Binder for electrode, electrode mixture, electrode, and secondary battery

Abstract

This binder for an electrode comprises a solid composition including primary particles containing a first polymer and a second polymer, wherein the second polymer is a non-melt-moldable fluorine-containing polymer containing a unit based on tetrafluoroethylene, the first polymer is different from the second polymer, and the content of the first polymer is 0.01-4.0 mass% with respect to the total mass of the first polymer and the second polymer.

Description

Electrode binder, electrode mixture, electrode, and secondary battery

[0001] The present invention relates to an electrode binder, an electrode mixture, an electrode, and a secondary battery. This application claims priority based on Japanese Patent Application No. 2024-017047, filed on February 7, 2024, the contents of which are incorporated herein by reference.

[0002] Fluorine-containing polymers such as tetrafluoroethylene copolymers are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. Patent Document 1 describes that polytetrafluoroethylene polymerized using a fluorine-containing surfactant is powdered and the powder is used as an electrode binder.

[0003] Patent No. 7303469

[0004] However, when a fluorine-containing polymer produced by a conventional method is used as an electrode binder, the binding strength with an electrode active material is insufficient. An object of the present invention is to provide an electrode binder that has excellent binding strength with an electrode active material, and an electrode mixture, an electrode, and a secondary battery that each contain the electrode binder.

[0005] The present invention has the following aspects. [1] An electrode binder comprising a solid composition containing primary particles including a first polymer and a second polymer, wherein the second polymer is a non-melt-formable fluorinated polymer containing units based on tetrafluoroethylene, the first polymer is a polymer different from the second polymer, and the content of the first polymer is 0.01 to 4.0 mass% relative to the total mass of the first polymer and the second polymer. [2] The electrode binder according to [1], wherein the first polymer contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [3] The electrode binder according to [2], wherein the content of the units based on perfluoro(alkyl vinyl ether) in the first polymer is 0.1 to 3.0 mol% relative to the total of all units of the first polymer and all units of the second polymer. [4] The electrode binder according to any one of [1] to [3], wherein the first polymer is water-insoluble. [5] The electrode binder according to any one of [1] to [4], wherein the content of the compound represented by the following formula (S1) and the content of the compound represented by the following formula (S2) are each 100 mass ppb or less, relative to the total mass of the first polymer and the second polymer: Formula (S1): H—(CF ２ ) ｎ１ -COOM Formula (S2): H-(CF ２ ) ｎ２ -SO ３ M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ wherein n1 represents an integer of 3 to 13, 15 or 17, and n2 represents an integer of 4 to 10, or 12. [6] The electrode binder according to any one of [1] to [5], wherein the aspect ratio of the primary particles is 1.5 or less. [7] An electrode mixture comprising the electrode binder according to any one of [1] to [6] and an electrode active material. [8] An electrode comprising the electrode mixture according to [7] and a current collector. [9] A secondary battery comprising the electrode according to [8].

[0006] According to the present invention, it is possible to provide an electrode binder that has excellent binding properties with an electrode active material, an electrode mixture containing the electrode binder, an electrode, and a secondary battery.

[0007] The following definitions of terms apply throughout the present specification and claims. A "unit" is a collective term for an atomic group derived from one molecule of the monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the atomic group. A "monomer-based unit" is also referred to simply as a "unit" below. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in this specification in stages, the upper or lower limit of a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of a certain numerical range may be replaced with a value shown in the Examples. The "average particle size of primary particles" is the average particle size (hydrodynamic diameter) calculated by cumulant analysis using an autocorrelation function obtained by dynamic light scattering. The "aspect ratio of particles" is the ratio (a / b) of the particle's major axis a to the longest diameter b perpendicular to the major axis a. "Non-melt moldable" means that the polymer does not exhibit melt fluidity. "Exhibiting melt fluidity" means that there is a temperature at which the melt flow rate is 0.1 to 1,000 g / 10 min at a temperature at least 20°C higher than the melting point of the resin under a load of 49 N. "Melt flow rate" refers to the melt mass flow rate (MFR) defined in JIS K 7210:1999 (ISO 1133:1997). "Standard specific gravity (hereinafter also referred to as "SSG")" is a value that serves as an index of average molecular weight; a larger value indicates a smaller molecular weight. It can be measured in accordance with ASTM D4895-04. The content (mass % or mol %) of each unit relative to the total units contained in the polymer is determined by analyzing the polymer using solid-state nuclear magnetic resonance spectroscopy (NMR). Typically, the content of each unit calculated from the amount of each monomer charged approximately matches the actual content of each unit. In this specification, each component may be a single substance corresponding to the component, or two or more substances may be used in combination. When two or more substances are used in combination for each component, the content of the component refers to the total content of the substances used in combination, unless otherwise specified.In this specification, a combination of two or more preferred aspects is a more preferred aspect.

[0008] The electrode binder of this embodiment includes a solid composition. The solid composition includes primary particles containing a first polymer and a second polymer. The second polymer is a non-melt-formable fluorine-containing polymer containing units based on tetrafluoroethylene. The first polymer is a polymer different from the second polymer. The content of the first polymer is 0.01 to 4.0 mass% relative to the total mass of the first polymer and the second polymer. The solid composition is preferably a powder composition.

[0009] <First Polymer> The first polymer is a polymer different from the second polymer. That is, the first polymer is not a non-melt-formable fluorine-containing polymer containing units based on tetrafluoroethylene. The first polymer may be a fluorine-containing polymer containing fluorine atoms, or a non-fluorine-containing polymer containing no fluorine atoms. Among these, the first polymer is preferably a fluorine-containing polymer. The glass transition temperature (hereinafter also referred to as "Tg") of the first polymer is preferably lower than the polymerization temperature of the second polymer. In one embodiment, it is preferable that the first polymer has neither a glass transition temperature nor a melting point of 20°C or higher.

[0010] The Tg of the first polymer is preferably 10°C or lower, more preferably 5°C or lower, even more preferably 3°C or lower, and particularly preferably 0°C or lower. When the Tg of the first polymer is the above upper limit or lower, primary particles containing the first polymer and the second polymer are easily formed. The Tg of the first polymer is preferably -50°C or higher, more preferably -45°C or higher, and even more preferably -40°C or higher. When the Tg of the first polymer is the above lower limit or higher, thermal stability after molding is improved. Examples of methods for adjusting the Tg of the first polymer within the above range include adjusting the type and amount of monomer used in producing the first polymer.

[0011] The first polymer is preferably an elastomer, more preferably a fluorine-containing elastomer. The term "elastomer" refers to an elastic copolymer having no melting point and exhibiting a storage modulus G' of 80 or more at 100°C and 50 cpm as measured in accordance with ASTM D6204.

[0012] The first polymer preferably has units based on a fluorine-containing monomer containing a fluorine atom. Examples of the fluorine-containing monomer constituting the first polymer include tetrafluoroethylene (hereinafter also referred to as "TFE"), perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), hexafluoropropylene (hereinafter also referred to as "HFP"), vinylidene fluoride (hereinafter also referred to as "VdF"), CH ２ =CF-CF ２ -O-Rf-COOH, CH ２ =CF-CF ２ —O—Rf—SO ３ H, C.F. ２ =CF-CF ２ -O-Rf-COOH, CF ２ =CF-CF ２ —O—Rf—SO ３ H, CH ２ =CF-O-Rf-COOH, CH ２ =CF-O-Rf-SO ３ H, C.F. ２ ═CF—O—Rf—COOH, and CF ２ =CF-O-Rf-SO ３ H (Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom between carbon atoms). Further, examples of other fluorine-containing polymers include perfluoroalkyl polyethers and perfluoropolyethers. The first polymer may consist solely of units based on a non-fluorine monomer, or may have units based on a non-fluorine monomer. Examples of non-fluorine monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride. The non-fluorine monomer may have a hydroxyl group and an ionic functional group as a substituent, which will be described later. Specifically, one or more hydrogen atoms of the non-fluorine monomer may be substituted with a hydroxyl group and an ionic functional group as described later.

[0013] The fluorine-containing monomer may have, as a substituent, a functional group that contributes to water solubility. Examples of the functional group that contributes to water solubility include a hydroxyl group and an ionic functional group. The ionic functional group may be either a cationic functional group or an anionic functional group. Specific examples of the ionic functional group include a carboxylic acid group (-COO － ), sulfonic acid group (—SO ３ － ), sulfate group (-SO ４ ２－ ), a phosphonic acid group (—PO ３ ２－ ), sulfonimide group (-N － (SO ２ )), and a phosphate group (-PO ４ ３－ ) and other anionic functional groups. The functional group that contributes to water solubility is preferably a monovalent group. The first polymer may have one or more functional groups that contribute to water solubility. The first polymer may have a functional group that contributes to water solubility in a side chain or at an end.

[0014] Preferably, the first polymer comprises TFE unit.When the first polymer comprises TFE unit, the content of TFE unit relative to the total units of the first polymer is preferably 30 mol% or more, more preferably 40 mol% or more, and even more preferably 50 mol% or more, because the more the content of TFE unit is, the more contributes to heat resistance.The upper limit of the content of TFE unit can be adjusted according to the type of unit other than TFE unit so as to obtain desired Tg.For example, it is preferably 90 mol% or less, more preferably 80 mol% or less, and even more preferably 70 mol% or less.

[0015] The first polymer is preferably water-insoluble in terms of ease of removal of the first polymer from water. In this specification, "water-insoluble" means that the solubility in 1,000 g of water at 25°C is less than 100 mg. When the first polymer contains a functional group that contributes to water solubility, the content thereof is preferably within a range that makes the first polymer water-insoluble. For example, the content of the functional group that contributes to water solubility is preferably 0 to 20 mol %, more preferably 0.000001 to 15 mol %, and even more preferably 0.0001 to 10 mol %, relative to all units constituting the first polymer.

[0016] The first polymer preferably contains TFE units and PAVE units, since it is easy to adjust the Tg to the above range and the effects of the present invention are more excellent.

[0017] The PAVE is preferably a monomer represented by formula (1) from the viewpoints of excellent polymerization reactivity in producing the first polymer and of enabling more efficient production of the second polymer. ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0018] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"). Among these, PMVE and PPVE are preferred, with PMVE being more preferred, from the viewpoint of enabling more efficient production of the second polymer.

[0019] When the first polymer contains TFE units and PAVE units, the content of PAVE units relative to the total of TFE units and PAVE units is preferably 20 to 60 mol %, more preferably 25 to 60 mol %, and even more preferably 30 to 55 mol %, from the viewpoints of easily adjusting Tg within the above range and more efficiently producing the second polymer. The suitable amount used is the same whether the PAVE units are PMVE units, PEVE units, or PPVE units, or whether a mixture of two or more of these is used.

[0020] When the first polymer contains TFE units and PAVE units, the first polymer may contain units based on other monomers other than TFE and PAVE. However, from the viewpoint of more efficient production of the second polymer, it is preferable that the first polymer does not substantially contain units based on other monomers. "Substantially not containing units based on other monomers" means that the content of units based on other monomers is 0.01 mol% or less, more preferably 0 mol%, based on the total units of the first polymer. When units based on other monomers are contained, HFP and propylene are preferred. When HFP is contained as the other monomer, the content of units based on HFP based on the total units of the first polymer is preferably more than 0 mol% and 10 mol% or less, more preferably more than 0 mol% and 5 mol% or less, and even more preferably more than 0 mol% and 1 mol% or less.

[0021] <Second Polymer> The second polymer is a non-melt-processable fluoropolymer containing TFE units. The second polymer may be a fluoropolymer consisting of TFE units only (PTFE), or may be a fluoropolymer further containing monomer units other than TFE units.

[0022] The monomer other than TFE may be a fluorine-containing monomer or a non-fluorine-containing monomer that does not contain a fluorine atom. Examples of the fluorine-containing monomer include chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), vinylidene fluoride (hereinafter also referred to as "VdF"), FAE, PAVE, hexafluoropropylene, perfluoro(2,2-dimethyl-1,3-dioxole), and perfluoro(4-methoxy-1,3-dioxole). Among these, CTFE, VdF, PAVE, perfluoroalkylethylene, and hexafluoropropylene are preferred, CTFE, VdF, perfluorobutylethylene, perfluoro(methyl vinyl ether), perfluoro(propyl butyl ether), and hexafluoropropylene are more preferred, and perfluorobutylethylene, perfluoro(methyl vinyl ether), and perfluoro(propyl butyl ether) are even more preferred. Examples of the non-fluorine-containing monomer include ethylene, propylene, vinyl chloride, and vinylidene chloride.

[0023] The content of TFE units contained in the second polymer is preferably 99.0 to 100.0 mol %, more preferably 99.5 to 100.0 mol %, and even more preferably 99.9 to 100.0 mol %, based on all units of the second polymer.

[0024] <Solid Composition> The content of the first polymer is 0.01 to 4.0 mass%, preferably 0.1 to 3.5 mass%, and more preferably 0.3 to 3.0 mass%, relative to the total mass of the first polymer and the second polymer. When the content of the first polymer is at least the lower limit of the above range, the emulsion stability of the second polymer is improved, and when it is at most the upper limit, the heat resistance of the second polymer can be maintained.

[0025] The content of the first polymer is preferably 0.1 to 4 mass%, more preferably 0.2 to 4 mass%, and even more preferably 0.3 to 3 mass%, relative to the total mass of the solid composition. The content of the second polymer is preferably 95 to 99.9 mass%, more preferably 96 to 99.8 mass%, and even more preferably 97 to 99.7 mass%, relative to the total mass of the solid composition. The combined content of the first polymer and the second polymer is preferably 99.0 to 100 mass%, more preferably 99.5 to 100 mass%, and even more preferably 99.8 to 100 mass%, relative to the total mass of the solid composition.

[0026] When the first polymer contains PAVE units, the content of PAVE units relative to the sum of all units of the first polymer and all units of the second polymer is preferably 0.1 to 3.0 mol%, more preferably 0.2 to 3.0 mol%, and even more preferably 0.3 to 2.0 mol%. When the content of PAVE units is equal to or greater than the lower limit of the above range, the stability of the aqueous dispersion during production of the second polymer is improved, and when it is equal to or less than the upper limit, the heat resistance is improved. When the content of TFE units is equal to or greater than the lower limit of the above range, the heat resistance is improved, and when it is equal to or less than the upper limit, the stability of the aqueous dispersion during production of the second polymer is improved.

[0027] The solid composition includes primary particles containing a first polymer and a second polymer. In the primary particles, the first polymer and a portion of the second polymer may be copolymerized. The primary particles containing the first polymer and the second polymer may contain impurities unavoidable during production in addition to the first polymer and the second polymer. The content of the impurities relative to the total mass of the first polymer and the second polymer is preferably less than 250 ppb by mass, more preferably less than 25 ppb by mass, even more preferably less than 1 ppb by mass, and particularly preferably less than 0.1 ppb by mass. The content of the impurities may be 0 ppb by mass.

[0028] In the solid composition, the content of the compound represented by the following formula (S1) and the content of the compound represented by the following formula (S2) are each preferably 100 ppb by mass or less, more preferably 50 ppb by mass or less, even more preferably 25 ppb by mass or less, and particularly preferably 0 ppb by mass, relative to the total mass of the first polymer and the second polymer.

[0029] Formula (S1): H-(CF ２ ) ｎ１ -COOM Formula (S2): H-(CF ２ ) ｎ２ -SO ３ In the formula (S1) and the formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ wherein n1 represents an integer of 3 to 13, 15, or 17, and n2 represents an integer of 4 to 10, or 12.

[0030] The compound represented by the formula (S1) and the compound represented by the formula (S2) are components that can be generated when a fluorine-containing monomer such as TFE is polymerized in the presence of a polymerization initiator, a chain transfer agent, and an emulsifier (particularly, a hydrocarbon-based emulsifier).When no emulsifier is used in the polymerization step of the second polymer in the method for producing the solid composition of this embodiment described below, the amount of the compound represented by the formula (S1) and the compound represented by the formula (S2) generated can be suppressed, and it becomes easy to set the content of these compounds within the above range.

[0031] The average particle size of the primary particles is preferably 100 to 400 nm, more preferably 150 to 300 nm, and even more preferably 170 to 270 nm. When the average particle size is at least the lower limit of the above range, productivity and mechanical properties are improved, and when it is at most the upper limit, emulsion stability can be maintained during production of the second polymer. The aspect ratio of the primary particles is preferably 1.5 or less, more preferably 1.0 to 1.5, even more preferably 1.1 to 1.5, and particularly preferably 1.2 to 1.5. When the aspect ratio is at most the upper limit of the above range, emulsion stability can be imparted.

[0032] The solid composition may be a powder composition containing secondary particles formed by aggregation of primary particles containing a first polymer and a second polymer. When the solid composition is a powder composition, the average primary particle size of the solid composition is preferably 100 to 400 nm, more preferably 150 to 300 nm, and even more preferably 170 to 270 nm. The powder composition containing the secondary particles may contain impurities unavoidable during production in addition to the first polymer and the second polymer. The content of the impurities relative to the total mass of the powder composition is preferably less than 250 ppb by mass, more preferably less than 100 ppb by mass, and even more preferably less than 25 ppb by mass.

[0033] The standard specific gravity (SSG) of the solid composition is preferably 2.13 to 2.23, more preferably 2.14 to 2.20, and even more preferably 2.15 to 2.17. When the SSG is equal to or less than the upper limit of the above range, the molecular weight is large, and the mechanical strength during processing is improved.

[0034] The extrusion pressure of the solid composition in the extrusion test described below is preferably 10 to 30 MPa, more preferably 15 to 25 MPa, and even more preferably 17 to 23 MPa. When the extrusion pressure is equal to or higher than the lower limit of the above range, the tensile strength is high, and when it is equal to or lower than the upper limit, the processability is excellent.

[0035] <<Method for Producing Solid Composition>> The method for producing a solid composition preferably includes a step of polymerizing a monomer (hereinafter also referred to as "second monomer") constituting a second polymer in an aqueous dispersion C containing a first polymer and an aqueous medium to produce an aqueous dispersion D containing the second polymer and the first polymer. It also preferably includes a step of aggregating the first polymer and the second polymer in the aqueous dispersion D. The polymerization step of the first polymer and the polymerization step of the second polymer will be described below. Furthermore, the aggregation step of the first polymer and the second polymer will be described. Hereinafter, reaction liquid A refers to an aqueous dispersion containing the first polymer and an aqueous medium, and refers to the aqueous dispersion immediately after the production of the first polymer. Aqueous dispersion B refers to an aqueous dispersion obtained by subjecting reaction liquid A to ion exchange treatment. Aqueous dispersion C refers to an aqueous dispersion containing the first polymer and an aqueous medium, and refers to an aqueous dispersion used as a polymerization reaction liquid for the second polymer, and may be a diluted version of aqueous dispersion B. The total mass of aqueous dispersion C is the sum of the first polymer, the aqueous medium, and optional additives, and does not include the mass of the second monomer, the polymerization initiator, and the chain transfer agent. Aqueous dispersion D is an aqueous dispersion containing primary particles containing the first polymer and the second polymer, and is obtained by the polymerization step of the second polymer.

[0036] <Polymerization step of first polymer> Two aspects of the polymerization step of the first polymer will be described below. The first aspect will also be referred to as polymerization step (1) of the first polymer, and the second aspect will also be referred to as polymerization step (2) of the first polymer. As polymerization step (1) of the first polymer, a method of polymerizing a monomer constituting the first polymer (hereinafter also referred to as "first monomer") in an aqueous medium in the presence of a polymerization initiator is preferred. By this method, a reaction liquid A containing the first polymer is obtained in an aqueous medium. Preferred aspects, such as the type and ratio of the first monomer, are determined based on the composition of the first polymer described above. The reaction liquid A is preferably a dispersion in which primary particles of the first polymer are dispersed in an aqueous medium.

[0037] The polymerization initiator used in producing the first polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate. Also preferred is a water-soluble oxidation-reduction catalyst described below.

[0038] The aqueous medium used in producing the first polymer is exemplified by water or a mixed solvent of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0039] The first monomer is supplied to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the first monomer may be supplied to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the first monomer may be dissolved in an aqueous medium, and the resulting solution may be supplied to the reaction system continuously or intermittently. The polymerization initiator may be supplied to the reaction system all at once or in portions.

[0040] The polymerization temperature is preferably 20 to 150° C., more preferably 50 to 100° C. The polymerization pressure is preferably 0 to 3.0 MPa, more preferably 1.0 to 2.0 MPa. In the case of batch processing, the polymerization time is preferably 1 to 120 minutes, more preferably 10 to 60 minutes.

[0041] The obtained reaction liquid A may be directly subjected to the polymerization step of the second polymer, or the reaction liquid A may be subjected to one or more treatments selected from the group consisting of a solvent adjustment treatment, a heating treatment, and an ion exchange treatment, and then subjected to the polymerization step of the second polymer.

[0042] Examples of the solvent adjustment treatment include adding another aqueous medium to the reaction liquid A, or replacing the solvent in the reaction liquid A and dispersing the first polymer in another aqueous medium.

[0043] When the heat treatment is performed, the polymerization initiator contained in the reaction solution A is deactivated, and therefore the polymerization step of the second polymer is less affected by the polymerization initiator used in producing the first polymer. As a result, a second polymer with a high molecular weight is more likely to be obtained. The heating temperature is preferably 70 to 100°C, more preferably 80 to 98°C, and even more preferably 85 to 95°C. When the heating temperature is within the above range, the deactivation of the polymerization initiator in the aqueous medium can be further promoted.

[0044] An example of the ion exchange treatment is contacting reaction liquid A with either or both of an anion exchange resin and a cation exchange resin to remove either or both of anions and cations, which are impurities contained in reaction liquid A.

[0045] An example of an anion impurity is sulfate ion. Sulfate ion originates from the polymerization initiator (particularly ammonium persulfate) and may be contained in reaction solution A. By subjecting reaction solution A to ion exchange treatment using an anion exchange resin to obtain aqueous dispersion B, the sulfate ion content in aqueous dispersion C after dilution can be reduced. The content of sulfate ion relative to the total mass of aqueous dispersion C is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less. The lower limit is not particularly limited, and may be 0 ppm by mass. It is believed that when the content of sulfate ion is equal to or less than the upper limit, the formation of terminal groups with low heat resistance in the second polymer can be suppressed. As a result, it is presumed that coloration of the second polymer (primary particles) is suppressed.

[0046] An example of an anion impurity is fluoride ion. Fluoride ion may be generated by the reaction between a polymerization initiator (e.g., ammonium persulfate) and a monomer used in producing the first polymer, and may be contained in the reaction solution A. By subjecting the reaction solution A to ion exchange treatment using an anion exchange resin to obtain aqueous dispersion B, the fluoride ion content in the diluted aqueous dispersion C can be reduced. The content of fluoride ion relative to the total mass of aqueous dispersion C is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less. The lower limit is not particularly limited and may be 0 ppm by mass. When the content of fluoride ion is equal to or less than the upper limit, polymerization is likely to be stable in the polymerization step of the second polymer.

[0047] An example of a cation impurity is ammonium ion. Ammonium ion may be derived from the polymerization initiator (particularly ammonium persulfate) and be contained in reaction solution A. By subjecting reaction solution A to ion exchange treatment using a cation exchange resin to obtain aqueous dispersion B, the ammonium ion content in aqueous dispersion C after dilution can be reduced. The content of ammonium ion relative to the total mass of aqueous dispersion C is preferably 20 ppm by mass or less, more preferably 10 ppm by mass or less. The lower limit is not particularly limited, and may be 0 ppm by mass. It is believed that when the content of ammonium ion is equal to or less than the upper limit, the ionic strength in the aqueous medium is reduced, thereby suppressing aggregation of the second polymer. As a result, it is predicted that the production efficiency of the second polymer is improved.

[0048] Next, the polymerization step (2) of the first polymer will be described. In the polymerization step (2) of the first polymer, a first monomer is polymerized in a first aqueous medium in the presence of compound (1) to produce a first polymer. This polymerization is preferably carried out in the presence of compound (1) and a polymerization initiator, and the same polymerization initiator as in the polymerization step (1) of the first polymer can be used as the polymerization initiator. As a result of the polymerization step (2) of the first polymer, a first post-polymerization dispersion is obtained, which is a dispersion containing the first polymer and the first aqueous medium.

[0049] <Compound (1)> Compound (1) is a compound represented by the following formula (2): CX １ X ２ =CX ３ -L-Z...(2) In formula (2), X １ and X ２ are each independently a hydrogen atom or an alkyl group, ３ represents a hydrogen atom, a fluorine atom, or an alkyl group; L represents a single bond or a divalent linking group; Z represents -SO ３ M １ , -OSO ３ M １ , -P(=O)(OM １ ) ２ , -OP(=O)(OM １ ) ２ , or -COOM １and M １ represents a hydrogen atom, a metal atom, N(R Ｍ１１ ) ４ or P(R Ｍ１２ ) ４ and M １ If there are multiple M １ may be the same or different from each other, R Ｍ１１ and R Ｍ１２ are each independently a hydrogen atom or a substituent, and R Ｍ１１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１１ may be the same or different from each other, R Ｍ１２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１２ may be the same or different from each other.

[0050] In formula (2), X １ and X ２ are each independently a hydrogen atom or an alkyl group. The alkyl group may be linear, branched, or cyclic. The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1. X １ and X ２ In terms of increasing the number of particles of the first polymer, it is preferable that each of X is a hydrogen atom. ３ is a hydrogen atom, a fluorine atom, or an alkyl group. Specific examples and preferred embodiments of the alkyl group are １ and X ２ The specific examples and preferred embodiments of the alkyl group in X are the same as those in X. ３ is preferably a fluorine atom or a hydrogen atom, more preferably a hydrogen atom, from the viewpoint of increasing the number of particles of the first polymer.

[0051] In formula (2), L is a single bond or a divalent linking group. Examples of the divalent linking group include an alkylene group, a carbonyl group, an ether bond, a thioether bond, a sulfonyl group, —NH—, and —SiH ２ -, phenylene group, -CF ２-, and groups combining two or more of these. Examples of the above groups combining two or more of these include an ester bond, a thioester bond, an amide bond, a sulfonamide bond, a combination of an alkylene group and an ether bond, a combination of an alkylene group and an ester bond, and a combination of an alkylene group and an amide bond. The alkylene group may be linear, branched, or cyclic, and is preferably linear or branched, and more preferably branched. The number of carbon atoms in the alkylene group may be, for example, 1 to 6, and preferably 1 to 4.

[0052] Specific examples of L include a single bond, an alkylene group, an ether bond, an ester bond, * Ｃ -CO-NH-R-* Ｚ and the like, and examples thereof include a single bond, an alkylene group having 1 to 6 carbon atoms, and * Ｃ -CO-NH-R-* Ｚ are preferred, and particularly preferred are a single bond, an alkylene group having 1 to 2 carbon atoms, and * Ｃ -CO-NH-R-* Ｚ is more preferable. Ｃ is the bonding site to the carbon atom in formula (2), and * Ｚ is the bonding site to Z in formula (2), and R is an alkylene group having 1 to 6 carbon atoms.

[0053] In formula (2), Z is —SO ３ M １ , -OSO ３ M １ , -P(=O)(OM １ ) ２ , -OP(=O)(OM １ ) ２ or -COOM １ From the viewpoint of stabilizing the dispersion and increasing the number of particles of the first polymer, Z is -SO ３ M １ and -COOM １ is preferred, and —SO ３ Na and —COONa are more preferred, and —SO ３ Na is more preferred.

[0054] M １ represents a hydrogen atom, a metal atom, N(R Ｍ１１ )４ or P(R Ｍ１２ ) ４ and R Ｍ１１ and R Ｍ１２ are each independently a hydrogen atom or a substituent. １ The metal atom represented by R is preferably a metal atom of Group 1, more preferably Li, Na, or K. Ｍ１１ and R Ｍ１２ The substituent represented by the formula (I) is preferably a monovalent organic group, more preferably a monovalent hydrocarbon group, and even more preferably an alkyl group or an aromatic hydrocarbon group. The substituent preferably has 1 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic. The aromatic hydrocarbon group is preferably a phenyl group.

[0055] The molecular weight of the compound (1) is, for example, 70 to 500, and from the viewpoint of dispersion stability, it is preferably 70 to 450, and more preferably 100 to 300.

[0056] Specific examples of compound (1) include vinyl sulfonic acid, vinyl phosphonic acid, (meth)acrylic acid, allyl sulfonic acid, allyl phosphonic acid, butenoic acid, crotonic acid, vinyl acetic acid, 2-sulfoethyl methacrylic acid, 4-vinyl benzene sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, N-tigloylglycine, 6-acrylamidohexanoic acid, 1,1-difluoro-2-methyl-2-[(1-oxo-2-propen-1-yl)amino]-1-propanesulfonic acid, 3-methyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2,3-dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, and metal salts thereof. Examples of the metal salts include M １ Examples of the metal salt include a metal salt of a metal atom represented by the following formula:

[0057] As compound (1), vinyl compounds having a sulfonic acid group, a phosphonic acid group, or a carboxy group, allyl compounds having a sulfonic acid group, a phosphonic acid group, or a carboxy group, (meth)acrylic acid, (meth)acrylamides having a sulfonic acid group, a phosphonic acid group, or a carboxy group, and metal salts thereof are preferred, and vinyl sulfonic acid, sodium vinyl sulfonate, allyl sulfonic acid, sodium allyl sulfonate, 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium 2-acrylamido-2-methyl-1-propanesulfonate, 2-methacrylamido-2-methyl-1-propanesulfonic acid, or sodium 2-methacrylamido-2-methyl-1-propanesulfonate are preferred. Note that the term "(meth)acrylic acid" encompasses both acrylic acid and methacrylic acid, and the term "(meth)acrylamide" encompasses both acrylamide and methacrylamide.

[0058] Before the polymerization of the first monomer is initiated, the content of compound (1) is preferably 1.0 to 1000 ppm by mass relative to the entire first aqueous dispersion. In terms of better effects of the present invention, 1.0 to 800 ppm by mass is more preferable, 3.0 to 500 ppm by mass is even more preferable, and 5.0 to 300 ppm by mass is particularly preferable. Note that the concept of the "first aqueous dispersion" before the polymerization of the first monomer is initiated includes compound (1) and an aqueous medium, but does not include the first monomer and polymerization initiator used in the polymerization of the first polymer. For example, even if the first aqueous dispersion containing compound (1) and an aqueous medium is mixed with the first monomer and the polymerization initiator before the polymerization of the first monomer is initiated, the "first aqueous dispersion" refers to a mixture of components excluding the first monomer and the polymerization initiator.

[0059] <First Aqueous Medium> Specific examples of the first aqueous medium include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0060] Before starting the polymerization of the first monomer, the content of the first aqueous medium is preferably 20 to 90% by volume, more preferably 40 to 80% by volume, based on the volume of the reactor.

[0061] <First Monomer> The first monomer used in the present production method includes at least one selected from the group consisting of tetrafluoroethylene (hereinafter also referred to as "TFE") and hexafluoropropylene (hereinafter also referred to as "HFP"). The first monomer may include a monomer other than TFE and HFP, and preferably includes a monomer other than TFE and HFP. Examples of the monomer other than TFE and HFP include perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), propylene, vinylidene fluoride (hereinafter also referred to as "VdF"), CH ２ =CF-CF ２ -O-Rf-COOH, CH ２ =CF-CF ２ —O—Rf—SO ３ H, C.F. ２ =CF-CF ２ -O-Rf-COOH, CF ２ =CF-CF ２ —O—Rf—SO ３ H, CH ２ =CF-O-Rf-COOH, CH ２ =CF-O-Rf-SO ３ H, C.F. ２ ═CF—O—Rf—COOH, and CF ２ =CF-O-Rf-SO ３ H (Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom between carbon atoms). When the first monomer contains TFE, the amount of TFE used is preferably 10 to 90 mol%, more preferably 30 to 85 mol%, and even more preferably 40 to 80 mol%, based on the amount of the first monomer used. When the first monomer contains HFP, the amount of HFP used is preferably 30 to 95 mol%, more preferably 40 to 90 mol%, and even more preferably 50 to 85 mol%, based on the amount of the first monomer used.

[0062] In terms of excellent polymerization reactivity of the first polymer and more excellent effects of the present invention, the first monomer preferably contains PAVE. In terms of excellent polymerization reactivity when producing the first polymer and more efficiently producing the second polymer, PAVE is preferably a monomer represented by formula (11).

[0063] CF ２ =CF-O-R ｆ１ (11) In formula (11), R ｆ１ is a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0064] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), and PMVE or PPVE are preferred, with PMVE being more preferred, from the viewpoint of enabling more efficient production of the second polymer.

[0065] When the first monomer contains PAVE, the amount of PAVE used is preferably 20 to 95 mol %, more preferably 25 to 80 mol %, and even more preferably 30 to 60 mol %, based on the amount of the first monomer used. The suitable amount is the same whether the PAVE is PMVE, PEVE, or PPVE, or a mixture of two or more of these.

[0066] In terms of excellent polymerization reactivity of the first polymer and better effects of the present invention, it is also preferable that the first monomer contains at least one selected from the group consisting of propylene and VdF.

[0067] When the first monomer contains propylene, the amount of propylene used is preferably 5 to 90 mol %, more preferably 8 to 70 mol %, and even more preferably 10 to 60 mol %, relative to the amount of the first monomer used. When the first monomer contains VdF, the amount of VdF used is preferably 5 to 90 mol %, more preferably 8 to 80 mol %, and even more preferably 10 to 70 mol %, relative to the amount of the first monomer used.

[0068] The first monomer preferably includes any combination of TFE and PAVE, TFE and propylene, or HFP and VdF. When the first monomer includes TFE and PAVE, the amount of PAVE used is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 60 mol%, based on the total amount of TFE and PAVE used. Whether the PAVE is PMVE, PEVE, or PPVE, or a mixture of two or more of these, the preferred amount is the same. When the first monomer includes TFE and PAVE, the total amount of TFE and PAVE used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on the total amount of the first monomer used. When the first monomer comprises TFE and propylene, the amount of propylene used is preferably 5 to 90 mol%, more preferably 8 to 70 mol%, and even more preferably 10 to 60 mol%, based on the total amount of TFE and propylene used. When the first monomer comprises TFE and propylene, the total amount of TFE and propylene used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on the total amount of the first monomer used. When the first monomer comprises HFP and VdF, the amount of VdF used is preferably 5 to 90 mol%, more preferably 8 to 80 mol%, and even more preferably 10 to 70 mol%, based on the total amount of HFP and VdF used. When the first monomer contains HFP and VdF, the total amount of HFP and VdF used is preferably 99.0 to 100.0 mol %, more preferably 99.5 to 100.0 mol %, and still more preferably 99.9 to 100.0 mol %, based on the amount of the first monomer used.

[0069] The first monomer may contain other monomers than those described above, or may be substantially free of other monomers in order to more efficiently produce the second polymer. "Substantially free of other monomers" means that the amount of other monomers used is 0.01 mol % or less, and preferably 0 mol %, relative to the amount of the first monomer used.

[0070] In the first aspect, the polymerization steps (1) and (2) of the first polymer are preferably carried out under conditions in which emulsifiers having fluorine atoms and emulsifiers not having fluorine atoms are substantially absent, in order to suppress a decrease in molecular weight of the resulting first polymer. In other words, it is preferable that the aqueous dispersion is substantially free of emulsifiers having fluorine atoms and emulsifiers not having fluorine atoms. The term "substantially free of emulsifiers having fluorine atoms and emulsifiers not having fluorine atoms" (hereinafter collectively referred to as "emulsifiers") means that the content of emulsifiers is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the first aqueous dispersion. The lower limit is 0 mass ppb. The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement methods described in paragraphs

[0721] to

[0732] of WO 2018 / 181904 can be mentioned.

[0071] Examples of the emulsifier having a fluorine atom and the emulsifier not having a fluorine atom include water-soluble emulsifiers. A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier means an emulsifier other than the above-mentioned water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or nonionic. Examples of the emulsifier having a fluorine atom and the emulsifier not having a fluorine atom include those not having a carbon-carbon double bond. Furthermore, compound (1), the first polymer described below, and the second fluorine-containing polymer described below do not fall under the category of emulsifiers.

[0072] Examples of emulsifiers having fluorine atoms include anionic fluorine-containing emulsifiers. Examples of anionic fluorine-containing emulsifiers include emulsifiers containing fluorine atoms whose total carbon number excluding anionic groups is 20 or less, and emulsifiers containing fluorine atoms whose anionic moiety has a molecular weight of 800 or less. The above-mentioned "anionic moiety" means the moiety excluding the cation of the fluorine-containing emulsifier.

[0073] The fluorine-free emulsifier is an emulsifier that does not contain fluorine atoms and has a hydrocarbon group such as an alkyl group as a hydrophobic moiety. It is also possible to substitute a hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier with a halogen atom other than a fluorine atom.

[0074] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0075] Anionic hydrocarbon emulsifiers refer to emulsifiers having a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon group, such as an alkyl group, as a hydrophobic moiety. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, and sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0076] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as their hydrophobic moieties. The hydrophilic moieties of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0077] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

[0052] of JP-A No. 2016-537499.

[0078] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier with silicon atom can include siloxane emulsifier.Siloxane emulsifier is a hydrocarbon-containing emulsifier with siloxane skeleton.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0079] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of the polymer emulsifier include a polymer having a hydrophilic group in a side chain. Examples of such a polymer emulsifier include a polymer containing a unit based on a compound having a site capable of polymerization reaction and a hydrophilic group. Further, even if the polymer does not originally have a hydrophilic group, a polymer containing a unit based on a compound having a group that can become a hydrophilic group and subjected to post-treatment such as hydrolysis may also be used.

[0080] When the first monomer is polymerized in the presence of an emulsifier having no fluorine atoms, typically, 0.1 to 15 parts by mass of the emulsifier having no fluorine atoms is used per 100 parts by mass of the aqueous medium.

[0081] <Polymerization step of second polymer> The polymerization step of the second polymer is preferably a method of polymerizing a second monomer in an aqueous dispersion C containing the first polymer and an aqueous medium. If necessary, a polymerization initiator and a chain transfer agent may be supplied. This method produces an aqueous dispersion D in which primary particles containing the first polymer and the second polymer are dispersed in an aqueous medium. Preferred aspects such as the type and ratio of the second monomer are determined based on the composition of the second polymer described above.

[0082] The content of the first polymer relative to the total mass of the aqueous dispersion C is preferably 0.01 to 4.0 mass%, more preferably 0.01 to 0.6 mass%, and even more preferably 0.01 to 0.5 mass%. When the content of the first polymer is within this range, the second polymer can be produced more efficiently. The content of the first polymer relative to the total mass of the aqueous dispersion C can be adjusted by the solvent adjustment treatment described above.

[0083] It is preferred that primary particles of the first polymer are dispersed in the aqueous medium of aqueous dispersion C. The average particle size of the primary particles of the first polymer is preferably 1 to 150 nm, more preferably 10 to 120 nm, and even more preferably 50 to 120 nm. When the average particle size of the first polymer is within the above range, the second polymer can be produced more efficiently. The average particle size of the primary particles of the first polymer is the average particle size (hydrodynamic diameter) obtained by measuring by a dynamic scattering method and analyzing by the cumulant method, and detailed measurement conditions are as described in the Examples section.

[0084] Examples of the aqueous medium contained in the aqueous dispersion C include the same aqueous media as those described in the production process of the reaction liquid A. The content of the aqueous medium relative to the total mass of the aqueous dispersion C is preferably 60 to 99.9 mass%, more preferably 80 to 99.9 mass%, and even more preferably 90 to 99.9 mass%.

[0085] The aqueous dispersion C may contain other components in addition to the first polymer and the aqueous medium. Specific examples of the other components include a pH adjuster, a wax, an emulsifier, and a reducing agent.

[0086] Examples of pH adjusters include inorganic salts. Examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium hydrogen carbonate and sodium carbonate. Preferred phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0087] The wax is preferably paraffin wax. Paraffin wax may be liquid, semi-solid, or solid at room temperature. Among them, saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is preferably 40 to 65°C, more preferably 50 to 65°C.

[0088] Examples of emulsifiers include fluorine-based emulsifiers and non-fluorine-based emulsifiers, but in this embodiment, it is preferable that the aqueous dispersion C does not substantially contain a fluorine-based emulsifier. That is, it is preferable that a fluorine-based emulsifier is not used in the polymerization step of the second polymer. A fluorine-based emulsifier refers to an emulsifier in which the hydrophobic moiety contains a fluorine atom in the hydrophilic moiety and the hydrophobic moiety of the emulsifier. Specific examples of fluorine-based emulsifiers include fluorine-containing alkanoates and fluorine-containing ether carboxylic acid compounds. A non-fluorine-based emulsifier refers to an emulsifier other than a fluorine-based emulsifier. Examples of non-fluorine-based emulsifiers include sodium lauryl sulfate, Perex SS-H manufactured by Kao Chemical Corporation, and Newcol 1305-SN manufactured by Nippon Nyukazai Co., Ltd.

[0089] "Substantially free of a fluorine-based emulsifier" means that the content of the fluorine-based emulsifier relative to the total mass of the First Polymer in the aqueous dispersion C is 100 ppm by mass or less, preferably 50 ppm by mass or less, more preferably 25 ppm by mass or less, and even more preferably 5 ppm by mass or less. The lower limit is not particularly limited, and may be 0 ppm by mass.

[0090] When aqueous dispersion C contains an emulsifier other than a fluorine-based emulsifier, the content of the emulsifier other than a fluorine-based emulsifier is preferably 0.01 to 5% by mass relative to the aqueous medium. In this embodiment, aqueous dispersion C preferably does not substantially contain an emulsifier. That is, it is preferable that no emulsifier is used in the polymerization step of the second polymer. "Substantially does not contain an emulsifier" means that the content of the emulsifier is 100 ppm by mass or less, preferably 10 ppm by mass or less, more preferably 100 ppb by mass or less, and even more preferably 1 ppb by mass or less, relative to the total mass of the first polymer and the second polymer. It may be 0.1 ppb by mass or less, or even 0 ppb by mass. When an emulsifier is not used, the generation amounts of the compound represented by formula (S1) and the compound represented by formula (S2) can be suppressed, making it easier to keep the content of these compounds within the above-mentioned range.

[0091] The method for producing a solid composition according to this embodiment allows efficient production of a second polymer without the use of an emulsifier. It is believed that during polymerization of the second monomer, the first polymer adsorbs the second monomer at its hydrophobic portion and incorporates it into the primary particles of the first polymer, thereby solubilizing the second monomer. As a result, it is believed that the second monomer is polymerized within or near the primary particles of the first polymer. Furthermore, it is believed that the first polymer contributes to dispersion stabilization in an aqueous medium.

[0092] When aqueous dispersion C contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium. When aqueous dispersion C contains a wax, the content of the wax is preferably 1 to 10 parts by mass per 100 parts by mass of the aqueous medium. When aqueous dispersion C contains a reducing agent, the amount of the reducing agent used is preferably 1 to 2000 ppm by mass per 100 parts by mass of the second monomer supplied.

[0093] The reaction is initiated by supplying a second monomer to the aqueous dispersion C, and optionally supplying a polymerization initiator. During the reaction, a chain transfer agent may be supplied.

[0094] The second monomer is supplied to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the second monomer may be supplied to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the second monomer may be dissolved in an aqueous medium, and the resulting solution may be supplied to the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be supplied to the reaction system all at once or in portions.

[0095] The amount of the second monomer supplied is preferably 1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass, relative to 100 parts by mass of the aqueous medium contained in the aqueous dispersion C.

[0096] Examples of polymerization initiators include oil-soluble radical initiators, water-soluble radical initiators, and water-soluble redox catalysts. Examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Examples of 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. Examples of water-soluble redox catalysts include combinations of oxidizing agents such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, and hydrogen peroxide with reducing agents such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, organic acids, and inorganic salts. Potassium persulfate and ammonium persulfate are preferred as persulfates. Sodium sulfite is preferred as sulfite. Examples of inorganic salts include combinations of sulfate anions, sulfite anions, and chloride anions with metal ions. Preferred metal ions are transition metals, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. Preferred inorganic salts are iron (II) sulfate. Preferred polymerization initiators are oil-soluble radical initiators and water-soluble radical initiators, with oil-soluble radical initiators being more preferred and oil-soluble organic peroxides being even more preferred in terms of more efficient production of fluorine-containing polymers. Two or more polymerization initiators may be used in combination.

[0097] The amount of the polymerization initiator to be supplied is preferably 1 to 1,000 ppm, more preferably 5 to 750 ppm, and even more preferably 10 to 500 ppm, relative to 100 parts by mass of the amount of the second monomer to be supplied.

[0098] Examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0099] The amount of the chain transfer agent supplied is preferably 0.1 to 5 parts by mass relative to 100 parts by mass of the aqueous medium, and is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the second monomer supplied.

[0100] 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. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0101] (Aqueous Dispersion D) Aqueous Dispersion D is an aqueous dispersion containing primary particles containing a first polymer and a second polymer, and is obtained by the polymerization step of the second polymer.

[0102] It is preferable that the aqueous dispersion D is substantially free of an emulsifier. Examples of the emulsifier include the above-mentioned fluorine-based emulsifiers and non-fluorine-based emulsifiers. "Substantially free of an emulsifier" in the aqueous dispersion D means that the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm, relative to the total mass of the aqueous dispersion D.

[0103] When no emulsifier is used in the polymerization step of the second polymer, aqueous dispersion D can easily be converted into a dispersion in an organic solvent such as N-methylpyrrolidone, acetone, etc. by solvent substitution. For example, aqueous dispersion D can be converted into a dispersion in an organic solvent by mixing it with an organic solvent and dehydrating it using evaporation or anhydrous sodium sulfate, etc.

[0104] The content of the first polymer is preferably 0.10 to 2.00% by mass, more preferably 0.15 to 1.50% by mass, and even more preferably 0.20 to 0.80% by mass, relative to the total mass of aqueous dispersion D. The content of the second polymer is preferably 10 to 40% by mass, more preferably 12 to 35% by mass, and even more preferably 15 to 30% by mass, relative to the total mass of aqueous dispersion D. The combined content of the first polymer and the second polymer is preferably 10 to 40% by mass, more preferably 12 to 35% by mass, and even more preferably 15 to 35% by mass, relative to the total mass of aqueous dispersion D.

[0105] The content of the aqueous medium relative to the total mass of the aqueous dispersion D is preferably from 50 to 99 mass %, more preferably from 60 to 99 mass %, and even more preferably from 70 to 99 mass %.

[0106] When the first polymer contains PAVE units, the content of PAVE units relative to the sum of all units of the first polymer and all units of the second polymer is preferably 0.1 to 5.0 mol %, more preferably 0.2 to 3.0 mol %, and even more preferably 0.3 to 2.0 mol %. When the content of PAVE units is at least the lower limit of the above range, excellent dispersibility is achieved, and when it is at most the upper limit, excellent heat resistance is achieved.

[0107] The content of TFE units relative to the total of all units of the first polymer and all units of the second polymer is preferably 90 to 99.8 mol %, more preferably 93 to 99.5 mol %, and even more preferably 95 to 99.0 mol %.

[0108] In the aqueous dispersion D, the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each preferably 100 ppb by mass or less, more preferably 50 ppb by mass or less, even more preferably 25 ppb by mass or less, and particularly preferably 0 ppb by mass, relative to the total mass of the first polymer and the second polymer.

[0109] The average particle size of the primary particles in aqueous dispersion D is preferably 100 to 400 nm, more preferably 150 to 300 nm, and even more preferably 170 to 270 nm. When the average particle size is at least the lower limit of the above range, productivity and mechanical properties are improved, and when it is at most the upper limit, emulsion stability can be maintained during production of the second polymer. The aspect ratio of the primary particles is preferably 1.5 or less, more preferably 1.0 to 1.5, even more preferably 1.1 to 1.5, and particularly preferably 1.2 to 1.5. When the aspect ratio is at most the upper limit of the above range, emulsion stability can be imparted.

[0110] <Step of aggregating first polymer and second polymer> The solid in aqueous dispersion D is agglomerated, and the dispersion medium such as an aqueous medium is removed to obtain a wet powder, which is then dried to obtain a dry powder solid composition. When aqueous dispersion D contains primary particles, the average particle size and aspect ratio of the primary particles in aqueous dispersion D can be considered to be the same as the average particle size and aspect ratio of the primary particles in the dry powder. The aggregating step, the step of removing the dispersion medium to obtain a wet powder, and the step of drying the wet powder to obtain a dry powder can be carried out using known techniques.

[0111] Aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, aggregation using a coagulant, and mechanical aggregation. In the case of freeze aggregation, the aggregation temperature is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which an acid-containing solution is added to aqueous dispersion D is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with hydrochloric acid being preferred. The acid concentration in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base aggregation, a method in which a base-containing solution is added to aqueous dispersion D is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The base concentration in the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, a compound of the general formula M'Al(SO ４ ) ２ ・12H ２ Examples of the alum include alum represented by the formula: ##STR00001## where M' is a monovalent cation other than lithium, calcium nitrate, and magnesium sulfate. Alum is preferred, and potassium alum, where M is potassium, is more preferred. Examples of mechanical agglomeration include known methods described in paragraph

[0032] of WO 2023 / 115278. Mechanical agglomeration is preferred as it can be easily performed.

[0112] <Electrode Binder> The electrode binder of this embodiment contains the solid composition described above. The content of the solid composition relative to the total mass of the electrode binder is preferably 80 mass% or more, more preferably 90 mass% or more, even more preferably 95 mass% or more, and may be 100 mass%. Examples of components that the electrode binder may contain other than the solid composition include fluororesins, polyimide resins, polyolefin resins, and the like, other than the first polymer and second polymer contained in the solid composition of this embodiment.

[0113] <Electrode Mix> The electrode mix of this embodiment contains an electrode binder and an electrode active material. The electrode active material may be a positive electrode active material or a negative electrode active material. That is, the electrode binder of this embodiment can be used for both positive and negative electrodes. The electrode mix may further contain a conductive additive and a solvent.

[0114] The positive electrode active material is LiNiO ２ (Lithium nickel oxide) based positive electrode active material, LiCoO ２ (Lithium cobalt oxide) based positive electrode active material, LiMnO ４ (Lithium manganese oxide) based positive electrode active material, LiFePO ４ Examples of positive electrode active materials include lithium iron phosphate (LiFePO4). Part of the nickel in lithium nickel oxide, part of the cobalt in lithium cobalt oxide, part of the manganese in lithium manganese oxide, and part of the iron in lithium iron phosphate may be substituted with other elements. Examples of other elements include nickel, cobalt, manganese, iron, copper, titanium, magnesium, tungsten, molybdenum, aluminum, niobium, zinc, tin, zirconia, gallium, vanadium, boron, phosphorus, sulfur, and silicon.

[0115] Examples of the negative electrode active material include carbon materials such as graphite, carbon black, carbon fiber, and baked organic polymers; chalcogen compounds such as oxides and sulfides; and nitrides. Other examples include metals and alloys. Examples of oxides include silicon oxide and tin oxide. Examples of metals include lithium metal, silicon metal, and tin metal.

[0116] Examples of the conductive aid include carbon black such as acetylene black, and carbon fiber.

[0117] Examples of the solvent include amine solvents such as N,N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; ester solvents such as methyl acetate; and amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).

[0118] In addition to the above, materials known in the art can be used as the positive electrode active material, negative electrode active material, conductive additive, and solvent. For example, materials described in Japanese Patent No. 7303469 can be used. The other known components preferably include a solid electrolyte, more preferably a sulfide-based solid electrolyte. Examples of solid electrolytes include sulfide-based solid electrolytes having an argyrodite-type crystal structure, oxide-based solid electrolytes, and halogen-based solid electrolytes. Examples of solid electrolytes also include solid electrolytes that constitute secondary batteries, which will be described later.

[0119] The content of the solid composition relative to the total mass of the electrode mixture excluding the solvent is preferably 0.5 to 3.5 mass%, more preferably 1.0 to 3.0 mass%, and even more preferably 1.5 to 2.5 mass%. The content of the electrode active material relative to the total mass of the electrode mixture excluding the solvent is preferably 92 to 98 mass%, more preferably 93 to 97 mass%, and even more preferably 94 to 96 mass%. The content of the conductive assistant relative to the total mass of the electrode mixture excluding the solvent is preferably 1.5 to 4.5 mass%, more preferably 2.0 to 4.0 mass%, and even more preferably 2.5 to 3.5 mass%.

[0120] <Electrode> The electrode of this embodiment includes an electrode mixture and a current collector. In the electrode, the electrode mixture is supported on the current collector. The positive electrode current collector may be a strip-shaped member made of a metal material such as aluminum metal, nickel metal, or stainless steel. The negative electrode current collector may be a strip-shaped member made of a metal material such as copper metal, nickel metal, or stainless steel.

[0121] An example of a method for supporting an electrode mixture on a current collector is to apply a paste-like electrode mixture to at least one surface of the current collector, dry it, and then pressurize it. The paste-like electrode mixture can be prepared using the above-mentioned solvent. A coating method known in the art can be used to apply the paste-like electrode mixture.

[0122] <Secondary Battery> The secondary battery of this embodiment includes an electrode. The electrode containing the above-mentioned solid composition may be a positive electrode, a negative electrode, or both a positive electrode and a negative electrode. The secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is sandwiched between the positive electrode and the negative electrode. The electrolyte is present between the positive electrode and the negative electrode. When the secondary battery is an all-solid-state battery, it includes a positive electrode, a negative electrode, and a solid electrolyte. Examples of secondary batteries include lithium-ion secondary batteries and nickel-metal hydride batteries.

[0123] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. In the following examples, Examples 1 to 3 are working examples, and Example 4 is a comparative example.

[0124] <Measurement method and evaluation method> [Glass transition temperature (Tg)] Tg was measured using a NEXTA DSC600 manufactured by Hitachi High-Technologies Corporation. Specifically, 5 mg of a sample for measurement was weighed into an aluminum sample pan, and the sample was heated to 100°C at a heating rate of 10°C / min under a nitrogen atmosphere. Thereafter, the sample was cooled to -60°C at a rate of 10°C / min. Once the predetermined temperature was reached, the temperature was again raised to 100°C at 10°C / min. Tg was estimated from the inflection point observed in this second heating operation.

[0125] [Proportion of each unit in the polymer] The proportion of each unit in the polymer is １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0126] [Solids concentration of aqueous dispersion] The solids concentration was determined by measuring the heating residue. Specifically, 7 to 8 g of the sample to be measured was weighed out and placed on an aluminum dish whose mass had been measured in advance, and heated at 120°C for 2 hours to evaporate the water. Next, the mass of the aluminum dish containing the solids remaining on the aluminum dish was measured. The solids concentration (unit: mass%) was calculated by dividing the mass of the solids by the mass of the sample used in the measurement.

[0127] [Average particle size of primary particles in aqueous dispersion] Measurement was performed by dynamic light scattering. The solid content of the aqueous dispersion to be measured was adjusted to 5.0% by mass to prepare a sample solution. However, when the solid content of the aqueous dispersion to be measured (stock solution) was less than 5%, the stock solution was used as the sample solution. Measurements were performed at 23°C, accumulating 125 times, using a particle size measurement system (Otsuka Electronics Co., Ltd. product name "ELSZ-neo"), and the average particle size determined by the cumulant method was used as the average particle size (unit: nm) of the primary particles. The refractive index of the solvent (water) was 1.333, and the viscosity of the solvent (water) was 0.93 mPa s.

[0128] [Number of Particles in Aqueous Dispersion] Using the relational equation, solid concentration of aqueous dispersion x = number of primary particles N × primary particle volume V × primary particle specific gravity ρ1 / specific gravity of aqueous dispersion ρ2, the number of primary particles per mL of aqueous dispersion was calculated using the following equation. Primary particles were considered to be true spheres. N = x ρ2 / V ρ1 N (unit: particles / mL): number of primary particles per mL x (unit: mass %): solid concentration of aqueous dispersion V (unit: mL / particle): volume of primary particles, V = 4 / 3 π (r / 2 × 10 －７ ) ３ r (unit: nm): primary particle diameter. ρ1 (unit: g / mL): density of primary particles. If it can be measured as PTFE, the value of SSG is used as ρ1, and if it cannot be measured as PTFE, ρ1 = 2.2. ρ2 (unit: g / mL): specific gravity of aqueous dispersion, empirically obtained value is ρ2 = 0.492x ２ +0.5319x +0.09992 was used, where x is the solid content concentration.

[0129] [Aspect Ratio] Aqueous Dispersion D was diluted to a solids concentration of 0.2% by mass to prepare a sample dispersion. The sample dispersion was dropped onto a substrate and dried, followed by Pt deposition. A scanning electron microscope (SEM, JEOL Ltd., JSM-IT700HR InTouchScope) was used to randomly select fields of view at a magnification of 20,000x so that particles did not overlap, and four or more observation images were saved. Using the image analysis software "MultiImage Tool," 800 or more elliptical particles were selected from the observation images. The brightness was adjusted and the particles and substrate were subjected to binarized image processing, after which the ratio of the long side to the short side of the particles (aspect ratio) was analyzed. The average aspect ratio of each particle was taken as the aspect ratio of the primary particles.

[0130] [Total Content of Compound (S1) Represented by Formula (S1) and Compound (S2) Represented by Formula (S2)] The content of the compounds represented by the above formulas (S1) and (S2) relative to the total mass of the fluoropolymer in the dry powder obtained in each example described below (hereinafter also referred to as "content M") was measured using a liquid chromatograph mass spectrometer as follows. 5 mL of methanol was added to 2.5 g of the dry powder obtained in each example described below, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate the fluoropolymer, and the supernatant was extracted as an extract. The extract was diluted with water or methanol as necessary and used for measurement. In this way, extract M to be used for measuring content M was obtained.

[0131] (Measurement Procedure) For extract M, the peak areas of the compounds represented by formula (S1) and formula (S2) with each carbon number were determined using MRM (Multiple Reaction Monitoring). Compounds in formula (S1) where n1 is 3 to 13, 15, and 17 were determined by converting them into perfluorocarboxylic acids with the same carbon number. Compounds in formula (S2) where n2 is 4 to 10, and 12 were determined by converting them into perfluorosulfonic acids with the same carbon number.

[0132] The measurement equipment and conditions are shown in Table 1. The MRM measurement parameters are shown in Tables 2 to 5. First, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations of 1 to 180 ng / g were prepared, and a was calculated using the following formula (A1) by using a first-order approximation from the respective sample concentrations and peak integral values: A = a × X (A1), where A is the peak area of ​​perfluorocarboxylic acid and perfluorosulfonic acid, and X is the concentration (ng / g) of perfluorocarboxylic acid and perfluorosulfonic acid.

[0133]

[0134]

[0135]

[0136]

[0137]

[0138] Next, the content of the compound having the carbon number (n1+1) in the extract M was calculated using the following formula (A2). Note that a in formula (A2) means a calculated using the above formula (A1). XCm = ACm / a × ρ1 / ρ2 (A2) XCm: content (ng / g) of the compound having the carbon number (n1+1) in the extract ACm: peak area of ​​the compound represented by the compound having the carbon number (n1+1) in the extract ρ1: density of methanol ρ2: density of the extract The quantitation limit in this measurement is 1 ng / g.

[0139] Furthermore, the content (ZCm) of each compound relative to the content of fluoropolymer in the solid composition was calculated by the following formula (A3) based on the XCm value of each compound obtained using extract M. ZCm = XCm × dilution ratio × W2a / W2b (A3) ZCm: content of the (n1+1) compound contained in the powder (relative to the fluoropolymer) W2a: mass (g) of extract M W2b: mass (g) of the dry powder used to prepare a sample of extract M The dilution ratio indicates the mass ratio at which the extract was diluted with water or methanol so that XCm was 180 ng / g or less. The ZCm values ​​of each compound were summed up to obtain the content M.

[0140] [Content of emulsifier in aqueous dispersion] The content of emulsifier in the aqueous dispersion was calculated from the charged amount.

[0141] [Content of First Polymer in Dry Powder] In the dry powder, the content of the first polymer relative to the total mass of the first polymer and the second polymer was calculated from the charged amounts, and the obtained value was defined as the content of the first polymer in the dry powder.

[0142] [Standard Specific Gravity (SSG)] Standard specific gravity (SSG) was measured in accordance with ASTM D4895-04. Specifically, 12.0 g of sample was weighed and compression molded in a cylindrical mold with an inner diameter of 28.6 mm to obtain a pellet sample. This was placed in an oven at 290 ° C and heated at 120 ° C / hour. After holding at 380 ° C for 30 minutes, the temperature was lowered at 60 ° C / hour and held at 294 ° C for 24 minutes. The sample was held in a desiccator at 23 ° C for 12 hours, and then the specific gravity value of the sample relative to water at 23 ° C was measured, and this was taken as the standard specific gravity. The smaller the SSG value, the larger the molecular weight.

[0143] [Extrusion Pressure (hereinafter also referred to as EP)] 100 g of the dried powder that had been left at room temperature for more than 2 hours was placed in a 500 mL glass bottle, 21.7 g of lubricating oil (Isopar H (registered trademark), manufactured by Exxon Corporation) was added, and the mixture was mixed for 3 minutes to obtain a mixture. The resulting mixture was then left in a 25°C thermostatic chamber for 2 hours, and then extruded at 25°C under the conditions of a reduction ratio (ratio of the cross-sectional area of ​​the die entrance to the cross-sectional area of ​​the exit) of 100 and an extrusion rate of 51 cm / min through an orifice with a diameter of 2.5 cm, a land length of 1.1 cm, and an entrance angle of 30° to obtain an extrusion bead (string-like material). The pressure required for extrusion at this time was measured and recorded as the extrusion pressure (unit: MPa).

[0144] [Tensile Strength] An extrusion bead was obtained in the same manner as in the measurement of extrusion pressure, and this was dried at 230°C for 30 minutes to remove the lubricant. Next, the extrusion bead was cut to an appropriate length, both ends were fixed so that the clamp distance was 3.8 cm, and the extrusion bead was heated to 300°C in an air circulating oven. Subsequently, the extrusion bead was stretched at a stretching speed of 1000% / sec and a stretch ratio of 2400% to obtain stretched porous body B (hereinafter also referred to as "stretched bead B"). A total of three samples, namely, samples cut from both ends of one stretched bead B (excluding neckdown within the clamp range, if any), and a sample cut from the center of stretched bead B, were measured for tensile breaking load using a tensile tester (manufactured by A&D Co., Ltd.), and the maximum stress generated until breakage was taken as the tensile strength (unit: N). Two stretched beads were measured, and the breaking strength was measured for a total of six samples (samples (1) to (6)). The average value of the breaking strength of the six samples is shown as the tensile strength in Table 8. In the measurement using the tensile tester, the sample was clamped and fixed between movable jaws having a gauge length of 5.0 cm, and the movable jaws were driven at a speed of 300 mm / min at room temperature (24°C) to apply a tensile stress.

[0145] [Stress Relaxation Time] Both ends of the stretched bead B were connected to fixtures to prepare a taut bead sample with a total length of 8 inches (20 cm). An oven was maintained at 390°C, and the fixture and bead sample were inserted into the oven through a (covered) slit on the side of the oven. The time required from the time of insertion into the oven until the bead sample broke was measured as the stress relaxation time (unit: seconds). A longer stress relaxation time indicates better heat resistance, and higher molecular weight and crystallinity after stretching.

[0146] <Preparation of electrode mixture> As an electrode active material (positive electrode active material), LiNi ０．６ Mn ０．２ Co ０．２ O ２The mixture was mixed with carbon black as a conductive additive using a pressure kneader at 30 rpm for 300 seconds to obtain Mixture 1. A dry powder was then added as a binder, and the mixture was stirred at 50 rpm for 300 seconds to obtain Mixture 2. The mass ratio of the components in Mixture 2 was adjusted to a positive electrode active material:binder:conductive additive = 95:2:3. Mixture 2 was then placed in a rolling mill, and a pressure of 10 MPa was applied. Mixture 2 emerging from the rolling mill was then placed in the rolling mill again, and this process was repeated five times to obtain 10 lumps of an electrode mixture (positive electrode mixture).

[0147] [Adhesion] A sieve with 2 mm openings and a tray underneath were placed in a shaker, and the electrode mixture was placed on the sieve. After operating the shaker at a speed of 240 rpm with an upper hammer vibration of 67 times / min for 20 minutes, the weight of the electrode mixture sieved onto the tray was measured. The adhesion to the electrode active material was calculated using the following formula and evaluated based on the ease of cohesion of the electrode mixture. Detachment rate = (W2 / W1) x 100 (%) W1: total mass (g) of the electrode mixture before the test W2: mass (g) of the sieved electrode mixture A: detachment rate less than 5% B: detachment rate 5% or more but less than 6% C: detachment rate 6% or more

[0148] [Production Example 1: Production of First Polymer P1-1] 33 kg of deionized water was charged into a 60 L stainless steel autoclave equipped with a baffle and a stirrer, and the autoclave was then purged with nitrogen and then reduced in pressure, followed by charging 2,450 g of PMVE. The temperature was raised to 90°C with stirring, and 324 g of TFE was charged and pressurized to 1.7 MPa. 150 g of ultrapure water in which 8.35 g of APS (ammonium persulfate) had been dissolved was injected to initiate polymerization. Polymerization was allowed to proceed while adding TFE to maintain the autoclave internal pressure at 1.62 MPa. The polymerization reaction was terminated when the amount of TFE added after the start of polymerization reached 60 g, and the autoclave was cooled. The TFE in the autoclave was then released into the atmosphere. The polymerization time was 24 minutes. Nitrogen was injected to 0.2 MPa, and the temperature was raised to 90°C. The autoclave was heated for 3 hours, cooled, and reaction liquid A1 was extracted. The first polymer P1-1 in the reaction liquid A1 was water-insoluble, and the reaction liquid A1 was an aqueous dispersion in which particles of the first polymer P1-1 were dispersed in an aqueous medium. The reaction liquid A1 was freeze-coagulated and then filtered. The obtained first polymer P1-1 was analyzed by NMR, and the ratio of TFE units to PMVE units was 62 / 38 (molar ratio). It was an elastomer, and its Tg was -5.5°C. The results are shown in Table 6 (the same applies hereinafter). This production was carried out twice.

[0149] Two ion exchange resin packed columns filled with Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 843 mL) and Purolite A300 (manufactured by Purolite, anion exchange resin, 843 mL) were prepared, and the reaction solution A1 was passed through them to remove impurities such as ionic species derived from the initiator and by-product ionic species, thereby obtaining an aqueous dispersion B1 of the first polymer P1-1. Using the methods described above, the solids concentration of the aqueous dispersion B1 (content of the first polymer), the average particle size of the primary particles in the aqueous dispersion B1, and the number of particles in the aqueous dispersion B1 were determined. The results are shown in Table 6 (the same applies hereinafter).

[0150] [Example 1: Production of Second Polymer P2-1] A 100 L stainless steel autoclave equipped with a baffle and a stirrer was charged with 1,500 g of paraffin wax, 47.6 kg of aqueous dispersion B1, and 11.4 L of deionized water. The autoclave was purged with nitrogen, then reduced in pressure and heated to 70°C. Stirring was initiated, and the pressure was increased to 1.86 MPa with TFE. 1 L of deionized water containing 3.36 g of DSAP (disuccinic acid peroxide) was added to initiate the polymerization reaction. Polymerization was continued while adding TFE to maintain the internal pressure of the autoclave at 1.86 MPa, synthesizing a second polymer P2-1 (PTFE). PTFE, a homopolymer of TFE, exhibits non-melt moldability. That is, the second monomer, TFE, was polymerized in aqueous dispersion C1, which was prepared by adding deionized water to aqueous dispersion B1.

[0151] The polymerization reaction was terminated when the amount of TFE added after the start of polymerization reached 13.1 kg, and the TFE in the autoclave was released into the atmosphere. The polymerization time was 150 minutes. The resulting reaction solution was cooled, and the supernatant paraffin wax was removed to obtain aqueous dispersion D1. The resulting aqueous dispersion D1 was diluted with deionized water to a solids concentration of 10% by mass, the temperature was adjusted to 16 ° C, and the mixture was stirred to flocculate and filtered to obtain a wet powder.

[0152] The obtained wet powder was dried at 195°C for 7.1 hours to obtain a dry powder. In the obtained dry powder, the content of the first polymer P1-1 relative to the total mass of the first polymer and the second polymer was 1.89% by mass. The results are shown in Table 8 (the same applies hereinafter). The composition of the dry powder was calculated using NMR, and the content of PAVE units relative to the total of TFE units and PAVE units (PMVE units in this example) was 1.2 mol%. The results are shown in Table 8 (the same applies hereinafter).

[0153] Table 7 shows the production conditions for the step of polymerizing the second monomer (TFE) in aqueous dispersion C1 (the same applies hereinafter). Specifically, Table 7 shows the content of the aqueous medium and the content of the first polymer in aqueous dispersion C1 before starting the polymerization of the second monomer. Table 7 shows the content of the paraffin wax per 100 parts by mass of the aqueous medium in aqueous dispersion C and the amount of the second monomer (TFE) used. Table 7 also shows the amount of the polymerization initiator used per 100 parts by mass of the second monomer used. Aqueous dispersion C1 does not contain any emulsifier, fluoride ion, sulfate ion, or ammonium ion.

[0154] Using the above methods, the solids concentration of aqueous dispersion D1, the average particle size of primary particles in aqueous dispersion D1, and the number of particles in aqueous dispersion D1 were determined. The results are shown in Table 8 (the same applies hereinafter). As shown in Tables 6 and 8, the number of particles in aqueous dispersion B1 and aqueous dispersion D1 was approximately the same, and the average particle size of the primary particles in aqueous dispersion D1 was larger. From this, it is believed that the second polymer P2-1 was produced while integrating with particles of the first polymer P1-1, and primary particles composed of the first polymer and the second polymer were formed. Note that the particle size of the primary particles in aqueous dispersion B and the particle size of the primary particles in aqueous dispersion C were the same. Table 8 shows the results of measuring the aspect ratio of the primary particles in aqueous dispersion D1. As shown in Table 8, the contents of compound (S1) and compound (S2) relative to the total mass of the primary particles in aqueous dispersion D1 were both below the detection limit, in the range of 100 ppb by mass or less.

[0155] The standard specific gravity (SSG) of the dry powder obtained in this example was measured using the method described above. The mixture (stretching composition) obtained by adding lubricating oil to the dry powder obtained in this example was measured for extrusion pressure (EP) using the method described above. Furthermore, stretched beads were formed from the mixture (stretching composition) using the method described above, and the tensile strength and stress relaxation time were measured. Furthermore, the dry powder obtained in this example was used as an electrode binder to prepare an electrode mixture, and its binding ability was evaluated. These results are shown in Table 8 (the same applies below).

[0156] [Production Example 2: Production of First Polymer P1-2] In this example, a first polymer was produced having a different molar ratio of TFE units / PMVE units and a different Tg from those in Production Example 1. 33 kg of deionized water was charged into a 60 L stainless steel autoclave equipped with a baffle and a stirrer, and the autoclave was then purged with nitrogen, reduced pressure, and 2441 g of PMVE was charged. The temperature was raised to 90°C with stirring, and 210 g of TFE was charged and pressurized to 1.40 MPa. 150 g of ultrapure water in which 8.35 g of APS had been dissolved was injected to initiate polymerization. Polymerization was also allowed to proceed while adding TFE so as to maintain the internal pressure of the autoclave at 1.40 MPa. The polymerization reaction was terminated when the amount of TFE added after the start of polymerization reached 120 g. The autoclave was cooled, and the TFE in the autoclave was then released into the atmosphere. The polymerization time was 84 minutes. Nitrogen was pressurized to 0.2 MPa, and the temperature was raised to 90°C. After heating the autoclave for 3 hours, it was cooled, and reaction liquid A2 was extracted. The first polymer P1-2 in reaction liquid A2 was water-insoluble. Reaction liquid A2 was freeze-coagulated and then filtered to obtain first polymer P1-2. The first polymer P1-2 had a TFE unit / PMVE unit ratio of 50 / 50 (molar ratio). It was an elastomer, and had a Tg of -5°C. This production was carried out twice.

[0157] In the same manner as in Production Example 1, the reaction liquid A2 was passed through an ion exchange resin to remove impurities, thereby obtaining an aqueous dispersion B2 of the first polymer P1-2.

[0158] [Example 2: Production of Second Polymer P2-2] In this example, TFE, the second monomer, was polymerized in aqueous dispersion C1, which was prepared by adding deionized water to aqueous dispersion B2. A 100 L stainless steel autoclave equipped with a baffle and a stirrer was charged with 1500 g of paraffin wax, 47.6 kg of aqueous dispersion B2, and 9.9 L of deionized water. The autoclave was purged with nitrogen, then reduced in pressure and heated to 70°C. Stirring was initiated, and the pressure was increased to 1.76 MPa with TFE. One liter of deionized water containing 2.80 g of DSAP was added to initiate the polymerization reaction. The polymerization was continued while adding TFE to maintain the internal pressure of the autoclave at 1.76 MPa, synthesizing second polymer P2-2 (PTFE). When the amount of TFE added after the start of polymerization reached 7.88 kg, one liter of deionized water containing 1.07 g of ammonium sulfite was added over 6 minutes. Thereafter, the temperature inside the autoclave was raised to 90°C at a rate of 15°C per hour. When the amount of TFE added after the start of polymerization reached 14.8 kg, the polymerization reaction was terminated, and the TFE inside the autoclave was released into the atmosphere. The polymerization time was 193 minutes. The resulting reaction solution was cooled, and the supernatant paraffin wax was removed to obtain aqueous dispersion D2. In the same manner as in Example 1, a wet powder was obtained from the resulting aqueous dispersion D2, and this was dried to obtain a dry powder.

[0159] [Production Example 3: Production of First Polymer P1-3] In this example, PPVE was used as PAVE, and a first polymer was produced having a different TFE unit / PAVE unit molar ratio and Tg from those of Production Examples 1 and 2. 61 kg of deionized water was charged into a 100 L stainless steel autoclave equipped with a baffle and a stirrer, and the autoclave was then purged with nitrogen and reduced pressure, followed by charging 2,470 g of PPVE (perfluoropropyl vinyl ether). The temperature was raised to 90°C with stirring, resulting in a pressure of 0.48 MPa. 900 g of TFE was charged thereto, and the pressure was increased to 0.82 MPa. 1,500 g of ultrapure water in which 19.1 g of APS had been dissolved was injected, and polymerization was initiated. The polymerization reaction was terminated when the internal pressure of the autoclave after the start of polymerization had decreased by 0.1 MPa since the addition of the aqueous APS solution, and the TFE in the autoclave was released into the atmosphere. The polymerization time was 19 minutes. Nitrogen was pressurized up to 0.5 MPa, and purging was repeated five times to cool the reaction solution, after which reaction solution A3 was withdrawn. The first polymer P1-3 in reaction solution A3 was water-insoluble. Reaction solution A3 was freeze-coagulated and then filtered to obtain first polymer P1-3. The first polymer P1-3 had a TFE unit / PPVE unit ratio of 56 / 44 (molar ratio). It was an elastomer, and its Tg was -5.5°C.

[0160] In the same manner as in Production Example 1, the reaction solution A3 was passed through an ion exchange resin to remove impurities, thereby obtaining an aqueous dispersion B3 of a first polymer P1-3.

[0161] Example 3: Production of Second Polymer P2-3 In this example, TFE, the second monomer, was polymerized in aqueous dispersion C3, which was prepared by adding deionized water to aqueous dispersion B3. A 100-liter stainless steel autoclave equipped with a baffle and a stirrer was charged with 1500 g of paraffin wax, 47.6 kg of aqueous dispersion B3, and 11.4 L of deionized water. The autoclave was purged with nitrogen, then reduced in pressure and heated to 70°C. Stirring was initiated, and the pressure was increased to 1.86 MPa with TFE. One liter of deionized water containing 3.36 g of DSAP was added to initiate the polymerization reaction. The polymerization was allowed to proceed while TFE was added to maintain the internal pressure of the autoclave at 1.86 MPa. The polymerization was terminated when the amount of TFE added after polymerization initiation reached 13.1 kg, and the TFE in the autoclave was released into the atmosphere. The polymerization time was 188 minutes. The resulting reaction solution was cooled, and the supernatant paraffin wax was removed to obtain aqueous dispersion D3. In the same manner as in Example 1, a wet powder was obtained from the resulting aqueous dispersion D3, and this was dried to obtain a dry powder.

[0162] [Example 4: Production of PTFE] This example is a comparative example in which PTFE was synthesized using a water-soluble fluorine-based emulsifier without using the first polymer. 760 g of paraffin wax, 53 L of ultrapure water, and C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４80 g of EEA (EEA) was charged. After heating to 65°C, the autoclave was purged with nitrogen and degassed, and TFE was introduced with stirring until the internal pressure reached 1.38 MPa. 1 L of a 0.5 mass% aqueous succinic acid peroxide solution was injected into the autoclave to initiate the polymerization reaction. The polymerization was carried out for 30 minutes while maintaining the polymerization pressure at 1.38 MPa while feeding TFE, and then the temperature was raised to 83°C at a heating rate of 6°C / hour. When 6.0 kg of TFE had been added, 1 L of a 14.2 mass% aqueous EEA solution was added. When the TFE addition amount reached 26.9 kg, the polymerization reaction was terminated, and the TFE in the autoclave was released into the atmosphere. The resulting reaction solution was cooled, and the supernatant paraffin wax was removed to obtain aqueous dispersion D4. In the same manner as in Example 1, a wet powder was obtained from the resulting aqueous dispersion D4, and this was dried to obtain a dry powder.

[0163] [Production Example 5: Production of First Polymer P1-5] 33 kg of deionized water and 1.66 g of a 50% by mass aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as "NaAAMPS") were charged into a 60 L stainless steel autoclave equipped with a baffle and a stirrer, and the autoclave was then purged with nitrogen, reduced pressure, and 2443 g of PMVE was charged. The temperature was raised to 90°C with stirring, and 243 g of TFE was charged and pressurized to 1.5 MPa. 400 g of ultrapure water in which 84.3 g of APS (ammonium persulfate) had been dissolved was injected, and polymerization was initiated. Furthermore, polymerization was allowed to proceed while adding TFE so as to maintain the internal pressure of the autoclave at 1.5 MPa. The polymerization reaction was terminated when the amount of TFE added after the start of polymerization reached 1200 g, and the autoclave was cooled, after which the TFE in the autoclave was released into the atmosphere. Nitrogen was pressurized to 0.2 MPa, and the temperature was raised to 90°C. After heating the autoclave for 3 hours, it was cooled, and reaction liquid A5 was extracted. The first polymer P1-5 in reaction liquid A5 was water-insoluble, and reaction liquid A5 was an aqueous dispersion in which particles of the first polymer P1-5 were dispersed in an aqueous medium. Reaction liquid A5 was freeze-aggregated and then filtered, and the obtained first polymer P1-5 was analyzed by NMR, and the result was that the ratio of TFE units / PMVE units was 63 / 37 (molar ratio). Tg was -6°C. It has no melting point. Except that reaction liquid A5 was diluted 5 times, reaction liquid A5 was passed through an ion exchange resin to remove impurities, and an aqueous dispersion B5 of the first polymer P1-5 was obtained in the same manner as in Production Example 1.

[0164] [Example 5: Production of Second Polymer P2-5] A 100 L stainless steel autoclave equipped with a baffle and a stirrer was charged with 1,500 g of paraffin wax, 33.7 kg of aqueous dispersion B5 containing 1.1% by mass of First Polymer P1-5, and 24.9 L of deionized water. The autoclave was purged with nitrogen, then reduced in pressure and heated to 65°C. Stirring was initiated, and the pressure was increased to 1.76 MPa with TFE. 1 L of deionized water containing 2.8 g of DSAP (disuccinic acid peroxide) was added to initiate the polymerization reaction. Furthermore, polymerization was allowed to proceed while adding TFE to maintain the internal pressure of the autoclave at 1.76 MPa, synthesizing Second Polymer P2-5 (PTFE). PTFE, a homopolymer of TFE, exhibits non-melt moldability. The polymerization reaction was terminated when the amount of TFE added after the start of polymerization reached 15.8 kg, and the TFE in the autoclave was released into the atmosphere. The resulting reaction solution was cooled, and the supernatant paraffin wax was removed to obtain Aqueous Dispersion D5. In the same manner as in Example 1, a wet powder was obtained from the resulting Aqueous Dispersion D5, and this was dried to obtain a dry powder.

[0165]

[0166]

[0167]

[0168] As shown in the results of Tables 6 to 8, the electrode binders containing the solid compositions obtained in Examples 1 to 3 and 5 had excellent binding properties with the electrode active material. The electrode binder containing the solid composition obtained in Example 4, in which the second monomer was polymerized without using the first polymer, had poor binding properties with the electrode active material.

Claims

1. An electrode binder comprising a solid composition containing primary particles comprising a first polymer and a second polymer, wherein the second polymer is a non-melt-formable fluorine-containing polymer containing units based on tetrafluoroethylene, the first polymer is a polymer different from the second polymer, and the content of the first polymer is 0.01 to 4.0% by mass relative to the total mass of the first polymer and the second polymer.

2. The electrode binder according to claim 1, wherein the first polymer comprises units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

3. The electrode binder according to claim 2, wherein the content of units based on perfluoro(alkyl vinyl ether) in the first polymer is 0.1 to 3.0 mol % relative to the sum of all units of the first polymer and all units of the second polymer.

4. The electrode binder of claim 1, wherein said first polymer is water-insoluble.

5. The electrode binder according to claim 1, wherein the content of the compound represented by the following formula (S1) and the content of the compound represented by the following formula (S2) are each 100 ppb by mass or less, relative to the total mass of the first polymer and the second polymer. Formula (S1): H-(CF ２ ) ｎ１ -COOM Formula (S2): H-(CF ２ ) ｎ２ -SO ３ M In formula (S1) and formula (S2), M each independently represents a hydrogen atom, Na, K, or NH ４ wherein n1 represents an integer of 3 to 13, 15 or 17, and n2 represents an integer of 4 to 10, or 12.

6. The electrode binder according to claim 1, wherein the aspect ratio of the primary particles is 1.5 or less.

7. An electrode mixture comprising the electrode binder according to any one of claims 1 to 6 and an electrode active material.

8. An electrode comprising the electrode mixture according to claim 7 and a current collector.

9. A secondary battery comprising the electrode according to claim 8.

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