JP2024027028A - Method for producing polytetrafluoroethylene mixed aqueous dispersion - Google Patents

Abstract

To provide a polytetrafluoroethylene mixed aqueous dispersion that can form a coating layer with a good appearance and resistance to crack or the like, and a method for producing the same.SOLUTION: A method for producing a polytetrafluoroethylene mixed aqueous dispersion includes mixing a predetermined polytetrafluoroethylene aqueous dispersion 1 with a predetermined polytetrafluoroethylene aqueous dispersion 2 so that the solid content mass ratio of the polytetrafluoroethylene aqueous dispersion 1 to the polytetrafluoroethylene aqueous dispersion 2 is 90/10-10/90.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a polytetrafluoroethylene mixed aqueous dispersion.

Fluorine-containing polymers are widely used to impart antifouling properties, weather resistance, and the like. For example, cloth sheets (covered woven fabrics), which are made by coating or impregnating fluorine-containing polymers on glass fiber woven fabrics and baking them to form coatings, are used as roofing materials for membrane structure buildings, conveyor belts in food production lines, etc. (For example, Patent Document 1).
In particular, polytetrafluoroethylene tends to have better heat resistance than other fluoropolymers, and is preferably used in applications that require heat resistance. The polytetrafluoroethylene coating is formed using, for example, an aqueous polytetrafluoroethylene dispersion.

However, since polytetrafluoroethylene coatings have low flexibility and poor flexibility, there is a problem in that the coating tends to peel off, crack, etc. in areas where large strains are applied. A similar problem also existed in cloth sheets using polytetrafluoroethylene as the fluoropolymer.

Patent No. 3118468

An object of the present invention is to provide a polytetrafluoroethylene mixed aqueous dispersion capable of forming a film that has an excellent appearance and is resistant to cracks, etc., and a method for producing the same.

As a result of intensive studies, the present inventors found that the above problem could be solved by the following configuration.

(1) The following polytetrafluoroethylene aqueous dispersion 1 and the following polytetrafluoroethylene aqueous dispersion 2 were prepared so that the solid content mass ratio was polytetrafluoroethylene aqueous dispersion 1/polytetrafluoroethylene aqueous dispersion 2 = 90/ A method for producing a polytetrafluoroethylene mixed aqueous dispersion, which comprises mixing at a ratio of 10 to 10/90.
[Polytetrafluoroethylene aqueous dispersion 1]
Step A1 of polymerizing a non-fluorinated monomer in an aqueous medium to obtain a solution 1 containing a polymer containing units based on the non-fluorinated monomer;
Step A2 of polymerizing tetrafluoroethylene in the solution 1 without substantially adding a surfactant to the solution 1 to obtain an aqueous emulsion containing polytetrafluoroethylene particles;
Obtained by a method comprising step A3 of adding a nonionic surfactant to the aqueous emulsion and then concentrating the aqueous emulsion to obtain a polytetrafluoroethylene aqueous dispersion,
An aqueous polytetrafluoroethylene dispersion, wherein the amount of the non-fluoromonomer used is 200 mass ppm or less relative to the amount of tetrafluoroethylene fed to the polymerization system.
[Polytetrafluoroethylene aqueous dispersion 2]
An aqueous dispersion different from polytetrafluoroethylene aqueous dispersion 1, comprising polytetrafluoroethylene particles and an aqueous medium.
(2) Step B1 in which the polytetrafluoroethylene aqueous dispersion 2 is subjected to emulsion polymerization of tetrafluoroethylene in an aqueous medium in the presence of a surfactant to obtain an aqueous emulsion; and a nonionic interface to the aqueous emulsion. The polytetrafluoroethylene mixed aqueous dispersion according to (1), which is the polytetrafluoroethylene aqueous dispersion 2 obtained from a method comprising step B2 of adding an activator and then concentrating the aqueous emulsion. manufacturing method.
(3) Polytetrafluoroethylene mixed aqueous dispersion containing the following polytetrafluoroethylene 1 and the following polytetrafluoroethylene 2 in a mass ratio of polytetrafluoroethylene 1/polytetrafluoroethylene 2 = 90/10 to 10/90. liquid.
[Polytetrafluoroethylene 1]
Polytetrafluoroethylene particles having an average primary particle diameter of 0.1 to 0.5 μm and containing no detectable CF ₂ chain oligomer group having 6 to 34 carbon atoms.
[Polytetrafluoroethylene 2]
Polytetrafluoroethylene particles having an average primary particle diameter of 0.1 to 0.5 μm and different from polytetrafluoroethylene 1.

According to the present invention, it is possible to provide a polytetrafluoroethylene mixed aqueous dispersion capable of forming a film that has an excellent appearance and is resistant to cracks and the like, and a method for producing the same.

The meanings of terms in the present invention are as follows.
"Unit" is a general term for an atomic group derived from one monomer molecule that is directly formed by polymerization of monomers.
A numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as lower and upper limits.

The method for producing a polytetrafluoroethylene (hereinafter also referred to as "PTFE") mixed aqueous dispersion of the present invention is to prepare a PTFE aqueous dispersion 1 and a PTFE aqueous dispersion 2, which will be described later, with a solid content mass ratio of PTFE aqueous dispersion. This is a method of mixing liquid 1/PTFE aqueous dispersion 2 in a ratio of 90/10 to 10/90.

PTFE aqueous dispersion 1 is prepared by polymerizing a non-fluorinated monomer in an aqueous medium to obtain a solution 1 containing a polymer containing units based on the non-fluorinated monomer, Step A1;
Step A2 of polymerizing tetrafluoroethylene in solution 1 without substantially adding a surfactant to solution 1 to obtain an aqueous emulsion containing polytetrafluoroethylene particles;
Obtained by a method comprising step A3 of adding a nonionic surfactant to an aqueous emulsion and then concentrating the aqueous emulsion to obtain a polytetrafluoroethylene aqueous dispersion,
This is an aqueous polytetrafluoroethylene dispersion in which the amount of non-fluoromonomer used is 200 mass ppm or less relative to the amount of tetrafluoroethylene supplied to the polymerization system.

<Step A1>
Step A1 is a step of polymerizing a non-fluorinated monomer in an aqueous medium to obtain a solution 1 containing a specific polymer.
Below, first, the materials used in step A1 will be explained in detail, and then the procedure of step A1 will be explained in detail.

(Non-fluorine monomer)
A non-fluorine monomer is a monomer that does not contain a fluorine atom.
The non-fluorine-based monomer usually has a polymerizable group, and the number of polymerizable groups is preferably 1 to 3, more preferably 1.
As the polymerizable group, an ethylenically unsaturated group is preferable. More specifically, examples include acryloyl group, methacryloyl group, vinyl ether group, vinyl ester group, vinyl group, and allyl group, with acryloyl group, methacryloyl group, vinyl ester group, and vinyl ether group being preferred.

As the non-fluorine monomer, a monomer represented by formula (1) is preferable.
Formula (1) CH ₂ =CR ¹¹ -L ¹ -R ¹²
R ¹¹ represents a hydrogen atom or an alkyl group. The number of carbon atoms in the alkyl group is preferably 1 to 3, more preferably 1.
L ¹ represents a single bond, -CO-O-*, -O-CO-* or -O-. * represents the bonding position with R ¹² . For example, when L ¹ is -CO-O-*, formula (1) represents CH ₂ =CR ¹¹ -CO-O-R ¹² .
R ¹² represents a hydrogen atom, an alkyl group, an alkenyl group or a nitrile group. However, when L ¹ is a single bond, R ¹² is a nitrile group.
The number of carbon atoms in the alkyl group and alkenyl group is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4.
The alkyl group may be chain or cyclic. When the alkyl group is cyclic, it corresponds to a cycloalkyl group.
The alkenyl group may be chain or cyclic.

The monomer represented by formula (1) includes a monomer represented by formula (1-1), a monomer represented by formula (1-2), and a monomer represented by formula (1-3). Monomers selected from the group consisting of monomers represented by formula (1-4) and monomers represented by formula (1-4) are preferred.
Formula (1-1) CH ₂ =CR ¹¹ -CO-O-R ¹³
Formula (1-2) CH ₂ =CR ¹¹ -O-CO-R ¹⁴
Formula (1-3) CH ₂ =CR ¹¹ -OR ¹⁵
Formula (1-4) CH ₂ =CR ¹¹ -R ¹⁶
The definition of R ¹¹ is as described above.
R ¹³ represents a hydrogen atom, an alkyl group or an alkenyl group, preferably an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 1 to 6 carbon atoms.
R ¹⁴ represents an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group.
R ¹⁵ represents an alkyl group, preferably a linear alkyl group or a cyclic alkyl group.
R ¹⁶ represents a nitrile group.

Examples of non-fluorine monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, Examples include methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, and cyclohexyl vinyl ether.
The non-fluorine monomers may be used alone or in combination of two or more.
As the non-fluorine monomer, a monomer represented by formula (1-1) or a monomer represented by formula (1-2) is preferable, and a monomer represented by formula (1-2) is preferable, and a monomer represented by formula (1-2) is preferred, and R ¹³ is an alkyl group. Monomers represented by 1) are more preferred. Since the monomer represented by formula (1-1) and the monomer represented by formula (1-2) have an ester group or a carboxy group that is a water-affinity group, the monomer or The polymer has water affinity. Therefore, especially at low concentrations, the monomers and their polymers are believed to be stably dispersed in aqueous media without the need for surfactants.

(Specific polymer)
The specific polymer is a polymer containing units based on non-fluoromonomers.
The specific polymer usually contains only units based on non-fluoromonomers, but may contain units based on fluoromonomers as long as the effects of the present invention are not impaired. That is, a fluorine-based monomer may be used in step A1 in addition to the non-fluorine-based monomer. The fluorine-based monomer is a monomer having a fluorine atom, and includes, for example, TFE.
The content of units based on non-fluorine monomers in the specific polymer is preferably 90% by mass or more, more preferably 95% by mass or more, based on the total units of the specific polymer. The upper limit is 100% by mass.

(aqueous medium)
Examples of the aqueous medium include water and a mixture of water and a water-soluble organic solvent.
Examples of water-soluble organic solvents include tert-butanol, propylene glycol, and dipropylene glycol. In the case of a mixture of water and a water-soluble organic solvent, the concentration of the water-soluble organic solvent is preferably 10% by mass or less.
It is preferable that the aqueous medium is only water.

(Polymerization initiator)
In step A1, a polymerization initiator may be used. That is, a polymerization initiator may be used during polymerization of the non-fluoromonomer.
As the polymerization initiator, water-soluble radical initiators and water-soluble redox catalysts are preferred.
Preferred water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide.
Water-soluble redox catalysts include oxidizing agents such as bromate or its salts, chloric acid or its salts, persulfuric acid or its salts, permanganic acid or its salts, hydrogen peroxide, sulfurous acid or its salts, and hydrogen sulfite. or a salt thereof, a combination with a reducing agent such as thiosulfuric acid or a salt thereof, or an organic acid is preferable. Among these, a combination of bromic acid or a salt thereof and sulfite or a salt thereof (eg ammonium sulfite), and a combination of permanganic acid or a salt thereof (eg potassium permanganate) and oxalic acid are more preferable.
As the polymerization initiator, ammonium persulfate alone or a mixed system of persulfate and disuccinic acid peroxide is preferable, and ammonium persulfate alone or a mixed system of ammonium persulfate and disuccinic acid peroxide is more preferable.
The polymerization initiators may be used alone or in combination of two or more.
As for the method of charging the polymerization initiator, the entire amount thereof may be charged into the polymerization system before starting the polymerization reaction, or it may be added continuously or intermittently to the polymerization system.

(Procedure of process A1)
In step A1, a non-fluorinated monomer is polymerized in an aqueous medium. Specifically, it is preferable to mix the non-fluoromonomer and an aqueous medium and polymerize the non-fluoromonomer in the resulting mixture.
Note that, as described above, a fluoromonomer may be used in combination, if necessary.

The amount of the non-fluorine-based monomer used is 200 mass ppm or less, and 1 to 150 mass ppm or less with respect to the amount of TFE supplied to the polymerization system (the amount of TFE used) used in step A2 described below. It is preferably 5 to 100 ppm by mass, more preferably 5 to 50 ppm by mass.
As a method for charging the non-fluorine monomer, initial batch addition is preferred, in which the entire amount is charged into the polymerization system before starting the polymerization reaction.

The content of the non-fluoromonomer in the dispersion obtained by mixing the non-fluoromonomer and the aqueous medium is preferably 0.000015 to 0.0030% by mass based on the total mass of the dispersion. , 0.000075 to 0.0023% by mass is more preferable.
Since the entire amount of the non-fluorine-based monomer is usually polymerized to form a specific polymer, the concentration of the specific polymer in the obtained solution 1 falls within the above numerical range.
The above non-fluorinated monomer concentration and specific polymer concentration are concentrations when the obtained solution 1 is used in step A2 without being diluted with an aqueous medium. When the obtained solution 1 is diluted with an aqueous medium to have the above specific polymer concentration and the diluted solution is used in step A2, a solution with a high concentration corresponding to the dilution ratio is produced in step A1. Although the dilution ratio is not particularly limited, it is preferably 10 times or less.

The amount of the polymerization initiator used is preferably 0.2 to 1000% by mass, more preferably 0.2 to 500% by mass, based on the total amount of non-fluoromonomers.

The amount of the polymerization initiator used is preferably 0.1 to 1000 mol%, more preferably 0.1 to 300 mol%, based on the total amount of non-fluorine monomers.

The polymerization temperature of the non-fluorine monomer is preferably 10 to 95°C, more preferably 50 to 90°C. The polymerization time is preferably 5 to 400 minutes, more preferably 5 to 300 minutes, even more preferably 5 to 200 minutes.
The pressure conditions during polymerization are preferably reduced pressure conditions or normal pressure conditions. Among these, 0 to 2.0 MPa is preferable, 0 to 1.0 MPa is more preferable, and 0 to 0.5 MPa is even more preferable.
Alternatively, the polymerization may be carried out using a TFE atmosphere as the atmosphere during the polymerization. Note that the polymerization of the non-fluorinated monomer in an aqueous medium usually proceeds with priority over the polymerization of TFE.

Through the above step A1, a solution 1 containing the specific polymer is obtained.
The specific polymer may be dissolved in the solution 1 or may be dispersed in the aqueous medium in the form of particles. During TFE polymerization in step A2, which will be described later, the specific polymer is not an emulsifier, but due to the balance of interfacial tension between the aqueous medium and the PTFE particles, the specific polymer exists at the boundary between the aqueous medium and the PTFE particles, and the aqueous medium of the PTFE particles It is presumed that this contributes to stabilizing the dispersion inside.
The particle diameter of the specific polymer particles is preferably 0.1 to 100 nm, more preferably 0.1 to 50 nm.

Note that the solution 1 obtained in step A1 may contain unreacted non-fluorine monomer. Further, the atmosphere in the polymerization system in step A1 may be a TFE-containing atmosphere in consideration of step A2. In such a case, it is considered that a part of the specific polymer in step A2 may become a polymer containing TFE units.
From another perspective, the PTFE particles obtained in step A2 are not limited to particles consisting of a physical mixture of a specific polymer and PTFE, but are TFE copolymers having units based on non-fluorine monomers. It is also considered that particles containing

<Step A2>
Step A2 is a step of polymerizing TFE in the solution 1 obtained in Step A1 without substantially adding a surfactant to the solution 1 to obtain an aqueous emulsion containing PTFE particles.
Below, first, the materials used in step A2 will be explained in detail, and then the procedure of step A2 will be explained in detail.

(TFE)
In step A2, TFE is used.

(other monomers)
In step A2, monomers other than TFE may be further used within a range that does not impair the effects of the present invention.
Other monomers include monomers having polar groups (hereinafter also simply referred to as "specific monomers"). Since the polar group in the specific monomer shows interaction with the aqueous medium, it is assumed that it is located between TFE and the aqueous medium during TFE polymerization and exhibits a surfactant-like function. . As a result, TFE polymerization progresses well and chain transfer is also suppressed.

Examples of the polar group contained in the specific monomer include a sulfonic acid group, a sulfonic acid group, a carboxylic acid group, a carboxylic acid group, a phosphonic acid group, and a phosphonic acid group. Among these, the group represented by formula (A) or the group represented by formula (B) is preferable, and the group represented by formula (A) is more preferable, since the generation of fluorine-based oligomers is further suppressed. .
Formula (A) -SO ₃ M
Formula (B) -COOM
In formula (A) and formula (B), M represents a hydrogen atom, NH ₄ or an alkali metal atom. Examples of the alkali metal atom include a lithium atom, a sodium atom, and a potassium atom.

The specific monomer usually has a polymerizable group, and the number of polymerizable groups is preferably 1 to 3, more preferably 1.
As the polymerizable group, an ethylenically unsaturated group is preferable. More specifically, examples include acryloyl group, methacryloyl group, vinyl ether group, vinyl ester group, vinyl group, and allyl group, with acryloyl group, methacryloyl group, vinyl ester group, and vinyl ether group being preferred.

As the specific monomer, a monomer represented by formula (3) is preferable since the production of fluorine-based oligomers is further suppressed.
Formula (3) CR ³¹ R ³² = CR ³³ -L ³ -R ³⁴
In formula (3), R ³¹ and R ³² each independently represent a hydrogen atom or a fluorine atom.

R ³³ represents a hydrogen atom, a fluorine atom, or an alkyl group optionally substituted with a fluorine atom. Among these, a hydrogen atom or a fluorine atom is preferable since copolymerizability with TFE is better.
The term "alkyl group optionally substituted with a fluorine atom" means an alkyl group in which at least one hydrogen atom may be substituted with a fluorine atom.
The number of carbon atoms in the alkyl group which may be substituted with a fluorine atom is preferably 1 to 3, more preferably 1.

L ³ represents a single bond or a divalent linking group. Among these, a single bond is preferred because it has better copolymerizability with TFE.
The divalent linking group may be, for example, a divalent hydrocarbon group (a divalent saturated hydrocarbon group, a divalent aromatic hydrocarbon group, an alkenylene group, an alkynylene group). The hydrogen group may be linear, branched or cyclic, and examples thereof include alkylene groups.The number of carbon atoms is preferably 1 to 20.Also, the divalent aromatic hydrocarbon group has a carbon number of 1 to 20. 5 to 20, and examples thereof include phenylene groups.Alkenylene groups having 2 to 20 carbon atoms and alkynylene groups having 2 to 20 carbon atoms may also be used.), divalent heterocyclic groups , -O-, -S-, -SO ₂ -, -C(O)-, -Si(R ^a ) ₂ -, -N(R ^b )-, and groups combining two or more of these are mentioned. It will be done. Here, R ^a represents an alkyl group (preferably having 1 to 10 carbon atoms) or a phenyl group. R ^b represents a hydrogen atom or an alkyl group (preferably having 1 to 10 carbon atoms).
Examples of groups combining two or more of the above-mentioned groups include -OC(O)-, -C(O)N(R ^b )-, alkylene group -O-alkylene group, alkylene group -OC(O)-alkylene group, alkylene group -Si(R ^a ) ₂ -phenylene group -Si(R ^a ) ₂ .
In addition, the said divalent hydrocarbon group may have a substituent. Examples of the substituent include halogen atoms (eg, fluorine atoms and chlorine atoms). That is, the hydrogen atom in the divalent hydrocarbon group may be substituted with a halogen atom.

R ³⁴ represents a group represented by the above formula (A) or a group represented by the above formula (B).

The monomer represented by formula (3) includes the monomer represented by formula (3-1), the monomer represented by formula (3-2), and the monomer represented by formula (3-3). from the monomer represented by the formula (3-4), the monomer represented by the formula (3-5), and the monomer represented by the formula (3-6). Monomers selected from the group consisting of: are preferred, and monomers represented by formula (3-1) are more preferred.
Formula (3-1) CR ³¹ R ³² =CR ³³ -R ³⁴
Formula (3-2) CR ³¹ R ³² =CR ³³ -(CF ₂ ) _m1 -R ³⁴
Formula (3-3) CR ³¹ R ³² =CR ³³ -(CF ₂ C(CF ₃ )F) _m2 - R ³⁴
Formula (3-4) CR ³¹ R ³² =CR ³³ -O-(CFR ³⁵ ) _m3 -R ³⁴
Formula (3-5) CR ³¹ R ³² =CR ³³ -O-(CF ₂ CFR ³⁵ O) _m4 -CF ₂ CF ₂ -R ³⁴
Formula (3-6) CR ³¹ R ³² =CR ³³ -CF ₂ -O-(CF(CF ₃ )CF ₂ O) _m5 -CF(CF ₃ )-R ³⁴

In formulas (3-1) to (3-6), the definitions of R ³¹ to R ³⁴ are as described above.
In formula (3-2), m1 represents an integer from 1 to 10.
In formula (3-3), m2 represents an integer from 1 to 5.
In formula (3-4), m3 represents an integer from 1 to 10. ^R35 represents a fluorine atom or _CF3 .
In formula (3-5), m4 represents an integer from 1 to 10. The definition of R ³⁵ is as described above.
In formula (3-6), m5 represents 0 or an integer from 1 to 10.

A specific example of the specific monomer is ammonium vinylsulfonate.
The specific monomers may be used alone or in combination of two or more.

(Polymerization initiator)
In step A2, a polymerization initiator may be used. That is, a polymerization initiator may be used during the polymerization of TFE.
Examples of the polymerization initiator used include the polymerization initiators described in step A1.
As the polymerization initiator, a mixed system of persulfate and disuccinic acid peroxide is preferable, and a mixed system of ammonium persulfate and disuccinic acid peroxide is more preferable.
The amount of the polymerization initiator used is preferably 0.10% by mass or more, more preferably 0.10 to 1.5% by mass, and 0.20 to 1.0% by mass, based on the total amount of TFE supplied to the polymerization system. % is more preferred.

(Stabilizing aid)
In step A2, a stabilizing aid may be used.
As the stabilizing aid, paraffin wax, fluorine solvent, and silicone oil are preferred, and paraffin wax is more preferred. Paraffin wax may be liquid, semi-solid, or solid at room temperature. Among these, saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of paraffin wax is preferably 40 to 65°C, more preferably 50 to 65°C.
The stabilizing aids may be used alone or in combination of two or more.

(others)
In addition, in step A2, monomers other than TFE and the specific monomer may be used within a range that does not impair the effects of the present invention, but since various properties of PTFE are superior, the amount of TFE used is , is preferably 99.5% by mass or more, more preferably 99.8% by mass or more, based on the total amount of monomers used in step A2.

(Procedure of step A2)
During step A2, substantially no surfactant is added to solution 1. That is, in step A2, TFE is polymerized in the solution 1 without substantially adding a new surfactant to the solution 1.
A surfactant is a compound having a hydrophilic group (eg, a polar group) and a hydrophobic group (eg, a hydrocarbon group). The definition of the polar group is the same as the definition of the polar group contained in the specific monomer.
Examples of the surfactant include known surfactants, including nonionic surfactants and ionic surfactants, and more specifically, hydrocarbon-containing surfactants and fluorine-containing surfactants. Can be mentioned. The definition of the hydrocarbon-containing surfactant is as described below.
In step A2, it is preferable that at least one selected from the group consisting of a hydrocarbon-containing surfactant and a fluorine-containing surfactant is not substantially added to the solution 1.
The above-mentioned "substantially not added" means that no surfactant is added, or even if it is added, the amount of surfactant added is 200 mass ppm or less with respect to the total mass of the solution 1. It means that. The lower limit is not particularly limited, but is preferably 0 mass ppm. That is, it is preferable that no surfactant is added to the solution 1 in step A2.

TFE is charged into the polymerization system (that is, the polymerization reaction vessel) by a conventional method. For example, TFE is continuously or intermittently introduced into the polymerization system so that the polymerization pressure is a predetermined pressure.
When using a polymerization initiator, the polymerization initiator may be added to the polymerization system all at once, or may be added in portions.

When using a specific monomer, the amount of the specific monomer used relative to the total amount of TFE is preferably 0.150% by mass or less. That is, the amount of the specific monomer charged relative to the total amount of TFE charged is preferably 0.150% by mass or less.
From the viewpoint of stability of the emulsion during polymerization, the amount of the specific monomer to be used based on the total amount of TFE is preferably 0.100% by mass or less, more preferably 0.090% by mass or less. Further, from the viewpoint of improving the molecular weight, the amount of the specific monomer to be used based on the total amount of TFE is preferably 0.005% by mass or more, and more preferably 0.010% by mass or more.
In addition, when using two or more types of specific monomers, the total usage amount of the specific monomers may be within the above range.

When using a specific monomer, the amount of the specific monomer used based on the total amount of TFE is preferably 0.150 mol% or less. In other words, the amount of the specific monomer charged relative to the total amount of TFE is preferably 0.150 mol% or less.
From the viewpoint of stability of the emulsion during polymerization, the amount of the specific monomer to be used relative to the total amount of TFE is preferably 0.100 mol% or less, more preferably 0.090 mol% or less. Further, from the viewpoint of improving the molecular weight, the amount of the specific monomer to be used relative to the total amount of TFE is preferably 0.001 mol% or more, more preferably 0.005 mol% or more.
In addition, when using two or more types of specific monomers, the total usage amount of the specific monomers may be within the above range.

The polymerization temperature is preferably 10 to 95°C, more preferably 15 to 90°C. The polymerization pressure is preferably 0.5 to 4.0 MPa, more preferably 0.6 to 3.5 MPa. The polymerization time is preferably 50 to 520 minutes, more preferably 50 to 450 minutes, even more preferably 50 to 300 minutes.

Note that Step A1 and Step A2 may be performed continuously in the same polymerization reaction vessel.
Further, in the production method of the present invention, it is sufficient that the specific polymer is formed in step A1, and step A2 may be performed before the non-fluorine monomer is completely consumed in step A1.

By the above procedure, an aqueous emulsion in which PTFE is dispersed in the form of particles (an aqueous emulsion containing PTFE particles) is obtained. The concentration of PTFE particles in the aqueous emulsion is preferably 10 to 45% by mass, more preferably 10 to 30% by mass, and even more preferably 10 to 25% by mass, based on the total amount of the aqueous emulsion. Within the above range, the PTFE particles in the aqueous emulsion can be coagulated more easily, and clouding of the coagulated liquid can be suppressed.
The average primary particle diameter of the PTFE particles is preferably 100 to 500 nm, more preferably 150 to 300 nm.
The average primary particle diameter of the PTFE particles corresponds to D50 measured by a laser scattering particle size distribution analyzer.

The PTFE in the PTFE particles obtained by the above procedure usually contains TFE units as a main component. The main component is intended to have a content of TFE units of 99.700% by mass or more, preferably 99.900% by mass or more, based on all the units of PTFE. The upper limit is 100% by mass.
When PTFE contains units based on specific monomers, the content of units based on specific monomers is preferably 0.005 to 0.150% by mass, and 0.010 to 0.0% by mass based on the total units of PTFE. .100% by mass is more preferable.
In addition, when using two or more types of specific monomers, the total content of units based on each specific monomer may be within the above range.
When PTFE contains units based on non-fluorine monomers, the content of units based on non-fluorine monomers is preferably 200 mass ppm or less, and 1 to 150 mass ppm based on the total units of PTFE. It is more preferably 5 to 100 ppm by mass, even more preferably 5 to 50 ppm by mass.
In addition, when using two or more types of non-fluorine monomers, the total content of units based on each non-fluorine monomer may be within the above range.

<Step A3>
Step A3 is a step of adding a nonionic surfactant to the aqueous emulsion obtained in Step A2, and then concentrating the aqueous emulsion to obtain a PTFE aqueous dispersion. That is, a nonionic surfactant is added to the PTFE low concentration aqueous dispersion (corresponding to the above aqueous emulsion) obtained in step A2, and then the PTFE low concentration aqueous dispersion is concentrated to produce a PTFE high concentration. This is a step of obtaining an aqueous dispersion (corresponding to the above-mentioned PTFE aqueous dispersion). By carrying out step A3, an aqueous PTFE dispersion having a PTFE particle concentration higher than that of the aqueous dispersion is obtained.
Below, first, the materials used in step A3 will be explained in detail, and then the procedure of step A3 will be explained in detail.

(Nonionic surfactant)
Examples of the nonionic surfactant include nonionic surfactants.
Moreover, as the nonionic surfactant, a nonionic surfactant represented by formula (4) and a nonionic surfactant represented by formula (5) are preferable.
Formula (4): R ⁴¹ -O-A-H
Formula (5): R ⁵¹ -C ₆ H ₄ -O-B-H
In the formula, R ⁴¹ represents an alkyl group having 8 to 18 carbon atoms. A represents a polyoxyalkylene chain composed of 5 to 20 oxyethylene groups and 0 to 2 oxypropylene groups.
In the formula, R ⁵¹ represents an alkyl group having 4 to 12 carbon atoms. B represents a polyoxyethylene chain composed of 5 to 20 oxyethylene groups.
Furthermore, as the nonionic surfactant, a nonionic surfactant represented by formula (6) is also preferable.
Formula (6): R ⁶¹ -ODH
In the formula, R ⁶¹ represents an alkyl group having 8 to 18 carbon atoms. D represents a polyoxyalkylene chain composed of 5 to 20 oxyethylene groups and 0.1 to 3 oxybutylene groups.

In formula (4), the alkyl group represented by R ⁴¹ has 8 to 18 carbon atoms, preferably 10 to 16 carbon atoms, and more preferably 12 to 16 carbon atoms. When the number of carbon atoms is 18 or less, the PTFE particles are difficult to sediment even when the PTFE aqueous dispersion is left for a long period of time, and the storage stability is excellent. Further, when the number of carbon atoms is 8 or more, the surface tension of the PTFE aqueous dispersion becomes low, and the permeability and wettability are excellent.
In formula (4), the hydrophilic group A is preferably a polyoxyalkylene chain composed of 7 to 12 oxyethylene groups and 0 to 2 oxypropylene groups. Among these, it is preferable that the number of oxypropylene groups in A is 0.5 to 1.5, since the defoaming property is good.

In formula (5), the alkyl group represented by R ⁵¹ has 4 to 12 carbon atoms, preferably 6 to 10 carbon atoms, and more preferably 8 to 9 carbon atoms. When the number of carbon atoms in the alkyl group is 4 or more, the surface tension of the aqueous PTFE dispersion becomes low, resulting in excellent permeability and wettability. When the number of carbon atoms is 12 or less, even if the PTFE aqueous dispersion is left for a long period of time, the PTFE particles are difficult to sediment, and the storage stability is excellent.
In formula (5), the number of oxyethylene groups in B, which is a hydrophilic group, is preferably 6 to 16, more preferably 7 to 12.

In formula (6), the alkyl group represented by R ⁶¹ has 8 to 18 carbon atoms, preferably 10 to 16 carbon atoms, and more preferably 12 to 16 carbon atoms. When the number of carbon atoms is 18 or less, the PTFE particles are difficult to sediment even when the PTFE aqueous dispersion is left for a long period of time, and the storage stability is excellent. Further, when the number of carbon atoms is 8 or more, the surface tension of the PTFE aqueous dispersion becomes low, and the permeability and wettability are excellent.
In formula (6), the hydrophilic group D is preferably a polyoxyalkylene chain having 7 to 12 oxyethylene groups and 0.1 to 3 oxybutylene groups. Among these, the case where the number of oxybutylene groups in D is 0.5 to 2 is preferable because the defoaming property is good. Further, the number of oxybutylene groups is more preferably 0.7 to 1.7, and even more preferably 0.9 to 1.5. The number of oxyethylene groups is preferably 6 to 15, more preferably 7 to 12.

The average molecular weight of the nonionic surfactant represented by formula (4), the average molecular weight of the nonionic surfactant represented by formula (5), and the nonionic interface represented by formula (6) The average molecular weight of each active agent is preferably 450 to 800, more preferably 500 to 750, and even more preferably 550 to 700.

Examples of the nonionic surfactant represented by formula (4) include 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 ) ₉ -OCH(CH ₃ )CH ₂ -OH, C ₁₆ H ₃₃ -( Examples thereof include OC ₂ H ₄ ) ₁₀ -OH and HC(C ₅ H ₁₁ )(C ₇ H ₁₅ )-(OC ₂ H ₄ ) ₉ -OH. Commercially available products include Tergitol (registered trademark) 15S series manufactured by Dow Corporation and Lionol (registered trademark) TD series manufactured by Lion Corporation.
Examples of the nonionic surfactant represented by formula (5) include C ₈ H ₁₇ -C ₆ H ₄ -(OC ₂ H ₄ ) ₁₀ -OH, C ₉ H ₁₉ -C ₆ H ₄ -( Examples include OC ₂ H ₄ ) ₁₀ -OH. Commercially available products include Triton (registered trademark) X series manufactured by Dow Corporation and Nikkor (registered trademark) OP series or NP series manufactured by Nikko Chemical Company.
Examples of the nonionic surfactant represented by formula (6) include C ₁₃ H ₂₇ OCH ₂ CH(C ₂ H ₅ )O(C ₂ H ₄ O) ₈ H, C ₁₀ H ₂₁ CH(CH ₃ ) _{CH2OCH2CH ( C2H5 ) O ( C2H4O ) 8H} , _C12H25OCH2CH ( _{C2H5 )} O _{( C2H4O} ) _8H , _C8 H ₁₇ OCH ₂ CH (C ₂ H ₅ ) O (C ₂ H ₄ O) ₁₀ H, C ₁₃ H ₂₇ OCH ₂ CH ₂ OCH ₂ CH (C ₂ H ₅ ) O (C ₂ H ₄ O) ₈ H, _C10H21CH ( _{CH3 )} CH2O _{( C2H4O ) 9CH2CH ( C2H5 ) OH , C16H33OC2H4OCH} ( _{C2H5 ) CH2O ( C2H4O} ) _9H , _{C12H25OCH2CH ( C2H5 ) O ( C2H4O ) 8CH2CH ( C2H5 )} OH, _{C13H27OCH ( CH3} )CH( _{CH3 )} O(C2H4O _{) 8H} , _C12H25OCH ( _{CH3 )} CH( _{CH3 )} O( _C2H4O ) _8H , _{C13H27O ( CH2} ) ₄ O(C ₂ H ₄ O) ₈ H, and C ₁₂ H ₂₅ O(CH ₂ ) ₂ CH(CH ₃ )O(C ₂ H ₄ O) ₈ H.

The nonionic surfactant represented by formula (4) and/or the nonionic surfactant represented by formula (5) may be used alone or in combination of two or more. Good too.
Further, the nonionic surfactants represented by formula (6) may be used alone or in combination of two or more.
Furthermore, the nonionic surfactant represented by formula (6) and the nonionic surfactant represented by formula (4) or the nonionic surfactant represented by formula (5) are mixed. It can be used as
Note that nonionic surfactants are a mixture of multiple substances with different molecular structures, and the number of carbon atoms in the alkyl group in the nonionic surfactant, oxyethylene groups, oxypropylene groups, and oxybutylene groups in the polyoxyalkylene chain Let us treat the number as an average value. Each numerical value is not limited to an integer.

(Procedure of step A3)
The method of concentrating the aqueous emulsion is not particularly limited, and conventionally known methods can be employed. Examples of the concentration method include centrifugal sedimentation, electrophoresis, and phase separation, as described on page 32 of the Fluororesin Handbook (edited by Takaomi Satokawa, published by Nikkan Kogyo Shimbun).

Electrophoresis is a method that utilizes the fact that PTFE particles are negatively charged. Specifically, a nonionic surfactant is dissolved in an aqueous emulsion in an amount of 1 to 10% by mass (preferably 2 to 8% by mass) based on the mass of PTFE. Next, a voltage of 50 to 500 V/m (preferably 100 to 300 V/m) is applied to the obtained aqueous emulsion in a container having a semipermeable membrane such as a cellulose membrane, and the PTFE particles are electrophoresed. This method collects the PTFE aqueous dispersion that accumulates on the surface of the semipermeable membrane and then settles to the bottom due to the difference in specific gravity. The pH of the aqueous emulsion before concentration is preferably 2 to 10, more preferably 3 to 9.

The phase separation method is a method in which PTFE particles are precipitated by heating and leaving for a certain period of time. Specifically, a nonionic surfactant is dissolved in an aqueous emulsion in an amount of 8 to 20% by mass (preferably 12 to 18% by mass) based on the mass of PTFE. Next, the obtained aqueous emulsion is heated at 50 to 100°C (preferably 60 to 90°C) and left to stand for 1 to 100 hours (preferably 5 to 20 hours). This is a method for recovering an aqueous PTFE dispersion.

In addition, when concentrating, anionic surfactants (for example, ammonium laurate, triethanolamine laurate, sodium lauryl sulfate, ammonium lauryl sulfate, triethanolamine lauryl sulfate, etc.) are added at 0.20% by mass based on the mass of PTFE. It may be added to the PTFE aqueous emulsion below to speed up concentration. Furthermore, these additives not only accelerate the concentration of the PTFE aqueous emulsion, but also have the effect of improving the viscosity and dispersion stability.

In addition, after adding the nonionic surfactant to the aqueous emulsion obtained in step A2 and before concentrating the aqueous emulsion, polymerization initiator residue etc. may be adsorbed and removed by an ion exchange resin etc. . This removes excess water-soluble ionic compounds, improves the coating performance of the PTFE aqueous dispersion, and facilitates its application to insulating materials.

The concentration of PTFE particles in the aqueous PTFE dispersion obtained by the above procedure is preferably 15 to 70% by mass, more preferably 20 to 70% by mass, based on the total mass of the aqueous PTFE dispersion. A PTFE aqueous dispersion with a PTFE particle concentration of 15 to 70% by mass can be used for impregnating cloth or string made of fibers such as glass fiber, for mixing with inorganic powder or plastic powder, and for paints. It can be preferably used in applications where a small amount is added.
Further, particularly in applications where a PTFE aqueous dispersion is coated or processed into PTFE fibers, the concentration of PTFE particles is preferably 50 to 70% by mass, more preferably 52 to 68% by mass.
The pH of the PTFE aqueous dispersion is preferably 2 to 13, more preferably 3 to 11.

The PTFE constituting the PTFE particles in the PTFE aqueous dispersion includes not only a homopolymer of TFE, but also a trace amount of halogenated ethylene such as chlorotrifluoroethylene, hexafluoropropylene, etc., which is practically impossible to melt process. Also included are so-called modified PTFEs containing polymerized units based on copolymerizable components that can be copolymerized with TFE, such as fluorovinyl ethers such as halogenated propylene and perfluoro(alkyl vinyl ether).

The content of the nonionic surfactant in the PTFE aqueous dispersion is preferably 1 to 20% by mass, more preferably 1.5 to 15% by mass, and even more preferably 2 to 10% by mass based on the mass of PTFE. .
When the content is 1% by mass or more, the PTFE aqueous dispersion has excellent mechanical stability and excellent wettability. Moreover, when the content is 20% by mass or less, cracks are less likely to occur in the coated film, and the durability of the PTFE product is excellent.
In particular, in order to improve wettability during coating and to prevent cracks from occurring, the content of the nonionic surfactant in the PTFE aqueous dispersion is particularly preferably 3 to 10% by mass.

The surface tension of the PTFE aqueous dispersion is preferably 24 to 35 mN/m, more preferably 25 to 32 mN/m. When the surface tension is 24 mN/m or more, it has excellent antifoaming properties, and when it is 35 mN/m or less, it is difficult to cause repellency.

The PTFE aqueous dispersion may contain one or more of a non-fluorine-containing emulsifier, various leveling agents, preservatives, colorants, fillers, organic solvents, aqueous ammonia, and other known components.
Furthermore, when the PTFE aqueous dispersion contains a polyethylene oxide or polyurethane-based viscosity modifier, the mechanical stability of the PTFE aqueous dispersion is excellent.

From the viewpoint of ease of application, the viscosity of the PTFE aqueous dispersion is preferably 300 mPa·s or less at 23°C, more preferably 3 to 100 mPa·s, and even more preferably 5 to 50 mPa·s.
The thickening temperature of the PTFE aqueous dispersion is preferably 30 to 60°C, more preferably 35 to 55°C, even more preferably 40 to 50°C. When the thickening temperature is within the above range, changes in viscosity due to fluctuations in coating temperature are less likely to occur, and repellency is less likely to occur.

The PTFE aqueous dispersion 2 contains PTFE particles and an aqueous medium, and may further contain a surfactant and other components as necessary. However, the PTFE aqueous dispersion 2 is a different aqueous dispersion from the PTFE aqueous dispersion 1.
The PTFE aqueous dispersion 2 can also be produced by a known method, but step B1 involves emulsion polymerization of tetrafluoroethylene in an aqueous medium in the presence of a surfactant to obtain an aqueous emulsion; It is preferable to obtain it by a method including step B2 of adding a surfactant and then concentrating the aqueous emulsion.

<Process B1>
Step B1 is a step of emulsion polymerizing tetrafluoroethylene in an aqueous medium in the presence of a surfactant to obtain an aqueous emulsion.
The aqueous emulsion of step B1 contains PTFE particles. PTFE particles are non-melt-formable TFE polymer particles, and are meant to include both TFE homopolymer particles and modified PTFE particles.

Comonomers used in the production of modified PTFE include hexafluoropropylene, perfluoro(alkyl vinyl ether), chlorotrifluoroethylene, (perfluoroalkyl)ethylene, vinylidene fluoride, perfluoro(alkenyl vinyl ether), perfluoro(2,2-dimethyl- 1,3-dioxole), perfluoro(4-alkyl-1,3-dioxole), and the like. The comonomers may be used alone or in combination of two or more.
As the comonomer, (perfluoroalkyl)ethylene is preferred, and (perfluoroalkyl)ethylene selected from the group consisting of (perfluoroethyl)ethylene, (perfluorobutyl)ethylene, and (perfluorohexyl)ethylene is more preferred.
The content of comonomer units in the modified PTFE is preferably 0.5% by mass or less, more preferably 0.4% by mass or less based on the total units.
In the production of modified PTFE, the total amount of TFE and comonomer consumed in the copolymerization reaction of TFE and comonomer is approximately equal to the amount of modified PTFE produced.

Examples of the surfactant include fluorine-containing anionic surfactants.
Examples of the fluorine-containing anionic surfactant include fluorine-containing alkyl carboxylic acids and salts thereof, fluorine-containing alkyl carboxylic acids having an etheric oxygen atom, and salts thereof.
Examples of the fluorine-containing alkylcarboxylic acid or its salt include ammonium perfluorooctanoate and ammonium perfluorohexanoate.
Examples of the fluorine-containing alkylcarboxylic acid or its salt having an etheric oxygen atom include a compound represented by the following formula 1.
F( _CF2 ) _pO (CF(X) _CF2O ) _qCF (X)COOA...Formula 1.
However, X is a fluorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms, A is a hydrogen atom, an alkali metal atom, or _NH4 , p is an integer of 1 to 10, and q is 0 to 3. is an integer.

Specific examples of the compound represented by Formula 1 are shown below.
F(CF ₂ ) ₂ OCF ₂ CF ₂ OCF ₂ COONH ₄ (hereinafter also referred to as EEA),
_{F ( CF2} ) _2O ( _CF2CF2O ) _{2CF2COONH4 ,}
F( _CF2 ) _3O (CF( _CF3 ) _CF2O ) _2CF ( _CF3 ) _COONH4 ,
_{F ( CF2 ) 3OCF2CF2OCF2COONH4 ,}
F _{( CF2} ) _{3O ( CF2CF2O} ) _{2CF2COONH4 ,
F ( CF2 ) 4OCF2CF2OCF2COONH4 ,}
F _{( CF2} ) _{4O ( CF2CF2O} ) _{2CF2COONH4 ,}
F( _CF2 ) _2OCF ( _CF3 ) _CF2OCF ( _CF3 ) _COONH4 ,
F _{( CF2 ) 2OCF2CF2OCF2COONa ,
F} ( _CF2 ) _2O ( _CF2CF2O ) _{2CF2COONa ,}
F _{( CF2 ) 3OCF2CF2OCF2COONa ,
F} ( _CF2 ) _3O ( _CF2CF2O ) _{2CF2COONa ,}
F _{( CF2 ) 4OCF2CF2OCF2COONa ,}
F( _CF2 ) _4O ( _CF2CF2O ) _{2CF2COONa , etc.}

Examples of emulsion polymerization include known methods such as those described in Japanese Patent No. 5,141,256.

The number average molecular weight of PTFE is preferably 300,000 to 30 million, more preferably 500,000 to 25 million. When the number average molecular weight of PTFE is at least the above lower limit, the mechanical properties of the film are better, and when it is at most the above upper limit, industrial production is easy.
The number average molecular weight of PTFE is a value determined by the method described in Suwa et al., Journal of Applied Polymer Science, 17, 3253 (1973) using crystallization heat.

The standard specific gravity (SSG) of PTFE is preferably 2.14 or more and less than 2.22, more preferably 2.15 to 2.21. When SSG is within the above range, the mechanical properties of the film are better.

The average primary particle diameter of the PTFE particles is preferably 0.1 to 0.5 μm, more preferably 0.18 to 0.45 μm, particularly preferably 0.20 to 0.35 μm. When the average primary particle diameter of the PTFE particles is at least the above lower limit, cracks are less likely to occur in the coating, and when it is at most the above upper limit, the PTFE particles are less likely to settle in the aqueous dispersion, resulting in excellent storage stability.

[Aqueous medium]
The aqueous medium includes water or a mixture of water and a water-soluble organic solvent.
As the water-soluble organic solvent, known ones can be used as appropriate, and examples thereof include alcohols such as tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.
When using a water-soluble organic solvent, it is preferable that the content of the water-soluble organic solvent in the aqueous medium is small. Specifically, the water-soluble organic solvent is preferably less than 1 part by mass, more preferably 0.5 parts by mass or less, and particularly preferably 0.1 parts by mass or less with respect to 100 parts by mass of water.
Most preferably, the aqueous medium is free of water-soluble organic solvents.

<Process B2>
Step B2 is a step of adding a nonionic surfactant to the aqueous emulsion and then concentrating the aqueous emulsion.
In step B2, it is preferable to use the same nonionic surfactant and the same concentration method as in step A3 of the PTFE aqueous dispersion 1.
As the PTFE aqueous dispersion 2, it is also possible to use a commercially available product.

The method for producing a PTFE mixed aqueous dispersion of the present invention involves preparing a PTFE aqueous dispersion 1 and a PTFE aqueous dispersion 2 at a solid content mass ratio of PTFE aqueous dispersion 1/PTFE aqueous dispersion 2 = 90/10 to 10/ Mix it so that it becomes 90%. The solid content mass ratio of PTFE aqueous dispersion 1/PTFE aqueous dispersion 2 is preferably 50/50 to 10/90, more preferably 20/80 to 10/90. When the content is within the above range, the coloring of the coating is suppressed and the appearance is excellent, and cracks are less likely to occur in the coating.
The method of mixing each aqueous dispersion is not particularly limited, and can be produced by a conventional method such as weighing each aqueous dispersion so as to have the above-mentioned solid content mass ratio, mixing and stirring.

The PTFE mixed aqueous dispersion of the present invention contains the following PTFE1 and PTFE2 at a mass ratio of PTFE1/PTFE2=90/10 to 10/90.
[PTFE1]
PTFE particles with an average primary particle diameter of 0.1 to 0.5 μm and no CF ₂ chain oligomer group having 6 to 34 carbon atoms detected.
[PTFE2]
PTFE particles having an average primary particle diameter of 0.1 to 0.5 μm and different from PTFE1.

The value of the oligomer group was measured by the following measurement method.
<Measurement method>
The sample (PTFE particles) was subjected to Soxhlet extraction with ethanol for 5 hours, and the ethanol extract was subjected to LC/MS analysis. A group of CF ₂ chain oligomers having 6 to 34 carbon atoms was quantified.
In the LC/MS analysis, Agilent 1260 series HPLC/6460MS was used, and the column was Imtakt's Cadenza CD-C18, 2 mmφ×100 mm, 3 μm particle size. Further, during the measurement, a gradient of ammonium acetate aqueous solution and methanol was applied.

The PTFE mixed aqueous dispersion of the present invention is preferably produced by the method for producing the PTFE mixed aqueous dispersion of the present invention described above.

The PTFE mixed aqueous dispersion of the present invention can be suitably used in the production of various PTFE products, such as films, sheets, and fibers containing PTFE as a main component, heat-resistant articles having a PTFE coating, and articles containing PTFE as a subcomponent. can.

PTFE products include, for example, packing made by impregnating a PTFE aqueous dispersion into a base material made of cloth or braided string made of glass fiber, aramid fiber, carbon fiber, and various other synthetic fibers or natural fibers and drying; glass; A heat-resistant belt for conveyance and a membrane structure for construction, made by impregnating a PTFE aqueous dispersion into a base material made of woven cloth or braided string of heat-resistant fibers such as fibers, aramid fibers, and carbon fibers and firing at a temperature higher than the melting point of PTFE. Materials for sheets, packing, and printed circuit boards; Kitchen equipment such as frying pans and electric kettles made by coating metal plates such as aluminum and stainless steel with a PTFE aqueous dispersion containing pigments and heat-resistant resin; and baking them; carbon, manganese dioxide, and water. Binder made by kneading battery active material powder such as nickel oxide and PTFE aqueous dispersion; Molding raw material mixed with PTFE aqueous dispersion to prevent plastic molded products such as polycarbonate and ABS resin from dripping during combustion. and molded product (anti-dripping agent); powder made by mixing PTFE aqueous dispersion with chemical fertilizer, lime, incineration ash, etc. to reduce dust generation; filler such as lead, zinc, carbon powder, etc. and PTFE aqueous dispersion Sliding materials such as oil-free bearing materials made by coating a porous material with a paste made by mixing a PTFE aqueous dispersion with a thickener such as viscose, and pressurizing it into a coagulation bath. Then fired PTFE fiber; PTFE ultra-thin sheet obtained by coating a heat-resistant sheet base material such as an aluminum plate or stainless steel plate with a PTFE aqueous dispersion and then peeling off the PTFE layer after firing; Casting from a PTFE aqueous dispersion A thin film obtained by film forming etc. that has heat resistance, high insulation properties, and low dielectric loss tangent ability, and is used as coil insulation, interlayer insulation film, and electrical insulation material for motors, transformers, relays, switches, etc.; PTFE water-based Examples include paints, resins, and rubber materials that have improved lubricity and antifouling properties by adding a dispersion liquid.

PTFE products are obtained by coating or mixing an aqueous PTFE dispersion, followed by drying or heat treatment at temperatures ranging from room temperature to 420°C. The temperature of the drying or heat treatment is preferably 50 to 400°C, more preferably 100 to 395°C.
The PTFE content in the PTFE product varies depending on the use, but is preferably 0.01 to 100% by mass, more preferably 0.1 to 100% by mass, and even more preferably 1 to 100% by mass.

The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited thereto.

[Coating test]
The mixed aqueous dispersion obtained by the procedure described below was applied onto an aluminum plate measuring 20 cm long, 15 cm wide, and 0.2 mm thick using an RDS #14 bar, and then placed in an oven at 120°C for 10 minutes. It was dried, baked in a 380°C oven for 10 minutes, and then cooled naturally.
On the formed PTFE layer, coating, drying, and baking were further performed, and this process was repeated twice to form a PTFE layer in which a total of three layers were overlaid.
After cooling, only the film layer was peeled off to produce a PTFE film.

[exterior]
The appearance of the PTFE film produced in the coating test was visually confirmed.

[crack]
The PTFE film produced in the coating test was dried at 120°C for 10 minutes, then fired at 380°C for 10 minutes, and the presence or absence of cracks was visually confirmed.

[Mechanical stability (rubbing stability)]
A Tygon tube with an outer diameter of 7.9 mm and an inner diameter of 4.8 mm is attached to a Cole Palmer tube pump, and both ends of the tube are placed in a 200 cc beaker containing 100 cc of PTFE aqueous dispersion. Cover the opening with foil. Using this device, the mixed aqueous dispersion obtained by the procedure described below was circulated for 1 hour at a room temperature of 23°C and a liquid feed rate of 200 cc per minute, and after completion of the circulation, it was filtered with a 200 mesh nylon filter to collect aggregates. , and the weight after drying at 120° C. for 1 hour was measured.

(Manufacturing example 1):
A 100 L stainless steel autoclave was charged with paraffin wax (1500 g) and deionized water (60 L). After the autoclave was purged with nitrogen, the pressure was reduced, and i-butyl methacrylate (i-BMA) (0.1 g) and deionized water (0.5 L) were poured into the autoclave.
Next, the inside of the autoclave was brought to a state below atmospheric pressure, and the temperature of the solution inside the autoclave was raised to 75° C. while stirring. Thereafter, a solution of ammonium persulfate (0.055 g), a polymerization initiator, dissolved in deionized water (1 L) was injected into the autoclave to polymerize i-butyl methacrylate.
After 20 minutes, the pressure was increased to 1.96 MPa using TFE, and ammonium persulfate (0.54 g) and disuccinic acid peroxide (concentration 80% by mass, remaining water) (53 g) were dissolved in warm water (1 L) at about 70 °C. The solution was injected into the autoclave.
After the internal pressure in the autoclave was reduced to 1.89 MPa, TFE was added to keep it at 1.96 MPa, and TFE polymerization was allowed to proceed.
The reaction was terminated when the amount of TFE added reached 9 kg, and the TFE in the autoclave was released into the atmosphere. Polymerization time was 94 minutes.
The solid content concentration (concentration of PTFE particles) of the aqueous emulsion was about 11% by mass. Further, the average primary particle diameter of the PTFE particles in the aqueous emulsion was 0.24 μm (240 nm).
A part of the obtained aqueous emulsion was adjusted to 20° C. and stirred to aggregate PTFE particles to obtain PTFE powder. Next, this PTFE powder was dried at 275° C. with an aqueous ammonium carbonate solution. The SSG of the obtained PTFE powder was 2.201.
Furthermore, no by-product fluorine-based oligomer was found in the obtained PTFE powder.
A nonionic surfactant (a) (Nukol 1308FA manufactured by Nippon Nyukazai Co., Ltd., C ₁₃ H ₂₇ -(OC ₂ H ₄ ) ₈ -OCH(CH ₃ )CH ₂ -OH) was added to the obtained aqueous emulsion. Ammonium laurate was dissolved in a proportion of 2.7% by mass based on the mass of PTFE, ammonium laurate was dissolved in a proportion of 0.06% by mass based on the mass of PTFE, and triethanolamine lauryl sulfate was dissolved in a proportion of 0.02% by mass based on the mass of PTFE. Concentration was performed by electrophoresis. The supernatant was removed to obtain a PTFE aqueous dispersion having a PTFE concentration of 65.8% by mass and a nonionic surfactant (a) concentration of 2.1% by mass based on the PTFE mass.
A nonionic surfactant (b) (Nukol G1301H manufactured by Nippon Nyukazai Co., Ltd., C ₁₃ H ₂₇ -OCH ₂ CH (C ₂ H ₅ )-(OC ₂ H ₄ ) ₈ -OH) was added to this PTFE aqueous dispersion. 1.2% by mass based on the mass of PTFE, nonionic surfactant (c) (Nukol FAA09801 manufactured by Nippon Nyukazai Co., Ltd., C ₁₃ H ₂₇ -OCH ₂ CH(C ₂ H ₅ )-(OC ₂ H ₄ ) ₁₁ -OH) to 1.2% by mass based on the PTFE mass, PEO 0.1% by mass based on the PTFE mass, water and aqueous ammonia, and the nonionic surfactant (a) based on the PTFE mass. A nonionic surfactant (a) was added so that the content was 2.4% by mass to obtain an aqueous PTFE dispersion 1-1 having a PTFE concentration of 60.5% by mass and a pH of 10.2. The obtained PTFE aqueous dispersion 1-1 had a viscosity at 23° C. of 25.8 mPa·s, a pH of 10.2, and a surface tension of 30 (mN/m).

(Production example 2):
A 100 L stainless steel autoclave was charged with 36 g of F(CF ₂ ) ₂ OCF ₂ CF ₂ OCF ₂ COONH ₄ , 555 g of paraffin wax (melting point 55° C.), and 61.3 liters of deionized water. After purging the inside of the autoclave with nitrogen and reducing the pressure, TFE monomer was introduced, and the temperature was raised to 62° C. with stirring. Furthermore, TFE monomer was injected until the internal pressure reached 1.765 MPa [gauge], and 26.3 g of disuccinic acid peroxide (concentration 80% by mass, the remainder was water) was dissolved in 1 liter of warm water at about 70°C and injected. .
After about 3 minutes, the internal pressure of the autoclave dropped to 1.716 MPa [gauge], so TFE monomer was pressurized to keep the internal pressure at 1.765 MPa [gauge] and polymerization proceeded. During the polymerization, EEA was dissolved in warm water and a total of 53 g of EEA was injected in two portions. The autoclave temperature was gradually raised to 72° C., and when the amount of TFE monomer injected reached 22 kg, the reaction was terminated, and the TFE in the autoclave was released into the atmosphere. Polymerization time was 105 minutes. After cooling, the paraffin wax solidified on the top was removed to obtain a PTFE aqueous emulsion. The PTFE concentration in the PTFE aqueous emulsion was about 25.0% by mass, and the EEA concentration was 0.40% by mass based on the PTFE mass. The average particle diameter of the PTFE particles in the aqueous emulsion was 0.26 μm. The average molecular weight of PTFE was 760,000, and the standard specific gravity of PTFE was 2.21.
A nonionic surfactant (a) (Nukol 1308FA manufactured by Nippon Nyukazai Co., Ltd., C ₁₃ H ₂₇ -(OC ₂ H ₄ ) ₈ -OCH(CH ₃ )CH ₂ -OH) was added to the obtained aqueous emulsion. Ammonium laurate was dissolved in a proportion of 2.7% by mass based on the mass of PTFE, ammonium laurate was dissolved in a proportion of 0.02% by mass based on the mass of PTFE, and triethanolamine lauryl sulfate was dissolved in a proportion of 0.01% by mass based on the mass of PTFE. Concentration was performed by electrophoresis. The supernatant was removed to obtain a PTFE aqueous dispersion having a PTFE concentration of 60.5% by mass and a nonionic surfactant (a) concentration of 2.2% by mass based on the PTFE mass.
A nonionic surfactant (b) (Nukol G1301H manufactured by Nippon Nyukazai Co., Ltd., C ₁₃ H ₂₇ -OCH ₂ CH (C ₂ H ₅ )-(OC ₂ H ₄ ) ₈ -OH) was added to this PTFE aqueous dispersion. 1.3% by mass based on the mass of PTFE, nonionic surfactant (c) (Nukol FAA09801 manufactured by Nippon Nyukazai Co., Ltd., C ₁₃ H ₂₇ -OCH ₂ CH(C ₂ H ₅ )-(OC ₂ H ₄ ) ₁₁ -OH) was 1.3% by mass based on the PTFE mass, PEO was 0.1% by mass based on the PTFE mass, water and aqueous ammonia were added, and the amount of nonionic surfactant (a) based on the PTFE mass was added. Nonionic surfactant (a) was added so that the content was 2.2% by mass to obtain PTFE aqueous dispersion 2.

(Production example 3):
Except that a nonionic surfactant (d) (Tergitol TMN100X manufactured by DOW, C ₁₂ H ₂₅ -(OC ₂ H ₄ ) ₁₀ -OH) was used instead of the nonionic surfactant (a). Following the same procedure as in Example 1, PTFE aqueous dispersion 1-2 was obtained.

(Manufacturing example 4)
A 100 L stainless steel autoclave was charged with paraffin wax (1500 g) and deionized (60 L). After the autoclave was purged with nitrogen, the pressure was reduced, and i-butyl methacrylate (i-BMA) (0.1 g) and deionized water (0.5 L) were poured into the autoclave.
Next, the inside of the autoclave was brought to a state below atmospheric pressure, and the temperature of the solution inside the autoclave was raised to 75° C. while stirring. Thereafter, a solution of ammonium persulfate (0.055 g), a polymerization initiator, dissolved in deionized water (1 L) was injected into the autoclave to polymerize i-butyl methacrylate.
After 20 minutes, the pressure was increased to 1.96 MPa using TFE, and ammonium persulfate (0.54 g) and disuccinic acid peroxide (concentration 80% by mass, remaining water) (53 g) were dissolved in warm water (1 L) at about 70 °C. The solution was injected into the autoclave. Next, TFE was added so as to maintain the internal pressure inside the autoclave at 1.96 MPa, and the polymerization of TFE was allowed to proceed. After adding 1 kg of TFE, a solution of ammonium vinyl sulfonate (5.0 g) dissolved in deionized water (1.5 L) was added so that ammonium vinyl sulfonate was 0.15 g per 1 kg of TFE supplied. Ammonium vinylsulfonate was supplied while checking the amount of TFE supplied using a flow meter.
The reaction was terminated when the amount of TFE added reached 9 kg, and the TFE in the autoclave was released into the atmosphere. Polymerization time was 97 minutes.
The solid content concentration (concentration of modified PTFE) of the aqueous emulsion was about 12% by mass. Moreover, the average primary particle diameter of the modified PTFE particles in the aqueous emulsion was 0.21 μm.
A part of the obtained aqueous emulsion was adjusted to 20° C. and stirred to aggregate modified PTFE particles to obtain modified PTFE powder. Next, this modified PTFE powder was dried at 275° C. with an aqueous ammonium carbonate solution. The SSG of the obtained modified PTFE powder was 2.193.
Furthermore, no by-product fluorine-based oligomer was observed in the modified PTFE powder obtained.
The aqueous emulsion obtained in Step A2 was concentrated in the same manner as in Production Example 1 to obtain PTFE aqueous dispersion 1-3. The average primary particle size of the PTFE particles in the PTFE aqueous dispersion 1-3 was the same as the average primary particle size of the PTFE particles measured in the aqueous emulsion.

(Manufacturing example 5)
PTFE aqueous dispersion 1-4 was obtained in the same manner as in Production Example 3, except that nonionic surfactant (d) was used instead of nonionic surfactant (a).

(Example 1)
The PTFE aqueous dispersion 1-1 obtained in Production Example 1 and the PTFE aqueous dispersion 2 obtained in Production Example 2 were mixed at a ratio of 20/80 (solid content mass ratio) to form a mixed aqueous dispersion. Obtained.
(Examples 2 to 12)
A mixed aqueous dispersion was obtained in the same manner as in Example 1, except that the solid content mass ratio in Example 1 was changed to the value shown in Table 1.

Claims (3)

The following polytetrafluoroethylene aqueous dispersion 1 and the following polytetrafluoroethylene aqueous dispersion 2 were prepared so that the solid content mass ratio was polytetrafluoroethylene aqueous dispersion 1/polytetrafluoroethylene aqueous dispersion 2 = 90/10 to 10. A method for producing a polytetrafluoroethylene mixed aqueous dispersion, the method of producing a polytetrafluoroethylene mixed aqueous dispersion.
[Polytetrafluoroethylene aqueous dispersion 1]
Step A1 of polymerizing a non-fluorinated monomer in an aqueous medium to obtain a solution 1 containing a polymer containing units based on the non-fluorinated monomer;
Step A2 of polymerizing tetrafluoroethylene in the solution 1 without substantially adding a surfactant to the solution 1 to obtain an aqueous emulsion containing polytetrafluoroethylene particles;
Obtained by a method comprising step A3 of adding a nonionic surfactant to the aqueous emulsion and then concentrating the aqueous emulsion to obtain a polytetrafluoroethylene aqueous dispersion,
An aqueous polytetrafluoroethylene dispersion, wherein the amount of the non-fluoromonomer used is 200 mass ppm or less relative to the amount of tetrafluoroethylene supplied to the polymerization system.
[Polytetrafluoroethylene aqueous dispersion 2]
An aqueous dispersion different from polytetrafluoroethylene aqueous dispersion 1, comprising polytetrafluoroethylene particles and an aqueous medium. The polytetrafluoroethylene aqueous dispersion 2 undergoes step B1 of emulsion polymerizing tetrafluoroethylene in an aqueous medium in the presence of a surfactant to obtain an aqueous emulsion, and adding a nonionic surfactant to the aqueous emulsion. The method for producing a polytetrafluoroethylene mixed aqueous dispersion according to claim 1, which is a polytetrafluoroethylene aqueous dispersion 2 obtained from a method including step B2 of adding a polytetrafluoroethylene mixed aqueous dispersion and then concentrating the aqueous emulsion. . A polytetrafluoroethylene mixed aqueous dispersion containing the following polytetrafluoroethylene 1 and the following polytetrafluoroethylene 2 in a mass ratio of polytetrafluoroethylene 1/polytetrafluoroethylene 2 = 90/10 to 10/90.
[Polytetrafluoroethylene 1]
Polytetrafluoroethylene particles having an average primary particle diameter of 0.1 to 0.5 μm and containing no detectable CF ₂ chain oligomer group having 6 to 34 carbon atoms.
[Polytetrafluoroethylene 2]
Polytetrafluoroethylene particles having an average primary particle diameter of 0.1 to 0.5 μm and different from polytetrafluoroethylene 1.