JP7654532B2 - Carbon fiber composite material and its manufacturing method - Google Patents

Description

The present invention relates to a carbon fiber composite material and a method for producing the same.

In recent years, composite materials that use carbon nanotubes to improve mechanical strength have been attracting attention. However, because carbon nanotubes have strong cohesive properties, they tend to form clumps, making it very difficult to use them as fibrous reinforcing materials in composite materials.

In response to this, a carbon fiber composite material has been proposed in which the elastomer molecules bond with the radicals at the ends of the carbon nanotubes during the process of kneading the carbon nanotubes into the elastomer, thereby weakening the cohesive force of the carbon nanotubes and compounding the carbon nanotubes in a defibrillated state (for example, Patent Document 1).

Sealing members using perfluoroelastomer (FFKM) as an elastomer for carbon fiber composite materials have also been proposed, and sealing members with excellent chemical resistance as well as high heat resistance that can be used in downhole equipment for exploring underground resources such as oil and natural gas have been proposed (for example, Patent Document 2).

Furthermore, a carbon fiber composite material with excellent blister resistance has been proposed by improving a carbon fiber composite material using a perfluoroelastomer (FFKM) (Patent Document 3).

JP 2005-97525 A Patent No. 5816474 Patent No. 6284394

In the semiconductor and chemical product fields, processing temperatures are becoming higher, and rubber products such as sealing materials for peripheral devices used in these fields tend to require relatively high heat resistance. However, while conventional carbon fiber composite materials using perfluoroelastomers have excellent mechanical properties at high temperatures, their compression set properties in high-temperature environments do not meet the performance requirements for rubber products in these fields.

The present invention aims to provide a carbon fiber composite material that has excellent mechanical properties at high temperatures and compression set properties in a high-temperature environment, and a method for producing the same.

The present invention has been made to solve at least some of the problems described above, and can be realized in the following aspects or application examples.

[1] One embodiment of the carbon fiber composite material according to the present invention is
A carbon fiber composite material containing carbon nanotubes with an average diameter of 0.7 nm to 30 nm and carbon black with an average particle diameter of 100 nm to 300 nm in a crosslinked perfluoroelastomer,
the amount of the carbon nanotubes is 0.1 parts by mass or more and 3.5 parts by mass or less based on 100 parts by mass of the perfluoroelastomer,
the amount of carbon black is 15 parts by mass or more and 50 parts by mass or less based on 100 parts by mass of the perfluoroelastomer,
the carbon fiber composite material has a plurality of continuous structures in which the distance between adjacent carbon nanotubes or the distance between the carbon nanotubes and the carbon black is 100 nm or less in a cross section thereof,
the number of the continuous structures per unit area in the cross section is 0.80 pieces/μm ² to 3.50 pieces/μm ² ;
The continuous structure has a maximum length in the cross section of 10 nm or more and 1000 nm or less.

[2] In one embodiment of the carbon fiber composite material,
The tensile strength measured in accordance with ASTM D1414, except in a 260°C environment, is 2.2 MPa or more, and the elongation at break is 60% or more.
The compression set after holding at 25% compression at 260° C. for 168 hours as measured in accordance with ASTM D395 may be less than 50%.

[3] In one embodiment of the carbon fiber composite material,
The international rubber hardness (IRHD) measured in accordance with JIS K6253 may be 68 or more and 82 or less.

[4] One embodiment of the method for producing a carbon fiber composite material according to the present invention comprises:
a first mixing step of kneading 100 parts by mass of a perfluoroelastomer before crosslinking with 0.1 parts by mass to 3.5 parts by mass of carbon nanotubes having an average diameter of 0.7 nm to 30 nm to obtain a first mixture;
a first thin passing step of feeding the first mixture into an open roll having a roll gap set to more than 0 mm and 0.5 mm or less and a roll temperature set to 0° C. to 50° C., and thin passing the first mixture to obtain a second mixture;
a second mixing step of kneading the second mixture with 15 parts by mass or more and 50 parts by mass or less of carbon black having an average particle size of 100 nm or more and 300 nm or less to obtain a third mixture;
a second thin-threading step of feeding the third mixture into an open roll having a roll gap set to more than 0 mm and not more than 0.5 mm and a roll temperature set to 0° C. to 50° C., and thin-threading the third mixture to obtain a carbon fiber composite material;
Including,
the carbon fiber composite material has a plurality of continuous structures in which the distance between adjacent carbon nanotubes or the distance between the carbon nanotubes and the carbon black is 100 nm or less in a cross section thereof,
the number of the continuous structures per unit area in the cross section is 0.80 pieces/μm ² to 3.50 pieces/μm ² ;
The continuous structure has a maximum length in the cross section of 10 nm or more and 1000 nm or less.

FIG. 2 is a schematic diagram illustrating a continuous structure in a cross section of a carbon fiber composite material. 1 is a SEM image of a tensile fracture surface of a carbon fiber composite material. 1 is a SEM image of a tensile fracture surface of a carbon fiber composite material to illustrate the continuous structure. FIG. 4 is a schematic diagram illustrating the continuous structure in FIG. 3 . FIG. 1 is a diagram illustrating a method for producing a carbon fiber composite material. FIG. 1 is a diagram illustrating a method for producing a carbon fiber composite material. FIG. 1 is a diagram illustrating a method for producing a carbon fiber composite material. FIG. 1 is a diagram illustrating a method for producing a carbon fiber composite material. FIG. 1 is a diagram illustrating a method for producing a carbon fiber composite material.

Below, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention described in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

1. Carbon Fiber Composite Material A carbon fiber composite material according to one embodiment of the present invention is a carbon fiber composite material comprising carbon nanotubes having an average diameter of 0.7 nm to 30 nm and carbon black having an average particle size of 100 nm to 300 nm in a crosslinked perfluoroelastomer, wherein the blending amount of the carbon nanotubes is 0.1 parts by mass to 3.5 parts by mass relative to 100 parts by mass of the perfluoroelastomer, and the blending amount of the carbon black is 15 parts by mass to 50 parts by mass relative to 100 parts by mass of the perfluoroelastomer, the cross section of the carbon fiber composite material has a plurality of continuous structures in which the distance between adjacent carbon nanotubes or the distance between the carbon nanotubes and the carbon black is 100 nm or less, the number of the continuous structures per unit area in the cross section is 0.80 pieces/μm ² to 3.50 pieces/μm ² , and the maximum length of the continuous structures in the cross section is 10 nm to 1000 nm, respectively.

The carbon fiber composite material may have an international rubber hardness (IRHD) measured in accordance with JIS K6253 of 68 or more and 82 or less, and may further be 70 or more and 80 or less. If the international rubber hardness is less than 68, the tensile strength at high temperatures is low, and if it exceeds 82, the compression set properties are reduced.

Carbon fiber composite materials have excellent heat resistance. Here, heat resistance can be evaluated as mechanical properties at high temperatures, and specifically, can be evaluated by tensile strength and elongation at break in a tensile test at high temperatures, for example, 260 ° C. The carbon fiber composite material can have a tensile strength of 2.2 MPa or more and an elongation at break of 60% or more measured in accordance with ASTM D1414 except in a 260 ° C. environment, and can further have a tensile strength of 2.5 MPa or more and 5.0 MPa or less and an elongation at break of 65% or more and 120% or less. If the tensile strength of the carbon fiber composite material is less than 2.2 MPa and the elongation at break is less than 60%, the durability of the rubber product tends to decrease when a rubber product such as a sealing material is manufactured from the carbon fiber composite material. In addition, the carbon fiber composite material can have a compression set of less than 50% after holding at 260 ° C., 168 hours, and 25% compression, measured in accordance with ASTM D395, and can further have a compression set of 48% or less. If the compression set of the carbon fiber composite material is 50% or more, the sealing material made from the carbon fiber composite material will collapse at high temperatures, making it difficult to maintain sealing properties. Carbon fiber composite materials with these properties are obtained by blending a relatively small amount of defibrated carbon nanotubes with a specified amount of carbon black using the manufacturing method described below.

In carbon fiber composite materials, carbon nanotubes are dispersed throughout in a defibrated state. Carbon fiber composite materials do not contain agglomerates of carbon nanotubes. If agglomerates exist, they can become the starting point of fracture, resulting in a decrease in mechanical strength.

1.1. Continuous structure The inventors of the present invention performed measurements of carbon fiber composite materials using a scanning electron microscope and found that:
It was found that carbon fiber composite materials with excellent compression set properties under high temperature conditions have a common structural feature.

The structural characteristics of carbon fiber composite material 50 will be described in detail with reference to Figures 1 to 4. Carbon fiber composite material 50 shown in Figures 1 to 4 is a sample of Example 3, which will be described later.

Figure 1 is a schematic diagram illustrating the structure in an image 90 of a cross section of a carbon fiber composite material 50, Figure 2 is an SEM image 90 of a tensile fracture surface of a carbon fiber composite material 50, Figure 3 is an image 90 showing a continuous structure 84 in the image 90 of Figure 2, and Figure 4 is a schematic diagram illustrating the continuous structure 84 in Figure 3. Note that the "cross section" may be a freeze fracture surface or a tensile fracture surface. Also, "SEM" is an abbreviation for Scanning Electron Microscope.

In FIG. 1, the carbon nanotubes 81 are shown as round black dots and the carbon black 82 is shown shaded to make it easier to understand the arrangement of the carbon nanotubes 81 and carbon black 82 in the cross section of the carbon fiber composite material 50. In addition, the continuous structure 84 is shown as one continuous structure by connecting adjacent carbon nanotubes 81 that are 100 nm or less apart, or adjacent carbon nanotubes 81 and carbon black 82 that are 100 nm or less apart, with straight dashed lines. Therefore, it can be seen that there are five continuous structures 84 within the range of FIG. 1. The remaining portion is perfluoroelastomer 30.

Figure 1 is an enlarged view of the area surrounded by the dashed line in Figure 4. Figure 4 is a view created to identify the continuous structures 84 based on the image 90 in Figure 2 and to count the number of them. A specific identification and measurement procedure will be described. First, the carbon nanotubes 81 and the carbon black 82 in the image 90 in Figure 2 are identified. In order to make it easier to measure the distance between the objects, as shown in Figure 3, the carbon nanotubes 81 appearing in the cross section of Figure 2 are marked with black dots and the carbon black 82 is filled in (white in Figure 3 but colored). This processing may be performed using image processing software or may be drawn using drawing software. Although the identification and measurement may be performed using Figure 3 as it is, in order to make it easier to understand, the image 90 before processing may be erased from Figure 3, and only the black dots and filled-in areas may be left to obtain Figure 4. Then, the distance L1 between the adjacent carbon nanotubes 81 on Figure 4 or the distance L1 between the carbon nanotubes 81 and the carbon black 82 on Figure 4 is measured. The portion where the distance L1 is 100 nm or less is indicated by drawing a straight dashed line to identify the continuous structures 84. Then, using FIG. 4, the number of continuous structures 84 can be counted to calculate the number per unit area, and the maximum length L2 of each continuous structure 84 can be measured. In these measurement processes, the carbon nanotubes 81 and carbon black 82 may be identified by binarizing the image 90 using image processing software, or the measurement of the distance L1 may be automated using a personal computer.

The carbon fiber composite material 50 shown in Figures 1 to 4 contains carbon nanotubes 81 with an average diameter of 0.7 nm to 30 nm and carbon black 82 with an average particle size of 100 nm to 300 nm in a crosslinked perfluoroelastomer 30. The carbon nanotubes 81 will be described later in Section "2.3. Carbon nanotubes," and the carbon black 82 will be described later in Section "2.2. Carbon black."

As shown in FIGS. 1 to 4, the cross section of the carbon fiber composite material 50 has a plurality of continuous structures 84 in which the distance L1 between adjacent carbon nanotubes 81 or the distance L1 between the carbon nanotube 81 and the carbon black 82 is 100 nm or less. The distance L1 is the distance between adjacent carbon nanotubes 81 or between the carbon nanotube 81 and the carbon black 82 at the position where they are closest to each other. In FIG. 1, the portion shown as connecting the carbon nanotube 81 and the carbon black 82 with a dashed straight line is the continuous structure 84. In the continuous structure 84, a certain carbon nanotube 81 is adjacent to another carbon nanotube 81 or carbon black 82 with a distance L1 of 100 nm or less, or the adjacent structures are continuous. When the distance L1 is 100 nm or less, it is considered that an interaction occurs between adjacent carbon nanotubes 81 or between adjacent carbon nanotubes 81 and the carbon black 82. Note that the interaction between the carbon blacks 82 is considered to be small, so even if the distance between the carbon blacks 82 is 100 nm or less, they are not treated as part of the continuous structure 84.

The average value of the distance L1 in the continuous structure 84 can be 10 nm or more and less than 100 nm, and further, the average value of the distance L1 can be 10 nm to 95 nm. If the average value of the distance L1 is less than 10 nm, the flexibility of the carbon fiber composite material 50 decreases. Furthermore, if the average value of the distance L1 is 100 nm or more, the interaction between the carbon nanotubes 81 or between the carbon nanotubes 81 and the carbon black 82 decreases, and the reinforcing effect decreases. The distance L1 is measured on the scanning electron microscope image 90.

The number of continuous structures 84 per unit area in the cross section of the carbon fiber composite material 50 is 0.80 pieces/μm ² to 3.50 pieces/μm ^2. Furthermore, the number of continuous structures 84 per unit area in the cross section of the carbon fiber composite material 50 can be 1.10 pieces/μm ² to 2.90 pieces/μm ^2. The number of continuous structures 84 is obtained by identifying the continuous structures 84 in the image 90 as shown in FIG. 4, counting the number of them, and converting it to the number per unit area (μm ² ). When the amount of carbon nanotubes 81 and carbon black 82 added is small, if the number of continuous structures 84 is less than 0.80 pieces/μm ² , the reinforcing property is significantly inferior, and if it exceeds 3.50 pieces/μm ² , the carbon nanotubes 81 may be partially aggregated, and physical properties such as tensile strength and elongation at break are reduced. Furthermore, when the amount of carbon nanotubes 81 and carbon black 82 added is large, if the number of continuous structures 84 is less than 0.80 pieces/ ^μm2 , it is considered that the continuous structures 84 are in a largely developed state, and therefore the compression set characteristics in a high temperature environment are deteriorated, and if the number exceeds 3.50 pieces/ ^μm2 , there is a possibility that the carbon nanotubes 81 are partially aggregated, resulting in deterioration of the physical properties.

The maximum length L2 of the continuous structure 84 in the cross section of the carbon fiber composite material 50 is 10 nm or more and 1000 nm or less. Furthermore, the maximum length L2 of the continuous structure 84 in the cross section of the carbon fiber composite material 50 can be 30 nm or more and 900 nm or less. The maximum length L2 of the continuous structure 84 is obtained by identifying the continuous structure 84 in the image 90 as shown in FIG. 4 and measuring the maximum length L2 of each of them. The maximum length L2 is a linear distance, and can also be said to be the maximum diameter when the continuous structure 84 is considered as one mass. If the maximum length L2 is less than 10 nm, most of the continuous structures 84 are composed of a pair of carbon nanotubes 81, so the physical properties are not improved. Also, if the maximum length L2 is 1000 nm or more, the continuous structure 84 develops too much, and the compression set characteristics in a high-temperature environment are reduced.

The continuous structure 84 has a higher elastic modulus than the phase of only the perfluoroelastomer 30, and is therefore presumed to behave like a single structure within the carbon fiber composite material 50. As a result, the continuous structure 84 bears the stress on the carbon fiber composite material 50, resulting in excellent tensile strength and elongation at high temperatures. It is believed that in the continuous structure 84, interactions occur due to the stress field between adjacent carbon nanotubes 81 or between the carbon nanotubes 81 and the carbon black 82. In addition, multiple continuous structures 84 are independently scattered within the carbon fiber composite material 50, and the perfluoroelastomer 30 is continuous, maintaining flexibility during deformation.

2. Raw Materials Next, the raw materials constituting the carbon fiber composite material will be described.

The perfluoroelastomer (FFKM) used in the carbon fiber composite material may have a Mooney viscosity ML ₍₁₊₁₀₎ at 121° C. of 30 to 80. When the Mooney viscosity of the perfluoroelastomer is within this range, it is relatively easy to process the perfluoroelastomer by kneading it with the carbon nanotubes.

The perfluoroelastomer used in the carbon fiber composite material can have a fluorine content of 72% or more. Perfluoroelastomers with a fluorine content in this range are preferred because they have excellent chemical resistance.

Examples of such perfluoroelastomers include tetrafluoroethylene (TFE)/perfluoroalkyl vinyl ether (PAVE) copolymers, and examples of the perfluoroalkyl vinyl ethers (PAVEs) that can be used here include perfluoromethoxy vinyl ether (PMOVE), perfluoromethyl vinyl ether (PMVE), perfluoroethyl vinyl ether (PEVE), perfluoropropyl vinyl ether (PPVE), and other similar compounds.

The perfluoroelastomer can be a peroxide crosslinked type, a triazine crosslinked type, etc.

The carbon black used in the carbon fiber composite material has an average particle size of 100 nm to 300 nm. The average particle size of carbon black can be determined by observing the particle diameters of 2,000 or more basic constituent particles using a scanning electron microscope and taking the arithmetic average.

As such carbon black, for example, reinforcing carbon black such as FT or MT can be used. By using carbon black having a relatively large particle size, it is possible to maintain the flexibility of the carbon fiber composite material while improving the compression set characteristics. It is preferable that the carbon black does not have a high structure, and for example, the DBP absorption (method A) can be 20 cm ³ /100g to 65 cm ³ /100g. This is because the development of the structure leads to the development of a continuous structure. For the carbon fiber composite material, MT grade carbon black can be used.

The amount of carbon black in the carbon fiber composite material is 15 parts by mass or more and 50 parts by mass or less per 100 parts by mass of perfluoroelastomer. The amount of carbon black in the carbon fiber composite material can be 20 parts by mass or more and 45 parts by mass or less per 100 parts by mass of perfluoroelastomer. If the amount of carbon black is less than 15 parts by mass, the rubber hardness and physical properties are low, and the mechanical strength is low. If the amount of carbon black is more than 50 parts by mass, the rubber hardness is high, and the tensile strength and elongation at break at high temperatures are low.

2.3. Carbon nanotubes The carbon nanotubes used in one embodiment of the present invention may have an average diameter (fiber diameter) of 0.7 nm to 30 nm, and may further be 2 nm to 20 nm. Such carbon nanotubes have a relatively small average diameter, so that they have a large specific surface area, and the surface reactivity with the perfluoroelastomer matrix is improved, which tends to improve poor dispersion of the carbon nanotubes in the perfluoroelastomer. Carbon nanotubes with a diameter of 0.7 nm or more are commercially available, and 3
If the average particle size is 0 nm or less, it has the effect of being excellent in tear fatigue property and wear resistance. The carbon nanotubes can be subjected to a known activation treatment in order to improve the reactivity of the surface with the perfluoroelastomer. The average diameter of the carbon nanotubes can be measured by observation with an electron microscope. In the detailed description of the present invention, the average diameter and average length of the carbon nanotubes can be obtained by measuring the diameter and length at 200 or more points from, for example, 5,000 times magnification imaging with an electron microscope (the magnification can be appropriately changed depending on the size of the carbon nanotubes) and calculating the arithmetic average value.

Carbon nanotubes are at least one of so-called multi-walled carbon nanotubes (MWCNT) and single-walled carbon nanotubes (SWCNT), which have a shape formed by rolling up one surface (graphene sheet) of carbon hexagonal mesh graphite into a cylindrical shape, and carbon materials partially having a carbon nanotube structure can also be used. Carbon nanotubes may include multi-walled carbon nanotubes and single-walled carbon nanotubes. In addition to the name carbon nanotubes, they are also called graphite fibril nanotubes and vapor-grown carbon fibers.

Carbon nanotubes can be obtained by vapor phase growth, also known as catalytic chemical vapor deposition (CCVD), which is a method of producing unprocessed carbon nanotubes by pyrolyzing a gas such as a hydrocarbon in the presence of a metal catalyst. To explain the vapor phase growth method in more detail, for example, the floating reaction method uses organic compounds such as benzene and toluene as raw materials and organic transition metal compounds such as ferrocene and nickelcene as metal catalysts, and introduces them together with a carrier gas into a reactor set at a high reaction temperature, for example, 400°C to 1000°C, to generate carbon nanotubes in a floating state or on the reactor wall, or the substrate reaction method, in which metal-containing particles previously supported on ceramics such as alumina or magnesium oxide are contacted with a carbon-containing compound at high temperature to generate carbon nanotubes on a substrate. For example, carbon nanotubes with an average diameter of 9 nm to 20 nm can be obtained by the catalyst support reaction method, and carbon nanotubes thicker than this can be obtained by the floating reaction method. The diameter of the carbon nanotubes can be adjusted, for example, by the size of the metal-containing particles and the reaction time.

The amount of carbon nanotubes is 0.1 to 3.5 parts by mass per 100 parts by mass of perfluoroelastomer. The amount of carbon nanotubes can be 0.5 to 3.0 parts by mass per 100 parts by mass of perfluoroelastomer. The amount of carbon nanotubes can be adjusted together with the amount of carbon black. If the amount of carbon nanotubes is less than 0.1 parts by mass, the tensile strength and elongation at break at high temperatures are low, and if it exceeds 3.5 parts by mass, the rubber hardness increases and the compression set properties in a high-temperature environment are reduced.

2.4. Other compounding agents Bituminous coal pulverized material may be further compounded with the perfluoroelastomer. Bituminous coal pulverized material is obtained by pulverizing general coal, including bituminous coal (classified as B1, B2, C in JIS M1002), a type of coal known as high-grade coal, to an average particle size of 1 μm to 100 μm. Furthermore, the average particle size of the bituminous coal pulverized material may be 1 μm to 10 μm, and in particular, the average particle size of the bituminous coal pulverized material may be 3 μm to 8 μm. The bituminous coal pulverized material may be 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of perfluoroelastomer. By including 1 part by mass or more of the bituminous coal pulverized material, an effect of excellent compression set is obtained, and if it includes more than 10 parts by mass, it tends to become brittle. Bituminous coal pulverized material is sometimes considered to be a type of carbon black, but here it is described as not being included in carbon black.

The average particle size of crushed bituminous coal is measured and published by the manufacturer if it is commercially available, but it can also be obtained by observing the crushed bituminous coal using a scanning electron microscope and measuring the particle diameters of 2,000 or more particles, each considered as a single particle (basic particle), to determine the arithmetic average value.

Furthermore, the specific gravity of the pulverized bituminous coal can be 1.6 or less, and even 1.35 or less.

In addition to the above components, the carbon fiber composite material can be used by appropriately adding compounding agents commonly used in the rubber industry, such as internal mold release agents, processing aids, metal oxides or hydroxides such as zinc oxide, acid acceptors which are hydrotalcite compounds, and plasticizers.

3. Manufacturing method of carbon fiber composite material A manufacturing method of a carbon fiber composite material according to one embodiment of the present invention includes a first mixing step of kneading 0.1 parts by mass to 3.5 parts by mass of carbon nanotubes having an average diameter of 0.7 nm to 30 nm with 100 parts by mass of perfluoroelastomer before crosslinking to obtain a first mixture, a first thin passing step of feeding the first mixture into an open roll having a roll gap set to more than 0 mm and 0.5 mm or less and a roll temperature set to 0° C. to 50° C. and thin passing the first mixture to obtain a second mixture, a second mixing step of kneading 15 parts by mass to 50 parts by mass of carbon black having an average particle diameter of 100 nm to 300 nm with the second mixture to obtain a third mixture, and a second mixing step of kneading the third mixture into the third mixture. and a second thin passing step of feeding the mixture into open rolls in which the roll gap is set to more than 0 mm and not more than 0.5 mm and the roll temperature is set to 0°C to 50°C, and thin passing is performed to obtain a carbon fiber composite material, wherein the carbon fiber composite material has a plurality of continuous structures in a cross section in which the distance between adjacent carbon nanotubes or the distance between the carbon nanotubes and the carbon black is 100 nm or less, the number of the continuous structures per unit area in the cross section is 0.80 pcs/μm2 to 3.50 pcs/μm2, and the maximum length of the continuous structures in the cross section is 10 nm or more and 1000 nm or less.

The method for producing a carbon fiber composite material according to this embodiment will be described in detail with reference to Figs. 5 to 9. Figs. 5 to 9 are schematic diagrams showing a method for producing a carbon fiber composite material by an open roll method according to one embodiment of the present invention. Note that the carbon fiber composite material, raw materials, and compounding amounts are the same as those described in 1 and 2 above, so duplicated explanations will be omitted.

As shown in Figures 5 to 9, the first roll 110 and the second roll 120 in the two-roll open roll 100 are arranged with a predetermined roll spacing d, for example, 0.5 mm to 1.5 mm, and rotate forward or backward at rotation speeds V1 and V2 in the directions shown by the arrows in Figures 5 to 9.

First, as shown in FIG. 5, the pre-crosslinked perfluoroelastomer 30 wound around the first roll 110 is masticated to appropriately cut the perfluoroelastomer molecular chains and generate free radicals. The perfluoroelastomer free radicals generated by mastication are in a state that makes them easy to bond with carbon nanotubes.

3.1. First Mixing Step Next, the first mixing step is carried out as shown in FIG. 6. In the first mixing step, carbon nanotubes 81 (0.1 parts by mass to 3.5 parts by mass) having an average diameter of 0.7 nm to 30 nm are added to a bank 34 of perfluoroelastomer 30 (100 parts by mass) before crosslinking wound around a first roll 110, and kneaded to obtain a first mixture 36 (FIG. 7). The temperature of the perfluoroelastomer 30 in this kneading can be, for example, 0° C. to 100° C., and can also be 0° C. to 50° C. The first mixing step is not limited to the open roll method, and can also be, for example, a closed kneading method or a multi-screw extrusion kneading method.

7, the first thin passing step is performed. In the first thin passing step, the first mixture 36 is fed into an open roll 100 having a roll gap d set to more than 0 mm and not more than 0.5 mm and a roll temperature set to 0° C. to 50° C., and thin passing is performed to obtain a second mixture 37.

The number of thin passes can be, for example, from 1 to 10 times.

If the surface speed of the first roll 110 is V1 and the surface speed of the second roll 120 is V2, the surface speed ratio (V1/V2) between the two during thin passing can be 1.05 to 3.00, and preferably 1.05 to 1.2. By using such a surface speed ratio, the desired shear force can be obtained.

The second mixture 37 extruded from between the narrow rolls in this way is significantly deformed as shown in FIG. 7 due to the restoring force caused by the elasticity of the perfluoroelastomer, and at that time, the carbon nanotubes move significantly together with the perfluoroelastomer.

In the first thin-threading process, in order to obtain the highest possible shear force, the roll temperature is set to a relatively low temperature, for example, between 0°C and 50°C, more preferably between 5°C and 30°C, and the actual measured temperatures of the first mixture 36 and the second mixture 37 can also be adjusted to between 0°C and 50°C.

The shear force thus obtained acts on the perfluoroelastomer, and the aggregated carbon nanotubes are separated from each other and defibrated as if they are pulled out one by one by the perfluoroelastomer molecules, and are dispersed in the perfluoroelastomer. In particular, the perfluoroelastomer has elasticity, viscosity, and chemical interaction with the carbon nanotubes, so that the carbon nanotubes can be easily dispersed. Thus, a second mixture 37 can be obtained that has excellent dispersibility and dispersion stability of the carbon nanotubes (resistance of the carbon nanotubes to re-aggregation).

More specifically, when perfluoroelastomer and carbon nanotubes are mixed on an open roll, the viscous perfluoroelastomer penetrates the carbon nanotubes, and specific parts of the perfluoroelastomer bond to the highly active parts of the carbon nanotubes through chemical interactions. If the surface activity of the carbon nanotubes is moderately high, they can bond particularly easily with perfluoroelastomer molecules. Next, when a strong shear force is applied to the perfluoroelastomer, the carbon nanotubes also move along with the movement of the perfluoroelastomer molecules, and further, the elasticity of the perfluoroelastomer causes the aggregated carbon nanotubes to separate and be dispersed in the perfluoroelastomer.

According to this embodiment, when the second mixture 37 is extruded between the narrow rolls, the second mixture 37 is deformed to a thickness greater than the roll gap d due to the restoring force caused by the elasticity of the perfluoroelastomer. It can be assumed that this deformation causes the second mixture 37, which is subjected to a strong shear force, to flow in a more complex manner, dispersing the carbon nanotubes in the perfluoroelastomer. Once dispersed, the carbon nanotubes are prevented from re-aggregating due to chemical interactions with the perfluoroelastomer, and can have good dispersion stability.

The first thin-passing process is not limited to the open roll method, and a closed kneading method or a multi-screw extrusion kneading method can also be used as long as the carbon nanotubes can be defibrated in the perfluoroelastomer by shear force. In short, this process only requires that a shear force capable of separating and defibrating the aggregated carbon nanotubes can be applied to the perfluoroelastomer. In particular, the open roll method is preferred because it allows not only control of the roll temperature, but also measurement and control of the actual temperature of the mixture.

3.3. Second mixing step Next, the second mixing step is performed as shown in Fig. 8. In the second mixing step, carbon black 82 (15 parts by mass or more and 50 parts by mass or less) having an average particle size of 100 nm to 300 nm is kneaded into the bank 34 of the second mixture 37 wound around the first roll 110 to obtain a third mixture 38 (Fig. 9). Here, the blending amount of carbon black 82 is the blending amount relative to 100 parts by mass of perfluoroelastomer. The processing method and processing conditions of the second mixing step are the same as those of the first mixing step.

9, the second thin passing step is carried out. In the second thin passing step, the third mixture 38 is fed into open rolls 100 in which the roll gap d is set to more than 0 mm and not more than 0.5 mm and the roll temperature is set to 0° C. to 50° C., and thin passing is carried out to obtain the carbon fiber composite material 50. The processing conditions, such as the number of thin passes and the surface speed, are the same as those in the first thin passing step.

The carbon fiber composite material 50 obtained by thin-threading may be rolled with a roll to separate it into a sheet of a predetermined thickness. A crosslinking agent can be mixed into the perfluoroelastomer before the first mixing step, during the first mixing step, before the second mixing step, during the second mixing step, or after the second mixing step.

3.5. Crosslinking process In the crosslinking process, the perfluoroelastomer in the carbon fiber composite material 50 (FIG. 9) obtained in the second thin-passing process is crosslinked to obtain a carbon fiber composite material. In the crosslinking process, for example, the carbon fiber composite material containing a crosslinking agent is placed in a mold, and the mold is heated to crosslink the perfluoroelastomer and press the carbon fiber composite material to form a rubber product (sealing material, etc.) of a desired shape. As the crosslinking agent, a known peroxide or crosslinking catalyst can be used. In the carbon fiber composite material obtained in the crosslinking process, the above-mentioned continuous structure can be observed in a scanning electron microscope image of the cross section.

As described above, the embodiments of the present invention have been described in detail, but it will be readily apparent to those skilled in the art that many modifications are possible that do not substantially depart from the novel features and effects of the present invention. Therefore, all such modifications are intended to be included within the scope of the present invention.

(1) Preparation of Samples The samples of Examples 1 to 7 and Comparative Examples 1 to 8 were prepared by the following steps.

Kneading process: 100 parts by mass (phr) of perfluoroelastomer shown in Tables 1 and 2 (shown as "FFKM1" and "FFKM2" in Tables 1 to 3) was placed into an open roll with a roll diameter of 6 inches (roll temperature 10°C to 20°C, roll spacing 0.5 mm to 1.0 mm) and wrapped around the roll for mastication (see Figure 5). The roll temperature in each of the following processes was 10°C to 20°C.

First mixing step: Next, the carbon nanotubes (referred to as "MWCNT1", "MWCNT2" and "SWCNT" in Tables 1 to 3) in the parts by weight (phr) shown in Tables 1 to 3 were added to the perfluoroelastomer (see FIG. 6) and kneaded to obtain a first mixture. At this time, the roll gap d was set to 1.5 mm.

First thin-passing process: The first mixture was removed from the rolls, the roll gap d was narrowed from 1.5 mm to 0.3 mm, and the first mixture was fed into an open roll for thin-passing to obtain a second mixture (see FIG. 7). At this time, the surface speed ratio of the two rolls was set to 1.1. Thin-passing was repeated five times. In Comparative Examples 1 and 7, carbon black was fed instead of carbon nanotubes in the first mixing process, and the second mixing process and the second thin-passing process were omitted.

Second mixing step: Next, the roll gap d was set to 1.5 mm, and the parts by weight (phr) of carbon black (referred to as "HS-CB" and "MT-CB" in Tables 1 to 3) and pulverized bituminous coal (referred to as "Austin Black" in Tables 1 to 3) shown in Tables 1 to 3 were added to the second mixture (see Figure 8) and kneaded to obtain a third mixture.

Second thin-threading process: The third mixture was removed from the rolls, the roll gap d was narrowed from 1.5 mm to 0.3 mm, and the third mixture was fed into an open roll for thin-threading to obtain a carbon fiber composite material (see Figure 9). At this time, the surface speed ratio of the two rolls was set to 1.1. Thin-threading was repeated five times.

Furthermore, peroxide or a crosslinking catalyst was added as a crosslinking initiator to separate out a 1 mm thick pre-crosslinked carbon fiber composite material.

The separated sheet was placed in an O-ring mold and molded by press crosslinking and secondary crosslinking to obtain an O-ring of AS568C-214 (hereinafter referred to as "sample"). Here, the samples of Examples 1 to 6 were primary crosslinked at 170°C for 24 minutes and secondary crosslinked at 300°C (9 hours of heating + 4 hours of holding), while the sample of Example 7 was primary crosslinked at 165°C for 10 minutes and secondary crosslinked at 290°C (8 hours of heating + 16 hours of holding). The samples of Comparative Examples 1 to 6 were primary crosslinked at 170°C for 24 minutes and secondary crosslinked at 300°C (9 hours of heating + 4 hours of holding), while the samples of Comparative Examples 7 and 8 were primary crosslinked at 165°C for 10 minutes and secondary crosslinked at 290°C (8 hours of heating + 16 hours of holding).

The details of the perfluoroelastomer and various compounding ingredients in the compounding column of the table are as follows:

FFKM1: Mooney viscosity ML ₁₊₁₀ 121°C (center value) 80 crosslinking catalyst system;
FFKM2: Mooney viscosity ML ₁₊₁₀ 121°C (center value) 75 peroxide crosslinking system,
HS-CB: High structure SRF grade carbon black, average particle size 70 nm, DBP absorption (method A) 152 cm ³ /100 g,
MT-CB: MT grade carbon black, average particle size 200 nm;
Austin Black: Bituminous coal pulverized material with an average diameter of 5 μm;
MWCNT1: multi-wall carbon nanotube, average diameter 15.3 nm;
MWCNT2: multi-wall carbon nanotube, average diameter 18 nm;
SWCNT: single-wall carbon nanotube, average diameter 5 nm;
It was.

The carbon black was mixed in such a way that the hardness of each sample was adjusted to be between 68 and 82.

The test samples of Examples 1 to 7 and Comparative Examples 1 to 8 were subjected to the various tests described below, and the test results are shown in Tables 1 to 3.

(2) Basic property test For each sample of the examples and comparative examples, the international rubber hardness (Hs (IRHD)) was measured according to JIS
Measurement was based on K 6253.

For each sample in the examples and comparative examples, a tensile test was performed in a high temperature atmosphere (260±2°C) based on ASTM D1414 at a tensile speed of 500 mm/min using a Shimadzu Autograph AG-X tensile tester, and the tensile strength (TS/260°C (MPa)), elongation at break (Eb/260°C (%)), and 25% stress (M25/260°C (MPa)) were measured. The measurement results are shown in each column of the table.

(3) Compression set test For each sample of the examples and comparative examples, the compression set after holding at 260°C and a compression ratio of 25% for 70 hours, 168 hours, and 336 hours (CS 260°C 70 hr, 168 hr, and 336 hr (%)) was measured in accordance with ASTM D395. The measurement results are shown in each column of the table.

(4) SEM Measurement Images of the fracture surfaces of each sample after the tensile test in the Examples and Comparative Examples were taken with a SEM. The distance between adjacent carbon nanotubes or between the carbon nanotube and the carbon black in each image was measured, and adjacent carbon nanotubes and carbon black with a distance of 100 nm or less were identified as continuous structures. The number of continuous structures in each image was counted, and the number of continuous structures per unit area was calculated. The calculation results are shown in Tables 1 to 3. In addition, the maximum length of all continuous structures in each image was measured, and the maximum and minimum values are shown in Tables 1 to 3.

According to Tables 1 to 3, the samples of Examples 1 to 7 had an international rubber hardness of 74 or more and 81 or less.

According to Tables 1 to 3, the samples of Examples 1 to 7 had a tensile strength (TS) of 2.5 MPa or more at 260°C, and an elongation at break (Eb) of 65% or more at 260°C. The samples of Comparative Examples 1, 2, and 7 had a tensile strength (TS) of 2.0 MPa or less at 260°C, and the samples of Comparative Examples 1 to 8 had an elongation at break (Eb) of 58% or less at 260°C.

According to Tables 1 to 3, the samples of Examples 1 to 7 had a compression set of 48% or less when held for 168 hours at 260°C and a compression ratio of 25%. The samples of Comparative Examples 3 to 6 and 8 had a compression set of 53% or more when held for 168 hours at 260°C and a compression ratio of 25%.

According to Tables 1 to 3, the number of continuous structures per unit area of the samples of Examples 1 to 7 was 1.22 to ^2.80 /μm ^2. The number of continuous structures per unit area of the samples of Comparative Examples 4, 6, and 8 was 0.76/μm ² or less.

According to Tables 1 to 3, the maximum length of the continuous structure of the samples of Examples 1 to 7 was 32 μm to 865 μm. The maximum length of the continuous structure of the samples of Comparative Examples 2, 4 to 6, and 8 was 1,341 μm or more, and the samples of Comparative Examples 1 and 7 did not contain carbon nanotubes and therefore did not have a continuous structure.

30...perfluoroelastomer, 34...bank, 36...first mixture, 37...second mixture, 38...third mixture, 50...carbon fiber composite material, 81...carbon nanotubes, 82...carbon black, 84...continuous structure, 90...image, 100...open roll, 110...first roll, 120...second roll, d...roll spacing, L1...distance, L2...maximum length, V1, V2...rotation speed

Claims (4)

A carbon fiber composite material containing carbon nanotubes with an average diameter of 0.7 nm to 30 nm and carbon black with an average particle diameter of 100 nm to 300 nm in a crosslinked perfluoroelastomer,
the amount of the carbon nanotubes is 0.1 parts by mass or more and 3.5 parts by mass or less based on 100 parts by mass of the perfluoroelastomer,
the amount of carbon black is 15 parts by mass or more and 50 parts by mass or less based on 100 parts by mass of the perfluoroelastomer,
the carbon fiber composite material has a plurality of continuous structures in which the distance between adjacent carbon nanotubes or the distance between the carbon nanotubes and the carbon black is 100 nm or less in a cross section thereof,
the number of the continuous structures per unit area in the cross section is 0.80 pieces/μm ² to 3.50 pieces/μm ² ;
The carbon fiber composite material, wherein the maximum length of the continuous structure in the cross section is 10 nm or more and 1,000 nm or less. In claim 1,
The tensile strength measured in accordance with ASTM D1414, except in a 260°C environment, is 2.2 MPa or more, and the elongation at break is 60% or more.
A carbon fiber composite material having a compression set of less than 50% after being held at 25% compression at 260° C. for 168 hours as measured in accordance with ASTM D395. In claim 1 or 2,
A carbon fiber composite material having an international rubber hardness (IRHD) of 68 or more and 82 or less, as measured in accordance with JIS K6253. a first mixing step of kneading 100 parts by mass of a perfluoroelastomer before crosslinking with 0.1 parts by mass to 3.5 parts by mass of carbon nanotubes having an average diameter of 0.7 nm to 30 nm to obtain a first mixture;
a first thin passing step of feeding the first mixture into an open roll having a roll gap set to more than 0 mm and 0.5 mm or less and a roll temperature set to 0° C. to 50° C., and thin passing the first mixture to obtain a second mixture;
a second mixing step of kneading the second mixture with 15 parts by mass or more and 50 parts by mass or less of carbon black having an average particle size of 100 nm or more and 300 nm or less to obtain a third mixture;
a second thin-threading step of feeding the third mixture into an open roll having a roll gap set to more than 0 mm and not more than 0.5 mm and a roll temperature set to 0° C. to 50° C., and thin-threading the third mixture to obtain a carbon fiber composite material;
Including,
the carbon fiber composite material has a plurality of continuous structures in which the distance between adjacent carbon nanotubes or the distance between the carbon nanotubes and the carbon black is 100 nm or less in a cross section thereof,
the number of the continuous structures per unit area in the cross section is 0.80 pieces/μm ² to 3.50 pieces/μm ² ;
wherein the maximum length of the continuous structure in the cross section is 10 nm or more and 1,000 nm or less.

Images