JP7699989B2 - Carbon fiber composite material and method for producing the same - Google Patents

Description

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

Silicone rubber has a very wide temperature range compared to other rubbers because its properties change little over a wide temperature range from low to high temperatures. However, it has the problem of low mechanical strength. Therefore, by blending carbon nanotubes instead of silica particles into silicone rubber as a reinforcing material, and further increasing the adhesive strength between the carbon nanotubes and the silicone rubber molecules using a silane coupling agent, etc., a carbon fiber composite material with improved tensile strength and tensile fatigue durability that cannot be achieved by blending ordinary silica particles was successfully developed (Patent Document 1).

In addition, a carbon fiber composite material has been proposed that has high rubber flexibility and loss tangent (tan δ) by blending a small amount of carbon nanotubes into silicone rubber (Patent Document 2).

JP 2017-82145 A JP 2019-65269 A

However, the carbon fiber composite material of Patent Document 1 has limited applications due to its low flexibility and high hardness, while the carbon fiber composite material of Patent Document 2 has excellent flexibility but is prone to tearing when its hardness is low.

The present invention aims to provide a carbon fiber composite material that has low hardness but excellent tear strength, and a method for producing the carbon fiber composite material.

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 in a crosslinked silicone rubber,
a cellular structure formed by the carbon nanotubes and their interphase surrounding a first silicone rubber region, and a continuous structure in which a plurality of the cellular structures are continuously formed in an annular shape so as to surround a second silicone rubber region,
In a cross section of the carbon fiber composite material, the continuous structure is a region in which the number of the carbon nanotubes per 1 ^μm2 exceeds two,
In the cross section, the second silicone rubber region has an area of 0.1 ^μm2 or more and 10 μm2 ^or less , and the number of the carbon nanotubes per 1 ^μm2 is two or less,
the total area occupied by the second silicone rubber region is 45% or more and 80% or less;
The second silicone rubber region has a maximum width of 0.1 μm or more and 6 μm or less .

[ 2 ] In one embodiment of the carbon fiber composite material,
The width of the continuous structure may be between 0.01 μm and 5 μm.

[ 3 ] In one embodiment of the carbon fiber composite material,
The carbon nanotubes may have an average diameter of 2 nm to 30 nm.

[ 4 ] In one embodiment of the carbon fiber composite material,
The carbon nanotubes may be included in an amount of 0.5 parts by mass to 7.0 parts by mass based on 100 parts by mass of the silicone rubber.

[ 5 ] In one embodiment of the carbon fiber composite material,
The hardness based on JIS K6253 may be 65 degrees to 78 degrees.

[ 6 ] In one embodiment of the carbon fiber composite material,
The stress at 50% elongation in a tensile test based on JIS K6251 at room temperature may be 2.0 MPa to 5.0 MPa.

[ 7 ] In one embodiment of the carbon fiber composite material,
The tear strength (Tr) at room temperature in a tear test based on JIS K6252 can be 45 N/mm to 65 N/mm.

[ 8 ] One embodiment of the method for producing a carbon fiber composite material according to the present invention is
a first mixing step of mixing the silicone rubber with the carbon nanotubes to obtain a mixture;
a first kneading step of feeding the mixture into open rolls 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 kneading the mixture thinly to obtain a first composite rubber;
a second mixing step of further mixing a silicone rubber with the first composite rubber to obtain a second composite rubber;
a second kneading step in which the second composite rubber is fed 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-kneaded to obtain a carbon fiber composite material;
Including,
The carbon nanotubes have an average diameter of 2 nm to 30 nm;
The first mixing step includes mixing 3 parts by mass to 15 parts by mass of the carbon nanotubes with 100 parts by mass of silicone rubber;
The second mixing step is characterized in that the silicone rubber is mixed so that the second composite rubber contains 0.5 to 7 parts by mass of the carbon nanotubes per 100 parts by mass of the silicone rubber .

FIG. 2 is a schematic diagram illustrating a cross-sectional structure of a carbon fiber composite material. FIG. 2 is an enlarged view of the dashed-line frame in FIG. 1 . 1 is a flowchart of 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. FIG. 1 is a diagram illustrating a method for producing a carbon fiber composite material. 1 is a SEM image of a tensile fracture surface of a sample of Example 2. FIG. 10 is a diagram for explaining carbon nanotubes and the like in the image of FIG. 9 .

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 containing carbon nanotubes in cross-linked silicone rubber, and includes a cell structure formed by the carbon nanotubes and their interfacial phase surrounding a first silicone rubber region, and a continuous structure in which a plurality of the cell structures are continuously formed in a ring shape so as to surround a second silicone rubber region.

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.

The carbon fiber composite material can have a hardness of 65 to 78 degrees based on JIS K6253. By achieving a relatively low hardness of 78 degrees or less while retaining the reinforcing effect of carbon nanotubes, it is possible to expand the range of applications, uses, and markets for carbon fiber composite materials in silicone rubber products.

The carbon fiber composite material may have a stress of 2.0 MPa to 5.0 MPa at 50% elongation in a tensile test based on JIS K6251 at room temperature. When the stress of the carbon fiber composite material at 50% elongation is 2.0 MPa or more, it has excellent resistance to instantaneous elongation deformation, and material destruction can be suppressed. It is more preferable that the stress of the carbon fiber composite material at 50% elongation in a tensile test based on JIS K6251 at room temperature is 2.2 MPa to 4.5 MPa.

The carbon fiber composite material may have a tear strength (Tr) of 45 N/mm to 65 N/mm in a tear test based on JIS K6252 at room temperature. When the tear strength of the carbon fiber composite material is 45 N/mm or more at room temperature, the material has excellent mechanical strength. This makes it possible to suppress breakage of the carbon fiber composite material when it is demolded during molding. It is more preferable that the carbon fiber composite material has a tear strength of 48 N/mm to 61 N/mm in a tear test based on JIS K6252 at room temperature.

Next, we will explain the materials that make up carbon fiber composite materials.

1.1. Silicone rubber Silicone rubber is not particularly limited, but may be organopolysiloxane raw rubber, the main chain of which is composed of siloxane bonds, and the side chain may have alkyl groups such as methyl, ethyl, propyl, and butyl groups, cycloalkyl groups such as cyclohexyl groups, alkenyl groups such as vinyl, allyl, butenyl, and hexenyl groups, aryl groups such as phenyl and tolyl groups, aralkyl groups such as benzyl and γ-phenylpropyl groups, or groups in which some or all of the hydrogen atoms bonded to the carbon atoms of these groups have been substituted with halogen atoms, cyano groups, etc., such as chloromethyl groups, trifluoropropyl groups, and cyanoethyl groups. The molecular structure of silicone rubber may be linear, or may be linear with some branches.

A known crosslinking agent can be used for silicone rubber. For example, a condensation reaction, an addition reaction, or a peroxide reaction can be used as the crosslinking form, with peroxide crosslinking being preferred. By crosslinking silicone rubber with a crosslinking agent, a carbon fiber composite material with excellent heat resistance and chemical resistance can be produced.

Silicone rubber also includes silicone rubber compounds that already contain silica. Commercially available silicone rubber usually contains silica. Silicone rubber is characterized by its excellent properties over a wide range of temperatures, from low to high, but because it has low physical strength, compounds that already contain silica particles are generally used.

1.2. Carbon nanotubes Carbon nanotubes can have an average diameter (fiber diameter) of 2 nm to 30 nm, and can further be 9 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 elastomer matrix is improved, and the poor dispersion of the carbon nanotubes in the elastomer tends to be improved. Carbon nanotubes with a diameter of 2 nm or more are commercially available, and those with a diameter of 30 nm or less have the effect of being excellent in tear strength and tensile product retention after heating. Carbon nanotubes can be subjected to a known activation treatment in order to improve the reactivity of their surface with the elastomer. 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 an image taken with an electron microscope at, for example, 5,000 times (the magnification can be changed appropriately 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 a vapor phase growth method, also known as catalytic chemical vapor deposition (CCVD), which is a method for producing raw 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, a floating reaction method is used in which an organic compound such as benzene or toluene is used as a raw material, and an organic transition metal compound such as ferrocene or nickelcene is used as a metal-based catalyst, and these are introduced into a reactor set at a high reaction temperature, for example, 400°C to 1000°C, together with a carrier gas, to generate carbon nanotubes in a floating state or on the reactor wall, or a substrate reaction method is used 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 can be adjusted according to the required hardness, for example, and can be 0.5 to 7.0 parts by mass per 100 parts by mass of silicone rubber. It is more preferable to mix 2 to 5 parts by mass of carbon nanotubes, and even more preferable to mix 3 to 5 parts by mass of carbon nanotubes, per 100 parts by mass of silicone rubber. If the amount of carbon nanotubes is 7.0 parts by mass or less, the carbon fiber composite material can be cost-competitive, and the rubber hardness can be easily adjusted to 78 degrees or less while maintaining elongation and flexibility, and the tear strength can be excellent due to the reinforcement by the carbon nanotubes. In addition, by mixing 0.5 parts by mass or more of carbon nanotubes with 100 parts by mass of silicone rubber and compounding them in a defibrated state, a microcellular structure and continuous structure, which will be described later, are formed in the carbon fiber composite material, thereby exerting a reinforcing effect.

1.3. Other compounding agents General compounding agents used in rubber, such as metal oxides such as silica, alumina, magnesium oxide, and zinc oxide, reinforcing agents such as carbon black, fillers such as talc, clay, graphite, and calcium silicate, processing aids such as stearic acid, palmitic acid, and paraffin wax, antioxidants, plasticizers, and coupling agents, can be added to silicone rubber as needed. Carbon black and graphite have almost no effect on the mechanical reinforcement of carbon fiber composite materials, but are expected to improve kneading processability.

The coupling agent used in this embodiment can be one or more types selected from the group consisting of titanate-based coupling agents, silane-based coupling agents, aluminate-based coupling agents, and zirconate-based coupling agents.

Silane coupling agents that can be used include those manufactured by Shin-Etsu Chemical Co., Ltd., Toray Industries, Inc., Momentive Performance Materials, Inc., etc., such as silane-1:3-methacryloxypropyltrimethoxysilane, silane-2:3-glycidoxypropyltrimethoxysilane, and silane-3:3-mercaptopropyltrimethoxysilane.

Titanate-based coupling agents, aluminate-based coupling agents, and zirconate-based coupling agents can be those manufactured by Ajinomoto Co., Ltd., KENRICH Co., Ltd., etc., and examples of titanate-based agents that can be used include tetra(2,2-diallyloxymethyl)butyl and di(ditridecyl)phosphite titanate, examples of aluminate-based agents that can be used include alkylacetoacetate aluminum diisopropylate, and examples of zirconate-based agents that can be used include tetra(2,2-diallyloxymethyl)butyl and di(ditridecyl)phosphite zirconate.

1.4 Structural Features The inventors of the present invention performed measurements of carbon fiber composite materials using a scanning electron microscope and found that carbon fiber composite materials with a hardness of 78 degrees or less and excellent mechanical strength have common structural features.

The structural features of the carbon fiber composite material 50 will be described in detail with reference to Figures 1 and 2. Figure 1 is a schematic diagram for explaining the structure in an image 90 of a cross section of the carbon fiber composite material 50, and Figure 2 is an enlarged view of the dashed frame in Figure 1. The image 90 is a photograph obtained by photographing a cross section of the carbon fiber composite material 50, and the cross section may be a freeze-fracture cross section or a tensile fracture cross section. The image 90 is obtained by observing and photographing with a scanning electron microscope (SEM).

The carbon fiber composite material 50 shown in Figures 1 and 2 contains multiple carbon nanotubes 20 in cross-linked silicone rubber 30. The carbon nanotubes 20 are present in the silicone rubber 30 in a defibrated state.

The carbon fiber composite material 50 includes a cellular structure 60 formed by carbon nanotubes 20 and their interphase 62 surrounding a first silicone rubber region 64, and a continuous structure 70 formed in a ring shape such that a plurality of cellular structures 60 are continuously arranged to surround a second silicone rubber region 72. The interphase 62 is something like a bound rubber that is formed around the carbon nanofibers, including the interface between the elastomer and the carbon nanofibers.

In the cross section of the carbon fiber composite material 50, the continuous structure 70 is a region where the number of carbon nanotubes 20 per 1 μm ² exceeds two. Since the continuous structure 70 is a dense state where the number of carbon nanotubes 20 exceeds two per 1 μm ² , it is considered that the interface phases 62 around the carbon nanotubes form a continuous state. The silicone rubber 30 having a small volume surrounded by the adjacent carbon nanotubes 20 and the interface phases 62 becomes the first silicone rubber region 64. The first silicone rubber region 64 becomes a part of the cell structure 60, and deformation is suppressed. The continuous structure 70 forms a three-dimensional mesh structure throughout the carbon fiber composite material 50 to restrain the deformation of the carbon fiber composite material 50, but since the amount of carbon nanotubes 20 mixed is small, the effect on the flexibility of the carbon fiber composite material 50 is relatively small. Since the continuous structure 70 is formed throughout the carbon fiber composite material 50, the mechanical strength, especially the tear strength, can be excellent.

The width of the continuous structure 70 can be 0.01 μm to 5 μm, and can also be 0.05 μm to 3 μm. This width is the distance between adjacent second silicone rubber regions 72 sandwiching the continuous structure 70, and is the shortest distance at each of the multiple measurement points at the boundary between the continuous structure 70 and the second silicone rubber region 72.

In the cross section of the carbon fiber composite material 50, the second silicone rubber region 72 is a region having an area of 0.1 ^μm2 or more and containing two or less carbon nanotubes per 1 ^μm2 . The second silicone rubber region 72 has a larger area than the first silicone rubber region 64. Since the number of carbon nanotubes 20 in the large-area second silicone rubber region 72 is two or less, it is considered that the second silicone rubber region 72 has excellent flexibility. The second silicone rubber region 72 and the first silicone rubber region 64 constituting the continuous structure 70 do not have a clear boundary, and are compatible because they are composed of the same silicone rubber 30.

The area of the second silicone rubber region 72 can be 0.1 ^μm2 or more and 10 ^μm2 or less. Since the second silicone rubber region 72 is a region surrounded by the continuous structure 70, the area will not be less than 0.1 ^μm2 . Furthermore, since the area is 10 ^μm2 or less, the carbon fiber composite material 50 can have excellent mechanical strength, particularly tear strength. The area of the second silicone rubber region 72 can be 0.2 μm2 or ^more and ⁸ μm2 or less, or 0.2 ^μm2 or more and 6 ^μm2 or less.

The total area occupied by the second silicone rubber regions 72 in the cross section of the carbon fiber composite material 50 can be 45% or more and 80% or less, and the total area can be 50% or more and 75% or less. The maximum width of the second silicone rubber regions 72 can be 0.1 μm or more and 6 μm or less. If the total area is less than 45%, the continuous structure 70 develops, and the hardness tends to increase and the flexibility tends to decrease. If the ratio of the total area to the whole exceeds 80%, the continuous structure 70 tends to be interrupted in many places, and the reinforcing property of the carbon nanotubes 20 tends to decrease. The total area can be measured as the total area of the second silicone rubber regions 72 in the image 90, and the whole area is the area of the image 90.

The second silicone rubber region 72 is specified by using image editing software to draw dots where the carbon nanotubes 20 are present in the image 90, and to draw a line to surround the region where the number of carbon nanotubes 20 per 1 ^μm2 is two or less. Then, the region in the image 90 other than the second silicone rubber region 72 can be specified as the continuous structure 70. As the images 90 used to measure the area of the second silicone rubber region 72, it is preferable to use a plurality of images 90 obtained by photographing a plurality of locations (e.g., three locations) of the cross section of the sample of the carbon fiber composite material 50. The images 90 are photographed at a magnification at which the carbon nanotubes 20 can be confirmed, for example, 10,000 times.

2. Manufacturing Method of Carbon Fiber Composite Material The manufacturing method of the carbon fiber composite material will be described in detail with reference to FIGS.

Figure 3 is a flowchart of the method for producing a carbon fiber composite material according to this embodiment, and Figures 4 to 8 are diagrams that show the schematic diagram of the method for producing a carbon fiber composite material according to this embodiment.

As shown in FIG. 3, the method for producing a carbon fiber composite material includes a first mixing step (S10), a first kneading step (S20), a second mixing step (S30), and a second kneading step (S40). The method for producing a carbon fiber composite material may further include a mastication step and/or a molding step.

As shown in Figures 4 to 8, the method for producing a carbon fiber composite material according to this embodiment will be described by using an example of an open roll 100. The first roll 110 and the second roll 120 of 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 4 to 6.

First, as shown in FIG. 4, the silicone rubber 30 wound around the first roll 110 is masticated to appropriately cut the silicone rubber molecular chains and generate free radicals. The free radicals in the silicone rubber generated by mastication are in a state that makes them easy to bond with the carbon nanotubes.

2.1. First Mixing Step Next, as shown in FIG. 5, in the first mixing step (S10), carbon nanotubes 20 are mixed into a bank 34 of silicone rubber 30 wound around a first roll 110 to obtain a mixture 36 (FIG. 6). In the first mixing step (S10), 3 to 15 parts by mass of carbon nanotubes 20 can be mixed with 100 parts by mass of silicone rubber 30. The carbon nanotubes 20 can be defibrated with appropriate elasticity and viscosity, as described below. Silicone rubber 30 is originally a material with low elasticity, but by including 3 parts by mass or more of carbon nanotubes 20, the elasticity of the entire material can be improved, and the defibration of carbon nanotubes 20 can be promoted. In addition, if there are too many carbon nanotubes 20, the viscosity of the entire material becomes too high, making processing difficult, but if there are 15 parts by mass or less of carbon nanotubes 20, the carbon nanotubes 20 can be defibrated with appropriate viscosity.

2.2. First kneading step Next, as shown in FIG. 6, in the first kneading step (S20), the mixture 36 is fed into open rolls 100 in which the roll gap d is set to be greater than 0 mm and not more than 0.5 mm and the roll temperature is set to be 0° C. to 50° C., and the mixture is passed through the open rolls 100 at a low temperature to obtain a first composite rubber 37.

The thin pass can be performed, for example, 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 first composite rubber 37 extruded from between the narrow rolls in this way is significantly deformed as shown in Figure 6 due to the restoring force caused by the elasticity of the silicone rubber, and at that time the carbon nanotubes move significantly together with the silicone rubber.

The first composite rubber 37 obtained by thin-threading may be rolled with a roll to be cut into a sheet of a predetermined thickness.

In this thin-threading process, in order to obtain the highest possible shear force, the roll temperature is set to a relatively low temperature, for example, 0 to 50°C, more preferably 5 to 30°C, and the actual temperature of the silicone rubber can also be adjusted to 0 to 50°C.

The shear force thus obtained acts on the silicone rubber, and the aggregated carbon nanotubes are separated from each other and defibrated as if they are pulled out one by one into the silicone rubber molecules, and are dispersed in the silicone rubber. In particular, silicone rubber has elasticity, viscosity, and chemical interaction with the carbon nanotubes, so that the carbon nanotubes can be easily dispersed. Thus, a first composite rubber 37 can be obtained that has excellent carbon nanotube dispersibility and dispersion stability (the carbon nanotubes are less likely to re-aggregate).

More specifically, when silicone rubber and carbon nanotubes are mixed on the open roll 100, the viscous silicone rubber penetrates the carbon nanotubes, and specific parts of the silicone rubber 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 silicone rubber molecules. Next, when a strong shear force is applied to the silicone rubber, the carbon nanotubes move along with the movement of the silicone rubber molecules, and further, the restoring force of the silicone rubber due to its elasticity after shearing separates the aggregated carbon nanotubes and disperses them in the silicone rubber.

According to this embodiment, when the first composite rubber 37 is extruded from between the narrow rolls, the first composite rubber 37 is deformed to a thickness greater than the roll gap d due to the restoring force caused by the elasticity of the silicone rubber. This deformation causes the first composite rubber 37, which is subjected to a strong shearing force, to flow in an even more complex manner, dispersing the carbon nanotubes in the silicone rubber. Once dispersed, the carbon nanotubes are prevented from re-aggregating due to chemical interactions with the silicone rubber, and can have good dispersion stability.

The first kneading step (S20) 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 silicone rubber by shear force. In short, this step only requires that a shear force capable of separating and defibrating the aggregated carbon nanotubes can be applied to the silicone rubber. In particular, the open roll method is preferred because it allows not only the roll temperature to be controlled, but also the actual temperature of the mixture to be measured and controlled.

7, in the second mixing step (S30), silicone rubber 30 is further mixed into the bank 34 of the first composite rubber 37 wound around the first roll 110 to obtain a second composite rubber 38 (FIG. 8). In the second mixing step (S30), the silicone rubber 30 can be mixed so that the second composite rubber 38 contains 0.5 to 7 parts by mass of carbon nanotubes per 100 parts by mass of silicone rubber.

8, in the second kneading step (S40), the second composite rubber 38 is fed into an open roll 100 in which the roll distance 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 is passed through the open roll 100 at a low temperature to obtain a carbon fiber composite material 50. The second kneading step (S40) can be performed in the same manner as the first kneading step (S20).

Since the carbon nanotubes have already been defibrated in the first composite rubber 37 and a uniform structure has developed throughout, the second mixing step (S30) alone does not completely mix the additional silicone rubber 30 with the first composite rubber 37, and does not result in the special structure of the continuous structure and the second silicone rubber region surrounded by the continuous structure as described above. However, by going through the second kneading step (S40), the carbon fiber composite material 50 has the special structure of the continuous structure and the second silicone rubber region surrounded by the continuous structure as described above.

The carbon fiber composite material 50 obtained by thin-threading may be rolled with a roll to be cut into a sheet of a predetermined thickness.

The carbon fiber composite material 50 obtained from the second kneading step (S40) is in an uncrosslinked state, so it can be crosslinked and molded at a predetermined temperature after mixing with a crosslinking agent. The crosslinking agent can be mixed as appropriate before or during mixing of the silicone rubber and carbon nanotubes, or before separation after thin-passing.

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 6 and Comparative Examples 4 and 5 were prepared by the following steps.

Mastication process: 100 parts by weight (phr) of silicone rubber shown in Tables 1 and 2 was placed on an open roll with a roll diameter of 6 inches (roll temperature 10 to 20°C) and wound around the roll (see Figure 4).

First mixing step: Next, 8 parts by mass of carbon nanotubes (referred to as "CNT-1", "CNT-2" and "CNT-3" in Tables 1 and 2) per 100 parts by mass of silicone rubber and compounding agents such as a silane coupling agent were added to the silicone rubber (see FIG. 5). At this time, the roll distance d was set to 1.5 mm. The silicone rubber mixture with the carbon nanotubes mixed in was taken out from the rolls.

First kneading process: The roll gap d was narrowed from 1.5 mm to 0.3 mm, and the mixture was fed into rolls whose roll temperatures were set to 10°C to 20°C, and thin passing was performed to obtain a first composite rubber (see Figure 6). At this time, the surface speed ratio of the two rolls was set to 1.1. Thin passing was repeated five times.

Second mixing process: The roll distance d was changed from 0.3 mm to 1.5 mm, and the first composite rubber was fed into the open rolls. Silicone rubber was then mixed in to obtain the composition shown in Table 1 to obtain the second composite rubber (see Figure 7).

Second kneading process: The roll gap d was narrowed from 1.5 mm to 0.3 mm, and the second composite rubber was fed into the open rolls and thin-passed to obtain a carbon fiber composite material (see Figure 8). At this time, the surface speed ratio of the two rolls was set to 1.1. Thin-passing was repeated five times.

Furthermore, DS-8 (2,5-dimethyl-2,5-di(t-butylperoxy)hexane) manufactured by Asahi Kasei Wacker Silicone was added as a crosslinking agent at a content of 50% (0.5 parts by mass per 100 parts by mass of silicone rubber) to the carbon fiber composite material, and the rolls were set at a predetermined interval (2.1 mm to 2.2 mm) to separate the uncrosslinked carbon fiber composite material.

In Comparative Examples 1 and 2, carbon nanotubes were not blended, so a crosslinking agent was added after the mastication process to obtain an uncrosslinked sample. In Comparative Example 3, 3 parts by mass of carbon nanotubes were added to 100 parts by mass of silicone rubber in the first mixing process, and a crosslinking agent was added to the mixture obtained by carrying out the first kneading process to obtain an uncrosslinked sample.

Molding process: For Examples 1 to 6 and Comparative Examples 1 to 5, the uncrosslinked carbon fiber composite material (Comparative Examples 1 and 2 are uncrosslinked rubber compositions) was placed in a vacuum press and press molded (primary crosslinking) at 170°C to 180°C for 5 to 10 minutes.

The carbon fiber composite material was then transferred to an oven and subjected to secondary crosslinking at 200°C for 2 hours to obtain crosslinked sheet-like carbon fiber composite material samples of Examples 1 to 6 and Comparative Examples 1 to 5 (Comparative Examples 1 and 2 were crosslinked rubber composition samples).

The amount of carbon nanotubes in each sample in Examples 1 to 6 was adjusted so that the rubber hardness (Hs) was about 70 degrees ± 5 degrees. The sample in Comparative Example 2 had a rubber hardness of 70 degrees without the addition of carbon nanotubes.

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

CNT-1: multi-walled carbon nanotube (average diameter 15.3 nm),
CNT-2: multi-walled carbon nanotube (fiber diameter 18.5 nm),
CNT-3: multi-walled carbon nanotube (fiber diameter 17.0 nm),
Silane coupling agent: Silane coupling agent KMB-503 (3-methacryloxypropyltrimethoxysilane), manufactured by Shin-Etsu Chemical Co., Ltd.
It was.

The test samples of Examples 1 to 6 and Comparative Examples 1 to 5 were subjected to the various tests described below, and the test results are shown in Tables 1 and 2.

(2) Basic Property Tests For each sample of the examples and comparative examples, rubber hardness (Hs (JIS-A)) was measured in accordance with JIS K 6253.

Furthermore, for the test pieces punched out into a JIS No. 3 dumbbell shape for each sample of the examples and comparative examples, a tensile test was carried out in accordance with JIS K6251 at 23±2°C and a tensile speed of 500 mm/min using a Shimadzu Autograph AG-X tensile tester, and the tensile strength (TS (MPa)), breaking elongation (Eb (%)), stress at 50% elongation (M50 (MPa)), and stress at 100% elongation (M100 (MPa)) were measured. The measurement results are shown in each column of the table.

(3) Tear test Each sample of the examples and comparative examples was punched out into an angle-shaped test piece without a notch as specified in JIS K6252, and a tear test was carried out at room temperature at a tensile speed of 500 mm/min in accordance with JIS K6252 using an Autograph AG-X manufactured by Shimadzu Corporation, and the tear strength (Tr (N/mm)) was calculated for the samples in the grain and anti-grain directions. The measurement results are shown in each column of the table.

(4) SEM Measurement The fracture surface of each sample after the tensile test of the Example and Comparative Example was photographed by SEM at 10,000 times magnification. FIG. 9 shows an image 90 (photograph) obtained by SEM of the tensile fracture surface of the sample of Example 2. The white thin thread-like parts and white dots in each image are carbon nanotubes. Next, as shown in FIG. 10, image editing software was used to draw dots at the locations of the carbon nanotubes 20 in each image 90, and further, the second silicone rubber region 72 was specified by drawing a line around the area where the number of carbon nanotubes 20 per 1 μm ² was two or less. As a result, the area other than the second silicone rubber region 72 in each image 90 could be specified as the continuous structure 70. In addition, three different locations were photographed for each sample to obtain three images 90, and the second silicone rubber region 72 and the continuous structure 70 were similarly specified in each image 90. Incidentally, no aggregates of carbon nanotubes 20 were confirmed in the sample of the Example.

Next, in each image 90, the maximum width of the second silicone rubber region 72 ("maximum width" in the table, μm), the area of the second silicone rubber region 72 ("area" in the table, μm ² ), the ratio of the total area to the entire image 90 ("ratio" in the table, %), and the width of the continuous structure 70 ("width" in the table, μm) were measured. The maximum width was measured using image editing software by drawing the longest straight line passing through the center of gravity of each second silicone rubber region 72 and connecting the opposing outer edges, and the length of the straight line was taken as the maximum width, and the maximum and minimum values of the maximum width of all the second silicone rubber regions 72 were extracted. The area was measured by measuring the area of the second silicone rubber region 72 in the image 90 using image editing software, and the maximum and minimum values were extracted. The ratio was calculated by dividing the total measured area by the area of the image 90. The width was determined by using image editing software to draw multiple straight lines between the outer edges of adjacent second silicone rubber regions 72 in each image 90, and finding the maximum and minimum lengths of the straight lines. The straight line was the shortest straight line drawn from any point on the outer edge of the second silicone rubber region 72 to the outer edge of the adjacent second silicone rubber region 72. The results are shown in Tables 1 and 2.

According to Tables 1 and 2, the samples of Examples 1 to 6 and Comparative Examples 1 to 4 had a hardness of 74 degrees or less. Comparative Example 5 had a hardness of 91 degrees.

According to Tables 1 and 2, the samples of Examples 1 to 6 showed a stress at 50% elongation (M50) of 2.2 MPa or more, and a stress at 100% elongation (M100) of 2.7 MPa or more. The samples of Comparative Examples 1 to 4 showed a stress at 50% elongation (M50) of 1.9 MPa or less, and a stress at 100% elongation (M100) of 2.1 MPa or less, and the sample of Comparative Example 5 showed a stress at 50% elongation (M50) and a stress at 100% elongation (M100) values greater than those of the Examples.

According to Tables 1 and 2, the samples of Examples 1 to 6 had tear strengths (Tr) of 48.6 N/mm or more at room temperature. The samples of Comparative Examples 1 to 5 had tear strengths at room temperature that were smaller than those of the Examples.

According to Tables 1 and 2, in the samples of Examples 1 to 6, the ratio of the area of the second silicone rubber region 72 to the area of the image 90 was 52.3% to 74.8%. In the samples of Comparative Examples 1 and 2, the second silicone rubber region 72 was not present, and in the samples of Comparative Examples 3 to 5, the ratio of the area of the second silicone rubber region 72 to the area of the image 90 was 33.6% to 89.3%.

According to Tables 1 and 2, the areas of the second silicone rubber regions 72 of the samples of Examples 1 to 6 were 0.24 μm ² to 5.54 μm ^2. The areas of the second silicone rubber regions 72 of the samples of Comparative Examples 3 and 4 were 0.92 μm ² to 13.8 μm ² , and the area of the second silicone rubber regions 72 of the sample of Comparative Example 5 was 0.23 μm ² to 1.85 μm ² .

According to Tables 1 and 2, the samples of Examples 1 to 6 had a maximum width of the second silicone rubber region 72 of 0.50 μm to 4.42 μm. The samples of Comparative Examples 3 and 4 had a maximum width of the second silicone rubber region 72 of 1.21 μm to 9.43 μm, and the sample of Comparative Example 5 had a maximum width of the second silicone rubber region 72 of 0.37 μm to 2.55 μm.

According to Tables 1 and 2, the width of the continuous structure 70 in the samples of Examples 1 to 6 was 0.05 μm to 2.70 μm. The samples of Comparative Examples 3 and 4 did not have the continuous structure 70, and the sample of Comparative Example 5 had a width of the continuous structure 70 of 1.13 μm to 6.70 μm.

20...carbon nanotubes, 30...silicone rubber, 34...bank, 36...mixture, 37...first composite rubber, 38...second composite rubber, 50...carbon fiber composite material, 60...cell structure, 62...interphase, 64...first silicone rubber region, 70...continuous structure, 72...second silicone rubber region, 90...image, 100...open roll, 110...first roll, 120...second roll, d...roll spacing, V1, V2...rotation speed

Claims (8)

A carbon fiber composite material containing carbon nanotubes in a crosslinked silicone rubber,
a cellular structure formed by the carbon nanotubes and their interphase surrounding a first silicone rubber region, and a continuous structure in which a plurality of the cellular structures are continuously formed in an annular shape so as to surround a second silicone rubber region,
In a cross section of the carbon fiber composite material, the continuous structure is a region in which the number of the carbon nanotubes per 1 ^μm2 exceeds two,
In the cross section, the second silicone rubber region has an area of 0.1 ^μm2 or more and 10 μm2 ^or less , and the number of the carbon nanotubes per 1 ^μm2 is two or less,
the total area occupied by the second silicone rubber region is 45% or more and 80% or less;
A carbon fiber composite material , wherein the second silicone rubber region has a maximum width of 0.1 μm or more and 6 μm or less . In claim 1 ,
The carbon fiber composite material, wherein the width of the continuous structure is 0.01 μm to 5 μm. In claim 1 or 2 ,
The carbon nanotubes have an average diameter of 2 nm to 30 nm. In any one of claims 1 to 3 ,
The carbon nanotubes are contained in a carbon fiber composite material in an amount of 0.5 to 7.0 parts by mass per 100 parts by mass of the silicone rubber. In any one of claims 1 to 4 ,
A carbon fiber composite material having a hardness of 65 degrees to 78 degrees based on JIS K6253. In any one of claims 1 to 5 ,
A carbon fiber composite material having a stress at 50% elongation of 2.0 MPa to 5.0 MPa in a tensile test based on JIS K6251 at room temperature. In any one of claims 1 to 6 ,
A carbon fiber composite material having a tear strength (Tr) of 45 N/mm to 65 N/mm at room temperature in a tear test based on JIS K6252. a first mixing step of mixing the silicone rubber with the carbon nanotubes to obtain a mixture;
a first kneading step of feeding the mixture into open rolls 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 kneading the mixture thinly to obtain a first composite rubber;
a second mixing step of further mixing a silicone rubber with the first composite rubber to obtain a second composite rubber;
a second kneading step in which the second composite rubber is fed 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-kneaded to obtain a carbon fiber composite material;
Including,
The carbon nanotubes have an average diameter of 2 nm to 30 nm;
The first mixing step includes mixing 3 parts by mass to 15 parts by mass of the carbon nanotubes with 100 parts by mass of silicone rubber;
In the second mixing step, silicone rubber is mixed so that the second composite rubber contains 0.5 to 7 parts by mass of carbon nanotubes per 100 parts by mass of silicone rubber .

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