JPWO2019188050A1 - Method of manufacturing composite materials - Google Patents

Abstract

A method for producing a composite material, which includes a pre-kneading step of kneading rubber and a fibrous carbon nanostructure to obtain a pre-kneaded product, and a main kneading step of further kneading the pre-kneaded product after the pre-kneading step. is there. Then, the kneading temperature in the pre-kneading step is made higher than the kneading temperature in the main kneading step.

Description

The present invention relates to a method for producing a composite material, and more particularly to a method for producing a composite material containing rubber and a fibrous carbon nanostructure.

Fibrous carbon nanostructures such as carbon nanotubes (hereinafter sometimes referred to as "CNT") are excellent in conductivity, thermal conductivity, sliding properties, mechanical properties, etc., and therefore their application to a wide range of applications is being studied. ing.
In recent years, by taking advantage of the excellent properties of fibrous carbon nanostructures and combining rubber and fibrous carbon nanostructures, rubber properties such as workability and strength and fibrous carbon nanostructures such as reinforcing properties have been used. The development of technology to provide composite materials that combine the characteristics of the body is underway.

Here, from the viewpoint of satisfactorily improving the mechanical properties of the composite material, it is necessary to uniformly disperse the fibrous carbon nanostructures such as CNTs in the rubber matrix. Therefore, a composite material is prepared in a rubber matrix by using a prepared dispersion prepared by uniformly dispersing fibrous carbon nanostructures in a dispersion medium and a dispersion prepared by mixing rubber. A technique for obtaining a composite material in which fibrous carbon nanostructures are uniformly dispersed has been proposed.

Specifically, for example, in Patent Document 1, an elastomer such as rubber is dissolved in a dispersion liquid obtained by dispersing a carbonaceous material such as CNT in a solvent to obtain an elastomer solution, and then the solvent is used from the elastomer solution. It is disclosed to remove to produce an elastomeric composition comprising a carbonaceous material.

JP-A-2017-8244

By the way, composite materials used in the automobile industry, the chemical industry, the machine-related industry, and the like may be required to have high tensile strength under high temperature conditions. However, the composite material obtained by the conventional method does not always have sufficient tensile strength under high temperature conditions. Therefore, there is room for improvement in the conventional method for producing a composite material containing rubber and fibrous carbon nanostructures.

Therefore, an object of the present invention is to provide a method for producing a composite material having excellent tensile strength under high temperature conditions.

The present inventors have made extensive studies to achieve the above object. Then, the present inventors kneaded the composite mixture containing the rubber and the fibrous carbon nanostructures in at least two kneading steps having different kneading temperatures to improve the tensile strength under high temperature conditions. We have found that a material can be obtained and completed the present invention.

That is, the present invention aims to advantageously solve the above problems, and the method for producing a composite material of the present invention is to knead a composite mixture containing rubber and a fibrous carbon nanostructure. The kneading temperature in the pre-kneading step is higher than the kneading temperature in the main kneading step. It is also characterized by being expensive. In this way, a pre-kneading step of kneading a composite mixture containing rubber and a fibrous carbon nanostructure to obtain a pre-kneaded product, and a main kneading step of further kneading the pre-kneaded product after the pre-kneading step. By including at least two steps of kneading, a composite material having excellent tensile strength under high temperature conditions can be obtained.

Here, in the method for producing a composite material of the present invention, the composite mixture is prepared by dispersing a composition containing the rubber, a poor solvent for the rubber, and the fibrous carbon nanostructures. It may be obtained through a procedure for obtaining the mixture and a procedure for removing the poor solvent from the obtained dispersion. If the composite mixture obtained through such a procedure is used, a composite material having excellent tensile strength under high temperature conditions can be efficiently obtained.

Further, in the method for producing a composite material of the present invention, the composite mixture is dispersed by dispersing a composition containing the rubber, a good solvent capable of dissolving the rubber, and the fibrous carbon nanostructures. It may be obtained through a procedure for obtaining a product and a procedure for removing the good solvent from the obtained dispersion. Even as a composite mixture obtained through such a procedure, a composite material having excellent tensile strength under high temperature conditions can be efficiently obtained.

In the method for producing a composite material of the present invention, the composite mixture may contain a particulate filler. Even as a composite mixture containing a particulate filler, a composite material having excellent tensile strength under high temperature conditions can be efficiently obtained.

Here, in the method for producing a composite material of the present invention, the rubber has a complex viscosity of 200,000 Pa · s or less under the condition of a shear rate of 0.1 (1 / s) at the kneading temperature of the pre-kneading step. It is preferable to have. When the complex viscosity of the rubber is not more than the above upper limit value, a composite material having a higher tensile strength under high temperature conditions can be efficiently obtained.

Further, in the method for producing a composite material of the present invention, the kneading temperature in the pre-kneading step is preferably 80 ° C. or higher. When the kneading temperature in the pre-kneading step is 80 ° C. or higher, a composite material having further excellent tensile strength under high temperature conditions can be efficiently obtained.

Further, in the method for producing a composite material of the present invention, the rubber is preferably at least one selected from the group consisting of fluororubber, nitrile rubber and hydrogenated nitrile rubber. By using such rubber, a composite material having excellent oil resistance, aging resistance and the like can be obtained.

Further, in the method for producing a composite material of the present invention, it is preferable that the fibrous carbon nanostructure contains carbon nanotubes. By using the fibrous carbon nanostructures containing carbon nanotubes, a composite material having excellent tensile strength under high temperature conditions can be obtained even when the amount of the fibrous carbon nanostructures contained in the composite material is small. be able to.

In the method for producing a composite material of the present invention, the fibrous carbon nanostructure preferably has a BET specific surface area of 600 m ² / g or more. When the BET specific surface area of the fibrous carbon nanostructure is 600 m ² / g or more, it is possible to provide a composite material having sufficiently excellent tensile strength under high temperature conditions.

According to the method for producing a composite material of the present invention, a composite material having excellent tensile strength under high temperature conditions can be efficiently produced.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the composite material of the present invention is used in producing a composite material containing rubber, a fibrous carbon nanostructure, and an arbitrary particulate filler. The composite material produced by using the method for producing a composite material of the present invention is excellent in tensile strength under high temperature conditions. Therefore, for example, it is used for various applications such as sheet materials and sealing materials that require high tensile strength under high temperature conditions.

(Manufacturing method of composite material)
The method for producing a composite material of the present invention includes a pre-kneading step of kneading a composite mixture containing rubber, a fibrous carbon nanostructure, and an arbitrary particulate filler to obtain a pre-kneaded product, and after the pre-kneading step. Further, the kneading temperature in the pre-kneading step is higher than that in the kneading step in the main kneading step, including the main kneading step of kneading the pre-kneaded product. In addition, the method for producing a composite material of the present invention optionally comprises a preparation step of preparing a composite mixture containing rubber, a fibrous carbon nanostructure, and an arbitrary particulate filler before the pre-kneading step. Further may be included.

The method for producing a composite material of the present invention includes a pre-kneading step of kneading a composite mixture containing rubber, a fibrous carbon nanostructure, and an arbitrary particulate filler to obtain a pre-kneaded product, and a pre-kneading process. After the step, the pre-kneaded product is further kneaded by a kneading step of at least two steps with the main kneading step of kneading the pre-kneaded product, and the kneading temperature in the pre-kneading step is higher than the kneading temperature in the main kneading step. A composite material having excellent strength can be obtained.
Here, the reason why the composite material obtained by the production method of the present invention is excellent in tensile strength under high temperature conditions is not clear, but it is presumed as follows. That is, in the pre-kneading step performed at a higher temperature than the main kneading step, the rubber easily invades the gap between the fibrous carbon nanostructures and the fibrous carbon nanostructures due to the heat during kneading. The fibrous carbon nanostructures are defibrated and easily dispersed. Therefore, it is presumed that the fibrous carbon nanostructures are well dispersed by carrying out the main kneading step after the pre-kneading step.

<Preparation process>
The preparation step is a step that can be arbitrarily included in the method for producing a composite material of the present invention. Then, in the preparation step, a composite mixture containing rubber, fibrous carbon nanostructures, and an arbitrary particulate filler is prepared.

<< Preparation of complex mixture >>
The composite mixture containing the rubber, the fibrous carbon nanostructures, and any particulate filler to be kneaded in the pre-kneading step can be obtained, for example, by the method (1) or (2) below.
(1) A procedure for obtaining a dispersion by dispersing a composition containing rubber, a poor solvent for the rubber, a fibrous carbon nanostructure, and an arbitrary particulate filler, and poor from the obtained dispersion. Method including step of removing solvent (2) A composition containing a rubber, a good solvent capable of dissolving the rubber, a fibrous carbon nanostructure, and an arbitrary particulate filler is dispersed and dispersed. A method comprising a procedure for obtaining a substance and a procedure for removing a good solvent from the obtained dispersion.

[Rubber]
Here, the rubber is not particularly limited, and a known rubber can be used, but the rubber is preferably at least one selected from the group consisting of fluororubber, nitrile rubber, and hydrogenated nitrile rubber. .. By using such rubber, a composite material having excellent oil resistance, aging resistance and the like can be obtained. In addition, these rubbers may be used individually by 1 type, and may use 2 or more types together.

-Fluororubber-
Examples of the fluororubber include ethylene tetrafluoroethylene-propylene rubber (FEPM), vinylidene fluoride rubber (FKM), ethylene tetrafluoroethylene-perfluoromethyl vinyl ether rubber (FFKM), and tetrafluoroethylene rubber. (TFE) and the like. Among these, ethylene tetrafluoroethylene-propylene rubber (FEPM) and vinylidene fluoride rubber (FKM) are preferable.

-Nitrile rubber-
Examples of the nitrile rubber include acrylonitrile butadiene rubber (NBR), carboxyl-modified acrylonitrile butadiene (XNBR), and acrylonitrile butadiene isoprene rubber (NBIR). Among these, acrylonitrile butadiene rubber (NBR) is preferable.

-Hydrogenated nitrile rubber-
Further, examples of the hydrogenated nitrile rubber include hydrogenated acrylonitrile butadiene rubber (HNBR).

[Complex viscosity (η ^* )]
^{The rubber preferably has a complex viscosity (η *} ) of 200,000 Pa · s or less under the condition of a shear rate of 0.1 (1 / s) at the kneading temperature of the pre-kneading step of the present invention. It is more preferably 000 Pa · s or less, further preferably 65,000 Pa · s or less, and particularly preferably 40,000 Pa · s or less. When the complex viscosity of the rubber is not more than the above upper limit value, a composite material having a higher tensile strength under high temperature conditions can be efficiently obtained. The complex viscosity of rubber can be measured by using the measuring method described in the examples of the present specification.

[Fibrous carbon nanostructures]
Further, the fibrous carbon nanostructure is not particularly limited, and a conductive fibrous carbon nanostructure can be used. Specifically, the fibrous carbon nanostructures include, for example, cylindrical carbon nanostructures such as carbon nanotubes (CNTs) and carbon nanostructures in which a six-membered ring network of carbon is formed in a flat tubular shape. Non-cylindrical carbon nanostructures such as bodies can be used. These may be used alone or in combination of two or more.

And among the above-mentioned, as the fibrous carbon nanostructure, it is more preferable to use the fibrous carbon nanostructure containing CNT. By using the fibrous carbon nanostructures containing CNTs, a composite material having excellent tensile strength under high temperature conditions can be provided even when the amount of the fibrous carbon nanostructures contained in the mixed solution is small. be able to.

Here, the fibrous carbon nanostructure containing CNT may be composed of only CNT, or may be a mixture of CNT and a fibrous carbon nanostructure other than CNT.
The CNTs in the fibrous carbon nanostructures are not particularly limited, and single-walled carbon nanotubes and / or multi-walled carbon nanotubes can be used, but the CNTs are carbon nanotubes having one to five layers. It is preferable that it is a single-walled carbon nanotube, and it is more preferable that it is a single-walled carbon nanotube. As the number of carbon nanotube layers is smaller, a composite material having excellent tensile strength can be efficiently produced even when the amount of fibrous carbon nanostructures contained in the mixed solution is small.

The average diameter of the fibrous carbon nanostructures is preferably 1 nm or more, preferably 60 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. When the average diameter of the fibrous carbon nanostructures is 1 nm or more, the dispersibility of the fibrous carbon nanostructures can be enhanced. Further, when the average diameter of the fibrous carbon nanostructures is 60 nm or less, the composite having excellent tensile strength under high temperature conditions even when the amount of the fibrous carbon nanostructures contained in the composite mixture is small. The material can be manufactured efficiently.
In the present invention, the "average diameter of fibrous carbon nanostructures" is determined by measuring the diameter (outer diameter) of, for example, 20 fibrous carbon nanostructures on a transmission electron microscope (TEM) image. , It can be obtained by calculating the number average value.

Further, as the fibrous carbon nanostructure, the ratio (3σ / Av) of the value (3σ) obtained by multiplying the standard deviation (σ: sample standard deviation) of the diameter by 3 with respect to the average diameter (Av) is more than 0.20. It is preferable to use a fibrous carbon nanostructure of less than 0.80, more preferably a fibrous carbon nanostructure having a 3σ / Av of more than 0.25, and a fibrous having a 3σ / Av of more than 0.40. It is more preferred to use carbon nanostructures. By using a fibrous carbon nanostructure having a 3σ / Av of more than 0.20 and less than 0.80, the performance of the produced composite material can be further improved.
The average diameter (Av) and standard deviation (σ) of the fibrous carbon nanostructures may be adjusted by changing the manufacturing method and manufacturing conditions of the fibrous carbon nanostructures, or may be obtained by different manufacturing methods. It may be adjusted by combining a plurality of types of the obtained fibrous carbon nanostructures.

As the fibrous carbon nanostructures, those measured as described above are usually plotted with the diameter measured on the horizontal axis and the frequency on the vertical axis, and when approximated by Gaussian, a normal distribution is usually used. Will be done.

Further, the fibrous carbon nanostructure preferably has an average length of 10 μm or more, more preferably 50 μm or more, further preferably 80 μm or more, preferably 600 μm or less, and preferably 550 μm. It is more preferably 5 μm or less, and further preferably 500 μm or less. When the average length is 10 μm or more, the tensile strength of the composite material can be improved even when the amount of the fibrous carbon nanostructures contained in the composite mixture is small. When the average length is 600 μm or less, the dispersibility of the fibrous carbon nanostructure can be enhanced in the dispersion treatment described later.
In the present invention, the average length of the "fibrous carbon nanostructures" is determined by measuring the length of, for example, 20 fibrous carbon nanostructures on a scanning electron microscope (SEM) image. It can be obtained by calculating the average value.

Furthermore, fibrous carbon nanostructures typically have an aspect ratio greater than 10. The aspect ratio of the fibrous carbon nanostructures was determined by measuring the diameter and length of 100 randomly selected fibrous carbon nanostructures using a scanning electron microscope or a transmission electron microscope. It can be obtained by calculating the average value of the ratio (length / diameter) to the length.

-BET specific surface area-
Further, the fibrous carbon nanostructure preferably has a BET specific surface area of 600 m ² / g or more, more preferably 800 m ² / g or more, preferably 2500 m ² / g or less, and 1200 m ^{2 or less.} More preferably, it is / g or less. If the BET specific surface area of the fibrous carbon nanostructure is within the above range, it is possible to provide a composite material having a higher tensile strength under high temperature conditions.
In the present invention, the "BET specific surface area" refers to the nitrogen adsorption specific surface area measured by using the BET method.

Further, it is preferable that the fibrous carbon nanostructure has an upwardly convex shape in the t-plot obtained from the adsorption isotherm. The "t-plot" can be obtained by converting the relative pressure into the average thickness t (nm) of the nitrogen gas adsorption layer in the adsorption isotherm of the fibrous carbon nanostructure measured by the nitrogen gas adsorption method. Can be done. That is, the above conversion is performed by obtaining the average thickness t of the nitrogen gas adsorption layer corresponding to the relative pressure from a known standard isotherm obtained by plotting the average thickness t of the nitrogen gas adsorption layer with respect to the relative pressure P / P0. Provides a t-plot of fibrous carbon nanostructures (t-plot method by de Boer et al.).

Here, in a substance having pores on the surface, the growth of the nitrogen gas adsorption layer is classified into the following processes (1) to (3). Then, the slope of the t-plot changes due to the following processes (1) to (3).
(1) Single-molecule adsorption layer formation process of nitrogen molecules on the entire surface (2) Multi-molecule adsorption layer formation and accompanying capillary condensation and filling process in the pores (3) Apparently the pores are filled with nitrogen Process of forming a multi-molecule adsorption layer on a non-porous surface

In the t-plot showing an upwardly convex shape, the plot is located on a straight line passing through the origin in the region where the average thickness t of the nitrogen gas adsorption layer is small, whereas when t is large, the plot is the straight line. The position is shifted downward from. The fibrous carbon nanostructures having such a t-plot shape have a large ratio of the internal specific surface area to the total specific surface area of the fibrous carbon nanostructures, and are abundant in the carbon nanostructures constituting the fibrous carbon nanostructures. It shows that the opening of is formed.

The bending point of the t-plot of the fibrous carbon nanostructure is preferably in the range satisfying 0.2 ≦ t (nm) ≦ 1.5, and 0.45 ≦ t (nm) ≦ 1.5. It is more preferable that it is in the range of 0.55 ≦ t (nm) ≦ 1.0. If the inflection point of the t-plot of the fibrous carbon nanostructure is within such a range, the dispersibility of the fibrous carbon nanostructure can be enhanced. Specifically, if the bending point value is less than 0.2, the fibrous carbon nanostructures are likely to aggregate and the dispersibility is lowered, and if the bending point value is more than 1.5, the fibrous carbon nanostructures are likely to aggregate. There is a risk that the structures will be easily entangled with each other and the dispersibility will be reduced.
The "position of the bending point" is the intersection of the approximate straight line A in the process (1) described above and the approximate straight line B in the process (3) described above.

Further, in the fibrous carbon nanostructure, the ratio (S2 / S1) of the internal specific surface area S2 to the total specific surface area S1 obtained from the t-plot is preferably 0.05 or more and 0.30 or less. When the value of S2 / S1 of the fibrous carbon nanostructure is within such a range, the dispersibility of the fibrous carbon nanostructure is enhanced, and the high temperature condition of the composite material obtained by the production method of the present invention is used in a small amount. The tensile strength underneath can be increased.
Here, the total specific surface area S1 and the internal specific surface area S2 of the fibrous carbon nanostructure can be obtained from the t-plot. Specifically, first, the total specific surface area S1 can be obtained from the slope of the approximate straight line in the process (1), and the external specific surface area S3 can be obtained from the slope of the approximate straight line in the process (3). Then, the internal specific surface area S2 can be calculated by subtracting the external specific surface area S3 from the total specific surface area S1.

Incidentally, the measurement of the adsorption isotherm of the fibrous carbon nanostructure, the creation of the t-plot, and the calculation of the total specific surface area S1 and the internal specific surface area S2 based on the analysis of the t-plot can be performed by, for example, a commercially available measuring device. "BELSORP (registered trademark) -mini" (manufactured by Nippon Bell Co., Ltd.) can be used.

Further, the fibrous carbon nanostructures containing CNTs suitable as fibrous carbon nanostructures preferably have a Radial Breathing Mode (RBM) peak when evaluated using Raman spectroscopy. RBM does not exist in the Raman spectrum of the fibrous carbon nanostructure composed of only three or more layers of multi-walled carbon nanotubes.

Further, in the fibrous carbon nanostructure containing CNT, the ratio (G / D ratio) of the G band peak intensity to the D band peak intensity in the Raman spectrum is preferably 0.5 or more and 5.0 or less. When the G / D ratio is 0.5 or more and 5.0 or less, the performance of the composite material obtained by the production method of the present invention can be further improved.

The fibrous carbon nanostructure containing CNT is not particularly limited, and is produced by using a known CNT synthesis method such as an arc discharge method, a laser ablation method, or a chemical vapor deposition method (CVD method). can do. Specifically, in the fibrous carbon nanostructure containing CNT, for example, a raw material compound and a carrier gas are supplied on a substrate having a catalyst layer for producing carbon nanotubes on the surface, and a chemical vapor deposition method (CVD) is performed. When CNTs are synthesized by the method), the catalytic activity of the catalyst layer is dramatically improved by the presence of a trace amount of oxidizing agent (catalyst activator) in the system (super growth method; International Publication No. 2006). It can be efficiently manufactured according to (see No. 011655). In the following, the carbon nanotubes obtained by the super growth method will be referred to as "SGCNT".
The fibrous carbon nanostructures produced by the super growth method may be composed of only SGCNTs, or in addition to SGCNTs, for example, other carbon nanostructures such as non-cylindrical carbon nanostructures. May include.

[Particular filler]
Further, the particulate filler that the composite mixture can optionally contain in the present invention is not particularly limited. Then, for example, a non-carbon filler can be used as the material of the particulate filler, and among them, talc (Mg ₃ Si ₄ O ₁₀ (OH) ₂ ), calcium carbonate (CaCO ₃ ), zinc oxide (ZnO) and the like are used. It is preferable, and it is more preferable to use talc. These may be used alone or in combination of two or more. In the present invention, the "particle shape" includes a spherical shape, an elliptical shape, a polygonal shape, a scaly shape, and the like.

-Average particle size-
Here, the average particle size of the particulate filler is preferably 0.5 μm or more, more preferably 1 μm or more, preferably 10 μm or less, and more preferably 8.5 μm or less. Further, it may be 5 μm or less. When the average particle size of the particulate filler is within the above range, a composite material having excellent tensile strength under high temperature conditions can be obtained. When the particulate filler is not spherical, the major axis of the particulate filler is the particle size of the particulate filler.
In addition, the average particle size of the particulate filler can be measured by using the measuring method described in the examples of the present specification.

-Mohs hardness-
Further, the Mohs hardness of the particulate filler is preferably 0.5 or more, more preferably 1.0 or more, preferably 3.5 or less, and more preferably 3.0 or less. It is preferably 2.0 or less, and more preferably 2.0 or less. When the Mohs hardness of the particulate filler is at least the above lower limit value, damage to the particulate filler can be prevented and a composite material having improved tensile strength can be obtained. Further, when the Mohs hardness of the particulate filler is not more than the above upper limit value, it is possible to prevent damage to the fibrous carbon nanostructures and provide a composite material having improved tensile strength.
Here, the Mohs hardness of the particulate filler can be measured using the method described in the examples of the present specification.

[Poor solvent]
When the method (1) described above is adopted in the preparation of the composite mixture, examples of the poor solvent to be used include water and cyclohexane. These can be used individually by 1 type or in combination of 2 or more types. Here, the poor solvent means a solvent having a rubber solubility of 10 g / 100 g or less at a temperature of 30 ° C. Specifically, for example, when FEPM is used as the rubber, cyclohexane, water, alcohols (isopropyl alcohol, methanol, etc.), ketones (methyl ethyl ketone, acetone, etc.) and the like can be mentioned as the poor solvent. When FKM is used as the rubber, cyclohexane, water and the like can be mentioned as the poor solvent. When NBR is used as the rubber, cyclohexane, water, alcohols (isopropyl alcohol, methanol, etc.) and the like can be mentioned as the poor solvent.

[Good solvent]
When the method (2) described above is adopted in the preparation of the composite mixture, examples of the good solvent to be used include tetrahydrofuran (THF) and methyl ethyl ketone (MEK). These can be used individually by 1 type or in combination of 2 or more types. Here, the good solvent means a solvent having a rubber solubility of 90 g / 100 g or more at a temperature of 30 ° C. Specifically, for example, when FEPM is used as the rubber, THF and the like can be mentioned as a good solvent. When FKM is used as the rubber, MEK or the like can be mentioned as a good solvent. When NBR is used as the rubber, MEK or the like can be mentioned as a good solvent.

-Content ratio of rubber and fibrous carbon nanostructures in the composite mixture-
The ratio of the content of rubber to the content of fibrous carbon nanostructures in the composite mixture is preferably 5 or more and 10 or more in terms of mass ratio (rubber / fibrous carbon nanostructures). Is more preferable, 15 or more is further preferable, 120 or less is preferable, 50 or less is more preferable, and 30 or less is further preferable. When the content ratio of the rubber and the fibrous carbon nanostructures in the composite mixture is within the above range, a composite material having increased tensile strength under high temperature conditions can be obtained.

-Content ratio of rubber and particulate filler in the composite mixture-
The ratio of the rubber content to the particulate filler content in the composite mixture is preferably 5 or more, more preferably 10 or more, and 15 or more in terms of mass ratio (rubber / particulate filler). It is more preferably 120 or less, more preferably 50 or less, and even more preferably 30 or less. When the content ratio of the rubber and the particulate filler in the composite mixture is within the above range, a composite material having higher tensile strength under high temperature conditions can be obtained.

-Content ratio of fibrous carbon nanostructures and particulate filler in the composite mixture-
Further, the ratio of the content of the fibrous carbon nanostructures to the content of the particulate fillers in the composite mixture is preferably 0.1 or more in terms of mass ratio (fibrous carbon nanostructures / particulate fillers). , 0.2 or more, more preferably 0.4 or more, particularly preferably 0.6 or more, preferably 12 or less, and more preferably 5 or less. It is more preferably 2 or less, and particularly preferably 1 or less. When the content ratio of the fibrous carbon nanostructure and the particulate filler in the composite mixture is within the above range, a composite material having further increased tensile strength under high temperature conditions can be obtained.

-Rubber solids concentration in composite mixture-
The solid content of the rubber in the composite mixture is preferably 2% by mass or more, more preferably 4% by mass or more, and 8% by mass or more in the composite mixture (100% by mass). It is more preferably 20% by mass or less, more preferably 16% by mass or less, and further preferably 12% by mass or less. When the concentration of the solid content of the rubber in the composite mixture is at least the above lower limit value, each component can be efficiently dispersed in the subsequent dispersion treatment. On the other hand, when the concentration of the solid content of the rubber in the composite mixture is not more than the above upper limit value, the solvent can be easily removed when the solvent is later removed.

Here, in the preparation of the composite mixture, the mixing of each component may be carried out by a known method. The order in which each of the above-mentioned components is mixed is not particularly limited, and all the components may be mixed at once, or a part of the components may be mixed and then the remaining components may be added and further mixed. You may.

When the method (1) described above is adopted in the preparation of the composite mixture, for example, a mixture containing a lump of rubber and an arbitrary particulate filler is pulverized to obtain a rubber and a particulate filler. After obtaining the pulverized mixture mixed with the above, the pulverized mixture and the remaining components may be mixed together. Alternatively, for example, rubber particles prepared by a known method such as pulverization or emulsion polymerization, fibrous carbon nanostructures, a poor solvent, and an arbitrary particulate filler may be mixed.

-Average particle size of rubber-
At that time, the mixture containing the lump of rubber and the particulate filler is pulverized until the rubber obtained by pulverization becomes rubber particles having an average particle size of preferably 1 mm or less, more preferably 0.5 mm or less. It is preferable to do so. By pulverizing the rubber into rubber particles having an average particle size of 1 mm or less, the dispersibility of the rubber in the composite material can be further enhanced.

The method for crushing the mixture containing the rubber lump and the particulate filler is not particularly limited, and the mixture containing the rubber lump and the particulate filler is crushed using a known crusher such as a freeze crusher. be able to. Further, the crushing conditions such as the crushing strength may be appropriately adjusted according to the desired particle size of the rubber particles obtained by crushing.

[Distributed processing]
Then, when the method (1) described above is used in the preparation of the composite mixture, a composition containing rubber, a poor solvent for rubber, fibrous carbon nanostructures, and an arbitrary particulate filler is dispersed. Process to obtain dispersion.
Further, when the method (2) described above is used in the preparation of the composite mixture, a composition containing rubber, a good solvent capable of dissolving the rubber, fibrous carbon nanostructures, and an arbitrary particulate filler. Disperse the material to obtain a dispersion.

The method for the dispersion treatment is not particularly limited, but the dispersion treatment is preferably performed by applying a shearing force to the composite mixture from the viewpoint that each component in the composite mixture can be uniformly dispersed.

Here, regarding the dispersion treatment in which a shearing force is applied to the composite mixture, a wet dispersion treatment using a medialess high-speed shearing machine will be described below as an example, but in the method for producing a composite material of the present invention, the dispersion treatment is performed. The method is not limited to the following example.

-Medialess high-speed shear machine-
As the medialess high-speed shearing machine, a known medialess high-speed shearing machine such as a high-speed stirrer, a homogenizer, and an in-line mixer, which can perform dispersion processing using a wet high-speed shearing force without using a dispersion medium, is used. be able to. By using a medialess high-speed shearing machine, it is possible to disperse a large amount of mixed liquid at one time in a short time as compared with a high-pressure type high-speed shearing machine such as a jet mill.

− Pressure −
Here, the pressure applied to the composite mixture in the wet dispersion treatment, that is, the pressure applied to the mixture from the supply of the composite mixture to the medialess high-speed shearing machine to the end of the wet dispersion treatment is 5 MPa in gauge pressure. It is preferably less than or equal to, and more preferably 4 MPa or less. Further, it is more preferable that the dispersion treatment of the mixed solution is performed under no pressure. When the pressure applied to the composite mixture is not more than the above upper limit value, damage to the fibrous carbon nanostructures and the particulate filler can be suppressed.

From the viewpoint of satisfactorily dispersing the fibrous carbon nanostructures and particulate filler under the condition that the pressure (gauge pressure) applied to the composite mixture is 5 MPa or less, the rotary medialess high speed shearing machine has a rotary medialess high speed. A shear machine is preferred, and a rotary homogenizer or an in-line rotor-stator mixer with a fixed stator and a rotor that rotates at high speed against the stator is preferred.

When a rotary homogenizer is used as the medialess high-speed shearing machine, the wet dispersion treatment is preferably performed under the condition that the blade peripheral speed is 5 m / sec or more. When the blade peripheral speed is 5 m / sec or more, the fibrous carbon nanostructures and the particulate filler can be sufficiently dispersed. The processing time is preferably 10 minutes or more and 300 minutes or less. Further, as the shape of the rotating portion, for example, a saw blade, a closed rotor, and a rotor / stator type are preferable. The slit width of the closed rotor or the minimum clearance of the rotor / stator is preferably 3 mm or less, and more preferably 1 mm or less.

Further, when an in-line rotor-stator type mixer is used as the medialess high-speed shearing machine, the wet dispersion treatment is preferably performed under the condition that the peripheral speed is 5 m / sec or more. When the peripheral speed is 5 m / sec or more, the fibrous carbon nanostructures and the particulate filler can be sufficiently dispersed. Further, the number of times the mixed solution passes through the rotating portion is preferably 10 times or more. By passing the mixed solution through the rotating portion 10 times or more, the fibrous carbon nanostructures and the particulate filler can be uniformly and satisfactorily dispersed. Further, the processing time is preferably 10 minutes or more and 300 minutes or less. Further, as the shape of the rotating portion, a slit type is preferable. The minimum rotor / stator clearance is preferably 3 mm or less, more preferably 1 mm or less. The slit width is preferably 2 mm or less, and more preferably 1 mm or less.

The wet dispersion treatment is preferably completed when the average bundle diameter of the fibrous carbon nanostructures in the dispersion obtained by the wet dispersion treatment is 10 μm or less, and is terminated when the average bundle diameter is 0.1 μm or less. It is more preferable to do so. When the average bundle diameter of the fibrous carbon nanostructures in the dispersion is 10 μm or less, the bundles of the fibrous carbon nanostructures are dispersed in a sufficiently loosened state. Here, if the average bundle diameter of the fibrous carbon nanostructures in the dispersion is 3 nm or more, the fibrous carbon nanostructures are dispersed without impairing the fiber shape. From this, it is preferable to end the wet dispersion treatment so that the average bundle diameter of the fibrous carbon nanostructures is 3 nm or more.

The average bundle diameter of the fibrous carbon nanostructures in the dispersion was 20 fibrous carbon nanostructures randomly selected by observing the dispersion separated during the wet dispersion treatment with a microscope. The bundle diameter of the bundle of structures can be measured and calculated by the arithmetic mean.

At the end of the wet dispersion treatment, the average bundle diameter of the fibrous carbon nanostructures can be used as an index.

[Removal of solvent]
Then, when the method (1) described above is used in the preparation of the composite mixture, the poor solvent is removed from the dispersion obtained by the dispersion treatment.
When the method (2) described above is used in the preparation of the composite mixture, the good solvent is removed from the dispersion obtained by the dispersion treatment.
Thereby, when any of the methods (1) and (2) is used, a composite mixture containing rubber, fibrous carbon nanostructures, and an arbitrary particulate filler can be obtained.

Here, the method for removing the poor solvent or the good solvent from the dispersion is not particularly limited, and a known method such as drying or filtration can be used. Above all, as a method for removing a poor solvent or a good solvent, it is preferable to combine filtration and drying. As the filtration, a known filtration method such as natural filtration, vacuum filtration, pressure filtration, and centrifugal filtration may be used. As the drying, vacuum drying, drying by flowing an inert gas, drying using a spray dryer and drying using a CD dryer are preferable, and vacuum drying, drying using a spray dryer and drying using a CD dryer are more preferable. ..

<Preliminary kneading process>
Then, in the method for producing a composite material of the present invention, in the pre-kneading step, a composite mixture containing rubber, fibrous carbon nanostructures, and an arbitrary particulate filler is kneaded. At this time, the kneading temperature needs to be higher than the kneading temperature in the main kneading step which is a subsequent step.
The composite mixture used in the pre-kneading step may contain rubber, fibrous carbon nanostructures, and an arbitrary particulate filler, and the method for preparing the composite mixture is limited to the above-mentioned preparation method. is not it. Therefore, a composite mixture may be prepared using commercially available rubber particles, fibrous carbon nanostructures, and an arbitrary particulate filler, and a pre-kneading step may be carried out, or the above-mentioned preparation method may be used. The pre-kneading step may be carried out using the composite mixture. It should be noted that each component contained in the composite mixture used in the pre-kneading step can be assumed to have been contained in the composite mixture in the above-mentioned method for preparing the composite mixture, and their preferred abundance ratios are described above. It is the same as the preferred abundance ratio of each component in the composite mixture.

[Kneading temperature]
The kneading temperature in the pre-kneading step needs to be higher than the kneading temperature in the main kneading step as a subsequent step. The kneading temperature in the pre-kneading step is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, further preferably 150 ° C. or higher, most preferably 200 ° C. or higher, and 300. The temperature is preferably 280 ° C. or lower, more preferably 250 ° C. or lower, and even more preferably 250 ° C. or lower. When the kneading temperature in the pre-kneading step is at least the above lower limit value, the rubber, the particulate filler, and the fibrous carbon nanostructures can be sufficiently kneaded. On the other hand, if the kneading temperature in the pre-kneading step is not more than the above upper limit value, decomposition and deterioration of the rubber can be suppressed.

[Kneading time]
The kneading time in the preliminary kneading step is not particularly limited, and may be, for example, 1 minute or more and 60 minutes or less.

[Kneading method]
Further, the pre-kneading method in the pre-kneading step is not particularly limited, and a known kneading device such as a kneader; a mixer such as a hovered mixer, a Bambari mixer, or a high-speed mixer; a biaxial kneading machine; a roll; is used. It can be carried out.

<Main kneading process>
Then, in the main kneading step, after the pre-kneading step, the pre-kneaded product obtained by the pre-kneading step is further kneaded at a temperature lower than the kneading temperature in the pre-kneading step.

[Kneading temperature]
Here, the kneading temperature in the main kneading step needs to be lower than the kneading temperature in the pre-kneading step. The kneading temperature in this kneading step is preferably 60 ° C. or lower, more preferably 50 ° C. or lower, further preferably 40 ° C. or lower, preferably 5 ° C. or higher, and 10 ° C. The above is more preferable. When the kneading temperature in the main kneading step is within the above range, the rubber, the particulate filler, and the fibrous carbon nanostructures can be sufficiently kneaded.
[Kneading time]
The kneading time in the main kneading step is not particularly limited, and can be, for example, 1 minute or more and 60 minutes or less.

[Kneading method]
Further, the main kneading method in the main kneading step is not particularly limited, and can be carried out by using the known kneading apparatus exemplified in the preliminary kneading step. According to the present invention, a composite material having excellent tensile strength under high temperature conditions can be obtained after the kneading step.
The obtained composite material is further mixed with, for example, a cross-linking agent, a reinforcing material, an antioxidant, etc. as an arbitrary compounding agent for rubber, kneaded, and molded and cross-linked to obtain a desired molded product. You can also. Here, kneading, molding and crosslinking can be carried out using known methods and devices. Since the main kneading step is carried out at a kneading temperature lower than that of the pre-kneading step, for example, even when a cross-linking agent is added, the fibrous carbon nanostructures can be cross-linked while being well dispersed. ..

The composite material obtained by the method for producing a composite material of the present invention conforms to JIS K7194 and has a volume resistivity of 1.0 × 10 ² Ωcm or less measured by a four-probe method using a resistivity meter. It is preferable to have. Here, the reason why the volume resistance of the composite material obtained by the production method of the present invention is low is not clear, but the viscosity of the rubber decreases due to the heat during kneading in the pre-kneading step, and the fibrous carbon nanostructures. Invasion of rubber into the gap between the fibrous carbon nanostructure and the fibrous carbon nanostructure disperses the fibrous carbon nanostructure and contributes to the formation of a network of the fibrous carbon nanostructure, and the volume resistance of the composite material It is presumed that it contributes to the decrease in.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.
The average particle size and Mohs hardness of the filler in the examples, the complex viscosity of the rubber in each example and each comparative example, the ratio of rubber to CNT, the ratio of CNT to filler, and the ratio of CNT to filler, and each example and The tensile strength of the rubber sheet produced in each comparative example was measured using the following method.

<Average particle size of filler>
The average particle size of the fillers used in Examples and Comparative Examples was measured by the sedimentation method. Specifically, the particle size distribution was measured by the centrifugal sedimentation method according to JIS R1619. Then, the median diameter in the obtained particle size distribution was taken as the average particle size of the filler.

<Mohs hardness>
The Mohs hardness of the fillers used in Examples and Comparative Examples was measured by a Mohs hardness tester. Here, the Mohs hardness tester is an instrument used to measure the "scratch hardness" of minerals, and is composed of 10 types of standard minerals having different hardnesses. In this example and the comparative example, in order to measure the Mohs hardness of the filler, the surface of the filler was scratched using a standard mineral of a Mohs hardness tester, and it was confirmed whether or not the surface was scratched. When the surface of the filler was not scratched, the scratching operation was repeated until the surface of the filler was scratched using a standard mineral having a higher hardness. When the surface of the filler is scratched, the scratched filler scratches the surface of the standard mineral of the Mohs hardness tester, and the hardness of the standard mineral when both the filler and the standard mineral are scratched. Was defined as the hardness of the filler.

<Complex viscosity (η ^* )>
As a rheometer, a viscoelasticity measuring device (manufactured by Alpha Technologies, product name "Rubber Process Analyzer RPA-2000") was used under the condition of a shear rate of 0.1 (1 / s) at the kneading temperature of the pre-kneading step. , The complex viscosity (η ^* ) of rubber was measured. The results are shown in Table 1.

<Ratio of rubber to CNT, ratio of CNT to filler, and ratio of CNT to filler>
Using the amounts of rubber, filler and CNT used in Examples and Comparative Examples, the ratio of rubber to CNT, the ratio of CNT to filler, and the ratio of CNT to filler were determined. The results are shown in Table 1.

<Tensile strength>
The obtained rubber sheet was punched into a dumbbell test piece (JIS No. 3) to prepare a test piece. Using a tensile tester (Strograph VG, manufactured by Toyo Seiki Co., Ltd.), the test temperature is 230 ° C, 200 ° C or 120 ° C, the test humidity is 50%, and the tensile speed is 500 ± 50 mm / min in accordance with JIS K6251: 2010. A tensile test was performed below, and the tensile strength (the maximum tensile force recorded when the test piece was pulled until it was cut divided by the initial cross-sectional area of the test piece) was measured. The larger the tensile strength value, the better the tensile strength under high temperature conditions.

(Example 1)
FKM as fluororubber (vinylidene fluoride rubber, manufactured by Chemers, product name "Baiton GBL600S" 100 parts by mass and talc as filler (manufactured by Takehara Chemical Industry Co., Ltd., product name "TT talc", composition: Mg ₃ Si ₄ O ₁₀ (OH) ₂ , average particle size: 8.5 μm, talc hardness: 1) 5 parts by mass was put into a freezing crusher (manufactured by Powder Giken Co., Ltd., liquid nitrogen cooling), and the average particle size. The mixture was pulverized until FKM particles having a size of about 400 μm were obtained to obtain a pulverized mixture containing FKM and talc.
Next, 55 g (105 parts by mass) of the obtained pulverized mixture, 495 g of ion-exchanged water as a poor solvent for FKM, and carbon nanotubes as fibrous carbon nanostructures (manufactured by Zeon Nanotechnology) were placed in a 0.9 L glass bottle. , Product name "ZEONANO SG101", SGCNT, specific gravity: 1.7, average diameter: 3.5 nm, average length: 400 μm, BET specific surface area: 1050 m ² / g, G / D ratio: 2.1, t-plot (Convex upward) 2.2 g (4 parts by mass) was added and these were mixed.
Then, using a medialess shearing machine (manufactured by Primix Corporation, stirring blade "Neomixer (registered trademark)" rotor / stator, minimum clearance 0.5 mm), the temperature is 40 ° C. and the rotation speed is 17,000 rpm (blade peripheral speed: 24 m / sec). The dispersion treatment was carried out for 30 minutes to obtain a slurry-like mixed solution containing FKM, talc, ion-exchanged water, and carbon nanotubes (rubber solid content concentration in the mixed solution: 10% by mass). This dispersion treatment was repeated until a required amount of slurry was obtained.
Then, the obtained slurry was air-dried to remove ion-exchanged water as a poor solvent. Then, it was vacuum-dried at a temperature of 80 ° C. for 12 hours using a vacuum dryer (manufactured by Yamato Scientific Co., Ltd.) to obtain a composite mixture containing FKM, talc, and carbon nanotubes.
Next, 87.4 g of the obtained composite mixture was kneaded at a kneading temperature of 100 ° C. for 3 minutes using a lab plast mill (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name “10C100”, capacity: 60 ml, 50 rpm). , Kneaded (preliminary kneading process).
Further, 109 parts by mass of the pre-kneaded product (100 parts by mass of FKM / 5 parts by mass of talc / 4 parts by mass of CNT), 3 parts by mass of zinc oxide (zinc oxide type 2) as a cross-linking aid, and 3 parts by mass of zinc oxide as a first cross-linking agent. Triallyl isocyanurate (manufactured by Nihon Kasei Co., Ltd., product name "TAIC (registered trademark)") 3 parts by mass and 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as a second cross-linking agent (Manufactured by Nihon Kasei Co., Ltd., product name "Perhexa 25B-40") After adding 2 parts by mass, knead them with a roll at a kneading temperature of 5 ° C while cooling them with water (main kneading step), and perform primary vulcanization. Treatment with (160 ° C., 15 minutes) and secondary vulcanization (232 ° C., 2 hours) was performed to obtain a rubber sheet having a thickness of 2 mm.
Using the obtained rubber sheet, a tensile strength test was conducted at a test temperature of 200 ° C. The results are shown in Table 1.

(Example 2)
A rubber sheet was obtained in the same manner as in Example 1 except that the kneading temperature in the pre-kneading step was changed to 150 ° C. Then, using the obtained rubber sheet, a tensile strength test was conducted at a test temperature of 200 ° C. The results are shown in Table 1.

(Example 3)
A rubber sheet was obtained in the same manner as in Example 1 except that the kneading temperature in the pre-kneading step was changed to 200 ° C. Then, using the obtained rubber sheet, a tensile strength test was conducted at a test temperature of 200 ° C. The results are shown in Table 1.

(Example 4)
A rubber sheet was obtained in the same manner as in Example 1 except that the kneading temperature in the pre-kneading step was changed to 230 ° C. Then, using the obtained rubber sheet, a tensile strength test was conducted at a test temperature of 200 ° C. The results are shown in Table 1.

(Example 5)
Instead of FKM, FEPM (tetrafluoroethylene-propylene rubber, manufactured by AGC, product name "Afras 100S", 100% insoluble in cyclohexane) was used. Further, the amount of carbon nanotubes to be added was changed so that the amount of carbon nanotubes added as the fibrous carbon nanostructure was 3 parts by mass. Further, 495 g of cyclohexane was used instead of ion-exchanged water as a poor solvent. Other than that, a composite mixture was obtained in the same manner as in Example 1. Then, the pre-kneading step was performed in the same manner as in Example 1 except that the kneading temperature in the pre-kneading step was changed to 230 ° C.
Further, 108 parts by mass of pre-kneaded product (100 parts by mass of FEPM / 5 parts by mass of talc / 3 parts by mass of CNT), 5 parts by mass of carbon black (manufactured by Cancurve, product name "Thermax (registered trademark) MT") and 5 parts by mass. 5 parts by mass of triallyl isocyanurate (manufactured by Nihon Kasei Co., Ltd., product name "TAIC (registered trademark)") as the first cross-linking agent and 1,3-bis (t) which is an organic peroxide as the second cross-linking agent. -Butyl peroxyisopropyl) benzene (manufactured by Nihon Kasei Co., Ltd., product name "Peroxymon F-40") 2.5 parts by mass and 1 part by mass of Ca stearate are added, and these are kneaded at a kneading temperature of 5 ° C. while cooling with water. , Kneaded using a roll (main kneading step), and subjected to primary vulcanization (170 ° C., 20 minutes) and secondary vulcanization (200 ° C., 4 hours) to obtain a rubber sheet having a thickness of 2 mm. ..
Using the obtained rubber sheet, the tensile strength was measured at a test temperature of 230 ° C. The results are shown in Table 1.

(Example 6)
Instead of the FKM lump, a lump of NBR (nitrile rubber, manufactured by Zeon Corporation, product name "Nipol (registered trademark) DN3350", 100% insoluble in cyclohexane) was used. Further, the amount of carbon nanotubes to be added was changed so that the amount of carbon nanotubes added as the fibrous carbon nanostructure was 10 parts by mass. Further, 495 g of cyclohexane was used instead of ion-exchanged water as a poor solvent. Other than that, a composite mixture was obtained in the same manner as in Example 1, and a pre-kneading step was performed.
Further, 115 parts by mass of the pre-kneaded product (100 parts by mass of NBR / 5 parts by mass of talc / 10 parts by mass of CNT), 5 parts by mass of zinc oxide (two types of zinc oxide) as a cross-linking aid, and 1 part by mass of stearic acid. , 0.5 parts by mass of sulfur (S # 325) as a vulcanizing agent, and tetramethylthiuram disulfide (manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., product name "Noxeller TT") as a first vulcanization accelerator 1.5 After adding 1.5 parts by mass and 1.5 parts by mass of N-cyclohexyl-2-benzothiazolyl sulfeneamide (manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., product name "Noxeller CZG") as a second vulcanization accelerator. These were kneaded with a roll at a kneading temperature of 50 ° C. (main kneading step) and vulcanized (160 ° C. for 10 minutes) to obtain a rubber sheet having a thickness of 2 mm.
Using the obtained rubber sheet, the tensile strength was measured at a test temperature of 120 ° C. The results are shown in Table 1.

(Comparative Example 1)
A rubber sheet having a thickness of 2 mm was obtained in the same manner as in Example 1 except that the pre-kneading step was not performed. Using the obtained rubber sheet, a tensile strength test was conducted at a test temperature of 200 ° C. The results are shown in Table 1.

(Comparative Example 2)
A rubber sheet having a thickness of 2 mm was obtained in the same manner as in Example 5 except that the pre-kneading step was not performed. Using the obtained rubber sheet, a tensile strength test was conducted at a test temperature of 230 ° C. The results are shown in Table 1.

(Comparative Example 3)
A rubber sheet having a thickness of 2 mm was obtained in the same manner as in Example 6 except that the pre-kneading step was not performed. Using the obtained rubber sheet, a tensile strength test was conducted at a test temperature of 120 ° C. The results are shown in Table 1.

In Table 1 shown below, "CNT" indicates carbon nanotubes, "FKM" indicates vinylidene fluoride rubber, "FEPM" indicates ethylene tetrafluoride-propylene rubber, and "NBR" indicates acrylonitrile. Indicates butadiene rubber, and "CHX" indicates cyclohexane.

From Table 1, in Examples 1 to 6 in which the pre-kneading step and the main kneading step were performed and the kneading temperature in the pre-kneading step was higher than the kneading temperature in the main kneading step, the tensile strength of the obtained rubber sheet was high. You can see that.
On the other hand, in Comparative Example 1, since the pre-kneading step was not performed, the tensile strength of the obtained rubber sheet was lower than the tensile strength of the rubber sheets of Examples 1 to 4 obtained by using the same type of rubber. You can see that it is doing.
Further, in Comparative Example 2, since the pre-kneading step was not performed, the tensile strength of the obtained rubber sheet was lower than the tensile strength of the rubber sheet of Example 5 obtained by using the same type of rubber. You can see that there is.
Further, in Comparative Example 3, since the pre-kneading step was not performed, the tensile strength of the obtained rubber sheet was lower than the tensile strength of the rubber sheet of Example 6 obtained by using the same type of rubber. You can see that there is.

According to the method for producing a composite material of the present invention, a composite material having excellent tensile strength under high temperature conditions can be produced.

Claims (9)

A pre-kneading step of kneading a composite mixture containing rubber and a fibrous carbon nanostructure to obtain a pre-kneaded product,
After the pre-kneading step, the main kneading step of kneading the pre-kneaded product is further included.
A method for producing a composite material, wherein the kneading temperature in the pre-kneading step is higher than the kneading temperature in the main kneading step. The composite mixture is
A procedure for obtaining a dispersion by dispersing a composition containing the rubber, a poor solvent for the rubber, and the fibrous carbon nanostructures.
The method for producing a composite material according to claim 1, which is obtained through a procedure for removing the poor solvent from the obtained dispersion. The composite mixture is
A procedure for obtaining a dispersion by dispersing a composition containing the rubber, a good solvent capable of dissolving the rubber, and the fibrous carbon nanostructures.
The method for producing a composite material according to claim 1, which is obtained through a procedure for removing the good solvent from the obtained dispersion. The method for producing a composite material according to any one of claims 1 to 3, wherein the composite mixture contains a particulate filler. The rubber has a complex viscosity of 200,000 Pa · s or less under the condition of a shear rate of 0.1 (1 / s) at the kneading temperature of the pre-kneading step, according to any one of claims 1 to 4. The method for producing a composite material according to the description. The method for producing a composite material according to any one of claims 1 to 5, wherein the kneading temperature in the pre-kneading step is 80 ° C. or higher. The method for producing a composite material according to any one of claims 1 to 6, wherein the rubber is at least one selected from the group consisting of fluororubber, nitrile rubber and hydrogenated nitrile rubber. The method for producing a composite material according to any one of claims 1 to 7, wherein the fibrous carbon nanostructure contains carbon nanotubes. The method for producing a composite material according to any one of claims 1 to 8, wherein the fibrous carbon nanostructure has a BET specific surface area of 600 m ^{2 / g or more.}