Metal bonding agent and metal bonding method using the same

Abstract

To provide a metal bonding agent which can obtain high adhesive strength without requesting a metal substrate to have high heat resistance, and a metal bonding method using the same.SOLUTION: A metal bonding agent 10 bonds the same or different kinds of metal substrates 11. The metal bonding agent 10 contains a water-soluble polymer solution, and resin powder which is added to the polymer solution and is formed of a thermoplastic resin dissoluble in water.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, welding, brazing, and the like are well known as methods for joining the same or different metal substrates. All of these methods use a bonding agent for joining the metal substrates separately. In addition to these, diffusion bonding is also known, which bonds metal substrates by utilizing the diffusion of metal atoms. Patent Document 1 discloses a technique for bonding a pair of metal substrates by sandwiching a metal foil for bonding between the metal substrates.

[0003] However, all of the above-mentioned conventional bonding methods for metal substrates require heating at high temperatures and maintaining high temperatures. Therefore, the metal substrate is required to have heat resistance, and there is a problem that it is difficult to apply the method to metal substrates that do not have sufficient heat resistance. In addition, when bonding metal substrates with low heat resistance, resin-based adhesives such as epoxy resins are used. However, conventional resin-based adhesives have a problem that it is difficult to ensure sufficient adhesive strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-321961 A Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore an object of the present invention to provide a metal bonding agent that can provide high adhesive strength without requiring high heat resistance from the metal substrate, and a metal bonding method using the same. [Means for solving the problem]

[0006] A metal bonding agent according to one embodiment bonds similar or different metal substrates, and includes a water-soluble polymer solution and a resin powder formed of a thermoplastic resin that is insoluble in water, added to the polymer solution.

[0007] The resin powder is preferably a powder formed of one or more resins selected from polyamide, polyphenylene sulfide, liquid crystal polyester, and polybutylene terephthalate. More preferably, the resin powder is a powder formed of polyamide. The metal bonding agent according to one embodiment preferably further contains a silane coupling agent. The metal bonding agent according to one embodiment preferably further comprises a metal additive. The metal additive is preferably formed in the form of a film on the surface of the resin powder. The metal additive is preferably Ag.

[0008] A metal bonding method using a metal bonding agent according to one embodiment includes the steps of applying the metal bonding agent to at least one of a pair of metal substrates to be bonded, drying the metal bonding agent applied to the metal substrates, stacking the pair of metal substrates with the dried metal bonding agent in between, and heating and pressurizing the stacked pair of metal substrates. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a pair of metal substrates bonded together using a metal bonding agent according to an embodiment; [Diagram 2] FIG. 1 is a schematic diagram showing a configuration of a metal bonding agent according to one embodiment; [Diagram 3] FIG. 1 is a schematic cross-sectional view showing a resin powder in a metal bonding agent according to an embodiment. [Figure 4] FIG. 1 is a schematic cross-sectional view showing a pair of metal substrates bonded together using a metal bonding agent according to an embodiment; [Diagram 5]FIG. 1 is a schematic cross-sectional view showing a pair of metal substrates bonded together using a metal bonding agent according to an embodiment; [Figure 6] FIG. 1 is a schematic cross-sectional view showing a chemical bond layer formed in a metal bonding agent according to an embodiment; [Figure 7] Schematic cross-sectional view showing a metal bonding agent according to one embodiment. [Figure 8] FIG. 1 is a schematic cross-sectional view showing a laminate in which a plurality of metal substrates are laminated using a metal bonding agent according to an embodiment. [Figure 9] Schematic diagram showing examples and comparative examples of metal additives according to one embodiment. [Figure 10] Schematic diagrams showing examples and comparative examples of a metal bonding agent according to one embodiment. [Figure 11] Schematic diagram showing the bonding strength of examples of metal bonding agents according to one embodiment. [Figure 12] Schematic diagram showing shear tensile strength of example metal bonding agents according to one embodiment. [Figure 13] FIG. 1 is a schematic diagram showing a measuring device for measuring the thermal resistance of a laminate using a metal bonding agent according to one embodiment. [Figure 14] Schematic diagram illustrating the thermal resistance of example metallic bonding agents according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the metal bonding agent will be described in detail with reference to the drawings. 1, a metal bonding agent 10 is applied between a pair of metal substrates 11. The metal bonding agent 10 forms a hardened bonding layer 12 between the pair of metal substrates 11. In this way, the metal bonding agent 10 bonds the pair of metal substrates 11 together.

[0011] The metal substrate 11 may be made of various metals and alloys, such as aluminum (Al), aluminum alloys, copper (Cu), Cu alloys, nickel (Ni), Ni alloys, iron (Fe), cold rolled steel sheets (SPCC), galvanized steel sheets (SECC, SGCC, SEHC, etc.), carbon tool steels (SK materials), carbon steels for mechanical construction (SC materials), stainless steels, general mild steel materials, ultra-high tensile steels, etc. The pair of metal substrates 11 may be made of the same type of material or different types of materials. The pair of metal substrates 11 may be made of any shape, such as a plate, a cylinder, or a column.

[0012] The metal bonding agent 10 includes a water-soluble polymer and a resin powder. The water-soluble polymer includes a resin component that forms a chemical bond with the surface of the metal substrate 11. That is, the water-soluble polymer forms a chemical bond with the surface of the metal substrate 11 by a functional group contained in the structure. Specifically, the water-soluble polymer is a polymer that has sufficient solubility in water, such as sodium polyacrylate, sodium carboxymethyl cellulose, polyvinyl alcohol, etc. The water-soluble polymer is not limited to these examples, and may be any polymer that is water-soluble and contains a resin component that forms a chemical bond with the metal substrate 11, such as polyacrylic acid amide.

[0013] The metal bonding agent 10 may contain an inorganic solvent that dissolves the water-soluble polymer. Water is typically used as the inorganic solvent. Although the metal bonding agent 10 does not necessarily need to be dissolved in an inorganic solvent, the addition of an inorganic solvent improves the coating performance. The metal bonding agent 10 may contain additives such as liquid paraffin, surfactants, and alcohol. Liquid paraffin promotes the clouding of the metal bonding agent 10, and contributes to improving the coating performance with improved visibility. The surfactant can be used to adjust the viscosity of the metal bonding agent 10. The alcohol contributes to reducing oxidation of the metal bonding agent 10. In addition, polyhydric alcohols such as glycols chemically react with the water-soluble polymer. Therefore, the polyhydric alcohol contributes to the formation of a thin organic film when the metal bonding agent 10 is dried. It is preferable to avoid the use of organic solvents as much as possible when using the metal bonding agent 10.

[0014] The metal bonding agent 10 contains a resin powder 22 dispersed in a water-soluble polymer 21 as shown in FIG. 2. The resin powder 22 is formed of a thermoplastic resin that is not dissolved in water. Although there is no particular limit to the particle size of the resin powder 22, it is preferable that the resin powder 22 is sufficiently fine to be uniformly dispersed throughout the metal bonding agent 10. The resin powder 22 is preferably formed of a resin selected from, for example, polyamide, polyphenylene sulfide, or liquid crystal polyester. The resin powder 22 may be one of these resins or a mixture of two or more of them. It is more preferable to use polyamide as the resin powder 22 in terms of the strength for bonding the metal substrate 11, ease of handling, and the like.

[0015] There is no limitation on the mass ratio between the water-soluble polymer 21 and the resin powder 22. On the other hand, if the mass ratio of the resin powder 22 is too large, the bonding effect of the water-soluble polymer 21 is reduced, and if the mass ratio of the resin powder 22 is too small, the bonding effect of the resin powder 22 is reduced. For this reason, the mass ratio between the water-soluble polymer 21 and the resin powder 22 is preferably about 1 to 10 when the resin powder 22 is taken as 1.

[0016] The metal bonding agent 10 may further contain a silane coupling agent in addition to the water-soluble polymer 21 and the resin powder 22. The silane coupling agent is a compound containing silicon (Si) and has both a site that reacts with an organic compound and a site that reacts with an inorganic compound in its structure. The silane coupling agent contributes to improving the bonding strength of the metal bonding agent 10 between a pair of metal substrates 11.

[0017] In addition, the metal bonding agent 10 may further include a metal additive 23 as shown in FIG. 3. The metal additive 23 added to the metal bonding agent 10 is not limited to a single metal, but may also include an alloy and a compound of a metal. The metal constituting the metal additive 23 may be the same type of metal as the pair of metal substrates 11 to be bonded, or may be a different type of metal. The metal additive 23 is formed in a film shape on the surface of the resin powder 22. That is, the metal additive 23 is coated on the surface of the resin powder 22. The metal additive 23 is coated on the surface of the resin powder 22 by, for example, plating. Since the metal additive 23 contributes to the transfer of heat in the metal bonding agent 10, it is preferable that the metal additive 23 contains a metal with high thermal conductivity, such as Ag, Cu, Al, or Sn. It is more preferable that the metal additive 23 is Cu or Ag. Specifically, the metal additive 23 is preferably Ag, which has a higher thermal conductivity, but since Ag is expensive, it may be inexpensive Cu, which has a slightly lower thermal conductivity than Ag.

[0018] Next, a method for bonding metal bases 11 using the metal bonding agent 10 having the above-mentioned configuration will be described. The metal bonding agent 10 is applied to a pair of target metal substrates 11 as shown in FIG. 4 and FIG. 5. In this case, the metal bonding agent 10 may be applied to either one of the pair of metal substrates 11 as shown in FIG. 4, or may be applied to both as shown in FIG. 5. The metal bonding agent 10 is in a paste form by mixing a water-soluble polymer 21, a resin powder 22, and other additives. The metal bonding agent 10 is applied to the metal substrate 11 by a coating device such as a die coater. The metal bonding agent 10 may also be applied by dropping the metal bonding agent 10 onto the metal substrate 11 and spreading it out. In addition, the metal bonding agent 10 may also be applied by dipping the metal substrate 11, for example, or by spraying it with a spray.

[0019] The metal bonding agent 10 applied to the metal substrate 11 forms a coating layer 31 as shown in Fig. 4 and Fig. 5. The coating layer 31 preferably has a sufficient thickness. The thickness of the coating layer 31 is preferably 50 µm or more, and more preferably 100 µm or more. The upper limit of the thickness of the coating layer 31 is not particularly specified, but is preferably several mm or less.

[0020] The coating layer 31 is applied to the metal substrate 11 and then dried. As a result, the metal bonding agent 10 constituting the coating layer 31 forms a chemically bonded layer 32 that is fixed to the surface of the metal substrate 11 by chemical bonding, as shown in FIG. 6. According to the findings of the inventors of the present invention, when the metal bonding agent 10 is dried, a dehydration condensation reaction occurs, and the functional groups of the water-soluble polymer 21 contained in the metal bonding agent 10 are covalently bonded to the chemically active groups present on the entire surface of the metal substrate 11. As a result, it is considered that a chemically bonded layer 32 is formed between the water-soluble polymer 21 contained in the metal bonding agent 10 and the surface of the metal substrate 11. It is also considered that the functional groups contained in the water-soluble polymer 21 form ester bonds with the hydroxyl groups (OH groups) fixed on the surface of the metal substrate 11.

[0021] In this case, the metal base 11 may be subjected to a plasma treatment before applying the metal bonding agent 10. By subjecting the surface of the metal base 11 to a plasma treatment, the number of hydroxyl groups on the surface of the metal base 11 increases. This improves the adhesion of the chemically bonded layer 32 to the metal base 11.

[0022] After drying the coating layer 31, a pair of metal substrates 11 are stacked as shown in Fig. 7. At this time, the pair of metal substrates 11 are stacked with the coating layer 31 formed by the metal bonding agent 10 sandwiched between them. Also, three or more metal substrates 11 may be stacked with the coating layer 31 sandwiched between them as shown in Fig. 8.

[0023] The metal substrates 11 stacked with the coating layer 31 sandwiched therebetween are heated and pressed. The heating and pressing are performed, for example, by hot pressing. At this time, the heating temperature is preferably set to a temperature equal to or higher than the softening temperature of the resin powder 22. Specifically, the heating temperature is preferably 180°C or higher, which is equal to or higher than the melting point of the resin powder 22, and is preferably 250°C to 350°C depending on the type of resin powder 22 used. The stacked metal substrates are maintained at 250°C to 350°C for several minutes, and then further cooled to about 150°C to 200°C, which is equal to or lower than the melting point, and maintained for several minutes to several tens of minutes, and then naturally cooled. When heating by a laser or ultrasonic waves is used, heating may be performed for about several seconds.

[0024] In this way, by heating and pressing the coating layer 31 together with the superposed metal substrates 11, the resin powder 22 contained in the metal bonding agent 10 forming the coating layer 31 melts. That is, since the resin powder 22 is formed of a thermoplastic resin, it melts by heating. The thermoplastic resin originating from the melted resin powder 22 penetrates into the chemical bonding layer 32 formed between the metal substrates 11 and is mixed with the chemical bonding layer 32, forming a bonding layer 12 that bonds the metal substrates 11 as shown in FIG. 1. As a result, the pair of metal substrates 11 are bonded by the bonding layer 12 formed by the metal bonding agent 10. Here, the pair of metal substrates 11 bonded by the metal bonding agent 10 are heated to about the melting point of the resin powder 22 contained in the metal bonding agent 10. The temperature during this heating is 180°C to 350°C, although it depends on the melting point of the thermoplastic resin that forms the resin powder 22. Therefore, the temperature during heating is lower than, for example, bonding by soldering or welding, or bonding using diffusion. Therefore, by using the metal bonding agent 10 of this embodiment, high adhesive strength can be obtained without requiring the metal base material 11 to have high heat resistance.

[0025] By adding the metal additive 23 to the metal bonding agent 10, heat generated by heating is effectively transferred in the coating layer 31 formed by the metal bonding agent 10. That is, the metal additive 23 is formed of a metal having high thermal conductivity. Therefore, the metal additive 23 contributes to smooth transfer of heat in the coating layer 31 formed as a heat transfer medium during heating. As a result, the temperature of the coating layer 31 rises quickly and uniformly during heating, and melting of the resin powder 22 contained in the coating layer 31 is promoted. In addition, the metal additive 23 contained in the metal bonding agent 10 also contributes to smooth transfer of heat in the bonding layer 12 that bonds a pair of metal substrates 11. As a result, by bonding the metal substrates 11 with the metal bonding agent 10, even if a bonding layer 12 is interposed between the pair of metal substrates 11, the transfer of heat between the metal substrates 11 is promoted. As described in FIG. 8, even if a plurality of metal substrates 11 are stacked, the transfer of heat between the metal substrates 11 is promoted. For example, in transformers, heat sinks, and the like, a plurality of plate materials for heat dissipation may be stacked and used. In such cases, by using the metal bonding agent 10 of the present embodiment, heat transfer is promoted even when a plurality of plate materials of metal base materials 11 are stacked and bonded. Therefore, by using the metal bonding agent 10 of the present embodiment, the heat dissipation of a device in which a plurality of metal base materials 11 are stacked can be improved.

[0026] Several examples of this embodiment will now be described. (Terminology explanation) First, the abbreviations and materials used in Figs. 9 and 10 will be explained. "PAN7", "PAN2", "CMC", and "PVA" all indicate substances constituting the water-soluble polymer 21. "PAN7" and "PAN2" indicate aqueous solutions of sodium polyacrylate. "PAN7" is an aqueous solution in which sodium polyacrylate and purified water are mixed in a mass ratio of 5:50. "PAN2" is an aqueous solution in which sodium polyacrylate and purified water are mixed in a mass ratio of 2.5:20. Sodium polyacrylate manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. was used. "CMC" indicates an aqueous solution of sodium carboxymethylcellulose, which is an aqueous solution in which sodium carboxymethylcellulose and purified water are mixed in a mass ratio of 1:50. Sodium carboxymethylcellulose manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. was used. "PVA" indicates an aqueous solution of polyvinyl alcohol, which is an aqueous solution in which polyvinyl alcohol and purified water are mixed in a mass ratio of 5:50. The polyvinyl alcohol used was manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0027] "PG" indicates propylene glycol as an additive, manufactured by Hayashi Pure Chemical Industries Co., Ltd. "SF" indicates a surfactant as an additive, manufactured by Kao Corporation, manufactured by Emulgen 707. "PA", "PPS", and "LCP" all indicate the substances that make up the resin powder. "PA" is a polyamide resin powder, manufactured by Nikko Rica Corporation, manufactured by SP500. "PPS" is a polyphenylene sulfide resin powder, manufactured by Polyplastics Co., Ltd., manufactured by FL-D10. "LCP" is a liquid crystal polymer resin powder, manufactured by Polyplastics Co., Ltd., manufactured by LC-D20S. "KBP" indicates a silane coupling agent, manufactured by Shin-Etsu Chemical Co., Ltd., manufactured by KBP-90. In addition, in Figs. 9 and 10, the numerical values ​​shown for the water-soluble polymer, additive, purified water, KBP, and resin powder indicate the mass (g) of each material prepared in the examples and comparative examples.

[0028] (Verification of resin powder addition) The effect of the metal bonding agent 10 of this embodiment in which the resin powder 22 is added to the water-soluble polymer 21 was verified using Examples 1 to 3. In Examples 1 to 3, the resin powder 22 is added to the water-soluble polymer 21 as shown in FIG. 9. Specifically, the metal bonding agent 10 of Example 1 has the polyamide resin powder 22 added to the water-soluble polymer 21. The metal bonding agent 10 of Example 2 has the polyphenylene sulfide resin powder 22 added to the water-soluble polymer 21. The metal bonding agent 10 of Example 3 has the liquid crystal polymer resin powder 22 added to the water-soluble polymer 21. Comparative Example 1 contains the same water-soluble polymer 21 as Examples 1 to 3 as a main component, and does not contain the resin powder 22.

[0029] In Examples 1 to 3 and Comparative Example 1, the metal bonding agent 10 was applied to a pair of metal substrates 11, and then the metal bonding agent 10 was dried, and heated and pressed by hot pressing to bond the metal substrates. The thickness of the coating layer 31 of the metal bonding agent 10 when dried was 100 μm. The metal substrate 11 was made of A5052, which is mainly composed of Al. The temperature during bonding in Examples 1 to 3 and Comparative Example 1 was changed according to the melting point of the resin powder 22 contained in the metal bonding agent 10. Specifically, Example 1, which includes polyamide resin powder 22, was heated to 250° C. and maintained for several minutes, then held at 150° C., and naturally cooled. Example 2, which includes polyphenylene sulfide resin powder 22, was heated to 310° C. and maintained for several minutes, then held at 250° C., and naturally cooled. Example 3, which includes liquid crystal polymer resin powder 22, was heated to 340° C. and maintained for several minutes, then held at 250° C., and naturally cooled. Comparative Example 1 not containing the resin powder 22 was heated to 250° C. and maintained for several minutes, then held at 190° C. and naturally cooled.

[0030] These Examples 1 to 3 all exhibited high bonding strengths of 4.0 MPa to 10.0 MPa, as shown in Figures 9 and 11. In contrast, Comparative Example 1 exhibited only such a weak bonding strength that the pair of metal bases 11 were separated by simply pulling with hands, and the bonding strength could not be measured. Thus, the metal bonding agent 10 of the present embodiment, which contains the resin powder 22 in addition to the water-soluble polymer 21, exhibited high bonding strength to the pair of metal substrates 11.

[0031] (Verification of electrical insulation) Using Example 1 and Comparative Example 1, the electrical insulation of the metal bonding agent 10 was verified. In both Example 1 and Comparative Example 1, A5052 containing Al as the main component was used as the metal substrate 11, and the thickness of the coating layer 31 formed by the metal bonding agent 10 was set to 50 μm. In these Example 1 and Comparative Example 1, the applied metal bonding agent 10 was dried at 220 ° C., and then heated and pressed to bond a pair of metal substrates 11. In Example 1 and Comparative Example 1, electricity was passed through both ends of a pair of metal substrates 11 sandwiching the bonding layer 12 made of the metal bonding agent 10, and the resistance value was measured. As a result, Example 1 was almost insulated, and no current was confirmed. On the other hand, Comparative Example 1 was in a state close to insulation, but a weak current was confirmed. Thus, Example 1 using the metal bonding agent 10 of this embodiment showed high electrical insulation between the pair of metal substrates 11 to be bonded.

[0032] (Verification of thermal resistance) Next, examples 4 to 6 of this embodiment will be described. In Example 4 of the metal bonding agent 10, Ag is added as a metal additive 23 to the water-soluble polymer 21 in addition to the resin powder 22 as shown in FIG. 10. In Examples 5 and 6 of the metal bonding agent 10, "KBP" is added as a silane coupling agent to the water-soluble polymer 21 in addition to the resin powder 22. In Example 6 of the metal bonding agent 10, Ag is added as a metal additive 23. The metal additive 23 in Examples 4 and 6 is coated on the surface of the polyamide resin powder 22. Specifically, in Example 4, the polyamide resin powder 22 is added to the water-soluble polymer 21, and the resin powder 22 is coated with Ag. In Example 5, the polyamide resin powder 22 is added to the water-soluble polymer 21 and KBP is added. In Example 6, the polyamide resin powder 22 is added to the water-soluble polymer 21, and the resin powder 22 is coated with Ag and KBP is added. Comparative Example 2 corresponds to a conventional example in which a pair of metal substrates 11 is simply bonded with an epoxy resin. The metal base 11 used in Examples 4 to 6 and Comparative Example 2 was made of A5052 having a thickness of 1 mm. In Comparative Example 3, the two metal bases 11 were equivalent to one sheet of A5052 having a thickness of 2 mm.

[0033] In Examples 4 to 6, the metal bonding agent 10 was applied to a pair of metal substrates 11, and then the metal bonding agent 10 was dried, and the metal substrates 11 were heated and pressed by hot pressing to bond the metal substrates 11 to each other. The thickness of the coating layer 31 of the metal bonding agent 10 when dried was 100 μm. The metal substrates 11 were made of A5052, which is mainly composed of Al. The temperature during bonding in Examples 4 to 6 was all 250°C, and the metal substrates 11 were heated and pressed for several minutes, and then the pressing was stopped when the metal substrates 11 were naturally cooled to 170°C. In Comparative Example 2, the pair of metal substrates 11 were bonded with epoxy resin, and therefore heating and pressing were not performed. In Comparative Example 3, the pair of metal substrates 11 were simply stacked and not bonded to each other.

[0034] The tensile strength (N) was measured for Examples 4 to 6 and Comparative Example 2. The tensile strength is a shear tension force. As a result, Examples 4 to 6 exhibited sufficiently large tensile strength compared to Comparative Example 2, which is a conventional example, as shown in FIG. 12. Thus, in Examples 4 to 6 as well, the pair of metal base materials 11 bonded with the metal bonding agent 10 exhibited high bonding strength.

[0035] Furthermore, the thermal resistance was verified using Example 5, Example 6, and Comparative Example 3. The thermal resistance was measured between a pair of metal bases 11 stacked as shown in Fig. 13 by heating one of the pair of metal bases 11 to 100°C and cooling the other to 20°C. Comparative Example 3 was used as the standard for measuring the thermal resistance because no bonding layer 12 was interposed between the metal bases 11 and the thermal resistance was the smallest. The thermal resistance of Comparative Example 3 was 0.39 K / W.

[0036] As shown in FIG. 14, Example 5, in which KBP was added to the metal bonding agent 10, had a slightly larger value of 0.63 K / W compared to Comparative Example 3. On the other hand, Example 6, in which KBP and the metal additive 23 were added to the metal bonding agent 10, had a value of 0.39 K / W, which was almost equivalent to Comparative Example 3. This indicates that Example 6 has a thermal resistance equivalent to Comparative Example 3, in which a pair of metal bases 11 are simply stacked without using the metal bonding agent 10. In other words, although Example 6 has the bonding layer 12 of the metal bonding agent 10 between the pair of metal bases 11, it has a thermal resistance equivalent to Comparative Example 3, in which the bonding layer 12 is not present. In this way, by adding KBP and the metal additive 23 to the metal bonding agent 10, it was possible to reduce the thermal resistance as well as to achieve high bonding strength.

[0037] The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist of the invention. [Explanation of symbols]

[0038] In the drawing, 10 denotes a metal binder, 11 denotes a metal substrate, 21 denotes a water-soluble polymer, 22 denotes a resin powder, and 23 denotes a metal additive.

Claims

1. A metal bonding agent for bonding metal substrates of the same or different types, an aqueous polymer solution; a resin powder formed of a thermoplastic resin that is added to the polymer solution and is insoluble in water; Including, Metallic bonding agent.

2. The resin powder is a powder formed of one or more resins selected from polyamide, polyphenylene sulfide, liquid crystal polyester, and polybutylene terephthalate. The metal bonding agent according to claim 1.

3. The resin powder is a powder formed of polyamide. The metal bonding agent according to claim 2.

4. Further comprising a silane coupling agent, The metal bonding agent according to claim 1.

5. Further comprising a metal additive, The metal bonding agent according to claim 1.

6. The metal additive is formed in the form of a film on the surface of the resin powder. The metal bonding agent according to claim 5.

7. The metal additive is Ag. The metal bonding agent according to claim 6.

8. A metal bonding method using the metal bonding agent according to any one of claims 1 to 7, applying the metal bonding agent to at least one of the pair of metal base materials to be joined; drying the metal bonding agent applied to the metal base material; stacking a pair of the metal substrates with the dried metal bonding agent between them; applying heat and pressure to the pair of stacked metal substrates; A metal joining method comprising the steps of:

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