Adhesive composition, adhesive structure, laminate, and motor

Abstract

This adhesive composition contains a radically polymerizable compound (A), a radical polymerization initiator (B), and a polymerization inhibitor (C). The polymerization inhibitor (C) contains an aromatic compound (C-1) which comprises a phenolic hydroxyl group and at least one of a nitroso group and a nitro group. This adhesive structure has a plurality of adherends and an adhesive layer which is interposed between the adherends that are adjacent to each other. The adhesive layer is composed of a cured product of the adhesive composition.

Description

Adhesive composition, bonded structure, laminate and motor

[0001] The present invention relates to an adhesive composition, an adhesive structure, a laminate, and a motor.

[0002] Radical polymerization adhesives are used in a variety of fields, taking advantage of their characteristic of rapid curing reaction. For example, Patent Document 1 describes a radical polymerizable adhesive composition for adhesively bonded laminated steel sheets, which has a tensile shear bond strength of 8.0 MPa or more as determined by a tensile shear bond strength test on electrical steel sheets, and which contains component (A): a radical polymerizable compound, component (B): a radical polymerization initiator, and component (C): a phosphate ester compound having a group represented by the following general formula (1) or (2):

[0003] International Publication No. 2019 / 123885

[0004] Incidentally, the radical polymerization initiator contained in a radical polymerization adhesive may generate radicals for various reasons, such as during storage of the adhesive. When radicals are generated in the adhesive, a polymerization reaction proceeds with the radicals as the starting point, which may result in the adhesive curing at an unintended time, such as during storage. To prevent such unintended curing of the adhesive and improve storage stability, a polymerization inhibitor that inhibits the progress of the radical polymerization reaction is usually added to radical polymerization adhesives.

[0005] However, polymerization inhibitors also hinder the progress of radical polymerization reactions when the adhesive is to be intentionally cured, and therefore, when an attempt is made to increase the storage stability of the adhesive by using a polymerization inhibitor, there is a problem in that the progress of the curing reaction slows down.

[0006] The present invention has been made in view of the above background, and aims to provide an adhesive composition having excellent storage stability and a fast curing rate, as well as an adhesive structure, a laminate, and a motor obtained using this adhesive composition.

[0007] A first aspect of the present invention resides in adhesive compositions according to the following items [1] to [8].

[0008] [1] An adhesive composition comprising: a radically polymerizable compound (A); a radical polymerization initiator (B); and a polymerization inhibitor (C), wherein the polymerization inhibitor (C) comprises an aromatic compound (C-1) having at least one of a nitroso group and a nitro group, and a phenolic hydroxyl group.

[0009] [2] The adhesive composition according to [1], wherein the aromatic compound (C-1) has at least one of a nitroso group bonded to an aromatic ring and a nitro group bonded to an aromatic ring. [3] The adhesive composition according to [2], wherein the nitroso group, the nitro group, and the phenolic hydroxyl group in the aromatic compound (C-1) are bonded to the same aromatic ring. [4] The adhesive composition according to [3], wherein the aromatic compound (C-1) is one or more compounds selected from the group consisting of 2,4-dinitrosoresorcinol, 1-nitroso-2-naphthol, 2-nitrophenol, and 2-nitroresorcinol.

[0010] [5] The adhesive composition according to any one of [1] to [4], wherein the content of the aromatic compound (C-1) is 0.0020% by mass or more and 0.080% by mass or less. [6] The adhesive composition according to any one of [1] to [5], wherein the content of the polymerization inhibitor (C) is 0.0020% by mass or more and 0.10% by mass or less. [7] The adhesive composition according to any one of [1] to [6], wherein the adhesive composition is configured to be cured under an anaerobic atmosphere. [8] The adhesive composition according to [7], wherein the adhesive composition further comprises one or more anaerobic curing catalysts (D) selected from the group consisting of saccharin, saccharin derivatives, amine compounds, azole compounds, mercaptan compounds, hydrazine compounds, and salts of hydrazine compounds.

[0011] A second aspect of the present invention is an adhesive structure according to the following items [9] to

[10] .

[0012] [9] An adhesive structure having a plurality of adherends and an adhesive layer interposed between adjacent adherends, wherein the adhesive layer is made of a cured product of the adhesive composition according to any one of [1] to [8].

[10] An adhesive structure having an adherend with a screw hole, a screw inserted into the screw hole, and an adhesive layer interposed between the adherend and the screw, wherein the adhesive layer is made of a cured product of the adhesive composition according to any one of [1] to [8].

[0013] A third aspect of the present invention is a laminate according to the following items

[11] to

[12] .

[0014]

[11] A laminate having a plurality of adherends stacked on top of one another and an adhesive layer interposed between adjacent adherends, wherein the adhesive layer is composed of a cured product of the adhesive composition according to any one of [1] to [8].

[12] The laminate according to

[11] , wherein the adherend is a steel plate.

[0015] A fourth aspect of the present invention is a motor according to the following item

[13] .

[0016]

[13] A motor including the laminate according to

[12] .

[0017] The polymerization inhibitor (C) in the adhesive composition contains at least the aromatic compound (C-1) having the specific functional group. By using the aromatic compound (C-1) as the polymerization inhibitor (C), the adhesive composition can improve storage stability while suppressing a decrease in curing time.

[0018] Therefore, according to the above-described embodiment, it is possible to provide an adhesive composition having excellent storage stability and a fast curing rate, and an adhesive structure, a laminate, and a motor obtained using this adhesive composition.

[0019] (Adhesive Composition) The adhesive composition is configured to be cured by radicals generated from a radical polymerization initiator. The trigger for initiating the curing reaction of the adhesive composition is not particularly limited. For example, the adhesive composition may be a thermosetting adhesive composition configured to initiate curing when triggered by heat. Alternatively, the adhesive composition may be a photocurable adhesive composition configured to initiate curing when triggered by light. Furthermore, the adhesive composition may be an anaerobic curing adhesive composition configured to initiate curing when oxygen is blocked.

[0020] The adhesive composition is preferably a so-called anaerobic curing adhesive composition that is configured to cure in an anaerobic atmosphere. Anaerobic curing adhesive compositions do not cure in an oxygen-containing atmosphere, but are configured to cure upon contact with metal ions in an anaerobic atmosphere. On the other hand, impurities containing metal ions may be mixed into the adhesive composition during its production process. Therefore, anaerobic curing adhesive compositions generally have the property of being prone to unintended curing during storage.

[0021] In contrast, the adhesive composition can effectively suppress the progression of unintended curing reactions by using a polymerization inhibitor (C) containing the specific aromatic compound (C-1). Therefore, by configuring the adhesive composition as an anaerobic curing adhesive composition, the above-mentioned effects can be more effectively utilized, and storage stability can be improved while suppressing a decrease in curing rate.

[0022] [Radical Polymerizable Compound (A)] As the radical polymerizable compound (A), a compound having a radical polymerizable functional group such as an acryloyl group, a methacryloyl group, a maleimide group, or a vinyl group can be used. The radical polymerizable compound (A) may be a monomer, an oligomer, or a polymer. More specifically, as the radical polymerizable compound (A), (meth)acrylic acid ester, maleimide, unsaturated carboxylic acid, unsaturated carboxylic acid anhydride, urethane (meth)acrylate, epoxy (meth)acrylate, ester (meth)acrylate, isoprene-based (meth)acrylate, hydrogenated isoprene-based (meth)acrylate, and (meth)acrylic group-containing acrylic polymer can be used. These radical polymerizable compounds (A) may be used alone, or two or more types of radical polymerizable compounds (A) may be used in combination.

[0023] The (meth)acrylic acid ester may be a monofunctional (meth)acrylate having one (meth)acryloyl group in one molecule, or a polyfunctional (meth)acrylate having two or more (meth)acryloyl groups in one molecule.

[0024] Examples of monofunctional (meth)acrylates include lauryl (meth)acrylate, stearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, caprolactone-modified tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, nonylphenoxyethyl (meth)acrylate, nonylphenoxytetraethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, butoxyethyl (meth)acrylate, butoxytriethylene glycol (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylhexyl Examples of the acrylate include polyethylene glycol (meth)acrylate, nonylphenyl polypropylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, glycerol (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, modified butyl (meth)acrylate, epichlorohydrin-modified phenoxy (meth)acrylate, ethylene oxide-modified succinic acid (meth)acrylate, caprolactone-modified 2-hydroxyethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, morpholino (meth)acrylate, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, and monohydroxyethyl acrylate phthalate.

[0025] From the viewpoint of adhesive strength to metal materials, the adhesive composition preferably contains, as the radical polymerizable compound (A), at least one monofunctional (meth)acrylate selected from the group consisting of 2-hydroxyethyl (meth)acrylate, isobornyl (meth)acrylate, morpholino (meth)acrylate, and tetrahydrofurfuryl (meth)acrylate.

[0026] As the polyfunctional (meth)acrylate, a di(meth)acrylate having two (meth)acryloyl groups per molecule, a tri(meth)acrylate having three (meth)acryloyl groups per molecule, and a (meth)acrylate having four or more (meth)acryloyl groups per molecule can be used.

[0027] Examples of di(meth)acrylates include 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexane glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, ethylene oxide-modified neopentyl glycol di(meth)acrylate, and propylene oxide-modified neopentyl glycol di(meth)acrylate. Examples of the di(meth)acrylate include cholesteryl di(meth)acrylate, hydroxypivalate neopentyl glycol diacrylate, caprolactone-modified hydroxypivalate neopentyl glycol diacrylate, neopentyl glycol-modified trimethylolpropane di(meth)acrylate, stearic acid-modified pentaerythritol di(meth)acrylate, dicyclopentenyl di(meth)acrylate, ethylene oxide-modified dicyclopentenyl di(meth)acrylate, di(meth)acryloyl isocyanurate, and dimethyloltricyclodecane di(meth)acrylate.

[0028] Examples of trimethacrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, epichlorohydrin-modified trimethylolpropane tri(meth)acrylate, epichlorohydrin-modified glycerol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0029] Examples of (meth)acrylates having four or more (meth)acryloyl groups per molecule include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, alkyl-modified dipentaerythritol pentaacrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified dipentaerythritol hexa(meth)acrylate.

[0030] From the viewpoint of adhesive strength at high temperatures, the adhesive composition may contain, as the radical polymerizable compound (A), a polyfunctional (meth)acrylate having 3 to 10 (meth)acryloyl groups per molecule. From the same viewpoint, the adhesive composition may contain, as the radical polymerizable compound (A), a polyfunctional (meth)acrylate having 3 to 9 (meth)acryloyl groups per molecule.

[0031] Furthermore, from the viewpoints of heat resistance and adhesive strength, the adhesive composition preferably contains, as the radically polymerizable compound (A), at least one polyfunctional (meth)acrylate selected from the group consisting of dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate.

[0032] Examples of maleimides include N-phenylmaleimide, N-(4-hydroxyphenyl)maleimide, N-(4-acetylphenyl)maleimide, N-(4-methoxyphenyl)maleimide, N-(4-ethoxyphenyl)maleimide, N-(4-chlorophenyl)maleimide, N-(4-bromophenyl)maleimide, and N-benzylmaleimide.

[0033] Examples of unsaturated carboxylic acids include unsaturated monocarboxylic acids such as (meth)acrylic acid and cinnamic acid, unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, crotonic acid and citraconic acid, and monoalkyl esters of unsaturated dicarboxylic acids. Examples of unsaturated carboxylic acid anhydrides include acid anhydrides of these unsaturated carboxylic acids.

[0034] From the viewpoint of heat resistance and adhesion to metal materials, the adhesive composition preferably contains (meth)acrylic acid as the radical polymerizable compound (A).

[0035] Examples of urethane (meth)acrylates include products produced by polyaddition of polyhydric alcohols, polyisocyanates, and hydroxy(meth)acrylates, and products produced by polyaddition of polyisocyanates and hydroxy(meth)acrylate compounds.

[0036] Examples of polyhydric alcohols used in the polyaddition of urethane (meth)acrylate include polyether polyols such as polypropylene glycol and polytetramethylene glycol, polyester polyols obtained by reacting a polyhydric alcohol with a polybasic acid, caprolactone polyols obtained by reacting a polyhydric alcohol with a polybasic acid and ε-caprolactone, and polycarbonate polyols (for example, polycarbonate polyols obtained by reacting 1,6-hexanediol with diphenyl carbonate).

[0037] Examples of organic polyisocyanates used in the polyaddition of urethane (meth)acrylate include alicyclic polyisocyanates such as isophorone diisocyanate and dicyclopentanyl diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; and aromatic polyisocyanates such as tolylene diisocyanate, xylylene diisocyanate, and diphenylmethane-4,4'-diisocyanate.

[0038] From the viewpoint of adhesiveness, the urethane (meth)acrylate preferably has structural units derived from one or more polyhydric alcohols selected from the group consisting of polyether polyols, polyester polyols, and polycarbonate polyols. From the same viewpoint, the urethane (meth)acrylate preferably has structural units derived from one or more polyhydric isocyanates selected from the group consisting of isophorone diisocyanate, hexamethylene diisocyanate, and xylene diisocyanate.

[0039] Furthermore, examples of the urethane (meth)acrylate that can be used include urethane (meth)acrylates having a polybutadiene skeleton, urethane (meth)acrylates having a hydrogenated polybutadiene skeleton, urethane (meth)acrylates having a polycarbonate skeleton, urethane (meth)acrylates having a hydrogenated bisphenol A skeleton, urethane (meth)acrylates having a polyether skeleton, urethane (meth)acrylates having a polyester skeleton, and urethane (meth)acrylates having a castor oil skeleton.

[0040] As the epoxy (meth)acrylate, for example, a reaction product of an epoxy resin such as an aromatic epoxy resin, an alicyclic epoxy resin, or an aliphatic epoxy resin with (meth)acrylic acid can be used.

[0041] From the viewpoint of adhesive strength, the adhesive composition preferably contains, as the radical polymerizable compound (A), at least one polymer selected from the group consisting of urethane (meth)acrylate, epoxy (meth)acrylate, ester (meth)acrylate, isoprene-based (meth)acrylate, hydrogenated isoprene-based (meth)acrylate, and (meth)acrylic group-containing acrylic polymer, more preferably at least one polymer of urethane (meth)acrylate and epoxy (meth)acrylate, even more preferably urethane (meth)acrylate, and particularly preferably urethane methacrylate.

[0042] [Radical Polymerization Initiator (B)] As the radical polymerization initiator (B), a thermal radical polymerization initiator, a photoradical polymerization initiator, or the like can be used. As the thermal radical polymerization initiator, an organic peroxide, an azo compound, or the like can be used. The adhesive composition may contain one type of radical polymerization initiator (B), or may contain two or more types of radical polymerization initiators (B).

[0043] Examples of organic peroxides include hydroperoxides such as cumene hydroperoxide, t-butyl hydroperoxide, p-methane hydroperoxide, methyl ethyl ketone peroxide, cyclohexane peroxide, dicumyl peroxide, and diisopropylbenzene hydroperoxide; ketone peroxides; diallyl peroxides; and peroxy esters.

[0044] Examples of the azo compound include azobisisobutyronitrile, azobisisovaleronitrile, and azobisisocapronitrile.

[0045] From the viewpoint of the curing rate, the adhesive composition preferably contains a hydroperoxide as the radical polymerization initiator (B).

[0046] Furthermore, when the adhesive composition is configured as an anaerobic curing adhesive composition, the radical polymerization initiator (B) preferably contains an organic peroxide having a one-hour half-life temperature of 80° C. or higher and 300° C. or lower, and more preferably contains an organic peroxide having a one-hour half-life temperature of 100° C. or higher and 200° C. or lower. Examples of such organic peroxides include hydroperoxides such as p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, and t-butyl hydroperoxide.

[0047] The anaerobic curability of the adhesive composition can be further improved by using an organic peroxide having a one-hour half-life temperature within the above-mentioned specific range as the radical polymerization initiator (B). The one-hour half-life temperature of the organic peroxide can be obtained by dissolving the organic peroxide in benzene, using a sample solution having an initial concentration of 0.1 mol / L, and thermally decomposing the organic peroxide in the sample solution.

[0048] When the adhesive composition is configured as an anaerobic curing adhesive composition, the adhesive composition preferably contains a thermal radical polymerization initiator as the radical polymerization initiator (B), and more preferably contains an organic peroxide, which can further enhance the anaerobic curability of the adhesive composition.

[0049] Examples of the photoradical generator that can be used include an acetophenone-based photoradical polymerization initiator, a benzoin-based photoradical polymerization initiator, a benzophenone-based photoradical polymerization initiator, a thioxanthone-based photoradical polymerization initiator, an acylphosphine oxide-based photoradical polymerization initiator, and a titanocene-based photoradical polymerization initiator.

[0050] Examples of acetophenone-based photoradical polymerization initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, benzyl dimethyl ketal, 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, and 2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone oligomer.

[0051] In addition, as the acetophenone-based photoradical polymerization initiator, commercially available products such as Omnirad (registered trademark) 184, Omnirad 1173, Omnirad 2959, and Omnirad 127 (all manufactured by IGM Resins B.V.) and ESACUREKIP-150 (manufactured by Lamberti s.p.a.) can also be used.

[0052] Examples of the acylphosphine oxide-based photoradical polymerization initiator include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0053] Furthermore, as the acylphosphine oxide-based photoradical polymerization initiator, commercially available products such as Omnirad TPO, Omnirad 819, and Omnirad 819DW (all manufactured by IGM Resins B.V.) can also be used.

[0054] The content of the radical polymerization initiator (B) can be appropriately set, for example, within a range of 10 mass% or less, relative to the total mass of the adhesive composition. From the viewpoints of anaerobic curability and adhesive strength, the content of the radical polymerization initiator (B) is preferably 0.01 mass% or more and 8.0 mass% or less, more preferably 0.05 mass% or more and 4.0 mass% or less, and even more preferably 0.1 mass% or more and 2.0 mass% or less, relative to the total mass of the adhesive composition.

[0055] [Polymerization inhibitor (C)] The adhesive composition contains one or more polymerization inhibitors (C) including an aromatic compound (C-1) having at least one of a nitroso group and a nitro group, and a phenolic hydroxyl group. By using the specific aromatic compound (C-1) as the polymerization inhibitor (C), the adhesive composition can improve storage stability while suppressing a decrease in curing rate.

[0056] The reason why the aromatic compound (C-1) provides such an effect is not entirely clear at present, but the following reasons are thought to be possible. The nitro group, nitroso group, and phenolic hydroxyl group possessed by the aromatic compound (C-1) are thought to have the ability to capture radicals generated from the radical polymerization initiator (B) and radicals of the radically polymerizable compound (A) and its polymer generated during the radical polymerization process. Therefore, by incorporating the aromatic compound (C-1) into the adhesive composition, it is thought that the progression of unintended radical polymerization reactions that occur during storage, etc. can be prevented. Furthermore, the aromatic compound (C-1) is thought to have the ability to chelate metal ions. Therefore, when the adhesive composition has anaerobic curing properties, it is thought that the generation of radicals that serve as initiation points for radical polymerization can be suppressed. These properties of the aromatic compound (C-1) are thought to contribute to the aforementioned effect of suppressing a decrease in curing rate while improving storage stability.

[0057] In the aromatic compound (C-1), the number of carbon atoms between the nitroso group and the phenol group and the number of carbon atoms between the nitro group and the phenol group are preferably from 2 to 5, more preferably from 2 to 4, and even more preferably from 2 to 3. By using such an aromatic compound (C-1) as the polymerization inhibitor (C), the above-mentioned effects can be more easily obtained.

[0058] From the same viewpoint, the aromatic compound (C-1) preferably has at least one of a nitroso group bonded to an aromatic ring and a nitro group bonded to an aromatic ring, i.e., the nitroso group and the nitro group in the aromatic compound (C-1) are preferably bonded to the aromatic ring.

[0059] In addition, the nitroso group, nitro group, and phenolic hydroxyl group in the aromatic compound (C-1) are preferably bonded to the same aromatic ring. Furthermore, the aromatic compound (C-1) is more preferably one or more compounds selected from the group consisting of 2,4-dinitrosoresorcinol, 1-nitroso-2-naphthol, 2-nitrophenol, and 2-nitroresorcinol, and even more preferably 2,4-dinitrosoresorcinol.

[0060] The content of the aromatic compound (C-1) is preferably 0.0020% by mass or more and 0.080% by mass or less, based on the total mass of the adhesive composition. By making the content of the aromatic compound (C-1) preferably 0.0020% by mass or more, more preferably 0.0030% by mass or more, even more preferably 0.0040% by mass or more, and particularly preferably 0.0045% by mass or more, it is possible to more reliably suppress the progress of unintended curing reactions and further improve the storage stability of the adhesive composition.

[0061] On the other hand, if the content of aromatic compound (C-1) is too high, the progress of the curing reaction may be excessively hindered, which may lead to a decrease in the curing rate. By setting the content of aromatic compound (C-1) to preferably 0.080 mass% or less, more preferably 0.050 mass% or less, even more preferably 0.030 mass% or less, and particularly preferably 0.010 mass% or less, it is possible to more easily avoid such problems and more reliably avoid a decrease in the curing rate of the adhesive composition.

[0062] When determining a preferred range for the content of the aromatic compound (C-1) in the adhesive composition, the above-described upper and lower limits for the content of the aromatic compound (C-1) can be combined in any manner. For example, the preferred range for the content of the aromatic compound (C-1) may be 0.0030% by mass or more and 0.050% by mass or less, 0.0040% by mass or more and 0.030% by mass or less, or 0.0045% by mass or more and 0.010% by mass or less.

[0063] The adhesive composition may further contain a polymerization inhibitor (C-2) other than the aromatic compound (C-1). In this case, an adhesive composition having excellent storage stability and a fast curing rate can be more easily obtained. Examples of the polymerization inhibitor (C-2) other than the aromatic compound (C-1) that can be used include a chelating agent and a radical scavenger. From the viewpoint of further enhancing the above-described effects, it is preferable that the adhesive composition contains a chelating agent as the polymerization inhibitor (C-2). Examples of chelating agents include oxalic acid, ethylenediaminetetraacetic acid disodium salt, acetylacetone, and o-aminophenol. Among these, it is preferable to use oxalic acid as the chelating agent.

[0064] Examples of radical scavengers include quinones such as p-benzoquinone, t-butylhydroquinone, hydroquinone, and hydroquinone monomethyl ether; phenols such as 4-t-butylpyrocatechol, p-methoxyphenol, and 2,6-di-t-butyl-4-methylphenol; amines such as phenothiazine; nitroso compounds such as N-nitroso-N-phenylhydroxylamine aluminum salt; and N-oxime compounds such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL). These compounds may be used alone, or two or more types of compounds may be used in combination.

[0065] The content of the polymerization inhibitor (C-2) other than the aromatic compound (C-1) is preferably 0.0050% by mass or more and 0.050% by mass or less, based on the total mass of the adhesive composition. By making the content of the polymerization inhibitor (C-2) preferably 0.0050% by mass or more, more preferably 0.0060% by mass or more, even more preferably 0.0070% by mass or more, and particularly preferably 0.0080% by mass or more, it is possible to more reliably suppress the progress of unintended curing reactions and further improve the storage stability of the adhesive composition.

[0066] On the other hand, if the content of the polymerization inhibitor (C-2) is excessively high, the progress of the curing reaction may be excessively hindered, which may lead to a decrease in the curing rate. By setting the content of the polymerization inhibitor (C-2) to preferably 0.040% by mass or less, more preferably 0.030% by mass or less, and even more preferably 0.020% by mass or less, it is possible to more easily avoid such problems and more reliably suppress a decrease in the curing rate of the adhesive composition.

[0067] When determining a preferred range for the content of the polymerization inhibitor (C-2) other than the aromatic compound (C-1) in the adhesive composition, the above-described upper and lower limits for the content of the polymerization inhibitor (C-2) can be combined in any manner. For example, a preferred range for the content of the polymerization inhibitor (C-2) may be 0.0060% by mass or more and 0.040% by mass or less, 0.0070% by mass or more and 0.030% by mass or less, or 0.0080% by mass or more and 0.020% by mass or less.

[0068] The content of the polymerization inhibitor (C), i.e., the sum of the content of the aromatic compound (C-1) and the content of the polymerization inhibitor (C-2) other than the aromatic compound (C-1), is preferably 0.0020% by mass or more and 0.10% by mass or less, based on the total mass of the adhesive composition. By setting the content of the polymerization inhibitor (C) to preferably 0.0020% by mass or more, more preferably 0.0030% by mass or more, even more preferably 0.0040% by mass or more, and particularly preferably 0.0045% by mass or more, it is possible to more reliably suppress the progress of unintended curing reactions and further improve the storage stability of the adhesive composition.

[0069] On the other hand, if the content of the polymerization inhibitor (C) is excessively high, the progress of the curing reaction may be excessively hindered, which may lead to a decrease in the curing rate. By setting the content of the polymerization inhibitor (C) to preferably 0.090 mass% or less, more preferably 0.070 mass% or less, even more preferably 0.050 mass% or less, and particularly preferably 0.030 mass% or less, it is possible to more easily avoid such problems and more reliably suppress a decrease in the curing rate of the adhesive composition.

[0070] When determining a preferred range for the content of the polymerization inhibitor (C) in the adhesive composition, the above-described upper and lower limits for the content of the polymerization inhibitor (C) can be combined in any manner. For example, the preferred range for the content of the polymerization inhibitor (C) may be 0.0030% by mass or more and 0.090% by mass or less, 0.0040% by mass or more and 0.070% by mass or less, or 0.0045% by mass or more and 0.030% by mass or less.

[0071] [Anaerobic Curing Catalyst (D)] The adhesive composition preferably further contains one or more anaerobic curing catalysts (D) selected from the group consisting of saccharin, saccharin derivatives, amine compounds, azole compounds, mercaptan compounds, hydrazine compounds, and salts of hydrazine compounds. By blending the anaerobic curing catalyst (D) with the adhesive composition, the adhesive composition is imparted with anaerobic curing properties, thereby obtaining an anaerobic curing adhesive composition. From the viewpoint of further enhancing anaerobic curing properties, it is more preferable that the adhesive composition contains, as the anaerobic curing catalyst (D), at least one compound selected from saccharin and saccharin derivatives, and at least one compound selected from hydrazine compounds and salts thereof.

[0072] Examples of saccharin derivatives include N-methylsaccharin.

[0073] Examples of the amine compound include heterocyclic secondary amines such as 1,2,3,4-tetrahydroquinoline and 1,2,3,4-tetrahydroquinaldine; heterocyclic tertiary amines such as quinoline, methylquinoline, quinaldine and quinoxalinephenazine; and aromatic tertiary amines such as N,N-dimethyl-anisidine, N,N-dimethylaniline and N,N'-dimethyl-p-toluidine.

[0074] Examples of the azole compound include 1,2,4-triazole, oxazole, oxadiazole, thiadiazole, benzotriazole, hydroxybenzotriazole, benzoxazole, 1,2,3-benzothiadiazole, and 3-mercaptobenzotriazole.

[0075] Examples of the mercaptan compound include linear mercaptans such as n-dodecyl mercaptan, ethyl mercaptan, and butyl mercaptan.

[0076] Examples of the hydrazine compound include 1-acetyl-2-phenylhydrazine, 1-acetyl-2(p-tolyl)hydrazine, 1-benzoyl-2-phenylhydrazine, 1-(1',1',1'-trifluoro)acetyl-2-phenylhydrazine, 1,5-diphenyl-carbohydrazine, 1-formyl-2-phenylhydrazine, 1-acetyl-2-(p-bromophenyl)hydrazine, 1-acetyl-2-(p-nitrophenyl)hydrazine, 1-acetyl-2-(2'-phenylethylhydrazine), p-nitrophenylhydrazine, and p-trisulfonylhydrazide.

[0077] Examples of the salts of hydrazine compounds include 4-methylsulfonylphenylhydrazine hydrochloride, hydrazine monohydrochloride, p-tolylhydrazine hydrochloride, and the like.

[0078] From the viewpoints of anaerobic curability and curing rate, the content of the anaerobic curing catalyst (D) is preferably from 0.05% by mass to 30% by mass, more preferably from 0.1% by mass to 20% by mass, and even more preferably from 0.2% by mass to 10% by mass, relative to the total mass of the adhesive composition.

[0079] [Acid and Acid Anhydride] The adhesive composition may contain an acid and / or acid anhydride that does not have a radically polymerizable functional group. Known acids or acid anhydrides can be used as the acid or acid anhydride. Among known acids and acid anhydrides, the adhesive composition preferably contains an organic acid and / or organic acid anhydride, and more preferably a carboxylic acid and / or a carboxylic acid anhydride. Suitable examples of the acid or acid anhydride include pyromellitic acid and trimellitic anhydride.

[0080] The adhesive composition may contain one or more acids, one or more acid anhydrides, or one or more acids and one or more acid anhydrides.

[0081] From the viewpoint of anaerobic curability and adhesive properties, the total content of the acid and the acid anhydride in the adhesive composition is preferably 0.01 mass % or more and 10 mass % or less, and more preferably 0.05 mass % or more and 5 mass % or less, relative to the total mass of the adhesive composition.

[0082] [Additives] The adhesive composition may contain additives such as fillers, various elastomers, antioxidants, light stabilizers, heavy metal deactivators, silane coupling agents, tackifiers, plasticizers, antifoaming agents, pigments, rust inhibitors, leveling agents, dispersants, rheology modifiers, and flame retardants, provided the additives do not impair the effects described above.

[0083] Adding a filler to the adhesive composition can improve the elastic modulus, flowability, etc. of the cured product. Examples of fillers that can be used include organic powders and inorganic powders. Examples of inorganic powders include glass, fumed silica, alumina, mica, ceramics, silicone rubber powder, calcium carbonate, aluminum nitride, boron nitride, carbon powder, kaolin clay, dried clay minerals, and dried diatomaceous earth.

[0084] Among these inorganic powders, fumed silica is blended for the purpose of adjusting the viscosity of the adhesive composition or improving the mechanical strength of the cured product. The fumed silica is preferably surface-treated with dimethylsilane, trimethylsilane, alkylsilane, methacryloxysilane, organochlorosilane, polydimethylsiloxane, hexamethyldisilazane, or the like.

[0085] In addition, as the fumed silica, for example, commercially available products such as Aerosil (registered trademark) R972, R972V, R972CF, R974, R976, R976S, R9200, RX50, NAX50, NX90, RX200, RX300, R812, R812S, R8200, RY50, NY50, RY200S, RY200, RY300, R104, R106, R202, R805, R816, T805, R711, RM50, and R7200 (all manufactured by Nippon Aerosil Co., Ltd.) can also be used.

[0086] The content of the inorganic powder is preferably 0.1 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the radical polymerizable compound (A).

[0087] Examples of the organic powder include polyethylene, polypropylene, polyamide, cross-linked acrylic, cross-linked polystyrene, polyester, polyvinyl alcohol, polyvinyl butyral, polycarbonate, etc. The content of the organic powder is preferably 0.1 parts by mass or more and 100 parts by mass per 100 parts by mass of the radical polymerizable compound (A).

[0088] Examples of antioxidants include phosphorus-based compounds such as tris(2,4-di-tert-butylphenyl)phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, tetrakis(2,4-di-tert-butylphenyl)[1,1-bisphenyl]-4,4′-diylbisphosphonite, and 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenz[d,f][1,3,2]dioxaphosphine; and sulfur-based compounds such as dilauryl 3,3′-thiodipropionate, distearyl 3,3′-thiodipropionate, pentaerythrityl tetrakis(3-laurylthiopropionate), and 2-mercaptobenzimidazole. The content of the antioxidant is preferably 0.1 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the radical polymerizable compound (A).

[0089] Examples of silane coupling agents include γ-chloropropyltrimethoxysilane, octenyltrimethoxysilane, glycidyloxyoctyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, p-styryltrimethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, mercaptopropylmethoxysilane, etc. From the viewpoint of adhesion to metal materials, the content of the silane coupling agent is preferably 0.05 parts by mass or more and 30 parts by mass or less, and more preferably 0.2 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the radical polymerizable compound (A).

[0090] The method for producing the adhesive composition can take various forms. For example, when producing the adhesive composition, first, a radical polymerizable compound (A), a radical polymerization initiator (B), a polymerization inhibitor (C) containing an aromatic compound (C-1), and other components used as needed are appropriately blended. The adhesive composition can then be obtained by mixing the above-mentioned components using a mixing means such as a mixer. The mixing temperature can be appropriately set, for example, within a range of 10°C or higher and 100°C or lower. The mixing time can be appropriately set, for example, within a range of 0.1 hours or higher and 5 hours or lower.

[0091] The viscosity of the adhesive composition at 25°C is preferably 100,000 mPa·s or less, more preferably 5 mPa·s or more and 50,000 mPa·s or less, even more preferably 10 mPa·s or more and 10,000 mPa·s or less, and particularly preferably 15 mPa·s or more and 5,000 mPa·s or less, from the viewpoints of ease of spreading on the adherend and preventing the adhesive composition from excessively squeezing out from the bonding surface during lamination. The viscosity of the adhesive composition is measured using an E-type viscometer.

[0092] (Bonded Structure) A bonded structure can be obtained by bonding a plurality of adherends using the adhesive composition. The bonded structure has, for example, a plurality of adherends and an adhesive layer interposed between adjacent adherends, the adhesive layer being composed of a cured product of the adhesive composition.

[0093] The material of the adherend in the bonded structure is not particularly limited. For example, the adherend may be metal or resin. The method for bonding the adherends with the adhesive composition may be selected from known methods appropriate for the curing method of the adhesive composition. For example, when the adhesive composition is configured to be cured by heat, the adhesive composition is applied to the adhesive surface of one of the multiple adherends, and then the other adherend is placed on the adhesive composition. Thereafter, the adherends are heated to cure the adhesive composition, thereby forming an adhesive layer between the multiple adherends.

[0094] Furthermore, for example, when the adhesive composition is configured to be cured by light, the adhesive composition is applied to the adhesive surface of one of a plurality of adherends, and then the adhesive composition is irradiated with light to initiate curing of the adhesive composition. The other adherend is then placed on the adhesive composition, thereby bonding the plurality of adherends via an adhesive layer. Furthermore, when at least one of the plurality of adherends is made of a light-transmitting material, the adhesive composition is applied to the adhesive surface of one of the adherends, and then the adherend is placed on the adhesive composition. The adherend is then irradiated with light, and the adhesive composition can be cured by the light that has passed through the adherend.

[0095] Furthermore, for example, when the adhesive composition has anaerobic curing properties, the adhesive composition is first applied to one of a plurality of adherends. Then, the other adherend is placed on top of the adhesive composition, preventing the adhesive composition present between the adherends from coming into contact with an oxygen-containing atmosphere. At this time, if a metal is exposed on the surface of one of the adherends, contact with the adherend can generate radicals in the adhesive composition. Even if no metal is exposed on the surface of either of the adherends, radicals can be generated in the adhesive composition by contact with the metal ions in the primer composition by applying a primer composition containing metal ions to the surface of the adherend in advance. As a result, the adhesive composition can be cured. Furthermore, when the adhesive composition has anaerobic curing properties and is configured to be cured by light, and at least one of the adherends is made of a light-transmitting material, the adhesive composition can be cured by irradiating the adherend with light, even with the light transmitted through the adherend. Furthermore, in this case, the adhesive composition can also be cured by irradiating light on the adhesive composition that has spilled over the side of the adherend.

[0096] The primer composition may be a known composition for use in an anaerobic curing adhesive composition. For example, the primer composition may contain an organometallic complex and a solvent. The primer composition may further contain an oil.

[0097] Examples of central metals in organometallic complexes include iron, cobalt, nickel, vanadium, copper, manganese, titanium, cerium, zirconium, zinc, tin, and bismuth. Examples of ligands in organometallic complexes include 2-ethylhexanoic acid, butyl phosphate, and acetylacetone. More specifically, examples of organometallic complexes that can be used include copper ethylhexanoate, iron pentadione, cobalt pentadione, copper pentadione, propylenediamine copper, ethylenediamine copper, iron naphthate, nickel naphthate, cobalt naphthate, copper naphthate, copper octate, iron hexoate, iron propionate, vanadium acetylacetonate, and a reaction product of vanadium pentoxide and dibutyl phosphate.

[0098] As the solvent, for example, organic solvents such as ethanol, toluene, acetone, and hepton, and oils such as mineral spirits and press processing oil can be used.

[0099] The primer composition may further contain an adhesion promoter containing a functional group or element capable of chemically or physically interacting with the metal contained in the adherend, such as a silane coupling agent, an aluminum chelate, a phosphate ester compound, a compound containing a nitrogen atom, or a thiol-containing compound.

[0100] The specific structure of the bonded structure is not particularly limited and can take various forms. For example, the bonded structure may include an adherend with a screw hole, a screw inserted into the screw hole, and an adhesive layer interposed between the adherend and the screw. By adhering the screw inserted into the screw hole to the adherend in this way, loosening of the screw can be suppressed for a long period of time. In such a bonded structure, an anaerobic atmosphere is likely to be formed between the screw and the adherend. Therefore, an adhesive composition having anaerobic curing properties can be suitably used to bond the screw and the adherend.

[0101] (Laminate) A laminate can also be obtained by laminating multiple adherends using the adhesive composition. The laminate has, for example, multiple adherends stacked on top of each other and an adhesive layer interposed between adjacent adherends, the adhesive layer being composed of a cured product of the adhesive composition.

[0102] As with the bonding method for the bonded structure described above, the method for bonding the adherends together may be an appropriate method such as heating, light irradiation, or blocking of an oxygen-containing atmosphere, depending on the composition of the adhesive composition. Furthermore, when bonding the adherends together, a primer composition or the like may also be used as needed.

[0103] The adhesive composition used to prepare the laminate preferably has anaerobic curing properties. When adherends are stacked in the production of the laminate, the gap between the adherends naturally becomes an anaerobic atmosphere. Therefore, by providing an anaerobic curing adhesive composition between the adherends, the adherends can be bonded together by the simple operation of stacking the adherends. Furthermore, in this case, the adherends can be bonded together at a temperature relatively close to room temperature, so stress concentration and strain concentration are less likely to occur in the laminate after bonding. Therefore, by producing a laminate using an anaerobic curing adhesive composition, the reliability of the adhesive layer can be further improved.

[0104] The material of the adherend used in the laminate is not particularly limited, and various materials such as metal and resin can be used. Among these, the adhesive composition is suitably used for bonding adherends made of metal. The adherend is more preferably a steel sheet. As the steel sheet, a cold-rolled steel sheet, an electromagnetic steel sheet, or the like can be used. The electromagnetic steel sheet may be a directional electromagnetic steel sheet or a non-directional electromagnetic steel sheet.

[0105] Although the use of the laminate is not particularly limited, it is preferable that the laminate be used as a motor component such as a motor core, rotor, or stator. In this case, it is preferable to use an electromagnetic steel sheet, and more preferably a non-oriented electromagnetic steel sheet, as the adherend. Since the laminate is insulated between the adherends by the adhesive layer, current loss can be reduced and motor performance can be further improved. Therefore, motors including the laminate have high performance.

[0106] In particular, laminates bonded with an anaerobic curing adhesive composition have excellent reliability because they are less susceptible to stress concentration and strain concentration, as described above. Therefore, by using a laminate produced using an anaerobic curing adhesive composition in a motor core or the like, it is possible to improve the performance and reliability of the motor.

[0107] The method for producing a laminate using an anaerobic curing adhesive composition and a primer composition can take various forms as shown below. Note that the production method shown below is one example, and the method for producing a laminate is not limited to the method shown below. Furthermore, in the production method shown below, unless otherwise specified, the order and conditions of the steps can be changed as appropriate depending on the structure of the laminate, etc. Furthermore, further steps may be added as necessary.

[0108] In a first embodiment of the method for producing a laminate, an adherend having a surface coated with a primer composition and an adherend having a surface coated with an adhesive composition are superimposed and bonded together so that the primer composition and the adhesive composition come into contact with each other, thereby producing a laminate. The lamination and bonding of the adherends may be performed sequentially or all at once. Furthermore, the method for applying the primer composition to the adherend and the method for applying the adhesive composition to the adherend may be the same or different from each other.

[0109] For example, a first aspect of the manufacturing method may include a first adherend preparation step of preparing a first adherend having a primer composition applied to at least one surface thereof; a second adherend preparation step of preparing a second adherend having the adhesive composition applied to at least one surface thereof; and a lamination and bonding step of overlapping and bonding the surface of the first adherend having the primer composition applied to the surface of the second adherend having the adhesive composition applied to the surface of the second adherend.

[0110] In this case, the laminate having the desired number of layers can be obtained by repeating the first adherend preparation step, the second adherend preparation step, and the lamination and bonding step a desired number of times. The first adherend may be a veneer, or may be a laminate obtained by performing the first adherend preparation step, the second adherend preparation step, and the lamination and bonding step. Similarly, the second adherend may be a veneer or a laminate.

[0111] The number of times the first adherend preparation step, the second adherend preparation step, and the lamination and adhesion step are repeated may be appropriately set depending on the desired number of layers in the laminate. For example, a laminate having a two-layer structure can be obtained by performing each of the first adherend preparation step, the second adherend preparation step, and the lamination and adhesion step once. Furthermore, a laminate having a multi-layer structure of three or more layers can be obtained by repeating the first adherend preparation step, the second adherend preparation step, and the lamination and adhesion step multiple times.

[0112] Furthermore, a first aspect of the manufacturing method may include an adherend preparation step of preparing a plurality of adherends each having a first surface coated with a primer composition and a second surface coated with the adhesive composition; and a stacking and bonding step of bonding the plurality of adherends together by stacking the plurality of adherends so that the first surface and the second surface are in contact with each other.

[0113] Furthermore, the first aspect of the manufacturing method may include a first adherend preparation step of preparing a first adherend having a primer composition applied to both sides thereof, a second adherend preparation step of preparing a second adherend having the adhesive composition applied to both sides thereof, and a lamination bonding step of alternately stacking the first adherend and the second adherend to bond a plurality of the adherends together.

[0114] In a second embodiment of the laminate manufacturing method, adherends are stacked to form a laminate, and then at least one of a primer composition and an adhesive composition is supplied into the gaps between the adherends, thereby bonding the multiple adherends together. In the second embodiment, when the adherends are stacked, gaps are formed between the adherends that allow the primer composition or adhesive composition to penetrate. Therefore, by supplying the primer composition or adhesive composition into the gaps between the adherends from the side of the laminate, these compositions can penetrate into the gaps between the adherends. Then, the primer composition and the adhesive composition come into contact with each other between the adherends, thereby curing the adhesive composition.

[0115] In the second aspect, the method for supplying the primer composition or adhesive composition into the gap between the adherends is not particularly limited and may take various forms. For example, the primer composition or adhesive composition may be sprayed onto the side of the laminate of adherends using a sprayer, allowing the composition to penetrate into the gap between the adherends. Alternatively, the laminate of adherends may be immersed in the primer composition or adhesive composition to allow the composition to penetrate into the gap between the adherends. Furthermore, the primer composition or adhesive composition may be injected by inserting an injection nozzle into the gap between the adherends. When supplying the primer composition or adhesive composition into the gap between the adherends, it is desirable to externally restrain the laminate in order to prevent the adherends from shifting position.

[0116] For example, a second aspect of the manufacturing method may include a lamination step of overlapping a plurality of adherends to form a laminate; a primer composition supplying step of supplying a primer composition into gaps between the adherends in the laminate; and an adhesive composition supplying step of supplying an adhesive composition into gaps between the adherends in the laminate.

[0117] In this case, the primer composition supplying step may be performed before or after the adhesive composition supplying step. In either case, the adherends can be bonded as long as the primer composition and the adhesive composition come into contact with each other in the gap between the adherends.

[0118] Furthermore, a second aspect of the manufacturing method may include an adherend preparation step of preparing a plurality of adherends each having either a primer composition or an adhesive composition applied to both sides thereof; a step of stacking the plurality of adherends to form a laminate; and an adhesion step of supplying, into the gaps between the adherends in the laminate, the primer composition and the adhesive composition that are not present in the gaps between the adherends, thereby adhering the adherends.

[0119] When manufacturing a laminate using electromagnetic steel sheets as adherends, a commonly used method is to continuously or intermittently feed a hoop material while punching and laminating the resulting adherends in sequence. Even in this case, it is possible to employ any of the above-mentioned methods to continuously laminate and bond electromagnetic steel sheets from the hoop material.

[0120] More specifically, when a laminate is produced using a hoop material according to the first embodiment, a coating process is performed in which a primer composition is applied to the first surface of the hoop material and an adhesive composition is applied to the second surface of the hoop material. This is followed by a punching process in which the hoop material is punched into the desired shape to produce an adherend. The adherends thus obtained are then laminated so that the first and second surfaces are in contact with each other in a lamination and bonding process. If necessary, a processing oil application process may be performed before the punching process in which press processing oil is applied to at least one surface of the hoop material. Note that press processing oil is an oil used to prevent galling and seizure. While the components of the press processing oil are not particularly limited, press processing oils often contain mineral oil or synthetic oil as their main components.

[0121] When the diluent contained in the primer composition is a press oil, the primer composition can also be used as the press oil, which allows the application of the press oil and the primer composition to be carried out in a single step, making it possible to efficiently produce a laminate.

[0122] When the primer composition is used as a press processing oil, the mass ratio of the press processing oil in the diluent is preferably 70 mass % or more, more preferably 90 mass % or more, and may be 100 mass %.

[0123] Examples of the adhesive composition are described below. In these examples, the adhesive composition was prepared using the following raw materials.

[0124] (Radical polymerizable compound (A)) Radical polymerizable compound a1: alicyclic bifunctional urethane methacrylate containing a structural unit derived from isophorone diisocyanate (maximum value of tan δ: −10° C. (measurement frequency in DMA measurement: 1 Hz, heating rate: 2° C. / min)) Radical polymerizable compound a2: 2-hydroxyethyl methacrylate Radical polymerizable compound a3: isobornyl methacrylate

[0125] (Radical polymerization initiator (B)) Radical polymerization initiator b1: cumene hydroperoxide ("Percumyl (registered trademark) H" manufactured by NOF Corporation)

[0126] (Polymerization inhibitor (C)) Aromatic compound (C-1) Polymerization inhibitor c11: 2,4-dinitrosoresorcinol Polymerization inhibitor c12: 1-nitroso-2-naphthol Polymerization inhibitor c13: 2-nitrophenol Polymerization inhibitor c14: 2-nitroresorcinol

[0127] Polymerization inhibitors (C-2) other than aromatic compounds (C-1) Polymerization inhibitor c21: oxalic acid Polymerization inhibitor c22: N-nitroso-N-phenylhydroxylamine aluminum salt Polymerization inhibitor c23: ethylenediaminetetraacetic acid disodium salt Polymerization inhibitor c24: hydroquinone monomethyl ether Polymerization inhibitor c25: phenothiazine Polymerization inhibitor c26: 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl

[0128] (Anaerobic curing catalyst (D)) Anaerobic curing catalyst d1: saccharin

[0129] (Other components) Acid e1: acrylic acid Hydrolysis inhibitor f1: acetylacetone

[0130] (Examples 1 to 16, Comparative Examples 1 to 9) The above-described substances were blended in the mass ratios shown in Tables 1 to 3, and then mixed by stirring for 60 minutes in an environment at approximately 25°C. In this manner, adhesive compositions of Examples 1 to 16 and Comparative Examples 1 to 9 shown in Tables 1 to 3 were obtained. All of the adhesive compositions of Examples 1 to 16 and Comparative Examples 1 to 9 were anaerobic curable.

[0131] The adhesive compositions obtained above were evaluated for viscosity, storage stability and rapid curing properties by the following methods.

[0132] (Viscosity) The viscosity of the adhesive composition at 25° C. was measured by a method in accordance with JIS Z8803: 2011. The viscosity was measured using an E-type rotational viscometer ("TVE22" manufactured by Toki Sangyo Co., Ltd.).

[0133] (Storage Stability) The storage stability of the adhesive composition was evaluated based on the number of days until gelation, measured by the following method. First, 50% of the adhesive composition was poured into a polyethylene container, and the container was then sealed. The container was then heated in an oven set to a temperature of 60°C, and the fluidity of the adhesive composition in the container was visually confirmed every day. The number of days from the start of heating until a lump of the adhesive composition formed in the container was then measured. The number of days until a lump of the adhesive composition formed for the adhesive compositions of the Examples and Comparative Examples is shown in the "Number of days until gelation" column in Tables 1 to 3.

[0134] In the "Storage stability" column of Tables 1 to 3, the symbol "A" is entered when the number of days until gelation is 4 days or more, the symbol "B" is entered when the number of days until gelation is 1 day or more but less than 4 days, and the symbol "C" is entered when the number of days until gelation is less than 1 day. When the storage stability of an adhesive composition is high, the curing reaction of the adhesive composition does not progress easily during heating, and the number of days until gelation is long. Therefore, an adhesive composition that takes a long time to gel has excellent storage stability.

[0135] (Rapid Curing Property) The rapid curing property of the adhesive composition was evaluated based on the tensile shear adhesive strength measured by a method conforming to JIS K6850:1999. Specifically, first, two acetone-degreased electromagnetic steel sheets were prepared as adherends. A primer composition containing metal ions ("AT Quicka VA" manufactured by Toagosei Co., Ltd.) was applied to one side of the first of these electromagnetic steel sheets. The adhesive composition was also applied to one side of the second electromagnetic steel sheet. Next, the two electromagnetic steel sheets were overlapped so that the surface of the first electromagnetic steel sheet coated with the primer composition and the surface of the second electromagnetic steel sheet coated with the adhesive composition were in contact. Thereafter, the two electromagnetic steel sheets were bonded together by clamping the laminated portions with clips for a predetermined period of time.

[0136] Using the test pieces thus obtained, a tensile test was performed 5 minutes after the start of clamping with the clips to measure the tensile shear bond strength of the cured adhesive composition. The tensile shear bond strengths of the adhesive compositions of the Examples and Comparative Examples are shown in the "Tensile shear bond strength" column of Tables 1 to 3.

[0137] If the adhesive composition has a fast curing rate, the adhesive composition will cure sufficiently within 5 minutes of the start of clamping, allowing the two magnetic steel sheets to be bonded together. On the other hand, if the adhesive composition has a slow curing rate, the adhesive composition will not have cured sufficiently by the time 5 minutes have passed since the start of clamping, preventing the two magnetic steel sheets from being bonded together sufficiently. Therefore, in the "Curing Speed" column of Tables 1 to 3, a tensile shear bond strength of 0.6 MPa or greater is recorded as "Good," and a tensile shear bond strength of less than 0.6 MPa is recorded as "Poor."

[0138]

[0139]

[0140]

[0141] As shown in Tables 1 and 2, the adhesive compositions of Examples 1 to 16 contain a radically polymerizable compound (A), a radical polymerization initiator (B), and a polymerization inhibitor (C). The polymerization inhibitor (C) also contains an aromatic compound (C-1) having at least one of a nitroso group and a nitro group, and a phenolic hydroxyl group. Therefore, the adhesive compositions of Examples 1 to 16 have excellent storage stability and a fast curing rate.

[0142] On the other hand, as shown in Table 3, the adhesive compositions of Comparative Examples 1 to 9 did not contain the aromatic compound (C-1), and therefore were unable to achieve both a fast curing rate and excellent storage stability.

[0143] Although the above describes aspects of the adhesive composition based on examples, the specific aspects of the adhesive composition according to the present invention are not limited to the aspects of the examples, and the configuration can be changed as appropriate within the scope that does not impair the spirit of the present invention.

Claims

1. An adhesive composition comprising: a radically polymerizable compound (A); a radical polymerization initiator (B); and a polymerization inhibitor (C), wherein the polymerization inhibitor (C) comprises an aromatic compound (C-1) having at least one of a nitroso group and a nitro group, and a phenolic hydroxyl group.

2. The adhesive composition according to claim 1, wherein the aromatic compound (C-1) has at least one of a nitroso group bonded to an aromatic ring and a nitro group bonded to an aromatic ring.

3. The adhesive composition according to claim 2, wherein the nitroso group, the nitro group, and the phenolic hydroxyl group in the aromatic compound (C-1) are bonded to the same aromatic ring.

4. The adhesive composition according to claim 3, wherein the aromatic compound (C-1) is one or more compounds selected from the group consisting of 2,4-dinitrosoresorcinol, 1-nitroso-2-naphthol, 2-nitrophenol, and 2-nitroresorcinol.

5. The adhesive composition according to claim 1, wherein the content of the aromatic compound (C-1) is 0.0020% by mass or more and 0.080% by mass or less.

6. The adhesive composition according to claim 1, wherein the content of the polymerization inhibitor (C) is 0.0020% by mass or more and 0.10% by mass or less.

7. The adhesive composition of claim 1, which is adapted to cure in an anaerobic atmosphere.

8. The adhesive composition according to claim 6, further comprising one or more anaerobic curing catalysts (D) selected from the group consisting of saccharin, saccharin derivatives, amine compounds, azole compounds, mercaptan compounds, hydrazine compounds, and salts of hydrazine compounds.

9. An adhesive structure having a plurality of adherends and an adhesive layer interposed between adjacent adherends, wherein the adhesive layer is composed of a cured product of the adhesive composition according to any one of claims 1 to 8.

10. An adhesive structure having an adherend with a screw hole, a screw inserted into said screw hole, and an adhesive layer interposed between said adherend and said screw, wherein said adhesive layer is composed of a cured product of the adhesive composition according to any one of claims 1 to 8.

11. A laminate having a plurality of adherends stacked on top of one another and an adhesive layer interposed between adjacent adherends, wherein the adhesive layer is composed of a cured product of the adhesive composition according to any one of claims 1 to 8.

12. The laminate according to claim 11, wherein the adherend is a steel plate.

13. A motor comprising the laminate of claim 12.

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