Electroplated carbon fiber having electroplated layer and method for producing thereof

Abstract

An object is to provide an electroplated carbon fiber having a stable electroplated layer. Another object is to provide a method for readily producing an electroplated carbon fiber having a stable electroplated layer. An electroplated carbon fiber having an electroplated layer on a surface of a carbon fiber via an amorphous carbon layer. A method for producing an electroplated carbon fiber, the method includes a step of preparing a carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon, a step of subjecting the carbon-fiber tow to an opening process to obtain carbon fiber monofilaments, and a step of subjecting the carbon fiber monofilaments to electroplating.

Description

TECHNICAL FIELD

[0001] The present invention relates to an electroplated carbon fiber having an electroplated layer, a carbon-fiber-reinforced metal comprising the electroplated carbon fiber, an electrically-conductive material comprising the electroplated carbon fiber, an electromagnetic wave absorption material comprising the electroplated carbon fiber, and a method for producing an electroplated carbon fiber.BACKGROUND ART

[0002] Subjecting carbon fibers to metal plating has been considered to contribute to improvement of usability of the carbon fibers. Carbon fibers having been subjected to metal plating can be used as a material of a carbon-fiber-reinforced metal (CFRM) by being mixed with a matrix metal, for example. In accordance with the kind of the metal plating to which the carbon fibers are subjected, various characteristics can be imparted to the carbon fibers. For example, carbon fibers imparted with electric conductivity can be used as an electrically-conductive material for reducing the weight of a wire harness and the like, and can be used as a lightning protection material if the carbon fibers are attached to a surface layer portion and the like of an aircraft airframe. Carbon fibers imparted with electromagnetic wave absorption property can be used as a material of electronic devices and the like. Carbon fibers imparted with heat resistance or oxidation resistance can be used as a material of heat resistant packings, mechanical seals, and the like.

[0003] As a technology for subjecting carbon fibers to metal plating, for example, Patent Document 1 describes a method in which: a compound having an aromatic ring is caused to undergo oxidative polymerization to generate a fibril-like polymer; and carbon fibers generated by calcining the fibril-like polymer are subjected to surface treatment with an alkaline degreasing liquid and then electroplating. In the method, performing calcination at 500 to 3000° C. is recommended. Patent Document 2 discloses a plated fiber obtained by subjecting a carbon fiber having a surface concentration of oxygen controlled in a predetermined range, to metal plating. In Patent Document 2, it is indicated that the surface oxygen amount of the carbon fiber can be changed by exposing the carbon fiber to carbon dioxide in a supercritical state, and it is recommended to perform electroplating such that the carbon fiber is metal-plated.RELATED ART DOCUMENTPatent DocumentPatent Document 1: JP-A-2007-186823

[0005] Patent Document 2: JP-A-2016-194176SUMMARY OF THE INVENTIONProblems to be Solved by the Invention

[0006] In Patent Document 1, it was necessary to perform calcination at 500 to 3000° C. and then perform surface treatment using an alkaline degreasing liquid, and thus, the operation was complicated. In Patent Document 2, it was necessary to prepare carbon dioxide in a supercritical state, which caused increase in size of the apparatus. In both Patent Documents, it was not easy to say that a stable plating structure was formed.

[0007] An object of the present invention is to provide an electroplated carbon fiber having a stable electroplated layer.

[0008] Another object of the present invention is to provide a method for readily producing an electroplated carbon fiber having a stable electroplated layer.Solutions to the Problems

[0009] The present invention is as follows.

[0010] [1] An electroplated carbon fiber having an electroplated layer on a surface of a carbon fiber via an amorphous carbon layer.

[0011] [2] The electroplated carbon fiber according to [1], in which the electroplated layer has an average thickness of 1 μm to 10 μm.

[0012] [3] The electroplated carbon fiber according to [1] or [2], in which the electroplated layer includes a base layer and a surface layer, the base layer contains Ni and P, and

[0013] the surface layer contains at least one element selected from the group consisting of Cu, Ni, Cr, Co, and Fe.

[0014] [4] The electroplated carbon fiber according to any one of [1] to [3],

[0015] in which the carbon fiber having the amorphous carbon layer on the surface thereof has a residual carbon content of 0.5 to 6 mass % measured by heating the carbon fiber under conditions of 600° C.×60 minutes.

[0016] [5] A carbon-fiber-reinforced metal including the electroplated carbon fiber according to any one of [1] to [4] and a matrix metal.

[0017] [6] An electrically-conductive material including the electroplated carbon fiber according to [3] or [4] as a component, in which the surface layer contains Cu.

[0018] [7] A lightning protection material including the electrically-conductive material according to [6].

[0019] [8] An electromagnetic wave absorption material including the electroplated carbon fiber according to [3] or [4] as a component, [1] in which the surface layer contains at least one element selected from the group consisting of Ni, Cr, Co, and Fe.

[0020] [9] A method for producing an electroplated carbon fiber, the method including: a step of preparing a carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon;

[0021] a step of subjecting the carbon-fiber tow to an opening process to obtain carbon fiber monofilaments; and

[0022] a step of subjecting the carbon fiber monofilaments to electroplating.Advantageous Effects of the Invention

[0023] According to the present invention, since the amorphous carbon layer is provided between the carbon fiber and the electroplated layer, an electroplated carbon fiber in which the electroplated layer is uniformly formed on the surface of the carbon fiber can be provided. In addition, according to the present invention, a method that can produce such an electroplated carbon fiber in a simple manner can be provided.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1(a) of FIG. 1 is a photograph, substituting for a drawing, of the cross-section of an electroplated carbon fiber according to the present invention, and (b) of FIG. 1 is an enlarged view of a main part of (a) of FIG. 1.

[0025] FIG. 2 is a photograph, substituting for a drawing, of the cross-section of a carbon fiber obtained by performing a base treatment and a surface treatment to a new carbon fiber monofilament.DESCRIPTION OF EMBODIMENTS

[0026] Since the surface of a carbon fiber is electrically inactive, adhesiveness between the carbon fiber and an electroplated layer is poor even if the surface of the carbon fiber is to be electroplated, and thus, a stable electroplated layer has not been able to be formed on the surface of the carbon fiber. The present inventors conducted studies and found that, when a carbon fiber having an amorphous carbon layer formed on the surface thereof is subjected to electroplating, adhesiveness of the electroplated layer to the carbon fiber is improved. The reason for this is considered to be that the surface of the amorphous carbon is electrically active. In addition, amorphous carbon is also chemically active, and it was found that, when the amorphous carbon layer is formed on the surface of the carbon fiber, adhesiveness between the carbon fiber and the amorphous carbon layer is also improved. Hereinafter, the present invention will be described in detail.

[0027] An electroplated carbon fiber as an embodiment of the present invention has an electroplated layer on the surface of a carbon fiber via an amorphous carbon layer. The amorphous carbon layer is formed on the surface of the carbon fiber, preferably on 80 area % or more of the surface of the carbon fiber, and particularly preferably on the entire surface of the carbon fiber. Here, “forming” means that, for example: in a process of recovering carbon fibers from carbon-fiber-reinforced resin in order to reuse them, when amorphous carbon has been generated through pyrolysis of thermosetting resin or thermoplastic resin covering the carbon fibers, the amorphous carbon is not completely removed, but instead, a mild treatment that allows some of the amorphous carbon to remain is performed, thereby consequently realizing a state where an amorphous carbon layer is formed; or alternatively, a state where an amorphous carbon layer is formed on a newly produced carbon fibers is intentionally realized.

[0028] The amount of the amorphous carbon layer formed on the surface of the carbon fiber can be obtained as a residual carbon content measured by heating the carbon fiber under conditions of 600° C.×60 minutes, for example. The residual carbon content refers to, when the mass of a carbon fiber having an amorphous carbon layer formed on the surface thereof is 100%, the amount of amorphous carbon contained in the carbon fiber, and the proportion of amorphous carbon that is removed through oxidation due to heating under the above temperature conditions, relative to the carbon fiber before being heated.

[0029] Preferably, the residual carbon content is in a range of 0.5 to 6 mass %. In a case where the residual carbon content is 0.5 mass % or more, adhesiveness between the amorphous carbon layer and the electroplated layer and adhesiveness between the amorphous carbon layer and the carbon fiber can be improved. The residual carbon content is preferably 1 mass % or more, and more preferably 2 mass % or more. However, when the residual carbon content is excessively large, adhesiveness between the amorphous carbon layer and the electroplated layer may deteriorate instead. Therefore, the residual carbon content is preferably 6 mass % or less, more preferably 5 mass % or less, and further preferably 4 mass % or less.

[0030] The residual carbon content may be measured by a differential gravimetric analysis method. For example, when change in the mass when carbon fibers having amorphous carbon layers formed on the surfaces thereof have been heated is measured by using a thermogravimetry (TG) apparatus, the residual carbon content can be calculated according to the following formula based on the mass before heating at 600° C. for 60 minutes and the mass after the heating. The atmosphere in which the thermogravimetry is performed is not particularly limited, and may be an air atmosphere in a static state, for example.Residual⁢ carbon⁢ content⁢ (mass⁢ %)=[⁠mass⁢ before⁢ heating-mass⁢ after⁢ heating]⁢⁠ / [mass⁢ before⁢ heating]×100

[0031] The residual carbon content may be measured by the differential gravimetric analysis method, but may also be calculated based on the above formula, for example, by putting a sample in a crucible, heating the sample with a lid put on the crucible at 600° C. for 60 minutes in the air, and measuring the masses before and after the heating.

[0032] Preferably, the electroplated layer is multiple layers composed of two or more layers. In a case where the electroplated layer is composed of two layers, the electroplated layer may include a base layer and a surface layer, the base layer may contain Ni (particularly, Ni and P), and the surface layer may contain at least one element selected from the group consisting of Cu, Ni, Cr, Co, and Fe.Base Layer

[0033] The base layer is a layer for enhancing adhesiveness between the amorphous carbon layer and the surface layer. As the base layer, in a case where a layer containing Ni, particularly, a layer containing Ni and P, is formed, the base layer can be uniformly formed on the surface of the amorphous carbon layer.

[0034] When the mass of the base layer is 100%, the content of Ni in the base layer may be 80 mass % or more and less than 100 mass %, for example. In a case where the content of Ni is 80 mass % or more, adhesiveness between the base layer and the surface layer is improved. The content of Ni is preferably 83 mass % or more, and further preferably 85 mass % or more. However, when the content of Ni is 100 mass %, adhesiveness between the base layer and the amorphous carbon layer may deteriorate instead. Therefore, the content of Ni is preferably less than 100 mass %, more preferably 95 mass % or less, and further preferably 90 mass or less.

[0035] When the mass of the base layer is 100%, the content of P in the base layer may be more than 0 mass % and 20 mass % or less, for example. In a case where the content of P is more than 0 mass %, the base layer is uniformly formed on the surface of the amorphous carbon layer. The content of P is more preferably 0.01 mass % or more, further preferably 1 mass % or more, particularly preferably 5 mass % or more, and most preferably 10 mass % or more. However, when the content of P is more than 20 mass %, adhesiveness between the base layer and the surface layer may deteriorate. Therefore, the content of P is preferably 20 mass % or less, more preferably 18 mass % or less, and further preferably 15 mass % or less.

[0036] The thickness of the base layer is not particularly limited, and the average thickness of the base layer may be from 0.1 μm to 0.5 μm. In a case where the average thickness of the base layer is 0.1 μm or more, adhesiveness between the amorphous carbon layer and the surface layer can be improved. The thickness of the base layer is more preferably 0.15 μm or more, and further preferably 0.2 μm or more. On the other hand, when the base layer is made excessively thick, the adhesiveness improvement effect is saturated. Therefore, the thickness of the base layer is preferably 0.5 μm or less, and more preferably 0.4 μm or less.

[0037] In the above description, preferable functions of the base layer containing Ni and P is described. However, depending on the procedure of forming the electroplated layer, technological means, and the like, there are cases where the base layer need not necessarily be present, and forming the electroplated layer in three or more layers is not necessarily excluded.Surface Layer

[0038] The surface layer is a layer for imparting various characteristics to the carbon fiber, and may be a pure metal layer consisting of one element selected from the group consisting of Cu, Ni, Cr, Co, and Fe, or may be an alloy layer containing two or more elements selected from the group consisting of Cu, Ni, Cr, Co, and Fe. The pure metal layer and the alloy layer may contain inevitable impurities.

[0039] In a case where the surface layer is an alloy layer, when the mass of the surface layer is 100%, the total amount of the two or more elements selected from the group consisting of Cu, Ni, Cr, Co, and Fe may be, for example, 95 to 100 mass %. In a case where the total amount is 95 mass % or more, characteristics of the alloy can be exhibited. The total amount is more preferably 96 mass % or more, and further preferably 97 mass % or more. The total amount may be 100 mass %, 99 mass % or less, and 98 mass % or less.

[0040] The thickness of the surface layer is not particularly limited, and the average thickness thereof may be from 0.9 μm to 9.9 μm. In a case where the average thickness of the surface layer is 0.9 μm or more, characteristics of the metal element forming the surface layer can be exhibited. The average thickness of the surface layer is more preferably 1.3 μm or more, and further preferably 1.5 um or more. On the other hand, when the surface layer is excessively thick, stability of the surface layer may be impaired. Therefore, the average thickness of the surface layer is preferably 9.9 μm or less, more preferably 9 μm or less, and further preferably 8 μm or less.

[0041] The thickness of the electroplated layer is not particularly limited, and the average thickness of the entirety of the electroplated layer may be about from 1 μm to 10 μm. In a case where the electroplated layer is multiple layers, the average thickness refers to the total thickness of the multiple layers. In a case where the average thickness of the electroplated layer is 1 μm or more, characteristics derived from the electroplated layer can be exhibited. The average thickness of the electroplated layer is more preferably 2 μm or more, and further preferably 3 μm or more. On the other hand, when the electroplated layer is excessively thick, stability of the electroplated layer may be impaired. Therefore, the average thickness of the electroplated layer is preferably 10 μm or less, more preferably 9 μm or less, and further preferably 8 μm or less.

[0042] The average thickness of the electroplated layer may be obtained by: observing a cross-section perpendicular to the longitudinal direction of the electroplated carbon fiber with a scanning electron microscope; measuring the thickness of the electroplated layer at at least three places; and averaging these.

[0043] The electroplated carbon fiber can be mixed with a matrix metal, for example, to be used as a raw material of a carbon-fiber-reinforced metal. That is, the present invention also includes a carbon-fiber-reinforced metal containing the electroplated carbon fiber and a matrix metal. The carbon-fiber-reinforced metal can be used as a vehicle body material for vehicles, an airframe material for aircraft, and the like, for example.

[0044] The kind of the matrix metal is not particularly limited, and examples thereof include at least one element selected from the group consisting of Ni, Cr, Co, and Fe. The matrix metal that is mixed with the electroplated carbon fiber may be an aluminum alloy that contains at least one element selected from the group consisting of Li, Mg, Zn, Si, Cu, Mn, and Fe, with the remainder being Al, for example. In a case where an aluminum alloy is used as the matrix metal, direct forming can be performed by using a 3D printer or the like.

[0045] The electroplated carbon fiber in which the electroplated layer is composed of two layers, i.e., the base layer and the surface layer, the base layer contains Ni in a range of 80 mass % or more and less than 100 mass % and P in a range of more than 0 mass % and 20 mass % or less, and the surface layer contains Cu, has electric conductivity. And thus, the electroplated carbon fiber can be used as a component of an electrically-conductive material, for example.

[0046] The electrically-conductive material can be used as a material of a wire harness and the like. The electrically-conductive material can be used as a lightning protection material by being attached to a surface layer portion of an aircraft airframe and the like, for example.

[0047] The electroplated carbon fiber in which the electroplated layer is composed of two layers, i.e., the base layer and the surface layer, the base layer contains Ni in a range of 80 mass % or more and less than 100 mass % and P in a range of more than 0 mass % and 20 mass % or less, and the surface layer contains at least one element selected from the group consisting of Ni, Cr, Co, and Fe, has electromagnetic wave absorption property. And thus, the electroplated carbon fiber can be used as a component of an electromagnetic wave absorption material, for example.

[0048] The electroplated carbon fiber that has electromagnetic wave absorption property can be used as a material of an electronic device and the like, for example. Metal lamination of an Al alloy and the like onto the electroplated carbon fiber by a 3D printer enables development of a carbon fiber composite (new FRM concept: CFRM) that could not be obtained in a conventional 3D metal laminate, The obtained CFRM reinforces a thin metal lamination structure with an arbitrary UDCF sheet, and thus, significantly improves the strength and rigidity of a 3D laminate produced by a conventional method.

[0049] Next, a method for producing the electroplated carbon fiber in the embodiment of the present invention will be described. The electroplated carbon fiber in the embodiment of the present invention can be produced by subjecting a carbon fiber monofilament having an amorphous carbon layer on the surface thereof, to electroplating.

[0050] As the carbon fiber monofilament having the amorphous carbon layer on the surface thereof, for example, monofilaments of unused carbon fibers (virgin product) to which amorphous carbon is attached may be used, or carbon fiber monofilaments obtained by subjecting, to an opening process, a recycled-carbon-fiber tow that has been recovered by subjecting a carbon-fiber-containing resin molded body to various recovery processes such as heat treatment, and in which carbon fibers are bundled into a tow via amorphous carbon, may be used.

[0051] The monofilaments of unused carbon fibers (virgin product) to which amorphous carbon is attached can be produced by, for example, covering the unused carbon fibers with thermosetting resin or thermoplastic resin of various kinds, and then performing a dry distillation treatment or a carbonization treatment on the resultant carbon fibers.

[0052] The carbon fiber monofilaments obtained by subjecting, to an opening process, the carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon can be produced through, for example: a step (hereinafter, sometimes referred to as a preparation step) of preparing a carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon; a step (hereinafter, sometimes referred to as an opening step) of subjecting the carbon-fiber tow to an opening process to obtain carbon fiber monofilaments; and a step (hereinafter, sometimes referred to as an electroplating step) of subjecting the carbon fiber monofilament to electroplating. In the following, the steps will be described.Preparation Step

[0053] In the preparation step, a carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon is prepared. As the carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon, for example, a recycled carbon fiber (hereinafter, sometimes referred to as rCF) tow recovered from a carbon-fiber-reinforced thermosetting resin (hereinafter, sometimes referred to as CFRP) molded body that has been molded by compounding and blending carbon fibers in thermosetting matrix resin can be used. A recycled-carbon-fiber tow recovered from a carbon-fiber-reinforced thermoplastic resin molded body may be used, but in the following, a case of a recycled-carbon-fiber tow recovered from a carbon-fiber-reinforced thermosetting resin molded body is mainly described.

[0054] Amorphous carbon is a solid that is generated by heating thermosetting resin and that is rich in carbon which is not melted or softened. In the present specification, amorphous carbon is not spherical mesophase carbon but a precursor in which micro crystals of carbon are entangled in a ribbon-like shape, and has a reactive group. When the precursor is further heated to 800° C., the precursor becomes glass-like carbon while maintaining the entanglement in a ribbon-like shape. Amorphous carbon has a structure significantly different from that of graphite in which crystals are two dimensionally arrayed via ordinary mesophase carbon. The presence or absence of amorphous carbon can be confirmed by using a scanning electron microscope or small-angle scattered X-rays. Amorphous carbon has a variety of amorphous states, porosities, and surface activities, depending on the staring raw material thereof, and a staring raw material is selected according to the purpose.

[0055] The tow refers to a bundle-like form in which a large number of carbon fibers are aligned. The number of carbon fibers constituting the tow is, but is not particularly limited to, for example, preferably 1000 to 48000 from the viewpoint of further enhancing handleability. The number of carbon fibers is more preferably 2000 or more, further preferably 3000 or more, more preferably 40000 or less, and further preferably 24000 or less.

[0056] The CFRP molded body is a composite of carbon fibers as a reinforcing member in a thermosetting resin molded body, and can also be referred to as carbon fibers bound by thermosetting resin. Examples of thermosetting resin serving as a binder include unsaturated polyester resin, epoxy resin, vinylester resin, bismaleimide resin, phenol resin, cyanate resin, and polyimide resin.

[0057] The CFRP molded bodies are used, for example, for aerospace planes (for example, rockets, artificial satellites, military aircrafts, passenger aircrafts, helicopter blades, etc. ,), racing cars, motorbikes, bicycles, railroad vehicles, deep ocean survey vehicles, racing boats, measurement devices, robot arms for transportation, wind power blade, compressed natural gas tanks (CNG tanks), golf shafts, tennis rackets, fishing rods, wheelchairs, structures such as artificial bones, and casings of mobile devices such as note book personal computer, tablets, and mobile phones.

[0058] The CFRP molded body may be a recovered used product or a recovered expired product. All recovered products of CFRP molded bodies such as a prepreg end material generated during production and a product excluded by trimming can be used.

[0059] The method for producing the carbon-fiber tow (recycled-carbon-fiber tow) in which carbon fibers are bundled into a tow via amorphous carbon, from the carbon-fiber-reinforced thermosetting resin (CFRP) molded body, is not particularly limited. For example, the carbon-fiber tow can be produced by: (1) heating the CFRP molded body to a predetermined temperature in a temperature range of 400° C. or higher and 480° C. or lower; at that time, (2) the concentration of oxygen in atmosphere gas is caused to be from 15 to 19 volume % in a period up to the end of the heating after the temperature reaches 300° C.; (3) the CFRP molded body is maintained for at least one hour in a period after the temperature reaches 300° C. until the temperature reaches 400° C.; and (4) the CFRP molded body is maintained for at least 30 minutes in a temperature range of 400° C. or higher. In the following, the method will be described in detail.(1) Heating Temperature

[0060] Preferably, the CFRP molded body is heated to a predetermined temperature in a temperature range of 400° C. or higher and 480° C. or lower. In a case where the temperature reached by heating during heating is in a temperature range of 400 to 480° C., the residual carbon content can be controlled to be in the above range. That is, in a case where the temperature reached by heating is 400° C. or higher, it is possible to prevent amorphous carbon from being left in an excessively large amount. Therefore, the carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon is easily opened into carbon fiber monofilaments. Therefore, the temperature reached by heating is preferably 400° C. or more, more preferably 410° C. or more, and further preferably 420° C. or more. However, when the temperature reached by heating is higher than 480° C., heating is excessively performed, amorphous carbon is excessively removed, the surfaces of carbon fibers become inactive smooth surfaces, no bundling force is exerted, uniformity for removing amorphous carbon cannot be maintained, wettability with matrix resin, which is required for obtaining the CFRP molded body or the like, is lost, and as a result, the rCF tow that is stable is less likely to be obtained. Therefore, the temperature reached by heating is preferably 480° C. or less, and more preferably 470° C. or less.

[0061] In a case where a plated layer or a coated layer is formed on the surface of the CFRP molded body, such as in a tennis racket, the plated layer or the coated layer is preferably removed in advance before the heating, but the plated layer or the coated layer may be separated from the carbon fiber after the heating.(2) Concentration of Oxygen in Atmosphere Gas

[0062] When the CFRP molded body is heated to a temperature range of 400 to 480° C., the concentration of oxygen in atmosphere gas is preferably 15 to 19 volume % in a period up to the end of the heating after the temperature reaches 300° C. In a case where the concentration of oxygen in the above period is 15 volume % or more, the decomposition rate of thermosetting resin is increased, amorphous carbon is generated, and carbon fibers can be bundled into a tow. Further, since decomposition gas is generated in a short time, closed pores are less likely to be generated, the pyrolysis rate is not reduced, and a uniform phase is generated. Therefore, the concentration of oxygen in the above period is more preferably 16 volume % or more, and further preferably 17 volume % or more. However, when the concentration of oxygen in the above period is more than 19 volume %, the decomposition rate of the thermosetting resin becomes excessively high, a part of the thermosetting resin is burned without generating amorphous carbon, and oxidized and removed, and thus, the carbon fibers cannot be bundled into uniform tows, and a cotton-like product and a lumped product coexist. Therefore, the concentration of oxygen in the above period is preferably 19 volume % or less, and further preferably 18 volume % or less.

[0063] The above concentration of oxygen in atmosphere gas in a period up to the end of the heating after the temperature reaches said 300° C. may be controlled so as to be constant, or may be varied. In a case where the concentration of oxygen is varied, the above period may be divided into some temperature periods, and the concentration of oxygen may be controlled in each temperature period. For example, the above period may be divided into a temperature period after the temperature reaches 300° C. until the temperature reaches 400° C., and a temperature period up to the end of the heating after the temperature reaches 400° C., and the concentration of oxygen in atmosphere gas may be controlled. Alternatively, the above period may be divided into a temperature period after the temperature reaches 300° C. until the temperature reaches 350° C., a temperature period after the temperature reaches 350° C. until the temperature reaches 400° C., and a temperature period up to the end of the heating after the temperature reaches 400° C., and the concentration of oxygen in atmosphere gas may be controlled.

[0064] When the CFRP molded body is heated, the concentration of oxygen in atmosphere gas in the period until the temperature reaches 300° C. is not particularly limited, and the concentration of oxygen is preferably controlled in a range of 13 to 19 volume %, for example. In a case where the concentration of oxygen in the above period is 13 volume % or more, incomplete combustion gas can be prevented from being discharged. The concentration of oxygen in the above period is more preferably 14 volume % or more, and further preferably 15 volume % or more. However, when the concentration of oxygen in the above period is more than 19 volume %, the combustion may become non-uniform, or explosion may occur in a dry distillation furnace. Therefore, the concentration of oxygen in the above period is preferably 19 volume % or less, and further preferably 18 volume % or less.

[0065] After the end of the heating, cooling may be performed. The concentration of oxygen in atmosphere gas during cooling is not particularly limited, and cooling may be performed in the air.(3) Maintaining Time in the Period in Which the Temperature is from 300 to 400° C.

[0066] When the CFRP molded body is heated to a temperature in a temperature range of 400 to 480° C., the CFRP molded body is preferably maintained for at least one hour in the period after the temperature reaches 300° C.. until the temperature reaches 400° C. In a case where maintaining is performed for at least one hour in the above period, pyrolysis temperature of the thermosetting resin can be reached while the thermosetting resin is allowed to progress into C-stage.

[0067] The maintaining time in the period after the temperature reaches 300° C. until the temperature reaches 400° C. is more preferably 1.5 hours or longer. The upper limit of the maintaining time in the above period is, but is not particularly limited to, preferably five hours or shorter, more preferably four hours or shorter, and further preferably three hours or shorter, when productivity is taken into consideration.

[0068] When maintaining is performed for a predetermined time in the period after the temperature reaches 300° C. until the temperature reaches 400° C., heating may be gradually performed until the temperature reaches 400° C. from 300° C., heating and maintaining may be repeated, or heating may be stopped immediately before 400° C. is reached and maintaining may be performed. In the above temperature period, cooling may be performed.

[0069] The average temperature increase rate in the period after the temperature reaches 300° C. until the temperature reaches 400° C. is preferably 70° C. / minute or less (not including 0° C. / minute), for example. The average temperature increase rate in the period is more preferably 60° C. / minute or less, and further preferably 50° C. / minute or less. The lower limit of the average temperature increase rate in the period is, but not particularly limited to, preferably 0.1 C. / minute or more, more preferably 0.5° C. / minute or more, and further preferably 1° C. / minute or more.

[0070] When the CFRP molded body is heated to a temperature in a temperature range of 400 to 480° C., it is preferable that the decomposed state of the CFRP molded body is confirmed at a time point when the temperature reaches 350° C., and then the CFRP molded body is continuously heated to be higher than 350° C. The end of the decomposition of the CFRP molded body may be confirmed by the fact that the discharged gas has no odor, the fact that no white smoke is generated, and the like, as well as the fact that the concentration of oxygen is confirmed to be stable by an oxygen sensor or the like. When heating to a temperature higher than 350° C. is performed before the end of the decomposition of the CFRP molded body, the CFRP molded body is rapidly oxidized, and thus, temperature control becomes difficult, and white smoke or unusual odor may be caused. In addition, due to the rapid oxidation, a tow may not be formed. Furthermore, since the temperature of the CFRP molded body is rapidly increased, an explosion may be caused.

[0071] When the CFRP molded body is heated, the average temperature increase rate until the temperature reaches 300° C. is, but is not particularly limited to, for example, preferably 10° C. / minute or more, more preferably 30° C. / minute or more, and further preferably 50° C. / minute or more, when productivity is taken into consideration. The upper limit of the average temperature increase rate is, for example, preferably 100° C. / minute or less, more preferably 70° C. / minute or less, and further preferably 55° C. / minute or less.

[0072] The average temperature increase rate in the temperature period up to the end of the heating after the temperature reaches 400° C. is, but is also not particularly limited to, for example, preferably 70° C. / minute or more, more preferably 75° C. / minute or more, and further preferably 80° C. / minute or more, when productivity is taken into consideration. The upper limit of the average temperature increase rate is, for example, preferably 100° C. / minute or less, more preferably 90° C. / minute or less, and further preferably 85° C. / minute or less.

[0073] When the CFRP molded body is heated, the average temperature increase rate until the temperature reaches 300° C., the average temperature increase rate in the temperature period after the temperature reaches 300° C. until the temperature reaches 400° C., and the average temperature increase rate in the temperature period up to the end of the heating after the temperature reaches 400° C. may be controlled so as to be constant, or may be varied.(4) Maintaining Time in the Period in Which the Temperature is from 400 to 480° C.

[0074] A maintaining time in a temperature range of 400° C. or higher and 480° C. or lower is preferably at least 30 minutes. In a case where the maintaining time in this temperature range is 30 minutes or more, an amorphous carbon content for binding carbon fibers of the rCF tow to each other can be appropriately adjusted so that the tow can be precisely adjusted so as to have a preferable hardness. The upper limit of the maintaining time is, but is not particularly limited to, for example, preferably 180 minutes or shorter, more preferably 150 minutes or shorter, and further preferably 120 minutes or shorter from the viewpoint of productivity. The maintaining time refers to a residence time in the temperature range from a time point when the temperature reaches 400° C. to a time point when the temperature reaches less than 400° C.

[0075] After maintaining has been performed in the above temperature range, cooling to 300° C. or lower may be performed.

[0076] As described above, when the CFRP molded body is heated, in a first step, the maintaining time and the concentration of oxygen in atmosphere gas in the period after the temperature reaches 300° C. until the temperature reaches 400° C. are appropriately controlled, whereby a state where carbon fibers are bundled into a tow via amorphous carbon derived from the thermosetting resin can be maintained, and in a second step, heating is performed to a temperature in a temperature range of 400° C. or higher and 480° C. or lower, and the concentration of oxygen in atmosphere gas in this temperature range is controlled, and then, maintaining is performed for a predetermined time, whereby the amount of amorphous carbon that contributes to bundling carbon fibers into a tow can be adjusted.

[0077] The above heating is performed together with pyrolytic gas (monomer of resin, pyrolytic hydrocarbons, etc.) derived from the above molded body, or the heating is preferably performed while oxygen-containing gas is mixed with CO2 obtained by the reaction and combustion of these pyrolysis gases with oxygen. By mixing oxygen-containing gas, a concentration of oxygen in atmosphere gas can be controlled. Slight increase of a concentration of oxygen and circulation of atmosphere gas progress pyrolysis of resin and oxidation of pyrolytic gas without greatly changing chemical equilibrium, so that matrix resin can be converted to amorphous carbon. Furthermore, by gradually progressing the reaction, while decomposition gas involving odor is, for example, introduced into a combustion chamber, subjected to complete combustion, and used as a heat source, a part of the decomposition gas is recirculated in a carbon fiber recovering furnace and the remaining part of the decomposition gas may be discharged through a deodorization device to the outside of the system, as combustion gas that does not substantially require additional exhaust gas treatment.

[0078] As oxygen-containing gas to be mixed, for example, air may be used. However, oxygen gas, inert gas containing oxygen gas, or the like may be used. As the inert gas, for example, nitrogen gas may be used.

[0079] Preferably, the CFRP molded body is heated in atmosphere gas that is flowing. In a case where atmosphere gas is caused to flow, pyrolysis and combustion of decomposition gas are allowed to gradually progress, and thus, the resin with which the carbon fibers is impregnated can be removed, while uniformity is maintained.

[0080] For performing heating in flowing atmosphere gas, gas may be supplied to a dry distillation furnace having the CFRP molded body placed therein, the atmosphere gas in a dry distillation furnace may be agitated, or the atmosphere gas in a dry distillation furnace may be discharged to the outside of the dry distillation furnace and then returned to the dry distillation furnace again, to be circulated, for example.

[0081] Preferably, the average flow rate of atmosphere gas is from 0.03 to 20 m / minute, for example. In a case where the average flow rate is 0.03 m / minute or more, the CFRP molded body can be uniformly heated without unevenness. The average flow rate is more preferably 0.04 m / minute or more, and further preferably 0.05 m / minute or more. However, when the average flow rate is excessively high, heat in a dry distillation furnace is taken out to the outside of the system. Thus, soaking becomes difficult, the flow rate in the entirety of the inside of the system becomes excessively high, and stability of combustion of the burner in the heat generation part of the dry distillation furnace may be impaired. Therefore, the average flow rate is preferably 20 m / minute or less, more preferably 10 m / minute or less, and further preferably 8 m / minute or less.

[0082] In a case where the CFRP molded body has a tubular shape, inactive gas may be supplied to the inside of the tubular CFRP molded body when heating is performed. In a case where inactive gas is supplied to the inside of the tubular CFRP molded body, excessive combustion due to excessively high temperature caused in the inside is inhibited, and the resin in the inside can be vaporized and recovered as a monomer. As the inactive gas, for example, nitrogen gas may be used.Opening Step

[0083] In the opening step, the carbon-fiber tow prepared in the preparation step is subjected to an opening process to produce carbon fiber monofilaments. In a case where the carbon-fiber tow is made into carbon fiber monofilaments, electroplating can be uniformly performed onto the entire periphery of the carbon fiber monofilaments in the electroplating step described later. The method of the opening process is not particularly limited, and, for example, use of a roll-type opening machine is preferable. The carbon-fiber tow prepared in the preparation step is wound around a bobbin, this bobbin is mounted to a roll-type opening machine, and then opening may be performed.Electroplating Step

[0084] In the electroplating step, the carbon fiber monofilaments obtained in the opening step are subjected to electroplating. In a case where electroplating is performed after the opening process is performed, electroplating can be uniformly provided around the carbon fiber monofilaments.

[0085] The conditions of electroplating are not particularly limited, and, for example, it is preferable to adjust the voltage applied from an energizing roll so as to be in a range of from 2 to 5 V. Preferably, the electroplating time is adjusted such that the average moving speed of carbon fibers is from 0.001 to 10 m / minute per unit length (meter) of the plating bath.

[0086] As the plating liquid, those containing at least one element selected from the group consisting of Cu, Ni, Cr, Co, and Fe can be used. In a case where the base layer and the surface layer are formed as the electroplated layer, it is preferable to use a plating liquid that contains Ni, in particular, a plating liquid that contains Ni and P, in order to form the base layer, and it is preferable to use a plating liquid that contains at least one element selected from the group consisting of Cu, Ni, Cr, Co, and Fe, in order to form the surface layer.

[0087] This application claims the benefit of the priority date of Japanese patent application No. 2023-177672 filed on Oct. 13, 2023. All of the contents of the Japanese patent application No. 2023-177672 are incorporated by reference herein.

[0088] Hereinafter, the present invention will be more specifically described by means of examples. However, the present invention is not limited by the following examples and can also be carried out with modifications being made within the scope of the gist described above and below, and each of these modifications are included in the technical scope of the present invention.EXAMPLESExperiment 1

[0089] A carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon was subjected to the opening process to produce carbon fiber monofilaments, and the obtained carbon fiber monofilaments were subjected to electroplating. The carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon was prepared according to the following procedure.

[0090] As the carbon-fiber-reinforced thermosetting resin molded body, a used gas tank (type 4: a gas tank whose inner liner is nylon resin) was prepared. The cylindrical gas tank had a diameter of about 40 cm×a length of about 152 cm×a thickness of about 1 cm. Metal pipes were inserted into both ends of the gas tank, and then, the both ends of the gas tank were each sealed. The metal pipes protruding from the gas tank were caused to be outside a dry distillation furnace, nitrogen gas was introduced from one of the metal pipes, and heating was performed while the inside of the gas tank was filled with nitrogen gas. In the heating, maintaining was performed at from 300° C. to 400° C. for 90 minutes, whereby the resin content constituting the gas tank was carbonized. During this time, from the inside of the gas tank, a molten liquid or pyrolysis gas having caprolactam as a main component was purged by nitrogen gas and collected. After the pyrolysis gas and the liquid generated from the inner liner were no longer observed, temperature increase was started, and heating was performed to a temperature in a range of 400° C. or higher and 470° C. or lower. When heating was performed to 400° C. or higher, supply of nitrogen gas to the inside of the gas tank was stopped, a circulating pump was operated, the gas in the dry distillation furnace was also introduced to the inside of the gas tank, and a carbonized layer of the matrix resin was started to be removed also from the inside of the gas tank.

[0091] The detailed heating conditions are as follows. A lid of the dry distillation furnace was closed, and a heat-resistant fan disposed at an exhaust portion of the dry distillation furnace was operated, and combustion gas was circulated in the dry distillation furnace in a period from a time point when the temperature in the dry distillation furnace reached 300° C. to the end of heating. An average flow rate of the combustion gas in the dry distillation furnace was 0.05 m / second. Air was taken from a variable speed blower disposed in the dry distillation furnace, and a concentration of oxygen in atmosphere gas in the dry distillation furnace was measured by a zirconia-type oxygen sensor. The concentration of oxygen in atmosphere gas in the dry distillation furnace was particularly 18 volume % from a time point when the temperature in the dry distillation furnace reached 300° C. to a time point when the temperature reached 400° C., and was 16 volume % in a period from 400° C. to the end of the heating. A maintaining time in a period from a time point when the temperature in the dry distillation furnace reached 300° C. to a time point when the temperature reached 400° C. was 1.5 hours. An average temperature increase rate in a period from a time point when the temperature in the dry distillation furnace reached 300° C. to a time point when the temperature reached 400° C. was 50° C. / minute. Immediately before the temperature reached 400° C., a decomposed state of the gas tank was confirmed in advance in an experimental furnace. In a case where the decomposition ended, the heating was subsequently performed to increase the temperature. The end of the decomposition was determined by both confirmation in the experimental furnace and observation as to presence or absence of fuming. In a case where no fuming occurred, the decomposition was determined to have ended. Presence or absence of unusual odor was also checked, and absence of the unusual odor was also confirmed. After the end of the decomposition was confirmed, the temperature reached by heating was set to 470° C. and heating was performed. In a temperature range of 400° C. or higher and 470° C. or lower, the maintaining time was 30 minutes. After the end of the heating, cooling was performed and carbon-fiber tow were obtained. The carbon fibers constituting the obtained carbon-fiber tow was converged in a tow-like configuration via amorphous carbon derived from thermosetting resin. An average fiber length of the carbon fibers constituting the carbon-fiber tow was 3000 m, and the number of the carbon fibers was about 3000.

[0092] Next, a bobbin around which the obtained carbon-fiber tow was wound was mounted to an opening machine to subject the carbon-fiber tow to the opening process. As the opening machine, “roll-to-roll continuous opening machine (apparatus name)” manufactured by AIKI RIOTECH was used. The condition for the opening process was set to 10 m / minute, and the carbon-fiber tow was opened such that the width became 200% relative to the original width of the carbon-fiber tow, to obtain carbon fiber monofilaments. The width of the carbon-fiber tow wound around the bobbin was 6 mm, and the width of the carbon fiber monofilaments obtained through the opening process was 9 mm.

[0093] The fiber bundle of the carbon fiber monofilaments obtained through the opening process was placed in a crucible having a lid and heated at 600° C. for 60 minutes in the air, the masses before and after the heating were measured, and the residual carbon content was measured. As a result, when the entirety of the carbon fiber monofilaments was 100 mass %, the residual carbon content was 3 mass %.

[0094] Electric conductivity of the fiber bundle of the obtained carbon fibers was evaluated. The electric conductivity was evaluated based on a result of measurement of the surface resistance value according to a four-terminal method, using “Loresta (apparatus name)” manufactured by Mitsubishi Chemical Corporation (formerly Mitsubishi Petrochemical Engineering Co., Ltd.). As a result, the surface resistance value of the fiber bundle of the carbon fiber monofilaments was 1×103 Ω. On the other hand, as a comparison, when the surface resistance value of a fiber bundle of new carbon fibers was measured, the surface resistance value was 1×102 Ω.

[0095] Next, the obtained carbon fiber monofilaments were subjected to electroplating, to produce electroplated carbon fibers. In the electroplating, base treatment was performed, and then, surface treatment was performed.

[0096] In the base treatment, a plating liquid containing Ni and P was used. As the plating liquid, “TOPNICORON BL” manufactured by OKUNO CHEMICAL INDUSTRIES CO., LTD. was used. The amount of Ni contained in the plating liquid was 85 mass %, and the amount of P in the plating liquid was 15 mass %. The base treatment was performed for 20 minutes, with the voltage applied from the energizing roll set in a range of 3 to 3.5 V.

[0097] With respect to the carbon fiber monofilaments subjected to the base treatment, the surface resistance value was measured under the same conditions as the above, and electric conductivity was evaluated. As a result, the surface resistance value of the carbon fiber monofilaments subjected to the base treatment was 1×100 Ω. On the other hand, as a comparison, new carbon fiber monofilaments were subjected to the base treatment, and then, the surface resistance value was measured. The base treatment was performed under the same conditions as the above. As a result, the surface resistance value was about 1×102 Ω and hardly changed as compared with that when the base treatment was not performed.

[0098] Next, the carbon fiber monofilaments subjected to the base treatment were subjected to the surface treatment. In the surface treatment, a plating liquid containing Cu was used. As the plating liquid, “CU-BRITE EP-30” manufactured by JCU CORPORATION was used. The plating liquid contained 225 g / L of copper sulfate pentahydrate, 55 g / L of sulfuric acid, and 60 mg / L of chlorine ions. The electrodeposited amount of Cu was 3 μm in average. The surface treatment was performed, with the voltage applied from the energizing roll set in a range of 2.5 to 3 V, and the average moving speed of carbon fibers per unit length (per 1000 mm) of the plating bath set to 10 mm / minute.

[0099] When a cross-section perpendicular to the longitudinal direction of the obtained electroplated carbon fiber was observed with a scanning electron microscope, a base layer containing Ni and P and having an average thickness of 0.2 μm was formed on the surface of the carbon fiber monofilament, and a surface layer containing Cu and having an average thickness of 3 μm was formed on the surface of the base layer. The base layer contained 85 mass % of Ni and 15 mass % of P, with the remainder being inevitable impurities, and the surface layer was composed of Cu and inevitable impurities.

[0100] Next, the obtained electroplated carbon fiber was hardened with resin, and a photograph of a cross-section perpendicular to the axial direction of the electroplated carbon fiber was taken. (a) of FIG. 1 is a photograph, substituting for a drawing, of the cross-section taken at a magnification of 10000 times. (b) of FIG. 1 is an enlarged view of a main part showing, in an enlarged manner, the portion surrounded by a square in (a) of FIG. 1. As shown in FIG. 1, it is seen that an electroplated layer composed of a base layer and a surface layer is formed on the surface of the carbon fiber monofilament. In FIG. 1, No. 1 indicates the base layer, No. 2 indicates the surface layer, the thickness of the base layer was 328.9 nm (0.3289 μm), and the thickness of the surface layer was 517.5 nm (0.5175 μm). It was separately confirmed that an amorphous carbon layer was present between the surface of the carbon fiber monofilament and the base layer.

[0101] As a comparison, new carbon fiber monofilaments were prepared, and the monofilaments were subjected to electroplating under the same conditions as the above, to produce electroplated carbon fibers. In the electroplating, the base treatment was performed, and then, the surface treatment was performed. The obtained electroplated carbon fiber was hardened with resin, and a photograph of a cross-section perpendicular to the axial direction of the electroplated carbon fiber was taken. The taken photograph substituting for a drawing is shown in FIG. 2. FIG. 2 is a photograph, substituting for a drawing, of the cross-section taken at a magnification of 5000 times. As is clear from FIG. 2, on the surface of the carbon fiber monofilament, hardly any base layer or surface layer was formed.

[0102] Next, with the conditions of the surface treatment changed, the surface layer was formed on the carbon fiber monofilaments subjected to the above base treatment, to produce electroplated carbon fibers having different thicknesses of the surface layer. With respect to the obtained electroplated carbon fibers, the surface resistance value was measured under the same conditions as the above, and electric conductivity was evaluated. As a result, the surface resistance value when the average thickness of the surface layer (Cu layer) was 0.1 μm was 1.90×10-1 Ω, the surface resistance value when the average thickness of the surface layer (Cu layer) was 0.5 μm was 3.29×10-2 0, the surface resistance value when the average thickness of the surface layer (Cu layer) was 5 μm was 3.55×10-3 Ω, and the surface resistance value when the average thickness of the surface layer (Cu layer) was 10 μm was 2.50×10-3 Ω. Thus, since the electroplated carbon fibers having a surface layer (Cu layer) whose average thickness is from 0.5 to 10 μm has electric conductivity, a sheet produced by impregnating these electroplated carbon fibers with epoxy resin can be used as a lightning protection material, by being attached to a surface layer portion of an aircraft airframe.Experiment 2

[0103] Each type of the electroplated carbon fibers having a different thickness of the surface layer obtained in Experiment 1 was covered with a resin coat to produce resin-coated electroplated carbon fibers, and electric conductivity of the obtained resin-coated electroplated carbon fibers was evaluated. As the resin, polyvinyl chloride (PVC) was used, and the average thickness of the covering resin coat was 500 μm.

[0104] Electric conductivity of the obtained resin-coated electroplated carbon fibers was evaluated under the same conditions as Experiment 1. As a result, the surface resistance value when the average thickness of the surface layer (Cu layer) was 0.1 μm was 1.90×10-1 Ω, the surface resistance value when the average thickness of the surface layer (Cu layer) was 0.5 μm was 3.29×10-2 Ω, the surface resistance value when the average thickness of the surface layer (Cu layer) was 5 μm was 3.55×10-3 Ω, and the surface resistance value when the average thickness of the surface layer (Cu layer) was 10 μm was 2.50×10-3 Ω. On the other hand, as a comparison, electric conductivity of a Cu electric wire manufactured by Furukawa Electric Co., Ltd. was evaluated under the same conditions as Experiment 1. As a result, the surface resistance value of the Cu electric wire was 3.05×10-3 Ω. Thus, the resin-coated electroplated carbon fibers having a surface layer (Cu layer) whose average thickness is from 0.5 to 10 μm has electric conductivity at a level similar to that of the Cu electric wire, and can be used as a harness electric wire for an electronic circuit.Experiment 3

[0105] The carbon fiber monofilaments obtained in Experiment 1 were subjected to electroplating, to produce electroplated carbon fibers. In the electroplating, base treatment was performed, and then, surface treatment was performed.Base Treatment

[0106] In the base treatment, a plating liquid containing Ni and P was used. As the plating liquid, “TOPNICORON BL” manufactured by OKUNO CHEMICAL INDUSTRIES CO., LTD. was used. The amount of Ni contained in the plating liquid was 85 mass %, and the amount of P in the plating liquid was 15 mass %. The base treatment was performed for 20 minutes, with the voltage applied from the energizing roll set in a range of 3 to 3.5 V.Surface Treatment

[0107] In the surface treatment, a plating liquid containing Ni was used. As the plating liquid, Watts bath composed of nickel sulfate, nickel chloride, and boric acid was used. The content of Ni was 15 mass %. The surface treatment was performed for 20 minutes, with the voltage applied from the energizing roll set in a range of 2.5 to 3 V, and the average moving speed of carbon fibers per unit length (per 1000 mm) of the plating bath set to 10 mm / minute.

[0108] When a cross-section perpendicular to the longitudinal direction of the obtained electroplated carbon fiber was observed with a scanning electron microscope, a base layer containing Ni and P and having an average thickness of 0.2 μm was formed on the surface of the carbon fiber monofilament, and a surface layer containing Ni and having an average thickness of 5 μm was formed on the surface of the base layer. The base layer contained 85 mass % of Ni and 15 mass % of P, with the remainder being inevitable impurities, and the surface layer was composed of Ni and inevitable impurities.

[0109] On the other hand, as a comparison, the carbon fiber monofilaments obtained in Experiment 1 were subjected to electroless plating, to produce electroless plated carbon fibers. In the electroless plating, as the plating liquid, “TOPNICORON BL” manufactured by OKUNO CHEMICAL INDUSTRIES CO., LTD. was used, and in this plating liquid, the carbon fiber monofilaments obtained in Experiment 1 were immersed for 20 minutes, with the temperature of the plating liquid set to 40° C. When a cross-section perpendicular to the longitudinal direction of the obtained electroless plated carbon fiber was observed with a scanning electron microscope, an electroplated Ni layer having an average thickness of 0.5 μm was formed on the surface of the carbon fiber monofilament.

[0110] Next, stability of the electroplated carbon fibers and the electroless plated carbon fibers was evaluated. The stability was evaluated such that the electroplated carbon fibers or the electroless plated carbon fibers were put in a crucible and heated for one hour in an electric furnace set at 600° C., and change in shapes before and after the heating was visually observed. As a result, no change in shape was observed in the electroplated carbon fibers before and after the heating, and the stability was good. With respect to the electroless plated carbon fibers, oxidation was observed in the electroless plated Ni layer. In addition, a part of the electroless plated Ni layer was separated from the surface of the carbon fiber monofilament. Thus, stability of the electroless plated Ni carbon fibers was poor.Experiment 4

[0111] The carbon fiber monofilaments obtained in Experiment 1 were subjected to electroplating, to produce electroplated carbon fibers. In the electroplating, base treatment was performed, and then, surface treatment was performed.Base Treatment

[0112] In the base treatment, a plating liquid containing Ni and P was used. As the plating liquid, “TOPNICORON BL” manufactured by OKUNO CHEMICAL INDUSTRIES CO., LTD. was used. The amount of Ni contained in the plating liquid was 85 mass %, and the amount of P in the plating liquid was 15 mass %. The base treatment was performed for 20 minutes, with the voltage applied from the energizing roll set in a range of 3 to 3.5 VSurface Treatment

[0113] In the surface treatment, a plating liquid containing Ni was used. As the plating liquid, Watts bath composed of nickel sulfate, nickel chloride, and boric acid was used. The content of Ni was 15 mass %. The surface treatment was performed for 20 minutes, with the voltage applied from the energizing roll set to 3.5 V, and the average moving speed of carbon fibers per unit length (per 1000 mm) of the plating bath set to 10 mm / minute.

[0114] When a cross-section perpendicular to the longitudinal direction of the carbon fiber monofilament obtained through surface treatment was observed with a scanning electron microscope, a base layer containing Ni and P and having an average thickness of 0.2 μm was formed on the surface of the carbon fiber monofilament, and a surface layer containing Ni and having an average thickness of 2 μm was formed on the surface of the base layer. The base layer contained 85 mass % of Ni and 15 mass % of P, with the remainder being inevitable impurities, and the surface layer was composed of Ni and inevitable impurities.

[0115] A sheet having a thickness of 200 μm was produced using the obtained electroplated carbon fibers and epoxy resin. Electromagnetic wave shielding property of the obtained sheet was evaluated based on the KEC method. The measurement frequency for the shielding effect was set to from 50 kHz to 1 GHz. As a result, the obtained sheet exhibited electromagnetic wave shielding property. Therefore, the electroplated carbon fibers can be used as a raw material of an electromagnetic wave absorption material.

[0116] Next, on both surfaces of the obtained electroplated carbon fibers, an Al alloy was 3D-printed as a matrix metal, to produce a carbon-fiber-reinforced metal. The content of the electroplated carbon fibers relative to Al of the matrix metal was set to 50 mass %. As a result, a composite of the electroplated carbon fibers and the Al alloy was formed, whereby mechanical characteristics of Al were improved.

Claims

1. An electroplated carbon fiber having an electroplated layer on a surface of a carbon fiber via an amorphous carbon layer.

2. The electroplated carbon fiber according to claim 1,wherein the electroplated layer has an average thickness of 1 μm to 10 μm.

3. The electroplated carbon fiber according to claim 1,wherein the electroplated layer includes a base layer and a surface layer,the base layer contains Ni and P, andthe surface layer contains at least one element selected from the group consisting of Cu, Ni, Cr, Co, and Fe.

4. The electroplated carbon fiber according to claim 1,wherein the carbon fiber having the amorphous carbon layer on the surface thereof has a residual carbon content of 0.5 to 6 mass % measured by heating the carbon fiber under conditions of 600° C.×60 minutes.

5. A carbon-fiber-reinforced metal comprising the electroplated carbon fiber according to claim 1 and a matrix metal.

6. An electrically-conductive material comprising the electroplated carbon fiber according to claim 3 as a component,wherein the surface layer contains Cu.

7. A lightning protection material comprising the electrically-conductive material according to claim 6.

8. An electromagnetic wave absorption material comprising the electroplated carbon fiber according to claim 3 as a component,wherein the surface layer contains at least one element selected from the group consisting of Ni, Cr, Co, and Fe.

9. A method for producing an electroplated carbon fiber, the method comprising:a step of preparing a carbon-fiber tow in which carbon fibers are bundled into a tow via amorphous carbon;a step of subjecting the carbon-fiber tow to an opening process to obtain carbon fiber monofilaments; anda step of subjecting the carbon fiber monofilaments to electroplating.

Images