JP7316760B2 - carbon nanotube wire - Google Patents

Description

The present invention relates to a carbon nanotube wire.

Carbon nanotubes (hereinafter sometimes referred to as “CNT”) are materials having various properties and are expected to be applied to many fields.

CNT is a three-dimensional network structure composed of a single layer of cylindrical bodies having a hexagonal lattice network structure or multiple layers arranged substantially coaxially, and is lightweight and has electrical conductivity, thermal conductivity, It has excellent properties such as mechanical strength and current density. For this reason, it is demanded to use CNT in the form of a wire. When CNTs are used as an electric wire material, it is useful to use a CNT wire having a twisted wire structure by twisting strands of a plurality of CNTs (Patent Document 1).

JP 2017-171546 A

Single CNTs are rigid linear molecules, but their aggregates are agglomerated by intermolecular forces. Therefore, a CNT wire made of a CNT aggregate does not have the rigidity of a copper wire cable made of metal-bonded crystals or a glass fiber made of covalently-bonded crystals, and hangs down under its own weight. Moreover, when spinning the CNT wire, a dry method or a wet method is generally used. In the case of the dry method, it is difficult to control the state of agglomeration of single CNTs when pulling them out of a furnace, substrate, or the like. In the case of the wet method, it is difficult to control the aggregation state of single CNTs when extracting the dispersion solvent from the dispersion. In other words, no matter which spinning method is used, it is difficult to produce a CNT wire with a uniform diameter and roundness. CNT strands having a uniform diameter and lacking rigidity were twisted together. Therefore, it has been difficult to produce a CNT wire having a perfectly circular cross section, and at the same time, it has been difficult to produce a CNT wire having a high-density structure because gaps are formed between the CNT wires. Furthermore, there is also a problem that the CNT wire is crushed during winding of such a CNT wire, resulting in a flattened shape.
Due to these circumstances, when a voltage is applied to the CNT wire as described above and a current is passed, the gaps between the CNT wires hinder the flow of electrons, and there are cases where the conductivity of the entire CNT wire is reduced. . In addition, since the cross section of the CNT wire is not circular, the stress concentrates on a specific portion of the CNT wire, making it easy to bend.

In order to solve the above problems, the present invention has the following embodiments.
[1] A stranded conductor having a carbon nanotube element wire composed of one or more carbon nanotube aggregates composed of a plurality of carbon nanotubes;
a conductive binding portion covering at least a part of the surface of the carbon nanotube wire;
A carbon nanotube wire having
A carbon nanotube wire, wherein the ratio of the area of the stranded conductor in the cross section of the carbon nanotube wire is 40% or more.
[2] The carbon nanotube wire according to [1] above, wherein the ratio of the area of the interstices in the cross section of the carbon nanotube wire is 5% or less.
[3] The carbon nanotube wire according to [1] or [2] above, wherein the conductive binding portion contains a resin and a conductive aid.
[4] The carbon nanotube wire according to [3] above, wherein the resin is at least one resin selected from the group consisting of polyolefin resins, acrylic resins, polyester resins, polyurethanes, and polyimides. .
[5] The carbon nanotube wire according to [3] or [4] above, wherein the conductive aid is at least one material selected from the group consisting of metals, carbon nanotubes, graphene, and carbon black.
[6] The carbon nanotube wire according to any one of [1] to [5] above, wherein the circularity of the cross section of the carbon nanotube wire is 0 to 0.3.

A carbon nanotube wire having excellent electrical conductivity and mechanical strength can be provided.

It is explanatory drawing of the CNT wire which concerns on one Embodiment. FIG. 2 is an explanatory diagram of a CNT wire used for a CNT wire according to one embodiment;

1. CNT Wire Below, a CNT wire according to one embodiment will be described with reference to the drawings.

FIG. 1(a) is a perspective view of a CNT wire 1 of one embodiment, and FIG. 1(b) is a cross-sectional view of the CNT wire 1 of FIG. 1(a). The outer peripheral portion of the CNT wire 1 is indicated by a dotted line. The CNT wire 1 of FIG. 1 has gaps 6 (FIG. 1(b)). A CNT wire 1 according to one embodiment includes a stranded conductor 3 having a CNT wire 2 consisting of one or more CNT aggregates composed of a plurality of CNTs, and covering at least a part of the surface of the CNT wire 2. and a conductive binding portion 4 . For example, the conductive binding portion 4 may cover at least a portion of the outer circumference of the CNT wire 2 and exist between the CNT wires 2 . The ratio of the area of the stranded conductor 3 in the cross section of the CNT wire 1 in FIG. 1(b) is 40% or more.

A conventional stranded conductor in which CNT wires are twisted has fine voids between the CNT wires, which is one of the factors that reduce the mechanical strength of the CNT wire. In addition, since the voids between the CNT strands have low electrical conductivity, the electrical conductivity of the entire CNT wire is lowered. On the other hand, in the CNT wire 1 of one embodiment, the conductive binding part 4 is provided so as to cover at least a part of the surface of the CNT wire 2, and also between the twisted CNT wires 2 Adjacent CNT strands 2 are bound due to the presence of the conductive binding portion 4 . Therefore, the mechanical strength of the CNT wire 1 as a whole can be improved to make it less likely to bend, and the durability against external force can be improved. Moreover, since the conductive binding portion 4 has high electrical conductivity, the electrical conductivity of the CNT wire 1 as a whole can be made excellent.

The ratio of the area of the stranded conductor 3 in the cross section of the CNT wire 1 is 40% or more. As a result, both the electrical conductivity and the mechanical strength of the CNT wire 1 can be improved. The ratio of the area of the stranded conductor 3 in the cross section of the CNT wire 1 is preferably 40 to 95%, more preferably 60 to 90%, and even more preferably 80 to 85%. By setting the ratio of the area of the stranded conductor 3 within the above range, the electrical conductivity and mechanical strength of the CNT wire 1 can be further improved. The equivalent circle diameter of the stranded conductor 3 is not particularly limited, but is, for example, 0.1 mm or more and 15 mm or less.

As shown in FIG. 1(b), gaps 6 exist within the CNT wire 1 in some cases. The gap 6 means a region judged to be a space or groove of 5 μm ² or more when the cross section of the CNT wire is observed with a microscope at a field of view of 2000 times. The ratio of the area of the gap 6 in the cross section of the CNT wire 1 is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. When the ratio of the area of the gap portion 6 is within the above range, the contact area between the adjacent CNT wires 2 and between the CNT wires 2 and the conductive binding portion 4 is increased. Mechanical strength can be further improved.

The roundness of the cross section of the CNT wire 1 is preferably 0 to 0.3, more preferably 0 to 0.2, and even more preferably 0 to 0.1. When the circularity of the cross section of the CNT wire 1 is within the above range, the anisotropy of deformation is eliminated when the CNT wire 1 is deformed by an external force, thereby improving workability. The roundness of the cross section of the CNT wire 1 can be calculated by the following formula by measuring the minor axis and the major axis of the cross-sectional image of the CNT wire obtained with a microscope.
Roundness = 1 - minor radius/major radius As shown in the above formula, when the cross section of the CNT wire 1 is a perfect circle, the roundness is 0. The more different the shapes, the closer the roundness is to 1.

Below, each part constituting the CNT wire 1 according to one embodiment will be described in detail.

(CNT wire)
FIG. 2 is an explanatory diagram of a CNT wire used for the CNT wire according to one embodiment. As shown in FIG. 2, the CNT wire 2 is formed from a single CNT assembly 11 composed of a plurality of CNTs 11a, 11a, . ing. Here, the CNT aggregate and the CNT wire mean those having a CNT ratio of 90% by mass or more. Plating and dopants are excluded from the calculation of the CNT ratio in the CNT wire. In FIG. 2, the CNT wire 2 has a configuration in which a plurality of CNT aggregates 11 are bundled. The longitudinal direction of the CNT aggregate 11 forms the longitudinal direction of the CNT wire 2 . Therefore, the CNT aggregate 11 is linear. The plurality of CNT aggregates 11, 11, . Therefore, the plurality of CNT aggregates 11, 11, . . . in the CNT wire 2 are oriented. The equivalent circle diameter of the CNT wire 2 is not particularly limited, but is, for example, 0.01 mm or more and 4.0 mm or less.

The CNT aggregate 11 is a bundle of CNTs 11a having a layered structure of one or more layers. The longitudinal direction of the CNTs 11 a forms the longitudinal direction of the CNT aggregate 11 . A plurality of CNTs 11a, 11a, . Therefore, the plurality of CNTs 11a, 11a, . . . in the CNT aggregate 11 are oriented. The equivalent circle diameter of the CNT aggregate 11 is, for example, 20 nm or more and 1000 nm or less, more typically 20 nm or more and 80 nm or less. The width dimension of the outermost layer of the CNTs 11a is, for example, 1.0 nm or more and 5.0 nm or less.

(stranded conductor)
The stranded conductor 3 is obtained by twisting a plurality of CNT strands 2, and is composed of a plurality of CNT strands 2 in one example. The average diameter, number, twisting method, etc. of the CNT wires 2 that constitute the stranded conductor 3 are not particularly limited, and a desired one can be appropriately selected according to the type, diameter, application, etc. of the CNT wire 1. . Moreover, the stranded conductor 3 may further have strands made of a material other than CNT.

(Conductive binding part)
The conductive binding portion 4 is provided so as to cover at least part of the surface of the CNT wire 2 . The conductive binding portion 4 is provided, for example, so as to cover the outer peripheral portion of the CNT wire 2 and may exist between adjacent CNT wire 2 . Since the conductive binding portion 4 bonds the CNT wires 2 together, the mechanical strength of the CNT wire 1 can be improved. Moreover, since the conductive binding portion 4 itself has high conductivity, the conductivity of the CNT wire 1 as a whole can be improved. In addition, the conductive binding part indicates the binding property to the CNT wire 2. For example, when the material of the conductive binding part is made into a sheet with a roll mixer and measured and calculated with a resistance measuring machine, It shall exhibit a volume resistivity of 6.0×10 ⁻⁴ Ω·cm or less.

The conductive binding portion 4 preferably contains a resin and a conductive aid. The CNT wire 1 can be easily molded by the conductive binding portion 4 containing the resin and the conductive aid. The resin constituting the conductive binding portion 4 is not particularly limited, and either a thermoplastic resin or a thermosetting resin can be used.

Examples of thermoplastic resins include polyolefin resins such as polyethylene and polypropylene, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, polyolefin copolymers such as ABS, and acrylic resins such as polyacrylate and polymethacrylate. resins, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polylactic acid, polyacetal resins, fluorine resins, polyvinyl chloride, polyphenylene ether, polyphenylene sulfide, polyether ether ketone, thermoplastic polyurethane, thermoplastic Examples include polyimide and thermoplastic polyamideimide.
Examples of thermosetting resins include phenol resins, urea resins, melamine resins, epoxy resins, unsaturated polyester resins, polyurethanes, polyimides, and silicone resins.
Among these resins, it is preferable to use at least one resin selected from the group consisting of polyolefin-based resins, acrylic-based resins, polyester-based resins, polyurethanes, and polyimides because of its excellent workability.

The conductive aid imparts conductivity to the conductive binding portion 4, and is not particularly limited as long as it has excellent workability and affinity with the resin. It is preferably at least one material selected from the group consisting of: Note that the CNT, which is the conductive additive, is present in the conductive binding portion and is not in the shape of a long line like the CNT wire, and therefore has a shape different from that of the CNT that constitutes the CNT wire. Therefore, the CNTs forming the CNT wire can be clearly distinguished from the CNTs forming the conductive aid. Examples of metals include copper, silver, and aluminum. The shape of the conductive aid is not particularly limited as long as it is excellent in processability, and examples thereof include powdery and fibrous shapes. The average particle size of the powdery conductive aid is preferably 10 nm to 100 μm, more preferably 10 nm to 10 μm, even more preferably 10 nm to 1 μm. The fiber length of the fibrous conductive additive is preferably 10 nm to 1000 μm, more preferably 10 nm to 100 μm, even more preferably 10 nm to 1 μm.

Next, a manufacturing example of the CNT wire 1 according to one embodiment will be described. For the CNT wire 1, first, the CNTs 11a are produced, and the CNT wire 2 is formed from the obtained plurality of CNTs 11a. Next, the CNT wire 1 is obtained by supplying the material of the conductive binding part onto the surface of the CNT wire 2 and twisting the CNT wire 2 while melting the material.

The CNT 11a can be produced by a method such as a floating catalyst method (Japanese Patent No. 5819888) or a substrate method (Japanese Patent No. 5590603). Moreover, a commercial item can be used suitably. The CNT strand 2 is dry spinning (Patent No. 5819888, Patent No. 5990202, Patent No. 5350635), wet spinning (Patent No. 5135620, Patent No. 5131571, Patent No. 5288359), It can be produced by liquid crystal spinning (Japanese Patent Publication No. 2014-530964) or the like.

The CNT wire 1 is obtained by supplying the material of the conductive binding part onto the surface (for example, the outer peripheral surface) of the CNT wire 2 obtained as described above and twisting the CNT wire 2 while melting the material. get More specifically, the CNT wire 2 and the material of the conductive binding portion are supplied to a twister, and the CNT wire 1 is obtained by twisting while heating and melting the material of the conductive binding portion. can be done.

The CNT wire 1 according to one embodiment can be used as a general electric wire such as a wire harness, and a general electric wire using the CNT wire 1 may be used to produce a cable.

(Examples 1-7 and Comparative Examples 1-2)
Using the floating catalyst vapor deposition (CCVD) method, the carbon source benzene, toluene, naphthalene, and A raw material solution containing one selected from the group consisting of decahydronaphthalene or a mixture thereof, ferrocene as a catalyst, and thiophene as a reaction accelerator was supplied by spraying. Hydrogen was supplied as carrier gas at 9.5 L/min. The CNTs produced by the above method were collected while being continuously wound to obtain a CNT wire having a diameter of about 50 μm and a length of 2 m. Next, the obtained CNT wire was heated to 500° C. in the atmosphere and further subjected to an acid treatment for high purification. Thereafter, the highly purified CNT wire was doped with nitric acid to obtain a CNT wire with an average diameter of 50 μm. Next, 19 CNT strands were bundled, and the material of the conductive binding portion shown in Table 1 below was supplied onto the surface of the CNT strands. In addition, in the examples using the conductive aid, powdery conductive aid was used in all cases. After that, in a state in which the material of the conductive binding portion is heated to the temperature shown in Table 1 below and melted, one end of the bundled CNT wires is fixed and the other end is twisted to twist the CNT wires. A stranded conductor was also obtained. Thereafter, the stranded conductor was cooled to harden the material of the conductive binding portion to form the conductive binding portion, thereby obtaining a CNT wire having the area ratio of the stranded conductor shown in Table 2.
The materials used in each example and comparative example are shown in Table 1 below.

(Evaluation method)
The CNT wires obtained in the above examples and comparative examples were evaluated as follows.
(1) Area Ratio of Twisted Wire Conductor, Conductive Bonding Portion, and Gap in Cross Section of CNT Wire After cutting the CNT wire in the cross-sectional direction, the cross section is processed by a polishing method. This cross section is observed with a microscope in a field of view of 2000 times, and in the obtained cross section image, the area ratio of the stranded conductor, the conductive binding portion, and the gap portion is quantified using image processing software. At this time, gaps of 5 μm ² or more that could be judged as spaces or grooves were counted.
(2) Volume Resistivity of CNT Wire A CNT wire was connected to a resistance measuring machine (manufactured by Keithley, device name “DMM2000”), and the resistance was measured by the four-terminal method. The volume resistivity was calculated based on the formula r=RA/L (R: resistance value, A: cross-sectional area of CNT wire, L: measured length).
(3) Roundness Similar to the above cross-sectional evaluation, in the cross-sectional image of the CNT wire obtained by observation with a 50x field of view with a microscope, measure the minor axis and major axis, and use the following formula to determine the true Circularity was calculated.
Roundness = 1 - minor radius/major radius (4) Bending resistance of CNT wire L ² / D = 75000 (L: wire length, D: wire diameter) was installed protruding from the work table, and X/L was evaluated as the self-weight deflection degree, where X was the distance from the original position of the tip of the line that hung down due to its own weight. When X/L was less than 0.1, it was rated as "good", and when it was 0.1 or more, it was rated as "x".
The above evaluation results are shown in Table 2 below.

As shown in Examples 1 to 7 in Table 2, the CNT wire was excellent because the ratio of the area of the stranded conductor in the cross section of the CNT wire was 40% or more and the CNT wire had a conductive binding portion. It can be seen that the mechanical strength (bending resistance) is exhibited. In particular, as shown in Examples 1 to 5, the ratio of the area of the stranded conductor in the cross section of the CNT wire is 70% or more, and the CNT wire has a conductive binding portion, resulting in excellent mechanical strength (bending resistance). and good electrical conductivity.

1 CNT wire 2 CNT element wire 3 stranded wire conductor 4 conductive binding portion 6 gap portion 11 CNT aggregate 11a CNT

Claims (4)

a stranded conductor having a carbon nanotube strand composed of a plurality of carbon nanotube aggregates composed of a plurality of carbon nanotubes;
a conductive binding portion covering at least a part of the surface of the carbon nanotube wire;
A carbon nanotube wire having
The conductive binding portion exists between the carbon nanotube strands,
The conductive binding part contains a resin and a conductive aid,
The proportion of the area of the stranded conductor in the cross section of the carbon nanotube wire is 40% or more,
A carbon nanotube wire, wherein the ratio of the area of the interstices in the cross section of the carbon nanotube wire is 5% or less. 2. The carbon nanotube wire according to claim 1 , wherein said resin is at least one resin selected from the group consisting of polyolefin resin, acrylic resin, polyester resin, polyurethane, and polyimide. 3. The carbon nanotube wire according to claim 1 , wherein said conductive aid is at least one material selected from the group consisting of metals, carbon nanotubes, graphene, and carbon black. The carbon nanotube wire according to any one of claims 1 to 3 , wherein the carbon nanotube wire has a cross-sectional circularity of 0 to 0.3.