JP2013177574A - Sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing material capable of retaining a high compression restorability and of retaining air tightness and liquid tightness of a container, even in a severe environment.SOLUTION: The sealing material consists of a fluorine-containing polymer having a polymerization unit based on tetrafluoroethylene and a polymerization unit based on one or more types of perfluoro (alkyl vinyl ether), wherein, for the fluorine-containing polymer, the polymerization unit based on the perfluoro (alkyl vinyl ether) is 4.0 mass% or less with respect to the total polymerization unit, and a melt flow rate is 1-100 g/10 min.

Description

The present invention relates to a sealing material. More specifically, the present invention relates to an electrolyte sealing material that can be suitably used for a secondary battery such as a lithium ion secondary battery.

Non-aqueous storage devices, such as non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries and non-aqueous electric double layer capacitors, normally seal the opening of the battery can body that contains the positive electrode, negative electrode, and electrolyte It has a sealed structure by sealing with the body. From the viewpoint of preventing a short circuit between the positive electrode and the negative electrode, the battery can body and the sealing body need to be electrically insulated. In addition, the non-aqueous electrolyte secondary battery is required to have high air tightness and liquid tightness in order to prevent leakage of contents such as the electrolyte and to prevent intrusion of air and moisture from the outside. It is done.

In order to maintain such battery airtightness, liquid tightness, and electrical insulation between the positive and negative electrodes, the battery can body and the sealing body are fixed via a sealing material. As the material of the sealing material, polyethylene, polypropylene, etc., which are conventionally excellent in chemical resistance, elasticity, creep resistance, good moldability and can be produced at low cost, are used. Since the demand for secondary batteries is expanding to applications used in harsh environments, fluororesins such as polytetrafluoroethylene (PTFE), which has better heat resistance and chemical resistance, are attracting attention. Yes. On the other hand, fluororesins such as PTFE are prone to creep phenomenon due to their materials, and are not suitable for use in places where a large load is applied. Various attempts have been made to use fluororesins as sealing materials. Has been done.

For example, with regard to sealing materials for sealing flanges of pipes and various devices, the creep phenomenon is made more advanced while ensuring the familiarity (followability) by controlling the porosity of the expanded porous PTFE sheet to be low. It is disclosed that a sealing material excellent in compression recovery characteristics can be obtained (see, for example, Patent Document 1).

In addition, regarding the sealing material used in places where high clamping pressure cannot be applied, such as glass tubes, a high compression rate and restoration rate can be achieved by applying a specific heat treatment to the sheet formed from the fluororesin powder and the inorganic filler. It is disclosed that the soft fluororesin sheet | seat which has is obtained (for example, refer patent document 2).

In addition, by using tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) whose fluorine content is specified as a sealing material for batteries such as lithium ion secondary batteries, moisture intrusion or It has been disclosed that leakage can be prevented (for example, see Patent Document 3).

JP 2008-184586 A Japanese Patent Laid-Open No. 5-8317 JP 2011-71003 A

As described above, various fluororesins for use in various sealing materials have been studied, and certain effects have been obtained in secondary batteries used in consumer electronic devices such as mobile phones and laptop computers. There is also.

However, in the case of a secondary battery for storing regenerative power, a secondary battery for accumulating wind power, an electric double layer capacitor for regenerative power, an in-vehicle lithium ion secondary battery, etc., it is large and has a large amount of current. Since it is large, internal heat generation is large due to internal resistance, and it is used under more severe conditions such as high temperature. Therefore, there is a possibility that the airtightness and liquid tightness inside the battery cannot be sufficiently maintained with the conventional sealing material.

In-vehicle secondary batteries are sometimes exposed to temperatures as high as 85 ° C or higher in the usage environment, and in order to maintain airtightness and liquid-tightness inside the battery, they are sealed even under such severe usage conditions. It is important that the stopper material retains sufficient compressibility and maintains high adhesion between the battery can body and the sealing body.
In this regard, the conventional sealing material has room for further improvement in performance.

The present invention has been made in view of the above-described situation, and provides a sealing material capable of maintaining excellent compression / restorability even in a harsh environment and maintaining the hermeticity and liquid tightness of a container. It is for the purpose.

In various investigations on a sealing material excellent in compression recovery, the present inventor has a polymer unit based on tetrafluoroethylene, and a fluoropolymer having a polymer unit based on perfluoro (alkyl vinyl ether) has an insulating property, We focused on the excellent basic characteristics required for sealing materials for secondary batteries, such as sealing properties, chemical resistance, and low moisture permeability. And, if the ratio of perfluoro (alkyl vinyl ether) in PFA and the melt flow rate are within a specific range, the resulting sealing material retains excellent compressibility even under high temperature conditions such as 85 ° C or higher. I found what I could do. Furthermore, when the sealing material is applied to a secondary battery such as a lithium ion secondary battery, cold flow (creep) can be sufficiently suppressed even under a severe environment such as a high temperature. As a result, the battery It was found that the internal gas tightness and liquid tightness can be maintained. And it has also been found that such a sealing material is particularly useful as a sealing material for a non-aqueous power storage device having a large capacity and a large energization amount, and the present invention has been achieved.

That is, the present invention is a sealing material comprising a fluoropolymer having a polymer unit based on tetrafluoroethylene and a polymer unit based on one or more types of perfluoro (alkyl vinyl ether), wherein the fluoropolymer Has a polymerization unit based on perfluoro (alkyl vinyl ether) of 4.0% by mass or less based on the total polymerization unit and a melt flow rate of 0.1 to 100 g / 10 min. It is a stopping material.
The present invention is described in detail below.

The sealing material of the present invention comprises a fluoropolymer having polymerized units based on tetrafluoroethylene [TFE] and polymerized units based on one or more types of perfluoro (alkyl vinyl ether) [PAVE].

As the PAVE, the following general formula:
CF ₂ = CF-ORf ¹
(Wherein Rf ¹ represents a perfluoroalkyl group having 1 to 5 carbon atoms) is preferred.

Specific examples of the PAVE include perfluoro (methyl vinyl ether) [PMVE], perfluoro (ethyl vinyl ether) [PEVE], perfluoro (propyl vinyl ether) [PPVE], perfluoro (butyl vinyl ether) and the like. 1 type, or 2 or more types of these can be used. PAVE is advantageous in that the side chain (the site represented by -ORf ¹ in the above formula) is longer in terms of improving the compression recovery property of the obtained sealing material and suppressing cold flow. The longer the chain, the more expensive and the manufacturing costs will increase. In the present invention, various types of PAVE can be used, but PPVE is preferably used from the viewpoint described above.

In the fluoropolymer, the polymerized unit based on the PAVE is 4.0% by mass or less based on the total polymerized units. Thereby, the obtained sealing material has an excellent compression recovery property even in a high temperature environment, and cold flow at a high temperature can be sufficiently suppressed. As a result, even in a harsh environment, a battery or the like using the sealing material can maintain sufficient airtightness and liquid tightness. More preferably, it is 3.7 mass% or less, More preferably, it is 3.5 mass% or less, Most preferably, it is 3.0 mass% or less.
The content of polymerized units based on PAVE in the fluoropolymer can be measured by ¹⁹ F-NMR method.
When two or more types of TFE-PAVE copolymers are used in combination, or when other fluorine-containing polymers such as TFE homopolymers are used in combination with TFE-PAVE copolymers, these It is preferable that the content of PAVE units in the mixture is in the above-mentioned range. The content of PAVE units in the above mixture can also be measured by ¹⁹ F-NMR method.

The polymer unit based on the PAVE is preferably 1.0% by mass or more based on the total polymer units. More preferably, it is more than 1.0 mass%, More preferably, it is 1.5 mass% or more, Especially preferably, it is 2.0 mass% or more, Most preferably, it is 2.5 mass% or more.

The fluoropolymer may further include a polymer unit based on a monomer copolymerizable with TFE and PAVE, in addition to a polymer unit based on TFE and a polymer unit based on PAVE. Examples of the monomer include ethylene, vinylidene fluoride [VdF], hexafluoropropylene [HFP], CX ¹ X ² = CX ³ (CF ₂ ) _n X ⁴ (wherein X ¹ , X ² and X ³ are , The same or different, each represents a hydrogen atom or a fluorine atom, X ⁴ represents a hydrogen atom, a fluorine atom or a chlorine atom, and n represents an integer of 1 to 10, and CF ₂ = CF—OCH ₂ —Rf ² (wherein Rf ² represents a perfluoroalkyl group having 1 to 5 carbon atoms), and the like. Among them, HFP It is preferable that

As the alkyl perfluorovinyl ether derivative, those in which Rf ² is a perfluoroalkyl group having 1 to 3 carbon atoms are preferable, and CF ₂ = CF—OCH ₂ —CF ₂ CF ₃ is more preferable.

In the fluoropolymer, the polymer units based on monomers copolymerizable with TFE and PAVE are preferably 0 to 10% by mass with respect to the total polymer units. More preferably, it is 0-5 mass%. Most preferably, it is 0% by mass, that is, the fluorine-containing polymer is composed only of TFE and PAVE.

The fluoropolymer may further contain a fluoropolymer other than those described above (hereinafter also referred to as other fluoropolymers). Examples of other fluorine-containing polymers include TFE polymers and TFE-HFP copolymers. The content of the other fluoropolymer is preferably 30% by mass or less with respect to the total amount of the fluoropolymer.

Above all, the fluoropolymer is preferably a copolymer of TFE and PAVE (PFA). That is, it is one of the preferred embodiments of the present invention that the fluoropolymer is a PFA having a polymer unit based on TFE and one or more polymer units based on PAVE.

The fluorine-containing polymer can be obtained by a conventionally known polymerization method such as suspension polymerization, solution polymerization, emulsion polymerization, bulk polymerization and the like. In the above polymerization, each condition such as temperature and pressure, polymerization initiator, chain transfer agent, solvent and other additives can be appropriately set according to the composition and amount of the desired fluoropolymer.

As said polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical initiator can be used.

The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, such as diisopropyl peroxydicarbonate (IPP), dinormal propyl peroxydicarbonate (NPP), disec-butyl peroxydi. Dialkyl peroxycarbonates such as carbonate, peroxyesters such as t-butylperoxyisobutyrate and t-butylperoxypivalate, dialkylperoxides such as di-t-butylperoxide, etc. (Ω-hydro-dodecafluoroheptanoyl) peroxide, di (ω-hydro-tetradecafluoroheptanoyl) peroxide, di (ω-hydro-hexadecafluorononanoyl) peroxide, di (perfluorobutyryl) Peroxide, di ( -Furpaleryl) 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-hydro-dodecafluoroheptanoyl-ω-hydro Hexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di (dichroic) Pentafluorobutanoyl) peroxide, di (trichlorooctafluorohexanoyl) peroxide, di (tetrachloroundecafluorooctanoyl) peroxide, di (pentachlorotetradecafluorodecanoyl) peroxide, di (undecachloro) Typical examples include dotriacontafluorodocosanoyl) peroxide di [perfluoro (or fluorochloro) acyl] peroxides and the like.

The water-soluble radical polymerization initiator may be a known water-soluble peroxide, for example, ammonium salts such as persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, percarbonate, potassium salts, sodium salts. , T-butyl permaleate, t-butyl hydroperoxide and the like. A reducing agent such as sulfites and sulfites may be used in combination with the peroxide, and the amount used may be 0.1 to 20 times the peroxide.

Examples of the chain transfer agent include hydrocarbons such as ethane, isopentane, n-hexane, and cyclohexane; aromatics such as toluene and xylene; ketones such as acetone; and acetates such as ethyl acetate and butyl acetate; Examples include alcohols such as methanol and ethanol; mercaptans such as methyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, chloroform, methylene chloride, and methyl chloride. The amount added may vary depending on the size of the chain transfer constant of the compound used, but is usually used in the range of 0.01 to 20 parts by weight with respect to the polymerization solvent.

Examples of the solvent include water, a mixed solvent of water and alcohol, and the like.

In the suspension polymerization, a fluorine-based solvent may be used in addition to water. Examples of the fluorine-based solvent include hydrochlorofluoroalkanes such as CH ₃ CClF ₂ , CH ₃ CCl ₂ F, CF ₃ CF ₂ CCl ₂ H, CF ₂ ClCF ₂ CFHCl; CF ₂ ClCFClCF ₂ CF ₃ , CF ₃ CFClCFClCF _3, etc. Perfluoroalkanes such as perfluorocyclobutane, CF ₃ CF ₂ CF ₂ CF ₃ , CF ₃ CF ₂ CF ₂ CF ₂ CF ₃ , CF ₃ CF ₂ CF ₂ CF ₂ CF ₂ CF ₃ , etc. Among them, perfluoroalkanes are preferable. The amount of the fluorine-based solvent used is preferably 10 to 100 parts by weight with respect to the aqueous medium from the viewpoint of suspendability and economy.

It does not specifically limit as polymerization temperature, It may be 0-100 degreeC. The polymerization pressure is appropriately determined according to other polymerization conditions such as the type, amount and vapor pressure of the solvent to be used, the polymerization temperature, etc., but may usually be 0 to 9.8 MPaG.

The fluorine-containing polymer has a melt flow rate (MFR) of 0.1 to 100 g / 10 minutes. Thereby, the compression restoring property at the time of high temperature can be improved, maintaining favorable moldability. As said MFR, 0.1-16 g / 10min is preferable, 0.1-10 g / 10min is more preferable, 1.5-5 g / 10min is still more preferable.
The said MFR shows the value at the time of implementing on condition of 372 degreeC and a 5-kg load using a melt indexer (made by Toyo Seiki Seisakusho).

The fluorinated polymer preferably has a melting point of 305 to 320 ° C. More preferably, it is 306-317 degreeC, More preferably, it is 307-315 degreeC.
The fluoropolymer may have a plurality of melting points.
The said melting | fusing point is calculated | required as temperature corresponding to the maximum value in a heat of fusion curve when it heats up at a speed | rate of 10 degree-C / min using DSC apparatus (made by SII nanotechnology Co., Ltd.).

The fluorine-containing polymer preferably has a weight average molecular weight of 200,000 to 2,000,000. More preferably, it is 300,000 to 1,500,000, and still more preferably 400,000 to 1,000,000.
The said weight average molecular weight calculates | requires the zero shear viscosity in 340 degreeC of the compression molding sheet | seat of sample thickness 0.5mm using melt viscoelasticity measuring apparatus MCR-500 (made by Anton Paar). The viscosity is substituted into the zero shear viscosity of the calculation formula (see the following formula) represented by “Macromolecules 1985, 18, 2023-30”, and the weight average molecular weight is calculated.
η ₀ = 2.04 × 10 ⁻¹² × Mw
η ₀ : Zero shear viscosity Mw: Weight average molecular weight

The sealing material of this invention may further contain other components other than the said fluoropolymer. Examples of other components include fillers, plasticizers, pigments, colorants, antioxidants, ultraviolet absorbers, flame retardants, anti-aging agents, antistatic agents, and antibacterial agents.

Among these other components, a filler is preferable. Examples of the filler include silica, kaolin, clay, organic clay, talc, mica, alumina, calcium carbonate, calcium terephthalate, titanium oxide, calcium phosphate, calcium fluoride, lithium fluoride, crosslinked polystyrene, potassium titanate, Examples thereof include carbon, boron nitride, carbon nanotube, and glass fiber. Among these, boron nitride is preferable.

As described above, the sealing material of the present invention can further contain various additives in addition to the fluoropolymer. However, from the viewpoint of fully exhibiting the characteristics based on the above-mentioned fluoropolymer, it is preferable that the content of the additive is small, and it is most preferable that the additive is not included. Specifically, it is preferable that an additive is 30 mass% or less with respect to the sealing material of this invention. More preferably, it is 10% by mass or less, and most preferably 0% by mass, that is, no additive is contained.
It is one of the preferred embodiments of the present invention that the sealing material is composed only of the fluoropolymer.

The encapsulating material of the present invention can be produced by molding the encapsulating material composition comprising the above fluoropolymer or the above fluoropolymer and an additive into a desired shape and size. .

As the method for producing the composition for a sealing material, a method of mixing the powder comprising the fluoropolymer with the additive in a dry manner, or mixing the fluoropolymer and the additive in advance with a mixer, And a kneading method using a kneader or a melt extruder.

The method for molding the fluoropolymer or the sealing material composition is not particularly limited, and examples thereof include an injection molding method, an extrusion molding method, a compression molding method, and a blow molding method.

The sealing material of the present invention has an excellent compression recovery property even in a high temperature environment.

The sealing material preferably has a restoration rate at 85 ° C. of 10.0% or more. When the sealing material has such a restoration rate, the airtightness and liquid tightness of the container using the sealing material can be sufficiently maintained even under a high temperature environment. More preferably, it is 12% or more, More preferably, it is 15% or more.
The restoration rate is a value measured at 85 ° C. by a measurement method based on ASTM D395, and will be described in detail later.

The size and shape of the sealing material may be appropriately set depending on the application, and are not particularly limited.

As described above, since the sealing material of the present invention is excellent in characteristics at high temperatures, it exhibits particularly excellent effects when used in an environment at high temperatures. Specifically, the sealing material is preferably used in an environment where the maximum temperature is 50 ° C. or higher. More preferably, it is used in an environment where the maximum temperature is 70 ° C. or higher.

Since the sealing material of the present invention can maintain the airtightness and liquid-tightness of the container using the sealing material even in a high temperature environment, the various sealing devices used in the high temperature environment It can be used as a sealing material for piping. Among them, it is preferably used as a sealing material for non-aqueous storage devices such as non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries and non-aqueous electric double layer capacitors, and particularly as a sealing material for lithium ion secondary batteries. It is preferable to use it. Further, the sealing material of the present invention is preferably used as a sealing material for non-aqueous power storage devices for vehicles such as automobiles and trains that are likely to be used at high temperatures, and is particularly applicable to lithium ion secondary batteries for vehicles. Is preferred.

The present invention is also a non-aqueous electrolyte secondary battery including the sealing material of the present invention.

As the configuration other than the sealing material of the nonaqueous storage device such as the nonaqueous electrolyte secondary battery such as the lithium ion secondary battery or the nonaqueous electric double layer capacitor, a conventionally known one may be adopted.

The non-aqueous electrolyte secondary battery includes, for example, a positive electrode, a negative electrode, a positive electrode current collector, a negative electrode current collector, a non-aqueous electrolyte solution, a separator, an overcurrent prevention element, a positive electrode terminal, a negative electrode terminal, or both The positive electrode terminal, the negative electrode terminal, or both are attached to the battery lid via the sealing material of the present invention. As a result, the battery can be sealed at the same time as the case and the electrode are insulated while ensuring electrical continuity with the current collector inside the battery.

The positive electrode material used for the positive _{electrode, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Co b V 1-b O z, Li x Co b _{Fe 1-b O 2, Li} x Mn 2 O 4, Li x Mn c Co 2-c O 4, Li x Mn c Ni 2-c O 4, Li x Mn c V 2-c O4, Li x Mn c Fe _{2-c O 4} (wherein x = 0.02~1.2, a = 0.1~0.9, b = 0.8~0.98, c = 1.6~1.96, z = 2.01 to 2.3).

Examples of the negative electrode material used for the negative electrode include compounds represented by the following general formula.
M ¹ M ² _p M ⁴ _q M ⁶ _r
In the formula, M ¹ and M ² are different and are at least one selected from Si, Ge, Sn, Pb, P, B, Al, and Sb. M ⁴ is at least one selected from Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. M ⁶ is at least one selected from O, S, and Te. p and q are 0.001-10, respectively. r is 1.00-50.

Examples of the material of the positive electrode or the positive electrode current collector include aluminum, stainless steel, nickel, titanium, or an alloy thereof. The material of the negative electrode or the negative electrode current collector includes copper, stainless steel, nickel, titanium, Or these alloys are mentioned. Examples of the positive electrode current collector and the negative electrode current collector include foil, expanded metal, punching metal, and wire mesh.

The non-aqueous electrolyte solution dissolves LiCF ₃ SO ₃ , LiClO ₄ , LiBF ₄ and / or LiPF ₆ in a non-aqueous solvent appropriately mixed with ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate or diethyl carbonate. And the like. The amount of the non-aqueous electrolyte solution added to the battery is not particularly limited, but can be set as appropriate depending on the amount of the positive electrode material and the negative electrode material and the size of the battery.

The separator has a high ion permeability, has a predetermined mechanical strength, and may be an insulating thin film. The material is olefin polymer, fluorine polymer, cellulose polymer, polyimide, nylon, glass fiber, alumina. Examples of the form include non-woven fabric, woven fabric, and microporous film.

Examples of the overcurrent prevention element include a fuse, a bimetal, and a PTC element.

The sealing material of the present invention also includes a sealing material for a stationary lithium secondary battery used for residences, a sealing material for a lithium secondary battery for wind power generation and storage of solar power, an uninterruptible power supply It can also be suitably used as a sealing material for a secondary battery as a power supply, and as a sealing material for an electric double layer capacitor or a secondary battery incorporated in an automobile, a forklift, a power shovel, a bulldozer or the like.

As the sealing material, a gasket or packing is preferable. In addition to the non-aqueous power storage device described above, it can also be used for a flange portion of a pipe and a seal portion of a metal joint.

The sealing material of the present invention has the above-described configuration, and has excellent compression recovery property even under a high temperature environment, and sufficiently suppresses cold flow (creep) even under such a severe environment. It is something that can be done. When the above sealing material is used, the airtightness and liquid tightness inside the container can be maintained even in a harsh environment. Therefore, the sealing material is a secondary battery, an electric double layer capacitor, etc. that has a large capacity and a large current. It is extremely useful as a sealing material in non-aqueous power storage devices.

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “parts” means “parts by weight”.

The equipment and measurement conditions used for the evaluation of physical properties are as follows.

<Measurement of copolymer composition>
^{It is} measured by ¹⁹ F-NMR method.

<Measurement of melt flow rate (MFR)>
Mass of polymer flowing out per unit time (10 minutes) from a nozzle having a diameter of 2.1 mm and a length of 8 mm under a 5 kg load at 372 ° C. using a melt indexer (manufactured by Toyo Seiki Seisakusho) under a 5 kg load. (G) was measured.

<Measurement of melting point>
The temperature is determined as the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is raised at a rate of 10 ° C./min using a DSC apparatus (made by SII Nanotechnology Inc.).

<Measurement of restoration rate>
The restoration rate is indicated by 100%-(compression set). Compression set (compression set) is measured by the method shown in ASTM D395-03 test method-B.
A test piece having a size of 13φ × 6 mmt is used.
Heating and pressing are performed at 85 ° C. for 1000 hours.
The compression ratio is 50% (that is, a 6 mm thick sample is compressed to 3 mm).
However, in ASTM D395, the test piece is allowed to cool after the sample is removed from the compression jig. However, in the test method employed in this example, the test piece is kept fixed to the compression jig for 3 hours or more at room temperature. After cooling to room temperature, the test piece is removed and the size of the test piece is measured 30 minutes later.

Synthesis example 1
A jacket type autoclave equipped with a stirrer and capable of containing 174 parts of water was charged with 26.6 parts of decarboxylated and demineralized water. The space inside the autoclave was sufficiently replaced with pure nitrogen gas and then evacuated to 30.4 parts perfluorocyclobutane (hereinafter referred to as “C-318”), 0.6 parts methanol as a chain transfer agent and 0.5 parts PPVE. Was charged. Next, the inside of the autoclave was kept at 35 ° C. while stirring, and TFE was injected to make the internal pressure 0.58 MPaG. Polymerization was initiated by adding 0.010 part of dinormalpropyl peroxydicarbonate (hereinafter referred to as “NPP”) as a polymerization initiator. Since the pressure in the autoclave decreased with the progress of the polymerization, TFE was injected to maintain the internal pressure at 0.58 MPaG. In addition, PPVE was also added as appropriate in order to make the polymerization composition uniform.
After 7.1 hours from the start of polymerization, the stirring was stopped, and at the same time, the unreacted monomer and C-318 were discharged to stop the polymerization. The white powder produced in the autoclave was washed with water and dried at 150 ° C. for 12 hours to obtain a polymer product.
The obtained polymer product was melt-extruded at 360 ° C. by a screw extruder (trade name: PCM46, manufactured by Ikekai Co., Ltd.) to produce pellets.
About the obtained pellet, when the copolymer composition, melting | fusing point, MFR, and the weight average molecular weight were measured, it was as follows.
Copolymer composition (mass%): TFE / PPVE = 97.5 / 2.5
Melting point: 315.1 ° C
MFR: 4.8 g / 10 minutes Weight average molecular weight: 520000

Synthesis Examples 2 to 11
Polymer product pellets were produced in the same manner as in Synthesis Example 1 except that the amount of the reactants and the reaction time were changed as shown in Table 1.
About the obtained pellet, copolymer composition (ratio of PPVE), melting | fusing point, MFR, and the weight average molecular weight were measured. The results are shown in Table 1.

Example 1
The polymer product pellets obtained in Synthesis Example 1 were preheated at 350 ° C. for 1 hour and then pressurized at 1 MPaG for 1 minute to form a 20 mm thick sheet, which was then allowed to cool to room temperature to obtain a sample sheet.
The sample sheet was cut to 13φ × 6 mmt to obtain a test piece.

The restoration rate of the test piece was measured by the method described above. The results are shown in Table 2.

Examples 2-8, Comparative Examples 1-3
Using the polymer product pellets obtained in Synthesis Examples 2 to 11, test pieces were prepared in the same manner as in Example 1, and the restoration rate of the obtained test pieces was measured. The results are shown in Table 2.

Claims (11)

A sealing material comprising a fluoropolymer having a polymer unit based on tetrafluoroethylene and a polymer unit based on one or more types of perfluoro (alkyl vinyl ether),
The fluoropolymer has a polymerization unit based on perfluoro (alkyl vinyl ether) of 4.0% by mass or less based on the total polymerization unit, and a melt flow rate of 0.1 to 100 g / 10 min. A sealing material characterized by 2. The sealing material according to claim 1, wherein the fluoropolymer has a polymerization unit based on perfluoro (alkyl vinyl ether) of 3.5% by mass or less based on all polymerization units. The sealing material according to claim 1 or 2, wherein the fluoropolymer has a melt flow rate of 0.1 to 16 g / 10 min. The sealing material according to claim 1, 2 or 3, wherein the fluoropolymer has a melt flow rate of 0.1 to 10 g / 10 min. The sealing material according to claim 1, wherein the perfluoro (alkyl vinyl ether) is perfluoro (propyl vinyl ether). The sealing material according to claim 1, 2, 3, 4, or 5, wherein the fluoropolymer has a melting point of 305 to 320 ° C. The encapsulating material according to claim 1, 2, 3, 4, 5, or 6, wherein the fluoropolymer has a weight average molecular weight of 300,000 or more. The sealing material according to claim 1, wherein the restoration rate at 85 ° C. is 10.0% or more. The sealing material according to claim 1, 2, 3, 4, 6, 7, or 8, which is used in an environment where the maximum temperature is 50 ° C. or higher. The sealing material according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, which is used for a non-aqueous power storage device. The sealing material according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, which is used for a vehicle-mounted non-aqueous power storage device.