Adhesive structure, adhesive, and refrigerator

Abstract

This adhesive comprises: a matrix adhesive including an acrylic adhesive as a main component; and thermally expandable fine particles which expand when heated, wherein the volume of the thermally expandable fine particles becomes 10 times or more of the original volume thereof after expansion. The matrix adhesive forms a phase structure during curing. The phase structure has: an acrylic hard phase formed by an acrylic component in the matrix adhesive; and an elastomer phase formed by an elastomer included in the matrix adhesive. The elastomer phase has: a granular elastomer phase obtained by a granular elastomer having a double bond portion; and a non-granular elastomer phase formed by a liquid elastomer.

Description

Adhesive structure, adhesive, and refrigerator

[0001] The present disclosure relates to a bonded structure, which is a structure obtained by bonding, an adhesive that enables the bonded structure to be disassembled, and a refrigerator having the bonded structure.

[0002] When a bonded structure, which is a structure obtained by bonding a plurality of adherends, is dismantled and the dismantled adherends are put into industrial use for recycling or reuse, etc., dismantling by heat is practical from the viewpoint of equipment, etc. In this case, in order to minimize the impact on areas other than the bonded parts during dismantling for the purpose of recycling, etc., it is important that the heating temperature and heating time of the product to be dismantled are not too high and that it can be easily and reliably dismantled after cooling to room temperature.

[0003] Patent Document 1 discloses an adhesive that uses polyurethane, rubber, acrylic resin, or epoxy resin as a binder and contains the following thermal expansion material. The thermal expansion material is, for example, a thermal expansion microcapsule that has a spherical shell made of thermoplastic resin and is approximately 10 to 100 μm in size, and liquefied gas is sealed inside it. When articles bonded with the adhesive are heated by microwaves, the thermal expansion material expands and the adhesive layer becomes weak, allowing the adherends to be separated.

[0004] JP 2008-56843 A

[0005] However, when attempting to construct an easily dismantled bonded structure using an adhesive that uses an acrylic resin as a binder and contains a heat-expandable spherical filler, if the adhesive has good adhesion to the adherends, it may not be possible to effectively separate the adherends even if the dismantlable adhesive is expanded under heating conditions of about 150 to 200°C.

[0006] Furthermore, when disassembling a bonded structure and recycling the adherends that constitute the bonded structure industrially, it is important that the disassembly can be performed using a simple process. A versatile and desirable method is to disassemble a product by subjecting it to temperatures that cannot be achieved in the product's usage environment. However, if the adhesive contains a resin that softens and melts, unintended welding may occur, making disassembly difficult.

[0007] When dismantling by heat while avoiding the above-mentioned problems, it is important to heat the bonded structure to about 150 to 200°C for only a short time so as to affect parts other than the bonded parts as little as possible, and to ensure that the adherends can be easily and reliably separated and dismantled manually after cooling to room temperature.

[0008] The present disclosure provides an adhesive structure, an adhesive, and a refrigerator having the adhesive structure that can be more reliably dismantled by low-temperature heating without reducing the adhesive strength between the adherend and the adhesive.

[0009] The bonded structure according to the present disclosure is a bonded structure obtained by bonding a plurality of adherends with an adhesive, the adhesive comprising a matrix adhesive primarily composed of an acrylic adhesive and thermally expandable microparticles that expand upon heating to a volume 10 times or more of their original volume after expansion, the hardened matrix adhesive comprising an acrylic hard phase due to the acrylic component in the matrix adhesive and an elastomer phase due to the elastomer component contained in the matrix adhesive, the elastomer phase comprising two or more phases, a granular elastomer phase and a non-granular elastomer phase.

[0010] The adhesive according to the present disclosure comprises a matrix adhesive that contains an acrylic monomer as a main component and that contains a nitrile-butadiene elastomer and a methacrylate-butadiene-styrene copolymer as elastomer components, and thermally expandable microparticles that expand at 120°C or higher and reach a volume that is at least 10 times their original volume after expansion, wherein the specific gravity of the matrix adhesive before curing is 0.9 to 1.2, and when the matrix adhesive contains an inorganic filler, the thermally expandable microparticles are added in an amount that is 10 to 35% by weight of the matrix adhesive excluding the inorganic filler.

[0011] The refrigerator according to the present disclosure includes the above-described adhesive structure as a component.

[0012] According to the bonded structure, adhesive, and refrigerator of the present disclosure, the presence of the non-particulate elastomer phase makes it easy to disassemble by low-temperature heating without reducing the adhesiveness of the bonded portions in the bonded structure.

[0013] FIG. 1 is a diagram schematically showing a first adhesive state using the adhesive according to Example 1. FIG. 2 is a diagram schematically showing a second adhesive state using the adhesive according to Example 1. FIG. 3 is a diagram showing a TEM image of a cured product of the adhesive according to Example 1. FIG. 4 is a diagram showing a TEM image of a cured product of the adhesive according to Comparative Example 1. FIG. 5 is a diagram schematically showing an adhesive state using the adhesive according to Example 2. FIG. 6 is a perspective view schematically showing a refrigerator incorporating the adhesive structure according to Example 3. FIG. 7 is a diagram schematically showing an adhesive state using the adhesive according to Example 4.

[0014] Embodiments. Hereinafter, embodiments of the bonded structure, adhesive, and refrigerator according to the present disclosure will be described. Note that the adherend to be bonded by the adhesive according to the embodiments may be any object that can be bonded by the adhesive according to the embodiments and conventional adhesives. Specifically, the adhesive according to the embodiments is obtained by kneading a matrix adhesive containing a second-generation acrylic adhesive as a main component with thermally expandable microparticles that are fine particles with thermal expansion properties. The acrylic adhesive according to the embodiments has a phase structure that is prone to exhibit a decrease in strength at 120 to 180°C due to the thermally expandable microparticles.

[0015] The thermally expandable microparticles are preferably microparticles in which a hydrocarbon gas is covered with a resin coating, and the resin coating softens and expands when heated. The type of resin coating may be any, and specific examples include the Advancel EM series manufactured by Sekisui Chemical, the F series or FN series of Matsumoto Microsphere manufactured by Matsumoto Oil & Fat, the H series or S series of Kureha Microsphere manufactured by Kureha Chemical, the Expancel series manufactured by Nippon Phillite, and the M series or H series of Dieform manufactured by Dainichiseika Chemicals.

[0016] Examples of the hydrocarbon gas encapsulated 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, and hexanedecane, or a mixture of two or more of these gases. The hydrocarbon gas is particularly preferably isobutane, n-butane, n-pentane, isopentane, n-hexane, isooctane, or isododecane, or a mixture thereof. The gas encapsulated in the resin coating may be CCl 2 instead of the hydrogen carbonate gas described above. ３ F, CCl ２ F ２ , CClF ３ , or CClF ２ -CClF ２ The thermally expandable fine particles may be chlorofluorocarbons such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane, or tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, or trimethyl-n-propylsilane, or may be a mixture of at least one of these with the hydrocarbon gas. All of the thermally expandable fine particles may contain the same gas among the above-mentioned gases encapsulated in the resin coating, or some of the thermally expandable fine particles may contain a gas different from the gas contained in the other thermally expandable fine particles encapsulated in the resin coating.

[0017] The particle size of the thermally expandable microparticles is not limited, but from the perspective of mixing with the matrix adhesive and the need to maintain the adhesive thickness within a practical range, a particle size of approximately 5 μm to 500 μm is desirable, and approximately 10 μm to 250 μm is particularly desirable. The thermally expandable microparticles must be capable of stably maintaining a level that allows the bonded structure obtained by bonding multiple adherends with the adhesive to withstand a thermal aging test as a product. Because the thermally expandable microparticles need to expand when the matrix resin of the matrix adhesive softens, their expansion initiation temperature is preferably 90°C or higher, and particularly 120°C or higher. Here, if the degree of expansion of the thermally expandable microparticles is too small, the force of the thermally expandable microparticles contributing to the disassembly of the adhesive layer is weakened, making it difficult to disassemble the bonded structure manually. Therefore, the degree of expansion of the thermally expandable microparticles is preferably at least 5 times, and particularly preferably at least 20 times, their original size after expansion.

[0018] The thermally expandable particles in the adhesive according to the embodiment may be of the same type, or may have different expansion starting temperatures or expansion ratios. The adhesive according to the embodiment may also contain other particles that have expandability in addition to the thermally expandable particles. A specific example of such other particles is expandable graphite.

[0019] Here, the matrix adhesive is an elastomer-modified acrylic adhesive. The adhesive according to the embodiment contains thermally expandable particles blended into the matrix resin in an amount of approximately 5 to 50% by weight. The adhesive layer formed by the adhesive according to the embodiment, which contributes to disassembly, can have a thickness of approximately 15 μm to 10 mm, but a practical range is approximately 50 μm to 2 mm. The adhesive layer to be disassembled may itself bond adherends together, or may be formed by forming a coating-like disassembly layer on the adherend using the adhesive according to the embodiment, and then fixing the disassembly layer to other parts with a separate adhesive. Forming the disassembly layer in a coating-like form has the advantage of allowing parts used in conventional assembly to be reused as is, except for the disassembly layer.

[0020] The adhesive strength of the adhesive layer and the disassembly layer to the adherend is not limited as long as the product is viable. However, even when another adhesive is used to fix the adherends together, it is desirable that the adhesive strength be about 3 MPa or more at room temperature when not disassembled so that the performance of the other adhesive can be exerted.

[0021] Examples of monomers for the acrylic adhesive used as the matrix resin include (meth)acrylic monomers. Examples of (meth)acrylic monomers 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, and (meth)acrylic monomers having a carboxyl group such as (meth)acrylic acid.

[0022] Examples of elastomers used to impart flexibility to acrylic adhesives include thermoplastic resins and liquid rubbers. Examples of such thermoplastic resins include polymethyl methacrylate, polyvinyl butyral, acrylonitrile-styrene copolymers (AS resins), acrylonitrile-butadiene-styrene copolymers (ABS resins), methyl methacrylate-butadiene copolymers, methyl methacrylate-butadiene-styrene copolymers (MBS resins), and methyl methacrylate-butadiene-acrylonitrile-styrene copolymers (MBAS resins). Examples of liquid rubbers include 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, as well as liquid polybutadiene, (meth)acrylic-modified liquid polybutadiene, and (meth)acrylic-modified acrylonitrile-butadiene liquid rubber.

[0023] Examples of peroxides in acrylic adhesives include benzoyl peroxide, lauroyl peroxide, methyl ethyl ketone peroxide, tert-butyl peroxide, pinene hydroperoxide, balamenthane peroxide, diisopropyl peroxide, and cumene hydroperoxide.

[0024] Examples of materials that can cause a redox reaction with the peroxide include metal complexes such as vanadyl acetylacetonate, and thiourea compounds.

[0025] Examples of materials for improving the stability of acrylic adhesives include radical polymerization inhibitors such as hydroquinone, methoxyhydroquinone, methylhydroquinone, 1,4-benzoquinone, 1,4-naphthoquinone, 2,6-di-t-butyl-4-methylphenol, and 2,2-methylenebis(4-methyl-6-t-butylphenol).

[0026] The acrylic adhesive may contain other additives such as paraffin to improve the curing properties of the surface that comes into contact with air, or 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 to improve adhesion.

[0027] The elastic modulus of the acrylic adhesive must be such that it does not become too hard when the thermally expandable particles begin to expand. Specifically, if the storage modulus or dynamic modulus of the acrylic adhesive is 50 MPa or less just before the temperature at which the thermally expandable particles begin to expand, dismantling is possible. However, to ensure more reliable dismantling, a value of 0.5 to 10 MPa is desirable. The storage modulus here is measured using a nanoindenter at a frequency of 10 Hz.

[0028] Here, when inorganic fine particles are added to the matrix adhesive, a high storage modulus is measured, so the evaluation value of the resin part that is not affected by the inorganic fine particles can be used, using a nanoindenter or AFM (Atomic Force Microscopy).

[0029] When the matrix adhesive is predominantly resinous, the specific gravity of the cured matrix adhesive is typically 0.9 to 1.2, which is almost the same as the specific gravity of the thermally expandable microparticles before expansion. In this case, the weight and volume ratios of the matrix adhesive and the thermally expandable microparticles are also almost the same. Therefore, to obtain the adhesive according to the embodiment, the weight of the thermally expandable microparticles added to the matrix adhesive is preferably approximately 5 to 50% of the weight of the matrix adhesive, and the volume of the thermally expandable microparticles added to the matrix adhesive is preferably approximately 5 to 50% of the volume of the matrix adhesive. Note that a ratio of the thermally expandable microparticles below 5% may impair dismantling capabilities. While there is no upper limit for the ratio of the thermally expandable microparticles, a ratio exceeding 50% may impair application. When the specific gravity of the matrix adhesive is 0.9 to 1.2 and the inorganic filler content is low, the weight of the thermally expandable microparticles is preferably 5 to 50% of the weight of the matrix resin, and more preferably 10 to 35% from the standpoints of workability and dismantling. When inorganic filler particles are added to the matrix adhesive and the specific gravity of the matrix adhesive becomes greater than 1.2, the weight of the thermally expandable particles should be 10 to 35% of the weight of the matrix resin as a volume fraction relative to the resin portion obtained by removing the inorganic filler from the matrix adhesive, based on that specific gravity.

[0030] The adhesive used to form the disassembly layer may be any material that can be bonded, such as metal, glass, ceramics, fiber-reinforced plastic, thermosetting resin, thermoplastic resin, or liquid crystal polymer.

[0031] When adhering an adherend with an adhesive forming a disassembly layer according to an embodiment, it is desirable to subject the adherend to a surface treatment to improve reliability. The surface treatment may be, but is not limited to, wiping the adherend's surface with a rag, an alcohol-based degreaser, acetone, or a hydrocarbon solvent, or sanding the adherend's surface with abrasive paper. Alternatively, shot blasting may be used. Alternatively, short-wavelength ultraviolet treatment, plasma treatment under vacuum, plasma treatment under atmospheric pressure, corona discharge treatment, excimer lamp treatment, laser treatment, or flame radiation treatment may be used. A combination of treatment using a silane coupling agent and flame radiation treatment may also be used. If the adherend is a metal material, a chemical conversion treatment may be used. If the adherend is a magnesium alloy or aluminum alloy, an anodizing treatment may be used. Alternatively, zinc phosphate treatment, iron phosphate treatment, zirconium-based chemical conversion treatment, or chromate-based treatment may be used.

[0032] If the adherend has a metal coating that can be formed into a film, a disassembly layer may be formed on the metal coating surface of the adherend. Examples of metal coatings include Ni plating, zinc plating, Ni-Zn alloy plating, Ni-P electroless plating, chromium plating, copper plating, and vapor-deposited films of aluminum or aluminum alloys.

[0033] If the adherend is paintable, a painted surface may be formed on the surface of the adherend, and the adhesive according to the embodiment may be applied to the painted surface. Examples of methods for painting the surface of the adherend include spray painting, powder painting, and electrodeposition painting. The component painted on the adherend may be any type of component as long as it is adhesive, similar to the adhesive according to the embodiment. Examples of components painted on the adherend include epoxy, urethane, polyester, melamine, acrylic, amide-imide, and natural oils and fats. If the adherend has been surface-treated to improve adhesion, the coating component may be a silicone-based or fluorine-based paint.

[0034] To improve the reliability of adhesion, an adhesive agent or primer may be used to improve adhesion. Specifically, a silane coupling agent or a titanate-based treatment agent may be applied to the surface of the adherend. Other methods for improving adhesion include etching with acid or cleaning with alkali.

[0035] When the demolition layer is formed into a coating and a separate adhesive is applied to the surface of the demolition layer to fix the adherend, the surface of the formed demolition layer may be subjected to treatment to improve the adhesiveness. Specifically, solvent degreasing, sanding, shot blasting with a weak force that does not peel off, short-wave ultraviolet treatment, plasma treatment under vacuum or atmospheric pressure, corona discharge treatment, treatment with an excimer lamp, treatment with a laser, flame radiation treatment, and a combination of silane coupling treatment and flame radiation treatment may be used.

[0036] The other adhesive to be adhered to the coated disassembly layer is not particularly limited, and specific examples of the other adhesive include 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.

[0037] The dismantling conditions for a bonded structure are that the adhesive portion of the dismantling layer of the product to be dismantled must be heated to a predetermined temperature, such as 120°C, and that the product must be dismantled within a predetermined time. Specifically, when the adhesive portion is heated using a conventional thermostatic oven, the product must be dismantled within a range of 1 minute to 12 hours, depending on the size or heat capacity of the product. It is desirable for the dismantled state to be reached within 20 minutes in order to efficiently dismantle the product, reduce the amount of gas generated from the parts, and minimize damage to components to be recycled or reused after dismantling.

[0038] Products to which the adhesives according to the embodiments can be applied include, but are not limited to, airplane parts, helicopter parts, automobile parts, railway vehicle 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 such as motors, various housings, or antenna parts.

[0039] Examples are described below. [Example 1] The adhesive according to Example 1 contains an acrylic adhesive matrix resin and thermally expandable microparticles. The acrylic resin component is a mixture of acrylic monomers, primarily composed of all or part of methyl methacrylate, 2-(hydroxyethyl) methacrylate, and dicyclopentenyloxyethyl methacrylate. The elastomer components are a nitrile-butadiene elastomer and a methacrylate-styrene-butadiene copolymer elastomer. The adhesive according to Example 1 also contains cumene hydroperoxide added as a peroxide and a thiourea compound added as a reducing agent. The adhesive according to Example 1 also contains trace amounts of a silane coupling agent and / or paraffin wax for airtightness. The thermally expandable microparticles contained in the adhesive according to Example 1 are microparticles in which hydrocarbons are encapsulated in an acrylic resin. The particle diameter is 17 to 52 μm, and the microparticles expand at 125°C or higher, becoming more than 20 times their original size. The thermally expandable microparticles were mixed and kneaded in an amount of 15 parts by weight per 100 parts by weight of the matrix resin component in the adhesive of Example 1. The storage modulus of the cured matrix resin was measured at 125°C and a frequency of 10 Hz to be 3.0 MPa.

[0040] Fig. 1 is a diagram schematically showing a first bonding state using the adhesive according to Example 1. Fig. 2 is a diagram schematically showing a second bonding state using the adhesive according to Example 1. The adhesive layer 5 shown in Figs. 1 and 2 is a layer obtained by hardening the adhesive according to Example 1, and has an average thickness of 0.25 mm. The adhesive layer 5 contains thermally expandable fine particles 7 and a matrix resin 8.

[0041] In Fig. 1, glass 4 and ABS resin 6 are bonded together using the adhesive of Example 1. The glass 4 is, for example, borosilicate glass. The thickness of the glass 4 is 0.5 mm, and the thickness of the ABS resin 6 is 3 mm. The bonding area between the glass 4 and the ABS resin 6 is 15 cm x 30 cm.

[0042] In Fig. 2, a glass plate 4 having a thickness of 0.5 mm and a stainless steel plate 9 having a thickness of 3 mm are bonded together using the adhesive of Example 1. The thickness of the glass plate 4 is 0.5 mm, and the thickness of the stainless steel plate 9 is 0.6 mm. The bonding area between the glass plate 4 and the stainless steel plate 9 is 15 cm x 30 cm.

[0043] The bonded structure of Example 1 obtained by bonding glass 4 to ABS resin 6 and stainless steel plate 9 using the adhesive of Example 1 was left at room temperature for one week. It was then confirmed that the glass 4 to ABS resin 6 and stainless steel plate 9 were securely bonded by the adhesive of Example 1. The bonded structure of Example 1 was then disassembled as follows. First, the bonded structure of Example 1 was placed in a thermostatic chamber set at 200°C for 10 minutes. The temperature of the bonded structure of Example 1 to be evaluated reached 180°C. The bonded structure of Example 1 was then removed from the thermostatic chamber and cooled. After the temperature of the bonded structure of Example 1 reached 40°C or below, at which point it was possible to perform work, an attempt was made to separate the glass 4 from the ABS resin 6 and stainless steel plate 9 using a scraper with a force of 98.1 N (10 kgf) or less, and separation was successful.

[0044] Comparative Example 1 The adhesive of Comparative Example 1 includes an acrylic adhesive matrix resin and thermally expandable microparticles. The adhesive of Comparative Example 1 includes an acrylic adhesive matrix resin and thermally expandable microparticles. The matrix resin of the adhesive of Comparative Example 1 is primarily composed of both or one of phenoxyethyl methacrylate and 2-hydroxypropyl methacrylate, and includes a methacrylate-styrene-butadiene copolymer elastomer component as an elastomer component. It also includes cumene hydroperoxide added as a peroxide and a vanadium complex added as a reducing agent. Furthermore, the matrix resin of Comparative Example 1 includes trace amounts of both or one of a silane coupling agent and paraffin wax for airtightness. The thermally expandable microparticles in the adhesive of Comparative Example 1 have a particle size distribution of 17 to 52 μm, expand at temperatures above 120°C, and expand to more than 20 times their original size. In Comparative Example 1, the storage modulus of the cured matrix resin was 2.5 MPa when measured at 120°C and a measurement frequency of 10 Hz.

[0045] In Comparative Example 1, similar to Example 1, glass 4 was bonded to ABS resin 6 and stainless steel plate 9 using the adhesive of Comparative Example 1, and the adhesive was allowed to cure at room temperature for one week. It was confirmed that the glass 4 was reliably bonded to the ABS resin 6 and stainless steel plate 9. Furthermore, similar to Example 1, the bonded structure obtained using the adhesive of Comparative Example 1 was placed in a thermostatic oven set at 200°C for 10 minutes. At this time, the temperature of the bonded structure of Comparative Example 1 reached 180°C. The bonded structure of Comparative Example 1 was then removed from the thermostatic oven and cooled. After the temperature of the bonded structure of Comparative Example 1 had fallen to a workable temperature of 40°C or below, an attempt was made to separate the glass 4 from the ABS resin 6 and stainless steel plate 9 using a scraper with a force of 98.1 N (10 kgf), but separation was unsuccessful.

[0046] Cured products of the adhesive according to Example 1, the adhesive according to Comparative Example 1, and the adhesive according to Comparative Example were processed into thin plates using a cryomicrotome. The resulting thin plates were stained with osmium tetroxide and then observed under a transmission electron microscope (TEM). Fig. 3 shows a TEM image of the cured product of the adhesive according to Example 1. Fig. 4 shows a TEM image of the cured product of the adhesive according to Comparative Example 1.

[0047] Here, when each of the adhesives according to Example 1 and Comparative Example 1 was stained with osmium tetroxide, the images obtained by TEM showed that the double bonds in each of the adhesives according to Example 1 and Comparative Example 1 appeared black. The portion where the acrylic component polymerized to form a hard phase had almost no double bonds, and the double bonds remained in the elastomer component, which is why it appeared black.

[0048] As shown in Figure 3, the adhesive of Example 1 forms a phase structure having white, gray, and black regions. The white regions are acrylic hard phase 1, i.e., the hard phase derived from the acrylic component. The gray regions are non-granular elastomer phase 2 derived from the liquid elastomer. As shown in Figure 3, the acrylic hard phase 1 is connected via the gray regions to form a single aggregate. The black regions are granular elastomer phase 3 derived from the granular elastomer. The black granular elastomer phase 3 is widely distributed so as to be present around the aggregate, and white or gray regions are present between the particles.

[0049] As shown in FIG. 4 , the phase structure formed by the adhesive according to Comparative Example 1 contained an acrylic hard phase 1 in the white portion and a granular elastomer phase 3 in the black portion, but no non-granular elastomer phase 2 in the gray portion.

[0050] Although sufficient adhesive strength was obtained with both the adhesive of Example 1 and the adhesive of Comparative Example 1, it is believed that the difference in phase structure as described above caused a significant difference to become apparent when dismantling was performed by thermal expansion using a material made by mixing a polymerizable modified acrylic adhesive and fine particles of a thermally expandable adhesive. The phase structure of Example 1 is such that the white portion is in contact with the gray portion so as to cover it, and it is presumed that the structural relationship between the acrylic hard phase 1 and the surrounding non-particulate elastomer phase 2 affects the decrease in strength due to the expansion of the thermally expandable fine particles.

[0051] The matrix resins in Example 1 and Comparative Example 1 had a storage modulus of 2 to 3 MPa at 120 to 180°C, indicating advanced softening. However, the bonded structure of Example 1 was easy to disassemble manually, while the bonded structure of Comparative Example 1 was impossible to disassemble manually. The ease of disassembly varies depending on the thermally expandable microparticles, and softening of the material is a necessary condition for facilitating disassembly. However, simply lowering the elastic modulus of the matrix resin and expanding the thermally expandable microparticles upon heating is difficult to achieve. In other words, when a force that causes the thermally expandable microparticles to expand within the adhesive layer is applied, it is difficult to reduce the strength to a level that would allow the bonded structure to be easily destroyed manually unless the composition of the hard phase and the soft phase is adjusted.

[0052] Comparative Example 2 The adhesive of Comparative Example 2 contains a matrix resin and thermally expandable particles, and the matrix resin is the same as that of Example 1. The thermally expandable particles in Comparative Example 2 have a particle size distribution of 5 to 12 μm, expand at 125°C or higher, and after expansion, become approximately three times their original size. In the adhesive of Comparative Example 2, the thermally expandable particles were blended and kneaded so that the weight of the matrix resin component was 30 parts by weight, assuming that the weight of the matrix resin component was 100 parts by weight.

[0053] The glass 4 was bonded to the ABS resin 6 and the stainless steel plate 9 using the adhesive of Comparative Example 2, and then cured at room temperature for one week. It was confirmed that the adhesive was also securely bonded in Comparative Example 2. Next, the bonded structure of Comparative Example 2 was placed in a constant temperature bath at 200°C for 10 minutes, as in Example 1, and heated. At this time, the temperature of the bonded structure of Comparative Example 2, which was the evaluation target, reached 180°C. The bonded structure of Comparative Example 2 was then cooled to room temperature, and after it reached 40°C or below, dismantling was attempted using a scraper. However, the bonded structure of Comparative Example 2 could not be dismantled with a force of 98.1 N (10 kgf).

[0054] The adhesive of Comparative Example 2 contains a matrix resin whose strength can be reduced by the expansion of the thermally expandable microparticles, but because the expansion ratio of the thermally expandable microparticles is less than 5 times, which is not very large, it does not cause a reduction in strength sufficient to make the adhesive dismantlable.

[0055] Example 2 The matrix resin contained in the adhesive of Example 2 is the same as that of Example 1. Therefore, the phase structure obtained by the adhesive of Example 2 is the same as that of Example 1, as shown in Figure 3. The adhesive of Example 2 contains two types of thermally expandable particles. The first type of thermally expandable particles has a particle size distribution of 12 to 30 μm, expands at 135°C or higher, and becomes 30 times or more its original size after expansion. The second type of thermally expandable particles has a particle size distribution of 16 to 25 μm, expands at 120°C or higher, and becomes approximately 9 times its original size after expansion. The adhesive of Example 2 contains 10% by weight of the first type of thermally expandable particles and 10% by weight of the second type of thermally expandable particles, based on the weight of the matrix resin, which are then blended and kneaded together. The storage modulus of the cured matrix resin was 3.0 MPa when measured at 120°C and a frequency of 10 Hz, and 2.5 MPa when measured at 135°C and a frequency of 10 Hz.

[0056] 5 is a diagram schematically illustrating the bonding state using the adhesive according to Example 2. The adherends in Example 2 are glass 4 whose surface has been decoratively painted with an epoxy paint, and glass fiber reinforced epoxy resin 15. The thickness of the glass 4 is 0.6 cm, and the area of ​​the glass 4 is 15 cm x 30 cm. The glass fiber reinforced epoxy resin 15 is a glass fiber reinforced resin with an epoxy resin matrix.

[0057] First, the adhesive according to Example 2 was thinly applied as a coating to the epoxy-coated surface, which was the surface of the epoxy-based paint coating 10 applied to the glass 4, and then cured to form a demolition layer 11. The average thickness of the demolition layer 11 was 0.15 mm. The demolition layer 11 contained thermally expandable particles 7 and a matrix resin 8.

[0058] Next, the disassembly layer 11 and the glass fiber reinforced epoxy resin 15 were bonded with a two-component mixed type epoxy adhesive 13, and the glass 4 and the glass fiber reinforced epoxy resin 15 were fixed.

[0059] Furthermore, the bonded structure according to Example 2 shown in FIG. 5 was heated in a constant temperature bath at 200°C for 10 minutes, as in Example 1. At this time, the temperature of the bonded structure according to Example 2 reached 180°C. Thereafter, the bonded structure according to Example 2 was cooled to room temperature, and after the temperature reached 40°C or less, dismantling work was attempted using a scraper. The bonded structure according to Example 2 could be dismantled with a force of 98.1 N (10 kgf) or less.

[0060] Example 3 The matrix resin contained in the adhesive of Example 3 is the same as that of Example 1. The thermally expandable microparticles contained in the adhesive of Example 3 have a particle size distribution of 12 to 30 μm, expand at 170°C or higher, and become 30 times or more their original size after expansion. The thermally expandable microparticles were blended and kneaded into the adhesive of Example 3 so that the weight of the matrix resin component was 15 parts by weight, assuming that the weight of the matrix resin component was 100. In Example 3, the storage modulus of the cured matrix resin was 1.88 MPa when measured at 170°C and a measurement frequency of 10 Hz.

[0061] Fig. 6 is a diagram showing a typical bonding state using an adhesive according to Example 3. The adherends in Example 3 are tempered glass 16 whose surface is painted with a decorative epoxy paint, and an ABS resin housing 17. The tempered glass 16 is 0.6 cm thick and has an area of ​​15 cm x 30 cm. The surface of the epoxy paint applied to the tempered glass 16 is treated with atmospheric pressure plasma. The ABS resin housing 17 is made by molding ABS resin into a housing shape.

[0062] The adhesive of Example 3 was applied as a coating to the epoxy-coated surface, which was the surface of the epoxy-based paint-coated portion 10 applied to the tempered glass 16, and then cured to form a demolition layer 11. The average thickness of the demolition layer 11 was 0.2 mm. The demolition layer 11 contained thermally expandable particles 7 and a matrix resin 8.

[0063] Disassembly layer 11 was bonded to ABS resin housing 17 with urethane foam resin 18 and urethane-based hot melt adhesive 19, and tempered glass 16 was fixed to ABS resin housing 17. Note that urethane foam resin 18 has adhesive properties. Adhesive structure 21 according to Example 3, which includes tempered glass 16 and ABS resin housing 17 obtained in this manner, can be incorporated as a part of a refrigerator.

[0064] FIG. 7 is a perspective view schematically illustrating a refrigerator 20 incorporating an adhesive structure 21 according to Example 3.

[0065] The bonded structure 21 according to Example 3 was heated in a constant temperature bath at 200°C for 10 minutes, as in Example 1. At this time, the temperature of the bonded structure 21 according to Example 3 reached 180°C. Thereafter, the bonded structure 21 was cooled to room temperature, and after the temperature reached 40°C or less, dismantling work was attempted using a scraper. The bonded structure 21 could be dismantled with a force of 98.1 N (10 kgf) or less.

[0066] Example 4 Fig. 8 is a diagram schematically illustrating the bonding state using an adhesive according to Example 4. The matrix resin contained in the adhesive according to Example 4 is the same as that in Example 1. The thermally expandable fine particles contained in the adhesive according to Example 4 are fine particles in which hydrocarbons are encapsulated in an acrylic resin, with a particle size distribution of 17 to 52 µm, and expand at 125°C or higher, with the size after expansion being 30 times or more the original size. In addition to these thermally expandable fine particles, the adhesive according to Example 4 also contains the following fine particles. The fine particles are expandable graphite with an average particle size of 250 µm, i.e., 80 mesh or less, that begins to expand at 160°C, and has an expansion ratio of 30 times or more.

[0067] The thermally expandable fine particles and the expandable graphite were added to the matrix resin and kneaded so that the weight of the thermally expandable fine particles was 10 and the weight of the expandable graphite was 10, assuming the weight of the matrix resin to be 100. The storage modulus of the cured matrix resin was 1.87 MPa when measured at 160°C and a measurement frequency of 10 Hz.

[0068] An aluminum plate 23 and a phenolic resin 22 were bonded together using the adhesive of Example 4. As shown in Fig. 8, an adhesive layer 25 formed using the adhesive of Example 4 contains expanded graphite particles 24 and thermally expandable particles 7. Here, the aluminum plate 23 is an aluminum 5052 plate that has been subjected to a zirconium-based chemical conversion treatment.

[0069] The bonded structure including the aluminum plate 23 and the phenolic resin 22 was placed in a constant temperature bath at 200°C for 10 minutes and heated. At this time, the temperature of the bonded structure according to Example 4 reached 185°C. Thereafter, the bonded structure according to Example 4 was cooled to room temperature, and after the temperature reached 40°C or less, dismantling work was attempted using a scraper. The bonded structure according to Example 4 could be dismantled with a force of 98.1 N (10 kgf) or less.

[0070] The effects of the bonded structure, adhesive, and refrigerator according to the embodiment are described below. The bonded structure according to the embodiment is obtained by bonding multiple adherends with an adhesive. The adhesive according to the embodiment includes a matrix adhesive and thermally expandable microparticles. The matrix adhesive is primarily composed of an acrylic adhesive. The thermally expandable microparticles expand when heated, and after expansion, their volume becomes at least 10 times their original volume. The cured matrix adhesive has an acrylic hard phase and an elastomer phase. The acrylic hard phase is due to the acrylic component in the matrix adhesive, and the elastomer phase is due to the elastomer contained in the matrix adhesive. The elastomer phase includes two or more phases: a granular elastomer phase and a non-granular elastomer phase.

[0071] According to the above-mentioned configuration, the presence of the non-particulate elastomer phase makes it easy to dismantle the bonded structure by low-temperature heating without reducing the adhesiveness of the bonded portions in the bonded structure.

[0072] In embodiments, the non-particulate elastomer phase is present in the cured matrix adhesive in a state where it coats the acrylic hard phase, which makes it easier to disassemble the bonded structure by low-temperature heating.

[0073] The matrix adhesive according to the embodiment has a specific gravity of 0.9 to 1.2. The thermally expandable microparticles are added in an amount of 10 to 35% of the weight of the matrix adhesive. This improves the workability and dismantling properties of the bonded structure.

[0074] The bonded structure according to the embodiment further contains fine particles of thermally expandable graphite, which makes the bonded structure easier to disassemble.

[0075] An adhesive according to an embodiment includes a matrix adhesive and thermally expandable microparticles. The matrix adhesive contains an acrylic monomer as a main component and a nitrile-butadiene elastomer and a methacrylate-butadiene-styrene copolymer as elastomer components. The thermally expandable microparticles expand at temperatures of 120°C or higher, and after expansion, reach a volume 10 times or more of its original volume. In an adhesive according to an embodiment, the matrix adhesive has a specific gravity of 0.9 to 1.2 before curing, and when the matrix adhesive contains an inorganic filler, the thermally expandable microparticles are added in an amount of 10 to 35% by weight of the matrix adhesive excluding the inorganic filler.

[0076] According to the above configuration, it is possible to improve the dismantling ability of the bonded structure without impairing the adhesiveness.

[0077] DESCRIPTION OF SYMBOLS 1 Acrylic hard phase, 2 Non-granular elastomer phase, 3 Granular elastomer phase, 4 Glass, 5, 25 Adhesive layer, 6 ABS resin, 7 Thermally expandable microparticles, 8 Matrix resin, 9 Stainless steel plate, 10 Painted portion, 11 Disassembly layer, 13 Epoxy adhesive, 15 Glass fiber reinforced epoxy resin, 16 Reinforced glass, 17 ABS resin housing, 18 Urethane foam resin, 19 Urethane-based hot melt adhesive, 20 Refrigerator, 21 Adhesive structure, 22 Phenolic resin, 23 Aluminum plate, 24 Expanded graphite microparticles.

Claims

1. An adhesive structure obtained by bonding a plurality of adherends with an adhesive, The adhesive is a matrix adhesive containing an acrylic adhesive as its main component; thermally expandable particles that expand when heated and have a volume 10 times or more of their original volume after expansion; Including, The cured matrix adhesive comprises: The matrix adhesive has an acrylic hard phase due to an acrylic component and an elastomer phase due to an elastomer component contained in the matrix adhesive, The elastomer phase is An adhesive structure comprising two or more phases: a particulate elastomer phase and a non-particulate elastomer phase.

2. The non-particulate elastomer phase is The adhesive structure according to claim 1 , wherein the acrylic hard phase is present in the cured matrix adhesive in a coating state.

3. The matrix adhesive is The specific gravity is 0.9 to 1.2, The thermally expandable fine particles are The adhesive structure according to claim 1 or 2, wherein the weight of the adhesive agent added is 10 to 35% of the weight of the matrix adhesive.

4. The bonded structure according to claim 1 or 2, further comprising fine particles of thermally expandable graphite.

5. a matrix adhesive containing an acrylic monomer as a main component and a nitrile-butadiene elastomer and a methacrylate-butadiene-styrene copolymer as elastomer components; thermally expandable particles that expand at 120°C or higher and have a volume 10 times or more of their original volume after expansion; Including, An adhesive in which the specific gravity of the matrix adhesive before hardening is 0.9 to 1.2, and if the matrix adhesive contains an inorganic filler, the thermally expandable microparticles are added in an amount of 10 to 35% by weight of the matrix adhesive excluding the inorganic filler.

6. A refrigerator comprising the adhesive structure according to claim 1 or 2 as a component.