JP2020167160A - Connection structure - Google Patents

Abstract

To provide a connection structure and a connection method in which smooth connection work is realized and electrical resistance is reduced in electrical connection between carbon nanotubes and metal terminals or the like.SOLUTION: In a connection structure 1, a carbon-based coating layer 30 having the thickness of 1 μm or more and 800 μm or less is formed on a base material 20, and a carbon nanotube wire rod 11 and the base material 20 are electrically connected via the carbon-based coating layer 30.SELECTED DRAWING: Figure 1

Description

The present invention relates to a connection structure formed by connecting a carbon nanotube wire rod and a metal base material.

As power lines and signal lines in various fields such as automobiles and industrial equipment, electric wires made of one or more wire rods and an insulating coating covering the core wires are used. Copper or a copper alloy is generally used as the material of the wire rod constituting the core wire from the viewpoint of electrical characteristics. However, in recent years, there has been an increasing need for miniaturization and weight reduction in automobile motors, medical fields, etc., and in order to meet this need, wire rods that replace conventional metal wires such as copper are desired in power lines and the like.

In order to meet such demands, for example, a technique for utilizing carbon nanotubes as a wire rod has been proposed (see, for example, Patent Document 1). The specific gravity of carbon nanotubes is about 1/5 of the specific gravity of copper (about 1/2 of the specific gravity of aluminum), and the electrical resistivity is higher than that of copper (electric resistivity 1.68 x ^10-6 Ω · cm). Is small and shows high conductivity. Therefore, by twisting carbon nanotubes to form a carbon nanotube wire rod, it is expected to realize miniaturization, weight reduction, and high conductivity of products such as automobile motors utilizing the wire rod.

Solder for carbon is used to electrically connect the carbon nanotube wire rod as described above to the metal terminal. Solder for carbon has good wettability with carbon nanotubes, but not with metal. Therefore, in order to electrically connect carbon nanotubes and metal terminals using carbon solder, after wetting the metal terminals with ordinary solder (solder containing lead and tin as the main components), , It is common to bond carbon nanotubes using solder for carbon.

JP-A-2017-171545

As described above, when using ordinary solder and solder for carbon in the electrical connection between the carbon nanotube wire and the metal terminal, the soldering process is required twice, which takes a lot of time and effort for the connection work. There was a problem. Further, since two types of solder are interposed between the carbon nanotube wire rod and the metal base material, the contact interface increases as compared with the case where only one type of solder is used, which may lead to an increase in connection resistance. It was.

An object of the present invention has been made in view of the above problems, and provides a connection structure that realizes smooth connection work and reduces electrical resistance in electrical connection between carbon nanotubes and metal terminals and the like. To do.

That is, the above object is achieved by the following invention.
(1) A connection structure formed by electrically connecting a carbon nanotube wire rod and a metal base material, and a carbon-based coating layer having a thickness of 1 μm or more and 800 μm or less is formed on the base material. The connection structure is characterized in that the carbon nanotube wire rod and the base material are electrically connected via the carbon-based coating layer.
(2) The connection structure according to (1) above, wherein the carbon-based coating layer has a thickness of 1 μm or more and 500 μm or less.
(3) The connection structure according to (1) above, wherein the carbon-based coating layer has a thickness of 2 μm or more and 10 μm or less.
(4) The connection structure according to any one of (1) to (3) above, wherein the carbon nanotube wire rod and the carbon-based coating layer are electrically connected by solder for carbon. ..
(5) The connection structure according to any one of (1) to (4) above, wherein the number of twists of the carbon nanotube wire rod is 1000 T / m or less.
(6) The connection structure according to any one of (1) to (4) above, wherein the number of twists of the carbon nanotube wire rod is 700 T / m or less.
(7) The connection structure according to any one of (1) to (4) above, wherein the number of twists of the carbon nanotube wire rod is 50 T / m or more and 400 T / m or less.
(8) The connection structure according to any one of (1) to (4) above, wherein the number of twists of the carbon nanotube wire rod is 80 T / m or more and 200 T / m or less.

According to the aspect of the present invention, since the base material such as a metal terminal and the carbon nanotube are electrically connected via the carbon-based coating layer, the workability at the time of connection is improved and the electrical resistance is reduced. Reduction can be achieved.

It is a perspective view which shows the connection structure of the carbon nanotube and the metal base material which concerns on this embodiment. It is sectional drawing which shows the connection structure of the carbon nanotube and the metal base material which concerns on this embodiment.

A preferred embodiment of the present invention will be described with reference to the drawings. The embodiment shown below is an example, and various forms can be taken within the scope of the present invention.

<Connection structure between carbon nanotubes and metal base material>
The connection structure between the carbon nanotube and the metal base material according to the present embodiment will be described with reference to FIGS. 1 and 2. The connection structure 1 is configured by connecting the carbon nanotube wire rod (hereinafter referred to as CNT wire rod) 11 constituting the carbon nanotube electric wire (hereinafter referred to as CNT electric wire) 10 and the metal base material 20.
In this connection structure 1, a carbon-based coating layer 30 is formed on a part of the base material 20. The carbon nanotube wire 11 and the base material 20 are electrically connected to each other via a carbon-based coating layer 30.
Further, in the connection structure 1, the carbon nanotube wire rod 11 and the carbon-based coating layer 30 are electrically connected to each other by using the carbon solder 40.

(CNT wire)
As shown in FIG. 1, the CNT wire rod 11 is formed by twisting CNT bundles 11a formed by bundling a plurality of carbon nanotubes (hereinafter, referred to as CNTs) having a layer structure of one or more layers. The outer diameter of the CNT wire rod 11 is, for example, 0.01 to 1 mm. The CNT wire rod 11 may be formed by twisting a plurality of carbon nanotube composites obtained by doping the CNT bundle 11a with different elements.

Here, the CNT is a tubular body having a single-walled structure or a multi-walled structure, and is called SWNT (single-walled nanotube) and MWNT (multi-walled nanotube), respectively. For example, a CNT having a two-walled structure is a three-dimensional network structure in which two tubular bodies having a network structure of a hexagonal lattice are arranged substantially coaxially, and is called a DWNT (double-walled nanotube). The hexagonal lattice, which is a constituent unit, is a six-membered ring in which carbon atoms are arranged at its vertices, and these are continuously bonded adjacent to other six-membered rings.

The properties of CNTs depend on the chirality of the tubular body as described above. Chirality is roughly classified into armchair type, zigzag type, and other chiral types. The armchair type is metallic, the chiral type is semiconducting, and the zigzag type is intermediate. Therefore, the conductivity of CNTs varies greatly depending on which chirality they have, and in order to improve the conductivity of CNT aggregates, it has been important to increase the proportion of armchair-type CNTs that exhibit metallic behavior. It was. On the other hand, it is known that by doping a chiral type CNT having a semiconductor property with a substance having an electron donating property or an electron accepting property (dissimilar element), it exhibits metallic behavior. Further, in a general metal, by doping a dissimilar element, conduction electrons are scattered inside the metal and the conductivity is lowered. Similarly, when a dissimilar element is doped in a metallic CNT, the dissimilar element is doped. , Causes a decrease in conductivity.

In the CNT bundle 11a composed of an aggregate of a plurality of CNTs, the ratio of the sum of the number of CNTs having a two-layer structure or a three-layer structure to the number of a plurality of CNTs is preferably 50% or more, preferably 75%. The above is more preferable. That is, the total number of all CNTs constituting one CNT bundle is N _TOTAL , the sum of the number of CNTs (2) having a two-walled structure among all the CNTs is N _{CNT (2)} , and the three-walled structure among all the CNTs. When the sum of the numbers of CNTs (3) having is N _{CNT (3)} , it can be expressed by the following equation (1).
(N _{CNT (2)} + N _{CNT (3)} ) / N _TOTAL × 100 (%) ≧ 50 (%) ・ ・ ・ (1)

A CNT having a small number of layers, such as a two-layer structure or a three-layer structure, has a relatively higher conductivity than a CNT having a larger number of layers. Further, the dopant is introduced inside the innermost layer of CNTs or in a gap between CNTs formed by a plurality of CNTs. The interlayer distance of CNTs is equivalent to 0.335 nm, which is the interlayer distance of graphite, and in the case of multi-walled CNTs, it is difficult for the dopant to enter between the interlayers in terms of size. From this, the doping effect is exhibited by introducing the dopant inside and outside the CNT, but in the case of the multi-walled CNT, the doping effect of the tube located inside not in contact with the outermost layer and the innermost layer is less likely to be exhibited. .. For the above reasons, when the CNTs having a multi-layer structure are individually doped, the doping effect of the CNTs having a two-layer structure or a three-layer structure is the highest. In addition, the dopant is often a highly reactive reagent that exhibits strong electrophile or nucleophile. A CNT having a single-walled structure has a weaker rigidity than a multi-walled one, and is inferior in chemical resistance. Therefore, when doping treatment is performed, the structure of the CNT itself may be destroyed. Therefore, in the present invention, attention is paid to the number of CNTs having a two-layer structure or a three-layer structure contained in the CNT aggregate. Further, when the ratio of the sum of the number of CNTs having a two-layer or three-layer structure is less than 50%, the ratio of CNTs having a single-wall structure or a four-wall structure becomes high, and the doping effect becomes small as a whole CNT aggregate. , It becomes difficult to obtain high conductivity. Therefore, the ratio of the sum of the number of CNTs having a two-layer or three-layer structure is set to a value within the above range.

The dopant doped in CNT is not particularly limited as long as the conductivity is improved, and is, for example, one or more dissimilar elements selected from the group consisting of nitric acid, sulfuric acid, iodine, bromine, potassium, sodium, boron and nitrogen. It is a molecule.

Further, the outer diameter of the outermost layer of the CNTs constituting the CNT bundle 11a is preferably 5.0 nm or less. If the outer diameter of the outermost layer of the CNTs constituting the CNT bundle 11a exceeds 5.0 nm, the porosity due to the gaps between the CNTs and the innermost layer increases and the conductivity decreases, which is not preferable. Therefore, the outer diameter of the outermost layer of the CNTs constituting the CNT bundle 11a is set to 5.0 nm or less.

Further, the number of twists of the CNT wire rod 11 (CNT bundle 11a) is preferably 1000 T / m or less. When the number of twists of the CNT wire 11 exceeds 1000 T / m, it becomes difficult for the carbon solder 40 described later to permeate between the adjacent CNT bundles 11a that have been twisted. As a result, the connection resistance between the CNT wire rod 11 and the base material 20 via the carbon solder 40 increases, and the conductivity decreases, which is not preferable. Further, since the carbon solder 40 does not easily penetrate between the CNT bundles 11a, the amount of the solder present at the connection interface between the CNT wire 11 and the carbon-based coating layer 30 is reduced. As a result, the adhesive effect of the carbon solder is weakened, and the strength at the interface between the CNT wire 11 and the carbon-based coating layer 30 is lowered (the peeling strength is lowered), which is not preferable. The number of twists of the CNT wire 11 is more preferably 700 T / m or less, and further preferably 50 to 400 T / m or less, from the viewpoint of the connection resistance between the CNT wire 11 and the base material 20 and the peeling strength. It is preferably 80 T / m or more and 200 T / m or less.
Further, the number of stranded wires of the CNT wire rod 11 (CNT bundle 11a) is preferably 10 or more and 200 or less. When the number of stranded wires is 10 or more and 200 or less, the carbon solder 40 easily permeates between the CNT bundles 11a, and the adhesive effect can be enhanced.
Further, the diameter of the wire constituting the CNT wire rod 11 (CNT bundle 11a) is preferably 20 μm or more and 100 μm or less. When the diameter of the strands is 20 μm or more and 100 μm or less, the carbon solder 40 easily permeates between the CNT bundles 11a, and the adhesive effect can be enhanced.

(Metal base material)
The metal base material 20 is, for example, a terminal that is electrically connected to an external terminal (not shown). The base material 20 is made of a metal material (copper, aluminum, iron, an alloy containing these as a main component, or the like). The base material 20 may be composed of only a metal material, or may be formed by providing a plating layer containing a metal as a main component on the base material in order to secure conductivity and strength.

(Carbon coating layer)
The carbon-based coating layer 30 contains carbon as a main component. The carbon content in the carbon-based coating layer 30 is preferably 70% by weight or more. The carbon contained is not particularly limited, and for example, carbon black, graphite (artificial graphite, scaly graphite, expanded graphite), graphene, carbon nanoflake, carbon nanofiber, carbon nanohorn, carbon nanocone, carbon nanotube, Examples thereof include carbon nanocoils, carbon microcoils, carbon nanowalls, carbon nanochaplets, fullerenes, diamonds, amorphous carbons and derivatives thereof.
In the present embodiment, the carbon-based coating layer 30 preferably contains carbon black or graphite, and more preferably contains carbon black and graphite (particularly expanded graphite).
Further, the carbon-based coating layer 30 may contain a conductive material other than carbon.

The thickness of the carbon-based coating layer 30 is preferably 1 μm or more and 800 μm or less. A part of the carbon component contained in the carbon-based coating layer 30 is transferred to the carbon solder 40 side, which will be described later, which is used for connecting the CNT wire rod 11 and the carbon-based coating layer 30. If the thickness of the carbon-based coating layer 30 is less than 1 μm, an exposed portion without carbon coating is generated in a part of the carbon-based coating layer 30 due to the migration of the carbon component to the outside of the coating layer. As a result, in the exposed portion, the wettability with the carbon solder 40 deteriorates, and the connection resistance between the CNT wire rod 11 and the base material increases, which is not preferable. On the other hand, when the thickness of the carbon-based coating layer 30 exceeds 800 μm, the mechanical properties of the connection structure 1 between the CNT wire rod 11 and the base material 20 are likely to be controlled by the mechanical properties of the carbon-based coating layer 30. As a result, fracture (cracking) starting from the carbon-based coating layer 30 is likely to occur, and the peeling strength is lowered, which is not preferable. The thickness of the carbon-based coating layer 30 is more preferably 1 μm or more and 500 μm or less, and further preferably 2 μm or more and 10 μm or less, from the viewpoint of the connection resistance between the CNT wire rod 11 and the base material 20 and the peeling strength. preferable.

(Solder for carbon)
The solder 40 for carbon is a solder having good wettability with respect to the carbon material. Examples of the solder 40 for carbon include C-Solder (manufactured by Cammetics).

Hereinafter, examples according to the embodiment of the present invention will be described. The following examples are merely examples for explaining the embodiments of the present invention, and the present invention is not limited to the examples.

(Examples 1 to 13 and Comparative Examples 1 to 2)
Copper or aluminum terminals were used as the metal substrate. A carbon-based coating layer was formed on the surface of this terminal using a carbon coater EC-32010CC (manufactured by JEOL Ltd.). Solder for carbon (C-Solder (Cametics)) with CNT wire (wire diameter 0.1 mm, wire density 1.8 g / cm ³ , number of twisted CNT bundles 18) in contact with the coating layer. The coating layer and the CNT wire rod were electrically connected using (manufactured by)). By the above method, a connection structure formed by electrically connecting a carbon nanotube wire rod and a metal base material was produced.

Next, the characteristics of the connection structure were evaluated by the following method.

(A) Connection resistivity Using a source meter (Keithley 2400 (manufactured by Keithley)), measure the resistance value when a current of 0.1 mA is passed between the terminal and the wire, and determine the connection resistance value of the above connection structure. I measured it. Four samples were measured, and the average value of the connection resistance values was calculated.

(B) Peeling strength Using a micro autograph (manufactured by Shimadzu Corporation), fix the terminals and stranded wires with grippers, and test speed in the direction of separating the terminals and stranded wires in parallel with the longitudinal method of the stranded wires. A peeling test was carried out at a test speed of 0.05 mm / min. The wire rod was 10 cm. Four samples were measured, and the average value of the tensile test strength was calculated.

(C) Corrosion The corrosive treatment was carried out according to the following procedure. A 5% aqueous sodium chloride solution was sprayed onto the structure at a test temperature of 35 ° C. for 96 hours, and then maintained at a test temperature of 80 ° C. and a humidity of 95% for 96 hours. After that, the connection resistance value was measured. Four samples were used, and the average value of the connection resistance values was calculated.
When the average value of the connection resistance value after the corrosion treatment was less than twice the connection resistance value before the corrosion treatment, it was evaluated as “◯”, and when it was 2 times or more and less than 10 times, it was evaluated as “Δ”.

Table 1 shows the measurement and evaluation results of Examples 1 to 13 and Comparative Examples 1 and 2.

As shown in Table 1, in the connection structures of Examples 1 to 13, the connection resistance between the CNT wire rod and the metal base material was 65 mΩ or less, showing good connection resistance. In particular, in the connection structures of Examples 1 to 12 in which the thickness of the carbon-based coating layer is 500 μm or less, even better connection resistance was exhibited. Further, the connection resistance was better when copper was used as the terminal as the base material.

Further, in the connection structures of Examples 1 to 12, the peeling strength of the CNT wire rod was 2.4N or more, and the peeling strength was good. In particular, in Examples 2, 5, 8 and 11 in which the number of twists of the CNT wire was 50 T / m or more and 400 T / m or less, even better peel strength was exhibited. Further, the peeling strength was better when copper was used as the terminal as the base material.

Further, in the connection structures of Examples 1 to 13, the corrosiveness was good.

On the other hand, as shown in Table 1, in the connection structures of Comparative Examples 1 and 2, the connection resistance was 200 mΩ or more, showing a high connection resistance. In the connection structures of Comparative Examples 1 and 2, the thickness of the carbon-based coating layer was less than 1 μm, and a state in which a part of the carbon-based coating layer was peeled off occurred at the connecting portion between the CNT wire and the carbon-based coating layer. As a result, the carbon solder did not get wet in the portion, which was caused by the increase in connection resistance. Further, in the connection structures of Comparative Examples 1 and 2, the peeling strength was less than 1N, and sufficient connection strength could not be obtained. Further, the connection structures of Comparative Examples 1 and 2 were not sufficiently corrosive.

1 Connection structure 11 CNT wire rod 20 Metal base material 30 Carbon-based coating layer 40 Carbon solder

Claims (8)

It has a connection structure in which a carbon nanotube wire rod and a metal base material are electrically connected.
A carbon-based coating layer having a thickness of 1 μm or more and 800 μm or less is formed on the base material.
A connection structure characterized in that the carbon nanotube wire rod and the base material are electrically connected via the carbon-based coating layer. The connection structure according to claim 1, wherein the carbon-based coating layer has a thickness of 1 μm or more and 500 μm or less. The connection structure according to claim 1, wherein the carbon-based coating layer has a thickness of 2 μm or more and 10 μm or less. The connection structure according to any one of claims 1 to 3, wherein the carbon nanotube wire rod and the carbon-based coating layer are electrically connected by solder for carbon. The connection structure according to any one of claims 1 to 4, wherein the number of twists of the carbon nanotube wire rod is 1000 T / m or less. The connection structure according to any one of claims 1 to 4, wherein the number of twists of the carbon nanotube wire rod is 700 T / m or less. The connection structure according to any one of claims 1 to 4, wherein the number of twists of the carbon nanotube wire rod is 50 T / m or more and 400 T / m or less. The connection structure according to any one of claims 1 to 4, wherein the number of twists of the carbon nanotube wire rod is 80 T / m or more and 200 T / m or less.

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