (Xg) of the sample is placed in an aluminum cup with a diameter of 5 cm, and heated residue (Yg) heated at 100 ° C for 1 hour, and the obtained heated residue (Yg) is further heated at 300 ° C for 1 hour. Heated residue (Z 8) was calculated from the equation ^ = [−2) 2] 100 (%).

 (5) Viscosity

 Using a B-type rotational viscometer (manufactured by Tokyo Keiki Co., Ltd.), the viscosity at 25 ° C or 35 ° C was measured in accordance with JIS K 6893.

[0035] (6) Mechanical stability

 50g of fluoropolymer aqueous dispersion was subjected to high-speed shearing with a homogenizer CM-1 00 (manufactured by Azwan Co., Ltd.) at 15000rpm for 5 minutes, and then filtered through a 400 mesh stainless steel wire mesh to collect the aggregates. Dry and weigh at 100 ° C. The percentage of the aggregate relative to the fluoropolymer in the aqueous fluoropolymer dispersion was determined as mechanical stability. The smaller this value, the more stable the fluoropolymer aqueous dispersion is against shearing.

 (7) Crack limit thickness (CCT)

 Degreased aluminum plate (size: 10cm x 15cm) is immersed in 100ml of fluoropolymer aqueous dispersion, dried at room temperature on a 45 ° slope for 5 minutes, further dried at 380 ° C for 10 minutes, and then cooled to room temperature Check for cracks with a 10X magnifier. Of the immersed aluminum plates that did not generate cracks, the maximum film thickness was measured with a film thickness meter to obtain CCT.

 (8) Storage stability

 500 ml of an aqueous fluoropolymer dispersion was placed in a plastic container and allowed to stand in a temperature-controlled room at 25 ° C or 40 ° C for 2 months. After standing, the mixture was gently stirred and then filtered through a stainless steel 400 mesh, and the agglomerate remaining on the mesh was dried. Those with poor storage stability generate a large amount of agglomerates.

[0036] Synthesis Example 1 Polytetrafluoroethylene [PTFE (TFE homopolymer; the same shall apply hereafter)] dispersion (PTFE content) in a cylindrical glass container with an inner volume of 5 L and a diameter of 16 cm equipped with a paddle type stirrer with a diameter of 6 cm 25%, average particle size 240nm, perfluorooctanoic acid ammonium [PFOA] content: amount equivalent to 2000ppm of PTFE) After adding 2000g and adjusting pH to 9 with 10% aqueous ammonia solution, 120rpm Polyoxyethylene alkyl ether type nonionic surfactant Neugen TDS-80 (Daiichi Kogyo Seiyaku Co., Ltd.) 125g was added as a fluorine-free surfactant under stirring of Mixed. Subsequently, the temperature of the hot water bath was raised while stirring, the internal temperature reached 70 ° C, the stirring was stopped, the internal temperature was maintained at 70 ° C for 6 hours, and then the separated supernatant phase was removed, The PTFE aqueous dispersion phase was separated.

 The resulting PTFE aqueous dispersion (concentrated aqueous dispersion) has a PTFE concentration of 70.5%, a fluorine-free surfactant content equivalent to 3.0% of PTFE, and a PFOA content of 48 ppm of PTFE. The amount was equivalent to

 Neugen TDS-80 and ion-exchanged water are added to this aqueous dispersion to adjust the PTFE content to 60% and the fluorine-free surfactant to an amount equivalent to 6.0% of PTFE. It was.

 [0037] Synthesis Example 2

 The same as Synthesis Example 1 except that PTFE was changed to modified PTFE (perfluoropropyl butyl ether [PP VE] modified, modified amount 0.1 mol%, average particle size 240 nm) in Synthesis Example 1. Thus, a concentrated aqueous dispersion having a modified PTFE concentration of 69.5%, a fluorine-free surfactant concentration of 2.8%, and a modified PFOA amount of 45 ppm was obtained.

 To this aqueous dispersion, Neugen TDS-80 and ion-exchanged water are added so that the modified PTFE content is 60% and the fluorine-free surfactant is equivalent to 6.0% of the modified PTFE. Adjusted.

[0038] Synthesis Example 3

Only the ion-exchanged water is added to the concentrated aqueous dispersion obtained in Synthesis Example 2, and the modified PTFE content is 60%, and the concentration of the fluorine-free surfactant is 2.8% of the modified PTFE. An aqueous dispersion was prepared. [0039] Synthesis Example 4

 PTFE dispersion (i) (PTFE content 30%, average particle diameter 220nm, PFOA content: PTFE equivalent to 2000ppm, fluorine-free surfactant (product name: Genapol X080, Clariant) content: An amount equivalent to 5% of PTFE) 2000g, an anion exchange resin (product name: Amberlite IRA402J, manufactured by Rohm 'And' Haas) 50ml in a column (diameter 2cm) filled with a temperature of 50 ° C, space Through the conditions of speed [SV] 2, the PTFE concentration is 30%, the fluorine-free surfactant content is equivalent to 4.9% of PTFE, and the PFOA content is equivalent to lOppm of PTFE. 1980 g of PTFE dispersion (ii) was obtained.

[0040] 60 g of a fluorine-free surfactant (product name: Genapol X080, manufactured by Clariant) was added to the PTFE dispersion (ii) and mixed uniformly at 40 ° C in a hot water bath. Subsequently, the temperature of the hot water bath was raised while stirring, and the internal temperature reached 60 ° C. Then, stirring was stopped and the internal temperature was maintained at 60 ° C for 4 hours to remove the separated supernatant phase. The PTFE aqueous dispersion separated from the PTFE aqueous dispersion phase has a PTFE concentration of 69.8%, a fluorine-free surfactant content, an amount equivalent to 2.5% of SpTFE, and a PFOA content of 2 ppm of PTFE. Is equivalent to o

 Ion exchange water and Genapol X080 were added to this to adjust the amount of PTFE 60% and fluorine-free surfactant to 6% of PTFE.

[0041] Synthesis Example 5

 Except for changing PTFE to modified PTFE (0.05 mol% modified with HFP, average particle size 220 nm), ion exchange treatment and concentration were performed in the same manner as in Synthesis Example 4 to obtain a modified PTFE concentration of 70.5. %, A fluorine-free surfactant content corresponding to 2.5% of the modified PTFE, and a PFOA content corresponding to 2 ppm of the modified PTFE were obtained.

 Ion exchange water and the above-mentioned non-fluorine-containing surfactant were added thereto, and the modified PTFE 60% and the content of non-fluorine-containing surfactant were adjusted to an amount corresponding to 6% of the modified PTFE.

[0042] Synthesis Example 6

Modified PTFE 60%, fluorine-free surfactant so that the concentration of surfactant containing no fluorine is 4.8% A fluoropolymer aqueous dispersion was prepared in the same manner as in Synthesis Example 5 except that the surfactant and water were added.

[0043] Synthesis Example 7

 In addition to the aqueous fluoropolymer dispersion of Synthesis Example 6, the alkylsulfonic acid Na salt [SAS]

(Manufactured by Clariant) was added in an amount corresponding to lOOOOppm of the modified PTFE.

[0044] Examples and Comparative Examples

 Viscosity, mechanical stability, crack limit thickness [CCT] and storage stability were measured for the aqueous dispersions of each synthesis example.

 Table 1 shows the measurement results.

[0045] [Table 1]

[0046] In Table 1, the content of each surfactant is expressed as a ratio to the fluoropolymer. When the results were compared, all of the aqueous dispersions of each example were excellent in storage stability and could suppress an increase in viscosity accompanying an increase in the liquid temperature. The viscosity increased remarkably with the increase, and in particular, the storage stability at 40 ° C was inferior. Industrial applicability

[0047] Since the aqueous fluoropolymer dispersion of the present invention has the above-described configuration, the content of the fluorine-containing surfactant and the fluorine-free surfactant is extremely low, and the fluoropolymer mono has a high concentration. Furthermore, it is excellent in dispersion stability and storage stability, and can suppress an increase in viscosity accompanying an increase in liquid temperature.

Claims

The scope of the claims  [1] A fluoropolymer aqueous dispersion in which particles made of a fluoropolymer are dispersed in an aqueous medium in the presence of a fluorine-free surfactant.  The particles made of the fluoropolymer are 35 to 70% by mass of the aqueous fluoropolymer dispersion,  The fluorine-containing surfactant in the aqueous fluoropolymer dispersion is below the amount corresponding to 50 ppm of the solid content of the fluoropolymer,  The fluorine-free surfactant is an amount corresponding to 1% by mass or more and 5% by mass or less of the solid content of the fluoropolymer,  The fluoropolymer is a modified polytetrafluoroethylene  An aqueous fluoropolymer dispersion characterized by the above. [2] The aqueous fluoropolymer dispersion according to claim 1, wherein the fluorine-free surfactant is in an amount corresponding to 1 to 3.5% by mass of the particles having a fluoropolymer power. [3] The fluorine-free surfactant is a fluorine-free non-ionic surfactant, or 2. The aqueous fluoropolymer dispersion according to 2. [4] The fluoropolymer aqueous dispersion according to any one of [1] to [3], wherein the non-fluorine-containing surfactant comprises a non-fluorine-containing compound having no hydrophobic group and a benzene ring. [5] The aqueous fluoropolymer dispersion according to any one of claims 1 to 4, wherein the fluorine-containing surfactant comprises a fluorine-containing compound having a molecular weight of 1000 or less. [6] The aqueous fluoropolymer dispersion according to any one of claims 1 to 5, wherein the fluorine-containing surfactant is composed of a fluorine-containing compound having 5 to 12 carbon atoms. 7. The aqueous fluoropolymer dispersion according to any one of claims 1 to 6, wherein the fluorine-containing surfactant also has perfluorocarboxylic acid or a salt power thereof.