Radical-curable sealing member and radical-curable sealing member for fuel cell

Abstract

To provide a radical-curable sealing member that can suppress the deterioration of mechanical properties under high temperature and high humidity conditions. [Solution] A radical-curable sealing member comprising a crosslinked body of a radical-curable composition containing the following components (A) to (D), wherein the total content (A+B+C) of the following components (A) to (C) is a monofunctional (meth)acrylic monomer (a) having an alkyl group having 6 to 9 carbon atoms in component (A). A (a) The total content of the constituent units derived from (a) and the content of component (B) A The content ratio of +B) ([a A A radical-curable sealing member having 80% by mass or more of (A) monofunctional (meth)acrylic monomer (a) having alkyl groups with 6 to 9 carbon atoms. A (B) A (meth)acrylic polymer whose main constituent unit is derived from ) (C) Monofunctional (meth)acrylic monomer having alkyl groups with 6 to 9 carbon atoms (D) Polyfunctional (meth)acrylic monomer.

Description

Technical Field

[0001] The present invention relates to a radical curable seal member used for sealing components of a fuel cell and the like.

Background Art

[0002] Various seal members are used for the components constituting a fuel cell and the like. For example, in a solid polymer fuel cell for automobiles, in order to prevent leakage of gas and refrigerant and to maintain a wet state inside the cell, a seal member is used to ensure sealing performance around a membrane electrode assembly (MEA) and a porous layer and between separators.

[0003] As the above seal member, a radical curable seal member is used as one that is excellent in productivity and can be made into a thin film. As the above radical curable seal member, various types have been proposed in recent years. For example, there are those using polymers such as polyisobutylene polymer and (meth)acrylic polymer having a (meth)acryloyl group at the molecular chain end (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the power generation reaction of a fuel cell involves the generation of water, the seal member for a fuel cell is always used in an environment exposed to warm water. Under such high temperature and high humidity, there are concerns about hydrolysis and deterioration of mechanical properties (for example, decrease in elongation due to embrittlement, increase in hardness, etc.), and it is required to improve the product durability of the seal member for a fuel cell.

[0006] This invention has been made in view of these circumstances, and aims to provide a radical-curable sealing member that can suppress the deterioration of mechanical properties under high temperature and high humidity conditions and has excellent product durability. [Means for solving the problem]

[0007] The inventors diligently conducted research to solve the above problems. As a result, they found that in a radical-curable sealing member consisting of a crosslinked radical-curable composition, by using a component derived from a specific monofunctional (meth)acrylic monomer as the material constituting the radical-curable composition and controlling the content ratio of said component within a specific range, it is possible to suppress the deterioration of mechanical properties under high temperature and high humidity conditions, and a significant improvement in product durability can be obtained.

[0008] The gist of this invention is as follows: [1] to

[11] . [1] A radical-curable sealing member comprising a crosslinked body of a radical-curable composition containing the following components (A) to (D), The total content (A+B+C) of the following components (A) to (C) is the monofunctional (meth)acrylic monomer (a) having an alkyl group with 6 to 9 carbon atoms in component (A). A (a) The total content of the constituent units derived from (a) and the content of component (B) A The content ratio of +B) ([a A A radical-curable sealing member in which [A+B+C] × 100) is 80% by mass or more. (A) Monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms (a A (Meth)acrylic polymer whose main constituent units are derived from ) (B) Monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms. (C) Polyfunctional (meth)acrylic monomer. (D) Radical polymerization initiator. [2] The above component (A) is a monofunctional (meth)acrylic monomer (a) having an alkyl group with 6 to 9 carbon atoms. A The radical-curable sealing member according to [1] is a (meth)acrylic polymer containing 80% by mass or more of constituent units derived from ). [3] The above monofunctional (meth)acrylic monomer (a) having an alkyl group with 6 to 9 carbon atoms A The radical-curable sealing member according to [1] or [2], wherein the is at least one selected from the group consisting of hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate. [4] The radical-curable sealing member according to any one of [1] to [3], wherein the above component (A) is a (meth)acrylic polymer further containing monomer-derived structural units having a carboxyl group. [5] The radical-curable sealing member according to any one of [1] to [4], wherein the content of component (B) is 10 to 50 parts by mass per 100 parts by mass of component (A). [6] The radical-curable sealing member according to any one of [1] to [5], wherein the above component (B) is at least one selected from the group consisting of hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate. [7] The radical-curable sealing member according to any one of [1] to [6], wherein the above-mentioned component (C) is at least one selected from the group consisting of 1,9-nonanediol diol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, and polypentaerythritol poly(meth)acrylate. [8] The radical-curable sealing member according to any one of [1] to [7], wherein the content of component (C) is 1 to 20 parts by mass per 100 parts by mass of component (A). [9] A radical-curable sealing member according to any one of [1] to [8], wherein the content of component (D) is 0.01 to 10 parts by mass per 100 parts by mass of component (A).

[10] The radical-curable sealing member described above is a radical-curable sealing member for fuel cells, as described in any of [1] to [9].

[11] The radical-curable sealing member according to any one of [1] to

[10] , wherein the glass transition temperature of the radical-curable sealing member is -10°C or lower. [Effects of the Invention]

[0009] The radical-curable sealing member of the present invention can suppress the deterioration of mechanical properties under high temperature and high humidity conditions, resulting in superior product durability. Therefore, it can exhibit excellent performance as a sealing member for fuel cells, for example. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing an example in which the radical-curable sealing member for fuel cells of the present invention is used as a sealing body. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below. However, the present invention is not limited to these embodiments. In the present specification, "(meth)acryl" is a term used as a concept encompassing both acrylic and methacrylic, "(meth)acrylate" is a term used as a concept encompassing both acrylate and methacrylate, and "(meth)acryloyl group" is a term used as a concept encompassing both acryloyl group and methacryloyl group. Further, "polymer" is a term used as a concept encompassing copolymers and oligomers. Furthermore, in the present specification, "X and / or Y (where X and Y are arbitrary configurations)" means at least one of X and Y, and means three cases: only X, only Y, and X and Y.

[0012] The radical curable seal member for a fuel cell according to one embodiment of the present invention (hereinafter sometimes referred to as "this seal member") is, as described above, a radical curable seal member composed of a crosslinked body of a radical curable composition containing components (A) to (D) (hereinafter sometimes referred to as "this radical curable composition"), and the content of the structural unit derived from the monofunctional (meth)acrylic monomer (a A ) having an alkyl group with 6 to 9 carbon atoms in component (A) and the total content of the content of component (B) (a A + B) ([a A + B] / [A + B + C] × 100) is 80% by mass or more. (A) A (meth)acrylic polymer having a structural unit derived from a monofunctional (meth)acrylic monomer (a A ) having an alkyl group with 6 to 9 carbon atoms as a main structural unit. (B) A monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms. (C) A polyfunctional (meth)acrylic monomer. (D) A radical polymerization initiator.

[0013] In the process of diligently studying how to suppress the deterioration of mechanical properties under high temperature and high humidity conditions, the inventors focused on hydrophobic monomer components as materials used in radical-curable sealing members from the viewpoint of improving hydrolysis resistance. As a result of their studies, the inventors found that while the use of hydrophobic monomer components resulted in improved hydrolysis resistance, the hardness and elongation properties were still unsatisfactory, making it difficult to obtain radical-curable sealing members with excellent product durability. Based on this finding, the inventors further diligently conducted experiments and found that by focusing on components derived from monofunctional (meth)acrylic monomers having alkyl groups with 6 to 9 carbon atoms as constituent materials of the radical-curable composition, and by controlling the content of these components within a specific range, the deterioration of mechanical properties under high temperature and high humidity conditions can be suppressed, and a significant improvement in product durability can be obtained.

[0014] In other words, as in the present invention, the total content (A+B+C) of the above components (A) to (C) is a monofunctional (meth)acrylic monomer (a) having an alkyl group with 6 to 9 carbon atoms in component (A). A (a) The total content of constituent units derived from (B) monofunctional (meth)acrylic monomers having alkyl groups with 6 to 9 carbon atoms (a A The content ratio of +B) ([a A By setting the ratio of (+B) / [A+B+C]×100) to 80% by mass or more, the deterioration of mechanical properties under high temperature and high humidity conditions can be suppressed, and an improvement in product durability can be obtained.

[0015] The above content ratio ([a A The ratio of [A+B+C] × 100) can be set appropriately within the above range, but for example, 80-98% by mass, 85-97% by mass, 90-96% by mass, etc. are preferred.

[0016] Furthermore, in one preferred embodiment of the present invention, it is particularly preferred that component (A) and / or component (B) do not have heat-sensitive structural sites or structural sites that serve as starting points for hydrolysis. Specifically, in component (A), monofunctional (meth)acrylic monomer (a) having an alkyl group having 6 to 9 carbon atoms is preferred. A (B) preferably does not have a hydrophilic group, and also, monofunctional (meth)acrylic monomers having an alkyl group with 6 to 9 carbon atoms also preferably do not have a hydrophilic group.

[0017] <<Radical-curable sealing material>> This sealing member is a crosslinked material of a radical-curable composition containing components (A) to (D). The individual component materials used in the radical-curable composition will be described in detail below.

[0018] <(A) component> Monofunctional (meth)acrylic monomers having an alkyl group with 6 to 9 carbon atoms (a A (Meth)acrylic polymer (A), whose main constituent units are derived from ), is the main component of this radical-curable composition. The content of component (A) is, for example, 50% by mass or more, preferably 50-85% by mass, and more preferably 55-75% by mass, based on the total amount (100% by mass) of this radical-curable composition.

[0019] (A) In component (a), a monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms A The constituent units derived from ) are the main constituent units. Here, "monofunctional (meth)acrylic monomer" means a (meth)acrylate compound having one (meth)acryloyl group in its molecular structure, and "main constituent unit" means the monofunctional (meth)acrylic monomer (a) relative to the total constituent units (100% by mass) of component (A). A This means that it contains 60% or more by mass of constituent units derived from ).

[0020] In this sealing member, from the viewpoint of suppressing the deterioration of mechanical properties under high temperature and high humidity conditions, a monofunctional (meth)acrylic monomer (a) having an alkyl group with 6 to 9 carbon atoms is selected.A The content of constituent units derived from (a) is preferably 80% by mass or more, more preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably about 94-98% by mass, relative to the total constituent units of component (A) (100% by mass). A If the content of constituent units derived from ) is within the above range, the material tends to have particularly excellent hydrolysis resistance or heat aging resistance.

[0021] Also, monofunctional (meth)acrylic monomers having an alkyl group with 6 to 9 carbon atoms (a A From the viewpoint of suppressing the deterioration of mechanical properties under high temperature and high humidity, it is preferable that the ) is a monofunctional (meth)acrylic monomer that does not have a hydrophilic group. Examples of the hydrophilic group include hydroxyl group, ether group, amine group, amide group, etc.

[0022] Also, monofunctional (meth)acrylic monomers having an alkyl group with 6 to 9 carbon atoms (a A The glass transition temperature (Tg) of the material is preferably -10°C or lower, more preferably -30°C or lower, and even more preferably -50°C or lower, from the viewpoint of suppressing increased hardness and a decrease in elongation properties. The glass transition temperature (Tg) can be appropriately set within the above range, for example, -52°C or lower, -54°C or lower, -56°C or lower, etc. The lower limit of the glass transition temperature (Tg) is not particularly limited, but it is, for example, -80°C or higher.

[0023] Monofunctional (meth)acrylic monomers having an alkyl group with 6 to 9 carbon atoms (a AThe glass transition temperature (Tg) of the above monofunctional (meth)acrylic monomer is measured using a differential scanning calorimeter (DSC) with a homopolymer of the above monofunctional (meth)acrylic monomer. Specifically, using a Seiko Instruments SSC-5200 differential scanning calorimeter (DSC), the sample is first heated to 150°C at a rate of 20°C / min, held for 5 minutes, and then pre-adjusted by lowering the temperature to -90°C at a rate of 10°C / min. Measurements are then taken while the temperature is raised to 150°C at a rate of 20°C / min, and the integral value is obtained from the resulting DSC curve. The glass transition temperature is then determined from the point of maximum value.

[0024] Monofunctional (meth)acrylic monomers having an alkyl group with 6 to 9 carbon atoms (a A Preferred examples of these, from the viewpoint of significantly demonstrating the effects of the present invention, include, for example, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, etc. These may be used individually or in combination of two or more. Among these, hexyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, hexyl acrylate and 2-ethylhexyl acrylate are more preferred, and 2-ethylhexyl acrylate is even more preferred.

[0025] (Other monomer components) (A) Component (a) is a monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms, to the extent that it does not inhibit the effects of the present invention. A ) may contain monomer components copolymerizable with (A). However, the content of copolymerizable monomer components is, for example, 15% by mass or less, 10% by mass or less, 5% by mass or less, etc., relative to the total constituent units of component (A) (100% by mass).

[0026] Examples of copolymerizable monomer components include, but are not limited to, monomers having a carboxyl group, monomers having a glycidyl group, monomers having a functional group containing a nitrogen atom (amino group, amide group), monomers having an isocyanate group, monomers having an acetoacetyl group, monomers having a hydroxyl group, and so on.

[0027] Examples of monomers having a carboxyl group include (meth)acrylic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, monomethyl maleate, and monomethyl itaconic acid. Among these, (meth)acrylic acid is preferred from the viewpoint of hydrolysis resistance and heat aging resistance.

[0028] The content of constituent units derived from monomers having a carboxyl group is not particularly limited, but is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, relative to the total constituent units of component (A) (100% by mass). The content of constituent units derived from monomers having a carboxyl group can be appropriately set within the above range, and may be, for example, 1 to 2% by mass.

[0029] Examples of monomers having a glycidyl group include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate. The content of constituent units derived from monomers having a glycidyl group is not particularly limited, but is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, relative to the total constituent units (100% by mass) of component (A). The content of constituent units derived from monomers having a glycidyl group can be appropriately set within the above range, for example, 2 to 4% by mass.

[0030] (A) A preferred embodiment of component (A) is, for example, a (meth)acrylic polymer whose main constituent units are one or more constituent units selected from the group consisting of hexyl (meth)acrylate and 2-ethylhexyl (meth)acrylate. Furthermore, a more preferred embodiment of component (A) is a (meth)acrylic polymer that contains as its main constituent units one or more constituent units selected from the group consisting of hexyl (meth)acrylate and 2-ethylhexyl (meth)acrylate, and also contains constituent units derived from monomers having a carboxyl group. Furthermore, a more preferred embodiment of component (A) is, for example, a (meth)acrylic polymer that contains as its main constituent units one or more selected from the group consisting of hexyl (meth)acrylate and 2-ethylhexyl (meth)acrylate, and also contains constituent units derived from monomers having a carboxyl group and constituent units derived from monomers having a glycidyl group.

[0031] (Method of manufacturing component (A)) (A) As a method for producing component (A), known polymerization methods can be appropriately employed. For example, a monofunctional alkyl (meth)acrylic monomer (a) having an alkyl group with 6 to 9 carbon atoms is mixed in an organic solvent such as methyl isobutyl ketone. A ), and polymerization methods include mixing or dropwise adding copolymerizable monomer components and polymerization initiators such as azo polymerization initiators as needed.

[0032] In the polymerization method described above, appropriate methods for supplying the monomers can be a batch-feeding method in which the entire amount of monomer components is supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc. The polymerization temperature can be set as appropriate, but for example, it is 30°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, preferably 120°C or lower, more preferably 100°C or lower, and even more preferably 90°C or lower. The organic solvent is not particularly limited, but examples include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; hydrocarbon solvents such as cyclohexane, hexane, heptane, and methylcyclohexane; aromatic solvents such as toluene and xylene; and ester solvents such as butyl acetate, ethyl acetate, and methyl acetate. The above organic solvent may be a mixed solvent containing two or more organic solvents.

[0033] (A) A preferred method for producing component (a) is, for example, a monofunctional (meth)acrylic monomer (a A Examples include a copolymer consisting of a monomer and copolymerizable monomer components, mixed with a monomer having a carboxyl group, and obtained by an addition reaction of the monomer having a carboxyl group. In the above addition reaction, an organic solvent and a catalyst can be used as appropriate.

[0034] The above-mentioned organic solvents can be used as appropriate. Furthermore, while there are no particular limitations on catalysts, examples include basic catalysts such as pyridine, pyrrole, triethylamine, diethylamine, dibutylamine, and amines such as ammonia; phosphines such as tributylphosphine and triphenylphosphine; metal alkoxide compounds such as copper naphthenate, cobalt naphthenate, zinc naphthenate, tributoxyaluminum, and tetrabutoxytrititanium; Lewis acids such as aluminum chloride; and organotin compounds such as dibutyltin dilaurate.

[0035] (Physical properties of component (A)) The glass transition temperature (Tg) of component (A) is not particularly limited, but is preferably -45°C or lower. If the glass transition temperature (Tg) of component (A) is higher than the above temperature, it tends to have poor low-temperature sealing properties, for example. The glass transition temperature (Tg) of component (A) can be set appropriately within the above range, for example, -50°C or lower, -52°C or lower, etc. The lower limit of the glass transition temperature (Tg) of component (A) is not particularly limited, but for example, it is -80°C or higher.

[0036] The glass transition temperature (Tg) of component (A) is measured by differential scanning calorimeter (DSC). Specifically, using a Seiko Instruments SSC-5200 differential scanning calorimeter (DSC), the sample is first heated to 150°C at a rate of 20°C / min, held for 5 minutes, and then lowered to -90°C at a rate of 10°C / min as a preliminary adjustment. Measurements are then taken while the sample is heated to 150°C at a rate of 20°C / min, and the integral value is obtained from the resulting DSC curve. The glass transition temperature is then determined from the point of maximum value.

[0037] (A) The number-average molecular weight (Mn) of component (A) is preferably 30,000 to 700,000, more preferably 50,000 to 600,000, and even more preferably 80,000 to 200,000, from the viewpoint of significantly demonstrating the effects of the present invention and from the viewpoint of balancing strength and viscosity. The number-average molecular weight (Mn) is measured by gel permeation chromatography (GPC). Specifically, chloroform is used as the mobile phase, and the measurement is performed on a polystyrene gel column. The number-average molecular weight can then be determined in terms of polystyrene equivalent.

[0038] <(B) component> This radical-curable composition contains (B) a monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms. Component (B) may be used alone or in combination of two or more.

[0039] In this radical-curable composition, (B) the content of monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms, and (A) the monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms in component (a A ) Total content of constituent units derived from (a A It is important to specify the content of +B) within a particular range. The above content ratio ([a A If the ratio of [A+B+C] × 100 is 80% by mass or more, the deterioration of mechanical properties under high temperature and high humidity conditions can be suppressed, resulting in superior product durability.

[0040] (B) Content of component and (A) monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms (a A ) Total content of constituent units derived from (a A The content ratio of component (B) relative to +B (B / [a A The above content ratio (B / [a A +B] × 100) can be set appropriately within the above range, for example, 8 to 48 mass%, 10 to 45 mass%, 15 to 42 mass%, 20 to 40 mass%, etc.

[0041] Component (B) is preferably a monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms, and preferably a monofunctional (meth)acrylic monomer that does not have a hydrophilic group. If the monofunctional (meth)acrylic monomer of component (B) has a hydrophilic group, the effect of suppressing the deterioration of mechanical properties under high temperature and high humidity tends to decrease. Examples of the above hydrophilic group include hydroxyl group, ether group, amine group, amide group, etc.

[0042] The glass transition temperature (Tg) of component (B) is preferably -10°C or lower, more preferably -30°C or lower, and even more preferably -50°C or lower, from the viewpoint of suppressing increased hardness and reduced elongation. The glass transition temperature (Tg) can be appropriately set within the above range, for example, -52°C or lower, -54°C or lower, -56°C or lower, etc. The lower limit of the glass transition temperature (Tg) is not particularly limited, but it is, for example, -80°C or higher.

[0043] The glass transition temperature (Tg) of component (B) is measured using a differential scanning calorimeter (DSC) with a homopolymer of the monofunctional (meth)acrylic monomer described above. Specifically, a Seiko Instruments SSC-5200 differential scanning calorimeter (DSC) is used. The sample is first heated to 150°C at a rate of 20°C / min, held for 5 minutes, and then lowered to -90°C at a rate of 10°C / min as a preliminary adjustment. Measurements are then taken while the sample is heated to 150°C at a rate of 20°C / min. The integral value is obtained from the resulting DSC curve, and the glass transition temperature is determined from its maximum point.

[0044] (B) Preferred specific examples of component include, for example, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, etc. These may be used individually or in combination of two or more. Among these, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, isooctyl acrylate, isononyl acrylate, and isodecyl acrylate are preferred from the viewpoint of significantly exhibiting the effects of the present invention.

[0045] (B) The content of component (B) is preferably 10 to 50 parts by mass per 100 parts by mass of component (A) from the viewpoint of significantly achieving the effects of the present invention. The content of component (B) can be appropriately set within the above range, for example, 20 to 50 parts by mass, 30 to 50 parts by mass, 40 to 50 parts by mass, etc.

[0046] <(C) component> (C) The polyfunctional (meth)acrylic monomer is a (meth)acrylate compound having two or more (meth)acryloyl groups in its molecular structure. Specifically, known ethylenically unsaturated polyfunctional monomers are included, and examples of (meth)acrylic monomers having two (meth)acryloyl groups in their molecular structure include 1,6-hexanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol diol 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, and butylethylpropional Examples include alkanediol di(meth)acrylates such as cindiol di(meth)acrylate, 3-methyl-1,7-octanediol di(meth)acrylate, 2-methyl-1,8-octanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated cyclohexanedimethanol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, and 1,1,1-trishydroxymethylethane di(meth)acrylate.

[0047] Examples of (meth)acrylic monomers having three or more (meth)acryloyl groups include trimethylolpropane tri(meth)acrylate, trimethylolpropaneethoxytri(meth)acrylate, trimethylolpropanepropoxytri(meth)acrylate, glycerinpropoxytri(meth)acrylate, tetramethylolmethanetri(meth)acrylate, tetramethylolmethanetetra(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, and pentaerythritol acrylate compounds having a pentaerythritol structure and a (meth)acrylate structure, such as monopentaerythritol(meth)acrylate, dipentaerythritol(meth)acrylate, tripentaerythritol(meth)acrylate, and polypentaerythritol(meth)acrylate.

[0048] Among these (C) components, from the viewpoint of significantly exhibiting the effects of the present invention, alkanediol di(meth)acrylates such as 1,6-hexanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol diol 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 pentaerythritol acrylate compounds are preferred. Among these, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol diol di(meth)acrylate, and pentaerythritol acrylate compounds are more preferred, with 1,9-nonanediol diol di(meth)acrylate being particularly preferred.

[0049] These (C) components may be used individually or in combination of two or more. For example, a mixture of tripentaerythritol acrylate, dipentaerythritol acrylate, monopentaerythritol acrylate, and polypentaerythritol acrylate may be used as the pentaerythritol acrylate compound.

[0050] (C) The content of component (C) is preferably 1 to 20 parts by mass, and more preferably 2 to 12 parts by mass, per 100 parts by mass of component (A), from the viewpoint of significantly exhibiting the effects of the present invention and enhancing crosslinkability, etc.

[0051] <(D) component> The radical polymerization initiator of component (D) is not particularly limited as long as it is a compound that generates radicals when irradiated with energy rays. Specific examples of component (D) are not limited to the following, but include, for example, benzophenone-type compounds such as benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, methyl orthobenzoylbenzoate, and 4-phenylbenzophenone; anthraquinone-type compounds such as t-butylanthraquinone and 2-ethylanthraquinone; 2-hydroxy-2-methyl-1-phenylpropan-1-one; oligo{2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone}; benzyldimethyl ketal; 1-hydroxycyclohexylphenyl ketone; benzoin methyl ether; 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone; 2-hydroxy-1-{ Examples include alkylphenone-type compounds such as 4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one, thioxanthone-type compounds such as 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, diethylthioxanthone, and isopropylthioxanthone, acylphosphine oxide-type compounds such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and phenylglyoxylate-type compounds such as phenylglyoxylic acid methyl ester. Among these, alkylphenone-type compounds are preferred from the viewpoint of excellent reactivity, and 2-hydroxy-2-methyl-1-phenylpropan-1-one is particularly preferred. These (D) components may be used individually or in combination of two or more.

[0052] The content of component (D) is not particularly limited, but for example, it is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 8 parts by mass, and even more preferably 1 to 6 parts by mass, per 100 parts by mass of component (A).

[0053] <Thickening agent ingredients (thickeners)> In addition to components (A) to (D), this radical-curable composition may contain thickening agents such as fillers and fatty acid amides as needed. These thickening agents are useful when it is necessary to increase the viscosity of the composition during the manufacture of this sealing member. The thickening agents may be used alone or in combination of two or more.

[0054] The filler is not particularly limited, but examples include silica, carbon black, calcium carbonate, titanium dioxide, talc, clay, and glass balloons. Furthermore, from the viewpoint of improving dispersibility, silica hydrophobized with a surface treatment agent is also possible. As silica hydrophobized with a surface treatment agent, for example, silica surface-treated with a silane compound is preferred, and dimethylsilylated silica surface-treated with dimethylsilane, trimethylsilylated silica surface-treated with trimethylsilane, octylsilylated silica surface-treated with octylsilane, and methacrylsilylated silica surface-treated with methacryloxysilane are more preferred, with trimethylsilylated silica and methacrylsilylated silica being particularly preferred.

[0055] Examples of fatty acid amides include caproic acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, oleic acid amide, erucic acid amide, methylenebisstearamide, and ethylenebisstearamide.

[0056] If a thickening agent component is included, its content is usually 0.1 to 50 parts by mass per 100 parts by mass of component (A). The content of the thickening agent component can be appropriately set within the above range, for example, 0.5 to 40 parts by mass, 1 to 30 parts by mass, 1 to 20 parts by mass, 1 to 10 parts by mass, etc.

[0057] <Various Additives> This radical-curable composition may contain various additives, such as antioxidants, compatibilizers, curing modifiers, lubricants, pigments, foaming agents, light stabilizers, and surface modifiers, to the extent that they do not impair the effects of the present invention. Furthermore, it is desirable that this radical-curable composition not contain amines, sulfur, or phosphorus-based materials, as these may inhibit the power generation of fuel cells or contaminate the platinum catalyst of the fuel cell.

[0058] (a) A (a) The total content of constituent units derived from (B) monofunctional (meth)acrylic monomers having alkyl groups with 6 to 9 carbon atoms (a A The content ratio of +B) ([a A The ratio of [+B] / total amount of radical-curable composition × 100) is preferably 80% by mass or more. By setting it within the above range, the decrease in mechanical properties under high temperature and high humidity conditions can be suppressed, and an improvement in product durability can be obtained. The above content ratio ([a A The ratio of +B] / total amount of radical-curable composition × 100) can be set appropriately within the above range, for example, 82-95% by mass, 84-96% by mass, 86-94% by mass, etc.

[0059] <<Method for producing radical-curable compositions>> This radical-curable composition is manufactured by adding components (A) to (D) and other components, and mixing and stirring them using a mixer such as a planetary mixer.

[0060] As one embodiment of the present invention, a radical-curable sealing member obtained by crosslinking a radical-curable composition containing 10 to 50 parts by mass of component (B), 1 to 20 parts by mass of component (C), and 0.01 to 10 parts by mass of component (D) per 100 parts by mass of component (A) is preferred. (A) Monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms (a A (Meth)acrylic polymer whose main constituent units are derived from ) (B) Monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms. (C) Polyfunctional (meth)acrylic monomer. (D) Radical polymerization initiator.

[0061] <<Curing method (crosslinking method)>> This radical-curable composition is cured (crosslinked) by active energy rays such as electron beams or ultraviolet rays. Among these, ultraviolet rays are preferred as they cause less damage to the substrate. The active energy source is not particularly limited and known sources can be used, for example, high-pressure mercury lamps, black lights, LEDs, fluorescent lamps, etc. can be preferably used.

[0062] <<Physical properties of this sealing material>> <Glass transition temperature (Tg) of this sealing material> The glass transition temperature (Tg) of the sealing member made of the crosslinked radical curable composition is preferably -10°C or lower, from the viewpoint of significantly exhibiting the effects of the present invention. If the glass transition temperature (Tg) is higher than the above temperature, for example, the low-temperature sealing performance tends to be poor. The lower limit of the glass transition temperature (Tg) of the sealing member is not particularly limited, but for example, it is -50°C or higher. The glass transition temperature (Tg) of this sealing member is measured, for example, using a dynamic viscoelasticity measuring device by the method described in the examples below.

[0063] <Elongation at break of this sealing material (Eb)> The sealing member made of the crosslinked radical curable composition exhibits excellent suppression of the deterioration of mechanical properties under high temperature and high humidity conditions, for example, ΔEb measured by the method described in the examples below. 1t The (decrease rate after immersion at 120°C for 1000 hours) is preferably within 20%, and more preferably within 15%. Furthermore, the ΔEb of the sealing member, as measured by the method described in the following examples, is also specified. 2t The rate of decrease (after immersion at 120°C for 2000 hours) is preferably 20% or less, and more preferably 15% or less.

[0064] <This sealing component has an M50 (50% modulus)> The sealing member made of the crosslinked radical curable composition can suppress the deterioration of mechanical properties under high temperature and high humidity conditions. For example, the sealing member can achieve a ΔM50 measured by the method described in the examples below. 1t The change after immersion at 120°C for 1000 hours is preferably within 0.5 MPa, and more preferably within 0.3 MPa. Furthermore, the sealing member has a ΔM50 measured by the method described in the following examples. 2t The change (after immersion at 120°C for 2000 hours) is preferably within 0.5 MPa, and more preferably within 0.3 MPa.

[0065] <<Sealing Method>> The sealing method for the above-mentioned radical-curable composition can be, for example, by applying the radical-curable composition to the components of a fuel cell and curing it by irradiating it with active energy rays. Various methods can be used for application, such as dispensers, sprays, inkjet printers, and screen printing. More specifically, sealing methods such as FIPG (foam-in-place gasket), CIPG (cure-in-place gasket), and MIPG (mold-in-place gasket) can be used.

[0066] Since the above radical-curable composition can be crosslinked in a short time (for example, several tens of seconds), using the above radical-curable composition to seal the components of a fuel cell according to the above sealing method results in excellent productivity. Furthermore, this sealing member can be easily made into a film-like sealing member, and by making the sealing member thinner, it is possible to miniaturize the fuel cell.

[0067] <<Applications>> This sealing member, which consists of a crosslinked material of the above-mentioned radical-curable composition, is suitably used as a component of a fuel cell.

[0068] <<Manufacturing of this sealing component (radical-curable sealing component for fuel cells)>> This sealing member can be manufactured by preparing a composition containing components (A) to (D), and other components as needed, applying it to various components such as fuel cell separators using a dispenser, and curing it by irradiation with active energy rays. Furthermore, the fuel cell can also be manufactured by applying the above-mentioned radical-curable composition to a surface on which adhesive has been applied to various components of the fuel cell, and then curing it by irradiating it with active energy rays. Furthermore, the sealing material can be molded into a predetermined shape according to the shape of the parts of the fuel cell components that need to be sealed. For example, if it is molded into a film, the sealing material can be attached to the various components of the fuel cell with an adhesive and used for sealing.

[0069] The fuel cell components sealed by this sealing member vary depending on the type and structure of the fuel cell, but examples include separators (metal separators, carbon separators, etc.), gas diffusion layers, and MEAs (electrolyte membranes, electrodes).

[0070] Figure 1 shows an example in which this sealing member is used as a seal. Figure 1 mainly shows a single cell 1 in a fuel cell in which multiple cells are stacked, and cell 1 comprises an MEA 2, a gas diffusion layer 3, a sealing member 4, a separator 5, and an adhesive layer 6. The sealing member 4 is this sealing member.

[0071] Furthermore, the components for the fuel cell may include, for example, a separator 5 and a sealing member 4 bonded together via an adhesive layer 6, or a separator 5 and a self-adhesive sealing member 4 bonded together.

[0072] MEA2, although not shown in the diagram, consists of an electrolyte membrane and a pair of electrodes positioned on both sides of the electrolyte membrane in the stacking direction. The electrolyte membrane and the pair of electrodes are rectangular thin plates. Gas diffusion layers 3 are positioned on both sides of MEA2 in the stacking direction. The gas diffusion layers 3 are porous layers and are rectangular thin plates.

[0073] The separator 5 is preferably a carbon separator or a metal separator, and from the viewpoint of conductivity 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 has a rectangular plate shape and has numerous grooves extending in the longitudinal direction. Due to these grooves, the cross-section of the separator 5 has an uneven shape. The separator 5 is arranged opposite 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 electrode is defined using the uneven shape.

[0074] The sealing member 4 has a rectangular frame shape. The sealing member 4 is bonded to the peripheral edges of the MEA 2 and gas diffusion layer 3, and to the separator 5 via the adhesive layer 6, thereby sealing the peripheral edges of the MEA 2 and gas diffusion layer 3. In the example shown in Figure 1, the sealing member 4 uses two separate members, one above the other. However, it is also possible to use a single sealing member made by combining both of these members.

[0075] Materials used to form the adhesive layer 6 include, for example, rubber glue, a rubber composition that is liquid at room temperature (23°C), and a primer. Methods for applying the above materials include, for example, dispenser application, and are usually applied under room temperature conditions. The thickness of the adhesive layer 6 is typically 0.01 to 1 mm when using the liquid rubber composition.

[0076] During operation of fuel cells such as polymer electrolyte fuel cells, fuel gas and oxidizer gas are supplied through gas passages 7, respectively. Here, the periphery of the MEA 2 is sealed by a sealing member 4 via an adhesive layer 6. Therefore, gas mixing and leakage do not occur. [Examples]

[0077] The following describes the examples along with comparative examples. However, the present invention is not limited to these examples unless it exceeds the essence of the invention.

[0078] First, we prepared the following materials.

[0079] <(A) component> [Acrylic Polymer A1] • Synthesis process 1 (Synthesis of the main polymer) A 1 L round-bottom flask equipped with a stirrer, reflux condenser, argon inlet, monomer dropper port, and polymerization initiator port was charged with 156.12 g of solvent (methyl isobutyl ketone), and the mixture was bubbling with argon gas for 0.5 hours to degas it. Then, 150 g of 2-ethylhexyl acrylate, 4.03 g of glycidyl methacrylate, and 2.09 g of polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile)) were added at a temperature below 30°C, and the mixture was homogenized by stirring with a blunt force. The flask was then heated to 65°C, and the polymerization reaction was carried out for 8 hours while stirring with a blunt force. After the polymerization reaction, the mixture was cooled to room temperature, and solid-liquid separation of the polymer was performed using methanol. After that, the polymer was thoroughly washed with methanol and dried in a vacuum dryer at 40°C for 24 hours. • Synthesis process 2 (addition of acrylic groups) In a 1 L round-bottom flask equipped with a stirrer, reflux condenser, argon inlet, monomer dropper port, and polymerization initiator port, 156.12 g of solvent (methyl isobutyl ketone) and 0.39 g of catalyst (triphenylphosphine) were charged and dissolved by stirring at 40°C. Then, the entire amount of the polymer obtained in synthesis step 1 was added and redissolved by stirring at 40°C. Next, 2.14 g of acrylic acid was added, the flask was heated to 80°C, and the polymerization reaction was carried out for 8 hours with stirring. After the polymerization reaction, the mixture was cooled to room temperature, and solid-liquid separation of the polymer was performed using methanol. After thoroughly washing the polymer with methanol, it was dried in a vacuum dryer at 40°C for 24 hours to obtain acrylic polymer A1 (polyacrylate 2-ethylhexyl polymer) (Tg: -69°C, number-average molecular weight (styrene equivalent): approximately 100,000).

[0080] [Acrylic Polymer A2] • Synthesis process 1 (Synthesis of the main polymer) A 1 L round-bottom flask equipped with a stirrer, reflux condenser, argon inlet, monomer dropper port, and polymerization initiator port was charged with 157.22 g of solvent (methyl isobutyl ketone), and the mixture was bubbling with argon gas for 0.5 hours to degas it. Then, 150 g of hexyl acrylate, 4.75 g of glycidyl methacrylate, and 2.47 g of polymerization initiator (2'-azobis(2,4-dimethylvaleronitrile)) were added at a temperature below 30°C, and the mixture was homogenized by stirring with a blunt force. The flask was then heated to 65°C, and the polymerization reaction was carried out for 8 hours while stirring with a blunt force. After the polymerization reaction, the mixture was cooled to room temperature, and solid-liquid separation of the polymer was performed using methanol. The polymer was then thoroughly washed with methanol and dried in a vacuum dryer at 40°C for 24 hours. • Synthesis process 2 (addition of acrylic groups) In a 1 L round-bottom flask equipped with a stirrer, reflux condenser, argon inlet, monomer dropper port, and polymerization initiator port, 157.22 g of solvent (methyl isobutyl ketone) and 0.46 g of catalyst (triphenylphosphine) were charged and dissolved by stirring at 40°C. Then, the entire amount of the polymer obtained in synthesis step 1 was added and redissolved by stirring at 40°C. Next, 2.53 g of acrylic acid was added, the flask was heated to 80°C, and the polymerization reaction was carried out for 8 hours with stirring. After the polymerization reaction, the mixture was cooled to room temperature, and solid-liquid separation of the polymer was performed using methanol. After thoroughly washing the polymer with methanol, it was dried in a vacuum dryer at 40°C for 24 hours to obtain acrylic polymer A2 (hexyl polyacrylate polymer) (Tg: -57°C, number-average molecular weight (styrene equivalent): approximately 100,000).

[0081] <Acrylic polymers other than component (A)> [Acrylic polymer (1)] • Synthesis process 1 (Synthesis of the main polymer) 158.8 g of solvent (methyl isobutyl ketone) was charged into a 1 L round-bottom flask equipped with a stirrer, reflux condenser, argon inlet, monomer dropper port, and polymerization initiator port. The mixture was bubbling with argon gas for 0.5 hours and then degassed. Subsequently, 150 g of butyl acrylate, 5.79 g of glycidyl methacrylate, and 3.01 g of polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile)) were added at a temperature below 30°C, and the mixture was homogenized by stirring with a blunt force. The flask was then heated to 65°C, and the polymerization reaction was carried out for 8 hours while stirring with a blunt force. After the polymerization reaction, the mixture was cooled to room temperature, and solid-liquid separation of the polymer was performed using methanol. After thoroughly washing the polymer with methanol, it was dried in a vacuum dryer at 40°C for 24 hours. • Synthesis process 2 (addition of acrylic groups) In a 1 L round-bottom flask equipped with a stirrer, reflux condenser, argon inlet, monomer dropper port, and polymerization initiator port, 158.8 g of solvent (methyl isobutyl ketone) and 0.56 g of catalyst (triphenylphosphine) were charged and dissolved by stirring at 40°C. Then, the entire amount of polymer obtained in synthesis step 1 was added and redissolved by stirring at 40°C. Subsequently, 3.08 g of acrylic acid was added, the flask was heated to 80°C, and the polymerization reaction was carried out for 8 hours with stirring. After the polymerization reaction, the mixture was cooled to room temperature, and solid-liquid separation of the polymer was performed using methanol. After thoroughly washing the polymer with methanol, it was dried in a vacuum dryer at 40°C for 24 hours to obtain acrylic polymer (1) (polyacrylate-butyl polymer) (Tg: -54°C, number-average molecular weight (styrene equivalent): approximately 100,000).

[0082] <(B) component> Monofunctional acrylic monomer B1: 2-ethylhexyl acrylate (Tg: -70℃) Monofunctional acrylic monomer B2: Hexyl acrylate (Tg: -58℃) Monofunctional acrylic monomer B3: Octyl acrylate (Tg: -65℃) Monofunctional acrylic monomer B4: Isononyl acrylate (Tg: -58℃) Monofunctional acrylic monomer B5: Isodecyl acrylate (Tg: -62℃)

[0083] <Acrylic monomers other than component (B)> • Monofunctional acrylic monomer (1): Butyl acrylate (Tg: -58℃) • Monofunctional acrylic monomer (2): Lauryl acrylate (Tg: -3℃) • Monofunctional acrylic monomer (3): Isovonyl acrylate (Tg: 97℃)

[0084] <(C) component> • Polyfunctional acrylic monomer C1: Pentaerythritol tetraacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) • Polyfunctional acrylic monomer C2:1,9-nonanedioldiol diacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) • Polyfunctional acrylic monomer C3: Polypentaerythritol polyacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.)

[0085] <(D) component> • Polymerization initiator D1: Omnirad184 (manufactured by iGM RESINS)

[0086] <Other ingredients> • Thickening agent (1): Silica (Aerosil RM50, manufactured by Nippon Aerosil Co., Ltd.) • Thickening agent (2): Fatty acid amide (Flonon RCM300TL, manufactured by Kyoeisha Chemical Co., Ltd.)

[0087] [Examples 1-13, Comparative Examples 1-4] A radical-curable composition was prepared by mixing the components shown in Table 1 in the proportions shown in the table and kneading them in a planetary mixer (manufactured by Inoue Seisakusho Co., Ltd.). Next, the radical-curable composition is applied to a predetermined thickness using a bar coater, and then irradiated with ultraviolet light using a high-pressure mercury UV irradiator (Heraeus, F600V-10) (irradiation intensity: 250 mW / cm²). 2 Total luminous intensity: 3000 mJ / cm² 2 A test sample (crosslinked material) with a thickness of 1 mm was prepared.

[0088] <Glass transition temperature (Tg)> The dynamic viscoelasticity (temperature dependence) of the test sample was measured using a dynamic viscoelasticity analyzer (Reogel-E4000F, UBM). The measurement conditions were tensile mode, with a measurement temperature of -70 to 200°C, a measurement frequency of 1 Hz, an amplitude of 10 μm, and a heating rate of 3°C / min. The tanδ peak temperature obtained was defined as the glass transition temperature (Tg). The glass transition temperature (Tg) was evaluated according to the following criteria. The results are shown in Tables 1 and 2. For samples showing multiple tanδ peak temperatures or broad peaks, those with the highest temperature peak below -20°C were evaluated as "○", and those above -20°C were evaluated as "×". (Evaluation Criteria) ×...Glass transition temperature (Tg) is above -20°C ○...Glass transition temperature (Tg) is below -20℃

[0089] In Table 1, "-" in the evaluation column indicates that measurement was not taken, and "*" indicates that the measurement was broadened.

[0090] <Durability Test (Heat Aging Resistance & Hydrolysis Resistance Test)> Tensile tests were performed on the test samples, and the elongation at break (Eb) and 50% modulus (M50) were measured. (1) Initial durability testing A JIS No. 3 dumbbell was prepared from a test sample, and the initial elongation at break (Eb) [%] and modulus 50 (M50) [MPa] were measured in accordance with JIS K 6251 under a 23°C atmosphere. (2) Durability test after immersion at 120°C for 1000 hours A JIS No. 3 dumbbell was prepared from a test sample, immersed in pure water (120°C) in a heat-resistant container for 1000 hours, and then air-dried at room temperature for more than 3 days. After air-drying, the elongation at break (Eb) was measured in accordance with JIS K 6251 at an atmosphere of 23°C. 1t )[%] and 50% modulus (M50 1t The pressure [MPa] was measured. (3) Durability test after immersion at 120°C for 2000 hours A JIS No. 3 dumbbell was prepared from a test sample, immersed in pure water (120°C) in a heat-resistant container for 2000 hours, and then air-dried at room temperature for more than 3 days. After air-drying, the elongation at break (Eb) was measured in accordance with JIS K 6251 at an atmosphere of 23°C. 2t )[%] and 50% modulus (M50 2t The pressure [MPa] was measured.

[0091] [Elongation at severance (Eb)] The elongation at the time of cutting (Eb) 1t or Eb 2t The rate of decrease in [%] was calculated according to the following formula and evaluated according to the following criteria. The results are shown in Tables 1 and 2. ΔEb 1t ={(Eb-Eb 1t ) / Eb}×100 ΔEb 2t ={(Eb-Eb 2t ) / Eb}×100 (Evaluation Criteria) ×…ΔEb 1t over 20% ○…ΔEb 1t within 20% ◎...ΔEb 2t within 20%

[0092] [50% Modulus] The above 50% modulus (M50 1t or M50 2t The change in ) was calculated according to the following formula and evaluated according to the following criteria. The results are shown in Tables 1 and 2. ΔM50 1t =M50-M50 1t (MPa) ΔM50 2t =M50-M50 2t (MPa) (Evaluation Criteria) ×…ΔM50 1t is over 0.5 MPa ○…ΔM50 1t within 0.5 MPa ◎...ΔM50 2twithin 0.5 MPa

[0093] For Examples 3, 7-13, and Comparative Example 4, the elongation at break and 50% modulus based on the above "(3) Durability test after immersion at 120°C for 2000 hours" were not evaluated, so the evaluation criteria were set to "○" or "×", and the results are shown in the table. Also, for Comparative Examples 1 and 2, it was not possible to measure the elongation at break and 50% modulus based on the above "(3) Durability test after immersion at 120°C for 2000 hours", so the evaluation criteria were set to "○" or "×", and the results are shown in the table.

[0094] <Hydrolysis Evaluation Test> JIS No. 3 dumbbells were prepared from test samples and immersed in pure water (120°C) in a heat-resistant container for 1000 hours, followed by air drying at room temperature for at least 3 days. After air drying, the hydrolysis properties of the test specimens were evaluated using Fourier transform infrared spectroscopy (FT-IR) according to the following criteria. The results are shown in Tables 1 and 2. This evaluation test assesses whether or not acrylic acid is produced due to the hydrolysis of acrylic acid esters. ·Measurement area: 500~4000cm -1 ·Measurement method: ATR method (Evaluation Criteria) ×...1700cm -1 A clear peak (a peak derived from acrylic acid) was observed. 〇…1700cm -1 No clear peak (a peak derived from acrylic acid) was observed.

[0095] [Table 1]

[0096] [Table 2]

[0097] Note that in the table, "(a A"(A+B+C) × 100" is the ratio of the total content of components (A) to (C) to the monofunctional (meth)acrylate monomer (a) having an alkyl group with 6 to 9 carbon atoms in component (A). A This is the content ratio of the total content of the constituent units derived from () and the content of component (B).

[0098] From the results in Table 1 above, it can be seen that the sealing members of the embodiments that satisfy each requirement of the present invention all have a sufficiently low glass transition temperature and excellent resistance to heat aging and hydrolysis.

[0099] In contrast, the sealing member of Comparative Example 1 contains an acrylic polymer whose main constituent unit is a monofunctional alkyl (meth)acrylic monomer having an alkyl group with 4 carbon atoms, and (A) monofunctional alkyl (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms as defined in the present invention (a A It does not contain (meth)acrylic polymer whose main constituent unit is a constituent unit derived from ). The sealing member of Comparative Example 1 contains a specific content ratio ([a A The value of [+B] / [A+B+C]×100) is low, indicating poor resistance to heat aging and hydrolysis.

[0100] Furthermore, the sealing member of Comparative Example 2 contains a monofunctional alkyl acrylic monomer having an alkyl group with 4 carbon atoms, and does not contain the monofunctional alkyl (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms as defined in the present invention. The sealing member of Comparative Example 2 contains the specific content ratio ([a A The value of [+B] / [A+B+C]×100) is low, indicating poor resistance to heat aging and hydrolysis.

[0101] Furthermore, the sealing members of Comparative Examples 3 and 4 are monofunctional alkyl (meth)acrylic monomers (a) having an alkyl group with 6 to 9 carbon atoms as defined in the present invention. A It does not contain the specific content ratio ([a AThe ratio of [A+B+C] × 100) is low, and the glass transition temperature is high, which means that the hardening at low temperatures in the operating environment cannot be suppressed, making it unsuitable as a sealing material. [Industrial applicability]

[0102] The sealing member of the present invention is used in components constituting a fuel cell, for example, in a fuel cell seal body in which a rubber sealing member that seals a fuel cell component such as a metal separator is bonded to it via an adhesive layer, or in a fuel cell seal body in which the sealing members are bonded to each other via an adhesive layer. [Explanation of symbols]

[0103] 1 cell 2 MEA 3. Gas diffusion layer 4. Sealing member 5 Separators 6 Adhesive layer 7 Gas flow path

Claims

1. A radical-curable sealing member comprising a crosslinked body of a radical-curable composition containing the following components (A) to (D), The total content (A + B + C) of the components (A) to (C) below is the monofunctional (meth)acrylic monomer (a) having an alkyl group with 6 to 9 carbon atoms in component (A) below. Ａ (a) The total content of the constituent units derived from (a) and the content of component (B) Ａ The content ratio of +B) ([a Ａ A radical-curable sealing member having a ratio of 80% or more by mass of [A + B + C] × 100. (A) Monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms (a Ａ (Meth)acrylic polymer whose main constituent units are derived from ) (B) Monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms. (C) Polyfunctional (meth)acrylic monomer. (D) Radical polymerization initiator.

2. The above component (A) is a monofunctional (meth)acrylic monomer (a) having an alkyl group having 6 to 9 carbon atoms. Ａ The radical-curable sealing member according to claim 1, which is a (meth)acrylic polymer containing 80% by mass or more of constituent units derived from ).

3. The above monofunctional (meth)acrylic monomer having an alkyl group with 6 to 9 carbon atoms (a Ａ The radical-curable sealing member according to claim 1 or 2, wherein the is at least one selected from the group consisting of hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate.

4. The radical-curable sealing member according to claim 1 or 2, wherein the above component (A) is a (meth)acrylic polymer further comprising monomer-derived structural units having a carboxyl group.

5. The radical-curable sealing member according to claim 1 or 2, wherein the content of component (B) is 10 to 50 parts by mass per 100 parts by mass of component (A).

6. The radical-curable sealing member according to claim 1 or 2, wherein component (B) is at least one selected from the group consisting of hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate.

7. The radical-curable sealing member according to claim 1 or 2, wherein the above-mentioned component (C) is at least one selected from the group consisting of 1,9-nonanediol diol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, and polypentaerythritol poly(meth)acrylate.

8. The radical-curable sealing member according to claim 1 or 2, wherein the content of component (C) is 1 to 20 parts by mass per 100 parts by mass of component (A).

9. The radical-curable sealing member according to claim 1 or 2, wherein the content of component (D) is 0.01 to 10 parts by mass per 100 parts by mass of component (A).

10. The radical-curable sealing member according to claim 1 or 2, wherein the radical-curable sealing member is a radical-curable sealing member for a fuel cell.

11. The radical-curable sealing member according to claim 1 or 2, wherein the glass transition temperature of the radical-curable sealing member is -10°C or lower.

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