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

Abstract

Provided is a polytetrafluoroethylene-based resin that is mixed with a living material or the like to produce an electrode binder and is excellent in the thickness uniformity of a sheet obtained using the electrode binder. 【Solution means】A polytetrafluoroethylene-based resin used as a binder for a secondary battery, having an angle of repose of 32 to 44° and a pore volume of 0.2 to 9.0 cm 3 / g, the polytetrafluoroethylene-based resin.

Description

Technical Field

[0001] The present invention relates to a polytetrafluoroethylene-based resin, an electrode binder, an electrode, and a secondary battery.

Background Art

[0002] Secondary batteries such as lithium-ion secondary batteries are used in small and 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, low memory effect, and the ability to achieve ultra-lightweight. They are also used as in-vehicle drive power sources and stationary large-scale power sources for automobiles.

[0003] The electrodes of non-aqueous electrolyte secondary batteries such as lithium-ion batteries are generally manufactured by applying an electrode binder containing an active material, a binder, etc. to a current collector. On the other hand, in recent years, for the purpose of reducing the environmental load during manufacturing and improving oxidation resistance, a dry method has been studied in which the electrode binder is stretched and formed into a sheet, and this sheet is bonded to a current collector to manufacture an electrode. In the case of the dry method, it is not necessary to use an organic solvent such as N-methyl-2-pyrrolidone.

[0004] Patent Document 1 discloses a polytetrafluoroethylene-based resin used as an electrode binder.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When the characteristics of a sheet obtained using an electrode binder containing a polytetrafluoroethylene-based 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. When the sheet thickness is not uniform, when charging and discharging as a secondary battery are repeated, an electric field may concentrate in the thin portion and short circuit easily.

[0007] An object of the present invention is to provide a polytetrafluoroethylene-based resin that is mixed with an active material or the like to produce an electrode binder and has excellent uniformity in the thickness of a sheet obtained using the electrode binder. Another object of the present invention is to provide an electrode binder, an electrode, and a secondary battery.

Means for Solving the Problems

[0008] As a result of intensive studies, 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, having an angle of repose of 32 to 44°, and a pore volume of 0.2 to 9.0 cm 3 / g, a polytetrafluoroethylene-based resin. 〔2〕 The polytetrafluoroethylene-based resin according to 〔1〕, having a pore median diameter of 10 μm or more. 〔3〕 The polytetrafluoroethylene-based resin according to 〔1〕 or 〔3〕, having a withstand voltage of 5 kV or more. 〔4〕 An electrode binder containing the polytetrafluoroethylene-based resin according to 〔1〕 or 〔2〕 and an active material. 〔5〕 Furthermore, containing a sulfide-based solid electrolyte, The electrode binder according to 〔4〕, wherein the content of the polytetrafluoroethylene-based resin is 1 to 10 parts by mass with respect to 100 parts by mass of the sulfide-based solid electrolyte. 〔6〕 The electrode binder according to 〔4〕 or 〔5〕, which is in a sheet form. [7] Furthermore, it contains a conductive auxiliary agent, wherein the content of the polytetrafluoroethylene-based resin is 0.5 to 10% by mass based on the total mass of the electrode binder, the content of the active material is 88 to 99% by mass based on the total mass of the electrode binder, and the content of the conductive auxiliary agent is 0.5 to 10% by mass based on the total mass of the electrode binder. The electrode binder according to any one of [4] to [6]. [8] An electrode comprising a current collector and an electrode layer containing the electrode binder according to any one of [4] to [7] disposed on the current collector. [9] A secondary battery comprising the electrode according to [8]. [Advantages of the Invention]

[0009] According to the present invention, it is possible to provide a polytetrafluoroethylene-based resin which is mixed with an active material or the like to produce an electrode binder, and which is excellent in the thickness uniformity of a sheet obtained by using the electrode binder. Further, according to the present invention, it is possible to provide an electrode binder, an electrode, and a secondary battery. [Embodiments for Carrying Out the Invention]

[0010] The meanings of the terms in the present invention are as follows. A numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another stepwise numerical range. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In this specification, each component may be used alone as one kind of substance corresponding to each component, or two or more kinds may be used in combination. Here, when two or more kinds of substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. The term "unit" is a general term for an atomic group derived from one molecule of the monomer, which is directly formed by polymerization of the monomer, and an atomic group obtained by chemically converting a part of the atomic group. The "unit based on the monomer" is hereinafter also simply referred to as "unit". The content (mass% or mol%) of each unit with respect to all the units contained in the polymer (polytetrafluoroethylene-based resin) is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR). Usually, the content of each unit calculated from the addition amount of each monomer is substantially consistent with the actual content of each unit.

[0011] [Polytetrafluoroethylene-based 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, having an angle of repose of 32 to 44° and a pore volume of 0.2 to 9.0 cm 3 / g.

[0012] The present inventors found that in a sheet obtained using a conventional electrode binder, the fluidity and the like are inferior, so that the uniformity of the sheet thickness is inferior. On the other hand, the present inventors surprisingly found that when the angle of repose and the pore volume of the PTFE-based resin are within a certain range, the dispersibility during mixing with the active material is improved, and as a result, a sheet having excellent fluidity and a uniform thickness can be manufactured. By making the sheet thickness uniform, it is expected to prevent the electric field from concentrating in the thin portion and being easily short-circuited when the charge and discharge of the secondary battery are repeated.

[0013] The form of the PTFE-based resin is not particularly limited, and examples thereof include granular and particulate forms, and the particulate form is preferred. Also, it may be in a powdery form in which granules and particles are aggregated. When the PTFE-based resin is particulate, 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, while suppressing the progress of fibrillation of the PTFE-based resin during mixing with the active material or the like, the average particle size of the PTFE-based resin can be reduced. The angle of repose of the PTFE-based resin can be measured by, for example, a known measurement method. For example, the powder of the PTFE-based resin to be measured is dropped from a funnel at a certain height onto a horizontal measurement table, and the bottom angle is calculated from the diameter and height of the generated conical deposit, and the above bottom angle can be used as the angle of repose. For example, it can be measured based on JIS-R931-2-2:1999 (equivalent international standard: ISO 920:1976). As a method for adjusting the angle of repose of the PTFE-based resin, for example, a method of performing a rotary kiln treatment in the production method of the PTFE-based resin described below can be mentioned. Specifically, when the treatment time of the rotary kiln treatment is lengthened, the angle of repose of the PTFE-based resin tends to become smaller. As another method, a method of cooling with a device capable of cooling while rotating, such as a rolling granulator or a fluid mixer, can be mentioned. The rotary kiln treatment is particularly preferable because excessive shear is less likely to be applied and the angle of repose is easy to adjust.

[0015] The pore volume of the PTFE-based resin is 0.2 to 9.0 cm 3 / g, preferably 0.4 to 8.0 cm 3 / g, more preferably 0.4 to 7.0 cm 3 / g. If the pore volume is within the above range, the intrusion of the active material and the conductive assistant into the pores of the PTFE-based resin is promoted and the disintegration of the PTFE-based resin is promoted, so that the mixability with the active material and the conductive assistant can be improved. The pore volume of the PTFE-based resin can be measured by, for example, the mercury intrusion method using a known analyzer (for example, AutoPoreIV 9520 manufactured by Micromeritics). As a method for adjusting the pore volume of the PTFE-based resin, for example, there is a method of performing plasma treatment in the method for producing the PTFE-based resin described below. Specifically, when the treatment time of the plasma treatment is lengthened, the pore volume of the PTFE-based resin tends to become smaller. As another method, microwave irradiation can be mentioned. Plasma treatment is particularly preferable because excessive heat is less likely to be applied and the pore volume is easy to adjust.

[0016] The average pore diameter of the PTFE-based resin is preferably 0.05 to 2.0 μm, more preferably 0.1 to 1.5 μm. The average pore diameter of the PTFE-based resin can be measured, for example, by the mercury intrusion method using a known analyzer. Specifically, when the pore volume is V (cm 3 / g) and the specific surface area is A (m 2 / g), the average pore diameter (μm) = 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 one-point method by the gas flow 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 nitrogen flow, and then using a nitrogen-helium mixed gas accurately adjusted so that the relative pressure value of nitrogen with respect to atmospheric pressure becomes 0.3.

[0017] The pore median diameter of the PTFE-based 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 adhesion. The upper limit is preferably 100 μm or less, more preferably 90 μm or less. The pore median diameter of the PTFE-based resin is the pore diameter when the cumulative value becomes 50% by volume of the pore volume in the pore distribution profile obtained by the mercury intrusion method using a known analyzer. As a method for adjusting the pore median diameter of the PTFE-based resin, for example, there is a method of adjusting the plasma treatment temperature in the method for producing the PTFE-based resin described below. Specifically, when the plasma treatment temperature is increased, the behavior of the pore median diameter changes, micro-melting of the PTFE-based resin occurs, and the change from larger pores to smaller pores of the PTFE-based resin is promoted, so the pore median diameter of the PTFE-based resin tends to decrease.

[0018] The charging voltage of the PTFE-based resin is preferably -2000 to -14000 V, more preferably -5000 to -12000 V, and even more preferably -200 to -3000 V in terms of better wall adhesion. If the charging voltage is within the above range, the PTFE-based resins repel each other due to electrostatic repulsion during the mixing step with the active material or the like, and the dispersibility can be improved. Also, the wall adhesion can be excellent. The charging voltage can be measured by a digital electrostatic potential measuring instrument MODEL KSD-1000 (manufactured by Kasuga Electric Co., Ltd.). The charging voltage can be adjusted by various ionizers and mechanical friction. When charging by applying mechanical friction, it can be efficiently charged by applying vibration in contact with a nylon material due to the relationship of the charging series. Among them, it is easy to adjust the charging voltage by charging the dried PTFE-based resin into a pot mill and rotating it at a speed of 10 to 50% of the critical rotation speed. The critical rotation speed means the rotation speed at which the contents are rotated with the container by centrifugal force, and is expressed by the following formula. N (critical rotation speed, unit: rpm) = 42.4 / √D (inner diameter of the container, unit: m)

[0019] In terms of improving the adhesion and 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 diameter is the volume-based median diameter obtained by a laser scattering method 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 diameter 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 even more preferably 2.130 to 2.180. Although SSG is used as a measure of the relative molecular weight, the lower the value, the higher the molecular weight. In addition, when the introduction amount of monomers other than tetrafluoroethylene in the PTFE-based resin is large, the amorphous structure further increases, the density decreases, and the SSG value tends to be small. Note that SSG is measured in accordance with ASTM D4895-10. Specifically, a 12.0 g sample is weighed and molded into a sample by holding it at 34.5 MPa for 2 minutes in a cylindrical mold with an inner diameter of 28.6 mm. This is placed in an oven at 290 °C and 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 for 12 hours in a desiccator at 23 °C, the specific gravity value of the molded product and water at 23 °C is measured, and this is taken as SSG.

[0022] The extrusion pressure in the extrusion test of the PTFE-based resin 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 by the following method. 100 g of a PTFE-based resin left standing at room temperature for 2 hours or more is placed in a glass bottle with an internal volume of 500 mL, 21.7 g of a lubricating oil (Isopar H (registered trademark), manufactured by Exxon) is added, and the mixture is obtained by mixing for 3 minutes. After leaving the obtained mixture in a constant temperature bath at 25°C for 2 hours, at 25°C under the conditions of a reduction ratio (the ratio of the cross-sectional area of the die inlet to the cross-sectional area of the outlet) of 100 and an extrusion speed of 51 cm / min, through an orifice with a diameter of 2.5 cm, a land length of 1.1 cm, and an introduction angle of 30°, paste extrusion is performed to obtain an extrusion bead (string-like object). The pressure required for extrusion at this time is measured and taken as the extrusion pressure (unit: MPa).

[0023] The withstand voltage of the molded body of the PTFE-based resin 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 at or above the above lower limit value, the electrochemical resistance of the PTFE-based resin increases, and the durability improves when the PTFE powder is used as the binder of the negative electrode. The upper limit value of the withstand voltage is not particularly limited, and it 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 by the following method. The detailed measurement method will be described in the examples. The withstand voltage varies depending on impurities contained, crystallinity, the presence or absence of monomer units other than tetrafluoroethylene, the molecular weight distribution of the PTFE-based resin, etc. Also, by not using nitric acid during the aggregation of the PTFE aqueous dispersion, impurities are reduced, and the withstand voltage tends to increase.

[0024] The water content of the PTFE-based 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, based on the total mass of the PTFE-based resin. The above water content is measured by the following method. The mass of the PTFE-based resin before and after heating at 150°C for 2 hours is measured and calculated according to the following formula. Three samples are taken, each calculated, and then the average is obtained and the average value is adopted. 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 and 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 below. Also, 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 below.

[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, 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").

[0029] (TFE units) PTFE-based resins are resins containing TFE units, and the content of TFE units 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, based on all the units of the resin. The upper limit is 100% by mass. Also, 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, based on all the units of the PTFE-based resin. The upper limit is 100 mol%.

[0030] (Units based on other monomers) The PTFE-based resin may contain units based on other monomers other than TFE units. Examples of other monomers include 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 ether; (fluoroalkyl)ethylene (FAE); and ethylene. Among them, as other monomers, HFP, VdF, FAE, or PAVE is preferable. Also, the other monomers may be monomers used in the method for producing PTFE powder described below.

[0031] As PAVE, the monomer represented by formula (PA) is preferable. CF2=CF-O-Rf 1 (PA) In formula (PA), Rf 1 represents a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms of the perfluoroalkyl group represented by Rf 1 is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3, from the viewpoint of more excellent 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] As the FAE, a monomer represented by formula (FA) is preferred. 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 from 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, relative to all 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 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less, relative to all units of the PTFE-based resin.

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

[0036] The content of each type of unit in the PTFE-based resin 19 can be measured by a known method such as the F-NMR (nuclear magnetic resonance analysis) method.

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

[0038] 〔Method for producing PTFE-based resin〕 The method for producing the PTFE-based resin is not particularly limited as long as it can produce the above-described PTFE-based resin. As a method for producing the PTFE-based resin, for example, a method for producing the PTFE-based resin including step A of obtaining an aqueous dispersion containing the PTFE-based resin and step B of obtaining the PTFE-based resin from the aqueous dispersion is preferable.

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

[0040] As the step of preparing the aqueous dispersion, a step of polymerizing a monomer that is a unit constituting the PTFE-based resin in an aqueous medium can be mentioned. The above monomer can be appropriately selected according to the desired PTFE-based resin. Examples of the polymerization method include known polymerization methods.

[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 the 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 only water.

[0043] (First monomer) The first monomer contains TFE. The first monomer may contain the other monomers described above other than TFE. The content of TFE is preferably 70 mol% or more, more preferably 80 mol% or more, still 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] Examples of the polymerization method of the first monomer include emulsion polymerization, solution polymerization, and suspension polymerization. It can be carried out by heating the above monomers in the presence of an aqueous medium and a polymerization initiator. An emulsifier may or may not be contained in the aqueous medium.

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

[0046] Examples of the oil-soluble radical polymerization initiator include dialkyl peroxydicarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate; peroxy esters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate; dialkyl peroxides such as di-t-butyl peroxide; di(ω-hydroxy-dodecafluorooctanoyl) peroxide, di(ω-hydroxy-tetradecafluorooctanoyl) peroxide, di(ω-hydroxy-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro-hexafluorobutyryl) peroxide, di(ω-chloro-decafluorohexanoyl) peroxide, di(ω-chloro-tetradecafluorooctanoyl) peroxide, ω-hydroxy-dodecafluorooctanoyl-ω-hydroxy-hexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydroxy-dodecafluorooctanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(tetrachloroundecafluorooctanoyl) peroxide, di(pentachlorotetradecafluorodecanoyl) peroxide, di(undecachlorodotriacontapentafluorodocosanoyl) peroxide, and di[perfluoro(or fluorochloro)acyl] peroxides;

[0047] As the water-soluble radical polymerization initiator, a water-soluble radical initiator or a water-soluble redox catalyst is preferable. Examples of the water-soluble radical initiator preferably include persulfates such as ammonium persulfate and potassium persulfate, water-soluble organic peroxides such as disuccinic peroxide, bisglutaric peroxide, and tert-butyl hydroperoxide. As the water-soluble redox catalyst, a combination of an oxidizing agent such as bromic acid or its salt, chloric acid or its salt, persulfuric acid or its salt, permanganic acid or its salt, hydrogen peroxide, etc., and a reducing agent such as sulfurous acid or its salt, bisulfite or its salt, thiosulfuric acid or its salt, organic acid, etc. is preferable. Among them, a combination of bromic acid or its salt and sulfurous acid or its salt (e.g., ammonium sulfite), and a combination of permanganic acid or its salt (e.g., potassium permanganate) and oxalic acid are more preferable. As the polymerization initiator, ammonium persulfate alone or a mixed system of a persulfate and disuccinic peroxide is preferable, and ammonium persulfate alone or a mixed system of ammonium persulfate and disuccinic peroxide is more preferable. The polymerization initiator may be used alone or in combination of two or more. Note that as the charging method of the polymerization initiator, the whole amount may be charged into the polymerization system before starting the polymerization reaction, or it may be added to the polymerization system continuously or intermittently.

[0048] The usage amount of the polymerization initiator is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and further preferably 0.01 to 2 parts by mass with respect to 100 parts by mass of the usage amount of the first monomer.

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

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

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

[0052] The decomposing agent for the polymerization initiator may be any compound that can decompose the polymerization initiator used. Examples 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 preferable, succinic acid, malonic acid, glutaric acid, adipic acid or pimelic acid is more preferable, and succinic acid is even more preferable.

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

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

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

[0057] <Step 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. It is preferable to obtain the PTFE-based resin by performing a coagulation treatment and a drying treatment on the aqueous dispersion. More preferably, a PTFE wet powder is obtained by performing a coagulation treatment on the aqueous dispersion, and then the PTFE-based resin is obtained by drying the PTFE wet powder.

[0058] Examples of the coagulation treatment include freeze coagulation, acid coagulation, base coagulation, mechanical coagulation, and coagulation using a coagulant. In the case of freeze coagulation, the coagulation temperature is preferably -20 to 0 °C. The coagulation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid coagulation, a method of adding a solution containing an acid to the aqueous dispersion is preferable. 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 preferable. The concentration of the acid in the solution containing the acid is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base coagulation, a method of adding a solution containing a base to the aqueous dispersion is preferable. Examples of the base to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferable. 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 coagulation with a coagulant, known coagulants can be used. Examples of known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, 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 can be mentioned, with alum being preferable and potassium alum where M is potassium being more preferable. As the coagulation method, acid coagulation or freeze coagulation is preferable.

[0059] As the drying treatment, a treatment for drying the PTFE wet powder obtained by the coagulation treatment is preferable. 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 longer, and preferably 3 hours or longer. The upper limit is preferably 100 hours or shorter, more preferably 50 hours or shorter, and even more preferably 30 hours or shorter. The drying time is preferably 1 to 100 hours, more preferably 1 to 50 hours, and even more preferably 3 to 30 hours. Also, the water content of the PTFE wet powder, which is the object 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 with respect to 100 parts by mass of the PTFE wet powder. The upper limit is preferably 150 parts by mass or lower, and more preferably 100 parts by mass or lower. The water content of the PTFE wet powder, which is the object 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 with respect to 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, an electric furnace such as a parallel flow box-type electric furnace, a vented box-type electric furnace, a vented conveyor-type electric furnace, a band electric furnace, a radiation conveyor-type electric furnace, a fluidized bed electric furnace, a vacuum electric furnace, a stirred electric furnace, an air flow type electric furnace, and a hot air circulation type electric furnace, or a steam furnace corresponding to the above (a device obtained by replacing the electric furnace in the device name of each of the above electric furnaces with a steam furnace) can be used. In terms of more efficiently removing moisture and unreacted monomers, etc., a parallel flow box-type electric furnace, a vented box-type electric furnace, a vented conveyor-type electric furnace, a band electric furnace, a fluidized bed electric furnace, a hot air circulation type electric furnace, or a steam furnace corresponding to the above (a device obtained by replacing the electric furnace in the device name of each of the above electric furnaces with a steam furnace) is preferred.

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

[0062] (Rotary kiln treatment) In the rotary kiln treatment, a PTFE-based resin is treated using a rotary kiln. By performing the rotary kiln treatment, the angle of repose can be adjusted. In the following, the rotary kiln treatment will be described. As described above, even if the treatment is performed using an apparatus that can be cooled while rotating, the angle of repose can be adjusted in the same manner. Examples of such an apparatus include a rolling granulator and a fluidized mixer. The method of the rotary kiln treatment is not particularly limited, but in a cylindrical rotary furnace that rotates around the central axis of the rotary kiln, the PTFE-based resin is rolled while being passed through the rotary furnace for treatment. Generally, a rotary kiln is an apparatus that treats while heating and fluidizing, but in the present invention, it is preferable to roll while contacting the resin of the system with the inner surface of the rotary furnace while cooling. The temperature during cooling 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 by more than -200 °C and equal to or lower than the glass transition temperature of the PTFE-based resin by -5 °C, still more preferably higher than -200 °C and equal to or lower than 10 °C, and particularly preferably -50 to 0 °C. If the PTFE-based resin is treated at the above temperature, while suppressing the fibrillation of the resin of the system, the denseness can be further increased, and the angle of repose of the PTFE-based resin can be decreased. As a result, the fluidity and the disintegratability during mixing are likely to increase. The inclination angle of the rotary furnace with respect to the horizontal direction (the grounding surface of the rotary kiln) is preferably 0.01 to 5°, more preferably 0.1 to 3°. If the rotary furnace is inclined at an inclination angle within the above range, the passing time of the PTFE-based resin in the rotary furnace (the residence time of the resin of the system in the rotary furnace) can be ensured to be sufficiently long. As a result, the PTFE-based resin can be treated more uniformly and sufficiently. The treatment time of the PTFE-based resin (the treatment time in the rotary furnace) is preferably 1 to 50 minutes, more preferably 5 to 40 minutes, and still more preferably 20 to 40 minutes in terms of being easy to adjust the angle of repose to an appropriate range. In this case, the cooling time and the rolling time of the PTFE-based resin can be sufficiently ensured. The rotation speed of the rotary furnace is preferably 1 to 20 rpm, more preferably 3 to 10 rpm. In this case, since it is difficult for excessive impact force to be applied to the PTFE resin, unintentional crushing and fibrillation of the PTFE resin during rolling (flowing) can be prevented. The charging speed of the PTFE resin into the rotary furnace is preferably a speed at which the filling rate of the PTFE resin in the rotary furnace is 0.1 to 40%, more preferably a speed at which it is 1 to 20%. In this case, the treatment of the PTFE resin can be carried out sufficiently and with high efficiency. Examples of the above rotary kiln include devices manufactured by Noritake Company Limited and devices manufactured by San-Ai Kacchu Co., Ltd. Instead of the heater covering the rotary furnace of these devices, a pipe can be wound in a spiral shape, and cooling can be achieved by flowing a cooling medium through it. In addition, in order to prevent condensation, it is preferable that the installation environment of this device has a dew point below the treatment temperature.

[0063] (Plasma treatment) The plasma treatment treats the PTFE resin using a plasma device. By carrying out the plasma treatment, the pore volume of the PTFE resin can be adjusted, and by appropriately applying the plasma treatment, the fine shape of the surface is likely to change. As described above, the pore volume of the PTFE resin can also be adjusted by performing microwave irradiation instead of the plasma treatment. The device and conditions used for plasma irradiation may be the devices and conditions commonly used for various industrially utilized plasma treatments. In many cases, the mechanism of industrial equipment that generates plasma ionizes gas by applying an electric field between electrodes in a reduced-pressure environment of 0.1 to 150 Pa. There are various forms of applying such an electric field in such a reduced-pressure environment, but it is often a DC discharge in which two electrodes, positive and negative, are placed in a dilute gas atmosphere and a voltage is applied. There is no particular limitation as long as it is a device capable of exposing the PTFE resin to the plasma generated by ionizing the atmospheric gas by a discharge phenomenon, but a device using glow discharge is preferable in terms of easily adjusting the micro pores on the particle surface of the PTFE resin.

[0064] From the perspective that the introduced PTFE-based resin and the plasma generated by glow discharge come into more uniform contact, a rotary tabletop vacuum plasma device equipped with a rotary drum-type treatment tank with a rotating shaft as the glow discharge electrode may be used. By rotating the treatment tank and generating plasma in its internal space, it is possible to irradiate the plasma uniformly on the particle surface of the PTFE-based resin while stirring the introduced PTFE-based resin. The rotation speed may be 10 to 100 rpm. The rotating shaft of the treatment tank may be horizontal or inclined. The method of plasma irradiation is not particularly limited, but effects can also be obtained by, for example, thinly placing the PTFE-based resin on a plane 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) can be microscopically dissolved or decomposed microscopically to adjust the pore volume, and it is easy to adjust to a suitable range.

[0065] As a cooling method, in the case of a drum-type treatment tank, a cooling tube can be arranged along the outer wall of the drum, and the inside of the chamber can be cooled by flowing a chiller. The temperature during cooling is preferably below the glass transition temperature of the PTFE-based resin, more preferably above the glass transition temperature of the PTFE-based resin - 200 °C and below the glass transition temperature of the PTFE-based resin - 5 °C, even more preferably above - 200 °C and below 10 °C, and particularly preferably - 50 to 0 °C in terms of easily adjusting the pore median diameter to a suitable range. For rotary plasma irradiation, for example, after introducing 250 to 300 g of the PTFE-based resin into the treatment tank, evacuation is performed with a vacuum pump to 5 Pa or less, and while maintaining the evacuated state by the pump, an atmospheric gas is introduced at a predetermined flow rate, adjusted so that the inside of the treatment tank is maintained in the range of 70 ± 10 Pa, and a voltage is applied between the electrodes in the range of 100 to 800 V.

[0066] <First Aspect> The manufacturing method of the PTFE-based resin may be the first aspect. A first aspect of a method for producing a PTFE-based resin is a method for producing a PTFE-based resin having step C, step D, and step 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 substantially 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. Further, the first aspect may further include the above-described other steps after step E.

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

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

[0069] As the non-fluorine-based monomer, a monomer represented by formula (NF) is preferable. Formula (NF) CH2=CR 11 -L 1 -R 12 R 11 represents a hydrogen atom or an alkyl group. The number of carbon atoms of the alkyl group is preferably 1 to 3, more preferably 1. L1 represents a single bond, -C(=O)-O-*, -O-C(=O)-* or -O-. * is R 12 and represents the bonding position with. For example, L 1 when is -C(=O)-O-*, formula (1) is CH2=CR 11 -C(=O)-O-R 12 represents. R 12 represents a hydrogen atom, an alkyl group, an alkenyl group or a nitrile group. However, when L 1 is a single bond, R 12 is a nitrile group. The number of carbon atoms in the alkyl group and the alkenyl group is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4. 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] As the monomer represented by the above formula (NF), a monomer selected from the group consisting of a monomer represented by formula (NF-1), a monomer represented by formula (NF-2), a monomer represented by formula (NF-3), and a monomer represented by formula (NF-4) is preferred. Formula (NF-1) CH2=CR 11 -C(=O)-O-R 13 Formula (NF-2) CH2=CR 11 -O-C(=O)-R 14 Formula (NF-3) CH2=CR 11 -O-R 15 Formula (NF-4) CH2=CR 11 -R 16 R 11 is defined as described above. R 13 represents a hydrogen atom, an alkyl group or an alkenyl group, and an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms is preferred. 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 the non-fluorine-based monomer 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-based monomer may be used alone or in combination of two or more. As the non-fluorine-based monomer, a monomer represented by the formula (NF-1) or a monomer represented by the formula (NF-2) is preferable, and R 13 A monomer represented by the formula (NF-1) in which is an alkyl group is more preferable. Since the monomer represented by the formula (NF-1) and the monomer represented by the formula (NF-2) have an ester group or a carboxy group which is a hydrophilic group, the monomer and its polymer have hydrophilicity. Therefore, particularly at a low concentration, it is considered that the monomer and its polymer are stably dispersed in an aqueous medium without requiring a surfactant.

[0072] - Specific polymer C - The specific polymer C is a polymer containing units based on a non-fluorine-based monomer. The specific polymer C usually contains only units based on a non-fluorine-based monomer, but may 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 examples thereof include TFE. The content of the unit based on the non-fluorine monomer in the specific polymer C is preferably 90% by mass or more, more preferably 95% by mass or more, based on all the units of the specific polymer C. The upper limit is 100% by mass.

[0073] -aqueous medium- Examples of the aqueous medium include the aqueous medium in the above-mentioned step A.

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

[0075] -Procedure of step C- In step C, the polymerization of the non-fluorine monomer is carried out in an aqueous medium. Specifically, it is preferable to mix the non-fluorine monomer and the aqueous medium and carry out the polymerization of the non-fluorine monomer in the obtained mixed solution. As described above, a fluorine monomer may be used in combination as necessary.

[0076] The usage amount of the non-fluorine monomer is preferably 200 mass ppm or less, more preferably 1 to 150 mass ppm or less, still more preferably 5 to 100 mass ppm, and particularly preferably 5 to 50 mass ppm, based on the supply amount of TFE (usage amount of TFE) used in step D described later. As for the charging method of the non-fluorine monomer, it is preferable to charge the whole amount into the polymerization system before starting the polymerization reaction, that is, initial batch addition.

[0077] The content of the non-fluorine monomer in the dispersion obtained by mixing the non-fluorine monomer and the aqueous medium is preferably 0.000015 to 0.0030% by mass, more preferably 0.000075 to 0.0023% by mass, based on the total mass of the dispersion. Since usually the whole amount of the non-fluorine monomer polymerizes to become the specific polymer C, the concentration of the specific polymer C in the obtained solution 1 falls within the above numerical range. The above non-fluorine monomer concentration and the concentration of the specific polymer C are the concentrations when the obtained solution 1 is used in step D without dilution with an aqueous medium. When the obtained solution 1 is diluted with an aqueous medium to obtain the above specific polymer C concentration and the diluted solution is used in step D, a high-concentration solution corresponding 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 0.2 to 1000% by mass, more preferably 0.2 to 500% by mass, based on the total amount of the non-fluorine 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 the non-fluorine monomers.

[0080] The polymerization temperature of the non-fluorine monomer is preferably 10 to 95°C, more preferably 50 to 90°C. The polymerization time is preferably 5 to 400 minutes, more preferably 5 to 300 minutes, and even more preferably 5 to 200 minutes. The pressure conditions during polymerization are preferably reduced pressure conditions or normal pressure conditions. Among them, 0 to 2.0 MPa is preferable, 0 to 1.0 MPa is more preferable, and 0 to 0.5 MPa is even more preferable. Also, the polymerization may be carried out with the atmosphere during polymerization being a TFE atmosphere. Usually, the polymerization of the non-fluorine monomer in the aqueous medium proceeds preferentially over the polymerization of TFE.

[0081] By the above step C, a solution 1 containing the 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 step D described later, although the specific polymer C is not an emulsifier, it is presumed that due to the balance of the interfacial tension with respect to both the aqueous medium and the PTFE-based resin, the specific polymer C exists at the boundary between the two and contributes to the dispersion stabilization of the PTFE-based resin in the aqueous medium. The average particle diameter of the particles of the specific polymer C is preferably 0.1 to 100 nm, more preferably 0.1 to 50 nm.

[0082] In addition, the solution 1 obtained in step C may contain unreacted non-fluorine monomers. Further, the atmosphere in the polymerization system of step C may be carried out under 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 be a polymer containing TFE units. Also, from another perspective, the PTFE particles obtained in step D are not limited to particles composed of a physical mixture of the specific polymer C and PTFE, but may also be particles containing a TFE copolymer having units based on non-fluorine monomers.

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

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

[0085] -Other monomers- In step D, other monomers other than TFE may be further used as long as the effects of the present invention are not impaired. Examples of other monomers include monomers having a polar group (hereinafter also referred to as "specific monomer D"). Since the polar group in the specific monomer D shows an interaction with the aqueous medium, it is presumed to be located between TFE and the aqueous medium during the polymerization of TFE and exhibit a surfactant-like function. As a result, the polymerization of TFE proceeds well and the occurrence of chain transfer is also 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 these, the group represented by the formula (A) or the group represented by the formula (B) is preferable, and the group represented by the formula (A) is more preferable in terms of further suppressing the formation of the fluorine-based oligomer. Formula (A) -SO3M Formula (B) -COOM In the formula (A) and the formula (B), M represents a hydrogen atom, NH4, or an alkali metal atom. Examples of the alkali metal atom 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 polymerizable groups is preferably 1 to 3, and more preferably 1. As the polymerizable group, an ethylenically unsaturated group is preferable. More specifically, an acryloyl group, a methacryloyl group, a vinyl ether group, a vinyl ester group, a vinyl group, and an allyl group can be mentioned, and an acryloyl group, a methacryloyl group, a vinyl ester group, or a vinyl ether group is preferable.

[0088] In terms of further suppressing the formation of the fluorine-based oligomer, as the specific monomer D, the monomer represented by the formula (3) is preferable. Formula (3) CR 31 R 32 =CR 33 -L 3 -R 34 In the 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 which may be substituted with a fluorine atom. Among these, a hydrogen atom or a fluorine atom is preferable in terms of better copolymerizability with TFE. The "alkyl group which may be substituted with a fluorine atom" means an alkyl group in which at least one hydrogen atom in the alkyl group may be substituted with a fluorine atom. The number of carbon atoms of the alkyl group which may be substituted with a fluorine atom is preferably 1 to 3, more preferably 1.

[0090] L 3 represents a single bond or a divalent linking group. Among them, a single bond is preferred in that the copolymerizability with TFE is better. Examples of the divalent linking group include a divalent hydrocarbon group, a divalent heterocyclic group, -O-, -S-, -SO2-, -C(O)-, -Si(R a )2-, -N(R b )-, and groups formed by combining two or more of these. R a represents an alkyl group (preferably having 1 to 10 carbon atoms) or a phenyl group. R b represents a hydrogen atom or an alkyl group (preferably having 1 to 10 carbon atoms). 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 an alkylene group. 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. In addition, an alkenylene group having 2 to 20 carbon atoms or an alkynylene group having 2 to 20 carbon atoms may also be used. Examples of the group formed by combining two or more of the above include -OC(O)-, -C(O)N(R b )-, an alkylene group -O- alkylene group, an alkylene group -OC(O)- alkylene group, and an alkylene group -Si(R a )2-phenylene group -Si(R a )2. Note that the above divalent hydrocarbon group may have a substituent. Examples of the substituent include a halogen atom (for example, a fluorine atom, a chlorine atom). That is, a hydrogen atom in the above 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] As the monomer represented by the formula (3), a monomer selected from the group consisting of a monomer represented by the formula (3-1), a monomer represented by the formula (3-2), a monomer represented by the formula (3-3), a monomer represented by the formula (3-4), a monomer represented by the formula (3-5), and a monomer represented by the formula (3-6) is preferable, and a monomer represented by the formula (3-1) is more preferable. 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), the definitions of R 31 ~R 34 are as described above. In formula (3-2), m1 represents an integer from 1 to 10. In formula (3-3), m2 represents an integer from 1 to 5. In formula (3-4), m3 represents an integer from 1 to 10. R 35 represents a fluorine atom or CF3. In formula (3-5), m4 represents an integer from 1 to 10. R 35 is defined as described above. In formula (3-6), m5 represents 0 or an integer from 1 to 10.

[0094] Specific examples of the specific monomer D include ammonium vinyl sulfonate. The specific monomer D may be used alone or in combination of two or more.

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

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

[0097] -Others- In step D, monomers other than TFE and specific monomer D may be used as long as the effects of the present invention are not impaired. However, in terms of more excellent various properties of the PTFE-based resin, the usage amount of TFE is preferably 99.5% by mass or more, more preferably 99.8% by mass or more, based on the total usage amount of the monomers used in step D.

[0098] -Procedure of step D- During step D, a surfactant is not substantially added to solution 1. That is, in step D, the 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 (for example, a polar group) and a hydrophobic group (for example, a hydrocarbon group). The definition of the polar group is the same as the definition of the polar group contained in specific monomer D. Examples of the surfactant include known surfactants, nonionic surfactants, and ionic surfactants. More specifically, hydrocarbon-containing surfactants and fluorine-based surfactants are included. The definition of the hydrocarbon-containing surfactant is as described later. In step D, it is preferable not to substantially add at least one selected from the group consisting of a hydrocarbon-containing surfactant and a fluorine-based surfactant to solution 1. The above "not substantially added" means that no surfactant is added, or even if added, the addition amount of the surfactant is 200 mass ppm or less based on the total mass of solution 1. The lower limit is not particularly limited, but 0 mass ppm is preferable. That is, in step D, it is preferable not to add a surfactant to solution 1.

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

[0100] When using the specific monomer D, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.150% by mass or less. That is, the amount of the specific monomer D charged relative to the total charged amount of TFE is preferably 0.150% by mass or less. From the viewpoint of the stability of the emulsion during polymerization, the amount of the 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 the molecular weight, the amount of the 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. In addition, when using two or more specific monomers D, the total amount of the specific monomers D used may be within the above range.

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

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

[0103] In addition, steps C and D may be continuously carried out in the same polymerization reaction vessel. In the production method of the present invention, it is only necessary that the specific polymer C is formed in step C, and step D may be carried out before all the non-fluorine monomers are consumed in step C.

[0104] By the above procedure, an aqueous emulsion in which the PTFE-based resin is dispersed in particulate form (aqueous emulsion containing the PTFE-based resin) is obtained. 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 with respect to 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 the turbidity of the condensate can be suppressed. The average primary particle diameter of the PTFE-based resin is preferably 100 to 500 nm, and more preferably 150 to 300 nm. The average primary particle diameter of the PTFE-based resin corresponds to D50 measured by a laser scattering method particle size distribution analyzer.

[0105] (Step E) Step E is a step of obtaining the PTFE-based resin from the aqueous emulsion obtained in step D. As step E, it can be carried out under the procedures and conditions in step B described above.

[0106] <Second Aspect> The production method of the PTFE-based resin may also be the following second aspect. The second aspect of the production method of the PTFE-based resin is a production method of the PTFE-based resin having step F and step 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 fluorine-containing polymer and an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin different from the first fluorine-containing polymer. Step G: A step of obtaining the PTFE-based resin from the aqueous dispersion obtained in step F. Also, the second aspect may further include the other steps described above after step E.

[0107] (Step 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 fluorine-containing polymer and an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin different from the above first fluorine-containing polymer.

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

[0109] -First fluorine-containing polymer- The first fluorine-containing polymer is presumed to solubilize the specific monomer F by adsorbing and incorporating the specific monomer F in the hydrophobic part during the polymerization of the specific monomer F, and adding a polymerization initiator thereto causes the specific monomer F to polymerize inside the particles of the first fluorine-containing polymer. Also, the first fluorine-containing polymer is presumed to contribute to the dispersion stabilization in the 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, more preferably 5 °C or lower, even more preferably 3 °C or lower, and particularly preferably 0 °C or lower from the viewpoint of efficiently adsorbing the specific monomer F. The Tg of the first fluorine-containing polymer is preferably -50 °C or higher, more preferably -45 °C or higher, and even more preferably -40 °C or higher from the viewpoint of the thermal stability after molding. The glass transition temperature of the first fluorine-containing polymer 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). Examples of the method for setting the Tg of the first fluorine-containing polymer within the above range include a method of adjusting the type and amount of monomers used in the production of the first fluorine-containing polymer.

[0111] The first fluorine-containing polymer preferably contains a TFE unit and a unit based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE") (hereinafter also referred to as "PAVE unit") in terms of being easily adjusted to the above range of Tg.

[0112] PAVE is preferred as the monomer represented by the above formula (PA) because it is excellent in polymerization reactivity when producing the first fluorine-containing polymer and can produce PTFE-based resins more efficiently. The monomer represented by formula (PA) has the same meaning as the monomer represented by formula (PA) in the above PTFE-based resin, and the preferred embodiments are also the same.

[0113] When the first fluorine-containing polymer contains TFE units and PAVE units, in the first fluorine-containing polymer, the PAVE units are preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and even more preferably 30 to 55 mol% based on the total of the TFE units and PAVE units, because it is easy to adjust the Tg within the above range and PTFE-based resins can be produced more efficiently.

[0114] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, but it is preferably substantially free of units based on other monomers in terms of more efficiently producing PTFE-based resins. Substantially free of units based on other monomers means that the content of units based on other monomers is 0.01 mol% or less based on the total units of the first fluorine-containing polymer, and 0 mol% is more preferred. When containing units based on other monomers, hexafluoropropylene is preferred as the other monomer.

[0115] Before starting the polymerization of the monomer used for the polymerization of the PTFE-based resin, the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass based on the total mass of the aqueous medium in the aqueous dispersion, and from the point of more efficiently producing the second fluorine-containing polymer, 0.01 to 0.6% by mass is preferred, and 0.01 to 0.5% by mass is more preferred.

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

[0117] Before starting the polymerization of the monomer used in the polymerization of the PTFE-based resin, the concentration of sulfate ions is preferably 10 mass ppm or less, more preferably 5 mass ppm or less, from the viewpoint of suppressing the coloring of the PTFE-based resin, based on the total mass of the aqueous medium in the aqueous dispersion. The lower limit may be 0 mass ppm. As an example of a method for setting the concentration of sulfate ions to the above value, a method of removing sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer can be mentioned. Here, sulfate ions are derived from, for example, the polymerization initiator (especially ammonium persulfate) used during the production of the first fluorine-containing polymer and may be contained in the aqueous dispersion containing the first fluorine-containing polymer. By the content of sulfate ions being 10 mass ppm or less (especially 5 mass ppm or less), it is presumed that the formation of end groups with low heat resistance in the PTFE-based resin is suppressed, and as a result, the coloring of the PTFE-based resin is suppressed.

[0118] Before starting the polymerization of the monomer used in the polymerization of the PTFE-based resin, the concentration of ammonium ions is preferably 20 mass ppm or less, more preferably 10 mass ppm or less, from the viewpoint of suppressing the aggregation of the PTFE-based resin, based on the total mass of the aqueous medium in the aqueous dispersion. The lower limit may be 0 mass ppm. As an example of a method for setting the concentration of ammonium ions to the above value, a method of removing ammonium ions using a cation exchange resin during the production of the first fluorine-containing polymer can be mentioned. Here, the ammonium ions are derived from, for example, an initiator (particularly ammonium persulfate) used in the production of the first fluorine-containing polymer, and may be contained in the aqueous dispersion containing the first fluorine-containing polymer. When the content of ammonium ions is 20 mass ppm or less, the ionic strength in the aqueous medium decreases, and as a result, it is presumed that the production efficiency of the PTFE-based resin is improved.

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

[0120] As a method for producing the first fluorine-containing polymer, a method of polymerizing a monomer (preferably a monomer mixture containing TFE and PAVE) in an aqueous medium in the presence of a polymerization initiator is preferable. Thereby, a first fluorine-containing polymer dispersed in a particulate form in the aqueous medium can be obtained. The aqueous medium in which the particles of the first fluorine-containing polymer thus obtained are dispersed may be used as it is as the above aqueous dispersion, or another aqueous medium may be further added and used as the above aqueous dispersion. Alternatively, the solvent may be replaced to disperse the first fluorine-containing polymer in another aqueous medium and used as the above aqueous dispersion.

[0121] As the polymerization initiator used in the production of the first fluorine-containing polymer, a water-soluble polymerization initiator is preferable, and persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, and organic polymerization initiators such as disuccinic peroxide and azobisisobutylamidine dihydrochloride are more preferable, persulfates are even more preferable, and ammonium persulfate is particularly preferable.

[0122] Examples of the aqueous medium used for producing the first fluorine-containing polymer include the aqueous medium in the above-described Step A. The aqueous medium contained in the aqueous dispersion may be the polymerization solvent used during the production of the first fluorine-containing polymer. Before initiating the polymerization of the monomer used for the polymerization of the PTFE-based resin, the content of the aqueous medium is preferably 60 to 99.9% by mass, more preferably 96 to 99.9% by mass, and even more preferably 98 to 99.9% by mass, relative to the total mass of the aqueous dispersion.

[0123] The production method of the first fluorine-containing polymer preferably includes a heating step of heating the aqueous medium in which the first fluorine-containing polymer is dispersed, after obtaining the aqueous medium. Thereby, since the polymerization initiator present in the system is deactivated, during the polymerization of the PTFE-based resin, it becomes less susceptible to the influence of the polymerization initiator used during the production of the first fluorine-containing polymer. As a result, it becomes easier to obtain a PTFE-based resin with a high molecular weight. From the viewpoint of further promoting the deactivation of the polymerization initiator in the aqueous medium, 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.

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

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

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

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

[0128] Specific examples of the 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 with respect to 100 parts by mass of the aqueous medium. Further, 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 still more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the amount of the specific monomer F described below. When the aqueous dispersion contains an emulsifier other than the fluorine-based emulsifier, the content of the emulsifier other than the fluorine-based emulsifier is preferably 0.01 to 5 parts by mass with respect 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 with respect 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 with respect to 100 parts by mass of the aqueous medium.

[0130] Before starting the polymerization of the monomer used for the polymerization of the PTFE-based resin, the concentration of the fluorine-based emulsifier is 100 mass ppm or less with respect to the total mass of the first fluorine-containing polymer in the aqueous dispersion. From the viewpoint of more excellent effects of the present invention, it is preferably 50 mass ppm or less, more preferably 25 mass ppm, and still more preferably 5 mass ppm or less. The lower limit is 0 mass ppm. A fluorine-based emulsifier means an emulsifier in which the hydrophobic part of the hydrophilic and hydrophobic parts of the emulsifier contains a fluorine atom. Specific examples of the fluorine-based emulsifier include fluorinated alkanoate and fluorinated ether carboxylic acid compounds. As an example of a method for setting the concentration of the fluorine-based emulsifier within the above range, a method for producing an aqueous dispersion without using a fluorine-based emulsifier can be mentioned.

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

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

[0133] Specific monomer F may contain a fluorine-containing monomer other than TFE, or may not substantially contain a fluorine-containing monomer other than TFE. Not substantially containing a fluorine-containing monomer other than TFE means that the usage amount of the fluorine-containing monomer other than TFE is 0.0001% by mass or less, based on the usage amount of specific monomer F, and may be 0% by mass. Examples of fluorine-containing monomers other than TFE include chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), vinylidene fluoride (hereinafter also referred to as "VdF"), fluoroalkyl ethylene, PAVE, and hexafluoropropylene. Fluorine-containing monomers other than TFE may be used in combination of two or more.

[0134] The specific monomer F may contain other monomers other than fluorine-containing monomers, but it is preferably free of other monomers. Substantially free of other monomers means that the usage amount of other monomers is 0.0001% by mass or less based on the usage amount of the specific monomer F, and 0% by mass is more preferable. Specific examples of other monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride. Other monomers may be used in combination of two or more.

[0135] The usage amount of the specific monomer F 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 with respect to 100 parts by mass of the aqueous medium contained in the above aqueous dispersion.

[0136] -Polymerization initiator- In the second aspect, 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 in the above step A.

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

[0138] -Other components- When polymerizing the specific monomer F, components other than the above (hereinafter also referred to as "other components") may be further used. Specific examples of other components include reducing agents. The usage amount of other components is preferably 1 to 2000 mass ppm with respect to 100 parts by mass of the specific monomer F.

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

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

[0141] The specific monomer F is introduced into the reaction system (that is, the polymerization reaction vessel) by a conventional method. For example, the specific monomer F may be continuously or intermittently introduced into the reaction system so that the polymerization pressure becomes a predetermined pressure. Alternatively, the specific monomer F may be dissolved in an aqueous medium, and the resulting solution may be continuously or intermittently introduced into the reaction system. 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 10 to 95 °C, more preferably 15 to 90 °C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1000 minutes, more preferably 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 and common surfactants. The substantial absence of an emulsifier means an environment where the content of the emulsifier is 0.03 mass ppm or less with respect to the total mass of the aqueous medium contained in the above aqueous dispersion, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm.

[0144] As described above, since 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, 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. Further, 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 still more preferably 1.0% by mass or more with respect to the total mass of the electrode binder. The upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, and still 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 still more preferably 1.0 to 10% by mass with respect to the total mass of the electrode binder. Within the above range, the retention of the active material and the mechanical strength of the electrode binder sheet are sufficient, the battery performance such as cycle characteristics is also good, and the decrease in battery capacity or conductivity can be more suppressed. Since the PTFE-based resin has excellent adhesion, even if the content is small, the active material can be sufficiently retained in the electrode binder.

[0149] <Active material> The electrode binder contains an active material. Examples of the active material include a positive electrode active material and a negative electrode active material, which can be appropriately selected according to the target electrode.

[0150] (Positive electrode active material) When the electrode binder is a positive electrode binder, the positive electrode binder contains a positive electrode active material. In addition to the PTFE-based resin and the positive electrode active material, the positive electrode binder may contain at least one selected from the group consisting of a binder other than the PTFE-based resin, a conductive material, a thickener, and an additive. As the positive electrode active material, a material that electrochemically intercalates and deintercalates lithium ions is used. 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 viewpoint of high average discharge voltage and cost advantage, the positive electrode active material may be a lithium-containing transition metal oxide.

[0151] A surface adherent material having a composition different from that of the positive electrode active material may be adhered to the surface of the positive electrode active material. Examples of the surface-attached 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] Examples of the shape of the particles of the positive electrode active material include massive, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar shapes. Further, 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, and more preferably 25 μm or less. d50 is preferably from 0.3 to 30 μm, more preferably from 0.5 to 30 μm, and even more preferably from 1.0 to 25 μm. When within the above range, high tap density products are easily obtained, or the diffusion time of lithium in the particles becomes appropriate, so that a decrease in battery performance can be more effectively suppressed. In terms of improving the filling property during the production of the positive electrode, two or more 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 by a known laser diffraction / scattering particle size distribution measuring device. When using LA-920 manufactured by HORIBA as the particle size distribution meter, as the dispersion medium used in the measurement, an aqueous solution of 0.1 mass% sodium hexametaphosphate is used, and after ultrasonic dispersion for 5 minutes, the measurement refractive index 1.24 is set for measurement.

[0155] The BET specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more, and more preferably 0.3 m 2 / g or more. The upper limit is preferably 50 m 2 / g or less, and preferably 30 m 2It is more preferable that it is below / g. The BET specific surface area of the positive electrode active material is 0.1 to 50 m 2 / g is preferable, and 0.3 to 30 m 2 / g is more preferable. The above BET specific surface area is defined as a value measured by the nitrogen adsorption BET one-point method by the gas flow 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 nitrogen flow, and then using a nitrogen-helium mixed gas accurately adjusted so that the relative pressure value of nitrogen with respect to atmospheric pressure becomes 0.3.

[0156] The positive electrode active material may be used alone or in combination of two or more. When using two or more positive electrode active materials, suitable combinations include LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Combinations with ternary systems such as O2; combinations of LiCoO2 with LiMn2O4 or those in which a part of this Mn is replaced with other transition metals, etc.; combinations of LiFePO4 with LiCoO2 or those in which a part of this Co is replaced with other transition metals, etc.

[0157] The content of the positive electrode active material is preferably 50 to 99.5% by mass, more preferably 80 to 99% by mass, based on the total mass of the electrode binder, 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 proceed with the occlusion and release of lithium ions, the desorption and insertion (intercalation) of lithium ions, or the doping and dedoping of the counter anion of lithium ions. Specifically, carbon-based materials such as lithium metal, 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 are mentioned.

[0159] As the negative electrode active material, a negative electrode active material containing silicon is preferable in terms of being able to produce a high-capacity battery. As the negative electrode active material containing silicon, silicon particles, particles having a structure in which fine silicon 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 are preferable. Silicon oxide is a general term for amorphous silicon oxides, and silicon oxide is represented by, for example, 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 cooling and depositing silicon monoxide gas generated by heating a mixture of silicon dioxide and metallic silicon.

[0160] The negative electrode active material containing silicon may be coated with carbon. By coating with carbon, conductivity can be imparted and battery characteristics can be improved. Examples of methods for imparting conductivity include a method of mixing with conductive particles such as graphite, a method of coating the surface of the negative electrode active material containing silicon with a carbon film, and a method of combining both. However, a method of coating with a carbon film is preferable, and a method of chemical vapor deposition (CVD) is more preferable.

[0161] Examples of the shape of the particles of the negative electrode active material include a massive shape, a polyhedral shape, a spherical shape, an ellipsoidal shape, a plate shape, a needle shape, and a columnar shape. Further, the negative electrode active material may be either primary particles or secondary particles.

[0162] The average particle diameter 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 diameter is the weight average particle diameter in the particle size distribution measurement by the laser diffraction method.

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

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

[0165] <Conductive aid The electrode mixture may contain a conductive aid. Examples of the conductive aid include metal materials such as copper and nickel; graphite (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; amorphous carbon such as needle coke, carbon nanotubes, fullerenes, and vapor-grown carbon fibers.

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

[0167] The electrode mixture is an electrode mixture containing a PTFE-based resin, an active material, and a conductive aid, wherein the content of the PTFE-based resin is 0.5 to 10% by mass based on the total mass of the electrode mixture, the content of the active material is 88 to 99% by mass based on the total mass of the electrode mixture, and the content of the conductive aid is preferably 0.5 to 10% by mass based on the total mass of the electrode mixture. More preferably, the content of the PTFE-based resin is 1 to 10% by mass based on the total mass of the electrode mixture, the content of the active material is 88 to 96% by mass based on the total mass of the electrode mixture, and the content of the conductive aid is 1 to 10% by mass based on the total mass of the electrode mixture.

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

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

[0170] <Other components> The electrode mixture may contain other components in addition to the above-described various components. As the other components, for example, at least one selected from the group consisting of a solid electrolyte, a binder other than the above, a conductive material, a thickener, and an additive may be included. Examples of the solid electrolyte include sulfide solid electrolytes having an argyrodite-type crystal structure, oxide solid electrolytes, and halogenated solid electrolytes. Examples of the binder include, as elastomers, styrene-butadiene rubber, acrylic rubber, styrene-ethylene-butadiene-styrene, and the like. Also, examples of the fiber component include cellulose, carboxymethyl cellulose, cellulose nanofiber, aramid fiber, and the like. In the case of the fiber component, it is preferably mixed as a powder, and if it is finely pulverized (microfibrillated) in advance by various pulverization methods, the miscibility with the PTFE powder is improved, which is preferable. By adding the fiber component, the strength of the formed sheet is likely to increase.

[0171] The electrode mixture preferably does not substantially contain an organic solvent. Specifically, the content of the organic solvent is preferably 1.0% by mass or less, more preferably 0.1% by mass or less, based on the total mass of the electrode mixture. The lower limit may be 0% by 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. In particular, the electrode mixture is suitable for lithium-ion secondary batteries. When used in a secondary battery, the electrode mixture is usually used in a sheet form.

[0174] [Manufacturing method of electrode mixture] The manufacturing method of the electrode mixture is not particularly limited as long as it can manufacture the above-mentioned electrode mixture. Among them, as a manufacturing method of the electrode mixture, a manufacturing method of the 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 auxiliary agent is preferable. With the above manufacturing method of the electrode mixture, the electrode mixture can be obtained in a relatively short process. Further, it is also preferable that the manufacturing method of the electrode mixture further includes a 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 can be obtained.

[0175] (Step X1) Step X1 is a step of mixing a binder containing a PTFE-based resin, an active material, and, if necessary, a raw material composition containing a conductive auxiliary agent. As a mixing method, a method of mixing using a mixing device is preferable. Examples of the mixing device 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 preferable in terms of achieving both the disintegration of the PTFE-based resin and the suppression of fibrillation. Examples of the jet mill include a collision type that pulverizes by colliding particles with each other or with a collision body (target), a swirling air flow type and a loop type that pulverize by mutual collision of particles in a pulverization zone formed by a plurality of pulverization nozzles arranged in a circulating air flow, a fluidized bed type that pulverizes by collision or friction between particles in a fluidized bed, and a supersonic type. Details of the collision type, swirling air flow type, loop type, and fluidized bed type jet mills are described on page 162 of "Advanced Pulverization Technology and Applications" edited by the Japan Resin Industry Technology Association and published by NGT Co., Ltd. Examples of impact jet mills include a mill that discharges a fluid such as compressed air from a nozzle and causes particles to collide with each other in a high-speed turbulent air flow formed in the jet mill for pulverization, and a mill that conveys resin particles with a high-speed air flow and causes them to collide with a collision body for pulverization.

[0176] Examples of commercially available jet mills include Cross Jet Mill (manufactured by Kurimoto Iron Works Co., Ltd.); Jet-O-Mill, A-O Jet Mill, Sanitary AOM, Co-Jet, Single Track Jet Mill, Super STJ Mill (all manufactured by Seishin Enterprise Co., Ltd.); Current Jet Mill (manufactured by Nisshin Engineering Co., Ltd.); Ulmax (manufactured by Nippon Catalytic Chemical Industries Co., Ltd.); Supersonic Jet Pulverizer PJM type, Supersonic Jet Pulverizer CPY type, Supersonic Jet Pulverizer LJ-3 type, Supersonic Jet Pulverizer I type (all manufactured by Nippon Pneumatic Mfg. Co., Ltd.); Counter Jet Mill, Micro Jet T type, Spiral Jet Mill, Micron Jet MJQ (all manufactured by Hosokawa Micron Corporation); Fluidized Bed Jet Mill (manufactured by Nippon Coke & Engineering Co., Ltd.); Nanogrinding Mill (manufactured by Tokuju Works Co., Ltd.), and EX-Mini Jet Mill (M-Tech Chemical). As a jet mill, a Single Track Jet Mill is preferable 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 terms of achieving both disintegration and suppression of fibrillation.

[0178] (Step 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 Step X2 include a method of rolling using a roll press, a flat plate press, a calendar roll, etc. The rolling conditions are not particularly limited and can be appropriately selected according to the thickness and density of the target electrode binder.

[0179] [Electrode] The electrode of the present invention includes a current collector and an electrode layer containing an electrode binder disposed on the current collector. A conductive carbonaceous material may be disposed between the current collector and the electrode layer as needed.

[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 aluminum, titanium, tantalum, stainless steel, and nickel, or alloys thereof; carbon materials such as carbon cloth and carbon paper. Metal materials are preferred, and aluminum or its alloy is more preferred. When the electrode is a negative electrode, examples of the current collector include metal materials such as copper, nickel, titanium, tantalum, and stainless steel, or alloys thereof; carbon materials such as carbon cloth and carbon paper. Metal materials are preferred, and copper, nickel, or their alloys are more preferred.

[0181] Examples of the shape of the current collector include, in the case of a metal material, metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, and foamed metal; in the case of a carbon material, carbon plate, carbon thin film, and carbon cylinder. Among these, the shape of the current collector is preferably metal foil. Note that the metal foil may be appropriately formed in a mesh shape. 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, it can have excellent handleability and strength.

[0182] Also, it is preferable that a conductive aid is applied to the surface of the current collector in terms of reducing the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of the conductive aid include noble metals such as carbon, gold, platinum, and silver.

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

[0184] The density of the positive electrode layer is preferably 3.00 g / cm 3 or more, more preferably 3.10 g / cm 3 or more, and even more preferably 3.20 g / cm 3 or more. The upper limit is preferably 3.80 g / cm 3 or less, more preferably 3.75 g / cm 3 or less, and even more preferably 3.70 g / cm 3 or less. The density of the positive electrode layer is preferably 3.00 to 3.80 g / cm 3 more preferably 3.10 to 3.75 g / cm 3 even more preferably 3.20 to 3.70 g / cm 3 is even more preferable. The density of the negative electrode layer is preferably 1.3 g / cm 3 or more, more preferably 1.4 g / cm 3 or more, and even more preferably 1.5 g / cm 3 or more. The upper limit is preferably 2.0 g / cm 3 or less, more preferably 1.9 g / cm 3 or less, and even more preferably 1.8 g / cm 3 or less. The density of the negative electrode layer is preferably 1.3 to 2.0 g / cm 3 more preferably 1.4 to 1.9 g / cm 3 even more preferably 1.5 to 1.8 g / cm 3 is even more preferable. Within the above range, the permeability of the electrolyte to the vicinity of the interface between the current collector and the active material is excellent, and the charge and discharge characteristics at a particularly high current density can be excellent. Also, the conductivity between the active materials can be excellent.

[0185] The thickness of the electrode layer (positive electrode layer and negative electrode layer) is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoints 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 layer 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 electrodes. The secondary battery may be a secondary battery using an electrolytic solution or a solid secondary battery. Examples of the secondary battery include non-aqueous secondary batteries such as non-aqueous electrolyte secondary batteries, all-solid-state batteries, and fuel cells. Specifically, 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 can be mentioned.

[0187] The secondary battery preferably includes a positive electrode, a negative electrode, an electrolytic solution, 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 a structure formed by bundling the metal core portions of each electrode layer and welding them to a terminal. When the secondary battery has a wound structure, a plurality of lead structures are provided on the positive electrode and the negative electrode respectively, and by bundling them to the terminal, the internal resistance can be reduced.

[0188] Examples of the shape of the secondary battery include a cylindrical shape, a rectangular shape, a laminate shape, a coin shape, and a large size shape. Note that the shapes and configurations of the positive electrode, the negative electrode, and the separator can be changed according to the shape of each battery and used.

[0189] Examples of the above separator include porous films such as polyethylene and polypropylene; and non-woven fabrics made of resins such as polypropylene, non-woven fabrics such as glass fiber non-woven fabrics, and the like. The material or shape of the separator is not particularly limited as long as it is stable in the electrolytic solution and has excellent liquid retention properties. Among them, the material of the separator is preferably a resin, glass fiber, or an inorganic substance. The shape of the separator is preferably a porous sheet or a non-woven fabric shape. 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] As the electrolyte, a non-aqueous electrolyte is preferred. Examples of the non-aqueous electrolyte include those obtained by dissolving a known electrolyte salt in a known organic solvent for dissolving the electrolyte salt. 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, fluoroether, and fluorinated carbonate. Examples of the electrolyte salt include LiClO4, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, LiFSI (LiN(SO2F)2), LiBOB (LiB(C2O4)2), LiDFOB (LiBF2(C2O4)), LiPF2(C2O4)2, LiPF4(C2O4), and LiN(SO2C2F5)2. In terms of good cycle characteristics, LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, or a combination thereof is preferred.

[0191] The solid secondary battery is preferably an all-solid-state secondary battery. The solid secondary battery is also 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 binder for the solid secondary battery may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0193] The above 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 above oxide-based solid electrolyte, a compound containing oxygen atoms, having ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and having 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 of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, 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 of C, S, Al, Si, Ga, Ge, In, 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 (However, 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 from 0 or more to 0.1 or less, and M ee represents a divalent metal atom. D 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 、Li3PO (4-3 / 2w) N w (w is w < 1), Li having a LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO4, La having a perovskite type crystal structure 0.51 Li 0.34 TiO 2.94 、La0.55 Li 0.35 TiO3, LiTi2P3O having a NASICON (Natrium super ionic conductor) 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 having a garnet crystal structure 12 (LLZ). Also, ceramic materials obtained by substituting elements in LLZ are also known. For example, LLZ-based ceramic materials obtained by substituting 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)) in LLZ are also included. Further, phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li3PO4), LiPON obtained by substituting part of the oxygen in lithium phosphate with nitrogen, LiPOD 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.) are included. Also, LiA 1 ON (A 1 is at least one selected from Si, B, Ge, Al, C, Ga, etc.) is also included. Specific examples include, for example, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2 and Li2O - Al2O3 - SiO2 - P2O5 - TiO2.

[0196] The above oxide-based solid electrolytes preferably contain lithium. The oxide-based solid electrolytes containing lithium are those used in solid batteries using lithium ions as carriers, and are preferable in terms of electrochemical devices having high energy density.

[0197] The above oxide-based solid electrolyte is preferably an oxide having a crystal structure. An oxide having a crystal structure is preferable in terms of good Li ion conductivity. Examples of the oxide having a crystal 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 (LLZ) etc.). Among them, the NASICON type is preferable.

[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 still more preferably 2 to 8 parts by mass with respect to 100 parts by mass of the sulfide-based solid electrolyte.

Examples

[0199] Hereinafter, the present invention will be described in detail with examples. Examples 1 to 4 and 10 to 12 are 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 methods and evaluation methods are as follows.

[0201] <Angle of Repose> The PTFE-based resin obtained in each of the examples described below was measured by the injection method using a multi-tester MT-02 (manufactured by Seishin Enterprise Co., Ltd.). In addition, the PTFE-based resin was sieved through a sieve with an aperture of 2360 μm in advance and then measured. Note that the above PTFE-based resin is intended to be the PTFE-based resin used in the electrode binder of each of the examples described below. For example, in Example 1, the angle of repose of the PTFE-based resin 1C was measured.

[0202] <Pore Volume and Pore Median Diameter> Regarding the PTFE-based resins obtained in each of the examples described below, measurements were carried out by the mercury intrusion method under the following conditions. 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> Regarding the aqueous dispersions obtained in each of the examples described below, measurements were carried out using a laser scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name "LA-920") with the aqueous dispersions as samples. 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 F-NMR analysis and infrared absorption spectrum analysis.

[0205] <Solid content concentration of aqueous dispersion> Regarding the solid content concentration of the aqueous dispersions obtained in each of the examples described below, after heating 2.0 g of the aqueous dispersion at 170 °C for 20 minutes, the mass of the residue was weighed, and the solid content concentration was calculated by the following formula. "Solid content concentration (mass%) = 100 × mass of 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, 12.0 g of the sample was weighed and formed into a sample by holding it at 34.5 MPa for 2 minutes using a cylindrical mold with an inner diameter of 28.6 mm. This was placed in an oven at 290 °C and heated at a rate of 120 °C / hr, held at 380 °C for 30 minutes, then cooled at a rate of 60 °C / hr and held at 294 °C for 24 minutes. After holding in a desiccator at 23 °C for 12 hours, the specific gravity value of the molded product and water at 23 °C was measured and taken as the SSG.

[0207] <Dielectric strength> The dielectric strength was measured in accordance with JIS K6892:1995. The specific procedure is as follows. The PTFE powder obtained in each example was left at a temperature of 25 ± 2 °C for 1 hour or more, then sieved well with a sieve having an opening of 1.7 mm at the above temperature, and 100 ± 0.1 g of the passed material was weighed as a 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 so as not to wet the wall of the container, stoppered, and shaken well for 3 minutes to mix the sample and toluene. The obtained mixture was placed in a preforming mold, gently pressed so that the moving speed of the push rod did not exceed 50 mm / min, and preformed by holding at a forming pressure of 0.98 MPa for 1 minute. The preformed product was taken out of 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 preformed product set was attached to a hydraulic press with a capacity of 3 tons, and the ram was moved at a speed of 5 - 10 mm / min to perform extrusion molding. The dimensions were an outer diameter of 5 mm and an inner diameter of 4 mm. Approximately 1 m was cut off after the molded product started to come out, and 15 pieces of the subsequent molded products were cut into lengths of 25 ± 1 cm with a sharp blade, inserted into the rod of the sample holder, and left at room temperature for 12 - 24 hours. Next, the sample holder was placed in an electric furnace maintained at 365 ± 5 °C, heated for 30 ± 3 minutes after the temperature in the furnace reached 365 ± 5 °C again for firing, then taken out and allowed to cool at room temperature. The obtained molded product was used as a test piece, a metal rod was inserted into the test piece as an internal electrode, and a metal foil was wound around the center as an external electrode. A high-voltage application lead wire was connected to the external electrode, and the internal electrode was grounded. The applied voltage was quickly increased to a predetermined voltage, and it was examined whether it could withstand this voltage for 1 minute. The predetermined voltage was increased by 1 kV at a time, and the maximum voltage that could be withstood for 1 minute was taken as the breakdown voltage.

[0208] <Preparation of Positive Electrode Composite> NMC622 (manufactured by Baokan Co., average particle size 10 μm, positive electrode active material), the PTFE-based resin of each example, and acetylene black (manufactured by Sigma Aldrich) were mixed at a mass ratio of 96:3:1, and pulverization and mixing were carried out with 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 an electrode composite (positive electrode composite). After the mixing was completed, the adhesion to the piping was visually confirmed during disassembly and cleaning. 50 g of the obtained electrode composite was passed through a roll press at a temperature of 90 °C and 3 t only once to form a sheet, and a positive electrode composite sheet with an average thickness of 200 μm was obtained.

[0209] <Wall Adhesion> After preparing the electrode composite by mixing the resin using a jet mill in <Preparation of Positive Electrode Composite>, the presence or absence of deposits on the piping and the container wall was visually confirmed, and the wall adhesion was evaluated according to the following evaluation criteria. "A": No deposits were seen. "B": Deposits were seen.

[0210] <Thickness Uniformity> The positive electrode mixture sheet obtained in <Production of Positive Electrode Mixture> was cut into pieces of 4.5 cm × 4.5 cm to obtain cut pieces. Next, from the 2.5 cm × 2.5 cm area excluding the 1 cm area from the peripheral edge of the obtained cut pieces, cutting into 0.5 cm × 0.5 cm was repeatedly performed to obtain a total of 25 measurement samples. The thickness at any one location of each measurement sample was measured, the X value was calculated according to the following formula, and the thickness uniformity was evaluated. From the obtained measured 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 according to the following evaluation criteria for the X value. A is considered qualified. X value (%) = 100 × (maximum value - minimum value) / arithmetic mean value "A": The X value is 10% or less. "B": The X value is more than 10% and 20% or less. "C": No sheet was obtained or holes occurred in the sheet, or the X value is more than 20%.

[0211] <Capacity Retention Rate> Graphite QC-6 (manufactured by Takizawa Shoten) and the PTFE-based resin of each example (Example 1, 10, and 11) were preliminarily mixed at a mass ratio of 96:4 using a V blender, and then pulverized and mixed using 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 the mixing was completed, the obtained negative electrode mixture was passed through a roll press at a temperature of 100°C and 3 t three times in the order of roll gap of 1 mm → 0.5 mm → 0.2 mm to form a sheet, and a negative electrode mixture sheet with an average thickness of 180 μm (average basis weight: 15.5 mg / cm 2 ) was obtained. In this process, the above <Wall Adhesion> and <Thickness Uniformity> were evaluated. This negative electrode mixture sheet was punched out to a diameter of 16 mm, laminated with a 12-μm-thick copper foil by pressing at 100°C and 1 MPa, and then incorporated into an HS flat cell (manufactured by Takizawa Shoten) with the following configuration to form a half cell. (Configuration) Working electrode: Negative electrode mixture sheet Counter electrode: Metallic lithium (100 μm, manufactured by Honjo Chemical Co., Ltd.) Separator: GA55 (glass separator manufactured by Advantec) 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 was measured when charging and discharging were repeated 5 cycles at 0.05C between 2.0 - 0.0V vs Li electrode, and this was taken as the initial capacity. After evaluating the initial capacity as described 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 Note that 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-regulating 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). While heating to 70°C, the inside of the autoclave was purged with nitrogen gas to remove oxygen. TFE was injected to set the internal pressure to 0.78 MPaG, and the internal temperature was maintained at 70°C while stirring. Next, an aqueous solution prepared by dissolving 14.0 mg of ammonium persulfate in 20 g of water was injected with TFE to initiate the polymerization reaction. As the polymerization reaction proceeded, the internal pressure decreased, but TFE was added to maintain the internal temperature at 70°C and the internal pressure at 0.78 MPaG. When 433 g of TFE had been consumed since the start of polymerization, an aqueous solution prepared by dissolving 17.0 mg of hydroquinone in 20 g of water was injected with TFE as a radical scavenger. Polymerization continued thereafter. When the polymerization amount of TFE reached 1273 g since the start of polymerization, stirring and the supply of TFE were stopped, and immediately the gas inside the system was released to normal pressure to terminate the polymerization reaction, obtaining an aqueous dispersion. The obtained aqueous dispersion was taken out, cooled, and the paraffin wax was separated to obtain an aqueous dispersion A containing a PTFE-based resin. The average primary particle diameter of the PTFE-based resin in the obtained aqueous dispersion A containing the PTFE-based resin was 295 nm, and the solid content concentration was 26.5 mass%.

[0213] Next, the aqueous dispersion A was diluted with water to a solid content concentration of 13 mass%, and while stirring in a container, the PTFE-based resin was coagulated and then separated from water by filtration to obtain a PTFE wet resin. The water content of the PTFE wet resin was 40 mass%. The obtained PTFE wet resin was placed on a stainless steel mesh tray (placement amount: 2.0 g / cm 2 ), and the mesh tray was heat-treated in a hot air circulation type electric furnace at 180°C. After 5 hours, the mesh tray was taken out, air-cooled, and PTFE resin 1A was obtained. 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 a 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 solution was poured into the chiller. The chiller was set at -10°C, and the PTFE-based resin 1A was fed into and passed through the rotary furnace of the rotary kiln for treatment. The rotary furnace was rotated at a rotation speed of 7 rpm so that the residence time (treatment time) of the PTFE-based resin 1A in the rotary furnace was 30 minutes. The PTFE-based resin 1A was fed at a rate such that the filling rate of the PTFE-based resin 1A in the rotary furnace was 10%, and the inclination angle of the rotary furnace with respect to the horizontal direction was 0.2°. The angle of repose of the PTFE-based resin 1B after passing through the rotary furnace 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 a 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 rotary drum-type treatment tank with the rotation axis 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 atmospheric pressure inside the treatment tank was set to 5 Pa, the atmosphere was Ar, and plasma was generated in the internal space while rotating. The rotation speed was 10 rpm, and the rotation axis of the treatment tank was tilted 20 degrees from the horizontal for 5 minutes to obtain PTFE-based resin 1C. The angle of repose was 32°, and the pore volume was 0.5 cm. 3 / g, and the pore median diameter was 50 μm. Using the obtained PTFE powder, the above evaluation was performed. The results are shown in Tables 1 and 2 (hereinafter, similarly shown in Tables 1 to 3).

[0216] Also, when the ratio of each unit in the PTFE-based resin 1C was measured by the above method, the content of the TFE unit was 99% by mass or more based on all the units of the PTFE-based resin 1C.

[0217] 〔Examples 2 to 9〕 Regarding the electrode binder sheets of Examples 2 to 9, each electrode binder sheet was obtained in the same procedure as in Example 1, except that the conditions shown in Table 1 were changed. Note that in Example 5, neither the rotary kiln treatment nor the plasma treatment was performed. In Example 8, the plasma treatment was performed without performing the rotary kiln treatment. In Example 9, the rotary kiln treatment was performed and the plasma treatment was not performed. Also, when the ratio of each unit in each PTFE-based resin was measured by the above method, in any of the PTFE-based resins, the content of the TFE unit was 99% by mass or more based on all the units of each PTFE-based resin.

[0218] 〔Example 10〕 Into a 100 L stainless steel autoclave equipped with a baffle plate and a stirrer, 70 g of C2F5OC2F4OCF2COONH4 (Ammonium perfluoro-3,6-dioxaoctanoate, hereinafter referred to as "APFDO"), 872 g of paraffin wax, and 59 liters of deionized water were charged. After the autoclave was purged with nitrogen and then depressurized, 2 g of CH2=CH-(CF2)4F (hereinafter referred to as "PFBE") and 300 g of deionized water were both aspirated and charged. Then, it was pressurized with TFE and heated to 70 °C while stirring. Next, the pressure was increased to 1.765 MPa with TFE, and 5.0 g of dicumyl peroxide (concentration 80% by mass, the rest being water) was dissolved in 1 liter of warm water at about 70 °C and injected. Then, polymerization was allowed to proceed while adding TFE so as to keep the internal pressure of the autoclave at 1.765 MPa. APFDO was dissolved in warm water and a total of 125 g of APFDO was added during the polymerization. Also, ammonium sulfite was dissolved in water and a total of 4 g of ammonium sulfite was added during the polymerization. The temperature was lowered to 65 °C in the middle and raised to 90 °C in the latter half of the polymerization. When the added amount of TFE reached 23 kg, the reaction was terminated, and the TFE in the autoclave was vented to the atmosphere. The obtained PTFE aqueous emulsion was cooled, and the supernatant paraffin wax was removed. The solid content concentration of the PTFE aqueous emulsion was about 26% by mass. The APFDO used was 8478 ppm by mass based on the final PTFE yield. Also, the added amount of PFBE was 0.0087% by mass based on the final PTFE yield. Also, the coagulum in the reactor was trace level. And the average primary particle diameter of the PTFE fine particles was 250 nm, This PTFE aqueous emulsion was diluted with pure water to a concentration of 10% by mass, adjusted to 20 °C, stirred and aggregated to obtain a PTFE wet resin. Then this PTFE wet resin was dried at 180 °C. Rotary kiln treatment and plasma treatment were carried out in the same manner as in Example 1 to obtain a PTFE resin 10C. The SSG of the PTFE resin 10C was 2.14 and the breakdown voltage was 10 kV.

[0219] 〔Example 11〕 Into a 6-liter stainless-steel autoclave equipped with a stainless-steel stirring blade and a temperature-regulating jacket, 3600 g of deionized water, 180 g of paraffin wax, 5.4 g of the ammonium salt of perfluoroether carboxylic acid B (CF3CF2OCF2CF2OCF2COONH4), 0.108 g of succinic acid, and 0.0252 g of oxalic acid were charged, and while heating to 70 °C, the inside of the polymerization tank was purged with nitrogen gas to remove oxygen. After maintaining the temperature inside the tank at 70 °C while stirring, TFE was introduced to a pressure of 2.7 MPaG. While stirring the contents, deionized water in which 3.5 mg of potassium permanganate was dissolved was continuously added at a constant rate, and TFE was continuously supplied so that the pressure inside the polymerization tank became constant at 2.7 MPaG. When the TFE consumption reached 184 g, 3.8 g of the ammonium salt of perfluoroether carboxylic acid B was added, and when the TFE consumption reached 900 g, the total amount of deionized water in which 3.5 mg of the above potassium permanganate was dissolved was added. When the TFE consumption reached 1543 g, stirring and TFE supply were stopped, the TFE inside the polymerization tank was purged, the polymerization reaction was terminated, and a dispersion was obtained. The obtained dispersion was taken out, cooled, the paraffin wax was separated, and an aqueous dispersion containing a PTFE-based resin was obtained. The average primary particle diameter 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 mass%. Further, the obtained aqueous dispersion was diluted to a solid content concentration of 13 mass%, nitric acid was added while stirring in a container to coagulate the PTFE-based resin, and then separated from water by filtration to obtain a PTFE wet resin. The water content of the PTFE wet resin was 40 mass% with respect to the total mass of the PTFE wet resin. The obtained PTFE wet resin was placed on a stainless-steel mesh tray (placement amount: 2.0 g / cm 2 ), and the mesh tray was heat-treated in a hot air circulation type electric furnace at 180 °C. After 5 hours, the mesh tray was taken out, air-cooled, and PTFE-based resin 11A was obtained. The rotary kiln treatment and plasma treatment were performed in the same manner as in Example 1 to obtain PTFE-based resin 11C of Example 11. The SSG of the PTFE-based resin 11C was 2.15, and the withstand voltage was 4 kV.

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

[0221] [Example 13] A cathode composite sheet was produced in the same manner as in Example 12, except that the PTFE resin 5C of Example 5 was used instead of the PTFE resin 10C, and the obtained cathode composite sheet was evaluated for <Wall 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 when the PTFE-based resin of the present invention was used, the obtained sheet was excellent in thickness uniformity. Further, from the comparison of Examples 1 to 4 shown in Table 1, it was confirmed that when the pore median diameter of the PTFE-based resin was 10 μm or more, the wall adhesion was more excellent. Also, from the same comparison, it was confirmed that when the temperature of the plasma treatment was -50 to 0°C, the above effects were more excellent. Furthermore, as shown in Table 2, in Examples 1 and 10 with withstand voltages of 6 kV and 10 kV respectively, the capacitance retention rate was higher than that of Example 11 with a withstand voltage of 4 kV.< / ssg>

Claims

1. A polytetrafluoroethylene-based resin used as a binder for a secondary battery, The content of units based on tetrafluoroethylene in the total units of the polytetrafluoroethylene-based resin is 99% by mass or more, The angle of repose is 32 to 44°, Pore ​​volume is 0.2 to 9.0 cm ３ / g polytetrafluoroethylene resin.

2. The polytetrafluoroethylene resin according to claim 1, having a median pore diameter of 10 μm or more and 100 μm or less.

3. A polytetrafluoroethylene-based resin used as a binder for a secondary battery, comprising: The angle of repose is 32 to 44°, The pore volume is 0.2 to 9.0 cm 3 / g; A polytetrafluoroethylene resin having a median pore diameter of 10 μm or more and 100 μm or less.

4. A polytetrafluoroethylene resin described in any one of claims 1 to 3, wherein a hollow cylindrical molded body having an outer diameter of 5 mm and an inner diameter of 4 mm has a withstand voltage of 5 kV or more.

5. An electrode mixture comprising the polytetrafluoroethylene resin according to any one of claims 1 to 3 and an active material.

6. Further, the present invention includes a sulfide-based solid electrolyte, The electrode mixture according to claim 5, 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.

7. The electrode mixture according to claim 5 , which is in the form of a sheet.

8. Further contains a conductive additive, The content of the polytetrafluoroethylene resin is 0.5 to 10% by mass based on the total mass of the electrode mixture, The content of the active material is 88 to 99% by mass based on the total mass of the electrode mixture, The electrode mixture according to claim 5, wherein the content of the conductive assistant is 0.5 to 10 mass% with respect to the total mass of the electrode mixture.

9. An electrode comprising: a current collector; and an electrode layer comprising the electrode mixture according to claim 5 disposed on the current collector.

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

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