Adhesive composition

Abstract

The present invention addresses the problem of providing an adhesive composition having excellent tensile lap-shear strength and T-peel strength, and being capable of maintaining adhesion performance even when lap length is increased, while having high adhesive strength at joints. As a solution, provided is an adhesive composition characterized in that the fracture energy per unit area is 0.035 J / mm2 or more in a tensile lap-shear adhesion test when the fracture region is an adhesive layer.

Description

adhesive composition

[0001] The present invention relates to an adhesive composition, and more particularly to an adhesive composition that exhibits excellent fracture energy at a joint.

[0002] Structural adhesives are defined in JIS K 6800, Adhesives and Bonding Terminology, as "reliable adhesives that can withstand heavy loads for long periods of time," and epoxy-based adhesives, acrylic-based adhesives, urethane-based adhesives, etc. are commonly used to join metal components. However, conventional structural adhesives are insufficient in achieving both adhesive strength and tenacity (toughness), and adhesives with high elastic modulus and high adhesive strength have poor elongation (ductility), resulting in sudden fracture of the joint after reaching maximum adhesive strength. On the other hand, when elongation (ductility) is important, conventional technology produces soft and sticky adhesives, but the adhesive strength is insufficient for use in structural joining.

[0003] For example, when two plates are simply overlapped and glued together, it is known that shear stress concentrates at the bonded edges due to shear force (Non-Patent Document 1). One known method to address this phenomenon is to use an adhesive with rubber elasticity to reduce stress concentration (Non-Patent Document 2). However, while this method can reduce stress concentration at the bonded edges, it does not achieve high adhesive strength and often reduces the rigidity of the joint, making it unsuitable for structural bonding.

[0004] Because epoxy adhesives are brittle, the addition of modifiers and control of the crosslink density of the cured product have been widely investigated. For example, as in Patent Document 1, attempts have been made to improve toughness by incorporating rubber components such as CTBN (carboxyl-containing butadiene-acrylonitrile liquid rubber) to introduce flexible chains into the resulting cured product, but the effect is still insufficient.

[0005] Japanese Patent Application Publication No. 5-148337

[0006] Sato, C., Network Polymer Journal, 2018, Vol. 39, No. 4, pp. 91-96; Arai, Y., Journal of the Japan Welding Society, 2006, Vol. 75, No. 5, pp. 330-332

[0007] There is a demand for adhesives that combine high tensile shear bond strength with tenacity (toughness). When designing joints, calculating the amount of adhesive needed in the tensile direction based on the bond strength per unit area makes structural design easier. However, in reality, stress concentrations at the bonded edge become the starting point for fracture, and increasing the adhesive lap length (overlap length) to increase the applied area does not result in the expected increase in bond strength. Therefore, there is a need for adhesives that maintain high bond strength and adhesive performance even with increased lap length. Furthermore, in the construction and civil engineering fields, where on-site heating is difficult, there is a demand for adhesives that cure quickly at room temperature (25°C ± 5°C).

[0008] An object of the present invention is to provide an adhesive composition that has high adhesive strength and can maintain its adhesive performance even when the lap length is increased.

[0009] The inventors have conducted extensive research to solve the above problems, and as a result have found that an adhesive having a constant fracture energy is an adhesive composition that is excellent in tensile shear bond strength and T-peel bond strength, has high bond strength at the joint, and can maintain adhesive performance even with an increase in lap length, and have completed the present invention. That is, the present invention relates to an adhesive composition that has a fracture energy per unit area of ​​0.035 J / mm when the fracture region is the adhesive layer in a tensile shear adhesion test. ２ The present invention provides an adhesive composition characterized by the above-mentioned properties and members bonded using the adhesive composition.

[0010] [Item 1] In a tensile shear adhesion test, when the fracture site is the adhesive layer, the fracture energy per adhesive unit area is 0.035 J / mm ２ [Item 2] The adhesive composition has a tensile shear adhesive strength of 20 N / mm or more. ２Item 1, wherein the adhesive composition has a tensile shear strength of 20 N / mm or more and / or a T-peel adhesive strength of 8 N / mm or more. [Item 3] The adhesive composition of item 1 or 2, wherein the adhesive composition is room temperature curable. [Item 4] The adhesive composition of any one of items 1 to 3, wherein the adhesive composition is an acrylic adhesive composition. [Item 5] The adhesive composition of any one of items 1 to 4, wherein the adhesive composition is an acrylic adhesive composition containing, as essential components, (A) an oligomer having a terminal (meth)acrylate group and having a weight average molecular weight of 2,000 or more, (B) a polymerizable vinyl monomer, (C) an organic peroxide, and (D) a reducing agent. [Item 6] The adhesive composition of any one of items 1 to 4, wherein the adhesive composition has a tensile shear adhesive strength of 20 N / mm or more and / or a T-peel adhesive strength of 8 N / mm or more. ２ A room temperature curable adhesive composition having a T-peel adhesive strength of 8 N / mm or more and a T-peel adhesive strength of 8 N / mm or more. [Item 7] The adhesive composition according to Item 6, wherein the adhesive composition is an acrylic adhesive composition. [Item 8] The adhesive composition according to Item 6 or 7, wherein the adhesive composition is an acrylic adhesive composition comprising, as essential components, (A) an oligomer having a terminal (meth)acrylate group and having a weight average molecular weight of 2,000 or more, (B) a polymerizable vinyl monomer, (C) an organic peroxide, and (D) a reducing agent. [Item 9] A member bonded with the adhesive composition according to any one of Items 1 to 8. [Item 10] A member characterized in that at least one of the adherends bonded with the adhesive composition according to any one of Items 1 to 8 is a steel material. [Item 11] A member characterized in that the adherends bonded with the adhesive composition according to any one of Items 1 to 8 are steel materials.

[0011] The present invention provides an adhesive composition that has high adhesive strength and can maintain its adhesive performance even when the lap length is increased, and that is excellent in adhesive strength and adhesive reliability.

[0012] Test force (N)-displacement (mm) curves for Example 1 and Comparative Example 9.

[0013] The adhesive composition of the present invention and members bonded with the adhesive composition will be described below. In the present invention, "(meth)acrylic" means "acrylic" and "methacrylic", "(meth)acrylate" means "acrylate" and "methacrylate", and "(meth)acryloyl" means "acryloyl" and "methacryloyl", respectively.

[0014] [Tensile Shear Adhesion Test] The tensile shear adhesion test of the present invention can be any test that can measure the load value and displacement when a load (force) is applied to the bonded portion in the shear direction. Measurements may be performed according to various standards and specifications, such as JIS, ISO, and ASTM. Alternatively, the adherends, test equipment, loading method and speed, and measurement methods for the load value and displacement of the test specimen may be arbitrarily set depending on the actual bonded portion. In the tensile shear adhesion test, the fracture energy of the adhesive bond is calculated as the integral (work load) of the force relative to the movement during the dissociation process of the bonded surface, i.e., the area under the force-displacement curve (Patent Publication No. 2011-526947, paragraph 0056). By dividing the fracture energy obtained by this by the applied area of ​​the adhesive, the fracture energy per unit area of ​​adhesion can be determined when the fractured portion is the adhesive layer in the tensile shear adhesion test.

[0015] As a general method for the tensile shear adhesion test, it is preferable to measure in accordance with standards such as JIS K 6850 Test method for tensile shear bond strength between adhesive and rigid adherend, ASTM D1002 Lap shear strength test of adhesive amount, ISO 4587 Tensile shear strength of adhesive-rigid material combination bond, etc. Among these, it is more preferable to measure in accordance with JIS K 6850:1999 Test method for tensile shear bond strength between adhesive and rigid adherend.

[0016] In tensile shear adhesion tests, if the strength of the adherend is significantly lower than the adhesive strength, the adherend itself may break. In that case, the fracture energy of the adherend itself is being measured. If the strength of the adherend is insufficient, measures such as increasing the thickness of the adherend or reducing the adhesive application area must be taken to conduct the test under conditions where the fracture occurs in the adhesive layer (conditions that lead to fracture in the adhesive), in order to determine the fracture energy of the joint.

[0017] The greater the fracture energy per unit area of ​​adhesion, the greater the energy required to fracture the bonded portion, resulting in increased fracture resistance and superior adhesive reliability. The fracture energy per unit area of ​​adhesion was 0.035 J / mm ２ It is preferable that the saturation voltage is 0.040 J / mm or more. ２ More preferably, it is 0.050 J / mm or more. ２ More preferably, it is equal to or greater than this.

[0018] Examples of adherends used in the test include metal materials such as aluminum, iron, titanium, and stainless steel, various resins, resin materials such as carbon fiber reinforced plastics, wood, various ceramics, etc. The adherends used may be the same material or different materials.

[0019] When measuring according to JIS K 6850, the size of the adherend is generally as specified in JIS K 6850:1999, and a test piece 100 mm long and 25 mm wide is used. The thickness of the adherend is preferably 1 to 3 mm, depending on the type of adherend. In accordance with JIS K 6850:1999, 1.6 mm is more preferable for metals. As the adherend, cold-rolled steel plate (SPCC) measuring 1.6 mm x 25 mm x 100 mm is preferably used because it is inexpensive and easily available. Since the typical adhesive application thickness specified in JIS K 6850:1999 is 0.2 mm, it is preferable for the thickness to be around this range. In practice, 0.1 mm to 0.3 mm is preferred, and 0.15 mm to 0.25 mm is more preferred, but this is not necessarily the case as long as sufficient fracture energy per unit area is exhibited. The overlapping portion of the adhesive is preferably 12.0 mm to 13.0 mm, and more preferably 12.25 mm to 12.75 mm.

[0020] Since fracture energy is expressed as force × displacement, it is preferable that either force ≒ adhesive strength or displacement ≒ displacement, or both, are large. It is preferable that the joint has a larger adhesive strength or has excellent displacement followability and fractures ductilely. The displacement of the joint may be measured by attaching a displacement meter directly to the members, or may be measured by an optical method such as a laser. For convenience, the crosshead displacement of the measuring device may be used.

[0021] When the adhesive composition of the present invention is used as a structural adhesive composition, it is necessary to "withstand a large load." Therefore, the adhesive composition should have a tensile shear adhesive strength of 20 N / mm ２ and / or T-peel adhesive strength is preferably 8 N / mm or more. ２ More preferably, 30 N / mm ２ The T-peel adhesive strength is more preferably 10 N / mm or more.

[0022] [Curing at Room Temperature] The room temperature curable adhesive composition of the present invention cures within one week at room temperature (25°C ± 5°C) and has a viscosity of 1 N / mm ２ Preferably, the adhesive exhibits a tensile shear adhesive strength of 1 N / mm or more after 3 days at room temperature (25°C ± 5°C). ２ More preferably, the adhesive strength is 1 N / mm or more after 24 hours. ２ More preferably, the adhesive strength is 10 N / mm after 24 hours. ２ When the adhesive composition of the present invention does not exhibit an adequate curing rate when cured at room temperature, it may be heated using a heating device or equipment such as a heater, a dryer, a burner, infrared heating, high-frequency heating, induction heating, or a drying furnace in order to accelerate curing.

[0023] [Adhesive Composition] The adhesive of the present invention is not particularly limited as long as it has a predetermined fracture energy, and can be appropriately selected depending on the application. Examples include epoxy-based adhesives, urethane-based adhesives, and acrylic-based adhesives. Among these, acrylic adhesives are preferred in terms of curing speed, workability, and heat resistance. Second-generation acrylic adhesives (SGA) are even more preferred because they have high adhesive strength, do not require precise blending of two components, can cure even with incomplete blending or mixing, and have excellent workability. SGA is an adhesive that cures by a polymerization reaction caused by the action of an organic peroxide and a reducing agent.

[0024] Furthermore, it is preferable that the adhesive composition be an acrylic adhesive containing, as essential components, (A) an oligomer having a terminal (meth)acrylate group and a weight average molecular weight of 2,000 or more, (B) a polymerizable vinyl monomer, (C) an organic peroxide, and (D) a reducing agent, because this has excellent fracture energy.

[0025] (A) Oligomers Having Terminal (Meth)acrylate Groups and a Weight-Average Molecular Weight of 2,000 or More The (A) oligomers having terminal (meth)acrylate groups and a weight-average molecular weight of 2,000 or more are reactive oligomers in which (meth)acrylate groups are introduced to the molecular terminals of oligomers having a weight-average molecular weight of 2,000 or more via urethane bonds, urea bonds, ester bonds, etc., and the main chains of the oligomers include polyether-based, polyester-based, polycarbonate-based, polyamide-based, epoxy-based, saturated or unsaturated hydrocarbon-based, vinyl chloride-based, and other oligomers. Among these, polyether-based, polyester-based, and polycarbonate-based oligomers are preferred because they are easily available and can be easily mixed with (B) polymerizable vinyl monomers. Polyether-based oligomers are more preferred because the resulting adhesive compositions have low viscosity and excellent workability. Among polyether-based oligomers, polytetramethylene glycol-based oligomers are more preferred because they have excellent heat resistance and water resistance.

[0026] If the weight-average molecular weight is less than 2,000, the ductility of the cured product of the adhesive composition will be poor, and sufficient fracture energy will not be obtained. (A) The oligomer having a weight-average molecular weight of 2,000 or more and having a (meth)acrylate group at its terminal is not particularly limited, as long as the weight-average molecular weight is 2,000 or more. Since the adhesive composition obtained will have excellent adhesive strength, the weight-average molecular weight is preferably 5,000 or more, more preferably 10,000 or more. However, since the adhesive composition may have a high viscosity and poor workability, the weight-average molecular weight is, for example, 100,000 or less, preferably 50,000 or less.

[0027] (A) The oligomer having a weight-average molecular weight of 2,000 or more and having (meth)acrylate group at its end is generally commercially available as urethane (meth)acrylate, and can be easily obtained.The example of commercially available urethane (meth)acrylate can be listed as the urethane (meth)acrylate manufactured by Kyoeisha Chemical Co., Ltd., the urethane (meth)acrylate manufactured by Shin-Nakamura Chemical Co., Ltd., the urethane (meth)acrylate manufactured by Taisei Fine Chemical Co., Ltd., the urethane (meth)acrylate manufactured by Daiichi Kogyo Seiyaku Co., Ltd., the urethane (meth)acrylate manufactured by Arkema, the urethane (meth)acrylate manufactured by Resonac Co., Ltd., the urethane (meth)acrylate manufactured by Daicel Allnex Co., Ltd., the urethane (meth)acrylate manufactured by Negami Chemical Industrial Co., Ltd., the urethane (meth)acrylate manufactured by Mitsubishi Chemical Corporation, and the urethane (meth)acrylate manufactured by DIC Corporation, and these products can also be used.

[0028] <(B) Polymerizable Vinyl Monomer> As the (B) polymerizable vinyl monomer, various polymerizable vinyl monomers can be used without particular limitation. Specifically, various polymerizable vinyl monomers capable of radical polymerization can be used. Examples of polymerizable vinyl monomers include (meth)acrylic acid esters, styrene, α-alkylstyrene, divinylbenzene, vinyl ether, divinyl ether, maleic anhydride, maleic acid esters, maleimide compounds, vinyl acetate, diallyl phthalate, diallyl fumarate, triallyl isocyanurate, vinylbenzyl butyl ether, vinylbenzyl hexyl ether, divinylbenzyl ether, allyl (meth)acrylate, acrylamide compounds, N-vinylpyrrolidone, 2-vinylpyridine, vinyl acetate, and vinyl propionate. Specific examples of these polymerizable vinyl monomers include those described in paragraphs 0026 to 0027 of JP 2018-188602 A and paragraphs 0016 to 0025 of WO 2022 / 249965 A. Among these, (meth)acrylic acid esters and acrylamide compounds are preferred from the viewpoint of good reactivity.

[0029] It is preferable to use a (meth)acrylic acid ester or acrylamide compound having a hydroxyl group, an alicyclic alkyl group, or an aromatic alkyl group as the polymerizable vinyl monomer (B) because the cured adhesive has high heat resistance and excellent adhesive strength. Also, from the viewpoint of availability, methyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, isobornyl (meth)acrylate, and acryloylmorpholine are preferable.

[0030] The blending amount of the polymerizable vinyl monomer (B) is not particularly limited. When the total amount of the components (A) and (B) is 100 parts by weight, the blending amount is preferably 40 to 95 parts by weight, and more preferably 50 to 90 parts by weight. If the blending amount of the polymerizable vinyl monomer is less than 40 parts by weight, the viscosity of the adhesive increases, which tends to deteriorate workability and may also reduce adhesion.

[0031] Furthermore, it is preferable to include methacrylic acid as the polymerizable vinyl monomer (B), since this provides excellent adhesive strength and also improves heat resistance. The amount of methacrylic acid is not particularly limited. When the total amount of the components (A) and (B) is 100 parts by weight, the amount is preferably 0.1 to 30 parts by weight, and more preferably 5 to 25 parts by weight. If the amount of methacrylic acid exceeds 30 parts by weight, the peel strength of the cured product may decrease.

[0032] Because excellent adhesion and adhesive strength to metal members are obtained, it is preferable that the polymerizable vinyl monomer (B) contains a (meth)acrylic acid ester containing a phosphate ester group. Specific examples include 2-(meth)acryloyloxyethyl acid phosphate, 2-(meth)acryloyloxypropyl acid phosphate, and bis(2-(meth)acryloyloxyethyl acid)phosphate. The amount of the (meth)acrylic acid ester containing a phosphate ester group is not particularly limited. When the total amount of the components (A) and (B) is 100 parts by weight, the amount is preferably 0.1 to 10 parts by weight, and more preferably 0.3 to 5 parts by weight. If the amount of the (meth)acrylic acid ester containing a phosphate ester group is less than 0.1 part by weight, the improvement in adhesion to metal members may be insufficient, while if the amount exceeds 10 parts by weight, not only is it economically disadvantageous but the storage stability of the adhesive composition may also be reduced.

[0033] <(C) Organic Peroxide> As the (C) organic peroxide, various organic peroxides can be used, such as t-butyl peroxybenzoate, t-butyl peroxydecanoate, cumene hydroperoxide, p-menthane hydroperoxide, t-butyl hydroperoxide, diisopropylbenzene dihydroperoxide, methyl ethyl ketone peroxide, and benzoyl peroxide.

[0034] These organic peroxides can be used alone or in combination of two or more. Among these, hydroperoxides are preferred because they are stable at room temperature (25°C ± 5°C), easy to handle, and easily initiate a reaction at room temperature when used in combination with a reducing agent. Cumene hydroperoxide is particularly preferred because of its excellent stability.

[0035] The amount of the organic peroxide (C) is preferably 0.05 to 10 parts by weight, and more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the total amount of the components (A) and (B). If the amount of the organic peroxide (C) is less than 0.05 parts by weight, the curing rate may decrease, and if it exceeds 10 parts by weight, the storage stability of the adhesive composition may deteriorate.

[0036] <(D) Reducing Agent> As the (D) reducing agent, various compounds that react with an organic peroxide to generate radicals can be used. Examples of the (D) reducing agent include a reaction condensation product of an amine and an aldehyde, triethylamine, tripropylamine, tributylamine, N,N-dimethyl-p-toluidine, 2-mercaptobenzimidazole, methylthiourea, dibutylthiourea, tetramethylthiourea, ethylenethiourea, cobalt compounds such as cobalt octylate, cobalt naphthenate, cobalt acetylacetone, and cobalt acetoacetate ethyl ester, copper compounds such as copper naphthenate and copper versatate, and vanadium compounds.

[0037] Examples of vanadium compounds include vanadyl acetylacetonate, vanadyl stearate, vanadium naphthenate, vanadium acetylacetonate, vanadium benzoylacetonate, etc. Among these, vanadyl acetylacetonate and ethylenethiourea are preferred because of their good reactivity with hydroperoxide.

[0038] These (D) reducing agents can be used alone or in combination of two or more. The amount of the (D) reducing agent is preferably 0.01 to 10 parts by weight, and more preferably 0.04 to 5 parts by weight, relative to 100 parts by weight of the total amount of the (A) component and the (B) component. If the amount of the (D) reducing agent is less than 0.01 part by weight, the curing rate may be slow, and if it exceeds 10 parts by weight, the storage stability may be reduced when the reducing agent is used together with a polymerizable vinyl monomer.

[0039] <(E) Fine Rubber Particles> In addition to the components (A) to (D), the adhesive composition of the present invention may contain (E) fine rubber particles, preferably core-shell rubber particles. The (E) fine rubber particles adjust the viscosity of the adhesive composition, impart thixotropy, and also serve as an impact buffer for the adhesive layer after curing. The (E) fine rubber particles may be either fine particles containing at least rubber, or core-shell rubber particles having a core layer made of rubber and a shell layer further covered with a resin layer.

[0040] (Core-shell Rubber Microparticles) Various core-shell rubber microparticles can be used as the core-shell rubber microparticles. Polymer microparticles can be synthesized by graft polymerizing a graft-copolymerizable monomer component in the presence of a core layer to form a shell layer. Examples of rubbers that can be used for the core layer include, but are not limited to, silicone rubber, butadiene rubber, styrene-butadiene rubber, acrylic rubber, acrylonitrile-butadiene-styrene rubber (ABS), methyl methacrylate-butadiene-styrene rubber (MBS), methyl methacrylate-butadiene rubber (MB), methyl methacrylate-butyl acrylate rubber (MBA), methyl methacrylate-butyl acrylate-styrene rubber (MBAS), and acrylonitrile-butyl acrylate-styrene rubber (AAS). For the shell layer, generally, a (meth)acrylate monomer, an aromatic vinyl monomer, acrylonitrile, or the like is used, but other monomers may also be used. One or more types of rubber for the core layer and monomers for the shell layer may be used depending on the desired properties.

[0041] The amount of (E) rubber fine particles, for example, core-shell rubber fine particles, is not particularly limited and is preferably 2 to 50 parts by weight, more preferably 5 to 30 parts by weight, relative to 100 parts by weight of the total amount of the (A) component and the (B) component.

[0042] <Other Additives> In addition to the components (A) to (E), the adhesive composition of the present invention may further contain various additives ("other additives"). Examples of other additives include one or more selected from the group consisting of elastomers that impart toughness or flexibility to the cured product, thixotropic agents, storage stabilizers (polymerization inhibitors, antioxidants, etc.), epoxy resins, fillers, organic solvents (volatile liquids such as alcohols, esters, and hydrocarbons), flame retardants, anti-sagging agents, anti-precipitation agents, curing accelerators, antioxidants, heat stabilizers, light stabilizers, UV absorbers, fragrances, lubricants (waxes, etc.), antibacterial agents, antifungal agents, leveling agents, colorants, lustrous materials, adhesion promoters, tackifying resins, surface conditioners, surfactants, antifoaming agents, wetting agents, rust inhibitors, chain transfer agents (polythiol compounds, etc.), viscosity modifiers, sensitizers, adhesion improvers (silane coupling agents, etc.), plasticizers, and antistatic agents. The amount of these additives to be added is not particularly limited as long as they do not impair the properties of the adhesive composition, and any amount necessary to impart the desired properties can be used.

[0043] Furthermore, paraffin, beeswax, etc. may be added to improve the curing properties of the air-contacting surface, or various reaction accelerators and regulators may be added to adjust the curing rate. Specific examples of these additives include those described in paragraphs 0041 to 0045 of WO 2022 / 249965.

[0044] <Applications> The adhesive composition of the present invention has excellent bond strength at the joint and excellent fracture toughness, resulting in tenacious and ductile fracture at the final fracture stage of the joint. It has excellent adhesion to various adherends, such as metals, resins, glass, ceramics, fibers, wood, and bamboo, and is particularly reliable when joining metals such as iron and aluminum, wood, concrete, and composite plastics such as CFRP, GFRP, and FRP. The adhesive composition of the present invention can be used in a variety of fields, including various electrical and electronic applications, automobiles, airplanes, ships, motorcycles, trains, machinery, buildings, civil engineering, office supplies, and household goods. In particular, it can be suitably used as a structural adhesive for civil engineering, construction, and automobiles, as a "reliable adhesive that can withstand heavy loads for long periods of time."

[0045] [Members] Various members are provided as members bonded with the adhesive composition of the present invention. Examples include members in which adherends are bonded with the adhesive composition of the present invention. In particular, due to the excellent fracture toughness of the bonded joint, it is preferable that at least one of the adherends is a steel material, and it is even more preferable that the adherends are both steel materials. Various structural steel materials such as SS material, SN material, SM material, and S-C material are used as the steel material. The bonded joint may use only the adhesive composition of the present invention, or may be used in combination with other bonding members such as bolts, high-strength bolts, or welds. Temporary fixation using a vice, clamp, clip, magnet, or the like may also be used in combination.

[0046] The following examples will be used to provide a more detailed explanation. It should be noted that these examples are merely illustrative and should not be construed as limiting. Unless otherwise specified, "%" means "% by weight" and "parts" means "parts by weight."

[0047] [Measurement Method] <Weight Average Molecular Weight> The weight average molecular weight of the urethane (meth)acrylate compound was measured using a high-speed GPC device (HLC-8320GPC manufactured by Tosoh Corporation).

[0048] <Tensile Testing Apparatus> The following tensile tests were performed using a Shimadzu Corporation precision universal testing machine, Autograph AGX-V 100kN, and data processing was performed using a Shimadzu Corporation TRAPEZIUMX-V. <Tensile Shear Adhesion Strength> Unless otherwise specified, tensile shear adhesion strength was measured in accordance with JIS K 6850:1999, Adhesives - Rigid Adherends, using a cold-rolled steel plate (SPCC) measuring 25mm wide x 100mm long x 1.6mm thick as the adherend. The adherend was surface-polished by sandblasting and then surface-treated with acetone. The mixed adhesive composition was uniformly applied to a 25mm wide x 12.5mm long x 0.2mm thick specimen, which was then bonded to another SPCC steel plate to prepare a test specimen. The specimen was then clamped using small eye clips and aged for at least one day at 23°C. According to JIS K 6850, the tensile shear adhesive strength was measured at 23°C and a pulling speed of 2.5 mm / min. The work load (J) required for fracture was calculated from the obtained test force (N)-displacement (mm) curve, and the adhesive area (312.5 mm ２ ) to determine the fracture energy per unit area of ​​the joint.

[0049] <T-peel adhesive strength> Two SPCC steel plates (25 mm wide x 150 mm long x 0.5 mm thick) were prepared, the surfaces of which had been polished by sandblasting and then treated with acetone. The mixed adhesive composition was uniformly applied to one of the plates, and then the plate was bonded to the other SPCC steel plate to prepare a test specimen. The thickness of the adhesive layer was adjusted to 0.2 mm. The specimen was aged for at least one day in an environment of 23°C while clamped using small eye clips, and the T-peel adhesive strength was measured at 23°C and a tensile speed of 50 mm / min in accordance with JIS K 6854.

[0050] <Tensile shear test with a lap length of 30 mm> In the same manner as in the method for measuring tensile shear adhesive strength, a cold-rolled steel plate (SPCC) with a width of 25 mm, a length of 100 mm, and a thickness of 1.6 mm was used as the adherend, and the adhesive composition was uniformly applied to an area of ​​25 mm in width, 30 mm in length, and 0.2 mm in thickness. After curing and curing, a tensile shear test was carried out at 23°C and a pulling rate of 100 mm / min, and the state of failure of the test specimen was evaluated.

[0051] [Synthesis Examples] <Synthesis Example 1> (Synthesis of urethane methacrylate compound UA1 having a terminal methacrylate group) 51.6 mmol of polytetramethylene glycol having a molecular weight of 2,900 as a polyol compound was weighed into a 500 mL four-neck separable flask equipped with a stirrer, thermometer, and condenser, and stirred under high vacuum at 120°C for 3 hours to remove moisture contained in the polyol. After cooling the system to room temperature, 150 g of toluene, 19.6 mmol of hexamethylene diisocyanate as a polyisocyanate compound, and 100 ppm of tin catalyst relative to the polyol compound were added under a nitrogen stream. A reaction was carried out for 3 hours at 80°C under a nitrogen stream to synthesize a urethane prepolymer. The temperature of the reaction solution was cooled to below 50°C, and 96.7 mmol of 2-methacryloyloxyethyl isocyanate was added as a terminal (meth)acrylate agent, and the reaction was carried out for 2 hours at 80°C. The solvent and excess 2-methacryloyloxyethyl isocyanate were removed by distillation under reduced pressure to obtain a urethane methacrylate compound UA1, which had a weight average molecular weight of 14,800.

[0052] Synthesis Example 2 Synthesis of urethane methacrylate compound UA2 having a methacrylate group at a terminal Except for using diphenylmethane diisocyanate as the polyisocyanate compound, a urethane methacrylate compound UA2 was obtained in the same manner as in Synthesis Example 1. The weight average molecular weight of the obtained compound UA2 was 15,500.

[0053] Synthesis Example 3 Synthesis of urethane methacrylate compound UA3 having a methacrylate group at its terminal A urethane methacrylate compound UA3 was obtained in the same manner as in Synthesis Example 1, except that a terminal isocyanate prepolymer was synthesized using 83.6 mmol of hexamethylene diisocyanate as the polyisocyanate compound, and then 96.0 mmol of 2-hydroxypropyl methacrylate was added as a terminal (meth)acrylate agent. The weight-average molecular weight of the obtained compound UA3 was 31,100.

[0054] Synthesis Example 4 Synthesis of urethane methacrylate compound UA4 having a methacrylate group at its terminal Except for using 72.9 mmol of polytetramethylene glycol having a molecular weight of 650 as the polyol compound and 168 mmol of 2-methacryloyloxyethyl isocyanate as the isocyanate compound, urethane methacrylate compound UA4 was obtained in the same manner as in Synthesis Example 1. The weight average molecular weight of the obtained compound UA4 was 1,700.

[0055] [Other components of the adhesive composition] UV-6640B: Shikoh UV-6640B, manufactured by Mitsubishi Chemical Corporation, urethane acrylate, Mw=5,000 UV-3000B: Shikoh UV-3000B, manufactured by Mitsubishi Chemical Corporation, urethane acrylate, Mw=18,000 IBXMA: Light Ester IB-X (isobornyl methacrylate), manufactured by Kyoeisha Chemical Co., Ltd. MA: Methacrylic acid, manufactured by Mitsubishi Chemical Corporation HPMA: Light Ester HOP (2-hydroxypropyl methacrylate), manufactured by Kyoeisha Chemical Co., Ltd. PM1: Light Ester P-1M (2-ethyl methacrylic acid phosphate (phosphate group-containing methacrylic monomer)), manufactured by Kyoeisha Chemical Co., Ltd.

[0056] CHP: Percumyl H80 (cumene hydroperoxide), manufactured by NOF Corporation Kane Ace M521: Methyl methacrylate-butadiene-styrene copolymer resin (core-shell rubber fine particles), manufactured by Kaneka Corporation Paraffin Wax 115: Waxy wax, manufactured by Nippon Seiro Co., Ltd. Paraffin Wax 125: Waxy wax, manufactured by Nippon Seiro Co., Ltd. EDTA: Chelest 400 (ethylenediaminetetraacetic acid sodium tetrahydrate), manufactured by Chelest Corporation Narcem Vanadyl: Vanadyl acetylacetone complex, manufactured by Nippon Chemical Industries Co., Ltd. Malic acid: Reagent, manufactured by Tokyo Chemical Industry Co., Ltd. Benzoquinone: Reagent, manufactured by Tokyo Chemical Industry Co., Ltd. Hydroquinone: Reagent, manufactured by Tokyo Chemical Industry Co., Ltd. AO-60: Hindered phenol antioxidant, manufactured by ADEKA Corporation QS20: Reolosil QS20 (hydrophilic silica), manufactured by Tokuyama Corporation NN#500: Heavy calcium carbonate manufactured by Nitto Funka Kogyo Co., Ltd.

[0057] [Commercially available products used in comparative examples] Adhesive A: Bond E258R (manufactured by Konishi Corporation, heat-resistant two-component epoxy resin adhesive for steel structures) Adhesive B: Bolt Lock 1 (manufactured by Denka Corporation, two-component acrylic adhesive for steel plates) Adhesive C: Scotch Weld Metal Grip (manufactured by 3M Japan, two-component acrylic adhesive for structure) Adhesive D: Scotch Weld DP6330NS (manufactured by 3M Japan, two-component urethane adhesive for structure) Adhesive E: Metal Lock Y612 BLACK (manufactured by Cemedine, two-component acrylic adhesive for structure) Adhesive F: Metal Lock Y618LD (manufactured by Cemedine, flexible two-component acrylic adhesive for structure) Adhesive G: Metal Lock Y630D (manufactured by Cemedine, two-component acrylic adhesive for structure)

[0058] Example 1 The following raw materials were used to prepare a two-component acrylic adhesive. (A) 30 parts by weight of urethane methacrylate compound UA1 was used in both Agents A and B. (B) 35 parts by weight of isobornyl methacrylate, 35 parts by weight of 2-hydroxypropyl methacrylate, 18 parts by weight of methacrylic acid, and 1.5 parts by weight of 2-ethyl methacrylic acid phosphate were used in both Agents A and B. (C) 0.4 parts by weight of CHP (cumene hydroperoxide) was used in Agent A. (D) 0.4 parts by weight of nursem vanadyl was used in Agent B. (E) 12 parts by weight of Kane Ace M521 was used as the rubber microparticles in both Agents A and B. As other additives, 3 parts by weight of QS20 was used in both Agents A and B, and 0.1 parts by weight of malic acid was used in Agent A.

[0059] The raw materials were thoroughly mixed and stirred to prepare two-component acrylic adhesives, Parts A and B (Adhesive X). Parts A and B were filled into a two-component cartridge at a ratio of 1:1, and the mixture was mixed using a static mixer at the tip and discharged. Tensile shear bond strength and T-peel bond strength were measured, and a tensile shear test was conducted with a lap length of 30 mm. The results are shown in Table 1.

[0060] [Examples 2 to 7] Two-component acrylic adhesives, components A and B, were prepared by adding the raw materials in the proportions shown in Table 1 and thoroughly mixing and stirring. Tensile shear bond strength and T-peel bond strength were measured in the same manner as in Example 1, and a tensile shear test with a lap length of 30 mm was conducted. The results are shown in Table 1.

[0061]

[0062] [Comparative Examples 1 to 4] Two-component acrylic adhesives, components A and B, were prepared by adding the raw materials in the proportions shown in Table 2 and thoroughly mixing and stirring. Tensile shear adhesive strength and T-peel adhesive strength were measured in the same manner as in Example 1, and a tensile shear test with a lap length of 30 mm was conducted. The results are shown in Table 2.

[0063]

[0064] Comparative Examples 5 to 11 Using the commercially available room-temperature curing structural adhesives shown in Table 3, the tensile shear bond strength and T-peel bond strength were measured and a tensile shear test with a lap length of 30 mm was carried out in the same manner as in Example 1. The results are shown in Table 3.

[0065]

[0066] As is clear from Examples 1 to 7, the fracture energy per unit area is 0.035 J / mm ２ If the lap length is increased to 30 mm, the 1.6 mm steel plate (SPCC) will break, demonstrating that this adhesive is a tenacious and highly reliable adhesive that can follow the extension of the steel plate. On the other hand, if the fracture energy per unit area is 0.035 J / mm ２ When the lap length was less than 30 mm, the adhesive layer broke before the 1.6 mm steel plate (SPCC) broke when the lap length was increased to 30 mm. Even when the tensile shear adhesive strength was almost the same (for example, Example 1 and Comparative Example 1), differences in the state of failure were observed when the lap length was 30 mm depending on the magnitude of the fracture energy. The tensile strength of a 1.6 mm SPCC steel plate (25 mm wide) was 14 to 15 kN, and when bonded with a lap length of 30 mm, the tensile strength was 20 N / mm ２ If the tensile shear adhesive strength is equal to or greater than 20 N / mm２ x 25 mm x 30 mm = 15 kN) exceeds the strength of the steel plate, and one would expect the steel plate to break, but in reality, stress concentrates at the adhesive end, or the steel plate deforms and a force other than shear force (peel force) is applied, and an adhesive with small fracture energy breaks or peels off while the steel plate is being stretched.

[0067] Existing structural adhesives generally available on the market (Comparative Examples 5 to 11) all had poor fracture energy, and even adhesives with high adhesive strength (Adhesives A, E, and G) were unable to maintain adhesive performance and fractured in a 30 mm lap length tensile test. Furthermore, adhesives with excellent ductility (Adhesives B, C, D, and F) had relatively high T-peel adhesive strength, but were unable to maintain adhesive performance and fractured in a 30 mm tensile test. Figure 1 shows the test force-displacement curves for Example 1 and Comparative Example 9 as representative examples. The area below the solid and dashed lines represents the fracture energy.

[0068] [Example 8] Using adhesive X of Example 1, tensile shear bond strength was measured on 1.5 mm thick SUS304 plates and 3 mm thick aluminum alloy plates (A7075P) as adherends in the same manner as in Example 1, except that the surfaces of the adherends were polished with #120 sandpaper. As a result, the tensile shear bond strength for SUS304 was 31.7 N / mm ２ , fracture energy is 0.044 J / mm ２ In the case of aluminum alloy plates, the tensile shear adhesive strength was 32.3 N / mm ２ , fracture energy is 0.036 J / mm ２ It was.

[0069] [Example 9] Using adhesive X of Example 1, the tensile shear bond strength was measured in the same manner as in Example 1, except that a 1.6 mm thick SPCC plate and a 3 mm thick aluminum alloy plate (A7075P) were used as adherends, the adhesive was applied to a thickness of 1 mm, and the surface of the aluminum alloy plate was polished with #120 sandpaper. As a result, the tensile shear bond strength of the SPCC was 24.1 N / mm ２ , fracture energy is 0.043 J / mm ２ In the case of aluminum alloy plates, the tensile shear adhesive strength was 28.2 N / mm ２, fracture energy is 0.060 J / mm ２ It was.

[0070] [Example 10] Using adhesive X of Example 1, the tensile shear bond strength was measured in the same manner as in Example 1, except that a 4.5 mm thick steel plate (SS400) was used as the adherend. The results for the adhesive lap length, coating thickness, tensile shear bond strength, and fracture energy are shown in Table 4.

[0071]

[0072] Comparative Examples 12 to 14 Using Adhesives A, B, and F and a 4.5 mm thick steel plate (SS400) as the adherend, the tensile shear bond strengths at lap lengths of 12.5 mm and 40 mm and their ratio (tensile shear bond strength at lap length 40 mm / tensile shear bond strength at lap length 12.5 mm) were determined as the adhesive strength retention rate (%). The results are shown in Table 5. In Example 10, a 4.5 mm thick steel plate (SS400) was used as the adherend, and the tensile shear bond strengths at lap lengths of 12.5 mm and 40 mm and their ratio (tensile shear bond strength at lap length 40 mm / tensile shear bond strength at lap length 12.5 mm) were determined as the adhesive strength retention rate (%). The results are also shown in Table 5. It is clear that with conventional adhesives, when the lap length is increased, a high adhesive strength retention rate is only achieved when the adhesive strength is low, and Example 10 is the only adhesive that can achieve both high adhesive strength and high adhesive strength retention rate.

[0073]

[0074] [Example 11] Using adhesive X of Example 1, the tensile shear bond strength was measured in the same manner as in Example 1, except that the test was conducted at tensile speeds of 25 mm / min and 250 mm / min. As a result, at a tensile speed of 25 mm / min, the tensile shear bond strength was 33.0 N / mm ２ , fracture energy is 0.112 J / mm ２ When the tensile speed was 250 mm / min, the tensile shear adhesive strength was 35.9 N / mm ２ , fracture energy is 0.112 J / mm ２ In the case of aluminum alloy plates, the tensile shear adhesive strength was 28.2 N / mm２ , fracture energy is 0.147 J / mm ２ It was.

[0075] [Example 12] The tensile shear bond strength was measured in the same manner as in Example 1, except that 30 parts by weight of the urethane methacrylate compound UA1 was used in both Agents A and B as the component (A) and 0.5 parts by weight of nursem vanadyl was used in Agent B as the component (D). The tensile shear bond strength was 30.7 N / mm ２ , fracture energy is 0.095 J / mm ２ It was.

[0076] [Example 13, Comparative Examples 15 to 17] The adhesive composition used in Example 5 (adhesive Y) was used as Example 13, and adhesives A, B, and E were used as Comparative Examples 15, 16, and 17. A tensile shear bond strength test was carried out at a tensile speed of 200 mm / min using a steel plate (SS400) measuring 40 mm wide x 200 mm long x 3.2 mm thick as the adherend, with a lap length of 100 mm and an adhesive coating thickness of 0.2 mm. As a result, the steel plate broke when adhesive Y was used, but the adhesive itself broke when adhesives A, B, and E were used.

[0077] The adhesive composition of the present invention, which has a certain level of fracture energy, is excellent in tensile shear bond strength and T-peel bond strength, and is an adhesive composition that can maintain adhesive performance even as the lap length increases while maintaining high adhesive strength at the joint. The adhesive composition of the present invention also has excellent adhesion to oily surfaces. Furthermore, it has excellent durability in terms of heat aging resistance, moist heat aging resistance, and hot water aging resistance. At the same time, it provides an adhesive with good impact resistance and high reliability.

Claims

1. In a tensile shear adhesion test, when the fracture site is the adhesive layer, the fracture energy per unit adhesion area is 0.035 J / mm ２ The adhesive composition characterized by the above.

2. The adhesive composition has a tensile shear adhesive strength of 20 N / mm ２ 2. The adhesive composition according to claim 1, wherein the adhesive composition has a T-peel adhesion strength of 8 N / mm or more.

3. The adhesive composition according to claim 1 or 2, which is curable at room temperature.

4. The adhesive composition according to claim 1 or 2, wherein the adhesive composition is an acrylic adhesive composition.

5. The adhesive composition according to claim 1 or 2, which is an acrylic adhesive composition comprising, as essential components, (A) an oligomer having a terminal (meth)acrylate group and a weight average molecular weight of 2,000 or more, (B) a polymerizable vinyl monomer, (C) an organic peroxide, and (D) a reducing agent.

6. Tensile shear adhesive strength of 20N / mm ２ and a T-peel adhesive strength of 8 N / mm or more.

7. The adhesive composition of claim 6, wherein the adhesive composition is an acrylic adhesive composition.

8. The adhesive composition according to claim 6 or 7, which is an acrylic adhesive composition comprising as essential components: (A) an oligomer having a terminal (meth)acrylate group and a weight average molecular weight of 2,000 or more; (B) a polymerizable vinyl monomer; (C) an organic peroxide; and (D) a reducing agent.

9. A member bonded with the adhesive composition according to claim 1 or 6.

10. A member, characterized in that at least one of the adherends bonded with the adhesive composition according to claim 1 or 6 is a steel material.

11. A member characterized in that the adherends joined with the adhesive composition according to claim 1 or 6 are steel materials.

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