Conductive paper and method for manufacturing the same, metal bonded body and method for manufacturing the same

Abstract

The present invention relates to an electrically conductive paper, a method for producing the same, a metal bonded body, and a method for producing the same, the electrically conductive paper comprising: a paper base material containing at least carbon fibers and fibrillated fibers, the content of the fibrillated fibers being 10 to 120 mass% relative to the carbon fibers; and a cured product of a thermosetting resin, at least a part of which is impregnated in the paper base material. Further, the present invention relates to a method for producing an electrically conductive paper, wherein a slurry containing carbon fibers and fibrillated fibers, the content of the fibrillated fibers being 10 to 120 mass% relative to the carbon fibers, is prepared, the slurry is papered to obtain a paper base material, a thermosetting resin is impregnated in the paper base material, and the paper base material impregnated with the thermosetting resin is heated to cure the thermosetting resin.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrically conductive paper and a method for manufacturing the same, and a metal bonded body and a method for manufacturing the same.

[0002] This application claims priority based on Japanese Patent Application No. 2024-071548 filed on April 25, 2024, and the contents thereof are incorporated herein. BACKGROUND

[0003] An electrically conductive paper containing an electrically conductive material such as a carbon fiber is used for electric conduction between product constituent members, and since it can utilize the properties of paper to impart functions other than electrical conductivity, it can be used for various purposes such as a ground brush of a complex shape, a separator of a fuel cell, a gas diffusion electrode material, an electromagnetic wave absorbing material, and the like.

[0004] Patent Literature 1 discloses a porous electrically conductive sheet obtained by papermaking a slurry containing electrically conductive particles having a particle diameter of less than 1 μm, electrically conductive particles having a particle diameter of 5 to 100 μm, carbon fibers, and organic fibers, and an electrode material using the same.

[0005] Patent Literature 2 discloses a separator for a fuel cell obtained by sandwiching a resin composition containing an ethylene-vinyl alcohol copolymer and an electrically conductive material between a plurality of composite sheets obtained by papermaking a slurry containing a polyolefin-based resin fiber, a particulate electrically conductive material, and a fibrous electrically conductive material, and integrally bonding by fusion.

[0006] In recent years, with the continuous advancement of the practicalization of electric vehicles, a potential difference and a current are sometimes generated between a rotating member such as a shaft and a fixed member such as a housing, causing problems. For example, an electric motor of an inverter drive type generates a shaft voltage caused by a potential difference between a stator and a rotor, and when a current derived from the shaft voltage passes through a rolling bearing that supports the shaft, the rolling bearing is damaged, and a problem called "electric erosion" occurs. In addition, a voltage and a current generated from various electronic control parts located near the rotating member are sometimes generated as noise components of a switch or the like, and via the rotating member, the other electronic control parts are affected, causing an electromagnetic compatibility problem.

[0007] The above are problems caused by the absence of an electrically conductive path between the rotating member and the fixed member, and as a countermeasure, in addition to the use of high-strength materials such as metal materials and crosslinked rubber materials, the use of an electrically conductive paper as a paper material has been studied. Electrically conductive paper is high in flexibility and processability, and in addition, is thin in thickness, and thus is excellent in attachability and can be attached to members of various shapes. In addition, since it is low in hardness, in the case where there is a differential rotational speed with the counter surface (metal member), it is possible to suppress the abrasion of the counter surface. It is also high in its own abrasion resistance. In addition, since it is porous, it can exclude an oil film and exhibit electrical conductivity, and thus is also suitable for members that are subjected to oil lubrication.

[0008] However, the electrical conductivity of conventional electrically conductive paper is significantly inferior to that of metal members. Therefore, in order to ensure sufficient electrical conductivity, it is necessary to increase the area and increase the load. Increasing the area and increasing the load can result in an increase in drag torque and a decrease in durability, and the like.

[0009] In addition, the electrically conductive path between the rotating member and the fixed member is also required to have strength that can cope with shear deformation caused by a differential rotational speed with the counter surface, and heat resistance that can withstand sliding heat, but conventional electrically conductive paper does not satisfy these requirements. For example, the porous electrically conductive sheet of Patent Literature 1 and the fuel cell separator of Patent Literature 2 are reinforced by resin, but since the resin is a thermoplastic resin, it softens due to sliding heat, thereby reducing the strength. Also, the fuel cell separator of Patent Literature 2 sandwiches a resin composition between the composite sheets, and thus is poor in oil film exclusion and has poor electrical conductivity in an oil environment.

[0010] Prior Art Documents

[0011] Patent Literature

[0012] Patent Literature 1: Japanese Patent Application Laid-Open No. 2014-103030

[0013] Patent Literature 2: Japanese Patent Application Laid-Open No. 2020-145014 SUMMARY

[0014] PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] The present application was completed in view of the above, and aims to provide an electrically conductive paper that is excellent in electrical conductivity, strength, and heat resistance, a method for manufacturing the same, and a metal bonded body using the same and a method for manufacturing the same.

[0016] SOLUTION TO THE PROBLEM

[0017] The present application has the following solutions.

[0018] [1] An electroconductive paper, wherein: a paper base material containing at least carbon fibers and fibrillated fibers at a content of 10 to 120 mass% relative to the carbon fibers; and a cured product of a thermosetting resin, at least a part of which is impregnated in the paper base material.

[0019] [2] The electroconductive paper according to the [1], wherein the proportion of the carbon fibers contained in the paper base material is 35 to 90 mass%.

[0020] [3] The electroconductive paper according to the [1] or [2], wherein the proportion of the cured product of the thermosetting resin contained in the electroconductive paper is 10 to 55 mass%.

[0021] [4] A method for manufacturing an electroconductive paper, wherein: a slurry containing at least carbon fibers and fibrillated fibers at a content of 10 to 120 mass% relative to the carbon fibers is prepared, the slurry is subjected to papermaking to obtain a paper base material, a thermosetting resin is impregnated in the paper base material, and the paper base material impregnated with the thermosetting resin is heated to cure the thermosetting resin.

[0022] [5] The method for manufacturing an electroconductive paper according to the [4], wherein the proportion of the carbon fibers contained in the paper base material is 35 to 90 mass%.

[0023] [6] The method for manufacturing an electroconductive paper according to the [4] or [5], wherein the proportion of the cured product of the thermosetting resin contained in the electroconductive paper is 10 to 55 mass%.

[0024] [7] A metal bonded body, wherein: a metal member; and the electroconductive paper according to any one of the [1] to [3] is chemically or mechanically bonded to a surface of the metal member.

[0025] [8] A method for manufacturing a metal bonded body, wherein the electroconductive paper according to any one of the [1] to [3] is chemically or mechanically bonded to a surface of a metal member.

[0026] Effects of Invention

[0027] According to the present application, it is possible to provide an electroconductive paper excellent in electroconductivity, strength, and heat resistance, a method for manufacturing the same, and a metal bonded body using the electroconductive paper and a method for manufacturing the same. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present application will be described. The present application is not limited to the following embodiments, and various modifications can be made without departing from the spirit of the present application.

[0029] In the present specification, "~" indicating a numerical range means that the numerical values recited before and after it are included as lower limit values and upper limit values.

[0030] [Conductive paper]

[0031] The conductive paper of one embodiment of the present application includes a paper base material and a cured product of a thermosetting resin. At least a part of the cured product of the thermosetting resin is impregnated in the paper base material.

[0032] [Paper base material]

[0033] The paper base material contains at least carbon fibers and fibrillated fibers.

[0034] The carbon fibers are fibrous carbon-based substances.

[0035] The carbon fibers constitute the skeleton of the paper base material. In addition, the carbon fibers form a conductive network in the paper base material, and exhibit conductivity.

[0036] The fiber length of the carbon fibers in the paper base material is preferably 0.1 mm to 6.5 mm, more preferably 0.3 mm to 2.0 mm. When the fiber length is greater than or equal to the lower limit value, the carbon fibers easily form a mesh structure in the paper base material, and there is a tendency that the conductivity of the conductive paper is improved. When the fiber length is less than or equal to the upper limit value, the reinforcing effect of the fibrillated fibers is increased, and there is a tendency that the strength of the conductive paper is improved.

[0037] The fiber length of the carbon fibers in the paper base material and the conductive paper is measured by the following method: the carbon fibers are taken out by thermal decomposition and stirring, and the taken-out fibers are subjected to image analysis.

[0038] The fiber diameter of the carbon fibers is preferably 6 to 15 μm, more preferably 7 to 10 μm. When the fiber diameter is greater than or equal to the lower limit value, the amount of charges that can move in a single fiber is increased, and there is a tendency that the conductivity of the single fiber is excellent. When the fiber diameter is less than or equal to the upper limit value, the number of carbon fibers included in the paper base material is increased relative to the weight of the carbon fibers, and there is a tendency that the conductive network property is excellent. The range of the fiber diameter of the carbon fibers is determined in balance between the improvement of the conductivity of the single fiber and the improvement of the conductive network property.

[0039] The fiber diameter is measured by microscopic observation of the cross section of the carbon fibers generated by laser light or the like with an electron microscope or the like. In the case of fibers having a flat cross section, the average of the major axis and the minor axis is set to the fiber diameter.

[0040] As the carbon fibers used in this embodiment, polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, phenol-based carbon fibers, rayon-based carbon fibers, and the like can be given.

[0041] The carbon fibers can be used alone or in combination of two or more kinds.

[0042] The proportion of the carbon fiber contained in the paper base material is preferably 35 to 90 mass% and more preferably 50 to 80 mass% relative to the total mass of the paper base material. When the proportion of the carbon fiber is equal to or greater than the lower limit value, the electrically conductive network property of the carbon fiber is improved, and the electrically conductive paper has a tendency to have more excellent electric conductivity. When the proportion of the carbon fiber is equal to or less than the upper limit value, the proportion of the fibrillated fiber that can be incorporated is increased, and the strength of the electrically conductive paper is improved.

[0043] The fibrillated fiber is a fiber in which the fibril component of the organic fiber is made to be in a fluffed state by beating the organic fiber.

[0044] The fibrillated fiber forms a skeleton of the paper base material together with the carbon fiber. In addition, since the paper base material contains the fibrillated fiber, the entanglement between the fibers is increased, and the strength of the paper base material and the electrically conductive paper is improved. Furthermore, the content of the carbon fiber in the paper base material is reduced by containing the fibrillated fiber, but the contact points between the carbon fibers are increased due to the entanglement improvement effect of the fibrillated fiber, and thus the electrically conductive network property of the paper base material is improved, and the electrically conductive paper has improved electric conductivity.

[0045] The degree of fibrillation of the fibrillated fiber is quantified based on the degree of filtration and the specific surface area. In particular, quantification based on the degree of filtration is simple, and serves as an index of the ease of entanglement, and thus is often used to evaluate the degree of fibrillation.

[0046] The degree of filtration of the fibrillated fiber is preferably 50 to 700 mL and more preferably 150 to 600 mL. The degree of filtration is one of the indices of fibrillation. When the degree of filtration is equal to or less than the upper limit value, the fibers are sufficiently entangled with each other, and the electrically conductive paper has a tendency to have more excellent strength and electric conductivity. When the degree of filtration is equal to or greater than the lower limit value, the oil film removal property is maintained, and the electrically conductive paper has a tendency to have more excellent electric conductivity under oil lubrication.

[0047] The degree of filtration is the Canadian Standard Freeness determined in accordance with JIS P 8121-2:2012.

[0048] As the organic fiber in the fibrillated fiber, any fiber that can be fibrillated can be used, and examples thereof include cellulose fibers, aramid fibers, acrylic fibers, and polyolefin fibers.

[0049] As the cellulose fiber, for example, plant cellulose fibers classified into seed hair fibers, bast fibers, and leaf vein fibers, using cotton, hemp, and the like as the main raw material; regenerated cellulose fibers obtained by extracting cellulose from trees and wood and chemically treating the cellulose; and acetates obtained by acetylating part or all of the hydroxyl groups in cellulose through a chemical reaction with respect to cellulose, i.e., semi-synthetic fibers.

[0050] As the aramid fiber (aromatic polyamide fiber), for example, there can be mentioned: poly-p-phenylene terephthalamide, copoly-p-phenylene-3,4' oxydiphenylene-p-terephthalamide, poly-m-phenylene isophthalamide.

[0051] As the acrylic fiber, for example, there can be mentioned: polyacrylonitrile, acrylonitrile polymer, acrylonitrile copolymer.

[0052] As the polyolefin fiber, for example, there can be mentioned: polyethylene, polypropylene, ethylene-propylene copolymer, polycycloolefin, polymethylpentene.

[0053] As the organic fiber, from the viewpoint of heat resistance, it is preferable to use an aramid fiber, an acrylic fiber, a polyolefin fiber.

[0054] The fibrillated fiber can be used singly or in combination of two or more kinds.

[0055] The content of the fibrillated fiber is 10 to 120 mass% relative to the carbon fiber, and more preferably 30 to 100 mass%. When the content of the fibrillated fiber is equal to or more than the lower limit value, the fibers are sufficiently entangled with each other, and the strength and the conductivity of the conductive paper are excellent. When the content of the fibrillated fiber is equal to or less than the upper limit value, the conductive network property of the carbon fiber can be sufficiently ensured, and the conductivity is excellent.

[0056] In a range not obstructing the object of the present application, the paper base material can further contain other components in addition to the carbon fiber and the fibrillated fiber.

[0057] As the other components, for example, there can be mentioned: a fiber dispersing agent, a paper strength agent, a coagulant, a thermoplastic resin having a function as a so-called binder component, a fibrous or particulate organic compound, a fibrous or particulate inorganic compound.

[0058] The other components can be used singly or in combination of two or more kinds.

[0059] <Curds of thermosetting resin>

[0060] The curds of the thermosetting resin function as a reinforcing material for reinforcing the paper base material. At least a part of the curds of the thermosetting resin is impregnated in the paper base material, whereby the strength of the conductive paper is excellent. Further, the curds of the thermosetting resin have excellent heat resistance as compared with the thermoplastic resin, and therefore even in a case where the temperature is increased due to sliding heat or the like, the strength of the conductive paper is not easily reduced, and the heat resistance of the conductive paper is excellent.

[0061] As the thermosetting resin, as long as it is a substance in a varnish state capable of being impregnated and subjected to heat curing, for example, there can be mentioned: a phenol resin, a modified phenol resin, an epoxy resin, a modified epoxy resin, a polyimide resin, a silicone resin, a polyester resin, a polyurethane resin, a rubber resin.

[0062] As the modifying component of the modified phenol resin, modified epoxy resin, there can be mentioned oil, rubber, Cashew, acrylic acid, a component of natural origin.

[0063] As the rubber resin, a cured product of liquid rubber is suitable. As the liquid rubber, there can be mentioned, for example, liquid butadiene rubber, liquid isoprene rubber, liquid styrene butadiene rubber, liquid fluororubber, liquid silicone rubber, liquid urethane rubber. In addition to the use of a crosslinking agent such as isocyanate, various agents for promoting crosslinking reaction can be used for the curing of the liquid rubber.

[0064] In a range not obstructing the object of the present application, a component other than the resin component can also be added to the thermosetting resin. As the component other than the resin component, there can be mentioned, for example, a surface tension adjusting agent contained or added in the resin solution for improving the impregnability, a fibrous or particulate organic compound or inorganic compound.

[0065] As the thermosetting resin, from the viewpoint of heat resistance, oil resistance, strength, a phenol resin, modified phenol resin is preferred.

[0066] The thermosetting resin can be used singly or in combination of two or more.

[0067] The proportion of the cured product of the thermosetting resin contained in the conductive paper is preferably 10 to 55 mass%, more preferably 20 to 40 mass% relative to the total mass of the conductive paper. When the proportion of the cured product of the thermosetting resin is equal to or more than the lower limit value, there is a tendency that the strength is more excellent. When the proportion of the cured product of the thermosetting resin is equal to or less than the upper limit value, there is a tendency that the conductivity, oil film exclusion property is more excellent.

[0068] <Properties of the conductive paper>

[0069] The porosity of the conductive paper is preferably 30 to 95%, more preferably 50 to 90%. When the porosity is equal to or less than the upper limit value, the strength, conductivity is more excellent. When the porosity is equal to or more than the lower limit value, the oil film exclusion property is improved, the conductivity under oil lubrication is more excellent.

[0070] The porosity is a value measured by a mercury porosimeter.

[0071] The conductive paper of the present embodiment is preferably a conductive paper capable of withstanding the differential rotational speed with the rotating member, and as an index of the strength, there can be mentioned the shear strength.

[0072] The shear strength of the conductive paper is preferably 0.1 MPa or more, more preferably 0.2 MPa or more. When the shear strength is equal to or more than the lower limit value, the load capacity to the conductive paper is improved, and therefore it is useful in applications requiring high conductivity.

[0073] The thickness of the conductive paper is preferably 0.2 to 1.5 mm, more preferably 0.3 mm to 1.0 mm. When the thickness of the conductive paper is equal to or greater than the lower limit value, the durability life is more excellent due to abrasion and collapse. When the thickness is equal to or less than the upper limit value, the distance of the electric conduction in the thickness direction of the conductive paper is shortened, and thus the electric conductivity in the thickness direction of the conductive paper is more excellent.

[0074] <Method for producing conductive paper>

[0075] The conductive paper of the present embodiment can be produced by, for example, the following method.

[0076] A slurry containing at least carbon fibers and fibrillated fibers in an amount of 10 to 120 mass% relative to the carbon fibers is prepared, a paper base material is obtained by papermaking the slurry, a thermosetting resin is impregnated in the paper base material, and the paper base material impregnated with the thermosetting resin is heated to cure the thermosetting resin.

[0077] (Preparation of slurry)

[0078] The slurry can be prepared by dispersing the carbon fibers, the fibrillated fibers, and other components as needed in water.

[0079] The carbon fibers, the fibrillated fibers, and other components can each be commercially available or can be produced by a publicly known method. The fibrillated fibers are obtained by, for example, fibrillating fibers by a publicly known method. As the method for fibrillating, for example, a method of beating fibers using a beater, a refiner, or the like can be exemplified.

[0080] The dispersing method is not particularly limited, and a method conventionally used for preparing a paper slurry in the production of paper can be applied. For example, a disintegrator (pulper), a beater, a refiner, or the like can be used.

[0081] (Papermaking)

[0082] The papermaking (wet papermaking) of the slurry can be performed by a publicly known method. For example, a Fourdrinier former or a cylinder former can be used.

[0083] As needed, in order to improve the strength of the paper base material, a solution of a thermoplastic resin can be impregnated in a papermaking material formed by the papermaking to obtain a paper base material by coating or impregnation.

[0084] In addition, components other than the resin component can be contained in the solution of the thermoplastic resin within a range not impeding the object of the present application. As the components other than the resin component, for example, a surface tension adjusting agent, a fibrous or particulate organic compound, or an inorganic compound contained or added in the resin solution for improving the impregnation can be exemplified.

[0085] (impregnation of thermosetting resin)

[0086] As a method of impregnating the thermosetting resin into the paper base material, a method of impregnating a varnish containing the thermosetting resin and a solvent into the paper base material by coating or dipping and drying (removing the solvent) is preferable. By thus impregnating the thermosetting resin, the paper base material as a whole can be uniformly strengthened by the thermosetting resin, as compared with the case where the thermosetting resin is internally added to the paper base material.

[0087] As the solvent of the varnish, any solvent can be used as long as it can dissolve the thermosetting resin. In order to improve the impregnability into the paper base material, a solvent having a low viscosity is preferable, and in order to easily remove the solvent, a solvent having a high volatility is preferable.

[0088] In a range not obstructing the object of the present application, a component other than the resin component can be contained in the varnish. As the component other than the resin component, for example, a surface tension adjusting agent, a fibrous or particulate organic compound or inorganic compound contained or added in the resin solution for improving the impregnability can be exemplified.

[0089] As a method of impregnating the varnish into the paper base material, for example, a method of coating the varnish on one side or both sides of the paper base material, a method of dipping the paper base material in the varnish can be exemplified.

[0090] As the drying, any drying can be used as long as the solvent of the varnish can be removed, and can be heating drying or air drying. The temperature of the heating drying is, for example, 50 to 200°C.

[0091] (curing)

[0092] As the heating condition of the paper base material impregnated with the thermosetting resin, any condition can be used as long as the thermosetting resin can be cured, and can be appropriately selected depending on the thermosetting resin used. In the case of a phenol resin, it is generally 120 to 300°C for 10 to 100 minutes or so.

[0093] After the curing, surface polishing, additional heating, compression molding, hot-pressing, chemical or mechanical adhesion to a metal or non-metal member, or the like can be performed as needed.

[0094] <Usage of conductive paper>

[0095] The conductive paper of the present embodiment is excellent in conductivity, strength, and heat resistance. Therefore, it is preferably used for a use requiring these properties.

[0096] As one preferable example of the use of the conductive paper of the present embodiment, formation of a conductive path between a rotating member and a fixed member can be exemplified. Among them, formation of a conductive path for preventing electric erosion of a bearing supporting an inverter control motor is preferable.

[0097] In the conductive path use, for example, the conductive paper is chemically or mechanically bonded to the surface of the metal member, and becomes a metal bonded body. In this metal bonded body, the conductive paper can be used as a conductive path. For example, metal members having a potential difference can be grounded by the conductive paper.

[0098] The metal member is not particularly limited, and for example, as a rotating member, a bearing, a shaft, a housing, a shaft accessory, and a housing accessory can be cited.

[0099] The metal bonded body of the present embodiment can be manufactured by a method in which the conductive paper of the present embodiment is chemically or mechanically bonded to the surface of the metal member.

[0100] As the method of chemically or mechanically bonding the conductive paper, for example, a method of bonding the conductive paper to the metal member by chemical reaction with an adhesive, a method of chemically adsorbing and bonding the conductive paper to the metal member by the adhesive component of a tape, and a method of mechanically fixing and bonding the conductive paper to the metal member by riveting or concave-convex can be cited.

[0101] [EXAMPLES]

[0102] The present application is specifically described below by examples, but the present application is not limited to the following description.

[0103] (Production of conductive paper)

[0104] First, the conductive paper of Example 1 and Comparative Examples 1 to 3 was produced.

[0105] Example 1 satisfies all of the following conditions: the condition in the present application that the content of fibrillated fibers in the paper base material is 43 mass% relative to the carbon fibers; the condition that the proportion of the carbon fibers contained in the paper base material is 66 mass%; the condition that the proportion of the cured product of the thermosetting resin in the conductive paper obtained from the same paper base material is 20 mass%; and the condition of the manufacturing method of obtaining the paper base material by papermaking of the slurry, impregnating the thermosetting resin therein, and curing it. Specifically, in the conductive paper of Example 1, the content of fibrillated fibers in the paper base material is 43 mass% relative to the carbon fibers, the content proportion of the carbon fibers in the paper base material is 66 mass%, and the content proportion of the cured product of the thermosetting resin in the conductive paper is 20 mass%. In addition, in the manufacturing method of the conductive paper of Example 1, a slurry containing carbon fibers, fibrillated fibers, and other components, the content of fibrillated fibers being 43 mass% relative to the carbon fibers, is prepared, the paper base material is obtained by papermaking of the slurry, a varnish of the thermosetting resin is impregnated into the paper base material, and the paper base material impregnated with the thermosetting resin is heated to cure the thermosetting resin.

[0106] Comparative Example 1 does not satisfy the condition of the content of the fibrillated fiber with respect to the carbon fiber in the present application, and the paper base material does not contain the fibrillated fiber. Specifically, in the conductive paper of Comparative Example 1, the content of the fibrillated fiber in the paper base material with respect to the carbon fiber is 0 mass%, the content ratio of the carbon fiber in the paper base material is 95 mass%, and the content ratio of the cured product of the thermosetting resin in the conductive paper is 20 mass%. In addition, in the production method of the conductive paper of Comparative Example 1, a slurry containing the carbon fiber and other components is prepared, the paper base material is obtained by papermaking the slurry, the varnish of the thermosetting resin is impregnated in the paper base material, and the thermosetting resin is cured by heating the paper base material impregnated with the thermosetting resin.

[0107] Comparative Example 2 does not satisfy the condition of the content of the fibrillated fiber with respect to the carbon fiber in the present application, and the content of the fibrillated fiber in the paper base material with respect to the carbon fiber is small. Specifically, in the conductive paper of Comparative Example 2, the content of the fibrillated fiber in the paper base material with respect to the carbon fiber is 5 mass%, the content ratio of the carbon fiber in the paper base material is 90 mass%, and the content ratio of the cured product of the thermosetting resin in the conductive paper is 20 mass%. In addition, in the production method of the conductive paper of Comparative Example 2, a slurry containing the carbon fiber, the fibrillated fiber, and other components is prepared, the content of the fibrillated fiber with respect to the carbon fiber is 5 mass%, the paper base material is obtained by papermaking the slurry, the varnish of the thermosetting resin is impregnated in the paper base material, and the thermosetting resin is cured by heating the paper base material impregnated with the thermosetting resin.

[0108] Comparative Example 3 does not satisfy the condition of the content of the fibrillated fiber with respect to the carbon fiber in the present application, and the content of the fibrillated fiber in the paper base material with respect to the carbon fiber is large. Specifically, in the conductive paper of Comparative Example 3, the content of the fibrillated fiber in the paper base material with respect to the carbon fiber is 156 mass%, the content ratio of the carbon fiber in the paper base material is 37 mass%, and the content ratio of the cured product of the thermosetting resin in the conductive paper is 20 mass%. In addition, in the production method of the conductive paper of Comparative Example 3, a slurry containing the carbon fiber, the fibrillated fiber, and other components is prepared, the content of the fibrillated fiber with respect to the carbon fiber is 156 mass%, the paper base material is obtained by papermaking the slurry, the varnish of the thermosetting resin is impregnated in the paper base material, and the thermosetting resin is cured by heating the paper base material impregnated with the thermosetting resin.

[0109] That is, Comparative Examples 1 to 3 are conductive papers produced by the same production method as that of Example 1, but do not satisfy the condition of the content of the fibrillated fiber in the paper base material with respect to the carbon fiber, and are outside the scope of the present application.

[0110] The raw materials used in Example 1 and Comparative Examples 1 to 3 were completely the same. As the carbon fiber, PAN-based carbon fiber having a fiber diameter of 7 μm and a fiber length of 2 mm was used in the paper base material, as the fibrillated fiber, aramid fiber having a filterability of 300 mL was used, and as the other components, a thermoplastic resin, a paper strength agent, and a coagulant were used in the same amounts of the components and in a total content of 5 mass% in the paper base material.

[0111] Further, the thickness of the conductive paper of Example 1 and Comparative Examples 1 to 3 was set to 0.5 mm.

[0112] (Evaluation of the conductive paper)

[0113] Next, the strength and the conductivity of the conductive paper of Example 1 and Comparative Examples 1 to 3 were evaluated. The results are shown in Table 1.

[0114] The strength was evaluated by a shear strength measurement of the conductive paper. The shear strength measurement was performed by the following method: the front and back surfaces of the conductive paper were fixed to iron plates, respectively, the iron plates were moved in the shear direction, i.e., in a direction perpendicular to the thickness direction of the conductive paper, and the iron plates of the front and back surfaces were moved in opposite directions, whereby the conductive paper was sheared and deformed, and the maximum shear stress at which the conductive paper was broken by shearing was taken as the shear strength.

[0115] The size of the conductive paper at the time of the shear strength measurement was performed in a Φ3 mm.

[0116] The conductivity was evaluated by the following method: a ring-shaped conductive paper having an inner diameter of φ38.5 mm and an outer diameter of φ55.8 mm was prepared, the front and back surfaces of the inner diameter side of the ring-shaped conductive paper were sandwiched with a ring-shaped copper plate having an inner diameter of φ33 mm and an outer diameter of φ45 mm, and the front and back surfaces of the outer diameter side of the ring-shaped conductive paper were sandwiched with a ring-shaped copper plate having an inner diameter of φ49 mm and an outer diameter of 61 mm, an electrically conductive path from the copper plate of the inner diameter side of the conductive paper to the copper plate of the outer diameter side of the conductive paper was formed on the conductive paper, and the resistance value, i.e., the impedance, of the alternating current of the electrically conductive path was measured. Here, the sandwiching pressure of the copper plates was set to 50 N on the inner diameter side and the outer diameter side of the conductive paper, respectively. Further, the reciprocal of the measured impedance was evaluated for the conductivity.

[0117] The evaluation results for the strength and the conductivity were represented by the relative values in the case where the value of Comparative Example 1 was taken as 100, and in the case where the evaluation value was greater than 100, it was judged that the performance was improved.

[0118] [Table 1]

[0119]

[0120] From Table 1, in Example 1, the evaluation values of strength and conductivity are greater than 100, and are the highest among Comparative Examples 1 to 3. The performance of Comparative Example 2 is improved relative to Comparative Example 1, but the effect is not sufficiently large. The conductivity of Comparative Example 3 is reduced relative to Comparative Example 1. Thus, the conductive paper of Example 1 can sufficiently improve strength and conductivity.

Claims

1. An electrically conductive paper, wherein, contains: a paper base material containing at least carbon fibers and fibrillated fibers, the content of the fibrillated fibers being 10 to 120 mass% relative to the carbon fibers; and a cured product of a thermosetting resin, at least a part of which is impregnated in the paper base material, the fiber length of the carbon fibers is 0.3 mm to 2.0 mm, the water permeability of the fibrillated fibers is 150 to 600 mL, the proportion of the cured product of the thermosetting resin contained in the conductive paper is 10 to 55 mass%.

2. The conductive paper according to claim 1, wherein the proportion of the carbon fibers contained in the paper base material is 35 to 90 mass%.

3. A method for producing a conductive paper, wherein a slurry containing at least carbon fibers and fibrillated fibers, the content of the fibrillated fibers being 10 to 120 mass% relative to the carbon fibers, is prepared, a paper base material is obtained by papermaking the slurry, a thermosetting resin is impregnated in the paper base material, the paper base material impregnated with the thermosetting resin is heated to cure the thermosetting resin, the fiber length of the carbon fibers is 0.3 mm to 2.0 mm, the water permeability of the fibrillated fibers is 150 to 600 mL, the proportion of the cured product of the thermosetting resin contained in the conductive paper is 10 to 55 mass%.

4. The method for producing a conductive paper according to claim 3, wherein the proportion of the carbon fibers contained in the paper base material is 35 to 90 mass%.

5. A metal bonding body, wherein, provided with: a metal member; and a conductive paper chemically or mechanically bonded to a surface of the metal member, the conductive paper contains: a paper base material containing at least carbon fibers and fibrillated fibers, the content of the fibrillated fibers being 10 to 120 mass% relative to the carbon fibers; and a cured product of a thermosetting resin, at least a part of which is impregnated in the paper base material, the fiber length of the carbon fibers is 0.3 mm to 2.0 mm, the water permeability of the fibrillated fibers is 150 to 600 mL.

6. A metal bonding body, wherein provided with: a metal member; and the conductive paper according to claim 1 or 2 chemically or mechanically bonded to a surface of the metal member.

7. A method for producing a metal-bonded body, wherein a conductive paper is chemically or mechanically bonded to a surface of a metal member, the conductive paper contains: a paper base material containing at least carbon fibers and fibrillated fibers, the content of the fibrillated fibers being 10 to 120 mass% relative to the carbon fibers; and a cured product of a thermosetting resin, at least a part of which is impregnated in the paper base material, the fiber length of the carbon fibers is 0.3 mm to 2.0 mm, the water permeability of the fibrillated fibers is 150 to 600 mL.

8. A method for producing a metal-bonded body, wherein the conductive paper according to claim 1 or 2 is chemically or mechanically bonded to a surface of a metal member.

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