Method for producing prepreg for forming carbon fiber-reinforced plastic, method for producing carbon fiber-reinforced plastic, joined body of metal and thermosetting carbon fiber-reinforced plastic and method for producing joined body

Abstract

This method for producing a prepreg for forming a thermosetting carbon fiber-reinforced plastic, the prepreg containing a carbon fiber and an epoxy resin, comprises: an electrodeposition step (S1) in which, in a state in which a carbon fiber material obtained by combining carbon fibers is immersed in a cationic electrodeposition coating material obtained by dispersing an electrolytic active epoxy resin in water, a voltage is applied using the carbon fiber material as a cathode to precipitate the electrolytic active epoxy resin on the surface of the carbon fiber; and a heating dehydration step (S2) in which the carbon fiber material coated with the cationic electrodeposition coating material is heated at a temperature of 180°C or lower to remove moisture.

Description

Manufacturing method of prepreg for forming carbon fiber reinforced plastic, manufacturing method of carbon fiber reinforced plastic, joint of metal and thermosetting carbon fiber reinforced plastic and manufacturing method thereof

[0001] The present invention relates to a method for producing a prepreg for forming a carbon fiber reinforced plastic, a method for producing a carbon fiber reinforced plastic, a bonded body of a metal and a thermosetting carbon fiber reinforced plastic, and a method for producing the same.

[0002] Carbon fiber reinforced plastics (CFRP), which use carbon fiber as a reinforcing material in a plastic base material, have traditionally been lighter and stronger than metal materials such as iron and aluminum. For this reason, great expectations are being placed on CFRP as a material that can achieve both weight reduction and strength improvement in parts when used as a material for various industrial products, including automobiles.

[0003] CFRP can be divided into two types: thermoplastic CFRP, which uses a thermoplastic resin as the base plastic, and thermosetting CFRP, which uses a thermosetting resin such as epoxy resin as the base plastic. Thermoplastic CFRP retains the properties of thermoplastic resin, softening when heated and hardening when cooled, so it can be molded into the desired shape of a part using a production method with short takt time, such as hot pressing. Therefore, thermoplastic CFRP is easy to mold into the shape of the part or component to be used, and can be provided as a material with excellent mass productivity for secondary processing.

[0004] Furthermore, because thermoplastic CFRP has the property of softening when heated and hardening when cooled, it offers a high degree of freedom in molding and processing, and is relatively easy to bond with adhesives, so the use of thermoplastic CFRP is being considered exclusively for the composite and multi-material combination of CFRP and metal materials.To join thermoplastic CFRP and metal materials, the vicinity of the joint is heated using a hot press, laser, friction, etc. to melt the thermoplastic CFRP and thermally fuse them.

[0005] There are two methods for producing thermoplastic CFRP: one is to prepare a laminate by sandwiching a thermoplastic resin film between bundles or woven carbon fiber material, and then to mold the entire prepreg laminate by pressurizing and heating it so that the heat-molten thermoplastic resin film is impregnated between the carbon fibers and adhered to the surfaces of the carbon fibers; and the other is to mold the entire carbon fiber laminate, in which bundles or woven carbon fiber material are layered, by pressurizing it so that the heated and melted thermoplastic resin is impregnated. Both methods utilize the property of thermoplastic resins, which soften and become fluid when heated above their melting point, in order to allow the resin impregnated between the carbon fibers to adhere uniformly to the carbon fiber surfaces.

[0006] However, if the thermoplastic resin does not penetrate the fine details of the carbon fiber material sufficiently, uniform adhesion to the surface of the carbon fiber is not achieved, resulting in the formation of voids and other defects within the carbon fiber. These voids become defects that significantly reduce the strength of the CFRP. Therefore, the production of thermoplastic CFRP requires not only the fluidity of the thermoplastic resin through heating, but also a long-term, high-pressure heating and pressurization process. This long-term heating and pressurization process requires large-scale equipment such as an autoclave, which increases costs and significantly reduces the productivity of thermoplastic CFRP.

[0007] On the other hand, thermosetting CFRP mainly uses epoxy resin, a thermosetting resin, and is highly reliable because it retains the excellent heat resistance, chemical resistance, and mechanical properties such as rigidity that epoxy resin has.It is expected to be an optimal material that can achieve both lightweight and high strength in parts and components of various industrial products.

[0008] One method for producing thermosetting CFRP involves first mixing a low-molecular-weight thermosetting resin with a curing agent, additives, and the like to create a low-viscosity, highly fluid coating material. This coating material is then applied to a bundle or woven carbon fiber material to form a composite sheet called a prepreg. The prepreg is then molded into the desired shape in a single layer or laminated state, while being heated to the curing temperature of the thermosetting resin to cure. This method ensures that the coating material wets the carbon fiber surface, allowing the coating material to easily penetrate between the carbon fibers and adhere uniformly to the surface. Therefore, unlike thermoplastic CFRP, thermosetting CFRP does not require the long-term heating and high-pressure processes required for impregnation and adhesion.

[0009] Patent No. 7162925 Publication JP-A-10-195349

[0010] Saito Takao: Color Materials, 72(3), 156(1999)

[0011] However, because the thermosetting coating materials used in thermosetting CFRP have high curing reactivity, their pot life for processing, such as impregnation, is short, and prepregs coated with thermosetting coating materials must be refrigerated or frozen for storage. This makes prepregs coated with thermosetting coating materials difficult to handle and work with. Furthermore, cured molded products do not possess the same properties as thermoplastic CFRP, which soften when heated and harden when cooled. Therefore, molding thermosetting CFRP into the desired shape for a particular part or component requires complex and difficult secondary processing steps, such as cutting, polishing, and assembly, resulting in long cycle times and poor mass productivity.

[0012] Therefore, Patent Document 1 discloses a configuration for producing thermosetting CFRP without forming a prepreg by utilizing the electrical conductivity of carbon fiber material. Specifically, Patent Document 1 discloses a configuration for producing a thermosetting CFRP having a desired three-dimensional shape by first forming a carbon fiber material as a precursor of the thermosetting CFRP into a desired three-dimensional shape, then immersing the carbon fiber material in an electrodeposition paint and applying a voltage to electrodeposit the surface of the carbon fiber. Thereafter, unreacted electrodeposition paint is removed from the carbon fiber material, and the carbon fiber material is heated to a temperature equal to or higher than the curing temperature of the resin to cure the resin. Patent Document 1 also discloses another configuration for producing a thermosetting CFRP having a desired three-dimensional shape by applying a voltage to a carbon fiber material immersed in an electrodeposition paint to electrodeposit the surface of the carbon fiber, forming the carbon fiber into a desired three-dimensional shape while the unreacted electrodeposition paint remains, and then removing the unreacted electrodeposition paint from the carbon fiber material and heating to a temperature equal to or higher than the curing temperature of the resin to cure the resin.

[0013] However, since the configuration disclosed in Patent Document 1 does not use prepregs, each time a thermosetting CFRP is produced, it is necessary to form a carbon fiber material into a desired three-dimensional shape, impregnate the carbon fiber material with an electrodeposition paint, apply a voltage, and heat the material to the curing temperature of the electrodeposition paint. As such, a configuration that does not use prepregs is difficult to work with and has low mass productivity.

[0014] Moreover, in recent years, there has been an increasing demand for higher mechanical properties, such as greater heat resistance and rigidity, even for multi-material materials made of metal and CFRP. As the thermoplastic plastics used in thermoplastic CFRP are expected to be highly crystalline super engineering plastics such as PPS and PEAK, joining by thermal fusion as described above has become extremely difficult.

[0015] On the other hand, thermosetting CFRP uses prepregs in which carbon fibers are pre-impregnated with a coating material containing a thermosetting resin. Because prepreg materials have high curing reactivity, they have a short pot life and require refrigeration or freezing during storage. This makes prepregs difficult to handle and work with. Due to these factors, there has been little research to date into using thermosetting CFRP instead of thermoplastic CFRP to create multi-material structures with metal materials.

[0016] For example, Patent Document 1 discloses a method for producing thermosetting CFRP by directly applying and curing a thermosetting electrodeposition paint without using a prepreg, utilizing the conductivity of the thermosetting electrodeposition paint and carbon fiber material, and also discloses the joining of thermosetting CFRP with metal materials. However, this method, which does not form an adhesive layer between the metal and thermosetting CFRP, makes it difficult to obtain sufficient and reliable adhesion, and therefore cannot be used as a multi-material technology.

[0017] As other thermosetting electrodeposition paints, for example, Non-Patent Document 1 and Patent Document 2 disclose electrolytically activated electrodeposition paints.

[0018] The present invention has been made in view of the above background, and aims to provide a method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic, which has excellent storage stability, workability, and mass productivity, and also to provide a joined body of metal and carbon fiber reinforced plastic, which has excellent joint strength, heat resistance, and chemical resistance at the joint, and has high mechanical strength.

[0019] A first aspect of the present invention is a method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic, which contains carbon fibers and an epoxy resin, comprising: an electrodeposition step of immersing a carbon fiber material formed by combining carbon fibers in a cationic electrodeposition paint in which an electrolytically activated epoxy resin is dispersed in water, and applying a voltage using the carbon fiber material as a cathode to deposit the electrolytically activated epoxy resin on the surface of the carbon fibers; and a thermal dehydration step of heating the carbon fiber material electrodeposited with the cationic electrodeposition paint at a temperature of 180°C or less to remove moisture.

[0020] A second aspect of the present invention is a method for producing a thermosetting carbon fiber reinforced plastic, comprising: a molding step of deforming the carbon fiber reinforced plastic forming prepreg produced by the method for producing a prepreg for thermosetting carbon fiber reinforced plastic of the above-mentioned one aspect along a molding die to form it into a target shape; and a curing step of heating the carbon fiber reinforced plastic forming prepreg molded into the target shape at a temperature of 180°C or higher to cure the electrolytically activated epoxy resin.

[0021] A third aspect of the present invention is a joined body of metal and thermosetting carbon fiber reinforced plastic, comprising: a first member made of metal; a second member made of thermosetting carbon fiber reinforced plastic; and an adhesive layer made of an electrodeposition coating film formed on the surface of the first member, wherein the first member and the second member are joined to each other via the adhesive layer.

[0022] A fourth aspect of the present invention is a method for producing a bonded body of metal and carbon fiber reinforced plastic, comprising: an adhesive layer forming step of immersing a first member made of metal in an electrodeposition paint comprising an electrolytically activated epoxy resin dispersed in water, applying a voltage using the first member as a cathode to precipitate the electrolytically activated epoxy resin on the surface of the first member, and heating the first member electrodeposited with the electrodeposition paint at a temperature of 180°C or less to remove moisture, thereby forming an adhesive layer made of the electrodeposition paint on the surface of the first member; a superposing step of superposing the prepreg for forming thermosetting carbon fiber reinforced plastic on the first member so that the prepreg for forming thermosetting carbon fiber reinforced plastic comes into contact with the adhesive layer; and a curing step of heating the superposed first member and the prepreg for forming thermosetting carbon fiber reinforced plastic at a temperature of 180°C or more to cure the electrolytically activated epoxy resin.

[0023] In the first aspect of the method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic, the electrolytically activated epoxy resin has electrodeposition latency with respect to the curing reaction of the coating. Electrodeposition latency refers to a property of the coating that the curing reaction is initially latent and requires an electrodeposition step to become active. In other words, to initiate the curing reaction of the coating, it is essential to first apply a voltage in the electrodeposition step to cause an electrochemical reaction; the curing reaction does not proceed by simply heating without applying a voltage. Furthermore, the progress of the curing reaction after the electrodeposition step is slow below the curing temperature of the epoxy resin, and in particular, it hardly progresses at room temperature, and is also slow in the temperature range of 100 to 180°C.

[0024] In the manufacturing method of the first aspect, the carbon fiber material that has been electrodeposited in an electrodeposition step with a cationic electrodeposition paint obtained by dispersing an electrolytically activated epoxy resin in water is heated at a temperature of 180° C. or less to remove moisture remaining in the carbon fiber material, thereby manufacturing a prepreg. Because the curing reaction does not actively proceed at this heating temperature, the epoxy resin in the manufactured prepreg is in a semi-cured state, and the prepreg can be maintained in a semi-cured state at room temperature.

[0025] Therefore, the prepreg produced by the manufacturing method of the first aspect does not require refrigeration or freezing during storage as conventional prepregs do, resulting in a long pot life and improved workability. Furthermore, because the prepreg is in a semi-cured state at room temperature, it can be easily molded into the shape of a part or component to which the thermosetting CFRP is to be applied. As a result, takt time can be shortened and mass productivity is high.

[0026] As described above, according to the first aspect, it is possible to provide a method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic, which is excellent in storage stability, workability and mass productivity.

[0027] Furthermore, according to the method for producing a thermosetting carbon fiber reinforced plastic of the second aspect, the prepreg for forming a thermosetting carbon fiber reinforced plastic produced by the production method of the first aspect can be easily molded into the shape of a desired part or component, thereby shortening the takt time and improving mass productivity. Furthermore, since the thermosetting carbon fiber reinforced plastic uses an epoxy resin as the thermosetting resin, it has excellent mechanical properties such as heat resistance, chemical resistance, and rigidity, making it highly reliable and able to contribute to achieving both weight reduction and high strength in parts and components of various industrial products.

[0028] In the bonded body of metal and thermosetting carbon fiber reinforced plastic of the third aspect, the adhesive layer has high bond strength and adhesion to the metal due to electrodeposition coating, and also has high bond strength and adhesion to the thermosetting carbon fiber reinforced plastic because it is a resin-to-resin bond. Furthermore, the epoxy resin constituting the adhesive layer has excellent heat resistance and chemical resistance. Therefore, by bonding a first member made of metal and a second member made of thermosetting carbon fiber reinforced plastic via the adhesive layer, the bonded portion has excellent bond strength, heat resistance, and chemical resistance, and a bonded body with a metal having high mechanical strength can be formed.

[0029] As described above, according to the third aspect, it is possible to provide a joined body of metal and carbon fiber reinforced plastic which has excellent joining strength, heat resistance, and chemical resistance at the joint and high mechanical strength.

[0030] In the manufacturing method of the fourth aspect, the electrolytically activated epoxy resin forming the adhesive layer has electrodeposition latency with respect to the curing reaction of the coating. Electrodeposition latency refers to a property of the coating that the curing reaction is initially latent and requires an electrodeposition process to become active. In other words, in order to initiate the curing reaction of the coating, it is essential that a voltage be applied in advance in the electrodeposition process to cause an electrochemical reaction; the curing reaction does not proceed by simply heating without applying a voltage. Furthermore, the progress of the curing reaction after the electrodeposition process is slow below the curing temperature of the epoxy resin, and in particular, it hardly progresses at room temperature, and is also slow in the temperature range of 100 to 180°C.

[0031] Therefore, in the manufacturing method of the fourth aspect, the first member electrodeposited in the adhesive layer formation step with a cationic electrodeposition paint comprising an electrolytically activated epoxy resin dispersed in water is heated at a temperature of 180°C or less to remove any remaining moisture from the first member and form an adhesive layer, which makes it easy for the adhesive layer to maintain a semi-cured state at room temperature before bonding. This results in a long usable time (pot life) and improved workability. Furthermore, by joining the first member made of metal and the second member made of thermosetting carbon fiber reinforced plastic via the adhesive layer, the joint can form a joint with the metal that has excellent bonding strength, heat resistance, and chemical resistance, and high mechanical strength.

[0032] 1 is a flow diagram showing a method for manufacturing a prepreg for forming a thermosetting carbon fiber reinforced plastic in Embodiment 1. (a) A conceptual perspective view of carbon fiber and a prepreg in Embodiment 1, and (b) A conceptual perspective view illustrating a prepreg joining step. Conceptual diagram illustrating an electrodeposition step in Embodiment 1. FIG. 2 is a flow diagram showing a method for manufacturing a thermosetting carbon fiber reinforced plastic in Embodiment 1. FIG. 3 is a conceptual perspective view of a molded product of a thermosetting carbon fiber reinforced plastic in Embodiment 1. (a) A conceptual perspective view illustrating a joining step of a first member and a prepreg, and (b) A conceptual perspective view of a bonded body of a first member and a second member in Embodiment 2. (a) A conceptual cross-sectional view illustrating a joining step of a first member and a prepreg, and (b) A conceptual cross-sectional view of a bonded body of a first member and a second member in Embodiment 2. FIG. 3 is a flow diagram showing a method for manufacturing a bonded body of a metal and a thermosetting carbon fiber reinforced plastic in Embodiment 2. Conceptual diagram illustrating an adhesive layer forming step in Embodiment 2. FIG. 4 is a flow diagram showing a method for manufacturing a prepreg for forming a thermosetting carbon fiber reinforced plastic in Embodiment 2. FIG. 10 is a conceptual diagram illustrating a confirmation test in the second embodiment.

[0033] In the method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic according to the first aspect, the heating temperature in the thermal dehydration step is preferably 100° C. or higher and 180° C. or lower. In this case, the produced prepreg can be easily brought to a semi-cured state early on without being completely cured.

[0034] In the method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic according to the first aspect, the electrolytically activated epoxy resin is preferably a novolac phenol polyepoxy resin. In this case, the thermosetting carbon fiber reinforced plastic formed using the produced prepreg has superior heat resistance, chemical resistance, and mechanical properties such as rigidity, as well as light weight, thereby further improving reliability.

[0035] Furthermore, the method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic of the first aspect can include, after the heating and dehydration step, a joining step of laminating a plurality of the sheet-like carbon fiber materials electrodeposited with the cationic electrodeposition paint, heating the laminate at a temperature of 180° C. or less, and rolling the laminate to join the carbon fiber materials to each other. In this case, rolling can form a prepreg having a smooth surface and closely packed carbon fibers.

[0036] In the method for producing a thermosetting carbon fiber reinforced plastic according to the second aspect, the molding step and the curing step can be carried out in parallel, thereby shortening the time required to produce the thermosetting carbon fiber reinforced plastic.

[0037] In the method for producing a thermosetting carbon fiber reinforced plastic according to the second aspect, the heating temperature in the curing step is preferably 180° C. or higher and 300° C. or lower. In this case, the prepreg in a semi-cured state can be cured at an early stage, further shortening the takt time and further improving mass productivity.

[0038] In the third aspect of the bonded body of metal and thermosetting carbon fiber reinforced plastic, the electrodeposition coating film in the adhesive layer is preferably made of an electrolytically activated epoxy resin. In this case, by using an electrolytically activated epoxy resin for the adhesive layer, the first member to which a cationic electrodeposition paint made by dispersing the electrolytically activated epoxy resin in water has been electrodeposited is heated at a temperature of 180°C or less to remove moisture remaining in the first member, thereby forming an adhesive layer. This makes it easy to maintain the adhesive layer in a semi-cured state at room temperature before bonding. This results in a long usable time (pot life) and improved workability.

[0039] In the third embodiment of the bonded body of metal and thermosetting carbon fiber reinforced plastic, the thermosetting carbon fiber reinforced plastic preferably comprises carbon fiber and an electrolytically activated epoxy resin. In this case, the cationic electrodeposition paint, which is a water dispersion of the electrolytically activated epoxy resin, is heated at a temperature of 180°C or less to the carbon fiber material that has been electrodeposited in the electrodeposition step, thereby removing the moisture remaining in the carbon fiber material and forming an adhesive layer. This makes it easy for the thermosetting carbon fiber reinforced plastic that constitutes the second member to maintain a semi-cured state at room temperature. This results in a long usable time (pot life) and improved workability.

[0040] In the bonded body of metal and thermosetting carbon fiber reinforced plastic according to the third aspect, the electrolytically activated epoxy resin is preferably a novolac phenol polyepoxy resin. In this case, the thermosetting carbon fiber reinforced plastic constituting the adhesive layer and the second member can be easily maintained in a semi-cured state at room temperature, thereby extending the usable time (pot life) and improving workability.

[0041] In the fourth aspect of the method for producing a bonded body of metal and thermosetting carbon fiber reinforced plastic, the prepreg for forming a thermosetting carbon fiber reinforced plastic is preferably produced by a prepreg production method including: a prepreg electrodeposition step in which a carbon fiber material formed by combining carbon fibers is immersed in an electrodeposition paint comprising an electrolytically activated epoxy resin dispersed in water, and a voltage is applied using the carbon fiber material as a cathode to deposit the electrolytically activated epoxy resin on the surface of the carbon fiber; and a prepreg heating and dehydration step in which the carbon fiber material electrodeposited with the cationic electrodeposition paint is heated at a temperature of 180°C or less to remove moisture. In this case, the curing reaction does not actively proceed in the prepreg at a heating temperature of 180°C or less, so the epoxy resin in the prepreg is in a semi-cured state, and the prepreg can be maintained in a semi-cured state at room temperature. Furthermore, since refrigeration or freezing is not required for storage, the usable time (pot life) is extended and workability is improved. Furthermore, because the prepreg is in a semi-cured state at room temperature, it can be easily molded to fit the first component to which the thermosetting CFRP is to be applied, even if the first component has a complex shape. As a result, takt time can be shortened and mass productivity is high.

[0042] In the method for producing a joined body of metal and thermosetting carbon fiber reinforced plastic according to the fourth aspect, the heating temperature in the adhesive layer forming step is preferably 100° C. or higher and 180° C. or lower. In this case, the adhesive layer before joining can be maintained in a semi-cured state early, improving workability.

[0043] In the method for producing a bonded body of metal and thermosetting carbon fiber reinforced plastic according to the fourth aspect, in the overlapping step, it is preferable to overlap the prepreg for forming thermosetting carbon fiber reinforced plastic onto the first member while heating at a temperature of not more than 180° C. In this case, when overlapping the first member and the prepreg for forming thermosetting carbon fiber reinforced plastic, the adhesive layer can be maintained in a semi-cured state at room temperature, improving the workability and compatibility of the adhesive layer.

[0044] In the method for producing a joined body of metal and thermosetting carbon fiber reinforced plastic according to the fourth aspect, the heating temperature in the overlapping step is 100° C. or higher and 180° C. or lower. In this case, the adhesive layer before joining can be maintained in a semi-cured state early, improving workability.

[0045] In the method for producing a joined body of metal and thermosetting carbon fiber reinforced plastic according to the fourth aspect, the heating temperature in the curing step is 180° C. or higher and 300° C. or lower. In this case, the adhesive layer can be cured early after the laminating step is completed, which further shortens the takt time and further improves mass productivity.

[0046] (Embodiment 1) 1. Prepreg for forming thermosetting carbon fiber reinforced plastic A prepreg for forming thermosetting carbon fiber reinforced plastic (hereinafter, in this specification, also simply referred to as "prepreg") is a composite of carbon fiber and a thermosetting resin for forming a thermosetting carbon fiber reinforced plastic, and is in a state where the carbon fiber material is pre-impregnated with the thermosetting resin.

[0047] 2. Carbon Fiber Material Carbon fiber materials are formed by combining carbon fibers in a bundle or woven form. The structure of the carbon fiber material is not limited, and examples include planar carbon fiber sheets and bundle-like carbon fiber bundles. Carbon fiber sheets can be formed by weaving multiple carbon fibers crosswise in perpendicular directions. The weaving pattern is not limited, and known weaves such as plain weave and twill weave can be used. In addition, carbon fiber sheets can be formed by arranging carbon fibers in a linear or curved pattern. The average fiber diameter of each carbon fiber is preferably within the range of 0.001 to 50 μm, from the viewpoint of sufficient precipitation of the epoxy resin described below. In this embodiment, a plain-woven carbon fiber sheet 10 shown in FIG. 1( a) is used as the carbon fiber material. The longitudinal and lateral dimensions of the carbon fiber sheet 10 are not limited, and the thickness of the carbon fiber sheet 10 is also not limited.

[0048] 3. Cationic Electrodeposition Paint The cationic electrodeposition paint used in the manufacturing method of thermosetting carbon fiber reinforced plastic is an electrolytically activated epoxy resin dispersed in water. Hereinafter, this cationic electrodeposition paint will also be referred to as "electrolytically activated electrodeposition paint." Electrolytically activated epoxy resins are made of epoxy resins that are electrolytically activated by an electrode reaction. More specifically, electrolytically activated epoxy resins form an epoxy resin coating by applying a voltage in the electrodeposition process, and the electrode reaction triggered by the voltage application generates activated chemical species in the coating, which promote the progress of the curing reaction of the coating. Furthermore, the progress of the curing reaction after voltage application is slow below the curing temperature of the epoxy resin, and in particular, progresses almost nonexistently at room temperature, and is also slow in the temperature range of 100 to 180°C.

[0049] The epoxy resin used in such electrolytically activated electrodeposition paints is a resin composition having sulfonium groups and propargyl groups in addition to the epoxy groups that constitute the epoxy resin. The resin composition in the electrolytically activated epoxy resin may, but does not necessarily, have both sulfonium groups and propargyl groups in one molecule containing an epoxy group. For example, it may have only one of sulfonium groups or propargyl groups in one molecule. In this case, the resin composition as a whole has these two types of functional groups. That is, the resin composition may consist of a resin having sulfonium groups and propargyl groups, or a mixture of a resin having only sulfonium groups and a resin having only propargyl groups, or a mixture of all of these.

[0050] The epoxy resin that forms the backbone of the electrolytically activated epoxy resin is preferably one having at least two epoxy groups per molecule, and specific examples include epibis-type epoxy resins and those chain-extended with diols, dicarboxylic acids, diamines, etc.; epoxidized polybutadienes; novolac phenol-type polyepoxy resins; novolac cresol-type polyepoxy resins; polyglycidyl acrylate; polyglycidyl ethers of aliphatic polyols or polyether polyols; and polyglycidyl esters of polybasic carboxylic acids. Of these, novolac phenol-type polyepoxy resins, novolac cresol-type polyepoxy resins, and polyglycidyl acrylate are preferred because they can be easily multifunctionalized to enhance curability.

[0051] Examples of electrolytically activated electrodeposition paints containing such electrolytically activated epoxy resins include Insulead (registered trademark) 1000 and Insulead (registered trademark) 3000 manufactured by Nippon Paint Industrial Coatings Co., Ltd. Insulead 1000 and Insulead 3000 contain phenolic resin (novolac resin) as a polymer compound, and can impart insulating properties and heat resistance by precipitating the epoxy resin. In this embodiment, Insulead 3000 is used as the electrolytically activated electrodeposition paint.

[0052] 4. Method for Manufacturing Prepreg for Forming Thermosetting Carbon Fiber Reinforced Plastic The method for manufacturing a prepreg for forming a thermosetting carbon fiber reinforced plastic according to the first embodiment includes an electrodeposition step S1, a heat dehydration step S2, and a joining step S3, as shown in FIG.

[0053] 4-1. Electrodeposition Step In the electrodeposition step S1 shown in Fig. 2, first, in step S11, the carbon fiber material is impregnated with an electrolytically activated electrodeposition paint. In the present embodiment 1, as shown in Fig. 3, the carbon fiber material 10 is immersed in an electrolytically activated electrodeposition paint 20 of a predetermined concentration stored in a reaction tank 30. As a result, the electrolytically activated electrodeposition paint 20 penetrates between the carbon fibers constituting the carbon fiber material 10. An electrode 31 is also immersed in the reaction tank 30. The configuration of the electrode 31 is not limited, and the material may be any conductive material, for example, stainless steel, aluminum, carbon, etc.

[0054] Thereafter, in step S12, a voltage is applied to the carbon fiber material 10. In the present embodiment 1, as shown in Fig. 3, the carbon fiber material 10 in the reaction tank 30 and an electrode 31 are electrically connected via a power supply 32, and the output of the power supply 32 is controlled by a controller 33 to apply a voltage from the power supply 32 so that the carbon fiber material 10 serves as the cathode. As a result, the epoxy resin present as a polymer compound colloid in the electrolytically activated electrodeposition paint 20 adheres to the surface of the carbon fiber material 10 by electrophoresis, and is insolubilized and precipitated (electrodeposited) by an electrode reaction.

[0055] The voltage and current applied to the carbon fiber material are not particularly limited and can be appropriately selected depending on the type of electrolytically activated electrodeposition paint. In particular, the applied voltage is preferably 90 to 500 V, more preferably 100 to 300 V, from the viewpoint of more sufficiently depositing the epoxy resin on each carbon fiber while further suppressing the electrolysis of water. The applied current depends on the size, thickness, etc. of the carbon fiber material, but is preferably 0.01 to 1.0 A, more preferably 0.05 to 0.5 A, from the viewpoint of more sufficiently depositing the epoxy resin on each carbon fiber while further suppressing the electrolysis of water.

[0056] The time for applying the voltage is not particularly limited and can be appropriately selected depending on the type of electrolytically activated electrodeposition paint. In particular, from the viewpoint of more sufficiently depositing the epoxy resin on each carbon fiber while further suppressing the electrolysis of water, the time is preferably 1 to 300 minutes, and more preferably 5 to 120 minutes.

[0057] 4-2. Heat Dehydration Step In the heat dehydration step S2 shown in FIG. 1, the carbon fiber material after the electrodeposition step S1 is heated at a temperature of 180°C or less. This removes moisture derived from the electrolytically activated electrodeposition paint adhering to the carbon fiber material. The heating temperature in the heat dehydration step S2 is 180°C or less, and more preferably in the range of 100 to 180°C. By setting the heating temperature in the range of 100 to 180°C, moisture can be removed quickly while suppressing resin curing in the carbon fiber material after the electrodeposition step S1. The heating time in the heat dehydration step S2 is not limited as long as it is long enough to sufficiently remove moisture. Once the moisture has been sufficiently removed, a prepreg for forming a thermosetting carbon fiber reinforced plastic is completed. The prepreg has a shape that reflects the shape of the carbon fiber material, and in this embodiment, it has the same shape as the carbon fiber sheet 10 shown in FIG. 2.

[0058] In the thermal dehydration step S2, as described above, the heating temperature is 180°C or less, so the curing of the electrolytically activated epoxy resin does not actively proceed, and the completed prepreg is in a semi-cured state. As described above, the curing reaction of the electrolytically activated epoxy resin after the electrodeposition step S1 hardly progresses at room temperature, so the completed prepreg 10a can be stored in a semi-cured state at room temperature.

[0059] 4-3. Bonding Step In this embodiment 1, the heating and dehydration step S2 is followed by the bonding step S3 shown in Fig. 1. In the bonding step S3, as shown in Fig. 2(b), a plurality of completed prepregs are stacked, heated at a temperature of 180°C or less, and rolled to be pressed in the direction indicated by arrow P and bonded together. The heating temperature in the bonding step S3 can be the same as the heating temperature in the heating and dehydration step S2. There is no limitation on the number of prepregs 10a to be stacked, and any desired number can be used.

[0060] 5. Method for Manufacturing Thermosetting Carbon Fiber Reinforced Plastic Next, a detailed description will be given of a method for manufacturing a thermosetting carbon fiber reinforced plastic according to the present embodiment 1. The method for manufacturing a thermosetting carbon fiber reinforced plastic includes a molding step S4 and a curing step S5.

[0061] In the molding step S4 shown in Fig. 4, the prepreg 10a for forming a thermosetting carbon fiber reinforced plastic is deformed along a molding die and molded into a target shape. In this embodiment, a plurality of prepregs 10a for forming a thermosetting carbon fiber reinforced plastic are set in a molding die (not shown) and molded into the channel shape shown in Fig. 5.

[0062] 5-2. Curing Step After the molding step S4, the curing step S5 shown in FIG. 4 is performed. In the curing step S5, the prepreg 10a for forming a thermosetting carbon fiber reinforced plastic is heated at a temperature of 180°C or higher to cure the electrolytically activated epoxy resin. The heating temperature in the curing step S5 can be 180°C or higher and 300°C or lower. This makes it possible to obtain a molded product of thermosetting carbon fiber reinforced plastic 100 (see FIG. 5) having the target shape molded in the molding step S4.

[0063] The molding step S4 and the curing step S5 may be performed in parallel. That is, the prepreg 10a for forming a thermosetting carbon fiber reinforced plastic may be deformed along the molding die to form a target shape, while the electrolytically activated epoxy resin is cured by heating at a temperature of 180°C or higher.

[0064] 6. Effects and Benefits The effects and benefits of the method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic according to the first embodiment are described below. According to the method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic according to the first embodiment, a carbon fiber material that has been electrodeposited in an electrodeposition step with a cationic electrodeposition paint comprising an electrolytically activated epoxy resin dispersed in water is heated at a temperature of 180°C or less to remove moisture remaining in the carbon fiber material, thereby producing the prepreg 10a. Because the curing reaction does not actively proceed at this heating temperature, the epoxy resin in the produced prepreg 10a is in a semi-cured state, and the prepreg 10a can be maintained in a semi-cured state at room temperature.

[0065] Therefore, unlike conventional prepregs, the prepreg 10a does not require refrigeration or freezing during storage, resulting in a longer pot life and improved workability. Furthermore, because the prepreg 10a is in a semi-cured state at room temperature, it can be easily molded into the shape of a part or component to which thermosetting CFRP is to be applied. As a result, takt time can be shortened and mass productivity is improved.

[0066] In the first embodiment, the heating temperature in the thermal dehydration step S2 is 100° C. or higher and 180° C. or lower. This allows the prepreg 10a to be produced in a semi-cured state early on, without being completely cured.

[0067] In this embodiment, the electrolytically activated epoxy resin is a specially modified novolac epoxy resin. As a result, the thermosetting carbon fiber reinforced plastic 100 formed using the prepreg 10a produced thereby has superior heat resistance, chemical resistance, and mechanical properties such as rigidity, as well as light weight, thereby further improving reliability.

[0068] Furthermore, in this embodiment 1, after the heating and dehydration step S2, a joining step S3 is included in which a plurality of sheet-shaped carbon fiber materials 10 electrodeposited with cationic electrodeposition paint are stacked, heated at a temperature of 180° C. or less, and rolled to join the carbon fiber materials to each other. As a result, the surface of the prepreg 10a is smooth and the carbon fibers are closely packed by the rolling.

[0069] As described above, according to the first embodiment, it is possible to provide a method for producing the prepreg 10a for forming a thermosetting carbon fiber reinforced plastic, which is excellent in storage stability, workability, and mass productivity.

[0070] The method for producing a thermosetting carbon fiber reinforced plastic according to the first embodiment includes a molding step S4 in which the prepreg 10a produced by the method for producing a prepreg for forming a carbon fiber reinforced plastic is deformed along a molding die to form a target shape, and a curing step S5 in which the prepreg 10a is heated at a temperature of 180°C or higher to cure the electrolytically activated epoxy resin. This allows the prepreg 10a for forming a thermosetting carbon fiber reinforced plastic according to the first embodiment to be easily molded into the shape of a desired part or component, thereby shortening takt time and improving mass productivity. Furthermore, because the thermosetting carbon fiber reinforced plastic uses an epoxy resin as the thermosetting resin, it has excellent heat resistance, chemical resistance, rigidity, and other mechanical properties, making it highly reliable and contributing to achieving both weight reduction and high strength in parts and components of various industrial products.

[0071] Furthermore, in the present embodiment 1, the molding step S4 and the curing step S5 can be performed in parallel, which can shorten the time required to produce the thermosetting carbon fiber reinforced plastic.

[0072] Furthermore, in the method for producing a thermosetting carbon fiber reinforced plastic according to the first embodiment, the heating temperature in the curing step S5 is 180° C. or higher and 300° C. or lower. This allows the prepreg 10a, which is in a semi-cured state, to be cured early, further shortening the takt time and further improving mass productivity.

[0073] Furthermore, according to the method for producing a thermosetting carbon fiber reinforced plastic of this embodiment 1, the prepreg for forming a thermosetting carbon fiber reinforced plastic produced by the production method of the above aspect can be easily molded into the shape of a desired part or component, thereby shortening the takt time and improving mass productivity. Furthermore, because the thermosetting carbon fiber reinforced plastic uses an epoxy resin as the thermosetting resin, it has excellent mechanical properties such as heat resistance, chemical resistance, and rigidity, making it highly reliable and able to contribute to achieving both weight reduction and high strength in parts and components of various industrial products.

[0074] As described above, according to the first embodiment, it is possible to provide a thermosetting carbon fiber reinforced plastic that can contribute to achieving both weight reduction and high strength.

[0075] (Embodiment 2) 7. Joined Body of Metal and Thermosetting Carbon Fiber Reinforced Plastic The following describes in detail a joined body of metal and thermosetting carbon fiber reinforced plastic according to this embodiment 2. A joined body 200 of metal and thermosetting carbon fiber reinforced plastic according to this embodiment 2 (hereinafter also referred to as "joint body 200") includes a first member 210 made of metal and a second member 220 made of thermosetting carbon fiber reinforced plastic, as shown in Fig. 6, joined via an adhesive layer 230 as shown in Fig. 6.

[0076] 7-1. First Member The metal constituting the first member 210 is not particularly limited, and various metals such as aluminum alloy, copper alloy, stainless steel alloy, and titanium alloy can be used. The shape of the first member 210 is also not limited, and can be a shape depending on the application of the joined body 200. In the second embodiment, the first member 210 is flat, as shown in FIGS. 6 and 7.

[0077] 7-2. Adhesion Layer As shown in FIG. 7(a), the adhesion layer 230 is made of an electrodeposition coating formed on the surface of the first member 210. The electrodeposition coating constituting the adhesion layer 230 is formed by electrodeposition coating with a cationic electrodeposition paint in which an electrolytically activated epoxy resin is dispersed in water. The cationic electrodeposition paint in this embodiment 2 is also called an "electrolytically activated electrodeposition paint" and can be the same as that described in "3. Cationic electrodeposition paint" in the above-mentioned embodiment 1. In this embodiment 2, Insulead 3000 is used as the electrolytically activated electrodeposition paint.

[0078] 7-3. Adhesive Layer Forming Step As shown in FIG. 8, the adhesive layer forming step S210 for forming the adhesive layer 230 includes an electrodeposition step S21 and a heating and dehydration step S22.

[0079] 7-3-1. Electrodeposition Step In the electrodeposition step S21 shown in Fig. 8, first, in step S211, the first member 210 is immersed in an electrolytically activated electrodeposition paint. In the second embodiment, as shown in Fig. 9, the first member 210 is immersed in an electrolytically activated electrodeposition paint 240 of a predetermined concentration stored in a reaction tank 250. This brings the electrolytically activated electrodeposition paint 240 into contact with the entire surface of the first member 210. An electrode 251 is also immersed in the reaction tank 250. The configuration of the electrode 251 is not limited, and it may be made of any conductive material, such as stainless steel, aluminum, or carbon.

[0080] Thereafter, in step S212 shown in Fig. 8 , a voltage is applied to the first member 210. In the second embodiment, as shown in Fig. 9 , the first member 210 and an electrode 251 in the reaction tank 250 are electrically connected via a power supply 252, and the output of the power supply 252 is controlled by a controller 253 to apply a voltage from the power supply 252 so that the first member 210 serves as the cathode. As a result, the epoxy resin present as a polymer compound colloid in the electrolytically activated electrodeposition paint 240 adheres to the surface of the first member 210 by electrophoresis, and is insolubilized and precipitated (electrodeposited) by an electrode reaction.

[0081] Since the cationic electrodeposition paint in which the electrolytically activated epoxy resin is dispersed in water remains on the surface of the deposited epoxy resin, in step S213 shown in FIG. 8, this is washed away with deionized water to clean the epoxy resin surface.

[0082] The voltage and current applied to the carbon fiber material are not particularly limited and can be appropriately selected depending on the type of electrolytically activated electrodeposition paint. In particular, the applied voltage is preferably 90 to 500 V, more preferably 100 to 300 V, from the viewpoint of more sufficiently depositing the epoxy resin on each carbon fiber while further suppressing the electrolysis of water. The applied current depends on the size, thickness, etc. of the carbon fiber material, but is preferably 0.01 to 1.0 A, more preferably 0.05 to 0.5 A, from the viewpoint of more sufficiently depositing the epoxy resin on each carbon fiber while further suppressing the electrolysis of water.

[0083] The time for applying the voltage is not particularly limited and can be appropriately selected depending on the type of electrolytically activated electrodeposition paint. In particular, from the viewpoint of more sufficiently depositing the epoxy resin on each carbon fiber while further suppressing the electrolysis of water, the time is preferably 1 to 300 minutes, and more preferably 5 to 120 minutes.

[0084] 8, the first member 210 after the electrodeposition step S21 is heated at a temperature of 180°C or less. This removes moisture derived from the electrolytically activated electrodeposition paint adhering to the first member 210. The heating temperature in the heat dehydration step S22 is 180°C or less, and more preferably in the range of 100 to 180°C. By setting the heating temperature in the range of 100 to 180°C, moisture can be removed quickly while suppressing hardening of the adhesive layer 230 in the first member 210 after the electrodeposition step S21. The heating time in the heat dehydration step S22 is not limited as long as it is a time that allows moisture to be sufficiently removed. Once the moisture has been sufficiently removed, the adhesive layer 230 is completed.

[0085] In the thermal dehydration step S22, as described above, the heating temperature is 180° C. or less, so that the curing of the electrolytically activated epoxy resin does not actively proceed, and the completed adhesive layer 230 is in a semi-cured state. As described above, the curing reaction of the electrolytically activated epoxy resin after the electrodeposition step S21 hardly progresses at room temperature, so that the adhesive layer 230 can be stored in a semi-cured state at room temperature.

[0086] 7-4. Second Member Made of Thermosetting Carbon Fiber Reinforced Plastic The thermosetting carbon fiber reinforced plastic constituting the second member 220 is made of a carbon fiber material and a thermosetting resin. The thermosetting carbon fiber reinforced plastic can be formed from a prepreg for forming thermosetting carbon fiber reinforced plastic. The prepreg for forming thermosetting carbon fiber reinforced plastic in this embodiment 2 (hereinafter also simply referred to as "prepreg" in this specification) is a composite of carbon fiber and thermosetting resin for forming thermosetting carbon fiber reinforced plastic, in which the carbon fiber material is pre-impregnated with the thermosetting resin.

[0087] 7-4-1. Carbon Fiber Material The carbon fiber material in this embodiment 2 can be the same as the carbon fiber material in the above-described embodiment 1. In this embodiment 2, a plain woven carbon fiber sheet is used as the carbon fiber material. The dimensions of the carbon fiber sheet in the longitudinal and lateral directions are not limited, and the thickness of the carbon fiber sheet is also not limited.

[0088] The electrodeposition paint used to form the thermosetting carbon fiber reinforced plastic in the second member 220 is an electrolytically activated epoxy resin dispersed in water, and can be the same as the electrodeposition paint in the adhesive layer 230 described above. In this second embodiment, Insulead 3000 is used as the electrolytically activated electrodeposition paint in the second member 220.

[0089] 7-5. Manufacturing Method of Prepreg for Forming Thermosetting Carbon Fiber Reinforced Plastic The manufacturing method of the prepreg for forming the thermosetting carbon fiber reinforced plastic that constitutes the second member 220 includes a prepreg electrodeposition step S21a and a prepreg heating and dehydration step S22a, as shown in Fig. 10. The prepreg electrodeposition step S21a (steps S211a, S212a, and S213a) and the prepreg heating and dehydration step S22a are equivalent to replacing the first member 210 with a carbon fiber sheet in the electrodeposition step S21 and the heating and dehydration step S22 of the adhesive layer formation step S210 described above and shown in Fig. 8, and detailed description thereof will be omitted.

[0090] In the second embodiment, as shown in Fig. 10, a prepreg bonding step S23a is performed after the prepreg heating and dehydrating step S22a. In the prepreg bonding step S23a, a plurality of prepregs 220a for forming thermosetting carbon fiber reinforced plastics (hereinafter referred to as "prepregs 220a") formed in the prepreg heating and dehydrating step S22a are stacked and heated at a temperature of 180°C or less, followed by rolling to bond them together. The number of prepregs 220a to be stacked is not limited and can be any desired number.

[0091] 8. Manufacturing Method of Joined Body of Metal and Thermosetting Carbon Fiber Reinforced Plastic Next, a detailed description will be given of a manufacturing method of the joined body 200 of metal and thermosetting carbon fiber reinforced plastic according to the present embodiment 2. As shown in Fig. 8, the manufacturing method of the joined body 200 includes the above-mentioned adhesive layer forming step S210, the overlapping step S220, and the curing step S230.

[0092] 8-1. Overlaying Step The overlaying step S220 shown in Fig. 8 is performed after the adhesive layer forming step S210 described above. In the overlaying step S220, as shown in Fig. 7(b), the prepreg 220a for forming a thermosetting carbon fiber reinforced plastic is overlaid on the first member 210 so that the prepreg 220a for forming a thermosetting carbon fiber reinforced plastic contacts the adhesive layer 230. In the overlaying step S220, rolling may be performed after overlaying.

[0093] In the overlapping step S220, the first member 210 and the prepreg 220a for forming a thermosetting carbon fiber reinforced plastic may be overlapped while being heated at a temperature of 180° C. or less. The heating temperature in the overlapping step S220 may be 100° C. or more and 180° C. or less.

[0094] 8-2. Curing Step After the overlapping step S220, the curing step S230 shown in FIG. 8 is performed. In the curing step S30, the overlapping first member 210 and the thermosetting carbon fiber reinforced plastic forming prepreg 220a are heated at a temperature of 180°C or higher to cure the electrolytically activated epoxy resin in the adhesive layer 230 and the prepreg 220a. The heating temperature in the curing step S230 can be 180°C or higher and 300°C or lower. This bonds the first member 210 and the second member 220 via the adhesive layer 230. A bonded body 200 of metal and thermosetting carbon fiber reinforced plastic can be manufactured.

[0095] 9. Verification Test Next, a verification test of the adhesive strength of the bonded body 200 of metal and thermosetting carbon fiber reinforced plastic according to the second embodiment was conducted as follows. First, as described above, a prepreg 220a was produced according to the prepreg electrodeposition step S21a and prepreg heating and dehydration step S22a shown in FIG. 10 . Then, in the prepreg bonding step S23a, five prepregs 220a cut into 25 mm × 100 mm pieces were stacked together, pressed together under a load of approximately 10 kg, and then dried at 105°C for 10 minutes to remove moisture, producing the uncured laminated prepreg 220b shown in FIG. 11( a). The thickness of the laminated prepreg 220b was 1.0 mm.

[0096] Next, aluminum, copper, and SUS metal plates (each 1.0 mm thick) were prepared as the first members 210 and cut into 25 mm x 100 mm pieces. Each first member 210 was electrocoated in a region extending 25 mm from its tip according to the electrodeposition step S1 and thermal dehydration step S2 shown in FIG. 3 , forming an adhesive layer 230 as shown in FIG. 11( a). Each metal plate constituting the first member 210 utilized the surface of a cold-rolled material as is, and the surface of the first member 210 was a smooth, flat surface with a surface roughness of Ra 1.0 or less. The area where the adhesive layer 230 was formed measured 25 mm x 25 mm.

[0097] 8, the laminated prepreg 220b was laminated on the first member 210 as shown in FIG. 11(b), and then the laminated prepreg 220b was baked for 20 minutes or longer at a temperature of 170° C. or higher and 180° C. or lower in accordance with the curing step S230. This produced a bonded body 200 of the first member 210 and the laminated prepreg 220b.

[0098] Each of the bonded structures 200 prepared as described above was subjected to a tensile tester to check the shear stress at the bonded portion of each bonded structure 200. The shear stress at the bonded portion between the aluminum first member 210 and the laminated prepreg 20b was 4.6 MPa, the shear stress at the bonded portion between the copper first member 210 and the laminated prepreg 20b was 4.8 MPa, and the shear stress at the bonded portion between the SUS first member 210 and the laminated prepreg 220b was 4.4 MPa. This confirmed that a sufficiently high bond strength could be obtained in all cases.

[0099] 10. Effects and Benefits The effects and benefits of the joined body of metal and thermosetting carbon fiber reinforced plastic of the second embodiment are described below. According to the joined body 200 of metal and thermosetting carbon fiber reinforced plastic of the second embodiment, the adhesive layer 230 has high bonding strength and adhesion to the metal due to the electrodeposition coating, and also has high bonding strength and adhesion to the thermosetting carbon fiber reinforced plastic because it is a resin-to-resin bond. In addition, the epoxy resin constituting the adhesive layer 230 has excellent heat resistance and chemical resistance. Therefore, by joining the first member 210 made of metal and the second member 220 made of thermosetting carbon fiber reinforced plastic via the adhesive layer 230, the joint has excellent bonding strength, heat resistance, and chemical resistance, and a joined body 200 with metal having high mechanical strength can be formed.

[0100] Furthermore, in the second embodiment, the electrodeposition coating film in the adhesive layer 230 is made of an electrolytically activated epoxy resin. By using an electrolytically activated cationic epoxy electrodeposition paint for the adhesive layer 230, the first member 210, which has been electrodeposited with a cationic electrodeposition paint made by dispersing an electrolytically activated epoxy resin in water, is heated at a temperature of 180°C or less to remove the moisture remaining in the first member 210 and form the adhesive layer 230. This makes it easy to maintain the adhesive layer 230 in a semi-cured state at room temperature before bonding. This results in a long usable time (pot life) and improved workability.

[0101] In the second embodiment, the thermosetting carbon fiber reinforced plastic is made of carbon fiber and an electrolytically activated epoxy resin. By heating the carbon fiber material, which has been electrodeposited with a cationic electrodeposition paint made of an electrolytically activated epoxy resin dispersed in water, at a temperature of 180°C or less, the moisture remaining in the carbon fiber material is removed and an adhesive layer is formed. This makes it easy for the thermosetting carbon fiber reinforced plastic constituting the second member to maintain a semi-cured state at room temperature. This results in a long usable time (pot life) and improved workability.

[0102] In addition, in the present embodiment 2, the electrolytically activated epoxy resin is a novolac phenol polyepoxy resin, which makes it easy to maintain the thermosetting carbon fiber reinforced plastic constituting the adhesive layer 230 and the second member 220 in a semi-cured state at room temperature, thereby extending the usable time (pot life) and improving workability.

[0103] In the method for manufacturing a bonded body of metal and thermosetting carbon fiber reinforced plastic according to the second embodiment, the first member 210, which has been electrodeposited with a cationic electrodeposition paint comprising an electrolytically activated epoxy resin dispersed in water in the adhesive layer formation process, is heated at a temperature of 180°C or less to remove any moisture remaining in the first member 210 and form the adhesive layer 230. This makes it easy for the adhesive layer 230 to maintain a semi-cured state at room temperature before bonding. This results in a long usable time (pot life) and improved workability. Furthermore, bonding the first member 210 made of metal and the second member 220 made of thermosetting carbon fiber reinforced plastic via the adhesive layer 230 provides excellent bonding strength, heat resistance, and chemical resistance.

[0104] In this second embodiment, the prepreg 220a for forming a thermosetting carbon fiber reinforced plastic is manufactured by a prepreg manufacturing method including a prepreg electrodeposition step S21a in which a carbon fiber material formed by combining carbon fibers is immersed in a cationic electrodeposition paint in which an electrolytically activated epoxy resin is dispersed in water, and a voltage is applied using the carbon fiber material as a cathode to precipitate the electrolytically activated epoxy resin on the surface of the carbon fiber; and a prepreg heating and dehydration step S22a in which the carbon fiber material electrodeposited with the cationic electrodeposition paint is heated at a temperature of 180°C or less to remove moisture. As a result, the curing reaction does not actively proceed in the prepreg 220a at a heating temperature of 180°C or less, so the epoxy resin in the prepreg 220a becomes semi-cured, and the prepreg 220a can be maintained in a semi-cured state at room temperature. Furthermore, since refrigeration or freezing is not required for storage, the usable time (pot life) is extended and workability is improved. Furthermore, since the prepreg 220a is in a semi-cured state at room temperature, it can be easily molded to fit the first member 210, even if the first member 210 to which the thermosetting CFRP is to be applied has a complex shape. As a result, the takt time can be shortened and mass productivity is high.

[0105] In the second embodiment, the heating temperature in the adhesive layer forming step S210 is 100° C. or higher and 180° C. or lower. This allows the adhesive layer 230 to be maintained in a semi-cured state before bonding at an early stage, improving workability.

[0106] In the second embodiment, in the overlapping step S220, the prepreg 220a for forming thermosetting carbon fiber reinforced plastic is overlapped on the first member 210 while being heated at a temperature of 180° C. or less. This allows the adhesive layer 230 to be maintained in a semi-cured state at room temperature when the first member 210 and the prepreg 220a for forming thermosetting carbon fiber reinforced plastic are overlapped, improving workability.

[0107] In the second embodiment, the heating temperature in the overlapping step S220 is 100° C. or higher and 180° C. or lower. This allows the adhesive layer 230 to be maintained in a semi-cured state before bonding at an early stage, improving workability.

[0108] In the second embodiment, the heating temperature in the curing step S230 is 180° C. or higher and 300° C. or lower. This allows the adhesive layer 230 to be cured early after the completion of the overlapping step S220, further shortening the takt time and further improving mass productivity.

[0109] As described above, according to the second embodiment, it is possible to provide a joined body 200 of metal and carbon fiber reinforced plastic having excellent joining strength, heat resistance, and chemical resistance at the joint and high mechanical strength.

[0110] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention.

Claims

1. A method for producing a prepreg for forming a carbon fiber reinforced plastic, which contains carbon fibers and an epoxy resin, comprising: an electrodeposition step in which a carbon fiber material formed by combining carbon fibers is immersed in a cationic electrodeposition paint in which an electrolytically activated epoxy resin is dispersed in water, and a voltage is applied using the carbon fiber material as a cathode to deposit the electrolytically activated epoxy resin on the surface of the carbon fiber; and a thermal dehydration step in which the carbon fiber material electrodeposited with the cationic electrodeposition paint is heated at a temperature of 180°C or less to remove moisture.

2. The method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic according to claim 1, wherein the heating temperature in the thermal dehydration step is 100°C or higher and 180°C or lower.

3. A method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic according to claim 1 or 2, wherein the electrolytically activated epoxy resin is a novolac phenol polyepoxy resin.

4. A method for producing a prepreg for forming a thermosetting carbon fiber reinforced plastic according to claim 1 or 2, which includes, after the heating and dehydration step, a joining step in which a plurality of sheets of the carbon fiber material electrocoated with the cationic electrocoating paint are stacked, heated at a temperature of 180°C or less, and rolled to join the carbon fiber materials to each other.

5. A method for producing thermosetting carbon fiber reinforced plastics, comprising: a molding step of deforming the prepreg for forming carbon fiber reinforced plastics, produced by the method for producing a prepreg for forming carbon fiber reinforced plastics according to claim 1 or 2, along a molding die to form it into a target shape; and a curing step of heating the prepreg for forming carbon fiber reinforced plastics at a temperature of 180°C or higher to cure the electrolytically activated epoxy resin.

6. The method for producing a thermosetting carbon fiber reinforced plastic according to claim 5, wherein the molding step and the curing step are carried out in parallel.

7. The method for producing thermosetting carbon fiber reinforced plastics according to claim 5, wherein the heating temperature in the curing step is 180°C or higher and 300°C or lower.

8. A joint of metal and thermosetting carbon fiber reinforced plastic, comprising: a first member made of metal; a second member made of thermosetting carbon fiber reinforced plastic; and an adhesive layer made of an electrodeposition coating film formed on the surface of the first member, wherein the first member and the second member are joined to each other via the adhesive layer.

9. A joint between metal and thermosetting carbon fiber reinforced plastic according to claim 8, wherein the electrodeposition coating in the adhesive layer is made of an electrolytically activated epoxy resin.

10. A joint between metal and thermosetting carbon fiber reinforced plastic according to claim 9, wherein the thermosetting carbon fiber reinforced plastic comprises carbon fiber and electrolytically activated epoxy resin.

11. A joint between metal and thermosetting carbon fiber reinforced plastic according to claim 9 or 10, wherein the electrolytically activated epoxy resin is a novolac phenol polyepoxy resin.

12. A method for manufacturing a bonded body of metal and thermosetting carbon fiber reinforced plastic, comprising: an adhesive layer forming step of immersing a first member made of metal in a cationic electrodeposition paint made of electrolytically activated epoxy resin dispersed in water, applying a voltage using the first member as a cathode to precipitate the electrolytically activated epoxy resin on the surface of the first member, and heating the first member electrodeposited with the cationic electrodeposition paint at a temperature of 180°C or less to remove moisture, thereby forming an adhesive layer made of the electrodeposition paint on the surface of the first member; an overlapping step of overlapping the prepreg for forming thermosetting carbon fiber reinforced plastic on the first member so that the prepreg for forming thermosetting carbon fiber reinforced plastic comes into contact with the adhesive layer; and a curing step of heating the overlapped first member and the prepreg for forming thermosetting carbon fiber reinforced plastic at a temperature of 180°C or more to cure the electrolytically activated epoxy resin.

13. A method for producing a joint of metal and thermosetting carbon fiber reinforced plastic according to claim 12, wherein the prepreg for forming thermosetting carbon fiber reinforced plastic is produced by a prepreg production method including: a prepreg electrodeposition process in which a carbon fiber material formed by combining carbon fibers is immersed in a cationic electrodeposition paint in which an electrolytically activated epoxy resin is dispersed in water, and a voltage is applied using the carbon fiber material as a cathode to precipitate the electrolytically activated epoxy resin on the surface of the carbon fiber; and a prepreg heating and dehydration process in which the carbon fiber material electrodeposited with the cationic electrodeposition paint is heated at a temperature of 180°C or less to remove moisture.

14. A method for manufacturing a joint between metal and thermosetting carbon fiber reinforced plastic as set forth in claim 12 or 13, wherein the heating temperature in the adhesive layer forming step is 100°C or higher and 180°C or lower.

15. A method for producing a joint between metal and thermosetting carbon fiber reinforced plastic as described in claim 12 or 13, wherein in the overlapping step, the prepreg for forming thermosetting carbon fiber reinforced plastic is overlapped on the first member while being heated at a temperature of 180°C or less.

16. A method for producing a joint between metal and thermosetting carbon fiber reinforced plastic as set forth in claim 15, wherein the heating temperature in the overlapping step is 100°C or higher and 180°C or lower.

17. A method for producing a joint between metal and thermosetting carbon fiber reinforced plastic as set forth in claim 12 or 13, wherein the heating temperature in the curing step is 180°C or higher and 300°C or lower.

Images