JP7763702B2 - Hot melt adhesive - Google Patents

Description

The present invention relates to a hot melt adhesive.

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), as well as their adhesiveness, flexibility, processability, and ease of various molecular designs in room temperature ranges (25±10°C).
The polyurethane-based adhesives include those that contain polyester polyol or acrylic polyol as a main component and polyisocyanate as a crosslinking agent, and are used by generating urethane bonds by promoting a crosslinking reaction between the main component and the crosslinking agent, and those that contain polyurethane having a certain chain length (so-called polyurethane prepolymer) as a main component and an isocyanate-based crosslinking agent as a crosslinking agent, and are used by promoting a crosslinking reaction between the main component and the crosslinking agent to cause curing.

Furthermore, Patent Document 1 below describes an adhesive that has excellent moisture and heat resistance as a two-component adhesive that contains a polyurethane resin as a base agent, an epoxy resin, and an isocyanate-based crosslinking agent.
In recent years, hot melt adhesives have been increasingly used to bond members because they are easier to handle than liquid adhesives such as those described in Patent Document 1 below.

International Publication No. 2013/157604

Improved moisture and heat resistance (heat resistance) is required not only for two-component adhesives such as those described in Cited Document 1, but also for hot melt adhesives.

In addition, although there is a demand for hot melt adhesives to have improved resistance to acids and alcohols, these demands have not been met.

The present invention was made in consideration of these problems with the prior art, and its objective is to provide a hot melt adhesive that can be thermocompression bonded, has excellent adhesion to substrates, and is also highly resistant to hot water, acids, and alcohols.

As a result of extensive research, the present inventors have found that by forming a hot melt adhesive into a hot melt adhesive containing a crosslinked product of an adhesive composition containing a crosslinking agent, the hot melt adhesive contains a polyurethane resin (A), an epoxy resin (B), and an isocyanate-based crosslinking agent (C), the epoxy resin (B) contains a hydroxyl group-containing epoxy resin having an epoxy equivalent of 450 g/eq or more and 3000 g/eq or less and having hydroxyl groups, and the polyurethane resin (A) contains a structural unit derived from a polyol (a1) whose skeleton has 8 or more carbon atoms, the hot melt adhesive can be thermocompression bonded, has excellent adhesion to a substrate, and is excellent in heat resistance (hot water resistance), acid resistance, and alcohol resistance.
As a result, the present invention was conceived.

That is, the hot melt adhesive according to the present invention is
The composition contains a polyurethane resin (A), an epoxy resin (B), and an isocyanate-based crosslinking agent (C),
the epoxy resin (B) contains a hydroxyl group-containing epoxy resin having an epoxy equivalent of 450 eq/g or more and 3000 eq/g or less and having a hydroxyl group;
The polyurethane resin (A) has a structural unit derived from a polyol (a1) having a skeleton with 8 or more carbon atoms.

With this configuration, the hot melt adhesive can be thermocompressed, has excellent adhesion to the substrate, and is also highly heat-resistant, acid-resistant, and alcohol-resistant.

In the hot melt adhesive,
The polyurethane resin (A) contains a hydroxyl group-containing polyurethane resin having a hydroxyl group,
The hydroxyl value of the hydroxyl-containing polyurethane resin is preferably 0.1 mgKOH/g or more and 20 mgKOH/g or less.

With this configuration, the hot melt adhesive is easier to bond by thermocompression, has better adhesion to the substrate, and is also more heat-resistant, acid-resistant, and alcohol-resistant.

In the hot melt adhesive,
The polyurethane resin (A) preferably has an aromatic diisocyanate as a constituent unit.

With this configuration, the hot melt adhesive is easier to bond by thermocompression, has better adhesion to the substrate, and is also more heat-resistant, acid-resistant, and alcohol-resistant.

In the hot melt adhesive,
The epoxy resin (B) contained in the adhesive composition is preferably 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the polyurethane resin (A).

With this configuration, the hot melt adhesive is easier to bond by thermocompression, has better adhesion to the substrate, and is also more heat-resistant, acid-resistant, and alcohol-resistant.

In the hot melt adhesive,
The weight average molecular weight Mw of the polyurethane resin (A) is preferably 1,000 or more and 100,000 or less.

With this configuration, the hot melt adhesive is easier to bond by thermocompression, has better adhesion to the substrate, and is also more heat-resistant, acid-resistant, and alcohol-resistant.

In the hot melt adhesive,
The amount of the isocyanate-based crosslinking agent (C) contained in the adhesive composition is preferably 2 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the total amount of the polyurethane resin (A) and the epoxy resin (B).

With this configuration, the hot melt adhesive is easier to bond by thermocompression, has better adhesion to the substrate, and is also more heat-resistant, acid-resistant, and alcohol-resistant.

In the hot melt adhesive,
It is used to bond components whose surfaces are made of resin,
The resin is preferably at least one selected from the group consisting of polyethylene terephthalate resin, polyethylene naphthalate resin, and polybutylene terephthalate resin.

In the hot melt adhesive,
Used to bond a first member and a second member,
At least the surfaces of the first member and the second member to be bonded are made of resin,
the resin in the first member is at least one selected from the group consisting of polyethylene terephthalate resin, polyethylene naphthalate resin, and polybutylene terephthalate resin;
The resin in the second member is preferably a perfluorocarbon sulfonic acid resin.

The present invention provides a hot melt adhesive that can be thermocompressed, has excellent adhesion to substrates, and is also highly resistant to hot water, acids, and alcohols.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

The hot melt adhesive according to this embodiment is a hot melt adhesive containing a crosslinked product of an adhesive composition containing a crosslinking agent.
The hot melt adhesive according to this embodiment contains a polyurethane resin (A), an epoxy resin (B), and an isocyanate-based crosslinking agent (C).
In the hot melt adhesive according to this embodiment, the epoxy resin (B) contains a hydroxyl group-containing epoxy resin having an epoxy equivalent of 450 g/eq or more and 3000 g/eq or less and having hydroxyl groups.
In the hot melt adhesive according to this embodiment, the polyurethane resin (A) has a structural unit derived from a polyol (a1) having a skeleton with 8 or more carbon atoms.

(Polyurethane resin (A))
The polyurethane resin (A) is obtained by urethane bonding reaction components including a polyol component (a) having two or more hydroxyl groups in one molecule and a polyisocyanate component (b) having two or more isocyanate groups in one molecule.
In this embodiment, as described above, the polyurethane resin (A) has, as the polyol component (a), a structural unit derived from a polyol (a1) having a skeleton with 8 or more carbon atoms.

The polyurethane resin (A) preferably contains a hydroxyl group-containing polyurethane resin having hydroxyl groups to react with the isocyanate-based crosslinking agent (C).
The hydroxyl group-containing polyurethane resin preferably has a hydroxyl group at its terminal.
The hydroxyl value of the hydroxyl-containing polyurethane resin is preferably 0.1 mgKOH/g or more and 20 mgKOH/g or less, and more preferably 1 mgKOH/g or more and 15 mgKOH/g or less.

In the hot melt adhesive according to this embodiment, the polyurethane resin (A) is crosslinked together with the epoxy resin (B) by the isocyanate-based crosslinking agent (C).
Specifically, in the hot melt adhesive according to this embodiment, the polyurethane resin (A) and the epoxy resin (B) are crosslinked by the isocyanate-based crosslinking agent (C) at a relatively low temperature (a temperature of 60°C or less).
That is, in the hot melt adhesive according to this embodiment, the polyurethane resin (A) and the epoxy resin (B) are contained in a state crosslinked by the isocyanate-based crosslinking agent (C) at a relatively low temperature (a temperature of 60°C or less).
In this way, the polyurethane resin (A) and the epoxy resin (B) are in a state of being crosslinked by the isocyanate-based crosslinking agent (C), and therefore can be easily thermocompression bonded.

The polyol component (a) preferably contains a polyol (a1) having a skeleton with 8 or more carbon atoms and a general polyol (a2).
In the following, the general polyol (a2) may be simply referred to as polyol (a2).
In this specification, the polyol (a1) having 8 or more carbon atoms in the skeleton means a polyol in which the number of carbon atoms between hydroxyl groups is 8 or more, and the 8 or more carbon atoms between the hydroxyl groups may be bonded via a heteroatom, and adjacent carbon atoms may be bonded via a saturated or unsaturated bond.
The polyol (a1) having a skeleton with 8 or more carbon atoms is preferably a polycarbonate polyol.
In the polyol (a1) having a skeleton with 8 or more carbon atoms, the number of heteroatoms contained in the portion containing 8 or more carbon atoms is preferably 2 or less.
Furthermore, the polyol (a1) having a skeleton of 8 or more carbon atoms preferably has a residue in the molecule obtained by removing multiple hydrogen atoms from a saturated or unsaturated hydrocarbon having 8 or more carbon atoms.
The polyol (a1) having a skeleton with 8 or more carbon atoms preferably has an alkylene group with 6 or more carbon atoms.

Examples of polyols (a1) having a skeleton with 8 or more carbon atoms include polyester polyols obtained by condensation polymerization of monomers containing dicarboxylic acids (such as sebacic acid (10 carbon atoms), azelaic acid (9 carbon atoms), isophthalic acid (8 carbon atoms), and terephthalic acid (8 carbon atoms)) and glycols (such as 1,9-nonanediol (9 carbon atoms) and 1,4-bishydroxymethylcyclohexane (8 carbon atoms)).

Examples of polyols (a1) having a skeleton with 8 or more carbon atoms include polycarbonate polyols such as poly(1,4-cyclohexanedimethylene carbonate) diol (carbon number 8), polyoctamethylene carbonate diol (carbon number 8), polynonamemethylene carbonate diol (carbon number 9), and polydecamethylene carbonate diol (carbon number 10), as well as random/block copolymers of monomers containing these.

Furthermore, examples of the polyol (a1) having a skeleton of 8 or more carbon atoms include polyols derived from dimer acids.
The dimer acid is a dicarboxylic acid having 36 carbon atoms obtained by dimerizing an unsaturated fatty acid having 18 carbon atoms, such as oleic acid or linoleic acid, and is a fatty acid derived from plants.
A typical structure of the dimer acid is represented by the following formula (1).
The dimer acid may include a trimer acid.
Trimer acid is a tricarboxylic acid having 54 carbon atoms obtained by trimerizing the above-mentioned unsaturated fatty acid having 18 carbon atoms. It is also produced as a by-product during the production of dimer acid, and commercially available dimer acid usually contains trimer acid.

Dimer diol, which is a polyol derived from dimer acid, is a polyol having 36 carbon atoms obtained by reducing the carboxyl groups of the dimer acid to hydroxyl groups.
The polyol may or may not have an unsaturated bond in its molecule.
A specific example of such a dimer polyol is dimer diol.
Similarly, trimer triol is a polyol obtained by reducing the carboxyl group of a trimer acid to a hydroxyl group.
Commercially available dimer diols typically contain trimer triols.
Therefore, the polyols derived from dimer acids, dimer polyols, and dimer diols may contain trimer triols.

Furthermore, examples of the polyol (a1) having a skeleton of 8 or more carbon atoms include polyolefin polyols.
Polyolefin polyol is a polymer obtained by polymerizing one or more polyolefins each having a plurality of hydroxyl groups.
Specific examples of such polyolefin polyols include polyethylene butylene diol, polybutadiene diol, and hydrogenated polybutadiene diol.
These polyols have extremely long carbon chains because the carbon chains are polymerized together.

When the hot melt adhesive contains, as the polyurethane resin (A), a structural unit derived from the polyol (a1) having 8 or more carbon atoms in its skeleton, the hydrophobicity of the hot melt adhesive can be improved compared to a hot melt adhesive that does not contain a structural unit derived from the polyol (a1) having 8 or more carbon atoms in its skeleton.
This makes the hot melt adhesive excellent in hot water resistance, acid resistance, and alcohol resistance.

As the polyol (a2), any known polyol that is used in the synthesis of polyurethane resins can be used.
Specific examples of the polyol (a2) include polyester polyols, polyether polyols, polycarbonate polyols, and other polyols.

Examples of polyester polyols include those obtained by condensation polymerization of aliphatic dicarboxylic acids (e.g., succinic acid, adipic acid, glutaric acid, etc.) and low-molecular-weight glycols (e.g., ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, neopentyl glycol, etc.).
The polyester polyols described above may be copolymerized with dicarboxylic acids or glycols having 8 or more carbon atoms.

Specific examples of such polyester polyols include polyethylene adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, polyneopentyl adipate diol, polyethylene/butylene adipate diol, polyneopentyl/hexyl adipate diol, poly-3-methylpentane adipate diol, polybutylene isophthalate diol, polycaprolactone diol, and poly-3-methylvalerolactone diol.
Polyester polyols have superior heat resistance compared to polyether polyols.
Therefore, polyester polyols are more advantageous than polyether polyols in terms of imparting excellent heat resistance to the resulting hot melt adhesive.

Specific examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and random/block copolymers thereof.
Polyether polyols have superior hydrolysis resistance compared to polyester polyols.
Therefore, polyether polyols are more advantageous than polyester polyols in providing the resulting hot melt adhesive with excellent hydrolysis resistance.

Specific examples of polycarbonate polyols include polytetramethylene carbonate diol, polypentamethylene carbonate diol, polyneopentyl carbonate diol, polyhexamethylene carbonate diol, and random/block copolymers thereof.
The above polycarbonate polyol may be copolymerized with a diol having 8 or more carbon atoms.
By using the various polycarbonate diols as described above as the polycarbonate polyol, the polyurethane resin (A) can be provided with structural units of the carbonate diol.
Polycarbonate polyol has excellent hydrolysis resistance and heat resistance.
This is advantageous in that the resulting hot melt adhesive has excellent hydrolysis resistance and heat resistance.
Among polycarbonate polyols, polyhexamethylene carbonate is preferred from the viewpoints of cost and ease of availability as a material.

Specific examples of other polyols include acrylic polyols, epoxy polyols, polyetherester polyols, siloxane-modified polyols, α,ω-polymethyl methacrylate diol, α,ω-polybutyl methacrylate diol, and siloxane-modified polyols.

To summarize the above description of the polyol (a2), from the viewpoint of making the resulting hot melt adhesive excellent in hot water resistance, it is preferable to use a polycarbonate polyol that has excellent hydrolysis resistance and heat resistance.
Moreover, from the viewpoint of cost and availability as a material, it is particularly preferable to use polyhexamethylene carbonate among the above polycarbonate polyols.

The number average molecular weight Mn (measured by a terminal functional group determination method) of the polyol (a1) and the polyol (a2) is not particularly limited, but is preferably 500 or more and 6,000 or less.
When the number average molecular weights Mn of the polyol (a1) and the polyol (a2) are within the above-mentioned ranges, the cohesive force due to the urethane bond is easily exhibited in the hot melt adhesive of this embodiment.
This provides the hot melt adhesive of this embodiment with excellent mechanical properties.
Furthermore, if the number average molecular weight Mn of the crystalline polyol is too large, when the hot melt adhesive of the present embodiment is formed into a film, the film may undergo whitening.
Therefore, when a crystalline polyol is used alone as the polyol (a1) and the polyol (a2), it is preferable to use one having a number average molecular weight Mn of 3,000 or less.
The polyol (a1) and the polyol (a2) may each be used alone or in combination of two or more.

The polyol (a1) is preferably blended in an amount of 10% by mass or more and 60% by mass or less when the polyol component (a) is taken as 100% by mass.
By blending the polyol (a1) in a proportion of 10 mass % or more, the hot melt adhesive according to this embodiment can be made to have sufficient hot water resistance, acid resistance, and alcohol resistance.
Furthermore, by blending the polyol (a1) in an amount of 60 mass% or less, the compatibility between the urethane resin (A) and the epoxy resin (B) is improved, and the resulting hot melt adhesive can have excellent adhesion to polyethylene terephthalate films, polyethylene naphthalate films, polybutylene terephthalate films, and resin films formed from perfluorocarbon sulfonic acid resins.
When the polyol component (a) is a copolymer of a monomer having a skeleton carbon number of 8 or more and a monomer having a skeleton carbon number of 7 or less, the parts by mass of the monomer having a skeleton carbon number of 8 or more are calculated as the parts by mass of the polyol (a1), and the parts by mass of the monomer having a skeleton carbon number of 7 or less are calculated as the parts by mass of the polyol (a2).

As the polyol component (a), in addition to the polyol (a1) and the polyol (a2), a short-chain diol (a3) can be used as necessary.
Specific examples of the short-chain diol (a3) include aliphatic glycols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, and neopentyl glycol, and low molar alkylene oxide adducts thereof (number average molecular weight Mn of less than 500 as determined by terminal functional group determination method); alicyclic glycols such as 1,4-bishydroxymethylcyclohexane and 2-methyl-1,1-cyclohexanedimethanol, and low molar alkylene oxide adducts thereof (number average molecular weight Mn of less than 500, same as above); aromatic glycols such as xylylene glycol, and low molar alkylene oxide adducts thereof (number average molecular weight Mn of less than 500, same as above); and bisphenols such as bisphenol A, thiobisphenol, and sulfonebisphenol, and low molar alkylene oxide adducts thereof (number average molecular weight Mn of less than 500, same as above).
Among the above short-chain diols (a3), it is preferable to use ethylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, neopentyl glycol, etc., and it is particularly preferable to use ethylene glycol, 1,3-butylene glycol, and 1,4-butylene glycol.
These short-chain diols (a3) may be used singly or in combination of two or more.

When producing the polyurethane resin (A), a polyhydric alcohol compound can also be used as a material for the polyurethane resin (A), similar to the short-chain diol (a3).
Specific examples of the polyhydric alcohol compounds include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, tris-(2-hydroxyethyl)isocyanurate, 1,1,1-trimethylolethane, and 1,1,1-trimethylolpropane.

If necessary, a hydroxyl group-containing compound (a4) having a carboxyl group may be used.
The hydroxyl group-containing compound (a4) having a carboxyl group usually has two or more hydroxyl groups in one molecule.
Furthermore, the hydroxyl group-containing compound (a4) having a carboxyl group usually has two or more hydroxyl groups in one molecule, and therefore reacts with a polyisocyanate component (b) having two or more isocyanate groups in one molecule to produce a polyurethane resin.

Examples of the hydroxyl group-containing compound (a4) having a carboxyl group include dimethylolpropanoic acid, dimethylolbutanoic acid, and low molar alkylene oxide adducts thereof (number average molecular weight Mn less than 500), low molar γ-caprolactone adducts (number average molecular weight Mn less than 500), half esters derived from acid anhydrides and glycerin, and compounds derived by a free radical reaction between a monomer containing a hydroxyl group and an unsaturated group and a monomer containing a carboxyl group and an unsaturated group.
Among these various compounds, it is preferable to use dimethylolpropanoic acid or dimethylolbutanoic acid, and it is particularly preferable to use dimethylolpropanoic acid.
These compounds may be used alone or in combination of two or more.
Here, the number average molecular weight Mn means a value measured by a terminal functional group determination method.
The various compounds described above are examples of preferred compounds in the present invention.
Therefore, the hydroxyl group-containing compound (a4) having a carboxyl group used in the present invention is not limited to the various compounds described above.
Therefore, in addition to the various compounds described above, any hydroxyl-containing compound (a4) having a carboxyl group that is currently commercially available and easily available on the market can be used in the present invention.

As the polyisocyanate component (b), any known polyisocyanate component that has been used in the production of polyurethane resins can be used.
Specific examples of the polyisocyanate component (b) include toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, mixtures thereof, 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, 2,4-diisocyanate diphenyl ether, 4,4'-methylenebis(phenylene isocyanate) (MDI), and crude or polymeric MDI, jurylene diisocyanate, xylylene diisocyanate (XDI), 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine Examples of the diisocyanate include aromatic diisocyanates such as methylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 1,10-decamethylene diisocyanate; alicyclic diisocyanates such as 1,4-cyclohexylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,5-tetrahydronaphthalene diisocyanate, isophorone diisocyanate, and hydrogenated XDI; and polyurethane prepolymers obtainable by reacting these diisocyanates with low-molecular-weight polyols so that the terminals are isocyanate groups.

Among these polyisocyanate components (b), from the viewpoint of industrially stably obtaining a hot melt adhesive that is inexpensive and has excellent heat resistance, it is preferable to use aromatic isocyanates, and it is particularly preferable to use toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, mixtures thereof, 4,4'-methylenebis(phenylene isocyanate) (MDI), and crude or polymeric MDI.
By using an aromatic isocyanate as the polyisocyanate component (b), the polyurethane resin (A) can be provided with structural units of an aromatic diisocyanate.
These polyisocyanate components (b) may be used singly or in combination of two or more.

(Method for producing polyurethane resin (A))
The polyurethane resin (A) can be produced by a conventionally known method for producing polyurethanes.
Specifically, first, a reaction composition containing, as reaction components, the polyol (a1) having 8 or more carbon atoms in its skeleton, the polyol (a2), the polyisocyanate component (b), and a short-chain diol (a3) used as a chain extender as needed, is reacted in the presence or absence of an organic solvent not containing active hydrogen in the molecule to obtain the polyurethane resin (A).
In addition, when obtaining the polyurethane resin (A), the hydroxyl group-containing compound (a4) having a carboxyl group may be used, if necessary.
The reaction composition generally has a compounding composition in which the equivalent ratio of isocyanate groups to hydroxyl groups is 0.8 to 1.25.
The reaction may be carried out by a one-shot method or a multi-stage method, usually at 20 to 150°C, preferably 60 to 110°C.

The weight average molecular weight Mw of the polyurethane resin (A) obtained as described above is preferably 1,000 or more and 100,000 or less.
When the weight average molecular weight Mw of the polyurethane resin (A) is within the above range, the hot melt adhesive containing the polyurethane resin (A) can more effectively exhibit properties such as adhesion to substrates, hot water resistance, acid resistance, and alcohol resistance.
The mass average molecular weight Mw of the polyurethane resin (A) means a value measured by gel permeation chromatography (GPC).
The mass average molecular weight Mw of the polyurethane resin (A) can be measured, for example, using the following apparatus and conditions.

Measurement equipment and conditions
・Equipment: Product name “HLC-8020” (manufactured by Tosoh Corporation)
Column: Product names "TSKgel G2000HXL", "G3000HXL", "G4000GXL" (manufactured by Tosoh Corporation)
Solvent: THF
・Flow rate: 1.0ml/min
Sample concentration: 2 g/L
・Injection volume: 100μL
・Temperature: 40℃
Detector: Model number "RI-8020" (manufactured by Tosoh Corporation)
Standard material: TSK standard polystyrene (manufactured by Tosoh Corporation)

In this embodiment, a catalyst can be used as needed in the synthesis of the polyurethane resin.
Examples of the catalyst include salts of metals with organic or inorganic acids, such as dibutyltin laurate, dioctyltin laurate, stannous octoate, zinc octoate, and tetra-n-butyl titanate; organometallic derivatives; organic amines, such as triethylamine; and diazabicycloundecene catalysts.
The catalyst accelerates the synthesis reaction of the polyurethane resin.
On the other hand, if the catalyst is used in excess, there is a risk that a decomposition reaction that decomposes substances other than the polyurethane resin will be induced, and as a result, there is a risk that the resulting hot melt adhesive will have poor long-term heat resistance.
Therefore, when the catalyst is used, it is preferable to use an appropriate amount of the catalyst.

The polyurethane resin (A) may be synthesized without using an organic solvent, or may be synthesized using an organic solvent.
As the organic solvent, an organic solvent inactive to an isocyanate group or an organic solvent less active than the reactive component to an isocyanate group can be used.
Specific examples of the organic solvent include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbon solvents such as toluene, xylene, Swazol (trade name, manufactured by Cosmo Oil Co., Ltd.), and Solvesso (trade name, manufactured by Exxon Chemical Co., Ltd.); aliphatic hydrocarbon solvents such as n-hexane; alcohol-based solvents such as methanol, ethanol, and isopropyl alcohol; ether-based solvents such as dioxane and tetrahydrofuran; ester-based solvents such as ethyl acetate, butyl acetate, and isobutyl acetate; carbonate-based solvents such as dimethyl carbonate, diethyl carbonate, and ethylene carbonate; glycol ether ester-based solvents such as ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, 3-methyl-3-methoxybutyl acetate, and ethyl-3-ethoxypropionate; amide-based solvents such as dimethylformamide and dimethylacetamide; and lactam-based solvents such as N-methyl-2-pyrrolidone.
Toluene, methyl ethyl ketone, and ethyl acetate are particularly preferred from the viewpoint of increasing the solubility of the polyurethane resin and from the viewpoint of easy volatilization when obtaining a hot melt adhesive.

(Epoxy resin (B))
In the hot melt adhesive according to this embodiment, the proportion of the epoxy resin (B) contained in the adhesive composition is preferably 10 parts by mass or more and 100 parts by mass or less, and more preferably 20 parts by mass or more and 80 parts by mass or less, per 100 parts by mass of the polyurethane resin (A).
When the proportion of the epoxy resin (B) is 10 parts by mass or more, the resulting hot melt adhesive exhibits sufficient hot water resistance, acid resistance, and alcohol resistance, and also exhibits sufficient adhesion to polyethylene terephthalate films, polyethylene naphthalate films, polybutylene terephthalate films, and resin films formed from perfluorocarbon sulfonic acid resins.
Furthermore, by making the proportion of the epoxy resin (B) 100 parts by mass or less, the resulting hot melt adhesive can fully exhibit the flexibility inherent to the urethane resin system.
This makes it possible to prevent the resulting hot melt adhesive from becoming too hard after curing (after the crosslinking reaction) and becoming unable to perform hot melt bonding.

In the hot melt adhesive of this embodiment, as described above, the epoxy resin (B) has an epoxy equivalent of 450 g/eq or more and 3000 g/eq or less and contains a hydroxyl group-containing epoxy resin having hydroxyl groups.
Since the epoxy equivalent is within the above numerical range, the hot melt adhesive of the present embodiment has excellent adhesion to substrates, cures at relatively low temperatures (e.g., 60°C or lower), and can be thermocompressed after curing (after the crosslinking reaction).
The epoxy equivalent can be determined in accordance with JIS K 7236.

The hydroxyl value is preferably 50 mgKOH/g or more and 250 mgKOH/g or less, and more preferably 100 mgKOH/g or more and 220 mgKOH/g or less.
When the hydroxyl value is 50 mgKOH/g or more, the crosslinking density can be further increased after the hydroxyl group-containing epoxy resin, together with the polyurethane resin (A), is crosslinked with the isocyanate-based crosslinking agent (C).
This allows the hot melt adhesive obtained as a cured product after the crosslinking reaction to have even better resistance to hot water, acid, and alcohol.
Furthermore, by making the hydroxyl value 250 mgKOH/g or less, it is possible to prevent the crosslink density from becoming excessively high.
This prevents the hot melt adhesive obtained as a cured product after the crosslinking reaction from becoming excessively poor in flexibility, making it difficult to perform thermocompression bonding.
Furthermore, by having a hydroxyl value of 250 mgKOH/g or less, the amount of unreacted hydroxyl groups can be made relatively small.
This prevents the relatively large number of remaining unreacted hydroxyl groups from reacting with the water contained in hot water or acid, thereby preventing the resulting hot melt adhesive from having a reduced resistance to hot water, acid, and alcohol.

The epoxy resin (B) may be a bisphenol A epoxy resin, a bisphenol F epoxy resin, or a bisphenol S epoxy resin, and these may be used alone or in combination of two or more.

In addition to the above, phenoxy resin, phenol novolac epoxy resin, rubber-modified epoxy resin, etc. can also be used in combination with the epoxy resin (B).

The epoxy resin (B) is preferably dissolved in an organic solvent and mixed with the polyurethane resin (A).

ether solvents such as dioxane and tetrahydrofuran; ester solvents such as ethyl acetate, butyl acetate, and isobutyl acetate; carbonate solvents such as dimethyl carbonate, diethyl carbonate, and ethylene carbonate; glycol ether ester solvents such as ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, 3-methyl-3-methoxybutyl acetate, and ethyl-3-ethoxypropionate; amide solvents such as dimethylformamide and dimethylacetamide; and lactam solvents such as N-methyl-2-pyrrolidone.
Toluene, methyl ethyl ketone, and ethyl acetate are particularly preferred from the viewpoint of increasing the solubility of the epoxy resin and from the viewpoint of easy volatilization when obtaining a hot melt adhesive.
Furthermore, toluene, methyl ethyl ketone, and ethyl acetate are preferred from the viewpoint that they are less likely to deactivate the isocyanate group than alcohol-based solvents.

(Isocyanate-based crosslinking agent (C))
In the hot melt adhesive of this embodiment, the proportion of the isocyanate-based crosslinking agent (C) contained in the adhesive composition is preferably 2 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the total amount of the polyurethane resin (A) and the epoxy resin (B).
By ensuring that the content of the isocyanate-based crosslinking agent (C) is within the above-mentioned range, it is possible to prevent the crosslinking reaction from proceeding excessively, which would result in the coating film becoming hard and brittle and difficult to be thermocompressed when the adhesive composition is applied to obtain a hot melt adhesive.
This provides the hot melt adhesive according to this embodiment with sufficient thermocompression bonding properties (hot melt properties).

The isocyanate-based crosslinking agent (C) is not particularly limited, and any of the conventionally used known crosslinking agents having a polyfunctional isocyanate group, such as an isocyanurate, biuret, adduct, or polymeric crosslinking agent, can be used.
Examples of such polyisocyanates include a dimer of 2,4-toluylene diisocyanate, triphenylmethane triisocyanate, tris-(p-isocyanatophenyl)thiophosphite, blocked polyisocyanates such as polyfunctional aromatic isocyanates, polyfunctional aromatic aliphatic isocyanates, polyfunctional aliphatic isocyanates, fatty acid-modified polyfunctional aliphatic isocyanates, and blocked polyfunctional aliphatic isocyanates, and polyisocyanate prepolymers.

Among these isocyanate-based crosslinking agents (C), diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate are preferred as aromatic crosslinking agents.
Among the aliphatic compounds, modified products such as hexamethylene diisocyanate and isophorone diisocyanate are preferred.
The isocyanate crosslinking agent (C) preferably contains three or more isocyanate groups in one molecule.
Furthermore, as the isocyanate-based crosslinking agent (C), a polymer of the above-mentioned polyisocyanate, an adduct with another compound, or a urethane prepolymer obtained by reacting a low-molecular-weight polyol with a polyamine so that the molecular terminal is an isocyanate group, can also be preferably used.
Examples of compounds preferred as the isocyanate-based crosslinking agent (C) are shown below as formulas (2) to (9).
However, the isocyanate-based crosslinking agent (C) is not limited to the compounds represented by the following formulas (2) to (9).

The hot melt adhesive according to this embodiment may further contain additives as needed.
Examples of additives include antioxidants (hindered phenols, phosphites, thioethers, etc.), light stabilizers (hindered amines, etc.), ultraviolet absorbers (benzophenones, benzotriazoles, etc.), gas discoloration stabilizers (hydrazines, etc.), metal deactivators, silane coupling agents, and tackifiers.
These additives may be used singly or in combination of two or more.

The hot melt adhesive according to this embodiment can be obtained by mixing the polyurethane resin (A), the epoxy resin (B), and the isocyanate-based crosslinking agent (C).
The epoxy resin (B) is preferably contained in a proportion of 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the polyurethane resin (A).
The isocyanate-based crosslinking agent (C) is preferably contained in an amount of 2 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the total amount of the polyurethane resin (A) and the epoxy resin (B).

The hot melt adhesive according to this embodiment obtained as described above is preferably used for bonding members at least the surface of which is made of resin.
The resin is preferably at least one selected from the group consisting of polyethylene terephthalate resin, polyethylene naphthalate resin, and polybutylene terephthalate resin.
The member may be a resin film (plastic film).
When the member is a resin film, the resin film is preferably at least one selected from the group consisting of a polyethylene terephthalate film, a polyethylene naphthalate film, and a polybutylene terephthalate film.

Furthermore, the hot melt adhesive of this embodiment is used to bond a first member and a second member, and it is preferable that at least the surfaces to be bonded of each of the first member and the second member are made of resin.
The resin in the first member is preferably at least one selected from the group consisting of polyethylene terephthalate resin, polyethylene naphthalate resin, and polybutylene terephthalate resin.
The resin in the second member is preferably a perfluorocarbon sulfonic acid resin.
The first member and the second member may be a resin film (plastic film).
When the first member is a resin film, the resin film is preferably at least one first resin film selected from the group consisting of a polyethylene terephthalate film, a polyethylene naphthalate film, and a polybutylene terephthalate film.
When the second member is a resin film, the resin film is preferably a film formed from a 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.
The perfluorocarbon sulfonic acid resin is, for example, a resin having a polymer structure represented by the following formula (1).
Regarding m, n, and x in the following formula (1), for example, in the "Nafion", m≧1, n=2, x=5 to 13.5; in the "Aciplex", m=0, 1, n=2 to 5, x=1.5 to 14; and in the "Flemion", m=0, 1, n=1 to 5.

The hot melt adhesive according to this embodiment can be obtained in the form of a sheet by applying a resin solution containing the polyurethane resin (A), the epoxy resin (B), and the isocyanate-based crosslinking agent (C), as well as an organic solvent such as toluene or methyl ethyl ketone, to a resin film (e.g., the first resin film) and drying the solution.
The resin solution can be applied by a conventionally known coating method, such as gravure or spray coating.
The coating is preferably carried out so that the thickness of the coating film after drying is 1 μm or more and 50 μm or less.
After the hot melt adhesive is processed into a sheet, the sheet-shaped hot melt adhesive is cured at a relatively low temperature (a temperature of 60°C or less) so that the polyurethane resin (A) and the epoxy resin (B) are crosslinked by the isocyanate-based crosslinking agent (C).
This allows the hot melt adhesive sheet processed into a sheet form to be stored for a long period of time while maintaining its quality on the resin film.
Furthermore, the polyurethane resin (A) and the epoxy resin (B) are cured in a crosslinked state by the isocyanate-based crosslinking agent (C), thereby preventing the resulting composition from becoming excessively tacky.
As a result, such a hot melt adhesive has excellent handling properties.
Furthermore, since the polyurethane resin (A) and the epoxy resin (B) are cured in a crosslinked state by the isocyanate-based crosslinking agent (C), the hot melt adhesive is easily thermocompressed and has excellent adhesion to the substrate, and further has the effects of being excellent in hot water resistance, acid resistance, and alcohol resistance.

The hot melt adhesive according to this embodiment is applied to a resin film, dried, and then cured in a crosslinked state at a relatively low temperature (a temperature of 60°C or less). In other words, after the hot melt adhesive has cured as a hot melt adhesive layer on the resin film, it is preferable that one hot melt adhesive layer be brought into contact with another hot melt adhesive layer and heated at a temperature of 120°C to 180°C to achieve thermocompression bonding (hot melt bonding).

Furthermore, after the hot melt adhesive according to this embodiment is applied to a resin film and dried, and then cured in a crosslinked state at a relatively low temperature (a temperature of 60°C or less), i.e., after the hot melt adhesive has cured in a state in which it forms a hot melt adhesive layer on the resin film, it is preferable that a resin film formed from a perfluorocarbon sulfonic acid resin be superimposed on the exposed surface of the hot melt adhesive layer (the surface not in contact with the resin film), and the hot melt adhesive layer be thermocompression bonded (hot melt bonded) to the resin film formed from the perfluorocarbon sulfonic acid resin by heating at a temperature of 120°C to 180°C.

The hot melt adhesive may also be used in a polymer electrolyte fuel cell by being attached to a solid electrolyte membrane formed from a perfluorocarbon sulfonic acid resin.
Specifically, in a membrane electrode assembly (MEA) configured by laminating a positive electrode and a negative electrode, each having a planar dimension smaller than that of a solid electrolyte membrane, on opposite sides of the solid electrolyte membrane, the hot melt adhesive may be attached to the solid electrolyte membrane exposed at the outer peripheral edge of the membrane electrode assembly (MEA).
Furthermore, when attaching the hot melt adhesive to the solid electrolyte membrane exposed at the outer peripheral end of the membrane electrode assembly (MEA), the solid electrolyte membrane may be sandwiched from both sides between two resin sheets with hot melt adhesive layers, so that a subgasket is formed by the two resin sheets with hot melt adhesive layers.

The hot melt adhesive according to the present invention is not limited to the above embodiment.
Furthermore, the hot melt adhesive according to the present invention is not limited to the above-mentioned effects.
The hot melt adhesive according to the present invention can be modified in various ways without departing from the gist of the present invention.

The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. Note that "parts" and "%" in the examples, reference examples, and comparative examples are by weight unless otherwise specified.

[Synthesis Example of Polyurethane Resin (A)]
<Synthesis example of polyurethane resin: A1>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the inside of a reaction vessel was purged with nitrogen, 300.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Corporation), 200.0 g of polycyclohexanedimethanol/hexanediol copolymer carbonate diol (trade name "ETERNACOLLUM-90 (3/1)", manufactured by Ube Industries, Ltd., hydroxyl value = 112.2 mg KOH/g, cyclohexanedimethanol/hexanediol = 3/1 molar ratio), and 10.0 g of 1,3-butylene glycol were charged.
Next, 207.3 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred.
After the system became homogeneous, 111.8 g of 4,4'-diphenylmethane diisocyanate (MDI) was charged at 50°C and reacted at 80°C to obtain a reaction liquid.
The viscosity of the reaction solution was adjusted by diluting the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm ⁻¹ due to free isocyanate groups measured by infrared absorption spectroscopy disappeared, thereby obtaining a resin solution AA1 containing polyurethane resin A1.
The obtained resin solution AA1 had a solid content of 30% by mass, and the polyurethane resin A1 had a hydroxyl value of 2.5 mg KOH/g and contained 29.7% by mass of polyol (a1) having a skeleton with 8 or more carbon atoms.
The weight average molecular weight of the polyurethane resin A1 measured by GPC was 72,000.

<Synthesis example of polyurethane resin: A2>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the inside of a reaction vessel was purged with nitrogen, 300.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Corporation), 200.0 g of polycyclohexanedimethanol/hexanediol copolymer carbonate diol (trade name "ETERNACOLLUM-90 (3/1)", manufactured by Ube Industries, Ltd., hydroxyl value = 112.2 mgKOH/g), 10.0 g of 1,3-butylene glycol, and 16 g of dimethylolpropanoic acid were charged.
Next, 222.3 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred.
After the system became homogeneous, 140.8 g of 4,4'-diphenylmethane diisocyanate (MDI) was charged at 50°C and reacted at 80°C to obtain a reaction liquid.
The viscosity of the reaction solution was adjusted by diluting the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm ⁻¹ due to free isocyanate groups measured by infrared absorption spectroscopy disappeared, thereby obtaining a resin solution AA2 containing a polyurethane resin A2.
The resulting resin solution AA2 had a solids content of 30% by mass, and the polyurethane resin A2 had a hydroxyl value of 2.9 mgKOH/g and an acid value of 10.0 mgKOH/g.
The weight average molecular weight of the polyurethane resin A2 measured by GPC was 61,000.
In the polyurethane resin A2, the polyol having a skeleton with 8 or more carbon atoms accounted for 29.7% by mass.

<Synthesis example of polyurethane resin: A3>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the inside of a reaction vessel was purged with nitrogen, 300.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Corporation), 200.0 g of polydecamethylene carbonate diol having hydroxyl groups at both ends (hydroxyl value = 56.1 mgKOH/g), and 10.0 g of 1,3-butylene glycol were charged.
Next, 199.2 g of methyl ethyl ketone (MEK) was charged as a solvent and the system was stirred. After the system became homogeneous, 87.6 g of 4,4'-diphenylmethane diisocyanate (MDI) was charged at 50°C and reacted at 80°C to obtain a reaction liquid.
The viscosity of the reaction solution was adjusted by diluting the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm ⁻¹ due to free isocyanate groups measured by infrared absorption spectroscopy disappeared, thereby obtaining a resin solution AA3 containing a polyurethane resin A3.
The obtained resin solution AA3 had a solid content of 30% by mass, and the polyurethane resin A3 had a hydroxyl value of 2.0 mgKOH/g and contained 30.6% by mass of polyol (a1) having a skeleton with 8 or more carbon atoms.
The weight average molecular weight of the polyurethane resin A3 measured by GPC was 76,000.

<Synthesis example of polyurethane resin: A4>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the inside of a reaction vessel was purged with nitrogen, 300.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Corporation), 200 g of dimer diol (trade name "Pripol 2033", manufactured by Croda Japan, OHv = 207 mg KOH/g), and 10.0 g of 1,3-butylene glycol were charged.
Next, 220.9 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred.
After the system became homogeneous, 152.8 g of 4,4'-diphenylmethane diisocyanate (MDI) was charged at 50°C and reacted at 80°C to obtain a reaction liquid.
The viscosity of the reaction solution was adjusted by diluting the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm ⁻¹ due to free isocyanate groups measured by infrared absorption spectroscopy disappeared, thereby obtaining a resin solution AA4 containing a polyurethane resin A4.
The obtained resin solution AA4 had a solid content of 30% by mass, and the polyurethane resin A4 had a hydroxyl value of 3.2 mg KOH/g and contained 39.2% by mass of polyol (a1) having a skeleton with 8 or more carbon atoms.
The weight average molecular weight of the polyurethane resin A1 measured by GPC was 56,000.

<Synthesis example of polyurethane resin: A5>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the inside of a reaction vessel was purged with nitrogen, 300.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Corporation), 200 g of hydrogenated polybutadiene polyol (trade name "GI-1000", manufactured by Nippon Soda Co., Ltd., OHv=66 mgKOH/g), and 10.0 g of 1,3-butylene glycol were charged.
Next, 200.6 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred.
After the system became homogeneous, 91.8 g of 4,4'-diphenylmethane diisocyanate (MDI) was added at 50°C, and the mixture was allowed to react at 80°C to obtain a reaction liquid.
The viscosity of the reaction solution was adjusted by diluting the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm ⁻¹ due to free isocyanate groups measured by infrared absorption spectroscopy disappeared, thereby obtaining resin solution AA5 containing polyurethane resin A5.
The obtained resin solution AA5 had a solid content of 30% by mass, and the polyurethane resin A5 had a hydroxyl value of 2.1 mg KOH/g and contained 39.2% by mass of polyol (a1) having a skeleton carbon chain of 8 or more.
The weight average molecular weight of the polyurethane resin A5 measured by GPC was 84,000.

<Synthesis example of polyurethane resin: A6>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the inside of the reaction vessel was purged with nitrogen, 200.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (Duranol: T6002, manufactured by Asahi Kasei Chemicals Corporation, number average molecular weight measured by terminal functional group determination method=2,000) and 10.0 g of 1,3-butylene glycol were charged.
Next, 87.1 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred.
After the system became homogeneous, 51.2 g of 4,4'-diphenylmethane diisocyanate (MDI) was added at 50°C, and the mixture was allowed to react at 80°C to obtain a reaction liquid.
The viscosity of the reaction solution was adjusted by diluting the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm ⁻¹ due to free isocyanate groups measured by infrared absorption spectroscopy disappeared, thereby obtaining a resin solution AA6 containing a polyurethane resin A6.
The resulting resin solution AA6 had a solids content of 30% by mass, and the polyurethane resin A6 had a hydroxyl value of 2.7 mgKOH/g.
The weight average molecular weight of the polyurethane resin A6 measured by GPC was 65,000.
The polyurethane resin A6 does not contain a polyol (a1) having a skeleton with 8 or more carbon atoms.

<Synthesis example of polyurethane resin: A7>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the inside of a reaction vessel was purged with nitrogen, 300.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Corporation), 20.0 g of polycyclohexanedimethanol/hexanediol copolymer carbonate diol (trade name "ETERNACOLLUM-90 (3/1)", manufactured by Ube Industries, Ltd., hydroxyl value = 112.2 mg KOH/g, cyclohexanedimethanol/hexanediol = 3/1 molar ratio), and 6.4 g of 1,3-butylene glycol were charged.
Next, 128.3 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred.
After the system became homogeneous, 58.5 g of 4,4'-diphenylmethane diisocyanate (MDI) was added at 50°C and reacted at 80°C to obtain a reaction liquid.
The viscosity of the reaction solution was adjusted by diluting the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm ⁻¹ due to free isocyanate groups measured by infrared absorption spectroscopy disappeared, thereby obtaining resin solution AA7 containing polyurethane resin A7.
The obtained resin solution AA7 had a solids content of 30% by mass, and the polyurethane resin A7 had a hydroxyl value of 2.1 mgKOH/g and contained 4.8% by mass of polyol (a1) having a skeleton with 8 or more carbon atoms.
The weight average molecular weight of the polyurethane resin A7 measured by GPC was 85,000.

<Synthesis example of polyurethane resin: A8>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the inside of a reaction vessel was purged with nitrogen, 300.0 g of polyhexamethylene carbonate diol having hydroxyl groups at both ends (DURANOL: T6002, manufactured by Asahi Kasei Chemicals Corporation), 1700 g of polycyclohexanedimethanol/hexanediol copolymer carbonate diol (trade name "ETERNACOLLUM-90 (3/1)", manufactured by Ube Industries, Ltd., hydroxyl value = 112.2 mg KOH/g, cyclohexanedimethanol/hexanediol = 3/1 molar ratio), and 40 g of 1,3-butylene glycol were charged.
Next, 865.5 g of methyl ethyl ketone (MEK) was charged as a solvent, and the system was stirred.
After the system became homogeneous, 556.4 g of 4,4'-diphenylmethane diisocyanate (MDI) was charged at 50°C and reacted at 80°C to obtain a reaction liquid.
The viscosity of the reaction solution was adjusted by diluting the reaction solution with methyl ethyl ketone (MEK) as a solvent, and the reaction was allowed to proceed until the absorption at 2,270 cm ⁻¹ due to free isocyanate groups measured by infrared absorption spectroscopy disappeared, thereby obtaining a resin solution AA8 containing a polyurethane resin A8.
The obtained resin solution AA8 had a solids content of 30% by mass, and the polyurethane resin A8 had a hydroxyl value of 3.0 mgKOH/g and contained 65.0% of polyol (a1) having a skeleton with 8 or more carbon atoms.
The weight average molecular weight of the polyurethane resin A8 measured by GPC was 60,000.

[Example of dissolution of epoxy resin (B)]
<Example of dissolving epoxy resin: B1>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the atmosphere inside a reaction vessel was replaced with nitrogen, 400.0 g of bisphenol A-type epoxy resin (epoxy equivalent: 450 g/eq, jER1001: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B1) was charged, and while stirring, 600.0 g of methyl ethyl ketone (MEK) was charged as a solvent. The temperature inside the system was raised to 60°C to completely dissolve the epoxy resin B1, thereby obtaining a solution BB1 of epoxy resin B1 (hereinafter referred to as epoxy resin solution BB1).
The resulting epoxy resin solution BB1 had a solids content of 40% by mass.

<Example of dissolving epoxy resin: B2>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the atmosphere inside a reaction vessel was replaced with nitrogen, 400.0 g of bisphenol A-type epoxy resin (epoxy equivalent: 925 g/eq, jER1004: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B2) was charged, and while stirring, 600.0 g of methyl ethyl ketone (MEK) as a solvent was charged. The temperature inside the system was raised to 60°C to completely dissolve the epoxy resin B2, thereby obtaining a solution BB2 of epoxy resin B2 (hereinafter referred to as epoxy resin solution BB2).
The resulting epoxy resin solution BB2 had a solids content of 40% by mass.

<Epoxy resin dissolution example: B3>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the atmosphere inside a reaction vessel was replaced with nitrogen, 400.0 g of bisphenol A-type epoxy resin (epoxy equivalent: 1975 g/eq, jER1007: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B3) was charged, and while stirring, 600.0 g of methyl ethyl ketone (MEK) was charged as a solvent. The temperature inside the system was raised to 60°C until the epoxy resin B3 was completely dissolved, thereby obtaining a solution BB3 of epoxy resin B3 (hereinafter referred to as epoxy resin solution BB3).
The resulting epoxy resin solution BB3 had a solids content of 40 mass %.

<Example of dissolving epoxy resin: B4>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the atmosphere inside a reaction vessel was replaced with nitrogen, 400.0 g of bisphenol A-type phenoxy resin (epoxy equivalent: 8500 g/eq, jER1256: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B4) was charged, and while stirring, 600.0 g of methyl ethyl ketone (MEK) was charged as a solvent. The temperature inside the system was raised to 60°C to completely dissolve the epoxy resin B4, thereby obtaining a solution of epoxy resin B4 BB4 (hereinafter referred to as epoxy resin solution BB4).
The resulting epoxy resin solution BB4 had a solids content of 40 mass %.

<Example of dissolving epoxy resin: B5>
A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen inlet tube, and a manhole was prepared.
While the atmosphere inside a reaction vessel was replaced with nitrogen, 800.0 g of a bisphenol A novolac epoxy resin (tri- or higher functional) (epoxy equivalent: 200 g/eq, jER157S70: manufactured by Mitsubishi Chemical Corporation; hereinafter referred to as epoxy resin B5) was charged, and 200.0 g of methyl ethyl ketone (MEK) as a solvent was charged while stirring. The temperature inside the system was raised to 60°C to completely dissolve the epoxy resin B5, thereby obtaining a solution of epoxy resin B5 BB5 (epoxy resin solution BB5).
The resulting epoxy resin solution BB5 had a solids content of 80 mass %.

[Preparation of hot melt adhesive]
The materials shown in Table 1 below were used in the blending ratios shown in Table 1 below to obtain hot melt adhesives according to each example.

Resin solutions AA1 to AA8 shown in Synthesis Examples A1 to A8 above were used as the resin solutions containing polyurethane resin (A).

The epoxy resin solutions BB1 to BB5 shown in the epoxy resin dissolution examples B1 to B5 above were used as the epoxy resin solutions containing epoxy resin (B).

The isocyanate-based crosslinking agents (C) used were a TMP adduct of XDI (C1) (D-110N: manufactured by Mitsui Chemicals, Inc.), a TMP adduct of TDI (C2) (D-101E: manufactured by Mitsui Chemicals, Inc.), and an isocyanurate of HDI (C3) (D-170N: manufactured by Mitsui Chemicals, Inc.).

[Coating of the compounded liquid onto a film]
The liquid mixture of each example was diluted with methyl ethyl ketone (MEK) to a solids content of 30% by mass.
In Example 1, the diluted mixture was applied to the entire surface of one side of a PET film (length: 210 mm, width: 150 mm, thickness: 100 μm, Lumirror: manufactured by Panac Corporation), and after application, the film was dried at 100° C. for 1 minute and then left in an oven at 40° C. for 48 hours to allow the curing reaction to proceed, thereby producing a PET film with a hot-melt adhesive layer.
The coating was carried out so that the thickness of the hot melt adhesive layer after drying was 20 μm.
In Example 2, coating was carried out in the same manner as in Example 1, except that the PET film was replaced with a PEN film (length: 210 mm, width: 150 mm, thickness: 100 μm, Teonex: manufactured by Toyobo Film Solutions Co., Ltd.).
Furthermore, in Example 3, coating was carried out in the same manner as in Example 1, except that the PET film was changed to a PBT film (length: 210 mm, width: 150 mm, thickness: 25 μm, Bobblet: manufactured by Kohjin Film & Chemicals Co., Ltd.).
In Examples 4 to 14 and Comparative Examples 1 to 5, coating was carried out in the same manner as in Example 1, except that the PET film was replaced with a PEN film, as in Example 2.
In Comparative Example 4, the PET film was replaced with a PEN film, as in Example 2, and coating was carried out in the same manner as in Example 1, except that the curing reaction of leaving the film in an oven at 40° C. for 48 hours was not carried out.

[Preparation of adhesive sheet E]
Two films with a hot melt adhesive layer of each example were prepared, and the two films with a hot melt adhesive layer were superimposed on each other so that the hot melt adhesive layers were in contact with each other.
Using a laminator adjusted to 140° C., two sheets of the film with the hot melt adhesive layer of each example were bonded together by thermocompression bonding to prepare an adhesive sheet E according to each example.
In Comparative Example 4, after lamination, the laminate was left in an oven at 40° C. for 48 hours to undergo a curing reaction.

[Creation of adhesive sheet F]
The film with the hot melt adhesive layer of each example was superimposed on a perfluorocarbon sulfonic acid resin sheet so that the exposed surface of the hot melt adhesive layer of the film with the hot melt adhesive layer of each example was in contact with one side of a perfluorocarbon sulfonic acid resin sheet (tetrafluoroethylene/perfluoro[2-(fluorosulfonylethoxy)propylvinylether] copolymer membrane (manufactured by DuPont, product name "NAFIONN-115")) (same shape as the film with the hot melt adhesive layer).
Using a laminator adjusted to 140°C, the film with the hot melt adhesive layer of each example and a perfluorocarbon sulfonic acid resin sheet were bonded together by thermocompression bonding to produce an adhesive sheet F according to each example.
In Comparative Example 4, after lamination, the laminate was left in an oven at 40° C. for 48 hours to undergo a curing reaction.

[Method for measuring adhesive strength]
The adhesive strength was measured using an autograb (Shimadzu Corporation, Autograph AGS-J500N).
The test was carried out by a T-peel test under a temperature condition of 25° C., and the pulling speed was 50 mm/min.

[Initial Adhesion 1]
For each example of adhesive sheet E, initial adhesion 1 was evaluated using an autograb.
A test specimen measuring 10 mm wide x 80 mm long was cut out from the adhesive sheet E of each example, and the adhesive strength of the test specimen was measured using an autograph.
In addition, when the adhesive strength value is 3 N/10 mm or more, it can be evaluated as being sufficient adhesive strength, and when the adhesive strength value is 4 N/10 mm or more, it can be evaluated as being even more sufficient adhesive strength.
The same applies below.
The measurement results are shown in Table 2 below. In Table 2 below, the unit of values is N/10 mm.

[Hot water resistance 1]
For the adhesive sheet E of each example, a test specimen measuring 10 mm wide x 80 mm long was cut out from the adhesive sheet of each example, and the test specimen was immersed in hot water at 95°C for 100 hours. After cooling to room temperature, the adhesive strength of the test specimen was measured using an autograph.
The measurement results are shown in Table 2 below.

[Acid resistance 1]
For the adhesive sheet E of each example, a test specimen measuring 10 mm wide x 80 mm long was cut out from the adhesive sheet of each example, and the test specimen was immersed in dilute sulfuric acid of pH 2 at 95°C for 100 hours. After cooling to room temperature, the adhesive strength of the test specimen was measured using an autograph.
The measurement results are shown in Table 2 below.

[Alcohol resistance 1]
For the adhesive sheet E of each example, a test specimen measuring 10 mm wide x 80 mm long was cut out from the adhesive sheet of each example, and the test specimen was immersed in ethylene glycol at 95°C for 100 hours. After cooling to room temperature, the adhesive strength of the test specimen was measured using an autograph.
The measurement results are shown in Table 2 below.

[Initial Adhesion 2]
For each example of adhesive sheet F, initial adhesion 2 was evaluated using an autograb.
A test specimen measuring 10 mm wide x 80 mm long was cut out from the adhesive sheet, and the adhesive strength of the test specimen was measured using an autograph.
The measurement results are shown in Table 2 below.

[Hot water resistance 2]
For the adhesive sheet F of each example, a test specimen measuring 10 mm wide x 80 mm long was cut out from the adhesive sheet of each example, and the test specimen was immersed in hot water at 95°C for 100 hours. After cooling to room temperature, the hot water resistance of each test specimen was evaluated according to the following criteria.

・Good: No peeling observed after immersion.
△: After immersion, no peeling was observed, but some lifting was observed.
×: Peeling was observed after immersion.

The evaluation results are shown in Table 2 below.

[Acid resistance 2]
For the adhesive sheet F of each example, a test specimen measuring 10 mm wide x 80 mm long was cut out from the adhesive sheet of each example, and the test specimen was immersed in dilute sulfuric acid of pH 2 at 95°C for 100 hours. After cooling to room temperature, the acid resistance of each test specimen was evaluated according to the following criteria.

・Good: No peeling observed after immersion.
△: After immersion, no peeling was observed, but some lifting was observed.
×: Peeling was observed after immersion.

The evaluation results are shown in Table 2 below.

[Alcohol resistance 2]
For the adhesive sheet F of each example, a test specimen measuring 10 mm wide x 80 mm long was cut out from the adhesive sheet of each example, and the test specimen was immersed in ethylene glycol at 95°C for 100 hours. After cooling to room temperature, the alcohol resistance of each test specimen was evaluated according to the following criteria.

・Good: No peeling observed after immersion.
△: After immersion, no peeling was observed, but some lifting was observed.
×: Peeling was observed after immersion.

The evaluation results are shown in Table 2 below.

[tack]
The surface of the adhesive layer of the film with the hot melt adhesive layer in each example was touched with a finger, and the tackiness was evaluated according to the following criteria.

・Good: Does not stick to fingers and the surface remains smooth.
・△: Doesn't stick to fingers, but leaves finger marks.
・×: There is enough tack to stick to your fingers.

The evaluation results are shown in Table 2 below.

From the results shown in Table 2, it can be seen that the hot melt adhesive of the present invention can be thermocompressed, has excellent adhesion to substrates, and is a hot melt adhesive that is also excellent in hot water resistance, acid resistance, alcohol resistance, and tackiness.

Claims (6)

A hot melt adhesive comprising a crosslinked product of an adhesive composition comprising a crosslinking agent,
The composition contains a polyurethane resin (A), an epoxy resin (B), and an isocyanate-based crosslinking agent (C),
the epoxy resin (B) contains a hydroxyl group-containing epoxy resin having an epoxy equivalent of 450 g/eq or more and 3000 g/eq or less, a hydroxyl value of 50 mgKOH/g or more and 250 mgKOH/g or less, and having a hydroxyl group;
the polyurethane resin (A) contains a hydroxyl group-containing polyurethane resin having a structural unit derived from a polyol (a1) having a skeleton with 8 or more carbon atoms and having a hydroxyl group;
a ratio of the epoxy resin (B) contained in the adhesive composition is 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the polyurethane resin (A),
The proportion of the isocyanate-based crosslinking agent (C) contained in the adhesive composition is 2 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the total amount of the polyurethane resin (A) and the epoxy resin (B).
Hot melt adhesive. The hot melt adhesive according to claim 1 , wherein the hydroxyl group-containing polyurethane resin has a hydroxyl group value of 0.1 mgKOH/g or more and 20 mgKOH/g or less. The hot melt adhesive according to claim 1 or 2, wherein the polyurethane resin (A) has an aromatic diisocyanate as a constituent unit. The hot melt adhesive according to any one of claims 1 to 3 , wherein the polyurethane resin (A) has a mass average molecular weight Mw of 1,000 or more and 100,000 or less. It is used to bond components whose surfaces are made of resin,
The hot melt adhesive according to any one of claims 1 to 4 , wherein the resin is at least one selected from the group consisting of polyethylene terephthalate resin, polyethylene naphthalate resin, and polybutylene terephthalate resin. Used to bond a first member and a second member,
At least the surfaces of the first member and the second member to be bonded are made of resin,
the resin in the first member is at least one selected from the group consisting of polyethylene terephthalate resin, polyethylene naphthalate resin, and polybutylene terephthalate resin;
The hot melt adhesive according to claim 1 , wherein the resin in the second member is a perfluorocarbon sulfonic acid resin.