JP7820838B2 - Electrically conductive members and interlayer thermal conductive materials - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. Published on page 111 of the abstracts of the 59th Fullerenes, Nanotubes, and Graphene General Symposium published by the Fullerenes, Nanotubes, and Graphene Society on September 10, 2020. Published at the 59th Fullerenes, Nanotubes, and Graphene General Symposium hosted by the Fullerenes, Nanotubes, and Graphene Society on September 18, 2020.

The present invention relates to a modified carbon nanotube forest (modified CNT forest), a continuous carbon nanotube body (CNT continuous body) comprising a spun body of the modified CNT forest, a gas-permeable sheet comprising the CNT continuous body, a catalyst electrode for a fuel cell comprising the gas-permeable sheet, a conductive member and a filamentous conductive member comprising the modified CNT forest or the CNT continuous body, an interlayer thermal conductive material comprising the conductive member, and a method for producing the modified CNT forest.

In this specification, "CNT forest" refers to a type of synthetic structure of multiple carbon nanotubes (CNTs) (hereinafter, the individual shape of the CNTs that gives rise to such a synthetic structure is referred to as the "primary structure," and the synthetic structure is also referred to as the "secondary structure"), and refers to an aggregate of CNTs formed by growth in which multiple CNTs are oriented in a specific direction (a specific example is a direction approximately parallel to a normal to one of the surfaces of the substrate) for at least a portion of their longitudinal axes. Patent Document 1 and Non-Patent Document 1 disclose a method of producing a CNT forest using iron chloride (gas-phase catalytic method). Non-Patent Document 2 discloses a method of obtaining a CNT forest by providing catalyst fine particles on a substrate and growing CNTs from the catalyst fine particles (solid-phase catalytic method).

In this specification, a "CNT continuum" refers to a structure formed by continuously extracting multiple CNTs from a CNT forest by pinching a portion of the CNTs and pulling them away from the CNT forest (this process is also referred to as "spinning" in the same way as the conventional process of producing yarn from fibers). The structure has multiple CNTs connected to each other along the spinning direction. Patent Document 2 discloses a secondary structure in which multiple CNTs are connected together in a thread-like overall shape (this CNT continuum is referred to as a "CNT yarn" in this specification). The CNTs that make up the CNT yarn are oriented along the extension direction of the CNT yarn (corresponding to the spinning direction). Patent Document 2 also discloses a secondary structure in which multiple CNTs are connected together in a web-like overall shape (this CNT continuum is referred to as a "CNT web" in this specification). The CNTs that make up the CNT web are oriented along one of the in-plane directions of the CNT web (corresponding to the spinning direction). Figure 29 shows the state of a CNT web being spun from a CNT forest produced by the gas-phase catalytic method.

Patent Document 3 discloses a carbon nanotube electrode comprising: a plurality of carbon fibers extending in an extension direction, each containing a carbon nanotube; and a plurality of metal particles supported on the carbon fibers, the metal particles being dispersed throughout the carbon fibers in the extension direction and electrically connecting each carbon fiber to other carbon fibers.

Patent Document 4 discloses a metal-composite carbon nanotube twisted yarn made by twisting together metal-coated nanotube fibers, in which the surfaces of carbon nanotube fibers are coated with metal and the ends of multiple carbon nanotubes are bonded together, and the metal-coated carbon nanotube fibers are fused together at the contact points.

JP 2009-196873 A Patent No. 5664832 Japanese Patent Application Laid-Open No. 2020-102352 JP 2018-53408 A

Adrian Ghemes, Yoshitaka Minami, Junichi Muramatsu, Morihiro Okada, Hidenori Mimura, Yoku Inoue. Fabrication and mechanical properties of carbon nanotube yarns spun from ultra-long multi-walled carbon nanotube arrays. Carbon 2012;50:4579-4587. Toshiya Kinoshita, Motoyuki Karita, Takayuki Nakano, Yoku Inoue. Two step floating catalyst chemical vapor deposition including in situ fabrication of catalyst nanoparticles and carbon nanotube forest growth with low impurity level. Carbon 2019;144:152-160.

The present invention aims to provide modified CNT forests in which CNT forests are modified with other substances, CNT continuous bodies comprising a spun body of the modified CNT forest, gas-permeable sheets comprising the CNT continuous bodies, fuel cell catalyst electrodes comprising the gas-permeable sheets, conductive members and filamentous conductive members comprising the modified CNT forests or CNT continuous bodies, interlayer thermal conductive materials comprising the conductive members, and methods for producing the modified CNT forests.

In order to solve the above problems, the present invention includes the following aspects.
[1] A modified carbon nanotube forest comprising carbon nanotubes oriented in a predetermined direction and microparticles supported on the carbon nanotubes, characterized in that the modified carbon nanotube forest is spinnable.

[2] A modified carbon nanotube forest described in [1] above, in which the ratio R defined by the following formula (1) using the adjacent gap D1 of the carbon nanotubes and the average particle diameter D2 of the microparticles is 3 or more.
R=D1/D2 (1)
Here, the adjacent gap D1 is expressed by the following formula (2) using the number density A (unit: pieces/ ^m2 ) of the modified carbon nanotube forest and the average diameter D3 of the carbon nanotubes, and the average particle size D2 and the average diameter D3 are, respectively, the arithmetic mean of the diameters of the microparticles at 10 or more locations and the arithmetic mean of the diameters of the carbon nanotubes at 10 or more locations measured by observing the modified carbon nanotube forest using an electron microscope.
D1=A ^-1/2 -D3 (2)

[3] The modified carbon nanotube forest described in [1] or [2] above, wherein the microparticles are electrically conductive.

[4] A modified carbon nanotube forest described in any one of [1] to [3] above, wherein the microparticles contain an oxide.

[5] A continuous carbon nanotube body comprising a spun body of the modified carbon nanotube forest described in any one of [1] to [4] above.

[6] The continuous carbon nanotube body described in [5] above, wherein the continuous carbon nanotube body has a web shape.

[7] The continuous carbon nanotube body described in [5] above, wherein the continuous carbon nanotube body has a thread-like shape.

[8] The carbon nanotube continuum described in [7] above, which is twisted.

[9] A gas-permeable sheet comprising the web-shaped continuous carbon nanotube body described in [6] above, wherein at least some of the carbon nanotubes constituting the continuous carbon nanotube body are adjacent to each other with gaps in a direction intersecting their orientation direction.

[10] The gas-permeable sheet described in [9] above, wherein the carbon nanotubes support fine particles containing one or more elements selected from the group consisting of Pt and Co.

[11] A catalyst electrode for a fuel cell comprising the gas permeable sheet described in [9] or [10] above.

[12] A conductive member comprising the modified carbon nanotube forest described in any one of [1] to [3] above, and a plating substance deposited on carbon nanotubes located inside the modified carbon nanotube forest.

[13] An interlayer thermally conductive material comprising the conductive member described in [12] above.

[14] A conductive member comprising the continuous carbon nanotube structure described in any one of [5] to [8] above, and a plating substance deposited on the carbon nanotubes located inside the continuous carbon nanotube structure.

[15] The conductive member described in [14] above, wherein the carbon nanotubes of the continuous carbon nanotube structure support conductive microparticles.

[16] A method for producing a modified carbon nanotube forest according to any one of [1] to [4] above, comprising: supplying a gaseous metal element-containing substance to a carbon nanotube forest; decomposing the metal element-containing substance to produce a metal-based substance; and supporting the fine particles formed from the metal-based substance on the carbon nanotube forest.

[17] A filamentous conductive member comprising a continuous carbon nanotube body having the filamentous shape described in [6] or [7] above, and a plating material deposited on at least a portion of the carbon nanotubes that make up the continuous carbon nanotube body.

[18] The filamentous conductive member according to the above [17], having a current capacity of 10 ⁵ A/cm ² or more.

[19] The filamentous conductive member according to [17] or [18], wherein when the conductivity in the longitudinal direction is measured, the temperature coefficient of resistance in the range of 300 K to 450 K is 1.8×10 ⁻³ K ⁻¹ or less.

[20] A filamentous conductive member according to any one of [17] to [19] above, in which the specific conductivity calculated based on the conductivity measured in the longitudinal direction is higher than the specific conductivity of copper wire at 400 K or higher.

[21] A filamentous conductive member according to any one of [17] to [20] above, having a tensile strength of 1.0 times or more and a Young's modulus of 1.5 times or more, based on a blank carbon nanotube continuum corresponding to the material obtained by removing the plating substance from the filamentous conductive member.

The present invention provides a modified CNT forest, a CNT continuous body comprising a spun body of the modified CNT forest, a gas-permeable sheet comprising the CNT continuous body, a fuel cell catalyst electrode comprising the gas-permeable sheet, an electrically conductive member and a filamentous electrically conductive member comprising the modified CNT forest or the CNT continuous body, an interlayer thermal conductive material comprising the electrically conductive member, and a method for producing the modified CNT forest.

This is a conceptual diagram of an example of a manufacturing apparatus for obtaining a modified CNT forest from a CNT forest. A figure showing observations of a portion of the side of a CNT forest. FIG. 1 shows a partial side view of a modified CNT forest. FIG. 4 is a partial enlarged view of FIG. 3 . FIG. 5 is a view showing the results of observation of the side surface shown in FIG. 4 by a backscattered electron image. This figure shows the results of observing a portion of a cross section obtained by removing a portion of a CNT forest. FIG. 7 is a diagram showing the results of observation of the side surface shown in FIG. 6 using a backscattered electron image. FIG. 1 is a conceptual diagram illustrating the spinning of a modified CNT forest. (a) A diagram showing the process of twisting the CNT yarn obtained by spinning the modified CNT forest to produce a CNT twisted yarn, and (b) a conceptual diagram showing the configuration of the device used to spin the modified CNT forest. FIG. 1 shows the observation results of a CNT twisted yarn. FIG. 11 is a partially enlarged view of FIG. 12(a) is an observation diagram of a cross section of a CNT twisted yarn, and (b) is a partially enlarged view of the central part of the cross section of FIG. 12(a) observed using backscattered electrons. FIG. 1 is a diagram conceptually illustrating the configuration of an apparatus for plating a CNT twisted yarn by electroplating in a copper sulfate bath. FIG. 1 shows the observation results of a modified CNT forest. FIG. 1 shows the observation results of a modified CNT forest. FIG. 1 shows the observation results of a modified CNT forest. FIG. 1 shows the observation results of a modified CNT forest. 10 is a histogram showing the measurement results of particle diameters of fine particles. FIG. 2 is an observation view of the appearance of a conductive member. FIG. 20 is an enlarged view of the conductive member of FIG. 19 . FIG. 1 is an observational view showing a cross section of a conductive member fabricated by plating at a current density of 5 mA/cm ² . FIG. 10 is an observation view showing a cross section of a comparative conductive member produced without modification with copper fine particles. 23(a) is an observational view showing a cross section of a conductive member produced by plating at a current density of 4 mA/ ^cm2 , and FIG. 23(b) is a partially enlarged view of the central portion of the cross section of FIG. 23(a). FIG. 1 is an observation view showing a cross section of a comparative conductive member without modification with copper fine particles. 1 is a graph showing the measurement results of the conductivity (unit: S/cm) of a conductive member. 1 is a graph showing the measurement results of the specific conductivity (unit: S·m ² ·kg ⁻¹ ) of a conductive member. 1 is a graph showing the measurement results of the current capacity (unit: A/cm ² ) of a conductive member. 1 is a graph showing the measurement results of the specific current capacity (unit: A·cm·kg ⁻¹ ) of a conductive member. FIG. 1 shows a CNT web spun from a CNT forest produced by a gas-phase catalytic method. Figure 1 shows a secondary electron image of a CNT forest carrying copper nanoparticles, produced using 10 mg of Cu(acac) ₂ . FIG. 1 shows a secondary electron image of a CNT forest carrying copper nanoparticles, produced using 30 mg of Cu(acac) ₂ . Figure 1 shows a secondary electron image of a CNT forest carrying copper nanoparticles, produced using 100 mg of Cu(acac) ₂ . FIG. 1 shows a cross-sectional secondary electron image of a composite yarn in which copper is deposited on a CNT twisted yarn carrying Cu-NPs. FIG. 10 is a diagram showing a cross-sectional secondary electron image of a composite yarn in which copper is deposited on a CNT twisted yarn that does not support Cu-NPs. FIG. 1 is a diagram showing a transmission electron image of an orthogonal cross section of a composite yarn in which copper is deposited on a CNT twisted yarn carrying Cu-NPs. FIG. 33 is a diagram showing a high-magnification image of FIG. 32(A). FIG. 1 shows a transmission electron image of a parallel cross section of a composite yarn in which copper is deposited on a CNT twisted yarn carrying Cu-NPs. FIG. 34 shows a high-magnification image of FIG. 33(A). 1 is a graph showing the electrical conductivity of a composite yarn in which copper is deposited on a CNT twisted yarn carrying Cu-NPs and a composite yarn in which copper is deposited on a CNT twisted yarn not carrying Cu-NPs. This is a graph in which the vertical axis of FIG. 34(A) is on a linear scale. 1 is a graph showing the temperature dependence of the electrical resistivity of each sample, normalized by the value at 300K. 1 is a graph showing the temperature dependence of the specific conductivity of a composite yarn in which copper is deposited on a CNT twisted yarn carrying Cu-NPs, and a copper wire. 10 is a graph showing the current capacity of each sample. 1 is a graph showing the relationship between the specific conductivity and the specific current capacity of each sample. FIG. 1 is a stress-strain diagram of each sample. 1 is a graph showing the relationship between Young's modulus and tensile strength of various samples. FIG. 1 shows a secondary electron image of a tensile fracture site of a composite yarn in which copper is precipitated on a Cu-NPs-loaded CNT twisted yarn. FIG. 10 is a diagram showing a secondary electron image of a tensile fracture portion of a composite yarn in which copper is precipitated on a CNT twisted yarn that does not support Cu-NPs. FIG. 1 shows a secondary electron image of a composite yarn in which copper is deposited on a CNT twisted yarn carrying Cu-NPs. FIG. 10 is a diagram showing a secondary electron image of a buckling portion of a composite yarn in which copper is precipitated on a CNT twisted yarn that does not support Cu-NPs.

The following describes an embodiment of the present invention.

A modified CNT forest (modified carbon nanotube forest) according to one embodiment of the present invention comprises a CNT forest with CNTs aligned in a predetermined direction and microparticles supported on the CNTs, and is spinnable. The CNT forest can be produced by the manufacturing method (gas-phase catalytic method) disclosed in Patent Document 1 or Non-Patent Document 1, or the manufacturing method (solid-phase catalytic method) disclosed in Non-Patent Document 2. In these cases, the predetermined direction is along the normal direction of the CNT forest formation surface of the substrate used to form the CNT forest.

The modified CNT forest has a ratio R of 3 or more, defined by the following formula (1) using the gap D1 between adjacent CNTs and the average particle size D2 of the microparticles.
R=D1/D2 (1)

Here, the adjacent gap D1 is expressed by the number density A (unit: pieces/ ^m2 ) of the modified CNT forest and the average diameter D3 of the CNTs, as shown in formula (2) below. The average particle size D2 and average diameter D3 are the arithmetic mean of the diameters of the microparticles at 10 or more locations and the arithmetic mean of the diameters of the carbon nanotubes at 10 or more locations, respectively, measured by observing the modified CNT forest from the side using an electron microscope.
D1=A ^-1/2 -D3 (2)

By appropriately configuring the method for supporting the microparticles, the adjacent gap D1 in the modified CNT forest can be made substantially equal to the adjacent gap D1' in the CNT forest (D1 = D1'). As described in Non-Patent Document 1, the adjacent gap D1' in a CNT forest produced by a gas-phase catalytic method is approximately 275 nm, since the number density A is approximately ¹⁰¹³ fibers/ ^m2 and the average diameter D3 is approximately 40 nm. On the other hand, as described in Non-Patent Document 2, the adjacent gap D1' in a CNT forest produced by a solid-phase catalytic method is approximately 20 nm, since the number density A is approximately 1.5 x ¹⁰¹⁵ fibers/ ^m2 and the average diameter D3 is approximately 7 nm. With the solid-phase catalytic method, it is possible to produce CNT forests with a number density A of approximately 5 x ¹⁰¹⁵ fibers/m2 and ^an average diameter D3 of approximately 4 nm, so the adjacent gap D1' can also be approximately 10 nm.

It is important that the average particle size D2 of the microparticles is sufficiently smaller than the adjacent gap D1 in order to ensure stable spinnability of the modified CNT forest. Specifically, the ratio R defined by the above formula (1) is preferably 3 or greater, more preferably 6 or greater, even more preferably 7 or greater, particularly preferably 8 or greater, and extremely preferably 9 or greater. A large average particle size D2 increases the likelihood that microparticles will exist between adjacent CNTs in the direction intersecting the orientation direction in the modified CNT forest, connecting adjacent CNTs. Adjacent CNTs should be separated during spinning, but when microparticles connect adjacent CNTs as described above, it can be difficult to separate adjacent CNTs, which can result in poor spinning.

As mentioned above, according to Non-Patent Document 1, the adjacent gap D1' in CNT forests produced by gas-phase catalytic method is approximately 275 nm, so the ratio R is 3 or greater when the average particle size D2 of the microparticles carried by CNTs in modified CNT forests formed from CNT forests produced by gas-phase catalytic method is 90 nm or less. Furthermore, according to Non-Patent Document 2, the adjacent gap D1' in CNT forests produced by gas-phase catalytic method is approximately 20 nm, so the ratio R is 3 or greater when the average particle size D2 of the microparticles carried by CNTs in modified CNT forests formed from CNT forests produced by gas-phase catalytic method is 6.7 nm or less. Gas-phase catalytic method can also produce CNT forests with an adjacent gap D1' of approximately 10 nm, in which case the ratio R is 3 or greater when the average particle size D2 of the microparticles is 3.3 nm or less.

The microparticles carried by the CNTs in a modified CNT forest may be electrically conductive. A typical example of electrically conductive microparticles is one made of a metallic material. When the microparticles are made of a metallic material, there are no particular restrictions on the constituent metal elements. Examples include Au, Ag, Cu, Pt, Ni, Co, Fe, Al, Ti, Zn, W, and Cr.

The fine particles carried by the CNTs in the modified CNT forest may contain oxides. Specific examples of oxides contained in the fine particles include aluminum oxide and titanium oxide. The oxide contained in the fine particles may contain multiple metal elements.

The modified CNT forest of one embodiment of the present invention can be produced by any manufacturing method as long as it is possible to load microparticles of a specified size onto the CNTs of the CNT forest, which is one of the raw materials, and the resulting modified CNT forest is spinnable. The method described below makes it possible to efficiently produce modified CNT forests.

A method for producing a modified CNT forest according to one embodiment of the present invention comprises supplying a metal element-containing substance in a gaseous state to a CNT forest, decomposing the metal element-containing substance to produce a metal-based substance, and supporting the microparticles formed from the metal-based substance on the CNT forest.

CNT forests can be produced by known methods. Specific examples include the gas-phase catalytic method described in Patent Document 1 and Non-Patent Document 1, and the solid-phase catalytic method described in Non-Patent Document 2. CNT forests produced by these methods can be spun.

Metal element-containing substances are substances that can be decomposed in the gas phase and can form fine particles from the decomposition product, a metal-based substance. Examples of metal element-containing substances include organometallic complexes such as copper(II) acetylacetonate and platinum acetylacetonate, and metal halides.

The metal element-containing substance does not need to be in the gas phase when supplied; in order to improve handleability, it may be preferable for it to be in the solid or liquid phase. In this case, in order to put the metal element-containing substance into the gas phase, it may be preferable to heat the metal element-containing substance or reduce the pressure in the space in which the metal element-containing substance is placed. The decomposition of the metal element-containing substance occurs when energy is applied from the outside. Specifically, the metal element-containing substance may be heated, or may be irradiated with a laser or a high-energy beam such as an electron beam.

Metal-based substances, which are the decomposition products of metal-element-containing substances, may be composed of metal-based materials including alloys and intermetallic compounds, or may be composed of oxides. The resulting metal-based substances aggregate or function as autocatalysts, forming fine particles.

Figure 1 is a conceptual diagram of an example of a manufacturing apparatus for obtaining a modified CNT forest from a CNT forest. The manufacturing apparatus 100 includes a glass tube 10, the interior of which serves as a reaction chamber RC, and a heater 20 that covers the side of the glass tube 10. A metal element-containing material RS is placed in the reaction chamber RC, and a CNT forest 30 is placed around the metal element-containing material RS.

The reaction chamber RC is depressurized and heated by the heater 20 to convert the metal element-containing material RS into a gaseous state. The gaseous metal element-containing material RS diffuses and is supplied to the CNT forest 30, where it thermally decomposes to produce a metal-based material. The fine particles based on the metal-based material are supported by the CNTs in the CNT forest 30, resulting in a modified CNT forest 40.

The particle size of the microparticles can be adjusted by the amount of metal element-containing material RS placed in the reaction chamber RC, the total pressure of the reaction chamber RC, the temperature of the reaction chamber RC, etc. The specific numerical ranges of these parameters are set appropriately depending on the type of metal element-containing material RS so as to achieve the average particle size D2 set by the adjacent gap D1 of the modified CNT forest. It is also possible to set the loading density of the CNT microparticles by adjusting these parameters.

In the manufacturing method of this embodiment, the metal element-containing material used as the microparticle raw material is supplied to the carbon nanotube forest in a gaseous state, allowing for highly uniform modification of CNTs with microparticles across the CNTs that make up the CNT forest. In other words, the manufacturing method of this embodiment allows for stable modification of CNTs located inside the CNT forest with microparticles, and the resulting modified CNT forest is spinnable. In contrast, in Patent Document 2, for example, Ag nanometal ink is dripped onto the CNT forest when manufacturing carbon nanotube electrodes. As a result, more microparticles (Ag in Patent Document 2) adhere to the outermost CNTs of the CNT forest, while the microparticles are less likely to adhere to the innermost CNTs. Furthermore, in the method disclosed in Patent Document 2, a liquid (ink) is dripped onto the CNT forest to attach the microparticles to the CNTs that make up the CNT forest. During this process, the CNTs that make up the CNT forest come into contact with each other due to the cohesive force of the liquid. Because of the strong interactions between CNTs that come into contact with each other, they are no longer able to be separated. In other words, the modified CNT forest described in Patent Document 2 cannot be spinnable.

Figure 2 shows the results of observing a portion of the side of a CNT forest. Hereinafter, unless otherwise specified, "observation" refers to observation using an electron microscope or an optical microscope. Figure 2 is a secondary electron image. This CNT forest was produced using a gas-phase catalytic method, and its number density A is approximately 10 ¹³ fibers/m ² , and the average CNT diameter D3 is approximately 35 nm. Therefore, the adjacent gap D1 in the CNT forest is approximately 280 nm. Figure 3 shows the results of observing a portion of the side of a modified CNT forest formed from a CNT forest produced using the same production method as the CNT forest in Figure 2. Figure 4 is a partial enlargement of Figure 3.

As shown in Figure 3, the CNTs in the CNT forest do not change morphologically even when they are loaded with microparticles. Therefore, the adjacent gap D1 in the modified CNT forest is substantially equal to the adjacent gap D1' in the CNT forest. Because the modified CNT forest shown in Figure 3 was formed from a CNT forest produced by gas-phase catalytic processing, the adjacent gap D1 is approximately 280 nm. Furthermore, as shown in Figure 4, the diameter of the microparticles loaded on the CNTs is well below 100 nm. As described later in the Examples, the average particle size D2 of the microparticles is 29.2 nm. Therefore, the ratio R in the modified CNT forest shown in Figure 4 is 9 or greater, and the modified CNT forest can be said to have particularly stable spinnability.

Figure 5 shows the results of backscattered electron imaging of the side surface shown in Figure 3, with the fine particles (made of a Cu-based conductive material) attached to the CNTs being observed as bright spots. Figure 6 shows the results of an observation of a portion of the cross section (i.e., the interior of the CNT forest) obtained by removing a portion of the CNT forest along the plane containing the CNT alignment direction. Figure 7 shows the results of backscattered electron imaging of the side surface shown in Figure 6, with the fine particles attached to the CNTs being observed as bright spots. Comparing Figure 5 and Figure 7, the density of bright spots is slightly higher in Figure 5, but a sufficient number of bright spots are also observed in Figure 7, confirming that the modified CNT forest also supports fine particles on the CNTs located within it.

A continuous carbon nanotube structure (CNT structure) according to one embodiment of the present invention comprises a spun body of the above-described modified CNT forest. Figure 8 is a conceptual diagram illustrating the process of spinning a modified CNT forest. CNTs 50 located on a portion of the side of a modified CNT forest 40 on a substrate SB are pulled out in direction D, resulting in a continuous connection of CNTs 50 aligned in direction D (spinning direction), forming a CNT structure 60. As shown in Figure 8, the microparticles 70 attached to the CNTs 50 that make up the modified CNT forest 40 maintain their state even after spinning. Therefore, the CNTs 50 that make up the CNT structure 60 obtained by spinning the modified CNT forest 40 are also highly uniformly modified with the microparticles 70.

The shape of the CNT continuum is determined by the spinning process. It may have a web shape or a thread shape.

A web-shaped CNT continuum (CNT web) can be obtained by pulling out one of the sides of the modified CNT forest so that it does not converge. The pulled CNT web can be continuously spun, for example, by winding it up on a drum.

The CNTs that make up a CNT web are aligned along the spinning direction. The connection between adjacent CNTs in the spinning direction (i.e., the orientation direction) is maintained by van der Waals forces between each CNT at their ends. Therefore, the CNTs that make up a CNT web are not connected to adjacent CNTs in the direction intersecting the spinning direction (the cross direction) except at their ends, and there are gaps between adjacent CNTs in the cross direction. In other words, a CNT web has a mesh-like structure, even though the CNTs that make it up are modified with fine particles. The length of these gaps depends on the number density of the CNT forest and the spinning method (especially the tension during spinning), but can be set in the range of several nanometers to several micrometers, for example. Therefore, by appropriately adjusting the gaps in the CNT web, it is possible to create a gas-permeable sheet that allows gas to pass through but not liquid.

This gas-permeable sheet allows for interaction between the fine particles and the gas passing through the sheet, since the CNTs that make up the sheet are modified with these particles. Furthermore, the gas-permeable sheet is conductive in the in-plane direction. Specifically, because the CNTs are aligned in the spinning direction, the conductivity along the alignment direction is higher than the conductivity in the direction perpendicular to the alignment direction. Therefore, by using an appropriate conductive catalyst material (such as a Pt-Co alloy containing Pt and Co) as the fine particles that modify the CNTs, this gas-permeable sheet can be used as a component of the catalyst electrode in a fuel cell.

A thread-shaped CNT continuum (CNT yarn) is obtained by pulling out CNTs from one side of a modified CNT forest to form a CNT web, then converging this CNT web in the spinning direction to further pull out CNTs. The CNTs that make up the CNT yarn formed in this way are oriented along the extension direction of the CNT yarn's thread shape. For this reason, compared to thread-shaped structures made by, for example, ejecting a liquid containing CNTs with short axial lengths from a die, the CNT yarn produced by the production method of this embodiment has high electrical conductivity along the extension direction of the thread shape and excellent mechanical properties.

As mentioned above, in a modified CNT forest, even the CNTs located inside are modified with microparticles, and so the CNTs in a CNT yarn are modified with microparticles even down to their center. In contrast, in the manufacturing method disclosed in Patent Document 3, for example, a dispersion containing metal particles is applied to a CNT fiber (corresponding to a CNT yarn) drawn from a CNT array (corresponding to a CNT forest), thereby attaching metal particles to the CNTs. As a result, metal particles are more likely to attach to CNTs located on the outer side of the CNT fiber, and less likely to attach to CNTs located in the center of the CNT fiber. In other words, the CNT yarn manufactured by the manufacturing method according to this embodiment is more uniformly modified with microparticles than the CNT yarn manufactured by the manufacturing method disclosed in Patent Document 3.

The CNT yarn obtained by spinning can be wound onto a bobbin as is, or can be wound while undergoing additional processing. One example of this processing is twisting. Figure 9(a) is a diagram showing the process of twisting the CNT yarn obtained by spinning a modified CNT forest to produce a twisted yarn (CNT twisted yarn). Figure 9(b) is a conceptual diagram showing the configuration of an apparatus for spinning a modified CNT forest. Figure 10 is a diagram showing the results of observation of the CNT twisted yarn, and Figure 11 is a partially enlarged view of Figure 10. Figure 12(a) is a cross-sectional view of the CNT twisted yarn. Figure 12(b) is a partially enlarged view of the central portion of the cross section of Figure 12(a) observed using backscattered electrons. Twisting increases the mechanical strength of the CNT yarn and may also improve its electrical properties (conductivity). As shown in Figures 11 and 12, even the CNTs located at the center of the CNT twisted yarn are modified with microparticles.

A method for manufacturing a conductive member according to one embodiment of the present invention comprises plating a CNT continuum having CNTs carrying conductive microparticles as described above, and depositing a plating substance on the CNTs located inside the CNT continuum.

The plating material may be deposited by electroplating or electroless plating. The plating material is selected as needed. A non-limiting example of a plating process is electroplating using a copper sulfate bath. FIG. 13 is a conceptual diagram illustrating the configuration of an apparatus for plating a CNT twisted yarn by electroplating in a copper sulfate bath. In the plating apparatus 100A shown in FIG. 13, a CNT twisted yarn 120 held by a mica sheet (mica foil) 110 is immersed in a copper sulfate bath 130. One end of the CNT twisted yarn 120 that is not immersed in the copper sulfate bath 130 is clamped with a clip 141, and a wiring 151 connected to the clip 141 is electrically connected to a cathode terminal 161 of a power source 160. An anode 170 made of U-shaped copper foil is immersed in the copper sulfate bath 130. A portion of the anode 170 that is not immersed in the copper sulfate bath 130 is clamped with a clip 142, and a wiring 152 connected to the clip 142 is electrically connected to an anode terminal 162 of the power source 160. By passing a current from the power supply 160, the CNT yarn 120 is copper-plated, resulting in the conductive member 200.

The conductive member obtained in this manner has sufficiently high conductivity as is, but the plating material can be reduced by heat-treating the conductive member in a reducing atmosphere, further increasing the conductivity of the conductive member. Heat-treatment conditions are set appropriately; a non-limiting example is 700°C for 1 hour under a hydrogen gas flow (100 sccm).

Another embodiment of the conductive member of the present invention comprises the modified CNT forest described above and a plating substance deposited on carbon nanotubes located within the modified carbon nanotube forest. As described above, the CNTs that make up the modified CNT forest support fine particles generated by the decomposition of metal-element-containing substances, and therefore the CNTs located within the modified CNT forest are also modified by the fine particles. Therefore, by plating the modified CNT forest, the plating substance is deposited so as to fill the gaps in the CNT forest. If the fine particles supported on the CNTs are conductive, the deposition of the plating substance can be achieved more stably. If copper, which has high thermal conductivity, is selected as the plating substance, the conductive member obtained by plating will have high thermal conductivity in the extension direction of the CNTs, making it suitable for use as an interlayer thermal conduction material.

The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the scope of the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

The present invention will be explained in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.
Example 1

Conductive components were manufactured using the manufacturing equipment shown in Figure 1 and the plating equipment shown in Figure 13.

Using the manufacturing method disclosed in Patent Document 1 and other documents, a CNT forest with a growth height of approximately 0.8 mm was obtained on the CNT-formed surface of the substrate under the following conditions.
Carbon source: acetylene Catalyst: solid FeCl ₂

The CNTs that made up the obtained CNT forest had diameters of 30 to 40 nm. When the CNT-formed surface of the substrate was observed after the CNT forest was removed, the number density of the CNT forest was found to be approximately ¹⁰¹³ / ^m2 . When the crystallinity of the CNTs that made up the CNT forest was evaluated by Raman scattering measurement, the ratio I _G /I _D of the G peak intensity of the graphene in-plane vibration mode to the D peak intensity due to its disordered vibration was found to be 2 to 3.

Using the manufacturing apparatus 100 shown in Figure 1, a modified CNT forest was obtained by modifying a CNT forest 30 with copper microparticles using copper(II) acetylacetonate (Cu(acac) ₂ ) as the metal element-containing substance RS. Specifically, a CNT forest 30 was placed in a sealable reaction chamber RC, and Cu(acac) ₂ , the metal element-containing substance RS, was placed nearby. Next, the reaction chamber RC was filled with argon gas and its pressure was maintained at 30 Torr. Next, the heater 20 was used to heat the reaction chamber RC at 400°C for 15 minutes. The CNTs in the CNT forest 30 were modified with copper microparticles generated by the separation of Cu(acac) ₂ at 200°C, resulting in a modified CNT forest 40. The images shown in Figures 3 to 7 are observations of the manufactured modified CNT forest 40. The microparticles observed in these figures were made of a Cu-based conductive material.

Modified CNT forests manufactured using the same method were observed using a scanning transmission electron microscope to measure the diameters of the CNTs and the particle sizes of the microparticles. Figures 14 to 17 show the results of the observations of the modified CNT forests, and Figure 18 is a histogram showing the particle size measurements of the microparticles. The diameters of 13 CNTs randomly selected from the images shown in Figures 14 to 17 were measured, and the average diameter (average diameter D3) was 36 nm with a standard deviation of 8.6 nm. Based on these measurement results, the number density A of the modified CNT forest was approximately 10 ¹³ CNTs/m ² , and therefore the adjacent spacing D1 of the modified CNT forest was 280 nm (= (10 ¹³ m ^-2 ) ^-1/2 - 36 nm). Furthermore, the particle sizes of 62 microparticles randomly selected from the images shown in Figures 14 to 17 were measured, and the average particle size (average particle size D2) was 29.2 nm with a standard deviation of 10.7 nm. Therefore, the ratio R defined by the above formula (1) was 9.7.

The resulting modified CNT forest was spun as shown in Figure 9 to obtain CNT twisted yarn. The diameter of the resulting CNT twisted yarn was 30-35 μm.

A sample prepared by cutting a portion of the resulting CNT twisted yarn was subjected to copper plating using the apparatus shown in Fig. 13. The specific conditions were as follows:
Plating bath: Copper sulfate aqueous solution ("Microfab Cu300" sold by Tanaka Kikinzoku Co., Ltd.)
Current density: 4 mA/cm ² or 5 mA/cm ²
・Plating time: 1 hour

A conductive member formed by depositing copper plating on twisted CNT yarn was heated in a hydrogen gas flow (100 sccm) at 700°C for 1 hour. This resulted in the conductive member to be evaluated. Figure 19 is an observation image of the external appearance of the conductive member thus obtained, and Figure 20 is an enlarged observation image of the external appearance of the conductive member.

Fig. 21 is an observational view showing a cross section of a conductive member produced by plating at a current density of 5 mA/cm ^2. Fig. 22 is an observational view showing a cross section of a comparative conductive member produced by plating at a current density of 5 mA/cm ² a CNT yarn obtained by spinning a CNT forest not modified with copper microparticles. Fig. 23 is an observational view showing a cross section of a conductive member produced by plating at a current density of 4 mA/cm ^2. Fig. 19 is an observational view showing a cross section of a comparative conductive member produced by plating at a current density of 4 mA/cm ² a CNT yarn obtained by spinning a CNT forest not modified with copper microparticles.

As is clear from a comparison between Figures 21 and 22, and between Figures 23 and 24, the use of modified CNT forests resulted in a conductive component with a relatively high copper density near the center.

By adjusting the plating conditions, several conductive members with different copper volume fractions (unit: vol%) were produced. The conductivity (unit: S/cm), specific conductivity (unit: S·m ² ·kg ⁻¹ ), current carrying capacity (unit: A/cm ² ), and specific current carrying capacity (unit: A·cm·kg ⁻¹ ) of these conductive members were measured. The results are shown in Figures 25 to 28. For comparison, Figures 23 to 28 also show the measurement results of a CNT yarn obtained by spinning a CNT forest not modified with copper microparticles (Cu fraction: 0 vol%) and the results of a typical pure copper wiring (Cu fraction: 100 vol%).

As shown in Figures 23 to 28, it was confirmed that the conductive member had electrical properties superior to those of CNT yarns formed solely from CNTs. Specifically, when the volume fraction of copper in the conductive member was 30 vol% or higher, electrical conductivity and specific conductivity substantially similar to those of copper were obtained, and when the volume fraction of copper was 35 vol% or higher, current carrying capacity and specific current carrying capacity substantially similar to those of copper were obtained.

Example 2
(1) Spinnable CNT Forest Synthesis Vertically aligned CNTs were grown on a substrate using a two-step floating catalyst CVD method. Details of the spinnable CNT forest synthesis method have been described in previous reports. In the first step, an ethanol solution containing ferrocene, the CNT catalyst precursor, was ultrasonically atomized and transported to a Si substrate in a CVD chamber using Ar as a carrier gas. Ferrocene was thermally decomposed on the Si substrate at 700°C, forming Fe nanoparticles in situ. In the second step, acetylene was supplied as the carbon source gas, and chlorine gas was supplied to elongate the CNTs. CNT forests with diameters of 10 nm and forest lengths of approximately 300 μm were synthesized at a CNT growth temperature of 700°C and a growth pressure of 18 Torr. The resulting CNT forests were spinnable.

(2) Cu Nanoparticle Supporting on CNT Forests. Copper nanoparticles (hereinafter also referred to as "Cu-NPs") were supported on CNT forests. Cu(acac) ₂ , a precursor of Cu-NPs, and spinnable CNT forests were placed in a CVD chamber and maintained at 400°C for 15 minutes in a 100% Ar atmosphere at 30 Torr. During this process, Cu(acac) ₂ evaporated, diffused, and thermally decomposed on the CNT surface. Subsequently, Cu-NPs nucleated on the CNT surface through thermal decomposition. Because the Cu(acac) ₂ vapor diffused homogeneously throughout the CNT forest, Cu-NPs were also uniformly deposited on the CNTs within the CNT forest. After the Cu-NPs were supported, the chamber was evacuated and reduced at 350°C for 1 hour in a 100 Torr argon:hydrogen (4:1) atmosphere. Furthermore, the amount of Cu-NPs supported on the CNT forest was controlled by changing the amount of Cu(acac) _2. Hereinafter, the spinnable CNT forest obtained in this way will also be referred to as the "Cu-NPs-supported CNT forest."

(3) Preparation of Cu-NPs-loaded CNT twisted yarn As in Example 1, when one end of the Cu-NPs-loaded CNT forest was pulled out, a CNT bundle (herein, a partial structure of a CNT forest in which several CNTs are closely spaced and bundled) was continuously pulled out, forming a unidirectionally aligned CNT linkage (CNT web). A CNT twisted yarn was prepared by pulling out the CNT web with a slider while twisting it. The spindle rotation speed was 14,000 rpm, and the pull-out speed was 50 mm/s. Hereinafter, the CNT twisted yarn obtained in this manner will also be referred to as "Cu-NPs-loaded CNT twisted yarn." For comparison, a CNT twisted yarn was also prepared from a CNT forest that did not load Cu-NPs. Hereinafter, this CNT twisted yarn will be referred to as "unloaded CNT twisted yarn."

(4) Copper Plating Treatment To deposit copper on the CNT twisted yarn, the Cu-NPs-supported CNT twisted yarn and the unsupported CNT twisted yarn were electroplated using a copper sulfate solution. A direct current was supplied to the copper plate as the anode and the CNT twisted yarn as the cathode. A current density of 0.2 A/ ^dm² was supplied for two hours. Furthermore, to reduce any copper oxide that may be present and to smooth the contact between the CNT and copper, a heat treatment was performed at 500 Torr and 700°C for one hour while supplying 400 sccm of argon and 100 sccm of hydrogen. In this way, a filamentous conductive member (hereinafter also referred to as "CNT/Cu-wire") was obtained, comprising a filament-shaped CNT continuum (CNT twisted yarn) and a plating material deposited on at least a portion of the CNTs that make up the CNT twisted yarn. In this specification, the term "plating-based substance" refers collectively to plating substances (substances formed by plating) and substances based on plating substances (corresponding to the reduced form of copper plating in this example).

(5) Characterization A field emission scanning electron microscope (Hitachi, Ltd., "SU-8030") was used to observe the CNTs. A cross-section polisher (JEOL, "IB-09020 CP") was used to polish the cross section of the CNT/Cu-wire to a high quality in order to observe cross-sectional secondary electron images of the CNT/Cu-wire. A transmission electron microscope (JEOL, "JEM-2100F") was used to observe the cross section of the CNT/Cu-wire at high magnification. A thin film of the CNT/Cu-wire was prepared using an FIB (JEOL, "JIB-4700F") to observe the transmission electron image. The electrical conductivity was measured using the four-terminal method under atmospheric pressure. The current capacity was measured using the two-terminal method under high vacuum. If the measurement length of the two-terminal method is short, heat will escape to the electrode, so the measurement length was set to 1 cm in order to measure the current capacity of the actual sample. The current density at which the yarn broke was taken as the current capacity. Tensile properties were measured using a tensile tester (Shimadzu Corporation, "EZ-L") with 5 measurements, a measurement length of 1 cm, and a tensile speed of 0.05 mm/min. Tensile strain was measured using a non-contact extensometer (Shimadzu Corporation, "TRViewX").

The measurement results of the CNT/Cu-wire obtained by the above manufacturing method are shown below.
(1) Dry-spinning CNT twisted yarn from Cu-NPs-loaded CNT forests. The Cu-NPs loading method according to this example makes it possible to control the amount of Cu-NPs loaded and particle size by adjusting parameters such as the amount of precursor and temperature. Cu(acac) ₂ is a sublimable organic compound that sublimes and thermally decomposes at relatively low temperatures. Therefore, it can be said to be suitable as a precursor for diffusing it into the interior of a CNT forest by vapor and loading Cu-NPs onto the CNT surface throughout the entire CNT forest.

However, the conditions for uniformly supporting Cu-NPs all the way to the interior of the CNT forest must be carefully controlled. The thermal decomposition rate of Cu(acac) ₂ varies greatly depending on the pressure and temperature inside the chamber. At high temperatures, the thermal decomposition rate is fast, so the Cu-NPs are supported from the sides of the CNT forest, resulting in failure to support them inside the CNT forest. In this example, the conditions for supporting Cu-NPs were carefully examined, and a spinnable CNT forest was obtained in which the Cu-NPs were uniformly supported all the way to the interior of the CNT forest.

Figures 30(A) to 30(C) show secondary electron images of CNT forests loaded with Cu-NPs when the amount of Cu(acac) ₂ was varied to 10 mg, 30 mg, and 100 mg. As shown in Figure 30(A), when the amount of Cu(acac) ₂ was as low as 10 mg, the amount of Cu-NPs loaded on the CNT surface was small, and some CNTs did not support Cu-NPs. However, spinnability was high, similar to that of CNT forests not loaded with Cu-NPs.

As shown in Figure 30(C), when the amount of Cu(acac) ₂ was as high as 100 mg, the amount of Cu-NPs supported on the CNT surface was extremely high. In this case, the CNTs were bonded to each other by Cu-NPs, and the entire CNT forest was formed into a single bonded entity. When the CNT forest end was pulled out, the CNT bundle adjacent to the pulled CNT was strongly bonded to the CNT forest and could not be separated from the CNT forest. Therefore, continuous dry spinning did not occur, and when the amount of Cu(acac) ₂ was 100 mg, it was impossible to produce a CNT twisted yarn.

As shown in Figure 30(B), by using 30 mg of Cu(acac) ₂ , Cu-NPs were evenly supported on the CNT surface, and a CNT forest with high spinnability was obtained. In this example, because it was necessary to spin the CNT twisted yarn, the CNT twisted yarn was produced using a CNT forest manufactured with 30 mg of Cu(acac) ₂ .

In this example, Cu(acac) ₂ was used as the precursor because the objective was to form a composite with copper. However, by using other acetylacetonate complexes (Pt(acac) ₂ , Ni(acac) ₂ , Zn(acac) ₂ , etc.), nanoparticles of various metals can be similarly supported on the CNT forest. Therefore, the method according to this example can be used not only for wiring materials, but also for applications such as electrode materials for batteries and capacitors.

In this example, dry spinning was achieved in which Cu-NPs were loaded entirely onto the CNT forest, resulting in a uniform loading of Cu-NPs on the drawn CNT web. In this example, Cu-NPs were loaded at the spinnable CNT forest stage, where the distance between CNT bundles was wider than in the CNT twisted yarn. This enabled Cu-NPs to be loaded more uniformly into the CNT twisted yarn, compared to when Cu-NPs were loaded after the CNT twisted yarn was produced. Because the method of this example loaded nanoparticles onto the CNT forest in advance, it has a wide range of applications, including Cu-NPs-loaded CNT forests, Cu-NPs-loaded CNT sheets, and Cu-NPs-loaded CNT twisted yarns. The method used in this example also offers excellent handling and user convenience.

(2) Structural Analysis of CNT/Cu-wire A copper luster was observed on the surface of the CNT/Cu-wire obtained in this example. Figure 31(A) is a cross-sectional secondary electron image of a composite yarn (hereinafter, sometimes referred to as "Mixed CNT/Cu-wire") in which copper was precipitated on a CNT twisted yarn (Cu-NPs-supported CNT twisted yarn) that was previously loaded with Cu-NPs using CNTs with a diameter of approximately 10 nm. Figure 31(B) is a cross-sectional secondary electron image of a composite yarn (hereinafter, sometimes referred to as "Unmixed CNT/Cu-wire") in which copper was precipitated on a CNT twisted yarn (unloaded CNT) that was not previously loaded with Cu-NPs, although it is common to both in that CNTs with a diameter of approximately 10 nm are used. In this specification, the term "CNT/Cu composite yarn" may be used as a general term for mixed CNT/Cu-wire and unmixed CNT/Cu-wire.

As shown in Figure 31(A), in the mixed CNT/Cu-wire, copper was deposited uniformly from the outer periphery to the interior of the CNT twisted yarn. Furthermore, high-magnification images reveal that copper was densely deposited. In contrast, in the unmixed CNT/Cu-wire, as shown in Figure 31(B), a core-clad structure (the CNT twisted yarn is the core, and the copper is the clad) was formed, with a large amount of copper deposited on the outer periphery of the CNT twisted yarn. Furthermore, copper was also deposited in island-like patterns inside the CNT twisted yarn. Comparing Figures 31(A) and 31(B) confirms that copper can be deposited uniformly all the way to the interior of the CNT twisted yarn by first loading Cu-NPs onto the CNT twisted yarn and then plating it.

Copper ions in the plating solution tend to precipitate as metallic copper on the surface of Cu-NPs, which have stable surface energy. In this example, Cu-NPs are formed throughout the entire CNT twisted yarn, and copper ions diffused inside the CNT twisted yarn during plating precipitate as metallic copper on the Cu-NPs surface. Furthermore, since the distance between CNT bundles in the CNT twisted yarn is approximately 200 nm, it is believed that copper ions are sufficiently diffused throughout the entire CNT twisted yarn by immersion in the plating solution before applying current. Furthermore, because the current density during plating is low, the rate-determining process is not ion diffusion but copper deposition on the CNT surface. Therefore, even after plating begins, ions continue to migrate inward, continuing deposition, which is thought to be why a homogeneous CNT/Cu-wire was produced in this example.

Figure 32(A) shows a transmission electron image of an orthogonal cross section (a cross section perpendicular to the CNT extension direction) of the mixed CNT/Cu-wire, and Figure 32(B) shows its corresponding high-magnification image. As shown in these figures, the particle size of the precipitated copper is several hundred nanometers. It can also be seen that copper precipitated between the CNT bundles and adhered closely to the CNT surface. While almost no voids were observed between the copper and the CNT, nanovoids of several tens of nanometers in size were present between the CNT bundles. Furthermore, the high-magnification image (Figure 32(B)) revealed that the CNTs covered by the copper matrix had a slightly crushed shape. This observation confirmed that even though copper begins electrolytic deposition from the Cu-NPs supported on the CNT surface, by the end of plating, copper precipitates to surround the CNT.

A transmission electron image of a parallel cross section (cross section in the plane including the extension direction of the CNT) of the mixed CNT/Cu-wire is shown in Figure 33(A), and its high-magnification image is shown in Figure 33(B). As shown in these figures, the CNT and copper were continuously adhered to each other in the longitudinal direction.
(3) Electrical conductivity of CNT/Cu-wire

Figure 34(A) shows the room temperature conductivity of mixed CNT/Cu-wire and unmixed CNT/Cu-wire. For comparison, data for twisted CNT yarn and copper wire (99.99% purity) are also shown. The copper volume content of the CNT/Cu-wire, shown on the horizontal axis of Figure 34(A), was calculated by calculating the volume of copper precipitated in the CNT/Cu-wire from the weight difference between the CNT/Cu-wire and the CNT twisted yarn before copper deposition, and then dividing this by the volume of the CNT/Cu-wire. Figure 34(B) is a graph of Figure 34(A) with the vertical axis on a linear scale.

As shown in Figure 34(A), the conductivity of the mixed CNT/Cu-wire was 2.41 x ¹⁰⁵ S/cm, and that of the unmixed CNT/Cu-wire was 4.26 x ¹⁰⁴ S/cm. The conductivity of the CNT twisted yarn was 2.35 x ¹⁰² S/cm, three orders of magnitude lower than that of copper wire (4.5 x ¹⁰⁵ S/cm). The conductivity of the CNT/Cu-wire increased as the volume fraction of copper increased. In the linear scale plot shown in Figure 34(B), the mixed CNT/Cu-wire exhibited a nearly linear relationship with the copper wire, with free electrons moving in the copper matrix being the dominant carriers. Note that the conductivity of the unmixed CNT/Cu-wire was lower than the linear relationship. The cross-sectional secondary electron image in Figure 31(B) shows copper precipitated in islands inside the CNT/Cu-wire, which indicates the presence of copper that does not contribute to conductivity. As a result, it is believed that the conductivity decreased relative to the copper content.

Figure 35 shows the temperature dependence of electrical resistivity for each sample, normalized by the value at 300 K. As shown in Figure 35, the electrical resistivity of copper wire (dashed line) increases in proportion to temperature due to phonon scattering, and the temperature coefficient of resistance (TCR) was 3.3 x ^10-3 K ^-1 . The electrical resistivity of mixed CNT/Cu-wire (solid line) and the electrical resistivity of unmixed CNT/Cu-wire (dotted line) increase with increasing temperature, but the TCRs are 1.2 x ^10-3 K ^-1 and 2.0 x ^10-3 K ^-1 , respectively, which are smaller than that of copper wire. This suggests that phonon scattering of electrons is suppressed by CNT. Furthermore, because Mixed CNT/Cu-wire, which has a larger contact surface area between the CNT and the copper matrix, has a smaller TCR than Unmixed CNT/Cu-wire, it is expected that phonon scattering of free electrons is reduced near the interface between the CNT and copper. As shown in Figure 35, when measuring the electrical conductivity in the longitudinal direction, the temperature coefficient of resistance (TCR) in the range of 300 K to 450 K is preferably 1.8 × 10 ^-3 K ^-1 or less, more preferably 1.5 × 10 ^-3 K ^-1 or less, and particularly preferably 1.2 × 10 ^-3 K ^-1 or less.

Figure 36 shows the temperature dependence of the specific conductivity of mixed CNT/Cu-wire and copper wire. At room temperature (300K), the specific conductivity of mixed CNT/Cu-wire (solid line) is lower than that of copper wire (dashed line) because CNT does not contribute to electrical conduction. However, because the TCR of mixed CNT/Cu-wire is lower than that of copper, the specific conductivity of mixed CNT/Cu-wire surpasses that of copper wire at 370K. In other words, it was confirmed that the specific conductivity of mixed CNT/Cu-wire is consistently higher than that of copper wire at temperatures above 400K.

On the other hand, as shown in Figure 35, the electrical resistivity of the CNT twisted yarn (dashed line) decreased linearly with increasing temperature, and its TCR was -0.6 × 10 ^-3 K ^-1 . This negative linear temperature dependence of the electrical resistance is thought to be due to the influence of Friedel oscillations.

Figure 37 shows the current capacity of each sample. The current capacity of the mixed CNT/Cu-wire was 1.3 x 10 ⁵ A/cm ² , and the current capacity of the unmixed CNT/Cu-wire was 5.32 x 10 ⁴ A/cm ² . Despite the copper volume content of 56.7%, the current capacity of the mixed CNT/Cu-wire was about 2.2 times higher than that of copper wire (5.8 x 10 ⁴ A/cm ² ). When the current density supplied to the CNT/Cu-wire is increased, the electrical resistance increases due to the generation of Joule heat in the CNT/Cu-wire. As mentioned above, the conductivity of the CNT/Cu-wire is higher than that of copper in the high temperature range of 370 K or higher, so Joule heating relative to the current density is smaller than that of copper wire. As a result, the temperature rise was reduced and the current capacity was increased. As such, it was confirmed from Figure 37 that the current capacity of the mixed CNT/Cu-wire is preferably 10 ⁵ A/cm ² or more.

Figure 38 shows a graph showing the relationship between the specific conductivity and specific current-carrying capacity of each sample. The specific conductivity of the mixed CNT/Cu-wire was 4.31 x 10 ⁴ S·cm ² /g, which is similar to that of copper wire (4.87 x 10 ⁴ S·cm ² /g) and more than two orders of magnitude higher than that of CNT twisted yarn (4.40 x 10 ² S·cm ² /g). The specific conductivity was almost entirely dependent on the copper content. This also supports the idea that the carriers in the composite material are free copper electrons. Meanwhile, the specific current-carrying capacity of the mixed CNT/Cu-wire was 2.32 x 10 ⁴ A·cm/g, 3.6 times larger than that of the copper wire (6.5 x 10 ³ A·cm/g). Due to the suppression of resistance increase at high temperatures in the CNT/Cu, the transport capacity was significantly improved, even though the current flowed through the copper matrix, similar to that of a copper wire.

The largest value was observed for CNT twisted yarn (2.85 x 10 ⁴ A cm/g). CNT twisted yarn has a sublimation temperature much higher than copper and a high infrared emissivity, so it can transport current up to higher temperatures than copper, and although its specific conductivity is two orders of magnitude smaller than that of copper, it is known to exhibit a high specific current capacity. From the above, mixed CNT/Cu-wire is lightweight yet has high conductivity, and has a current capacity that surpasses that of copper wire, so it is expected to be used as a thin-diameter wiring capable of supplying high power.

(4) Mechanical Properties of CNT/Cu Wire Table 1 shows the properties of the CNT yarn, CNT/Cu composite yarn, and copper wire.

Figure 39(A) shows stress-strain curves for mixed CNT/Cu-wire and unmixed CNT/Cu-wire manufactured using CNTs with a diameter of approximately 10 nm. For comparison, the stress-strain curves for CNT twisted yarn and copper wire manufactured using CNTs with a diameter of approximately 10 nm are also shown. The tensile strength of the mixed CNT/Cu-wire was 699 MPa and the Young's modulus was 70.4 GPa. The tensile strength of the copper wire was 191 MPa and the Young's modulus was 83.5 GPa, while the tensile strength of the CNT twisted yarn was 666 MPa and the Young's modulus was 32.2 GPa. Compared to the CNT twisted yarn, the tensile strength and Young's modulus of the mixed CNT/Cu-wire were both improved due to the homogeneous composite with copper. The tensile strength of the unmixed CNT/Cu-wire was 182.9 MPa and the Young's modulus was 25.8 GPa, and both the tensile strength and Young's modulus decreased. Figure 39(B) is a graph showing the relationship between the Young's modulus and tensile strength of various samples obtained from the stress-strain diagram of Figure 39(A). As shown in Figure 39(B), when the CNT twisted yarn is used as the reference, the mixed CNT/Cu-wire had a significantly increased Young's modulus and a tensile strength that was equal to or greater than that of the CNT twisted yarn. In contrast, the unmixed CNT/Cu-wire had a significantly decreased tensile strength and a decreased Young's modulus. In other words, a comparison between mixed CNT/Cu-wire and unmixed CNT/Cu-wire showed that the mixed CNT/Cu-wire thread-shaped conductive member preferably has a tensile strength of 1.0 or more and a Young's modulus of 1.5 or more times that of a blank carbon nanotube continuum, which corresponds to the material obtained by removing the plating substance from this thread-shaped conductive member, i.e., a CNT twisted yarn. It is more preferable that the Young's modulus of the mixed CNT/Cu-wire be 2.0 or more times that of the CNT twisted yarn.

Figure 40(A) shows a secondary electron image of a tensile fractured portion of Mixed CNT/Cu-wire, while Figure 40(B) shows a secondary electron image of a tensile fractured portion of Unmixed CNT/Cu-wire. As shown in Figure 40(A), the fractured portion of Mixed CNT/Cu-wire showed a short CNT pull-out period. On the other hand, as shown in Figure 40(B), the copper in the outer cladding of Unmixed CNT/Cu-wire broke and slipped, resulting in a long CNT twist pull-out period. Compared to copper wire, Mixed CNT/Cu-wire exhibits significantly improved Young's modulus and tensile strength, indicating that not only is copper precipitated homogeneously within the CNT twisted yarn, but it also has good adhesion to the CNT bundle surface, and copper acts as a matrix to effectively transmit load between CNT bundles. In other words, by comparing Figures 40(A) and 40(B), it was confirmed that Mixed CNT/Cu-wire can be considered a fiber-reinforced composite material with copper as the matrix.

Figure 41(A) shows a secondary electron image of a composite yarn in which copper has been deposited on a CNT twisted yarn loaded with Cu-NPs. Figure 41(B) shows a secondary electron image of the buckling area of a composite yarn in which copper has been deposited on a CNT twisted yarn not loaded with Cu-NPs. As shown in Figure 41(A), the mixed CNT/Cu-wire can be deformed with a small curvature. This composite yarn is flexible because it is a homogeneous medium in which CNT and copper are uniformly mixed. On the other hand, as shown in Figure 41(B), the unmixed CNT/Cu-wire easily buckles and fractures. This is thought to be because, although the CNT twisted yarn remains intact in the center of the unmixed CNT/Cu-wire, the CNT twisted yarn cannot withstand the compressive load caused by bending, and the outer copper cladding on the surface easily buckles.

As described above, in Example 2, a CNT/Cu composite yarn containing a homogeneous high proportion of CNTs was produced. Due to the synergistic effect of CNT and copper, it is an innovative new material with high electrical conductivity, low TCR, high current carrying capacity, high tensile properties, and high flexibility. Homogeneous CNT/Cu wire is expected to be a new lightweight wiring material for drone motors, earphones, small coils for small actuators, and wiring for high-energy-density small electronic device systems. Furthermore, the dry CNT spinning technique with vapor-phase nanoparticle deposition demonstrated in this example to obtain a homogeneous composite material is a new technology that adds a new dimension to CNT applications. Nanoparticle-loaded CNTs can be used to form a variety of structures, including long fibers, sheets, and three-dimensional structures, potentially enabling CNT applications with diverse functionality in the future.

10: Glass tube 20: Heater 30: CNT forest 40: Modified CNT forest 50: CNT
60: CNT continuum 70: Microparticles 100: Manufacturing apparatus 100A: Plating apparatus 110: Mica sheet 120: CNT twisted yarn 130: Copper sulfate bath 141, 142: Clips 151, 152: Wiring 160: Power source 161: Cathode terminal 162: Anode terminal 170: Anode 200: Conductive member D: Direction RC: Reaction chamber RS: Metal element-containing material SB: Substrate

Claims (2)

a modified carbon nanotube forest that is spun and includes carbon nanotubes oriented in a predetermined direction, and particles supported on the carbon nanotubes, and the modified carbon nanotube forest is spun and includes the carbon nanotubes positioned inside the modified carbon nanotube forest also supporting the particles;
a plating-based material deposited on the carbon nanotubes located inside the modified carbon nanotube forest; and
A conductive member comprising: An interlayer thermally conductive material comprising the electrically conductive member according to claim 1 .