JP5308210B2 - Biaxially oriented polyester film for reinforcing solid polymer electrolyte membrane and solid polymer electrolyte membrane reinforcing member comprising the same - Google Patents

Description

  The present invention relates to a biaxially oriented polyester film excellent in hot water resistance and gas sealing properties and suitable as a reinforcing material for a solid polymer electrolyte membrane of a solid polymer electrolyte fuel cell, and a solid polymer electrolyte membrane reinforcing member comprising the same.

  In recent years, fuel cells have been actively developed from the viewpoint of environmental problems. Various types of fuel cells such as a solid polymer electrolyte type, a phosphoric acid type, a molten carbonate type, and a solid oxide type are known depending on the type of electrolyte used. Among these, solid polymer electrolyte fuel cells are attracting attention because of their relatively low reaction temperatures.

  A solid polymer electrolyte fuel cell is a fuel cell that utilizes the function as a proton conductive electrolyte when a polymer resin membrane having proton (hydrogen ion) exchange groups in the molecule is hydrated to a saturated state. is there. A solid polymer type fuel cell has a polymer electrolyte membrane made of a polymer ion exchange membrane (cation exchange membrane), and a fuel cell structure having an anode side electrode and a cathode side electrode respectively disposed on both sides of the electrolyte. The body (fuel cell) is sandwiched between separators. The fuel gas, for example, hydrogen supplied to the anode side electrode is hydrogen ionized on the catalyst electrode and moves to the cathode side electrode side through the polymer electrolyte membrane that is appropriately humidified. Electrons generated in the meantime are taken out to an external circuit and used as direct current electric energy. Since the oxidant gas, for example, oxygen gas or air is supplied to the cathode side electrode, water reacts with the hydrogen ions, the electrons and oxygen to generate water.

  As the polymer electrolyte membrane, a perfluorosulfonic acid resin membrane (for example, “Nafion” (a registered trademark of DuPont)) is used, so that high power generation efficiency can be obtained by reducing the resistivity of the polymer ion exchange membrane. In order to achieve this, it is normally operated at a temperature condition of about 50 to 100 ° C. This polymer electrolyte membrane is required to improve conductivity and reduce costs, and because it is an extremely thin film material, it is difficult to handle, and when joining to each electrode, a plurality of single cells are used. During assembly operations such as stacking and combining as a stack, wrinkles are generated at the peripheral edge, and the mechanical strength of the constituent members of the stack is the lowest so that it is easily damaged.

  Therefore, in Patent Document 1, the electrolyte membrane is mechanically reinforced at the peripheral portion of the fuel battery cell, and the reinforcement is airtightly bonded so that fuel gas and oxidant gas do not leak from the boundary surface with the electrolyte membrane. It is preferable to provide a frame and a reinforcing frame having required mechanical strength, corrosion resistance, etc. even at an operating temperature. For example, polycarbonate, other polyethylene terephthalate, thermosetting plastic such as glass fiber reinforced epoxy resin, titanium, etc. Corrosion-resistant metals such as carbon or carbon are disclosed. Patent Document 2 discloses that a frame member having airtightness is used at the outer peripheral end of a porous body fixed on both surfaces of a solid polymer electrolyte membrane. Examples of the material include thermoplastic resins such as polycarbonate, ethylene propylene copolymer, polyester, modified polyphenylene oxide, polyphenylene sulfide, or acrylonitrile styrene.

Patent Document 3 discloses a solid polymer electrolyte membrane that has high mechanical strength, excellent heat-resistant dimensional stability in the processing temperature / use temperature range, and excellent hydrolyzability in a high humidity use environment. As the film, a biaxially oriented polyester film containing polyethylene naphthalene dicarboxylate as a main component is disclosed.
Patent Document 4 discloses that a seal-integrated membrane electrode assembly used in a fuel cell has a reinforcing member having rigidity higher than that of the sealing member inside the sealing member, and polyethylene resin as a resin constituting the reinforcing member. Examples include phthalate, polyethylene terephthalate, polyphenylene sulfide, polyether sulfone, polyether ether ketone, polyimide, polypropylene, and polyimide.

  As described above, various resins have been studied as a solid polymer electrolyte reinforcing member mainly from the viewpoint of mechanical strength. Among such materials, polyethylene naphthalate has been attracting attention as a material having high mechanical strength and hydrolysis resistance. However, as the durability of fuel cells has increased, it has further improved hydrolysis resistance. A material excellent in long-term durability is desired. In addition to excellent hydrolysis resistance and reinforcing strength, the reinforcing member has higher confidentiality (gas) that prevents gas leakage of fuel gas and oxidant gas while suppressing damage to the electrolyte membrane due to the fastening pressure of the fuel cell. At present, sealing properties are required.

JP 7-65847 A JP 10-199551 A JP 2007-103170 A JP 2007-250249 A

  The object of the present invention is to eliminate such problems of the prior art, have excellent hot water resistance in high temperature and high humidity usage environments in addition to the conventional reinforcement strength, and damage the electrolyte membrane due to the fastening pressure of the fuel cell. An object of the present invention is to provide a biaxially oriented polyester film suitable for a reinforcing material for a solid polymer electrolyte membrane of a solid polymer electrolyte fuel cell that is excellent in gas sealing properties while being suppressed, and a solid polymer electrolyte membrane reinforcing member comprising the same.

  Furthermore, another object of the present invention is to provide a gas-sealing property while having excellent hot water resistance in a high temperature / high humidity use environment in addition to the conventional reinforcing strength and suppressing damage to the electrolyte membrane due to the fastening pressure of the fuel cell. A biaxially oriented polyester film suitable as a reinforcing material for a solid polymer electrolyte membrane of a solid polymer electrolyte fuel cell and having excellent adhesion to the solid polymer electrolyte membrane and a diffusion layer, and a solid polymer electrolyte comprising the same The object is to provide a membrane reinforcing member.

  As a result of intensive studies to solve the above problems, the present inventors have found that a biaxially oriented polyester film containing polytrimethylene naphthalene dicarboxylate as a constituent material is excellent in elastic recoverability. As a result, it is possible to protect the solid polymer electrolyte membrane without applying a load to the electrolyte membrane, and because the film is excellent in gas impermeability, it has high confidentiality. It has been found that it has a gas sealing property and is excellent in hot water resistance and can maintain a high mechanical strength over a long period of time even in a high temperature / high humidity use environment, and has completed the present invention.

That is, according to the present invention, an object of the present invention, the polytrimethylene naphthalenedicarboxylate Ri Do at least one layer comprising a layer whose main component, the breaking strength in the MD direction is represented by the following formula (1) holds The time required for the rate to reach 50% exceeds 200 hours
Breaking strength retention ratio (%) = (breaking strength X / initial breaking strength X ₀ ) × 100 (1)
(In the formula (1), the breaking strength X is the breaking strength after treatment for a predetermined time under the conditions of 121 ° C., 2 atm and 100% RH (unit: MPa), and the breaking strength X ₀ is the initial breaking strength (unit) : MPa))
This is achieved by a biaxially oriented polyester film for reinforcing a solid polymer electrolyte membrane.

In addition, the biaxially oriented polyester film for reinforcing a solid polymer electrolyte membrane of the present invention preferably has polytrimethylene naphthalene dicarboxylate as polytrimethylene-2,6-naphthalene dicarboxylate, The content of methylene naphthalene dicarboxylate is 90% by weight or more based on the layer containing polytrimethylene naphthalene dicarboxylate ,
It elastic recovery rate represented by the following following formula (2) is not less than 65%,
Elastic recovery rate (%) = ((L1-L2) / L1) × 100 (2)
(In Formula (2), L1 represents the amount of deformation (mm) at the time of 10% elongation, and L2 represents the amount of strain (mm) remaining when the elongation is restored to the initial position after 10% elongation)
An easy adhesion layer containing an acrylic resin is laminated on at least one surface of a layer mainly composed of polytrimethylene naphthalene dicarboxylate, the acrylic resin is an acrylic resin containing an amide group, and easy adhesion A layer comprising at least one of the following: a layer containing polytrimethylene naphthalene dicarboxylate as a main component is applied before the completion of crystal orientation of the layer is also included as a preferred embodiment.
Furthermore, this invention includes the solid polymer electrolyte membrane reinforcement member containing the above-mentioned biaxially oriented film for solid polymer electrolyte membrane reinforcement.

  The biaxially oriented polyester film of the present invention has mechanical strength as a polyester, is excellent in elastic recovery, gas impermeability, hot water resistance in a high temperature / high humidity environment, and is a solid polymer electrolyte fuel cell. When used as a reinforcing member for polymer electrolyte membranes, it can maintain mechanical strength for a long time even in high-temperature and high-humidity environments, and maintain confidentiality (gas sealability) without imposing a load on the electrolyte membrane. Therefore, it is useful as a solid polymer electrolyte membrane reinforcing film.

The present invention will be described in detail below.
<Biaxially oriented polyester film>
The biaxially oriented polyester film of the present invention comprises at least one layer including a layer containing polytrimethylene naphthalene dicarboxylate as a main component. Here, “main” means 90% by weight or more based on the layer containing polytrimethylene naphthalene dicarboxylate, more preferably 95% by weight, particularly preferably 97% by weight or more.

(Polytrimethylene naphthalene dicarboxylate)
In the polytrimethylene naphthalene dicarboxylate constituting the film of the present invention, naphthalene dicarboxylic acid or a derivative thereof is used as a main dicarboxylic acid component, and trimethylene glycol is used as a main glycol component. Examples of naphthalenedicarboxylic acid include 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, and 1,5-naphthalenedicarboxylic acid. Among these, 2,6-naphthalenedicarboxylic acid is preferable. Here, “main” means 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more of all repeating units in the polymer constituting the film of the present invention.

  In the present invention, by using polytrimethylene naphthalene dicarboxylate as a polymer component constituting the film, in addition to mechanical strength as a polyester, it exhibits high elastic recovery, gas impermeability, and hydrolysis resistance. And a film suitable for the reinforcing member can be provided.

The polytrimethylene naphthalene dicarboxylate of the present invention may be a polytrimethylene naphthalene dicarboxylate copolymer having a copolymerization component within 20 mol%. As the copolymer component, a compound having two ester-forming functional groups in the molecule can be used. Examples of such a compound include oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid, terephthalic acid, Dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, tetralindicarboxylic acid, decalindicarboxylic acid, diphenyletherdicarboxylic acid, p-oxy Oxycarboxylic acids such as benzoic acid, p-oxyethoxybenzoic acid, or ethylene oxide of ethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexane dimethanol, bisphenol sulfone A dihydric alcohol such as a side adduct, an ethylene oxide adduct of bisphenol A, diethylene glycol, or polyethylene oxide glycol can be preferably used.
These copolymerization components may be used alone or in combination of two or more. Of these, the acid component is preferably isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid, p-oxybenzoic acid, and the glycol component is ethylene glycol, It is an ethylene oxide adduct of hexamethylene glycol, neopentyl glycol, and bisphenol sulfone.

The polytrimethylene naphthalene dicarboxylate may be a blend with other polyesters. Examples of such blend components include polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polyethylene-2,7-naphthalene dicarboxylate, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene-4,4′-tetramethylene diphenyl. Mention may be made of polyesters such as dicarboxylate, polyneopentylene-2,6-naphthalene dicarboxylate, poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalene dicarboxylate.
Among these blend components, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, and poly (bis (4-ethyleneoxyphenyl) sulfone) -2,6-naphthalenedicarboxylate are particularly preferred. It is mentioned as a preferable component. These blend components are preferably used in a range of 20 mol% or less based on the number of moles of all repeating structural units of the polymer constituting the layer comprising polytrimethylene naphthalene dicarboxylate as the main component. Even if it exists, you may use 2 or more types together.

  The polytrimethylene naphthalene dicarboxylate of the present invention may be one in which a terminal hydroxyl group and / or a carboxyl group is partially or entirely blocked with a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. . Further, it may be copolymerized within a range in which a substantially linear polymer is obtained with a very small amount of a trifunctional or higher functional ester-forming compound such as glycerin and pentaerythritol.

The polytrimethylene naphthalene dicarboxylate of the present invention can be produced by applying a known method. For example, it can be produced by a method in which a diol, a dicarboxylic acid and, if necessary, a copolymerization component are esterified, and then a reaction product obtained is polycondensed to form a polyester. Alternatively, these raw material monomer derivatives may be transesterified, and then the resulting reaction product may be subjected to a polycondensation reaction to obtain a polyester.
Alternatively, polytrimethylene naphthalene dicarboxylate obtained by such melt polymerization can be chipped and subjected to solid phase polymerization under heating under reduced pressure or in an inert gas stream such as nitrogen. By performing solid phase polymerization, the hydrolysis resistance of the biaxially oriented film is further improved.

  The intrinsic viscosity of the polytrimethylene naphthalene dicarboxylate of the present invention is preferably 0.50 dl / g or more and 0.90 dl / g or less. Such intrinsic viscosity is more preferably 0.52 dl / g or more and 0.85 dl / g or less, and particularly preferably 0.53 dl / g or more and 0.80 dl / g or less. When the intrinsic viscosity is less than the lower limit, breakage during film formation is likely to occur, and the obtained film may become brittle, or the hydrolysis characteristics may be deteriorated. Further, if the intrinsic viscosity of polytrimethylene naphthalene dicarboxylate exceeds the upper limit, the intrinsic viscosity of the polymer needs to be considerably increased, and a normal synthesis method requires a long time for polymerization, resulting in poor productivity.

  The intrinsic viscosity of the polytrimethylene naphthalene dicarboxylate after forming into a biaxially oriented film is preferably 0.45 dl / g or more and 0.85 dl / g or less, more preferably 0.47 dl / g or more and 0. .80 g / dl or less, particularly preferably 0.50 dl / g or more and 0.75 g / dl or less. The intrinsic viscosity is a value (unit: dl / g) measured at 35 ° C. using o-chlorophenol as a solvent. Polytrimethylene naphthalene dicarboxylate subjected to solid phase polymerization is o-chlorophenol. Insoluble in water is represented by a value measured at a temperature of 35 ° C. after dissolving in a phenol: tetrachloroethane mixed solvent having a weight ratio of 6: 4.

(Other additives)
In order to improve the handleability of the biaxially oriented polyester film of the present invention, inert particles or the like may be added within a range not impairing the effects of the invention. As the inert particles, for example, inorganic particles (for example, kaolin, alumina, titanium oxide, calcium carbonate, silicon dioxide, etc.) containing the elements of Periodic Tables IIA, IIB, IVA, and IVB, a crosslinked silicone resin, Particles made of a polymer having high heat resistance such as crosslinked polystyrene and crosslinked acrylic resin particles can be contained. When the inert particles are contained, the average particle diameter of the inert particles is preferably in the range of 0.001 to 5 μm, and 0.01 to 10 based on the weight of the layer containing polytrimethylene naphthalene dicarboxylate as a main component. It is preferable to contain in the range of weight%. Further, the content of the particles is more preferably 0.01 to 5% by weight, and particularly preferably 0.1 to 3% by weight.
The biaxially oriented polyester film of the present invention may contain a small amount of an ultraviolet absorber, an antioxidant, an antistatic agent, a light stabilizer, and a heat stabilizer as necessary.

<Heat resistant water>
The biaxially oriented polyester film of the present invention is in contact with the electrolyte membrane surface in a water-containing state and is used in a temperature range of about 50 ° C. to 100 ° C. It is preferable that a decrease in strength due to decomposition is small, and it is preferable that the time required for the fracture strength retention in the MD direction represented by the following formula (1) to be 50% exceeds 200 hours.
Breaking strength retention ratio (%) = (breaking strength X / initial breaking strength X ₀ ) × 100 (1)
(In the formula (1), the breaking strength X is the breaking strength after treatment for a predetermined time under the conditions of 121 ° C., 2 atm and 100% RH (unit: MPa), and the breaking strength X ₀ is the initial breaking strength (unit) : MPa))

The time required for the fracture strength retention represented by formula (1) to be 50% is more preferably 220 hours or more, and even more preferably 250 hours or more. Further, the upper limit of the time required for the fracture strength retention represented by the formula (1) to be 50% is preferably 350 hours or less from the viewpoint of the polymer material.
If the time required for the fracture strength retention rate to reach 50% is less than the lower limit value, sufficient strength and confidentiality as a reinforcing member may not be maintained for a long period of time in a high temperature / high humidity use environment. Such hydrolysis resistance is achieved by using polytrimethylene naphthalene dicarboxylate among polyesters.

<Elastic recovery rate>
The biaxially oriented polyester film of the present invention preferably has an elastic recovery rate represented by the following formula (2) of 65% or more.
Elastic recovery rate (%) = ((L1-L2) / L1) × 100 (2)
(In Formula (2), L1 represents the amount of deformation (mm) at the time of 10% elongation, and L2 represents the amount of strain (mm) remaining when the elongation is restored to the initial position after 10% elongation)
The elastic recovery rate can be measured using an apparatus usually used for measuring the tensile strength. The test piece is pulled to an elongation of 10% and then returned to the original length at the same speed. From the average value of five measurements , Represented by a value obtained according to the equation (2).

A higher elastic recovery rate is preferable, but the upper limit is naturally limited due to the characteristics of the material, and is in the range of 85% or less, further 70% or less.
Due to the elastic recovery rate being within such a range, when used as a reinforcing member for a solid polymer electrolyte membrane, there is little deformation due to the fastening pressure during the production of the fuel cell, and the polymer electrolyte membrane is not subject to any load on the electrolyte membrane. Can be protected. Moreover, since it has high confidentiality when used as a reinforcing member, fuel gas and oxidant gas leakage can be prevented, and high gas sealing performance can be maintained.

<Gas impermeability>
The biaxially oriented polyester film of the present invention preferably has an oxygen gas permeability of 0 to 7 cc.cm/cm ² .sec.cmHg. When the oxygen gas permeability is in such a range, the gas sealing property can be improved when used as a reinforcing member for the solid polymer electrolyte membrane. Such gas impermeability is achieved by using polytrimethylene naphthalene dicarboxylate.

<Film thickness>
The film thickness of the biaxially oriented polyester film of the present invention is preferably 1 μm or more and 100 μm or less. The lower limit of the film thickness is more preferably 2 μm or more, and further preferably 5 μm or more. The upper limit of the film thickness is more preferably 75 μm or less, and further preferably 50 μm or less. When the film thickness is less than the lower limit, a sufficient reinforcing effect as a reinforcing material for the electrolyte membrane may not be obtained. When the film thickness exceeds the upper limit, it may be difficult to reduce the battery size.

<Easily adhesive layer>
In the biaxially oriented polyester film of the present invention, an easy adhesion layer containing an acrylic resin is preferably laminated on at least one surface of a layer containing polytrimethylene naphthalene dicarboxylate as a main component.
Such an easy-adhesion layer is preferably laminated on at least one side of a layer containing polytrimethylene naphthalene dicarboxylate as a main component, and may be laminated on both sides.

  The biaxially oriented polyester film is used as a reinforcing member for the electrolyte membrane by being bonded to the peripheral portion of the electrolyte membrane in a frame shape. In the solid polymer electrolyte fuel cell, electrode layers are arranged on both sides of the electrolyte. The electrode layer is smaller in size than the electrolyte membrane, and the frame-shaped reinforcing member made of the biaxially oriented polyester film of the present invention is usually It arrange | positions so that the outer edge of a catalyst layer may be enclosed. Since a diffusion layer having a size larger than that of the electrode layer is further disposed outside these electrode layers, one surface of the reinforcing member made of the biaxially oriented polyester film has a peripheral portion of the electrolyte membrane and the other surface. The surface is in contact with the peripheral edge of the diffusion layer.

When the biaxially oriented polyester film has an easy adhesion layer on one side, the easy adhesion layer may be on either the electrolyte membrane side or the diffusion layer side. Further, the easy-adhesion layer and the electrolyte membrane or the diffusion layer may be directly bonded or may be further bonded via an adhesive layer.
When the biaxially oriented polyester film is firmly bonded to at least one of the electrolyte membrane and the diffusion layer, the performance as a reinforcing member is further enhanced. In addition, high adhesion can be maintained over a long period even in a high humidity usage environment.
In the case of using an adhesive layer, the type is not particularly limited, but examples include an adhesive mainly composed of a polymer constituting the electrolyte membrane, specifically, a perfluorosulfonic acid polymer.

  Examples of the acrylic resin contained in the easy-adhesion layer include acrylic resins composed of acrylic monomer components exemplified below. That is, alkyl acrylate, alkyl methacrylate (alkyl groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.); Mention may be made of hydroxy-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; monomers such as glycidyl acrylate and glycidyl methacrylate; acrylic acid and methacrylic acid. One or more of these monomers can be used as a copolymerization component. Particularly preferred acrylic monomers include methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and the like.

  Such an acrylic resin further contains, as a copolymerization component, carboxy such as itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.). Monomers containing a group or a salt thereof; monomers of acid anhydrides such as maleic anhydride and itaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene, α-methylstyrene, vinyl methyl ether, vinyl ethyl ether, vinyl trialkoxysilane, Alkyl maleic acid monoester, alkyl fumaric acid monoester, alkylitaconic acid monoester, acrylonitrile, methacrylonitrile, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, butadiene and the like may be used. The copolymerization ratio of the copolymer component is preferably in the range of 0.1 to 60 mol% based on all monomer units of the acrylic resin. The upper limit of the copolymerization ratio is more preferably 50 mol%. Further, the lower limit of the copolymerization ratio is more preferably 1 mol%.

  More preferably, the acrylic resin contains an amide group. As an acrylic resin containing an amide group, for example, an acrylic monomer component having the following amide group can be obtained by introducing it into the acrylic resin as a copolymerization component.

  Examples of the acrylic monomer component having an amide group include acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N, N-dialkylacrylamide, N, N-dialkylmethacrylamide (the alkyl group is a methyl group). , Ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.), N-alkoxyacrylamide, N-alkoxymethacrylamide, N, N- Dialkoxyacrylamide, N, N-dialkoxymethacrylamide (alkoxy groups include methoxy group, ethoxy group, butoxy group, isobutoxy group, etc.), N-methylolacrylamide, N-methylolmethacrylamide, N-phenylacrylate Ruamido, N- phenyl methacrylamide, can be exemplified acryloyl morpholine.

  When the acrylic resin is an acrylic resin containing an amide group (hereinafter sometimes referred to as an acrylic copolymer), it is sufficient that at least one monomer having the above amide group is included. Due to the presence of the amide group in the acrylic copolymer, the adhesion with the electrolyte membrane, the diffusion layer, or the adhesive layer is further improved, and the gas sealing property is improved.

  Particularly preferred acrylic monomers having an amide group include acrylamide, methacrylamide, N-alkyl acrylamide, N, N-dialkyl acrylamide, N, N-dialkyl methacrylamide (the alkyl groups include methyl, ethyl, n-propyl). Group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.), N-methylolacrylamide, N-methylolmethacrylamide, and acryloylmorpholine.

  When the acrylic resin is an acrylic copolymer containing an amide group, the copolymerization ratio of the acrylic monomer component having an amide group is in the range of 0.2 to 20 mol% based on the total monomer units of the acrylic resin. It is preferable. The upper limit of the copolymerization ratio is more preferably 10 mol%, particularly preferably 5 mol%. Further, the lower limit of the copolymerization ratio is more preferably 1 mol%, and particularly preferably 2 mol%. When the copolymerization ratio of the acrylic monomer component having an amide group is within the above range, the adhesion with the electrolyte membrane, the diffusion layer, or the adhesive layer can be further improved.

  For easy adhesion, in addition to the above-mentioned acrylic resin, a polyester copolymer, a urethane resin, or the like, or an acrylic-modified polyester, acrylic-modified urethane, or the like, which is a modified body thereof, may be mixed as a binder component. Preferably mixing with a polyester copolymer is mentioned. In the case of a mixture with a polyester copolymer, the mixing ratio is preferably 80 to 20% by weight of the polyester copolymer with respect to 20 to 80% by weight of the acrylic resin, based on the weight of the binder component in the coating layer. . The amount of the binder component in the easy-adhesion layer is preferably 50% by weight to 100% by weight, more preferably 60% by weight to 95% by weight, and particularly preferably 80% by weight to 90% by weight.

  A cross-linking agent such as an epoxy compound, oxazoline, melamine, isocyanate, silane coupling agent, zirco-aluminum coupling agent may be added to the easy adhesion layer as a cross-linking component in order to improve heat resistance. . Of these, epoxy is particularly preferred.

  The coating solution used for coating the easy-adhesion layer is preferably a water-dispersible or aqueous coating solution. Further, as long as it does not affect the acrylic resin and other additives, it may contain some organic solvent. This coating solution can be used by adding a necessary amount of a surfactant such as an anionic surfactant, a cationic surfactant, a nonionic surfactant, etc., for example, 1% by weight or more based on the weight of the easy adhesion layer The range is preferably 15% by weight or less, more preferably 5% by weight or more and 10% by weight or less.

  Such surfactants are preferably those that can reduce the surface tension of aqueous coating solutions to 40 mN / m or less and promote wetting on polyester films, such as polyoxyethylene-fatty acid esters, sorbitan fatty acid esters, glycerin fatty acid esters, fatty acids. Examples thereof include metal soaps, alkyl sulfates, alkyl sulfonates, alkyl sulfosuccinates, quaternary ammonium chloride salts, alkylamine hydrochlorides, and betaine surfactants.

  As a method for forming an easy-adhesion layer, for example, an aqueous coating solution containing a component that forms an easy-adhesion layer on one or both sides of the polyester film is applied before the crystal orientation of the polyester film is completed, and then drying and stretching are necessary. It can be laminated by heat treatment according to the above. Here, before the crystal orientation is completed, it is an unstretched polyester film, a uniaxially stretched polyester film, or a polyester film that is biaxially stretched at a low stretch ratio, and among these, a longitudinally stretched uniaxially in the extrusion direction (longitudinal direction) of the film. A stretched polyester film is particularly preferred.

As a method of applying an easy-adhesion layer to a polyester film, in addition to the method of applying at the above-mentioned timing in the film forming process, there is also a method of performing a process separated from the film manufacturing process on a polyester film thermally fixed after biaxial stretching. Although it is normally performed, since it is easy to entrain dust, dust and the like when performed in a process separated from the film production process, application in a clean atmosphere, that is, application in the film production process is preferable.
As a coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, and a curtain coating method can be used alone or in combination.

<Film formation>
The polyester film of the present invention needs to be biaxially oriented. By being biaxially oriented, the properties relating to mechanical strength, dimensional change, and hydrolysis resistance are improved, and sufficient performance as a reinforcing member for the solid polymer electrolyte membrane can be exhibited.

  If the biaxially oriented polyester film of the present invention is biaxially stretched, it can be produced using a known film-forming method. For example, a sufficiently dried polytrimethylene-2,6-naphthalate has a melting point. It can be produced by melt extrusion at a temperature of ˜ (melting point + 70) ° C., quenching on a casting drum to form an unstretched film, and then successively or simultaneously biaxially stretching the unstretched film and heat setting. When forming a film by sequential biaxial stretching, the unstretched film is stretched in the longitudinal direction at 60 to 110 ° C. in a range of 2.3 to 6.5 times, more preferably in a range of 2.5 to 5.0 times, and then a stenter. The film is stretched in the transverse direction at 80 to 110 ° C. in the range of 2.3 to 5.5 times, more preferably 2.5 to 5.0 times. The heat setting is preferably performed at a temperature of 110 to 260 ° C., more preferably 130 to 180 ° C. under tension or limited shrinkage, and the heat setting time is preferably 1 to 1000 seconds. In the case of simultaneous biaxial stretching, the above stretching temperature, stretching ratio, heat setting temperature and the like can be applied. Moreover, you may perform a relaxation | loosening process after heat setting.

<Reinforcing member>
The biaxially oriented film of the present invention is used as a reinforcing film for a solid polymer electrolyte membrane of a solid polymer electrolyte fuel cell having an operating temperature of about 50 to 100 ° C. As such a solid polymer electrolyte fuel cell, specifically, a fuel cell for a moving body can be exemplified, and further, it can be suitably used as a reinforcing film for a solid polymer electrolyte membrane of an automobile fuel cell.

  The biaxially oriented film of the present invention is preferably used as a solid polymer electrolyte membrane reinforcing member. The biaxially oriented film is used as a reinforcing member for the electrolyte membrane by being bonded to the peripheral portion of the electrolyte membrane in a frame shape. In the solid polymer electrolyte fuel cell, electrode layers are arranged on both sides of the electrolyte, the electrode layer has a smaller dimension than the electrolyte membrane, and the frame-shaped reinforcing member including the biaxially oriented film of the present invention is a normal electrode. It is arranged to surround the outer edge of the layer. Since a diffusion layer having a size larger than that of the electrode layer is further disposed outside these electrode layers, one surface of the reinforcing member including the biaxially oriented film is a peripheral portion of the electrolyte membrane, and the other surface is It contacts each peripheral edge of the diffusion layer.

  The solid polymer electrolyte membrane reinforcing member can be used by attaching at least one biaxially oriented film to at least one surface of the electrolyte membrane. The solid polymer electrolyte membrane reinforcing member can preferably be used by superposing at least two biaxially oriented films. When superposing at least two biaxially oriented films, specifically, an embodiment in which one biaxially oriented film is used on each of both surfaces of the electrolyte membrane via the peripheral edge. Further, two or more biaxially oriented films may be overlapped and used on both surfaces of the electrolyte membrane via the peripheral edge.

  The biaxially oriented polyester film of the present invention has mechanical strength as a polyester and is excellent in elastic recovery, gas impermeability, and hot water resistance, so that the polymer electrolyte membrane of a solid polymer electrolyte fuel cell When used as a reinforcing member, it can maintain mechanical strength over a long period of time even in high-temperature and high-humidity environments, and can maintain confidentiality (gas-sealability) without imposing a load on the electrolyte membrane. The service life can be increased.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

(1) Hot water resistance A strip-shaped sample piece cut into a 150 mm length × 10 mm width so that the film MD direction is the measurement direction is stainless steel in an environmental test machine set at 121 ° C., 2 atm, wet saturation mode, and 100% RH. Suspend with a plastic clip. Then, a sample piece is taken out every predetermined time, and the breaking strength in the film MD direction is measured. Tensileon UCT-100 manufactured by Orientec Co., Ltd. was used to measure the breaking strength in a room adjusted to a temperature of 20 ° C. and a humidity of 50%, with a chuck of 100 mm and a tensile speed of 100 mm / min and a chart speed of 500 mm / min. The strength at break was determined.
The measurement was performed 5 times, the average value was obtained, and the hot water resistance was evaluated by obtaining the time until the fracture strength retention in the MD direction represented by the following formula (1) reached 50% of the initial value. As a measuring device, Tensilon UCT-100 type manufactured by Orientec Co., Ltd. was used.
Breaking strength retention ratio (%) = (breaking strength X / initial breaking strength X ₀ ) × 100 (1)
(In the formula (1), the breaking strength X is the breaking strength after treatment for a predetermined time under the conditions of 121 ° C., 2 atm and 100% RH (unit: MPa), and the breaking strength X ₀ is the initial breaking strength (unit) : MPa))

(2) Elastic recovery property Using a test piece obtained by cutting the film into a length of 150 mm × 10 mm, and using a Tensilon UCT-100 type manufactured by Orientec, between chucks in a room adjusted to a temperature of 20 ° C. and a humidity of 50% The tensile speed was 10 mm / min, the chart speed was 500 mm / min, and the elongation was 10%. After that, the traveling direction of the crosshead was immediately reversed and returned to the original length at the same speed. The measurement was performed 5 times, the average value was calculated | required, and the elastic recovery rate represented by following formula (2) was calculated | required.
Elastic recovery rate (%) = ((L1-L2) / L1) × 100 (2)
(In Formula (2), L1 represents the amount of deformation (mm) at the time of 10% elongation, and L2 represents the amount of strain (mm) remaining when the elongation is restored to the initial position after 10% elongation)

(3) Gas permeability The oxygen permeability at 25 ° C. was measured using a gas permeability measuring device (manufactured by Toyo Seiki Co., Ltd., MC-1 type) according to JIS K-7126.

(4) Adhesion A 50 mm square perfluorosulfonic acid resin (manufactured by DuPont: Nafion 117) was used as the electrolyte membrane, and a polyester film of the same size was layered on one side and joined at 140 ° C. by hot pressing. When the polyester film had an easy-adhesion layer, they were stacked so that the easy-adhesion layer was in contact with the electrolyte membrane. The corner of the surface of the obtained test piece on the electrolyte membrane side was rubbed 10 times with a finger to evaluate the presence or absence of peeling of the electrolyte membrane.

(5) Gas sealing property as a reinforcing frame 100 mm square perfluorosulfonic acid resin (manufactured by DuPont: Nafion 117) is used as an electrolyte membrane, and a frame-like polyester film (outer circumference 100 mm × 100 mm, inner circumference 80 mm × 80 mm) and joined by hot pressing at 140 ° C., assembled in a fuel cell, submerged in water, and compressed air was sent to one side of the cell so that bubbles were generated from the opposite side. At that time, the pressure of the compressed air was gradually increased from 0 MPa.
The pressure at which bubbles were generated was determined, and the gas sealability was evaluated by relative evaluation with respect to the case where the PEN film of Comparative Example 2 was used.
◎: 1.2 times or more compared with PEN film ○: 0.8 times or more and less than 1.2 times compared with PEN film △: Less than 0.8 times compared with PEN film

(6) Reinforcing performance evaluation of reinforcing members (A)
A 100 mm square perfluorosulfonic acid resin (manufactured by DuPont: Nafion 117) is used as the electrolyte membrane, and a frame-like biaxially oriented film (outer periphery 100 mm × 100 mm, inner periphery 80 mm × 80 mm) is stacked on both surfaces at 140 ° C. Joined by hot pressing.
The structure of the electrolyte membrane and the reinforcing member is fixed to a vibration tester, and the amplitude is 0.75 mm (longitudinal direction) at 90 ° C., 10 Hz → 55 Hz → 10 Hz is swept in 60 seconds, and this is 10 cycles. Changes such as wrinkles, tearing, and breakage of the electrolyte membrane after cycling were visually observed and evaluated according to the following criteria.
○: No changes such as wrinkles, tears, and breakage are observed in the electrolyte membrane portion, and the reinforcing performance is excellent. ×: At least one of wrinkles, tears, and breakage is observed in the electrolyte membrane portion, and the reinforcement performance is high. Not enough

(7) Reinforcing performance evaluation of reinforcing members (B)
The structure of the electrolyte membrane and the reinforcing member prepared by the method of (6) was placed in an environmental test machine set to 121 ° C., 2 atm, wet saturation mode, and 100% RH, and treated for 200 hours.
The sample after treatment was fixed to a vibration testing machine, and the amplitude was 0.75 mm (longitudinal direction), 10 Hz → 55 Hz → 10 Hz was swept in 60 seconds in an atmosphere of 90 ° C., and this was performed 10 cycles as one cycle. Changes such as wrinkles, tearing, and breakage of the subsequent electrolyte membrane and the reinforcing frame were visually observed and evaluated according to the following criteria.
○: No changes such as wrinkles, tears, and breakage were observed in the electrolyte membrane and the reinforcing frame portion, and the reinforcing performance was excellent. ×: At least one of wrinkles, tearing, and breakage occurred in the electrolyte membrane or the reinforcing frame portion. Observed, reinforcing performance is not enough

[Example 1]
100 parts by weight of dimethyl 2,6-naphthalenedicarboxylate, 60 parts by weight of trimethylene glycol, 0.03 part by weight of manganese acetate tetrahydrate as a transesterification catalyst, and 0.03 part of calcium carbonate particles having an average particle size of 0.5 μm as a lubricant. 25 wt%, 0.06 wt% spherical silica particles having an average particle diameter of 0.2 μm, and 0.1 wt% spherical silica particles having an average particle diameter of 0.1 μm were added, An exchange reaction was allowed to occur. Each lubricant shows the compounding quantity with respect to film weight. Thereafter, 0.042 parts by weight of triethylphosphonoacetate was added to substantially complete the transesterification reaction. Subsequently, 0.024 parts by weight of antimony trioxide was added, and then the polymerization reaction was carried out in a conventional manner under high temperature and high vacuum, so that polytrimethylene-2,6-naphthalenedicarboxylate having an intrinsic viscosity of 0.60 dl / g. (Tg = 73 ° C.) was obtained. The polytrimethylene-2,6-naphthalenedicarboxylate polymer was dried at 160 ° C. for 3 hours, then supplied to an extruder, melted at a melting temperature of 240 ° C., extruded from a die slit, and then surface temperature of 25 ° C. An unstretched film was prepared by cooling and solidifying on a casting drum set to 1.

This unstretched film was stretched 3.0 times in the longitudinal direction (continuous film forming direction) at 105 ° C. to obtain a uniaxially stretched film. On one side of the uniaxially stretched film, 4 g / m ² of aqueous coating solution A having a solid content concentration of 3% by weight was applied by kiss coating. The coating liquid A is 90% by weight of an acrylic copolymer composed of 70% by mole of methyl methacrylate / 22% by mole of ethyl acrylate / 4% by mole of N-methylolacrylamide / 4% by mole of N, N-dimethylacrylamide as a solid content. , 10% by weight of polyoxyethylene lauryl ether (n = 7) is mixed.
Thereafter, the film is biaxially stretched by a factor of 3.2 in the transverse direction (width direction) at 100 ° C., heat-set at 145 ° C., and further reheated while shrinking 1% in the transverse direction at 140 ° C., A biaxially oriented polyester film having a thickness of 25 μm was obtained. The properties of the obtained film and the reinforcing member are shown in Table 1. The obtained film was excellent in hot water resistance, elastic recovery, and oxygen impermeability. Moreover, the adhesiveness with the electrolyte membrane was also excellent. In addition, when used as a reinforcing member, it was excellent in gas sealing properties and maintained mechanical strength for a long time even in high temperature and high humidity usage environments.

[Example 2]
A biaxially oriented polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the coating solution was not applied to one side of the uniaxially stretched film. The properties of the obtained film and the reinforcing member are shown in Table 1.

[Example 3]
Example 1 except that the unstretched film was stretched 3.5 times in the longitudinal direction at 105 ° C., then successively biaxially stretched 3.9 times in the transverse direction at 95 ° C., and heat-set at 150 ° C. Similarly, a biaxially oriented polyester film having a thickness of 25 μm was obtained. The properties of the obtained film and the reinforcing member are shown in Table 1.

[Comparative Example 1]
0.1% by weight of spherical silica having an average particle diameter of 0.3 μm was added to polyethylene terephthalate (PET) having an intrinsic viscosity of 0.61 dl / g. A lubricant shows the compounding quantity with respect to a film weight.
This PET polymer was dried at 170 ° C. for 3 hours, then supplied to an extruder, melted at a melting temperature of 280 ° C., extruded through a die slit, and then cooled and solidified on a casting drum set at a surface temperature of 20 ° C. A stretched film was prepared. This unstretched film was stretched 3.0 times in the longitudinal direction at 110 ° C. to obtain a uniaxially stretched film. Thereafter, the film was biaxially stretched 3.2 times in the transverse direction at 120 ° C., heat-fixed at 220 ° C., and re-heat treated while shrinking 2% in the transverse direction at 210 ° C. An axially oriented polyester film was obtained. The properties of the obtained film and the reinforcing member are shown in Table 1. The obtained film was insufficient in hot water resistance, elastic recovery and oxygen impermeability. Further, when used as a reinforcing member, the gas sealability is not sufficient, and the strength retention for a long period of time in a high temperature / high humidity usage environment is not sufficient.

[Comparative Example 2]
Polyethylene-2,6-naphthalenedicarboxylate (PEN) having an intrinsic viscosity of 0.60 dl / g is composed of 0.25% by weight of calcium carbonate particles having an average particle size of 0.5 μm and spherical silica particles having an average particle size of 0.2 μm. 0.1% by weight was added. A lubricant shows the compounding quantity with respect to a film weight.
This PEN polymer was dried at 175 ° C. for 5 hours, then supplied to an extruder, melted at a melting temperature of 300 ° C., extruded through a die slit, and then cooled and solidified on a casting drum set at a surface temperature of 55 ° C. An unstretched film was created. This unstretched film was stretched 3.0 times in the longitudinal direction at 140 ° C. to obtain a uniaxially stretched film. Thereafter, the film was sequentially biaxially stretched 3.2 times in the transverse direction at 135 ° C., heat-set at 245 ° C., and further reheated while shrinking 2% in the transverse direction at 240 ° C. An axially oriented polyester film was obtained. The properties of the obtained film and the reinforcing member are shown in Table 1. Although the obtained film was excellent in hot water resistance, the elastic recovery was not sufficient. Further, the oxygen impermeability was lowered as compared with the Examples. When used as a reinforcing member, the gas sealability was lower than in the Examples, and the strength retention for a long period was not sufficient in a high temperature / high humidity usage environment.

  The biaxially oriented polyester film of the present invention has mechanical strength as a polyester, is excellent in elastic recovery, gas impermeability, hot water resistance in a high temperature / high humidity environment, and is a solid polymer electrolyte fuel cell. When used as a reinforcing member for polymer electrolyte membranes, it can maintain mechanical strength for a long time even in high-temperature and high-humidity environments, and maintain confidentiality (gas sealability) without imposing a load on the electrolyte membrane. Therefore, it is useful as a solid polymer electrolyte membrane reinforcing film.

Claims (8)

Ri Do at least one layer comprising a layer of the polytrimethylene naphthalenedicarboxylate a main component, the following formula MD direction breaking strength retention time of 200 hours required to become 50% of the formula (1) Over
Breaking strength retention ratio (%) = (breaking strength X / initial breaking strength X ₀ ) × 100 (1)
(In the formula (1), the breaking strength X is the breaking strength after treatment for a predetermined time under the conditions of 121 ° C., 2 atm and 100% RH (unit: MPa), and the breaking strength X ₀ is the initial breaking strength (unit) : MPa))
A biaxially oriented polyester film for reinforcing a solid polymer electrolyte membrane.   The biaxially oriented polyester film for reinforcing a solid polymer electrolyte membrane according to claim 1, wherein the polytrimethylene naphthalene dicarboxylate is polytrimethylene-2,6-naphthalene dicarboxylate.   The biaxially oriented polyester film for reinforcing a solid polymer electrolyte membrane according to claim 1 or 2, wherein the content of polytrimethylene naphthalene dicarboxylate is 90% by weight or more based on the layer containing polytrimethylene naphthalene dicarboxylate. . The biaxially oriented polyester film for reinforcing a solid polymer electrolyte membrane according to any one of claims 1 to 3 , wherein an elastic recovery rate represented by the following formula (2) is 65% or more.
Elastic recovery rate (%) = ((L1-L2) / L1) × 100 (2)
(In Formula (2), L1 represents the amount of deformation (mm) at the time of 10% elongation, and L2 represents the amount of strain (mm) remaining when the elongation is restored to the initial position after 10% elongation) The solid polymer electrolyte membrane reinforcing material according to any one of claims 1 to 4 , wherein an easy-adhesion layer containing an acrylic resin is laminated on at least one surface of a layer containing polytrimethylene naphthalene dicarboxylate as a main component. Biaxially oriented polyester film. The biaxially oriented polyester film for reinforcing a solid polymer electrolyte membrane according to claim 5 , wherein the acrylic resin is an acrylic resin containing an amide group. The biaxially oriented polyester film for reinforcing a solid polymer electrolyte membrane according to claim 5 or 6 , wherein the easy-adhesion layer is applied before completion of crystal orientation of a layer containing polytrimethylene naphthalene dicarboxylate as a main component. A solid polymer electrolyte membrane reinforcing member comprising the biaxially oriented film for reinforcing a solid polymer electrolyte membrane according to any one of claims 1 to 7 .