Radical curable sealing member for fuel cell

Abstract

Provided is a radical-curable sealing member (4) for fuel cells, which has excellent compression crack resistance. The radical-curable sealing member (4) for a fuel cell is formed from a crosslinked product of a radical-curable composition containing the following components (A) to (D): (A) a polyisobutylene polymer having a (meth) acryloyl group at the molecular chain end, (B) a polyisobutylene polymer having a (meth) acryloyl group at the molecular chain end, and (D) a polyisobutylene polymer having a (meth) acryloyl group at the molecular chain end, with respect to 100 parts by mass of the component (A) being contained in an amount of 5 to 20 parts by mass relative to 100 parts by mass of the component (A); (B) a polyfunctional (meth) acrylic monomer having five or more functional groups; (C) a monofunctional (meth) acrylic monomer; and (D) a radical polymerization initiator.

Description

Technical Field

[0001] The present invention relates to a radical curable sealing member for sealing constituent members of a fuel cell. Background Art

[0002] A fuel cell generates electricity through an electrochemical reaction of gases, has high power generation efficiency, emits clean gases, and has little impact on the environment. Among them, a polymer electrolyte fuel cell can operate at a relatively low temperature and has a large output density. Therefore, the above-mentioned polymer electrolyte fuel cell can be expected to be used for various purposes such as power generation and power sources for motor vehicles.

[0003] In a polymer electrolyte fuel cell, a single cell formed by sandwiching a membrane electrode assembly (MEA) with separators and the like serves as a power generation unit. The MEA is composed of a polymer membrane (electrolyte membrane) as an electrolyte and a pair of electrode catalyst layers (fuel electrode (anode) catalyst layer, oxygen electrode (cathode) catalyst layer) disposed on both sides in the thickness direction of the electrolyte membrane. A porous layer for gas diffusion is also disposed on the surfaces of the pair of electrode catalyst layers. A fuel gas such as hydrogen is supplied to the fuel electrode side, and an oxidant gas such as oxygen or air is supplied to the oxygen electrode side. Power generation is performed through an electrochemical reaction at the three-phase interface of the supplied gas, electrolyte, and electrode catalyst layer. A polymer electrolyte fuel cell is constituted by fastening a single cell laminate formed by laminating a plurality of the above-mentioned single cells with end plates and the like disposed at both ends in the single cell lamination direction.

[0004] Flow paths for gases supplied to each electrode and flow paths for a refrigerant for mitigating heat generation during power generation are formed in the separator. For example, if the gases supplied to each electrode are mixed, problems such as a decrease in power generation efficiency occur. In addition, the electrolyte membrane has proton conductivity in a state containing water. Therefore, during operation, it is necessary to keep the electrolyte membrane in a moist state. Thus, in order to prevent gas mixing, gas and refrigerant leakage, and keep the inside of the single cell in a moist state, it is important to ensure the sealing performance around the MEA and the porous layer and between adjacent separators. As a sealing member for sealing these constituent members, for example, a radical curable sealing member containing a polymer such as a polyisobutene polymer or a (meth)acrylic acid polymer having a (meth)acryloyl group at the molecular chain end has been proposed (for example, refer to Patent Document 1).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2017 / 029978 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, a fuel cell is formed by stacking, for example, 200 to 300 single cells and fastening the above-described sealing member while highly compressing it (for example, a compression ratio of 50%), and thus excellent compression crack resistance (compression destruction resistance) is required.

[0010] As a method for improving compression crack resistance, a method of adding silica to the material of the sealing member is considered. However, if silica is added to the material of the sealing member, a tendency for improvement in compression crack resistance is observed. On the other hand, the Si (silicon) component from silica elutes from the sealing member over time. Therefore, for example, there is a concern that various properties of the sealing member and the fuel cell may be affected. Therefore, development of a new method different from the above-described method of adding silica is required.

[0011] The present invention has been made in view of such circumstances, and provides a radically curable sealing member for a fuel cell having excellent compression crack resistance.

[0012] Means for Solving the Problem

[0013] In the process of repeatedly conducting in-depth research based on the above circumstances, the inventors of the present invention focused on polyfunctional (meth)acrylate in the material constituting the sealing member from the viewpoint of improving compression crack resistance. The inventors of the present invention further conducted research from the viewpoint of highly balancing both the mechanical strength and the elongation rate characteristics of the sealing member, and as a result, found that when a crosslinked body formed from a radically curable composition is used as the radically curable sealing member for a fuel cell, an unexpectedly significant improvement effect in compression crack resistance can be obtained. The radically curable composition is obtained by blending a specific polyfunctional (meth)acrylic acid monomer, that is, a polyfunctional (meth)acrylic acid monomer having 5 or more functional groups, with a polyisobutene polymer having a (meth)acryloyl group at the molecular chain end in a specific content ratio.

[0014] The gist of the present invention lies in the following [1] to [6]. [1]

[0016] A radically curable sealing member for a fuel cell, which is formed from a crosslinked body of a radically curable composition containing the following components (A) to (D), and the content of the component (B) is 5 to 20 parts by mass with respect to 100 parts by mass of the component (A).

[0017] (A) A polyisobutene polymer having a (meth)acryloyl group at the molecular chain end.

[0018] (B) A polyfunctional (meth)acrylic acid monomer having 5 or more functional groups.

[0019] (C) Monofunctional (meth) acrylic monomer,

[0020] (D) Free radical polymerization initiator. [2]

[0022] The free radical curable sealing member for a fuel cell according to [1], wherein the content of the component (B) is 8 to 20 parts by mass with respect to 100 parts by mass of the component (A). [3]

[0024] The free radical curable sealing member for a fuel cell according to [1] or [2], wherein the component (B) is a polyfunctional (meth) acrylic monomer having a pentaerythritol skeleton and having 5 or more functional groups. [4]

[0026] The free radical curable sealing member for a fuel cell according to any one of [1] to [3], wherein the glass transition temperature of the free radical curable sealing member for a fuel cell is -40°C or lower. [5]

[0028] The free radical curable sealing member for a fuel cell according to any one of [1] to [4], wherein the free radical curable composition is a free radical curable composition not containing silica. [6]

[0030] The free radical curable sealing member for a fuel cell according to any one of [1] to [5], wherein no cracks are generated in the free radical curable sealing member for a fuel cell after the following compression heating treatment,

[0031] [Compression heating treatment]

[0032] Compression ratio: 50%

[0033] Heating temperature: 120°C

[0034] Heating time: 100 hours.

[0035] Advantages of the Invention

[0036] The free radical curable sealing member for a fuel cell of the present invention has excellent compression crack resistance. Therefore, it can exhibit excellent performance as a sealing member for a fuel cell. Description of the Drawings

[0037] Figure 1 It is a cross-sectional view showing an example of using the free radical curable sealing member for a fuel cell of the present invention as a sealing body. Detailed Description

[0038] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to this embodiment.

[0039] In addition, in this specification, “(meth)acrylic acid” is a term used as a concept including both acrylic acid and methacrylic acid, “(meth)acrylate” is a term used as a concept including both acrylate and methacrylate, and “(meth)acryloyl” is a term used as a concept including both acryloyl and methacryloyl. Further, “polymer” is a term used as a concept including copolymers and oligomers.

[0040] As described above, the radical curable sealing member for a fuel cell (hereinafter, sometimes referred to as “this sealing member”) according to one embodiment of the present invention is formed of a crosslinked body of a radical curable composition (hereinafter, sometimes referred to as “this radical curable composition”), and the radical curable composition contains the following components (A) to (D), and the content of the component (B) is 5 to 20 parts by mass with respect to 100 parts by mass of the component (A).

[0041] (A) A polyisobutene polymer having a (meth)acryloyl group at the molecular chain end.

[0042] (B) A polyfunctional (meth)acrylic acid monomer having 5 or more functional groups.

[0043] (C) A monofunctional (meth)acrylic acid monomer.

[0044] (D) A radical polymerization initiator.

[0045] By using the crosslinked body of this radical curable composition as the radical curable sealing member for a fuel cell, it is possible to significantly obtain an improvement effect in compression crack resistance. The reason for obtaining such an effect is not necessarily clear, but it is considered that by using a crosslinked body of a radical curable composition obtained by mixing a polyfunctional (meth)acrylic acid monomer (B) having 5 or more functional groups and further a monofunctional (meth)acrylic acid monomer (C) and a radical polymerization initiator (D) in a specific content ratio with respect to the polyisobutene polymer (A) having a (meth)acryloyl group at the molecular chain end, it is possible to highly balance both the mechanical strength and the elongation property of the sealing member, and as a result, it is possible to significantly obtain an improvement effect in compression crack resistance.

[0046] For example, when a polyfunctional (meth)acrylic acid monomer having 4 or less functional groups is used in place of the component (B) for the sealing member, although the compression crack resistance can be improved to some extent, it is difficult to highly balance both the mechanical strength and the elongation property, and thus it is impossible to significantly obtain an improvement effect in compression crack resistance.

[0047] Moreover, even if silica is not used as the material of this sealing member, it is highly useful in terms of being able to significantly obtain an improvement effect in compression crack resistance. That is, the methods for improving the compression crack resistance of the sealing member are limited. In reality, a method of incorporating silica is envisioned. However, when silica is used as the material of the sealing member, the Si (silicon) component from silica dissolves out of the sealing member over time. For example, there are concerns about affecting various properties of the sealing member and the fuel cell. Even if silica is not used as the material of this sealing member, the improvement effect in compression crack resistance can be significantly obtained, thus alleviating the above concerns.

[0048] In addition, when silica is used as the material of the sealing member, due to deviations in its particle size and surface state, there is a tendency for various properties of the sealing member to deviate, so there are concerns about quality stability. However, this sealing member can exhibit excellent compression crack resistance even without using silica, so its quality stability is excellent.

[0049] Furthermore, when silica is used as the material of the sealing member, due to its aggregability, the dispersion treatment process in the manufacturing process requires corresponding man-hours. However, this sealing member can exhibit excellent compression crack resistance even without using silica, so the man-hours required for dispersion treatment can be reduced, and the productivity and economy are excellent.

[0050] Hereinafter, each component material used in this sealing member will be described in detail.

[0051] <Component (A)>

[0052] The polyisobutene polymer having a (meth)acryloyl group at the molecular chain end is the main component of the radical curable composition used as the material of this sealing member. Generally, it is a component that accounts for 50% by mass or more, preferably 50 - 85% by mass, and more preferably about 60 - 75% by mass relative to the total amount (100% by mass) of the above composition. Compared with acrylic polymers and the like, this component (A) has excellent hydrolysis resistance and can suppress changes in mechanical properties caused by hydrolysis (such as a decrease in elongation rate due to embrittlement and an increase in hardness). Therefore, the product durability of this sealing member is excellent.

[0053] Component (A) can be used alone or in combination of two or more.

[0054] Component (A) only needs to be a polyisobutene polymer having a (meth)acryloyl group as a radical curable functional group at the molecular chain end. From the viewpoint of improving radical curability, a polyisobutene polymer having (meth)acryloyl groups at both ends of its molecular chain is preferred.

[0055] The average number of (meth)acryloyl groups introduced into each molecule of component (A) is not particularly limited, and is preferably, for example, 1.5 to 4, more preferably 1.7 to 2.5.

[0056] (A) The glass transition temperature (Tg) of the component is not particularly limited, and is preferably, for example, -40°C or lower, more preferably -50°C or lower. When the glass transition temperature (Tg) of component (A) is higher than the above temperature, a tendency for poor low-temperature sealing performance can be observed. In addition, the lower limit value of the glass transition temperature (Tg) of component (A) is not particularly limited, and is, for example, -80°C or higher.

[0057] (A) The glass transition temperature (Tg) of the component can be measured by a known method, for example, by using a differential scanning calorimeter (DSC). Specifically, using a differential scanning calorimeter (DSC) SSC-5200 manufactured by Seiko Instruments Inc., after lowering the temperature of the sample to -90°C, the measurement is carried out during the period of raising the temperature to 200°C at a heating rate of 20°C / minute, and the glass transition temperature is determined from the obtained DSC curve.

[0058] From the viewpoint of significantly exerting the effects of the present invention, the number average molecular weight (Mn) of component (A) is preferably, for example, 2000 to 100000, more preferably 3000 to 50000. When the number average molecular weight (Mn) is less than the above range, a tendency for poor compression crack resistance can be observed.

[0059] From the viewpoint of significantly exerting the effects of the present invention, the molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of component (A) is preferably, for example, 1.1 to 1.6, more preferably 1.1 to 1.4.

[0060] In addition, the above number average molecular weight (Mn) and weight average molecular weight (Mw) are measured by gel permeation chromatography (GPC). Specifically, chloroform is used as the mobile phase, the measurement is carried out using a polystyrene gel column, and the number average molecular weight and the like can be obtained by conversion to polystyrene.

[0061] From the viewpoint of significantly exerting the effects of the present invention, the viscosity of component (A) at 23°C (viscosity based on an E-type viscometer) is preferably, for example, 100 to 10000 Pa·s, more preferably 500 to 6000 Pa·s, and even more preferably 1000 to 5000 Pa·s.

[0062] (A) The specific structure of the component is not particularly limited as long as it has a (meth)acryloyl group at the molecular chain end and has a polyisobutylene backbone (-[CH2C(CH3)2]n-, where n is 2 or more). For example, known structures having the structures shown in the following formulas (1) to (4) can be cited.

[0063] [Chemical formula 1]

[0064]

[0065] In formula (1), R 1 represents an aromatic hydrocarbon group or an aliphatic hydrocarbon group with a valence of 2 or more. A represents a polyisobutylene backbone containing -[CH2C(CH3)2]- units. R 2 represents a divalent saturated hydrocarbon group with 2 to 6 carbon atoms and no heteroatoms. R 3 , R 4 each represent hydrogen, a monovalent hydrocarbon group with 1 to 20 carbon atoms, or an alkoxy group. R 5 represents hydrogen or methyl. n represents an integer of 2 or more.

[0066] [Chemical formula 2]

[0067]

[0068] [Chemical formula 3]

[0069]

[0070] [Chemical formula 4]

[0071]

[0072] In formulas (2) to (4), R 1 represents an aromatic hydrocarbon group or an aliphatic hydrocarbon group with a valence of 2 or more. A represents a polyisobutylene backbone containing -[CH2C(CH3)2]- units. R 3 , R 4 each represent hydrogen, a monovalent hydrocarbon group with 1 to 20 carbon atoms, or an alkoxy group. R 5 represents hydrogen or methyl. n represents an integer of 2 or more.

[0073] (A) The component can be a synthetic product or a commercially available product. As a commercially available product, for example, EP400V manufactured by KANEKA Corporation can be cited. In addition, as a synthesis method (manufacturing method) of the (A) component, for example, known methods described in Japanese Patent Application Laid-Open No. 2013-035901 and International Publication No. 2013-047314 can be cited.

[0074] <(Component B)>

[0075] (B) The polyfunctional (meth)acrylic monomer having 5 or more functional groups refers to a (meth)acrylate compound having 5 or more (meth)acryloyl groups in its molecular structure. As described above, from the viewpoint of exhibiting excellent compression crack resistance, it is important that this radically curable composition contains (B) the polyfunctional (meth)acrylic monomer having 5 or more functional groups, and the content of component (B) is 5 to 20 parts by mass with respect to 100 parts by mass of component (A).

[0076] As component (B), it is not limited to the following, but from the viewpoint of significantly exhibiting the effects of the present invention, a polyfunctional (meth)acrylic monomer having 5 or more functional groups having a pentaerythritol skeleton is preferred. The polyfunctional (meth)acrylic monomer having 5 or more functional groups having a pentaerythritol skeleton refers to a compound having one or more pentaerythritol skeletons (the skeleton part in pentaerythritol: C(CH2 - O - )4 residue) in the molecule and having 5 or more (meth)acryloyl groups in the molecule.

[0077] Specific examples of component (B) include, but are not limited to, dipentaerythritol penta(meth)acrylate, tripentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol hepta(meth)acrylate, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol nona(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, and their alkylene oxide-modified compounds, etc. Among them, dipentaerythritol pentacrylate and dipentaerythritol hexaacrylate are preferred.

[0078] These component (B) can be used alone or in combination of two or more.

[0079] As described above, from the viewpoint of exhibiting the effects of the present invention, it is important that the content of component (B) is 5 to 20 parts by mass with respect to 100 parts by mass of component (A). The content of component (B) can be appropriately set within the above range. From the viewpoint of significantly exhibiting the effects of the present invention, with respect to 100 parts by mass of component (A), it is preferably 6 to 20 parts by mass, more preferably 8 to 20 parts by mass, and particularly preferably 10 to 15 parts by mass.

[0080] This sealing member may contain a polyfunctional (meth)acrylic monomer having 2 to 4 functional groups as the polyfunctional (meth)acrylic monomer within the range not impairing the effects of the present invention. However, the content of the polyfunctional (meth)acrylic monomer having 2 to 4 functional groups is preferably 5 parts by mass or less, more preferably 3 parts by mass or less with respect to 100 parts by mass of component (A). When the content of the polyfunctional (meth)acrylic monomer having 2 to 4 functional groups is higher than the above range, there is a tendency for the compression crack resistance to deteriorate.

[0081] The above-mentioned difunctional to tetrafunctional polyfunctional (meth)acrylic monomers are (meth)acrylate compounds having 2 to 4 (meth)acryloyl groups in the molecular structure. Specific examples of the difunctional to tetrafunctional polyfunctional (meth)acrylic monomers include, for example, 1,6-hexanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 2,4-diethyl-1,5-pentanediol di(meth)acrylate, butylethylpropanediol di(meth)acrylate, 3-methyl-1,7-octanediol di(meth)acrylate, 2-methyl-1,8-octanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate and other alkanediol di(meth)acrylates, ethoxylated cyclohexanedimethanol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, 1,1,1-trimethylol ethane di(meth)acrylate, etc.

[0082] In addition, for example, there can be mentioned trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxytri(meth)acrylate, trimethylolpropane propoxytri(meth)acrylate, glycerol propoxytri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, bis-trimethylolpropane tetra(meth)acrylate, etc.

[0083] <(C) component>

[0084] The monofunctional (meth)acrylic monomer as the component (C) is a (meth)acrylate compound having one (meth)acryloyl group in its molecular structure. Specifically, known ethylenically unsaturated monofunctional monomers can be cited, for example, but not limited to methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate and other acrylic alkyl ester monomers. Among them, n-octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, and isodecyl acrylate are preferred, and 2-ethylhexyl acrylate is more preferred.

[0085] These components (C) can be used alone or in combination of two or more.

[0086] The content of the component (C) is not particularly limited. For example, relative to 100 parts by mass of the component (A), it is preferably 5 to 70 parts by mass, more preferably 10 to 50 parts by mass.

[0087] The glass transition temperature (Tg) of the component (C) is not particularly limited, and is preferably -40°C or lower, more preferably -50°C or lower. When the glass transition temperature (Tg) of the component (C) is higher than the above temperature, a tendency for poor low-temperature sealing performance can be observed. In addition, the lower limit value is not particularly limited, for example, it is -80°C or higher.

[0088] The glass transition temperature (Tg) of this component (C) can be measured for the homopolymer of the monofunctional (meth)acrylic monomer as the component (C) using a differential scanning calorimeter (DSC) in the same manner as described above.

[0089] <Component (D)>

[0090] The radical polymerization initiator as component (D) is not particularly limited as long as it is a compound that generates radicals upon irradiation with energy rays. Specific examples of component (D) include, but are not limited to, benzophenone-type compounds such as benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, anthraquinone-type compounds such as tert-butylanthraquinone, 2-ethylanthraquinone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, oligo{2-hydroxy-2-methyl-1-[4-(1-methylethenyl)phenyl]propanone}, benzil dimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, benzoin methyl ether, 2-methyl-[4-(methylthio)phenyl]-2-morpholin-1-propanone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropanoyl)benzyl]phenyl}-2-methylpropan-1-one and other alkylbenzophenone-type compounds, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, diethylthioxanthone, isopropylthioxanthone and other thioxanthone-type compounds, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and other acylphosphine oxide-type compounds, methyl phenylglyoxylate and other phenylglyoxylate-type compounds, etc. Among them, from the viewpoint of excellent reactivity, alkylbenzophenone-type compounds are preferred, and 2-hydroxy-2-methyl-1-phenylpropan-1-one and the like are preferred.

[0091] These components (D) can be used alone or in combination of two or more.

[0092] The content of component (D) is not particularly limited. For example, relative to 100 parts by mass of component (A), it is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass.

[0093] <Silica>

[0094] In addition to the above components (A) to (D), this radical curable composition as the material of this sealing member may contain silica, but the Si component from silica may elute from the sealing member over time, which may cause potential adverse effects on the physical properties of the sealing member and various properties of the fuel cell. Therefore, it is preferably free of silica.

[0095] When the radical curable composition contains silica, its content is preferably less than 8% by mass, more preferably less than 5% by mass, still more preferably less than 1% by mass, particularly preferably less than 0.5% by mass, and most preferably 0% by mass relative to the total amount (100% by mass) of this radical curable composition.

[0096] As the above-mentioned silica, for example, it also includes silica surface-treated with a silane compound, dimethylsilylated silica surface-treated with dimethylsilane, trimethylsilylated silica surface-treated with trimethylsilane, octylsilylated silica surface-treated with octylsilane, methacryloylsilylated silica surface-treated with methacryloyloxysilane, etc.

[0097] <Various additives>

[0098] In this free-radical curable composition, in addition to the above components (A) to (D), various additives such as fillers other than silica, anti-aging agents, compatibilizers, curability regulators, lubricants, pigments, defoamers, foaming agents, light stabilizers, and surface modifiers can be incorporated within the range that does not impair the effects of the present invention.

[0099] In addition, in this free-radical curable composition, there is a risk of hindering the power generation of the fuel cell or contaminating the platinum catalyst of the fuel cell, so it is preferably free of substances such as amine, sulfur, and phosphorus-based materials.

[0100] <Method for producing the free-radical curable composition>

[0101] This free-radical curable composition is produced by adding the above components (A) to (D) and other components and mixing and stirring them using a mixer such as a planetary mixer.

[0102] <Curing method (crosslinking method)>

[0103] This free-radical curable composition is cured (crosslinked) by active energy rays such as electron beams and ultraviolet rays. Among them, ultraviolet rays that cause less damage to the substrate are preferred. As the active energy source, there is no particular limitation, and a publicly known active energy source can be used. For example, a high-pressure mercury lamp, a black light, an LED, a fluorescent lamp, etc. can be preferably used.

[0104] <Glass transition temperature (Tg) of this sealing member>

[0105] From the viewpoint of significantly exhibiting the effects of the present invention, the glass transition temperature (Tg) of the sealing member formed from the crosslinked product of this free-radical curable composition is preferably -40°C or lower, more preferably -50°C or lower. When the above glass transition temperature (Tg) is higher than the above temperature, a tendency for poor low-temperature sealing performance can be observed. The lower limit value of the glass transition temperature (Tg) of this sealing member is not particularly limited, for example, it is -80°C or higher.

[0106] In addition, the glass transition temperature (Tg) of this sealing member is measured in the same manner as above using a differential scanning calorimeter (DSC).

[0107] <Compressive Crack Resistance of this Sealing Member>

[0108] This sealing member formed from the crosslinked product of this radically curable composition exhibits excellent compressive crack resistance. For example, this sealing member does not develop cracks even after the following compression heating treatment.

[0109] [Compression Heating Treatment]

[0110] Compression ratio: 50%

[0111] Heating temperature: 120 °C

[0112] Heating time: 100 hours

[0113] In addition, this sealing member formed from the crosslinked product of this radically curable composition preferably does not develop cracks even when the compression ratio is changed to 60% in the above compression heating treatment.

[0114] <Elongation at Break (Eb) of this Sealing Member>

[0115] This sealing member formed from the crosslinked product of this radically curable composition has good elongation characteristics. For example, the elongation at break (Eb) of this sealing member measured in an atmosphere at 23 °C in accordance with JIS K 6251 is 100% or more, preferably 140% or more, and more preferably 150% or more.

[0116] <Si Dissolution Amount (ppm) and Volume Change Rate (%) of this Sealing Member>

[0117] This sealing member exhibits excellent compressive crack resistance even without incorporating silica into this radically curable composition as its material.

[0118] Therefore, for example, the Si dissolution amount of this sealing member determined by the method described in the examples below is less than 1 ppm, more preferably less than 0.1 ppm, and even more preferably less than 0.01 ppm.

[0119] In addition, for example, the volume change rate (%) of this sealing member determined by the method described in the examples below is preferably in the range of 98 to 102%.

[0120] <Sealing Method>

[0121] As a method for sealing the above-described radically curable composition, for example, the radically curable composition is applied to a constituent member of a fuel cell, and then irradiated with active energy rays to cure it. As the coating method, various methods such as a dispenser, a sprayer, inkjet, and screen printing can be used. More specifically, sealing methods such as FIPG (Form-in-Place Gasket), CIPG (Cure-in-Place Gasket), and MIPG (Mold-in-Place Gasket) can be used.

[0122] The above-described radically curable composition can crosslink in a short time (for example, about several tens of seconds). Therefore, by using the above-described radically curable composition and sealing the constituent members of the fuel cell according to the above-described sealing method, the productivity becomes excellent. In addition, this sealing member can be easily formed into a film-like sealing member, and by thinning the sealing member, miniaturization of the fuel cell can be achieved.

[0123] <Use>

[0124] This sealing member formed from a crosslinked product of the above-described radically curable composition is used for a constituent member of a fuel cell.

[0125] <Production of This Sealing Member (Radically Curable Sealing Member for Fuel Cell)>

[0126] This sealing member can be produced as follows: After preparing a composition containing components (A) to (D) and other components as needed, for example, using a dispenser or the like to coat various constituent members such as a separator of a fuel cell, and then irradiating with active energy rays to cure it.

[0127] Alternatively, it can also be produced by applying the above-described radically curable composition to the surface of a constituent member of a fuel cell coated with an adhesive and irradiating with active energy rays to cure it.

[0128] Furthermore, it can also be preformed into a predetermined shape according to the shape of the sealed portion of various constituent members of the fuel cell. For example, if formed into a film shape, the sealing member can be pasted onto various constituent members of the fuel cell using an adhesive for use.

[0129] The constituent members of the fuel cell sealed by this sealing member vary depending on the type, structure, etc. of the fuel cell, and examples include separators (metal separators, carbon separators, etc.), gas diffusion layers, MEA (electrolyte membranes, electrodes), etc.

[0130] In Figure 1 an example of forming this sealing member into a sealed body is shown. Figure 1Mainly shows a single unit cell 1 in a fuel cell formed by stacking multiple unit cells. The unit cell 1 includes an MEA 2, a gas diffusion layer 3, a sealing member 4, a separator 5, and an adhesive layer 6. Moreover, the above-mentioned sealing member 4 is this sealing member.

[0131] In addition, as a constituent member for a fuel cell, for example, it may also be a member formed by bonding the separator 5 and the sealing member 4 via the adhesive layer 6, a member formed by bonding the separator 5 and a sealing member 4 having self-adhesive properties, etc.

[0132] Although not shown in the figure, the MEA 2 is composed of an electrolyte membrane and a pair of electrodes arranged on both sides in the stacking direction with the electrolyte membrane interposed therebetween. The electrolyte membrane and the pair of electrodes are in the shape of rectangular thin plates. The gas diffusion layers 3 are arranged on both sides in the stacking direction with the MEA 2 interposed therebetween. The gas diffusion layer 3 is a porous layer and is in the shape of a rectangular thin plate.

[0133] The separator 5 is preferably a carbon separator or a metal separator, and from the viewpoint of conduction reliability, a metal separator having a carbon thin film such as a DLC film (diamond-like carbon film) or a graphite film is particularly preferred. The separator 5 is in the shape of a rectangular thin plate and is recessed with a plurality of grooves extending in the long side direction. Through these grooves, the cross-section of the separator 5 has an uneven shape. The separator 5 is arranged opposite to each other on both sides in the stacking direction of the gas diffusion layer 3. Between the gas diffusion layer 3 and the separator 5, a gas flow path 7 for supplying gas to the electrodes is defined by the uneven shape.

[0134] The sealing member 4 is in the shape of a rectangular frame. Moreover, the sealing member 4 is bonded to the MEA 2, the peripheral portion of the gas diffusion layer 3, and the separator 5 via the adhesive layer 6 to seal the peripheral portion of the MEA 2 and the gas diffusion layer 3.

[0135] In addition, in Figure 1 the example of, the sealing member 4 uses two members separated up and down, but it may also be a single sealing member formed by combining the two.

[0136] As the material for forming the adhesive layer 6, for example, rubber paste, a rubber composition that is liquid at normal temperature (23 °C), a primer, etc. are used. As the coating method of the above materials, for example, dispensing coating, etc. can be cited, and it is usually coated under normal temperature conditions. When using the above-mentioned liquid rubber composition, the thickness of the above-mentioned adhesive layer 6 is usually 0.01 to 1 mm.

[0137] When a fuel cell such as a polymer electrolyte fuel cell operates, a fuel gas and an oxidant gas are respectively supplied through the gas flow path 7. Here, the peripheral portion of the MEA 2 is sealed by the sealing member 4 via the adhesive layer 6. Therefore, gas mixing and leakage do not occur.

[0138] Examples

[0139] Hereinafter, examples will be described together with comparative examples. However, the present invention is not limited to these examples as long as it does not exceed its gist.

[0140] First, before the examples and comparative examples, the materials shown below were prepared.

[0141] In addition, each value (measurement value, etc.) shown for each material is a value obtained according to the criteria described above.

[0142] <Component (A)>

[0143] (a1) Polyisobutene polymer having an acryloyl group at the molecular chain end (manufactured by KANEKA CORPORATION, EP400V)

[0144] <Component (B)>

[0145] (b1) Dipentaerythritol pentaacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., A-DPH)

[0146] (b2) Dipentaerythritol hexaacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., A-9550)

[0147] (b3) Poly(pentaerythritol polyacrylate) (manufactured by Shin-Nakamura Chemical Co., Ltd., TPOA-50)

[0148] <Component (B’) (2-4 functional polyfunctional (meth)acrylic acid monomer)>

[0149] (b’1) Trimethylolpropane triacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., Viscoat#295)

[0150] (b’2) Bis(trimethylolpropane) tetraacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AD-TMP)

[0151] <Component (C)>

[0152] (c1) 2-Ethylhexyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., 2EHA)

[0153] <Component (D)>

[0154] (d1) 2-Hydroxy-2-methyl-1-phenylpropan-1-one (manufactured by iGM RESINS Co., Ltd., Omnirad1173)

[0155] <Other components>

[0156] Methacrylsilylated silica

[0157] [Examples 1 to 10, Comparative Examples 1 to 8]

[0158] (Preparation of Free Radical Curable Sealing Member (Test Sample) for Fuel Cell)

[0159] Each component shown in Table 1 below was compounded in the mass ratio shown in the table and kneaded using a planetary mixer (manufactured by Inoue Manufacturing Co., Ltd.) to prepare a free radical curable composition.

[0160] Next, the above free radical curable composition was coated with a bar coater to a predetermined thickness, and ultraviolet rays were irradiated (irradiation intensity: 250 mW / cm 2 , cumulative light quantity: 3000 mJ / cm 2 ) using a high-pressure mercury UV irradiator (manufactured by Heraeus, F600V-10) to produce a sheet.

[0161] <Compression Crack Resistance>

[0162] The sheet produced above was blanked to obtain each test sample having a circular shape in plan view with a diameter of 10 mm and a thickness of 1 mm. For each of these test samples, the compression crack resistance was evaluated in accordance with JIS K 6262 (2007). That is, each test sample was compressed at a compression rate of 50% or 60%, and after heating at 120 °C for 100 hours in this state, the presence or absence of cracks in each test sample after decompression was visually confirmed and evaluated according to the following criteria. The results are shown in Table 1. In addition, "crack" means that cracks occurred on the appearance of each test sample.

[0163] 〔Evaluation Criteria〕

[0164] ◎ (Excellent): No cracks were confirmed at a compression rate of 60%.

[0165] 〇 (Very Good): Cracks were confirmed at a compression rate of 60%. No cracks were confirmed at a compression rate of 50%.

[0166] × (Poor): Cracks were confirmed at a compression rate of 50%.

[0167] <Si Dissolution Amount>

[0168] Test pieces having dimensions of 30 mm in width, 50 mm in length, and 1 mm in thickness were cut out from the sheet produced above to obtain each test sample. Each of these test samples was immersed in an aqueous sulfuric acid solution (pH 3, temperature 95 °C, 100 mL) for 1000 hours, and the Si dissolution amount after immersion was measured by ICP analysis and evaluated according to the following criteria. The results are shown in Table 1.

[0169] 〔Evaluation Criteria〕

[0170] ◎ (Excellent): Si dissolution amount is less than 0.01 ppm.

[0171] 〇(Very good): The Si dissolution amount is 0.01 ppm or more and less than 0.1 ppm.

[0172] ×(Poor): The Si dissolution amount is 0.1 ppm or more.

[0173] <Volume change rate>

[0174] Test pieces with dimensions of 30 mm in width, 50 mm in length, and 1 mm in thickness are cut from the above-prepared sheet to obtain each test sample. Each of these test samples is immersed in warm water (95 °C, 100 mL) for 1000 hours, and the volume change rate is calculated from the volume V1 before immersion and the volume V2 after immersion, and evaluated according to the following criteria. The results are shown in Table 1.

[0175] Volume change rate (%) = (Volume V2 after immersion) ÷ (Volume V1 before immersion) × 100

[0176] 〔Evaluation criteria〕

[0177] 〇(Very good): The volume change rate is 98% or more and 102% or less.

[0178] ×(Poor): The volume change rate is less than 98% or greater than 102%.

[0179] <Elongation at break (Eb)>

[0180] According to JIS K 6251 (2017), the elongation at break (Eb) is evaluated. That is, for each dumbbell-shaped test sample cut from the above-prepared sheet, the elongation at break (Eb) is measured in an atmosphere of 23 °C and evaluated according to the following criteria. The results are shown in Table 1.

[0181] 〔Evaluation criteria〕

[0182] ◎(Excellent): The value of Eb is 140% or more.

[0183] 〇(Very good): The value of Eb is less than 140% and 100% or more.

[0184] ×(Poor): The value of Eb is less than 100%.

[0185] <Glass transition temperature (Tg)>

[0186] For each test sample cut from the above-prepared sheet, the glass transition temperature (Tg) is measured using a differential scanning calorimeter (DSC). The results are shown in Table 1.

[0187]

[0188] As can be seen from the results shown in Table 1 above, the compression crack resistance of the sealing members of the embodiments that meet the various requirements specified in the present invention is excellent.

[0189] In addition, as can be seen from the results shown in Table 1 above, the sealing members of the embodiments that meet the various requirements specified in the present invention have obtained good results in the evaluations of elongation at break, Si elution amount, and volume change rate.

[0190] In contrast, it can be seen that the sealing members of Comparative Example 1 and Comparative Examples 3 to 6 do not contain the polyfunctional (meth)acrylic monomer having 5 or more functional groups specified in the present invention, and as a result, the compression crack resistance is poor. In addition, it can be seen that although the sealing member of Comparative Example 2 contains the polyfunctional (meth)acrylic monomer having 5 or more functional groups specified in the present invention, the polyfunctional (meth)acrylic monomer having 5 or more functional groups is contained in a range of 30 parts by mass with respect to 100 parts by mass of the component (A), and as a result, the compression crack resistance is poor.

[0191] In addition, it can be seen that the sealing members of Comparative Examples 7 to 8 do not contain the polyfunctional (meth)acrylic monomer having 5 or more functional groups specified in the present invention, but contain silica, and as a result, although an improvement effect is confirmed in terms of compression crack resistance, the Si elution amount (ppm) and volume change rate (%) increase.

[0192] In the above embodiments, specific modes in the present invention are shown, but the above embodiments are merely examples and are not to be construed in a limiting sense. Various deformation intentions obvious to those skilled in the art are included in the scope of the present invention.

[0193] Industrial Applicability

[0194] The sealing member of the present invention is used for a member constituting a fuel cell, for example, for a fuel cell seal formed by bonding a fuel cell component such as a metal separator and a rubber sealing member for sealing it via an adhesive layer, or for the above sealing member of a fuel cell seal formed by bonding the above sealing members via an adhesive layer.

[0195] Explanation of Reference Numerals

[0196] 1: Single cell;

[0197] 2: MEA;

[0198] 3: Gas diffusion layer;

[0199] 4: Sealing member;

[0200] 5: Separator;

[0201] 6: Adhesive layer;

[0202] 7: Gas flow path.

Claims

1. A free radical curable sealing member for a fuel cell, wherein, The free radical curable sealing member for a fuel cell is formed from a crosslinked body of a free radical curable composition, and the free radical curable composition contains the following components (A) to (D). The content of component (B) is 5 to 20 parts by mass with respect to 100 parts by mass of component (A). (A) A polyisobutene polymer having a (meth)acryloyl group at the molecular chain end. (B) A polyfunctional (meth)acrylic acid monomer having 5 or more functional groups. (C) A monofunctional (meth)acrylic acid monomer. (D) A free radical polymerization initiator.

2. The free radical curable sealing member for a fuel cell according to claim 1, wherein The content of component (B) is 8 to 20 parts by mass with respect to 100 parts by mass of component (A).

3. The radical curable sealing member for a fuel cell according to claim 1 or 2, wherein Component (B) is a polyfunctional (meth)acrylic acid monomer having 5 or more functional groups with a pentaerythritol skeleton.

4. The radical curable sealing member for a fuel cell according to any one of claims 1 to 3, wherein, The glass transition temperature of the free radical curable sealing member for a fuel cell is -40°C or lower.

5. The free radical curable sealing member for a fuel cell according to any one of claims 1 to 4, wherein, The free radical curable composition is a free radical curable composition that does not contain silica.

6. The radical curable sealing member for a fuel cell according to any one of claims 1 to 5, wherein, The free radical curable sealing member for a fuel cell does not generate cracks after the following compression heating treatment. [Compression heating treatment] Compression ratio: 50% Heating temperature: 120°C Heating time: 100 hours.

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