Adhesive structure and adhesion method using same

Abstract

An adhesive structure (100) according to the present disclosure comprises: a first matrix adhesive (1) which contains a matrix resin (11) having an acrylic resin as a main component, and thermally expandable microparticles (12) having a foaming initiation temperature of 115°C or higher; and a second matrix adhesive (2) which is provided with the first matrix adhesive (1) and in which the elastic modulus at a temperature below the aforementioned foaming initiation temperature is higher than the elastic modulus of the first matrix adhesive (1).

Description

Adhesion structure and adhesion method using same

[0001] The present disclosure relates to a bonded structure and a bonding method using the same.

[0002] When dismantling a bonded structure and industrially reusing or recycling the adherends, thermal dismantling is practical from the viewpoint of equipment, etc. For thermal dismantling of bonded parts, it is known to use thermally expandable particles, and various forms of this method are being put to practical use.

[0003] In Patent Document 1, adhesives are used with polyurethane, rubber, acrylic resin, and epoxy resin as binders, and thermally expandable microfillers are mixed with thermoplastic resin spheres of approximately 10-100 μm in size that contain liquefied gas. When this is heated with microwaves or the like, the storage modulus of the adhesive binder becomes 5 MPa or less at 90°C to 150°C, and an adhesive structure suitable for dismantling is obtained.

[0004] JP 2008-56843 A

[0005] However, the method described in Patent Document 1 has the problem that it is difficult to ensure the strength of products that may be used in such temperature ranges. Also, when trying to use a product while maintaining the strength and rigidity of the adhesive joint in high temperature ranges, the elastic modulus of the adhesive itself also increases, which causes the adhesive matrix to not soften sufficiently around the temperature when the microparticles expand, making disassembly difficult.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an adhesive structure that can be used in products over a wide temperature range, and an adhesive method using the same, assuming that adhesive joints are dismantled using thermally expandable microparticles.

[0007] The adhesive structure disclosed herein is characterized by comprising: a first matrix adhesive containing a matrix resin primarily composed of an acrylic resin and thermally expandable microparticles having a foaming initiation temperature of 115°C or higher; and a second matrix adhesive having the first matrix adhesive and a higher elastic modulus at temperatures below the foaming initiation temperature than the elastic modulus of the first matrix adhesive.

[0008] The bonding method using an adhesive structure according to the present disclosure is characterized by including the steps of kneading thermally expandable microparticles having a foaming initiation temperature of 115°C or higher into a matrix resin primarily composed of an acrylic resin, followed by curing to form a first matrix adhesive; pulverizing the cured first matrix adhesive; dispersing the pulverized first matrix adhesive in a second matrix adhesive having a higher elastic modulus than the first matrix adhesive at a temperature below the foaming initiation temperature, curing the second matrix adhesive, and bonding objects to each other via the second matrix adhesive in which the pulverized first matrix adhesive has been dispersed.

[0009] The bonding method using the adhesive structure disclosed herein is characterized by including the steps of kneading thermally expandable microparticles having a foaming initiation temperature of 115°C or higher into a matrix resin whose main component is an acrylic resin, forming the resin into a sheet having a plurality of through holes, and curing the resin; sandwiching the hardened first matrix adhesive into the sheet form between a second matrix adhesive having a higher elastic modulus than the first matrix adhesive at temperatures below the foaming initiation temperature, curing the second matrix adhesive, and bonding objects to each other via the second matrix adhesive sandwiched between the first matrix adhesive hardened into the sheet form.

[0010] According to the present disclosure, not only can the range of applications for products be expanded, but also the product can be easily disassembled by heating.

[0011] Figures 1A and 1B are cross-sectional views showing the configuration of the bonded structures of Examples 1 and 2. Figures 2A to 2E are views showing a method for manufacturing the bonded structures of Examples 2 and 4. Figures 3A and 3B are cross-sectional views showing a method for manufacturing the bonded structure of Example 3. Figure 4 is a cross-sectional view showing the adhesive state of the bonded structure of Example 4. Figure 5 is a perspective view showing a refrigerator in which the bonded structure of Example 4 is incorporated. Figure 6 is a view showing a TEM image of a cured product of the first matrix adhesive of Example 1. Figure 7 is a view showing a TEM image of a cured product of the first matrix adhesive of Comparative Example 1.

[0012] Hereinafter, embodiments of the adhesive structure according to the present disclosure will be described. Note that the adherend to be bonded by the adhesive structure according to the embodiment may be any object as long as it can be bonded by the adhesive structure according to the embodiment or a conventional adhesive structure.

[0013] Specifically, the bonded structure according to the embodiment is obtained by curing a mixture of a first matrix adhesive, the main component of which is a second-generation acrylic adhesive having a specific phase structure, and thermally expandable fine particles, and then placing or sandwiching this cured mixture in a second matrix adhesive, which is then cured to obtain a bonded structure.

[0014] The acrylic adhesive that serves as the first matrix adhesive in this embodiment has a phase structure that is prone to exhibiting a decrease in strength when heated to 140 to 200° C. due to the thermal expansion fine particles.

[0015] The thermally expandable microparticles are preferably those that are made by covering hydrocarbon gas with resin coating, and when heated, the resin coating softens and expands.The type of the resin coating can be any, and specifically, can be mentioned the ADVANCEL (registered trademark) EM series manufactured by Sekisui Chemical, the F series or FN series of Matsumoto Microsphere (registered trademark) manufactured by Matsumoto Oil & Fat, the H series or S series of Kureha Microsphere (registered trademark) manufactured by Kureha Chemical, the EXPANCEL (registered trademark) series manufactured by Nippon Phillite, or the M series or H series of Daiform (registered trademark) manufactured by Dainichiseika Chemicals.

[0016] Examples of hydrocarbon gases contained in the resin coating include ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, isooctane, octane, decane, isododecane, dodecane, hexanedecane, etc., or mixtures of two or more of these gases. In addition, isobutane, n-butane, n-pentane, isopentane, n-hexane, isooctane, isododecane, or mixtures thereof are particularly preferred as hydrocarbon gases. The gas encapsulated in the resin coating may be, instead of the bicarbonate-based gas described above, a chlorofluorocarbon such as CClF, CClF, CClF, or CClF-CClF, or a tetraalkylsilane such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, or trimethyl-n-propylsilane, or at least one of these may be mixed with the hydrocarbon-based gas described above. All of the thermally expansive particles may contain the same gas encapsulated in the resin coating, or some of the thermally expansive particles may contain a gas encapsulated in the resin coating that is different from the gas contained in the other thermally expansive particles.

[0017] The particle size of the thermally expandable microparticles is not limited, but from the viewpoint of mixing with the first matrix adhesive, a particle size of about 5 μm to 500 μm is desirable, and a particle size of about 10 μm to 100 μm is particularly desirable. The thermally expandable microparticles must be stable enough to withstand a thermal aging test as a product when the cured product obtained by bonding multiple adherends with the first matrix adhesive is cured.

[0018] The thermally expandable microparticles must expand when the matrix resin of the first matrix adhesive softens. In the present disclosure, thermally expandable microparticles that expand by foaming are used, and the foaming initiation temperature is preferably 115°C or higher, particularly preferably 130°C or higher. The foaming initiation temperature of the thermally expandable microparticles is determined taking into account the target temperature (the temperature at which the product is used) of the product using the adhesive structure of the present disclosure and the temperature of the manufacturing process for the product. The foaming initiation temperature is determined so that the strength of the adhesive structure is maintained at the product's operating temperature. If the degree of expansion of the thermally expandable microparticles is too small, the force exerted by the thermally expandable microparticles that contributes to the disassembly of the adhesive layer is weakened, making it difficult to disassemble the adhesive structure manually. Therefore, the degree of expansion of the thermally expandable microparticles is preferably at least 5 times, particularly preferably at least 20 times, their original size after expansion.

[0019] The thermally expandable particles may be used alone or in combination with a plurality of particles having different foaming initiation temperatures and expansion ratios. The thermally expandable particles may also be used in combination with other thermally expandable particles, such as expandable graphite.

[0020] An elastomer-modified acrylic adhesive is used as the first matrix adhesive for preparing the thermally expandable microparticles and the primary cured product. The thermally expandable microparticles are mixed in a ratio of about 10 to 200 parts by weight per 100 parts by weight of the first matrix adhesive. If the ratio is less than 10 parts, the expansion will not provide sufficient dismantling ability. If the ratio is more than 200 parts, the cured product will be brittle and not have sufficient toughness when mixed, which will result in poor handling when the second matrix adhesive is added and bonded to an adherend. From the standpoint of dismantling ability and handling ability, a blending amount of about 20 to 120 parts is particularly desirable.

[0021] The elastic modulus of the acrylic-based first matrix adhesive must not become too hard as the thermally expandable particles expand. Specifically, the storage modulus or dynamic modulus of the acrylic-based first matrix adhesive is 50 MPa or less just before the temperature at which the thermally expandable particles begin to expand, making it possible to dismantle it. However, to ensure more reliable dismantling, a modulus of 0.5 to 40 MPa is desirable. A modulus of less than 0.5 MPa is not practical for practical use in the case of a material in which a hard matrix is ​​combined with an elastomer, as this reduces strength. The storage modulus here is calculated using a nanoindenter, using an indenter with a tip radius of 50 μm, at a frequency of 10 Hz, and calculated using the Hertz contact equation.

[0022] Examples of monomer components of the acrylic resin used in the first matrix adhesive include (meth)acrylic acid, (meth)acrylic acid alkyl esters, phenoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, dicyclopentenyloxyethyl methacrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, (meth)acrylic acid hydroxyalkyl esters, poly(meth)acrylates of polyhydric alcohols, epoxy (meth)acrylates obtained by addition reaction of (meth)acrylic acid with epoxy resins, urethane (meth)acrylates, polyester (meth)acrylates, di(meth)acrylates of alkylene oxide adducts of bisphenol A, (meth)acrylic acid monomers having a carboxyl group such as (meth)acrylic acid, and (meth)acrylic acid hydroxyalkyl esters.

[0023] Examples of elastomers for imparting flexibility include thermoplastic resins such as polymethyl methacrylate, polyvinyl butyral, acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), methyl methacrylate-butadiene copolymer, methyl methacrylate-butadiene-styrene copolymer (MBS resin), and methyl methacrylate-butadiene-acrylonitrile-styrene copolymer (MBAS resin); unvulcanized rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), nitrile rubber (NBR), acrylic rubber, ethylene-acrylic rubber, and epichlorohydrin rubber; and liquid rubbers such as liquid polybutadiene, (meth)acrylic-modified liquid polybutadiene, and (meth)acrylic-modified acrylonitrile-butadiene liquid rubber.

[0024] Examples of peroxides include benzoyl peroxide, lauroyl peroxide, methyl ethyl ketone peroxide, tert-butyl peroxide, pinene hydroperoxide, palamenthane peroxide, diisopropyl peroxide, and cumene hydroperoxide.

[0025] Materials that can be reacted with peroxides to cause a redox reaction include metal complexes such as vanadyl acetylacetonate and thiourea compounds.

[0026] Examples of materials that can improve the stability of the adhesive include the addition of a radical polymerization inhibitor such as hydroquinone, methoxyhydroquinone, methylhydroquinone, 1,4-benzoquinone, 1,4-naphthoquinone, 2,6-di-t-butyl-4-methylphenol, or 2,2-methylenebis(4-methyl-6-t-butylphenol).

[0027] As other additives, paraffin may be blended to improve the curing properties of the surface that comes into contact with air, and a silane coupling agent such as vinyltris(2-methoxyethoxy)silane, or a phosphoric acid compound such as 2-methacryloyloxyethyl phosphate or bis(2-methacryloyloxyethyl)phosphate may be added to improve adhesion.

[0028] The second matrix adhesive may be any adhesive such as an epoxy-based, acrylic-based, urethane-based, polyimide-based, cyanoacrylate-based, modified silicone, hot melt-based, or a hybrid of these.

[0029] The adhesive structure of the present disclosure is particularly useful in adhesives that are difficult to dismantle simply by adding thermally-expandable microparticles. Specifically, it is particularly effective for materials in which the modulus of elasticity of the second matrix adhesive exceeds 40 MPa, particularly 100 MPa, in the temperature range corresponding to the foaming initiation temperature of the thermally-expandable microparticles. A specific example of the foaming initiation temperature of the thermally-expandable microparticles is approximately 115°C to 140°C, and it is preferable to use a second matrix adhesive whose modulus of elasticity exceeds 100 MPa in this temperature range. The modulus of elasticity of the second matrix adhesive is preferably higher than that of the first matrix adhesive below the foaming initiation temperature of the thermally-expandable microparticles. The foaming initiation temperature range of the thermally-expandable microparticles may include a temperature slightly above the foaming initiation temperature.

[0030] Since an acrylic material is used for the first matrix adhesive, the second matrix adhesive may be any type that has good adhesion to the cured acrylic adhesive. An acrylic adhesive of the same type is preferred.

[0031] Any method can be used to mix the first matrix adhesive and the thermally expandable microparticles. If the amount used is not large, manual mixing is also possible. For individual batch methods, a kneader, heat kneader, Banbury mixer, kneader, etc. can be used. For continuous processing, a rudder, extruder, twin-axis tapered screw, etc. can be used. Any method can be used for crushing, pulverizing, or pulverizing, including a mill, crusher, and freeze-pulverizing. Grinding can also be performed using a method such as an agate mortar and pestle, or a stamp mill.

[0032] When the kneaded material of the first matrix adhesive and the thermally expandable microparticles is formed into a sheet, it can be compressed in contact with a releasable material such as a fluororesin so that it can be released after hardening. The releasable material can be not only a fluororesin, but also a metal or resin with a non-adhesive coating such as Teflon (registered trademark), or a surface treatment that imparts releasability to the surface. When perforating the sheet, an embossed, debossed, punched, or mesh-like material can be used.

[0033] The pressure may be applied by any method, such as vacuum pressing, press molding, air pressure molding, or rolling. A vice, weight, clamp, hand vice, or the like may also be used.

[0034] Since the sheet-shaped molded product will then be bonded with the second matrix adhesive, it is necessary to avoid using a jig containing a release agent to form the sheet, in order to avoid adverse effects.

[0035] Furthermore, the cured product obtained by kneading the first matrix adhesive and the thermally expandable fine particles, whether in sheet or powder form, may be subjected to a treatment to improve the adhesiveness of the surfaces of the first matrix adhesive and the thermally expandable fine particles before being combined with the second matrix adhesive. Specifically, this treatment may include short-wavelength ultraviolet treatment, plasma treatment under vacuum, plasma treatment under atmospheric pressure, corona discharge treatment, treatment with an excimer lamp, treatment with a laser, flame radiation treatment, or a combination of a silane coupling agent and flame radiation treatment.

[0036] The bonded structure of the present disclosure is basically composed of a cured product obtained by kneading the first matrix adhesive and the thermally expandable microparticles, and a second matrix adhesive, but these may also be formed into a coating on the adherend, and a third adhesive may be applied to the coating to fasten the components together. When the bonded structure of the present disclosure is used as a coating to contribute to disassembly, the coating thickness can be set to approximately 40 μm to 10 mm, but in practice, a practical range is approximately 80 μm to 2 mm.

[0037] As described above, the adhesive structure according to the first embodiment includes a first matrix adhesive containing a matrix resin primarily composed of an acrylic resin and thermally expandable microparticles having a foaming initiation temperature of 115°C or higher, and a second matrix adhesive containing the first matrix adhesive and having a higher elastic modulus at temperatures below the foaming initiation temperature than the first matrix adhesive. Therefore, even when the adhesive layer undergoes a thermal history in which the temperature exceeds the foaming initiation temperature of the thermally expandable microparticles, the adhesive structure can maintain a high level of strength due to the effect of the second matrix adhesive. This not only broadens the range of applicable products but also allows for easy disassembly by heating. Specifically, when the temperature of the adhesive layer exceeds the foaming initiation temperature of the thermally expandable microparticles, the thermally expandable microparticles begin to foam, causing the first matrix adhesive to begin softening. The second matrix adhesive has a higher elastic modulus than the first matrix adhesive and has a layered structure in which the first matrix adhesive penetrates into the second matrix adhesive or is sandwiched between the second matrix adhesives. Therefore, even when the first matrix adhesive begins to soften, the second matrix adhesive maintains its strength. Therefore, the adhesive structure can maintain its strength. Further increases in temperature further accelerate the softening of the first matrix adhesive. Because the bonded structure has a layered structure in which the first matrix adhesive penetrates into the second matrix adhesive or the first matrix adhesive is sandwiched between the second matrix adhesives, as the first matrix adhesive softens, the second matrix adhesive also begins to soften, making the bonded structure easily dismantlable.

[0038] The adhesive structure of the present disclosure can be applied to any product regardless of its target. Specifically, it may be used for airplane parts, helicopter parts, automobile parts, railroad car parts, ship parts, submarine parts, various robot parts, processing machines, transformers, flying objects such as drones, air conditioner parts, refrigerators, cookers, video equipment, vacuum cleaners, smartphones, mobile phones, various communication devices, personal computers, tablets, elevators, escalator parts, platform fence parts, circuit board parts, rotating machines (motors), fixing parts for various housings, antenna parts, etc.

[0039] Examples of the bonded structure according to the present disclosure will be described below. The adherends to be bonded by the bonded structures according to the examples may be any as long as they can be bonded by the bonded structures according to the examples and conventional bonded structures. Specifically, the bonded structures according to the examples are obtained by kneading a first matrix adhesive containing a second-generation acrylic adhesive as a main component with thermally expandable microparticles.

[0040] Example 1 Fig. 1A is a cross-sectional view showing the configuration of an adhesive structure 100 according to this Example 1. Fig. 1B is a cross-sectional view taken along the line AA in Fig. 1A. A first matrix adhesive 1 used in the adhesive structure 100 contains an acrylic adhesive matrix resin 11 and thermally expandable fine particles 12.

[0041] The matrix resin 11 has an acrylic resin component that is a mixture of acrylic monomers whose main components are all or part of methyl methacrylate, 2-(hydroxyethyl) methacrylate, and dicyclopentenyloxyethyl methacrylate, and an elastomer component that is a nitrile-butadiene elastomer and a methacrylate-styrene-butadiene copolymer elastomer.

[0042] The first matrix adhesive 1 contains cumene hydroperoxide as a peroxide and a thiourea-based compound as a reducing agent, and also contains trace amounts of a silane coupling agent and / or paraffin wax for air barrier purposes.

[0043] The thermally expandable particles 12 contained in the first matrix adhesive 1 are particles in which hydrocarbons are encapsulated in an acrylic resin, with a particle diameter of 17 to 52 μm, and expand at 125° C. or higher, becoming 20 times or more their original size as a result of the expansion. In the first matrix adhesive 1, the thermally expandable particles 12 were mixed in an amount of 80 parts by weight to 100 parts by weight of matrix resin 11, and the mixture was placed in a mortar and kneaded with a pestle.

[0044] After kneading, before the matrix resin 11 hardened, the cured product obtained by kneading the thermally expandable microparticles 12 and the matrix resin 11 was sandwiched between fluororesin plates and pressed with a vice so as to have a thickness of 0.5 mm. In this state, the cured product was cured at room temperature for 1 hour and at 80°C for 1 hour, and then returned to room temperature. Thereafter, through holes with a diameter of 1.5 mm were drilled into the sheet-like cured product at 1 cm intervals. 2 The storage modulus of the cured product of First Matrix Adhesive 1 was measured at a measurement frequency of 10 Hz and a measurement temperature of 120°C, and was found to be 3.0 MPa.

[0045] The second matrix adhesive 2 was a modified acrylic adhesive having a storage modulus of 600 MPa at a measurement frequency of 10 Hz and a measurement temperature of 120° C. and 220 MPa at 140° C. The adhesive structure 100 was formed by sandwiching the sheet-shaped cured product of the first matrix adhesive 1 having the above-described through holes 1 a between the second matrix adhesive 2.

[0046] A 3.2 mm thick aluminum 5052 alloy plate was prepared as the adherend 4a, and a 1.6 mm thick stainless steel 304 plate was prepared as the adherend 4b. The adhesive joints of the adherends 4a and 4b were polished with 400 grit sandpaper and then degreased with ethanol. The adherends 4a and 4b were then bonded together using the adhesive structure 100, which was composed of the first matrix adhesive 1 and the second matrix adhesive 2 containing the thermally expandable microparticles 12, as described above.

[0047] A disassembly test of the bonded structure 100 in which the adherends 4a and 4b were bonded was carried out as follows. The bonded structure 100 in which the adherends 4a and 4b were bonded was placed in a heating furnace set at 200°C for 10 minutes and heated until the temperature of the bonded structure 100 reached 180°C. Thereafter, the bonded structure 100 in which the adherends 4a and 4b were bonded was removed from the heating furnace and allowed to cool to room temperature before a disassembly test was carried out. By applying this heat, the bonded structure 100 could be disassembled manually.

[0048] Under similar conditions, a specimen was prepared with the adhesive area adjusted to 25 x 10 mm so that strength could be measured. After curing, the shear adhesive strength was measured at a test speed of 10 mm / min, and the strength was 4.5 MPa at 120°C.

[0049] Example 2 In Example 2, the adhesive structure 100 shown in Fig. 1 was used, as in Example 1. In Example 2, in the first matrix adhesive 1 used in the adhesive structure 100, the matrix resin 11 was mixed in a ratio of 100 to 100 of thermally expandable fine particles 12.

[0050] The thermally expandable microparticles 12 and the matrix resin 11 were mixed separately into a component containing peroxide and a component containing thiourea, a reducing agent. The components were kneaded in a Banbury mixer. The peroxide component and the reducing agent component were then mixed in a hand mixer, and the mixture was formed into a sheet while still in a fluid state before hardening.

[0051] 2A to 2E are diagrams showing a process for forming a sheet of the first matrix adhesive 1 for the bonded structure 100 according to Example 2. The process for forming a sheet of the first matrix adhesive 1 for the bonded structure 100 according to Example 2 will be described below using FIGS.

[0052] First, as shown in Fig. 2A, stainless steel plates 7 and 8, the surfaces of which are treated with a release agent such as Teflon (registered trademark) coating, are prepared in order to form a sheet of a mixture of thermally expandable particles 12 and matrix resin 11. One of the stainless steel plates 8 has through holes with a diameter of 1.5 mm and a length of 1 cm. 2The protrusions 8a are provided so that 15 holes can be opened.

[0053] Next, as shown in FIG. 2B, the mixture 10 of the thermally expandable fine particles 12 and the matrix resin 11 in a fluid state before hardening is sandwiched between the stainless steel plates 7 and 8.

[0054] 2C, a sheet-like first matrix adhesive 1 having through holes 1a and a thickness of 0.3 mm was formed using a roller 30. The sheet was then cured at room temperature for 3 hours and at 60°C for 4 hours, and then returned to room temperature.

[0055] After the sheet-like first matrix adhesive 1 has hardened, the stainless steel plates 7 and 8 are removed as shown in Fig. 2D. Then, in order to improve the adhesiveness of the surface of the hardened sheet-like first matrix adhesive 1, a short-wavelength ultraviolet irradiation device is used to irradiate the surface with short-wavelength ultraviolet light from a low-pressure mercury lamp containing wavelengths of 185 nm and 254 nm at a dose of 10 mW / cm. 2 2E is a perspective view of the sheet-shaped first matrix adhesive 1. This completes the formation of the sheet of the first matrix adhesive 1.

[0056] An epoxy-coated carbon steel plate having a thickness of 1.6 mm was prepared as the adherend 4a, and an anodized aluminum 5052 alloy plate having a thickness of 3.2 mm was prepared as the adherend 4b on the opposite side.

[0057] The sheet-shaped cured product of the first matrix adhesive 1 with the above-described through holes 1a formed therein was sandwiched between the second matrix adhesive 2 to form the adhesive structure 100. The second matrix adhesive 2 used in Example 2 was the same as that used in Example 1.

[0058] A disassembly test of the bonded structure 100 in which the adherends 4a and 4b were bonded was carried out as follows. The bonded structure 100 in which the adherends 4a and 4b were bonded was placed in a heating furnace set at 200°C for 10 minutes and heated until the temperature of the bonded structure 100 reached 180°C. Thereafter, the bonded structure 100 in which the adherends 4a and 4b were bonded was removed from the heating furnace and allowed to cool to room temperature before a disassembly test was carried out. By applying this heat, the bonded structure 100 could be disassembled manually.

[0059] Under similar conditions, a specimen was prepared with the adhesive area adjusted to 25 x 10 mm so that strength could be measured. After curing, the shear adhesive strength was measured at a test speed of 10 mm / min, resulting in a strength of 4.5 MPa at 120°C.

[0060] Example 3 In Example 3, the mixture of thermally expandable fine particles 12 and matrix resin 11 in the first matrix adhesive 1 used in the bonded structure 100 was made into a sheet using the same composition and ratio as in Example 1.

[0061] The thickness of the sheet of first matrix adhesive 1 was 0.5 mm. The mixture was cured at room temperature for 3 hours and at 60°C for 4 hours, and then returned to room temperature. The cured first matrix adhesive 1 was then placed in a freeze-grinding device and powdered. The powder that passed through a sieve with a nominal mesh size of 250 μm was collected.

[0062] A 3.2 mm thick aluminum 5052 alloy plate was prepared as the adherend 4a, and a 1.6 mm thick stainless steel 304 plate was prepared as the adherend 4b. The adhesive joints of the adherends 4a and 4b were polished with 400 grit sandpaper and then degreased with ethanol.

[0063] 3A and 3B are diagrams illustrating a process for forming the bonded structure 100 according to Example 3. The process for forming the bonded structure 100 according to Example 3 will be described below with reference to FIGS. 3A and 3B.

[0064] The second matrix adhesive 2 was applied to the aluminum alloy plate of the adherend 4a, and a mixed powder 20 of thermally expandable microparticles 12 and matrix resin 11 obtained by sieving the second matrix adhesive 2 was dispersed over the entire surface of the second matrix adhesive 2a applied to the adherend 4a. The second matrix adhesive 2 was also applied to the stainless steel plate of the adherend 4b on the opposite side, and the second matrix adhesive 2 was bonded to the second matrix adhesive 2 applied to the aluminum alloy plate of the adherend 4a and cured.

[0065] A disassembly test of the bonded structure 100 in which the adherends 4a and 4b were bonded was carried out as follows. The bonded structure 100 in which the adherends 4a and 4b were bonded was placed in a heating furnace set at 200°C for 10 minutes and heated until the temperature of the bonded structure 100 reached 180°C. Thereafter, the bonded structure 100 in which the adherends 4a and 4b were bonded was removed from the heating furnace and allowed to cool to room temperature before a disassembly test was carried out. By applying this heat, the bonded structure 100 could be disassembled manually.

[0066] Example 4 For Example 4, a sheet-shaped molded product of the first matrix adhesive 1 containing thermally expandable fine particles 12 was prepared in the same configuration as Example 2 (see FIG. 2E). The sheet-shaped molded product of the first matrix adhesive 1 had a thickness of 0.3 mm and through holes with a diameter of 1.5 mm, each 1 cm long. 2 There are 15 per unit.

[0067] A tempered glass substrate coated with an epoxy-based decorative coating was prepared. Both sides of the sheet-shaped molded product of the first matrix adhesive 1 with through holes 1a were coated with the second matrix adhesive 2 to an average thickness of 0.4 mm, and the coated product was then cured to adhere to the decorative coating side of the tempered glass, forming an adhesive structure 100 as a disassembly layer.

[0068] Fig. 4 is a cross-sectional view showing the configuration of the bonded structure 100 of Example 4. As shown in Fig. 4, an ABS resin housing 25 was bonded to the surface of a dismantling layer 23 (bonded structure 100) bonded to the decorative coating 22 side of tempered glass 21, with a urethane foam resin 26 sandwiched in the middle, with the periphery bonded with a urethane-based hot melt adhesive 24 and the center bonded with the adhesive urethane foam resin 26. Fig. 5 is a perspective view showing a refrigerator having a portion 28 incorporating the dismantling layer 23 (bonded structure 100) of Example 4.

[0069] The disassembly test of the disassembly layer 23 (bonded structure 100) of Example 4 was carried out as follows. The part 28 incorporating the disassembly layer 23 (bonded structure 100) of Example 4 was placed in a thermostatic chamber set at 200°C for 10 minutes, and heated until the temperature of the part 28 incorporating the disassembly layer 23 (bonded structure 100) reached 180°C. The part 28 incorporating the disassembly layer 23 (bonded structure 100) was then removed from the heating furnace and allowed to cool to room temperature before a disassembly test was carried out. By applying this heat, the disassembly layer 23 (bonded structure 100) could be disassembled manually.

[0070] Comparative Example 1 In the bonded structure according to Comparative Example 1, the first matrix adhesive used was as follows: The same thermally expandable fine particles and second matrix adhesive as those used in Example 1 were used.

[0071] In Comparative Example 1, the first matrix adhesive is not an acrylic adhesive but is composed of an elastomer-modified epoxy adhesive and thermally expandable particles. The first matrix adhesive contains a modifying elastomer component, a bisphenol A-type epoxy resin, and an amine-based curing agent.

[0072] The thermally expandable particles contained in the first matrix adhesive were particles in which hydrocarbons were encapsulated in an acrylic resin, and had a particle diameter of 17 to 52 μm. The first matrix adhesive was mixed so that the weight of the thermally expandable particles was 80 parts by weight per 100 parts by weight of the matrix resin, and the mixture was placed in a mortar and kneaded with a pestle.

[0073] After kneading, but before the matrix resin hardened, the cured product obtained by kneading the thermally expandable microparticles and the matrix resin was sandwiched between fluororesin plates and pressed with a vice so as to form a sheet having a thickness of 0.5 mm. In this state, the cured product was left at room temperature for 6 hours, then cured at 80°C for 1 hour, and then returned to room temperature. Thereafter, through holes with a diameter of 1.5 mm were drilled into the sheet-like cured product at 1 cm intervals. 2 The storage modulus of the cured product of the first matrix adhesive was measured at a measurement frequency of 10 Hz and a measurement temperature of 120°C, and was found to be 21 MPa.

[0074] The sheet-shaped cured product of the first matrix adhesive having the through holes drilled therein was sandwiched between the same second matrix adhesive as used in Example 1 to form an adhesive structure.

[0075] A disassembly test of the bonded structure of Comparative Example 1 in which adherends 4a and 4b were bonded was carried out as follows. The bonded structure in which adherends 4a and 4b were bonded was placed in a heating furnace set at 200°C for 10 minutes and heated until the temperature of the bonded structure reached 180°C. The bonded structure in which adherends 4a and 4b were bonded was then removed from the heating furnace and allowed to cool to room temperature before a disassembly test was carried out. Even after heating in this manner, the bonded structure of Comparative Example 1 could not be disassembled manually.

[0076] Comparative Example 2 The matrix resin of the first matrix adhesive of the adhesive structure of Comparative Example 2 is mainly composed of either or both of phenoxyethyl methacrylate and 2-hydroxypropyl methacrylate, and also contains methacrylic acid to impart heat resistance, and contains a methacrylate-styrene-butadiene copolymer elastomer component as the elastomer component.

[0077] The first matrix adhesive 1 contains cumene hydroperoxide as a peroxide and a vanadium complex as a reducing agent, and also contains trace amounts of a silane coupling agent and / or paraffin wax for air barrier.

[0078] The thermally expandable particles contained in the first matrix adhesive were the same as those used in Example 1. In the first matrix adhesive, the thermally expandable particles were mixed so that the weight of the particles was 100 parts by weight relative to the weight of the matrix resin, and the mixture was placed in a mortar and kneaded with a pestle.

[0079] After kneading, but before the matrix resin hardened, the cured product obtained by kneading the thermally expandable microparticles and the matrix resin was sandwiched between fluororesin plates and pressed with a vice so as to form a sheet having a thickness of 0.5 mm. In this state, the cured product was cured at room temperature for 1 hour and at 80°C for 1 hour, and then returned to room temperature. Thereafter, through holes with a diameter of 1.5 mm were drilled into the sheet-like cured product at 1 cm intervals. 2The storage modulus of the cured product of the first matrix adhesive was measured at a measurement frequency of 10 Hz and a measurement temperature of 120°C, and was found to be 350 MPa.

[0080] The sheet-shaped cured product of the first matrix adhesive having the through holes drilled therein was sandwiched between the same second matrix adhesive as used in Example 1 to form an adhesive structure.

[0081] A disassembly test of the bonded structure of Comparative Example 2 in which adherends 4a and 4b were bonded was carried out as follows. The bonded structure in which adherends 4a and 4b were bonded was placed in a heating furnace set at 200°C for 10 minutes and heated until the temperature of the bonded structure reached 180°C. The bonded structure in which adherends 4a and 4b were bonded was then removed from the heating furnace and allowed to cool to room temperature before a disassembly test was carried out. Even after heating in this manner, the bonded structure of Comparative Example 2 could not be disassembled manually.

[0082] The cured products of the first matrix adhesive 1 of the bonded structure 100 according to Example 1 and the first matrix adhesive of the bonded structure according to Comparative Example 1 were each processed into thin plates using a cryomicrotome. The resulting thin plates were stained with osmium tetroxide and then observed with a transmission electron microscope (TEM).

[0083] Fig. 6 is a diagram showing a TEM image of a cured product of the first matrix adhesive 1 of the bonded structure 100 according to Example 1. Fig. 7 is a diagram showing a TEM image of a cured product of the first matrix adhesive of the bonded structure according to Comparative Example 1.

[0084] Here, when the first matrix adhesive 1 of the bonded structure 100 according to Example 1 and the first matrix adhesive of the bonded structure according to Comparative Example 1 are each stained with osmium tetroxide, the images obtained by TEM show that the double bonds in the first matrix adhesive 1 of the bonded structure 100 according to Example 1 and the first matrix adhesive of the bonded structure according to Comparative Example 2 appear black. The portion where the acrylic component polymerizes to form a hard phase has almost no double bonds, and the elastomer component has double bonds remaining, which is why it appears black.

[0085] The first matrix adhesive according to Example 1 forms a phase structure having white, gray, and black portions, as shown in Figure 6. The white portion W is an acrylic hard phase, i.e., a hard phase derived from the acrylic component. The gray portion G is a non-granular elastomer phase derived from the liquid elastomer. The acrylic hard phase is connected via the gray portion to form a single aggregate.

[0086] The black portion B is a granular elastomer phase derived from the granular elastomer. The black granular elastomer phase is widely distributed around the aggregates, with white or gray areas present between the particles.

[0087] As shown in Figure 7, the first matrix adhesive of the adhesive structure of Comparative Example 1 has small elastomer phases (black part BS) and large elastomer phases (black part BL) dispersed within the hard matrix (white part W), and no phases that form aggregates as seen in the example of Figure 6 are observed.

[0088] When bonding with the adhesive structure 100 used as a disassembly layer, it is desirable to perform a surface treatment on the adherend side to improve reliability. Any surface treatment is acceptable, including wiping with a rag, an alcohol-based degreaser, acetone, or a hydrocarbon-based solvent. Sanding with abrasive paper or shot blasting may also be performed. Treatments may include short-wavelength ultraviolet light treatment, plasma treatment under vacuum, plasma treatment under atmospheric pressure, corona discharge treatment, treatment with an excimer lamp, treatment with a laser, or flame radiation treatment, or a combination of a silane coupling agent and flame radiation treatment. Metallic materials may be subjected to chemical conversion treatment, and magnesium alloys and aluminum alloys may be subjected to anodizing treatment. Other treatments that may be performed include zinc phosphate treatment, iron phosphate treatment, zirconium-based chemical conversion treatment, and chromate-based treatment.

[0089] If the adherend is a metal on which a metal-based coating can be formed, a disassembly layer may be used on the metal-based coating surface, specifically, Ni plating, zinc plating, Ni-Zn alloy plating, Ni-P electroless plating, chromium plating, copper plating, aluminum, or an aluminum alloy vapor deposition film, etc.

[0090] If the adherend can be painted, it can be adhered to a painted surface. Examples include spray painting, powder painting, and electrodeposition painting. Any type of coating component can be used as long as it is adhesive, such as epoxy, urethane, polyester, melamine, acrylic, amide-imide, and natural oils. Silicone and fluorine-based paints can also be used if the surface is treated to improve adhesion.

[0091] To improve the reliability of adhesion, an adhesive agent or primer that improves adhesion may be used. Specifically, a silane coupling agent or a titanate-based treatment agent may be applied. Other methods for improving adhesion include etching with acid or cleaning with alkali.

[0092] Any adhesive may be used to adhere the coated disassembly layer, including, for example, second-generation acrylic adhesives, room temperature curing epoxy adhesives, heat curing epoxy adhesives, phenolic adhesives, urethane adhesives, cyanoacrylate adhesives, hot melt adhesives, reactive hot melt adhesives, anaerobic adhesives, ultraviolet curing adhesives, silicone adhesives, modified silicone adhesives, rubber adhesives, vinyl acetate adhesives, water-based emulsion adhesives, and polyimide adhesives.

[0093] The disassembly condition for a bonded body is that the adhesive portion of the disassembly layer of the product to be disassembled reaches a predetermined temperature, specifically 140°C or higher. When heating using a standard thermostatic oven, the disassembly time should be between 1 minute and 12 hours, depending on the size and heat capacity of the product. In order to efficiently disassemble the body, reduce the amount of gas generated from the parts, and minimize damage to components that are to be recycled or reused after disassembly, it is desirable for the disassembly state to be reached within 20 minutes.

[0094] The adhesive structure 100 of the present disclosure can be applied to any product regardless of its target. Specifically, it may be used for airplane parts, helicopter parts, automobile parts, railroad car parts, ship parts, submarine parts, various robot parts, processing machines, transformers, flying objects such as drones, air conditioner parts, refrigerators, cookers, video equipment, vacuum cleaners, smartphones, mobile phones, various communication devices, personal computers, tablets, elevators, escalator parts, platform fence parts, circuit board parts, rotating machines (motors), fixing the following types of housings, antenna parts, etc.

[0095] Although various exemplary embodiments and examples are described in this disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are contemplated within the scope of the technology disclosed in this disclosure specification. For example, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0096] 1 First matrix adhesive, 2 Second matrix adhesive, 11 Matrix resin, 12 Thermally expandable fine particles, 100 Adhesive structure.

Claims

1. An adhesive structure comprising: a first matrix adhesive containing a matrix resin whose main component is an acrylic resin and thermally expandable microparticles having a foaming initiation temperature of 115°C or higher; and a second matrix adhesive containing the first matrix adhesive and having a higher elastic modulus at temperatures below the foaming initiation temperature than the first matrix adhesive.

2. The bonded structure according to claim 1, wherein the first matrix adhesive has an elastic modulus of 0.5 MPa or more and 40 MPa or less.

3. The adhesive structure described in claim 1 or claim 2, characterized in that the first matrix adhesive has an acrylic hard phase made of an acrylic component and an elastomer phase made of an elastomer component, and the elastomer phase includes a granular elastomer phase and a non-granular elastomer phase.

4. A bonding method using an adhesive structure, comprising the steps of: kneading thermally expandable microparticles having a foaming initiation temperature of 115°C or higher into a matrix resin whose main component is an acrylic resin, and then curing the mixture to form a first matrix adhesive; pulverizing the cured first matrix adhesive; and dispersing the pulverized first matrix adhesive in a second matrix adhesive having a higher elastic modulus than the first matrix adhesive at a temperature below the foaming initiation temperature, curing the second matrix adhesive, and bonding objects to each other via the second matrix adhesive in which the pulverized first matrix adhesive has been dispersed.

5. A bonding method using an adhesive structure, comprising the steps of: kneading thermally expandable microparticles having a foaming initiation temperature of 115°C or higher into a matrix resin whose main component is an acrylic resin, forming the resin into a sheet having a plurality of through holes, and curing the sheet; sandwiching the hardened first matrix adhesive into a second matrix adhesive having a higher elastic modulus than the first matrix adhesive at temperatures below the foaming initiation temperature, curing the second matrix adhesive, and bonding objects to each other via the second matrix adhesive sandwiching the hardened first matrix adhesive into a sheet.

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