Joining method

Abstract

To join two resin bodies, at least one of which is an ester resin body, with high joining strength.SOLUTION: A bonding method according to the present invention is a method for bonding two resin bodies, at least one of which is an ester-based resin body, and includes a plasma treatment step of treating a bonding surface of the ester-based resin body with water plasma, a coating treatment step of applying a silane coupling agent to a bonding surface of at least one of the two resin bodies, and a thermal pressing treatment step of bringing the two resin bodies into contact with each other at the respective bonding surfaces, and heating and pressurizing the two resin bodies.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for bonding objects made of resins having ester bonds. [Background technology]

[0002] Resins such as polycarbonate (PC), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polyethylene (PE), polypropylene (PP), and cycloolefin polymer (COP) are used as materials for the substrates of microfluidic chips and the lens-equipped substrates that make up camera modules for smartphones.

[0003] Of these resins, PC and PET have ester bonds in their main chains, while PMMA has ester bonds in their side chains. Such resins having ester bonds in their main chains or side chains are referred to herein as ester-based resins. Furthermore, in this specification, an object (plate, shaped object, etc.) made of resin is referred to as a resin body, and an object made of an ester-based resin is particularly referred to as an ester-based resin body. Note that, in this specification, the term "ester bond" refers not only to an ester bond in the narrow sense formed by a condensation reaction between a carboxylic acid and an alcohol, but also to an ester bond in the broad sense formed by a condensation reaction between an organic or inorganic oxo acid and a compound having a hydroxy (OH) group.

[0004] Microfluidic chips and smartphone camera modules are manufactured by bonding resin substrates together. In this case, the bonding surfaces are sometimes treated with ultraviolet light or plasma to ensure a secure bond between the resin substrates.

[0005] In particular, when the resin body is an ester-based resin body, for example, Patent Document 1 describes treating at least one of the surfaces of two resin bodies such as PC, PET, and PMMA with water plasma. Also, Patent Document 2 describes irradiating the surface of a resin body such as PC with ultraviolet light, and then applying a solution containing a silane coupling agent. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 02-286222 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-019348 [Patent Document 3] Japanese Patent Publication No. 2022-190586 [Patent Document 4] International Publication No. 2016 / 147828 Summary of the Invention [Problem to be solved by the invention]

[0007] In microfluidic chips and smartphone camera modules, it is necessary to improve the impact resistance when dropped to the ground, etc., and to bond substrates with higher bonding strength. However, the methods described in Patent Documents 1 and 2 have limitations on the bonding strength that can be obtained.

[0008] The problem to be solved by the present invention is to bond two resin bodies, at least one of which is an ester-based resin body, with high bonding strength. [Means for solving the problem]

[0009] A bonding method according to the present invention, which has been made to solve the above problems, is a method for bonding two resin bodies, at least one of which is an ester-based resin body, comprising the steps of: a plasma treatment step of treating the bonding surface of the ester-based resin body with water plasma; a coating treatment step of applying a silane coupling agent to at least one of the joining surfaces of the two resin bodies; a heat pressing process in which the two resin bodies are brought into contact with each other at their joining surfaces and heated and pressurized; Includes:

[0010] As described above, an ester-based resin body is an object made of a resin having a broad ester bond formed by a condensation reaction between an organic or inorganic oxo acid and a compound having an OH group, and is, for example, a plate made of PC, PET, PMMA, etc.

[0011] In the bonding method according to the present invention, one of the two resin bodies is an ester-based resin body, but the other resin body may be the same or a different type of ester-based resin body, or may be a resin body other than an ester-based resin such as PE, PP, COP, etc. Examples of the resin body include a substrate for a microchannel chip and a substrate with a lens. [Effects of the Invention]

[0012] As will be described later, the present inventors have discovered that when an ester resin body is treated with ultraviolet light, ester bonds near its surface are cleaved and hydroxyl groups (OH groups) are introduced at the cleavage sites (a layer in this state will be referred to as a fragile layer), and that if a fragile layer is formed near the joining surface of the ester resin body, even if the resin bodies are joined together after applying a silane coupling agent, the fragile layer of the ester resin body will peel off when the resin bodies are pulled together, making it impossible to increase the joining strength between the resin bodies.The reason why ester bonds are cleaved when treated with ultraviolet light is not clear, but it is thought that the electron-withdrawing properties of ester bonds reduce the covalent bonding properties of the main chain of the resin body, making them more susceptible to cleavage.

[0013] Therefore, in the bonding method according to the present invention, before bonding two resin bodies, at least one of which is an ester-based resin body, by heat pressing, the ester-based resin body is treated with water plasma and then coated with a silane coupling agent. In the bonding method according to the present invention, the surface of the ester-based resin body is treated with water plasma instead of ultraviolet light, so no brittle layer is formed. Furthermore, coating the silane coupling agent after water plasma treatment further increases the bonding strength.

[0014] Therefore, according to the present invention, two resin bodies, at least one of which is an ester-based resin body, can be joined with higher joining strength. [Brief explanation of the drawings]

[0015] [Figure 1] 1A and 1B are diagrams showing the respective processing procedures of a joining method included in the present invention and a joining method not included in the present invention. [Figure 2] FIG. 1 is a diagram illustrating the water plasma treatment in this experiment. [Figure 3] FIG. 10 is a diagram illustrating the state of ultraviolet treatment in this experiment. [Figure 4] FIG. 1 is a diagram showing two bonded test pieces and a diagram illustrating a tensile test for measuring the bond strength between them. [Figure 5] FIG. 1 is a diagram schematically illustrating a microchannel chip. [Figure 6] 1A and 1B are diagrams showing the structure of a side surface of a camera module formed by stacking a plurality of lens-equipped substrates. DETAILED DESCRIPTION OF THE INVENTION

[0016] First, the method and results of the experiment conducted to confirm the effects of the present invention will be described with reference to the drawings.

[0017] <Test piece and its joining method> [Test piece] In this experiment, multiple test pieces 1 measuring 10 mm x 15 mm x 0.5 mm were prepared for each of PC, PET, PMMA, PE, and PP. For PC, PCSMPS610 manufactured by Takiron C.I. Co., Ltd. was used, for PET, Lumirror T60 manufactured by Toray Industries, Inc. was used, for PMMA, Acriplene HBS006H manufactured by Mitsubishi Chemical Corporation was used, for PE, PEN-050501 manufactured by AS ONE Corporation was used, and for PP, P922-1 manufactured by Hikari Corporation was used.

[0018] Figure 1 shows the respective processing steps of a bonding method included in the present invention (Figure 1(a)) and a bonding method not included in the present invention (Figures 1(b) and 1(c)). Each processing step shown in Figure 1 will be explained below.

[0019] [Water plasma treatment] For this treatment, an Aqua Plasma (registered trademark) cleaner AQ-500 manufactured by Samco Inc. was used. Figure 2 is a diagram illustrating the water plasma treatment in this experiment. As shown in Figure 2, the test piece 1 was placed, with the bonding surface facing up, on the lower electrode (ground electrode) 22 of the parallel plate type electrodes in the treatment chamber 21 of the same device. The plasma treatment conditions are as follows. Note that the water plasma treatment may also be performed under atmospheric pressure. Process gas: water vapor (H2O) Flow rate: 12sccm Pressure: approx. 7 Pa High frequency power: 50W Processing time: 20 seconds or 80 seconds

[0020] [Coating treatment] Test piece 1 was immersed in a solution of aminopropyltrimethoxysilane (APS), a silane coupling agent, for 5 seconds. After immersion, the bonding surface was washed with pure water (alcohol washing was also possible) and dried by spraying nitrogen gas (air could be used instead of nitrogen gas) to minimize the amount of silane coupling agent remaining on the surface of test piece 1. This resulted in an APS coating on the bonding surface of test piece 1. An aqueous solution of polyethyleneimine (PEI) may also be used as the silane coupling agent. Furthermore, to minimize the amount of silane coupling agent remaining on the surface of test piece 1, the solution is preferably diluted with water or alcohol to 10% (preferably 1%) or less.

[0021] [Press processing] At room temperature (25°C) and atmospheric pressure (approximately 0.1 MPa), the bonding surfaces of two test pieces 1,1 of the same type were placed together and brought into contact with each other. Then, a pressure of 1 MPa or less was applied using a hand roller for 3 minutes. This pressing process is preferably performed in a reduced-pressure (100 Pa or less) environment, allowing for the removal of air that had entered the bonding surfaces when the flow path plate and cover plate were placed together. Alternatively, the stacked test pieces 1,1 may be pressed at 1 MPa or more. The test pieces were then heated to 80°C for 30 minutes (heating treatment). While a heating temperature of 50°C to 160°C is sufficient for the heating process, a temperature of 70°C to 90°C is more preferable, and a temperature of 80°C is even more preferable. The pressing process may be performed while heated, rather than at room temperature. In this case, a separate heating treatment is not necessary. Heating in this manner promotes the dehydration condensation reaction between the silane coupling agent and the test pieces 1,1, resulting in a strong bond via siloxane bonding.

[0022] [UV treatment] For this treatment, a UV ozone cleaner UV-1 manufactured by Samco Inc. was used. Figure 3 is a diagram illustrating the ultraviolet treatment in this experiment. As shown in Figure 3, the test piece 1 was placed in the treatment chamber 31 of the device with the bonding surface facing up, and nitrogen (N2) gas was introduced into the treatment chamber 31 to create a nitrogen atmosphere at approximately atmospheric pressure (approximately 0.1 MPa). Then, low-pressure mercury lamps 32 with wavelengths of 253.7 nm and 184.9 nm were used to irradiate the test piece with ultraviolet light at an illuminance of 20 mW / cm. 2 Test piece 1 was irradiated with ultraviolet light of intensity of 1 for 3 minutes.

[0023] <Experimental Method> Figure 4 shows two bonded test pieces and explains the tensile test procedure for measuring their bond strength. As shown in Figure 4(a), two test pieces 1, 1 for each of PC, PET, PMMA, PE, and PP were bonded using the three methods shown in Figure 1, and then the bond strength and fracture location were confirmed using a tensile tester as shown in Figure 4(b). Specifically, the top and bottom of the bonded assembly were fixed to bolts, and one of the test pieces 1 was pulled vertically to confirm the bond strength. The tensile strength test was conducted in accordance with JIS K 6849, and the bond strength was measured using a force gauge ZTA-500N manufactured by Imada Co., Ltd.

[0024] In this experiment, an example in which PC test pieces 1, 1 were joined together using the method shown in FIG. 1(a) (a joining method included in the present invention) was designated Example 1, an example in which they were joined using the method shown in FIG. 1(b) (a joining method not included in the present invention) was designated Comparative Example 1, and an example in which they were joined using the method shown in FIG. 1(c) (a joining method not included in the present invention) was designated Comparative Example 2. Similarly, an example in which PET was joined using the method shown in FIG. 1(a) was designated Example 2, an example in which they were joined using the method shown in FIG. 1(b) was designated Comparative Example 3, an example in which PMMA was joined using the method shown in FIG. 1(a) was designated Example 3, and an example in which they were joined using the method shown in FIG. 1(b) was designated Comparative Example 4. Furthermore, examples in which PE and PP were joined using the method shown in FIG. 1(a) were designated Comparative Examples 5 and 6, respectively.

[0025] <Experimental Results> In the methods according to Examples 1 to 3, cohesive failure occurred in both cases where the plasma treatment time was 20 seconds and 80 seconds, and the bonding strength was 200 N / cm 2 On the other hand, in the methods according to Comparative Examples 1 to 6, when the plasma treatment time was either 20 seconds or 80 seconds, interfacial peeling occurred, and the bonding strength was 100 N / cm 2 As an example, the experimental results of Examples 1 to 3 and Comparative Examples 1 to 6 are shown below, where the unit of the numerical values ​​is N / cm. 2 , and ○ indicates a bonding strength of 100 N / cm 2 or more, × indicates a bonding strength of 100 N / cm 2 means less than. [Table 1]

[0026] The results of Example 1 and Comparative Example 1 show that when joining two resin bodies, at least one of which is an ester-based resin, by performing a water plasma treatment, followed by a coating treatment, and then a press treatment, the joining strength can be increased. Furthermore, the results of Examples 1 to 3 and Comparative Examples 2 to 4 show that when joining two resin bodies, at least one of which is an ester-based resin, by performing an ultraviolet treatment, the joining strength decreases. Furthermore, the results of Comparative Examples 5 and 6 show that when neither of the resin bodies is an ester-based resin, high joining strength cannot be obtained even if the water plasma treatment, coating treatment, and press treatment are performed. In other words, at least one of the resin bodies must be an ester-based resin.

[0027] As described in Patent Document 3, ultraviolet treatment usually has the effect of increasing the bonding strength between resin bodies, but this experiment revealed that when at least one of the bodies is an ester-based resin, such effect is not obtained and instead the bonding strength is reduced.Patent Document 4 describes that when bonding resin bodies such as cycloolefin resin, acrylic resin, and silicone resin, excessive irradiation with ultraviolet light decomposes part of the resin body near the surface, reducing the bonding strength, but does not clarify the detailed cause of this.

[0028] Therefore, the present inventors conducted extensive research and found that when an ester resin body is treated with ultraviolet light, ester bonds near its surface are cleaved, OH groups are introduced at the cleavage sites (hydrolysis), and a brittle layer (a layer of low-molecular-weight organic compounds formed near the surface of the ester resin body by hydrolysis) is formed. The present inventors then came up with the idea that if a brittle layer is formed near the surface of an ester resin body, even if the resin bodies are bonded together after being coated with a silane coupling agent, the brittle layer will peel off from the resin body when the resin bodies are pulled together, thereby reducing the bonding strength of the two resin bodies. The following describes the method and results of an experiment conducted to confirm this idea, with reference to the drawings.

[0029] <Experimental Method> Ester-based resins (PC, PET, PMMA) and non-ester-based resins (PE, PP, COP) were treated with water plasma (80 s), and UV light (2 or 3 min) and water plasma (80 s) were also treated. The water contact angle on the surface of the resins was measured before and after UV or water plasma treatment. For PC, PET, PMMA, PE, and PP, the same test pieces as described above were used, and for COP, ZEONEX690R manufactured by Zeon Corporation was used.

[0030] <Experimental Results> Table 2 shows the experimental results for water plasma treatment (80 s), UV treatment (3 min), and water plasma treatment (80 s). The numbers in the table represent the contact angle of water on the resin surface. When UV treatment was performed on ester-based resins, the contact angle was found to be reduced by 10° or more compared to when UV treatment was not performed, regardless of whether water plasma treatment was performed before or after (see columns AB and CD). On the other hand, for resins that are not ester-based resins, no reduction in contact angle due to UV treatment was observed. This experimental result can be explained by the fact that UV treatment breaks ester bonds near the surface of the ester-based resin, introducing OH groups, supporting the idea mentioned above. [Table 2]

[0031] Table 3 shows the experimental results for water plasma treatment (80 s), UV treatment (2 min), and water plasma treatment (80 s). The decrease in contact angle due to UV treatment was not as significant as when UV treatment was performed for 3 min, but it was still observed to some extent. Since the degree of decrease in contact angle differs depending on the treatment time of UV treatment, it is thought that the degree of formation of the brittle layer also depends on the UV irradiation time. [Table 3]

[0032] The reason why ester bonds are broken by treatment with ultraviolet light is not clear, but it is thought that the electron-withdrawing properties of ester bonds reduce the covalent bond strength of the main chain of the resin body, making them more susceptible to cleavage.

[0033] Next, exemplary embodiments of the bonding method according to the present invention will be described. In this specification, as examples, a case where a micro-channel chip is manufactured by bonding a channel plate and a cover plate (first embodiment) and a case where a camera module is manufactured by bonding a lens-equipped substrate (second embodiment) will be described.

[0034] First Embodiment As a first embodiment of the bonding method of the present invention, a method for producing a micro-channel chip will be described.

[0035] [Flow path plate and cover plate] Figure 5 is a schematic diagram of a microchannel chip. Figure 5 (a) shows the channel plate of the microchannel chip, (b) shows the cover plate, and (c) shows the side structure of the microchannel chip manufactured by bonding the channel plate and cover plate. Microchannel chips are generally manufactured by placing a separate transparent plate (cover plate) made of glass, resin, or the like on the surface of a plate (channel plate) on which channels are formed, made of a plate material such as resin or glass, and bonding the two together.

[0036] In this embodiment, the materials for the channel plate and cover plate constituting the microchannel chip can be ester-based resins such as PC, PET, and PMMA, or non-ester-based resins such as PE, PP, and COP. In this embodiment, at least one of the channel plate and cover plate is an ester-based resin such as PC, PET, or PMMA. For example, a COP plate cut from ZEONEX690R (glass transition temperature: 136°C) manufactured by Zeon Corporation to approximately 25 mm × 60 mm × 1 mm can be used as the channel plate, and a PC film cut from PCSMPS610 (manufactured by Takiron C.I. Co., Ltd.) to approximately 35 mm × 75 mm × 50 μm can be used as the cover plate. A flexible film with a thickness of approximately 20 μm to 200 μm is preferably used as the cover plate to improve conformability to the channel plate during bonding and reduce optical loss. The channel shown in FIG. 5(a) is formed by thermal imprinting using a silicon mold. The flow path can have a meandering section with a width of, for example, 300 μm, a depth of 50 μm, and a length of 150 mm.

[0037] The flow path plate and the cover plate are joined together using the method shown in Fig. 1(a). An example of the conditions for each step in these procedures will be described below.

[0038] [Water plasma treatment] As explained above, this treatment can be performed using the Aqua Plasma (registered trademark) Cleaner AQ-500 manufactured by Samco, Inc. As shown in Figure 2, the flow path plate and cover plate can be placed, with the bonding surface facing up, on the lower electrode (ground electrode) 22 of the parallel plate type electrodes in the treatment chamber 21 of the apparatus. The plasma treatment conditions for the water plasma treatment are as follows. Note that the water plasma treatment may also be performed under atmospheric pressure. Process gas: water vapor (H2O) Flow rate: 1sccm~50sccm Pressure: 1Pa~30Pa High frequency power: 50W~250W Processing time: 1s to 600s

[0039] [Coating treatment] Next, the cover plate is immersed in a solution of APS, a silane coupling agent, for approximately 5 seconds. After immersion, the bonding surface is washed with pure water or alcohol to minimize the amount of silane coupling agent remaining on the surface of the cover plate, and then dried by spraying with nitrogen gas or air. In this way, the bonding surface of the cover plate is coated with APS. Note that an aqueous solution of polyethyleneimine (PEI) may also be used as the silane coupling agent. Furthermore, to minimize the amount of silane coupling agent remaining on the surface of the cover plate, the solution is preferably diluted with water or alcohol to 10% (preferably 1%) or less.

[0040] [Press processing] The joining surfaces of the flow channel plate and the cover plate are brought into contact with each other at room temperature (25°C) and atmospheric pressure (approximately 0.1 MPa), and then maintained for 3 minutes while applying pressure (1 MPa or less) using, for example, a hand roller. This pressing process is preferably performed in a reduced-pressure (100 Pa or less) environment, since it allows for the removal of air that may have entered the joining surfaces when the flow channel plate and the cover plate are brought into contact with each other. Alternatively, the stacked flow channel plate and cover plate may be pressurized at 1 MPa or more. The mixture is then heated to 80°C for 30 minutes (heating process). While a heating temperature of 50°C to 160°C is sufficient for the heating process, a temperature of 70°C to 90°C is more preferable, and a temperature of 80°C is even more preferable. The pressing process may be performed while heating rather than at room temperature, in which case a separate heating process is not necessary. As mentioned above, heating after applying the silane coupling agent promotes the dehydration condensation reaction and forms a strong bond between the flow channel material and the cover material via siloxane bonds.

[0041] The microchannel chip obtained in this way does not form a brittle layer because the surface of the ester resin body is treated with water plasma instead of ultraviolet light. Furthermore, the silane coupling agent is applied after the water plasma treatment, which further increases the bonding strength.

[0042] According to the bonding method of the present invention, when at least one of the flow path plate and the cover plate is made of an ester-based resin, the flow path plate and the cover plate can be bonded together with high strength by carrying out the above-mentioned treatment.

[0043] Second Embodiment As a second embodiment of the bonding method of the present invention, a method for manufacturing a camera module by bonding a plurality of lens-fitted substrates will be described.

[0044] [Substrate with lens] Figure 6 is a diagram showing the side structure of a camera module made by stacking seven lens-fitted substrates (L1 to L7). The lens-fitted substrate is composed of a lens portion and a substrate portion that supports the lens portion at its outer periphery. As shown in Figure 6, a camera module is manufactured by stacking multiple lens-fitted substrates with their optical axes aligned and bonding the substrate portions together.

[0045] In this embodiment, the lens portion of the lens-fitted substrate can be molded from resins such as PC, PET, PMMA, PE, PP, and COP, while the substrate portion can be molded from resins such as PC, PET, PMMA, PE, PP, and COP, or a silicon plate. The lens portion and substrate portion can be integrally molded simultaneously using the same resin by injection molding to form a lens-fitted substrate. In Figure 6, lens-fitted substrates L2, L6, and L7 are integrally molded. Alternatively, the lens portion and substrate portion can be molded from different resins and then bonded together, or the lens portion can be bonded to a silicon substrate portion to form a lens-fitted substrate. In Figure 6, lens-fitted substrates L1, L3, L4, and L5 are lens-fitted substrates obtained by bonding a lens portion to a substrate portion. Since the bonding surface of the substrate portion will bond to the substrate portion of another lens-fitted substrate when stacked, it is preferable for it to have high flatness. In this embodiment, at least one of the substrate portions of adjacent lens-fitted substrates is made of an ester-based resin such as PC, PET, or PMMA.

[0046] These lens-equipped substrates are bonded together using the method shown in Fig. 1(a). An example of the conditions for each step in these procedures will be described below.

[0047] [Water plasma treatment] As explained above, this treatment can be performed using the Aqua Plasma® Cleaner AQ-500 manufactured by Samco, Inc. As shown in Figure 2, the lens-equipped substrate can be placed with the bonding surface facing up on the lower electrode (ground electrode) 22 of the parallel plate electrodes in the treatment chamber 21 of the apparatus. When bonding three or more lens-equipped substrates and treating both the front and back surfaces of the lens-equipped substrates, one surface can be treated first, then the substrate can be turned over and the other surface can be treated. Alternatively, the lens-equipped substrate can be placed vertically and both surfaces can be treated simultaneously. Simultaneous treatment of both surfaces improves bonding strength and shortens treatment time. The plasma treatment conditions for the water plasma treatment are as follows. The water plasma treatment can also be performed under atmospheric pressure. Process gas: water vapor (H2O) Flow rate: 1sccm~50sccm Pressure: 1Pa~30Pa High frequency power: 50W~250W Processing time: 1s to 600s

[0048] [Coating process] and [Pressing process] The coating process and pressing process can be performed in the same manner as in the case of the microchannel chip, and therefore a description thereof will be omitted.

[0049] In this embodiment, when the water plasma treatment and coating treatment are performed, it is preferable to mask the lens portion so as not to affect the optical properties of the lens portion. [Explanation of symbols]

[0050] 1...Test piece 21, 31...Processing chamber 22...Lower electrode 32...Low-pressure mercury lamp L1~L7...Lens-equipped board

Claims

1. A method for joining two resin bodies, at least one of which is an ester-based resin body, comprising the steps of: a plasma treatment step of treating the bonding surface of the ester-based resin body with water plasma; a coating treatment step of applying a silane coupling agent to at least one of the joining surfaces of the two resin bodies; a heat pressing process in which the two resin bodies are brought into contact with each other at their joining surfaces and heated and pressurized; A joining method comprising:

2. The bonding method according to claim 1 , wherein the two resin bodies are both ester-based resin bodies.

3. 3. The bonding method according to claim 1, wherein the plasma treatment time in the plasma treatment step is 80 seconds or less.

4. 4. The bonding method according to claim 3, wherein the plasma treatment time in the plasma treatment step is 20 seconds or more and 80 seconds or less.

5. The bonding method according to claim 1 or 2, wherein the heat pressing step is carried out under a reduced pressure atmosphere of 100 Pa or less.

6. The bonding method according to claim 1 or 2, wherein the heat pressing step is carried out at a temperature of 50°C to 160°C.

7. The bonding method according to claim 6, wherein the pressing step is carried out at a temperature of 70°C to 90°C.

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