Composite Material and Method for Producing the Same

Abstract

The present invention provides: a composite material which has further enhanced characteristics due to carbon nanotubes adhered to fibers; and a method for producing this composite material. With respect to a composite material 10 according to the present invention, a structure 12 which is composed of a plurality of carbon nanotubes 14 is formed on the surfaces of fibers 11 that constitute the composite material 10. Each carbon nanotube 14 has a curved shape. The carbon nanotubes 14 adhere, in various postures, to the surfaces of the fibers 11, said surfaces being curved surfaces; and the structure 12 is formed of much more carbon nanotubes 14 since spaces between the carbon nanotubes 14 and the surfaces of the fibers 11 and spaces (gaps) among the adhering carbon nanotubes 14 are filled with other carbon nanotubes 14.

Description

Technical Field

[0001] The present invention relates to a composite material and a method for manufacturing the same.

Background Art

[0002] There has been proposed a composite material having a structure composed of fibers and a plurality of carbon nanotubes (hereinafter referred to as CNTs) attached to the surface of the fibers (for example, Patent Document 1). The structure of the composite material forms a network structure in which a plurality of CNTs are connected to each other and is attached to the surface of the fiber. A fiber-reinforced molded body obtained by reinforcing a resin with such a composite material as a reinforcing fiber has higher strength and rigidity than a resin alone by including the fiber, and also has improved electrical conductivity, thermal conductivity, and mechanical properties due to the CNTs.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The applications of the above-described fiber-reinforced molded bodies have been expanding into various fields, and the requirements for fiber-reinforced molded bodies have become even higher. On the other hand, in the case of fibers having a small diameter, the improvement effect of mechanical properties and the like derived from CNTs is easily obtained, but in the case of fibers having a large diameter, the improvement effect of mechanical properties and the like derived from CNTs is difficult to obtain. Therefore, it is desired to further enhance the properties derived from CNTs.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a composite material and a method for manufacturing the same that can further enhance the properties derived from CNTs attached to fibers.

Means for Solving the Problems

[0006] The composite material of the present invention is composed of fibers and a plurality of carbon nanotubes, forms a network structure in which the carbon nanotubes are in direct contact with each other, and includes a structure in which the carbon nanotubes adhering to the surface of the fibers are directly attached to the surface of the fibers. The carbon nanotubes have a bent shape with bent portions.

[0007] The method for manufacturing the composite material of the present invention includes an ultrasonic step of applying ultrasonic vibration to a dispersion liquid in which a plurality of carbon nanotubes having a bent shape with bent portions are dispersed, and dipping continuous fibers into the dispersion liquid to which the ultrasonic vibration is applied, and attaching the plurality of carbon nanotubes to the fibers to form a structure on the surface of the fibers.

Advantages of the Invention

[0008] According to the present invention, since the carbon nanotubes adhering to the fibers have a bent shape with bent portions, the number of carbon nanotubes adhering to the fibers is increased, and the properties derived from the carbon nanotubes can be further enhanced.

[0009] According to the present invention, a composite material is manufactured by attaching carbon nanotubes having a bent shape with bent portions to the surface of fibers in a structure as if they were woven like the fibers of a non-woven fabric. Therefore, the number of carbon nanotubes adhering to the fibers can be increased, and a composite material with further enhanced properties derived from the carbon nanotubes can be manufactured.

Brief Description of the Drawings

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[0011] [First Embodiment] [Composite Material] In FIG. 1, the composite material 10 includes fibers 11 and a structure 12 formed on the surface of the fibers 11. The structure 12 is formed by intertwining a plurality of carbon nanotubes (hereinafter referred to as CNTs) 14. This composite material 10 can be, for example, a fiber (hereinafter referred to as a resin-impregnated fiber) obtained by impregnating the structure 12 with a resin or the like, or can be used as a single filament constituting a multifilament or a reinforcing fiber of a fiber-reinforced molded body. The composite material 10 and resin-impregnated fibers, multifilaments, fiber-reinforced molded bodies, etc. (hereinafter referred to as secondary products) produced using such a composite material 10 have improved mechanical properties and the like by having the structure 12 on the surface of the fibers 11. That is, the mechanical properties and the like are improved due to the CNTs 14 adhering to the surface of the fibers 11.

[0012] As shown in FIG. 2, which shows an example of a multifilament 15 using the composite material 10, the multifilament 15 has a plurality of composite materials 10 and a matrix resin 16. In FIG. 2, a multifilament 15 composed of six composite materials 10 is depicted, but the number of composite materials 10 is not particularly limited, and for example, the multifilament 15 can be composed of several thousand to several hundred thousand. Also, a plurality of composite materials 10 can be twisted together to form one multifilament 15.

[0013] As the matrix resin 16, for example, a resin such as polyurethane or an elastomer such as synthetic rubber can be used. The matrix resin 16 is interposed between the composite materials 10 to bond the composite materials 10 to each other. This matrix resin is impregnated up to the structure 12 of each composite material 10 and cured.

[0014] The fiber 11 is not particularly limited, and examples include resin fibers such as nylon, polyester, vinylon, and acrylic, as well as glass fibers and mineral fibers. Also, the diameter of the fiber 11 is not particularly limited, and those within the range of 5 μm or more and 100 μm or less can be preferably used, and those within the range of 5 μm or more and 30 μm or less can be more preferably used. The fiber 11 is preferably a long fiber, and its length is preferably 50 m or more, more preferably within the range of 100 m or more and 100,000 m or less, and even more preferably within the range of 100 m or more and 10,000 m or less. Note that, for example, the fiber 11 may be cut short after the formation of the structure 12.

[0015] The CNTs 14 constituting the structure 12 are evenly dispersed and intertwined over substantially the entire surface of the fiber 11 to form a network structure in which a plurality of CNTs 14 are connected in a state of being intertwined with each other. The connection referred to here includes physical connection (mere contact) and chemical connection. The CNTs 14 are in direct contact with each other, that is, there are no dispersants such as surfactants or inclusions such as adhesives between them, and the CNTs 14 are in direct contact with each other.

[0016] As schematically shown in FIG. 3, some of the CNTs 14 constituting the structure 12 are directly attached and fixed to the surface of the fiber 11. As a result, the structure 12 is directly attached to the surface of the fiber 11. The direct attachment of the CNTs 14 to the surface of the fiber 11 means that the CNTs 14 are directly attached to the fiber 11 without the presence of dispersants such as surfactants or adhesives between the surface of the CNTs 14, and the attachment (fixation) is due to the bond by van der Waals force. Since some of the CNTs 14 constituting the structure 12 are directly attached to the surface of the fiber 11, the structure 12 is in a state of direct contact with the surface of the fiber 11 without the intervention of dispersants or adhesives.

[0017] As CNT14, those having a bent shape are used. As a result, among the CNT14 that make up the structure 12, there are some that are not in direct contact with the surface of the fiber 11 but are fixed to the fiber 11 by entangling with other CNT14. Furthermore, there are some that are directly attached to the surface of the fiber 11 and are fixed to the fiber 11 by entangling with other CNT14. Hereinafter, the fixing of CNT14 to these fibers 11 will be collectively referred to as adhesion to the fibers 11 and described. Note that the state where CNT14 is entangled or intertwined includes a state where a part of CNT14 is pressed against other CNT14.

[0018] In addition to directly adhering to the surface of the fiber 11 as described above, some of the CNT14 that make up the structure 12 are not in direct contact with the surface of the fiber 11 but are fixed to the fiber 11 by intertwining with other CNT14 or the like. Therefore, the structure 12 in this example is composed of more CNT14 than a structure composed only of CNT directly attached to the surface of the fiber like a conventional composite material structure. That is, the number of CNT14 attached to the fiber 11 is larger than that of the conventional one, and the thickness of the structure 12 is also larger than that of the conventional one.

[0019] As described above, since a plurality of CNT14 are connected to each other's surfaces without inclusions to form the structure 12, the composite material 10 exhibits the electrical conductivity and thermal conductivity performance derived from CNT. Also, since CNT14 is attached to the surface of the fiber 11 without inclusions, the CNT14 that make up the structure 12 are difficult to peel off from the surface of the fiber 11, and the mechanical strength of the composite material 10 and secondary products containing the same is improved. Moreover, since the thickness of the structure 12 is large, the above-mentioned mechanical strength is further improved. For this reason, even for a fiber 11 with a large diameter, a composite material 10 and a secondary product with improved mechanical strength can be obtained. Hereinafter, the case of a fiber-reinforced molded body as a secondary product will be described, but the same applies to the case of resin-impregnated fibers and multifilaments.

[0020] For example, in a fiber-reinforced molded body, a matrix resin is impregnated into and cured in a fiber bundle composed of a plurality of composite materials 10 in which a structure 12 is formed. Since the matrix resin of this fiber-reinforced molded body impregnates and cures in the structure 12, the structure 12 of each composite material 10 is fixed to the matrix resin together with the surface of the fiber 11. As a result, each fiber 11 is firmly adhered to the matrix resin, and the peel strength between the composite material 10 and the matrix resin is improved. Further, since such adhesion to the matrix resin extends over the entire composite material 10, the fiber-reinforcing effect can be obtained throughout the fiber-reinforced molded body.

[0021] Around each fiber 11 in the fiber-reinforced molded body, there is a region (hereinafter referred to as a composite region) formed by impregnating and curing a matrix resin into CNTs 14 constituting the structure 12 as described above. Since there are CNTs 14 rising from the surface of the structure 12, the concentration (density) of the CNTs 14 in the composite region decreases as the distance from the composite material 10 increases. In such a composite region, the CNTs 14 and the matrix resin are combined to have high strength and flexibility derived from the CNTs 14. Further, due to such a composite region, effects such as a stress concentration relaxation effect, a restraint effect for suppressing displacement of the composite material 10, and an effect of efficiently absorbing external mechanical energy can be obtained.

[0022] For example, when energy such as vibration propagates between the fibers 11, the energy of the propagating vibration is absorbed and attenuated by the friction of the composite regions around the respective fibers 11. As a result, for example, the vibration damping characteristics (vibration isolation performance) of the fiber-reinforced molded body are improved. Further, when an external force is applied to the fiber-reinforced molded body and displacement occurs inside it, displacement occurs in the fibers 11 inside the fiber-reinforced molded body. Due to the displacement of the fibers 11, elongation occurs in the structure 12 of the composite region, and a restraint effect is obtained due to the network structure of the CNTs 14. As a result, the characteristics of the CNTs 14 are exhibited and the elastic modulus of the fiber-reinforced molded body is increased.

[0023] The properties derived from CNT14 in the fiber-reinforced molded body are manifested by the properties of the composite region as described above, the effects of the composite region, etc. Since the structure 12 increases the number of CNT14s attached to the fiber 11 as described above and has a structure in which the CNT14s are woven like the fibers of the nonwoven fabric, the properties derived from the CNTs in the fiber-reinforced molded body are higher than those of the composite material in which a structure like the structure 12 is not formed.

[0024] The structures 12 formed in each of the plurality of composite materials 10 have independent structures, and the structure 12 of one composite material 10 and the structure 12 of the other composite material 10 do not share the same CNT14. That is, the CNT14 included in the structure 12 provided on one fiber 11 is not included in the structure 12 provided on the other fiber 11.

[0025] For example, a sizing agent (not shown) is fixed to the surface of the CNT14 constituting the structure 12. This sizing agent is composed of a reaction-curable resin, a thermosetting resin, or a cured or uncured product of a thermoplastic resin. The sizing agent is formed by performing a sizing treatment.

[0026] The sizing agent covers the surface of the CNT14, and at the contact portion where the CNT14s are in contact with each other, an inclusion portion that wraps around the contact portion is formed. This inclusion portion makes the state in which the CNT14s are in contact with each other stronger and makes the structure 12 more difficult to collapse. In the inclusion portion, the sizing agent is fixed to each CNT14 in a state where it does not enter between the contacting CNT14s, so the CNT14s in the contact portion are in direct contact with each other.

[0027] In addition, in the structure 12, a plurality of CNTs 14 form voids (meshes) surrounded by them. In order not to prevent the impregnation of the matrix resin into the structure 12, it is preferable that the sizing agent does not block the voids. In order not to block the voids, the volume of the sizing agent is preferably 30% or less with respect to the volume of the CNTs 14 in the structure 12. The sizing agent is formed on the surface of the CNTs 14 and is different from a fixing resin portion described later that enters the structure 12 and fixes the CNTs 14 to the fibers 11. Further, it is not necessary to apply a sizing agent to the structure 12.

[0028] As described above, the CNTs 14 attached to the fibers 11 have a bent shape. This bent shape of the CNTs 14 is due to the presence of five-membered rings, seven-membered rings, etc. in the graphite structure of the CNTs 14, having bent portions (bending portions). It is a shape that can be evaluated as the CNTs 14 being curved, bent, etc. by observation with SEM. For example, the bent shape of the CNTs 14 means that there is at least one bending portion per average length in the range of use of the CNTs 14 described later. Even when such bent CNTs 14 are long, they adhere to the surface of the curved fibers 11 in various postures. Also, in the bent CNTs 14, a space (gap) is easily formed between the surface of the fibers 11 to which they are attached and between the attached CNTs 14, and other CNTs 14 enter this space. Therefore, by using bent CNTs 14, the number of CNTs 14 attached to the fibers 11 (the number of CNTs 14 forming the structure 12) is larger than when using CNTs having a highly linear shape.

[0029] The length of CNT14 is preferably in the range of 0.1 μm or more and 10 μm or less. If the length of CNT14 is 0.1 μm or more, CNT14s can be more surely intertwined with each other to form the structure 12 in direct contact or directly connected, and at the same time, the space into which other CNT14s can enter can be more surely formed as described above. Also, if the length of CNT14 is 10 μm or less, CNT14 will not span and adhere between the fibers 11. That is, as described above, CNT14 included in the structure 12 provided on one fiber 11 will not be included in the structure 12 provided on another fiber 11.

[0030] More preferably, the length of CNT14 is in the range of 0.2 μm or more and 5 μm or less. If the length of CNT14 is 0.2 μm or more, the number of CNT14s attached can be increased to thicken the structure 12, and if it is 5 μm or less, when CNT14 is attached to the fiber 11, CNT14 is less likely to aggregate and is more likely to be evenly dispersed. As a result, CNT14 adheres to the fiber 11 more uniformly.

[0031] Note that it does not exclude the mixing of CNTs with high linearity or CNTs outside the above length range as the CNTs attached to the fiber 11. Even if there is mixing, for example, by allowing CNTs with high linearity to enter the space formed by CNT14, the number of CNTs attached to the fiber 11 can be increased.

[0032] CNT14 preferably has an average diameter in the range of 1 nm or more and 15 nm or less, more preferably in the range of 3 nm or more and 10 nm or less. If the diameter of CNT14 is 15 nm or less, it is rich in flexibility, easily adheres along the surface of fiber 11, easily entangles with other CNT14s and is fixed to fiber 11, and further ensures the formation of structure 12. Also, if it is 10 nm or less, the bonding between CNT14s constituting structure 12 becomes strong. The diameter of CNT14 is the value measured using a transmission electron microscope (TEM) photograph. CNT14 can be either single-layer or multi-layer, but preferably multi-layer.

[0033] By forming CNT14 into a bent shape as described above, compared with the case of using a highly linear CNT, the number of CNT14s adhering to fiber 11 can be increased, the thickness of structure 12 can be increased, and a structure 12 is formed in which CNT14s are woven like non-woven fabric fibers. As a result, not only is the mechanical strength higher, but when an external force is applied to the secondary product and fiber 11 is displaced, the restraining effect of structure 12 is large, and the elastic modulus is further increased. Also, the mechanical energy absorption effect of the composite region around fiber 11 is increased, and the vibration damping characteristics of the secondary product are further improved.

[0034] As one of the improved mechanical strengths of the secondary product, an improvement in durability against repeated bending can be cited. As described above, in the fiber-reinforced molded body using the composite material 10 with CNTs 14 attached to the surface of the fibers 11, the durability against repeated bending is considered to be enhanced by the effect of improving the peel strength due to the interposition of the structure 12 and the effect of absorbing mechanical energy by the composite region. The improvement in this peel strength and the effect of absorbing mechanical energy are enhanced as the number of CNTs 14 attached to the surface of the fibers 11 increases, resulting in higher durability against repeated bending. The composite material 10 having such characteristics is suitable as a spring material such as a coil spring or a leaf spring to which a load is repeatedly applied, and the secondary product containing the composite material 10 can be applied to various springs such as a coil spring or a leaf spring.

[0035] In addition, in a secondary product using the composite material 10, for example, a fiber-reinforced molded body, a crosslinked structure that crosslinks the fibers 11 is formed by the composite regions in which the structure 12 is impregnated with the matrix resin and cured being fixed to each other. The composite region in which the impregnated matrix resin is cured has a higher hardness than the cured matrix resin alone and a large elastic limit, that is, high elasticity. In addition, the composite region has higher wear resistance than the matrix resin. By the bonding of such composite regions, the bonding between the composite materials 10 becomes strong, and the durability of the fiber-reinforced molded body using the composite material 10 against repeated bending is improved. Since the crosslinked structure is formed when the distance between the composite materials 10 is close to the extent that the structures 12 contact each other, the greater the thickness of the structure 12, the more advantageous it is to increase the crosslinking. Further, when the composite material 10 is formed into a fabric shape or bundled like a multifilament, the number of crosslinked portions where the composite regions are fixed to each other increases, and the effect of the crosslinked structure becomes greater.

[0036] The thickness of each part of the structure 12 (the length in the radial direction of the fiber 11) can be obtained, for example, by adhering a part of the structure 12 on the surface of the fiber 11 to cellophane tape or the like and then peeling it off, and measuring the cross-section of the structure 12 remaining on the surface of the fiber 11 by SEM or the like. The average of the thicknesses of the structure 12 measured at 10 locations within the measurement range is taken as the thickness of the structure 12 so as to substantially evenly cover a measurement range of a predetermined length along the fiber axis direction of the fiber 11. The length of the measurement range is, for example, set to be 5 times the upper limit of the length range of the above-described CNT14. The number of CNT14s attached to the fiber 11 can be evaluated by the thickness of the structure 12.

[0037] The thickness (average) of the structure 12 obtained as described above is in the range of 10 nm or more and 300 nm or less, preferably in the range of 15 nm or more and 200 nm or less, and more preferably in the range of 50 nm or more and 200 nm or less. If the thickness of the structure 12 is 200 nm or less, the impregnation property of the resin between the fibers 11 is better.

[0038] [Manufacturing Method of Composite Material] Next, the manufacturing of the composite material 10 will be described. In this example, the case of manufacturing the composite material 10 using a fiber bundle 20 (see FIG. 4) composed of a plurality of fibers 11 will be described, but the composite material 10 can be manufactured in the same manner using individual fibers 11 instead of the fiber bundle 20.

[0039] The fibers 11 constituting the fiber bundle 20 have their fiber axis directions aligned such that the fibers 11 do not substantially entangle with each other. The fiber axis direction is the direction (extended direction) of the axis of the fiber 11. In this example, the fiber bundle 20 is composed of a plurality of fibers 11. The number of fibers 11 constituting the fiber bundle 20 is not particularly limited, but can be, for example, in the range of 100 or more and 10 million or less.

[0040] The entanglement of the fibers 11 in the fiber bundle 20 can be evaluated by the degree of disorder of the fibers 11. For example, the fiber bundle 20 is observed at a certain magnification with a scanning electron microscope (SEM: Scanning Electron Microscope), and the lengths of a predetermined number (for example, 10) of the fibers 11 in the observed range (the range of a predetermined length of the fiber bundle 20) are measured. Based on the variation in the lengths of the predetermined number of fibers 11 obtained from this measurement result, the difference between the maximum value and the minimum value, and the standard deviation, the degree of disorder of the fibers 11 can be evaluated. Further, the fact that the fibers 11 are not substantially entangled can also be determined by measuring the degree of entanglement according to, for example, the method for measuring the degree of entanglement in JIS L1013:2010 "Test Methods for Chemical Fiber Filament Yarns". The smaller the measured degree of entanglement, the less entanglement there is between the fibers 11 in the fiber bundle 20.

[0041] A fiber bundle 20 in which the fibers 11 are not substantially entangled with each other or are less entangled is easy to uniformly fibrillate the fibers 11. As a result, it is easy to uniformly attach the CNTs 14 to each of the fibers 11, and the resin uniformly impregnates the fiber bundle 20, and each of the composite materials 10 contributes to the strength.

[0042] To form the structure 12 by attaching the CNTs 14 to each of the fibers 11 of the fiber bundle 20, the fiber bundle 20 is immersed in a CNT isolated dispersion liquid (hereinafter simply referred to as a dispersion liquid) in which the CNTs 14 are isolated and dispersed, and mechanical energy is applied to the dispersion liquid. Isolated dispersion means a state in which the CNTs 14 are physically separated one by one and are dispersed in the dispersion medium without being entangled, and refers to a state in which the ratio of aggregates in which two or more CNTs 14 are aggregated in a bundle shape is 10% or less. Here, if the ratio of the aggregates is 10% or more, the aggregation of the CNTs 14 in the dispersion medium is promoted, and the adhesion of the CNTs 14 to the fibers 11 is inhibited.

[0043] As shown in an example in FIG. 4, the adhesion device 21 is composed of a CNT adhesion tank 22, guide rollers 23 to 26, an ultrasonic generator 27, a traveling mechanism (not shown) for running the fiber bundle 20 at a constant speed, etc. A dispersion liquid 28 is accommodated in the CNT adhesion tank 22. The ultrasonic generator 27 irradiates ultrasonic waves on the dispersion liquid 28 in the CNT adhesion tank 22 from below the CNT adhesion tank 22.

[0044] A long fiber bundle 20 (for example, about 100 m in length) without the structure 12 formed thereon is continuously supplied to the adhesion device 21. The supplied fiber bundle 20 is wound around the guide rollers 23 to 26 in order and runs at a constant speed by the traveling mechanism. The adhesion device 21 is supplied with a fiber bundle 20 in which the sizing agent is not attached to each fiber 11. Here, the sizing agent is one that adheres to the surface of the fiber 11 to prevent entanglement of the fibers 11 and is different from the above-mentioned sizing agent and the fixed resin part.

[0045] The fiber bundle 20 is wound around the guide rollers 23 to 26 in an open-fiber state. The fiber bundle 20 wound around the guide rollers 23 to 26 has an appropriate tension acting thereon, thereby reducing the possibility of the fibers 11 being entangled. It is preferable that the winding of the fiber bundle 20 around the guide rollers 24 to 26 is at a smaller winding angle (90° or less).

[0046] The guide rollers 23 to 26 are all flat rollers. As shown in FIG. 5, the roller length (axial length) L1 of the guide roller 23 is made sufficiently larger than the width WL of the open-fiber fiber bundle 20. The same applies to the guide rollers 24 to 26, and their roller lengths are made sufficiently larger than the width WL of the open-fiber fiber bundle 20. For example, the guide rollers 23 to 26 are all of the same size. In the open-fiber fiber bundle 20, a plurality of fibers 11 are arranged in the thickness direction (radial direction of the guide roller).

[0047] Among the guide rollers 23 to 26, the guide rollers 24 and 25 are arranged in the CNT adhesion tank 22. Thereby, between the guide rollers 24 and 25, the fiber bundle 20 travels linearly at a certain depth in the dispersion liquid 28.

[0048] The traveling speed of the fiber bundle 20 is preferably in the range of 0.5 m / min or more and 10,000 m / min or less. The higher the traveling speed of the fiber bundle 20, the more the productivity can be improved. The lower the traveling speed, the more effective it is for the uniform adhesion of the CNTs 14, and it is also effective for suppressing the entanglement of the fibers 11. Also, the less the entanglement of the fibers 11, the higher the uniformity of the adhesion of the CNTs 14 to the fibers 11 can be. If the traveling speed of the fiber bundle 20 is 100 m / min or less, the entanglement of the fibers 11 can be more effectively suppressed, and the uniformity of the adhesion of the CNTs 14 can be made higher. Also, the traveling speed of the fiber bundle 20 is more preferably in the range of 5 m / min or more and 50 m / min or less.

[0049] The ultrasonic generator 27 applies ultrasonic vibration as mechanical energy to the dispersion liquid 28. Thereby, in the dispersion liquid 28, a reversible reaction state in which the dispersed state in which the CNTs 14 are dispersed and the aggregated state in which they are aggregated alternately changes is created. When the fiber bundle 20 is passed through the dispersion liquid 28 in this reversible reaction state, when shifting from the dispersed state to the aggregated state, the CNTs 14 adhere to each fiber 11 by van der Waals forces. The mass of the fiber 11 with respect to the CNT 14 is more than 100,000 times larger, and the energy for the adhered CNT 14 to desorb is larger than the energy by the ultrasonic vibration. Therefore, the CNTs 14 once adhered to the fiber 11 are not peeled off from the fiber 11 even by the ultrasonic vibration after adhesion. Note that since the masses of the CNTs 14 are all extremely small, they alternately change between the dispersed state and the aggregated state by the ultrasonic vibration.

[0050] By repeatedly transitioning from a dispersed state to an aggregated state, a large number of CNTs 14 adhere to each fiber 11, respectively, and the structure 12 is formed. As described above, by using CNTs 14 having a bent shape, other CNTs 14 enter the spaces formed between the CNT 14 and the surface of the fiber 11 to which it adheres, or between the adhered CNTs 14, etc., so that more CNTs 14 adhere to the fiber 11 and the structure 12 is formed.

[0051] The frequency of the ultrasonic vibration applied to the dispersion liquid 28 is preferably 40 kHz or more and 950 kHz or less. If the frequency is 40 kHz or more, the entanglement between the fibers 11 in the fiber bundle 20 is suppressed. Also, if the frequency is 950 kHz or less, the CNT 14 adheres well to the fiber 11. In order to further reduce the entanglement of the fibers 11, the frequency of the ultrasonic vibration is preferably 100 kHz or more, more preferably 130 kHz or more. Also, the frequency of the ultrasonic vibration is more preferably 430 kHz or less.

[0052] Also, the inventors have found that the number of CNTs 14 adhering to the fiber 11 becomes almost maximum while ensuring the uniformity of the adhesion of the CNT 14 to the fiber 11 when the number of transitions of the CNT 14 from the dispersed state to the aggregated state is 65,000 times. The maximum value of the number of adherences varies depending on the CNT concentration of the dispersion liquid 28, and the higher the CNT concentration of the dispersion liquid 28, the larger it becomes. However, when the CNT concentration of the dispersion liquid 28 becomes so high that the CNT 17 cannot be in a dispersed state when ultrasonic vibration is applied, the CNT 17 cannot adhere to the fiber 11.

[0053] Therefore, the length of the period during which the fiber bundle 20 travels in the dispersion liquid 28, that is, the time taken to travel between the guide rollers 24 and 25 (hereinafter referred to as the immersion time), is 65,000 times or more the period of the ultrasonic vibration applied to the dispersion liquid 28. It is preferable to determine the traveling speed of the fiber bundle 20, the distance that the fiber bundle 20 travels in the dispersion liquid 28 (the interval between the guide rollers 24 and 25), and the frequency of the ultrasonic vibration applied to the dispersion liquid 28. That is, when the frequency of the ultrasonic vibration is fs (Hz) and the immersion time is Ts (seconds), it is preferable to satisfy "Ts ≧ 65,000 / fs". For example, if the frequency of the ultrasonic vibration is 130 kHz and the distance that the fiber bundle 20 travels in the dispersion liquid 28 is 0.1 m, the traveling speed of the fiber bundle 20 may be 12 m / min or less. Also, even when the fiber bundle 20 is immersed in the dispersion liquid 28 in multiple portions, the total immersion time being 65,000 times or more the period of the ultrasonic vibration can make the number of CNTs 14 attached almost maximum.

[0054] As schematically shown in FIG. 6, a standing wave with a determined sound pressure (amplitude) distribution is generated in the dispersion liquid 28 in the CNT adhesion tank 22 by the ultrasonic vibration applied from the ultrasonic generator 27. In this adhesion device 21, the positions of the guide rollers 24 and 25 in the depth direction are adjusted so that the fiber bundle 20 travels at the node of the standing wave of the ultrasonic vibration, that is, at the depth where the sound pressure becomes extremely small, in the dispersion liquid 28. Therefore, the depth from the liquid surface of the dispersion liquid 28 in which the fiber bundle 20 travels in the dispersion liquid 28 is determined to satisfy "D = n·(λ / 2)", where D is the depth, λ is the wavelength of the standing wave of the ultrasonic vibration generated in the dispersion liquid 28, and n is an integer of 1 or more. The wavelength λ of the standing wave can be obtained based on the speed of sound in the dispersion liquid 28 and the frequency of the ultrasonic vibration applied from the ultrasonic generator 27.

[0055] As described above, by adjusting the depth of the fiber bundle 20 traveling in the dispersion liquid 28, the vibration of the fiber 11 caused by the sound pressure can be suppressed, the yarn entanglement due to yarn slack can be prevented, the rubbing between the fibers 11 or between the CNTs 14 attached to the surfaces of the respective fibers 11 can be suppressed, and the thick structure 12 can be formed. The larger the diameter of the fiber 11, the greater the influence of the vibration caused by the standing wave. Therefore, by satisfying the condition of the depth at which the fiber bundle 20 travels in the dispersion liquid 28, the effect of suppressing the vibration of the fiber 11 can be remarkably obtained. In addition, it is difficult for the fiber 11 to elongate in the fiber axis direction due to the sound pressure of the standing wave, and plastic deformation of the fiber 11 in the fiber axis direction can be prevented. Note that the depth at which the fiber bundle 20 travels in the dispersion liquid 28 may deviate slightly from the node of the standing wave. In that case, it is preferably in the range of n·λ / 2 - λ / 8 or more and n·λ / 2 + λ / 8 or less (n·λ / 2 - λ / 8 ≦ D ≦ n·λ / 2 + λ / 8). Thereby, the yarn entanglement due to the yarn slack of the fiber 11 can be made within an allowable range.

[0056] The fiber bundle 20 is dried after being drawn out from the dispersion liquid 28. By sequentially performing sizing treatment and drying on the dried fiber bundle 20, the sizing agent is applied to the structure 12. The sizing treatment can be performed by a general method.

[0057] The sizing agent is not particularly limited, and various reaction-curable resins, thermosetting resins, and thermoplastic resins can be used as described above. For example, examples of thermosetting resins include epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, alkyd resins, thermosetting polyimides, resins having reactive groups, and the like. Examples of thermoplastic resins include general-purpose resins such as polyethylene, polypropylene, polystyrene, acrylonitrile / styrene (AS) resins, acrylonitrile / butadiene / styrene (ABS) resins, methacrylic resins (such as PMMA), and vinyl chloride, engineering plastics such as polyamides, polyacetals, polyethylene terephthalate, ultra-high molecular weight polyethylene, and polycarbonate, and super engineering plastics such as polyphenylene sulfide, polyether ether ketone, liquid crystal polymer, polytetrafluoroethylene, polyether imide, polyarylate, and polyimide. In the sizing treatment, it is preferable to use a solution in which the resin serving as the sizing agent is dissolved, and the sizing agent is preferably attached to the CNT 14 of the structure 12 by applying the solution to the fiber bundle 20 or the like.

[0058] [Dispersion liquid] The dispersion liquid 28 used when attaching the CNT 14 to the composite material 10 is prepared, for example, by adding long CNTs (hereinafter referred to as material CNTs) to a dispersion medium and cutting the material CNTs into CNTs 14 of a desired length by a homogenizer, a shearing force, an ultrasonic disperser, or the like, and by making the dispersion of the CNT 14 uniform.

[0059] As the dispersion medium, water, alcohols such as ethanol, methanol, and isopropyl alcohol, organic solvents such as toluene, acetone, tetrahydrofuran (THF), methyl ethyl ketone (MEK), hexane, normal hexane, ethyl ether, xylene, methyl acetate, and ethyl acetate, and mixtures of these in any ratio can be used. The dispersion liquid 28 does not contain a dispersant or an adhesive.

[0060] The material CNT that is the source of the CNT14 with the bent shape as described above is in a bent shape. Such a material CNT preferably has uniform diameters of individual material CNTs. An example of the material CNT is shown in the SEM photograph of FIG. 7. The material CNT is preferably one that can isolate and disperse CNTs even if the lengths of the individual CNTs generated by cutting are large. Thereby, the dispersion liquid 28 in which the CNT14 satisfying the above-described length conditions is isolated and dispersed can be easily obtained.

[0061] In the composite material 10 of this example, as described above, since the bent-shaped CNT14 is adhered, other CNT14s enter the spaces formed between the CNT14 and the surface of the fiber 11 to which it is adhered, or between the adhered CNT14s. As a result, more CNT14s adhere to the fiber 11. Further, since the CNT14 firmly adheres to the fiber 11 to form the structure 12, it is more difficult for the CNT14 to peel off from the fiber 11. And the fiber-reinforced molded body produced using such a composite material 10 has higher characteristics derived from CNT.

[0062] The secondary product produced using the composite material 10 as described above has improved mechanical properties such as vibration damping characteristics (vibration isolation properties) and change characteristics of elastic modulus compared to the secondary product using the conventional composite material. Regarding the change characteristics of the elastic modulus, an increase in the elastic modulus of the fiber-reinforced molded body is suppressed with respect to an increase in the impact velocity on the fiber-reinforced molded body.

[0063] The concentration of CNT14 in the dispersion liquid 28 is preferably in the range of 0.003 wt% or more and 3 wt% or less. The concentration of CNT14 in the dispersion liquid 28 is more preferably 0.005 wt% or more and 0.5 wt% or less.

[0064] In the above embodiment, the fixation of CNTs to the surface of the fiber is due to the bonding by the van der Waals force between the fiber and the CNTs. In addition to this, a binding part for reinforcing the fixation of CNTs to the surface of the fiber may be provided. The binding part is, for example, an epoxy resin that has hardened in a state of entering the gap formed between the surfaces (circumferential surfaces) of the fiber and the CNTs directly attached (contacted) thereto. The epoxy resin is dissolved in a solvent such as toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), butanol, ethyl acetate or butyl acetate to form a solution. After immersing a fiber bundle containing the fiber in which the structure is formed in this solution, it is heated. Thereby, the uncured epoxy resin is allowed to enter the gap formed between the surfaces of the fiber and the CNT and cured.

[0065] In forming the binding part, an emulsion of the solution of the epoxy resin, which is the material of the binding part, may be used. For example, it can be emulsified by adding an emulsifier such as a nonionic emulsifier to a solution in which the epoxy resin is dissolved in a solvent. As the binding part, in addition to the epoxy resin, for example, a phenol resin, a polyurethane resin, a melamine resin, a urea resin, a polyimide resin, etc. may be used. Also, a silane coupling agent or an inorganic adhesive can be used as the binding part.

[0066] [Second Embodiment] The composite material of the second embodiment has a plurality of fixing resin parts that partially fix a part of the plurality of CNTs constituting the structure to the surface of the fiber. Since the composite material of the second embodiment is the same as the composite material of the first embodiment except that the fixing resin part is provided instead of the sizing agent, substantially the same members are denoted by the same reference numerals and the detailed description thereof is omitted.

[0067] In FIG. 8, the composite material 10A is provided with a plurality of fixing resin parts 38 that partially fix a part of the plurality of CNTs 14 constituting the structure 12 to the surface of the fiber 11. The composite material 10A is used as a resin-impregnated fiber, or as a single fiber constituting a multifilament or a reinforcing fiber of a fiber-reinforced molded body.

[0068] The fixed resin part 38 is formed by curing resin in a granular state that reaches from the surface of the structure 12 to the surface of the fiber 11. The fixed resin part 38 adheres to the surface of the fiber 11 to which its bottom part is attached, and also adheres to the CNT 14 of the structure 12 that covers the part above the bottom. In this way, the fixed resin part 38 fixes the CNT 14 to the fiber 11 by adhering to both the surface of the fiber 11 and a part of the CNT 14.

[0069] As described above, the fixed resin part 38 partially fixes a part of the plurality of CNTs 14 constituting the structure 12 to the surface of the fiber 11. It is provided so as to be scattered on the surface of the fiber 11, and fixes the CNT 14 of the structure 12 at each location. The fixed resin parts 38 provided in such a scattered manner have their upper parts exposed on the surface of the structure 12 and are also observed to be scattered on the surface of the structure 12.

[0070] As schematically shown in FIG. 9, the fixed resin part 38 is formed in a range that reaches from the surface of the structure 12 to the surface of the fiber 11 in the radial direction of the fiber 11 (the thickness direction of the structure 12). It adheres to the surface of the fiber 11 and also adheres to a part of the CNT 14 contained therein.

[0071] Regarding the CNT 14 of the structure 12, there are some cases where the part adhering to the surface of the fiber 11, the part overlapping or sandwiched by other CNTs 14 are adhered to the fixed resin part 38. Also, for some CNTs 14, their end parts or central parts are adhered to the fixed resin part 38. In this way, the CNT 14 adhered to the fixed resin part 38 is strongly fixed to the fiber 11 by the fixed resin part 38. The part of the CNT 14 not covered by the fixed resin part 38 adheres to the surface of the fiber 11 by van der Waals force as described above, so it is lifted away from the surface of the fiber 11 by the action of a weaker force compared to the part fixed by the fixed resin part 38 and can move on the surface of the fiber 11. Also, on the surface of the structure 12, the part of the CNT 14 not fixed by the fixed resin part 38 is in a free state where it can be lifted away from the surface of the structure 12.

[0072] As described above, by fixing the CNT 14 of the structure 12 with the fixing resin portion 38, partial detachment of the structure 12 is suppressed as compared with the case where the CNT 14 of the structure 12 is not fixed with the fixing resin portion 38. Thereby, the properties derived from the CNT of the fiber-reinforced molded body are further enhanced. Since the CNT 14 of the fixing resin portion 38 is constrained on the surface of the fiber 11, it becomes easy to flow an electric current from the fiber 11, and thus it can contribute to improving the conductivity of the fiber-reinforced molded body.

[0073] Note that all of the CNT 14 constituting the structure 12 may be fixed to the fiber 11 by the fixing resin portion 38, but it is sufficient if a part of the CNT 14 is fixed. That is, at least a part of the CNT 14 constituting the structure 12 may be fixed with the fixing resin portion 38. Since the CNT 14 forms a film as the structure 12 having a non-woven fabric structure, the performance can be exhibited if at least a part of the CNT 14 constituting the structure 12 is fixed.

[0074] The fixing resin portion 38 preferably has a number ratio N, which is the number per 5 μm square on the surface (outer peripheral surface) of the structure 12 in plan view, within a range of 27 or more and 130 or less. Further, on the surface of the structure 12 in plan view, the area ratio S of the fixing resin portion 38 is preferably within a range of 6% or more and 45% or less, and more preferably within a range of 7% or more and 30% or less. The area ratio S is the ratio of the area covered by the plurality of fixing resin portions 38 to the surface area of the structure 12 on the surface of the structure 12 in plan view, and is obtained by "S = S1 / S2 × 100 (%)", where S2 is the surface area of the structure 12 within a predetermined range and S1 is the area covered by each fixing resin portion 38 within the predetermined range on the surface of the structure 12. Plan view means observing the peripheral surface of the structure 12 in a planar manner from a direction orthogonal to the fiber axis direction of the fiber 11.

[0075] Since the thickness of the structure 12 is sufficiently smaller than the radius of the fiber 11, the surface of the structure 12 can be regarded as the surface of the fiber 11, and for each fixing resin portion 38, it can be regarded that the area of the fixing resin portion 38 covering the surface of the structure 12 and the area of the fixing resin portion 38 covering the surface of the fiber 11 are substantially the same. Therefore, the above-mentioned number ratio N and area ratio S can be regarded as the number ratio of the fixing resin portions 38 per 5 μm square on the surface (outer peripheral surface) of the fiber 11 in plan view, and the ratio of the area of the fixing resin portion 38 covering the surface of the fiber 11 to the surface area of the fiber 11 on the surface of the fiber 11 in plan view.

[0076] Actually, when counting the number ratio N and obtaining the area ratio S, for example, the structure 12 formed on the peripheral surface of the fiber 11 is observed planarly using an SEM photograph. Then, a 5 μm square observation frame is set on the planar observation image of the structure 12 in the SEM photograph, the number of the fixing resin portions 38 within the observation frame is counted, and this number is taken as the number ratio N. Similarly, the area of each fixing resin portion 38 observed within the observation frame is obtained respectively, and the area ratio S can be calculated by taking the sum of the areas of these fixing resin portions 38 as the area S1 and the area of the observation frame as the surface area S2. The observation frame G is preferably set such that its centroid coincides with the center in the radial direction of the fiber 11.

[0077] Increasing the number ratio N and the area ratio S can reliably fix the CNT 14 to the surface of the fiber 11 and reduce the partial detachment of the structure 12. Also, decreasing the number ratio N and the area ratio S increases the portion of the CNT 14 not fixed by the fixing resin portion 38, and increases the degree of freedom of the CNT 14, and thus the degree of freedom of the structure 12.

[0078] If the above-mentioned number ratio N is 27 or more or the area ratio S is 6% or more, the CNT 14 can be surely fixed to the fiber 11 by the fixing resin portion 38, the effect of reducing the partial dropout of the structure 12 can be surely obtained, and the characteristics derived from the CNT of the fiber-reinforced molded body can be further enhanced. Further, if the number ratio N is 130 or less or the area ratio S is 45% or less, the CNT 14 covered entirely with the fixing resin portion 38 can be made sufficiently small. Thereby, the characteristics derived from the CNT of the fiber-reinforced molded body, particularly the effect based on the fact that a part of the CNT 14 floats from the surface of the structure 12 can be surely obtained. It is preferable that the number ratio N and the area ratio S are simultaneously within the above ranges.

[0079] As will be described later, under certain conditions, the area ratio S can be increased or decreased substantially proportionally to the number ratio N, and the number ratio N and the area ratio S can be made to satisfy the above conditions simultaneously. When the above area ratio S is satisfied, the total area of the fixing resin portions 38 within a 5-μm square on the surface of the structure 12 in plan view is 1.5 μm 2 ~11.25 μm 2 within the range.

[0080] Further, the substantial area per one of the fixing resin portions 38 on the surface of the structure 12 is preferably within the range of 0.03 μm 2 or more and 1.12 μm 2 or less. If the individual area of the fixing resin portion 38 is 0.03 μm 2 or more, the fixing force for surely fixing the CNT 14 to the surface of the fiber 11 can be obtained. Also in this case, the effect of reducing the partial dropout of the structure 12 can be surely obtained. If the individual area of the fixing resin portion 38 is 1.12 μm 2 or less, sufficient freedom degree of the CNT 14 can be obtained.

[0081] The area ratio S, the number ratio N, and the individual substantial area of the fixing resin portion 38 in plan view can be obtained using image analysis software (for example, Winroof2015 (manufactured by Mitani Corporation)).

[0082] As described above, a fiber-reinforced molded body or the like produced from the composite material 10A including the structure 12 composed of the bent CNTs 14 has characteristics improved as compared with the conventional ones due to the CNTs 14.

[0083] The elastic modulus of the fiber-reinforced molded body using the composite material 10A is increased by the restraint effect that suppresses the displacement of the fibers 11 in the composite region. Further, in the fiber-reinforced molded body, due to the restraint effect in the composite region between the fibers, an increase in the elastic modulus of the fiber-reinforced molded body is suppressed with respect to an increase in the collision speed to the fiber-reinforced molded body. As a result, the velocity dependence of the elastic modulus is reduced. Furthermore, the progress resistance of the delamination crack can be made larger by the fixed resin portion 38.

[0084] The manufacturing process of the composite material 10A is the same as that of the first embodiment except that a fixed resin application process for forming the fixed resin portion 38 is performed instead of the sizing process of attaching a sizing agent to the surface of the structure 12. That is, the fixed resin portion 38 is formed by performing a fixed resin application process on the fiber bundle 20 dried after being drawn out from the dispersion liquid 28 (see FIG. 2). The fixed resin application process can be a process according to the material and form of the fixed resin portion 38.

[0085] As a preferable method of the fixed resin application process, there is one using an emulsion-type treatment liquid in which an uncured resin (polymer) that becomes the fixed resin portion 38 is dispersed in a liquid droplet form in a dispersion medium. In this method, an adhesion process of opening the fiber bundle 20 in which the structure 12 is formed on each fiber 11 and bringing it into contact with the treatment liquid to adhere the resin to the fiber bundle 20, and a curing process of evaporating the dispersion medium and curing the resin to form the fixed resin portion 38 are sequentially performed.

[0086] As the resin in the treatment liquid, a resin having a property of curing, that is, a curable resin is used. As the curable resin, any of a thermosetting resin, a reaction curable resin, etc. may be used. Note that the cured resin obtained by curing the curable resin may be a thermoplastic resin. Specifically, examples include epoxy resins, urethane resins, urea resins, polyimide resins, vinyl acetate, acrylic resins, olefin resins, vinyl chloride, phenol resins, melamine resins, rubber-based, silicone-based resins, and inorganic adhesives, etc., but are not limited thereto.

[0087] Note that the fixing resin part 38 preferably has a high affinity with the matrix resin. For this reason, it is preferable that the fixing resin part 38 and the matrix resin are, for example, a combination of polar resins or a combination of non-polar resins.

[0088] Examples of the dispersion medium of the treatment liquid include water, ethanol, acetone, MEK, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, toluene, and xylene, etc. These dispersion media can be used alone or in combination of two or more. From the viewpoints of handleability and safety, water is preferable as the dispersion medium. The concentration of the resin in the treatment liquid after dilution is appropriately adjusted so as to be the target adhesion amount of the fixing resin part 38 (the ratio (wt%) of the mass of the fixing resin part 38 to the composite material 10A). The adhesion amount of the fixing resin part 38 on the surface of the fiber 11 after the drying treatment is preferably in the range of 0.1 wt% or more and 5.0 wt% or less, more preferably in the range of 0.3 wt% or more and 3.0 wt% or less.

[0089] The particle size of the resin in the treatment liquid is preferably in the range of 0.05 μm or more and 1 μm or less, and more preferably in the range of 0.1 μm or more and 0.4 μm or less. The particle size of the resin in the treatment liquid can be determined by a laser analysis method. If the particle size of the resin in the treatment liquid is 0.05 μm or more, CNT14 can be surely fixed on the surface of the fiber 11. If it is 1 μm or less, the resin can surely enter between CNT14s constituting the structure 12, and it can be surely prevented that CNT14 is covered with the resin. Further, if it is 0.1 μm or more, it is a resin size sufficient to fix the non-woven fabric-like structure 12, and if it is 0.4 μm or less, partial fixing of the structure 12 becomes possible.

[0090] When an emulsion-type treatment liquid containing a resin having a particle size in the range of 0.1 μm or more and 0.4 μm or less is used, the fixing resin portions 38 each having an area in the range of 0.03 μm 2 or more and 1.12 μm 2 or less can be formed. When a treatment liquid adjusted so that the adhesion amount of the fixing resin portion 38 after the curing treatment is about 0.1 mass% to 5.0 mass% is used, the number ratio N can be in the range of 27 or more and 130 or less.

[0091] The method of the adhesion treatment using the treatment liquid is not particularly limited, and examples thereof include a roller dipping method, a roller contact method, a spray method, etc. Also, the method of the curing treatment is not particularly limited, and for example, hot air, a hot plate, a heating roller, various infrared heaters, etc. can be used.

[0092] Fig. 10 shows a flat belt 40 as an example of a product using the composite material 10. This flat belt 40 is used, for example, as a power transmission belt or the like. The flat belt 40 has a structure in which a reinforcing cloth 42 and a surface rubber layer 43 are laminated on both surfaces of an inner rubber layer 41, and a cord core wire 45 is embedded in the inner rubber layer 41.

[0093] The inner rubber layer 41 is formed of, for example, nitrile rubber, carboxylated nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, chlorosulfonated polyethylene, polybutadiene rubber, natural rubber, EPM, EPDM, urethane rubber, acrylic rubber, etc. The reinforcing cloth 42 is provided to improve the durability of the flat belt 40, and for example, woven fabrics or knitted fabrics such as polyester fiber, nylon fiber, aramid fiber, glass fiber, carbon fiber, and cotton are used. The surface rubber layer 43 is provided to obtain a predetermined frictional force between the flat belt 40 and the conveyed object or the power transmission device, and is formed of, for example, nitrile rubber, carboxylated nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, chlorosulfonated polyethylene, polybutadiene rubber, natural rubber, EPM, EPDM, urethane rubber, acrylic rubber, silicone rubber, etc.

[0094] As the cord core 45, the above-mentioned multifilament 15 in which the composite materials 10 are bonded to each other by the matrix resin 16 impregnated and cured up to the structure 12 is used. The fiber axis direction of the multifilament 15 of the cord core 45 coincides with the longitudinal direction of the flat belt 40 (the running direction of the flat belt 40, the arrow X direction). Further, the cord cores 45 are arranged at a predetermined pitch in the width direction orthogonal to the longitudinal direction of the flat belt 40. When twisted multifilaments are used as the cord cores 45, it is preferable to alternately arrange S-twisted and Z-twisted ones in order to suppress the skew of the belt. Thus, since the flat belt 40 uses the multifilament using the composite material 10 as the cord core 45, the elongation with respect to tension and compression is small, and the durability with respect to repeated bending is high.

[0095] In the above, an example of a flat belt has been described. However, a composite material can be used as the cord core of various belts. In particular, the composite material is suitable as the cord core of transmission belts such as toothed belts typified by timing belts, V-belts, and V-ribbed belts. The example shown in FIG. 11 uses a multifilament 15 as the cord core 45 of a V-belt 50, and the example shown in FIG. 12 uses a multifilament 15 as the cord core 45 of a timing belt 60. The V-belt 50 in FIG. 11 has a structure in which a bottom cloth 51, a bottom rubber layer 52, an adhesive rubber layer 53, a back rubber layer 54, and an upper cloth layer 55 are laminated, and the cord core 45 is embedded in the adhesive rubber layer 53. Further, the timing belt 60 in FIG. 12 has a rubber layer 61 composed of a belt main body portion 61a and a plurality of tooth portions 61b, and a tooth cloth 62 that covers the surface of the rubber layer 61 on the tooth portion 61b side, and has a structure in which the cord core 45 is embedded in the belt main body portion 61a.

[0096] FIG. 13 shows the results of evaluating the interfacial adhesion strength between glass fiber and matrix resin due to the difference in the presence or absence of CNT adhesion. In this evaluation, a plurality of test pieces A in which CNT composite fibers using glass fibers as fibers 11 were embedded in a soft epoxy resin and test pieces B in which glass fibers (raw yarns) were embedded in a soft epoxy resin were respectively prepared and evaluated by the fragmentation method.

[0097] For the test piece A, in the same procedure as described above, through the glass fiber (raw yarn) in the dispersion liquid 28 irradiated with ultrasonic waves, CNTs 14 were sufficiently and uniformly adhered to the glass fiber, and the fiber 11 having the structure 12 formed on its surface was obtained. Note that no sizing agent or binder was applied. The test piece A was prepared by taking out one glass fiber having the structure 12 formed on its surface and embedding the glass fiber in a soft epoxy resin. The diameter of the glass fiber (raw yarn) was about 16 μm. An SEM photograph of observing the structure 12 formed on the surface of the glass fiber used for the test piece A is shown in FIG. 14.

[0098] For test piece B, it was fabricated by embedding a single glass fiber (raw yarn) without CNT attached in a soft epoxy resin. The fabrication conditions of test piece B were the same as those of test piece A except that CNT was not attached to the glass fiber.

[0099] For each of test pieces A and B, a tensile load was applied until the glass fiber was no longer cut, and then the length of each cut piece of the glass fiber at a certain length in the test piece was measured for each individual test piece, and the average length of the cut pieces (cut fiber length) was determined for each test piece.

[0100] The cut fiber lengths of test pieces A and B measured by the fragmentation method as described above are shown in Fig. 13. Test piece A, that is, the one with CNT 14 attached to the glass fiber, has a shorter cut fiber length compared to test piece B, that is, the one without CNT attached to the glass fiber, indicating that the interfacial adhesion strength between the glass fiber and the matrix resin is high. In test pieces A and B, since the glass fiber has a diameter of 10 μm or more, stress concentration at the interface is significant. However, in test piece A, it is considered that the presence of CNT 14 on the surface of the glass fiber improves the resin elastic modulus at the interface and relaxes the stress concentration, thereby improving the interfacial adhesion strength.

Explanation of Symbols

[0101] 10, 10A Composite Material 11 Fiber 12 Structure 14 Carbon Nanotube 20 Fiber Bundle 38 Fixed Resin Part

Claims

1. a fiber and a structure composed of a plurality of carbon nanotubes, forming a network structure in which the carbon nanotubes are in direct contact with each other, and the carbon nanotubes adhering to the surface of the fiber are directly adhered to the surface of the fiber, and comprising the carbon nanotubes have a bent shape having a bent portion which is a portion bent due to the presence of pentagonal rings and heptagonal rings in the graphite structure of the carbon nanotubes, in the structure, a void portion surrounded by the plurality of carbon nanotubes is formed A composite material characterized by the above.

2. The composite material according to claim 1, wherein the structure has a thickness in the range of 10 nm or more and 300 nm or less.

3. The composite material according to claim 1 or 2, wherein the fiber has a diameter in the range of 5 μm or more and 100 μm or less.

4. A sizing agent is fixed on the surfaces of the plurality of carbon nanotubes, the volume of the sizing agent is 30% or less with respect to the volume of the plurality of carbon nanotubes of the structure, and the sizing agent is fixed so as not to block the void portion. The composite material according to claim 1 or 2.

5. an ultrasonic step of applying ultrasonic vibration to a dispersion liquid in which a plurality of carbon nanotubes having a bent shape with bent portions are dispersed; an adhesion step of immersing a fiber in the dispersion liquid to which the ultrasonic vibration is applied, attaching the plurality of carbon nanotubes to the fiber, and forming a structure on the surface of the fiber having In the adhesion step, the long fiber is run in the dispersion liquid, the depth from the liquid surface of the dispersion liquid in which the fiber runs is D, the wavelength of the standing wave of the ultrasonic vibration generated in the dispersion liquid by the ultrasonic step is λ, and when n is an integer of 1 or more, a method for manufacturing a composite material is characterized by satisfying n·λ / 2 - λ / 8 ≤ D ≤ n·λ / 2 + λ / 8.

6. The method for manufacturing a composite material according to claim 5, wherein the ultrasonic step is characterized in that the frequency of the ultrasonic vibration is in the range of 40 kHz or more and 950 kHz or less.

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