Bonding agent and bonding method using the same

Abstract

The objective is to provide a bonding agent that does not oxidize the metal substrate and produces a thin bonded layer after joining, as well as a bonding method using the same. [Solution] The bonding agent according to one embodiment is a bonding agent for bonding a metal substrate to a metal substrate of the same or different type as the metal substrate, or a non-metal substrate. This bonding agent consists of a polymer solution prepared with a water-insoluble polymer and an organic solvent, and the water-insoluble polymer is a thermoplastic polymer.

Description

Technical Field

[0001] The present invention relates to an adhesive for joining metal to metal or metal to non-metal materials, and a joining method using the same.

Background Art

[0002] Conventionally, welding, brazing, etc. are well-known as methods for joining the same or different metal substrates, and as methods for joining a metal substrate and a resin substrate which is a non-metal material, methods such as an adhesive using chemical bonding are well-known. All of these use an adhesive for joining separately from the substrate. Further, Patent Document 1 discloses a metal bonding agent capable of obtaining high bonding strength and a metal bonding method using the same.

[0003] However, since the bonding agent for metal substrates disclosed in Patent Document 1 contains a water-soluble polymer solution, there is a problem that rust occurs on the metal serving as the substrate when the bonding agent is dried during the bonding process. Further, when a conventional adhesive is used, there is a problem that the thickness of the adhesive layer becomes an obstacle in use.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, an object is to provide an adhesive which does not cause rust on the metal of the substrate even after a drying process after applying the adhesive to the metal serving as the bonding substrate, and a bonding method using the same, and which has a thin bonding layer thickness after bonding.

Means for Solving the Problems

[0006] One embodiment of the bonding agent is a bonding agent for bonding a metal substrate to a metal substrate of the same or different type as the metal substrate, or a non-metal substrate. This bonding agent consists of a polymer solution prepared with a water-insoluble polymer and an organic solvent, wherein the water-insoluble polymer is a thermoplastic polymer.

[0007] The water-insoluble polymer is preferably polyvinyl butyral. The organic solvent is preferably diethylene glycol monoethyl ether. Furthermore, the bonding agent may further contain propylene glycol, and may further contain at least one of conductive particles, inorganic particles, and plastic particles.

[0008] A bonding method using a bonding agent according to one embodiment includes the steps of: applying the bonding agent to at least one metal substrate to be bonded; preparing a pair of substrates by stacking the other metal substrate or non-metal substrate with the bonding agent in between; and heating and pressurizing the stacked pair of substrates. The method may also include the step of drying the bonding agent applied to the metal substrate. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic cross-sectional view showing the joining of a pair of substrates using a bonding agent according to one embodiment. [Figure 2] A schematic cross-sectional view showing the bonding process of a pair of substrates using a bonding agent according to one embodiment. [Figure 3] A schematic cross-sectional view showing a pressurization process of a pair of substrates using a bonding agent according to one embodiment. [Figure 4] A simulated cross-sectional view showing a laminate formed by stacking multiple metal substrates using a bonding agent according to one embodiment. [Figure 5] Schematic diagram showing an example of a bonding agent according to one embodiment. [Figure 6] A diagram showing the bonding strength when a metal substrate and a resin substrate are joined together. [Figure 7] A diagram showing the bonding strength when two metal substrates are joined together. [Figure 8] A diagram showing the heat resistance when two metal substrates are joined together. [Figure 9] Figure showing the measurement results of the bonding layer thickness. [Figure 10] Diagram showing the joint strength when steel is used as the base material. [Figure 11] This figure shows the bonding strength when using a bonding agent containing conductive particles. [Figure 12] A diagram showing the detailed shape of the joint used in the interlocking connection. [Modes for carrying out the invention]

[0010] The following describes embodiments of the bonding agent in detail with reference to the drawings. As shown in Figure 1, the adhesive 10 is applied between a pair of substrates 11 and 12. The adhesive 10 forms a thin, hardened bonding layer between these two substrates 11 and 12. In this way, the adhesive 10 bonds the pair of substrates 11 and 12 together.

[0011] Of the pair of base materials, one base material 11 is a metal base material, and various other metals and alloys can be used, such as aluminum (Al), aluminum alloys, copper (Cu), copper alloys, nickel (Ni), nickel alloys, iron (Fe), cold-rolled steel sheets (SPCC), galvanized steel sheets (SECC, SGCC, SEHC, etc.), carbon tool steel (SK material), carbon steel for machine structures (SC material), stainless steel (SUS), general mild steel, and ultra-high-strength steel.

[0012] The other base material 12 is a metallic or non-metallic base material. In the case of a metallic base material, it may be the same type of material as base material 11, or it may be a different type of metallic material. In the case of a non-metallic base material, polyamide (PA) resins such as PA6 and PA66, polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyethylene terephthalate (PET), carbon fiber reinforced thermoplastic resin (CFRTP), ABS resin, polyethylene (PE), polypropylene (PP), polyacetal (POM), polyvinyl chloride (PVC), other plastics and rubber, thermoplastic resins, synthetic resins that soften when heated, ceramics (such as alumina), glass, and other inorganic materials can be used.

[0013] These pair of base materials 11 and 12 can be used in any shape, such as a plate, a cylinder, or a columnar shape.

[0014] The bonding agent 10 is a polymer solution prepared with a water-insoluble polymer and an organic solvent. The water-insoluble polymer must be a thermoplastic polymer. This water-insoluble polymer contains a resin component that forms a chemical bond with the surface of the metal substrate to be bonded. That is, the water-insoluble polymer forms a chemical bond with the surface of the metal substrate due to the functional groups it contains structurally. Furthermore, this water-insoluble polymer contains a component that melts and mixes with the resin component upon heating to form a bond. Specifically, the water-insoluble polymer can be, for example, polyvinyl butyral (PVB). The water-insoluble polymer is not limited to this example, but can be any resin component that is water-insoluble and forms a chemical bond with the metal substrate, and if the substrate is a resin, it can contain a resin component that melts and mixes with the resin upon heating to form a bond.

[0015] The bonding agent 10 contains an organic solvent that dissolves the above-mentioned water-insoluble polymer. When using PVB as the water-insoluble polymer, the organic solvent can typically be an organic solvent that dissolves PVB, such as diethylene glycol monoethyl ether (DEGMEE). As an additive, the bonding agent 10 may be added with, for example, propylene glycol (PG) or a coupling agent. PG can be used as a means to adjust the physical properties such as the viscosity and adhesiveness of the bonding agent 10 and to improve the stability of the solution. In addition, the coupling agent improves the adhesiveness by chemical bonding and contributes to the improvement of mechanical properties such as the tensile strength of the pair of bonded base materials. Typically, a silane coupling agent containing silicon (Si) can be used as the coupling agent.

[0016] Further, the bonding agent 10 may further contain at least one of conductive particles, inorganic particles, and plastic particles. The conductive particles added to the bonding agent 10 are not limited to simple conductive metals, and may be alloys or metal compounds. The metal constituting the conductive particles may be the same type of metal as the pair of metal base materials to be joined, or different types of metals. Specifically, the conductive particles have a metal formed in a film shape on the surface of the resin powder. That is, the metal constituting the conductive particles is coated on the surface of the resin powder. For example, it is coated on the surface of the resin powder by plating or the like. Since the conductive particles contribute to electrical conduction in the bonding agent 10, it preferably contains a metal such as silver (Ag), copper (Cu), gold (Au), aluminum (Al), etc. Specifically, although Ag is preferable for the conductive particles, since Ag is expensive, Cu, which is inexpensive although its electrical conductivity is slightly inferior compared to Ag, may also be used.

[0017] By including, for example, aluminum powder with a particle size of about 3 μm in the bonding agent 10, a bonding agent with good heat conduction and good electrical conduction can be obtained. Also, by including, for example, aluminum nitride particles or silicon nitride particles with a particle size of about 1 to 10 μm in the bonding agent 10, the thermal conductivity can be increased while maintaining insulation. Further, when plastic particles such as nylon 12 are included in the bonding layer 10, the adhesion to the metal becomes good, and it is also possible to adjust the thickness of the bonding layer.

[0018] Next, a method for bonding substrates using the bonding agent 10 with the above configuration will be described. As shown in Fig. 2(a), the bonding agent 10 can be applied to one of the pair of substrates 11 and 12, and as shown in Fig. 2(b), it can also be applied to both of the pair of substrates 11 and 12. The bonding agent 10 is in a solution state by mixing a water-insoluble polymer and an organic solvent, or becomes a paste state by adding an additive. The bonding agent 10 is applied to the substrate by a coating device such as a die coater. Also, the bonding agent 10 may be applied, for example, by dropping it onto the substrate and spreading it. In addition to this, the bonding agent 10 may be applied, for example, by dipping the substrate or spraying it with a spray.

[0019] The bonding agent 10 applied to the substrate forms a coating film layer 20 as shown in Fig. 2. The coating film layer 20 preferably has a sufficient thickness. The thickness of the coating film layer 20 is preferably 50 μm or more, and more preferably 100 μm or more.

[0020] After the coating film layer 20 is applied to the metal substrate, it is dried. As a result, the bonding agent 10 constituting the coating film layer 20 generates a chemical bonding layer that adheres to the surface of the metal substrate by chemical bonding. Here, it is considered that a chemical bonding layer is generated between the water-insoluble polymer contained in the bonding agent 10 and the surface of the substrate.

[0021] After the coating layer 20 has dried, the pair of substrates 11 and 12 are stacked together as shown in Figure 3. At this time, the pair of substrates 11 and 12 are stacked with the coating layer 20 formed by the bonding agent 10 in between. Alternatively, three or more substrates 11 and 12 may be stacked with the coating layer 20 in between, as shown in Figure 4.

[0022] As shown in Figure 3, the pair of substrates stacked with the coating layer 20 in between are heated and pressurized. Heating and pressurizing are performed, for example, by hot pressing. The pair of substrates 11 and 12 placed on the heating plate 30 are pressed in the direction of arrow 40 while heated. At this time, it is preferable to set the heating temperature to a temperature above the softening point at which the non-water-soluble polymer softens. Specifically, if the non-water-soluble polymer is PVB, the heating temperature is preferably 150°C to 200°C or higher, which is the softening point. The stacked substrates are maintained at, for example, 250°C for several minutes, then cooled to 170°C in the pressurizing process, maintained under pressure for several minutes to several tens of minutes, and then allowed to cool naturally. When using laser or ultrasonic heating, heating for a few seconds may suffice.

[0023] In the case of joining metal to metal, or metal to inorganic material, the thermoplastic, water-insoluble polymer contained in the bonding agent 10 that forms the coating layer 20 melts when the coating layer 20 is heated and pressurized together with the stacked substrates 11 and 12, forming a bonding layer. On the other hand, in the case of joining metal to resin, the resin substrate is heated to a temperature above its melting point to melt it, and then fused to the chemical bonding layer by pressing it against it. As a result, the pair of substrates 11 and 12 are joined by the bonding layer formed by the bonding agent 10.

[0024] In the case of joining metal substrates, by adding conductive particles to the bonding agent 10, the bonding layer formed by the bonding agent 10 becomes conductive, and the electrical resistance between the pair of metal substrates 11 and 12 joined by the bonding layer can be reduced. This makes the present invention usable in bonding applications where conductivity is required. Furthermore, since the conductive particles are made of metals with high thermal conductivity, the addition of conductive particles also contributes to the smooth transfer of heat in the coating layer 20. As a result, the temperature of the coating layer 20 rises rapidly and uniformly when heated, not only promoting the melting of water-insoluble polymers, but also making it usable in bonding applications where heat transfer between the bonded substrates is required.

[0025] Several embodiments of this model will be described below. First, let's explain the constituent materials of the bonding agent shown in Figure 5. Polyvinyl butyral (PVB) manufactured by SIGMA-ALDRICH was used as the thermoplastic, water-insoluble polymer. As the organic solvent, diethylene glycol monoethyl ether (DEGMEE) manufactured by Hayashi Pure Chemical Industries, Ltd., which can dissolve PVB, was used, to which propylene glycol (PG) manufactured by Fujifilm Wako Pure Chemical Corporation was added. As the coupling agent, the silane coupling agent "KB P-90" (KBP) from Shin-Etsu Chemical Co., Ltd. was used. Figure 5 also shows the components of the bonding agents for Examples 1 to 6, and the numbers shown in the figure indicate the mass (g) of each material prepared in each example.

[0026] In Examples 1-6, the adhesive was applied to both metal substrates 11 and 12 when joining metals, and only to the metal substrate 11 when joining metals and nonmetals. The materials were then dried in a drying oven and joined by heating and pressurizing with a hot press. The application thickness of the adhesive 10 was 50 μm on one side, for a total of 100 μm on both sides.

[0027] (Bonding metal and resin) A metal substrate 11 and a resin substrate 12 were joined using the bonding agents described in Examples 1 to 6 above. The metal substrate was A5052, primarily composed of aluminum, and the resin substrate was polyamide 6 (PA6 GF30) containing 30% glass fiber. The bonded test specimens consisted of a 50mm long, 20mm wide, and 1mm thick metal substrate and an 80mm long, 10mm wide, and 4mm thick resin substrate. The bonding started at 250°C and ended at 170°C. The bonded specimens were allowed to cool naturally after bonding. The pressure applied during the bonding process was adjusted to suppress thermal deformation of the resin substrate.

[0028] Figure 6 shows the results of tensile tests on substrates joined using the bonding agents of Examples 1 to 6. In all cases, the bonding strength was high, ranging from approximately 3 MPa to 15 MPa, confirming that bonding can be performed without problems even when using water-insoluble polymers. Figure 6 also shows the elongation in each test, confirming that there are no practical problems.

[0029] (Joining metal to metal) Metal substrates 11 and 12, both made of the same metal, were joined using the bonding agents described in Examples 1 to 6 above. A5052, primarily composed of aluminum, was used as the metal substrate. The test specimen was a plate with dimensions of 50 mm in length, 20 mm in width, and 1 mm in thickness, and the joint area was 20 mm x 10 mm. The joining temperature was 250 degrees Celsius at the start and 170 degrees Celsius at the end. The joint was allowed to cool naturally after joining. The pressure applied during the joining process was 2 MPa.

[0030] Figure 7 shows the results of tensile tests on substrates joined using the adhesives of Examples 1 to 6. Here, a pattern with a thickness of 50 μm where adhesive 10 is applied only to the metal substrate 11 and a pattern with a thickness of 100 μm where adhesive 10 is applied to both metal substrates 11 and 12 are shown side by side. In both cases, the joint strength was high, at approximately 7 MPa to 11 MPa, confirming that joining can be performed without problems even when using water-insoluble polymers. Figure 7 also shows the elongation amount in each test, confirming that there are no practical problems.

[0031] Next, the heat resistance of the bonding strength was tested using the bonding agent of Example 6. The metal substrates 11 and 12 were A5052, and the dimensions of the test specimen were plate-shaped with a length of 100 mm, a width of 20 mm, and a thickness of 1 mm, with a bonding area of ​​20 mm × 10 mm. As shown in Figure 8, the bonding strength, which was approximately 13 MPa at room temperature, decreased as the temperature increased to 100°C, 150°C, and 200°C. Since the glass transition temperature of the water-insoluble polymer PVB used in this study is in the range of 70°C to 80°C, a slight decrease in bonding strength occurs at the test temperature of 100°C. Furthermore, since the softening point of the same polymer is in the range of 150°C to 200°C, the bonding strength decreases drastically at the test temperature of 200°C. This makes it possible to appropriately select the operating environment temperature when using PVB as a water-insoluble polymer.

[0032] (Thickness of the bonding layer) The thickness of the bonded layer was measured when bonding using adhesive 10. The substrate used was stainless steel (SUS) with a thickness of 0.15 mm. The thickness of two of these substrates stacked without applying adhesive 10 was 0.29 mm. Adhesive 6 of Example 6 was applied to both of these substrates to a thickness of 50 μm, and bonding was performed. The bonding start temperature was 250 degrees Celsius, the end temperature was 170 degrees Celsius, and the material was allowed to cool naturally after bonding. The pressure applied during the bonding process was 2 MPa.

[0033] Figure 9 shows the thickness measurement results. Bonding thickness test 1 shows the results when the applied adhesive was allowed to dry before bonding, while bonding thickness test 2 shows the results when the adhesive was not allowed to dry before bonding. The thickness of the bonded parts after bonding in both tests was 0.30 mm and 0.29 mm, which is almost the same as the thickness of the unbonded part (0.29 mm). In other words, the thickness of the bonded layer is thought to be 0.01 mm or less. This confirms that an extremely thin bonded layer can be achieved when bonding with adhesive 10.

[0034] (Joining steel materials) Joint tests were conducted using steel materials. The steel material used was SPCC. The joint tests were performed using the bonding agent of Example 6, with SPCC used for both substrates (SPCC / SPCC), with SPCC on one side and A5052 on the other (SPCC / A5052), and for comparison, with A5052 used for both sides (A5052 / A5052). The dimensions of the test specimens were plate-shaped with a length of 50 mm, a width of 20 mm, and a thickness of 1 mm, and the joint area was 20 mm × 10 mm. The starting temperature for joining was 250 degrees Celsius, and the ending temperature was 170 degrees Celsius. After joining, the joints were allowed to cool naturally. The pressure applied during the joining process was 2 MPa.

[0035] Figure 10 shows the results of joining tests using steel materials. A joint strength of approximately 13 MPa was obtained for SPCC / SPCC joining, and approximately 10 MPa was obtained for SPCC / A5052 joining. This strength is sufficient even when compared to the joint strength of A5052 / A5052, confirming that a strong bond can be formed without oxidation of the steel joint by using the water-insoluble polymer PVB.

[0036] Furthermore, a laminate bonding test was conducted using electrical steel sheets, as shown in Figure 4. The bonding agent from Example 6 was applied to seven 0.35 mm thick electrical steel sheets, and these were stacked and heated and pressurized. Other bonding conditions were the same as above. The bonding test results confirmed that the seven electrical steel sheets became one unit and a strong bond was achieved. This confirmed that by using a water-insoluble polymer PVB, it is possible to laminate and bond extremely thin metal sheets with an amorphous iron base that are prone to rusting, using an extremely thin bonding layer.

[0037] (Conductivity verification) Conductive particles were added to bonding agent 10, and the conductivity between the bonded pair of metal substrates was verified. A bonding agent was prepared by adding conductive particles to the bonding agent of Example 5. The mass ratio of PVB, DEGMEE, PG, and conductive particles in the bonding agent was 0.3:3:1:1. The conductive particles used were 4 μm in diameter and had silver (Ag) coated on their surface.

[0038] First, bonding was performed using the bonding agent of Example 6. The metals used for verification were aluminum (Al) and copper (Cu), and the thickness of the applied bonding agent was 120 μm on each side. Other bonding conditions were the same as above. Figure 11 shows the results of the bonding test. The results are for three types of bonding tests: Al to Al bonding (Al / Al), Al to Cu bonding (Al / Cu), and Cu to Cu bonding (Cu / Cu). In all cases, a bonding strength of approximately 10 MPa or higher was confirmed.

[0039] Next, conductivity tests were conducted. The tests were performed using a four-terminal method with a DC stabilized power supply and a voltmeter. In the case of a Cu-Cu junction, the measurement results showed a voltage of 0mV at a current of 1A, and the electrical resistance was calculated to be less than 1mΩ. In the case of a Cu / Al junction, a voltage of 1mV was obtained at a current of 1A, and the electrical resistance was calculated to be 1mΩ. Thus, it was confirmed that sufficient conductivity was achieved.

[0040] (Joining with a fitted shape) A joint test was conducted on the interlocking shape of metals. The detailed shape of the joint is shown in Figure 12. The metal base material used was an A5052 aluminum block. A projection with a diameter of φ9.97 mm and a height of 6 mm was formed on one aluminum block, and a hole with a diameter of φ9.99 mm and a depth of 6 mm was formed on the other aluminum block. The joining material of Example 6 was applied to the tip surface of the projection on one aluminum block, and the joint was made.

[0041] The starting temperature for bonding was 250 degrees Celsius, and the ending temperature was 170 degrees Celsius. The pressure applied during the bonding process was 4 MPa. The bonding test results showed that a tensile strength of 419 N was obtained by using the bonding material of Example 6. It is believed that the high tensile strength was achieved because the bonding material melted due to heating and pressurizing, and at the same time, the bonding material penetrated into the wall surface, increasing the bonding area.

[0042] (Joining metals and inorganic materials) A bonding test was conducted between alumina ceramic and aluminum. The alumina ceramic specimen was 2 mm thick, and the aluminum specimen was 1 mm thick. The bonding material from Example 6 was used for bonding. The bonding material was applied to the aluminum specimen to a thickness of 50 μm, dried, and then bonded by heating at 250 degrees Celsius using a hot press. The pressure applied during the bonding process was kept low enough not to crack the alumina ceramic. The bonding test results showed that the alumina ceramic and aluminum specimens were sufficiently bonded. Furthermore, bonding between glass and aluminum is also possible using the same method. The ability to join metals and inorganic materials makes it possible to join metal heat dissipation components with insulating components such as ceramics and resins in a state of high thermal conductivity, which opens up possibilities for applications in electronic components such as LEDs.

[0043] The present invention described above is not limited to the embodiments described above, and can be applied to various embodiments without departing from its spirit. [Explanation of symbols]

[0044] In the drawing, 10 indicates the adhesive, 11 the metal substrate, 12 the metal or non-metal substrate, 20 the coating layer, 30 the heating plate, and 40 the direction of pressure.

Claims

1. A bonding agent for joining a metal substrate to a metal substrate of the same or different type as the said metal substrate, or a non-metallic substrate, The aforementioned bonding agent consists of a polymer solution prepared with a water-insoluble polymer and an organic solvent. The aforementioned water-insoluble polymer is a thermoplastic polymer. A bonding agent characterized by the following features.

2. The aforementioned water-insoluble polymer is polyvinyl butyral. The bonding agent according to claim 1.

3. The aforementioned organic solvent is diethylene glycol monoethyl ether. The bonding agent according to claim 2.

4. Further containing propylene glycol, The bonding agent according to claim 3.

5. Further comprising at least one of conductive particles, inorganic particles, and plastic particles, The adhesive according to claim 4.

6. A bonding method using the bonding agent according to any one of claims 1 to 5, A step of applying the bonding agent to at least one of the metal substrates to be joined, The process of preparing a pair of substrates by placing the other metal substrate or non-metal substrate on top of the aforementioned bonding agent, A step of heating and pressurizing the stacked pair of substrates, A joining method that includes [a specific type of joining].

7. The process includes drying the bonding agent applied to the metal substrate. The joining method according to claim 6.

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