JP2023017551A - Resin composition for solid polymer type fuel cell seal material and seal material using resin composition, and solid polymer type fuel cell using seal material - Google Patents

Abstract

To provide a resin composition for a solid polymer type fuel cell seal material which suppresses deterioration of adhesive force under high temperatures, is excellent in durability under high temperature and high humidity, can suppress changes in a shape of a seal material and film thickness in hot press under high temperature and pressurization, and is excellent in shape stability and a seal material using the resin composition, and a solid polymer type fuel cell using the seal material.SOLUTION: A resin composition for a solid polymer type fuel cell seal material contains an acrylic resin (A) having an acid value of less than 15 mgKOH/g, an acrylic resin (B) having an acid value of 15 mgKOH/g or more, and a crosslinking agent.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a resin composition for a polymer electrolyte fuel cell sealing material, a sealing material using the resin composition, and a polymer electrolyte fuel cell using the sealing material.

A polymer electrolyte fuel cell (hereinafter sometimes referred to as a "fuel cell") electrochemically reacts a hydrogen-containing fuel gas with an oxygen-containing oxidant gas to generate electric power. It generates heat at the same time.
FIG. 1 shows a cross-sectional view of a cell 10, which is a structural unit of a typical fuel cell. A typical fuel cell is constructed by stacking several tens to hundreds of cells 10, sandwiching the stack with end plates via current collector plates and insulating plates, and tightening them from both ends with fastening bolts. be.
A fuel cell constructed in this way operates in a high-temperature and high-humidity state, and a very small amount of hydrofluoric acid elutes from the solid polymer electrolyte membrane (hereinafter sometimes referred to as "electrolyte membrane"). Therefore, the means disclosed in Patent Documents 1 to 3 have been proposed as the sealing material 16 used under such conditions.

JP-A-2002-42835 JP-A-2000-56694 JP 2008-171667 A

Patent document 1 uses urethane-based resin or liquid silicone rubber as a sealing material. However, the urethane resin has a problem of being hydrolyzed in a high-humidity environment. Polyurethane resins are broadly classified into polyester and polyether types, but both are weak against heat, with polyester resins losing their adhesive strength at temperatures below 100°C and polyether resins at around 70°C. rice field. Liquid silicone rubber has the problem that it has low mechanical strength and is easily hydrolyzed by acids and alkalis.
Patent document 2 uses an olefin-based resin or a soft epoxy-based resin as a sealing material. However, olefin resins do not have sufficient adhesive strength because the cohesive strength of the resin decreases in high temperature environments, and soft epoxy resins have the problem that adhesive strength decreases due to softening in high temperature environments. rice field.
Patent Document 3 uses a composition containing a styrene-based block polymerization elastomer and a tackifier as a sealing material. However, this composition has a lower adhesive strength in a high-temperature environment.
In addition, the sealing material may become thinner than designed due to exposure to high-temperature pressurization during hot pressing with the electrolyte membrane during fuel cell manufacturing, and it exhibits sufficient performance as a sealing material. Sometimes I couldn't.

The present invention suppresses a decrease in adhesive strength at high temperatures, has excellent durability at high temperatures and high humidity, and can suppress changes in the shape and film thickness of the sealing material due to hot press at high temperatures and high pressures. An object of the present invention is to provide a polymer electrolyte fuel cell sealing material excellent in shape stability, a sealing material using the resin composition, and a polymer electrolyte fuel cell using the sealing material. do.

In order to solve the above problems, the present invention provides the following [1] to [11].
[1] A resin composition for a polymer electrolyte fuel cell sealing material, containing an acrylic resin (A) having an acid value of less than 15 mgKOH/g, an acrylic resin (B) having an acid value of 15 mgKOH/g or more, and a cross-linking agent. .
[2] The polymer electrolyte fuel cell seal according to [1], wherein the mass ratio (A)/(B) of the resin (A) and the resin (B) is 20/80 or more and 80/20 or less. Resin composition for lumber.
[3] The resin (A) is obtained by copolymerizing raw material components containing 5% by mass to 40% by mass of styrene and 20% by mass to 60% by mass of methyl methacrylate, and has a weight average molecular weight of 300,000. The resin composition for polymer electrolyte fuel cell sealing material according to [1] or [2], which is the above copolymer resin.
[4] The polymer electrolyte fuel cell seal according to [3], wherein the raw material component of the resin (A) further contains one or more selected from glycidyl acrylate, glycidyl methacrylate, acrylic acid and methacrylic acid. Resin composition for lumber.
[5] The solid polymer type according to [3] or [4], wherein the raw material component of the resin (A) further contains an alkyl (meth)acrylate having an alkyl group with 2 or more carbon atoms. A resin composition for a fuel cell sealing material.
[6] The resin (B) is obtained by copolymerizing raw material components containing 30% by mass or more and 70% by mass or less of styrene and 5% by mass or more and 30% by mass or less of methyl methacrylate, and has a weight average molecular weight of 200,000. The resin composition for polymer electrolyte fuel cell sealing material according to any one of [1] to [5], which is the above copolymer resin.
[7] The polymer electrolyte fuel cell seal according to [6], wherein the raw material component of the resin (A) further contains one or more selected from glycidyl acrylate, glycidyl methacrylate, acrylic acid and methacrylic acid. Resin composition for lumber.
[8] The solid polymer type according to [6] or [7], wherein the raw material component of the resin (B) further contains an alkyl (meth)acrylate having an alkyl group with 2 or more carbon atoms. A resin composition for a fuel cell sealing material.
[9] The resin composition for polymer electrolyte fuel cell sealing material according to any one of [1] to [8], wherein the cross-linking agent is an amine epoxy cross-linking agent.
[10] A sealing material for polymer electrolyte fuel cells, formed from the resin composition according to any one of [1] to [9].
[11] A polymer electrolyte fuel cell comprising a sealing portion with the sealing material for a polymer electrolyte fuel cell according to [10].

According to the present invention, the adhesive strength is suppressed at high temperatures, and the durability is excellent at high temperatures and high humidity. It is possible to provide a polymer electrolyte fuel cell sealing material excellent in suppressible shape stability, a sealing material using the resin composition, and a polymer electrolyte fuel cell using the sealing material. can.

It is a cross-sectional view showing an example of a cell that constitutes a general fuel cell.

[Resin composition for polymer electrolyte fuel cell sealing material]
The resin composition for a polymer electrolyte fuel cell sealing material of the present invention comprises an acrylic resin (A) having an acid value of less than 15 mgKOH/g (hereinafter also referred to as "resin (A)") and an acid value of 15 mgKOH/g. It is characterized by containing the above acrylic resin (B) (hereinafter also referred to as "resin (B)") and a cross-linking agent.

In general, the acid value in a resin is an index of the content of acidic substituents such as carboxylic acid and hydroxyl groups in the resin, and generally, the higher the acid value, the greater the content of acidic substituents. Since this acidic substituent becomes a cross-linking point for a cross-linking reaction in a resin, cross-linking can be achieved by blending a resin having such an acidic substituent and using a cross-linking agent such as epoxy or isocyanate.

Conventional resin compositions for fuel cell sealing materials have used resin compositions that have not undergone a cross-linking reaction. Therefore, although problems such as peeling do not readily occur under high temperature and high humidity conditions, the shape of the sealing material is likely to change, so there have been cases where the function as a sealing material cannot be sufficiently exhibited.
On the other hand, in order to improve the shape change as described above, it has been practiced to use a resin composition for a fuel cell sealing material after cross-linking. For some reason, the curing of the resin composition as a whole impairs the fluidity, and thus the performance of the sealing material under high temperature and pressure conditions is impaired.

In the resin composition of the present invention, since the resin (A) has an acid value of less than 15 mgKOH/g, it is a resin with few cross-linking points, while the resin (B) has an acid value of 15 mgKOH/g or more. , is a resin with many cross-linking points. In the resin composition of the present invention, by blending two resins having different amounts of cross-linking points, the cross-linking of the resin composition becomes non-uniform. A change in shape can be suppressed. By having the above characteristics, the resin composition of the present invention suppresses a decrease in adhesive strength at high temperatures, has excellent durability at high temperatures and high humidity, and can be subjected to heat press etc. at high temperatures and high pressures. It is possible to obtain a sealing material excellent in shape stability that can suppress changes in the shape and film thickness of the sealing material.

The acid value of the resin (A) and the resin (B) of the present invention is determined by a neutralization titration method using potassium hydroxide or the like according to JIS K 0070 (1992).
In the present invention, when the acid value of resin (A) cannot be obtained as a measured value, the acid value of resin (A) is 0 mgKOH/g, indicating that the resin has few cross-linking points.

The acid value of the resin (A) is preferably 12 mgKOH/g or less, more preferably 10 mgKOH/g or less, and even more preferably 8 mgKOH/g or less, from the viewpoint of easily improving the flexibility of the resin composition under high temperature and high humidity conditions. . Moreover, the lower limit of the acid value of the resin (A) is preferably 0 mgKOH/g or more.
The lower limit of the acid value of the resin (B) is 15 mgKOH/g or more, preferably 16 mgKOH/g or more, and 17 mgKOH/g or more, from the viewpoint of easily improving the shape stability of the resin composition at high temperatures. is more preferable. Further, the upper limit of the acid value of the resin (B) is preferably 100 mgKOH/g or less, more preferably 95 mgKOH/g or less, more preferably 90 mgKOH/g or less, from the viewpoint of suppressing cross-linking of the resin composition and ensuring flexibility. More preferred.

The difference between the acid value of resin (A) and the acid value of resin (B) ([acid value of resin (B)] - [acid value of resin (A)]) is preferably 5 mgKOH/g or more, and 10 mgKOH/ g or more is more preferable, 15 mgKOH/g or more is still more preferable, and 20 mgKOH/g or more is even more preferable. When the difference between the acid value of the resin (A) and the acid value of the resin (B) is 5 mgKOH/g or more, the cross-linking of the resin composition tends to be non-uniform, so the resin composition can be used under high temperature and high humidity conditions. The flexibility and shape stability of the resin composition at high temperatures can be easily improved.
Further, the difference between the acid value of resin (A) and the acid value of resin (B) ([acid value of resin (B)] - [acid value of resin (A)]) is preferably 90 mgKOH/g or less, 80 mgKOH/g or less is more preferable, 75 mgKOH/g or less is still more preferable, and 70 mgKOH/g or less is even more preferable. When the difference between the acid value of the resin (A) and the acid value of the resin (B) is 90 mgKOH/g or less, it becomes easier to prevent the crosslink density of the resin composition from becoming too low, so It is possible to achieve both the flexibility of the resin composition in and the shape stability of the resin composition at high temperatures.

The acid values of resin (A) and resin (B) can be adjusted, for example, by increasing the ratio of carboxylic acid monomers in the monomer composition ratio during polymer polymerization.
By increasing the ratio of the carboxylic acid monomer, the acid values of the resin (A) and the resin (B) are increased, and the resin (A) and the resin (B) can be resins having many cross-linking points. On the other hand, by decreasing the ratio of the carboxylic acid monomer, the acid values of the resin (A) and the resin (B) are decreased, and the resin (A) and the resin (B) can be resins with few cross-linking points.

In the resin composition of the present invention, the mass ratio (A)/(B) of resin (A) and resin (B) is preferably 20/80 or more and 80/20 or less, and 30/70 or more and 70/30. The following are preferred. When the mass ratio (A)/(B) is within the above range, the flexibility of the resin composition under high temperature and high humidity and the shape stability at high temperature can be easily improved in a well-balanced manner.

[Resin (A) and Resin (B)]
Resin (A) is a copolymer having a weight average molecular weight of 300,000 or more obtained by copolymerizing raw material components containing 5% by mass or more and 40% by mass or less of styrene and 20% by mass or more and 60% by mass or less of methyl methacrylate. Resin is preferred.
The resin (B) is obtained by copolymerizing raw material components containing 30% by mass or more and 70% by mass or less of styrene and 5% by mass or more and 30% by mass or less of methyl methacrylate, and has a weight average molecular weight of 200,000 or more. A copolymer resin is preferred.
Since the resin (A) and the resin (B) have the above characteristics, it is possible to obtain a resin composition and a sealing material having excellent durability under high temperature and high humidity.
In addition, in this invention, a weight average molecular weight is a value which measured by the gel permeation chromatogram method (GPC method) and converted into polystyrene.

<Styrene>
The resin (A) and the resin (B) in the resin composition of the present invention preferably contain styrene (styrene monomer) as a raw material component.
Since styrene is a nonpolar component whose constituent element is CH, by introducing styrene into the resin (A) and the resin (B) in the present invention, a polar material (for example, an electrolyte membrane) and a nonpolar material It is possible to easily provide excellent adhesiveness and adhesion between the components of.
In addition, since styrene has a relatively high glass transition temperature (Tg), by introducing styrene into the copolymer resin of the present invention, it is easy to obtain heat-resistant adhesion due to the effect of improving cohesion.
A common technique for imparting heat-resistant adhesion to a resin composition is to add a silane coupling agent, a tackifier, etc. to the resin to impart adhesiveness, but the silane coupling agent seeps out ( bleed out), which may impair the reliability of the product. However, by incorporating it into the resin itself as a copolymer component, bleeding out can be easily suppressed.

The content of styrene in the raw material components of the resin (A) is preferably 5% by mass or more and 40% by mass or less, more preferably 7% by mass or more and 35% by mass or less, and 9% by mass or more and 30% by mass or less. More preferred.
By setting the content of styrene in the raw material components of the resin (A) to 5% by mass or more, it is possible to easily improve the adhesiveness and adhesion when the resin composition of the present invention is used as a sealing material. Further, by setting the content of styrene in the raw material components of the resin (A) to 40% by mass or less, the hardness of the resin composition of the present invention can be easily adjusted to follow the shape of the adherend. Moreover, since the proportion of methyl methacrylate, which will be described later, can be ensured, it is possible to further suppress a decrease in adhesive strength in a high-temperature environment and to improve acid resistance.

The styrene content in the raw material components of the resin (B) is preferably 30% by mass or more and 70% by mass or less, more preferably 35% by mass or more and 65% by mass or less, and 40% by mass or more and 60% by mass or less. More preferred.
By setting the content of styrene in the raw material component of the resin (B) to 30% by mass or more, it is possible to easily improve the adhesiveness and adhesion when the resin composition of the present invention is used as a sealing material. The shape stability of the resin composition can be easily improved. Further, by setting the content of styrene in the raw material components of the resin (B) to 70% by mass or less, the hardness of the resin composition of the present invention can be easily adjusted to follow the shape of the adherend. Moreover, since the proportion of methyl methacrylate, which will be described later, can be ensured, it is possible to further suppress a decrease in adhesive strength in a high-temperature environment and to improve acid resistance.

<Methyl methacrylate>
It is preferable that the resin (A) and the resin (B) in the resin composition of the present invention contain methyl methacrylate (methyl methacrylate monomer) as a raw material component.
By using methyl methacrylate together with styrene, the glass transition temperature (Tg) of the resin (A) and the resin (B) obtained by copolymerizing the raw material components can be finely adjusted, and the weight average molecular weight can be adjusted. can do. Therefore, in the resin composition containing the resin (A) and the resin (B), it is possible to easily control the adhesiveness and bonding conditions between materials having different polarities.
In addition, since the resin (A) and the resin (B) contain methyl methacrylate, it is possible to easily suppress the decrease in weight due to the decomposition of the resin composition by moisture and acid. It is possible to suppress the decrease in the cohesive strength and adhesive strength of.

The content of methyl methacrylate (methyl methacrylate monomer) in the raw material component of the resin (A) is preferably 20% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 55% by mass or less, More preferably, it is 20% by mass or more and 50% by mass or less.
By setting the content of methyl methacrylate in the raw material components of the resin (A) to 20% by mass or more, the softening point of the resin composition of the present invention can be increased, and the handleability when used as a sealing material can be easily improved. Furthermore, it is possible to easily improve the shape stability. Further, by setting the content of methyl methacrylate to 60% by mass or less, the hardness of the resin composition of the present invention can be easily adjusted to follow the shape of the adherend.

The content of methyl methacrylate (methyl methacrylate monomer) in the raw material component of the resin (B) is preferably 5% by mass or more and 30% by mass or less, more preferably 8% by mass or more and 25% by mass or less, More preferably, it is 10% by mass or more and 20% by mass or less.
By setting the content of methyl methacrylate in the raw material component of the resin (B) to 5% by mass or more, the softening point of the resin composition of the present invention can be increased, and the handleability when used as a sealing material can be easily improved. Furthermore, it is possible to easily improve the shape stability. Further, by setting the content of methyl methacrylate to 30% by mass or less, the hardness of the resin composition of the present invention can be easily adjusted to follow the shape of the adherend.

<Other monomers>
Resins (A) and (B) preferably further contain one or more selected from glycidyl acrylate, glycidyl methacrylate, acrylic acid and methacrylic acid as other monomers in the raw material components.
By containing other monomers in the raw material components of the resin (A), it becomes easier to secure the cohesive force of the resin while maintaining the adhesive force in a high-temperature environment.

As other monomers in the raw material components of the copolymer resin, any of the above compounds can be suitably used, but from the viewpoint of handling properties such as skin irritation, stability as a compound, and ease of synthesis. , glycidyl methacrylate and methacrylic acid are more preferred.

The content of other monomers in the raw material components of the resin (A) is preferably 0.5% by mass or more and 5% by mass or less, more preferably 0.8% by mass or more and 4% by mass or less, and 1% by mass or more and 3% by mass. % or less is more preferable. When the content of the other monomer in the raw material components of the resin (A) is 0.5% by mass or more, the cohesive force of the resin of the resin composition of the present invention can be more easily improved. In addition, since the content of other monomers in the raw material components of the resin (A) is 5% by mass or less, the copolymer resin is prevented from gelling, and the proportion of methyl methacrylate is ensured to ensure hot water resistance and acid resistance. It is easy to improve the quality. In addition, since the acid value of the resin (A) can be lowered, the resin (A) can be a resin with few cross-linking points, and the cross-linking of the resin composition of the present invention can be made uneven. It is possible to easily achieve both durability under high temperature and high humidity and shape stability under high temperature and pressure.

The content of other monomers in the raw material components of the resin (B) is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 12% by mass or less, and further preferably 3% by mass or more and 10% by mass or less. preferable. When the content of other monomers in the raw material components of the resin (B) is 1% by mass or more, the cohesive force of the resin of the resin composition of the present invention can be more easily improved. In addition, since the content of other monomers in the raw material components of the resin (A) is 15% by mass or less, the copolymer resin is prevented from gelling, and the proportion of methyl methacrylate is ensured to ensure hot water resistance and acid resistance. It is easy to improve the quality. In addition, since the acid value of the resin (B) can be increased, the resin (B) can be a resin having many cross-linking points, and the cross-linking of the resin composition of the present invention can be made uneven. It is possible to easily achieve both durability under high temperature and high humidity and shape stability under high temperature and pressure.

<Alkyl (meth)acrylate having an alkyl group having 2 or more carbon atoms>
It is preferable that the resin (A) and the resin (B) further contain an alkyl (meth)acrylate having an alkyl group having 2 or more carbon atoms among the raw material components.
By containing styrene and methyl methacrylate as raw material components, the resin (A) and the resin (B) can suppress deterioration due to moisture and acid, and can improve adhesive strength in a high-temperature environment. The softening point of the resin may become too high. Here, by containing an alkyl (meth)acrylate having an alkyl group with a carbon number of 2 or more as a raw material component, the softening point of the copolymer resin is lowered, and the sealing material is heat-sealed to the sealing portion of the fuel cell. workability can be improved.

As the alkyl (meth)acrylate having 2 or more carbon atoms, alkyl (meth)acrylates other than methyl methacrylate can be used, such as n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate. , butyl (meth)acrylate such as tert-butyl (meth)acrylate, ethyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, heptyl (meth)acrylate Acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate acrylates and the like.
The alkyl (meth)acrylate having 2 or more carbon atoms is preferably an alkyl acrylate from the viewpoint that it is easy to adjust the softening points of the resin (A) and the resin (B). Further, ethyl acrylate is preferable from the viewpoint of ease of copolymerization and industrial versatility.

The content of the alkyl (meth)acrylate having an alkyl group with 2 or more carbon atoms in the raw material components of the resin (A) and the resin (B) is preferably 20% by mass or more and 70% by mass or less, and 23% by mass or more and 60% by mass. % by mass or less is more preferable, and 25% by mass or more and 60% by mass or less is even more preferable.
By making the alkyl (meth)acrylate having 2 or more carbon atoms 20% by mass or more, the softening point of the copolymer resin can be lowered and the heat sealing work of the sealing material can be facilitated. By doing so, the ratio of methyl methacrylate and other monomers can be ensured, and adhesive strength, hot water resistance and acid resistance in a high temperature environment can be improved.

The resin (A) and the resin (B) are the above-mentioned styrene and methyl methacrylate, other monomers used as necessary, and an alkyl (meth)acrylate having an alkyl group having 2 or more carbon atoms and 2 or more carbon atoms. It is obtained by copolymerizing a raw material composition containing

Copolymerization methods include suspension polymerization, emulsion polymerization, and solution polymerization. Among these copolymerization methods, it is possible to obtain a polymer with a narrow molecular weight distribution and few residual monomers, a high molecular weight polymer can be obtained, there are few impurities because an emulsifier is not required, and water resistance is achieved while being polymerized in water. Suspension polymerization is preferred because it is easy to obtain a copolymer resin having excellent toughness and heat resistance.
As for the polymerization conditions, for example, in the case of suspension polymerization, it is preferable to carry out at 50 to 80° C. for 2 to 24 hours.
The form of the copolymer may be alternating, random, block, graft, or the like.

One or more suspension stabilizers may be used in the aqueous suspension polymerization for producing granules. For example, water-soluble polymers such as polyvinyl alcohol, partially saponified polyvinyl alcohol, polyvinylpyrrolidone, (meth)acrylate, polyacrylamide, partially saponified polyacrylamide, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, calcium phosphates, calcium carbonate, etc. Inorganic salt powder etc. are mentioned.

As for the polymerization initiator, it is preferable that the polymerization-initiating radical species after decomposition is oil-soluble. Typical radical polymerization initiators include azo radical polymerization initiators and peroxide radical polymerization initiators.
Azo radical polymerization initiators include 2,2′-azobispropane, 2,2′-dichloro-2,2′-azobispropane, 1,1′-azo(methylethyl)diacetate, 2,2 '-azobis(2-amidinopropane) hydrochloride, 2,2'-azobis(2-aminopropane) nitrate, 2,2'-azobisisobutane, 2,2'-azobisisobutyramide, 2,2'- azobisisobutyronitrile, methyl 2,2'-azobis-2-methylpropionate, 2,2'-dichloro-2,2'-azobisbutane, 2,2'-azobis-2-methylbutyronitrile, 2 , 2′-azobis dimethyl isobutyrate, 1,1′-azobis(1-methylbutyronitrile-3-sodium sulfonate), 2-(4-methylphenylazo)-2-methylmalonodinitrile 4,4′- Azobis-4-cyanovaleric acid, 3,5-dihydroxymethylphenylazo-2-allylmalonodinitrile, 2,2′-azobis-2-methylvaleronitrile, dimethyl 4,4′-azobis-4-cyanovalerate , 2,2′-azobis-2,4-dimethylvaleronitrile, 1,1′-azobiscyclohexanenitrile, 2,2′-azobis-2-propylbutyronitrile, 1,1′-azobiscyclohexanenitrile, 2,2'-azobis-2-propylbutyronitrile, 1,1'-azobis-1-chlorophenylethane, 1,1'-azobis-1-cyclohexanecarbonitrile, 1,1'-azobis-1-cycloheptane Nitrile, 1,1′-azobis-1-phenylethane, 1,1′-azobiscumene, 4-nitrophenylazobenzylcyanoethyl acetate, phenylazodiphenylmethane, phenylazotriphenylmethane, 4-nitrophenylazotriphenylmethane, 1,1'-azobis-1,2-diphenylethane, poly(bisphenol A-4,4'-azobis-4-cyanopentanoate), poly(tetraethylene glycol-2,2'-azobisisobutyrate ) and the like.
Peroxide-based radical polymerization initiators include acetyl peroxide, cumyl peroxide, tert-butyl peroxide, propionyl peroxide, benzoyl peroxide, 2-chlorobenzoyl peroxide, 3-chlorobenzoyl peroxide, and peroxide 4. - chlorobenzoyl, 2,4-dichlorobenzoyl peroxide, 4-bromomethylbenzoyl peroxide, lauroyl peroxide, potassium persulfate, diisopropyl peroxycarbonate, tetralin hydroperoxide, 1-phenyl-2-methylpropyl-1-hydroperoxide , tert-butyl pertriphenylacetate, tert-butyl hydroperoxide, tert-butyl performate, tert-butyl peracetate, tert-butyl benzoate, tert-butyl perphenylacetate, tert-butyl per-4-methoxyacetate, and tert-butyl N-(3-toluyl)carbamate. Examples of polymerization initiators include peroxides such as benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, methyl ethyl ketone peroxide and the like.

A mercapto compound can also be added as a chain transfer agent. For example, chain transfer agents having a hydroxyl group such as mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptopropanediol, mercaptobutanediol, hydroxybenzenethiol and derivatives thereof; 1-butanethiol, butyl-3-mercaptopropionate, methyl- 3-mercaptopropionate, 2,2-(ethylenedioxy)diethanethiol, ethanethiol, 4-methylbenzenethiol, dodecyl mercaptan, propanethiol, butanethiol, pentanethiol, 1-octanethiol, cyclopentanethiol, cyclohexanethiol, thioglycerol, 4,4-thiobisbenzenethiol, and the like.

The weight average molecular weights of resin (A) and resin (B) are preferably 200,000 or more. By setting the weight-average molecular weight to 200,000 or more, it is possible to improve the adhesive strength in a high-temperature environment. Moreover, the weight average molecular weight of the copolymer resin is preferably 1,500,000 or less from the viewpoint of suppressing gelation during polymerization and stabilizing the quality.
The weight average molecular weight of the resin (A) is preferably 200,000 or more and 1,500,000 or less, preferably 250,000 or more and 1,400,000 or less, and more preferably 300,000 or more and 1,300,000 or less.
The weight average molecular weight of the resin (B) is preferably 200,000 to 1,500,000, preferably 200,000 to 1,000,000, more preferably 200,000 to 800,000, and even more preferably 200,000 to 600,000.

The total content of the resin (A) and the resin (B) in the resin composition of the present invention is 50 mass of the total solid content of the resin composition of the present invention in order to sufficiently exhibit the effects of the present invention. % or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[Crosslinking agent]
The resin composition of the present invention further contains a cross-linking agent in addition to the resin (A) and resin (B) described above. By containing a cross-linking agent, it is possible to suppress a decrease in adhesive strength in a high-temperature environment and prevent the resin composition from deteriorating in a high-temperature environment and reducing its weight. Furthermore, when used as a sealing material, it is possible to suppress changes in shape due to hot press or the like under high temperature and pressure. Therefore, the sealing material using the resin composition of the present invention can stably maintain the performance of the fuel cell.

As the cross-linking agent in the resin composition of the present invention, an epoxy-based cross-linking agent is preferably used. Among them, it is preferable to use an amine-based epoxy cross-linking agent because of its high reactivity and easy progress of the cross-linking reaction.
Examples of amine-based epoxy crosslinking agents include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N',-tetraglycidyl-m-xylenediamine, N,N-bis (oxiranylmethyl)-4-(oxiranylmethoxy)aniline, 4,4′-methylenebis[N,N-bis(oxiranylmethyl)aniline and the like, among which 1,3-bis( More preferably, N,N-diglycidylaminomethyl)cyclohexane is used.

The content of the cross-linking agent in the resin composition of the present invention is 0.5 parts by mass or more and 10.0 parts by mass or less with respect to a total of 100 parts by mass of the resin (A) and the resin (B) in the resin composition. more preferably 0.8 parts by mass or more and 8.0 parts by mass or less, and even more preferably 1.0 parts by mass or more and 6.0 parts by mass or less.
By setting the content of the cross-linking agent in the resin composition to 0.5 parts by mass or more, it is possible to maintain the adhesiveness in a high-temperature environment, and the resin composition deteriorates in a high-temperature environment to reduce the weight of the resin. can be easily prevented. Further, by setting the content of the cross-linking agent in the resin composition to 10.0 parts by mass or less, it is possible to easily prevent the cross-linking agent from being eluted under the influence of heat or acid.

In addition, when the cross-linking agent is an epoxy-based cross-linking agent, the content of the cross-linking agent in the resin composition of the present invention is the epoxy group contained in the epoxy-based cross-linking agent and the acidity contained in the resin (A) and the resin (B). The equivalent ratio [epoxy group]/[acidic substituent] with the substituent is preferably 0.50 or more and 1.20 or less, more preferably 0.60 or more and 1.10 or less, and 0.70. It is more preferable that it is more than or equal to 1.00 or less. By setting the content of the cross-linking agent in the resin composition to 0.50 or more, it is possible to maintain the adhesiveness in a high-temperature environment and prevent the resin composition from deteriorating in a high-temperature environment and reducing the weight of the resin. It can be done easily. Further, by setting the content of the cross-linking agent in the resin composition to 1.20 or less, it is possible to easily prevent the cross-linking agent from eluting due to the influence of heat or acid.
The equivalent ratio [epoxy group]/[acidic substituent] is the number of moles of the acidic substituent contained in the resin (A) and the resin (B) in the resin composition to be blended, and the number of moles of the acidic substituent that reacts with the acidic substituent. It is calculated from the number of moles of epoxy groups in the cross-linking agent.

(Other additives)
The resin composition of the present invention contains additives such as pigments, flame retardants, ultraviolet absorbers, antioxidants, antistatic agents, silane coupling agents, tackifiers, etc., within a range that does not impair the effects of the present invention. may

The resin composition of the present invention is prepared by dissolving the resin (A), the resin (B), the cross-linking agent, and optionally other additives in a solvent and stirring and mixing them.

The resin composition of the present invention preferably has an ammonium ion elution amount contained in the total solid content of the resin composition of 1 ppm/g or less on a mass basis. By setting the ammonium ion elution amount to 1 ppm/g or less, it is possible to prevent cations from eluting from the sealing material and to prevent the performance of the fuel cell from being affected. The amount of ammonium ions eluted from the copolymer resin is more preferably 1 ppm/g or less, and more preferably not contained.
The nitrogen atomic weight in the copolymer resin can be measured, for example, by an ion chromatograph such as HIC-SP manufactured by Shimadzu Corporation.

[Seal material for polymer electrolyte fuel cell]
The sealing material of the present invention is formed from the resin composition of the present invention described above. The form of the sealing material is preferably solid such as particulate or sheet, and more preferably sheet from the viewpoint of handling.
When the sealing material of the present invention is formed into a sheet, from the viewpoint of ease of handling, the sealing material layer-forming composition obtained by dissolving the resin composition of the present invention in a solvent is coated on a base film, The sealing material layer is preferably formed by drying.
In the case of a sheet-shaped sealing material, the thickness of the sealing material layer varies depending on the separator, electrolyte membrane, etc. of the fuel cell, so it cannot be generalized. Note that the sealing material layer may be laminated as necessary.

The base film is not particularly limited as long as the sealing material can be formed into a sheet and has good workability when used as a sealing material for a fuel cell. Plastic films such as naphthalate, polyphenylene sulfide, polycarbonate, polyethylene, polypropylene, polystyrene, triacetyl cellulose, poly(meth)acrylate, and polyvinyl chloride are preferred, and polyethylene naphthalate is more preferred.

In addition, when the sealing material is formed in the form of a sheet, it is preferable that a peelable base material is attached on the sealing material layer of the sheet-like sealing material. By attaching the peelable base material to the sealing material, the surface of the sealing material can be easily protected from scratches and contamination before it is used as the sealing material for the fuel cell.
Releasable substrates are polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polystyrene, triacetyl cellulose, poly(meth)acrylate, polyvinyl chloride, etc. Plastic films and paper, etc. is preferably applied.
The thickness of the peelable substrate is preferably 10 to 100 μm, more preferably 25 to 75 μm, from the viewpoint of handleability. The releasable base material is preferably a base material treated with a non-silicone release agent in order to prevent adverse effects due to migration of the silicone component to the electrolyte membrane and sealing material layer. Non-silicone release agents include polyolefins.

Such a sealing material of the present invention can be used for a sealing portion of a fuel cell, more specifically, a sealing portion of a cell constituting a fuel cell. When in use, the sealing material is heated and melted to seal the sealing portion of the cell. In the case where the sealing material layer is sandwiched between peelable substrates, the sealing portion of the cell may be sealed by heating and melting the sealing material layer after peeling the substrates.

Conventional sealing materials for fuel cells, when undergoing a cross-linking reaction, required a batch treatment at a high temperature of 100° C. to 150° C. for 1 hour in order to exhibit sufficient performance as a sealing material. The manufacturing process was complicated, and it was difficult to improve the manufacturing efficiency.
On the other hand, the sealing material of the present invention is formed from the resin composition described above and uses an epoxy-based cross-linking agent. It is now possible to perform aging treatment in the same condition, making it easier to improve production efficiency. Furthermore, since aging treatment can be performed at a relatively low temperature of 45°C to 60°C, processing can be performed at a temperature lower than the heat-resistant temperature of the base material used for the body where the sealing material is formed in a sheet form. Since it is possible to request the occurrence of defects in the material, the yield can be improved.

[Polymer electrolyte fuel cell]
The polymer electrolyte fuel cell of the present invention comprises a portion sealed with the sealing material of the present invention.
FIG. 1 is a cross-sectional view showing an example of a cell that constitutes a general fuel cell.
The cell 10 is a composite (MEA: Membrane and Electrode Assembly) consisting of a solid polymer electrolyte membrane 11 and a pair of electrodes (anode, cathode) 12 and 13 arranged on both sides thereof, and arranged on both sides of the composite. separators (14, 15) formed with gas flow paths (14a, 15a) for supplying fuel gas and oxidant gas, respectively, and sealing between the composite and the separators (14, 15) It is composed of a sealing material 16 that seals as much as possible.
A typical fuel cell is constructed by stacking several tens to hundreds of cells 10, sandwiching the stack with end plates via current collector plates and insulating plates, and tightening them from both ends with fastening bolts. be.
The sealing material of the present invention can be suitably used as a sealing material in such general fuel cells. The position (sealed portion) of the sealing material in FIG. 1 is an example, and the position of the sealing material can be appropriately changed according to the configuration of the cells constituting the fuel cell.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. Each property value was measured and evaluated by the following methods.

1. Measurement and evaluation 1-1. Heat-resistant adhesive strength An electrolyte membrane (manufactured by DuPont, Nafion NRE-212, thickness 50 μm) is overlaid on the sealing material layer of the sheet-shaped sealing material obtained in Examples and Comparative Examples having a width of 5 cm and a length of 10 cm. They were put together and press-bonded under conditions of 2 MPa and 100° C. for 30 seconds. After press-bonding, it was cut into strips with a width of 1 cm to obtain samples for heat-resistant adhesion evaluation.
Next, the entire surface of the electrolyte membrane side of the heat-resistant adhesion evaluation sample was reinforced with a polyimide tape, and the polyimide tape and the electrolyte membrane were pulled by Tensilon under the conditions of an angle of 180°, a speed of 10 mm/min, and an atmosphere of 120°C. Peel strength was measured. The peel strength at this time was used as an index of the heat-resistant adhesive strength. It should be noted that the greater the peel strength at this time, the greater the heat-resistant adhesive strength and the better. Table 3 shows the evaluation results.

1-2. Heat and humidity durability An electrolyte membrane (Nafion NRE-212 manufactured by DuPont, thickness 50 μm) is placed on the sealing material layer of the sheet-shaped sealing material obtained in Examples and Comparative Examples having a width of 5 cm and a length of 10 cm. They were put together and press-bonded under conditions of 2 MPa and 100° C. for 30 seconds. After press-bonding, it was cut into strips with a width of 1 cm to obtain samples for heat and humidity durability tests.
Next, the heat and humidity durability test sample was left for 300 hours in an atmosphere with a temperature of 110° C. and a humidity of 100% RH to carry out a heat and humidity durability test.
The samples after the heat and humidity durability test were evaluated by the following procedure.
(1) Appearance Evaluation After the heat-and-humidity durability test, the state of the sealing material layer and the electrolyte membrane of the sample was visually confirmed to confirm whether or not peeling occurred, and the evaluation was made according to the following evaluation criteria. Table 3 shows the evaluation results.
A: No peeling occurred between the sealing material layer and the electrolyte membrane.
B: Separation was confirmed between the sealing material layer and the electrolyte membrane.
(2) Evaluation of adhesive strength after heat-and-humidity durability test After the heat-and-humidity durability test, the entire surface of the electrolyte membrane side of the sample was reinforced with polyimide tape, and the polyimide tape and electrolyte membrane were held at an angle of 180° and at a speed of 10 mm/min. , and the peel strength was measured by pulling with Tensilon under the conditions of 120°C atmosphere. The peel strength at this time was used as an index of the adhesive strength after the heat-and-humidity durability test. It should be noted that the greater the peel strength at this time, the greater the adhesive strength after the heat-and-moisture durability test, indicating that the film is favorable. Table 3 shows the evaluation results.

1-3. Shape Stability (1) Creep Test The sealing materials obtained in Examples and Comparative Examples were cut into 5 cm squares to prepare creep test samples.
The creep test evaluation sample was pressed with a hot press under conditions of 5 MPa and 100° C. for 24 hours, and the film thickness was measured.
From the film thickness of the sealing material of the creep test sample before and after the creep test, the change rate of the film thickness was obtained by the following formula, and used as an index for the creep test. Table 3 shows the evaluation results. If the rate of change at this time is less than 50%, the shape of the sealing material is maintained well even when the fuel cell is operated, so that the performance of the sealing material can be sufficiently exhibited. On the other hand, if the rate of change is 50% or more, the sealing material may creep during operation of the fuel cell, impairing the performance of the sealing material.
<Rate of change in creep test>
(Rate of change in creep test [%]) = {(Film thickness of sealing material before creep test [μm] - (Film thickness of sealing material after creep test [μm])} x 100/(Seal before creep test Material thickness [μm])
(2) Film thickness change test An electrolyte membrane (manufactured by DuPont, Nafion NRE-212, thickness 50 μm) was superimposed on the sealing material layer of the sheet-shaped sealing material obtained in Examples and Comparative Examples, and the pressure was 0.05 MPa. , and 170° C. for 1 minute, and the film thickness of the sealing material at that time was measured.
From the film thickness of the sealing material before and after press bonding, the change rate of the film thickness was obtained by the following formula, and used as an index of film thickness change. Table 3 shows the evaluation results. If the rate of change at this time is less than 50%, the shape of the sealing material is maintained well even when the fuel cell is operated, so that the performance of the sealing material can be sufficiently exhibited. On the other hand, if the rate of change is 50% or more, the film thickness of the sealing material may be insufficient during operation of the fuel cell, impairing the performance of the sealing material.
<Change rate of film thickness change test>
(Change rate of film thickness change test [%]) = {(film thickness of sealing material before film thickness change test [μm] - (film thickness of sealing material after film thickness change test [μm])} x 100/ (Film thickness of sealing material before creep test [μm])

1-4. Acid Value 1 g of the acrylic resin obtained in Production Example was dissolved in 100 g of isopropanol. The obtained solution was subjected to neutralization titration with 0.1N potassium hydroxide aqueous solution using phenolphthalein as an indicator, and the amount (mL) of potassium hydroxide aqueous solution required to neutralize 1 g of acrylic resin was determined. The acid value of the acrylic resin was obtained from the following formula.
Acid value (unit: mgKOH/g) = (5.611 x a x F)/S
In the formula, a is the titration amount (mL) of 0.1N potassium hydroxide-ethanol solution, F is the factor of 0.1N potassium hydroxide-ethanol solution, and S is the amount of acrylic resin collected (g). is. Table 1 shows the measurement results of the acid value of the acrylic resin.

1-5. Theoretical Tg
The theoretical Tg of the acrylic resin obtained in the production example was calculated as a theoretically calculated glass transition temperature (Tg) according to the following FOX formula. Table 1 shows the results.
(FOX style)
₁ /Tg ₌ W1 _/ Tg1 ₊ W2/Tg2+...+ _Wi / _Tg1 +...+ _Wn / _Tgn
In the above FOX formula, Tg _i (K) is the glass transition temperature of a homopolymer of each monomer constituting a polymer composed of n kinds of monomers, and W _i is the mass fraction of each monomer (W ₁ +W2 ₊ ...+Wi+... _{Wn =} 1).

1-6. Ion elution Put 50 g of deionized water into a heat-resistant container, add about 2 g of a sealing material layer cut into a size of 1 cm × 5 cm from the sheet-like sealing layer of Examples and Comparative Examples, and heat the heat-resistant container at 95 ° C. oven for 24 hours. Next, using the liquid in the heat-resistant container as a test liquid, the amount of eluted ions such as ammonium ions was measured by an ion chromatograph to calculate the content of ions in the sealing material layer. At this time, the thickness of the sealing material layer in Examples 1 to 4 and Comparative Examples 1 to 3 was set to 50 μm. Table 2 shows the results.

2. Preparation of acrylic resin <Production example 1>
In a separable flask with a capacity of 1 liter, 200 parts by mass of water containing 0.2% by mass of polyvinyl alcohol, 20 parts by mass of styrene monomer (ST), 40 parts by mass of methyl methacrylate monomer (MMA), glycidyl methacrylate monomer A uniform mixed solution containing 1 part by mass of (GMA), 39 parts by mass of ethyl acrylate monomer (EA), 0.1 part by mass of benzoyl peroxide as a polymerization initiator, and a chain transfer agent for adjusting the molecular weight was charged.
The mixture was heated to 70° C. while being stirred under a nitrogen atmosphere, and suspension polymerization was carried out for 4 hours. Water was then removed from the suspension by decantation. The solid matter was washed with water while being suction-filtered, and after removing moisture, it was vacuum-dried at 60° C. to obtain an acrylic resin of Production Example 1.
The weight-average molecular weight of the obtained acrylic resin was measured by a weight-average molecular weight measurement method and found to be 43.7×10 ⁴ . Table 1 shows the monomer composition and weight average molecular weight.

<Production Examples 2 to 8>
Acrylic resins of Production Examples 2 to 8 were obtained in the same manner as in Production Example 1, except that the monomer composition and weight average molecular weight of the acrylic resin were as shown in Table 1. Incidentally, the weight average molecular weight of the acrylic resin of each production example was adjusted by the amount of the chain transfer agent.

3. Preparation of sealing material <Example 1>
[Preparation of resin composition]
After dissolving 70 parts by mass of the acrylic resin of Production Example 1 as the acrylic resin (A) and 30 parts by mass of the acrylic resin of Production Example 5 as the acrylic resin (B) in ethyl acetate, an amine-based epoxy is added as a cross-linking agent. 2.24 parts by mass (equivalence ratio 0.75) of (1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, product name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was added, stirred and mixed, A resin composition of Example 1 was obtained.

[Preparation of sheet-like sealing material]
The resulting resin composition was melted and stirred in methyl ethyl ketone to prepare a composition for forming a sealing material layer. After applying the above sealing material layer-forming composition onto a PEN (polyethylene naphthalate) film having a thickness of 100 μm, it was dried at 100° C. for 2 minutes to form a sealing material layer having a thickness of 10 μm. A sheet-like sealing material of Example 1 was obtained.

<Examples 2 to 7, Comparative Examples 1 to 5>
Resin compositions and sheet-like sealing materials of Examples 2 to 7 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that the resin composition and the cross-linking agent of the resin composition were as shown in Table 2. rice field.

From the results in Table 3, the sealing materials of Examples 1 to 7, which have the characteristics of the present invention, have good heat-resistant adhesive strength and adhesive strength after heat and humidity durability, and also have excellent shape stability in a high-temperature atmosphere. Therefore, it was confirmed that it has excellent durability even in harsh environments such as high temperature and high humidity.
Furthermore, it was confirmed that the sealing materials of Examples 1 to 7 had little ion elution.

Reference Signs List 10: Cell 11: Electrolyte membranes 12, 13: Electrodes 14, 15: Separators 14a, 15a: Gas channel 16: Sealing material

Claims (11)

A resin composition for a polymer electrolyte fuel cell sealing material, comprising an acrylic resin (A) having an acid value of less than 15 mgKOH/g, an acrylic resin (B) having an acid value of 15 mgKOH/g or more, and a cross-linking agent. 2. The polymer electrolyte fuel cell sealing material according to claim 1, wherein the mass ratio (A)/(B) of the resin (A) and the resin (B) is 20/80 or more and 80/20 or less. Resin composition. The resin (A) is a copolymer having a weight average molecular weight of 300,000 or more, which is obtained by copolymerizing raw material components containing styrene from 5% by mass to 40% by mass and methyl methacrylate from 20% by mass to 60% by mass. 3. The resin composition for a polymer electrolyte fuel cell sealing material according to claim 1, which is a polymer resin. 4. The polymer electrolyte fuel cell sealing material according to claim 3, wherein the raw material component of the resin (A) further contains one or more selected from glycidyl acrylate, glycidyl methacrylate, acrylic acid and methacrylic acid. Resin composition. 5. The polymer electrolyte fuel cell sealing material according to claim 3, wherein the raw material component of the resin (A) further contains an alkyl (meth)acrylate having an alkyl group with 2 or more carbon atoms. of the resin composition. The resin (B) is a copolymer having a weight average molecular weight of 200,000 or more obtained by copolymerizing raw material components containing 30% by mass or more and 70% by mass or less of styrene and 5% by mass or more and 30% by mass or less of methyl methacrylate. The resin composition for polymer electrolyte fuel cell sealing material according to any one of claims 1 to 5, which is a polymer resin. 7. The polymer electrolyte fuel cell sealing material according to claim 6, wherein the raw material component of the resin (A) further contains one or more selected from glycidyl acrylate, glycidyl methacrylate, acrylic acid and methacrylic acid. Resin composition. 8. The polymer electrolyte fuel cell sealing material according to claim 6, wherein the raw material component of the resin (B) further contains an alkyl (meth)acrylate having an alkyl group with 2 or more carbon atoms. of the resin composition. The resin composition for a polymer electrolyte fuel cell sealing material according to any one of claims 1 to 8, wherein said cross-linking agent is an amine epoxy cross-linking agent. A sealing material for polymer electrolyte fuel cells, formed from the resin composition according to any one of claims 1 to 9. 11. A polymer electrolyte fuel cell comprising a sealing portion with the sealing material for a polymer electrolyte fuel cell according to claim 10.

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