Electrode binder, electrode mixture, electrode, and secondary battery

Abstract

An electrode adhesive comprising a solid composition comprising primary particles containing a first polymer and a second polymer, the second polymer being a non-melt-forming fluoropolymer comprising tetrafluoroethylene-based units, the first polymer being a different polymer from the second polymer, the content of the first polymer being 0.01 to 4.0 by mass relative to the total mass of the first polymer and the second polymer.

Description

Technical Field

[0001] This invention relates to adhesives for electrodes, electrode mixtures, electrodes, and secondary batteries.

[0002] 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. Background Technology

[0003] Because fluoropolymers such as tetrafluoroethylene copolymers have excellent heat resistance, chemical resistance, flame retardancy, and weather resistance, they are used in various industrial fields.

[0004] Patent document 1 describes the following: polytetrafluoroethylene polymerized with a fluorinated surfactant is powdered, and the powder is used as an electrode adhesive.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 7303469 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] However, when fluoropolymers manufactured using existing methods are used as electrode adhesives, their adhesion to the electrode active material is insufficient.

[0010] The technical problem of the present invention is to provide an electrode adhesive with excellent adhesion to electrode active materials, an electrode compound containing the electrode adhesive, an electrode, and a secondary battery.

[0011] Technical solutions adopted to solve technical problems

[0012] The present invention has the following technical content.

[0013] [1] An electrode adhesive comprising a solid composition comprising primary particles containing a first polymer and a second polymer, the second polymer being a non-melt-forming fluoropolymer comprising tetrafluoroethylene-based units, the first polymer being a polymer different from the second polymer, the content of the first polymer being 0.01 to 4.0 by mass relative to the total mass of the first polymer and the second polymer.

[0014] [2] The electrode adhesive as described in [1], wherein the first polymer comprises a tetrafluoroethylene-based unit and a perfluoro(alkyl vinyl ether)-based unit.

[0015] [3] The electrode adhesive as described in [2], wherein the content of the perfluoro(alkyl vinyl ether)-based unit 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.

[0016] [4] An electrode adhesive as described in any one of [1] to [3], wherein the first polymer is non-water-soluble.

[0017] [5] An electrode adhesive as described in any one of [1] to [4], wherein the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are each less than 100 ppb by mass relative to the total mass of the first polymer and the second polymer. Formula (S1): H-(CF2) n1 -COOM Formula (S2): H-(CF2) n2 -SO3M In formulas (S1) and (S2), M independently represents a hydrogen atom, Na, K or NH4, n1 represents an integer from 3 to 13, 15 or 17, and n2 represents an integer from 4 to 10 or 12.

[0018] [6] An electrode adhesive as described in any one of [1] to [5], wherein the aspect ratio of the primary particles is 1.5 or less.

[0019] [7] An electrode compound comprising an electrode binder and an electrode active substance as described in any one of [1] to [6].

[0020] [8] An electrode comprising the electrode mixture described in [7] and a current collector.

[0021] [9] A secondary battery comprising the electrodes described in [8].

[0022] Invention Effects

[0023] The present invention provides an electrode adhesive with excellent adhesion to electrode active materials, an electrode compound containing the electrode adhesive, an electrode, and a secondary battery. Detailed Implementation

[0024] The following definitions of terms apply to this specification and the claims.

[0025] "Unit" refers to the atomic group derived directly from a monomer molecule formed by monomer polymerization, and the atomic group obtained by chemically transforming a portion of the aforementioned atomic group. "Monomer-based unit" is also referred to as "unit" below.

[0026] The numerical range indicated by "~" refers to the range including the values ​​listed before and after "~" as both the lower and upper limits. In this specification, the upper or lower limit of a numerical range can be replaced by the upper or lower limit of another numerical range. Furthermore, the upper or lower limit of a numerical range can also be replaced by the values ​​shown in the embodiments. "Average particle size of primary particles" refers to the average particle size (hydrodynamic diameter) obtained using the autocorrelation function obtained by dynamic light scattering and calculated through cumulative analysis.

[0027] The aspect ratio of a particle is the ratio (a / b) of the particle's major diameter a to the longest diameter b among the diameters perpendicular to major diameter a.

[0028] "Non-melt formability" means that it does not exhibit melt flowability.

[0029] "Exhibiting melt flowability" refers to a temperature at which the melt flow rate is 0.1 to 1000 g / 10 minutes under a load of 49 N and a temperature more than 20 °C higher than the melting point of the resin.

[0030] "Mel flow rate" refers to the melt mass flow rate (MFR) specified in JIS K 7210:1999 (ISO 1133:1997).

[0031] "Standard specific gravity (hereinafter also referred to as "SSG")" is a value used as an indicator of average molecular weight; the higher the value, the smaller the molecular weight. It can be determined according to ASTM D4895-04.

[0032] The content (mass % or mole %) of each unit relative to all units contained in the polymer can be determined by analyzing the polymer using solid-state nuclear magnetic resonance (NMR). However, the content of each unit calculated from the amount of each monomer fed is usually roughly the same as the actual content of each unit.

[0033] In this specification, each component may be used alone as a single substance equivalent to that component, or it may be used in combination with two or more substances. In this document, when two or more substances are used in combination, unless otherwise specified, the content of the component refers to the total content of the substances used in combination. In this specification, a combination of two or more preferred forms is a more preferred form.

[0034] The electrode binder of this embodiment comprises a solid composition. The solid composition comprises primary particles containing a first polymer and a second polymer. The second polymer is a non-melt-forming fluoropolymer containing tetrafluoroethylene-based units. The first polymer is a different polymer from the second polymer. The content of the first polymer is 0.01 to 4.0% by mass relative to the total mass of the first and second polymers.

[0035] The solid composition is preferably a powder composition.

[0036] <First Polymer>

[0037] The first polymer is a different polymer from the second polymer. That is, the first polymer is not a non-melt-forming fluoropolymer containing tetrafluoroethylene-based units. The first polymer can be a fluoropolymer containing fluorine atoms or a non-fluoropolymer without fluorine atoms. Preferably, the first polymer is a fluoropolymer.

[0038] 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. Furthermore, in one embodiment, the first polymer preferably does not have either a glass transition temperature or a melting point above 20°C.

[0039] The Tg of the first polymer is preferably below 10°C, more preferably below 5°C, even more preferably below 3°C, and particularly preferably below 0°C. When the Tg of the first polymer is below the above-mentioned upper limit, primary particles comprising the first polymer and the second polymer are easily formed.

[0040] The thermal stability (Tg) of the first polymer is preferably above -50°C, more preferably above -45°C, and even more preferably above -40°C. When the Tg of the first polymer is above the above-mentioned lower limit, the thermal stability after molding and processing is improved.

[0041] As a method to bring the Tg of the first polymer within the aforementioned range, for example, methods for adjusting the type and amount of monomers used in the manufacture of the first polymer can be cited.

[0042] The first polymer is preferably an elastomer, more preferably a fluorinated elastomer. "Elastomer" refers to an elastic copolymer that has a storage modulus G' of 80 or more at 100°C and 50 cpm as determined by ASTM D6204, and does not have a melting point.

[0043] The first polymer preferably has units of fluorinated monomers based on fluorine atoms. Examples of fluorinated monomers 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"), CH2=CF-CF2-O-Rf-COOH, CH2=CF-CF2-O-Rf-SO3H, CF2=CF-CF2-O-Rf-COOH, CF2=CF-CF2-O-Rf-SO3H, CH2=CF-O-Rf-COOH, CH2=CF-O-Rf-SO3H, CF2=CF-O-Rf-COOH, and CF2=CF-O-Rf-SO3H (Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms, and the carbon atoms in the perfluoroalkyl group may have ether-like oxygen atoms between them). In addition, other fluoropolymers include perfluoroalkyl polyethers and perfluoropolyethers.

[0044] The first polymer may consist solely of units based on non-fluorinated monomers, or it may contain units based on non-fluorinated monomers. Examples of non-fluorinated monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride. Furthermore, non-fluorinated monomers may have hydroxyl groups and ionic functional groups as substituents, as described later. Specifically, one or more hydrogen atoms of the non-fluorinated monomer may be replaced by hydroxyl groups and ionic functional groups, as described later.

[0045] The aforementioned fluorinated monomers can have functional groups as substituents that enhance water solubility. Examples of functional groups that enhance water solubility include hydroxyl groups and ionic functional groups. Ionic functional groups can be either cationic or anionic. A specific example of an ionic functional group is a carboxylic acid group (-COO). - ), sulfonic acid group (-SO3) - ), sulfate group (-SO4) 2- ), phosphonic acid group (-PO3) 2- ), sulfonylimide group (-N) - (SO2)) and phosphate groups (-PO4) 3- Anionic functional groups such as ) are present. Furthermore, functional groups that contribute to improving water solubility are preferably monovalent groups.

[0046] The first polymer may have one or more functional groups that contribute to improving water solubility. Furthermore, the first polymer may have functional groups that contribute to improving water solubility on its side chains or at its ends.

[0047] The first polymer preferably contains TFE units.

[0048] When the first polymer contains TFE units, a higher content of TFE units is more beneficial for improving heat resistance. Therefore, the content of TFE units relative to the total number of units in the first polymer is preferably 30 mol% or more, more preferably 40 mol% or more, and even more preferably 50 mol% or more. The upper limit of the TFE unit content can be adjusted according to the types of units other than TFE units to obtain the 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.

[0049] From the viewpoint of easy removal of the first polymer from water, the first polymer is preferably non-water-soluble. In this specification, "non-water-soluble" means having a solubility of less than 100 mg in 1000 g of water at 25°C.

[0050] When the first polymer contains the aforementioned functional groups that help improve water solubility, its content is preferably within the range where the first polymer is non-water-soluble.

[0051] For example, the content of the functional groups that help improve water solubility is preferably 0 to 20 mol% relative to all units constituting the first polymer, more preferably 0.000001 to 15 mol%, and even more preferably 0.0001 to 10 mol%.

[0052] From the viewpoint that Tg can be easily adjusted to the above range, and from the viewpoint that the present invention has better effects, the first polymer preferably includes TFE units and PAVE units.

[0053] From the viewpoint of excellent polymerization reactivity when manufacturing the first polymer and the viewpoint of being able to manufacture the second polymer more efficiently, the monomer represented by PAVE formula (1) is preferred.

[0054] CF2 = CF-OR f1 (1)

[0055] In equation (1), R f1 This refers to perfluoroalkyl groups with 1 to 10 carbon atoms. From the perspective of superior polymerization reactivity, R... f1 The carbon number is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3.

[0056] Perfluoroalkyl groups can be straight-chain or branched.

[0057] 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"). From the viewpoint that the second polymer can be manufactured more efficiently, PMVE and PPVE are preferred, and PMVE is more preferred.

[0058] When the first polymer comprises TFE units and PAVE units, from the viewpoint of easily adjusting Tg to the above-mentioned range and from the viewpoint of manufacturing the second polymer more efficiently, 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%. The preferred amounts are the same when the PAVE units are PMVE units, PEVE units, or PPVE units, or when a mixture of two or more of them is used.

[0059] When the first polymer contains TFE units and PAVE units, the first polymer may also contain units based on monomers other than TFE and PAVE, but from the viewpoint that the second polymer can be manufactured more efficiently, it is preferable that it does not contain units based on other monomers.

[0060] "Substantially free of units based on other monomers" means that the content of units based on other monomers is less than 0.01 mol% relative to all units of the first polymer, more preferably 0 mol%.

[0061] When the unit includes units based on other monomers, HFP and propylene are preferred as other monomers. When HFP is included as an other monomer, the content of HFP-based units relative to all units of the first polymer is preferably greater than 0 mol% and less than 10 mol%, more preferably greater than 0 mol% and less than 5 mol%, and even more preferably greater than 0 mol% and less than 1 mol%.

[0062] <Second Polymer>

[0063] The second polymer is a non-melt-forming fluoropolymer containing TFE units.

[0064] The second polymer can be a fluoropolymer (PTFE) consisting only of TFE units, or it can be a fluoropolymer that also contains monomer units other than TFE units.

[0065] Monomers other than TFE can be either fluorinated monomers or non-fluorinated monomers that do not contain fluorine atoms.

[0066] Examples of fluorinated monomers include trifluorochloroethylene (hereinafter also referred to as "CTFE"), vinylidene fluoride (hereinafter also referred to as "VdF"), FAE, PAVE, hexafluoropropylene, perfluoro(2,2-dimethyl-1,3-dioxacyclopentene), and perfluoro(4-methoxy-1,3-dioxacyclopentene). 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.

[0067] Examples of non-fluorinated monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride.

[0068] The content of TFE units in the second polymer is preferably 99.0 to 100.0 mol% relative to all units of the second polymer, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%.

[0069] <Solid Composition>

[0070] The content of the first polymer relative to the total mass of the first polymer and the second polymer is 0.01 to 4.0% by mass, preferably 0.1 to 3.5% by mass, and more preferably 0.3 to 3.0% by mass. If the content of the first polymer is above the lower limit of the above range, the emulsion stability of the second polymer becomes good, and if it is below the upper limit, the heat resistance of the second polymer can be maintained.

[0071] The content of the first polymer relative to the total mass of the solid composition is preferably 0.1 to 4% by mass, more preferably 0.2 to 4% by mass, and even more preferably 0.3 to 3% by mass.

[0072] The content of the second polymer relative to the total mass of the solid composition is preferably 95-99.9% by mass, more preferably 96-99.8% by mass, and even more preferably 97-99.7% by mass. The combined content of the first polymer and the second polymer relative to the total mass of the solid composition is preferably 99.0-100% by mass, more preferably 99.5-100% by mass, and even more preferably 99.8-100% by mass.

[0073] When the first polymer contains PAVE units, the content of PAVE units relative to the total of all units in the first polymer and all units in 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%. If the content of PAVE units is above the lower limit of the above range, the aqueous dispersion stability of the second polymer during manufacturing is good; if it is below the upper limit, the heat resistance is good.

[0074] 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%. If the content of TFE units is above the lower limit of the above range, the heat resistance is good; if it is below the upper limit, the stability of the aqueous dispersion during the manufacture of the second polymer is good.

[0075] The solid composition comprises primary particles containing a first polymer and a second polymer. The first polymer may be copolymerized with a portion of the second polymer in the primary particles.

[0076] In addition to the first and second polymers, the primary particles containing the first polymer and the second polymer may also contain impurities that are unavoidable in manufacturing. The content of these impurities relative to the total mass of the first and second polymers 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 impurities may also be 0 ppb by mass.

[0077] In the solid composition, the content of the compound represented by formula (S1) and the content of the compound represented by formula (S2) are preferably 100 ppb or less by mass relative to the total mass of the first polymer and the second polymer, more preferably 50 ppb or less by mass, even more preferably 25 ppb or less by mass, and particularly preferably 0 ppb by mass.

[0078] Formula (S1): H-(CF2) n1 -COOM

[0079] Formula (S2): H-(CF2) n2 -SO3M

[0080] In the above formulas (S1) and (S2), M independently represents a hydrogen atom, Na, K or NH4, n1 represents an integer from 3 to 13, 15 or 17, and n2 represents an integer from 4 to 10 or 12.

[0081] The compounds represented by formula (S1) and formula (S2) above are components that may be generated when specific monomers such as TFE are polymerized in the presence of polymerization initiators, chain transfer agents, and emulsifiers (especially hydrocarbon emulsifiers). In the polymerization step of the second polymer in the method for manufacturing the solid composition of this embodiment described later, since the amount of compounds represented by formula (S1) and formula (S2) generated can be suppressed without the use of emulsifiers, it is easy to keep the content of these compounds within the above-mentioned range.

[0082] The average particle size of the primary particles is preferably 100–400 nm, more preferably 150–300 nm, and even more preferably 170–270 nm. If the average particle size is above the lower limit of the above range, the productivity and mechanical properties are good; if it is below the upper limit, the emulsion stability during the manufacture of the second polymer can be maintained.

[0083] 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. If the aspect ratio is below the upper limit of the above range, it can impart stability to the emulsion.

[0084] The solid composition may be a powder composition containing secondary particles, wherein the secondary particles are obtained by agglomeration 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 100–400 nm, more preferably 150–300 nm, and even more preferably 170–270 nm.

[0085] In addition to the first and second polymers, the powder composition containing secondary particles may also contain impurities that are unavoidable in manufacturing. The content of these 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.

[0086] 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. If the SSG is below the upper limit of the above range, the molecular weight increases and the mechanical strength during processing becomes better.

[0087] The extrusion pressure of the solid composition in the extrusion test described later is preferably 10 to 30 MPa, more preferably 15 to 25 MPa, and even more preferably 17 to 23 MPa. If the extrusion pressure is above the lower limit of the above range, the tensile strength is high; if it is below the upper limit, the processability is excellent.

[0088] Method for manufacturing solid compositions

[0089] The method for manufacturing the solid composition preferably includes the following steps: polymerizing a monomer constituting a second polymer (hereinafter also referred to as "second monomer") 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. More preferably, a step is included to agglomerate the first polymer and the second polymer in the aqueous dispersion D. Hereinafter, the polymerization steps of the first polymer and the second polymer will be described separately. The agglomeration step of the first polymer and the second polymer will also be described.

[0090] Hereinafter, reaction solution A refers to an aqueous dispersion containing a first polymer and an aqueous medium, and is an aqueous dispersion obtained immediately after the first polymer is manufactured.

[0091] Aqueous dispersion B refers to an aqueous dispersion obtained by ion exchange treatment of reaction solution A.

[0092] Aqueous dispersion C refers to an aqueous dispersion containing a first polymer and an aqueous medium, and is an aqueous dispersion that can be used as a polymerization reaction solution for a second polymer. It can also be an aqueous dispersion obtained by diluting aqueous dispersion B. The total mass of aqueous dispersion C is the sum of the first polymer, the aqueous medium, and any additives added as needed, but does not include the mass of the second monomer, polymerization initiator, and chain transfer agent.

[0093] Aqueous dispersion D is an aqueous dispersion containing primary particles of a first polymer and a second polymer, obtained through a polymerization process of the second polymer.

[0094] <Polymerization process of the first polymer>

[0095] The following describes two forms of the polymerization process of the first polymer. The first form is also called the polymerization process of the first polymer (1), and the second form is also called the polymerization process of the first polymer (2).

[0096] The polymerization step (1) of the first polymer is preferably a method of polymerizing the monomers constituting the first polymer (hereinafter also referred to as "first monomers") in an aqueous medium in the presence of a polymerization initiator. By this method, a reaction solution A containing the first polymer in an aqueous medium can be obtained. The preferred form, such as the type and proportion of the first monomer, can be determined based on the composition of the first polymer described above.

[0097] The reaction solution A is preferably a dispersion obtained by dispersing the primary particles of the first polymer in an aqueous medium.

[0098] As the polymerization initiator used in the manufacture of the first polymer, water-soluble polymerization initiators are preferred, persulfate-type initiators such as ammonium persulfate, sodium persulfate, and potassium persulfate are more preferred, organic polymerization initiators such as bis(2-di ...

[0099] In addition, water-soluble redox catalysts, which will be described later, are preferred.

[0100] Examples of aqueous media used in the manufacture of the first polymer include water, or a mixture of water and a water-soluble organic solvent. Examples of water-soluble organic solvents include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0101] The first monomer is supplied to the reaction system (i.e., the polymerization reactor) using conventional methods. For example, the first monomer can be supplied to the reaction system continuously or intermittently to bring the polymerization pressure to a specified level. Alternatively, the first monomer can be dissolved in an aqueous medium, and the resulting solution can be supplied to the reaction system continuously or intermittently.

[0102] The polymerization initiator can be supplied to the reaction system all at once or in batches.

[0103] The polymerization temperature is preferably 20–150°C, more preferably 50–100°C.

[0104] The polymerization pressure is preferably 0–3.0 MPa, more preferably 1.0–2.0 MPa. The polymerization time is preferably 1–120 minutes, more preferably 10–60 minutes, in the case of batch processing.

[0105] The resulting reaction solution A can be directly supplied to the polymerization process of the second polymer. The reaction solution A can be subjected to any one or more of the following treatments: solvent conditioning, heating, and ion exchange, before being supplied to the polymerization process of the second polymer.

[0106] As a solvent adjustment process, examples include adding other aqueous media to reaction solution A, or performing solvent displacement in reaction solution A to disperse the first polymer in other aqueous media.

[0107] If heat treatment is performed, the polymerization initiator contained in reaction solution A is deactivated. Therefore, the polymerization process of the second polymer is less affected by the polymerization initiator used in the manufacture of the first polymer. As a result, a second polymer with a high molecular weight is easily obtained.

[0108] The heating temperature is preferably 70–100°C, more preferably 80–98°C, and even more preferably 85–95°C. If the heating temperature is within the above range, the deactivation of the polymerization initiator in the aqueous medium can be further promoted.

[0109] As an ion exchange treatment, it can be exemplified by contacting the reaction solution A with either or both of anion exchange resin and cation exchange resin to remove impurities contained in the reaction solution A, namely either or both of anions and cations.

[0110] Anions that can be considered as impurities include sulfate ions. Sulfate ions originate from polymerization initiators (especially ammonium persulfate) and are sometimes present in reaction solution A. By treating reaction solution A with anion exchange resin to obtain an aqueous dispersion B, sulfate ions in the diluted aqueous dispersion C can be reduced. The sulfate ion content 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 can be 0 ppm by mass. It is believed that if the sulfate ion content is below the upper limit, the formation of heat-sensitive terminal groups in the second polymer can be suppressed. As a result, it is speculated that coloring of the second polymer (primary particles) can be suppressed.

[0111] Anions that can be cited as impurities include fluoride ions. Fluoride ions are generated by the reaction of a polymerization initiator (e.g., ammonium persulfate) with a monomer used in the manufacture of the first polymer, and are sometimes contained in reaction solution A. By treating reaction solution A with anion exchange resin to obtain aqueous dispersion B, the fluoride ions in the diluted aqueous dispersion C can be reduced. The content of fluoride ions 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 can be 0 ppm by mass. If the content of fluoride ions is below the above-mentioned upper limit, polymerization is easily stabilized in the polymerization process of the second polymer.

[0112] Ammonium ions can be exemplified as cations that are impurities. Ammonium ions originate from polymerization initiators (especially ammonium persulfate) and are sometimes present in reaction solution A. By treating reaction solution A with a cation exchange resin to obtain an aqueous dispersion B, the amount of ammonium ions in the diluted aqueous dispersion C can be reduced. The content of ammonium ions relative to the total mass of aqueous dispersion C is preferably 20 ppm or less, more preferably 10 ppm or less. The lower limit is not particularly limited and can be 0 ppm by mass. It is believed that if the content of ammonium ions is below the aforementioned upper limit, the ionic strength in the aqueous medium decreases, and the aggregation of the second polymer is suppressed. As a result, it is speculated that the manufacturing efficiency of the second polymer is improved.

[0113] Next, the polymerization process (2) of the first polymer will be described.

[0114] In the polymerization step (2) of the first polymer, the first monomer is polymerized in a first aqueous medium in the presence of compound (1) to produce the first polymer. This polymerization is preferably carried out in the presence of compound (1) and a polymerization initiator, and the same polymerization initiator as that used in the polymerization step (1) of the first polymer can be used as the polymerization initiator. After the polymerization step (2) of the first polymer, a dispersion containing the first polymer and the first aqueous medium is obtained, i.e., the first post-polymerization dispersion.

[0115] <Compound(1)>

[0116] Compound (1) is the compound represented by the following formula (2).

[0117] CX 1 X 2 =CX 3 -LZ...(2)

[0118] In equation (2), X 1 and X 2 Each is independently a hydrogen atom or an alkyl group. X 3 It can be a hydrogen atom, a fluorine atom, or an alkyl group. L is a single bond or a divalent linker. Z is -SO3M 1 -OSO3M 1 -P(=O)(OM) 1 )2、-OP(=O)(OM 1 )2 or -COOM 1 , M 1 For hydrogen atoms, metal atoms, N(R) M11 )4 or P(R M12 4. When there are multiple M 1 At that time, multiple M 1 They can be the same or they can be completely different.

[0119] R M11 and R M12 Each can be a hydrogen atom or a substituent, R. M11 Any two of them can be connected to each other to form a loop, and multiple Rs M11 They can be the same or different from each other, R M12 Any two of them can be connected to each other to form a loop, and multiple Rs M12 They can be the same or different from each other.

[0120] In equation (2), X 1 and X 2 Each is independently a hydrogen atom or an alkyl group.

[0121] The alkyl group can be any of the following: straight-chain, branched, or cyclic.

[0122] The number of carbon atoms in the alkyl group is preferably 1 to 10, more preferably 1 to 3, and even more preferably 1.

[0123] From the perspective of increasing the number of particles in the first polymer, X 1 and X 2 All are preferably hydrogen atoms.

[0124] In equation (2), X 3 Preferably, it contains hydrogen atoms, fluorine atoms, or alkyl groups.

[0125] Specific examples and preferred forms of the above-mentioned alkyl groups are the same as X. 1 and X 2 The specific examples and preferred forms of the alkyl groups are the same.

[0126] From the perspective of increasing the number of particles in the first polymer, X 3 Preferably, it contains fluorine atoms or hydrogen atoms, more preferably hydrogen atoms.

[0127] In formula (2), L is a single bond or a divalent linking group.

[0128] Examples of divalent linking groups include alkylene groups, carbonyl groups, ether bonds, thioether bonds, sulfonyl groups, -NH-, -SiH2-, phenylene groups, -CF2-, and groups formed by combining two or more of these. Examples of groups formed by combining two or more of these include ester bonds, thioester bonds, amide bonds, sulfonamide bonds, combinations of alkylene and ether bonds, combinations of alkylene and ester bonds, and combinations of alkylene and amide bonds.

[0129] The aforementioned alkylene group can be any of straight-chain, branched, or cyclic, preferably straight-chain or branched, and more preferably branched. Examples of the number of carbon atoms in the alkylene group include 1 to 6, preferably 1 to 4.

[0130] Specific examples of L include single bonds, alkylene bonds, ether bonds, ester bonds, etc. C -CO-NH-R- Z And so on, preferably single bonds, alkylene groups with 1 to 6 carbon atoms and C -CO-NH-R- Z More preferably, single bonds, alkylene groups having 1 to 2 carbon atoms, and C -CO-NH-R- Z .in, CIt is the bonding site with the carbon atom in formula (2). Z It is the bonding site with Z in formula (2), and R is an alkylene group with 1 to 6 carbon atoms.

[0131] In equation (2), Z is -SO3M 1 -OSO3M 1 -P(=O)(OM) 1 )2、-OP(=O)(OM 1 )2 or -COOM 1 .

[0132] From the viewpoint of stabilizing the dispersion and increasing the number of particles of the first polymer, Z is preferred -SO3M. 1 and -COOM 1 More preferably -SO3Na and -COONa, and even more preferably -SO3Na.

[0133] M 1 For hydrogen atoms, metal atoms, N(R) M11 )4 or P(R M12 )4, R M11 and R M12 Each can be a hydrogen atom or a substituent, independently.

[0134] M 1 The metal atom represented is preferably a group 1 metal atom, more preferably Li, Na, or K.

[0135] R M11 and R M12 The substituents represented are preferably monovalent organic groups, more preferably monovalent hydrocarbon groups, and even more preferably alkyl or aromatic hydrocarbon groups.

[0136] The number of carbon atoms in the above-mentioned substituents is preferably 1 to 10.

[0137] The alkyl group can be any of the following: straight-chain, branched, or cyclic.

[0138] The aforementioned aromatic hydrocarbon group can be either monocyclic or polycyclic. Phenyl is preferred as the aforementioned aromatic hydrocarbon group.

[0139] The molecular weight of compound (1) can be 70 to 500, for example, and 70 to 450 is preferred from the viewpoint of dispersion stability, and more preferably 100 to 300.

[0140] 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 acetate, 2-sulfoethyl methacrylic acid, 4-vinylbenzene sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, N-crotonylglycine, 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 their metal salts.

[0141] As an example of the aforementioned metal salts, M can be cited. 1 The metal salt representing the metal atom.

[0142] As compound (1), preferably, it is a vinyl compound having a sulfonic acid group, a phosphonic acid group, or a carboxyl group; an allyl compound having a sulfonic acid group, a phosphonic acid group, or a carboxyl group; (meth)acrylic acid; (meth)acrylamide having a sulfonic acid group, a phosphonic acid group, or a carboxyl group; and their metal salts, preferably 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-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulfonic acid, or sodium 2-methacrylamido-2-methyl-1-propanesulfonic acid. Furthermore, the term "(meth)acrylic acid" above includes both acrylic acid and methacrylic acid, and the term "(meth)acrylamide" above includes both acrylamide and methacrylamide.

[0143] Before the polymerization of the first monomer begins, the content of compound (1) relative to the first aqueous dispersion is preferably 1.0 to 1000 ppm by mass. From the viewpoint of better performance of the present invention, it is more preferably 1.0 to 800 ppm by mass, even more preferably 3.0 to 500 ppm by mass, and particularly preferably 5.0 to 300 ppm by mass.

[0144] Furthermore, the concept of "first aqueous dispersion" before the polymerization of the first monomer includes the compound (1) and the aqueous medium, but excludes the first monomer and polymerization initiator used in the polymerization of the first polymer. For example, even if the first aqueous dispersion containing the compound (1) and the aqueous medium is mixed with the first monomer and polymerization initiator before the polymerization of the first monomer begins, "first aqueous dispersion" refers to a mixture of components other than the first monomer and polymerization initiator.

[0145] <First Aqueous Medium>

[0146] Specific examples of the first aqueous medium include water, and mixtures of water and water-soluble organic solvents. Specific examples of water-soluble organic solvents include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0147] Before the polymerization of the first monomer begins, the content of the first aqueous medium is preferably 20 to 90% by volume relative to the reactor capacity, more preferably 40 to 80% by volume.

[0148] <First Monomer>

[0149] The first monomer used in this manufacturing method comprises at least one selected from tetrafluoroethylene (hereinafter also referred to as "TFE") and hexafluoropropylene (hereinafter also referred to as "HFP").

[0150] The first monomer may also contain monomers other than TFE and HFP, and preferably contains monomers other than TFE and HFP.

[0151] Other monomers besides TFE and HFP mentioned above include perfluoro(alkyl vinyl ether) (hereinafter also called "PAVE"), propylene, vinylidene fluoride (hereinafter also called "VdF"), CH2=CF-CF2-O-Rf-COOH, CH2=CF-CF2-O-Rf-SO3H, CF2=CF-CF2-O-Rf-COOH, CF2=CF-CF2-O-Rf-SO3H, CH2=CF-O-Rf-SO3H, CH2=CF-O-Rf-SO3H, CF2=CF-O-Rf-COOH, and CF2=CF-O-Rf-SO3H (Rf represents a perfluoroalkyl group with 1 to 10 carbon atoms, and the carbon atoms in the perfluoroalkyl group may have ether-like oxygen atoms).

[0152] When the first monomer contains TFE, the amount of TFE relative to the amount of the first monomer is preferably 10 to 90 mol%, more preferably 30 to 85 mol%, and even more preferably 40 to 80 mol%.

[0153] When the first monomer contains HFP, the amount of HFP relative to the amount of the first monomer is preferably 30-95 mol%, more preferably 40-90 mol%, and even more preferably 50-85 mol%.

[0154] From the viewpoint of superior polymerization reactivity of the first polymer and superior effects of the present invention, the first monomer preferably contains PAVE.

[0155] From the viewpoint of excellent polymerization reactivity when manufacturing the first polymer and the viewpoint of being able to manufacture the second polymer more efficiently, the monomer represented by PAVE formula (11) is preferred.

[0156] CF2 = CF-OR f1 (11)

[0157] In equation (11), R f1 It is a perfluoroalkyl group with 1 to 10 carbon atoms.

[0158] From the perspective of superior polymerization reactivity, R f1 The number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3.

[0159] Perfluoroalkyl groups can be linear or branched.

[0160] 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"). From the viewpoint that the second polymer can be manufactured more efficiently, PMVE or PPVE is preferred, and PMVE is more preferred.

[0161] When the first monomer contains PAVE, the amount of PAVE relative to the amount of the first monomer is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 60 mol%. When the PAVE is PMVE, PEVE, or PPVE, or when a mixture of two or more of these is used, the preferred amounts are the same.

[0162] From the viewpoint of superior polymerization reactivity of the first polymer and superior effects of the present invention, the first monomer preferably comprises at least one selected from propylene and VdF.

[0163] When the first monomer contains propylene, the amount of propylene used relative to the amount of the first monomer is preferably 5 to 90 mol%, more preferably 8 to 70 mol%, and even more preferably 10 to 60 mol%.

[0164] When the first monomer contains VdF, the amount of VdF relative to the amount of the first monomer is preferably 5 to 90 mol%, more preferably 8 to 80 mol%, and even more preferably 10 to 70 mol%.

[0165] The first monomer preferably comprises any combination of TFE and PAVE, TFE and propylene, and HFP and VdF.

[0166] When the first monomer comprises TFE and PAVE, the amount of PAVE relative to the total amount of TFE and PAVE is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 30 to 60 mol%. The preferred amounts are the same when PAVE is PMVE, PEVE, or PPVE, or when a mixture of two or more of these is used.

[0167] When the first monomer comprises TFE and PAVE, the total amount of TFE and PAVE relative to the amount of the first monomer 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%.

[0168] When the first monomer comprises TFE and propylene, the amount of propylene used relative to the total amount of TFE and propylene is preferably 5 to 90 mol%, more preferably 8 to 70 mol%, and even more preferably 10 to 60 mol%.

[0169] When the first monomer comprises TFE and propylene, the total amount of TFE and propylene relative to the amount of the first monomer 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%.

[0170] When the first monomer comprises HFP and VdF, the amount of VdF used relative to the total amount of HFP and VdF is preferably 5 to 90 mol%, more preferably 8 to 80 mol%, and even more preferably 10 to 70 mol%.

[0171] When the first monomer comprises HFP and VdF, the total amount of HFP and VdF relative to the amount of the first monomer 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%.

[0172] The first monomer may also contain other monomers besides those mentioned above, and from the viewpoint of manufacturing the second polymer more efficiently, it may be substantially free of other monomers.

[0173] "Substantially free of other monomers" means that the amount of other monomers used relative to the amount of the first monomer is less than 0.01 mol%, preferably 0 mol%.

[0174] In the polymerization steps (1) and (2) of the first polymer in the first form, from the viewpoint of suppressing the decrease in the molecular weight of the obtained first polymer, it is preferable to carry out the process under conditions where there are substantially no emulsifiers having fluorine atoms or emulsifiers without fluorine atoms. That is, the aqueous dispersion preferably does not contain substantially any emulsifiers having fluorine atoms or emulsifiers without fluorine atoms.

[0175] The absence of emulsifiers with and without fluorine atoms (hereinafter collectively referred to as "emulsifiers") means that the content of the emulsifier relative to the total mass of the first aqueous dispersion is less than 10 ppm by mass, preferably less than 150 ppb by mass, and more preferably less than 50 ppb by mass. The lower limit is 0 ppb by mass.

[0176] The content of various emulsifiers can be determined using a liquid chromatography mass analyzer. Specifically, the determination method described in paragraphs

[0721] to

[0732] of International Publication No. 2018 / 181904 can be cited as an example.

[0177] Examples of emulsifiers, both those with and without fluorine atoms, include water-soluble emulsifiers. A water-soluble emulsifier is defined as one with a solubility of 100 mg or more in 1000 g of water at 25°C. A non-water-soluble emulsifier is any emulsifier other than the water-soluble type mentioned above. Water-soluble emulsifiers can be either ionic or non-ionic.

[0178] Examples of emulsifiers that have fluorine atoms and those that do not include emulsifiers that do not have carbon-carbon double bonds.

[0179] In addition, compound (1), the first polymer described later and the second fluoropolymer described later are not emulsifiers.

[0180] Anionic fluorinated emulsifiers can be cited as examples of emulsifiers containing fluorine atoms.

[0181] Examples of anionic fluorinated emulsifiers include emulsifiers containing fluorine atoms in which the total number of carbon atoms in the portion excluding the anionic group is 20 or less, and emulsifiers containing fluorine atoms in which the molecular weight of the anionic portion is 800 or less. Furthermore, the term "anionic portion" refers to the portion of the fluorinated emulsifier that has had its cationic components removed.

[0182] Emulsifiers without fluorine atoms are those that do not have fluorine atoms but have alkyl or other hydrocarbon groups as hydrophobic moieties. Alternatively, halogen atoms other than fluorine atoms can replace the hydrogen atoms of the hydrocarbon groups in emulsifiers without fluorine atoms.

[0183] Examples of emulsifiers that do not have fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0184] Anionic hydrocarbon emulsifiers refer to emulsifiers that have negatively charged hydrophilic parts such as carboxylic acid groups, sulfonic acid groups, sulfuric acid groups, phosphonic acid groups, and phosphoric acid groups, as well as hydrocarbon groups such as alkyl groups that are hydrophobic parts.

[0185] Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acids supplied by Resolution Performance Products under the trademark Versatic 10, linear alkyl polyether sulfonates supplied by BASF under the trademark Avanel S series, and sulfonic acid succinate emulsifier Lankropol K8300 available from AkzoNobel Surface Chemistry LLC.

[0186] Nonionic hydrocarbon emulsifiers are emulsifiers that do not dissociate into ions in water and exhibit surface activity, and have alkyl or other hydrocarbon groups as hydrophobic parts.

[0187] Examples of water-soluble functional groups, such as polyethylene oxide chains obtained from the polymerization of ethylene oxide, can be cited as the hydrophilic portion of nonionic hydrocarbon emulsifiers. Examples of nonionic hydrocarbon emulsifiers include polyoxyolefin block copolymers, such as block copolymers containing polyethylene oxide and polypropylene oxide.

[0188] In addition, as other nonionic hydrocarbon emulsifiers, the emulsifiers described in paragraphs

[0043] to

[0052] of Japanese Patent Publication No. 2016-537499 can be cited as examples.

[0189] Emulsifiers containing fluorine atoms and those without fluorine atoms can contain silicon atoms. Examples of silicon-containing emulsifiers include siloxane emulsifiers. Siloxane emulsifiers are hydrocarbon-containing emulsifiers with a siloxane backbone.

[0190] Examples of siloxane emulsifiers include those described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0191] Emulsifiers containing fluorine atoms and those without fluorine atoms can be polymeric emulsifiers. Examples of polymeric emulsifiers include polymers with hydrophilic side chains. Examples of such polymeric emulsifiers include polymers comprising units based on compounds having sites that can undergo polymerization and hydrophilic groups. Furthermore, examples can be given of polymers obtained through post-treatment such as hydrolysis of polymers containing units based on compounds having groups that can be hydrophilic, even if they initially do not have hydrophilic groups.

[0192] When polymerizing the first monomer in the presence of an emulsifier that does not have fluorine atoms, 0.1 to 15 parts by mass of the emulsifier that does not have fluorine atoms are typically used relative to 100 parts by mass of the aqueous medium.

[0193] <Polymerization process of the second polymer>

[0194] The polymerization process of the second polymer is preferably carried out in an aqueous dispersion C containing the first polymer and an aqueous medium, wherein the second monomer is polymerized. A polymerization initiator and a chain transfer agent may also be supplied as needed. This method yields an aqueous dispersion D containing primary particles of both the first and second polymers dispersed in an aqueous medium. The preferred form, such as the type and proportion of the second monomer, can be determined based on the composition of the second polymer described above.

[0195] The content of the first polymer relative to the total mass of the aqueous dispersion C is preferably 0.01 to 4.0% by mass, more preferably 0.01 to 0.6% by mass, and even more preferably 0.01 to 0.5% by mass. If the content of the first polymer is within the above range, the second polymer can be manufactured more easily and 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.

[0196] Preferably, the primary particles of the first polymer are dispersed in an aqueous medium of aqueous dispersion C. The average particle size of the primary particles of the first polymer is preferably 1–150 nm, more preferably 10–120 nm, and even more preferably 50–120 nm. If the average particle size of the first polymer is within the above range, the second polymer can be manufactured more easily and efficiently. The average particle size of the primary particles of the first polymer is determined by dynamic scattering and analyzed by cumulative analysis (hydrodynamic diameter), and the detailed measurement conditions are described in the Examples section.

[0197] As an aqueous medium contained in aqueous dispersion C, an example can be the same aqueous medium described in the manufacturing process of reaction solution A.

[0198] The content of the aqueous medium relative to the total mass of the aqueous dispersion C is preferably 60 to 99.9% by mass, more preferably 80 to 99.9% by mass, and even more preferably 90 to 99.9% by mass.

[0199] The aqueous dispersion C may also contain other components besides the first polymer and the aqueous medium. Specific examples of other components include pH adjusters, waxes, emulsifiers, and reducing agents.

[0200] 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 bicarbonate and sodium carbonate. Among phosphates, disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate are preferred.

[0201] Paraffin wax is preferred as the wax. Paraffin wax can be liquid, semi-solid, or solid at room temperature. It is preferably a saturated hydrocarbon with 12 or more carbon atoms. The melting point of paraffin wax is preferably 40–65°C, more preferably 50–65°C.

[0202] Examples of emulsifiers include fluorinated and non-fluorinated emulsifiers, but in this embodiment, the aqueous dispersion C preferably does not contain fluorinated emulsifiers substantially. That is, fluorinated emulsifiers are preferably not used in the polymerization step of the second polymer. Fluorinated emulsifiers refer to emulsifiers whose hydrophobic sites contain fluorine atoms. Specific examples of fluorinated emulsifiers include fluorinated alkylates and fluorinated ether carboxylic acids. Non-fluorinated emulsifiers refer to emulsifiers other than fluorinated emulsifiers. Examples of non-fluorinated emulsifiers include sodium dodecyl sulfate, PELEX SS-H manufactured by Kao Chemical Co., Ltd., and NEWCOL 1305-SN manufactured by Nippon Emulsifier Co., Ltd.

[0203] "Substantially free of fluorinated emulsifiers" means that, relative to the total mass of the first polymer in the aqueous dispersion C, the content of fluorinated emulsifiers is less than 100 ppm by mass, preferably less than 50 ppm by mass, more preferably less than 25 ppm by mass, and even more preferably less than 5 ppm by mass. The lower limit is not particularly limited and can be 0 ppm by mass.

[0204] When the aqueous dispersion C contains emulsifiers other than fluorinated emulsifiers, the content of emulsifiers other than fluorinated emulsifiers is preferably 0.01 to 5% by mass relative to the aqueous medium. In this embodiment, the aqueous dispersion C is preferably substantially free of emulsifiers. That is, it is preferable not to use emulsifiers in the polymerization step of the second polymer. "Substantially free of emulsifiers" means that the content of emulsifiers is less than 100 ppm by mass relative to the total mass of the first polymer and the second polymer, preferably less than 10 ppm by mass, more preferably less than 100 ppb by mass, and even more preferably less than 1 ppb by mass. It can be less than 0.1 ppb by mass or even 0 ppb by mass. When emulsifiers are not used, the amount of compounds represented by formula (S1) and formula (S2) above can be suppressed, so it is easy to keep the content of these compounds within the above range.

[0205] In the method for manufacturing the solid composition of this embodiment, the second polymer can be manufactured efficiently even without the use of an emulsifier. It is presumed that during the polymerization of the second monomer, the first polymer adsorbs the second monomer through its hydrophobic portion, encapsulating it within the primary particles of the first polymer, thereby making the second monomer soluble. As a result, it is presumed that the second monomer polymerizes within or near the primary particles of the first polymer. Furthermore, it is presumed that the first polymer contributes to dispersion stabilization in aqueous media.

[0206] When the aqueous dispersion C contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass relative to 100 parts by mass of the aqueous medium.

[0207] When the aqueous dispersion C contains wax, the wax content is preferably 1 to 10 parts by mass relative to 100 parts by mass of the aqueous medium.

[0208] When the aqueous dispersion C contains a reducing agent, the amount of reducing agent used is preferably 1 to 2000 ppm by mass relative to 100 parts by mass of the second monomer supplied.

[0209] The reaction is initiated by supplying a second monomer to the aqueous dispersion C and, if necessary, a polymerization initiator. Alternatively, a chain transfer agent may be supplied during the reaction.

[0210] The second monomer is supplied to the reaction system (i.e., the polymerization reactor) using conventional methods. For example, the second monomer can be supplied to the reaction system continuously or intermittently to bring the polymerization pressure to a specified level. Alternatively, the second monomer can be dissolved in an aqueous medium, and the resulting solution can be supplied to the reaction system continuously or intermittently.

[0211] When using a polymerization initiator, the polymerization initiator can be supplied to the reaction system all at once or in batches.

[0212] The amount of the second monomer supplied is preferably 1 to 50 parts by mass relative to 100 parts by mass of the aqueous medium contained in the aqueous dispersion C, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass.

[0213] Examples of polymerization initiators include oil-soluble free radical initiators, water-soluble free radical initiators, and water-soluble redox catalysts.

[0214] Examples of oil-soluble free radical initiators include tert-butyl peroxypentanoate (hereinafter also known as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also known as "IPP"), among other oil-soluble organic peroxides.

[0215] Examples of water-soluble free radical initiators include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as bis(2-)peroxysuccinic acid, diglutaric acid peroxide, and tert-butyl hydroperoxide.

[0216] Examples of water-soluble redox catalysts include combinations of oxidants such as hydrobromic acid or its salts, hydrochloric acid or its salts, persulfate or its salts, permanganate or its salts, and hydrogen peroxide, with reducing agents such as sulfurous acid or its salts, bisulfite or its salts, thiosulfate or its salts, organic acids, and inorganic salts. Potassium persulfate and ammonium persulfate are preferred persulfates. Sodium sulfite is preferred as a sulfite. Combinations of sulfate anions, sulfite anions, chloride anions, and metal ions are possible as inorganic salts. Transition metal ions are preferred, including ions of manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver, with iron ions being more preferred. Ferrous sulfate is preferred as an inorganic salt. Oil-soluble free radical initiators and water-soluble free radical initiators are preferred as polymerization initiators. From the viewpoint of more efficient production of fluoropolymers, oil-soluble free radical initiators are more preferred, and oil-soluble organic peroxides are even more preferred.

[0217] Polymerization initiators can be used in combination of two or more.

[0218] The amount of polymerization initiator supplied relative to 100 parts by mass of the second monomer is preferably 1 to 1000 ppm, more preferably 5 to 750 ppm, and even more preferably 10 to 500 ppm.

[0219] Examples of chain transfer agents include ethyl acetate, methanol, ethanol, tert-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0220] The supply amount of the chain transfer agent is preferably 0.1 to 5 parts by mass relative to 100 parts by mass of the aqueous medium. The supply amount of the chain transfer agent is preferably 0.1 to 20 parts by mass relative to 100 parts by mass of the second monomer, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass.

[0221] The polymerization temperature is preferably 10–95°C, and more preferably 15–90°C.

[0222] The polymerization pressure is preferably 0.5 to 4.0 MPa, more preferably 0.6 to 3.5 MPa.

[0223] The polymerization time is preferably 90 to 1000 minutes, more preferably 90 to 700 minutes, in the case of batch processing.

[0224] (Aqueous dispersion D)

[0225] Aqueous dispersion D is an aqueous dispersion containing primary particles of a first polymer and a second polymer, obtained through a polymerization process of the second polymer.

[0226] The aqueous dispersion D preferably contains no emulsifier. Examples of emulsifiers include the fluorinated and non-fluorinated emulsifiers mentioned above.

[0227] The fact that the aqueous dispersion D is substantially free of emulsifier means that the content of emulsifier relative to the total mass of the aqueous dispersion D is less than 0.03 ppm by mass, preferably less than 0.02 ppm by mass, and more preferably 0 ppm by mass.

[0228] In the absence of an emulsifier in the polymerization process of the second polymer, the aqueous dispersion D can also be easily prepared into a dispersion of organic solvents such as N-methylpyrrolidone or acetone by solvent displacement.

[0229] For example, an organic solvent dispersion can be prepared by mixing an aqueous dispersion D with an organic solvent and then dehydrating it by evaporation or by using anhydrous sodium sulfate.

[0230] The content of the first polymer relative to the total mass of the aqueous dispersion D 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.

[0231] The content of the second polymer relative to the total mass of the aqueous dispersion D is preferably 10 to 40% by mass, more preferably 12 to 35% by mass, and even more preferably 15 to 30% by mass.

[0232] The combined content of the first polymer and the second polymer relative to the total mass of the aqueous dispersion D is preferably 10 to 40% by mass, more preferably 12 to 35% by mass, and even more preferably 15 to 35% by mass.

[0233] The content of the aqueous medium relative to the total mass of the aqueous dispersion D is preferably 50-99% by mass, more preferably 60-99% by mass, and even more preferably 70-99% by mass.

[0234] When the first polymer contains PAVE units, the content of PAVE units relative to the total of all units in the first polymer and all units in 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%. If the content of PAVE units is above the lower limit of the above range, the dispersibility is excellent, and if it is below the upper limit, the heat resistance is excellent.

[0235] 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%.

[0236] 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 preferably 100 ppb or less by mass relative to the total mass of the first polymer and the second polymer, more preferably 50 ppb or less by mass, even more preferably 25 ppb or less by mass, and particularly preferably 0 ppb by mass.

[0237] The average particle size of the primary particles in the aqueous dispersion D is preferably 100–400 nm, more preferably 150–300 nm, and even more preferably 170–270 nm. If the average particle size is above the lower limit of the above range, the productivity and mechanical properties are good; if it is below the upper limit, the emulsion stability during the manufacture of the second polymer can be maintained.

[0238] 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. If the aspect ratio is below the upper limit of the above range, it can impart stability to the emulsion.

[0239] <The coagulation process of the first and second polymers>

[0240] By agglomerating the solids in the aqueous dispersion D and removing the dispersion medium such as the aqueous medium, a moist powder is obtained, which is then further dried to obtain a dry powdered solid composition.

[0241] When the aqueous dispersion D contains primary particles, the average particle size and aspect ratio of the primary particles in the aqueous dispersion D can be considered to be the same as those of the primary particles in the dry powder.

[0242] The coagulation process, the process of removing the dispersion medium to obtain a wet powder, and the process of drying the wet powder to obtain a dry powder can be carried out using known methods.

[0243] Examples of coagulation methods include freeze coagulation, acid coagulation, alkali coagulation, and coagulation using coagulants, but these are not the only ones that can be mentioned.

[0244] In the case of freeze-coagulation, the coagulation temperature is preferably -20 to 0°C. The coagulation time is preferably 1 hour or more, more preferably 2 hours or more.

[0245] In the case of acid coagulation, it is preferable to add an acid-containing solution to the aqueous dispersion D. Examples of acids added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with hydrochloric acid being preferred. The concentration of the acid 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.

[0246] As a method for alkaline coagulation, it is preferable to add an alkaline solution to the aqueous dispersion D. Examples of the added alkaline include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the alkaline solution is preferably 0.1–50% by mass, more preferably 1–30% by mass, and even more preferably 1–10% by mass.

[0247] As a coagulation process using a coagulant, known coagulants can be used. Examples of known coagulants include ammonium salts, calcium salts, and magnesium salts. Specifically, examples include aluminum sulfate, alum represented by the general formula M'Al(SO4)2·12H2O [where M' is a monovalent cation other than lithium], calcium nitrate, and magnesium sulfate. Alum is preferred, and potassium alum, in which M is potassium, is more preferred.

[0248] As a mechanical cohesion, examples include well-known methods described in paragraph

[0032] of International Publication 2023 / 115278.

[0249] Mechanical coagulation is preferred as a coagulation method because it is easy to implement.

[0250] Adhesive for electrodes

[0251] The electrode adhesive of this embodiment comprises the above-described solid composition. The content of the solid composition relative to the total mass of the electrode adhesive is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may also be 100% by mass. In addition to the solid composition, other components that may be included in the electrode adhesive include, for example, fluoropolymers, polyimide resins, polyolefin resins, etc., other than the first and second polymers contained in the solid composition of this embodiment.

[0252] <Electrode Mixture>

[0253] The electrode mixture of this embodiment contains an electrode binder and an electrode active material. The electrode active material can be either a positive electrode active material or a negative electrode active material. That is, the electrode binder of this embodiment can be used in both positive and negative electrodes. The electrode mixture may also contain conductive additives and solvents.

[0254] Examples of positive electrode active materials include those based on LiNiO2 (lithium nickel oxide), LiCoO2 (lithium cobalt oxide), LiMnO4 (lithium manganese oxide), and LiFePO4 (lithium iron phosphate). A portion of the nickel in lithium nickel oxide, a portion of the cobalt in lithium cobalt oxide, a portion of the manganese in lithium manganese oxide, and a portion of the iron in lithium iron phosphate can be replaced by other elements. Examples of these other elements include nickel, cobalt, manganese, iron, copper, titanium, magnesium, tungsten, molybdenum, aluminum, niobium, zinc, tin, zirconium, gallium, vanadium, boron, phosphorus, sulfur, and silicon.

[0255] Examples of anode active materials include: carbon materials such as graphite, carbon black, carbon fiber, and sintered organic polymers; chalcogenide compounds such as oxides and sulfides; and nitrides. Metals and alloys can also be included. Examples of oxides include silicon oxide and tin oxide. Examples of metals include metallic lithium, metallic silicon, and metallic tin.

[0256] Examples of conductive additives include carbon black such as acetylene black and carbon fiber.

[0257] Examples of solvents 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).

[0258] In addition to the materials mentioned above, materials known in the art may also be used as positive electrode active materials, negative electrode active materials, conductive additives, and solvents. For example, the materials described in Japanese Patent No. 7303469 may be used.

[0259] Other known components preferably include a solid electrolyte, and more preferably a sulfide-based solid electrolyte.

[0260] Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes, which have a sulfide-germanium ore-type crystal structure. Furthermore, examples of solid electrolytes that constitute secondary batteries, as described later, also include solid electrolytes.

[0261] The content of the solid composition relative to the total mass of the electrode mixture after solvent removal is preferably 0.5 to 3.5% by mass, more preferably 1.0 to 3.0% by mass, and even more preferably 1.5 to 2.5% by mass.

[0262] The content of the electrode active material relative to the total mass of the electrode mixture after solvent removal is preferably 92-98% by mass, more preferably 93-97% by mass, and even more preferably 94-96% by mass.

[0263] The content of the conductive additive relative to the total mass of the electrode mixture after solvent removal is preferably 1.5 to 4.5% by mass, more preferably 2.0 to 4.0% by mass, and even more preferably 2.5 to 3.5% by mass.

[0264] <Electrode>

[0265] The electrode in this embodiment includes an electrode mixture and a current collector. The electrode mixture is carried in the current collector. Examples of positive current collectors include strip-shaped members made of metallic materials such as aluminum, nickel, or stainless steel. Examples of negative current collectors include strip-shaped members made of metallic materials such as copper, nickel, or stainless steel.

[0266] As a method for carrying an electrode mixture onto a current collector, an example is to coat a paste-like electrode mixture onto at least one side of the current collector and then dry and pressurize it. The paste-like electrode mixture can be prepared using the solvent described above. As a method for coating the paste-like electrode mixture, coating methods known in the art can be used.

[0267] Secondary batteries

[0268] The secondary battery of this embodiment includes electrodes. The electrode comprising the above-described solid composition can be a positive electrode or a negative electrode, or both. The secondary battery includes a positive electrode, a negative electrode, a spacer, and an electrolyte. The spacer is sandwiched between the positive and negative electrodes. The electrolyte is present between the positive and negative electrodes. In the case of an all-solid-state battery, the secondary battery 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.

[0269] Example

[0270] The present invention will be described in more detail below with reference to the embodiments, but the present invention is not limited to these embodiments. In the following examples, Examples 1 to 3 are embodiments, and Example 4 is a comparative example.

[0271] <Determination Methods and Evaluation Methods>

[0272] [Glass transition temperature (Tg)]

[0273] Tg was measured using a NEXTA DSC600 manufactured by Hitachi Advanced Technology Co., Ltd. Specifically, 5 mg of the sample was measured in an aluminum sample pan, and the sample was heated to 100°C at a rate of 10°C / min under a nitrogen atmosphere. It was then cooled to -60°C at a rate of 10°C / min. After reaching the specified temperature, it was heated again to 100°C at a rate of 10°C / min. Tg was estimated from the inflection point confirmed by this second heating operation.

[0274] [Proportion of each unit in the polymer]

[0275] The proportions of each unit in the polymer are determined by... 19 The results were obtained from F-NMR analysis and infrared absorption spectroscopy analysis.

[0276] [Concentration of solids in aqueous dispersion]

[0277] The concentration of the solid component is determined by heating the remaining portion. Specifically, 7–8 g of the test sample is measured in a pre-measured aluminum dish and heated at 120°C for 2 hours to evaporate the moisture. Then, the mass of the aluminum dish containing the remaining solid component is measured. The concentration of the solid component (unit: mass%) is calculated by dividing the mass of the solid component by the mass of the test sample used in the measurement.

[0278] [Average particle size of primary particles in aqueous dispersion]

[0279] The determination was performed using dynamic light scattering. The solids concentration of the aqueous dispersion of the test object was adjusted to 5.0% by mass to prepare the sample solution. However, if the solids concentration of the aqueous dispersion (stock solution) of the test object was less than 5%, the stock solution was used as the sample solution. A particle size analysis system (Otsuka Electronics Co., Ltd. product name "ELSZ-neo") was used, and measurements were performed 125 times at 23°C. The average particle size (unit: nm) was determined using the cumulative measurement method. The refractive index of the solvent (water) was 1.333, and the viscosity of the solvent (water) was 0.93 mPa. s.

[0280] [Number of particles in the aqueous dispersion]

[0281] Using the formula x = (concentration of solid component in aqueous dispersion) = number of primary particles N × volume of primary particles V × specific gravity of primary particles ρ1 / specific gravity of aqueous dispersion ρ2, the number of primary particles per mL of aqueous dispersion can be calculated. Primary particles are considered to be spherical.

[0282] N=x ρ2 / V ρ1

[0283] N (unit: particles / mL): number of particles per mL.

[0284] x (unit: mass%): concentration of solid components in the aqueous dispersion.

[0285] V (unit: mL / particle): Volume of a primary particle, V = 4 / 3 π (r / 2×10 -7 ) 3 r (unit: nm): Primary particle size.

[0286] ρ1 (unit: g / mL): density of primary particles. When it can be used as a PTFE metric, the value of SSG is ρ1. When it cannot be used as a PTFE metric, ρ1=2.2 is used.

[0287] ρ2 (unit: g / mL): The specific gravity of the aqueous dispersion, a value obtained empirically, using ρ2 = 0.492x 2 +0.5319x+0.09992. x is the concentration of the solid component mentioned above.

[0288] Aspect Ratio

[0289] Aqueous dispersion D was diluted to a solid content concentration of 0.2% by mass to prepare a sample dispersion. Pt vapor deposition was performed on the sample after the dispersion was dropped onto the substrate and dried. Using a scanning electron microscope (SEM, JSM-IT700HR InTouchScope, NEC Corporation), at least four images of non-overlapping particles at 20,000x magnification were randomly selected and saved. From these images, focusing on at least 800 elliptical particles, the brightness was adjusted using the image analysis software "MultiImage Tool," and binarization of the particles and substrate was performed. The aspect ratio (length to width) of each particle was then analyzed. The average aspect ratio of each particle was taken as the primary aspect ratio.

[0290] [The total content of compound (S1) represented by formula (S1) and compound (S2) represented by formula (S2)]

[0291] Using a liquid chromatography-mass spectrometry analyzer, the content (hereinafter also referred to as "content M") of the compounds represented by the above formulas (S1) and (S2) relative to the total mass of the fluoropolymers in the dried powders obtained in the examples described below is determined as follows.

[0292] In the examples described below, 2.5 g of the dried powder was added to 5 mL of methanol, and the mixture was ultrasonically treated at 50 °C for 2 hours. The mixture was then centrifuged (5000 rpm, 5 minutes) to allow the fluoropolymer to precipitate, and the supernatant was collected as the extract. The extract was diluted with water or methanol as needed for determination. Thus, extract M, used in the determination of content M, was obtained.

[0293] (Measurement Procedure)

[0294] For extract M, the peak areas of compounds represented by equations (S1) and (S2) for each carbon number were determined using the MRM (Multiple Reaction Monitoring) method.

[0295] Compounds with n1 in formula (S1) ranging from 3 to 13, 15, and 17 carbon atoms are determined by conversion to perfluorocarboxylic acids with the same number of carbon atoms. Compounds with n2 in formula (S2) ranging from 4 to 10 and 12 carbon atoms are determined by conversion to perfluorosulfonic acids with the same number of carbon atoms.

[0296] The measuring instruments and conditions are shown in Table 1. The MRM measurement parameters are shown in Tables 2-5.

[0297] First, prepare five standard methanol solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations of 1–180 ng / g. Use an approximation based on the sample concentration and peak integral value of each standard, and calculate a using the following formula (A1).

[0298] A = a × X (A1)

[0299] A: Peak area of ​​perfluorocarboxylic acids and perfluorosulfonic acids; X: Concentration of perfluorocarboxylic acids and perfluorosulfonic acids (ng / g).

[0300] [Table 1]

[0301] [Table 2]

[0302] [Table 3]

[0303] [Table 4]

[0304] [Table 5]

[0305] Next, the content of compounds with carbon number (n1+1) in extract M is calculated using the following formula (A2). Furthermore, 'a' in formula (A2) refers to 'a' calculated from the above formula (A1).

[0306] XCm=ACm / a×ρ1 / ρ2 (A2)

[0307] XCm: Content (ng / g) of compounds with a carbon number of (n1+1) in the extract.

[0308] ACm: Peak area of ​​compounds with the number of carbons (n1+1) in the extract.

[0309] ρ1: Density of methanol

[0310] ρ2: Density of the extract

[0311] The quantitation limit in this assay is 1 ng / g.

[0312] In addition, the content (ZCm) of each compound relative to the content of the fluoropolymer in the solid composition is determined by the following formula (A3) based on the XCm value of each compound obtained using the extract M.

[0313] ZCm = XCm × Dilution ratio × W2a / W2b (A3)

[0314] ZCm: The content of (n1+1) compounds in the powder (relative to fluoropolymers).

[0315] W2a: Mass of extract M (g)

[0316] W2b: Mass (g) of the dried powder used in sample preparation of extract M.

[0317] The dilution ratio indicates the mass ratio of the extract diluted with water or methanol to achieve an XCm of less than 180 ng / g.

[0318] The ZCm values ​​of each compound are summed and used as the content M.

[0319] [Emulsifier content in aqueous dispersions]

[0320] The emulsifier content in an aqueous dispersion is calculated from the amount added.

[0321] [Content of the first polymer in the dried powder]

[0322] In the dried powder, the content of the first polymer relative to the total mass of the first polymer and the second polymer is calculated based on the input amount, and the obtained value is taken as the content of the first polymer in the dried powder.

[0323] [Standard Specific Gravity (SSG)]

[0324] Standard specific gravity (SSG) is determined according to ASTM D4895-04. Specifically, a 12.0 g sample is weighed and compressed into granules within a cylindrical mold with an inner diameter of 28.6 mm. The sample is then placed in an oven at 290°C with a heating rate of 120°C / hour. Further, it is held at 380°C for 30 minutes, then cooled at 60°C / hour and held at 294°C for 24 minutes. After the sample is placed in a desiccator at 23°C for 12 hours, the specific gravity of the sample relative to water at 23°C is determined; this is the standard specific gravity. The smaller the SSG value, the larger the molecular weight.

[0325] [Extrusion pressure (hereinafter also referred to as EP)]

[0326] 100g of dried powder that has been left at room temperature for more than 2 hours was added to a 500mL glass bottle, along with 21.7g of lubricating oil (ISOPAR H (registered trademark), manufactured by ExxonMobil). The mixture was stirred for 3 minutes to obtain a final product. After the final product was placed in a 25°C constant temperature bath for 2 hours, extrusion was performed at 25°C through an orifice with a shrinkage ratio (the ratio of the inlet cross-sectional area to the outlet cross-sectional area of ​​the die) of 100 and an extrusion speed of 51cm / min to obtain extruded beads (rope-like objects). The pressure required for extrusion at this point was measured; this pressure is the extrusion pressure (unit: MPa).

[0327] Tensile strength

[0328] Extruded beads were obtained using the same method as for measuring extrusion pressure, and dried at 230°C for 30 minutes to remove the lubricant. The extruded beads were then cut to suitable lengths, with the two ends fixed so that the clamp spacing was 3.8 cm, and heated to 300°C in an air-circulating oven. Next, they were stretched at a stretching speed of 1000% / second and a stretching ratio of 2400% to obtain stretched porous body B (hereinafter also referred to as "stretched beads B").

[0329] Three samples were tested using a tensile testing machine (manufactured by Aiand Corporation): one sample was cut from both ends of a single tensile bead B (neckback was removed if present within the clamping area), and the other sample was cut from the center of the tensile bead B. The tensile breaking load was measured, and the maximum stress generated until fracture was taken as the tensile strength (unit: N). The number of tensile beads tested was changed to two, and the fracture strength of a total of six samples (samples (1) to (6)) was measured. The average fracture strength of these six samples was recorded as the tensile strength in Table 8.

[0330] In the tensile testing machine test, the sample is clamped in a movable jaw with a gauge length of 5.0 cm and fixed. The movable jaw is driven at a speed of 300 mm / min at room temperature (24℃) to apply tensile stress.

[0331] [Stress relaxation time]

[0332] The two ends of the aforementioned string bead B are connected to the fixing element to create a taut string bead sample with a total length of 8 inches (20 cm). The oven is maintained at 390°C, and the fixing element and string bead sample are inserted into the oven through a slit located on the side (covered). The time required from insertion into the oven until the string bead sample breaks is measured as the stress relaxation time (in seconds). A longer stress relaxation time indicates better heat resistance, higher molecular weight, and higher crystallinity after stretching.

[0333] <Preparation of Electrode Mixture>

[0334] LiNi will be used as the electrode active material (positive electrode active material). 0.6 Mn 0.2 Co 0.2 O2 and carbon black as a conductive additive were mixed in a pressure kneader at 30 rpm for 300 seconds to obtain mixture 1. Then, dry powder as a binder was added, and the mixture was stirred at 50 rpm for 300 seconds to obtain mixture 2. The ratio of the components in mixture 2, by mass, was positive electrode active material: binder: conductive additive = 95:2:3. Mixture 2 was fed into a rolling mill and a pressure of 10 MPa was applied. Mixture 2 removed from the rolling mill was fed back into the rolling mill, and this operation was repeated 5 times to obtain 10 block-shaped electrode mixtures (positive electrode mixtures).

[0335] [Adhesiveness]

[0336] A 2mm aperture sieve and a tray below it were set up on a vibrating machine, and the electrode mixture was placed into the sieve. After operating the upper pendulum at 240 rpm for 20 minutes at 67 times / minute, the weight of the electrode mixture that fell onto the tray was measured. The adhesion to the electrode active material was calculated according to the following formula, and the ease of adhesion of the electrode mixture was used as a benchmark for evaluation.

[0337] detachment rate = (W2 / W1) × 100 (%)

[0338] W1: Total mass (g) of the electrode mixture before the experiment

[0339] W2: Mass of electrode mixture that fell off during sieving (g)

[0340] A: The dropout rate is less than 5%.

[0341] B: Disengagement rate is above 5% and less than 6%.

[0342] C: The dropout rate is above 6%.

[0343] [Manufacturing Example 1: Manufacturing of the First Polymer P1-1]

[0344] After adding 33 kg of deionized water to a 60 L stainless steel autoclave equipped with baffles and a stirrer, the autoclave was purged with nitrogen and the pressure reduced. Then, 2450 g of PMVE was added. While stirring, the temperature was raised to 90 °C, 324 g of TFE was added, and the pressure was increased to 1.7 MPa. 150 g of ultrapure water containing 8.35 g of APS (ammonium persulfate) was then forced in to begin polymerization. TFE was added concurrently with polymerization to maintain the pressure inside the autoclave at 1.62 MPa.

[0345] The polymerization reaction was terminated when the TFE addition reached 60g. After cooling the autoclave, the TFE inside was released into the atmosphere. The polymerization time was 24 minutes. Nitrogen gas was introduced until the pressure reached 0.2MPa, and the temperature was raised to 90℃. After heating the autoclave for 3 hours, it was cooled, and the reaction solution A1 was extracted.

[0346] The first polymer P1-1 in reaction solution A1 is non-water-soluble, and reaction solution A1 is an aqueous dispersion in which the particles of the first polymer P1-1 are dispersed in an aqueous medium.

[0347] The reaction solution A1 was freeze-coagulated and then filtered for separation. NMR analysis revealed the first polymer P1-1 to be obtained, with a TFE unit / PMVE unit ratio of 62 / 38 (molar ratio). It is an elastomer with a Tg of -5.5℃. The results are shown in Table 6 (the same applies below). This manufacturing process was performed twice.

[0348] Two ion exchange resin packed towers were prepared, each filled with Dowex Monosphere 650C (manufactured by DuPont, cation exchange resin, 843 mL) and Purolite A300 (manufactured by Purolite Corporation, anion exchange resin, 843 mL). Reaction solution A1 was introduced to remove impurities such as ion species or byproduct ion species originating from the initiator, resulting in an aqueous dispersion B1 of the first polymer P1-1.

[0349] Using the above method, the solid component concentration (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 below).

[0350] [Example 1: Manufacturing of the second polymer P2-1]

[0351] 1500g of paraffin wax, 47.6kg of aqueous dispersion B1, and 11.4L of deionized water were added to a 100L stainless steel autoclave equipped with baffles and a stirrer. After purging the autoclave with nitrogen and reducing the pressure, the temperature was raised to 70℃, and stirring was initiated. The pressure was increased to 1.86MPa using TFE. 1L of deionized water containing 3.36g of DSAP (disuccinic acid peroxide) was added to initiate the polymerization reaction. Simultaneously, TFE was added to maintain the autoclave pressure at 1.86MPa, synthesizing the second polymer P2-1 (PTFE). The TFE homopolymer, i.e., PTFE, exhibits non-melt-forming properties.

[0352] That is, TFE, as the second monomer, is polymerized in aqueous dispersion C1 obtained by adding deionized water to aqueous dispersion B1.

[0353] The polymerization reaction was terminated when the TFE addition 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 paraffin in the supernatant was removed to obtain an aqueous dispersion D1.

[0354] Add deionized water to the obtained aqueous dispersion D1 to dilute it to a solid component concentration of 10% by mass, adjust the temperature to 16°C, stir to cause coagulation, filter and separate to obtain a wet powder.

[0355] The resulting 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 was 1.89% by mass relative to the total mass of the first and second polymers. The results are shown in Table 8 (the same applies below).

[0356] For the dry powder, the composition was calculated using NMR, and the result showed that the content of PAVE units was 1.2 mol% relative to the total of TFE units and PAVE units (PMVE units in this example). The results are shown in Table 8 (the same applies below).

[0357] The manufacturing conditions for the process of polymerizing the second monomer (TFE) in an aqueous dispersion C1 are shown in Table 7 (the same applies below).

[0358] Specifically, the content of the aqueous medium and the content of the first polymer in the aqueous dispersion C1 before the second monomer begins polymerization are shown in Table 7 above.

[0359] The paraffin content and the amount of the second monomer (TFE) relative to 100 parts by mass of the aqueous medium in aqueous dispersion C are shown in Table 7 above.

[0360] The amount of polymerization initiator relative to 100 parts by mass of the second monomer is shown in Table 7 above.

[0361] The aqueous dispersion C1 does not contain any of the following: emulsifier, fluoride ions, sulfate ions, or ammonium ions.

[0362] Using the above method, the solid content concentration, 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 below).

[0363] As shown in Tables 6 and 8, the number of particles in aqueous dispersions B1 and D1 is approximately the same, but the average particle size of the primary particles in aqueous dispersion D1 is larger. Therefore, it can be considered that the particles of the second polymer P2-1 and the first polymer P1-1 are integrally generated, forming primary particles composed of the first polymer and the second polymer.

[0364] In addition, the particle size of the primary particles in aqueous dispersion B is the same as that of the primary particles in aqueous dispersion C.

[0365] Table 8 shows the results of the aspect ratio determination of primary particles in aqueous dispersion D1.

[0366] As shown in Table 8, in the aqueous dispersion D1, the contents of compounds (S1) and (S2) relative to the total mass of primary particles are both below the detection limit, in the range of less than 100 ppb by mass.

[0367] The standard specific gravity (SSG) of the dried powder obtained in this example was determined using the method described above. The extrusion pressure (EP) of the mixture (stretching composition) obtained by adding lubricating oil to the dried powder obtained in this example was determined using the method described above. Furthermore, tensile beads were formed from the mixture (stretching composition) using the method described above, and the tensile strength and stress relaxation time were determined. Subsequently, an electrode adhesive was prepared using the dried powder obtained in this example as an electrode binder, and its adhesion was evaluated. The results are shown in Table 8 (the same applies below).

[0368] [Manufacturing Example 2: Manufacturing of the First Polymer P1-2]

[0369] In this example, a first polymer was manufactured with a different molar ratio of TFE units to PMVE units and a different Tg than that in Manufacturing Example 1.

[0370] After adding 33 kg of deionized water to a 60L stainless steel autoclave equipped with baffles and a stirrer, the autoclave was purged with nitrogen and the pressure reduced. Then, 2441 g of PMVE was added. While stirring, the temperature was raised to 90°C, 210 g of TFE was added, and the pressure was increased to 1.40 MPa. 150 g of ultrapure water containing 8.35 g of APS was then forced in to begin polymerization. Furthermore, TFE was added during polymerization to maintain the pressure inside the autoclave at 1.40 MPa.

[0371] The polymerization reaction was terminated when the TFE addition reached 120g. After cooling the autoclave, the TFE inside was released into the atmosphere. The polymerization time was 84 minutes. Nitrogen gas was introduced until the pressure reached 0.2MPa, and the temperature was raised to 90°C. After heating the autoclave for 3 hours, it was cooled, and reaction solution A2 was extracted. The first polymer P1-2 in reaction solution A2 is non-water-soluble.

[0372] After the reaction solution A2 was freeze-coagulated, it was filtered and separated to obtain the first polymer P1-2. In the first polymer P1-2, the molar ratio of TFE units to PMVE units is 50 / 50. It is an elastomer with a Tg of -5℃. This manufacturing process was carried out twice.

[0373] Similar to manufacturing example 1, the reaction solution A2 was passed through an ion exchange resin to remove impurities, resulting in an aqueous dispersion B2 of the first polymer P1-2.

[0374] [Example 2: Manufacturing of the second polymer P2-2]

[0375] In this example, TFE, as the second monomer, is polymerized in aqueous dispersion C1 obtained by adding deionized water to aqueous dispersion B2.

[0376] 1500g of paraffin wax, 47.6kg of aqueous dispersion B2, and 9.9L of deionized water were added to a 100L stainless steel autoclave equipped with baffles and a stirrer. After purging the autoclave with nitrogen and reducing the pressure, the temperature was raised to 70°C, and stirring was initiated. The pressure was increased to 1.76MPa using TFE. 1L of deionized water containing 2.80g of DSAP was added to initiate the polymerization reaction. Furthermore, TFE was added simultaneously with the polymerization to maintain the pressure inside the autoclave at 1.76MPa, thus synthesizing the second polymer P2-2 (PTFE).

[0377] When the TFE addition reaches 7.88 kg after the start of polymerization, add 1 L of deionized water containing 1.07 g of ammonium sulfite over 6 minutes. Then, raise the temperature inside the autoclave to 90 °C at a rate of 15 °C per hour.

[0378] The polymerization reaction was terminated when the TFE addition reached 14.8 kg, and the TFE in the autoclave was released into the atmosphere. The polymerization time was 193 minutes. The resulting reaction solution was cooled, and the paraffin in the supernatant was removed to obtain an aqueous dispersion D2.

[0379] Similar to Example 1, a wet powder was obtained from the resulting aqueous dispersion D2, which was then dried to obtain a dry powder.

[0380] [Manufacturing Example 3: Manufacturing of the First Polymer P1-3]

[0381] In this example, PPVE was used as PAVE to produce a first polymer with a TFE unit / PAVE unit molar ratio and Tg different from those in Examples 1 and 2.

[0382] After adding 61 kg of deionized water to a 100 L stainless steel autoclave equipped with baffles and a stirrer, the autoclave was purged with nitrogen and the pressure was reduced. Then, 2470 g of PPVE (perfluoropropyl vinyl ether) was added. While stirring, the temperature was raised to 90 °C, resulting in a pressure of 0.48 MPa. Next, 900 g of TFE was added, and the pressure was increased to 0.82 MPa. Finally, 1500 g of ultrapure water containing 19.1 g of APS was injected to initiate polymerization.

[0383] The polymerization reaction was terminated when the pressure inside the autoclave decreased by 0.1 MPa after the addition of the APS aqueous solution, and the TFE inside the autoclave was released into the atmosphere. The polymerization time was 19 minutes. Nitrogen gas was introduced to 0.5 MPa, and the reaction was repeated 5 times. After cooling the reaction solution, reaction solution A3 was extracted. The first polymer P1-3 in reaction solution A3 is not water-soluble.

[0384] After the reaction solution A3 was freeze-coagulated, it was filtered and separated to obtain the first polymer P1-3. In the first polymer P1-3, the molar ratio of TFE units to PPVE units is 56 / 44. It is an elastomer with a Tg of -5.5℃.

[0385] Similar to manufacturing example 1, the reaction solution A3 was passed through an ion exchange resin to remove impurities, resulting in an aqueous dispersion B3 of the first polymer P1-3.

[0386] [Example 3: Manufacturing of the second polymer P2-3]

[0387] In this example, TFE, as the second monomer, is polymerized in aqueous dispersion C3 obtained by adding deionized water to aqueous dispersion B3.

[0388] 1500g of paraffin wax, 47.6kg of aqueous dispersion B3, and 11.4L of deionized water were added to a 100L stainless steel autoclave equipped with baffles and a stirrer. After purging the autoclave with nitrogen and reducing the pressure, the temperature was raised to 70°C, and stirring was initiated. The pressure was increased to 1.86MPa using TFE. 1L of deionized water containing 3.36g of DSAP was added to begin the polymerization reaction. Furthermore, TFE was added simultaneously with the polymerization to maintain the pressure inside the autoclave at 1.86MPa.

[0389] The polymerization reaction was terminated when the TFE addition 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 paraffin in the supernatant was removed to obtain an aqueous dispersion D3.

[0390] Similar to Example 1, a wet powder was obtained from the resulting aqueous dispersion D3, which was then dried to obtain a dry powder.

[0391] [Example 4: Manufacturing of PTFE]

[0392] This example is a comparative example of synthesizing PTFE using a water-soluble fluorinated emulsifier instead of a first polymer.

[0393] 760g of paraffin wax, 53L of ultrapure water, and 80g of C2F5OCF2CF2OCF2COONH4 (EEA) were added to a 100L stainless steel autoclave equipped with baffles and a stirrer. After heating to 65℃, nitrogen purging was performed to degas the autoclave. TFE was introduced while stirring until the internal pressure reached 1.38MPa. 1L of a 0.5% by mass succinic acid peroxide aqueous solution was then injected to initiate the polymerization reaction. The polymerization pressure was maintained at 1.38MPa while supplying TFE, and polymerization proceeded for 30 minutes. The temperature was then increased to 83℃ at a rate of 6℃ / hour. 1L of a 14.2% by mass EEA aqueous solution was added at the point where 6.0kg of TFE was added. The polymerization reaction was terminated when the TFE addition reached 26.9kg, and the TFE in the autoclave was released into the atmosphere. The resulting reaction solution was cooled, and the paraffin wax supernatant was removed to obtain an aqueous dispersion D4.

[0394] Similar to Example 1, a wet powder was obtained from the resulting aqueous dispersion D4, which was then dried to obtain a dry powder.

[0395] [Manufacturing Example 5: Manufacturing of the First Polymer P1-5]

[0396] 33 kg of deionized water and 1.66 g of a 50% (w / w) aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as "NaAAMPS") were added to a 60 L stainless steel autoclave equipped with baffles and a stirrer. The autoclave was then purged with nitrogen and the pressure reduced, followed by the addition of 2443 g of PMVE. While stirring, the temperature was raised to 90 °C, 243 g of TFE was added, and the pressure was increased to 1.5 MPa. 400 g of ultrapure water containing 84.3 g of APS (ammonium persulfate) was then forced in to initiate polymerization. Furthermore, TFE was added during polymerization to maintain the pressure inside the autoclave at 1.5 MPa.

[0397] The polymerization reaction was terminated when the TFE addition reached 1200g. After cooling the autoclave, the TFE inside was released into the atmosphere. Nitrogen gas was introduced until the pressure reached 0.2MPa, and the temperature was raised to 90℃. After heating the autoclave for 3 hours, it was cooled, and reaction solution A5 was extracted.

[0398] The first polymer P1-5 in reaction solution A5 is non-water-soluble, and reaction solution A5 is an aqueous dispersion in which the particles of the first polymer P1-5 are dispersed in an aqueous medium.

[0399] After the reaction solution A5 was freeze-coagulated and filtered, the first polymer P1-5 obtained was analyzed by NMR, and the result was TFE unit / PMVE unit ratio of 63 / 37 (molar ratio). The Tg was -6℃. It has no melting point.

[0400] In addition to diluting the reaction solution A5 by 5 times, similar to Manufacturing Example 1, the reaction solution A5 was passed through an ion exchange resin to remove impurities, resulting in an aqueous dispersion B5 of the first polymer P1-5.

[0401] [Example 5: Manufacturing of the second polymer P2-5]

[0402] 1500g of paraffin wax, 33.7kg of an aqueous dispersion B5 containing 1.1% by mass of the first polymer P1-5, and 24.9L of deionized water were added to a 100L stainless steel autoclave equipped with baffles and a stirrer. After purging the autoclave with nitrogen and reducing the pressure, the temperature was raised to 65°C, and stirring was initiated. The pressure was increased to 1.76MPa using TFE. 1L of deionized water containing 2.8g of DSAP (disuccinic acid peroxide) was added to initiate the polymerization reaction. Simultaneously, TFE was added to maintain the autoclave pressure at 1.76MPa, synthesizing the second polymer P2-5 (PTFE). The TFE homopolymer, i.e., PTFE, exhibits non-melt-forming properties.

[0403] The polymerization reaction was terminated when the TFE addition reached 15.8 kg after the start of polymerization, and the TFE in the autoclave was released into the atmosphere. The resulting reaction solution was cooled, and the paraffin in the supernatant was removed to obtain an aqueous dispersion D5.

[0404] Similar to Example 1, a wet powder was obtained from the resulting aqueous dispersion D5, which was then dried to obtain a dry powder.

[0405] [Table 6]

[0406] [Table 7]

[0407] [Table 8]

[0408] As shown in Tables 6-8, the electrode binder containing the solid compositions obtained in Examples 1-3 and 5 exhibits excellent adhesion to the electrode active material.

[0409] The electrode adhesive in Example 4, which contains a solid composition in which a second monomer is polymerized without using a first polymer, has poor adhesion to the electrode active material.

Claims

1. An electrode adhesive comprising a solid composition, said solid composition comprising primary particles containing a first polymer and a second polymer. The second polymer is a non-melt-forming fluoropolymer comprising tetrafluoroethylene-based units, and the first polymer is a different polymer from the second polymer. The content of the first polymer is 0.01 to 4.0% of the total mass of the first polymer and the second polymer.

2. The electrode adhesive as claimed in claim 1, wherein, The first polymer comprises tetrafluoroethylene-based units and perfluoro(alkyl vinyl ether)-based units.

3. The electrode adhesive as described in claim 2, wherein, The content of the perfluorinated (alkyl vinyl ether)-based unit in the first polymer is 0.1 to 3.0 mol relative to the total of all units in the first polymer and all units in the second polymer.

4. The electrode adhesive as claimed in claim 1, wherein, The first polymer is non-water-soluble.

5. The electrode adhesive as claimed in claim 1, wherein, The contents of the compound represented by formula (S1) and the contents of the compound represented by formula (S2) are each less than 100 ppb by mass relative to the total mass of the first polymer and the second polymer. Formula (S1): H-(CF2) n1 -COOM Formula (S2): H-(CF2) n2 -SO3M In formulas (S1) and (S2), M independently represents a hydrogen atom, Na, K or NH4, n1 represents an integer from 3 to 13, 15 or 17, and n2 represents an integer from 4 to 10 or 12.

6. The electrode adhesive as claimed in claim 1, wherein, The aspect ratio of the primary particle is less than 1.

5.

7. An electrode binder comprising any one of claims 1 to 6 and an electrode active substance.

8. An electrode comprising the electrode mixture and current collector as described in claim 7.

9. A secondary battery comprising the electrode as claimed in claim 8.

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