JP2024052746A - Modified carbon nanotube forests, carbon nanotube continua and interlayer thermal conductive materials - Google Patents

Abstract

[Problem] To provide a modified carbon nanotube forest having a structure in which a carbon nanotube forest supports fine particles. [Solution] The modified carbon nanotube forest 40 comprises carbon nanotubes 50 oriented in a predetermined direction and fine particles 70 supported on the carbon nanotubes 50, is spinnable, and preferably has a ratio R defined by the following formula (1) using the adjacent gap D1 of the carbon nanotubes 50 and the average diameter D2 of the fine particles 70, which is 3 or more. It is preferable that the fine particles 70 are conductive. R=D1/D2 (1) The adjacent gap D1 is expressed by the following formula (2) using the number density A (unit: tubes/m2) of the modified carbon nanotube forest 40 and the average diameter D3 of the carbon nanotubes 50. D1=A-1/2-D3 (2) [Selected Figure] FIG. 3

Description

Application for application of Article 30, Paragraph 2 of the Patent Act has been filed. Published on page 111 of the Abstracts of the 59th Fullerene, Nanotube, and Graphene General Symposium published by the Fullerene, Nanotube, and Graphene Society on September 10, 2020. Published at the 59th Fullerene, Nanotube, and Graphene General Symposium hosted by the Fullerene, Nanotube, and Graphene Society on September 18, 2020.

The present invention relates to a modified carbon nanotube forest (modified CNT forest), a carbon nanotube continuous 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 of a fuel cell comprising the gas-permeable sheet, a conductive member and a filamentary conductive member comprising the modified CNT forest or 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 composite structure of multiple carbon nanotubes (CNTs) (hereinafter, the individual shape of the CNTs that gives such a composite structure is referred to as the "primary structure", and the above composite structure is also referred to as the "secondary structure"), and refers to an aggregate of CNTs that have grown so that multiple CNTs are oriented in a certain direction (a specific example is a direction approximately parallel to a normal line of one of the surfaces of the substrate) for at least a part of their longitudinal direction. 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 catalytic fine particles on a substrate and growing CNTs from the catalytic fine particles (solid-phase catalytic method).

In addition, in this specification, a structure in which multiple CNTs are connected to each other along the spinning direction, formed by continuously extracting multiple CNTs from a CNT forest by pinching a part of the CNTs in the CNT forest and pulling the CNTs away from the CNT forest (in this specification, this operation is also referred to as "spinning" following the operation of producing yarn from fibers in the prior art), is referred to as a "CNT continuum." Patent Document 2 discloses a secondary structure in which multiple CNTs are connected to each other along the spinning direction (in this specification, this CNT continuum is referred to as a "CNT yarn"). 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 to each other along the spinning direction (in this specification, this CNT continuum is referred to as a "CNT web"). 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 in which a CNT web is 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 along an extension direction, each of the carbon fibers including a carbon nanotube; and a plurality of metal particles supported on the plurality of carbon fibers, the plurality of 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 in which metal-coated nanotube fibers, in which the surfaces of carbon nanotube fibers in which the ends of multiple carbon nanotubes are joined together are coated with metal, are twisted together, and the contact portions of the metal coated carbon nanotube fibers are fused together.

JP 2009-196873 A Patent No. 5664832 JP 2020-102352 A 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 a modified CNT forest in which a CNT forest is modified with another substance, a CNT continuous body comprising a spun body of the modified CNT forest, a gas-permeable sheet comprising the CNT continuous body, a catalyst electrode of a fuel cell comprising the gas-permeable sheet, a conductive member and a filamentary 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 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, and characterized in that it is spinnable.

[2] The 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: tubes/ ^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 average of the diameters of the microparticles at 10 or more locations and the arithmetic average 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 conductive.

[4] The modified carbon nanotube forest described in any one of [1] to [3] above, wherein the fine particles include an oxide.

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

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

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

[8] A carbon nanotube continuum according to [7] above, which is twisted.

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

[10] The gas permeable sheet described in [9] above, in which 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 a modified carbon nanotube forest according to any one of [1] to [3] above, and a plating material deposited on the 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 a carbon nanotube continuous body as described in any one of [5] to [8] above, and a plating substance deposited on the carbon nanotubes located inside the carbon nanotube continuous body.

[15] The conductive member according to [14] above, in which the carbon nanotubes of the carbon nanotube continuum support conductive particles.

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

[17] A filamentary conductive member comprising a continuous carbon nanotube body having the filamentary 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], having a temperature coefficient of resistance of 1.8×10 ⁻³ K ⁻¹ or less in the range of 300 K to 450 K when the electrical conductivity is measured in the longitudinal direction.

[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 a copper wire at 400 K or higher.

[21] A filamentary conductive member according to any one of [17] to [20] above, which has 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 filamentary 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 catalyst electrode of a fuel cell comprising the gas-permeable sheet, a conductive member and a filamentary 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.

A conceptual diagram of an example of a manufacturing apparatus for obtaining a modified CNT forest from a CNT forest. A diagram showing observations of a portion of the side of a CNT forest. A diagram showing a partial observation of the side of a modified CNT forest. FIG. 4 is a partially enlarged view of FIG. 3 . FIG. 5 is a diagram showing a result of observing the side surface shown in FIG. 4 by a reflected 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 a result of observing the side surface shown in FIG. 6 by a backscattered electron image. FIG. 1 is a conceptual diagram illustrating how a modified CNT forest is spun. (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 for spinning 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 image of a cross section of a CNT twisted yarn, and (b) is an enlarged view of the central part of the cross section of FIG. 12(a) observed by reflected electrons. FIG. 1 is a schematic diagram showing the configuration of an apparatus for plating a CNT 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. 1 is a histogram showing the measurement results of particle diameters of fine particles. FIG. 2 is an observation view of the external appearance of a conductive member. FIG. 20 is an enlarged view of the conductive member of FIG. 19 . FIG. 2 is an observational view of a cross section of a conductive member produced by plating at a current density of 5 mA/cm ² . FIG. 2 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 ; (b) is a partially enlarged view of the central portion of the cross section of FIG. 23(a). FIG. 2 is an observational 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 electrical 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 being spun from a CNT forest produced by gas phase catalytic method. FIG. 2 shows a secondary electron image of a CNT forest carrying copper nanoparticles produced using 10 mg of Cu(acac) ₂ . FIG. 2 shows a secondary electron image of a CNT forest carrying copper nanoparticles produced using 30 mg of Cu(acac) ₂ . FIG. 2 shows a secondary electron image of a CNT forest carrying copper nanoparticles produced using 100 mg of Cu(acac) ₂ . FIG. 13 is a cross-sectional secondary electron image of a composite yarn in which copper is precipitated on a CNT twisted yarn carrying Cu-NPs. FIG. 13 is a cross-sectional secondary electron image of a composite yarn in which copper is precipitated on a CNT twisted yarn not carrying Cu-NPs. FIG. 13 is a transmission electron image of an orthogonal cross section of a composite yarn in which copper is precipitated on a CNT twisted yarn carrying Cu-NPs. FIG. 33 is a diagram showing a high magnification image of FIG. 32(A). FIG. 13 is a transmission electron image of a parallel cross section of a composite yarn in which copper is precipitated 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 twisted CNT yarn carrying Cu-NPs, and a composite yarn in which copper is deposited on a twisted CNT yarn not carrying Cu-NPs. The vertical axis of FIG. 34(A) is a graph in which the vertical axis is in a linear scale. 1 is a graph showing the temperature dependence of electrical resistivity of each sample normalized with the value at 300K. 1 is a graph showing the temperature dependence of the specific conductivity of a composite yarn and a copper wire in which copper is precipitated on a CNT twisted yarn carrying Cu-NPs. 1 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. 4 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. 13 is a secondary electron image of a tensile fracture portion of a composite yarn in which copper is precipitated on a CNT twisted yarn carrying Cu-NPs. FIG. 13 is a secondary electron image of a tensile fracture portion of a composite yarn in which copper was precipitated on a CNT twisted yarn not carrying Cu-NPs. FIG. 13 is a secondary electron image of a composite yarn in which copper is precipitated on a CNT twisted yarn carrying Cu-NPs. FIG. 13 is a secondary electron image of a buckling portion of a composite yarn in which copper is precipitated on a CNT twisted yarn not carrying Cu-NPs.

The following describes an embodiment of the present invention.

The modified CNT forest (modified carbon nanotube forest) according to one embodiment of the present invention comprises a CNT forest with CNTs oriented in a predetermined direction and microparticles supported on the CNTs, and can be spun. The CNT forest can be produced by the manufacturing method (gas phase catalyst method) disclosed in Patent Document 1 or Non-Patent Document 1, or the manufacturing method (solid phase catalyst 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 for forming the CNT forest.

The modified CNT forest has a ratio R, defined by the following formula (1) using the gap D1 between adjacent CNTs and the average particle size D2 of the microparticles, of 3 or more.
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 the following formula (2): The average particle size D2 and the average diameter D3 are the arithmetic mean of the diameters of fine particles at 10 or more locations and the arithmetic mean of the diameters of 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)

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

It is important that the average particle diameter 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 more, more preferably 6 or more, even more preferably 7 or more, particularly preferably 8 or more, and extremely preferably 9 or more. If the average particle diameter D2 is large, there is a high possibility that microparticles are present between adjacent CNTs in the direction intersecting the orientation direction in the modified CNT forest so as to connect adjacent CNTs. Adjacent CNTs should be separated when spun, but when the microparticles connect adjacent CNTs as described above, it may be difficult to separate the adjacent CNTs, which may cause poor spinning.

As described above, according to Non-Patent Document 1, the adjacent gap D1' in a CNT forest produced by gas-phase catalytic method is about 275 nm, so the ratio R is 3 or more when the average particle size D2 of the microparticles carried by the CNTs in the modified CNT forest formed from the CNT forest produced by the gas-phase catalytic method is 90 nm or less. Also, according to Non-Patent Document 2, the adjacent gap D1' in a CNT forest produced by gas-phase catalytic method is about 20 nm, so the ratio R is 3 or more when the average particle size D2 of the microparticles carried by the CNTs in the modified CNT forest formed from the CNT forest produced by the gas-phase catalytic method is 6.7 nm or less. With the gas-phase catalytic method, it is also possible to produce CNT forests with adjacent gaps D1' of about 10 nm, in which case the ratio R is 3 or more when the average particle size D2 of the microparticles is 3.3 nm or less.

The fine particles carried by the CNTs in the modified CNT forest may be conductive. A typical example of a fine particle with conductivity is one made of a metallic material. When the fine particle is made of a metallic material, the constituent metal elements are not particularly limited. 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 oxides of aluminum and titanium. The fine particles may contain multiple metal elements that constitute the oxide.

The modified CNT forest according to one embodiment of the present invention can be produced by any production method as long as the CNTs of the CNT forest, which is one of the raw materials, can carry microparticles of a predetermined size, and the resulting modified CNT forest has spinnability. The method described below makes it possible to efficiently produce the modified CNT forest.

A method for producing a modified CNT forest according to one embodiment of the present invention includes 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 a 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 at the supply stage, and 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 a gaseous state, 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 by applying energy 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.

The metal-based substance, which is the decomposition product of the metal-element-containing substance, may be composed of a metal-based material including an alloy or an intermetallic compound, or may be composed of an oxide. The resulting metal-based substance aggregates or acts as an autocatalyst to form 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 is a reaction chamber RC, and a heater 20 that is arranged to cover 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 put the metal element-containing material RS into a gaseous state. The metal element-containing material RS in the gaseous state diffuses and is supplied to the CNT forest 30, where the metal element-containing material RS is thermally decomposed to produce a metal-based material, and the fine particles based on the metal-based material are supported by the CNTs of the CNT forest 30, resulting in the 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 according to 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 according to the present embodiment, the metal element-containing material, which is the raw material for the microparticles, is supplied to the carbon nanotube forest in a gaseous state, so that the modification of the CNTs by the microparticles can be generated with high uniformity for the CNTs constituting the CNT forest. That is, according to the manufacturing method according to the present embodiment, the modification of the CNTs located inside the CNT forest by the microparticles can be stably realized, and the obtained modified CNT forest can be spun. In contrast, for example, in Patent Document 2, Ag nanometal ink is dripped onto the CNT forest when manufacturing a carbon nanotube electrode. Therefore, the more the CNTs located on the outside of the CNTs constituting the CNT forest, the more the microparticles (Ag in Patent Document 2) adhere to them, and the more difficult it is for the microparticles to adhere to the CNTs located inside the CNT forest. In addition, in the method disclosed in Patent Document 2, a liquid (ink) is dripped onto the CNT forest in order to adhere the microparticles to the CNTs constituting the CNT forest. At this time, the CNTs constituting 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 can no longer be separated. In other words, the modified CNT forest described in Patent Document 2 cannot be spinnable.

FIG. 2 is a diagram showing the results of observing a portion of the side of a CNT forest. Hereinafter, unless otherwise specified, "observation" means observation by an electron microscope or observation by an optical microscope. FIG. 2 is a secondary electron image. This CNT forest was produced by a gas-phase catalytic method, and its number density A is about 10 ¹³ pieces/m ² , and the average diameter D3 of the CNTs is about 35 nm. Therefore, the adjacent gap D1 of the CNT forest is about 280 nm. FIG. 3 is a diagram showing the results of observing a portion of the side of a modified CNT forest formed from a CNT forest produced by the same production method as the CNT forest of FIG. 2. FIG. 4 is a partial enlarged view of FIG. 3.

As shown in FIG. 3, the CNTs in the CNT forest do not change morphologically even when they support fine particles. Therefore, the adjacent gap D1 of the modified CNT forest is substantially equal to the adjacent gap D1' of the CNT forest. The modified CNT forest shown in FIG. 3 is formed from a CNT forest produced by a gas-phase catalytic method, so the adjacent gap D1 is about 280 nm. Also, as shown in FIG. 4, the diameter of the fine particles supported on the CNTs is sufficiently smaller than 100 nm. As will be described later in the examples, the average particle diameter D2 of the fine particles is 29.2 nm. Therefore, in the modified CNT forest shown in FIG. 4, the ratio R is 9 or more, and it can be said that the modified CNT forest has particularly stable spinnability.

Figure 5 shows the results of observation of the side shown in Figure 3 using a backscattered electron image, where the fine particles (made of Cu-based conductive material) attached to the CNTs are observed as bright spots. Figure 6 shows the results of observation of a portion of the cross section (i.e., the inside of the CNT forest) obtained by removing a portion of the CNT forest at a plane including the CNT orientation direction. Figure 7 shows the results of observation of the side shown in Figure 6 using a backscattered electron image, where the fine particles attached to the CNTs are 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, and it is confirmed that the modified CNT forest also supports fine particles on the CNTs located inside it.

The carbon nanotube continuum (CNT continuum) according to one embodiment of the present invention comprises a spun body of the modified CNT forest described above. FIG. 8 is a conceptual diagram showing how the modified CNT forest is spun. CNTs 50 located on a part of the side of the modified CNT forest 40 on the substrate SB are pulled out in the direction D, so that the CNTs 50 aligned in the direction D (spinning direction) are continuously connected to form the CNT continuum 60. As shown in FIG. 8, the microparticles 70 attached to the CNTs 50 constituting the modified CNT forest 40 maintain their state even after spinning. Therefore, the CNTs 50 constituting the CNT continuum 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) is obtained by drawing one of the sides of the modified CNT forest so that it does not converge. The drawn CNT web can be spun continuously, for example by winding it up on a drum.

The CNTs that make up the CNT web are aligned along the spinning direction. The connection state of adjacent CNTs in the spinning direction (i.e., the orientation direction) is maintained by the van der Waals forces that occur between each end of the CNTs and other CNTs. Therefore, the CNTs that make up the CNT web are not connected to adjacent CNTs in the direction that intersects the spinning direction (crossing direction) at parts other than their ends, and there are gaps between adjacent CNTs in the crossing direction. In other words, the CNTs that make up the CNT web have a mesh-like structure, even though they are modified with fine particles. The length of this gap depends on the number density of the CNT forest and the spinning method (especially the tension when spinning), but can be set in the range of several nm to several μm, for example. Therefore, by appropriately adjusting the gaps in the CNT web, a gas-permeable sheet that allows gas to pass through but not liquid can be formed.

This gas-permeable sheet is capable of generating an interaction between the gas passing through the sheet and the fine particles because the CNTs that make up the sheet are modified with fine particles. Moreover, the gas-permeable sheet is conductive in the in-plane direction. Specifically, because the CNTs are oriented in the spinning direction, the conductivity along the orientation direction is higher than the conductivity in the direction perpendicular to the orientation direction. Therefore, if an appropriate conductive catalyst material (e.g., a Pt-Co alloy containing Pt and Co) is selected as the fine particles that modify the CNTs, this gas-permeable sheet can be used as a component of the catalyst electrode of a fuel cell.

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

As described above, in the modified CNT forest, the CNTs located inside are also modified with fine particles, so that even the CNTs located at the center of the CNT yarn are modified with fine particles. In contrast, in the manufacturing method disclosed in Patent Document 3, for example, a dispersion liquid 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. For this reason, metal particles are more likely to attach to CNTs located on the outer side of the CNT fiber, and metal particles are 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 fine particles than the CNT yarn manufactured by the manufacturing method disclosed in Patent Document 3.

The CNT yarn obtained by spinning may be wound on a bobbin as it is, or may be wound while additional processing is performed. One of the additional processing is twisting. Figure 9 (a) is a diagram showing the state in which the CNT yarn obtained by spinning the modified CNT forest is twisted to produce a twisted yarn (CNT twisted yarn). Figure 9 (b) is a diagram conceptually showing the configuration of a device for spinning the modified CNT forest. Figure 10 is a diagram showing the observation result of the CNT twisted yarn, and Figure 11 is a partially enlarged view of Figure 10. Figure 12 (a) is an observation view of the cross section of the CNT twisted yarn. Figure 12 (b) is a partially enlarged view of the central part of the cross section of Figure 12 (a) observed by reflected electrons. By twisting, the mechanical strength of the CNT yarn is increased, and in some cases the electrical properties (conductivity) are improved. As shown in Figures 11 and 12, even the CNTs located at the center of the CNT twisted yarn are modified with fine particles.

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

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

The conductive member thus obtained has a sufficiently high conductivity as it is, but the plating material can be reduced by heat treating the conductive member in a reducing atmosphere, thereby further increasing the conductivity of the conductive member. The heat treatment conditions are set appropriately, and 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 includes the above-mentioned modified CNT forest and a plating material deposited on the carbon nanotubes located inside the modified carbon nanotube forest. As described above, the CNTs that make up the modified CNT forest carry fine particles generated by the decomposition of the metal element-containing substance, so that the CNTs located inside the modified CNT forest are also modified by the fine particles. Therefore, by plating the modified CNT forest, the plating material is deposited so as to fill the gaps in the CNT forest. If the fine particles carried by the CNTs are conductive, the plating material is deposited more stably. If copper, which has a high thermal conductivity, is selected as the plating material, the conductive member obtained by plating has high thermal conductivity in the extension direction of the CNTs, and can be suitably used as an interlayer thermal conductive material.

The above-described embodiments are described to facilitate understanding of the present invention, and are not described to limit 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 described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.
Example 1

The conductive member was manufactured using the manufacturing apparatus shown in Figure 1 and the plating apparatus 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 _FeCl2

The CNTs constituting the obtained CNT forest had diameters of 30 nm to 40 nm. When the CNT-formed surface of the substrate after removing the CNT forest was observed, the number density of the CNT forest was approximately ¹⁰¹³ / ^m2 . When the crystallinity of the CNTs constituting 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 2-3.

Using the manufacturing apparatus 100 shown in FIG. 1, the CNT forest 30 was modified with copper fine particles using copper (II) acetylacetonate (Cu(acac) ₂ ) as the metal element-containing material RS to obtain a modified CNT forest. Specifically, the CNT forest 30 was placed in a sealable reaction chamber RC, and the metal element-containing material RS, Cu(acac) ₂ , was placed nearby. Next, the reaction chamber RC was filled with argon gas and the pressure was kept at 30 Torr. Next, the inside of the reaction chamber RC was heated at a temperature of 400° C. for 15 minutes using the heater 20. The CNTs of the CNT forest 30 were modified with copper fine particles generated by the separation of Cu(acac) ₂ at 200° C., and the modified CNT forest 40 was obtained. The images shown in FIG. 3 to FIG. 7 are observational views of the manufactured modified CNT forest 40. The fine particles observed in these figures were made of a Cu-based conductive material.

A modified CNT forest produced by the same method was observed using a scanning transmission electron microscope to measure the diameter of the CNTs and the particle size of the particles. Figures 14 to 17 are diagrams showing the observation results of the modified CNT forest, and Figure 18 is a histogram showing the measurement results of the particle size of the particles. When the diameters of 13 CNTs selected from the images shown in Figures 14 to 17 were measured, the average diameter (average diameter D3) was 36 nm and the standard deviation was 8.6 nm. From the above measurement results, the number density A of the modified CNT forest was about 10 ¹³ /m ² , so the adjacent gap D1 of the modified CNT forest was 280 nm (= (10 ¹³ m ^-2 ) ^-1/2 - 36 nm). In addition, the particle size of 62 particles selected from the images shown in Figures 14 to 17 was measured, and the average particle size (average particle size D2) was 29.2 nm and the standard deviation was 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 part of the obtained 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: 4mA/ ^cm2 or 5mA/ ^cm2
・Plating time: 1 hour

The conductive member formed by depositing copper plating on the twisted CNT yarn was heated in a hydrogen gas flow (100 sccm) at 700°C for 1 hour. In this way, the conductive member to be evaluated was obtained. Figure 19 is an observational view of the appearance of the conductive member thus obtained, and Figure 20 is an enlarged observational view of the conductive member's appearance.

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, a number of conductive members with different copper volume fractions (unit: vol%) were produced. The electrical conductivity (unit: S/cm) and specific electrical conductivity (unit: S·m ² ·kg ⁻¹ ), as well as the 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 Figs. 25 to 28. For comparison, Figs. 23 to 28 also show the measurement results of a CNT yarn obtained by spinning a CNT forest not modified with copper fine particles (Cu fraction of 0 vol%) and the results of a general pure copper wiring (Cu fraction of 100 vol%).

As shown in Figures 23 to 28, it was confirmed that the conductive member has better electrical properties than CNT yarns formed only from CNTs. Specifically, when the volume fraction of copper in the conductive member is 30 vol% or more, the electrical conductivity and specific electrical conductivity are substantially similar to those of copper, and when the volume fraction of copper is 35 vol% or more, the current capacity and specific current capacity are substantially similar to those of copper.

Example 2
(1) Synthesis of spinnable CNT forest Vertically aligned CNTs were grown on a substrate by a two-step floating catalyst CVD method. The details of the synthesis method of spinnable CNT forest are described in a past report. In the first step, a solution containing ferrocene, which is a catalyst precursor of CNT, in ethanol is ultrasonically atomized and transported to a Si substrate in a CVD chamber by Ar carrier gas. Ferrocene was pyrolyzed on a Si substrate at 700°C to form Fe nanoparticles in-situ. In the second step, acetylene was supplied as a carbon source gas and chlorine gas was supplied for the purpose of lengthening CNTs. A CNT forest with a diameter of 10 nm and a forest length of about 300 μm was synthesized with a CNT growth temperature of 700°C and a growth pressure of 18 Torr. The CNT forest obtained in this way was spinnable.

(2) Cu nanoparticle loading on CNT forest Copper nanoparticles (hereinafter also referred to as "Cu-NPs") were loaded on the CNT forest. Cu(acac) ₂ , a precursor of Cu-NPs, and spinnable CNT forest were placed in a CVD chamber and held at 400 °C for 15 minutes in a 100% Ar atmosphere of 30 Torr. In this process, Cu(acac) ₂ evaporated and diffused to be thermally decomposed on the CNT surface. Then, it was thermally decomposed on the CNT surface, and Cu-NPs were nucleated. Since the vapor of Cu(acac) ₂ diffused homogeneously to the inside of the CNT forest, Cu-NPs were also uniformly deposited on the CNTs inside the CNT forest. After loading Cu-NPs, the chamber was evacuated and reduced at 350 °C for 1 hour in a 100 Torr argon:hydrogen = 4:1 atmosphere. In addition, 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 manner is also referred to as the "Cu-NPs-supported CNT forest."

(3) Preparation of Cu-NPs-supported CNT twisted yarn As in Example 1, when one end of the Cu-NPs-supported CNT forest was pulled out, a CNT bundle (in this specification, a partial structure of the CNT forest in which several CNTs are in close proximity and in a bundle) was continuously pulled out, and a connected body of CNTs oriented in one direction (CNT web) was formed. 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 thus obtained is also referred to as "Cu-NPs-supported CNT twisted yarn". For comparison, a CNT twisted yarn was also prepared from a CNT forest that did not support Cu-NPs. Hereinafter, this CNT twisted yarn is referred to as "unsupported CNT twisted yarn".

(4) Copper plating treatment In order 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 twisted CNT yarn with a copper plate as the anode and the twisted CNT yarn as the cathode. A current density of 0.2 A/ ^dm2 was supplied for 2 hours. In addition, in order to reduce copper oxide that may be present and to smooth the attachment of CNT and copper, a heat treatment was performed at 500 Torr and 700°C for 1 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, which includes a CNT continuum (CNT twisted yarn) having a thread shape and a plating-based substance deposited on at least a part of the CNTs constituting the twisted CNT 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 embodiment).

(5) Characteristic Evaluation A field emission scanning electron microscope (Hitachi, Ltd., "SU-8030") was used to observe the CNTs. A cross-section polisher (JEOL, Ltd., "IB-09020 CP") was used to process the cross section of the CNTs/Cu-wire to a high quality in order to observe the cross-sectional secondary electron image of the CNTs/Cu-wire. A transmission electron microscope (JEOL, Ltd., "JEM-2100F") was used to observe the cross section of the CNTs/Cu-wire at high magnification. A thin film of the CNTs/Cu-wire was prepared using an FIB (JEOL, Ltd., "JIB-4700F") to observe the transmission electron image. The electrical conductivity was measured using a four-terminal method under atmospheric pressure. The current capacity was measured using a two-terminal method under high vacuum. If the measurement length of the two-terminal method is short, heat will escape to the electrodes, so the measurement length was set to 1 cm for the purpose of measuring the current capacity of the true 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-supported CNT forest According to the Cu-NPs-supporting method of this embodiment, the amount of Cu-NPs supported and the particle size can be controlled by parameters such as the amount of precursor and temperature. Cu(acac) ₂ is a sublimable organic compound that sublimes and pyrolyzes at a relatively low temperature. Therefore, it can be said that it is suitable as a precursor that diffuses into the inside of the CNT forest with steam and supports Cu-NPs on the CNT surface throughout the CNT forest.

However, the conditions for uniformly supporting Cu-NPs to the inside of the CNT forest must be carefully controlled. The thermal decomposition rate of Cu(acac) ₂ varies greatly depending on the pressure and temperature in the chamber. When the temperature is high, the thermal decomposition rate is fast, so the support of Cu-NPs proceeds from the side of the CNT forest, and it is not possible to support Cu-NPs to the inside of the CNT forest. In this example, the support conditions for Cu-NPs were carefully examined, and a spinnable CNT forest was obtained in which Cu-NPs was uniformly supported to the inside of the CNT forest.

Secondary electron images of CNT forests carrying Cu-NPs when the amount of Cu(acac) ₂ was changed to 10 mg, 30 mg, and 100 mg are shown in Figures 30(A) to 30(C). As shown in Figure 30(A), when the amount of Cu(acac) ₂ was as small as 10 mg, the amount of Cu-NPs carried on the CNT surface was small, and there were CNTs that did not carry Cu-NPs. However, the spinnability was high, just like the CNT forests that did not carry Cu-NPs.

As shown in FIG. 30(C), when the amount of Cu(acac) ₂ was as large as 100 mg, the amount of Cu-NPs supported on the CNT surface was very large. In this case, the CNTs were bonded to each other by Cu-NPs, and the entire CNT forest was one bonded body. When the end of the CNT forest was pulled out, the CNT bundle adjacent to the pulled out CNT was strongly bonded to the CNT forest and could not be separated from the CNT forest. For this reason, 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 Fig. 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, since it was necessary to spin the CNT twisted yarn, the CNT twisted yarn was produced using the CNT forest produced with 30 mg of Cu(acac) ₂ .

In this example, Cu(acac) ₂ was used as the precursor because the purpose was to form a composite with copper, but other acetylacetonate complexes (Pt(acac) ₂ , Ni(acac) ₂ , Zn(acac) ₂ , etc.) can be used to similarly support nanoparticles of various metals 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 embodiment, dry spinning was achieved in which Cu-NPs was supported throughout the CNT forest and the drawn CNT web was also uniformly supported with Cu-NPs. In this embodiment, Cu-NPs was supported at the spinnable CNT forest stage, where the distance between CNT bundles is wider than in the CNT twisted yarn, so Cu-NPs can be supported uniformly in the CNT twisted yarn, in contrast to the case where Cu-NPs is supported after the CNT twisted yarn is produced. In the method according to this embodiment, nanoparticles are supported in advance in the CNT forest, so there is a wide range of applications, such as Cu-NPs-supported CNT forests, Cu-NPs-supported CNT sheets, and Cu-NPs-supported CNT twisted yarns. The method used in this embodiment has the advantage of being easy to handle and convenient for users.

(2) Structural analysis of CNT/Cu-wire A copper luster was observed on the surface of the CNT/Cu-wire obtained in this example. FIG. 31(A) is a cross-sectional secondary electron image of a composite yarn (hereinafter, also referred to as "Mixed CNT/Cu-wire") in which copper was precipitated on a CNT twisted yarn (Cu-NPs-supported CNT twisted yarn) that had Cu-NPs preliminarily supported by using CNTs with a diameter of about 10 nm. FIG. 31(B) is a cross-sectional secondary electron image of a composite yarn (hereinafter, also referred to as "Unmixed CNT/Cu-wire") in which copper was precipitated on a CNT twisted yarn (unsupported CNT) that had not previously supported Cu-NPs, although it is common in that CNTs with a diameter of about 10 nm were 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 FIG. 31(A), in the mixed CNT/Cu-wire, copper was precipitated uniformly from the outer periphery to the inside of the CNT twisted yarn. Also, from the high magnification image, it can be seen that copper was precipitated densely. In contrast, in the unmixed CNT/Cu-wire, as shown in FIG. 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 precipitated on the outer periphery of the CNT twisted yarn. Copper was also precipitated in islands inside the CNT twisted yarn. By comparing FIG. 31(A) and FIG. 31(B), it was confirmed that copper can be precipitated uniformly all the way to the inside of the CNT twisted yarn by first supporting Cu-NPs on the CNT twisted yarn and then plating it.

Copper ions in the plating solution are likely to precipitate as metallic copper on the surface of Cu-NPs, which is stable in terms of 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. In addition, 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 passing current. Furthermore, since the current density during plating is low, the rate-determining process is not ion diffusion but copper precipitation on the CNT surface. Therefore, even after plating begins, ions continue to move inside and precipitation continues, which is thought to be why a homogeneous CNT/Cu-wire was produced in this example.

A transmission electron image of an orthogonal cross section (cross section perpendicular to the extension direction of the CNT) of the mixed CNT/Cu-wire is shown in FIG. 32(A), and its high-magnification image is shown in FIG. 32(B). As shown in these figures, the grain size of the precipitated copper is several hundred nm. It can also be seen that copper precipitates between the CNT bundles and adheres closely to the CNT surface. There were almost no gaps between the copper and the CNT, but nanovoids of about several tens of nm existed between the CNT bundles. In addition, from the high-magnification image (FIG. 32(B)), it was observed that the CNTs covered with the copper matrix had a slightly crushed shape. From this observation, it was confirmed that even if copper begins to be electrolytically deposited from the Cu-NPs supported on the CNT surface, copper precipitates so as to surround the CNTs by the end of plating.

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 Fig. 33(A), and its high-magnification image is shown in Fig. 33(B). As shown in these figures, the CNT and copper were continuously adhered to each other in the longitudinal direction.
(3) Electrical conductivity properties of CNT/Cu-wire

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

As shown in FIG. 34(A), the conductivity of Mixed CNT/Cu-wire was 2.41×10 ⁵ S/cm, and that of Unmixed CNT/Cu-wire was 4.26×10 ⁴ S/cm. The conductivity of CNT twisted yarn was 2.35×10 ² S/cm, which is three orders of magnitude smaller than the conductivity of copper wire (4.5×10 ⁵ S/cm). The conductivity of CNT/Cu-wire increased as the volume ratio of copper increased. In the linear scale plot shown in FIG. 34(B), Mixed CNT/Cu-wire has an almost linear relationship with copper wire, and free electrons moving in the copper matrix are dominant as carriers. Note that the conductivity of Unmixed CNT/Cu-wire is lower than the linear relationship. In the cross-sectional secondary electron image of Fig. 31(B), copper precipitated in islands inside the CNT/Cu-wire is seen, which indicates that copper is present that does not contribute to electrical conductivity. As a result, it is believed that the electrical conductivity is reduced relative to the copper content.

Figure 35 shows the temperature dependence of electrical resistivity of each sample normalized by the value at 300K. As shown in Figure 35, the electrical resistivity of the copper wire (dashed line) increases in proportion to the temperature due to phonon scattering, and the temperature coefficient of resistance (TCR) was 3.3 x ^10-3 K ^-1 . The electrical resistivity of the Mixed CNT/Cu-wire (solid line) and the electrical resistivity of the Unmixed CNT/Cu-wire (dotted line) increase with increasing temperature, but the TCR is 1.2 x ^10-3 K ^-1 and 2.0 x ^10-3 K ^-1 , respectively, which is smaller than that of the copper wire. From this, it is considered that the phonon scattering of electrons is suppressed by the CNT. In addition, 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 Fig. 35, when the electrical conductivity in the longitudinal direction is measured, the temperature coefficient of resistance (TCR) in the range of 300K to 450K is preferably 1.8 x ^10-3 K ^-1 or less, more preferably 1.5 x ^10-3 K ^-1 or less, and particularly preferably 1.2 x ^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 smaller 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 smaller than that of copper, the specific conductivity of Mixed CNT/Cu-wire reversed that of copper wire at 370K. In other words, it was confirmed that the specific conductivity of Mixed CNT/Cu-wire is stably higher than that of copper wire at temperatures above 400K.

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 electrical resistance is thought to be due to the influence of Friedel oscillations.

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

FIG. 38 shows a graph showing the relationship between the specific conductivity and the specific current capacity of each sample. The specific conductivity of Mixed CNT/Cu-wire is 4.31×10 ⁴ S·cm ² /g, which is similar to that of copper wire (4.87×10 ⁴ S·cm ² /g) and is more than two orders of magnitude higher than that of CNT twisted yarn (4.40×10 ² S·cm ² /g). The specific conductivity is almost entirely dependent on the copper content. This also supports the idea that the carrier in the composite material is the free electron of copper. On the other hand, the specific current capacity of Mixed CNT/Cu-wire is 2.32×10 ⁴ A·cm/g, which is 3.6 times larger than that of copper wire (6.5×10 ³ A·cm/g). Due to the suppression of the increase in resistance at high temperatures in CNT/Cu, the transport capacity is greatly improved, even though the current flows through the copper matrix like that of copper wire.

The largest value was achieved for CNT twisted yarn (2.85 x 10 ⁴ A cm/g). CNT twisted yarn has a sublimation temperature much higher than copper, and also has a high infrared emissivity, so it can transport electric 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 the stress-strain curves of Mixed CNT/Cu-wire and Unmixed CNT/Cu-wire manufactured using CNTs with a diameter of about 10 nm. For comparison, the stress-strain curves of CNT twisted yarn and copper wire manufactured using CNTs with a diameter of about 10 nm are also shown. The tensile strength of Mixed CNT/Cu-wire was 699 MPa and Young's modulus was 70.4 GPa. The tensile strength of copper wire was 191 MPa and Young's modulus was 83.5 GPa, while the tensile strength of CNT twisted yarn was 666 MPa and Young's modulus was 32.2 GPa. Compared to CNT twisted yarn, the tensile strength and Young's modulus of Mixed CNT/Cu-wire were both improved by homogeneous compounding 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 the Young's modulus decreased. FIG. 39(B) is a graph showing the relationship between the Young's modulus and the tensile strength of various samples obtained from the stress-strain diagram of FIG. 39(A). As shown in FIG. 39(B), when the CNT twisted yarn is used as a reference, the Mixed CNT/Cu-wire had a significantly increased Young's modulus and the same or higher tensile strength. In contrast, the tensile strength of the unmixed CNT/Cu-wire decreased significantly, and the Young's modulus also decreased. That is, by comparing Mixed CNT/Cu-wire with Unmixed CNT/Cu-wire, it was shown that the thread-shaped conductive member Mixed CNT/Cu-wire preferably has a tensile strength of 1.0 times or more and a Young's modulus of 1.5 times or more based on the blank carbon nanotube continuum, which corresponds to the material obtained by removing the plating substance from this thread-shaped conductive member, i.e., CNT twisted yarn. It is more preferable that the Young's modulus of Mixed CNT/Cu-wire is 2.0 times or more based on the CNT twisted yarn.

A secondary electron image of the tensile fracture of Mixed CNT/Cu-wire is shown in Figure 40(A), and a secondary electron image of the tensile fracture of Unmixed CNT/Cu-wire is shown in Figure 40(B). As shown in Figure 40(A), the fracture of Mixed CNT/Cu-wire was short in CNT pull-out. On the other hand, as shown in Figure 40(B), the copper of the outer periphery (clad) of Unmixed CNT/Cu-wire broke and slipped, and the CNT twisted yarn was pulled out for a long time. Since Mixed CNT/Cu-wire shows a significant improvement in Young's modulus and tensile strength compared to copper wire, not only is copper precipitated homogeneously in the CNT twisted yarn, but it also has good adhesion to the CNT bundle surface, and copper transmits the load between the CNT bundles well as a matrix. 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 is precipitated on a CNT twisted yarn carrying Cu-NPs. Figure 41 (B) shows a secondary electron image of a buckling part of a composite yarn in which copper is precipitated on a CNT twisted yarn not carrying 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 homogeneously mixed. On the other hand, as shown in Figure 41 (B), the Unmixed CNT/Cu-wire easily buckles and breaks. 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 portion cannot bear the compressive load caused by bending, and the outer peripheral part (cladding) made of copper on the surface easily buckles.

As explained above, in Example 2, a CNT/Cu composite yarn containing a homogeneous high proportion of CNT was produced. Due to the synergistic effect of CNT and copper, it is an innovative new material that has high electrical conductivity, low TCR, high current 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 small electronic device systems with high energy density. In addition, the dry CNT spinning technology with vapor-phase nanoparticle deposition shown in this example to obtain a homogeneous composite material is a new technology that adds a new aspect to CNT applications. Nanoparticle-loaded CNTs can form a variety of structures such as long fibers, sheets, and three-dimensional structures, so in the future, CNT applications with various functions will be possible.

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 (10)

a carbon nanotube forest having carbon nanotubes oriented in a predetermined direction and capable of being spun;
and a particle supported on the carbon nanotube.
A modified carbon nanotube forest characterized by being spinnable. The modified carbon nanotube forest of claim 1 , wherein 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: tubes/ ^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) The modified carbon nanotube forest according to claim 1 or 2, wherein the microparticles are conductive. The modified carbon nanotube forest according to any one of claims 1 to 3, wherein the microparticles include an oxide. A carbon nanotube continuous body comprising a spun body of a modified carbon nanotube forest according to any one of claims 1 to 4. The carbon nanotube continuous body according to claim 5, wherein the carbon nanotube continuous body has a web shape. The carbon nanotube continuous body according to claim 5, wherein the carbon nanotube continuous body has a thread shape. The carbon nanotube continuum according to claim 7, which is twisted. A conductive member comprising a modified carbon nanotube forest according to any one of claims 1 to 3 and a plating material deposited on the carbon nanotubes located inside the modified carbon nanotube forest. An interlayer thermally conductive material comprising the conductive member described in claim 9.