Adhesive and bonding method using the same

Abstract

To provide an adhesive that contains a coordination polymer and enables adherends such as those made of metal to be bonded with high bonding strength.SOLUTION: An adhesive contains a liquid comprising a coordination polymer including a transition metal and an azole, and a deep eutectic solvent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive and a bonding method using the same. [Background technology]

[0002] In electronic component materials such as semiconductor elements and liquid crystal display elements, various members (adherends) are bonded together using adhesives. Polymer-based adhesives such as epoxy resin adhesives have traditionally been used as adhesives for such electronic component materials. However, polymer-based adhesives have a high linear expansion coefficient, and when used to bond metal adherends, there is a problem in that the bonded portions are damaged by temperature changes.

[0003] Therefore, Japanese Patent Laid-Open Publication No. 2022-530 (Patent Document 1) discloses an adhesive composition capable of suppressing peeling after high-temperature, high-humidity treatment, which contains (a) a thermoplastic resin, (b) a silane compound having a urethane bond and an alkoxysilyl group in the molecule, (c) a radically polymerizable compound, and (d) a radical polymerization initiator, and contains (e) a compound having a urethane bond as a component other than the (a), (c), and (d) components, or the (a), (b), (c), and (d) components, and the cured product has an average linear expansion coefficient of 800 ppm / K or less at 30 to 90 °C. It also discloses that adding an insulating filler to the adhesive composition further suppresses peeling after high-temperature, high-humidity treatment. However, the adhesive composition described in Patent Document 1 has a problem in that, even when an insulating filler is added, the average linear expansion coefficient is greater than the linear expansion coefficient of the metal, and therefore, when bonding metal adherends together, the bonded portion can be damaged by temperature changes. Furthermore, there is also the problem that the addition of insulating fillers reduces adhesive strength.

[0004] On the other hand, Yanyi Zhao et al., ACS Nano, 2017, Vol. 11, pp. 3662-3670 (Non-Patent Document 1), have investigated adhesives using the Hoffmann-type cyano-bridged coordination polymer Ni(HO)2[Ni(CN)4]·4HO. They disclose that nanoflakes of platelet crystals of this Ni(HO)2[Ni(CN)4]·4HO can be used to bond adherends such as glass, plastic, and metal. However, paste-type adhesives containing solid powders have the problem of insufficient adhesive strength due to the tendency for voids to form in the adhesive layer after the solvent is removed by drying or other methods. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-530 [Non-patent literature]

[0006] [Non-Patent Document 1] Yanyi Zhao et al., ACS Nano, 2017, Vol. 11, pp. 3662-3670 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the problems associated with the above-mentioned conventional technology, and aims to provide an adhesive that contains a coordination polymer and is capable of bonding adherends, such as metals, together with high adhesive strength, and a bonding method using the same. [Means for solving the problem]

[0008] As a result of extensive research to achieve the above-mentioned object, the inventors discovered that by using an adhesive containing a coordination polymer including a transition metal and an azole, and a liquid including a deep eutectic solvent, it is possible to bond adherends, such as those made of metal, together with high adhesive strength, and thus completed the present invention.

[0009] That is, the present invention provides the following aspects. [1] An adhesive comprising a coordination polymer containing a transition metal and an azole, and a liquid containing a deep eutectic solvent. [2] The adhesive according to [1], wherein the deep eutectic solvent contains choline chloride. [3] The adhesive according to [1] or [2], wherein the coordination polymer is ZIF-8. [4] A bonding method comprising forming an adhesive layer between adherends, the adhesive layer being made of the adhesive according to any one of [1] to [3], and then heating the adhesive layer at 100 to 300°C to dissolve at least a part of the coordination polymer in the adhesive layer, and then curing the adhesive layer. [5] The bonding method according to [4], wherein the adherend is at least one selected from the group consisting of a metal adherend, a metal oxide adherend, and a metal nitride adherend.

[0010] While the reason why the adhesive of the present invention enables bonding of metal and other adherends with high adhesive strength is not entirely clear, the inventors speculate as follows. Generally, once synthesis is complete, coordination polymers such as metal-organic frameworks do not readily dissolve in solvents that dissolve the synthesis raw materials of the coordination polymer. However, coordination polymers are known to dissolve in deep eutectic solvents. For example, the solubility of the metal-organic framework ZIF-8 is known to be 3 g at 170°C and 0.2 g or less at 110°C per 1 g of deep eutectic solvent (a eutectic mixture of choline chloride and urea) (Y. Wang et al., Microporous and Mesoporous Materials, 2014, Vol. 195, pp. 50-59). The adhesive of the present invention contains a coordination polymer that dissolves in such a deep eutectic solvent and a liquid containing the deep eutectic solvent. In an adhesive layer formed by such an adhesive, at least a portion of the coordination polymer dissolves in the deep eutectic solvent upon heat treatment, forming a liquid phase. This liquid adhesive easily spreads over the interface between the adherends, forming a uniform liquid adhesive layer between the adherends. When this uniform liquid adhesive layer is cooled, a solid component composed primarily of the coordination polymer precipitates, and the adherends are bonded together by this solid component. In the bonding method of the present invention, the solid component spreads uniformly over the bonding surfaces of the adherends, which is presumably why the adherends are bonded together with high adhesive strength. [Effects of the Invention]

[0011] According to the present invention, it is possible to bond adherends made of metal or the like together with high adhesive strength. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic perspective view showing the bonded bodies produced in Examples 1 and 2 and Comparative Example 3. [Figure 2] FIG. 1 is a schematic diagram showing an outline of the compression tests carried out in Examples 1 and 2 and Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below based on preferred embodiments thereof.

[0014] 〔glue〕 First, the adhesive of the present invention will be described. The adhesive of the present invention contains a coordination polymer (CP) containing a transition metal and an azole, and a liquid containing a deep eutectic solvent. The coordination polymer has a structure in which the azole is coordinated to the transition metal, and the polymer structure is formed by van der Waals forces and coordinate bonds. Note that a "coordination polymer (CP)" is a complex having a continuous structure consisting of multidentate ligands and metal ions, and a "metal-organic framework (MOF)" is a coordination polymer (CP) that has pores.

[0015] The transition metal is not particularly limited as long as it can form a coordination polymer with an azole coordinated thereto. From the viewpoints of environmental friendliness and rarity, however, Group 6 elements such as Cr, Group 7 elements such as Mn, Group 8 elements such as Fe, Group 9 elements such as Co, Group 10 elements such as Ni, Group 11 elements such as Cu, and Group 12 elements such as Zn and Cd are preferred, with Cr, Mn, Fe, Co, Ni, Cu, Zn, and Cd being more preferred, with Zn, Co, Mn, Ni, and Cu being even more preferred, and Zn and Co being particularly preferred.

[0016] The azoles are not particularly limited as long as they can be coordinated to the transition metal to form a coordination polymer, and examples thereof include pyrroles, diazoles (e.g., imidazoles, pyrazoles), triazoles, and tetrazoles. Among these azoles, from the viewpoint of coordination, imidazoles, pyrazoles, and triazoles are preferred, imidazoles and triazoles are more preferred, and imidazoles are particularly preferred. Examples of the imidazoles include imidazole, methylimidazole, and benzimidazole.

[0017] Furthermore, it is preferable that the decomposition temperature of the coordination polymer is higher than the heating temperature (hereinafter also referred to as the "curing temperature") when the adhesive of the present invention is cured. If the decomposition temperature of the coordination polymer is lower than the curing temperature, the coordination polymer will be decomposed by heating when curing the adhesive, which tends to make it difficult to form an adhesive layer with high adhesive strength. The decomposition temperature of the coordination polymer can be measured by thermal analysis such as thermogravimetry (TGA).

[0018] Furthermore, the coordination polymer preferably has a crystal linear expansion coefficient of 20 ppm / K or less, more preferably 10 ppm / K or less. An adhesive containing a coordination polymer whose crystals have such a linear expansion coefficient exhibits high reliability against temperature changes, even when bonding metal adherends together. The linear expansion coefficient of the coordination polymer crystal can be determined from the slope of the relationship between the lattice constant and temperature by measuring the temperature dependence of the lattice constant of the coordination polymer crystal, which is determined based on the XRD spectrum obtained by X-ray diffraction (XRD) measurement.

[0019] Specific examples of such coordination polymers include those shown in Table 1.

[0020] [Table 1]

[0021] Among these coordination polymers, from the viewpoints of heat resistance and ease of synthesis, coordination polymers belonging to the Zeolitic Imidazolate Framework (ZIF) are preferred, and [Zn(2-MeIm)2] (ZIF-8) is more preferred.

[0022] The adhesive of the present invention contains such a coordination polymer and a liquid containing a deep eutectic solvent. A deep eutectic solvent is a eutectic mixture of a hydrogen bond donor compound and a hydrogen bond acceptor compound, and is liquid at room temperature.

[0023] Examples of such deep eutectic solvents include eutectic mixtures of choline chloride and nitrogen-containing compounds, such as a eutectic mixture of choline chloride and urea and a eutectic mixture of choline chloride and imidazole; eutectic mixtures of choline chloride and ethylene glycol, a eutectic mixture of choline chloride and glycerol, a eutectic mixture of choline chloride and o-cresol, a eutectic mixture of choline chloride and 2,3-xylenol, a eutectic mixture of choline chloride and phenol, and a eutectic mixture of choline chloride and glucose. eutectic mixtures of choline chloride and hydroxyl-containing compounds, such as a eutectic mixture of choline chloride and acrylic acid, a eutectic mixture of choline chloride and citric acid, a eutectic mixture of choline chloride and malonic acid, a eutectic mixture of choline chloride and oxalic acid, a eutectic mixture of choline chloride and phenylacetic acid, a eutectic mixture of choline chloride and phenylpropanoid acid, and a eutectic mixture of choline chloride and succinic acid. Preferred deep eutectic solvents contain at least choline chloride.

[0024] In the adhesive of the present invention, the mass ratio of the coordinating polymer to the deep eutectic solvent (coordinating polymer:deep eutectic solvent) is preferably 100:1 to 100:100, more preferably 100:10 to 100:70, and even more preferably 100:40 to 100:60. If the mass ratio (coordinating polymer:deep eutectic solvent) is below the lower limit, the binding between the particles of the coordinating polymer tends to be insufficient. On the other hand, if the mass ratio (coordinating polymer:deep eutectic solvent) exceeds the upper limit, the liquid component tends to remain in a large amount, and the binding strength tends to decrease.

[0025] Furthermore, in the adhesive of the present invention, the solubility of the coordination polymer in the deep eutectic solvent is preferably 0.1 g or more, more preferably 0.5 g or more, and even more preferably 1 to 100 g, per 1 g of the deep eutectic solvent at 170° C. If the solubility of the coordination polymer is below the lower limit, the ratio of the solvent component in the adhesive must be increased, which tends to reduce the binding strength. On the other hand, if the solubility of the coordination polymer exceeds the upper limit, the adhesive strength tends to reduce due to the inclusion of trace amounts of solvent components.

[0026] Furthermore, in the adhesive of the present invention, from the viewpoint of adhesive strength, it is preferable to use only a deep eutectic solvent as the liquid containing the deep eutectic solvent. However, from the viewpoint of adjusting the concentration to a level suitable for application, a mixed solvent of a deep eutectic solvent and a diluent solvent may be used within a range that does not impair adhesive strength. Examples of the diluent solvent include polar solvents such as water, alcohols such as ethanol, carbonate solvents such as dimethyl carbonate, and ether solvents such as dimethoxyethane. Since these diluent solvents need to be removed when the adhesive layer is heated, it is preferable to appropriately select and use a diluent solvent with a boiling point lower than the heating temperature of the adhesive layer.

[0027] [Adhesion method] Next, the bonding method of the present invention will be described. The bonding method of the present invention is a method in which an adhesive layer made of the adhesive of the present invention is formed between adherends, and then the adhesive layer is heated at 100 to 300°C to dissolve at least a portion of the coordination polymer in the adhesive layer, and then the adhesive layer is cured.

[0028] (Adhesive layer formation process) In the bonding method of the present invention, first, an adhesive layer made of the adhesive of the present invention is formed between the adherends. Specifically, an appropriate amount of the adhesive of the present invention is applied to an adherend (preferably a metal adherend), and another adherend (preferably a metal adherend) is placed on top of it, thereby forming the adhesive layer between the adherends.

[0029] (melting process) Next, the adhesive layer formed between the adherends is heated at 100 to 300°C to dissolve at least a portion of the coordination polymer in the adhesive layer. This forms a liquid phase in which the coordination polymer is dissolved in the deep eutectic solvent. This liquid phase easily spreads between the adherends, forming a uniform liquid adhesive layer over the entire bonding surface.

[0030] The lower limit of the heating temperature of the adhesive layer is preferably 150°C or higher, more preferably 200°C or higher, from the viewpoint of removing the deep eutectic solvent component. Furthermore, when the liquid contained in the adhesive used contains a diluent solvent such as water, the lower limit of the heating temperature of the adhesive layer is preferably equal to or higher than the boiling point of the diluent solvent, from the viewpoint of reliably removing the diluent solvent from the adhesive layer. On the other hand, the upper limit of the heating temperature of the adhesive layer is preferably a temperature lower than the decomposition temperature of the coordination polymer, because thermal decomposition of the coordination polymer may change the adhesive principle and result in a decrease in adhesive strength. Therefore, a temperature 30°C lower than the decomposition temperature of the coordination polymer is more preferable.

[0031] (hardening process) Next, the adhesive layer is continuously heated, and the liquid containing the deep eutectic solvent is removed from the liquid adhesive layer (liquid phase), thereby precipitating a solid component mainly composed of the coordination polymer, and hardening the adhesive layer. In the bonding method of the present invention, the solid component is precipitated from the uniform liquid adhesive layer over the entire bonding surface, and the adhesive layer hardens, so that the adherends are bonded together with high adhesive strength. [Example]

[0032] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0033] Example 1 First, 1.40 g (10.0 mmol) of choline chloride (manufactured by Tokyo Chemical Industry Co., Ltd., purity: 98.0%) and 1.22 g (20.3 mmol) of urea (manufactured by Tokyo Chemical Industry Co., Ltd., purity: 99.0%) were mixed in a screw tube in the atmosphere, and then the pressure was reduced in a dry oven and the mixture was heated at 100°C until it became a transparent liquid. After that, the mixture was allowed to cool, and a transparent deep eutectic solvent was obtained.

[0034] Next, ZIF-8 (Sigma-Aldrich's "Basolite Z1200") as a coordination polymer and the deep eutectic solvent were mixed in a mortar in air at a mass ratio of 10:5 to prepare a powder adhesive. The solubility of ZIF-8 in 1 g of the deep eutectic solvent is 3 g at 170 °C and 0.2 g or less at 110 °C.

[0035] Next, two copper discs were bonded using this adhesive as shown in Figure 1. Specifically, an appropriate amount of the adhesive was applied to the center (5 cm diameter) of a disc-shaped test piece of oxygen-free copper C1020 (adherend A in Figure 1, 10 mm diameter, 5 mm thickness) with a spatula and spread evenly to form an adhesive layer. A disc-shaped test piece of oxygen-free copper C1020 (adherend B in Figure 1, 5 mm diameter, 3 mm thickness) was then placed on this adhesive layer, and then placed on a hot plate set at 220 °C. While lightly pressing the top of adherend B with a spatula, the bottom of adherend A was heated for 10 minutes to harden the adhesive layer, bonding the two copper discs (adherends A and B in Figure 1). The two bonded copper discs were then placed on aluminum foil and allowed to cool at room temperature.

[0036] One of the adherends of the obtained bonded body (adherends A and B bonded together) was picked up with tweezers and lifted up, but the bonded surfaces did not peel off and it was possible to lift it up.

[0037] Furthermore, a compression test was conducted on the bonded structure using a compression testing machine (homemade using a "Digital Force Gauge" manufactured by Imada Co., Ltd.) in air at a loading rate of 1 mm / min as shown in Figure 2, and the compressive shear strength was measured to be 4.5 MPa.

[0038] Furthermore, when the fracture surface was visually inspected after measuring the compressive shear strength, it was found to have a metallic luster and that a dark green solid had adhered to the periphery of adherend B.

[0039] Example 2 A suspension containing the adhesive was prepared by adding ion-exchanged water at a mass ratio of 1:1.5 to the powdered adhesive prepared in the same manner as in Example 1 and stirring the mixture. Two copper disks were bonded together in the same manner as in Example 1, except that this suspension was used.

[0040] One of the adherends of the resulting bonded structure (bonded together adherends A and B) was picked up with tweezers and lifted without peeling off the bonded surfaces. Furthermore, the compressive shear strength of the bonded structure was measured in the same manner as in Example 1, and was found to be 3.5 MPa. Furthermore, visual inspection of the fracture surface after measuring the compressive shear strength revealed a metallic luster, and a dark green solid was found attached to the periphery of adherend B.

[0041] Example 3 Two aluminum plates were bonded in the same manner as in Example 1, except that instead of the two copper discs, an aluminum plate (40 mm x 10 mm x 1.5 mm thick) was used as adherend A and an aluminum plate (4 mm x 4 mm x 1.5 mm thick) was used as adherend B.

[0042] One of the adherends of the obtained bonded structure (bonded together the adherends A and B) was picked up with tweezers and lifted without peeling off the bonded surfaces. Furthermore, the compressive shear strength of the bonded structure was measured in the same manner as in Example 1, and was found to be 3.6 MPa. Furthermore, visual inspection of the fracture surface after measuring the compressive shear strength revealed that there were areas with a metallic luster and areas with a milky white solid attached, and that a brown solid was attached to the periphery of the adherend B.

[0043] Example 4 Two alumina plates were bonded in the same manner as in Example 1, except that an alumina plate (20 mm x 15 mm x 1.5 mm thick) was used as adherend A and an alumina plate (15 mm x 8 mm x 1.5 mm thick) was used as adherend B instead of the two copper discs.

[0044] One of the adherends of the obtained bonded structure (bonded together the adherends A and B) was picked up with tweezers and lifted without peeling off the bonded surfaces. Furthermore, the compressive shear strength of the bonded structure was measured in the same manner as in Example 1, and was found to be 4.5 MPa. Furthermore, visual inspection of the fracture surface after measuring the compressive shear strength revealed that a brown solid had adhered to the periphery of the adherend B.

[0045] Example 5 Two aluminum nitride plates were bonded in the same manner as in Example 1, except that instead of the two copper discs, an aluminum nitride plate (20 mm x 20 mm x 0.5 mm thick) was used as adherend A and an aluminum nitride plate (10 mm x 10 mm x 0.5 mm thick) was used as adherend B.

[0046] One of the adherends of the obtained bonded structure (bonded together the adherends A and B) was picked up with tweezers and lifted without peeling off the bonded surfaces. Furthermore, the compressive shear strength of the bonded structure was measured in the same manner as in Example 1, and was found to be 3.7 MPa. Furthermore, visual inspection of the fracture surface after measuring the compressive shear strength revealed that a brown solid had adhered to the periphery of the adherend B.

[0047] Example 6 First, 3.59 g (25.7 mmol) of choline chloride (Tokyo Chemical Industry Co., Ltd., purity: 98.0%) and 3.96 g (63.8 mmol) of ethylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd., purity: 99.5%) were mixed in a screw tube in the atmosphere, and then stirred at room temperature for 8 hours to obtain a deep eutectic solvent.

[0048] Next, in the atmosphere, ZIF-8 (Sigma-Aldrich's "Basolite Z1200") as a coordination polymer and the deep eutectic solvent were mixed in a mass ratio of 1:1 using a mortar to prepare a paste-like adhesive.

[0049] Next, using this adhesive, two copper disks were bonded together in the same manner as in Example 1, except that the hot plate temperature was set to 250° C. and the heating time was changed to 6 minutes.

[0050] One of the adherends of the obtained bonded structure (bonded together the adherends A and B) was picked up with tweezers and lifted without peeling off the bonded surfaces. Furthermore, the compressive shear strength of the bonded structure was measured in the same manner as in Example 1, and was found to be 3.3 MPa. Furthermore, visual inspection of the fracture surface after measuring the compressive shear strength revealed that a solid had adhered to the periphery of the adherend B.

[0051] (Comparative Example 1) A powdered adhesive was prepared in the same manner as in Example 1, except that ion-exchanged water was used instead of the deep eutectic solvent, and two copper disks were bonded together using this adhesive.

[0052] When one of the adherends of the obtained bonded body (bonded together the adherends A and B) was picked up with tweezers and lifted, the bonded surface peeled off and it could not be lifted. Furthermore, when the peeled bonded surface was visually inspected, the adhesive remained in a powdery state.

[0053] (Comparative Example 2) A powder adhesive was prepared in the same manner as in Example 1, except that ethanol was used instead of the deep eutectic solvent, and two copper disks were then bonded together using this adhesive.

[0054] When one of the adherends of the obtained bonded body (bonded together the adherends A and B) was picked up with tweezers and lifted, the bonded surface peeled off and it could not be lifted. Furthermore, when the peeled bonded surface was visually inspected, the adhesive remained in a powdery state.

[0055] (Comparative Example 3) Two copper disks were bonded together in the same manner as in Example 1, except that urea (manufactured by Tokyo Chemical Industry Co., Ltd., purity: 99.0%) was used instead of the powder adhesive.

[0056] One of the adherends of the obtained bonded structure (bonded together the adherends A and B) was picked up with tweezers and lifted without peeling of the bonded surfaces. Furthermore, the compressive shear strength of the bonded structure was measured in the same manner as in Example 1, and was found to be 0.5 MPa or less. Furthermore, visual inspection of the fracture surface after measuring the compressive shear strength revealed that it had turned black and had no metallic luster.

[0057] Comparative Example 4 Two copper disks were bonded together in the same manner as in Example 1, except that choline chloride (Tokyo Chemical Industry Co., Ltd., purity: 98.0%) was used instead of the powdered adhesive.

[0058] When one of the adherends of the obtained bonded body (bonded together the adherends A and B) was picked up with tweezers and lifted, the bonded surface peeled off and could not be lifted. Furthermore, when the peeled bonded surface was visually inspected, black powder was found to be attached.

[0059] (Comparative Example 5) Two copper disks were bonded in the same manner as in Example 1, except that a deep eutectic solvent prepared in the same manner as in Example 1 was used instead of the powder adhesive. When one of the adherends of the resulting bonded body (adherends A and B bonded together) was picked up with tweezers and lifted, the bonded surface peeled off and could not be lifted. Furthermore, when the peeled bonded surface was visually observed, it had a metallic luster but was covered with liquid.

[0060] (Reference example 1) In the atmosphere, 5 g of ion-exchanged water or ethanol was placed in a screw bottle, and 50 mg of ZIF-8 (Sigma-Aldrich "Basolite Z1200") was added, followed by stirring at room temperature using a shaker. Visual observation of the inside of the screw bottle revealed that the contents were suspended in both ion-exchanged water and ethanol.

[0061] Next, the screw bottle was placed on a hot stirrer and heated to about 90° C. while stirring at 300 rpm, and then the screw bottle was removed from the hot stirrer and allowed to cool to 30° C. Visual observation of the inside of the screw bottle during heating and cooling revealed that the contents were in a suspended state both during heating and cooling in both the ion-exchanged water and ethanol cases.

[0062] Furthermore, the screw bottle was again placed on the hot stirrer and heated to about 90° C. while stirring at 300 rpm, and then the screw bottle was removed from the hot stirrer and allowed to cool to 30° C. Visual observation of the inside of the screw bottle during heating and cooling revealed that the contents were in a suspended state both during heating and cooling in both the ion-exchanged water and ethanol cases.

[0063] These results show that the solubility of ZIF-8 in water or ethanol is 50 mg / 5 g (i.e., 1 mass %) or less at any of the temperatures mentioned above.

[0064] (Reference example 2) In the atmosphere, 1 mg of ZIF-8 (Sigma-Aldrich "Basolite Z1200") was placed in a screw bottle, 100 ml of ion-exchanged water was added, and the mixture was stirred at 100 rpm at room temperature using a stirrer. During stirring, a laser beam was irradiated onto the screw bottle using a laser pointer, and a light path was observed inside the screw bottle, confirming the Tyndall phenomenon.

[0065] Next, the screw bottle was placed on a hot stirrer and stirred at 100 rpm while being heated to 60°C. When the screw bottle was irradiated with laser light using a laser pointer while being heated and stirred, a light path was observed inside the screw bottle, confirming the Tyndall phenomenon.

[0066] From these results, it was found that the Tyndall phenomenon occurred at all of the above temperatures, ZIF-8 was dispersed in water without dissolving, and the solubility of ZIF-8 in water was 1 mg / 100 g (i.e., 0.001 mass%) or less.

[0067] [Table 2]

[0068] As shown in Table 2, when an adhesive containing a coordination polymer and a liquid including a deep eutectic solvent was used (Examples 1 to 6), it was confirmed that adherends made of metal, metal oxide, metal nitride, etc. could be bonded with high adhesive strength. This is presumably because, upon heating at 220°C, the coordination polymer in the adhesive layer gradually dissolved in the deep eutectic solvent to form a liquid phase, which then wetted and spread to the interface between adherend A and adherend B, and then, upon cooling, solid components precipitated from the liquid phase, hardening the adhesive layer.

[0069] Furthermore, it was confirmed that even when the deep eutectic solvent was diluted with water (Example 2), the adherends could be bonded with high adhesive strength. This is presumably because, as in the case where the dilution solvent, water, was evaporated by heating at 220°C, the coordination polymer in the adhesive layer gradually dissolved in the deep eutectic solvent to form a liquid phase, which then spread to the interface between adherend A and adherend B, and then, by cooling, solid components precipitated from the liquid phase, hardening the adhesive layer. Furthermore, this suggests that even when diluted with a dilution solvent other than water, by heating at a temperature above the boiling point of the dilution solvent to evaporate (volatilize) the dilution solvent, adherends made of metals, metal oxides, metal nitrides, etc. can be bonded with high adhesive strength.

[0070] On the other hand, when using an adhesive containing a coordination polymer and water (Comparative Example 1) or an adhesive containing a coordination polymer and ethanol (Comparative Example 2), that is, an adhesive not containing a deep eutectic solvent, it was difficult to bond the adherend with high adhesive strength. This is because, as shown in Reference Examples 1 and 2, the solubility of ZIF-8 in water or ethanol is very low, and it is presumed that in the adhesives prepared in Comparative Examples 1 and 2, ZIF-8 is dispersed in water or ethanol. Even when such an adhesive is used to bond the adherend, the ZIF-8 does not dissolve by heat treatment, and the ZIF-8 particles do not bond to each other or to the adherend surface, or even if they do bond, it is presumed that the adhesion is very weak. [Industrial Applicability]

[0071] As described above, according to the present invention, it is possible to obtain an adhesive that contains a coordination polymer and is capable of bonding adherends made of metals, etc. with high adhesive strength. Therefore, a bonding method using the adhesive of the present invention is useful as a method for bonding metal members in electronic component materials such as semiconductor elements and liquid crystal display elements, aircraft brake linings, etc.

Claims

1. An adhesive comprising a coordination polymer containing a transition metal and an azole, and a liquid containing a deep eutectic solvent.

2. 2. The adhesive of claim 1, wherein the deep eutectic solvent comprises choline chloride.

3. 2. The adhesive according to claim 1, wherein the coordination polymer is ZIF-8.

4. A bonding method comprising forming an adhesive layer between adherends, the adhesive layer being made of the adhesive according to claim 1, and then heating the adhesive layer at 100 to 300°C to dissolve at least a portion of the coordination polymer in the adhesive layer, and then curing the adhesive layer.

5. 5. The bonding method according to claim 4, wherein the adherend is at least one selected from the group consisting of a metal adherend, a metal oxide adherend, and a metal nitride adherend.

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