JP7216519B2 - Composite fibers and fiber bundles - Google Patents

Description

The present invention relates to bicomponent fibers and fiber bundles.

In recent years, SiC whiskers with carbon nanotubes, carbon nanotube films, SiC substrates with carbon nanotube films, etc. using carbon nanotubes, which are carbon substances, have been studied with the aim of application in the field of electronic materials and the like (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. comprising carbon materials also have excellent thermal and electrical conductivity.

Japanese Patent Application Laid-Open No. 2003-171107

However, the shape of the object provided in Patent Document 1 is limited to specific shapes such as whiskers, films, and substrates, which limits the scope of application. On the other hand, fibers have conventionally been applied to various uses, and their application range is generally wide.
Therefore, a fiber with carbon material is desired, but to the best of our knowledge, no practical fiber with this configuration exists.
The present invention has been made in view of the above circumstances, and provides a composite fiber and a fiber bundle thereof, which are provided with a carbon material exhibiting high thermal conductivity and high electrical conductivity, and which are applicable to a wide range of applications. With the goal. The present invention can be implemented 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% by weight or less,
The carbon layer is made of graphene,
A conjugate fiber characterized in that, when the conjugate fiber is divided into sections of 30 μm in the longitudinal direction and observed, different numbers of layers of the graphene are observed in at least one section.

[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 obtained by bundling 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 fibrous shape, it can be applied to a wide range of uses. Moreover, according to the conjugate fiber of the present invention, since the conjugate fiber has a metal carbide content of 92% by weight or more, it is excellent in both heat resistance and strength. Furthermore, since the composite fiber has a carbon layer made of graphene covering the surface of the metal carbide-containing fiber, it is excellent in thermal conductivity and electrical conductivity.
Then, when observing sections of 30 μm in the longitudinal direction of the composite fiber, graphene with 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, by setting the oxygen content of the conjugate fiber to 1.2% by weight or less, the strength is further increased.
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 is resistant to displacement and is similar to ordinary fibers (resin fibers and Al ₂ O ₃ —SiO ₂ fibers, etc.).
When the average fiber diameter of the composite fiber is 6 μm to 50 μm, both the strength and resistance to displacement of the composite fiber 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 fifteen or more conjugate fibers are bundled to form a fiber bundle, variations in the individual conjugate fibers are canceled out, and variations in the strength, thermal conductivity, and electrical conductivity of the fiber bundle are reduced.

1 is a vertical cross-sectional view of a composite fiber in one embodiment of the present invention; FIG. 1 is a cross-sectional view of a composite fiber in one embodiment of the invention; FIG. 1 is a vertical cross-sectional view of a composite fiber in one embodiment of the present invention; FIG. FIG. 4 is an explanatory diagram for explaining a method for preparing a composite fiber;

The present invention will be described in detail below. In this specification, the description using "-" for the numerical range includes the lower limit and the upper limit 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 the 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 conjugate fiber 1 is divided into sections of 30 μm in the longitudinal direction and observed, graphene having different numbers of layers is observed within the same section in at least one section.

(1) Average Fiber Diameter and Aspect Ratio The average fiber diameter of the composite fiber 1 is not particularly limited. The average fiber diameter is preferably 6 μm to 50 μm, more preferably 10 μm to 30 μm, from the viewpoint of strength and flexibility.
The average length of the composite fiber 1 is not particularly limited. The average length is usually 200 μm or more, 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 the conjugate fiber 1 when it is bent The conjugate fiber 1 of the present invention preferably has a property that it does not break even when the bending angle is 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 SiC is particularly preferable. The type of metal carbide contained in the metal carbide-containing fiber 3 can be identified from a combination of the result of composition analysis by EPMA (electron probe microanalyzer) and the result of XRD measurement. When the metal carbide is SiC, the metal carbide-containing fiber 3 is preferably formed by bonding SiC particles of 3 nm to 25 nm from the viewpoint of flexibility. Such metal carbide-containing fibers 3 have grain boundaries.
When the metal carbide-containing fiber 3 is an aggregate of a plurality of metal carbide particles, the metal carbide-containing fiber 3 has flexibility. On the other hand, whiskers are single crystals grown from one grain and are hard (no flexibility). Thus, the metal carbide-containing fibers 3, which are aggregates of metal carbide particles, are different from whiskers.
The content of 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 metal carbide content 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 determined 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 JIS1616 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 determined. Then, considering the ratio of the number of metal atoms and the number of carbon atoms in the composition formula of the metal carbide, the metal atoms and carbon atoms involved in the composition of the metal carbide in the metal carbide-containing fiber 3 are determined. Determine the metal carbide content 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) and the number of carbon atoms constituting SiC is "1:1". Here, among the metal atoms (Si atoms) and carbon atoms contained in the metal carbide-containing fiber 3 whose number was determined by measurement, those involved in the composition of the metal carbide are one metal atom (Si atom) 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 surplus atoms that cannot form a pair between a metal atom (Si atom) and a carbon atom do not form a metal carbide. Specifically, for example, if the number of metal atoms (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. and the extra 5 carbon atoms are considered not to form SiC. Since the amounts of metal atoms (Si atoms) and carbon atoms constituting SiC are known in this manner, the content of metal carbide (SiC) contained in the metal carbide-containing fiber 3 can be calculated. Then, the content 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 thermal conductivity and electrical conductivity, the carbon layer 5 preferably covers 90% or more of the surface 3A of the metal carbide-containing fiber 3, more preferably 95% or more. preferable. Carbon layer 5 may cover 100% of surface 3A of 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 pattern. That is, graphene has a six-membered ring network formed by carbon atoms. Graphene may include not only 6-membered rings formed by carbon atoms, but also 5-membered rings formed by carbon atoms and 7-membered rings formed by carbon atoms.

In the conjugate fiber 1 of the present invention, when the metal carbide-containing fiber 3 is divided into sections of 30 μm in the longitudinal direction and observed, graphene having different numbers of layers is observed within the same section in at least one section. The concept of this structure is shown in FIG. FIG. 3 shows that five layers of graphene, four layers of graphene, seven layers of graphene, two layers of graphene, and three layers of graphene are arranged in this order from the left within a section of 30 μm. The number of layers observed in the 30 μm section should be two or more. FIG. 3 is an example in which five species are observed. In addition, the order in which graphene layers with different numbers of layers are arranged is not particularly limited.
In a configuration in which different numbers of graphene layers are observed within the same section of 30 μm, the followability of the conjugate fiber 1 to displacement 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 a bending stress is applied to the composite fiber 1, the bending stress is applied to the graphene as it is, and the graphene structure changes. presumed to be easily destroyed. On the other hand, in a configuration in which graphene with different numbers of layers is observed in the same section of 30 μm, bending stress can be released to the boundary between graphene with different numbers of layers, so it is speculated that the graphene structure is less likely to be destroyed. be.
Among 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 is preferably three or more layers, for example. Although the upper limit of the difference in the number of layers is not limited, it is usually 100 layers.

The plane formed by the six-membered ring network, which is a structure in which carbon atoms in graphene are arranged in a honeycomb pattern, is preferably 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. As shown in FIG. Note that FIG. 3 also shows how the graphene sheet 7 extends in the longitudinal direction of the metal carbide-containing fiber 3 . This structure contributes to improving the thermal conductivity and electrical conductivity of the composite fiber 1 .

The average radial thickness of the composite fibers 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, breakage of the carbon layer 5 when the composite fiber 1 is bent is suppressed. In addition, when the average thickness is within 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 Rate of Composite Fiber 1 The oxygen content rate of the conjugate 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 conjugate fiber 1 is within this range, the conjugate fiber 1 is used as a heating element, and resistance value change is less likely to occur 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 displacement of the metal carbide-containing fiber 3.
The porosity of the metal carbide-containing fiber 3 is measured by JIS R 7603:1999 carbon fiber--test method for density.

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

3. Method for Producing Composite 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 produced by a production method in which raw material fibers containing metal carbide (metal carbide-containing fibers) are heated under reduced pressure.
As the reduced pressure 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 preferably be 10 ^-3 Torr to 10 ^-4 Torr.
The heating temperature is, for example, preferably 1650°C to 1950°C, more preferably 1700°C to 1800°C.
It is desirable that the atmosphere in which the conjugate fiber 1 is produced does not contain oxygen.
The holding time at the above heating temperature is appropriately adjusted between 1 minute and 300 minutes. The number of types of layers observed in the 30 μm section in the longitudinal direction of the conjugate fiber 1 is affected by the degree of vacuum and the holding time. When the degree of vacuum is high and the retention time is short, the number of types of layer numbers 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 wrapped around a carbon rod and heated under reduced pressure.

EXAMPLES The present invention will be described more specifically by way of examples.
Note that Experimental Examples 1 to 20 correspond to Examples, and Experimental Examples 21 to 25 are Comparative Examples. As for the comparative examples, in Table 1, "*" such as "21*" is attached after the number indicating the number of the experimental example.

1. Preparation of Composite Fiber 1 (1) Experimental Examples 1-25
In Experimental Examples 1 to 25, various raw material fibers 12 (metal carbide-containing fibers) listed in Table 1 were held by 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 conditions of a degree of vacuum of 1×10 ⁻⁴ Torr and 1750° C. to obtain a composite fiber 1 of each experimental example.
The details of each raw material fiber described in Table 1 are as follows.
"TiC fibers" means TiC fibers with an average fiber diameter of 30 µm.
"ZrC fibers" means ZrC fibers with an average fiber diameter of 30 µm.
"CrC fibers" means CrC fibers with an average fiber diameter of 30 µm.
"SiC fiber" means SiC fiber with an average fiber diameter of 30 µm.
Each of these raw fibers is a combined body of particles having an average particle size described in the column of "Particle Size of Particles Constituting Metal Carbide-Containing Fiber" in Table 1.

2. Evaluation method (1) The content of metal carbide in the inner portion (metal carbide-containing fiber 3) of the composite fiber 1 than the carbon layer 5 is obtained by the method described in the above "(3) Metal carbide" column. rice field. The content (%) of this metal carbide was 92% by weight or more in all of Experimental Examples 1-25.
(2) The ratio of the carbon layer 5 covering the surface of the metal carbide-containing fiber 3, or the coverage, was calculated by observing 1 to 10 composite fibers with an SEM and calculating the average coverage by image analysis.
(3) The oxygen content of composite fiber 1 was determined using the method described in JIS 1616:2007, item 13.
(4) The particle diameter of the particles constituting the metal carbide-containing fiber 3 was obtained in the following manner. SEM observation is performed with a field of view of 0.5 μm×0.5 μm, and diagonal lines of the observed image are connected. The particle diameter is obtained by adding the long side and the short side of the particle existing on the diagonal line and dividing the result by 2. 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 according to JIS R 7603:1999 carbon fiber-density test method.
(6) TEM observation was used to confirm that graphene with different numbers of layers was observed within the same section of 30 μm. That is, the longitudinal section of the conjugate fiber 1 was observed with a TEM, and the conjugate fiber 1 was divided into a plurality of sections of 30 μm in the longitudinal direction for observation. The number of sections was set to three. In Table 1, when graphene with a different number of layers was observed in any of the observed sections, it was indicated as "O", and when it was not observed, it was indicated as "x". In the case of "x", only graphene with a specific number of layers was observed within the same section in any section.

(7) Displacement The resistance value was measured after bending fatigue was applied to the composite fiber 1 10 times. 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 the displacement property. Evaluation was performed as follows. It should be noted that the smaller the displaceability, the better the performance.

"△" ... 20% or more "〇" ... 10% or more and less than 20% "◎" ... 5% or more and less than 10% "★" ... less than 5%

(8) Tensile Strength, Tensile Elastic Modulus Tensile strength and tensile elastic modulus were evaluated according to JIS7606:2000 Test method for tensile properties of carbon fiber-single fiber.
Evaluation was performed 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 examples, satisfy all of the following requirements [1] to [4].
[1] Composite fiber 1 includes metal carbide-containing fiber 3 having a metal carbide content of 92% by weight or more, and carbon layer 5 covering surface 3A of 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 conjugate fiber 1 is divided into sections of 30 μm in the longitudinal direction and observed, different numbers of graphene layers are observed in at least one section.
In contrast, 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 21-23, the oxygen content is greater than 1.2% by weight.
Experimental Examples 24 and 25 do not satisfy the requirement of [4]. That is, in Experimental Examples 24 and 25, only graphene having a specific number of layers of one type was observed in each section observed by dividing the section of 30 μm.

Experimental Examples 1 to 20, which are examples, were superior in tensile strength and tensile modulus compared to Experimental Examples 21 to 23, which are comparative examples.
Experimental Examples 1 to 20, which are examples, were superior to Experimental Example 24, which is a comparative example, in terms of displacement and tensile modulus.
Experimental Examples 1 to 20, which are examples, were superior in displaceability compared to Experimental Example 25, which was a comparative example.

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

Among Experimental Examples 1 to 20, Experimental Examples 9 to 20 having an average fiber diameter of 6 μm to 50 μm exhibited extremely excellent displaceability.

Among Experimental Examples 1 to 20, Experimental Examples 14 to 20 with a coverage of 90% or more were extremely excellent in displaceability, tensile strength, and tensile elastic modulus.

<Other embodiments (modifications)>
It should be noted that the present invention is not limited to the examples and embodiments described above, and can be embodied in various forms without departing from the scope 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 transformers, motors, wiring boards, heat dissipation boards, wires and the like.

Reference Signs List 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% by weight or less,
The carbon layer is made of graphene,
A conjugate fiber characterized in that, when the conjugate fiber is divided into sections of 30 μm in the longitudinal direction and observed, different numbers of layers of the graphene are observed in at least one section. 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. 3. The composite fiber according to claim 1, wherein the average fiber diameter is 6 μm to 50 μm. The composite fiber according to any one of claims 1 to 3, wherein 90% or more of the surface of said metal carbide-containing fiber is covered with said carbon layer. A fiber bundle comprising 15 or more of the conjugate fibers according to any one of claims 1 to 4.

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