JP7476748B2 - Adhesives, cured products and laminates - Google Patents

Description

The present invention relates to an adhesive that has high coating strength and is excellent in flexibility, heat resistance, chemical resistance, and adhesion.

In the fields of automobiles, building materials, ships, aircraft, etc., various structural adhesives are used to bond and fix metals such as iron, aluminum, and stainless steel, resins, glass, ceramics, etc. In recent years, weight reduction has been promoted in the fields of automobiles and aircraft to improve fuel efficiency, and there has been a strong movement to increase the use of materials made of plastics and fiber-reinforced plastics (hereinafter abbreviated as FRP) and to replace iron with lighter aluminum, so there is a demand for adhesives that can firmly bond these materials. Furthermore, from the viewpoints of workability and reducing environmental impact, there is a demand for adhesives that do not contain volatile organic compounds.

However, for example, when bonding a metal such as aluminum to a material with a different linear expansion coefficient such as FRP, the difference in the expansion coefficient between the materials caused by temperature changes during the manufacturing process or in the operating temperature environment places high stress on the adhesive layer, accelerating the destruction or deterioration of the adhesive layer.

To address these issues, for example, Patent Documents 1 to 3 disclose a method of adding long-chain polyamines or nano-dispersed rubber particles to epoxy compounds that have high adhesion to metals and FRP for the purpose of stress relief. However, although these methods can impart a certain degree of flexibility, the resulting adhesive layer remains hard and brittle, and the effect is insufficient.

On the other hand, Patent Documents 4 to 6 disclose adhesive compositions that have high flexibility and coating strength by using a base agent containing a urethane polymer and a curing agent containing a non-crystalline polyol compound and a polyamine compound.

However, these methods use large amounts of amine compounds, making it difficult to adjust the curing speed, and they have issues such as nozzle clogging during application and uneven bonding when bonding large areas. In addition, the curing speed can be slowed down by reducing the amount of amine compounds used, but this reduces flexibility and coating strength. Furthermore, these methods have issues with insufficient heat resistance and chemical resistance such as oil resistance, because trace amounts of amino groups remain in the cured film.

JP 2018-506635 A International Publication No. 2007/025007 JP 2015-182248 A JP 2020-055921 A JP 2020-055922 A JP 2020-055923 A

The object of the present invention is to provide a structural adhesive that has high coating strength, excellent flexibility, heat resistance, chemical resistance, and adhesion, and is suitable for use in fields such as automobiles, building materials, ships, and aircraft.

The present invention relates to an adhesive that contains a urethane-acrylic composite resin (C) in which a urethane unit (A) and a (meth)acrylic unit (B) are linked by a chain transfer agent residue, a crosslinking agent (D), and a reactive diluent (E), in which the urethane unit (A) has a structural unit derived from a non-crystalline polyol (F) having a number average molecular weight of 500 or more and a structural unit derived from a crystalline polyol (G) having a number average molecular weight of 500 or more, and the (meth)acrylic unit (B) has a structural unit derived from a (meth)acrylic monomer (b1) having a hydroxyl group.

The present invention relates to the above adhesive, in which the polyol constituting the urethane unit (A) contains 30 to 65 mass% of non-crystalline polyol (F) and 35 to 70 mass% of crystalline polyol (G) based on the total mass of the polyol.

The present invention relates to the above adhesive, in which the urethane-acrylic composite resin (C) contains urethane units (A) in a range of 70 to 97% by mass based on the total mass of the urethane-acrylic composite resin (C).

The present invention relates to the above adhesive, in which the amorphous polyol (F) contains polypropylene glycol.

The present invention relates to the above adhesive, in which the crystalline polyol (G) contains at least one selected from the group consisting of polytetramethylene glycol and polycarbonate polyol.

The present invention relates to the above adhesive, in which the (meth)acrylic monomer (b1) having a hydroxyl group includes a (meth)acrylic monomer (b1a) having a hydroxyl group and a nitrogen atom.

The present invention relates to a cured product of the above adhesive.

The present invention relates to a laminate having a layer of the above-mentioned cured product on a substrate.

The present invention provides a structural adhesive that has high coating strength and is excellent in flexibility, heat resistance, chemical resistance, and adhesion.

<Adhesive>
The adhesive of the present invention contains a urethane-acrylic composite resin (C) in which a urethane unit (A) and a (meth)acrylic unit (B) are linked by a chain transfer agent residue, a crosslinking agent (D), and a reactive diluent (E), and the urethane unit (A) has a structural unit derived from a non-crystalline polyol (F) having a number average molecular weight of 500 or more and a structural unit derived from a crystalline polyol (G) having a number average molecular weight of 500 or more, and the (meth)acrylic unit (B) has a structural unit derived from a (meth)acrylic monomer (b1) having a hydroxyl group. By adopting such a configuration, the flexible urethane portion and the portion derived from the acrylic and reactive diluent crosslinked by the reaction with the crosslinking agent form a microphase separation structure, and excellent extensibility due to the urethane portion and excellent strength due to the portion derived from the crosslinked acrylic and reactive diluent are exhibited. As a result, the adhesive of the present invention can exhibit high coating strength, excellent flexibility, heat resistance, chemical resistance, and adhesion.
Therefore, the adhesive of the present invention is suitable for use in the fields of automobiles, building materials, ships, aircraft, etc. Furthermore, the adhesive of the present invention can be used as a liquid solvent-free adhesive, and is excellent in terms of safety and environmental friendliness.
In this specification, the term "chain transfer agent residue" refers to a partial structure of a composite resin that can be identified as being derived from a chain transfer agent.

<Urethane-acrylic composite resin (C)>
The urethane-acrylic composite resin (C) of the present invention may have a structure in which a urethane unit (A) having a constituent unit derived from a non-crystalline polyol (F) having a number average molecular weight of 500 or more and a constituent unit derived from a crystalline polyol (G) having a number average molecular weight of 500 or more, and a (meth)acrylic unit (B) having a constituent unit derived from a (meth)acrylic monomer (b1) having a hydroxyl group are linked by a chain transfer agent residue, and the production method thereof is not limited, but it can be preferably produced by the following method.
First, a polyol containing a non-crystalline polyol (F) and a crystalline polyol (G) is reacted with a polyisocyanate to form a urethane prepolymer having isocyanato groups at both ends (hereinafter, step 1).
Next, a chain transfer agent and a reactive diluent (E) are added to synthesize a urethane unit (A) having chain transfer agent residues at both ends of the urethane prepolymer (hereinafter, step 2).
Thereafter, an ethylenically unsaturated monomer including a (meth)acrylic monomer (b1) having a hydroxyl group is chain-transfer polymerized in the presence of a polymerization initiator using the chain transfer agent residue contained in the obtained urethane unit (A) to form a (meth)acrylic unit (B) (hereinafter, step 3).
In this way, a urethane-acrylic composite resin (C) can be obtained, which is a block polymer in which the urethane unit (A) and the (meth)acrylic unit (B) are linked by a chain transfer agent residue. All of these reactions may be carried out using a solvent or without using a solvent. However, when a solvent is used, it is preferable to remove the solvent under reduced pressure or normal pressure during or after the reaction. In this way, a solvent-free adhesive can be obtained.

<Urethane unit (A)>
First, the urethane unit (A) of the urethane-acrylic composite resin (C) will be described below.
The urethane unit (A) in the present invention can be obtained by reacting a urethane prepolymer obtained by reacting a polyol containing a non-crystalline polyol (F) having a number average molecular weight of 500 or more and a crystalline polyol (G) having a number average molecular weight of 500 or more, and a polyisocyanate in a solventless or solvent-free state with a chain transfer agent, preferably in the presence of a reactive diluent (E), to obtain a urethane unit (A) having a chain transfer agent residue at both ends. If the number average molecular weights of the polyols (F) and (G) constituting the urethane unit (A) are less than 500, the flexibility of the urethane portion decreases, so it is important to use a polyol having a number average molecular weight of 500 or more.
In this specification, "crystalline" means that the material is solid at -20°C, and "non-crystalline" means that the material is liquid at -20°C.

[Non-crystalline polyol (F)]
The non-crystalline polyol (F) having a number average molecular weight of 500 or more constituting the urethane unit (A) may be any polyol having the above-mentioned "non-crystalline" number average molecular weight of 500 or more, and examples thereof include polyether polyols, polyolefin polyols, vegetable oil-based polyols, and modified polyols thereof, etc. These may be used alone or in combination of two or more.

(Polyether polyol)
Examples of polyether polyols include polymers or copolymers of methylene oxide, ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, and the like, and glycols such as polyethylene glycol, polypropylene glycol, and poly(ethylene/propylene) glycol;
Condensates of hexanediol, methylhexanediol, heptanediol, octanediol, or mixtures thereof; and polyols obtained by adding an alkylene oxide, such as methylene oxide, ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, or polyoxytetramethylene oxide, to a compound having two or more active hydrogen groups.

Examples of the compound having two or more active hydrogen groups include low molecular weight polyols, aliphatic amine compounds, aromatic amine compounds, alkanolamines, and bisphenols.

The low molecular weight polyol may be, for example, a bifunctional low molecular weight polyol or a trifunctional or higher functional low molecular weight polyol.

The bifunctional low molecular weight polyol is not particularly limited, and examples thereof include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, hexanediol, octanediol, nonanediol, dipropylene glycol, diethylene glycol, triethylene glycol, 3-methyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octane Examples include diol, polyoxyethylene glycol (10 or less moles added), polyoxypropylene glycol (10 or less moles added), cyclohexanediol, cyclohexanedimethanol, tricyclodecane dimethanol, cyclopentadiene dimethanol, dimer diol, bisphenol A, N,N-bis(2-hydroxypropyl)aniline, dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, dihydroxypropionic acid, and dihydroxybenzoic acid.

The trifunctional or higher low molecular weight polyol is not particularly limited, and examples thereof include trimethylolethane, trimethylolpropane, 1,1,1-trimethylolbutane, 1,2,3-butanetriol, 1,2,4-butanetriol, 1,2,6-butanetriol, trimethylolbutene, trimethylolpentene, trimethylolhexene, trimethylolheptene, trimethyloloctene, trimethylolnonene, trimethyloldecene, trimethylolundecene, trimethyloldodecene, trimethyloltridecene, trimethylolpentadecene, trimethylolpentadecene, trimethylolbutene ... Tyrolhexadecene, Trimetrolheptadecene, Trimethyloloctadecene, 1,1,1-trimethylol-2-methyl-hexane, 1,1,1-trimethylol-3-methyl-hexane, 1,1,1-trimethylol-2-ethyl-hexane, 1,1,1-trimethylol-3-ethyl-hexane, Trimethylolhexene, 1,2,3-octanetriol, 1,3,7-octanetriol, 3,7-dimethyl-1,2,3-octanetriol, 1,1,1-, 1,1,1-trimethyloldecane, 1,2,10-decanetriol, 1,1,1 -Trimethylol isoheptadecane, 1,1,1-trimethylol-sec-butane, 1,1,1-trimethylol-tert-pentane, 1,1,1-trimethylol-tert-nonane, 1,1,1-trimethylol-tert-tridecane, 1,1,1-trimethylol-tert-heptadecane, 1,1,1-trimethylol-2-methyl-hexane, 1,1,1-trimethylol-3-methyl-hexane, 1,1,1-trimethylol-2-ethyl-hexane, 1,1,1-trimethylol-3-ethyl-hexane, 1,1,1-tri ...2-methyl-hexane, 1,1,1-trimethylol-3-ethyl-hexane, 1,1,1-trimethylol isoheptadecane, 1,1,1-trimethylol-2-methyl-hexane, 1,1,1-trimethylol-3-ethyl-hexane, 1,1,1-trimethylol isoheptadecane, 1,1,1-trimethylol-2-methyl-hexane, 1,1,1-trimethylol-3-ethyl-hexane, 1,1,1-trimethylol isoheptadecane, These include butadecane, 1,2,3,4-butanetetraol, pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, diglycerin, triglycerin, polyglycerin, ditrimethylolethane, ditrimethylolpropane, tris(2-hydroxyethyl)isocyanurate, benzene-1,3,5-triol, benzene-1,2,3-triol, stilbene-3,4',5-triol, sucrose, inositol, sorbitan, sorbitol, mannitol, saccharose, cellulose, and xylitol.

Examples of aliphatic amine compounds include ethylenediamine, triethylenetetramine, diethylenetriamine, and triaminopropane. Examples of aromatic amine compounds include toluenediamine and diphenylmethane-4,4-diamine. Examples of alkanolamines include ethanolamine and diethanolamine. Examples of bisphenols include bisphenol A, bisphenol AP, bisphenol B, bisphenol C, bisphenol E, and bisphenol F.

(Polyolefin polyol)
Examples of polyolefin polyols include hydroxyl-containing polybutadiene, hydrogenated hydroxyl-containing polybutadiene, hydroxyl-containing polyisoprene, hydrogenated hydroxyl-containing polyisoprene, hydroxyl-containing chlorinated polypropylene, and hydroxyl-containing chlorinated polyethylene.

(Vegetable oil-based polyol)
Examples of vegetable oil-based polyols include polyols made from castor oil, dimer acid, or soybean oil, which are derived from plants.

The number average molecular weight of the non-crystalline polyol (F) is 500 or more, preferably in the range of 500 to 30,000, and more preferably in the range of 800 to 3,000.

The non-crystalline polyol (F) preferably contains a polyether polyol, more preferably contains glycols, and even more preferably contains polypropylene glycol. Polypropylene glycol has side chains, which gives it excellent flexibility, and it is also highly compatible with the crystalline polyol (G) described below, which is why it is preferably used.

[Crystalline polyol (G)]
The crystalline polyol (G) having a number average molecular weight of 500 or more constituting the urethane unit (A) may be any polyol having the above-mentioned "crystallinity" and a number average molecular weight of 500 or more, and examples thereof include polyester polyols, polycarbonate polyols, polytetramethylene ether glycols, and modified polyols thereof, etc. These may be used alone or in combination of two or more.

(Polyester polyol)
The polyester polyol may be, for example, a polyester polyol obtained by a condensation reaction between the above-mentioned low molecular weight polyol and a dibasic acid component.
Examples of the dibasic acid component include aliphatic or aromatic dibasic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, adipic acid, azelaic acid, dimer acid, succinic acid, hydrogenated dimer acid, phthalic anhydride, maleic anhydride, itaconic anhydride, trimellitic acid, glutaric acid, pimelic acid, suberic acid, and sebacic acid, and their anhydrides.

In addition, polyester polyols obtained by ring-opening polymerization of cyclic ester compounds of lactones such as ε-caprolactone, poly(β-methyl-γ-valerolactone), and polyvalerolactone may be used as the polyester polyol.

(Polycarbonate polyol)
Examples of the polycarbonate polyol include those obtained by reacting the above-mentioned low molecular weight polyol with a carbonate compound such as a dialkyl carbonate, an alkylene carbonate, or a diaryl carbonate.
As the dialkyl carbonate, for example, dimethyl carbonate or diethyl carbonate can be used, as the alkylene carbonate, for example, ethylene carbonate can be used, and as the diaryl carbonate, for example, diphenyl carbonate can be used.

(Polytetramethylene ether glycol)
The polytetramethylene ether glycol is a polyether glycol having primary hydroxyl groups at both ends, and any conventionally known polytetramethylene ether glycol can be used without any particular limitation.
Examples of polytetramethylene ether glycol include ring-opening polymers obtained by cationic polymerization of tetrahydrofuran, and copolymers obtained by copolymerizing the above-mentioned bifunctional low-molecular-weight alcohols with polymer units of tetrahydrofuran, etc.
The polytetramethylene ether glycol may be of plant origin, using tetrahydrofuran as the starting material, which is produced from a plant-derived raw material such as furfural.

The number average molecular weight of the crystalline polyol (G) is 500 or more, preferably 500 to 30,000, and more preferably 800 to 3,000.

The crystalline polyol (G) preferably contains at least one selected from the group consisting of polytetramethylene ether glycol and polycarbonate polyol. Polytetramethylene ether glycol and polycarbonate polyol have high cohesive strength and can exhibit various resistances such as excellent coating strength, heat resistance, and water resistance while maintaining the flexibility of the urethane portion, and are therefore preferably used.

As described above, it is preferable that the polyol constituting the urethane unit (A) contains polypropylene glycol as the non-crystalline polyol (F) and at least one selected from the group consisting of polytetramethylene ether glycol and polycarbonate polyol as the crystalline polyol (G). By using such a specific polyol, a more ideal phase separation structure is formed, and high flexibility due to the polypropylene glycol and various resistances such as high cohesive force, coating strength, heat resistance, and water resistance due to the polytetramethylene ether glycol and polycarbonate polyol are exhibited.

In addition, from the viewpoint of coating film strength and flexibility, the polyol constituting the urethane unit (A) preferably contains 30 to 65 mass% of amorphous polyol (F) and 35 to 70 mass% of crystalline polyol (G) based on the total mass of the polyol, and more preferably contains 35 to 60 mass% of amorphous polyol (F) and 40 to 65 mass% of crystalline polyol (G). By using such a blending ratio, a tough cured film is obtained, which has excellent heat resistance, chemical resistance, and adhesion.

The polyol constituting the urethane unit (A) may contain a polyol having a number average molecular weight of less than 500 other than (F) and (G) for the purpose of adjusting the urethane bond concentration and introducing various functional groups, within a range that does not impair the effects of the present invention. Such polyols having a number average molecular weight of less than 500 are not particularly limited, and for example, the compounds exemplified as low molecular weight polyols described above can be used.

[Polyisocyanate]
Examples of the polyisocyanate constituting the urethane unit (A) include aromatic, aliphatic, and alicyclic diisocyanates. These may be used alone or in combination of two or more.

Examples of aromatic diisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, tolidine diisocyanate, xylylene diisocyanate, m-tetramethylxylene diisocyanate, p-tetramethylxylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, and 1,5-tetrahydronaphthalene diisocyanate.

Examples of aliphatic diisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, lysine ester triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate tetramethylene diisocyanate, pentamethylene diisocyanate, and trimethylhexamethylene diisocyanate.

Examples of alicyclic diisocyanates include isophorone diisocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,4-bis(isocyanatemethyl)cyclohexane, hydrogenated xylylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate.

The reaction between the polyol and the polyisocyanate can be carried out preferably in the absence of a solvent using a known urethane reaction, and by using an excess of polyisocyanate, a urethane prepolymer having isocyanato groups at both ends can be obtained. The molar ratio of isocyanato groups to hydroxyl groups (NCO moles/OH moles) during the reaction is preferably 1.05 to 2.00, more preferably 1.10 to 1.50.
In the urethanization reaction, a catalyst may be used for the purpose of adjusting the reactivity.

The catalyst may be a known metal catalyst, amine catalyst, or the like. Metal catalysts include dibutyltin dilaurate, tin octoate, dibutyltin di(2-ethylhexoate), lead 2-ethylhexoate, 2-ethylhexyl titanate, titanium ethyl acetate, iron 2-ethylhexoate, cobalt 2-ethylhexoate, zinc naphthenate, cobalt naphthenate, and tetra-n-butyltin. Amine catalysts include tertiary amines such as tetramethylbutanediamine. The amount of catalyst used is preferably in the range of 0.05 to 1 mol% based on the total mass of the polyol.

[Chain transfer agent]
The chain transfer agent constituting the urethane unit (A) is not particularly limited, but is preferably one having a functional group capable of reacting with an isocyanato group and a sulfanyl group in the molecule. When the chain transfer agent is used, the terminal isocyanato group in the urethane prepolymer reacts with the functional group capable of reacting with an isocyanato group in the chain transfer agent, forming a urethane unit (A) having sulfanyl groups at both ends. The chain transfer agent can be used alone or in combination of two or more of known chain transfer agents.

The functional group capable of reacting with the isocyanato group may be a hydroxyl group or an amino group, and from the viewpoint of reactivity, an amino group is preferred. Since the amino group is more reactive than the sulfanyl group, it reacts preferentially with the terminal isocyanato group of the urethane prepolymer to form a urea bond, and the sulfanyl group can be efficiently introduced into the terminal of the urethane unit (A).
The hydroxyl groups in the reactive diluent (E) described below may also react with the terminal isocyanato groups of the urethane prepolymer. However, the use of a chain transfer agent having an amino group, which is more reactive than a hydroxyl group, is preferable because it suppresses the reaction between a bifunctional or higher functional polyol and the isocyanato groups of the urethane prepolymer and enables efficient introduction of sulfanyl groups to the terminals of the urethane units (A).

Examples of compounds having one amino group and one sulfanyl group in the molecule include aminoalkanethiols such as 2-aminoethanethiol, 3-aminopropyl-1-thiol, 1-aminopropyl-2-thiol, and 4-amino-1-butanethiol; and aminobenzenethiols such as 2-aminothiophenol, 3-aminothiophenol, and 4-aminothiophenol. Among these, aminoalkanethiols are preferred, and 2-aminoethanethiol is more preferred.

[Content of urethane unit (A)]
The content of the urethane unit (A) is preferably 70 to 97% by mass, more preferably 80 to 95% by mass, based on the total mass of the urethane-acrylic composite resin (C). When the content of the urethane unit (A) is 70 to 975% by mass, excellent adhesive strength and flexibility are obtained, which is preferable.

The number weight average molecular weight of the urethane unit (A) is not particularly limited, but is preferably in the range of 3,000 to 200,000. If it is 3,000 or more, the adhesiveness of the resulting cured product will be excellent, and if it is 200,000 or less, the viscosity can be easily adjusted.

<Reactive Diluent (E)>
The reactive diluent (E) may be any liquid substance reactive with the crosslinking agent (D) described below, and is preferably a compound having a bifunctional or higher hydroxyl group. By including the reactive diluent (E) in the adhesive, the film formed by the adhesive becomes a stronger cured film, and excellent adhesive strength can be obtained.

As the reactive diluent (E), for example, various polyols listed in the above polyol section, as well as low molecular weight polyols used as raw materials thereof, can be used. The reactive diluent (E) may also be a condensate of these polyols and polyisocyanate. These may be used alone or in combination of two or more.
The reactive diluent (E) is preferably a polyether polyol, more preferably polypropylene glycol or polyethylene glycol.
As described above, the urethane unit (A) in step 2 is mainly composed of a reaction product between a urethane prepolymer and a chain transfer agent, and it is preferred that the majority of the reactive diluent (E) remains unreacted.

The content of the reactive diluent (E) is preferably 15 to 60% by mass, and more preferably 20 to 55% by mass, based on the total mass of the urethane-acrylic composite resin (C) and the reactive diluent (E). A content of the reactive diluent (E) of 15 to 60% by mass is preferable because it provides excellent flexibility and heat resistance.

The number average molecular weight of the reactive diluent (E) is preferably 200 to 2,000, more preferably 400 to 1,000. The hydroxyl value of the reactive diluent (E) is not particularly limited, but is preferably 50 to 500 mgKOH/g, more preferably 100 to 300 mgKOH/g. It is preferable that the number average molecular weight and hydroxyl value are within the above ranges, since they provide excellent adhesive strength, flexibility, heat resistance, and chemical resistance.

<(Meth)acrylic unit (B)>
The (meth)acrylic unit (B) has a structural unit derived from a (meth)acrylic monomer (b1) having a hydroxyl group, and is a structure obtained by polymerizing an ethylenically unsaturated monomer including the (meth)acrylic monomer (b1) having a hydroxyl group in the presence of a polymerization initiator.
Specifically, the composition containing the urethane unit (A) having chain transfer agent residues at both ends and the reactive diluent (E) obtained in step 2 and an ethylenically unsaturated monomer containing a (meth)acrylic monomer (b1) having a hydroxyl group are polymerized in the presence of a polymerization initiator, whereby it is possible to obtain a composition containing the urethane-acrylic composite resin (C), which is a block polymer in which the urethane unit (A) and the (meth)acrylic unit (B) are linked by a chain transfer agent residue, and the reactive diluent (E).

[(Meth)acrylic monomer having a hydroxyl group (b1)]
As the (meth)acrylic monomer having a hydroxyl group, a compound having at least one (meth)acryloyl group and a hydroxyl group in the molecule can be used, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxy-3-allyloxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, or caprolactone adducts of these monomers (the number of moles added is 1 to 5), polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, and glycerin mono(meth)acrylate. These may be used alone or in combination of two or more.

The content of the structural unit derived from the (meth)acrylic monomer (b1) having a hydroxyl group is preferably 50 to 100% by mass, and more preferably 70 to 100% by mass, based on the total mass of the ethylenically unsaturated monomers constituting the (meth)acrylic unit (B). If the content of the structural unit derived from the (meth)acrylic monomer (b1) having a hydroxyl group is 50 to 100% by mass, it is preferable because it has excellent flexibility and chemical resistance.

((Meth)acrylic monomer (b1a) having a hydroxyl group and a nitrogen atom)
From the viewpoint of the high adhesive strength and adhesion of amide group, the (meth)acrylic monomer (b1) having hydroxyl group preferably contains the (meth)acrylic monomer (b1a) having nitrogen atom in the molecule.As the (meth)acrylic monomer (b1a) having hydroxyl group and nitrogen atom in the molecule, a compound having at least one (meth)acryloyl group, hydroxyl group and nitrogen atom in the molecule can be used, for example, a (meth)acrylamide monomer, an amino group-containing (meth)acrylic monomer, a cyano group-containing (meth)acrylic monomer, or a (meth)acrylic monomer containing quaternary ammonium cation can be used.
Among these, (meth)acrylic monomers having a hydroxyl group are preferred, and examples of such monomers include N-(2-hydroxyethyl)(meth)acrylamide, N-methylol(meth)acrylamide, N,N-di(methylol)acrylamide, and N-methylol-N-methoxymethyl(meth)acrylamide. These may be used alone or in combination of two or more.

The content of the structural unit derived from the (meth)acrylic monomer (b1a) having a hydroxyl group and a nitrogen atom is
The content is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, based on the total mass of the (meth)acrylic monomer (b1) having a hydroxyl group. A content of 50 to 100% by mass is preferred because it provides excellent flexibility and strength at break.

[Other ethylenically unsaturated monomers]
The ethylenically unsaturated monomer other than the (meth)acrylic monomer (b1) having a hydroxyl group, which is used for forming the (meth)acrylic unit (B), is not particularly limited as long as it is copolymerizable with the (meth)acrylic monomer (b1), and can be appropriately selected from known ethylenically unsaturated monomers.
Examples of such other ethylenically unsaturated monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isoamyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cetyl (meth)acrylate, decyl (meth)acrylate, and isodecyl (meth)acrylate. linear or branched alkyl (meth)acrylates such as lauryl (meth)acrylate, tridecyl (meth)acrylate, isomyristyl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate; cyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and isobornyl (meth)acrylate; cyclic alkyl (meth)acrylates such as acrylate; fluoroalkyl (meth)acrylates such as trifluoroethyl (meth)acrylate, octafluoropentyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, and tetrafluoropropyl (meth)acrylate; (meth)acrylates having a heterocycle such as tetrahydrofurfuryl (meth)acrylate and 3-methyl-3-oxetanyl (meth)acrylate; benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxypolyethylene glycol ( (meth)acrylates having an aromatic ring, such as para-cumylphenoxyethyl (meth)acrylate, para-cumylphenoxypolyethylene glycol (meth)acrylate, and nonylphenoxypolyethylene glycol (meth)acrylate; methoxypolyethylene glycol mono(meth)acrylate, octoxypolyethylene glycol polypropylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, stearoxypolyethylene glycol mono(meth)acrylate, and phenoxypolyethylene glycol mono(meth)acrylate; (meth)acrylates having an alkyl ether group such as diethylene glycol mono(meth)acrylate, phenoxy polyethylene glycol polypropylene glycol mono(meth)acrylate, polyethylene glycol monomethyl ether (meth)acrylate, lauroxy polyethylene glycol mono(meth)acrylate, nonylphenoxy polyethylene glycol mono(meth)acrylate, nonylphenoxy polypropylene glycol mono(meth)acrylate, nonylphenoxy polyethylene glycol polypropylene glycol mono(meth)acrylate, phenoxy polyethylene glycol mono(meth)acrylate, methoxypolyethylene glycol (meth)acrylate, n-butoxyethyl (meth)acrylate, n-butoxydiethylene glycol (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate; vinyls such as styrene, α-methylstyrene, and vinyl acetate; (meth)acrylamide, N-methyl (meth)acrylamide, N-butyl (meth)acrylamide, diacetone (meth)acrylamide, N-methoxymethyl- (meth) Acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, N-pentoxymethyl-(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-dibenzyl(meth)acrylamide, methacrylformamide, N-methyl-N-vinylacetamide, N-vinylpyrrolidone, N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethyl(meth)acrylamide, N,N-di(ethoxymethyl)(meth)acrylamide and (meth)acrylates having a nitrogen atom such as N-ethoxymethyl-N-propoxymethyl(meth)acrylamide, N,N-di(propoxymethyl)(meth)acrylamide, N-butoxymethyl-N-(propoxymethyl)(meth)acrylamide, N,N-di(butoxymethyl)(meth)acrylamide, N-butoxymethyl-N-(methoxymethyl)(meth)acrylamide, N,N-di(pentoxymethyl)(meth)acrylamide, N-methoxymethyl-N-(pentoxymethyl)(meth)acrylamide, and cinnamic acid amide.
These may be used alone or in combination of two or more.

[Polymerization initiator]
As the polymerization initiator, known azo compounds and organic peroxides can be used. These may be used alone or in combination of two or more.
The azo compound is not particularly limited, and examples thereof include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl 1,1'-azobis(1-cyclohexanecarboxylate), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane].
The organic peroxide is not particularly limited, and examples thereof include benzoyl peroxide, t-butyl peroxy 2-ethylhexaate, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, (3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetyl peroxide.

The amount of polymerization initiator used is preferably 0.001 to 15% by mass based on the total mass of the ethylenically unsaturated monomer. A range of 0.001 to 15% by mass is preferable because chain transfer polymerization proceeds effectively.

[Weight average molecular weight of (meth)acrylic unit (B)]
The weight average molecular weight of the (meth)acrylic unit (B) is not particularly limited, but is preferably from 2,000 to 200,000. When it is 2,000 or more, the adhesiveness is excellent, and when it is 200,000 or less, the viscosity can be easily adjusted.

<Solvent>
Reactions for producing a urethane-acrylic composite resin, such as the reaction between a polyol and a polyisocyanate, the reaction between a urethane prepolymer and a chain transfer agent, and the reaction of polymerizing an ethylenically unsaturated monomer using a chain transfer agent residue, may be carried out using a solvent. These solvents may be used alone or in combination of two or more.
The solvent that may be used in the reaction of the polyol with the polyisocyanate is not particularly limited as long as it does not react with an isocyanato group, and examples thereof include acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, propyl acetate, toluene, xylene, anisole, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-vinylpyrrolidone, N-methylcaprolactam, dimethylsulfoxide, tetramethylurea, pyridine, dimethylsulfone, hexamethylsulfoxide, m-cresol, γ-butyrolactone, and γ-valerolactone.
As the solvent that may be used in the reaction between the urethane prepolymer and the chain transfer agent, in addition to the above-mentioned solvents, alcohols such as ethanol, isopropanol, tertiary butanol, and diacetone alcohol can be used.

<Weight average molecular weight of urethane-acrylic composite resin (C)>
The weight average molecular weight of the urethane-acrylic composite resin (C) is not particularly limited, but is preferably 5,000 to 300,000, and more preferably 10,000 to 100,000. When it is 5,000 or more, it is excellent in adhesion, and when it is 300,000 or less, it is easy to adjust the viscosity.

<Crosslinking Agent (D)>
The adhesive of the present invention further comprises a crosslinking agent (D) in addition to the composition containing the above-mentioned urethane-acrylic composite resin (C) and reactive diluent (E).
The crosslinking agent (D) is preferably one having a functional group capable of reacting with the functional group of the urethane-acrylic composite resin (C) or reactive diluent (E) contained in the adhesive, and is preferably a polyisocyanate. The polyisocyanate is not particularly limited as long as it is a compound having two or more isocyanato groups in the molecule, and includes the above-mentioned polyisocyanates, and their biuret bodies, nurate bodies, adduct bodies, and other condensation bodies. These crosslinking agents may be used alone or in combination of two or more.

Examples of biuret compounds include biuret compounds of hexamethylene diisocyanate (product name "Sumidur N-75", manufactured by Sumika Bayer Urethane Co., Ltd.; product name "Duranate 24A-100", manufactured by Asahi Kasei Chemicals Corporation).

Examples of nurates include hexamethylene diisocyanate nurate (product name "Sumidur N-3300", manufactured by Sumika Bayer Urethane Co., Ltd.), isophorone diisocyanate nurate (product name "Desmodur Z-4370", manufactured by Sumika Bayer Urethane Co., Ltd.), and tolylene diisocyanate nurate (product name "Coronate 2030", manufactured by Nippon Polyurethane Co., Ltd.).

Examples of adducts include bifunctional or higher isocyanate compounds obtained by reacting the above-mentioned polyisocyanates with the above-mentioned polyols or compounds having two or more active hydrogen groups, such as hexamethylene diisocyanate adducts of trimethylolpropane (product name "Takenate D-160N", manufactured by Mitsui Chemicals) and isophorone diisocyanate adducts of trimethylolpropane (product name "Takenate D-140N", manufactured by Mitsui Chemicals).

Other condensates include the polyfunctional, carbodiimide-modified, biuret-modified or allophanate-modified polyisocyanates mentioned above, such as polymethylene polyphenyl polyisocyanate (product name "PAPI27", manufactured by Dow), biuret of hexamethylene diisocyanate (product name "Takenate D-165N", manufactured by Mitsui Chemicals), and carbodiimide-modified diphenylmethane diisocyanate (product name "Isonate 143L", manufactured by Dow).

Among them, preferred crosslinking agents are trifunctional isocyanate compounds such as biuret of hexamethylene diisocyanate, isocyanurate of hexamethylene diisocyanate, trimethylolpropane adduct of tolylene diisocyanate, polymethylene polyphenyl polyisocyanate, trimethylolpropane adduct of xylylene diisocyanate, diphenylmethane diisocyanate, and tolylene diisocyanate, and these are preferred because they provide high cohesive strength. More preferred are isocyanurate of hexamethylene diisocyanate, trimethylolpropane adduct of tolylene diisocyanate, polymethylene polyphenyl polyisocyanate, and diphenylmethane diisocyanate.

The molar ratio of the isocyanato groups in the crosslinking agent (D) to the total hydroxyl groups contained in the adhesive (moles of isocyanato groups/moles of hydroxyl groups) is preferably 0.5 to 5.0, and more preferably 0.8 to 3.0. A molar ratio of 0.5 to 5.0 is preferred because it provides excellent adhesive strength and flexibility.

[Other ingredients]
The adhesive of the present invention may further contain known additives such as reaction accelerators, silane coupling agents, phosphoric acid or phosphoric acid derivatives, leveling agents or defoamers, fillers, propellants, plasticizers, superplasticizers, wetting agents, flame retardants, viscosity modifiers, preservatives, stabilizers, and colorants. Such additives may be used alone or in combination of two or more.

Examples of the reaction accelerator include metal catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, and dibutyltin dimaleate; tertiary amines such as 1,8-diaza-bicyclo(5,4,0)undecene-7, 1,5-diazabicyclo(4,3,0)nonene-5,6-dibutylamino-1,8-diazabicyclo(5,4,0)undecene-7; and reactive tertiary amines such as triethanolamine.
The amount of the reaction accelerator to be added is preferably 0.005 to 5% by mass based on the total mass of the urethane-acrylic composite resin (C).

Examples of the silane coupling agent include trialkoxysilanes having a vinyl group, such as vinyltrimethoxysilane and vinyltriethoxysilane; trialkoxysilanes having an amino group, such as 3-aminopropyltriethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane; trialkoxysilanes having a glycidyl group, such as 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane; trialkoxysilanes having an isocyanato group, such as 3-isocyanatepropyltriethoxysilane; and trialkoxysilanes having a mercapto group, such as 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane.
The amount of the silane coupling agent added is preferably 0.05 to 10% by mass based on the total mass of the urethane-acrylic composite resin (C).

Among phosphoric acid or phosphoric acid derivatives, phosphoric acid may be any one having at least one free oxygen acid, and examples thereof include phosphoric acids such as hypophosphorous acid, phosphorous acid, orthophosphoric acid, hypophosphoric acid, and condensed phosphoric acids such as metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, polyphosphoric acid, and ultraphosphoric acid. Examples of phosphoric acid derivatives include those obtained by partially esterifying the above-mentioned phosphoric acids with alcohols while leaving at least one free oxygen acid. Examples of these alcohols include aliphatic alcohols such as methanol, ethanol, ethylene glycol, and glycerin, and aromatic alcohols such as phenol, xylenol, hydroquinone, catechol, and phloroglucinol.
The amount of phosphoric acid or a derivative thereof added is preferably 0.005 to 5% by mass based on the total mass of the urethane-acrylic composite resin (C).

Examples of leveling agents include polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl-containing polydimethylsiloxane, polyetherester-modified hydroxyl-containing polydimethylsiloxane, acrylic copolymers, methacrylic copolymers, polyether-modified polymethylalkylsiloxane, acrylic acid alkyl ester copolymers, methacrylic acid alkyl ester copolymers, and lecithin.

Examples of antifoaming agents include known ones such as silicone resins, silicone solutions, and copolymers of alkyl vinyl ethers, alkyl acrylates, and alkyl methacrylates.

<Laminate, Cured Product>
The cured product of the present invention is preferably obtained by mixing a composition consisting of a urethane-acrylic composite resin (C) and a reactive diluent (E) with a crosslinking agent (D) by a known method. The laminate of the present invention has a layer consisting of the cured product of the adhesive of the present invention on a substrate. The method for producing the laminate is not particularly limited, and for example, the adhesive is applied to one surface of a substrate, and then another substrate is placed on the uncured adhesive surface, and a heat treatment is performed at about 20 to 150°C to cure the adhesive, thereby obtaining a laminate. The thickness of the adhesive layer after curing is preferably 0.1 μm to 300 mm.

The adhesive of the present invention can be used to bond a wide variety of substrates. Suitable substrates include, for example, metals such as aluminum, thermoplastic polymers such as polyethylene, polypropylene, polyurethane, polyacrylate, polycarbonate and copolymers thereof, thermosetting polymers such as vulcanized rubber, urea-formaldehyde foam, melamine resin, wood, carbon fiber reinforced plastic, glass fiber reinforced plastic and other fiber reinforced plastics. The substrates bonded via the adhesive layer may be the same or different.

The adhesive of the present invention has sufficient adhesion, flexibility, and adhesion to substrates, and laminates using the adhesive are useful as structural members (panel parts, frame parts, suspension parts, etc.) for automobiles, building materials, ships, aircraft, and other transportation equipment.

The present invention will be explained in more detail below with reference to examples, but the following examples do not limit the scope of the invention in any way. In the examples, "parts" means "parts by mass" and "%" means "% by mass" unless otherwise specified.

<Weight average molecular weight (Mw)>
The weight average molecular weight (Mw) of the resin was determined by gel permeation chromatography (GPC) as a converted value using standard polystyrene. The measurement was performed using a GPC-8020 (manufactured by Tosoh Corporation) as a GPC device, tetrahydrofuran as an eluent, and three TSKgel Super HM-M (manufactured by Tosoh Corporation) columns connected in series under the conditions of a flow rate of 0.6 ml/min, an injection amount of 10 μl, and a column temperature of 40° C.

<Measurement of Hydroxyl Value>
The hydroxyl value was determined by the following procedure. First, 1 g of sample was precisely weighed and placed in a stoppered Erlenmeyer flask, and 100 ml of pyridine was added to dissolve it. Then, exactly 5 ml of an acetylating agent (a solution of 25 g of acetic anhydride dissolved in pyridine to a volume of 100 ml) was added, and after stirring for 1 hour, the solution was titrated with a 0.5N alcoholic potassium hydroxide solution. Based on the above, the hydroxyl value (unit: mgKOH/g) was calculated by the following formula. The hydroxyl value was the value of the dried sample.

Hydroxyl value = [[{(b - a) x F x 28.05} / S] / (non-volatile content concentration / 100) + D] / (α / β)
S: Amount of sample collected (g)
a: Amount of 0.5N alcoholic potassium hydroxide solution consumed (ml)
b: Amount of 0.5N alcoholic potassium hydroxide solution consumed in a blank experiment (ml)
F: Factor of 0.5N alcoholic potassium hydroxide solution
D: Acid value (mg KOH / g)
α: the amount (g) of all ethylenically unsaturated monomers constituting the (meth)acrylic unit (B) used during production
β: Amount (g) of all components used in production

The abbreviations of compounds used in this specification are shown below.
<Non-crystalline polyol (F) having a number average molecular weight of 500 or more>
P-1000: Bifunctional polypropylene glycol, number average molecular weight 1,000, hydroxyl value 110 mgKOH/g, manufactured by ADEKA Corporation. P-2000: Bifunctional polypropylene glycol, number average molecular weight 2,000, hydroxyl value 67.5 mgKOH/g, manufactured by ADEKA Corporation.

<Crystalline polyol (G) having a number average molecular weight of 500 or more>
PTG-1000SN: bifunctional polytetramethylene ether glycol, number average molecular weight 1,000, hydroxyl value 112 mgKOH/g, manufactured by Hodogaya Chemical Co., Ltd. PTG-2000SN: bifunctional polytetramethylene ether glycol, number average molecular weight 2,000, hydroxyl value 56.8 mgKOH/g, manufactured by Hodogaya Chemical Co., Ltd. T6001: bifunctional polycarbonate polyol, number average molecular weight 1,000, hydroxyl value 116.5 mgKOH/g, manufactured by Asahi Kasei Corporation T5652: bifunctional polycarbonate polyol, number average molecular weight 2,000, hydroxyl value 56.6 mgKOH/g, manufactured by Asahi Kasei Corporation T5651: bifunctional polycarbonate polyol, number average molecular weight 1,000, hydroxyl value 113 mgKOH/g, manufactured by Asahi Kasei Corporation

<Polyol with a number average molecular weight of less than 500>
14BG: 1,4-butanediol, molecular weight 90.12, hydroxyl value 1245 mgKOH/g

<Polyisocyanate>
IPDI: Isophorone diisocyanate <chain transfer agent>
Cysteamine: 2-aminoethanethiol

<(Meth)acrylic monomer>
HEMA: 2-hydroxyethyl methacrylate HEAA: hydroxyethyl acrylamide BMA: n-butyl methacrylate

<Reactive Diluent (E)>
P-400: bifunctional polypropylene glycol, number average molecular weight 400, hydroxyl value 280 mgKOH/g, manufactured by ADEKA Corporation

<Crosslinking Agent>
Polymeric MDI: Polymethylene polyphenyl polyisocyanate, manufactured by Dow Corporation TDI-TMP adduct: Trimethylolpropane to toluene diisocyanate adduct, manufactured by Mitsui Chemicals, Inc.

<Production of urethane-acrylic composite resin>
(Production Example 1)
A reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser was charged with 65.0 parts of P-1000 as a non-crystalline polyol, 35.0 parts of PTG-1000SN as a crystalline polyol, 28.5 parts of isophorone diisocyanate as a polyisocyanate, and 0.02 parts of dibutyltin dilaurate as a catalyst, and after uniform stirring, the mixture was reacted at 90° C. for 5 hours under a nitrogen atmosphere to obtain a urethane prepolymer.
Next, the mixture was cooled to 80° C., and 55.1 parts of methyl ethyl ketone as a solvent, 71.2 parts of Adeca Polyether P-400 as a reactive diluent, and 4.3 parts of 2-aminoethanethiol as a chain transfer agent were added, followed by reaction for 2 hours at 75° C. to obtain a urethane unit. The end point of the reaction was confirmed by FT-IR based on the disappearance of the peak (near 2270 cm ⁻¹ ) derived from the isocyanato group.
Next, 26.6 parts of HEAA as a (meth)acrylic monomer (b1) having a hydroxyl group and 6.6 parts of BMA as another ethylenically unsaturated monomer were added and stirred uniformly, and then the mixture was heated to 75° C. under a nitrogen atmosphere. 0.1 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) as a polymerization initiator was added thereto in 13 divided portions every 30 minutes, and the reaction was continued for another 2 hours after the addition of the polymerization initiator to form a (meth)acrylic unit. The solvent was then completely removed under reduced pressure to obtain a composition (CE-1) consisting of a urethane-acrylic composite resin (C-1) and a reactive diluent.
The weight average molecular weight of the obtained urethane-acrylic composite resin (C-1), the proportion (%) of the urethane unit (A) in the urethane-acrylic composite resin (C-1), the proportion (%) of the (meth)acrylic monomer (b1) having a hydroxyl group in the (meth)acrylic unit (B), the proportion (%) of the (meth)acrylic monomer (b1a) having a hydroxyl group and a nitrogen atom in the (meth)acrylic monomer (b1) having a hydroxyl group, and the proportion (%) of the reactive diluent (E) in the urethane-acrylic composite resin (C) and the reactive diluent (E) are as shown in Table 1.

(Production Examples 2 to 27, Comparative Production Examples 1 to 2)
Except for changing the compounds and blending compositions shown in Tables 1 to 3, the same operation as in Production Example 1 was performed to obtain compositions (CE-2 to CE-29) composed of urethane-acrylic composite resins (C-2 to C-29) and reactive diluents of Production Examples 2 to 40, respectively.
The weight average molecular weight of the obtained urethane-acrylic composite resin (C), the proportion (%) of the urethane unit (A) in the urethane-acrylic composite resin (C), the proportion (%) of the (meth)acrylic monomer (b1) having a hydroxyl group in the (meth)acrylic unit (B), the proportion (%) of the (meth)acrylic monomer (b1a) having a hydroxyl group and a nitrogen atom in the (meth)acrylic monomer (b1) having a hydroxyl group, and the proportion (%) of the reactive diluent (E) in the urethane-acrylic composite resin (C) and the reactive diluent (E) are as shown in Tables 1 to 3.

<Production of Comparative Resin>
(Comparative Production Example 3) Urethane resin (J)
In a reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser, 65.0 parts of P-1000 as a non-crystalline polyol, 35.0 parts of PTG-1000SN as a crystalline polyol, 16.8 parts of isophorone diisocyanate as a polyisocyanate, and 0.02 parts of dibutyltin dilaurate as a catalyst were charged, and after uniform stirring, the mixture was reacted at 110 ° C. for 5 hours under a nitrogen atmosphere to obtain a urethane resin. Subsequently, 50.0 parts of Adeka polyether P-400 was added as a reactive diluent, and the mixture was thoroughly stirred and mixed to obtain a comparative urethane resin (J) containing a reactive diluent. The weight average molecular weight of the obtained urethane resin (J) was 42,000.

(Comparative Production Example 4) Acrylic resin (K)
In a reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser, 5.4 parts of Adeka Polyether P-400 as a reactive diluent, 10.0 parts of n-butyl methacrylate, 2.5 parts of 2-hydroxyethyl methacrylate, and 0.1 parts of 2-ethylhexyl thioglycolate were added and uniformly stirred, and then the temperature was raised to 75°C under a nitrogen atmosphere, and 0.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) as a polymerization initiator was added in 13 portions every 30 minutes, and after all of the polymerization initiator was added, the reaction was continued for another 2 hours, thereby obtaining a comparative acrylic resin (K) containing a reactive diluent. The weight average molecular weight of the obtained acrylic resin (K) was 22,000.

<Preparation of adhesive>
[Example 1]
The adhesive of Example 1 was prepared by mixing and stirring 10.0 parts of the mixed solution (CE-1) consisting of the urethane-acrylic composite resin (C-1) and the reactive diluent obtained in Production Example 1 and 4.0 parts of polymeric MDI as the crosslinking agent (B) at room temperature.

[Examples 2 to 28 and Comparative Examples 1 to 4]
The adhesives of Examples 2 to 28 and Comparative Examples 1 to 4 were prepared in the same manner as in Example 1, except that the compounding compositions were changed to those shown in Table 4. Note that the adhesive of Comparative Example 2 had a high viscosity, making it difficult to prepare a sample, and therefore testing could not be carried out.

<Adhesive evaluation>
The adhesives prepared in the Examples and Comparative Examples were subjected to the following tests. The results are shown in Table 4.

[Breaking stress/breaking elongation]
Each adhesive was filled into a sheet-like formwork having a thickness of 2 mm, the surface was smoothed, and after curing at 80° C. for one day, a dumbbell-shaped test piece for evaluation was prepared by punching it out with a dumbbell mold No. 3. Using this dumbbell piece, a tensile test was performed at a tensile speed of 50 mm/min, and the breaking stress (MPa) and breaking elongation (%) were measured and evaluated according to the following criteria.

(Evaluation Criteria for Breaking Stress)
◎: Breaking stress is 25 MPa or more (very good)
○: Breaking stress is 20 MPa or more and less than 25 MPa (good)
△: Breaking stress is 15 MPa or more and less than 20 MPa (usable)
×: Breaking stress is less than 15 MPa (unusable)

(Evaluation Criteria for Breaking Elongation)
◎: Breaking elongation is 500% or more (very good)
○: Breaking elongation is 400% or more and less than 500% (good)
△: Breaking elongation is 300% or more and less than 400% (usable)
×: Breaking elongation is less than 300% (unusable)

[Heat resistance to 120°C]
A dumbbell-shaped test piece was prepared in the same manner as in the above [Break stress and break elongation]. The dumbbell-shaped test piece was heat-treated for 100 hours in an environment of 120°C, and then a tensile test was carried out in the same manner as in the above [Break stress and break elongation] to measure the break stress (MPa) and the break elongation (%). The rate of change of the test piece before and after the test was calculated and judged according to the following criteria.

(Evaluation Criteria for Rate of Change in Breaking Stress)
◎: The rate of change is less than 10% (very good)
○: The rate of change is 10% or more and less than 30% (good)
△: The rate of change is 30% or more and less than 50% (usable)
×: The rate of change is 50% or more (unusable)

(Evaluation Criteria for Rate of Change in Breaking Elongation)
◎: The rate of change is less than 10% (very good)
○: The rate of change is 10% or more and less than 30% (good)
△: The rate of change is 30% or more and less than 50% (usable)
×: The rate of change is 50% or more (unusable)

[Oil resistance at 120°C]
A dumbbell-shaped test piece was prepared in the same manner as in the above [Breaking Stress and Elongation]. The dumbbell-shaped test piece was immersed in automatic transmission oil at 120°C for 100 hours, and then subjected to a tensile test in the same manner as in the above [Breaking Stress and Elongation] to measure the breaking stress (MPa) and breaking elongation (%). The rate of change of the test piece before and after the test was calculated and judged according to the following criteria.

(Evaluation Criteria for Rate of Change in Breaking Stress)
◎: The rate of change is less than 10% (very good)
○: The rate of change is 10% or more and less than 30% (good)
△: The rate of change is 30% or more and less than 50% (usable)
×: The rate of change is 50% or more (unusable)

(Evaluation Criteria for Rate of Change in Breaking Elongation)
◎: The rate of change is less than 10% (very good)
○: The rate of change is 10% or more and less than 30% (good)
△: The rate of change is 30% or more and less than 50% (usable)
×: The rate of change is 50% or more (unusable)

[Shear adhesive strength]
Each adhesive composition was applied to a stainless steel substrate (length 100 mm, width 25 mm, thickness 2 mm) to a width of 25 mm, length 10 mm, and thickness of 0.1 mm, and then bonded to a carbon fiber reinforced plastic substrate (length 100 mm, width 25 mm, thickness 2 mm), and aged at 80° C. for 1 day while being pressed to maintain a thickness of 0.1 mm to obtain a test specimen. The shear adhesive strength of the obtained test specimen was measured using a tensile tester at a temperature of 25° C. and a relative humidity of 50% at a tensile speed of 1 mm/min, and evaluated according to the following evaluation criteria.
(Evaluation criteria)
◎: Shear adhesive strength is 10 MPa or more (very good)
○: Shear adhesive strength is 7 MPa or more and less than 10 MPa (good)
△: Shear adhesive strength is 5 MPa or more and less than 7 MPa (usable)
×: Shear adhesive strength is less than 5 MPa (unusable)

The adhesive of the present invention exhibited good results in terms of breaking stress, breaking elongation, heat resistance at 120° C., oil resistance at 120° C., and shear adhesive strength. On the other hand, the adhesive of the comparative example exhibited results inferior to those of the examples in terms of some or all of breaking stress, breaking elongation, heat resistance at 120° C., oil resistance at 120° C., and shear adhesive strength.

Claims (8)

An adhesive comprising: a urethane-acrylic composite resin (C) in which a urethane unit (A) and a (meth)acrylic unit (B) are linked by a chain transfer agent residue; a crosslinking agent (D); and a reactive diluent (E),
the urethane unit (A) has a constituent unit derived from a non-crystalline polyol (F) having a number average molecular weight of 500 or more and a constituent unit derived from a crystalline polyol (G) having a number average molecular weight of 500 or more,
The (meth)acrylic unit (B) has a structural unit derived from a (meth)acrylic monomer (b1) having a hydroxyl group. The adhesive according to claim 1, wherein the polyol constituting the urethane unit (A) contains 30 to 65 mass% of non-crystalline polyol (F) and 35 to 70 mass% of crystalline polyol (G) based on the total mass of the polyol. The adhesive according to claim 1 or 2, wherein the urethane-acrylic composite resin (C) contains urethane units (A) in a range of 70 to 97% by mass based on the total mass of the urethane-acrylic composite resin (C). The adhesive according to any one of claims 1 to 3, wherein the amorphous polyol (F) contains polypropylene glycol. The adhesive according to any one of claims 1 to 4, wherein the crystalline polyol (G) includes at least one selected from the group consisting of polytetramethylene glycol and polycarbonate polyol. The adhesive according to any one of claims 1 to 5, wherein the (meth)acrylic monomer (b1) having a hydroxyl group includes a (meth)acrylic monomer (b1a) having a hydroxyl group and a nitrogen atom. A cured product of the adhesive described in any one of claims 1 to 6. A laminate having a layer of the cured product according to claim 7 on a substrate.