Adhesion method and conjugate

Abstract

To heighten adhesion strength between an object to be joined and a thermosetting adhesive agent to adhere the object to be adhered more stronger than ever.SOLUTION: A method includes a preparation step of preparing a pre-bonding structure by interposing an adhesive containing a thermosetting resin between two objects to be bonded; a preliminary curing step of heating the pre-bonding structure to a first temperature that is equal to or higher than room temperature but lower than the specified curing temperature of the adhesive, and keeping the pre-bonding structure in the first temperature environment at least until heat generation accompanying polymerization of the thermosetting resin is completed; and a main curing step of heating the pre-bonding structure to a second temperature that is higher than the first temperature, and keeping the pre-bonding structure in the second temperature environment for a predetermined time.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a bonding method, and more particularly to a bonding method and bonded article using a thermosetting adhesive. [Background technology]

[0002] There are two types of adhesives: room-temperature curing adhesives, which cure resin at room temperature to form bonds, and thermosetting adhesives, which cure resin by heating to form bonds. There are various types of room-temperature curing adhesives, most of which have a glass transition temperature (Tg) of around 50-60°C. Tg is the temperature at which the resin begins to soften, so the adhesive strength of the adhesive decreases significantly at temperatures above Tg. For this reason, room-temperature curing adhesives are not suitable for use in high-temperature environments.

[0003] On the other hand, some thermosetting adhesives can achieve a Tg of about 120°C by curing at about 120°C, and have better heat resistance than room temperature curing adhesives. For example, Patent Documents 1 to 3 describe adhesives whose Tg is further increased by mixing a different type of resin, filler, low molecular weight compound, etc. with the epoxy resin used in thermosetting adhesives. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-177013 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-231536 [Patent Document 3] Japanese Patent Application Publication No. 2017-31402 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, thermosetting adhesives have excellent heat resistance and are less likely to lose adhesive strength even in high-temperature environments. However, thermosetting adhesives generally have a problem in that their adhesive strength at room temperature is lower than that of room-temperature-curing adhesives.

[0006] The problem to be solved by the present invention is to increase the adhesive strength when objects to be joined are joined with a thermosetting adhesive. [Means for solving the problem]

[0007] In order to solve the above problems, the bonding method according to the present invention comprises: a preparation step of preparing a pre-bonding structure by interposing an adhesive containing a thermosetting resin between two objects to be bonded; a pre-curing step of heating the pre-bonding structure to a first temperature that is equal to or higher than room temperature and lower than a specified curing temperature of the adhesive, and placing the pre-bonding structure in the first temperature environment at least until heat generation associated with polymerization of the thermosetting resin is completed; a main curing step of heating the pre-bonding structure to a second temperature that is higher than the first temperature and placing the pre-bonding structure in an environment at the second temperature for a predetermined time; It has the following characteristics.

[0008] The specified curing temperature of an adhesive is, for example, the curing temperature recommended by the adhesive manufacturer, and is usually published on the manufacturer's website, catalog, etc. Generally, the recommended curing temperature is set within the range of 120°C to 180°C. According to the above configuration, in the preliminary curing step, the pre-bonding structure is heated to a first temperature that is equal to or higher than room temperature, thereby increasing the molecular mobility of the resin contained in the adhesive between the bonded objects. Furthermore, because the first temperature is lower than the specified curing temperature of the adhesive, the polymerization reaction of the resin does not proceed rapidly. As a result, as the polymerization reaction progresses, unreacted functional groups of the oligomers generated by the polymerization reaction interact with functional groups on the surfaces of the bonded objects, causing the oligomers to orient on the surfaces of the bonded objects. In this state, the pre-bonding structure is heated to a second temperature in the main curing step, thereby crosslinking the oligomers. As a result, a dense three-dimensional network structure is formed, and the bonded objects can be bonded with higher adhesive strength and a higher Tg than with conventional curing methods.

[0009] In the above bonding method, When the specified curing temperature is 120°C, the first temperature may be 60°C or higher and 90°C or lower.

[0010] In addition, in the above-mentioned bonding method, The second temperature may be at least 5° C. higher than the first temperature.

[0011] Furthermore, in the above-mentioned bonding method, The predetermined time may be 15 minutes or more.

[0012] Furthermore, the above-mentioned bonding method includes: In the main curing step, the pre-bonding structure may be heated to the second temperature within 120 minutes after the preliminary curing step.

[0013] As a result, the objects to be bonded can be bonded with a higher adhesive strength more reliably.

[0014] In the above bonding method, The second temperature may be lower than a specified curing temperature of the adhesive.

[0015] The bonded body obtained through the preliminary curing step and the main curing step is then naturally cooled. According to the above bonding method, thermal shrinkage of the adhesive during cooling can be suppressed, and even when bonding objects with different thermal expansion coefficients, peeling of the adhesive due to differences in thermal shrinkage rates is unlikely to occur. Therefore, the above method can be used to manufacture bonded bodies used in various applications requiring leak resistance. Furthermore, even when the preliminary curing step and the main curing step are performed at a temperature lower than the specified curing temperature, a higher Tg can be obtained than when one-stage curing is performed at the specified curing temperature.

[0016] In the above bonding method, The bonding surfaces of the two objects to be bonded may each be made of fiber reinforced plastic (FRP), heat resistant resin, or metal.

[0017] The above method can be used to manufacture junctions for various applications that require heat resistance, leak resistance, radiation resistance, and mechanical strength.

[0018] The above-mentioned bonding method is a measuring step of measuring, when a temperature-measurement adhesive having the same composition as the adhesive is heated to the first temperature, the time from when the first temperature is reached to when heat generation accompanying polymerization of the thermosetting resin ends, using a differential scanning calorimeter; In the pre-curing step, the pre-bonding structure may be heated to a first temperature and then placed in an environment at the first temperature for at least the period of time.

[0019] Typically, the adhesive layer in the pre-bonded structure is thin, making it difficult to directly confirm the temperature change of the adhesive layer. According to the above bonding method, the timing at which heat generation associated with polymerization of the thermosetting resin of the adhesive in the pre-bonded structure ends can be inferred from the temperature change when a temperature-measuring adhesive having the same composition as the adhesive used in the pre-bonded structure is heated to a first temperature.

[0020] The above-mentioned bonding method is In the pre-curing step, the end of heat generation due to polymerization of the thermosetting resin may be detected by measuring the temperature of a temperature-measuring adhesive having the same composition as the adhesive and placed in a container that is in thermally conductive contact with the pre-bonding structure, and detecting the maximum temperature.

[0021] According to the bonding method of the ninth aspect, the end of heat generation accompanying the polymerization of the thermosetting resin can be detected in situ.

[0022] The bonded body according to the present invention, which has been made to solve the above problems, is A bonded structure comprising two bonded bodies, each made of FRP, heat-resistant resin, or metal, and an adhesive containing a thermosetting resin interposed between the two bonded bodies, wherein the tensile shear adhesive strength between the bonded bodies and the adhesive at 80°C is 31 MPa or more.

[0023] In the above bonded body, The adhesive may have a glass transition temperature of 140°C or higher.

[0024] These bonded bodies firmly bond the objects to be bonded even in a high temperature environment. [Effects of the Invention]

[0025] According to the bonding method of the present invention, it is possible to increase the adhesive strength when objects to be bonded are bonded with a thermosetting adhesive. [Brief explanation of the drawings]

[0026] [Figure 1] 10A and 10B are diagrams illustrating a step of preparing a pre-bonding structure in Experimental Example 2. [Figure 2] FIG. 10 is a diagram for explaining a method for measuring the temperature of an adhesive in Experimental Example 2. [Figure 3]10 is a graph showing an example of a temperature profile of the temperature inside a heating furnace and the temperature of an adhesive in Experimental Example 2. [Figure 4] 10 is a diagram for explaining a method of leak measurement in Experimental Example 3. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] The bonding method according to the present invention includes a preparation step of preparing a pre-bonding structure by interposing an adhesive containing a thermosetting resin between two objects to be bonded; a preliminary curing step of heating the pre-bonding structure to a first temperature that is equal to or higher than room temperature but lower than the specified curing temperature of the adhesive, and keeping the pre-bonding structure in the first temperature environment at least until heat generation associated with polymerization of the thermosetting resin is completed; and a main curing step of heating the pre-bonding structure to a second temperature that is higher than the first temperature, and keeping the pre-bonding structure in the second temperature environment for a predetermined time.

[0028] <Preparation process> In the preparation process, a pre-bonding structure is prepared by placing an adhesive containing a thermosetting resin between two objects to be bonded. Here, thermosetting resin refers to a resin that hardens when heated and the polymer polymerizes to form a network structure. Examples of thermosetting resins contained in adhesives include epoxy resin, phenolic resin, acrylic resin, unsaturated polyester resin, melamine resin, urea resin, and urethane resin. Epoxy resin is preferred as the thermosetting resin due to its excellent adhesive strength, heat resistance, radiation resistance, electrical insulation, small heat-curing shrinkage, and mechanical strength after curing.

[0029] The type of epoxy resin is not particularly limited, but a multifunctional epoxy resin having two or more epoxy groups per molecule is preferred. Examples include bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, tert-butyl-catechol epoxy resins, naphthalene epoxy resins, glycidylamine epoxy resins, cresol novolac epoxy resins, biphenyl epoxy resins, biphenyl aralkyl epoxy resins, bisphenol A novolac epoxy resins, naphthalene diol epoxy resins, trisphenylol methane epoxy resins, tetrakisphenylol ethane epoxy resins, phenol biphenyl epoxy resins, dicyclopentadiene epoxy resins with hydrogenated aromatic rings, phenol dicyclopentadiene novolac epoxy resins with hydrogenated aromatic rings, triazine derivative epoxy resins, and alicyclic epoxy resins. Bisphenol A or bisphenol F epoxy resins are preferred because of their excellent adhesive strength, mechanical strength, and radiation resistance.

[0030] The curing reaction of thermosetting resins can be mediated by polymerization caused by a curing agent or self-polymerization caused by a catalyst, and both can occur simultaneously. Therefore, adhesives may contain additives such as curing agents and catalysts in addition to the thermosetting resin. Examples of curing agents include amine compounds, phenolic compounds, and acid anhydrides. These may be used alone or in combination. Furthermore, curing accelerators such as imidazole compounds, phosphorus compounds, and organometallic compounds may be used in addition to the curing agent. Examples of self-polymerization catalysts include anionic polymerization catalysts such as imidazole compounds and tertiary amines, and cationic polymerization catalysts such as boron trifluoride and sulfonium salts.

[0031] Thermosetting resin-containing adhesives include one-component adhesives in which the thermosetting resin and curing agent / catalyst are premixed, and two-component adhesives in which the thermosetting resin and curing agent / catalyst are mixed at the time of use. While the adhesive form is not particularly limited, one-component adhesives are preferred for ease of handling. Furthermore, one-component adhesives have the advantage of being less prone to trapping air bubbles because they do not require mixing. If air bubbles trap and create voids in the adhesive after curing, this can reduce mechanical strength and potentially become the starting point for dielectric breakdown when high voltage is applied, making them undesirable. Among one-component adhesives, those containing latent curing agents (e.g., imidazole compounds, dicyandiamide, organic acid dihydrazides, microencapsulated curing agents) that do not react at room temperature but release active species upon heating are more preferred.

[0032] The material of the objects to be joined is not particularly limited and may be metal, fiber-reinforced plastics (FRP), glass, ceramics, etc. Examples of metals include iron, steel, stainless steel, aluminum alloys, magnesium alloys, copper alloys, and titanium alloys. Examples of resin materials for FRP include thermosetting resins such as epoxy resin, unsaturated polyester resin, and phenolic resin. Alternatively, thermoplastic resins such as polyamide resin, polyphenylene sulfide resin, polyether ether ketone resin, polycarbonate resin, polyester resin, polystyrene resin, polypropylene resin, and ABS resin may also be used. Examples of fiber materials for FRP include glass fiber, carbon fiber, aramid fiber, polyethylene fiber, Zylon fiber, and boron fiber. The two objects to be joined may be of the same or different types. When at least one of the two objects to be joined is FRP using epoxy resin, the thermosetting resin contained in the adhesive is preferably epoxy resin.

[0033] Methods for preparing a pre-bonding structure include applying an adhesive to at least one of the surfaces to be bonded of two objects to be bonded and then joining the surfaces together, and sandwiching a sheet-like fibrous nonwoven mat pre-impregnated with an adhesive (referred to as a "prepreg" in the present invention) between two objects to be bonded. The method using a prepreg is preferred because it allows for easy preparation of a pre-bonding structure. In particular, the use of a prepreg is preferred when the objects to be bonded are large and the surface area of ​​the bonded surface is large.

[0034] Fiber types for the fibrous nonwoven mat used in the prepreg include inorganic fibers such as glass fiber, carbon fiber, and ceramic fiber, organic fibers such as aramid fiber, polyester fiber, polyamide fiber, rayon fiber, vinylon fiber, and high-strength cellulose fiber, and natural fibers such as cotton, hemp, and silk. Glass fiber and carbon fiber are preferred due to their properties of high strength, high elasticity, heat resistance, and dimensional stability.

[0035] A fibrous nonwoven mat is a sheet-like, smooth mat made by uniformly dispersing cut short fibers (several millimeters to several centimeters) in random directions on a flat surface. To maintain the mat shape after dispersion, it is preferable to use a mat that has been solidified with a small amount of binder. For example, a surface mat used for surface finishing of FRP can be used. The proportion of fibers in the bulk volume of the fibrous nonwoven mat itself before impregnation with adhesive is preferably 30% or less, and more preferably 20% or less. By keeping the fiber proportion 30% or less, both the upper and lower surfaces of the fibrous nonwoven mat layer are uniformly covered with adhesive, increasing the adhesive strength between the adhesive and the object to be joined.

[0036] <Preliminary curing process> In the pre-curing process, the pre-bonding structure is heated to a first temperature that is equal to or higher than room temperature but lower than the specified curing temperature of the adhesive, and the pre-bonding structure is kept in the first temperature environment at least until heat generation associated with polymerization of the thermosetting resin is completed.

[0037] The specified curing temperature for an adhesive is, for example, the curing temperature recommended by the adhesive manufacturer. The recommended curing temperature varies depending on the adhesive's composition, but is usually set within a range of 120°C to 180°C. Room temperature refers to the room temperature during the preparation process, generally ranging from 15°C to 30°C. In the pre-curing process, the pre-bonded structure must be left for a predetermined period of time in a state where the adhesive has high fluidity, where the polymerization reaction progresses to form oligomers, but the cross-linking reaction does not proceed rapidly. The first temperature may be 30°C or more lower than the specified curing temperature. For example, if the recommended curing temperature for the adhesive is 120°C, the first temperature is preferably 60°C to 90°C, and more preferably 70°C to 80°C. When the pre-bonded structure is placed in a first temperature environment, the first temperature may vary within a certain range (approximately 5°C). The pre-curing process may be performed in two or more stages.

[0038] The end of heat generation associated with the polymerization of the thermosetting resin can be determined by measuring the temperature of the adhesive in the pre-bonded structure and observing the temperature change. However, because adhesive layers are generally thin and heat generated in the adhesive quickly transfers to the bonded components, it is difficult to directly observe the temperature change of the adhesive in the pre-bonded structure. Therefore, in the present invention, a temperature-measurement adhesive having the same composition as the adhesive used in the pre-bonded structure is prepared, and the timing at which heat generation associated with the polymerization of the thermosetting resin in the adhesive in the pre-bonded structure ends can be inferred from the temperature change when this temperature-measurement adhesive is heated to a first temperature. For example, by using a differential scanning calorimeter to measure the temperature at multiple points from the time the temperature-measurement adhesive is heated until it reaches the first temperature and from the time the temperature rises and falls after reaching the first temperature, and by determining the temperature change pattern and temperature change rate, it is possible to predict the time from the time the first temperature is reached until the heat generation associated with the polymerization of the thermosetting resin ends. Alternatively, in the pre-curing step, a container with high thermal conductivity is placed in contact with the pre-bonded structure, and the temperature-measurement adhesive is placed in the container. The end of heat generation may be detected by measuring the temperature of the temperature-measuring adhesive using a thermocouple or the like and detecting when the temperature rises and then falls. In this case, the end of heat generation can be detected in situ. The time for which the pre-bonding structure is placed in the first temperature environment may be 30 minutes or more and 180 minutes or less. For example, if the time from when the adhesive reaches the first temperature to when the exothermic reaction due to polymerization of the thermosetting resin ends is approximately 60 minutes, the time should be 60 minutes or more and 140 minutes or less. This allows the objects to be bonded with sufficient adhesive strength even in a high-temperature environment.

[0039] As described above, if voids are generated in the cured adhesive, the mechanical strength may decrease and they may become the starting point of dielectric breakdown when a high voltage is applied. To prevent the generation of such voids, the pre-curing step may be performed in a vacuum. In the pre-curing step, the fluidity of the adhesive is high, so air bubbles in the adhesive are easily removed. When the pre-bonding structure is produced using a prepreg, this is preferable because air bubbles in the adhesive are removed along the fibers of the prepreg.

[0040] <Main curing process> In the main curing step, the pre-bonding structure is heated to a second temperature that is higher than the first temperature, and the pre-bonding structure is placed in an environment at the second temperature for a predetermined time.

[0041] The second temperature can be set appropriately depending on the type of adhesive, provided that it is higher than the first temperature. Generally, to ensure the crosslinking reaction of the adhesive proceeds reliably, the second temperature is set to at least 5°C, preferably at least 10°C, and more preferably at least 20°C higher than the first temperature. Furthermore, the second temperature is preferably lower than the specified curing temperature of the adhesive. For example, the second temperature may be at least 10°C lower than the specified curing temperature of the adhesive. The bonded body obtained through the preliminary curing step and the main curing step is then naturally cooled. The lower the second temperature, the smaller the thermal shrinkage rate during cooling. Therefore, even when bonding objects with different thermal expansion coefficients, adhesive peeling due to the difference in thermal shrinkage rate is unlikely to occur. As with the first temperature, when the pre-bonding structure is placed in a second temperature environment, the second temperature may vary within a certain range (approximately 5°C). Furthermore, the main curing step may be performed in two or more stages.

[0042] The time from the end of the preliminary curing step until the pre-bonded structure reaches the second temperature can be set appropriately depending on the type of adhesive. Generally, it is preferable to heat the pre-bonded structure to the second temperature within 120 minutes, more preferably within 60 minutes, after the end of the preliminary curing step. This reliably improves the adhesive strength. The time for which the pre-bonded structure is placed in the second temperature environment can be set appropriately depending on the type of adhesive. In order to ensure that the crosslinking reaction proceeds reliably, generally, 15 minutes or more is preferable, 30 minutes or more is more preferable, and 60 minutes or more is particularly preferable. This further improves heat resistance and adhesive strength. Although a longer period does not result in a decrease in adhesive strength, it is preferable to set the period to 120 minutes or less from the standpoint of work efficiency.

[0043] Although the details of the mechanism of the bonding method according to the present invention are unclear, the following is thought to be the mechanism. In the bonding method according to the present invention, in the preliminary curing step, the pre-bonding structure is heated to a first temperature that is equal to or higher than room temperature, thereby increasing the molecular mobility of the resin contained in the adhesive between the bonded objects. Furthermore, because the first temperature is lower than the specified curing temperature of the adhesive, the polymerization reaction of the resin does not proceed rapidly. As a result, as the polymerization reaction progresses, unreacted functional groups of the oligomers generated by the polymerization reaction interact with functional groups on the surfaces of the bonded objects, causing the oligomers to orient on the surfaces of the bonded objects. In this state, in the main curing step, the pre-bonding structure is heated to a second temperature, thereby crosslinking the oligomers. As a result, a dense three-dimensional network structure is formed, and the bonded objects are firmly bonded. [Example]

[0044] The bonding method according to the present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0045] <Experimental Example 1> (Preparation of junction) Surface mat (Central Glass FC-30C: fiber diameter 9 μm or less, thickness 0.13 mm, unit weight 30 g / m 2A pre-bonding structure was prepared by stacking four sheets of SUS304, impregnated with 90 wt% of a commercially available one-component curing agent-containing epoxy resin adhesive (XNR3688, manufactured by Nagase Chemtex, bisphenol A-type epoxy resin, recommended curing temperature 120°C), and sandwiching the pre-bonding structure between two SUS plates (2 cm x 10 cm). The pre-bonding structure was placed in a heating furnace, and the adhesive was cured in two stages under the conditions of temperature (T1: first temperature, T2: second temperature), holding time, and transition time shown in Table 1. The pre-bonding structure was then naturally cooled in the heating furnace, yielding the bonded structures of Examples 1 to 3 and Comparative Examples 5 to 8. Alternatively, the pre-bonding structure was placed in a heating furnace, and the adhesive was cured in one stage under the conditions of temperature (T1) and holding time shown in Table 1, and then naturally cooled, yielding the bonded structures of Comparative Examples 2 to 4. In addition, the above adhesive was replaced with a commercially available room temperature curing epoxy resin adhesive (manufactured by ThreeBond, model number 2082C), and the pre-bonded structure was prepared. The structure was placed in a heating furnace, and the adhesive was cured in one stage under the conditions of the temperature (T1) and holding time shown in Table 1, and then the structure was allowed to cool naturally, thereby obtaining a bonded body of Comparative Example 1.

[0046] (Measurement of adhesive strength) The tensile shear adhesive strength of the produced bonded bodies was measured at room temperature and at 80°C in accordance with the JIS K6850 test method. The results are shown in Table 1.

[0047] (Measurement of glass transition temperature) The uncured adhesive was cured under the same temperature and holding time conditions as in Table 1, and the specific heat was measured using a thermal analyzer (Shimadzu, model DSC-60 Plus). The inflection point within the range where the baseline of the DSC curve changes was determined as the glass transition temperature. The results are shown in Table 1.

[0048] [Table 1]

[0049] The results in Table 1 show that Examples 1 to 3, in which two-stage curing was performed under conditions where T1 was 80°C, T2 was 100°C, and the holding times in the preliminary curing step were 60, 90, and 105 minutes, had higher adhesive strengths and glass transition temperatures at room temperature and 80°C than Comparative Example 1, in which one-stage curing was performed using a room-temperature curing adhesive, and Comparative Examples 2 to 4, in which one-stage curing was performed using the same adhesive as Examples 1 to 3. On the other hand, Comparative Examples 5 and 6, in which the holding times in the preliminary curing step were 30 and 180 minutes, respectively, had lower adhesive strengths than Examples 1 to 3. Furthermore, Comparative Example 7, in which the transition time to T2 after the completion of the preliminary curing step was 150 minutes, and Comparative Example 8, in which the holding time in the main curing step was 10 minutes, had lower adhesive strengths at room temperature than Examples 1 to 3.

[0050] <Experimental Example 2> (Adhesive temperature measurement) As shown in FIG. 1, a pre-bonded structure was prepared by sandwiching the same prepreg 10 (containing a one-component curing agent-containing epoxy resin adhesive) as used in Experimental Example 1 between a cylindrical FRP (fiberglass-reinforced epoxy resin) structure 20 with a diameter of 260 mm and a disk-shaped stainless steel (SUS304) flange structure 30 with a diameter of 260 mm. The pre-bonded structure was placed in a heating furnace, and as shown in FIG. 2, a stainless steel container 40 was placed on top of the stainless steel flange structure 30. A temperature-measurement prepreg 50, identical to the prepreg 10 used in the pre-bonded structure, was placed in the container 40. The adhesive was subjected to two-stage curing under pre-curing conditions (T1: 80°C, holding time: 90 minutes) and main curing conditions (T2: 100°C, holding time: 60 minutes), with a transition time from T1 to T2 of 45 to 60 minutes, to obtain a bonded structure. The temperature of the temperature-measurement prepreg 50 was measured using a thermocouple. The temperature profile of the temperature-measurement prepreg 50 and the inside of the heating furnace is shown in FIG. 3. The horizontal axis of FIG. 3 represents the time (minutes) elapsed since the start of heating in the heating furnace, and the vertical axis represents the temperature (° C.).

[0051] 3, the temperature of the temperature-measurement prepreg 50 reached T1 (80°C) when approximately 70 minutes had elapsed since the start of heating, the temperature of the temperature-measurement prepreg 50 began to rise when approximately 100 minutes had elapsed, and the temperature of the temperature-measurement prepreg 50 began to fall when approximately 130 minutes had elapsed. From this, it was found that when the adhesive used in Experimental Example 1 was heated to T1 (80°C), heat generation due to polymerization of the thermosetting resin contained in the adhesive ended 60 minutes after the temperature of the adhesive reached T1.

[0052] <Experimental Example 3> (Preparation of junction) The same prepreg 10 (containing a one-component curing agent-containing epoxy resin adhesive or a room-temperature curing epoxy resin adhesive) as in Experimental Example 1 was placed between a 50 mm x 50 mm plate-shaped FRP (fiberglass reinforced epoxy resin) structure 20 and a disk-shaped stainless steel (SUS304) flange structure 30 with a diameter of 70 mm and a hole in the center, so as to surround the hole, to prepare a pre-bonding structure. Thereafter, bonded bodies of Examples 1-2 to 3-2 and Comparative Examples 2-2, 3-2, 5-2, and 6-2 were produced in the same manner as in Experimental Example 1. The "Example (Number-2)" and "Comparative Example (Number-2)" in Experimental Example 3 correspond to the Example and Comparative Example of Experimental Example 1 with the respective numbers.

[0053] (Leak test) To confirm the airtightness of the assembled body, the inside of the assembled body was evacuated through a hole provided in the stainless steel flange structure 30 as shown in Figure 4, and a leak test from the adhesive joint was performed using a He leak detector (manufactured by ULVAC, model number HELIOT900). The leak rate was 1.0 x 10 -10 Pa / m 2 The results are shown in Table 2.

[0054] [Table 2]

[0055] From the results in Table 2, it can be seen that in Examples 1-2 to 3-2 in Experimental Example 1, sufficient adhesive strength was obtained at room temperature and 80° C., and the results of the leak test were also good.

[0056] [Aspect] It will be apparent to those skilled in the art that the above-described exemplary embodiments are examples of the following aspects.

[0057] (Item 1) A bonding method according to one aspect of the present invention comprises: The method includes a preparation step of preparing a pre-bonding structure by interposing an adhesive containing a thermosetting resin between two objects to be bonded; a preliminary curing step of heating the pre-bonding structure to a first temperature that is equal to or higher than room temperature but lower than the specified curing temperature of the adhesive, and keeping the pre-bonding structure in the first temperature environment at least until heat generation accompanying polymerization of the thermosetting resin is completed; and a main curing step of heating the pre-bonding structure to a second temperature that is higher than the first temperature, and keeping the pre-bonding structure in the second temperature environment for a predetermined time.

[0058] According to the bonding method of the first aspect, when the bonded objects are bonded with a thermosetting adhesive, the bonding strength can be increased.

[0059] (Item 2) In the bonding method according to item 1, When the specified curing temperature is 120°C, the first temperature may be 60°C or higher and 90°C or lower.

[0060] (Item 3) In the bonding method according to item 1 or 2, The second temperature may be at least 5° C. higher than the first temperature.

[0061] (Item 4) In the bonding method according to any one of items 1 to 3, The predetermined time may be 15 minutes or more.

[0062] (Item 5) In the bonding method according to any one of Items 1 to 4, In the main curing step, the pre-bonding structure may be heated to the second temperature within 120 minutes after the preliminary curing step.

[0063] According to the bonding method of any one of items 2 to 5, the objects to be bonded can be bonded with higher adhesive strength.

[0064] (Item 6) In the bonding method according to any one of Items 1 to 5, The second temperature may be lower than the specified curing temperature.

[0065] According to the bonding method of item 6, thermal shrinkage of the adhesive during cooling can be suppressed, and even when bonding objects with different thermal expansion coefficients, peeling of the adhesive due to differences in thermal shrinkage rates is unlikely to occur. Therefore, the above method can be used to manufacture bonded bodies used in various applications that require leak resistance. Furthermore, even when the preliminary curing step and main curing step are performed at a temperature lower than the specified curing temperature, a higher Tg can be obtained than when curing in one step at the specified curing temperature.

[0066] (Item 7) In the bonding method according to any one of items 1 to 6, The bonding surfaces of the two objects to be bonded may each be made of fiber reinforced plastic (FRP), heat resistant resin, or metal.

[0067] The bonding method according to paragraph 7 can be used to manufacture bonded bodies for various applications that require heat resistance, leak resistance, radiation resistance, and mechanical strength.

[0068] (Item 8) In the bonding method according to any one of items 1 to 7, The method may include a measurement step in which, when a temperature-measuring adhesive having the same composition as the adhesive is heated to the first temperature, the time from when the first temperature is reached to when heat generation due to polymerization of the thermosetting resin ends is measured using a differential scanning calorimeter, and in the pre-curing step, after the pre-bonding structure is heated to the first temperature, it is placed in an environment at the first temperature for at least the aforementioned time.

[0069] Usually, the adhesive layer in the pre-bonded structure is thin, making it difficult to directly confirm the temperature change of the adhesive layer. According to the bonding method of item 8, the timing at which heat generation associated with polymerization of the thermosetting resin of the adhesive in the pre-bonded structure ends can be inferred from the temperature change when a temperature-measuring adhesive having the same composition as the adhesive used in the pre-bonded structure is heated to a first temperature.

[0070] (Item 9) In the bonding method according to any one of items 1 to 7, In the pre-curing step, the end of heat generation due to polymerization of the thermosetting resin can be detected by measuring the temperature of a temperature-measuring adhesive having the same composition as the adhesive and placed in a container that is in thermally conductive contact with the pre-bonding structure, and detecting the maximum temperature.

[0071] According to the bonding method of the ninth aspect, the end of heat generation accompanying the polymerization of the thermosetting resin can be detected in situ.

[0072] (Item 10) A conjugate according to one aspect of the present invention comprises: A bonded structure comprising two bonded objects, each made of FRP, heat-resistant resin, or metal, and an adhesive containing a thermosetting resin interposed between the two bonded objects, wherein the tensile shear adhesive strength between the bonded objects and the adhesive at 80°C is 31 MPa or more.

[0073] (Item 11) In the conjugate according to item 10, The adhesive may have a glass transition temperature of 140°C or higher.

[0074] In the bonded body according to the tenth or eleventh aspect, the bonded bodies are firmly bonded together even in a high temperature environment. [Explanation of symbols]

[0075] 10...Adhesive (prepreg) 20…Object to be joined (FRP structure) 30...Bonded body (stainless steel flange structure) 40…Container 50...Temperature measurement adhesive (prepreg)

Claims

1. a preparation step of preparing a pre-bonding structure by interposing an adhesive containing a thermosetting resin between two objects to be bonded; a pre-curing step of heating the pre-bonding structure to a first temperature that is equal to or higher than room temperature and lower than a specified curing temperature of the adhesive, and placing the pre-bonding structure in the first temperature environment at least until heat generation associated with polymerization of the thermosetting resin is completed; a main curing step of heating the pre-bonding structure to a second temperature that is higher than the first temperature and placing the pre-bonding structure in an environment at the second temperature for a predetermined time; The bonding method comprising the steps of:

2. The bonding method according to claim 1 , wherein when the specified curing temperature is 120° C., the first temperature is 60° C. or higher and 90° C. or lower.

3. 3. The bonding method according to claim 1, wherein the second temperature is at least 5°C higher than the first temperature.

4. 3. The bonding method according to claim 1, wherein the predetermined time is 15 minutes or more.

5. 3. The bonding method according to claim 1, wherein in the main curing step, the pre-bonding structure is heated to the second temperature within 120 minutes after the preliminary curing step.

6. 3. The bonding method according to claim 1, wherein the second temperature is lower than the specified curing temperature.

7. 3. The bonding method according to claim 1, wherein the bonding surfaces of the two objects to be bonded are made of fiber reinforced plastic (FRP), heat resistant resin, or metal.

8. a measuring step of measuring, when a temperature-measurement adhesive having the same composition as the adhesive is heated to the first temperature, the time from when the temperature reaches the first temperature to when heat generation accompanying polymerization of the thermosetting resin ends, using a differential scanning calorimeter; 3. The bonding method according to claim 1, wherein in the pre-curing step, the pre-bonding structure is heated to a first temperature and then placed in an environment at the first temperature for at least the period of time.

9. 3. The bonding method according to claim 1, wherein the completion of heat generation due to polymerization of the thermosetting resin in the pre-curing step is detected by measuring the temperature of a temperature-measuring adhesive having the same composition as the adhesive and placed in a container in thermally conductive contact with the pre-bonding structure, and detecting a maximum of the temperature.

10. A joined body having two joined bodies, each made of FRP, heat-resistant resin, or metal, and an adhesive containing a thermosetting resin interposed between the two joined bodies, wherein the tensile shear adhesive strength between the joined bodies and the adhesive at 80°C is 31 MPa or more.

11. 11. The bonded structure according to claim 10, wherein the adhesive has a glass transition temperature of 140°C or higher.

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