JP2020066812A - Composite fiber and fiber bundle - Google Patents

Abstract

To provide a composite fiber applicable to a wide range of use, as well as equipped with a carbon substance that exhibits high heat conductivity and high electrical conductivity, and a fiber bundle thereof.SOLUTION: A composite fiber 1 includes: a metal carbide-containing fiber 3 with a metal carbide content of 92 wt.% or more; and a carbon layer 5 covering a surface 3A of the metal carbide-containing fiber 3. The composite fiber 1 has an oxygen content of 1.2 wt.% or less. The carbon layer 5 includes graphene. The graphene having a different number of layers can be observed in at least one section, when the section of 30 μm divided in a longer direction of the metal carbide-containing fiber 3 is observed.SELECTED DRAWING: Figure 3

Description

  The present invention relates to composite fibers and fiber bundles.

  In recent years, SiC whiskers with carbon nanotubes using carbon nanotubes, which are carbon substances, carbon nanotube films, SiC substrates with carbon nanotube films, and the like have been studied with the aim of application in the field of electronic materials (see, for example, Patent Document 1). ). Since carbon materials such as carbon nanotubes exhibit high thermal conductivity and high electrical conductivity, whiskers, films, substrates, etc. provided with carbon materials are also excellent in thermal conductivity and electrical conductivity.

JP, 2003-171107, A

However, the shape of the object provided in Patent Document 1 is limited to a specific shape such as a whisker, a film, and a substrate, which limits the application range. On the other hand, fibers have been conventionally applied to various uses, and their application range is generally wide.
Therefore, a fiber provided with a carbon material is desired, but as far as the present inventors are aware, there is no practical fiber provided with this structure.
The present invention has been made in view of the above circumstances, and provides a composite fiber and a fiber bundle thereof that are provided with a carbon material that exhibits high thermal conductivity and high electrical conductivity and that can be applied to a wide range of applications. With the goal. The present invention can be realized as the following modes.

[1] A metal carbide-containing fiber having a metal carbide content of 92% by weight or more,
A composite fiber comprising a carbon layer covering the surface of the metal carbide-containing fiber,
The oxygen content is 1.2 wt% or less,
The carbon layer is made of graphene,
The composite fiber, wherein the graphene having different numbers of layers is observed in at least one section when the section of 30 μm is divided and observed in the longitudinal direction of the composite fiber.

[2] The metal carbide is SiC,
The composite fiber according to [1], wherein the metal carbide-containing fiber is formed by bonding SiC particles of 3 nm to 25 nm.

[3] The composite fiber according to [1] or [2], which has an average fiber diameter of 6 μm to 50 μm.

[4] The composite fiber according to any one of [1] to [3], wherein 90% or more of the surface of the metal carbide-containing fiber is covered with the carbon layer.

[5] A fiber bundle comprising 15 or more of the composite fibers according to any one of [1] to [4].

Since the conjugate fiber of the present invention has a fiber shape, it can be applied to a wide range of applications. Further, according to the composite fiber of the present invention, since the fiber having a metal carbide content of 92% by weight or more is provided, both the heat resistance and the strength are excellent. Furthermore, since the composite fiber is provided with the carbon layer made of graphene that covers the surface of the metal carbide-containing fiber, it has excellent thermal conductivity and electrical conductivity.
Then, when observing a section of 30 μm in the longitudinal direction of the composite fiber, graphene having different numbers of layers is observed in the same section in at least one section. The stress can be released and the followability to the displacement of the composite fiber is improved.
Further, when the oxygen content of the composite fiber is 1.2% by weight or less, the strength becomes higher.
When the metal carbide is SiC, and the metal carbide-containing fiber is formed by bonding SiC particles of 3 nm to 25 nm, it has resistance to displacement, and ordinary fiber (resin fiber or Al ₂ O ₃ —SiO _{2 2} fiber, etc.) and has the same suppleness.
When the average fiber diameter of the composite fiber is 6 μm to 50 μm, both the strength of the composite fiber and the resistance to displacement are good.
When 90% or more of the surface of the metal carbide-containing fiber is covered with the carbon layer, the strength of the composite fiber is further improved.
When 15 or more composite fibers are bundled into a fiber bundle, the dispersion of each composite fiber is offset, and the dispersion of the strength, thermal conductivity, and electric conductivity of the fiber bundle is reduced.

It is a longitudinal cross-sectional view of the conjugate fiber in one embodiment of the present invention. It is a cross-sectional view of the conjugate fiber in one embodiment of the present invention. It is a longitudinal cross-sectional view of the conjugate fiber in one embodiment of the present invention. It is explanatory drawing for demonstrating the preparation method of a conjugate fiber.

  Hereinafter, the present invention will be described in detail. In addition, in the present specification, the description using “to” for the numerical range includes the lower limit value and the upper limit value unless otherwise specified. For example, the description “10 to 20” includes both the lower limit “10” and the upper limit “20”. That is, “10 to 20” has the same meaning as “10 or more and 20 or less”.

1. Composite fiber 1
As shown in FIGS. 1 and 2, the composite fiber 1 includes a metal carbide-containing fiber 3 having a metal carbide content of 92% by weight or more, and a carbon layer 5 covering a surface 3A of the metal carbide-containing fiber 3. .
The composite fiber 1 has an oxygen content of 1.2% by weight or less. The carbon layer 5 is made of graphene. When the section of 30 μm is divided in the longitudinal direction of the composite fiber 1 and observed, in at least one section, graphene having a different number of layers is observed in the same section.

(1) Average Fiber Diameter, Aspect Ratio The average fiber diameter of the composite fiber 1 is not particularly limited. From the viewpoint of strength and flexibility, the average fiber diameter is preferably 6 μm to 50 μm, and more preferably 10 μm to 30 μm.
The average length of the composite fiber 1 is not particularly limited. The average length is usually 200 μm or more, and preferably 1 mm or more.
The aspect ratio of the composite fiber 1 is not particularly limited. The aspect ratio is usually 20 or more.

(2) Characteristics of Bending of Composite Fiber 1 It is preferable that the composite fiber 1 of the present invention has a property that it cannot be bent even when it is bent until the bending angle reaches 60 °.

(3) Metal Carbide The metal carbide is not particularly limited as long as it is a metal carbide. The metal constituting the metal carbide is preferably one or more selected from the group consisting of Si (silicon), Zr (zirconium), and Ti (titanium). From the viewpoint of improving the heat resistance and strength of the composite fiber 1, the metal carbide is preferably one or more selected from the group consisting of SiC, ZrC, and TiC, and particularly preferably SiC. The type of metal carbide contained in the metal carbide-containing fiber 3 can be specified from a combination of the composition analysis result by EPMA (electron probe microanalyzer) and the XRD measurement result. When the metal carbide is SiC, the metal carbide-containing fiber 3 is preferably formed by binding SiC particles of 3 nm to 25 nm from the viewpoint of having flexibility. Such metal carbide containing fiber 3 has a grain boundary.
When the metal carbide-containing fiber 3 is an aggregate of a plurality of metal carbide particles, the metal carbide-containing fiber 3 has suppleness. On the other hand, whiskers are single crystals in which one particle is grown and are hard (no flexibility). Thus, the metal carbide-containing fiber 3 that is an aggregate of metal carbide particles is different from the whiskers.
The content rate of the metal carbide in the metal carbide-containing fiber 3, that is, the purity of the metal carbide in the metal carbide-containing fiber 3 is 92% by weight or more. The content of the metal carbide in the metal carbide-containing fiber 3 is preferably 95% by weight or more. The metal carbide content may be 100% by weight.
The content of metal carbide in the metal carbide-containing fiber 3 can be obtained as follows. The amount of metal in the metal carbide containing fiber 3 is measured by ICP emission spectroscopy. The carbon content in the metal carbide-containing fiber 3 is measured by carbon content analysis. This carbon content analysis is performed according to JIS 1616 chemical analysis of silicon carbide.
From these measurement results, the number of metal atoms and the number of carbon atoms contained in the metal carbide-containing fiber 3 can be obtained. Then, in consideration of the ratio of the number of metal atoms and the number of carbon atoms in the composition formula of the metal carbide, the metal atom and the carbon atom involved in the constitution of the metal carbide in the metal carbide containing fiber 3 are obtained, and the inside of the metal carbide containing fiber 3 is obtained. Determine the content of the metal carbide of. For example, when the metal carbide contained in the metal carbide-containing fiber 3 is SiC, the ratio of the number of metal atoms (the number of Si atoms) constituting the SiC to the number of carbon atoms is “1: 1”. Here, among the metal atoms (Si atoms) and carbon atoms contained in the metal carbide-containing fiber 3 whose number has been determined by measurement, one metal atom (Si atom) is involved in the constitution of the metal carbide. On the other hand, there is one carbon atom, and a metal atom (Si atom) and a carbon atom form a pair. Therefore, it is considered that the metal atom (Si atom) and the carbon atom cannot form a pair and the surplus atom does not form a metal carbide. Specifically, for example, when the number of metal atoms (the number of Si atoms) obtained by measurement is 100 and the number of carbon atoms is 105, 100 metal atoms (Si atoms) and 100 carbon atoms form SiC. Therefore, it is considered that the surplus 5 carbon atoms do not form SiC. In this way, since the amounts of metal atoms (Si atoms) and carbon atoms constituting SiC are known, the content of metal carbide (SiC) contained in the metal carbide-containing fiber 3 can be calculated. Then, the content rate of the metal carbide is calculated from the content of the metal carbide and the weight of the metal carbide-containing fiber 3.

(4) Carbon layer 5
In the composite fiber 1 of the present invention, the carbon layer 5 covers the surface 3A of the metal carbide containing fiber 3. From the viewpoint of further increasing the thermal conductivity and the electrical conductivity, the carbon layer 5 preferably covers 90% or more of the surface 3A of the metal carbide-containing fiber 3, and more preferably 95% or more. preferable. The carbon layer 5 may cover 100% of the surface 3A of the metal carbide containing fiber 3.
The carbon layer 5 is made of graphene. Graphene forming the carbon layer 5 has a structure in which carbon atoms are arranged in a honeycomb shape. That is, graphene has a six-membered ring network formed by carbon atoms. Graphene may include not only a 6-membered ring formed by carbon atoms but also a 5-membered ring formed by carbon atoms and a 7-membered ring formed by carbon atoms.

In the conjugate fiber 1 of the present invention, when observed in a section of 30 μm in the longitudinal direction of the metal carbide-containing fiber 3, graphene having different numbers of layers is observed in the same section in at least one section. The concept of this structure is shown in FIG. In FIG. 3, five layers of graphene, four layers of graphene, seven layers of graphene, two layers of graphene, and three layers of graphene are sequentially arranged in order from the left within a section of 30 μm. The number of layers observed in the section of 30 μm may be two or more. FIG. 3 is an example in which 5 types are observed. Further, the order of arranging the graphenes having different numbers of layers is not particularly limited.
In the configuration in which graphene having different numbers of layers is observed in the same section of 30 μm, the followability to the displacement of the composite fiber 1 is improved. More specifically, the following phenomenon is presumed to occur. First, when this requirement is not satisfied, that is, when the number of graphene layers is the same in the longitudinal direction of the composite fiber 1, when bending stress is applied to the composite fiber 1, the bending stress is applied to the graphene as it is, and the graphene structure is Presumed to be easily destroyed. On the other hand, in the structure in which graphene having different numbers of layers is observed in the same section of 30 μm, bending stress can be released to the boundary of graphene having different numbers of layers, and it is presumed that the structure of graphene is less likely to be destroyed. It
Among the graphenes having different numbers of layers observed in the same section, the difference in the number of layers between the graphene having the minimum number of layers and the graphene having the maximum number of layers is not particularly limited, but for example, 3 or more layers are preferable. The upper limit of the difference in the number of layers is not limited, but is usually 100 layers.

It is preferable that the surface of the six-membered ring network, which is a structure in which carbon atoms in graphene are arranged in a honeycomb shape, is substantially parallel to the surface 3A of the metal carbide-containing fiber 3.
That is, the graphene sheet surface of the carbon layer 5 is preferably substantially parallel to the surface 3A of the metal carbide-containing fiber 3. FIG. 3 schematically shows that the sheet surface of the graphene sheet 7 is substantially parallel to the surface 3A of the metal carbide containing fiber 3. Note that FIG. 3 also shows that the graphene sheet 7 extends in the longitudinal direction of the metal carbide-containing fiber 3. This structure contributes to the improvement of the thermal conductivity and the electrical conductivity of the composite fiber 1.

  The average radial thickness of the composite fiber 1 of the carbon layer 5 is not particularly limited. The average thickness in the radial direction is preferably 10 nm to 500 nm, more preferably 30 nm to 100 nm. Within this range, damage to the carbon layer 5 when the composite fiber 1 is bent is suppressed. Further, when the average thickness is in this range, cracks (peeling) at the interface between the carbon layer 5 and the metal carbide-containing fiber 3 due to the carbon layer 5 being too thick are suppressed.

(5) Oxygen Content of Composite Fiber 1 The oxygen content of the composite fiber 1 is 1.2% by weight or less, and more preferably 0.8% by weight or less. The oxygen content of the composite fiber 1 may be 0% by weight.
When the oxygen content of the composite fiber 1 is within this range, the composite fiber 1 is used as a heating element, and the resistance value hardly changes when actually generating heat.

(6) Porosity of Metal Carbide-Containing Fiber 3 The porosity of the metal carbide-containing fiber 3 is not particularly limited. The porosity of the metal carbide-containing fiber 3 is preferably 5% to 20%, more preferably 8% to 15%, from the viewpoint of the strength and displaceability of the metal carbide containing fiber 3.
The porosity of the metal carbide containing fiber 3 is measured by the JIS R 7603: 1999 carbon fiber-density test method.

2. Fiber Bundle The fiber bundle of the present invention is made by bundling 15 or more of the above-mentioned composite fibers 1. Although the upper limit of the number of the composite fibers 1 constituting the fiber bundle is not limited, it is usually 50.

3. Method for producing conjugate fiber 1 The conjugate fiber 1 of the present invention can be produced, for example, by the following method. The composite fiber 1 can be manufactured by a manufacturing method in which raw material fibers containing metal carbide (metal carbide containing fibers) are heated under reduced pressure.
As the depressurization condition, for example, a condition where the degree of vacuum is 10 ⁻² Torr to 10 ⁻⁴ Torr can be preferably adopted. The degree of vacuum can be preferably 10 ⁻³ Torr to 10 ⁻⁴ Torr.
The heating temperature is, for example, preferably 1650 ° C to 1950 ° C, and preferably 1700 ° C to 1800 ° C.
It should be noted that it is desirable that the atmosphere for producing the composite fiber 1 does not contain oxygen.
The holding time at the heating temperature is appropriately adjusted to 1 minute to 300 minutes. The number of types of layers observed in a 30 μm section in the longitudinal direction of the composite fiber 1 is affected by the degree of vacuum and the holding time. When the degree of vacuum is high and the holding time is short, the number of types of layers tends to decrease.
When manufacturing the conjugate fiber 1, a single (one) raw material fiber may be heated under reduced pressure, or a plurality of raw material fibers may be bundled and heated under reduced pressure. Alternatively, the raw material fibers may be wound around a carbon rod and heated under reduced pressure.

The present invention will be described in more detail by way of examples.
Note that Experimental Examples 1 to 20 correspond to Examples, and Experimental Examples 21 to 25 are Comparative Examples. For the comparative example, in Table 1, “*” is added after the number indicating the number of the experimental example, such as “21 *”.

1. Preparation of Composite Fiber 1 (1) Experimental Examples 1 to 25
In Experimental Examples 1 to 25, various raw material fibers 12 (metal carbide-containing fibers) shown in Table 1 were held in the SiC bulk 10 as shown in FIG. In this state, the raw material fiber 12 was placed in a high temperature furnace and heated under the conditions of a vacuum degree of 1 × 10 ⁻⁴ Torr and 1750 ° C. to obtain the conjugate fiber 1 of each experimental example.
Details of each raw material fiber shown in Table 1 are as follows.
“TiC fiber” means TiC fiber having an average fiber diameter of 30 μm.
“ZrC fiber” means a ZrC fiber having an average fiber diameter of 30 μm.
“CrC fiber” means CrC fiber having an average fiber diameter of 30 μm.
“SiC fiber” means a SiC fiber having an average fiber diameter of 30 μm.
Each of these raw material fibers is a bonded body of particles having an average particle diameter described in the column of "particle diameter of particles constituting metal carbide-containing fiber" in Table 1.

2. Evaluation method (1) In the composite fiber 1, the content rate of the metal carbide in the portion inside the carbon layer 5 (the metal carbide-containing fiber 3) was obtained by the method described in the above-mentioned section "(3) Metal carbide". It was In each of Experimental Examples 1 to 25, the content (%) of the metal carbide was 92% by weight or more.
(2) The coverage, which is a ratio of the carbon layer 5 covering the surface of the metal carbide-containing fiber 3, was calculated as an average coverage by observing 10 composite fibers 1 by SEM and performing image analysis.
(3) The oxygen content of the composite fiber 1 was determined by using the method described in JIS 1616: 2007, item 13.
(4) The particle diameter of the particles forming the metal carbide-containing fiber 3 was obtained by the following procedure. Observe in a field of view of 0.5 μm × 0.5 μm by SEM observation, and connect diagonal lines of the observed image. The particle size is calculated by adding the long side and the short side of the particles existing on the diagonal line and dividing by two. The average particle diameter is obtained by averaging all the particles existing on the diagonal line.
(5) The porosity of the metal carbide containing fiber 3 was measured by the JIS R 7603: 1999 carbon fiber-density test method.
(6) It was confirmed by TEM observation that graphene having different numbers of layers was observed in the same section of 30 μm. That is, the longitudinal section of the composite fiber 1 was observed by TEM, and a plurality of sections of 30 μm in the longitudinal direction of the composite fiber 1 were observed. The number of sections was 3. In Table 1, the case where graphene having a different number of layers was observed in any of the observed sections was designated as “◯”, and the case where it was not observed was designated as “x”. In the case of “x”, only a certain number of graphenes were observed in the same section in any section.

(7) Displacement The composite fiber 1 was subjected to bending fatigue 10 times and then the resistance value was measured. Regarding the resistance value after bending fatigue, the rate of change with respect to the initial resistance value was obtained, and this was evaluated as displaceability. The evaluation is as follows. It should be noted that the smaller the displacement, the better the performance.

"△" ... 20% or more "○" ... 10% or more and less than 20% "◎" ... 5% or more and less than 10% "★" ... less than 5%

(8) Tensile Strength and Tensile Elastic Modulus Tensile strength and tensile elastic modulus were evaluated according to JIS 7606: 2000 Carbon Fiber-Single Fiber Tensile Property Test Method.
The evaluation is as follows.

Tensile strength "△" ... 2.1 GPa or more and less than 2.4 GPa "○" ... 2.4 GPa or more and less than 2.7 GPa "◎" ... 2.7 GPa or more and less than 3.0 GPa "★" ... 3.0 GPa or more

Tensile elastic modulus "△" ... less than 200 GPa "○" ... 200 GPa or more and less than 250 GPa "◎" ... 250 GPa or more and less than 300 GPa "★" ... 300 GPa or more

3. Evaluation results Table 1 also shows the evaluation results.

Experimental Examples 1 to 20, which are working examples, satisfy all the following requirements [1] to [4].
[1] The composite fiber 1 includes a metal carbide-containing fiber 3 having a metal carbide content of 92% by weight or more, and a carbon layer 5 covering a surface 3A of the metal carbide-containing fiber 3.
[2] The oxygen content is 1.2% by weight or less.
[3] The carbon layer 5 is made of graphene.
[4] When the section of 30 μm is divided in the longitudinal direction of the composite fiber 1 and observed, at least one section has different number of layers of graphene.
On the other hand, Experimental Examples 21 to 25, which are comparative examples, do not satisfy the following requirements.
Experimental Examples 21 to 23 do not satisfy the requirement [2]. That is, in Experimental Examples 21 to 23, the oxygen content rate is higher than 1.2% by weight.
Experimental Examples 24 to 25 do not satisfy the requirement [4]. That is, in Experimental Examples 24 to 25, in any of the sections observed by dividing the section of 30 μm, only one specific type of graphene was observed in the same section.

Experimental Examples 1 to 20, which are Examples, were superior in tensile strength and tensile elastic modulus as compared with Experimental Examples 21 to 23 which were Comparative Examples.
Experimental Examples 1 to 20, which are Examples, were excellent in displaceability and tensile elastic modulus as compared with Experimental Example 24 which was a Comparative Example.
Experimental Examples 1 to 20, which are Examples, were excellent in displaceability as compared with Experimental Example 25 which was a Comparative Example.

  Moreover, among Experimental Examples 1 to 20 which are Examples, Experimental Examples 5 to 20 in which the metal carbide-containing fiber 3 is a SiC fiber and particles of 3 nm to 25 nm (SiC particles) are bonded are displaceability and tensile strength. The strength and tensile modulus were particularly excellent.

  Moreover, among Experimental Examples 1 to 20 which are Examples, Experimental Examples 9 to 20 having an average fiber diameter of 6 μm to 50 μm were extremely excellent in displaceability.

  Further, among Experimental Examples 1 to 20 which are Examples, Experimental Examples 14 to 20 having a coverage of 90% or more were extremely excellent in displaceability, tensile strength, and tensile elastic modulus.

<Other Embodiments (Modifications)>
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the spirit of the invention.

  The conjugate fiber of the present invention can be used as a medium for electric conduction and heat conduction. Specifically, the composite fiber can be used for a transformer, a motor, a wiring board, a heat dissipation board, a wire, and the like.

DESCRIPTION OF SYMBOLS 1 ... Composite fiber 3 ... Metal carbide containing fiber 3A ... Surface 5 ... Carbon layer 7 ... Graphene sheet 10 ... SiC bulk 12 ... Raw material fiber

Claims (5)

A metal carbide-containing fiber having a metal carbide content of 92% by weight or more;
A composite fiber comprising a carbon layer covering the surface of the metal carbide-containing fiber,
The oxygen content is 1.2 wt% or less,
The carbon layer is made of graphene,
The composite fiber, wherein the graphene having different numbers of layers is observed in at least one section when the section of 30 μm is divided and observed in the longitudinal direction of the composite fiber. The metal carbide is SiC,
The composite fiber according to claim 1, wherein the metal carbide-containing fiber is formed by bonding SiC particles of 3 nm to 25 nm.   The composite fiber according to claim 1 or 2, which has an average fiber diameter of 6 µm to 50 µm.   90% or more of the surface of the said metal carbide containing fiber is covered with the said carbon layer, The conjugate fiber of any one of Claims 1-3 characterized by the above-mentioned.   A fiber bundle formed by bundling 15 or more of the composite fibers according to any one of claims 1 to 4.

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