Anaerobic adhesive composition for electromagnetic steel sheet

Abstract

The present invention addresses the problem of providing an anaerobic adhesive composition for an electromagnetic steel sheet, the composition having excellent peel strength, more specifically, cohesive failure resistance. This anaerobic adhesive composition for an electromagnetic steel sheet is characterized by comprising: 100 parts by weight of a polymerizable (meth)acrylic monomer (A) which contains, as main components, (a-1) hydroxyalkyl (meth)acrylate and (a-2) (meth)acrylic acid; 0.01-15 parts by weight of an organic peroxide (B); 0.01-10 parts by weight of a curing accelerator (C); and 0.1-30 parts by weight of polyalkyl (meth)acrylate (D).　

Description

Anaerobic adhesive composition for electrical steel sheets

[0001] The present invention relates to an anaerobic adhesive composition for electrical steel sheets.

[0002] Laminated electrical steel sheets used in energy conversion electrical equipment such as electric motors, generators, and transformers are manufactured by stacking multiple electrical steel sheets with insulating coatings and then integrating them by methods such as crimping or welding. However, in recent years, electrical steel sheets have become thinner in order to reduce energy loss and noise. In this case, not only is crimping or welding difficult, but the edges of the laminated electrical steel sheets are prone to opening, making it difficult to maintain the shape of the iron core. Therefore, a method of laminating multiple electrical steel sheets using an adhesive has been adopted. Acrylic anaerobic adhesives are often used as the adhesive used in this method.

[0003] Patent Document 1 describes a laminated electrical steel sheet formed by bonding the surfaces of two or more different types of electrical steel sheets together. As described above, the variety of laminated electrical steel sheets has been diversifying in recent years, and there has been an increasing demand for acrylic anaerobic adhesive compositions for electrical steel sheets that can bond to a wide variety of electrical steel sheets.

[0004] Patent Document 2 describes that if the surface roughness (SRz) of the electromagnetic steel sheets is less than 1.5 μm, the sliding resistance between the electromagnetic steel sheets in contact with each other decreases and the bonding strength of the adhesive varies greatly, and therefore, by making the surface roughness (SRz) 1.5 μm or more, the bonding strength of the adhesive becomes stable.

[0005] JP 2019-161765 JP 2003-282330

[0006] In view of the above-mentioned background art, an object of the present invention is to provide an anaerobic adhesive composition for electromagnetic steel sheets that can bond to multiple types (two or more types) of electromagnetic steel sheets, and that has excellent peel strength between the anaerobic adhesive and the electromagnetic steel sheets, more specifically, excellent cohesive fracture resistance, regardless of the surface roughness of the electromagnetic steel sheets.

[0007] Therefore, as means for solving the above-mentioned problems, the present invention provides an anaerobic adhesive composition for electrical steel sheets, characterized by comprising: (a) 100 parts by weight of a polymerizable (meth)acrylic monomer (A) containing, as main components, (a-1) a hydroxyalkyl (meth)acrylate and (a-2) (meth)acrylic acid; 0.01 to 15 parts by weight of an organic peroxide (B); 0.01 to 10 parts by weight of a curing accelerator (C); and 0.1 to 30 parts by weight of a polyalkyl (meth)acrylate (D); and (b) the anaerobic adhesive composition for electrical steel sheets according to (a), characterized in that the polymerizable (meth)acrylic monomer (A) comprises: 35 to 90% by weight of (a-1); 5 to 60% by weight of (a-2); and (a-3) 0 to 35% by weight of a (meth)acrylic acid ester other than (a-1) and (a-2), (c) There is provided an anaerobic adhesive composition for electrical steel sheets according to (a), wherein the polyalkyl(meth)acrylate (D) is a methyl acrylate polymer and / or a methyl methacrylate polymer; (d) There is provided an anaerobic adhesive composition for electrical steel sheets according to (a), wherein the polyalkyl(meth)acrylate (D) has a weight average molecular weight Mw of 10,000 or more and 350,000 or less; (e) There is provided an anaerobic adhesive composition for electrical steel sheets according to any one of (a) to (e), wherein the polyalkyl(meth)acrylate (D) is soluble in the polymerizable (meth)acrylic monomer (A); (f) There is provided an anaerobic adhesive composition for electrical steel sheets according to any one of (a) to (e), wherein, after curing, the anaerobic adhesive composition forms a sea-island structure in which the polyalkyl(meth)acrylate (D) serves as a dispersed phase in a continuous phase made of the polymerizable (meth)acrylic monomer (A); (g) There is provided the anaerobic adhesive composition for electrical steel sheets according to (f), characterized in that the dispersed phase has a substantially columnar or substantially disk shape.

[0008] The present invention provides an anaerobic adhesive composition for electrical steel sheets that can bond to multiple (two or more) types of electrical steel sheets. Furthermore, it is possible to provide an anaerobic adhesive composition for electrical steel sheets (hereinafter referred to as "anaerobic adhesive composition") that has excellent peel strength, more specifically, excellent cohesive fracture resistance, regardless of the surface roughness of the electrical steel sheets.

[0009] 2(a) and 2(b) are cross-sectional schematic diagrams for explaining in detail the mechanism by which a dispersed phase composed of polyalkyl(meth)acrylate (D) aggregates into a roughly columnar shape. Fig. 2(a) and 2(b) are SEM images of a cured product of the anaerobic adhesive composition according to the present invention, with Fig. 2(a) being an image taken at a magnification of 1,500 times and Fig. 2(b) being an image taken at a magnification of 10,000 times. Fig. 2(a) and 2(b) are cross-sectional schematic diagrams for explaining in detail the mechanism by which a dispersed phase composed of polyalkyl(meth)acrylate (D) aggregates into a roughly disc-shaped shape. Fig. 3(a) is a cross-sectional schematic diagram of a cured product of the anaerobic adhesive composition having a roughly disc-shaped dispersed phase, and Fig. 3(b) is a cross-sectional schematic diagram of a cured product of the anaerobic adhesive composition having no dispersed phase. 4(a) and 4(b) are diagrams for explaining a method for measuring peel strength in the present invention, in which Fig. 4(a) is a schematic plan view of a first electromagnetic steel sheet used in the peel strength measurement, Fig. 4(b) is a schematic plan view of a second electromagnetic steel sheet used in the peel strength measurement, Fig. 4(c) is a schematic plan view of the first and second electromagnetic steel sheets superimposed, and Fig. 4(d) is a schematic cross-sectional view showing an example of a peel strength measuring device. In the examples of the present invention, SEM images of the fracture interface after a peel test taken at 1,500 magnifications and the fracture state are shown. In the examples of the present invention, a cross section of the cured anaerobic adhesive composition was measured using a Raman spectrometer at 814 cm －１ 10 is a diagram showing the results of chemical mapping at wavelengths of 1000 nm and 1000 nm.

[0010] In this specification, "(meth)acrylic" or "(meth)acrylate" is a general term for acrylic and methacrylic, or a general term for acrylate and methacrylate, and means one or both of these.

[0011] In this specification, the term "to" means a range including both ends of the numerical value.

[0012] Furthermore, in the present invention, "after curing" refers to a state in which the reaction rate is 50% or more as measured by Fourier transform infrared spectroscopy (FT-IR). Specifically, for example, the measurement can be performed using a Fourier transform infrared spectroscopy device, Nicolet is5 (manufactured by Thermo Fisher Scientific Co., Ltd.). The measurement method can be, for example, the following method. (1) The 810 cm of the anaerobic adhesive composition before the reaction －１ The peak intensity Ia at 810 cm in the anaerobic adhesive composition after the reaction is measured by FT-IR. －１ The peak intensity Ib of the anaerobic adhesive composition after the reaction is measured by FT-IR. (3) The reaction rate of the anaerobic adhesive composition after the reaction is calculated using the following formula. If the reaction rate is 50% or higher, the composition is judged to be in a "cured" state. (Formula) Reaction rate of anaerobic adhesive composition after the reaction (%) = {1 - (Ib / Ia)} x 100

[0013] [Electromagnetic Steel Sheet] Electromagnetic steel sheet (electrical steel sheet) refers to a steel sheet of any composition, without particular limitations, that contains elements such as carbon (C), silicon (Si), manganese (Mn), aluminum (Al), phosphorus (P), sulfur (S), nitrogen (N), and tin (Sn), with the remainder being iron (Fe) and impurities, and that is adjusted to obtain desired magnetic properties by changing the resistivity. The impurities refer to components contained in raw materials or components mixed in during the manufacturing process, but are not intentionally included in the steel sheet.

[0014] Furthermore, in order to improve the workability of the magnetic steel sheet and the iron loss of the laminated magnetic steel sheet, an insulating coating may be formed on the surface of the magnetic steel sheet. The material constituting the insulating coating may be, for example, an inorganic compound, an organic resin, a mixture of an inorganic compound and an organic resin, or the like, and is not particularly limited. Specific examples of inorganic compounds include a complex of dichromate and boric acid, a complex of phosphate and silica, and the like. Examples of organic resins include, but are not particularly limited to, epoxy resin, acrylic resin, acrylic-styrene resin, polyester resin, silicone resin, fluororesin, and the like.

[0015] Furthermore, the surface of the electrical steel sheet on which the insulating coating is formed may be left untreated or may be pretreated. The pretreatment is optional, but degreasing treatment using an alkali or the like, and pickling treatment using hydrochloric acid, sulfuric acid, phosphoric acid, or the like are preferably applied.

[0016] The thickness of the electrical steel sheet is not particularly limited, but considering the iron loss characteristics of the laminated electrical steel sheet, it is preferably 0.10 mm or more and 0.65 mm or less, more preferably 0.10 mm or more and 0.35 mm or less, even more preferably 0.10 mm or more and 0.25 mm or less, and particularly preferably 0.10 mm or more and 0.20 mm or less. When an insulating coating is formed on the surface of the electrical steel sheet, the thickness of the insulating coating is also included in the thickness of the electrical steel sheet. The thickness of the electrical steel sheet can be measured, for example, using a micrometer.

[0017] In order to ensure the insulating performance of the electrical steel sheet, the thickness of the insulating coating is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.1 μm or more and 2 μm or less. The thickness of the insulating coating can be measured, for example, by observing a cross section obtained by cutting the electrical steel sheet in the thickness direction with a microscope or the like.

[0018] The insulating coating can be formed using a variety of methods commonly used in industry, such as a roll coater, flow coater, spray coater, knife coater, etc. The baking method can also be a commonly used method, such as a hot air method, an infrared method, or an induction heating method.

[0019] [Polymerizable (meth)acrylic monomer (A)] The polymerizable (meth)acrylic monomer (A) contains two components, (a-1) a hydroxyalkyl (meth)acrylate and (a-2) (meth)acrylic acid, as main components. In this specification, the term "main component" refers to a component that accounts for 50% by weight or more of the polymerizable (meth)acrylic monomer (A), and means that the two components, (a-1) a hydroxyalkyl (meth)acrylate and (a-2) (meth)acrylic acid, together account for 50% by weight or more.

[0020] The polymerizable (meth)acrylic monomer (A) can contain (a-1) 35 to 90% by weight of a hydroxyalkyl (meth)acrylate, (a-2) 5 to 60% by weight of (meth)acrylic acid, and (a-3) 0 to 35% by weight of a (meth)acrylic acid ester other than (a-1) and (a-2), and can also contain other polymerizable polymers.

[0021] (a-1) Hydroxyalkyl (meth)acrylate (a-1) Hydroxyalkyl (meth)acrylate has a hydroxyl group in the molecule, and is therefore characterized by excellent adhesion to adherends. Examples of hydroxyalkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, diethylene glycol mono(meth)acrylate, and polypropylene glycol (meth)acrylate. Among these, 2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate, which have high glass transition points (Tg), are preferred from the standpoint of heat resistance. These may be used alone or in combination of two or more.

[0022] The (a-1) hydroxyalkyl (meth)acrylate preferably contains 35 to 90% by weight of the polymerizable (meth)acrylic monomer (A), with the lower limit being preferably 40% by weight or more, 45% by weight or more, or 50% by weight or more from the viewpoint of adhesion, and the upper limit being preferably 85% by weight or less, 80% by weight or less, or 75% by weight or less from the viewpoint of heat resistance.

[0023] (a-2) (meth)acrylic acid (a-2) (meth)acrylic acid preferably contains 5 to 60% by weight of polymerizable (meth)acrylic monomer (A). The lower limit is preferably 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more from the viewpoint of further improving heat resistance and curing speed, and the upper limit is preferably 60% by weight or less, 50% by weight or less, 40% by weight or less, or 30% by weight or less from the viewpoint of skin irritation and metal corrosiveness.

[0024] (a-3) (Meth)acrylic acid esters other than (a-1) and (a-2) (a-3) (meth)acrylic acid esters other than (a-1) and (a-2) are not particularly limited as long as they are esters produced from acrylic acid and an alcohol (or phenol), and examples thereof include di(meth)acrylates of alkylene oxide adducts of bisphenol A such as ethoxylated bisphenol A dimethacrylate, isobornyl (meth)acrylate, (meth)acrylic acid alkyl esters, phenoxyethyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, poly(meth)acrylates of polyhydric alcohols, epoxy (meth)acrylates obtained by addition reaction of (meth)acrylic acid to epoxy resins, urethane poly(meth)acrylates, and polyester poly(meth)acrylates.

[0025] Further, examples of the (meth)acrylic acid ester other than (a-1) and (a-2) include acidic phosphate esters containing a (meth)acryloyloxy group. Examples of such esters include mono(meth)acryloyloxyethyl phosphates such as mono(2-hydroxyethyl methacrylate) phosphate, di(meth)acryloyloxyethyl phosphate, mono(meth)acryloyloxypropyl phosphate, di(meth)acryloyloxypropyl phosphate, mono(meth)acryloyloxy-β-chloropropyl phosphate, and di(meth)acryloyloxy-β-chloropropyl phosphate.

[0026] In addition, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, phenyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, glycidyl (meth)acrylate, caprolactone-modified tetrahydrofurfuryl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, ethoxycarbonylmethyl (meth)acrylate, phenol ethylene oxide modified (meth)acrylate, phenol (ethylene oxide 2 mol modified) (meth)acrylate, phenol (ethylene oxide 4 mol modified) (meth)acrylate, paracumylphenol ethylene oxide modified (meth)acrylate, nonylphenol ethylene oxide modified (meth)acrylate, nonylphenol (ethylene oxide (ethylene oxide 4 mol modified) (meth)acrylate, nonylphenol (ethylene oxide 8 mol modified) (meth)acrylate, nonylphenol (propylene oxide 2.5 mol modified) (meth)acrylate, 2-ethylhexyl carbitol (meth)acrylate, trifluoroethyl (meth)acrylate, β-(meth)acryloyloxyethyl hydrogen succinate, ω-carboxy-polycaprolactone mono(meth)acrylate, n-(meth)acryloyloxyalkyl hexahydrophthalimide, maleic acid, fumaric acid Acid, ω-carboxy-polycaprolactone mono(meth)acrylate, monohydroxyethyl phthalate (meth)acrylate, (meth)acrylic acid dimer, β-(meth)acryloyloxyethyl hydrogen succinate, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, methoxylated cyclodecatriene (meth)acrylate, 1,2-polybutadiene terminated urethane (meth)acrylate, 1,4-polybutadiene terminated urethane (meth)acrylate, polyisoprene terminated (meth)acrylate, polyester-based urethane (meth)acrylate, polyether-based urethane (meth)acrylate, polyester (meth)acrylate, bis-A type epoxy (meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexadiol di(meth)acrylate, 1,9-Nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, 2-ethyl-2-butyl-propanediol (meth)acrylate, neopentyl glycol modified trimethylolpropane di(meth)acrylate, stearic acid modified pentaerythritol diacrylate, polyethylene glycol modified bisphenol A di(meth)acrylate, polypropylene glycol modified bisphenol A di(meth)acrylate, polypropylene glycol di(meth)acrylate, 2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxypropyl) Examples of (meth)acrylic acid esters that can be used other than (a-1) and (a-2) include (meth)acrylic acid esters such as 2,2-bis(4-(meth)acryloxytetraethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxytetraethoxyphenyl)propane, trimethylolpropane tri(meth)acrylate, tris[(meth)acryloyloxyethyl]isocyanurate, dimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol ethoxy tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, and the above-mentioned esters can be used alone or in combination of two or more.

[0027] (a-3) (meth)acrylic acid esters other than (a-1) and (a-2) preferably contain 0 to 35 wt% of polymerizable (meth)acrylic monomer (A). The lower limit is preferably 0.01 wt% or more, and 0.1 wt% or more. The upper limit is preferably 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, 10 wt% or less, 5 wt% or less, or 3 wt% or less, from the viewpoint of improving peel strength, more specifically, cohesive failure resistance. By blending (a-3) (meth)acrylic acid esters other than (a-1) and (a-2) in the above-mentioned ratios and using (a-1) hydroxyalkyl (meth)acrylate and (a-2) (meth)acrylic acid as the main components, an anaerobic adhesive composition having excellent peel strength, more specifically, excellent cohesive failure resistance, can be obtained.

[0028] [Organic Peroxide (B)] The organic peroxide (B) functions as an initiator for radical polymerization of a (meth)acrylic monomer, and the following examples can be used alone or in combination of two or more.

[0029] Examples of the organic peroxide (B) include ketone peroxides, dialkyl peroxides, diacyl peroxides, peroxy esters, and hydroperoxides, among which hydroperoxides are preferred from the viewpoint of the curability and storage stability of the anaerobic adhesive composition. Examples of hydroperoxides include cumene hydroperoxide, p-menthane hydroperoxide, tertiary butyl hydroperoxide, and 1,1,3,3-tetramethylbutyl hydroperoxide.

[0030] From the viewpoint of curability, the content of the organic peroxide (B) in the anaerobic adhesive composition is 0.01 to 15 parts by weight per 100 parts by weight of the polymerizable (meth)acrylic monomer. From the viewpoint of further increasing the curing rate, the lower limit is preferably 0.05 parts by weight or more, 0.1 parts by weight or more, 1 part by weight or more, or 3 parts by weight or more, and from the viewpoint of further increasing the storage stability and peel strength of the anaerobic adhesive composition, the upper limit is preferably 10 parts by weight or less, 9 parts by weight or less, 8 parts by weight or less, or 7 parts by weight or less.

[0031] [Curing Accelerator (C)] The curing accelerator (C) is a component that accelerates the curing of the anaerobic adhesive composition, for example, by shortening the curing time of the anaerobic adhesive composition, accelerating the curing reaction, or improving the adhesiveness by modifying the adhesive surface. The curing accelerators exemplified below can be used alone or in combination of two or more.

[0032] Examples of the curing accelerator (C) 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), ethyl carbazate, p-nitrophenylhydrazine, and p-trisulfonyl hydrazine. hydroquinone compounds such as methylhydroquinone, dimethylhydroquinone, methoxyhydroquinone, 2-t-butylhydroquinone, and 2,5-di-t-butylhydroquinone; tertiary amines such as N,N-dimethyl orthotoluidine, N,N-dimethyl meta-toluidine, N,N-dimethyl para-toluidine, N,N-dimethylaniline, and N,N-dimethylnaphthylamine; heterocyclic amines such as quinoline, quinaldine, quinoxaline, tetrahydroquinoline, and tetrahydroquinaldine; benzoquinone; and saccharin.

[0033] In benzoquinone, the positional relationship of the two oxygen atoms in the six-membered carbon atom ring may be ortho, meta, or para. The positional relationship (para) of the two hydroxyl groups in the hydroquinone compound and the positional relationship of the two oxygen atoms in benzoquinone may be the same or different.

[0034] The content of the curing accelerator (C) in the anaerobic adhesive composition is preferably 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, or 0.2 parts by weight or more per 100 parts by weight of the polymerizable (meth)acrylic monomer (A) in order to further increase the curing rate of the anaerobic adhesive composition, and more preferably 10 parts by weight or less, 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, or 1 part by weight or less in order to further increase the storage stability of the anaerobic adhesive composition.

[0035] [Polyalkyl(meth)acrylate (D)] The polyalkyl(meth)acrylate (D) is soluble in the polymerizable (meth)acrylic monomer (A) and, when the anaerobic adhesive composition is cured, forms a dispersed phase in the continuous phase made of the polymerizable (meth)acrylic monomer (A), and is a component for improving the peel strength, or more specifically, the cohesive failure resistance.

[0036] The polyalkyl(meth)acrylate (D) is a polymer containing a methyl acrylate polymer and / or a methyl methacrylate polymer. The methyl acrylate polymer is preferably a homopolymer of methyl acrylate, and the methyl methacrylate polymer is preferably a homopolymer of methyl methacrylate.

[0037] The weight average molecular weight Mw of the polyalkyl (meth)acrylate (D) is 10,000 or more and 350,000 or less. From the viewpoint of increasing peel strength, more specifically, cohesive fracture resistance, the lower limit is preferably 20,000 or more, 30,000 or more, 40,000 or more, 50,000 or more, 60,000 or more, or 80,000 or more, and from the viewpoint of solubility, the upper limit is preferably 300,000 or less, 250,000 or less, or 200,000 or less.

[0038] A weight-average molecular weight Mw of 10,000 or more is preferred because, when the anaerobic adhesive composition cures, a dispersed phase in which the polyalkyl(meth)acrylate (D) is dispersed is easily formed, resulting in excellent peel strength, and more specifically, excellent cohesive fracture resistance. Furthermore, a weight-average molecular weight Mw of 350,000 or less is preferred because it is easily dissolved in the polymerizable (meth)acrylic monomer (A), allowing the anaerobic adhesive composition of the present invention to be efficiently obtained. The weight-average molecular weight Mw of the polyalkyl(meth)acrylate (D) can be measured, for example, by gel permeation chromatography (GPC). If a manufacturer's published value is available, this may be used as the weight-average molecular weight Mw.

[0039] The content of the polyalkyl (meth)acrylate (D) is 0.1 to 30 parts by weight per 100 parts by weight of the polymerizable (meth)acrylic monomer. From the viewpoint of increasing peel strength, more specifically, cohesive failure resistance, the lower limit is preferably 0.1 parts by weight or more, 0.5 parts by weight or more, 1 part by weight or more, 2 parts by weight or more, or 3 parts by weight or more. From the viewpoint of handling, the upper limit is preferably 25 parts by weight or less, 20 parts by weight or less, 19 parts by weight or less, or 18 parts by weight or less.

[0040] The polyalkyl(meth)acrylate (D) is completely dissolved in the polymerizable (meth)acrylic monomer (A) before curing, but when it aggregates and precipitates, it forms a dispersed phase in the shape of a column or a disk.

[0041] Here, the mechanism by which the dispersed phase of polyalkyl (meth)acrylate (D) aggregates into a generally columnar shape will be described below. FIG. 1 is a cross-sectional schematic diagram for explaining in detail the mechanism by which the dispersed phase of polyalkyl (meth)acrylate (D) aggregates into a generally columnar shape. As shown in FIG. 1, the polyalkyl (meth)acrylate (D) precipitates in a generally columnar shape between two electromagnetic steel sheets, forming a dispersed phase 2. The polyalkyl (meth)acrylate (D), which is completely dissolved before the anaerobic adhesive composition is cured, precipitates and aggregates during the curing process of the anaerobic adhesive composition. During aggregation, the polyalkyl (meth)acrylate (D) may precipitate so as to penetrate into the irregularities on the surface of the electromagnetic steel sheet 5. This is thought to produce an anchor effect and improve peel strength. In addition, as shown in FIG. 1, the aggregation of the polyalkyl (meth)acrylate into a generally columnar shape is thought to inhibit the progression of cohesive failure, resulting in excellent peel strength, and more specifically, excellent cohesive failure resistance.

[0042] As described above, the polyalkyl(meth)acrylate (D) dissolves in the polymerizable (meth)acrylic monomer (A), and as the anaerobic adhesive composition cures, the polyalkyl(meth)acrylate (D) precipitates and forms a dispersed phase in a sea-island structure within a continuous phase of the polymerizable (meth)acrylic monomer (A). Figure 2 shows SEM images of a cured product of the anaerobic adhesive composition, with Figure 2(a) being an image taken at 1,500 magnifications and Figure 2(b) being an image taken at 10,000 magnifications.

[0043] 2(a) shows that the cured product of the anaerobic adhesive composition has a sea-island structure in which polyalkyl(meth)acrylate (D) forms a dispersed phase 2 in a continuous phase 1 made of polymerizable (meth)acrylic monomer (A). Also, FIG. 2(b) shows that the dispersed phase 2 of polyalkyl(meth)acrylate (D) aggregates into a roughly disk-like shape. The thickness of the dispersed phase 2 shown in FIG. 2(b) was approximately 0.5 μm, and the diameter was approximately 8 μm.

[0044] 2(a) and 2(b) , a specific observation method was as follows: First, a mold was prepared by forming a 6 mm × 10 mm opening in a 6 mm thick plate, and this mold was placed on a release film. Next, the anaerobic adhesive composition described in Example 1 of Table 2 was blended with a photopolymerization initiator (Omnirad (registered trademark) 184, manufactured by IGM RESINS B.V.) and poured into the mold. The anaerobic adhesive composition was then cured by irradiating it with 20,000 mJ of ultraviolet light using an ultraviolet irradiation device. The surface of the cured anaerobic adhesive composition was then ground with a microtome, and the cross section was observed with an SEM (JSM-6510LA, manufactured by JEOL Ltd.).

[0045] 3A and 3B are cross-sectional schematic diagrams for explaining in detail the mechanism by which a dispersed phase made of polyalkyl(meth)acrylate (D) aggregates into an approximately disk-shaped form. FIG. 3A is a cross-sectional schematic diagram of a cured product of an anaerobic adhesive composition having an approximately disk-shaped dispersed phase made of polyalkyl(meth)acrylate (D), and FIG. 3B is a cross-sectional schematic diagram of a cured product of an anaerobic adhesive composition having no dispersed phase made of polyalkyl(meth)acrylate (D).

[0046] Comparing the fracture interfaces, it can be seen that in Figure 3(a), which has a dispersed phase 2 made of polyalkyl (meth)acrylate (D), the fracture interface is formed along the dispersed phase 2, making the fracture interface more complex than in Figure 3(b). In this way, the presence of the dispersed phase 2 inhibits the progression of fracture, and it is therefore thought that Figure 3(a), which has the dispersed phase 2, has superior peel strength, and more specifically, cohesive fracture resistance, than Figure 3(b), which does not have a dispersed phase.

[0047] Furthermore, since the polyalkyl(meth)acrylate (D) was completely dissolved in the anaerobic adhesive composition of the present invention before curing, it is believed that during the curing process of the anaerobic adhesive composition, the polyalkyl(meth)acrylate (D) aggregated into a roughly disk-shaped dispersed phase in the continuous phase consisting of the polymerizable (meth)acrylic monomer (A). When the polyalkyl(meth)acrylate (D) dissolved before curing precipitates and aggregates during the curing process of the anaerobic adhesive composition, it may precipitate so as to penetrate into the irregularities on the surface of the electrical steel sheet 5. This is believed to produce an anchor effect and improve the peel strength.

[0048] As described above, the polyalkyl(meth)acrylate (D) in the cured anaerobic adhesive composition aggregates into a generally columnar or generally discoid shape, thereby providing excellent peel strength, and more specifically, excellent cohesive failure resistance. The aggregate shape of the polyalkyl(meth)acrylate (D) in the cured anaerobic adhesive composition is not particularly limited; it may precipitate only in a generally columnar shape, or only in a generally discoid shape, or may precipitate in both a generally discoid shape and a generally discoid shape.

[0049] The dispersed phase 2 made of polyalkyl(meth)acrylate (D) may precipitate so as to penetrate into the irregularities on the surface of the electrical steel sheet, and therefore the thickness and diameter of the dispersed phase are not particularly limited, but for example, the thickness is about 0.1 to 3 μm, preferably about 0.5 to 1.5 μm, and the diameter is, for example, about 1 to 20 μm, preferably about 5 to 15 μm.

[0050] In this specification, the term "substantially columnar shape" refers to agglomeration and precipitation in a substantially columnar shape between two electromagnetic steel sheets as shown in FIG. 1, but the strict shape is not important. Furthermore, the term "disk shape" refers to a substantially circular and flat shape as shown in FIG. 2(b), but the strict shape is not important as long as the polyalkyl(meth)acrylate is aggregated in that shape. Incidentally, as a method for confirming whether the dispersed phase is polyalkyl(meth)acrylate (D), for example, measurement can be performed using Raman spectroscopy, FT-IR mapping, or the like.

[0051] Examples of the polyalkyl(meth)acrylate (D) include DIANAL (registered trademark) BR-75, BR-82, and BR-85 manufactured by Mitsubishi Chemical Corporation, the HYPERL (registered trademark) series manufactured by Negami Chemical Industrial Co., Ltd., and the TECHPOLYMER (registered trademark) MB series manufactured by Sekisui Plastics Co., Ltd.

[0052] [Other Components (P)] The anaerobic adhesive composition of an embodiment of the present invention may further contain other components in addition to those described above, as long as the effects of the present invention are obtained. Examples of other components (P) include stabilizers, adhesion improvers, strength improvers, and reducing agents, and the anaerobic adhesive composition may contain one or more of these.

[0053] The stabilizer is a component that enhances the storage stability of the anaerobic adhesive composition at room temperature. Examples of stabilizers include radical polymerization inhibitors and chelating agents, and more specifically, 2,6-di-t-butyl-4-methylphenol, 2,2-methylenebis(4-methyl-6-t-butylphenol), benzoquinone, quinhydrone, tetrasodium ethylenediaminetetraacetate, oxalic acid, N-methyl-N-nitrosoaniline, and N-nitrosodiphenylamine. The content of the stabilizer in the anaerobic adhesive composition can be determined appropriately from the viewpoint of sufficiently enhancing storage stability, and is not particularly limited, and may be, for example, 0.01 to 5 parts by weight per 100 parts by weight of the polymerizable (meth)acrylic monomer (A).

[0054] The adhesion improver is a component for improving the adhesiveness of the anaerobic adhesive composition and stabilizing the adhesive strength. Examples of the adhesion improver include thermoplastic resins such as polyvinyl butyral, acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), and methyl methacrylate-butadiene-styrene copolymer (MBS resin); rubbers such as styrene-butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), chloroprene rubber (CR), nitrile rubber (NBR), chlorinated rubber, acrylic rubber, epichlorohydrin rubber, and chlorosulfonated polyethylene; and liquid rubbers such as liquid polybutadiene, terminal acrylic-modified liquid polybutadiene, and liquid acrylonitrile-butadiene copolymer. The content of the adhesion improver in the anaerobic adhesive composition can be determined appropriately within a range in which the effect of improving adhesion can be obtained, and is not particularly limited, and may be, for example, 0 to 50 parts by weight, 5 to 40 parts by weight, or 10 to 30 parts by weight relative to 100 parts by weight of the polymerizable (meth)acrylic monomer (A).

[0055] The strength improver is, for example, a component for improving the mechanical strength of the cured product of the anaerobic adhesive composition. Examples of the strength improver include fillers. Fillers are organic particles such as resin particles, or inorganic particles as described below. Examples of fillers include various powders such as glass, silica, alumina, talc, mica, silicone rubber powder, calcium carbonate, aluminum nitride, carbon powder, kaolin clay, dried clay minerals, and dried diatomaceous earth.

[0056] The content of the filler in the anaerobic adhesive composition may be 0.1 to 100 parts by weight, or may be 1 to 10 parts by weight, relative to 100 parts by weight of the polymerizable (meth)acrylic monomer (A), and is not particularly limited.

[0057] Among these, silica is preferred from the viewpoint of preventing coating defects due to drying of the anaerobic adhesive composition. The silica may be, for example, hydrophobic silica or hydrophilic silica, but hydrophilic silica is more preferred from the viewpoint of preventing coating defects due to drying of the anaerobic adhesive composition.

[0058] The anaerobic adhesive composition of an embodiment of the present invention may be used in combination with a primer liquid containing a reducing agent in an organic solvent for the purpose of accelerating curing. Methods for using a primer liquid in combination with the anaerobic adhesive composition include, for example, a method of applying the primer liquid to the area where the anaerobic adhesive composition will be applied in advance, or a method of applying the primer liquid to the area that protrudes from the joining members and is in contact with oxygen.

[0059] Examples of organic solvents include hydrocarbons such as n-pentane, n-hexane, n-heptane, and cyclohexane; halogenated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride; methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl acetate, acetone, methyl methacrylate, and ethyl methacrylate.

[0060] The reducing agent is selected from those which form a redox catalyst system with an organic peroxide, and examples thereof include thiourea derivatives such as ethylene thiourea, diethyl thiourea, tetramethyl thiourea, monoacetyl thiourea, monobenzoyl thiourea, diphenyl thiourea, and dicyclohexyl thiourea, vanadium compounds such as vanadium acetylacetonate, vanadyl acetylacetonate, vanadyl stearate, vanadium naphthenate, vanadium benzoylacetonate, and vanadium pentoxide, and copper compounds such as copper acetylacetonate, copper chloride, copper acetate, copper naphthenate, and copper neodecanoate. These can be used alone or in combination of two or more.

[0061] Further, other additives such as a viscosity modifier, a colorant, an antibacterial agent, and a moisture cure accelerator may also be contained as other components (P).

[0062] [Production method and use] The anaerobic adhesive composition of an embodiment of the present invention can be prepared by mixing the various components described above. The anaerobic adhesive composition of an embodiment of the present invention may be in the form of a single liquid containing all of the various components described above, or in the form of two or more liquids containing some of the various components described above and all of the components as a whole. The anaerobic adhesive composition of an embodiment of the present invention can be used as an adhesive for electrical steel sheets, and can be used, for example, as an adhesive for laminated electrical steel sheets used in electric motors, generators, transformers, and other electrical equipment for energy conversion. There are no particular limitations on the use of the anaerobic adhesive composition as long as it is used to bond to electrical steel sheets.

[0063] [Effects] The anaerobic adhesive composition of an embodiment of the present invention is applied to, for example, electromagnetic steel sheets, and when the electromagnetic steel sheets are assembled, the anaerobic adhesive composition fills the gaps between the electromagnetic steel sheets and is isolated from air, allowing the anaerobic adhesive composition to harden in the gaps in an anaerobic environment.

[0064] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0065] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0066] Prior to the Examples, the surfaces (front and back) of the two types of electrical steel sheets P and Q used in the Examples were observed using a three-dimensional white light interference microscope (Contour GT-K, manufactured by Bruker Japan Co., Ltd.). Furthermore, the surface roughness (arithmetic mean height Sa of the surface, maximum peak height Sp, maximum valley depth Sv, maximum height Sz) of the electrical steel sheets P and Q were measured. The results are shown in Table 1.

[0067]

[0068] From Table 1, it can be seen that the arithmetic mean height Sa of the surface of electromagnetic steel sheet P is high and that there are streak-like height differences. On the other hand, electromagnetic steel sheet Q does not have the streak-like height differences seen in electromagnetic steel sheet P and has a smoother surface compared to electromagnetic steel sheet P, and it can be seen that the surface roughness of electromagnetic steel sheets P and Q is different.

[0069] [Material Preparation] The following materials were prepared. Polymerizable (meth)acrylic monomer (A): (a-1) 2-hydroxyethyl methacrylate [Acryester (registered trademark) HO, manufactured by Mitsubishi Chemical Corporation] (a-2) methacrylic acid [Methacrylic acid, manufactured by Mitsubishi Chemical Corporation] (a-3-1) Ethoxylated bisphenol A di(meth)acrylate [NK Ester BPE-200, manufactured by Shin-Nakamura Chemical Co., Ltd.] (a-3-2) Isobornyl (meth)acrylate [Acryester (registered trademark) IBX, manufactured by Mitsubishi Chemical Corporation] Organic peroxide (B): (b) Cumene hydroperoxide [Purmicle (registered trademark) H, manufactured by NOF Corporation] Curing accelerator (C): (c) 1-acetyl-2-phenylhydrazine [APH, manufactured by Sanuki Chemical Industry Co., Ltd.] Polymer beads containing polyalkyl (meth)acrylate (D): (d-1) Methyl acrylate polymer (manufactured by Mitsubishi Chemical Corporation, Dianal BR-75, weight average molecular weight Mw: 85,000, particle size: about 200 to 300 μm) (d-2) Methyl (meth)acrylate polymer [manufactured by Mitsubishi Chemical Corporation, Dianal BR-85, weight average molecular weight Mw: 200,000, particle size: about 200 to 300 μm] (d-3) Methyl (meth)acrylate polymer [manufactured by Mitsubishi Chemical Corporation, Dianal BR-82, weight average molecular weight Mw: 150,000, particle size: about 200 to 300 μm] Other polymer beads (X) not containing polyalkyl (meth)acrylate (D): (x) Styrene polymer [manufactured by Mitsubishi Chemical Corporation, Dianal BR-50, weight average molecular weight Mw: 60,000] Other components (P): (p-1) Hydrophilic silica [AEROSIL (registered trademark) 200, manufactured by Nippon Aerosil Co., Ltd.] (p-2) Methyl methacrylate-butadiene-styrene copolymer [Kane Ace (registered trademark) B-56, manufactured by Kaneka Corporation]

[0070] Next, the materials in the amounts (parts by weight) shown in Table 2 were mixed in a mixer to prepare the anaerobic adhesive compositions of Examples 1 to 6 and Comparative Examples 1 to 4.

[0071] In this example, the anaerobic adhesive compositions described in Examples 1 to 6 and Comparative Examples 1 to 4 in Table 2 were used to carry out the peel test described below. In addition, the peel strength (N) described below was measured for each of two types of electrical steel sheets (electrical steel sheets P and Q). The results are shown in Table 2.

[0072] [Peel Test] The method of the peel test will be described with reference to Figure 4. 0.8 to 1.2 mg of the prepared anaerobic adhesive composition 8 was applied to the central area of ​​25 mm wide x 25 mm long on the back of a first electromagnetic steel sheet 6 measuring 25 mm wide x 100 mm long x 0.3 mm thick (see Figure 4(a)). 2 mg of primer liquid 9 (8% copper naphthenate, manufactured by Toei Kako Co., Ltd., diluted 25 times with punching oil) was applied to the central area of ​​25 mm wide x 25 mm long on the front of a second electromagnetic steel sheet 7 measuring 25 mm wide x 100 mm long (see Figure 4(b)). Next, the first electromagnetic steel sheet 6 coated with the anaerobic adhesive composition 8 was attached to a jig 11 located below using double-sided tape 10, and the second electromagnetic steel sheet 7 coated with the primer liquid 9 was attached to a jig 11 located above using double-sided tape 10. At this time, the portions of the first electromagnetic steel sheet 6 coated with the anaerobic adhesive composition 8 and the portions of the second electromagnetic steel sheet 7 coated with the primer liquid 9 were overlapped, and the longitudinal directions of the first and second electromagnetic steel sheets were perpendicular to each other (see FIGS. 4( c) and 4(d)). The overlapped first and second electromagnetic steel sheets were then pressed with 300 N and allowed to stand for 3 minutes in an environment of 23°C and 50% RH. Next, using an autograph, the sheets were peeled at a speed of 3 mm / sec in an environment of 23°C and 50% RH, and the maximum peel strength was measured. The same test was performed three times, and the average value of the three measurements was taken as the peel strength (N).

[0073]

[0074] As is clear from Table 2, the anaerobic adhesive compositions of Examples 1 to 6 have a peel strength of 120 N or more, and are well bonded to two types of electromagnetic steel sheets, electromagnetic steel sheets P and Q, and are excellent in peel strength, more specifically, cohesive fracture resistance, with two types of electromagnetic steel sheets with different surface roughness. On the other hand, the anaerobic adhesive compositions of Comparative Examples 1 to 4 have an adhesive strength of less than 100 N with either electromagnetic steel sheet P or electromagnetic steel sheet Q, and are therefore unable to provide a good bond to the two electromagnetic steel sheets with different surface roughness.

[0075] [Confirmation of Precipitation State of Dispersed Phase 2] Next, the precipitation state of the dispersed phase 2 was confirmed. Specifically, the above-mentioned peel test was performed on the electrical steel sheet P using the anaerobic adhesive compositions described in Example 2 and Comparative Examples 1 to 3, and the fracture interface (side A, side B) after peeling was photographed at 1,500 magnification using an SEM (JSM-6510LA, manufactured by JEOL Ltd.). Fig. 5 shows an SEM image of the fracture interface observed after the peel test, and the fracture state after the peel test.

[0076] 5, a dispersed phase 2 having a generally columnar or generally discoid shape can be confirmed in Example 2, whereas no dispersed phase 2 can be confirmed in Comparative Examples 1 to 3. This shows that by using the anaerobic adhesive composition described in this specification, the cured anaerobic adhesive composition has a generally discoid dispersed phase 2. Furthermore, since a generally discoid dispersed phase 2 is present on the surface of the fracture interface after the peel test, it is inferred that cohesive failure progresses along the dispersed phase 2, and therefore the composition is considered to have excellent cohesive failure resistance.

[0077] On the other hand, in Comparative Examples 1 and 2, the surface of the electromagnetic steel sheet 5 could be confirmed, which shows that interfacial peeling between the surface of the electromagnetic steel sheet and the adhesive layer occurred before cohesive failure of the adhesive layer occurred. Furthermore, in Comparative Example 3, only the anaerobic adhesive composition 3 after curing could be confirmed, and it was not possible to confirm the dispersed phase 2 present in Example 2 or the surface of the electromagnetic steel sheet 5.

[0078] [Confirmation of Dispersed Phase 2 by Raman Spectroscopic Analysis] Here, Raman spectroscopic measurement was performed using the anaerobic adhesive composition of Example 2. First, as a preliminary preparation for the Raman spectroscopic measurement, the Raman peak of the anaerobic adhesive composition (d-1) of Example 2, a methyl acrylate polymer (manufactured by Mitsubishi Chemical Corporation, Dianall BR-75, weight average molecular weight Mw: 85,000) was measured, and a peak at 814 cm －１ It was confirmed that a characteristic absorption peak was observed. Next, a sample for Raman spectroscopic analysis was prepared. First, the anaerobic adhesive composition of Example 2 was applied to a polycarbonate resin plate to a thickness of 9 μm, and a release PET film was attached to the applied anaerobic adhesive composition to prepare a sample. Then, after confirming that the anaerobic adhesive composition of Example 2 had sufficiently cured, the Raman spectrum of the dispersed phase 2 in the cured anaerobic adhesive composition was measured using a Raman spectrometer (NRS-4500, manufactured by JASCO Corporation). The measurement results are described below. The dispersed phase 2 had the same 814 cm as (d-1) methyl acrylate polymer (Dianal BR-75, manufactured by Mitsubishi Chemical Corporation, weight average molecular weight Mw: 85,000). －１ An absorption peak was observed.

[0079] Furthermore, a cross section of the cured anaerobic adhesive composition was measured using a Raman spectrometer at 814 cm －１ The chemical mapping results are shown in Figure 6. As shown in Figure 6, －１ One of the aggregates was approximately disk-shaped, and the other was also approximately disk-shaped.

[0080] REFERENCE SIGNS LIST 1 Continuous phase 2 Dispersed phase 3 Anaerobic adhesive composition after curing 4 Cohesive failure interface 5 Electrical steel sheet 6 First electrical steel sheet 7 Second electrical steel sheet 8 Anaerobic adhesive composition 9 Primer liquid 10 Double-sided tape 11 Jig 12 Roughly columnar aggregate 13 Roughly disc-shaped aggregate

Claims

1. An anaerobic adhesive composition for electrical steel sheets, comprising: 100 parts by weight of a polymerizable (meth)acrylic monomer (A) containing as its main components (a-1) a hydroxyalkyl (meth)acrylate and (a-2) (meth)acrylic acid; 0.01 to 15 parts by weight of an organic peroxide (B); 0.01 to 10 parts by weight of a curing accelerator (C); and 0.1 to 30 parts by weight of a polyalkyl (meth)acrylate (D).

2. The anaerobic adhesive composition for electrical steel sheets according to claim 1, characterized in that the polymerizable (meth)acrylic monomer (A) contains 35 to 90% by weight of the (a-1), 5 to 60% by weight of the (a-2), and (a-3) 0 to 35% by weight of a (meth)acrylic acid ester other than the (a-1) and the (a-2).

3. The anaerobic adhesive composition for electrical steel sheets according to claim 1, characterized in that the polyalkyl(meth)acrylate (D) is a methyl acrylate polymer and / or a methyl methacrylate polymer.

4. The anaerobic adhesive composition for electrical steel sheets according to claim 1, characterized in that the polyalkyl (meth)acrylate (D) has a weight average molecular weight Mw of 10,000 or more and 350,000 or less.

5. An anaerobic adhesive composition for electrical steel sheets as described in any one of claims 1 to 4, characterized in that the polyalkyl (meth)acrylate (D) is soluble in the polymerizable (meth)acrylic monomer (A).

6. An anaerobic adhesive composition for electrical steel sheets as described in any one of claims 1 to 4, characterized in that after curing, the anaerobic adhesive composition forms a sea-island structure in which the polyalkyl (meth)acrylate (D) serves as a dispersed phase in a continuous phase consisting of the polymerizable (meth)acrylic monomer (A).

7. The anaerobic adhesive composition for electrical steel sheets according to claim 6, characterized in that the dispersed phase is generally columnar or generally disk-shaped.

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