Hot-melt adhesive sheet

Abstract

A hot-melt adhesive sheet comprising an adhesive layer laminated on at least one surface of a sheet-like substrate, wherein the adhesive layer is formed of a hot-melt adhesive comprising a moisture-curable polyurethane resin and an epoxy resin.

Description

Hot Melt Adhesive Sheet CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2024-117055, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a hot melt adhesive sheet.

[0003] Conventionally, polyurethane adhesives have been widely used as adhesives for various plastics due to their adhesive stability in low temperature ranges (e.g., −10° C. to 15° C.), adhesiveness, flexibility, processability, and ease of various molecular designs in room temperature ranges (25±10° C.). Examples of polyurethane adhesives include those containing polyester polyol, acrylic polyol, or the like as a base agent and polyisocyanate as a crosslinking agent, which are used by generating urethane bonds through a crosslinking reaction between the base agent and the crosslinking agent, and those containing polyurethanes with a certain chain length (so-called polyurethane prepolymers) as a base agent and an isocyanate-based crosslinking agent as a crosslinking agent, which are used by curing through a crosslinking reaction between the base agent and the crosslinking agent.

[0004] Also known is a two-component adhesive containing a polyurethane resin as a base agent, an epoxy resin, and an isocyanate-based crosslinking agent (see Patent Document 1). In recent years, hot melt adhesives have increasingly been used to bond components because they are easier to handle than liquid adhesives such as those described in Patent Document 1. The hot melt adhesive is often used in the form of a hot melt adhesive sheet, particularly because of its ease of handling. The hot melt adhesive sheet typically comprises a sheet-like substrate formed from a polymer sheet and an adhesive layer laminated on the sheet-like substrate and formed from the hot melt adhesive.

[0005] The hot melt adhesive sheet is produced by coating one or both sides of a sheet substrate with a coating liquid in which a hot melt adhesive is dissolved in an organic solvent or the like, drying the coating in a heating furnace, and then coating one or both sides of the sheet substrate with a solventless coating liquid that becomes a hot melt adhesive by a thermosetting reaction, and then thermosetting the coating in a heating furnace (aging treatment). However, if the aging treatment is insufficient, it is difficult to obtain a hot melt adhesive sheet with sufficient adhesive strength.

[0006] International Publication No. 2013 / 157604

[0007] However, when the aging treatment for promoting the crosslinking reaction in the production of the hot melt adhesive sheet is carried out by heating, there is a problem that the energy required for the heating increases the amount of carbon dioxide emitted. From the viewpoint of reducing such environmental load, it is desired that the hot melt adhesive sheet be produced by an aging treatment at room temperature without using heat.

[0008] However, conventional hot melt adhesive sheets cannot be subjected to sufficient aging treatment at room temperature, making it difficult to obtain good adhesion to difficult-to-adhere articles such as solid electrolyte membranes while producing them by aging treatment at room temperature.

[0009] Therefore, an object of the present invention is to provide a hot melt adhesive sheet that exhibits good adhesion to difficult-to-adhere articles even without aging treatment by heating.

[0010] The hot melt adhesive sheet according to the present invention comprises a sheet-like substrate having a sheet-like substrate on at least one surface thereof and an adhesive layer formed of a hot melt adhesive, the hot melt adhesive comprising a moisture-curable polyurethane resin and an epoxy resin.

[0011] 1 is a schematic cross-sectional view showing the configuration of a hot melt adhesive sheet according to an embodiment of the present invention, and a state in which the hot melt adhesive sheet according to an embodiment of the present invention is attached to a solid electrolyte membrane of a polymer electrolyte fuel cell.

[0012] Hereinafter, a hot melt adhesive sheet according to one embodiment of the present invention will be described with reference to the drawings. Hereinafter, one embodiment of the present invention will sometimes be simply referred to as the present embodiment.

[0013] As shown in Fig. 1, the hot melt adhesive sheet 10 according to this embodiment is a hot melt adhesive sheet in which an adhesive layer 10b formed of a hot melt adhesive is laminated on one side of a sheet-like substrate 10a. In the hot melt adhesive sheet 10 shown in Fig. 1, the adhesive layer 10b is laminated on only one side of the sheet-like substrate 10a, but the adhesive layer 10b may also be laminated on the other side of the sheet-like substrate 10a. In other words, the hot melt adhesive sheet 10 may be a hot melt adhesive sheet in which the adhesive layer 10b is laminated on both sides of the sheet-like substrate 10a.

[0014] The hot melt adhesive sheet 10 of this embodiment is a hot melt adhesive sheet in which an adhesive layer formed of a hot melt adhesive is laminated on at least one side of a sheet-like substrate, and the hot melt adhesive contains a moisture-curing polyurethane resin and an epoxy resin.

[0015] (Moisture-curable polyurethane resin (A)) The moisture-curable polyurethane resin (A) is obtained by urethane bonding reaction components including a polyol (a) having two or more hydroxyl groups per molecule and a polyisocyanate (b) having two or more isocyanate groups per molecule.

[0016] The moisture-curable polyurethane resin (A) is usually linear or branched and has two or more molecular ends. In one embodiment, the moisture-curable polyurethane resin (A) has an unreacted isocyanate group at one or two or more molecular ends. In another embodiment, the moisture-curable polyurethane resin (A) has an unreacted isocyanate group at the end of the main chain. In yet another embodiment, the moisture-curable polyurethane resin (A) has an unreacted isocyanate group at one end or both ends of the main chain.

[0017] The isocyanate group reacts with moisture in the air to convert it into an amino group and carbon dioxide. The amino group further reacts with other unreacted isocyanate groups in the moisture-curable polyurethane resin to form a urea bond, allowing the moisture-curable polyurethane resin (A) to cure even under room temperature conditions (e.g., 23°C).

[0018] In the hot melt adhesive sheet 10 according to this embodiment, the moisture-curable polyurethane resin (A) has a structural unit derived from a polyol (a) having an ester bond, a carbonate bond, or an ether bond. That is, the polyol (a) can be an ester bond-containing polyol (a1), a carbonate bond-containing polyol (a2), or an ether bond-containing polyol (a3).

[0019] As the ester bond-containing polyol (a1), a polyester obtained by a condensation reaction between a polycarboxylic acid and a polyhydric alcohol can be used.

[0020] Examples of the polycarboxylic acid include phthalic acid, isophthalic acid, terephthalic acid, maleic acid, itaconic acid, fumaric acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic acid, sebacic acid, azelaic acid, trimellitic acid, methylcyclohexene tricarboxylic acid, pyromellitic acid, dimer acids derived from unsaturated fatty acids, and acid anhydrides thereof.

[0021] Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, pentamethylene glycol, hexamethylene glycol, heptamethylene glycol, and octamethylene glycol.

[0022] The polyhydric alcohol may be a polyhydric alcohol having a carboxyl group (hereinafter also referred to as a carboxyl group-containing polyhydric alcohol). Examples of the carboxyl group-containing polyhydric alcohol include dimethylolpropionic acid, dimethylolbutanoic acid, and diphenolic acid. Furthermore, the polyhydric alcohol may be modified with a caprolactone compound such as ε-caprolactam.

[0023] Examples of the carbonate bond-containing polyol (a2) include polytetramethylene carbonate diol, polypentamethylene carbonate diol, polyneopentyl carbonate diol, polyhexamethylene carbonate diol, and random / block copolymers thereof.

[0024] The carbonate bond-containing polyol (a2) has excellent hydrolysis resistance and heat resistance. Therefore, when the moisture-curable polyurethane resin (A) contains structural units derived from the carbonate bond-containing polyol (a2), an adhesive layer 10b having excellent hot water resistance can be obtained.

[0025] Examples of the ether bond-containing polyol (a3) ​​include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and random / block copolymers thereof.

[0026] The ether bond-containing polyol (a3) ​​has better hydrolysis resistance than the ester bond-containing polyol (a1). Therefore, when the moisture-curable polyurethane resin (A) contains structural units derived from the ether bond-containing polyol (a3), an adhesive layer 10b having excellent hot water resistance can be obtained.

[0027] Examples of the polyisocyanate (b) include aliphatic isocyanate compounds, alicyclic isocyanate compounds, and aromatic isocyanate compounds.

[0028] Examples of the aliphatic isocyanate compound include hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, trimethylhexamethylene diisocyanate, and xylylene diisocyanate.

[0029] Examples of the alicyclic isocyanate compound include isophorone diisocyanate, methylcyclohexane diisocyanate, lysine diisocyanate, and cyclohexane-1,4-diisocyanate.

[0030] Examples of the aromatic isocyanate compound include tolylene diisocyanate, 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, tetraalkyldiphenylmethane isocyanate, dialkyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate.

[0031] The molar ratio of the polyisocyanate (b) to the polyol (a) is preferably 1.3 or more and 5.0 or less, more preferably 1.5 or more and 4.5 or less, and even more preferably 1.8 or more and 4.0 or less.

[0032] In the hot melt adhesive sheet 10 according to this embodiment, the molar ratio of polyisocyanate (b) to polyol (a) is within the above range, ensuring a sufficient amount of isocyanate groups for moisture curing. This allows the moisture-curable polyurethane resin to cure sufficiently even at room temperature, improving the hydrolysis resistance of the moisture-curable polyurethane resin (A) after curing and providing better adhesion under hot water conditions.

[0033] The content of the moisture-curable polyurethane resin (A) in the hot melt adhesive may be 20% by mass or more, 45% by mass or more, 70% by mass or more, or 90% by mass or more. In one aspect of the hot melt adhesive sheet 10 according to the present embodiment, the hot melt adhesive may be composed only of the moisture-curable polyurethane resin (A).

[0034] (Epoxy Resin (B)) The epoxy groups of the epoxy resin (B) react with amino groups derived from isocyanate groups generated when the moisture-curable polyurethane resin (A) cures. This increases the crosslink density of the hot melt adhesive sheet 10 according to this embodiment, resulting in superior adhesiveness under hot water conditions.

[0035] The epoxy resin (B) may be, for example, a triphenylmethane-type epoxy resin, a bisphenol-type epoxy resin, a novolac-type epoxy resin, or an alicyclic epoxy resin. Examples of the bisphenol-type epoxy resin include bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, and bisphenol S-type epoxy resin. The bisphenol-type epoxy resin may be a long-chain epoxy resin, such as a phenoxy resin. The bisphenol-type epoxy resin may be a modified product, such as a CTBN-modified or ATBN-modified product. Examples of the novolac-type epoxy resin include phenol novolac-type epoxy resin and cresol novolac-type epoxy resin. The novolac-type epoxy resin may contain a naphthalene skeleton or a naphthalene-skeleton-containing novolac-type epoxy resin. The alicyclic epoxy resin may be, for example, a dicyclopentadiene-type epoxy resin. These various epoxy resins may be used alone or in combination of two or more.

[0036] The epoxy resin (B) is preferably one or more epoxy resins selected from the group consisting of triphenylmethane-type epoxy resins, bisphenol A-type epoxy resins, and naphthalene skeleton-containing novolac-type epoxy resins, and more preferably a bisphenol A-type epoxy resin.

[0037] In the hot melt adhesive sheet 10 according to this embodiment, the epoxy equivalent of the epoxy resin (B) may be 100 g / eq or more and 1500 g / eq or less, preferably 100 g / eq or more and 1100 g / eq or less, more preferably 400 g / eq or more and 1100 g / eq or less, and even more preferably 800 g / eq or more and 1100 g / eq or less. The epoxy equivalent is determined by the method specified in JIS K7236.

[0038] The hot melt adhesive sheet 10 according to this embodiment has an epoxy equivalent of the epoxy resin (B) within the above range, and therefore exhibits even better adhesiveness under hot water conditions.

[0039] In one aspect, the hot melt adhesive sheet 10 according to this embodiment has an epoxy resin content of 5 parts by mass or more and 150 parts by mass or less, preferably 5 parts by mass or more and 100 parts by mass or less, more preferably 20 parts by mass or more and 80 parts by mass or less, and even more preferably 20 parts by mass or more and 60 parts by mass or less, relative to 100 parts by mass of the moisture-curing polyurethane resin.

[0040] The sheet-like substrate 10a used in the hot melt adhesive sheet 10 according to this embodiment is not particularly limited, but examples thereof include a PEN (polyethylene naphthalate) film, a perfluorocarbon sulfonic acid resin sheet (film), and a PPS (polyphenylene sulfide) film.

[0041] Next, referring to Figure 2, we will further explain the case where the adherend to which the adhesive layer 10b of the hot melt adhesive sheet 10 of this embodiment is adhered is a membrane electrode assembly (MEA) 20 of a solid polymer fuel cell.

[0042] The membrane electrode assembly (MEA) 20, which is the adherend, is configured to allow hydrogen gas to pass from the negative electrode side to the positive electrode side and to generate electricity by reacting the hydrogen with oxygen supplied to the positive electrode side.

[0043] 2 , in the membrane electrode assembly (MEA) 20, a cathode 202 and an anode 203 are laminated on opposite surfaces of a solid electrolyte membrane 201. The cathode 202 includes a cathode catalyst layer 202a and a cathode gas diffusion layer 202b laminated on the cathode catalyst layer 202a, with the cathode catalyst layer 202a laminated on one surface of the solid electrolyte membrane 201. The anode 203 includes an anode catalyst layer 203a and an anode gas diffusion layer 203b laminated on the anode catalyst layer 203a, with the anode catalyst layer 203a laminated on the other surface of the solid electrolyte membrane 201.

[0044] 2 , the positive electrode catalyst layer 202 a and the negative electrode catalyst layer 203 a are formed so as to have smaller planar dimensions than the solid electrolyte membrane 201, and the positive electrode gas diffusion layer 202 b and the negative electrode gas diffusion layer 203 b are also formed so as to have smaller planar dimensions than the positive electrode catalyst layer 202 a and the negative electrode catalyst layer 203 a. That is, in the membrane electrode assembly (MEA) 20, the planar dimensions of the positive electrode 202 and the negative electrode 203 are smaller than the planar dimensions of the solid electrolyte membrane 201. As described above, because the planar dimensions of the positive electrode 202 are smaller than the planar dimensions of the solid electrolyte membrane 201, a positive electrode-side electrolyte membrane exposed region 201 a is formed on the outer periphery of the positive electrode side (one side) of the membrane electrode assembly (MEA) 20, where the solid electrolyte membrane 201 extends outward beyond the positive electrode catalyst layer 202 a and the surface of the solid electrolyte membrane 201 is exposed. Furthermore, since the planar dimensions of the anode 203 are smaller than the planar dimensions of the solid electrolyte membrane 201, an anode-side electrolyte membrane exposed region 201b is formed on the outer periphery of the anode side (other surface side) of the membrane electrode assembly (MEA) 20, where the solid electrolyte membrane 201 extends outward beyond the anode catalyst layer 203a and the surface of the solid electrolyte membrane 201 is exposed.

[0045] Furthermore, a cathode-side catalyst layer exposed region 202a1 is formed on the cathode side of the membrane electrode assembly (MEA) 20, where the cathode catalyst layer 202a extends outward beyond the cathode gas diffusion layer 202b, exposing the surface of the cathode catalyst layer 202a. The cathode-side catalyst layer exposed region 202a1 is formed inside the cathode-side electrolyte membrane exposed region 201a and outside the cathode gas diffusion layer 202b. In this embodiment, the cathode-side electrolyte membrane exposed region 201a is formed in an annular shape that wraps around the outer periphery of the membrane electrode assembly (MEA) 20. The cathode-side catalyst layer exposed region 202a1 is formed in an annular shape that is smaller than the cathode-side electrolyte membrane exposed region 201a. That is, on the positive electrode side of the membrane electrode assembly (MEA), a second boundary line L2, which is the boundary line between the positive electrode-side electrolyte membrane exposed region 201a and the positive electrode-side catalyst layer exposed region 202a1, is formed inside a first boundary line L1, which is the boundary line between the positive electrode-side electrolyte membrane exposed region 201a and the positive electrode-side catalyst layer exposed region 202a1.

[0046] An anode-side catalyst layer exposed region 203a1 is formed on the anode side of the membrane electrode assembly (MEA) 20, where the anode catalyst layer 203a extends outward beyond the anode gas diffusion layer 203b, exposing the surface of the anode catalyst layer 203a. The anode-side catalyst layer exposed region 203a1 is formed inside the anode-side electrolyte membrane exposed region 201b and outside the anode gas diffusion layer 203b. In this embodiment, the anode-side electrolyte membrane exposed region 201b is formed in an annular shape that wraps around the outer periphery of the membrane electrode assembly (MEA) 20. The anode-side catalyst layer exposed region 203a1 is formed in an annular shape that is smaller than the anode-side electrolyte membrane exposed region 201b. That is, on the negative electrode side of the membrane electrode assembly (MEA) 20, a fourth boundary line L4, which is the boundary line between the negative electrode-side electrolyte membrane exposed region 201b and the negative electrode-side catalyst layer exposed region 203a1, is formed inside a third boundary line L3, which is the boundary line between the negative electrode-side electrolyte membrane exposed region 201b and the negative electrode-side catalyst layer exposed region 203a1.

[0047] In the state of use shown in Figure 2, two hot melt adhesive sheets 10, namely, a first hot melt adhesive sheet 10 adhered to the positive electrode side of the membrane electrode assembly (MEA) 20 and a second hot melt adhesive sheet 10 adhered to the negative electrode side of the membrane electrode assembly (MEA) 20, are used as subgasket materials for a solid polymer fuel cell.

[0048] The first hot melt adhesive sheet 10 is annular and has a shape such that when it is overlaid on the membrane electrode assembly (MEA) 20, its outer peripheral edge is on the outer side of the membrane electrode assembly (MEA) 20, and its inner peripheral edge fits within the positive electrode-side catalyst layer exposed region 202a1 and the negative electrode-side catalyst layer exposed region 203a1. In other words, the inner peripheral edge of the first hot melt adhesive sheet 10 has a shape that is slightly larger than the positive electrode gas diffusion layer 202b.

[0049] The second hot melt adhesive sheet 10 also has the same shape as the first hot melt adhesive sheet 10 .

[0050] In this embodiment, the first hot melt adhesive sheet 10 and the second hot melt adhesive sheet 10 are directly bonded to each other at the outer periphery of the adhesive layer 10b outside the membrane / electrode assembly (MEA) 20, and are used as the subgasket material.

[0051] The first hot melt adhesive sheet 10 has its inner periphery, excluding its outer periphery adhered to the second hot melt adhesive sheet 10, adhered to the outer periphery of the membrane electrode assembly (MEA) 20, and is adhered in a range from the positive electrode-side electrolyte membrane exposed region 201a across the first boundary line L1 to the positive electrode-side catalyst layer exposed region 202a1. Specifically, the surface of the adhesive layer 10b of the first hot melt adhesive sheet 10 used as the subgasket material has an adhesive surface that is adhered to the membrane electrode assembly (MEA) 20, which is the adherend. The first hot melt adhesive sheet 10 in this embodiment is annular as described above, and the adhesive surface of the adhesive layer 10b is also annular. In this embodiment, the radially outermost region of the annular adhesive surface of the first hot melt adhesive sheet 10 forms a first annular adhesive region that is adhered to the second hot melt adhesive sheet 10 having the same shape. The adhesive surface of the hot melt adhesive sheet 10 of this embodiment further includes a second annular adhesive region adhered to the positive electrode-side electrolyte membrane exposed region 201a and a third annular adhesive region adhered to the positive electrode-side catalyst layer exposed region 202a1. On the adhesive surface, the third annular adhesive region, the second annular adhesive region, and the first annular adhesive region are arranged in this order from the radially outer side, such that the first annular adhesive region surrounds the second annular adhesive region, and the second annular adhesive region surrounds the third annular adhesive region. The second hot melt adhesive sheet 10 is also adhered in the same manner as the first hot melt adhesive sheet 10.

[0052] By adhering (coating) the hot melt adhesive sheet 10 to the membrane electrode assembly (MEA) 20 as described above, a portion of the positive electrode gas can permeate through the positive electrode-side electrolyte membrane exposed region 201 a and a portion of the negative electrode gas can permeate through the negative electrode-side electrolyte membrane exposed region 201 b, thereby preventing a decrease in performance as a solid polymer fuel cell.

[0053] As explained above, in a polymer electrolyte fuel cell, electricity is generated by a reaction between hydrogen and oxygen in the membrane electrode assembly (MEA) 20. When hydrogen and oxygen react as described above, the temperature of the membrane electrode assembly (MEA) 20 reaches a relatively high temperature (e.g., 95°C). When the polymer electrolyte fuel cell is installed as a power source in an automobile, the central portion of the membrane electrode assembly (MEA) 20 is sufficiently cooled by circulating antifreeze solution contained in a radiator through a duct. However, since the duct is not usually extended to the edge portions of the membrane electrode assembly (MEA) 20, the edge portions of the membrane electrode assembly (MEA) 20 continue to maintain a high temperature.

[0054] In the hot melt adhesive sheet 10 according to this embodiment, the adhesive layer 10b is configured as described above, and therefore has excellent long-term hot water resistance. Therefore, when the hot melt adhesive sheet according to this embodiment is used as a subgasket material in a polymer electrolyte fuel cell installed in an automobile, even if the adhesive layer 10b comes into contact with water at a high temperature of 95°C, as described above, it can maintain adhesion to the solid electrolyte membrane 201 for a long period of time. Note that the solid electrolyte membrane 201 is typically made of a fluororesin such as perfluorocarbon sulfonic acid, as will be described later.

[0055] In the membrane electrode assembly (MEA) 20, the positive electrode catalyst layer 202 a and the negative electrode catalyst layer 203 a are generally formed using a catalyst ink composition containing a catalyst support material such as a carbon material supporting a catalyst, a proton-conductive polymer, and a solvent.

[0056] The solid electrolyte membrane 201 of the membrane electrode assembly (MEA) 20 is formed of a fluororesin such as perfluorocarbon sulfonic acid resin. Examples of the perfluorocarbon sulfonic acid resin include "Nafion" (trade name) manufactured by DuPont, "Flemion" (trade name) manufactured by Asahi Kasei Corporation, and "Aciplex" (trade name) manufactured by Asahi Glass Co., Ltd.

[0057] When the solid electrolyte membrane 201 of the membrane electrode assembly (MEA) 20 is formed of a perfluorocarbon sulfonic acid resin, the adhesive layer 10b exhibits excellent adhesion to the solid electrolyte membrane 201. This makes it difficult for water molecules to enter between the adhesive layer 10b and the solid electrolyte membrane 201, and the moisture-curable polyurethane resin (A) in the adhesive layer 10b is less likely to be hydrolyzed, so the hot melt adhesive sheet 10 according to this embodiment exhibits excellent hot water resistance.

[0058] When the hot melt adhesive contains the epoxy resin (B), the hot melt adhesive is thermally cured by thermocompression bonding the hot melt adhesive sheet 10 and the solid electrolyte membrane 201, and the adhesive layer 10b exhibits excellent adhesion to the solid electrolyte membrane 201. This makes it difficult for water molecules to enter between the adhesive layer 10b and the solid electrolyte membrane 201, and the moisture-curable polyurethane resin (A) in the adhesive layer 10b is less likely to be hydrolyzed, so the hot melt adhesive sheet 10 according to this embodiment exhibits excellent hot water resistance.

[0059] The positive electrode catalyst layer 202a and the negative electrode catalyst layer 203a are layers containing catalyst particles. Examples of the catalyst particles contained in the positive electrode catalyst layer 202a include platinum. Examples of the catalyst particles contained in the negative electrode catalyst layer 203a include platinum compounds. Examples of the platinum compounds include alloys of platinum with at least one metal selected from the group consisting of ruthenium, palladium, nickel, molybdenum, iridium, and iron.

[0060] The positive electrode gas diffusion layer 202b and the negative electrode gas diffusion layer 203b are made of a porous conductive substrate, such as carbon paper or carbon cloth.

[0061] The hot melt adhesive sheet 10 according to this embodiment can also be used in redox flow batteries, water electrolysis devices, etc. The hot melt adhesive sheet used in redox flow batteries is used to prevent permeation of the electrolyte.

[0062] The hot melt adhesive sheet according to the present invention is not limited to the above-described embodiment, nor is it limited by the above-described effects. The hot melt adhesive sheet according to the present invention can be modified in various ways without departing from the gist of the present invention.

[0063] The matters disclosed by this specification include the following.

[0064] (1) A hot melt adhesive sheet, comprising a sheet-like substrate and an adhesive layer formed of a hot melt adhesive laminated on at least one surface thereof, the hot melt adhesive comprising a moisture-curable polyurethane resin and an epoxy resin. (2) The hot melt adhesive sheet according to (1), wherein the content of the epoxy resin is 5 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the moisture-curable polyurethane resin. (3) The hot melt adhesive sheet according to (1) or (2), wherein the epoxy resin has an epoxy equivalent of 100 g / eq or more and 1500 g / eq or less. (4) The hot melt adhesive sheet according to any one of (1) to (3), wherein the epoxy resin is one or more epoxy resins selected from the group consisting of triphenylmethane-type epoxy resins, bisphenol A-type epoxy resins, and naphthalene-skeleton-containing novolac-type epoxy resins.

[0065] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0066] The moisture-curable polyurethane resin (A) and epoxy resin (B) used in the examples and comparative examples are as follows: (Polyurethane resin (A)) PU1: moisture-curing ester-based polyurethane resin, manufactured by Toyochem Co., Ltd., model number "RH-3143B4" PU2: moisture-curing carbonate-based polyurethane resin, manufactured by Toyochem Co., Ltd., model number "RH-3143B4C" PU3: polycarbonate-type polyurethane resin, manufactured by DIC Corporation, model number "TA-205FT" PU4: ester-type polyurethane resin, manufactured by Toyobo MC Co., Ltd., model number "UR-3210" (Epoxy resin (B)) EP1: bisphenol A-type epoxy resin, manufactured by Nan-A Plastics Co., Ltd., model number "NPES-304", epoxy equivalent 900-1000 g / eq EP2: bisphenol A-type epoxy resin, manufactured by Mitsubishi Chemical Corporation, model number "jER1001", epoxy equivalent 450-500 g / eq EP3: rubber-modified epoxy resin, manufactured by ADEKA Corporation, model number "EPR-1415-1", epoxy equivalent 400 g / eq EP4: bisphenol A type epoxy resin, manufactured by Nan-A Plastics Co., Ltd., model number "NPES-301", epoxy equivalent 450-550 g / eq EP5: triphenylmethane type epoxy resin, manufactured by Nippon Kayaku Co., Ltd., model number "EPPN-501HY", epoxy equivalent 167 g / eq EP6: naphthalene skeleton-containing novolac type epoxy resin, manufactured by Nippon Kayaku Co., Ltd., model number "NC-7000L", epoxy equivalent 232 g / eq (isocyanate crosslinking agent (C)) IC1: isocyanate crosslinking agent, manufactured by Mitsui Chemicals, Inc., model number "D-110N"

[0067] Example 1 A polyurethane resin (A) from Table 1 was dissolved in methyl ethyl ketone (MEK), and then an epoxy resin (B) from Table 1 was further added to obtain a resin composition solution. The resin composition solution was applied to the entire surface of one side of a PPS film (length: 300 mm, width: 200 mm, thickness: 25 μm, Torelina, manufactured by Toray Industries, Inc.) so that the adhesive layer would have a thickness of 20 μm after drying, and the film was dried at 100° C. for 1 minute. The film was then left to stand for 72 hours under conditions of room temperature and 50% relative humidity, to obtain a hot melt adhesive sheet.

[0068] The obtained hot melt adhesive sheet and perfluorocarbon sulfonic acid resin sheet were superimposed so that the exposed surface of the adhesive layer of the hot melt adhesive sheet abutted against one side of a perfluorocarbon sulfonic acid resin sheet (tetrafluoroethylene / perfluoro[2-(fluorosulfonylethoxy)propyl vinyl ether] copolymer membrane (manufactured by DuPont, product name "NAFIONN-115")) (same shape as the film with the hot melt adhesive layer). An adhesive sheet was produced by bonding the hot melt adhesive sheet and perfluorocarbon sulfonic acid resin sheet together by thermocompression using a laminator adjusted to 140°C.

[0069] Comparative Example 1: The polyurethane resin (A) in Table 1 was dissolved in methyl ethyl ketone (MEK), and then the epoxy resin (B) and isocyanate crosslinking agent (C) in Table 1 were further added to obtain a resin composition solution. The resin composition solution was applied to the entire surface of one side of a PPS film (length: 300 mm, width: 200 mm, thickness: 25 μm, Torelina, manufactured by Toray Industries, Inc.) so that the adhesive layer would have a thickness of 20 μm after drying, and then dried at 100°C for 1 minute. The resulting mixture was then left in a 40°C oven for 48 hours to obtain a hot melt adhesive sheet. An adhesive sheet was produced using the hot melt adhesive sheet in the same manner as in Example 1.

[0070] Table 1 shows the compositions of the adhesive sheets in Example 1 and Comparative Example 1, and the temperatures at which the aging treatment was carried out in the production of the adhesive sheets.

[0071]

[0072] In Example 1, which satisfied all of the constituent elements of the present invention, an adhesive sheet having adhesiveness equivalent to that of the adhesive sheet of Comparative Example 1 was obtained without carrying out the aging treatment by heating as in Comparative Example 1.

[0073] Examples 2 to 18, Comparative Examples 2 to 9 Adhesive sheets were prepared in the same manner as in Example 1, except that the types and amounts of polyurethane resin (A) and epoxy resin (B) were as shown in Table 2.

[0074] <Hot Water Resistance Test 1> Test specimens measuring 10 mm wide x 80 mm long were cut out from the adhesive sheets of Examples 1 to 18 and Comparative Examples 2 to 9, and the test specimens were immersed in hot water at 95°C for 72 hours. After cooling to room temperature, the hot water resistance of each test specimen was evaluated according to the following criteria: Good: No peeling was observed after immersion. Fair: No peeling was observed after immersion, but some lifting was observed. Poor: Peeling was observed after immersion.

[0075] The evaluation results of the hot water resistance test 1 for Examples 1 to 18 and Comparative Examples 2 to 9 are shown in Table 2.

[0076]

[0077] As can be seen from the results in Table 2, most of the examples showed better results in terms of hot water resistance than the comparative examples.

[0078] Furthermore, in Table 2, good hot water resistance was also obtained for the adhesive sheets of Examples 9 and 10, which used an epoxy resin (B) other than a bisphenol A-type epoxy resin, i.e., a triphenylmethane-type epoxy resin and a naphthalene skeleton-containing novolac-type epoxy resin.

[0079] Reference Examples 1 to 4 Adhesive sheets were prepared in the same manner as in Example 1, except that the moisture-curable polyurethane resin (A) and epoxy resin (B) in Table 3 were used.

[0080] <Hot Water Resistance Test 2> Test specimens measuring 10 mm wide x 80 mm long were cut out from the adhesive sheet of each Reference Example, and the test specimens were immersed in hot water at 120°C for 24 hours. After cooling to room temperature, the hot water resistance of each test specimen was evaluated according to the following criteria: Good: No peeling was observed after immersion. Fair: No peeling was observed after immersion, but some lifting was observed. Poor: Peeling was observed after immersion.

[0081] The evaluation results of the hot water resistance test 2 are shown in Table 3.

[0082]

[0083] The results in Table 3 show that by using a bisphenol A type epoxy resin as the epoxy resin in a hot melt adhesive sheet, an adhesive sheet with excellent hot water resistance can be obtained even under harsher conditions such as hot water at 120°C.

[0084] From the above, it can be seen that the present invention can provide a hot melt adhesive sheet that exhibits good adhesion to difficult-to-adhere articles even without aging treatment by heating.

[0085] 10 hot melt adhesive sheet, 20 membrane / electrode assembly (MEA), 201 solid electrolyte membrane, 202 positive electrode, 203 negative electrode, 10a sheet-like substrate, 10b adhesive layer, 201a positive electrode side electrolyte membrane exposed region, 201b negative electrode side electrolyte membrane exposed region, 202a positive electrode catalyst layer, 202b positive electrode gas diffusion layer, 203a negative electrode catalyst layer, 203b negative electrode gas diffusion layer, 202a1 positive electrode side catalyst layer exposed region, 203a1 negative electrode side catalyst layer exposed region, L1 first boundary line, L2 second boundary line, L3 third boundary line, L4 fourth boundary line.

Claims

1. A hot melt adhesive sheet comprising a sheet-like substrate and an adhesive layer formed of a hot melt adhesive laminated on at least one surface thereof, the hot melt adhesive comprising a moisture-curing polyurethane resin and an epoxy resin.

2. The hot melt adhesive sheet according to claim 1, wherein the content of the epoxy resin is 5 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the moisture-curing polyurethane resin.

3. The hot melt adhesive sheet according to claim 1, wherein the epoxy equivalent of the epoxy resin is 100 g / eq or more and 1500 g / eq or less.

4. The hot melt adhesive sheet according to any one of claims 1 to 3, wherein the epoxy resin is one or more epoxy resins selected from the group consisting of triphenylmethane-type epoxy resins, bisphenol A-type epoxy resins, and naphthalene skeleton-containing novolac-type epoxy resins.

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