JP6976554B2 - Adhesives and joining methods - Google Patents

Description

The present invention relates to adhesives and bonding methods.

Thermosetting adhesives are generally used for joining resin materials such as resins and resin composite materials. When resin materials are bonded to each other using an adhesive, the adhesive is heated at a high temperature for a long time to be cured by using a hot air furnace or the like, so that energy consumption is large.

Therefore, as a method of curing the adhesive while reducing the energy consumption at the time of joining the resin materials, for example, a method of using microwaves has been proposed.

For example, Patent Document 1 discloses an adhesive containing a microwave absorbing substance that absorbs microwaves and generates heat and an adhesive component, and uses carbon black or SiC as the microwave absorbing substance. It is described that by irradiating this adhesive with microwaves to cure it, even a structure to which adhesive joining is difficult can be adhered at low cost.

Japanese Unexamined Patent Publication No. 2008-156510

However, the adhesive described in Patent Document 1 does not describe increasing the curing speed and shortening the bonding time. In order to efficiently bond the resin materials to each other, it is important to cure the adhesive earlier.

One aspect of the present invention is to provide an adhesive capable of joining resin materials to each other in a shorter time.

The adhesive according to one aspect of the present invention is an adhesive that is cured by irradiation with microwaves and contains a thermosetting resin and carbon fibers, and the average length of the carbon fibers is 35 μm or more and 200 μm or less. When the total amount of the adhesive is 100% by volume, the content of the carbon fibers is 0. It is 5 % by volume or more and 20% by volume or less.

The bonding method according to one aspect of the present invention comprises a step of irradiating an adhesive containing a thermosetting resin and carbon fibers with microwaves to cure the adhesive, and the average length of the carbon fibers is increased. When it is 35 μm or more and 200 μm or less and the total amount of the adhesive is 100% by volume, the content of the carbon fiber is 0. It is 5 % by volume or more and 20% by volume or less.

According to one aspect of the present invention, the resin materials can be bonded to each other in a shorter time.

FIG. 1 is a diagram showing measurement results of the degree of curing of the adhesives of Examples 1-1 and 1-2 and Comparative Examples 1-1 to 1-4. FIG. 2 is a diagram showing the measurement results of the adhesive strength of the adhesives of Examples 1-1 and 1-2 and Comparative Examples 1-1 to 1-4. FIG. 3 is a diagram showing the measurement results of the degree of curing of the adhesives of Examples 2-1 to 2-4 and Comparative Example 2-1. FIG. 4 is a diagram showing the measurement results of the bending strength of the adhesives of Examples 3-1 and 3-2 and Comparative Examples 3-1 to 3-5.

Hereinafter, embodiments according to the present invention will be described.

<Adhesive>
The adhesive according to the embodiment of the present invention will be described. The adhesive according to this embodiment has a thermosetting resin and carbon fibers.

Examples of the thermosetting resin include epoxy resins, unsaturated polyester resins, vinyl ester resins, polyimide resins, bismaleimide resins, urethane resins, amino resins such as melamine, urea and phenol, and silicone resins. Fluorescent resin and the like can be mentioned. These may be used alone or in combination of two or more. Among these, epoxy resins and the like are preferable because they can be cured in a shorter time.

Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, flexible epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, alicyclic epoxy resin, brominated epoxy resin, and glycidyl ester. Examples thereof include a type epoxy resin, a glycidylamine type epoxy resin, a hydride-in type epoxy resin, an isocyanurate type epoxy resin, and an acrylic acid-modified epoxy resin. As the epoxy resin, these may be used alone or in combination of two or more.

The carbon fibers are contained in the thermosetting resin in a dispersed state. Carbon fibers have the property of absorbing microwaves and generating heat when irradiated with microwaves.

As the carbon fiber, pitch (PITCH) -based carbon fiber or polyacrylic nitrile (PAN) -based carbon fiber can be used alone or in combination of two or more.

Pitch-based carbon fiber is carbon fiber produced from by-products (PITCH) such as petroleum, coal, and coal tar. The PAN-based carbon fiber is a carbon fiber produced from a synthetic fiber containing PAN as a main component. Pitch-based carbon fibers are characterized by having a higher thermal conductivity than PAN-based carbon fibers. The PAN-based carbon fiber has a characteristic that it has high strength and is hard to cut even when mixed with a resin or the like. When the adhesive is cured, it is preferable to use pitch-based carbon fibers rather than PAN-based carbon fibers from the viewpoint of improving the thermal conductivity to the thermosetting resin. Further, by using the pitch-based carbon fiber and the PAN-based carbon fiber in combination as the carbon fiber, the curing of the adhesive can be promoted and the strength of the cured body obtained by curing the adhesive can be increased.

The average length of the carbon fibers is preferably 35 μm or more and 200 μm or less. When the average length of the carbon fibers is 35 μm or more, the adhesive can efficiently absorb microwaves, so that curing can be promoted. When the average length of the carbon fibers is 200 μm or less, the viscosity of the adhesive is suppressed, so that the adhesive can be stably applied to the surface of the adherend or between the adherends. The average length of the carbon fibers is more preferably 40 μm or more and 150 μm or less.

In the present embodiment, the average length of carbon fibers means the median value. The average length of carbon fibers means, for example, the average value of the lengths of carbon fibers measured by observing a plurality of carbon fibers (for example, about 1000) with an optical microscope or a scanning electron microscope.

The carbon fiber is contained in an amount of 0.1% by volume or more and 20% by volume or less when the total amount of the adhesive is 100% by volume. If the content of the carbon fiber is less than 0.1% by volume, the adhesive may not be sufficiently cured and sufficient adhesive strength may not be obtained. When the content of the carbon fiber exceeds 20% by volume, the viscosity of the adhesive becomes high, so that it becomes difficult to apply the adhesive on the surface of the adherend or between the adherends. The carbon fiber is preferably contained in an amount of 5% by volume or more and 20% by volume or less when the total amount of the adhesive is 100% by volume.

The adhesive according to the present embodiment contains a thermosetting resin and carbon fibers as main components, and may further contain a curing agent.

The curing agent cures the main agent of the thermosetting resin when heated together with the thermosetting resin. The curing agent is not particularly limited as long as it is a curing agent for a thermosetting resin, and known curing agents can be used. As the curing agent, for example, a carboxylic acid-based curing agent having a carboxyl group or a carboxylic acid anhydride group (acid anhydride-based curing agent); an amine-based curing agent having an amino group, an amide group, a ketoimine group, an imidazole group, a dicyandiamide group and the like. A curing agent; or a phenolic curing agent having a phenol group such as phenol novolak; or the like can be used.

Specific examples of the acid anhydride-based curing agent include succinic anhydride, maleic anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and methylnadic anhydride. Hexahydrohydride phthalic acid, methylhexahydrochloride anhydride, 1,2-cyclohexanedicarboxylic acid anhydride, 4-methylcyclohexane-1,2-dicarboxylic acid anhydride, 3,4,5,6-tetrahydrophthalic acid anhydride, Examples thereof include 2,3-naphthalenedicarboxylic acid anhydride. These can be used alone or in combination of two or more.

Specific examples of amine-based curing agents include aliphatic polyamines such as triethylenetetraamine, tetraethylenepentamine, m-xylenediamine, trimethylhexamethylenediamine, and 2-methylpentamethylenediamine; isophoronediamine, 1,3-. Alicyclic polyamines such as bisaminomethylcyclohexane, bis (4-aminocyclohexyl) methane, norbornenediamine, 1,2-diaminocyclohexane; N-aminoethylpiperazine, 1,4-bis (2-amino-2-methylpropyl). ) Piperazine-type polyamines such as piperazine; diethyltoluenediamine, dimethylthiotoludiamine, 4,4'-diamino-3,3'-diethyldiphenylmethane, bis (methylthio) toluenediamine, diaminodiphenylmethane, m-phenylenediamine, diaminodiphenyl Examples include aromatic polyamines such as sulfone, diethyltoluenediamine, trimethylenebis (4-aminobenzoate) and polytetramethylene oxide-di-p-aminobenzoate. Moreover, as a commercial product, jER cure ST-11 (trade name, manufactured by Mitsubishi Chemical Corporation) and the like can be mentioned. These can be used alone or in combination of two or more.

Specific examples of the phenol-based curing agent refer to monomers, oligomers, and polymers having a phenolic hydroxyl group, for example, phenol novolac resin, cresol novolac resin, phenol aralkyl (including phenylene and biphenylene skeleton) resin, naphthol aralkyl resin, and the like. Examples thereof include triphenol methane resin and dicyclopentadiene type phenol resin. These can be used alone or in combination of two or more.

The blending amount of the curing agent is appropriately set according to the type and blending amount of the thermosetting resin and carbon fiber, and is appropriately set according to the molding conditions, characteristics, etc. within the range in which the curing agent is usually used. ..

The adhesive according to the present embodiment may contain various known additives in addition to the above-mentioned components, if necessary.

Additives include, for example, softeners, antioxidants, stabilizers, adhesion promoters, leveling agents, defoaming agents, plasticizers, inorganic fillers, tackifier resins, usable time extenders, antioxidants, ultraviolet rays. Absorbents, antioxidants, fungicides, thickeners, plasticizers, colorants such as pigments, fillers and the like may be used in combination.

The method for applying the adhesive is not particularly limited, and a known method can be used. As a method for applying the adhesive, for example, a gravure coat, a roll coat, a spin coat, a reverse coat, a bar coat, a screen coat, a blade coat, an air knife coat, dipping, a dispensing and the like can be used.

As a method for preparing the adhesive according to the present embodiment, either a one-component type or a two-component type can be adopted. The one-component preparation method refers to a method in which all the ingredients are mixed in advance, stored in a sealed container, and then cured by the humidity in the air after construction. The two-component preparation method refers to a method in which a curing agent and a solvent, and if necessary, components such as a filler and a plasticizer are mixed, and the main agent and the curing agent are mixed before construction.

When the adhesive is a one-component type, all the components are premixed, so that if water is present in the adhesive, curing may proceed during storage. Therefore, it is preferable to dehydrate the components containing water by dehydrating and drying them in advance and then adding them or reducing the pressure in a mixed state.

When the adhesive is a two-component type, it is necessary to add a curing agent to the main agent, so even if the adhesive contains some water, there is little concern about the progress of curing (gelling), but for a long period of time. If storage stability is required, dehydration drying is preferred.

A joining method for joining the adherend using the adhesive according to the present embodiment will be described. The adhesive is applied to the adhesive surface of one of the adherends. As the method for applying the adhesive, the same method as described above can be used. Then, the other adherend is attached to the adhesive surface of one adherend via an adhesive. After that, the adhesive interposed between the adherends is irradiated with microwaves to cure the adhesive. This makes it possible to obtain a cured product in which the adhesive is cured.

The wavelength of the microwave irradiating the adhesive is preferably 300 MHz or more and 3000 MHz or less. When the wavelength of the microwave is within the above range, the adhesive can be heated almost uniformly as a whole when the adhesive is irradiated with the microwave.

The adhesive according to the present embodiment contains a thermosetting resin and carbon fibers, and the content of the carbon fibers is 0.1% by volume or more and 20% by volume or less when the total amount of the adhesive is 100% by volume. .. By irradiating the adhesive with microwaves, heat is generated from the carbon fibers. Since the heat generated from the carbon fibers can accelerate the curing of the thermosetting resin, the curing of the thermosetting resin can be accelerated. This allows the adhesive to cure in a shorter time, eg, a heating time of 1/10 or less of the curing time recommended for conventional adhesives (eg, 50 seconds or less). Therefore, the present adhesive can stably bond the resin materials to each other in a shorter time.

The adhesive according to the present embodiment can have a curing degree of 90% or more and 100% or less, preferably 92% or more and 100% or less, by being irradiated with microwaves.

The degree of curing of the cured product of the adhesive can be evaluated by using a known method. For example, a differential scanning calorimeter is used to measure the total calorific value required for heat curing of the adhesive applied to the adherend. Then, the adhesive after the heat hardening treatment is recovered from the adherend, and the residual calorific value is measured using a differential scanning calorimeter. The degree of curing (%) is obtained from the following formula (1).
Curing degree (%) = (total calorific value-residual calorific value) / total calorific value x 100 ... (1)

Further, the adhesive according to the present embodiment can accelerate the curing of the thermosetting resin by being irradiated with microwaves, so that the adhesive strength of the cured product is not contained in the adhesive. Compared with the case, for example, it can be increased by about 2 to 5 times.

For the adhesive strength of the cured body of this adhesive, for example, an adhesive is applied to the end of one of the two adherends so that the adhesive surface is within a predetermined range (for example, 100 mm ² ). do. Then, after superimposing the other adherend on the adhesive surface of one adherend, the adhesive is heat-cured. After that, using a universal testing machine (for example, AG-IS, manufactured by Shimadzu Corporation), hook the pulling jig of the universal testing machine on the tabs attached to the two adherends in advance, and reverse the two adherends. Pull in the direction at a tensile speed of 1 mm / min and 27 ° C. under the conditions. Adhesive strength is obtained by dividing the maximum stress when the two adherends are peeled off by the adhesive surface (for example, 100 mm ^2).

Further, since the adhesive according to the present embodiment contains a predetermined amount of carbon fibers in the thermosetting resin, the adhesive is fiber-reinforced. Therefore, the cured product of the present adhesive can increase the bending strength as compared with the case where the adhesive does not contain carbon fibers.

As a method for evaluating the bending strength of the adhesive, the bending strength of the cured product of the adhesive can be obtained by performing it in accordance with JIS K 7171.

Since the adhesive according to the present embodiment has the above-mentioned characteristics, it can be suitably used for vehicle parts such as automobiles and railways, aircraft parts, and the like. By using the adhesive according to the present embodiment for resins used in vehicles, aircraft, etc., carbon fiber reinforced resins, glass fiber reinforced resins, etc., vehicle parts and aircraft parts can be manufactured in a short time.

Hereinafter, embodiments will be described in more detail with reference to Examples and Comparative Examples, but the embodiments are not limited to these Examples.

<Example 1>
[Example 1-1]
(Preparation of adhesive)
A carbon fiber (XN-90C, manufactured by Nippon Graphite Fiber Corporation) having an average length of about 113 μm was mixed with an epoxy adhesive (PM-4, manufactured by Toto Kagaku Kogyo Co., Ltd.) in an amount of about 5% by volume to prepare an adhesive.
(Preparation of cured product)
Two adherends were prepared by molding with tabs using a carbon fiber reinforced thermoplastic resin composite material (manufactured by BONDLAMINATES). The size of the adherend other than the tab was 1 mm × 60 mm × 10 mm in thickness. About 0.04 g of the above adhesive was applied to one end (10 mm × 10 mm) of the two adherends, and the adherends were overlapped with each other. Then, the adhesive was irradiated with microwaves at 800 W for 30 seconds to heat and cure the adhesive to obtain a cured product.

(Confirmation of curing degree and curing strength of cured product)
The degree of curing and the curing strength of the cured product were confirmed by the following methods.
(Confirmation of the degree of curing of the cured product)
First, the total calorific value required for heat curing of the adhesive was measured using a differential scanning calorimeter. The adhesive after the heat hardening treatment was recovered from the adherend, and the residual calorific value was measured using a differential scanning calorimeter. As shown in the following formula (1), the degree of curing of the adhesive was determined by dividing the value obtained by subtracting the residual calorific value from the total calorific value by the total calorific value and multiplying by 100. The result of measuring the degree of curing is shown in FIG.
Curing degree (%) = (total calorific value-residual calorific value) / total calorific value x 100 ... (1)
(Confirmation of adhesive strength of cured product)
First, a tab (thickness 1 mm × 20 mm × 10 mm) was attached to an end portion different from the end portion to which the adhesive of the two adherends was applied. Then, after grasping the attached tab with the pulling jig of the universal testing machine, the two adherends were pulled in opposite directions. The maximum stress at which the ^two adhered bodies were peeled off was divided by the adhesive surface of 100 mm 2, and the adhesive strength of the cured body was determined. The results of measuring the adhesive strength are shown in FIG.

[Example 1-2]
A cured product was prepared in the same manner as in Example 1-1 except that the amount of carbon fiber added was changed to 20% by volume in Example 1-1, and the degree of curing and the adhesive strength of the cured product were measured. The result of measuring the degree of curing of the cured body is shown in FIG. 1, and the result of measuring the adhesive strength of the cured body is shown in FIG.

[Comparative Example 1-1]
In Example 1-1, a cured product was prepared in the same manner as in Example 1-1 except that carbon fiber powder was not added to the adhesive (0% by volume), and the degree of curing and the adhesive strength of the cured product were measured. did. The result of measuring the degree of curing of the cured body is shown in FIG. 1, and the result of measuring the adhesive strength of the cured body is shown in FIG.

[Comparative Examples 1-2 to 1-4]
Examples 1-1 and 1-2, and Comparative Example 1-1, respectively, except that the adhesive was changed to heat at 135 ° C. for 30 seconds in an electric oven, respectively. A cured product was prepared in the same manner as in Comparative Example 1-1, and the degree of curing and the adhesive strength of the cured product were measured. The result of measuring the degree of curing of the cured body is shown in FIG. 1, and the result of measuring the adhesive strength of the cured body is shown in FIG.

The types of thermosetting resins, carbon fiber content and average length, heating conditions, or the degree of curing and adhesive strength of the cured product of each of the above Examples and Comparative Examples are summarized in Tables 1, 1 and 2.

As shown in Table 1, FIG. 1 and FIG. 2, in the adhesives of Examples 1-1 and 1-2, the degree of curing of the cured product is about 94% or more, and the adhesive strength is about 2.3 MPa or more. The adhesive had hardened. On the other hand, in the adhesive of Comparative Example 1-1, the degree of curing of the cured product was about 90%, and the adhesive strength was about 0.7 MPa or less. Therefore, it was confirmed that even if microwaves are used to heat the adhesive, the cured product does not have high adhesive strength unless the adhesive contains carbon fibers.

Further, in the adhesives of Comparative Examples 1-2 and 2-3, the degree of curing of the cured product was about 4% or less, the adhesive strength was about 0.003 MPa or less, and the adhesive was not cured. Therefore, if the adhesive containing carbon fibers is irradiated with microwaves to cure the adhesive, the adherend will be adhered with high strength in a shorter time than when the adhesive is heated in an electric oven. It was confirmed that it can be said that it can be done.

<Example 2>
[Example 2-1]
(Preparation of adhesive)
Pitch-based carbon fiber (XN-90C, manufactured by Nippon Graphite Fiber Corporation) was crushed with a mixer to make an average length of about 36 μm. An epoxy resin (jER827 (registered trademark), manufactured by Mitsubishi Chemical Corporation) was used as the thermosetting resin which is the main component of the adhesive, and jER Cure ST-11 (manufactured by Mitsubishi Chemical Corporation) was used as the curing agent. About 0.1% by volume of carbon fiber was mixed in the main agent and the curing agent to prepare an adhesive.
(Preparation of cured product)
As an adherend, another 20 mm square silicon rubber sheet having a hole with a diameter of 15 mm was superposed on a 20 mm square silicon rubber sheet having a thickness of 1.5 mm to prepare a mold. About 0.3 g of the adhesive was put into this mold, and the adhesive was heat-cured by irradiating with microwaves at 800 W for 50 seconds to obtain a cured product.
(Confirmation of the degree of curing of the cured product)
The degree of curing of the cured product was determined using the adhesive structure obtained by adhering the two adherends with an adhesive. The degree of curing of the cured product was measured using the same method as in Example 1 above. The result of measuring the degree of curing is shown in FIG.

[Example 2-2]
A cured product was prepared in the same manner as in Example 2-1 except that the average length of the carbon fibers used in Example 2-1 was changed from about 36 μm to about 113 μm, and the degree of curing was measured. The result of measuring the degree of curing is shown in FIG.

[Example 2-3]
In Example 2-1 the curing agent used was changed from jER Cure ST-11 to 4-methylcyclohexane-1,2-dicarboxylic acid anhydride (4MCDA), and the amount of carbon fiber added was changed from 0.1% by volume. A cured product was prepared and the degree of curing was measured in the same manner as in Example 2-1 except that the microwave irradiation condition was changed from 50 seconds at 800 W to 50 seconds at 480 W by changing to 0.5% by volume. did. The result of measuring the degree of curing is shown in FIG.

[Example 2-4]
In Example 2-1 the curing agent was changed from jER Cure ST-11 to 4MCDA, the average length of the carbon fibers used was changed from about 36 μm to about 113 μm, and the amount of carbon fibers added was 0.1% by volume. To 0.5% by volume, a cured product was prepared in the same manner as in Example 2-1 except that the microwave irradiation condition was changed from 50 seconds at 800 W to 50 seconds at 480 W, and the degree of curing was adjusted. It was measured. The result of measuring the degree of curing is shown in FIG.

[Comparative Example 2-1]
In Example 2-1 the curing agent was changed from jER Cure ST-11 to 4MCDA, the average length of the carbon fibers used was changed from about 36 μm to about 13 μm, and the amount of carbon fibers added was 0.1% by volume. To 0.5% by volume, a cured product was prepared in the same manner as in Example 2-1 except that the microwave irradiation condition was changed from 50 seconds at 800 W to 50 seconds at 480 W, and the degree of curing was adjusted. It was measured. The result of measuring the degree of curing is shown in FIG.

Table 2 shows the types of thermosetting resins, the carbon fiber content and average length, the types of curing agents, microwave irradiation conditions, and the degree of curing in each of the above Examples and Comparative Examples.

As shown in Table 2 and FIG. 3, in the adhesives of Examples 2-1 to 2-4 in which the average length of the carbon fibers is 36 μm or 113 μm, the degree of curing of the cured product is about 92% or more. And the adhesive was cured. On the other hand, in the adhesive of Comparative Example 2-1 in which the average length of the carbon fibers was 13 μm, the degree of curing of the cured product was about 66%, and the adhesive was not cured. Therefore, it was confirmed that if the average length of the carbon fibers is 35 μm or more, it can be said that it contributes to efficiently absorbing microwaves and heating and curing the adhesive regardless of the type of the curing agent.

<Example 3>
[Example 3-1]
(Preparation of cured product)
A carbon fiber (XN-90C, manufactured by Nippon Graphite Fiber Corporation) having a length of about 113 μm was mixed with an epoxy adhesive (PM-4, manufactured by Tokyo Chemical Industry Co., Ltd.) in an amount of about 20% by volume to prepare an adhesive.
(Preparation of cured product)
The adhesive was press molded at 135 ° C. for 5 minutes using a mold (4 mm × 10 mm × 80 mm). Then, the adhesive was irradiated with microwaves for 5 minutes while adjusting the microwave output so as to reach 135 ° C., and the adhesive was heated and cured to obtain a cured product.
(Confirmation of bending strength of hardened body)
A three-point bending test was performed according to JIS K 7171, and the bending strength of the cured product was measured. The results of measuring the bending strength of the cured product are shown in FIG. In FIG. 4, the white coating is the case where the adhesive is heated by irradiating the adhesive with microwaves, and the broken line is the case where the adhesive is heated using an electric oven.

[Example 3-2]
A cured product was prepared in the same manner as in Example 3-1 except that the time for irradiating the adhesive with microwaves was changed from 5 minutes to 20 minutes in Example 3-1 and the bending strength of the cured product was measured. did. The results of measuring the bending strength of the cured product are shown in FIG.

[Comparative Example 3-1]
A cured product was prepared in the same manner as in Example 3-1 except that the adhesive was heated in an electric oven at 135 ° C. for 5 minutes to cure in Example 3-1 and the bending strength of the cured product was measured. did. The results of measuring the bending strength of the cured product are shown in FIG.

[Comparative Example 3-2]
A cured product was prepared in the same manner as in Example 3-1 except that the adhesive was heated at 135 ° C. for 20 minutes in Example 3-1 and cured, and the bending strength of the cured product was measured. did. The results of measuring the bending strength of the cured product are shown in FIG.

[Comparative Examples 3-3-3-5]
Except that in Example 3-1 the carbon fiber powder was not added to the adhesive (0% by volume) and the adhesive was heated in an electric oven at 135 ° C. for 30 minutes, 60 minutes, or 90 minutes to cure. A cured product was prepared in the same manner as in Example 3-1 and the bending strength of the cured product was measured. The results of measuring the bending strength of the cured product are shown in FIG.

Tables 3 and 4 show the types of thermosetting resins, carbon fiber content and average length, heating conditions, or bending strength of each of the above Examples and Comparative Examples.

As shown in Table 3 and FIG. 4, in the adhesives of Examples 3-1 and 3-2, the bending strength of the cured product was about 68 MPa or more. On the other hand, in the adhesives of Comparative Examples 3-1 and 3-2, the bending strength of the cured product was about 65 MPa or less. Therefore, it was confirmed that if the adhesive containing carbon fibers is irradiated with microwaves to cure the adhesive, it can be said that a cured product having high bending strength can be obtained in a shorter time.

Further, in the adhesives of Comparative Examples 3-3 to 3-5, the bending strength of the cured product was about 66 MPa or less. Therefore, if the adhesive containing carbon fibers is irradiated with microwaves to cure the adhesive, a cured product having higher bending strength can be obtained in a shorter time than when the adhesive is heated in an electric oven. It was confirmed that it can be said that it can be done.

As described above, the embodiments have been described, but the above embodiments are presented as examples, and the present invention is not limited to the above embodiments. The above-described embodiment can be implemented in various other embodiments, and various combinations, omissions, replacements, changes, and the like can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

Claims (4)

An adhesive that cures when exposed to microwaves.
Thermosetting resin and
Contains carbon fiber,
The average length of the carbon fibers is 35 μm or more and 200 μm or less.
When the total amount of the adhesive is 100% by volume, the content of the carbon fiber is 0. An adhesive characterized by having 5 % by volume or more and 20% by volume or less. The adhesive according to claim 1 , wherein the thermosetting resin contains a curing agent. It includes a step of irradiating an adhesive containing a thermosetting resin and carbon fibers with microwaves to cure the adhesive.
The average length of the carbon fibers is 35 μm or more and 200 μm or less.
When the total amount of the adhesive is 100% by volume, the content of the carbon fiber is 0. A joining method characterized by being 5 % by volume or more and 20% by volume or less. The joining method according to claim 3 , wherein the wavelength of the microwave is 300 MHz or more and 3000 MHz or less.

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