Structure

Abstract

The structure (1) comprises an aluminum substrate (111) and an adhesive layer (12) composed of an adhesive resin bonded to the surface of the aluminum substrate (111). The adhesive layer (12) comprises a hard layer (121) bonded to an adhesive interface (131) with the aluminum substrate (111) and a main body layer (123) bonded to the hard layer (121). The hard layer (121) is harder than the main body layer (123).

Description

[0001] Cross-reference to related applications

[0002] This application is based on Japanese application No. 2020-001210 filed on January 8, 2020, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to structures. Background Art

[0004] Conventionally, there has been widely known a structure including an aluminum substrate and an adhesive layer composed of an adhesive resin such as an epoxy resin that is bonded to the surface of the aluminum substrate.

[0005] Furthermore, as described in Patent Document 1, a structure in which a primer is applied between an aluminum substrate and an adhesive layer composed of an adhesive resin is also known.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-239644 Summary of the Invention

[0009] In conventionally known structures, the interface between the aluminum substrate and the adhesive layer is relatively fragile. Therefore, prolonged contact with solvents or thermal shock can cause delamination at the interface between the aluminum substrate and the adhesive layer.

[0010] An object of the present disclosure is to provide a structure that can exhibit high adhesive strength even when in contact with a solvent for a long time or when subjected to thermal shock.

[0011] One embodiment of the present disclosure is a structure including an aluminum substrate and an adhesive layer composed of an adhesive resin adhered to a surface of the aluminum substrate.

[0012] The adhesive layer includes a hard layer in contact with the bonding interface with the aluminum substrate and a main body layer in contact with the hard layer.

[0013] The hard layer is harder than the main body layer.

[0014] The bonding resin is epoxy resin or silicone resin.

[0015] According to the above structure, high adhesive strength can be exhibited even when it is in contact with a solvent for a long time or when thermal shock is applied.

[0016] It should be noted that the symbols in parentheses described in the scope of the claims indicate the correspondence relationship with the specific methods described in the embodiments described below, and do not limit the technical scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above-mentioned objects and other objects, features and advantages of the present disclosure will become more apparent through reference to the accompanying drawings and the following detailed description. The accompanying drawings are as follows:

[0018] Figure 1 is a diagram schematically showing a structure of Embodiment 1,

[0019] Figure 2 are explanatory diagrams of the inferred mechanism of improved bonding strength, wherein (a) schematically shows the state of the adhesive resin in the structure of Embodiment 1, and (b) schematically shows the state of the adhesive resin in the structure of a comparative embodiment.

[0020] Figure 3 is a diagram schematically showing the relationship between the distance from the bonding interface and the adsorption force or elastic modulus in the cross section of the adhesive layer.

[0021] Figure 4 is a diagram schematically showing a structure of Embodiment 2,

[0022] Figure 5 FIG. 1 is a diagram showing an adsorption force image of a cross section of the adhesive layer of Sample 1 obtained by surface observation using a scanning probe microscope in Experimental Example 1.

[0023] Figure 6 FIG. 1 is a diagram showing an adsorption force image of a cross section of the adhesive layer of Sample 1C obtained by surface observation using a scanning probe microscope in Experimental Example 1.

[0024] Figure 7 : is a diagram showing an elastic modulus image of the adhesive layer cross section of Sample 1 obtained by surface observation using a scanning probe microscope in Experimental Example 1.

[0025] Figure 8 : is a figure showing the elastic modulus image of the adhesive layer cross section of sample 1C obtained by surface observation using a scanning probe microscope in Experimental Example 1.

[0026] Figure 9 : is a graph showing the relationship between the distance from the bonding interface and the adsorption force in the cross section of the adhesive layer of Sample 1 and Sample 1C obtained in Experimental Example 2.

[0027] Figure 10 : is a graph showing the relationship between the distance from the bonding interface and the adsorption force in the cross section of the adhesive layer of Sample 2 and Sample 2C obtained in Experimental Example 2.

[0028] Figure 11 Graph showing the relationship between the distance from the bonding interface and the elastic modulus in the cross section of the adhesive layer of Sample 1 and Sample 1C obtained in Experimental Example 2.

[0029] Figure 12 Graph showing the relationship between the distance from the bonding interface and the elastic modulus in the cross section of the adhesive layer of Sample 2 and Sample 2C obtained in Experimental Example 2.

[0030] Figure 13 This is a graph showing the tensile shear strength of the structures of Sample 1 and Sample 1C obtained in Experimental Example 3 under various conditions. DETAILED DESCRIPTION

[0031] The structure of this embodiment comprises an aluminum substrate and an adhesive layer composed of an adhesive resin bonded to the surface of the aluminum substrate. The adhesive layer comprises a hard layer in contact with the bonding interface with the aluminum substrate and a main body layer in contact with the hard layer. The hard layer is harder than the main body layer.

[0032] The structure of this embodiment can mainly produce fractures in the main layer even when it is in contact with a solvent for a long time or subjected to thermal shock. That is, in the structure of this embodiment, it is mainly the base material of the main layer that breaks, rather than the interface fracture. It is believed that this is because, even if the bonding layer is composed of the same bonding resin, the resin properties of the bonding resin in the main layer do not change. On the other hand, the resin properties of the bonding resin fixed to the bonding interface in a manner that is harder than the main layer in the hard layer change, and the strength near the bonding interface increases.

[0033] Therefore, the structure according to this embodiment can exhibit high adhesive strength even when it is in contact with a solvent for a long time or is subjected to thermal shock. This will be described in detail below.

[0034] (Implementation 1)

[0035] For the structure of embodiment 1, use Figure 1 、 Figure 2 For explanation. Figure 1 As shown in FIG. 1 , the structure 1 of the present embodiment includes an aluminum substrate 111 and an adhesive layer 12 .

[0036] The aluminum referred to in the aluminum substrate 111 includes not only pure aluminum but also aluminum alloys. Specifically, examples of the aluminum substrate 111 include substrates of variously shaped components made of aluminum or aluminum alloys. Examples of aluminum alloys include 1000-series Al alloys, 2000-series Al alloys, 3000-series Al alloys, 4000-series Al alloys, 5000-series Al alloys, 6000-series Al alloys, 7000-series Al alloys, and aluminum die-casting alloys such as ADC12.

[0037] In the surface of the aluminum substrate 111, at least the bonding surface to which the bonding layer 12 is bonded can be modified. Specifically, the bonding surface can remove all or part of the oxide film layer (not shown). In addition, a modified layer (not shown) composed of silicate glass or the like can be provided on the surface of the bonding surface from which all or part of the oxide film layer has been removed. According to this structure, a covalent bond is easily formed between the modified layer and the adhesive resin, and combined with the strength-enhancing effect near the bonding interface 131, high bonding strength can be easily exerted. As silicate glass, for example, silicate glass having Al element solid dissolved therein, i.e., aluminosilicate glass, etc. can be exemplified.

[0038] The adhesive layer 12 is composed of an adhesive resin that adheres to the surface of the aluminum substrate 111. Specifically, the adhesive layer 12 may be formed partially on the surface of the aluminum substrate 111 or may be formed on the entire surface of the aluminum substrate 111.

[0039] As the adhesive resin, for example, epoxy resin, polyurethane resin, melamine resin, urea-formaldehyde resin, silicone resin, polyester resin, etc. can be cited. Among them, as the adhesive resin, epoxy resin or silicone resin can be used. Since epoxy resin and silicone resin can produce covalent bonds by chemical reaction with the OH group that may be present on the surface of the aluminum substrate 111, it is easy to improve the strength near the bonding interface 131. For example, as mentioned above, in the case where the aluminum substrate 111 has a modified layer composed of silicate glass on the surface, epoxy resin can produce covalent bonds by chemical reaction between the OH group on the surface of the modified layer and the epoxy group. In addition, silicone resin can produce covalent bonds with the OH group on the surface of the modified layer through dehydration condensation reaction. It should be noted that, as needed, the adhesive resin can contain one or more various additives applied to general resin-based adhesives.

[0040] The adhesive layer 12 includes a hard layer 121 and a main layer 123. The hard layer 121 is in contact with the bonding interface 131 with the aluminum substrate 111. The main layer 123 is in contact with the hard layer 121. Since both the hard layer 121 and the main layer 123 are part of the adhesive layer 12, they are essentially formed integrally from the same type of adhesive resin that constitutes the adhesive layer 12. However, the state of the polymer constituting the adhesive resin differs between the hard layer 121 and the main layer 123. Therefore, the hardness of the hard layer 121 and the main layer 123 differs. Specifically, the hard layer 121 is harder than the main layer 123.

[0041] The inferred mechanism by which a structure having such a configuration can exhibit high adhesive strength is explained. Figure 2As shown in (b), the adhesive layer 12' of the comparative structure 1' does not have a hard layer 121 and a main layer 123, and the adhesive layer 12' has a uniform hardness as a whole. In such a structure, the cross-linking density of the adhesive resin constituting the adhesive layer 12' is roughly the same in the thickness direction of the adhesive layer 12', and the strength near the adhesive interface 131 is not improved. Therefore, the previous structure 1' is prone to peeling at the adhesive interface 131. In contrast, the adhesive layer 12 of the structure 1 of this embodiment has a hard layer 121 and a main layer 123, and the hard layer 121 is harder than the main layer 123. In such a structure, the cross-linking density of the adhesive resin constituting the hard layer 121 is greater than the cross-linking density of the adhesive resin constituting the main layer 123, and the strength near the adhesive interface 131 is improved by increasing the cross-linking density. It should be noted that in Figure 2 , the intersections of the grids shown in the adhesive layers 12 and 12' represent crosslinking points. Thus, in the structure 1, fracture occurs first in the relatively low-strength main layer 123 (parent material fracture), making it less likely for interfacial fracture to occur at the adhesive interface 131. Consequently, the structure 1 can maintain high adhesive strength even when exposed to solvents for extended periods or subjected to thermal shock.

[0042] The hard layer 121 can be configured to bond to the surface of the aluminum substrate 111 via covalent bonds. With this configuration, compared to a configuration where the hard layer 121 is bonded to the surface of the aluminum substrate 111 via an anchoring effect or hydrogen bonding, solvents are less likely to penetrate into the bonding interface 131. Therefore, with this configuration, the strength of the bonding interface 131 is less likely to deteriorate, and the strength improvement effect of the bonding interface 131 can be ensured. Furthermore, the long-term bonding reliability of the bonding interface 131 is also improved. It should be noted that hydrogen bonds are severed by the attack caused by the solvent that penetrates the bonding interface 131, and the severed portions become new reaction points, causing a chain reaction. Therefore, bonds generated by hydrogen bonds are more susceptible to degradation of the bonding interface 131 with solvents such as organic solvents, compared to bonds generated by covalent bonds.

[0043] Here, as described above, the hardness of the adhesive layer 12 is related to the crosslinking density of the adhesive resin. Therefore, the relationship between the distance from the bonding interface 131 to the inner side of the adhesive layer 12 and the crosslinking density is directly measured. If the crosslinking density of the hard layer 121 is greater than the crosslinking density of the main layer 123, it can be said that the hard layer 121 is harder than the main layer 123. However, it is difficult to measure the crosslinking density distribution of the adhesive resin in the adhesive layer 12. Therefore, the present inventors repeated trial and error and found that the adsorption force or elastic modulus of the adhesive resin is selected as the resin property. When the adsorption force of the hard layer 121 is greater than the adsorption force of the main layer 123 and / or the elastic modulus of the hard layer 121 is greater than the elastic modulus of the main layer 123, the hard layer 121 can be harder than the main layer 123, and the above-mentioned effect can be achieved.

[0044] Specifically, if Figure 3As shown in the example, the structure 1 can be configured such that the adsorption force of the hard layer 121, as measured using a scanning probe microscope in a cross section of the adhesive layer 12 perpendicular to the adhesive interface 131, is greater than the adsorption force of the main body layer 123. Furthermore, the structure 1 can be configured such that the elastic modulus of the hard layer 121, as measured using a scanning probe microscope in a cross section of the adhesive layer 12 perpendicular to the adhesive interface 131, is greater than the elastic modulus of the main body layer 123. With these configurations, the above-described effects can be ensured.

[0045] The measurement of adsorption force and elastic modulus can be carried out as follows. A measurement sample having a cross section of the adhesive layer 12 perpendicular to the adhesive interface 131 is collected from the structure 1 of the measurement object. As a scanning probe microscope, a scanning probe microscope "SPM9500" manufactured by Shimadzu Corporation can be used. It should be noted that if this model has been discontinued and is not available, a subsequent model can be used. The probe uses an AFM cantilever made of Si3N4 ("SN-AF01" (spring constant 0.08N / m) manufactured by Hitachi High-Tech Science Company). The measurement mode of the scanning probe microscope is set to contact mode, and the action mode is set to force curve mode. The frequency during measurement is set to 1Hz, and the contact voltage is set to 0.5V. Using the above-mentioned scanning probe microscope, the force curve of each position of the adhesive layer 12 is measured while gradually increasing the distance from the adhesive interface 131 appearing on the cross section of the adhesive layer 12 in the measurement sample along the thickness direction of the adhesive layer 12 while measuring the force curve. That is, the distance from the bonding interface 131 in the bonding layer 12 to the inner side of the bonding layer 12 is gradually changed, and the force curve at each position of the cross section of the bonding layer 12 is measured. Next, the elastic modulus and the adsorption force at each position of the cross section of the bonding layer 12 are obtained from the force curve at each position of the cross section of the bonding layer 12. It should be noted that according to the measurement using a scanning probe microscope, if the cantilever is brought close to the surface of the measurement sample and the cantilever is brought into contact with the measurement sample, a deflection on the repulsive side occurs in the cantilever. Then, if the cantilever begins to leave the measurement sample, the deflection of the cantilever decreases, but due to the adsorption force generated between the surface of the measurement sample and the cantilever, a deflection on the attractive side occurs in the opposite direction to the above. Then, the cantilever completely detaches from the surface of the measurement sample. The elastic modulus can be obtained from the deflection amount of the force curve portion corresponding to the portion where the cantilever deflects toward the repulsive side. The adsorption force can be obtained from the deflection amount of the force curve portion corresponding to the portion where the cantilever deflects toward the attractive side and then detaches from the measurement sample. Thus, the following can be obtained: Figure 3, which illustrates a relationship between the distance from the bonding interface 131 and the adsorption force in a cross-section of the adhesive layer 12, and a relationship between the distance from the bonding interface 131 and the elastic modulus in a cross-section of the adhesive layer 12. In these relationship diagrams, the region where the adsorption force or elastic modulus barely changes with the distance from the bonding interface 131 corresponds to the main body layer 123, while the region where the adsorption force or elastic modulus is greater than that of the main body layer 123 and where the adsorption force or elastic modulus changes with the distance from the bonding interface 131 corresponds to the hard layer 121. Thus, the hard layer 121 in the adhesive layer 12 can be understood as a region where the adsorption force or elastic modulus of the adhesive resin fixed at the bonding interface 131 changes compared to the adsorption force or elastic modulus of the adhesive resin in the main body layer 123.

[0046] In the case where the adsorption force of the hard layer 121 in the structure 1 is greater than the adsorption force of the main layer 123, the adsorption force of the hard layer 121 can be configured to decrease as the distance from the bonding interface 131 is increased. This configuration ensures that the strength of the bonding interface 131 is increased, thereby ensuring the aforementioned effects. Furthermore, there are advantages such as gradually changing the state of the adhesive resin, reducing the number of areas where stress concentration occurs, making it less likely that force will be applied near the bonding interface 131. The adsorption force of the hard layer 121 can decrease gradually as the distance from the bonding interface 131 is increased, or it can decrease in stages (stepwise) as the distance from the bonding interface 131 is increased.

[0047] Similarly, in the case where the elastic modulus of the hard layer 121 is configured to be greater than the elastic modulus of the main layer 123 in the structure 1, the elastic modulus of the hard layer 121 can be configured to decrease as the distance from the bonding interface 131 increases. This configuration can reliably improve the strength of the bonding interface 131, thereby ensuring the above-mentioned effects. Furthermore, there is the advantage that, because the displacement caused by stress changes in stages, it is easy to prevent sudden stress concentration caused by displacement differences. The elastic modulus of the hard layer 121 can gradually decrease as the distance from the bonding interface 131 increases, or it can decrease in stages (stepwise) as the distance from the bonding interface 131 increases.

[0048] In the structure 1, the thickness of the hard layer 121 can be 0.5 μm or more. According to this structure, there are the following advantages: since the adsorption force and elastic modulus near the bonding interface 131 are high and the density of the bonding resin is high, it is easy to prevent the bonding resin near the bonding interface 131 from being weakened by the permeation of solvents and gases. From the viewpoint of easily preventing the permeation of solvents and gases into the bonding resin, the thickness of the hard layer 121 is preferably 1 μm or more, more preferably 2 μm or more, and further preferably 5 μm or more. In addition, in this case, if the bonding resin is hardened as a whole, there is a risk that the density of the bonding resin becomes high, the flexibility of the bonding resin decreases, and the bonding resin becomes weaker against thermal shock. From the viewpoint of easily preventing this situation, the thickness of the hard layer 121 is preferably 2 mm or less. It should be noted that the thickness of the hard layer 121 can be calculated as the distance from the bonding interface 131 to the interface between the hard layer 121 and the main layer 123 based on the relationship diagram between the distance from the bonding interface 131 in the cross section of the above-mentioned bonding layer 12 and the adsorption force, and the relationship diagram between the distance from the bonding interface 131 in the cross section of the bonding layer 12 and the elastic modulus.

[0049] The adhesive layer 12 in the structure 1 of the present embodiment can be used as, for example, a resin coating on the surface of the aluminum substrate 111 , a sealing material formed on the surface of the aluminum substrate 111 , or the like.

[0050] (Implementation Method 2)

[0051] For the structure 1 of the second embodiment, use Figure 4 It should be noted that, in the symbols used in Embodiment 2 and thereafter, unless otherwise specified, the same symbols as those used in the above embodiment denote the same constituent elements as those in the above embodiment.

[0052] like Figure 4 As shown in the example, the structure 1 of this embodiment has an aluminum substrate 111 and an adhesive layer 12, similar to the structure 1 of the first embodiment. The structure 1 of this embodiment further has an aluminum substrate 112. Specifically, the structure 1 of this embodiment has an aluminum substrate 111, an aluminum substrate 112, and an adhesive layer 12 disposed between these aluminum substrates 111 and 112 and composed of an adhesive resin that adheres to the surfaces of the aluminum substrates 111 and 112. In other words, the structure 1 of this embodiment is a bonded structure in which the aluminum substrates 111 and 112 are bonded via the adhesive layer 12.

[0053] like Figure 4More specifically, the adhesive layer 12 includes a hard layer 121 in contact with the adhesive interface 131 with the aluminum substrate 111, a hard layer 122 in contact with the adhesive interface 132 with the aluminum substrate 112, and a bulk layer 123 in contact with both hard layers 121 and 122. Furthermore, the hard layer 121 is harder than the bulk layer 123, and the hard layer 122 is harder than the bulk layer 123. The aluminum substrate 112, adhesive interface 132, and hard layer 122 can be configured similarly to the aluminum substrate 111, adhesive interface 131, and hard layer 121 described in Embodiment 1. It should be noted that the aluminum substrate 112 may be composed of the same aluminum alloy as the aluminum substrate 111, or a different aluminum alloy.

[0054] It should be noted that in this embodiment, the above-mentioned aluminum substrate 111 can also be called the first aluminum substrate, the aluminum substrate 112 can also be called the second aluminum substrate, the hard layer 121 can also be called the first hard layer, the hard layer 122 can also be called the second hard layer, the bonding interface 131 can also be called the first bonding interface, and the bonding interface 132 can also be called the second bonding interface.

[0055] According to the structure 1 of the present embodiment, a joined structure capable of exhibiting high adhesive strength even when in contact with a solvent for a long period of time or when subjected to thermal shock can be obtained.

[0056] In structure 1, the thickness of hard layers 121 and 122 can be 1 μm or greater. This configuration offers the following advantages: an increased elastic modulus, increased strength at bonding interfaces 131 and 132, and reduced resistance to shearing at and near bonding interfaces 131 and 132. To enhance the strength of bonding interfaces 131 and 132, the thickness of hard layers 121 and 122 is preferably 2 μm or greater, more preferably 3 μm or greater, and even more preferably 5 μm or greater. Furthermore, to prevent the elastic modulus from being too high, which could hinder the release of internal stress, the thickness of hard layers 121 and 122 is preferably 2 mm or less.

[0057] The structure 1 of this embodiment can be used to join aluminum components. More specifically, the structure 1 of this embodiment can be applied in various ways to join aluminum pipes to pipe components (e.g., joint components, fixing components, etc.), to join pipes together, to join heat exchanger components together, to join heat exchangers to pipes, and to join heat exchangers to surrounding components. Other configurations and effects are the same as those of the first embodiment.

[0058] (Experimental example)

[0059] <Experimental Example 1>

[0060] - Preparation of Sample 1 and Sample 1C -

[0061] An aluminum substrate with an oxide film having a length of 40 mm, a width of 10 mm, and a thickness of 1 mm was cleaned with alkali and then immersed in a sodium silicate aqueous solution with a pH of 12.4, a temperature of 50°C, and a sodium silicate concentration of 0.4 mol / L for 1 minute. The substrate was then rinsed with pure water. This modified layer on the aluminum substrate surface is a thin film composed of silicate glass containing Al in a solid solution, generated from the oxide film composed of Al2O3.

[0062] Next, the two aluminum substrates prepared as described above are arranged to overlap within a length of 10 mm in a state where a gap is formed between the substrate surfaces at each end. It should be noted that the spacing of the gap is 200 μm. Next, an adhesive resin material is applied to the end of the above-mentioned gap. The adhesive resin material uses an epoxy resin material composed of 2,2-bis(4-hydroxyphenyl)propylene diglycidyl ether (BPADGE) as a main agent and dicyandiamide (DYCI) as a curing agent. Then, by heating to 80°C, the adhesive resin material is made low in viscosity and flows and moves, filling the above-mentioned gap. Thus, a laminate having a laminated structure in which aluminum substrate / adhesive resin material / aluminum substrate is laminated in this order is obtained.

[0063] Next, the resulting laminate was heated and held at 135°C for 10 minutes. The temperature was then further increased and held at 155°C for 20 minutes to cure the adhesive resin material, followed by natural cooling. This resulted in a structure of Sample 1 comprising an aluminum substrate and an adhesive layer composed of an epoxy resin bonded to the surface of the aluminum substrate (specifically, a structure having a laminated structure stacked in the order of aluminum substrate / adhesive layer / aluminum substrate). It should be noted that in the structure of Sample 1, the adhesive resin in the hard layer was bonded to the surface of the modified aluminum substrate via a covalent bond.

[0064] Next, in the preparation of the structure of the above-mentioned sample 1, the same procedure was followed except that the aluminum substrate was not immersed in the sodium silicate aqueous solution, thereby obtaining a structure of sample 1C having an aluminum substrate and an adhesive layer composed of an epoxy resin bonded to the surface of the aluminum substrate (specifically, a structure having a stacked structure stacked in the order of aluminum substrate / adhesive layer / aluminum substrate).

[0065] - Preparation of Sample 2 and Sample 2C -

[0066] In the preparation of the structure of Sample 1, an epoxy-modified silicone resin material ("DOWSIL SE 1714," manufactured by Dow Toray Co., Ltd.) was used as the adhesive resin material. The silicone resin material was applied to the substrate surfaces at each end of two aluminum substrates, overlapping them within a length of 10 mm. The substrate surfaces at each end were then bonded together with a spacing of 200 μm between the substrate surfaces to form a laminate. The resulting laminate was heated at 140°C for 5 minutes, then the temperature was further increased to 170°C for 5 minutes, and then naturally cooled. The same procedures were followed, except that the heating process was repeated to obtain the structure of Sample 2, which comprises an aluminum substrate and an adhesive layer composed of the silicone resin bonded to the surface of the aluminum substrate. Note that in the structure of Sample 2, the adhesive resin in the hard layer was covalently bonded to the surface of the modified aluminum substrate.

[0067] Next, the same procedure was followed as in the preparation of the structure of Sample 2, except that the aluminum substrate was not immersed in the sodium silicate aqueous solution, to obtain a structure of Sample 2C having an aluminum substrate and an adhesive layer composed of the above-mentioned silicone resin adhered to the surface of the aluminum substrate.

[0068] - Adsorption force image measured using a scanning probe microscope -

[0069] A measurement sample having a cross section of an adhesive layer perpendicular to the bonding interface was collected from the structures of sample 1 and sample 1C. It should be noted that the measurement sample was cut into each structure with a wire saw and then a cross section was made using FIB. The same applies below. Next, the cross section of each adhesive layer was subjected to surface observation using a scanning probe microscope, and the adsorption force image of each adhesive layer was measured. It should be noted that the adsorption force image was obtained as follows: by performing a measurement based on the above-mentioned measurement conditions on the entire cross section, the adsorption force of each point in each part was calculated and mapped. The adsorption force image of the adhesive layer cross section of sample 1 is shown in Figure 5 The adsorption force image of the adhesive layer cross section of sample 1C is shown in Figure 6 .

[0070] like Figure 6 As shown in the figure, the adhesive layer of the structure of sample 1C has a roughly constant adsorption force throughout the entire adhesive layer. This shows that in the structure of sample 1C, the crosslinking density of the epoxy resin constituting the adhesive layer does not change in the thickness direction, and the entire adhesive layer has a uniform hardness. In other words, it can be seen that the adhesive layer of the structure of sample 1C does not have a hard layer and a main layer. In contrast, Figure 5As shown, in the adhesive layer of the structure of Sample 1, the adsorption force from the bonding interface between the aluminum substrate and the adhesive layer to a certain area on the side of the adhesive layer is greater than the adsorption force of the adhesive layer further inside the above-mentioned certain area. Therefore, it can be said that in the structure of Sample 1, the crosslinking density of the epoxy resin constituting the adhesive layer varies in the thickness direction, and the crosslinking density from the bonding interface to a certain area on the side of the adhesive layer is greater than the crosslinking density of the adhesive layer further inside the above-mentioned certain area. In other words, it can be seen that the adhesive layer of the structure of Sample 1 has an internal main layer and a hard layer that is harder than the main layer. It should be noted that the same results as those of the structures of Samples 1 and 1C were obtained for the structures of Samples 2 and 2C.

[0071] - Elastic modulus image measured using a scanning probe microscope -

[0072] From the structures of Sample 1 and Sample 1C, a measurement sample having a cross section of the adhesive layer perpendicular to the adhesive interface was collected. Next, the cross section of each adhesive layer was observed using a scanning probe microscope to measure the elastic modulus image of each adhesive layer. It should be noted that the elastic modulus image was obtained as follows: by performing a measurement based on the above-mentioned measurement conditions on the entire cross section, the elastic modulus of each point in each part was obtained and mapped. The elastic modulus image of the adhesive layer cross section of Sample 1 is shown in FIG. Figure 7 The elastic modulus image of the adhesive layer cross section of sample 1C is shown in Figure 8 .

[0073] like Figure 8 As shown in the figure, the elastic modulus of the adhesive layer of the structure of sample 1C is approximately constant throughout the adhesive layer. This shows that in the structure of sample 1C, the crosslinking density of the epoxy resin constituting the adhesive layer does not change in the thickness direction, and the entire adhesive layer has a uniform hardness. In other words, it can be seen that the adhesive layer of the structure of sample 1C has a hard layer and a main layer. In contrast, Figure 7 As shown, in the adhesive layer of the structure of sample 1, the elastic modulus of a certain area from the bonding interface between the aluminum substrate and the adhesive layer to the adhesive layer side is greater than the elastic modulus of the adhesive layer inside the above-mentioned certain area. Thus, it can be said that in the structure of sample 1, the crosslinking density of the epoxy resin constituting the adhesive layer changes in the thickness direction, and the crosslinking density of a certain area from the bonding interface to the adhesive layer side is greater than the crosslinking density of the adhesive layer inside the above-mentioned certain area. That is, it can be seen that the adhesive layer of the structure of sample 1 has an internal main body layer and a hard layer harder than the main body layer. It should be noted that for the structures of sample 2 and sample 2C, the same results as those of the structures of sample 1 and sample 1C are obtained.

[0074] <Experimental Example 2>

[0075] - Relationship between the distance from the bonding interface in the cross section of the adhesive layer and the adsorption force or elastic modulus -

[0076] From the structures of Sample 1 and Sample 1C, a measurement sample having a cross section of the adhesive layer perpendicular to the adhesive interface was collected. Next, the cross section of each adhesive layer was subjected to surface observation using a scanning probe microscope under the above-mentioned measurement conditions, and the relationship between the distance from the adhesive interface in the cross section of the adhesive layer and the adsorption force, and the relationship between the distance from the adhesive interface in the cross section of the adhesive layer and the elastic modulus were measured. The relationship between the distance from the adhesive interface in the cross section of the adhesive layer of Sample 1 and Sample 1C and the adsorption force is shown in FIG. Figure 9 The relationship between the distance from the bonding interface and the adsorption force in the cross section of the adhesive layer of Sample 2 and Sample 2C is shown in FIG. Figure 10 The relationship between the distance from the bonding interface and the elastic modulus in the cross section of the adhesive layer of Sample 1 and Sample 1C is shown in FIG. Figure 11 The relationship between the distance from the bonding interface and the elastic modulus in the cross section of the adhesive layer of Sample 2 and Sample 2C is shown in Figure 12 .

[0077] like Figure 9 and Figure 10 、 Figure 11 and Figure 12 As shown in the figure, it can be seen that the adsorption force and elastic modulus of the structures of Samples 1C and 2C are constant regardless of the distance from the bonding interface. This shows that in the structures of Samples 1C and 2C, the crosslinking density of the adhesive resin constituting the adhesive layer does not change in the thickness direction, and the entire adhesive layer has a uniform hardness. In contrast, Figure 9 and Figure 10 、 Figure 11 and Figure 12 As shown, in the adhesive layer of the structure of Sample 1 and Sample 2, the adsorption force and elastic modulus from the bonding interface between the aluminum substrate and the adhesive layer to a certain distance to the adhesive layer side are greater than the adsorption force and elastic modulus of the adhesive layer at a distance exceeding the above-mentioned certain distance. Therefore, it can be said that in the structure of Sample 1 and Sample 2, the crosslinking density of the adhesive resin constituting the adhesive layer changes in the thickness direction, and the crosslinking density from the bonding interface to a certain distance to the adhesive layer side is greater than the crosslinking density of the adhesive layer further inside the above-mentioned certain distance. In other words, it can be seen that the adhesive layer of the structure of Sample 1 and Sample 2 has an internal main layer and a hard layer that is harder than the main layer. In addition, the hard layer in the structure of Sample 1 and Sample 2 becomes smaller as it moves away from the bonding interface.

[0078] <Experimental Example 3>

[0079] The tensile shear strength was measured for the structures of sample 1 and sample 1C in the initial state, the structures of sample 1 and sample 1C immersed in tetrahydrofuran (THF) for 18 hours, and the structures of sample 1 and sample 1C subjected to 10 repeated thermal cycles of heating to 50°C and then cooling to -196°C. The measurement was performed using a universal testing device (manufactured by Shimadzu Corporation, "Autograph"). The measurement conditions were a tensile speed of 5 mm / min, a clamping width of 10 mm, and the number of measurements = 6. The results are shown in Figure 13 .

[0080] like Figure 13 As shown in the figure, the initial tensile shear strength of the structure of Sample 1 is higher than that of the structure of Sample 1C. This is because the adhesive layer of the structure of Sample 1C does not have a hard layer, and the adhesive resin is bonded to the surface of the aluminum substrate through anchoring effects, hydrogen bonds, etc. In contrast, the structure of Sample 1 is believed to have a higher initial tensile shear strength due to the effect of the adhesive resin in the hard layer bonding to the surface of the aluminum substrate through covalent bonds, in addition to the increased strength near the bonding interface by the hard layer.

[0081] In addition, if Figure 13 As shown, compared with the structure of sample 1C, the structure of sample 1 shows less decrease in tensile shear strength in either case after THF immersion or after thermal cycle loading, and is able to maintain high tensile shear strength. It should be noted that the fracture mode of sample 1 is mainly the fracture of the base material of the main layer, but the structure of sample 1C is mainly interface peeling. In addition, the structures of sample 2 and sample 2C also obtained the same results as the structures of sample 1 and sample 1C.

[0082] The present disclosure is not limited to the above-mentioned embodiments and experimental examples, and various changes can be made within the scope of the gist thereof. In addition, the various configurations shown in the various embodiments and experimental examples can be arbitrarily combined. That is, although the present disclosure has been described based on the embodiments, it should be understood that the present disclosure is not limited to the embodiments, structures, etc. The present disclosure also includes various modified examples and modifications within the equivalent scope. In addition, various combinations, methods, and other combinations and methods obtained by including only one element, above or below them are also within the scope and idea of ​​the present disclosure.

[0083] Examples of reference methods are described below.

[0084] Item 1.

[0085] A structure (1) comprising an aluminum substrate (111, 112) and an adhesive layer (12) made of an adhesive resin and adhered to the surface of the aluminum substrate.

[0086] The adhesive layer comprises a hard layer (121, 122) in contact with the adhesive interface (131, 132) with the aluminum substrate and a main body layer (123) in contact with the hard layer.

[0087] The hard layer is harder than the main body layer.

[0088] In item 1, examples of the adhesive resin include epoxy resin, polyurethane resin, melamine resin, urea resin, silicone resin, polyester resin, etc. Among them, epoxy resin and silicone resin are preferred as the adhesive resin.

[0089] Item 2.

[0090] The structure according to item 1, wherein, in a cross section of the adhesive layer perpendicular to the adhesive interface, the adsorptive force of the hard layer measured using a scanning probe microscope is greater than the adsorptive force of the main body layer.

[0091] Item 3.

[0092] The structure according to item 2, wherein the adsorption force of the hard layer decreases as the distance from the bonding interface increases.

[0093] Item 4.

[0094] The structure according to any one of items 1 to 3, wherein the elastic modulus of the hard layer measured using a scanning probe microscope in a cross section of the adhesive layer perpendicular to the adhesive interface is greater than the elastic modulus of the main body layer.

[0095] Item 5.

[0096] The structure according to item 4, wherein the elastic modulus of the hard layer decreases as the distance from the bonding interface increases.

[0097] Item 6.

[0098] The structure according to any one of items 1 to 5, wherein the adhesive resin is an epoxy resin or a silicone resin.

[0099] Item 7.

[0100] The structure according to any one of items 1 to 6, wherein the hard layer has a thickness of 0.5 μm or more.

[0101] Item 8.

[0102] The structure according to any one of items 1 to 6, wherein the hard layer has a thickness of 1 μm or more.

Claims

1. A structure (1) comprising an aluminum substrate (111, 112) and an adhesive layer (12) made of an adhesive resin adhered to a surface of the aluminum substrate, The adhesive layer comprises a hard layer (121, 122) in contact with the bonding interface (131, 132) with the aluminum substrate and a main body layer (123) in contact with the hard layer. The hard layer is harder than the main layer, The bonding resin is epoxy resin or silicone resin; The adsorption force of the hard layer measured using a scanning probe microscope on a cross section of the adhesive layer perpendicular to the adhesive interface is greater than the adsorption force of the main layer, or / and the elastic modulus of the hard layer measured using a scanning probe microscope on a cross section of the adhesive layer perpendicular to the adhesive interface is greater than the elastic modulus of the main layer; The aluminum substrate has a modified layer composed of silicate glass on its surface, the epoxy resin generates covalent bonds through a chemical reaction between the OH groups on the surface of the modified layer and the epoxy groups, the silicone resin generates covalent bonds with the OH groups on the surface of the modified layer through a dehydration condensation reaction, and the hard layer is bonded to the surface of the aluminum substrate through a covalent bond.

2. The structure according to claim 1, wherein The adsorption force of the hard layer decreases as it moves away from the bonding interface.

3. The structure according to claim 1 or 2, wherein The hard layer has a thickness of 0.5 μm or more.

4. The structure according to claim 1 or 2, wherein The hard layer has a thickness of 1 μm or more.

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