Polytetrafluoroethylene-based resin, electrode mixture, electrode, and secondary battery

Abstract

To provide a polytetrafluoroethylene-based resin excellent in uniformity of thickness of a sheet obtained by using an electrode mixture prepared by mixing with an active material or the like.SOLUTION: A polytetrafluoroethylene polymer used as a binder for secondary batteries, wherein the angle of repose is 32-44 °, and the pore volume is 0. 2-9. 0cm3 / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polytetrafluoroethylene resin, an electrode mixture, an electrode, and a secondary battery. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries are used in small, portable electrical and electronic devices such as notebook computers, mobile phones, smartphones, tablet computers, and ultrabooks because of their high voltage, high energy density, low self-discharge and memory effect, and the possibility of ultra-lightweight design. They are also used as on-board power sources for driving automobiles and large stationary power sources.

[0003] Electrodes for nonaqueous electrolyte secondary batteries such as lithium-ion batteries are generally produced by applying an electrode mixture containing an active material, a binder, and the like to a current collector. However, in recent years, with the aim of reducing the environmental impact during production and improving oxidation resistance, dry methods have been investigated in which the electrode mixture is stretched and formed into a sheet, which is then attached to a current collector to produce an electrode. The dry method does not require the use of organic solvents such as N-methyl-2-pyrrolidone.

[0004] Patent Document 1 discloses a polytetrafluoroethylene resin used as a binder for electrodes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-051888 Summary of the Invention [Problem to be solved by the invention]

[0006] When the characteristics of a sheet obtained using an electrode mixture containing a polytetrafluoroethylene resin and an active material described in Patent Document 1 were evaluated, it was found that there was room for improvement in the uniformity of the sheet thickness. If the sheet thickness is not uniform, when the secondary battery is repeatedly charged and discharged, the electric field may concentrate in the thinner parts, making it more likely to short-circuit.

[0007] An object of the present invention is to provide a polytetrafluoroethylene resin that can be mixed with an active material or the like to prepare an electrode mixture, and that has excellent thickness uniformity when used to obtain a sheet. Another object of the present invention is to provide an electrode mixture, an electrode, and a secondary battery. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that the above problems can be solved by the following configuration. [1] A polytetrafluoroethylene-based resin used as a binder for a secondary battery, The angle of repose is 32 to 44°. Pore ​​volume is 0.2 to 9.0 cm 3 / g of polytetrafluoroethylene-based resin. [2] The polytetrafluoroethylene resin according to [1], having a pore median diameter of 10 μm or more. [3] The polytetrafluoroethylene resin according to [1] or [3], which has a withstand voltage of 5 kV or more. [4] An electrode mixture comprising the polytetrafluoroethylene resin according to [1] or [2] and an active material. [5] Further, the battery contains a sulfide-based solid electrolyte, The electrode mixture according to [4], wherein the content of the polytetrafluoroethylene resin is 1 to 10 parts by mass per 100 parts by mass of the sulfide-based solid electrolyte. [6] The electrode mixture according to [4] or [5], which is in a sheet form. [7] Further containing a conductive additive, the content of the polytetrafluoroethylene resin is 0.5 to 10% by mass relative to the total mass of the electrode mixture; The content of the active material is 88 to 99% by mass relative to the total mass of the electrode mixture, The electrode mixture according to any one of [4] to [6], wherein the content of the conductive assistant is 0.5 to 10 mass % relative to the total mass of the electrode mixture. [8] An electrode comprising: a current collector; and an electrode layer disposed on the current collector and containing the electrode mixture according to any one of [4] to [7]. [9] A secondary battery comprising the electrode according to [8]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a polytetrafluoroethylene resin which can be mixed with an active material or the like to prepare an electrode mixture, and which has excellent thickness uniformity when used to obtain a sheet using the electrode mixture. Furthermore, the present invention can provide an electrode mixture, an electrode, and a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0010] The terms used in the present invention have the following meanings. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples. In this specification, each component may be a single substance corresponding to the component, or two or more substances may be used in combination. When two or more substances are used in combination for each component, the content of the component refers to the total content of the substances used in combination, unless otherwise specified. As used herein, a combination of two or more preferred embodiments is a more preferred embodiment. The term "unit" refers collectively to an atomic group derived from one molecule of the monomer that is formed directly by polymerizing the monomer, and an atomic group obtained by chemically converting a part of the atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to the total units contained in a polymer (polytetrafluoroethylene-based resin) is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer added is approximately the same as the actual content of each unit.

[0011] [Polytetrafluoroethylene resin] The polytetrafluoroethylene-based resin of the present invention (hereinafter also simply referred to as "PTFE-based resin") is a PTFE-based resin used as a binder for secondary batteries, and has an angle of repose of 32 to 44° and a pore volume of 0.2 to 9.0 cm3. 3 / g.

[0012] The present inventors have found that sheets obtained using conventional electrode mixtures have poor fluidity and therefore poor thickness uniformity. On the other hand, the present inventors have surprisingly found that by keeping the angle of repose and pore volume of the PTFE-based resin within a certain range, dispersibility when mixed with the active material is improved, resulting in the production of a sheet with excellent fluidity and a uniform thickness. A uniform sheet thickness is expected to prevent the electric field from concentrating in thin portions, which can easily cause short circuits, during repeated charge and discharge cycles as a secondary battery.

[0013] The form of the PTFE-based resin is not particularly limited, but examples thereof include granular and particulate forms, with particulate forms being preferred.Furthermore, the PTFE-based resin may be in the form of a powder, which is an aggregate of granular and particulate forms. When the PTFE-based resin is in a particulate form, the PTFE-based resin may be either primary particles or secondary particles.

[0014] The angle of repose of the PTFE-based resin is 32 to 44°, preferably 33 to 40°. If the angle of repose is within the above range, the average particle size of the PTFE-based resin can be reduced while suppressing the progression of fibrous formation of the PTFE-based resin during mixing with the active material, etc. The angle of repose of a PTFE-based resin can be measured, for example, by a known measurement method. For example, the PTFE-based resin powder to be measured is dropped from a funnel of a certain height onto a horizontal measurement table, and the base angle is calculated from the diameter and height of the resulting conical deposit. For example, the angle of repose can be measured based on JIS-R931-2-2:1999 (corresponding international standard: ISO 920:1976). An example of a method for adjusting the angle of repose of a PTFE-based resin is rotary kiln treatment in the manufacturing method of a PTFE-based resin described below. Specifically, the angle of repose of the PTFE-based resin tends to decrease when the treatment time of the rotary kiln treatment is extended. Other methods include cooling the resin using a device capable of cooling while rotating, such as a tumbling granulator or a fluidized mixer. Rotary kiln treatment is particularly preferred because it is less likely to apply excessive shear and makes it easy to adjust the angle of repose.

[0015] The pore volume of PTFE resin is 0.2 to 9.0 cm 3 / g, 0.4 to 8.0 cm 3 / g is preferred, and 0.4 to 7.0 cm 3 When the pore volume is within the above range, the penetration of the active material and the conductive additive into the pores of the PTFE-based resin is promoted, and the disintegration of the PTFE-based resin is accelerated, thereby improving the mixability of the active material and the conductive additive. The pore volume of the PTFE-based resin can be measured by, for example, mercury intrusion porosimetry using a known analytical device (for example, AutoPoreIV 9520 manufactured by Micromeritics). An example of a method for adjusting the pore volume of a PTFE-based resin is a method of performing plasma treatment in the manufacturing method of a PTFE-based resin described below. Specifically, the pore volume of the PTFE-based resin tends to decrease when the treatment time of the plasma treatment is extended. Another method is microwave irradiation. Plasma treatment is particularly preferred because it is less likely to be subjected to excessive heat and the pore volume can be easily adjusted.

[0016] The average pore size of the PTFE resin is preferably 0.05 to 2.0 μm, more preferably 0.1 to 1.5 μm. The average pore size of the PTFE-based resin can be measured, for example, by mercury intrusion porosimetry using a known analytical device. Specifically, the pore volume is expressed as V (cm 3 / g), and the specific surface area is A (m 2 When the average pore diameter (μm) is calculated as 4V / A, the average pore diameter (μm) is calculated as 4V / A. The specific surface area is the BET specific surface area. The BET specific surface area is defined as the value measured by the nitrogen adsorption BET single-point method using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.) after pre-drying the sample at 150°C for 30 minutes under a nitrogen flow, using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0017] The median pore diameter of the PTFE resin is preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more, in terms of excellent wall surface adhesion. The upper limit is preferably 100 μm or less, more preferably 90 μm or less. The median pore diameter of a PTFE-based resin is the pore diameter at which the cumulative value is 50% by volume of the pore volume in a pore distribution profile obtained by mercury intrusion porosimetry using a known analyzer. An example of a method for adjusting the median pore diameter of a PTFE-based resin is adjusting the plasma treatment temperature in the method for producing a PTFE-based resin described below. Specifically, increasing the plasma treatment temperature changes the behavior of the median pore diameter, causing micro-melting of the PTFE-based resin and promoting the transformation of large pores in the PTFE-based resin into smaller pores, which tends to reduce the median pore diameter of the PTFE-based resin.

[0018] The electrostatic potential of the PTFE resin is preferably -2000 to -14000 V, more preferably -5000 to -12000 V, and even more preferably -200 to -3000 V in terms of superior wall surface adhesion. If the electrostatic potential is within the above range, the PTFE resin particles repel each other due to electrostatic repulsion during the mixing process with the active material, etc., and dispersibility can be improved. In addition, wall surface adhesion can also be excellent. The electrostatic potential can be measured using a digital electrostatic potential meter, Model KSD-1000 (manufactured by Kasuga Electric Co., Ltd.). Charging voltage can be adjusted using various ionizers and mechanical friction. When charging by mechanical friction, due to the triboelectric series, charging can be done efficiently by vibrating the resin while it is in contact with a nylon material. In particular, charging voltage can be easily adjusted by placing dried PTFE resin in a pot mill and rotating it at a speed of 10 to 50% of the critical rotation speed. The critical rotation speed is the rotation speed at which the contents rotate along with the container due to centrifugal force, and is expressed by the following formula: N (critical rotation speed, unit: rpm) = 42.4 / √D (inner diameter of container, unit: m)

[0019] In order to improve the binding strength and the flexibility of the electrode, the average primary particle diameter of the PTFE powder is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less. The lower limit is preferably 100 nm or more, more preferably 150 nm or more, and even more preferably 180 nm or more. The average primary particle diameter of the PTFE powder is preferably 100 to 500 nm, more preferably 180 to 450 nm, and even more preferably 200 to 400 nm. The average primary particle size is a volume-based median size obtained by a laser scattering particle size distribution analyzer.

[0020] The average secondary particle diameter of the PTFE powder is preferably 280 μm or more, more preferably 300 μm or more, and even more preferably 320 μm or more. The upper limit is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 700 μm or less. The average secondary particle diameter of the PTFE powder is preferably 280 to 1000 μm, more preferably 300 to 800 μm, and even more preferably 320 to 700 μm. The average secondary particle size of the PTFE powder can be measured, for example, in accordance with JIS K 6891:1995.

[0021] The standard specific gravity (SSG) of the PTFE-based resin is preferably 2.120 to 2.190, more preferably 2.125 to 2.190, and further preferably 2.130 to 2.180. SSG is used as a relative measure of molecular weight, and the lower the value, the higher the molecular weight. Also, if a large amount of monomers other than tetrafluoroethylene is introduced into a PTFE-based resin, the amorphous structure increases further, the density decreases, and the SSG value tends to decrease. SSG is measured in accordance with ASTM D4895-10. Specifically, a 12.0 g sample is weighed and molded into a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes. This is placed in a 290°C oven, heated at 120°C / hr, held at 380°C for 30 minutes, then cooled at 60°C / hr and held at 294°C for 24 minutes. After holding the sample in a desiccator at 23°C for 12 hours, the specific gravity of the molded product relative to water is measured at 23°C, and this is the SSG.

[0022] The extrusion pressure of the PTFE resin in the extrusion test is preferably 5 to 60 MPa, more preferably 10 to 40 MPa, and even more preferably 15 to 25 MPa. The extrusion pressure is measured as follows. 100 g of PTFE-based resin that had been left at room temperature for at least two hours was placed in a 500 mL glass bottle, 21.7 g of lubricating oil (Isopar H (registered trademark), manufactured by Exxon Chemical) was added, and the mixture was mixed for three minutes to obtain a mixture. The resulting mixture was then left in a 25°C thermostatic chamber for two hours, and then extruded through an orifice with a diameter of 2.5 cm, a land length of 1.1 cm, and an entrance angle of 30° at 25°C under the conditions of a reduction ratio (ratio of the cross-sectional area of ​​the die entrance to the cross-sectional area of ​​the exit) of 100 and an extrusion speed of 51 cm / min to obtain an extrusion bead (string-like material). The pressure required for extrusion at this time was measured and recorded as the extrusion pressure (unit: MPa).

[0023] The withstand voltage of a PTFE-based resin molded article is preferably 4 kV or more, more preferably 5 kV or more, and even more preferably 6 kV or more. When the withstand voltage is equal to or greater than the above-mentioned lower limit, the electrochemical resistance of the PTFE-based resin is enhanced, improving durability when the PTFE powder is used as a negative electrode binder. The upper limit of the withstand voltage is not particularly limited, but may be 30 kV or less, or 20 kV or less. The withstand voltage is preferably 4 to 30 kV, more preferably 5 to 20 kV, and even more preferably 6 to 20 kV. The withstand voltage is measured in accordance with JIS K6892:1995 using the following method. Details of the measurement method are described in the examples. The withstand voltage varies depending on the impurities contained, as well as the crystallinity, the presence or absence of monomer units other than tetrafluoroethylene, and the molecular weight distribution of the PTFE-based resin. Furthermore, by not using nitric acid during aggregation of the PTFE aqueous dispersion, impurities are reduced and the withstand voltage tends to increase.

[0024] The water content of the PTFE resin is preferably 0.040% by mass or less, more preferably 0.020% by mass or less, even more preferably 0.010% by mass or less, particularly preferably 0.005% by mass or less, and most preferably 0.002% by mass or less, relative to the total mass of the PTFE resin. The moisture content is measured by the following method: the mass of the PTFE resin is measured before and after heating at 150°C for 2 hours, and the moisture content is calculated according to the following formula: Three samples are taken, and the moisture content is calculated for each sample, and the average value is calculated and used. Moisture content (mass %) = 100 × [(mass of PTFE resin before heating (g)) - (mass of PTFE resin after heating (g))] / (mass of PTFE resin before heating (g))

[0025] The bulk density of the PTFE resin is preferably 350 to 600 g / L, more preferably 400 to 550 g / L. The bulk density is measured in accordance with JIS K6892:1995.

[0026] The PTFE resin is used as a binder for secondary batteries. The PTFE resin is preferably used, for example, in a composition for forming a member or layer constituting a secondary battery. More preferably, it is used in an electrode mixture obtained by mixing the PTFE resin with an active material or the like. Note that the binder has the same meaning as a general binder, and examples include so-called binders, dispersants, and adhesives. Examples of the member or layer constituting the secondary battery include, for example, the electrode layer in the electrode described later. Further, the secondary battery is not particularly limited as long as it is a known secondary battery. Preferred embodiments of the secondary battery are as described later.

[0027] The PTFE resin can also be suitably used for other applications. Examples of other applications include, for example, ceramic capacitors such as low-temperature sintering type barium titanate. In the capacitor, barium titanate and a PTFE resin are mixed and formed into a sheet, and then a small amount of water is added, and a temperature of 100 to 200°C and a pressure of several hundred MPa are applied to densify it. By using the PTFE resin of the present invention, the strength after densification can be increased.

[0028] <PTFE resin> The PTFE resin means a resin containing units based on tetrafluoroethylene (hereinafter, "TFE units"). <Q

[0029] (TFE units)<Q The PTFE resin is a resin containing TFE units, and the content of TFE units relative to the total units of the resin is preferably 99% by mass or more, more preferably 99.5% by mass or more, and even more preferably 99.9% by mass or more. The upper limit can be 100% by mass. The content of TFE units is preferably 99 mol % or more, more preferably 99.5 mol % or more, and even more preferably 99.9 mol % or more, relative to all units in the PTFE resin. The upper limit can be 100 mol %.

[0030] (units based on other monomers) The PTFE-based resin may contain units based on other monomers than the TFE units. Other monomers include, for example, perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VdF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers such as perfluoro(alkyl vinyl ether) (PAVE); perfluoroallyl ethers; (fluoroalkyl)ethylenes (FAE); and ethylene. Among these, the other monomer is preferably HFP, VdF, FAE or PAVE. The other monomer may be a monomer used in the method for producing PTFE powder described below.

[0031] As the PAVE, a monomer represented by formula (PA) is preferred. CF2=CF-O-Rf 1 (PA) In formula (PA), Rf 1 represents a perfluoroalkyl group having 1 to 10 carbon atoms. 1 The number of carbon atoms in the perfluoroalkyl group represented by the following formula is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3, in terms of better polymerization reactivity. The perfluoroalkyl group may be linear or branched.

[0032] Specific examples of PAVE include CF2=CFOCF3 (PMVE), CF2=CFOCF2CF3 (PEVE), CF2=CFOCF2CF2CF3 (PPVE), CF2=CFOCF2CF2CF2CF3, and CF2=CFO(CF2)8F, with PMVE or PPVE being preferred.

[0033] The FAE is preferably a monomer represented by formula (FA). CZ2=CX(CF2) m Y (FA) In formula (FA), X, Y and Z each independently represent a hydrogen atom or a fluorine atom, and m represents an integer of 2 to 6. Specific examples of FAE include CH2=CH(CF2)2F, CH2=CH(CF2)3F, CH2=CH(CF2)4F(PFBE), CH2=CF(CF2)3H, and CH2=CF(CF2)4H, with PFBE or CH2=CH(CF2)2F being preferred, and PFBE being more preferred.

[0034] The content of units based on other monomers (preferably units based on PFBE) is preferably 1 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.1 mol% or less, based on the total units of the PTFE-based resin. The lower limit is preferably 0 mol% or more. The content of units based on other monomers is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, based on the total units of the PTFE-based resin.

[0035] The content of TFE units and PFBE-based units is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more, relative to the total mass of the PTFE-based resin. The upper limit can be 100% by mass.

[0036] The content of each unit in PTFE-based resin is as follows: 19 It can be measured by known methods such as F-NMR (nuclear magnetic resonance analysis).

[0037] The PTFE-based resin may have a core-shell structure. Examples of PTFE-based resins having a core-shell structure include PTFE-based resins containing a core of high-molecular-weight PTFE-based resin in the particles and a shell of lower-molecular-weight PTFE-based resin or PTFE-based resin containing other units.

[0038] [Method for producing PTFE-based resin] The method for producing the PTFE-based resin is not particularly limited as long as it is a method that can produce the above-mentioned PTFE-based resin. A preferred method for producing a PTFE-based resin includes, for example, a step A of obtaining an aqueous dispersion containing a PTFE-based resin, and a step B of obtaining a PTFE-based resin from the aqueous dispersion.

[0039] <Process A> Step A is a step of preparing an aqueous dispersion containing a PTFE-based resin.

[0040] The step of preparing the aqueous dispersion includes a step of polymerizing a monomer that will become a unit constituting the PTFE-based resin in an aqueous medium. The monomer can be appropriately selected according to the desired PTFE-based resin. The polymerization method can be, for example, a known polymerization method.

[0041] Step A is preferably a step of polymerizing a first monomer containing TFE in the presence of an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin.

[0042] (aqueous medium) Specific examples of the aqueous medium include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol. In the case of a mixture of water and a water-soluble organic solvent, the concentration of the water-soluble organic solvent is preferably 10% by mass or less. The aqueous medium is preferably water alone.

[0043] (First monomer) The first monomer comprises TFE. The first monomer may include the above-mentioned other monomers other than TFE. The content of TFE is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more, based on the total number of moles of the first monomer. The upper limit is preferably 100 mol% or less.

[0044] Methods for polymerizing the first monomer include, for example, emulsion polymerization, solution polymerization, and suspension polymerization. The polymerization can be carried out by heating the monomers in the presence of an aqueous medium and a polymerization initiator. The aqueous medium may or may not contain an emulsifier.

[0045] (Polymerization initiator) Examples of the polymerization initiator include an oil-soluble radical polymerization initiator and a water-soluble radical polymerization initiator.

[0046] Examples of the oil-soluble radical polymerization initiator include dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate; peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate; dialkyl peroxides such as di-t-butyl peroxide; di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, and di(ω-chloro-hexafluoro). di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chlorohexanoyl)peroxide, di(ω-chlorotetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0047] The water-soluble radical polymerization initiator is preferably a water-soluble radical initiator or a water-soluble oxidation-reduction catalyst. The water-soluble radical initiator is preferably a persulfate such as ammonium persulfate or potassium persulfate, or a water-soluble organic peroxide such as disuccinic acid peroxide, bisglutaric acid peroxide, or tert-butyl hydroperoxide. As the water-soluble oxidation-reduction catalyst, a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, or an organic acid, is preferred. Among these, a combination of bromic acid or a salt thereof and sulfurous acid or a salt thereof (e.g., ammonium sulfite), and a combination of permanganic acid or a salt thereof (e.g., potassium permanganate) and oxalic acid are more preferred. The polymerization initiator is preferably ammonium persulfate alone or a mixture of a persulfate and disuccinic acid peroxide, more preferably ammonium persulfate alone or a mixture of ammonium persulfate and disuccinic acid peroxide. The polymerization initiator may be used alone or in combination of two or more. The polymerization initiator may be charged in its entirety into the polymerization system before the start of the polymerization reaction, or may be added to the polymerization system continuously or intermittently.

[0048] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, relative to 100 parts by mass of the amount of the first monomer used.

[0049] (Other ingredients) In the polymerization of the first monomer, other components such as a nucleating agent, a chain transfer agent, a buffer, a pH adjuster, a stabilizing aid, a dispersion stabilizer, a radical scavenger, a decomposing agent for the polymerization initiator, and a dicarboxylic acid may be used.

[0050] Examples of the nucleating agent include fluoropolyethers such as perfluoropolyether acids, nonionic surfactants, and chain transfer agents. Examples of the perfluoropolyether acids include the perfluoropolyether acids described in J. Appl. Polymer Sci. 57, 797 (1995).

[0051] Examples of radical scavengers include aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride. Examples of aromatic hydroxy compounds include unsubstituted phenol, polyhydric phenols, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol. Examples of unsubstituted phenols include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, and p-nitrosophenol. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, and naphthresorcinol. Examples of aromatic amines include o-, m-, or p-phenylenediamine and benzidine. Examples of quinone compounds include o-, m-, or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Thiocyanates include ammonium thiocyanate (NH4SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).

[0052] The decomposer for the polymerization initiator may be any compound capable of decomposing the polymerization initiator used, and examples thereof include sulfites, bisulfites, bromates, diimines, diimine salts, oxalic acid, oxalates, copper salts, and iron salts.

[0053] As the dicarboxylic acid, for example, a compound represented by the general formula: HOOC-R-COOH (wherein R represents an alkylene group having 1 to 5 carbon atoms) is preferred, succinic acid, malonic acid, glutaric acid, adipic acid or pimelic acid is more preferred, and succinic acid is even more preferred.

[0054] In the polymerization of the first monomer, a stabilizing aid may be used. The stabilizing aid is preferably paraffin wax, a fluorine-based solvent, or silicone oil, and more preferably paraffin wax. Paraffin wax may be liquid, semi-solid, or solid at room temperature. Among them, saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C. The stabilizing aids may be used alone or in combination of two or more.

[0055] The polymerization temperature and polymerization pressure in the polymerization of the first monomer can be appropriately determined depending on the type of monomer used, the molecular weight of the desired PTFE-based resin, and the reaction rate. The polymerization temperature is preferably 5° C. or higher, more preferably 10° C. or higher, even more preferably 30° C. or higher, and particularly preferably 50° C. or higher. The upper limit is preferably 150° C. or lower, more preferably 120° C. or lower, and even more preferably 100° C. or lower. The polymerization temperature is preferably 5 to 150° C., more preferably 10 to 120° C., and even more preferably 50 to 100° C. The polymerization pressure is preferably 0.05 MPaG or more, more preferably 0.3 MPaG or more, and even more preferably 0.5 MPaG or more. The upper limit is preferably 5.0 MPaG or less, and more preferably 3.0 MPaG or less. The polymerization pressure is preferably 0.05 to 5.0 MPaG, more preferably 0.3 to 5.0 MPaG, and even more preferably 0.5 to 3.0 MPaG.

[0056] The content of the PTFE resin is preferably 5 to 50 mass %, more preferably 10 to 45 mass %, and even more preferably 10 to 30 mass %, based on the total mass of the aqueous dispersion. The solid content concentration of the aqueous dispersion is preferably from 5 to 50 mass %, more preferably from 10 to 45 mass %, and even more preferably from 10 to 30 mass %. The solids concentration of the aqueous dispersion can be measured, for example, by the following method. The solids concentration of the aqueous dispersion is calculated by heating 2.0 g of the aqueous dispersion at 170° C. for 20 minutes, weighing the mass of the residue, and calculating the solids concentration using the following formula. "Solid content concentration (mass%) = 100 × heating residue of aqueous dispersion (g) / mass of aqueous dispersion (2.0 g)"

[0057] <Process B> Step B is a step of obtaining a PTFE-based resin from the aqueous dispersion obtained in Step A. Examples of methods for obtaining a PTFE-based resin from an aqueous dispersion include known methods. Preferably, the PTFE-based resin is obtained by subjecting the aqueous dispersion to an aggregation treatment and a drying treatment, and more preferably, the PTFE-based resin is obtained by subjecting the aqueous dispersion to an aggregation treatment to obtain a wet PTFE powder and then drying the wet PTFE powder.

[0058] Examples of the flocculation treatment include freeze flocculation, acid flocculation, base flocculation, mechanical flocculation, and flocculation using a coagulant. In the case of freeze aggregation, the aggregation temperature is preferably −20 to 0° C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid coagulation, a method in which an acid-containing solution is added to an aqueous dispersion is preferred. Examples of the acid to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with hydrochloric acid or nitric 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. A preferred method for base coagulation is to add a solution containing a base to the aqueous dispersion. Examples of the base to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the base in the solution containing the base is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, 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, where M is potassium, is more preferred. The aggregation method is preferably acid aggregation or freeze aggregation.

[0059] As the drying treatment, a treatment of drying the PTFE wet powder obtained by the agglomeration treatment is preferred. The drying temperature is preferably 100° C. or higher, more preferably 150° C. or higher, and even more preferably 170° C. or higher. The upper limit is preferably 280° C. or lower, and more preferably 250° C. or lower. The drying temperature is preferably 100 to 280° C., more preferably 150 to 280° C., and even more preferably 170 to 250° C. The drying time is preferably 1 hour or more, and more preferably 3 hours or more. The upper limit is preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 30 hours or less. The drying time is preferably 1 to 100 hours, more preferably 1 to 50 hours, and even more preferably 3 to 30 hours. The water content of the PTFE wet powder to be dried is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the PTFE wet powder. The upper limit is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. The water content of the PTFE wet powder to be dried is preferably 10 to 150 parts by mass, more preferably 20 to 150 parts by mass, and even more preferably 30 to 100 parts by mass, per 100 parts by mass of the PTFE wet powder.

[0060] The drying treatment can be carried out using an electric furnace or a steam furnace. For example, it can be carried out using an electric furnace such as a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a radiant conveyor-type electric furnace, a fluidized-bed electric furnace, a vacuum electric furnace, an agitator-type electric furnace, an airflow-type electric furnace, or a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by substituting "steam furnace" for "electric furnace" in the apparatus name of each electric furnace above). In terms of being able to more efficiently remove moisture, unreacted monomers, etc., a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a fluidized-bed electric furnace, a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by substituting "steam furnace" for "electric furnace" in the apparatus name of each electric furnace above) is preferred.

[0061] <Other processes> The method for producing the PTFE-based resin may further include other steps. Other processes include, for example, rotary kiln treatment and plasma treatment. The other steps are preferably carried out after step B.

[0062] (Rotary kiln processing) Rotary kiln treatment is a method for treating PTFE-based resins using a rotary kiln. The angle of repose can be adjusted by performing the rotary kiln treatment. While the rotary kiln treatment will be described below, as mentioned above, the angle of repose can also be adjusted by treating the resin using a device that can cool the resin while rotating. Examples of such devices include a tumbling granulator and a fluidized bed mixer. The method of rotary kiln treatment is not particularly limited, but the PTFE-based resin is treated by passing it through a cylindrical rotary kiln while rolling in the rotary kiln, which rotates around the central axis of the rotary kiln. Generally, a rotary kiln is a device for treating by heating and fluidizing, but in the present invention, it is preferable to roll the PTFE-based resin while contacting it with the inner surface of the rotary kiln while cooling. The cooling temperature is preferably equal to or lower than the glass transition temperature of the PTFE resin, more preferably higher than the glass transition temperature of the PTFE resin −200°C, and equal to or lower than the glass transition temperature of the PTFE resin −5°C, still more preferably higher than −200°C and equal to or lower than 10°C, and particularly preferably −50 to 0°C. By treating the PTFE-based resin at the above temperature, the PTFE-based resin can be prevented from becoming fibrous, while the density can be increased and the angle of repose of the PTFE-based resin can be reduced, which tends to improve the fluidity and crushability during mixing. The tilt angle of the rotary kiln relative to the horizontal direction (the rotary kiln's ground surface) is preferably 0.01 to 5°, more preferably 0.1 to 3°. By tilting the rotary kiln at an angle within the above range, the passage time of the PTFE-based resin through the rotary kiln (the residence time of the PTFE-based resin in the rotary kiln) can be ensured to be sufficiently long. As a result, the PTFE-based resin can be treated more uniformly and thoroughly. The treatment time for the PTFE resin (treatment time in the rotary furnace) is preferably 1 to 50 minutes, more preferably 5 to 40 minutes, and even more preferably 20 to 40 minutes, since this makes it easier to adjust the angle of repose within an appropriate range. In this case, sufficient time can be ensured for cooling and rolling the PTFE resin. The rotation speed of the rotary furnace is preferably 1 to 20 rpm, more preferably 3 to 10 rpm. In this case, excessive impact force is unlikely to be applied to the PTFE-based resin, and therefore, undesired crushing and fiber formation of the PTFE-based resin during rolling (flowing) can be prevented. The rate at which the PTFE resin is introduced into the rotary furnace is preferably such that the filling rate of the PTFE resin in the rotary furnace is 0.1 to 40%, more preferably 1 to 20%, which allows the PTFE resin to be treated sufficiently and efficiently. Examples of the rotary kiln include devices manufactured by Noritake Company Limited and Sanai Chemical Industry Co., Ltd. Instead of a heater covering the rotary furnace of these devices, cooling can be achieved by spirally wrapping piping through which a cooling medium flows. In order to prevent condensation, it is preferable that the dew point of the installation environment of this apparatus be set to a temperature lower than the processing temperature.

[0063] (Plasma treatment) In the plasma treatment, a plasma device is used to treat the PTFE-based resin. By carrying out plasma treatment, the pore volume of the PTFE-based resin can be adjusted, and by applying plasma treatment appropriately, the fine shape of the surface can be easily changed. As mentioned above, the pore volume of the PTFE-based resin can also be adjusted by microwave irradiation instead of plasma treatment. The apparatus and conditions used for plasma irradiation may be those commonly used in various industrial plasma treatments. In many cases, industrial equipment mechanisms for generating plasma ionize gas by applying an electric field between electrodes in a reduced-pressure environment of 0.1 to 150 Pa. While various methods for applying an electric field in such a reduced-pressure environment are possible, DC discharge, in which a voltage is applied between two positive and negative electrodes placed in a rarefied gas atmosphere, is often used. There are no particular limitations on the apparatus as long as it is capable of exposing a PTFE-based resin to plasma generated by ionizing atmospheric gas through a discharge phenomenon, but glow discharge is preferred because it is easy to adjust the micropores on the surface of PTFE-based resin particles.

[0064] From the viewpoint of more even contact between the introduced PTFE-based resin and the plasma generated by glow discharge, a rotary tabletop vacuum plasma device equipped with a rotary drum-type treatment vessel whose rotating shaft serves as a glow discharge electrode may be used. By rotating the treatment vessel and generating plasma in its internal space, it is possible to more evenly irradiate the plasma onto the particle surfaces of the PTFE-based resin while stirring the introduced PTFE-based resin. The rotation speed may be 10 to 100 rpm. The rotation axis of the treatment tank may be horizontal or inclined. The plasma irradiation method is not particularly limited, but the effect can also be obtained by placing a thin layer of PTFE-based resin on a flat surface or stirring the placed PTFE-based resin at regular intervals. By treating in a cooled state, the pores in the PTFE-based resin (secondary particles) are micro-dissolved or micro-decomposed, allowing the pore volume to be adjusted and easily adjusted to a suitable range.

[0065] As a cooling method, in the case of a drum-type treatment tank, the inside of the chamber can be cooled by placing a cooling tube along the outer wall of the drum and running a chiller. The cooling temperature is preferably equal to or lower than the glass transition temperature of the PTFE-based resin, more preferably higher than the glass transition temperature of the PTFE-based resin −200°C, or equal to or lower than the glass transition temperature of the PTFE-based resin −5°C, even more preferably higher than −200°C and equal to or lower than 10°C, and particularly preferably −50 to 0°C, since this makes it easy to adjust the median pore diameter to an appropriate range. Rotary plasma irradiation can be carried out, for example, by introducing 250 to 300 g of PTFE-based resin into a treatment tank, evacuating the tank to 5 Pa or less using a vacuum pump, and then introducing atmospheric gas at a predetermined flow rate while maintaining the vacuum state using the pump, adjusting the pressure inside the treatment tank to be kept within the range of 70±10 Pa, and applying a voltage between the electrodes in the range of 100 to 800 V.

[0066] <First aspect> The method for producing a PTFE-based resin may be the first embodiment. The first embodiment of the method for producing a PTFE-based resin is a method for producing a PTFE-based resin, which comprises steps C, D, and E. Step C: A step of polymerizing a non-fluorine-based monomer in an aqueous medium to obtain a solution 1 containing a polymer containing units based on the non-fluorine-based monomer (hereinafter also referred to as "specific polymer C"). Step D: A step of polymerizing TFE in Solution 1 without adding a surfactant to Solution 1 to obtain an aqueous emulsion containing a PTFE-based resin. Step E: A step of obtaining a PTFE-based resin from the aqueous emulsion obtained in Step D. Furthermore, the first embodiment may further include the other steps described above after step E.

[0067] (Process C) Step C is a step of polymerizing a non-fluorinated monomer in an aqueous medium to obtain a solution 1 containing a specific polymer C. In the following, first, the materials used in step C will be described in detail, and then the procedure for step C will be described in detail.

[0068] -Non-fluorinated monomers- The non-fluorine-based monomer is a monomer that does not contain a fluorine atom. The non-fluorine-containing monomer usually has a polymerizable group, and the number of polymerizable groups is preferably 1 to 3, and more preferably 1. The polymerizable group is preferably an ethylenically unsaturated group, more specifically, an acryloyl group, a methacryloyl group, a vinyl ether group, a vinyl ester group, a vinyl group, or an allyl group, and an acryloyl group, a methacryloyl group, a vinyl ester group, or a vinyl ether group is preferred.

[0069] The non-fluorine-containing monomer is preferably a monomer represented by formula (NF). Formula (NF) CH2=CR 11 -L 1 -R 12 R 11 represents a hydrogen atom or an alkyl group. The alkyl group preferably has 1 to 3 carbon atoms, and more preferably 1 carbon atom. L1 represents a single bond, -C(=O)-O-*, -OC(=O)-* or -O-. * represents R 12 For example, L 1 is -C(=O)-O-*, then formula (1) is CH2=CR 11 -C(=O)-OR 12 Represents. R 12 represents a hydrogen atom, an alkyl group, an alkenyl group, or a nitrile group, provided that L 1 If is a single bond, R 12 is a nitrile group. The alkyl group and alkenyl group preferably have 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms. The alkyl group may be linear or cyclic. When the alkyl group is cyclic, it corresponds to a cycloalkyl group. The alkenyl group may be linear or cyclic.

[0070] The monomer represented by the formula (NF) is preferably a monomer selected from the group consisting of a monomer represented by the formula (NF-1), a monomer represented by the formula (NF-2), a monomer represented by the formula (NF-3), and a monomer represented by the formula (NF-4). Formula (NF-1) CH2=CR 11 -C(=O)-OR 13 Formula (NF-2) CH2=CR 11 -OC(=O)-R 14 Formula (NF-3) CH2=CR 11 -OR 15 Formula (NF-4) CH2=CR 11 -R 16 R 11 The definition of is as described above. R 13 represents a hydrogen atom, an alkyl group, or an alkenyl group, and is preferably an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms. R 14represents an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group. R 15 represents an alkyl group, preferably a linear alkyl group or a cyclic alkyl group. R 16 represents a nitrile group.

[0071] Examples of non-fluorine-based monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, and cyclohexyl vinyl ether. The non-fluorine-containing monomers may be used alone or in combination of two or more. As the non-fluorine-containing monomer, a monomer represented by formula (NF-1) or a monomer represented by formula (NF-2) is preferred, and R 13 is an alkyl group. The monomers represented by formula (NF-1) and formula (NF-2) have a hydrophilic group such as an ester group or a carboxy group, and therefore the monomers and their polymers have hydrophilicity. Therefore, it is believed that the monomers and their polymers can be stably dispersed in an aqueous medium without the need for a surfactant, particularly at low concentrations.

[0072] -Specific polymer C- The specific polymer C is a polymer containing units based on a non-fluorine-containing monomer. The specific polymer C usually contains only units based on a non-fluorine-based monomer, but may also contain units based on a fluorine-based monomer. That is, in addition to the non-fluorine-based monomer, a fluorine-based monomer may be used in step C. The fluorine-based monomer is a monomer having a fluorine atom, and an example of the fluorine-based monomer is TFE. The content of units based on a non-fluorine-containing monomer in the specific polymer C is preferably 90% by mass or more, more preferably 95% by mass or more, based on the total units of the specific polymer C. The upper limit may be 100% by mass.

[0073] -Aqueous medium- The aqueous medium may be the aqueous medium used in step A above.

[0074] -Polymerization initiator- A polymerization initiator may be used in the step C. That is, a polymerization initiator may be used when polymerizing the non-fluorine-based monomer. Examples of the polymerization initiator include the water-soluble radical polymerization initiator used in step A above.

[0075] -Step C Procedure- In the step C, the non-fluorine-based monomer is polymerized in an aqueous medium. Specifically, it is preferable to mix the non-fluorine-based monomer with the aqueous medium and polymerize the non-fluorine-based monomer in the resulting mixed liquid. As described above, a fluorine-containing monomer may be used in combination, if necessary.

[0076] The amount of the non-fluorinated monomer used is preferably 200 ppm by mass or less, more preferably 1 to 150 ppm by mass or less, still more preferably 5 to 100 ppm by mass, and particularly preferably 5 to 50 ppm by mass, relative to the amount of TFE supplied (amount of TFE used) used in step D described below. The non-fluorine-containing monomer is preferably added all at once in the initial stage, that is, the entire amount is added to the polymerization system before the polymerization reaction is started.

[0077] The content of the non-fluorine-based monomer in the dispersion obtained by mixing the non-fluorine-based monomer with the aqueous medium is preferably 0.000015 to 0.0030 mass %, more preferably 0.000075 to 0.0023 mass %, relative to the total mass of the dispersion. Since the entire amount of the non-fluorinated monomer is usually polymerized to become the specific polymer C, the concentration of the specific polymer C in the obtained solution 1 falls within the above-mentioned numerical range. The above-mentioned non-fluorinated monomer concentration and specific polymer C concentration are concentrations when the obtained solution 1 is used in step D without diluting it with an aqueous medium. When the obtained solution 1 is diluted with an aqueous medium to have the above-mentioned specific polymer C concentration and the diluted solution is used in step D, a high-concentration solution according to the dilution ratio is produced in step C. The dilution ratio is not particularly limited, but is preferably 10 times or less.

[0078] The amount of the polymerization initiator used is preferably from 0.2 to 1000 mass %, more preferably from 0.2 to 500 mass %, based on the total amount of non-fluorinated monomers.

[0079] The amount of the polymerization initiator used is preferably 0.1 to 1000 mol %, more preferably 0.1 to 300 mol %, based on the total amount of non-fluorinated monomers.

[0080] The polymerization temperature for the non-fluorine-based monomer is preferably 10 to 95° C., more preferably 50 to 90° C. The polymerization time is preferably 5 to 400 minutes, more preferably 5 to 300 minutes, and even more preferably 5 to 200 minutes. The pressure conditions during polymerization are preferably reduced pressure conditions or normal pressure conditions, and among these, 0 to 2.0 MPa is preferred, 0 to 1.0 MPa is more preferred, and 0 to 0.5 MPa is even more preferred. Alternatively, the polymerization may be carried out in a TFE atmosphere. Note that the polymerization of the non-fluorinated monomer in an aqueous medium usually proceeds preferentially over the polymerization of TFE.

[0081] By the above step C, a solution 1 containing a specific polymer C is obtained. The specific polymer C may be dissolved in the solution 1 or may be dispersed in the aqueous medium in the form of particles. During the polymerization of TFE in the step D described below, the specific polymer C is not an emulsifier, but it is presumed that the specific polymer C exists at the boundary between the aqueous medium and the PTFE-based resin due to the balance of interfacial tensions between the two, thereby contributing to the stabilization of the dispersion of the PTFE-based resin in the aqueous medium. The average particle size of the particles of the specific polymer C is preferably from 0.1 to 100 nm, more preferably from 0.1 to 50 nm.

[0082] The solution 1 obtained in step C may contain unreacted non-fluorinated monomers. In addition, the polymerization atmosphere in step C may be set to a TFE-containing atmosphere in consideration of step D. In such a case, it is considered that a part of the specific polymer C in step D may become a polymer containing TFE units. From another perspective, the PTFE particles obtained in step D are not limited to particles consisting of a physical mixture of specific polymer C and PTFE, but can also be considered to be particles containing a TFE copolymer having units based on a non-fluorinated monomer.

[0083] (Process D) Step D is a step of polymerizing TFE in the solution 1 obtained in step D without adding substantially any surfactant to the solution 1, thereby obtaining an aqueous emulsion containing a PTFE-based resin. In the following, first, the materials used in step D will be described in detail, and then the procedure for step D will be described in detail.

[0084] -TFE- In step D, TFE is used.

[0085] -Other monomers- In step D, a monomer other than TFE may be further used within the range that does not impair the effects of the present invention. The other monomer may be a monomer having a polar group (hereinafter also referred to as "specific monomer D"). The polar group in specific monomer D interacts with the aqueous medium, and is therefore presumed to function as a surfactant by being located between TFE and the aqueous medium during TFE polymerization. As a result, TFE polymerization proceeds smoothly and chain transfer is suppressed.

[0086] Examples of the polar group contained in the specific monomer D include a sulfonic acid group, a sulfonate group, a carboxylic acid group, a carboxylate group, a phosphonic acid group, and a phosphonate group. Among them, the group represented by formula (A) or the group represented by formula (B) is preferred, and the group represented by formula (A) is more preferred, in that the formation of fluorine-based oligomers is further suppressed. Formula (A) -SO3M Formula (B) -COOM In formula (A) and formula (B), M represents a hydrogen atom, NH4, or an alkali metal atom. Examples of alkali metal atoms include a lithium atom, a sodium atom, and a potassium atom.

[0087] The specific monomer D usually has a polymerizable group, and the number of the polymerizable groups is preferably 1 to 3, and more preferably 1. The polymerizable group is preferably an ethylenically unsaturated group, more specifically, an acryloyl group, a methacryloyl group, a vinyl ether group, a vinyl ester group, a vinyl group, or an allyl group, and an acryloyl group, a methacryloyl group, a vinyl ester group, or a vinyl ether group is preferred.

[0088] The specific monomer D is preferably a monomer represented by formula (3) in that the formation of fluorine-based oligomers is further suppressed. Formula (3) CR 31 R 32 =CR 33 -L 3 -R 34 In formula (3), R 31 and R 32 each independently represents a hydrogen atom or a fluorine atom.

[0089] R 33 represents a hydrogen atom, a fluorine atom, or an alkyl group optionally substituted with a fluorine atom. Among these, a hydrogen atom or a fluorine atom is preferred in terms of better copolymerizability with TFE. The term "alkyl group which may be substituted with a fluorine atom" refers to an alkyl group in which at least one hydrogen atom may be substituted with a fluorine atom. The alkyl group which may be substituted with a fluorine atom preferably has 1 to 3 carbon atoms, and more preferably 1 carbon atom.

[0090] L 3 represents a single bond or a divalent linking group. Among these, a single bond is preferred in that it has better copolymerizability with TFE. Examples of the divalent linking group include a divalent hydrocarbon group, a divalent heterocyclic group, -O-, -S-, -SO2-, -C(O)-, and -Si(R a )2-, -N(R b )-, and groups formed by combining two or more of these. a represents an alkyl group (preferably having 1 to 10 carbon atoms) or a phenyl group. b represents a hydrogen atom or an alkyl group (preferably having 1 to 10 carbon atoms). The divalent hydrocarbon group may be a divalent saturated hydrocarbon group, a divalent aromatic hydrocarbon group, an alkenylene group, or an alkynylene group. The divalent saturated hydrocarbon group may be linear, branched, or cyclic, and examples thereof include alkylene groups. The number of carbon atoms is preferably 1 to 20. The divalent aromatic hydrocarbon group preferably has 5 to 20 carbon atoms, and examples thereof include a phenylene group. Alternatively, the group may be an alkenylene group having 2 to 20 carbon atoms, or an alkynylene group having 2 to 20 carbon atoms. Examples of groups that combine two or more of these include -OC(O)-, -C(O)N(R b )-, alkylene group-O-alkylene group, alkylene group-OC(O)-alkylene group, and alkylene group-Si(R a )2-phenylene group -Si(R a )2 are listed. The divalent hydrocarbon group may have a substituent. Examples of the substituent include a halogen atom (e.g., a fluorine atom, a chlorine atom). In other words, the hydrogen atom in the divalent hydrocarbon group may be substituted with a halogen atom.

[0091] R 34 represents a group represented by the above formula (A) or a group represented by the above formula (B).

[0092] The monomer represented by formula (3) is preferably a monomer selected from the group consisting of a monomer represented by formula (3-1), a monomer represented by formula (3-2), a monomer represented by formula (3-3), a monomer represented by formula (3-4), a monomer represented by formula (3-5), and a monomer represented by formula (3-6), and more preferably a monomer represented by formula (3-1). Formula (3-1) CR 31 R 32 =CR 33 -R 34 Formula (3-2) CR 31 R 32 =CR 33 -(CF2) m1 -R 34 Formula (3-3) CR 31 R 32 =CR 33 -(CF2C(CF3)F) m2 -R 34 Formula (3-4) CR 31 R 32 =CR 33 -O-(CFR 35 ) m3 -R 34 Formula (3-5) CR 31 R 32 =CR 33 -O-(CF2CFR 35 O) m4 -CF2CF2-R 34 Formula (3-6) CR 31 R 32 =CR 33 -CF2-O-(CF(CF3)CF2O) m5 -CF(CF3)-R 34

[0093] In formulas (3-1) to (3-6), R 31 ~R 34 The definition of is as described above. In formula (3-2), m1 represents an integer of 1 to 10. In the formula (3-3), m2 represents an integer of 1 to 5. In formula (3-4), m3 represents an integer of 1 to 10. 35 represents a fluorine atom or CF3. In formula (3-5), m4 represents an integer of 1 to 10. 35 The definition of is as described above. In formula (3-6), m5 represents 0 or an integer of 1 to 10.

[0094] A specific example of the specific monomer D is ammonium vinyl sulfonate. The specific monomer D may be used alone or in combination of two or more.

[0095] -Polymerization initiator- A polymerization initiator may be used in step D. That is, a polymerization initiator may be used during polymerization of TFE. The polymerization initiator used may be the polymerization initiator described in step C. As the polymerization initiator, a mixture of persulfate and disuccinic acid peroxide is preferred, and a mixture of ammonium persulfate and disuccinic acid peroxide is more preferred. The amount of the polymerization initiator used is preferably 0.10% by mass or more, more preferably 0.10 to 1.5% by mass, and even more preferably 0.20 to 1.0% by mass, based on the total amount of TFE supplied to the polymerization system.

[0096] -Stabilizing agent- In step D, a stabilizing aid may be used. The stabilizing aid is preferably paraffin wax, a fluorine-based solvent, or silicone oil, and more preferably paraffin wax. Paraffin wax may be liquid, semi-solid, or solid at room temperature. Among them, saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C. The stabilizing aids may be used alone or in combination of two or more.

[0097] -others- In step D, a monomer other than TFE and specific monomer D may be used within a range that does not impair the effects of the present invention. However, in order to improve various properties of the PTFE-based resin, the amount of TFE used is preferably 99.5 mass % or more, and more preferably 99.8 mass % or more, based on the total amount of the monomers used in step D.

[0098] -Procedure for Process D- In step D, substantially no surfactant is added to solution 1. That is, in step D, polymerization of TFE is carried out in solution 1 without substantially adding a new surfactant to solution 1. A surfactant is a compound having a hydrophilic group (e.g., a polar group) and a hydrophobic group (e.g., a hydrocarbon group). The definition of the polar group is the same as that of the polar group contained in the specific monomer D. Examples of surfactants include known surfactants, such as nonionic surfactants and ionic surfactants, and more specifically, hydrocarbon-containing surfactants and fluorine-containing surfactants. The definition of hydrocarbon-containing surfactants is as described below. In step D, it is preferable that at least one selected from the group consisting of hydrocarbon-containing surfactants and fluorine-containing surfactants is not substantially added to solution 1. The above phrase "substantially no surfactant is added" means that no surfactant is added, or if a surfactant is added, the amount of surfactant added is 200 mass ppm or less relative to the total mass of Solution 1. There is no particular lower limit, but 0 mass ppm is preferred. In other words, it is preferred that no surfactant is added to Solution 1 in Step D.

[0099] TFE is added to the polymerization system (i.e., polymerization reaction vessel) by a conventional method. For example, TFE is added to the polymerization system continuously or intermittently so that the polymerization pressure becomes a predetermined pressure. When a polymerization initiator is used, the polymerization initiator may be added to the polymerization system all at once or in portions.

[0100] When the specific monomer D is used, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.150% by mass or less. In other words, the amount of the specific monomer D charged relative to the total amount of TFE charged is preferably 0.150% by mass or less. From the viewpoint of emulsion stability during polymerization, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.100% by mass or less, more preferably 0.090% by mass or less. Also, from the viewpoint of improving molecular weight, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.005% by mass or more, more preferably 0.010% by mass or more. When two or more specific monomers D are used, the total amount of the specific monomers D used may be within the above range.

[0101] When the specific monomer D is used, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.150 mol % or less. In other words, the amount of the specific monomer D charged relative to the total amount of TFE charged is preferably 0.150 mol % or less. From the viewpoint of emulsion stability during polymerization, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.100 mol% or less, more preferably 0.090 mol% or less. Furthermore, from the viewpoint of improving molecular weight, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.001 mol% or more, more preferably 0.005 mol% or more. When specific monomer D is used, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.100 to 0.100 mol%, more preferably 0.005 to 0.090 mol%. When two or more specific monomers D are used, the total amount of the specific monomers D used may be within the above range.

[0102] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPa, more preferably 0.6 to 3.5 MPa. The polymerization time is preferably 50 to 520 minutes, more preferably 50 to 450 minutes, and even more preferably 50 to 300 minutes.

[0103] Step C and step D may be carried out consecutively in the same polymerization reaction vessel. In the production method of the present invention, it is sufficient that the specific polymer C is formed in the step C, and the step D may be carried out before the non-fluorinated monomer is completely consumed in the step C.

[0104] The above procedure results in an aqueous emulsion in which the PTFE-based resin is dispersed in particulate form (aqueous emulsion containing the PTFE-based resin). The concentration of the PTFE-based resin in the aqueous emulsion is preferably 10 to 45% by mass, more preferably 10 to 30% by mass, and even more preferably 10 to 25% by mass, based on the total amount of the aqueous emulsion. Within the above range, the PTFE-based resin in the aqueous emulsion can be more easily coagulated, and clouding of the coagulated liquid can be suppressed. The average primary particle size of the PTFE resin is preferably 100 to 500 nm, more preferably 150 to 300 nm. The average primary particle size of the PTFE-based resin corresponds to D50 measured by a laser scattering particle size distribution analyzer.

[0105] (Process E) Step E is a step of obtaining a PTFE-based resin from the aqueous emulsion obtained in Step D. Step E can be carried out using the same procedures and conditions as in Step B above.

[0106] <Second mode> The method for producing a PTFE-based resin may be the following second embodiment. The second embodiment of the method for producing a PTFE-based resin is a method for producing a PTFE-based resin, which comprises steps F and G. Step F: A step of polymerizing a monomer containing tetrafluoroethylene (hereinafter also referred to as "specific monomer F") in an aqueous dispersion containing a first fluoropolymer and an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin different from the first fluoropolymer. Step G: A step of obtaining a PTFE-based resin from the aqueous dispersion obtained in Step F. Furthermore, the second embodiment may further include the other steps described above after step E.

[0107] (Process F) Step F is a step of polymerizing a monomer containing TFE (hereinafter also referred to as "specific monomer F") in an aqueous dispersion containing a first fluoropolymer and an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin different from the first fluoropolymer.

[0108] -Aqueous dispersion- In the second embodiment, an aqueous dispersion containing the first fluorine-containing polymer and an aqueous medium is used.

[0109] -First fluoropolymer- It is presumed that the first fluorine-containing polymer solubilizes specific monomer F by adsorbing and incorporating the specific monomer F at the hydrophobic portion during polymerization of the specific monomer F, and that by adding a polymerization initiator to this, the specific monomer F is polymerized within the particles of the first fluorine-containing polymer. It is also presumed that the first fluorine-containing polymer contributes to dispersion stabilization in an aqueous medium.

[0110] The glass transition temperature (hereinafter also referred to as "Tg") of the first fluorine-containing polymer is preferably 10°C or lower, and from the viewpoint of efficiently adsorbing the specific monomer F, more preferably 5°C or lower, even more preferably 3°C or lower, and particularly preferably 0°C or lower. From the viewpoint of thermal stability after molding, the Tg of the first fluoropolymer is preferably −50° C. or higher, more preferably −45° C. or higher, and even more preferably −40° C. or higher. The glass transition temperature of the first fluoropolymer is preferably −50 to 10° C., more preferably −45 to 5° C., and even more preferably −40 to 3° C. The Tg of the first fluorine-containing polymer is measured by differential scanning calorimetry (DSC). As a method for adjusting the Tg of the first fluoropolymer within the above range, for example, a method of adjusting the type and amount of the monomer used in producing the first fluoropolymer may be mentioned.

[0111] The first fluorine-containing polymer preferably contains TFE units and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE units") (hereinafter also referred to as "PAVE units"), since this makes it easier to adjust the Tg within the above range.

[0112] The PAVE is preferably a monomer represented by the above formula (PA) from the viewpoints of excellent polymerization reactivity in producing the first fluorine-containing polymer and of enabling more efficient production of a PTFE-based resin. The monomer represented by formula (PA) has the same meaning as the monomer represented by formula (PA) in the above PTFE-based resin, and preferred embodiments are also the same.

[0113] When the first fluorine-containing polymer contains TFE units and PAVE units, the content of PAVE units in the first fluorine-containing polymer relative to the total of TFE units and PAVE units is preferably 20 to 60 mol %, more preferably 25 to 60 mol %, and even more preferably 30 to 55 mol %, from the viewpoints that Tg can be easily adjusted to within the above range and that a PTFE-based resin can be produced more efficiently.

[0114] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, but preferably does not substantially contain units based on other monomers, in order to more efficiently produce a PTFE-based resin. Substantially free of units derived from other monomers means that the content of units derived from other monomers is 0.01 mol % or less, more preferably 0 mol %, based on the total units of the first fluorine-containing polymer. When units based on another monomer are contained, the other monomer is preferably hexafluoropropylene.

[0115] Before the start of polymerization of the monomers used in the polymerization of the PTFE-based resin, the content of the first fluorine-containing polymer is 0.01 to 4.0 mass% relative to the total mass of the aqueous medium in the aqueous dispersion, and from the viewpoint of more efficient production of the second fluorine-containing polymer, it is preferably 0.01 to 0.6 mass%, more preferably 0.01 to 0.5 mass%.

[0116] In this specification, "before starting polymerization of the monomers used in the polymerization of the PTFE-based resin" means immediately before the start of polymerization. Here, "the start of polymerization" includes the time when the monomers and the polymerization initiator are made to coexist in the reactor after the temperature inside the reactor is raised to the polymerization temperature or higher, and the time when the temperature inside the reactor is raised to the polymerization temperature or higher after the monomers and the polymerization initiator are made to coexist in the reactor.

[0117] Before starting polymerization of the monomers used in the polymerization of the PTFE-based resin, the concentration of sulfate ions is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion, in order to suppress coloration of the PTFE-based resin.The lower limit can be 0 ppm by mass. An example of a method for adjusting the sulfate ion concentration to the above range is to remove sulfate ions using an anion exchange resin during production of the first fluorine-containing polymer. Here, the sulfate ions are derived, for example, from the polymerization initiator (particularly ammonium persulfate) used in producing the first fluoropolymer, and may be contained in the aqueous dispersion containing the first fluoropolymer. It is presumed that by keeping the content of sulfate ions at 10 ppm by mass or less (particularly 5 ppm by mass or less), it is possible to prevent the formation of terminal groups with low heat resistance in the PTFE-based resin, thereby suppressing coloration of the PTFE-based resin.

[0118] Before starting polymerization of the monomers used in the polymerization of the PTFE-based resin, the concentration of ammonium ions is preferably 20 ppm by mass or less, more preferably 10 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion, in order to suppress aggregation of the PTFE-based resin.The lower limit can be 0 ppm by mass. An example of a method for adjusting the ammonium ion concentration to the above range is to remove ammonium ions using a cation exchange resin during the production of the first fluorinated polymer. Here, the ammonium ions are derived, for example, from the initiator (particularly ammonium persulfate) used in producing the first fluoropolymer, and may be contained in the aqueous dispersion containing the first fluoropolymer. It is presumed that the ammonium ion content of 20 ppm by mass or less reduces the ionic strength in the aqueous medium, thereby improving the production efficiency of the PTFE-based resin.

[0119] The first fluorine-containing polymer is preferably dispersed in the aqueous medium in the form of particles. In this case, the average particle size of the first fluoropolymer is preferably from 1 to 150 nm, more preferably from 10 to 120 nm, and even more preferably from 50 to 120 nm, from the viewpoint of more efficient production of the PTFE-based resin. The average particle size of the first fluoropolymer is determined by measuring the particle size distribution by a laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle population set to 100%, and measuring the particle size (D50) at the point on the cumulative curve where the cumulative volume is 50%; detailed measurement conditions are as described in the Examples section.

[0120] The method for producing the first fluorine-containing polymer is preferably a method in which a monomer (preferably a monomer mixture containing TFE and PAVE) is polymerized in an aqueous medium in the presence of a polymerization initiator, thereby obtaining the first fluorine-containing polymer dispersed in the aqueous medium in the form of particles. The aqueous medium thus obtained, in which the particles of the first fluorine-containing polymer are dispersed, may be used as the aqueous dispersion as it is, or another aqueous medium may be added thereto and the resulting mixture may be used as the aqueous dispersion. Alternatively, the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution and the resulting mixture may be used as the aqueous dispersion.

[0121] The polymerization initiator used in the production of the first fluorine-containing polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, further preferably a persulfate, and particularly preferably ammonium persulfate.

[0122] The aqueous medium used for producing the first fluorine-containing polymer includes the aqueous medium in step A described above. The aqueous medium contained in the aqueous dispersion may be the polymerization solvent used in producing the first fluorine-containing polymer. Before starting polymerization of the monomers used in the polymerization of the PTFE-based resin, the content of the aqueous medium is preferably 60 to 99.9 mass%, more preferably 96 to 99.9 mass%, and even more preferably 98 to 99.9 mass%, based on the total mass of the aqueous dispersion.

[0123] The method for producing the first fluoropolymer preferably includes a heating step of heating the aqueous medium having the first fluoropolymer dispersed therein after the aqueous medium is obtained. This deactivates the polymerization initiator present in the system, making it less susceptible to the influence of the polymerization initiator used in producing the first fluoropolymer during polymerization of the PTFE-based resin. As a result, a PTFE-based resin with a high molecular weight is more likely to be obtained. The heating temperature in the heating step is preferably 70 to 100°C, more preferably 80 to 98°C, and even more preferably 85 to 95°C, since this can further promote the deactivation of the polymerization initiator in the aqueous medium.

[0124] -Other ingredients- The aqueous dispersion used in the present production method may contain other components in addition to the first fluorine-containing polymer and the aqueous medium. Specific examples of other components that may be contained in the aqueous dispersion include a chain transfer agent, an emulsifier other than a fluorine-based emulsifier, a pH adjuster, and a wax.

[0125] Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0126] Specific examples of emulsifiers other than fluorine-based emulsifiers include sodium lauryl sulfate, Perex SS-H manufactured by Kao Chemical Corporation, and Newcol 1305-SN manufactured by Nippon Nyukazai Co., Ltd.

[0127] Specific examples of pH adjusters include inorganic salts. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. More preferred specific examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0128] Specific examples of wax include Parafffin Wax-155 and Parafffin Wax-150 (both manufactured by Nippon Seiro Co., Ltd.).

[0129] When the aqueous dispersion contains a chain transfer agent, the content 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 amount of the chain transfer agent used is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the specific monomer F described below. When the aqueous dispersion contains an emulsifier other than a fluorine-based emulsifier, the content of the emulsifier other than a fluorine-based emulsifier is preferably 0.01 to 5 parts by mass relative to 100 parts by mass of the aqueous medium. When the aqueous dispersion 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. When the aqueous dispersion contains a wax, the content of the wax is preferably 1 to 10 parts by mass per 100 parts by mass of the aqueous medium.

[0130] Before starting polymerization of the monomers used in polymerization of the PTFE-based resin, the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less, based on the total mass of the first fluorine-containing polymer in the aqueous dispersion, and from the viewpoint of achieving better effects of the present invention, it is preferably 50 ppm by mass or less, more preferably 25 ppm by mass or less, and even more preferably 5 ppm by mass or less. The lower limit is 0 ppm by mass. The fluorine-containing emulsifier refers to an emulsifier in which the hydrophobic moiety contains a fluorine atom, and specific examples of the fluorine-containing emulsifier include fluorine-containing alkanoates and fluorine-containing ether carboxylic acid compounds. One example of a method for adjusting the concentration of the fluorine-containing emulsifier to fall within the above range is to produce an aqueous dispersion without using a fluorine-containing emulsifier.

[0131] Before starting polymerization of the monomers used in the polymerization of the second fluorine-containing polymer, the concentration of fluoride ions is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, based on the total mass of the aqueous dispersion, from the viewpoint of polymerization stability. The lower limit is 0 ppm by mass. An example of a method for adjusting the fluoride ion concentration to the above range is to remove sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer. Here, the fluoride ions may be generated by the reaction between a polymerization initiator (for example, ammonium persulfate) and the monomer used in producing the first fluorine-containing polymer, and may be contained in the aqueous dispersion.

[0132] -Specific monomer F- The specific monomer F includes TFE. The amount of TFE used is preferably from 97 to 100% by mass, more preferably from 98 to 100% by mass, and even more preferably from 99 to 100% by mass, based on the amount of specific monomer F used.

[0133] The specific monomer F may contain a fluorine-containing monomer other than TFE, but may not substantially contain a fluorine-containing monomer other than TFE. "Substantially free of fluorine-containing monomers other than TFE" means that the amount of fluorine-containing monomers other than TFE used is 0.0001% by mass or less, and may be 0% by mass, relative to the amount of specific monomer F used. Examples of the fluorine-containing monomer other than TFE include chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), vinylidene fluoride (hereinafter also referred to as "VdF"), fluoroalkylethylene, PAVE, and hexafluoropropylene. Two or more types of the fluorine-containing monomer other than TFE may be used in combination.

[0134] The specific monomer F may contain other monomers in addition to the fluorine-containing monomer, but it is preferable that it does not contain any other monomers. "Substantially free of other monomers" means that the amount of other monomers used is 0.0001% by mass or less, more preferably 0% by mass, relative to the amount of specific monomer F used. Specific examples of the other monomer include ethylene, propylene, vinyl chloride, and vinylidene chloride. Two or more of the other monomers may be used in combination.

[0135] The amount of the specific monomer F used is preferably 1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass, relative to 100 parts by mass of the aqueous medium used in the aqueous dispersion.

[0136] -Polymerization initiator- In the second embodiment, the specific monomer F is preferably polymerized in the presence of a polymerization initiator. Examples of the polymerization initiator include the water-soluble radical polymerization initiator used in step A above.

[0137] The amount of the polymerization initiator used is preferably 1 to 1000 ppm by mass, more preferably 5 to 750 ppm by mass, and even more preferably 10 to 500 ppm by mass, relative to 100 parts by mass of the specific monomer F used.

[0138] -Other ingredients- Components other than those mentioned above (hereinafter also referred to as "other components") may be further used during polymerization of the specific monomer F. A specific example of the other component is a reducing agent. The amount of the other components used is preferably 1 to 2000 ppm by mass relative to 100 parts by mass of the specific monomer F used.

[0139] -Step F Procedure- In this production method, the specific monomer F is polymerized in the aqueous dispersion to produce a PTFE-based resin.

[0140] The PTFE-based resin obtained by this production method is as described above. The first fluorine-containing polymer and the PTFE-based resin may be copolymerized.

[0141] The specific monomer F is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer F may be added to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer F may be dissolved in an aqueous medium, and the resulting solution may be added to the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0142] The polymerization temperature is preferably from 10 to 95°C, more preferably from 15 to 90°C. The polymerization pressure is preferably from 0.5 to 4.0 MPaG, more preferably from 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably from 90 to 1000 minutes, more preferably from 90 to 700 minutes.

[0143] The polymerization of the specific monomer F is preferably carried out in the substantial absence of an emulsifier. Examples of the emulsifier include known emulsifiers, such as common surfactants. "In the substantial absence of an emulsifier" means an environment in which the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm, relative to the total mass of the aqueous medium contained in the aqueous dispersion.

[0144] As described above, it is presumed that the specific monomer F polymerizes within the particles of the first fluorine-containing polymer during the polymerization of the specific monomer F. Therefore, in this production method, it is considered that particles containing the first fluorine-containing polymer and the PTFE-based resin are generated. That is, according to this production method, it is estimated that the PTFE-based resin is obtained in the form of particles containing the first fluorine-containing polymer and the PTFE-based resin. In this case, an aqueous dispersion in which particles containing the first fluorine-containing polymer and the PTFE-based resin are dispersed in the above aqueous medium is obtained by this production method.

[0145] (Step G) Step G is a step of obtaining the PTFE-based resin from the aqueous dispersion obtained in Step F. As Step G, it can be carried out under the procedures and conditions in Step B described above.

[0146] 〔Electrode binder〕 The electrode binder of the present invention contains the above-mentioned PTFE-based resin and an active material. In addition, when the electrode binder is a negative electrode binder, it is preferable that the negative electrode binder contains a PTFE-based resin and a negative electrode active material. When the electrode binder is a positive electrode binder, it is preferable that the positive electrode binder contains a PTFE-based resin and a positive electrode active material.

[0147] <PTFE-based resin> The electrode binder contains a PTFE-based resin. The PTFE-based resin has the same meaning as the PTFE-based resin of the present embodiment described above, and the preferred embodiments are also the same.

[0148] The content of the PTFE-based resin is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, relative to the total mass of the electrode mixture. The upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less. The content of the PTFE-based resin is preferably 0.1 to 30% by mass, more preferably 0.5 to 30% by mass, and even more preferably 1.0 to 10% by mass, relative to the total mass of the electrode mixture. Within the above ranges, the retention of the active material and the mechanical strength of the electrode mixture sheet are sufficient, battery performance such as cycle characteristics is also good, and a decrease in battery capacity or conductivity can be further suppressed. PTFE-based resins have excellent binding properties, so even if the content is small, the active material can be sufficiently held within the electrode mixture.

[0149] <Active material> The electrode mixture includes an active material. Examples of the active material include a positive electrode active material and a negative electrode active material, and can be appropriately selected according to the intended electrode.

[0150] (Cathode active material) When the electrode mixture is a positive electrode mixture, the positive electrode mixture contains a positive electrode active material. The positive electrode mixture may contain, in addition to the PTFE resin and the positive electrode active material, at least one selected from the group consisting of a binder other than the PTFE resin, a conductive material, a thickener, and an additive. The positive electrode active material is a material that electrochemically absorbs and releases lithium ions. Examples of such materials include at least one selected from the group consisting of lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. From the viewpoints of high average discharge voltage and cost advantage, the positive electrode active material may be a lithium-containing transition metal oxide.

[0151] A surface-adhering substance having a different composition from the positive electrode active material may be adhered to the surface of the positive electrode active material. Examples of surface-adhering substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0152] The shape of the particles of the positive electrode active material may be blocky, polyhedral, spherical, oval sphere, plate-like, needle-like, columnar, etc. The positive electrode active material may be either primary particles or secondary particles.

[0153] The volume-based median diameter d50 of the particles (primary particles or secondary particles) of the positive electrode active material is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more. The upper limit is preferably 30 μm or less, more preferably 25 μm or less. d50 is preferably 0.3 to 30 μm, more preferably 0.5 to 30 μm, and even more preferably 1.0 to 25 μm. Within the above range, a high tap density product is easily obtained, or the diffusion time of lithium within the particles becomes appropriate, which can further suppress deterioration of battery performance. In order to improve the filling property when preparing the positive electrode, two or more types of positive electrode active materials having different median diameters d50 may be mixed as the positive electrode active material.

[0154] The median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using a HORIBA LA-920 as the particle size distribution analyzer, the measurement is performed using a 0.1% by mass aqueous solution of sodium hexametaphosphate as the dispersion medium, and after ultrasonic dispersion for 5 minutes, the measurement is performed with a refractive index set to 1.24.

[0155] The BET specific surface area of ​​the positive electrode active material is 0.1 m 2 / g or more is preferable, and 0.3m 2 / g or more is more preferable. The upper limit is 50m 2 / g or less is preferable, and 30m 2The BET specific surface area of ​​the positive electrode active material is preferably 0.1 to 50 m / g. 2 / g is preferred, and 0.3 to 30m 2 / g is more preferred. The BET specific surface area is defined as a value measured by a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.) using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, after which the sample is pre-dried at 150°C for 30 minutes under a nitrogen flow, by a nitrogen adsorption BET single-point method using a gas flow method.

[0156] The positive electrode active materials may be used alone or in combination of two or more. When two or more positive electrode active materials are used, a suitable combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 combinations of LiCoO2 with ternary systems such as O2; combinations of LiCoO2 with LiMn2O4 or with LiFePO4 with LiCoO2 or with LiFePO4 in which part of the Co has been substituted with other transition metals;

[0157] The content of the positive electrode active material is preferably 50 to 99.5 mass %, more preferably 80 to 99 mass %, based on the total mass of the electrode mixture, in terms of high battery capacity.

[0158] (Negative electrode active material) The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions, desorb and insert (intercalate) lithium ions, or dope and dedope counter anions of lithium ions. Specific examples include lithium metal, carbonaceous materials such as graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate.

[0159] As the negative electrode active material, a negative electrode active material containing silicon is preferable because it allows the production of a high-capacity battery. The silicon-containing negative electrode active material is preferably silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5≦x≦1.6), or a mixture thereof. Silicon oxide is a general term for amorphous silicon oxide, and is represented, for example, by the general formula SiOx (0.5≦x≦1.6). x is preferably 0.8≦x<1.6, and more preferably 0.8≦x<1.3. This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon to produce silicon monoxide gas, which is then cooled and precipitated.

[0160] The silicon-containing negative electrode active material may be coated with carbon. The carbon coating can provide electrical conductivity, improving battery performance. Methods for providing electrical conductivity include, for example, mixing with electrically conductive particles such as graphite, coating the surface of the silicon-containing negative electrode active material with a carbon coating, and combining both methods. The carbon coating method is preferred, and chemical vapor deposition (CVD) is more preferred.

[0161] The shape of the particles of the negative electrode active material may be blocky, polyhedral, spherical, oval sphere, plate-like, needle-like, columnar, etc. The negative electrode active material may be either primary particles or secondary particles.

[0162] The average particle size of the particles (primary particles or secondary particles) of the negative electrode active material is preferably 0.1 to 50 μm, more preferably 0.2 to 30 μm, and even more preferably 0.5 to 20 μm. The average particle size is a weight average particle size measured by particle size distribution measurement using a laser diffraction method.

[0163] The BET specific surface area of ​​the negative electrode active material is 0.5 to 100 m 2 / g is preferred, and 1 to 20m 2 / g is more preferred.

[0164] The content of the negative electrode active material is preferably 50 to 99.5 mass %, more preferably 80 to 99 mass %, based on the total mass of the electrode mixture.

[0165] <Conductive additive> The electrode mixture may contain a conductive additive. Examples of conductive additives include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; and amorphous carbon such as needle coke, carbon nanotubes, fullerene, and vapor-grown carbon fiber.

[0166] The content of the conductive additive is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more, relative to the total mass of the electrode mixture. The upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less. The content of the conductive additive is preferably 0.01 to 50% by mass, more preferably 0.1 to 30% by mass, and even more preferably 1 to 15% by mass, relative to the total mass of the electrode mixture.

[0167] The electrode mixture contains a PTFE-based resin, an active material, and a conductive auxiliary, and the content of the PTFE-based resin is preferably 0.5 to 10 mass% relative to the total mass of the electrode mixture, the content of the active material is 88 to 99 mass% relative to the total mass of the electrode mixture, and the content of the conductive auxiliary is preferably 0.5 to 10 mass% relative to the total mass of the electrode mixture, and more preferably the content of the PTFE-based resin is 1 to 10 mass% relative to the total mass of the electrode mixture, the content of the active material is 88 to 96 mass% relative to the total mass of the electrode mixture, and the content of the conductive auxiliary is 1 to 10 mass% relative to the total mass of the electrode mixture.

[0168] <Thermoplastic resin> The electrode mixture may contain a thermoplastic resin. Examples of thermoplastic resins include polyvinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide.

[0169] In the electrode mixture, the ratio of the thermoplastic resin content to the active material content (thermoplastic resin content / active material content × 100) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more. The upper limit is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less. The ratio of the thermoplastic resin content to the active material content is preferably 0.01 to 3.0% by mass, more preferably 0.05 to 2.5% by mass, and even more preferably 0.10 to 2.0% by mass.

[0170] <Other ingredients> The electrode mixture may contain other components in addition to the various components described above. The other components may include, for example, at least one selected from the group consisting of a solid electrolyte, a binder other than those mentioned above, a conductive material, a thickener, and an additive. Examples of the solid electrolyte include sulfide solid electrolytes having an argyrodite-type crystal structure, oxide solid electrolytes, and halogenated solid electrolytes. Examples of binders include elastomers such as styrene-butadiene rubber, acrylic rubber, and styrene-ethylene-butadiene-styrene. Fiber components include cellulose, carboxymethyl cellulose, cellulose nanofiber, and aramid fiber. Fiber components are preferably mixed as powders, and are preferably finely ground (microfibrillated) in advance by various grinding methods, as this improves the mixability with the PTFE powder. Adding fiber components tends to increase the strength of the molded sheet.

[0171] The electrode mixture preferably does not substantially contain an organic solvent. Specifically, the content of the organic solvent is preferably 1.0 mass % or less, more preferably 0.1 mass % or less, based on the total mass of the electrode mixture. The lower limit may be 0 mass %.

[0172] The electrode mixture is preferably in the form of a sheet.

[0173] The electrode mixture can be suitably used as an electrode mixture for secondary batteries. The electrode mixture is particularly suitable for lithium ion secondary batteries. When used in secondary batteries, the electrode mixture is usually used in the form of a sheet.

[0174] [Method for producing electrode mixture] The method for producing the electrode mixture is not particularly limited as long as it is a method that can produce the above-mentioned electrode mixture. Among these, the method for producing an electrode mixture is preferably a method for producing an electrode mixture including a step X1 of pulverizing and mixing a raw material composition containing a binder containing a PTFE-based resin, an active material, and, if necessary, a conductive additive. The above-mentioned method for producing an electrode mixture can obtain an electrode mixture in a relatively short number of steps. The method for producing an electrode mixture preferably further includes step X2 of rolling the raw material composition pulverized and mixed in step X1 into a sheet shape. When step X2 is included, a sheet-shaped electrode mixture is obtained.

[0175] (Process X1) Step X1 is a step of mixing a raw material composition containing a binder containing a PTFE-based resin, an active material, and, if necessary, a conductive additive. The mixing method is preferably a method in which a mixing device is used. Examples of mixing devices include a jet mill, a pin mill, a blender, a twin-screw extruder, and a mixer. A jet mill, a mixer, or a twin-screw extruder is preferred because it can simultaneously crush the PTFE-based resin and suppress the formation of fibers. Jet mills include collision types that crush particles by colliding them with each other or with a collision body (target), swirling airflow types and loop types that crush particles by collision of particles with each other in a crushing zone formed by multiple crushing nozzles arranged in a circulating airflow, fluidized bed types that crush particles by collision or friction of particles with each other in a fluidized bed, and supersonic types. Collision type, swirling air current type, loop type and fluidized bed type jet mills are described in detail in "Advanced Crushing Technology and Applications" edited by the Japan Plastics Industry Technology Association, published by NGT Ltd., p. 162. Collision-type jet mills include pulverizers that discharge a fluid such as compressed air from a nozzle and crush particles by causing them to collide with each other in the high-speed turbulent airflow formed in the jet mill, and pulverizers that transport resin particles in a high-speed airflow and crush them by causing them to collide with a collision body.

[0176] Commercially available jet mills include the Cross Jet Mill (manufactured by Kurimoto Iron Works); Jet-O-Mill, AO Jet Mill, Sanitary AOM, Cojet, Single Track Jet Mill, and Super STJ Mill (all manufactured by Seishin Enterprises); Current Jet Mill (manufactured by Nisshin Engineering); Urmax (manufactured by Nisso Engineering); Supersonic Jet Mill PJM Type, Supersonic Jet Mill CPY Type, Supersonic Jet Mill LJ-3 Type, and Supersonic Jet Mill I Type (all manufactured by Nippon Pneumatic Mfg. Co., Ltd.); Counter Jet Mill, Micro Jet T Type, Spiral Jet Mill, and Micron Jet MJQ (all manufactured by Hosokawa Micron Corporation); Fluidized Bed Jet Mill (manufactured by Nippon Coke and Engineering Co., Ltd.); Nano Grinding Mill (manufactured by Tokuju Kogyosho Co., Ltd.), and EX-Mini Jet Mill (M-Tech Chemical). As the jet mill, a single track jet mill is preferred in terms of excellent productivity.

[0177] The pulverization pressure in the jet mill is preferably 0.1 to 2 MPa, more preferably 0.2 to 0.9 MPa, in order to achieve both disintegration properties and suppression of fiber formation.

[0178] (Process X2) Step X2 is a step of rolling the raw material composition pulverized and mixed in step X1 into a sheet shape. Examples of the rolling method in the step X2 include rolling methods using a roll press, a plate press, a calender roll, and the like. The rolling conditions are not particularly limited and can be appropriately selected according to the thickness and density of the target electrode mixture.

[0179] 〔electrode〕 The electrode of the present invention includes a current collector and an electrode layer containing an electrode mixture disposed on the current collector. The electrode may have a conductive carbonaceous material disposed between the current collector and the electrode layer, if necessary.

[0180] <Current collector> The electrode includes a current collector. When the electrode is a positive electrode, examples of the current collector include metal materials such as metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or alloys thereof; and carbon materials such as carbon cloth and carbon paper, with metal materials being preferred and aluminum or its alloys being more preferred. When the electrode is a negative electrode, examples of the current collector include metal materials such as metals such as copper, nickel, titanium, tantalum, and stainless steel, or alloys thereof; and carbon materials such as carbon cloth and carbon paper, with metal materials being preferred, and copper, nickel, or alloys thereof being more preferred.

[0181] The shape of the current collector may be, for example, a metal foil, a metal cylinder, a metal coil, a metal plate, an expanded metal, a punched metal, or a foamed metal, for example, a carbon plate, a carbon thin film, or a carbon cylinder, for example, when made of a carbon material. Of these, a metal foil is preferred as the shape of the current collector. The metal foil may also be formed into a mesh, as appropriate. The thickness of the current collector is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The upper limit is preferably 1 mm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Within the above range, excellent handleability and strength can be achieved.

[0182] It is also preferable that the surface of the current collector is coated with a conductive additive, in order to reduce the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of the conductive additive include carbon and precious metals such as gold, platinum, and silver.

[0183] <Electrode layer> The electrode includes an electrode layer. The electrode layer is disposed on the current collector and contains the above-mentioned electrode mixture. The electrode layer may be either a positive electrode layer or a negative electrode layer, and can be appropriately selected depending on the active material contained in the electrode mixture, etc.

[0184] The density of the positive electrode layer is 3.00 g / cm 3 More than 3.10 g / cm is preferable. 3 More preferably, 3.20 g / cm or more 3 More preferably, the upper limit is 3.80 g / cm 3 Preferably less than 3.75 g / cm 3 Less than 3.70 g / cm is more preferable. 3 The density of the positive electrode layer is more preferably 3.00 to 3.80 g / cm 3 is preferred, and 3.10 to 3.75 g / cm 3 More preferably, 3.20 to 3.70 g / cm 3 is more preferable. The density of the negative electrode layer is 1.3 g / cm 3 More than 1.4 g / cm is preferable. 3 More preferably, 1.5 g / cm 3 More preferably, the upper limit is 2.0 g / cm 3 Preferably less than 1.9 g / cm 3 Less than 1.8 g / cm is more preferable. 3 The density of the negative electrode layer is more preferably 1.3 to 2.0 g / cm. 3 is preferred, and 1.4 to 1.9 g / cm 3 More preferably, 1.5 to 1.8 g / cm 3 is more preferable. Within the above range, the permeability of the electrolyte to the interface between the current collector and the active material is excellent, and the charge / discharge characteristics at high current densities in particular are excellent. Also, the conductivity between the active materials is excellent.

[0185] The thickness of the electrode layers (positive electrode layer and negative electrode layer) is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoint of high capacity and high output. The upper limit is preferably 500 μm or less, more preferably 450 μm or less. The thickness of the electrode layers is preferably 10 to 500 μm, more preferably 20 to 450 μm.

[0186] [Secondary battery] The secondary battery of the present invention includes the above-described electrode. The secondary battery may be a secondary battery that uses an electrolyte solution or a solid-state secondary battery. Examples of secondary batteries include non-aqueous secondary batteries such as non-aqueous electrolyte secondary batteries, all-solid-state batteries, and fuel cells. Specific examples include nickel-cadmium batteries, nickel-metal hydride batteries, lithium secondary batteries, sodium-ion secondary batteries, zinc-ion secondary batteries, fluoride-ion secondary batteries, alkali metal secondary batteries, halide secondary batteries, and lithium-air secondary batteries.

[0187] The secondary battery preferably includes a positive electrode, a negative electrode, an electrolyte, and a separator. The secondary battery may have either a laminated structure including a positive electrode, a separator, and a negative electrode in this order, or a wound structure in which a positive electrode, a separator, and a negative electrode are wound in a spiral shape. When the secondary battery has a laminated structure, the laminated structure is preferably formed by bundling metal core portions of the electrode layers and welding them to terminals. When the secondary battery has a wound structure, the internal resistance can be reduced by providing a plurality of lead structures on each of the positive electrode and the negative electrode and bundling them into a terminal.

[0188] The shape of the secondary battery may be, for example, cylindrical, square, laminated, coin-shaped, or large. The shapes and configurations of the positive electrode, negative electrode, and separator can be changed according to the shape of each battery.

[0189] Examples of the separator include porous membranes such as polyethylene and polypropylene; and nonwoven fabrics such as nonwoven fabrics made of resins such as polypropylene, and glass fiber nonwoven fabrics. The material or shape of the separator is not particularly limited as long as it is stable to the electrolyte and has excellent liquid retention properties. Among these, the separator is preferably made of a resin, glass fiber, or inorganic material, and is preferably in the form of a porous sheet or nonwoven fabric. The thickness of the separator is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more. The upper limit is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. The thickness of the separator is preferably 1 to 50 μm, more preferably 5 to 40 μm, and even more preferably 8 to 30 μm.

[0190] The electrolyte is preferably a non-aqueous electrolyte, such as one obtained by dissolving a known electrolyte salt in a known organic solvent for dissolving electrolyte salts. Examples of the organic solvent for dissolving the electrolyte salt include known hydrocarbon solvents such as vinylene carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and fluorine-based solvents such as fluoroethylene carbonate, fluoroethers, and fluorinated carbonates. Examples of electrolyte salts include LiClO4, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiFSI(LiN(SO2F)2), LiBOB(LiB(C2O4)2), LiDFOB(LiBF2(C2O4)), LiPF2(C2O4)2, LiPF4(C2O4), and LiN(SO2C2F5)2, and LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, or combinations thereof are preferred in terms of good cycle characteristics.

[0191] The solid state secondary battery is preferably an all-solid state secondary battery. The solid-state secondary battery is preferably a lithium-ion battery or a sulfide-based all-solid-state secondary battery. The solid secondary battery preferably includes a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode.

[0192] The solid electrolyte used in the solid secondary battery mixture may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0193] The sulfide-based solid electrolyte is not particularly limited, and examples include Li2S-P2S5, Li2S-P2S3, Li2S-P2S3-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, LiI-Li2S-SiS2-P2S5, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li3PS4-Li4GeS4, Li 3.4 P 0.6 Si 0.4 S4, Li 3.25 P 0.25 Ge 0.76 S4, Li 4-x Ge 1-x P x S4 (X = 0.6 to 0.8), Li 4+y Ge 1-y Ga y S4 (y = 0.2 to 0.3), LiPSCl, LiCl, Li 7-x-2y PS 6-x-y Cl x (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5), etc., or a mixture of two or more thereof can be used. Also, the sulfide-based solid electrolyte preferably contains lithium. The sulfide-based solid electrolyte containing lithium is used in a solid battery that uses lithium ions as carriers, and is preferable in terms of an electrochemical device having a high energy density.

[0194] As the oxide-based solid electrolyte, a compound that contains oxygen atoms, has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and has electron insulation is preferable.

[0195] Examples of the oxide-based solid electrolyte include Li xa La ya TiO3 [xa = 0.3 to 0.7, ya = 0.3 to 0.7] (LLT), Li xb La yb Zr zb M bb mb O nb (Mbb is at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, where xb satisfies 5≦xb≦10, yb satisfies 1≦yb≦4, zb satisfies 1≦zb≦4, mb satisfies 0≦mb≦2, and nb satisfies 5≦nb≦20.), Li xc B yc M cc zc O nc (M cc is at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn, where xc satisfies 0≦xc≦5, yc satisfies 0≦yc≦1, zc satisfies 0≦zc≦1, and nc satisfies 0≦nc≦6.), Li xd (Al,Ga) yd (Ti,Ge) zd Si ad P md O nd (where 1≦xd≦3, 0≦yd≦2, 0≦zd≦2, 0≦ad≦2, 1≦md≦7, 3≦nd≦15), Li (3-2xe) M ee xe D ee O(xe represents a number between 0 and 0.1, and M ee represents a divalent metal atom. ee represents a halogen atom or a combination of two or more halogen atoms.) Li xf Si yf O zf (1≦xf≦5, 0 <yf≦3、1≦zf≦10)、Li xg S yg O zg (1≦xg≦3, 0 <yg≦2、1≦zg≦10)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 , LiPO (4-3 / 2w) N w (w<1), Li with LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO4, La with perovskite crystal structure 0.51 Li 0.34 TiO 2.94 , La0.55 Li 0.35 TiO3, LiTi2P3O with NASICON (sodium super ionic conductor) type crystal structure 12 , Li 1+xh+yh (Al,Ga) xh (Ti,Ge) 2-xh Si yh P 3-yh O 12 (where 0≦xh≦1, 0≦yh≦1), and Li7La3Zr2O with a garnet-type crystal structure 12 (LLZ). Ceramic materials in which element substitution has been performed on LLZ are also known. For example, LLZ-based ceramic materials in which at least one of Mg (magnesium) and A (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)) has been substituted for LLZ are also known. Phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li3PO4), LiPON, LiPOD, in which part of the oxygen in lithium phosphate has been substituted with nitrogen, are also desirable. 1 (D 1 is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc. 1 ON(A 1 is at least one selected from Si, B, Ge, Al, C, Ga, etc. Specific examples include Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 and Li2O-Al2O3-SiO2-P2O5-TiO2.

[0196] The oxide-based solid electrolyte preferably contains lithium. The oxide-based solid electrolyte containing lithium is used in a solid-state battery that uses lithium ions as a carrier, and is preferred in terms of electrochemical devices having a high energy density.

[0197] The oxide-based solid electrolyte is preferably an oxide having a crystalline structure. Oxides having a crystalline structure are preferred in terms of good Li-ion conductivity. Examples of oxides having a crystalline structure include perovskite-type (La 0.51 Li 0.34 TiO 2.94 etc.), NASICON type (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, etc.), garnet type (Li7La3Zr2O 12 Among them, the NASICON type is preferred.

[0198] The content of the polytetrafluoroethylene powder is preferably 1 to 10 parts by mass, more preferably 1.5 to 9 parts by mass, and even more preferably 2 to 8 parts by mass, relative to 100 parts by mass of the sulfide-based solid electrolyte. [Example]

[0199] The present invention will be described in detail below with reference to examples. Examples 1 to 4 and 10 to 12 are working examples, and Examples 5 to 9 and 13 are comparative examples. However, the present invention is not limited to these examples.

[0200] [Measurement and evaluation methods] The various measurement and evaluation methods are as follows.

[0201] <Angle of repose> The PTFE-based resins obtained in each of the examples described below were measured by the injection method using a Multitester MT-02 (manufactured by Seishin Enterprise Co., Ltd.) The PTFE-based resins were passed through a sieve with 2360 μm openings before the measurement. The PTFE-based resin is intended to be the PTFE-based resin used in the electrode mixture in each example described below. For example, in Example 1, the angle of repose of PTFE-based resin 1C was measured.

[0202] <Pore volume and median pore diameter> For the PTFE-based resins obtained in each of the examples described below, measurements were carried out under the following conditions by the mercury intrusion method. The definitions of pore volume and pore median diameter are as described above. Note that the above PTFE-based resin refers to the PTFE-based resin used in the electrode binder of each of the examples described below. For example, in Example 1, the pore volume and pore median diameter of PTFE-based resin 1C were measured. · Pretreatment: Dry the PTFE-based resin at 150 °C for 2 hours · Equipment used: AutoPoreIV 9520 manufactured by Micromeritics · Measurement range: Approximately 4 nm to 500 μm · Analysis method: Washburn method · Surface tension: 480 dynes / cm · Contact angle: 140°

[0203] <Average primary particle diameter (PPS) of PTFE-based resin> Using the aqueous dispersion obtained in each of the examples described below as a sample, measurements were carried out using a laser scattering particle size distribution analyzer (manufactured by Horiba, Ltd., trade name "LA-920"). The average primary particle diameter is the median diameter based on volume.

[0204] <Ratio of each unit in PTFE-based resin> The ratio of each unit in the PTFE-based resin obtained in each of the examples described below was 19 determined from 19F-NMR analysis and infrared absorption spectrum analysis.

[0205] <Solid content concentration of aqueous dispersion> The solid content concentration of the aqueous dispersion obtained in each of the examples described below was calculated by weighing the mass of the residue after heating 2.0 g of the aqueous dispersion at 170 °C for 20 minutes and then calculating the solid content concentration using the following formula. "Solid content concentration (mass%) = 100 × Heating residue of aqueous dispersion (g) / Mass of aqueous dispersion (2.0 g)"

[0206] <ssg> The SSG was measured in accordance with ASTM D4895-10. Specifically, a 12.0 g sample was weighed and placed in a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes to form a molded sample. This sample was placed in a 290°C oven, heated at 120°C / hr, held at 380°C for 30 minutes, then cooled at 60°C / hr to 294°C for 24 minutes. After holding the sample in a desiccator at 23°C for 12 hours, the specific gravity of the molded product relative to water was measured at 23°C, and this was used as the SSG.

[0207] <Voltage resistance> The dielectric strength was measured in accordance with JIS K6892:1995. The specific procedure was as follows: The PTFE powder obtained in each example was left at a temperature of 25±2°C for at least 1 hour, then thoroughly sieved through a 1.7 mm mesh sieve at the same temperature. 100±0.1 g of the powder that passed through was weighed out and used as the sample. The sample was placed in a 500 mL wide-mouth glass bottle, and 25±0.1 g of toluene was added little by little, taking care not to wet the walls of the bottle. The bottle was then stoppered and shaken vigorously for 3 minutes to mix the sample and toluene. The resulting mixture was placed in a preforming mold, and gentle pressure was applied so that the push rod movement speed did not exceed 50 mm / min. A molding pressure of 0.98 MPa was maintained for 1 minute to perform preforming. The preforming product was removed from the preforming mold and immediately transferred to an extrusion molding tester. The lower part of the mold of the extrusion molding tester was maintained at a temperature of 60±5°C. Next, the extrusion molding tester with the preform set in place was attached to a 3-ton hydraulic press, and the ram was moved at a speed of 5-10 mm / min to perform extrusion molding. The dimensions were 5 mm outer diameter and 4 mm inner diameter. Approximately 1 m of the extrusion was removed from the extrusion, and 15 pieces of the extrusion were cut with a sharp blade into lengths of 25 ± 1 cm. These pieces were then inserted into rods on a sample holder and left at room temperature for 12-24 hours. The sample holder was then placed in an electric furnace maintained at 365 ± 5°C. After the temperature inside the furnace returned to 365 ± 5°C, the extrusion was baked for 30 ± 3 minutes, then removed and allowed to cool at room temperature. The resulting molded product was used as a test piece. A metal rod was inserted into the test piece to form the internal electrode, and metal foil was wrapped around the center to form the external electrode. A high-voltage lead wire was connected to the external electrode, and the internal electrode was grounded. The applied voltage was quickly increased to a specified voltage, and it was determined whether the specimen could withstand this voltage for one minute. The specified voltage was increased in 1 kV increments, and the maximum voltage that could be withstood for one minute was taken as the withstand voltage.

[0208] <Preparation of positive electrode mixture> NMC622 (Hosen Co., Ltd., average particle size 10 μm, positive electrode active material), the PTFE-based resin of each example, and acetylene black (Sigma-Aldrich) were mixed in a mass ratio of 96:3:1, and pulverized and mixed in an Ex-Mini Jet Mill (M-Tech Chemical Co., Ltd.) at a feed rate of 3 g / min and an air pressure of 0.4 MPa to obtain an electrode mixture (positive electrode mixture). After mixing, adhesion to the piping was visually confirmed during disassembly and cleaning. 50 g of the obtained electrode mixture was passed through a 3 ton roll press at a temperature of 90° C. only once to form a sheet, to obtain a positive electrode mixture sheet having an average thickness of 200 μm.

[0209] <Wall adhesion> After preparing an electrode mixture by mixing the resin using the jet mill in <Preparation of Positive Electrode Mix>, the presence or absence of adhesion to the piping and container walls was visually confirmed, and the wall adhesion was evaluated according to the following evaluation criteria. "A": No adhesion was observed. "B": Deposits were observed.

[0210] <Thickness uniformity> The positive electrode mixture sheet obtained in <Preparation of positive electrode mixture> was cut into 4.5 cm x 4.5 cm pieces. Next, a 1 cm area from the periphery of the obtained cut piece was removed, and within a 2.5 cm x 2.5 cm area, further cutting into 0.5 cm x 0.5 cm pieces was repeated to obtain measurement samples, resulting in a total of 25 measurement samples. The thickness of each measurement sample was measured at an arbitrary location, and the X value was calculated according to the following formula to evaluate the thickness uniformity. From the obtained measurement values, the maximum value, minimum value, and arithmetic mean value were calculated, and the X value was calculated according to the following formula. The thickness uniformity of the sheet was evaluated for the X value according to the following evaluation criteria. A was considered to be acceptable. X value (%) = 100 x (maximum value - minimum value) / arithmetic mean value "A": X value is 10% or less. "B": X value is more than 10% and less than 20%. "C": No sheet was obtained or holes were formed in the sheet, or the X value was more than 20%.

[0211] <Capacity maintenance rate> Graphite QC-6 (manufactured by Hosensha) and the PTFE-based resin of each example (Examples 1, 10, and 11) were premixed in a V-blender at a mass ratio of 96:4, and then pulverized and mixed in an Ex-mini jet mill (manufactured by M-Tech Chemical Co., Ltd.) at a feed rate of 3 g / min and an air pressure of 0.4 MPa to obtain a negative electrode mixture. After mixing, the resulting negative electrode mixture was passed through a 3-ton roll press at a temperature of 100°C, with the roll gap changed three times from 1 mm to 0.5 mm to 0.2 mm, to form a sheet with an average thickness of 180 μm (average basis weight: 15.5 mg / cm). 2 During this process, the above-mentioned "wall adhesion" and "thickness uniformity" were evaluated. This negative electrode mixture sheet was punched out to φ16 mm, laminated with 12 μm thick copper foil by pressing at 100° C. and 1 MPa, and then incorporated into an HS flat cell (manufactured by Hosen Co., Ltd.) in the following configuration to form a half cell. (composition) Working electrode: negative electrode mixture sheet Counter electrode: metallic lithium (Honjo Chemical Co., Ltd., 100 μm) Separator: GA55 (Advantec glass separator) Electrolyte: 1M LiPF6 / ethylene carbonate: dimethylene carbonate = 1:1 Impregnation conditions: -60 kPa, 3 min × 6 times (Evaluation) Using a charge-discharge evaluation device TOSCAT (manufactured by Toyo System Co., Ltd.), the capacity mAh / g when charging and discharging were repeated 5 cycles at 0.05C between 2.0 - 0.0V vs Li electrode was measured and taken as the initial capacity. After evaluating the initial capacity as above, the charge-discharge rate was increased to 0.5C and 20 cycles of charge-discharge were performed. Then it was returned to 0.05C again and 5 cycles of charge-discharge were performed. The capacity in the final cycle was confirmed as the capacity after cycling, and the capacity retention rate was calculated from the following formula. Capacity retention rate = Capacity after cycling / Initial capacity × 100 The evaluation criteria are as follows. A: 98% or more. B: Less than 98%.

[0212] [Example 1] [Preparation of PTFE-based resin] A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3480 g of deionized water, 100 g of paraffin wax, 15.75 g of CF3CF2OCF2CF2OCF2COONH4, and 35 mg of hydrophilic monomer D (Ammonium 2,3,3,3-tetrafluoro-2-[(1,1,2-trifluoro-2-propenyl)oxy]-Propanoate, structural formula: CH2=CFCF2OCF(CF3)COONH4). The autoclave was heated to 70°C and the atmosphere was purged with nitrogen gas to remove oxygen. TFE was introduced under pressure to adjust the system pressure to 0.78 MPaG, and the system temperature was maintained at 70°C with stirring. Next, an aqueous solution of 14.0 mg of ammonium persulfate dissolved in 20 g of water was introduced under pressure with TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 433 g of TFE had been consumed since the start of polymerization, an aqueous solution of 17.0 mg of hydroquinone (a radical scavenger) dissolved in 20 g of water was added under pressure with TFE. The polymerization continued, and when the amount of TFE polymerized reached 1,273 g from the start of polymerization, the stirring and TFE supply were stopped, and the gas in the system was immediately released to return to normal pressure, terminating the polymerization reaction and obtaining an aqueous dispersion. The resulting aqueous dispersion was removed, cooled, and the paraffin wax was separated to obtain an aqueous dispersion A containing a PTFE-based resin. The average primary particle size of the PTFE-based resin in the resulting aqueous dispersion A containing a PTFE-based resin was 295 nm, and the solids concentration was 26.5% by mass.

[0213] Next, aqueous dispersion A was diluted with water to a solids concentration of 13% by mass, and the PTFE resin was solidified while stirring in a container, and then the water was filtered off to obtain a wet PTFE resin. The water content of the wet PTFE resin was 40% by mass. The obtained wet PTFE resin was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 180° C. After 5 hours, the mesh tray was taken out and cooled in air to obtain PTFE-based resin 1A. The average particle size of PTFE resin 1A is 520 μm, the angle of repose is 47°, and the pore volume is 13.0 cm 3 / g, and the median pore diameter (volume) was 100 μm.

[0214] <Rotary kiln processing> The obtained PTFE-based resin 1A was subjected to rotary kiln treatment according to the following procedure. A rotary kiln (Motoyama RK-0330 with the heater removed and SUS304 tracing piping wrapped around it) and a chiller (Orion CLC250A, small chiller with water tank) were prepared, and an ethylene glycol aqueous solution was added to the chiller. The chiller temperature was set to -10°C, and PTFE-based resin 1A was fed into the rotary kiln of the rotary kiln and passed through it for treatment. The rotary kiln was rotated at a rotation speed of 7 rpm so that the residence time (treatment time) of PTFE-based resin 1A in the rotary kiln was 30 minutes. The PTFE-based resin 1A was introduced at a rate such that the filling rate of PTFE-based resin 1A in the rotary kiln was 10%, and the inclination angle of the rotary kiln with respect to the horizontal direction was 0.2°. After passing through the rotary kiln, the angle of repose of PTFE-based resin 1B was 32°, and the pore volume was 13.0 cm. 3 The SSG was 2.16 and the withstand voltage was 6 kV.

[0215] <Plasma treatment> The obtained PTFE-based resin 1B was further subjected to plasma treatment according to the following procedure. PTFE-based resin 1B was subjected to plasma treatment using a rotary tabletop vacuum plasma device YHS-DφS (manufactured by Sakigake Semiconductor) equipped with a rotating drum-type treatment tank with the rotation axis serving as a glow discharge electrode. A cooling tube was wrapped around the outside of the drum, and a -10°C refrigerant was circulated using a chiller circulation device. The pressure inside the treatment tank was set to 5 Pa, the atmosphere was Ar, and plasma was generated in the internal space while the tank was rotating. The rotation speed was 10 rpm, and the treatment was continued for 5 minutes with the rotation axis of the treatment tank tilted 20 degrees from the horizontal, yielding PTFE-based resin 1C. The angle of repose was 32°, and the pore volume was 0.5 cm. 3 / g, and the median pore diameter was 50 μm. The above evaluations were carried out using the obtained PTFE powder. The results are shown in Tables 1 and 2 (hereinafter, similarly shown in Tables 1 to 3).

[0216] Furthermore, when the proportion of each unit in PTFE-based resin 1C was measured by the above-mentioned method, the content of TFE units was 99 mass % or more relative to the total units of PTFE-based resin 1C.

[0217] [Examples 2 to 9] For the electrode mixture sheets of Examples 2 to 9, each electrode mixture sheet was obtained in the same procedure as in Example 1, except that the conditions were changed as shown in Table 1. In Example 5, neither rotary kiln treatment nor plasma treatment was performed. In Example 8, rotary kiln treatment was not performed but plasma treatment was performed. In Example 9, rotary kiln treatment was performed but plasma treatment was not performed. Furthermore, when the proportion of each unit in each PTFE-based resin was measured by the above-mentioned method, the content of TFE units in all PTFE-based resins was 99 mass % or more relative to the total units in each PTFE-based resin.

[0218] [Example 10] A 100 L stainless steel autoclave equipped with a baffle and a stirrer was charged with 70 g of C2F5OC2F4OCF2COONH4 (Ammonium perfluoro-3,6-dioxaoctanoate, hereinafter referred to as "APFDO"), 872 g of paraffin wax, and 59 L of deionized water. The autoclave was purged with nitrogen and then reduced in pressure. 2 g of CH2=CH-(CF2)4F (hereinafter referred to as "PFBE") and 300 g of deionized water were then added by suction. The autoclave was then pressurized with TFE and heated to 70 °C with stirring. The pressure was then increased to 1.765 MPa with TFE, and 5.0 g of disuccinic acid peroxide (80% by mass, remainder water) dissolved in 1 L of warm water at approximately 70 °C was added. Polymerization was then allowed to proceed while adding TFE to maintain the internal pressure of the autoclave at 1.765 MPa. APFDO was dissolved in warm water and added in total as APFDO, 125 g in total, during the polymerization. Ammonium sulfite was also dissolved in water and added in total as ammonium sulfite, 4 g in total, during the polymerization. The temperature was lowered to 65°C during the polymerization and raised to 90°C in the latter half of the polymerization. The reaction was terminated when the amount of TFE added reached 23 kg, and the TFE in the autoclave was released into the atmosphere. The resulting aqueous PTFE emulsion was cooled, and the supernatant paraffin wax was removed. The solids concentration of the aqueous PTFE emulsion was approximately 26% by mass. The amount of APFDO used was 8478 ppm by mass relative to the final PTFE yield. The amount of PFBE added was 0.0087% by mass relative to the final PTFE yield. The amount of coagulated material in the reactor was only traces. The average primary particle diameter of the PTFE microparticles was 250 nm. This aqueous PTFE emulsion was diluted with pure water to a concentration of 10% by mass, adjusted to 20°C, and stirred and coagulated to obtain a wet PTFE resin. This wet PTFE resin was then dried at 180°C. Rotary kiln treatment and plasma treatment were carried out in the same manner as in Example 1 to obtain PTFE resin 10C. PTFE resin 10C had an SSG of 2.14 and a withstand voltage of 10 kV.

[0219] [Example 11] A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-controlling jacket was charged with 3600 g of deionized water, 180 g of paraffin wax, 5.4 g of the ammonium salt of perfluoroethercarboxylic acid B (CF3CF2OCF2CF2OCF2COONH4), 0.108 g of succinic acid, and 0.0252 g of oxalic acid. The contents were heated to 70°C, and the atmosphere in the polymerization vessel was purged with nitrogen gas to remove oxygen. After maintaining the temperature at 70°C with stirring, TFE was introduced to adjust the pressure to 2.7 MPaG. While stirring the contents, deionized water containing 3.5 mg of potassium permanganate was continuously added at a constant rate, and TFE was continuously supplied to maintain a constant pressure of 2.7 MPaG in the polymerization vessel. When the TFE consumption reached 184 g, 3.8 g of the ammonium salt of perfluoroethercarboxylic acid B was added, and when the TFE consumption reached 900 g, the entire amount of deionized water containing 3.5 mg of potassium permanganate was added. When the TFE consumption reached 1,543 g, stirring and TFE supply were stopped, and the TFE in the polymerization vessel was purged to terminate the polymerization reaction and obtain a dispersion. The resulting dispersion was removed and cooled, and the paraffin wax was separated to obtain an aqueous dispersion containing a PTFE-based resin. The average primary particle size of the obtained aqueous dispersion containing the PTFE-based resin was 310 nm, and the solid content concentration of the aqueous dispersion was 30.6% by mass. The resulting aqueous dispersion was diluted to a solids concentration of 13% by mass, and nitric acid was added to the PTFE resin while stirring in a container to coagulate the PTFE resin, which was then filtered to separate the water, yielding a wet PTFE resin. The water content of the wet PTFE resin was 40% by mass relative to the total mass of the wet PTFE resin. The obtained wet PTFE resin was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm 2 The mesh tray was then heat-treated in a hot air circulating electric furnace at 180°C. After 5 hours, the mesh tray was removed and air-cooled to obtain PTFE-based resin 11A. Rotary kiln treatment and plasma treatment were carried out in the same manner as in Example 1 to obtain PTFE-based resin 11C of Example 11. PTFE-based resin 11C had an SSG of 2.15 and a withstand voltage of 4 kV.

[0220] [Example 12] In an environment with a dew point of -60°C or below, a sulfide solid electrolyte (Fine LPSCl manufactured by NEI) with an average particle size of 1 μm, lithium niobate-coated NCM111 particles (cathode active material) with an average particle size of 7 μm, a conductive additive, and PTFE resin 10C from Example 10 were mixed in a ratio of 20 parts by mass:75 parts by mass:2 parts by mass:3 parts by mass and formed into a sheet in the same manner as in <Preparation of Cathode Mix>. The obtained cathode mix sheet was evaluated for <wall adhesion> and <thickness uniformity>.

[0221] [Example 13] A positive electrode mixture sheet was produced in the same manner as in Example 12, except that PTFE resin 5C of Example 5 was used instead of PTFE resin 10C, and the positive electrode mixture sheet was evaluated for <wall surface adhesion> and <thickness uniformity>.

[0222] [Table 1]

[0223] [Table 2]

[0224] [Table 3]

[0225] As shown in Tables 1 to 3, it was confirmed that the use of the PTFE-based resin of the present invention resulted in a sheet with excellent thickness uniformity. Furthermore, a comparison of Examples 1 to 4 shown in Table 1 confirmed that when the PTFE-based resin pore median diameter is 10 μm or more, the wall surface adhesion is superior. Furthermore, a similar comparison confirmed that the above effect is also superior when the plasma treatment temperature is -50 to 0°C. Furthermore, as shown in Table 2, Examples 1 and 10, which had withstand voltages of 6 kV and 10 kV, respectively, had higher capacity retention rates than Example 11, which had a withstand voltage of 4 kV.< / ssg>

Claims

1. A polytetrafluoroethylene-based resin used as a binder for a secondary battery, The angle of repose is 32 to 44°, Pore ​​volume is 0.2 to 9.0 cm ３ / g of a polytetrafluoroethylene-based resin.

2. The polytetrafluoroethylene resin according to claim 1, wherein the median pore diameter is 10 μm or more.

3. The polytetrafluoroethylene resin according to claim 1 or 2, which has a withstand voltage of 5 kV or more.

4. An electrode mixture comprising the polytetrafluoroethylene resin according to claim 1 or 2 and an active material.

5. Further, the battery contains a sulfide-based solid electrolyte, 5. The electrode mixture according to claim 4, wherein the content of the polytetrafluoroethylene resin is 1 to 10 parts by mass per 100 parts by mass of the sulfide-based solid electrolyte.

6. The electrode mixture according to claim 4 , which is in the form of a sheet.

7. Further containing a conductive additive, The content of the polytetrafluoroethylene resin is 0.5 to 10% by mass relative to the total mass of the electrode mixture, The content of the active material is 88 to 99% by mass relative to the total mass of the electrode mixture, The electrode mixture according to claim 4, wherein the content of the conductive assistant is 0.5 to 10 mass% with respect to the total mass of the electrode mixture.

8. An electrode comprising: a current collector; and an electrode layer disposed on the current collector and comprising the electrode mixture according to claim 4.

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

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