JP2021147474A - Method for producing rubber composition - Google Patents

Abstract

To produce a rubber composition comprising a rubber and a fibrous carbon nanostructure and having high tensile strength and a low volume resistivity.SOLUTION: There is provided a method for producing a rubber composition which comprises: a mixing step of mixing rubber particles, a fibrous carbon nanostructure and a poor solvent of the rubber particles to obtain a mixed solution; a dispersion step of subjecting the mixed solution to dispersion treatment using a dispersion machine to obtain a dispersion liquid and a dispersion medium removing step of removing a poor solvent from the dispersion liquid, wherein the rubber particles are composed of a rubber having a loss modulus G" of 180 kPa or less at 70°C and have an average particle diameter of 0.01 mm or more and less than 0.1 mm and the absolute value of the difference (Ra1-Ra2) between the Hansen solubility parameter distance Ra1 between the rubber and the poor solvent and the Hansen solubility parameter distance Ra2 between the fibrous carbon nanostructure and the poor solvent is 4 or less.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a rubber composition, and more particularly to a method for producing a rubber composition containing rubber and fibrous carbon nanostructures.

Since fibrous carbon nanostructures such as carbon nanotubes (hereinafter sometimes referred to as "CNT") are excellent in conductivity, thermal conductivity, sliding properties, mechanical properties, etc., 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. Development of technology to provide composite materials that have both body characteristics 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, by preparing a composite material using a dispersion liquid in which the fibrous carbon nanostructures and rubber are dispersed in a dispersion medium, the fibrous carbon nanostructures are uniformly dispersed in the rubber matrix. Techniques for obtaining materials have been proposed.

Specifically, for example, in Patent Document 1, rubber particles having an average particle size of 0.10 mm or more and 2.00 mm or less, a fibrous carbon nanostructure, and a poor solvent for the rubber particles were mixed and obtained. It is disclosed that after the mixed solution is dispersed using a medialess disperser, the poor solvent is removed from the obtained dispersion to produce a rubber composition containing rubber and fibrous carbon nanostructures. Has been done.

International Publication No. 2019/180993

However, the rubber composition produced by the above-mentioned conventional production method has room for improvement in that the tensile strength is further increased and the volume resistivity is reduced to improve the conductivity.

Therefore, an object of the present invention is to provide a method for producing a rubber composition, which comprises a rubber and a fibrous carbon nanostructure and can produce a rubber composition having a high tensile strength and a low volume resistivity. do.

The present inventors have made extensive studies to achieve the above object. Then, the present inventors use a disperser to mix a mixed solution containing rubber particles having a predetermined average particle size made of rubber having a predetermined property, a fibrous carbon nanostructure, and a predetermined dispersion medium. The present invention has been completed by finding that a rubber composition in which fibrous carbon nanostructures are well dispersed can be produced by carrying out the dispersion treatment.

That is, the present invention aims to advantageously solve the above-mentioned problems, and the method for producing a rubber composition of the present invention is poor in rubber particles, fibrous carbon nanostructures, and the rubber particles. A mixing step of mixing a solvent to obtain a mixed solution, a dispersion step of dispersing the mixed solution using a disperser to obtain a dispersion, and a dispersion medium removing step of removing the poor solvent from the dispersion. The rubber particles are made of rubber having a loss elasticity G'' at 70 ° C. of 180 kPa or less, and have an average particle size of 0.01 mm or more and less than 0.1 mm, and the rubber and the poor solvent. The absolute value of the difference (Ra1-Ra2) between the Hansen solubility parameter distance Ra1 and the Hansen solubility parameter distance Ra2 between the fibrous carbon nanostructure and the poor solvent is 4 or less. As described above, if the poor solvent is removed from the dispersion obtained by dispersing the rubber particles having the predetermined properties, the fibrous carbon nanostructures, and the predetermined poor solvent, the fibrous carbon It is possible to produce a rubber composition having high tensile strength and low volumetric resistance in which nanostructures are well dispersed.
In the present invention, the “elastic modulus G''” and the “average particle size” can be measured by using the methods described in the examples.

Here, in the method for producing a rubber composition of the present invention, the mixed solution contains the fibrous carbon nanostructures in a proportion of 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber particles. Is preferable. When the content of the fibrous carbon nanostructures is within the above range, the dispersibility of the fibrous carbon nanostructures in the rubber composition can be further enhanced.

In addition, the method for producing a rubber composition of the present invention includes at least one of the rubber particles selected from the group consisting of fluororubber particles, silicone rubber particles, hydrogenated nitrile rubber particles, acrylic rubber particles and nitrile rubber particles. Is preferable. By using these rubber particles, it is possible to provide a rubber composition having excellent properties such as oil resistance and aging resistance.

Further, the method for producing a rubber composition of the present invention preferably includes a pulverization step of pulverizing the rubber in the absence of a dusting agent to obtain the rubber particles before the mixing step. By using the rubber particles obtained by crushing the rubber in the absence of a dusting agent, the tensile strength of the rubber composition can be further improved and the volume resistivity can be further reduced.

In the method for producing a rubber composition of the present invention, examples of the dusting agent include talc, barium sulfate, silica, calcium carbonate, clay and carbon black.

Then, in the method for producing a rubber composition of the present invention, it is preferable that the disperser uses a medium. By using a disperser that applies a collision force using a medium, the tensile strength of the rubber composition can be further improved and the volume resistivity can be further reduced.

According to the present invention, it is possible to produce a rubber composition having a high tensile strength and a low volume resistivity.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the method for producing a rubber composition of the present invention is used when producing a rubber composition containing a rubber and a fibrous carbon nanostructure. The rubber composition produced by using the method for producing a rubber composition of the present invention is particularly limited because the fibrous carbon nanostructures are well dispersed and have high tensile strength and low volumetric resistance. However, it is useful for manufacturing, for example, sealing materials, hoses, belts, anti-vibration rubbers, diaphragms, electrodes for wearable devices, and the like.

(Manufacturing method of rubber composition)
In the method for producing a rubber composition of the present invention, a rubber composition containing a rubber and a fibrous carbon nanostructure and optionally further containing an additive such as a dispersant is produced. The method for producing a rubber composition of the present invention comprises rubber having a loss elastic modulus G'' at 70 ° C. of 180 kPa or less and having an average particle size of 0.01 mm or more and less than 0.1 mm. , The mixing step of mixing the fibrous carbon nanostructure and the poor solvent of the rubber particles to obtain a mixed solution, and the mixed solution obtained in the mixing step are dispersed using a disperser to obtain a dispersion. It includes a dispersion step and a dispersion medium removal step of removing a poor solvent from the dispersion obtained in the dispersion step. Further, in the method for producing a rubber composition of the present invention, the difference between the Hansen solubility parameter distance Ra1 between the rubber and the poor solvent and the Hansen solubility parameter distance Ra2 between the fibrous carbon nanostructure and the poor solvent as the poor solvent ( A solvent having an absolute value of Ra1-Ra2) of 4 or less is used.

Then, according to the method for producing a rubber composition of the present invention, a mixed solution containing predetermined rubber particles, fibrous carbon nanostructures, and a predetermined poor solvent is dispersed and treated using a disperser. Therefore, it is possible to obtain a rubber composition in which the fibrous carbon nanostructures are well dispersed. Further, the rubber composition can be efficiently produced as compared with the case where rubber is added after preparing the dispersion liquid of the fibrous carbon nanostructures or the case where the dispersion treatment is performed under high pressure.

The method for producing the rubber composition of the present invention may include steps other than the above-mentioned steps. Specifically, the method for producing a rubber composition of the present invention is a crushing step of crushing rubber to obtain rubber particles having an average particle size of 0.01 mm or more and less than 0.1 mm as an optional step prior to the mixing step. May further be included.
Further, the rubber composition produced according to the method for producing a rubber composition of the present invention has a dusting agent (for example, talc, barium sulfate, silica, calcium carbonate, etc.) from the viewpoint of improving tensile strength and reducing volume resistivity. It is preferable that it does not contain particles such as clay or carbon black.

<Crushing process>
In the pulverization step, rubber having a loss elastic modulus G'' at 70 ° C. of 180 kPa or less is pulverized to obtain rubber particles having an average particle size of 0.01 mm or more and less than 0.1 mm. By including a step of crushing rubber into rubber particles having the average particle size, the production method of the present invention uses a desired rubber type regardless of whether the rubber particles having the average particle size are commercially available. Can be carried out.

Here, the rubber in the pulverization step is preferably pulverized by a freeze pulverization method. Specifically, the freeze-crushing method is a method in which a rubber mass is cooled to a temperature equal to or lower than the glass transition temperature (Tg) of the rubber and then crushed to obtain rubber particles.

The temperature at which freeze crushing is performed is not particularly limited as long as it is a temperature equal to or lower than the Tg of the rubber to be crushed, but is preferably a temperature 10 ° C. or higher lower than the Tg of the rubber, and a temperature 100 ° C. or higher lower than the Tg of the rubber. More preferred. By freezing and pulverizing at these temperatures, the rubber mass can be efficiently pulverized into the rubber particles having the above average particle size.
The crushing method is not particularly limited, and can be carried out using a known freezing crusher or the like.
The cooling method is not particularly limited, and a cooling agent suitable for the freeze crusher to be used may be selected. For example, it can be cooled by using liquid nitrogen (about -196 ° C.) or the like as a cooling agent.
The size and shape of the rubber block to be crushed are not particularly limited, and may be a size and shape that can be freeze-crushed by the freeze-crusher used. Specifically, one having a major axis diameter of more than 2.0 mm to 1.0 cm, which is the length of the longest axis in one rubber block, can be used. Further, the shape and the number of rubber lumps that can be used are not limited as long as they can be put into the freeze crusher.

In the pulverization step, it is preferable that no dusting agent (also referred to as “powder fluidity improver”) is used (that is, pulverization is performed in the absence of the dusting agent). If no dusting agent is used, the tensile strength of the obtained rubber composition can be further improved and the volume resistivity can be further reduced.
In the method for producing a rubber composition of the present invention, rubber having a loss elastic modulus G'' at 70 ° C. of 180 kPa or less is used, so that the obtained rubber particles can be obtained without using a dusting agent. It is hard to adhere and the rubber particles are easy to handle.

When a commercially available product is used as the rubber particles having a predetermined average particle size without performing the crushing step as an optional step, it is preferable to use the rubber particles to which the dusting agent particles are not attached.

Here, examples of the dusting agent include particles such as talc, barium sulfate, silica, calcium carbonate, clay, and carbon black, and in particular, particles such as talc, clay, and calcium carbonate.

<Mixing process>
In the mixing step, a mixed solution is prepared by mixing rubber particles having a predetermined average particle size made of rubber having predetermined properties, a fibrous carbon nanostructure, a poor solvent for the rubber particles, and an arbitrary additive. do.

[Rubber particles]
Here, the rubber particles are not particularly limited as long as they have a loss elastic modulus G'' at 70 ° C. of 180 kPa or less, and rubber particles derived from any of the known rubber types are used. Can be done. Above all, from the viewpoint of improving the characteristics of the obtained rubber composition, the rubber particles are selected from at least a group consisting of fluororubber particles, silicone rubber particles, hydride nitrile rubber particles, acrylic rubber particles and nitrile rubber particles. It is preferable to use one kind, and it is more preferable to use fluororubber particles. The elastic modulus G ″ of the rubber at 70 ° C. is preferably 160 kPa or less, and more preferably 150 kPa or less.
As the rubber particles, one type may be used alone, or two or more types may be used in combination.

The fluororubber constituting the fluororubber particles suitable as the rubber particles is not particularly limited, and is, for example, tetrafluoroethylene propylene-based rubber (FEPM), fluorovinylidene-based rubber (FKM), or tetrafluoride. Examples thereof include ethylene-perfluoromethylvinyl ether-based rubber (FFKM) and tetrafluoroethylene-based rubber (TFE). Among these, as the fluororubber, vinylidene fluoride-based rubber (FKM) and ethylene tetrafluoride-perfluoromethyl vinyl ether-based rubber (FFKM) are preferable.

The average particle size of the rubber particles needs to be in the range of 0.01 mm or more and less than 0.1 mm, the lower limit value is preferably 0.03 mm or more, and more preferably 0.05 mm or more. The upper limit is preferably 0.09 mm or less, and more preferably 0.08 mm or less. By setting the average particle size of the rubber particles within the above range, the dispersibility of the fibrous carbon nanostructures can be enhanced.
The rubber particles usually have an aspect ratio (major axis diameter / minor axis diameter) of 1 or more and 10 or less.

[Fibrous carbon nanostructures]
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 fibrous carbon nanostructures containing CNTs, it is possible to efficiently impart conductivity and excellent mechanical properties even with a small amount of compounding, improve the tensile strength of the rubber composition, and increase the volume. This is because the resistivity can be lowered.

Here, the fibrous carbon nanostructures containing CNTs may be composed of only CNTs, or may be a mixture of CNTs and fibrous carbon nanostructures other than CNTs.
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. This is because the smaller the number of layers of carbon nanotubes, the better the conductivity of the rubber composition and the lower the volume resistivity even if the blending amount 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 and the tensile strength of the rubber composition can be improved. Further, when the average diameter of the fibrous carbon nanostructures is 60 nm or less, conductivity can be efficiently imparted to the rubber composition even with a small blending amount. Therefore, if the average diameter of the fibrous carbon nanostructures is within the above range, the tensile strength of the rubber composition can be sufficiently improved and the volume resistivity can be sufficiently reduced.
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 0.60, 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 0.60, the performance of the produced rubber composition 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 rubber composition can be improved with a small blending amount. When the average length is 600 μm or less, the dispersibility in the rubber composition can be enhanced.
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.

In addition, 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.

Further, the fibrous carbon nanostructure preferably has a BET specific surface area of 200 m ² / g or more, more preferably 400 m ² / g or more, and further preferably 600 m ² / g or more. It is preferably 2000 m ² / g or less, ^{more preferably 1800 m 2} / g or less, and even more preferably 1600 m ² / g or less. When the BET specific surface area of the fibrous carbon nanostructure is 200 m ² / g or more, the dispersibility of the fibrous carbon nanostructure can be enhanced, and the tensile strength of the rubber composition can be increased with a small blending amount. Further, when the BET specific surface area of the fibrous carbon nanostructure is 2000 m ² / g or less, the conductivity of the rubber composition can be stabilized.
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" is 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 the accompanying condensing and filling process of capillary tubes 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 a region where the average thickness t of the nitrogen gas adsorption layer is small, whereas when t is large, the plot is in 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. When the bending 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, and the tensile strength of the rubber composition can be increased with a small blending amount. Specifically, if the value of the bending point is less than 0.2, the fibrous carbon nanostructures are likely to aggregate and the dispersibility is lowered, and if the value of the bending point 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 can be enhanced, and the tensile strength of the rubber composition can be increased with a small blending amount.
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, which are 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 produced rubber composition 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 phase growth 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). / 011655), it can be manufactured efficiently. In the following, the carbon nanotubes obtained by the super growth method may 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.

The amount of the fibrous carbon nanostructure to be blended in the mixed solution is preferably 0.1 part by mass or more, and more preferably 0.5 part by mass or more, per 100 parts by mass of the rubber particles described above. It is preferably 1.0 part by mass or more, more preferably 3.0 part by mass or more, further preferably 4.0 part by mass or more, and 20 parts by mass or less. Is more preferable, and it is more preferably 15 parts by mass or less, and further preferably 10 parts by mass or less. When the amount of the fibrous carbon nanostructures is at least the above lower limit value, the tensile strength of the rubber composition can be sufficiently improved and the volume resistivity can be sufficiently reduced. Further, when the amount of the fibrous carbon nanostructures is equal to or less than the above upper limit value, the dispersibility of the fibrous carbon nanostructures in the rubber composition is lowered and unevenness in the performance of the rubber composition is suppressed. be able to. Therefore, if the amount of the fibrous carbon nanostructures is within the above range, a rubber composition having high tensile strength and low volume resistivity can be obtained.

[Poor solvent]
In the production method of the present invention, a poor solvent for rubber particles is used as the dispersion medium, which does not dissolve the rubber particles but can disperse the rubber particles and the fibrous carbon nanostructures.
Here, the poor solvent of the rubber particles means that the rubber particles having the above-mentioned average particle size are immersed in the poor solvent having a mass of 5 times or more, and after 72 hours, the rubber particles are filtered through a 40-mesh net. It refers to a solvent in which the insoluble content remaining on the net is 80% by mass or more.
By using a poor solvent for rubber particles as the dispersion medium, most of the rubber particles remain undissolved in the mixed solution, and the rubber particles themselves are also loosened during the dispersion treatment while loosening the bundle of fibrous carbon nanostructures. By being pulverized, the fibrous carbon nanostructures can be satisfactorily dispersed.

As the poor solvent, the absolute value of the difference (Ra1-Ra2) between the Hansen solubility parameter distance Ra1 with the rubber constituting the rubber particles and the Hansen solubility parameter distance Ra2 with the fibrous carbon nanostructure is 4 or less. Use a poor solvent.
The absolute value of the above-mentioned difference (Ra1-Ra2) is preferably 0.5 or more and 3.5 or less.

Here, the Hansen solubility parameter distance Ra1 between the rubber and the poor solvent is preferably 7.5 or more, more preferably 8.0 or more, preferably 20.0 or less, and 17.5. The following is more preferable. When Ra1 is within the above range, the fibrous carbon nanostructures can be more well dispersed in the rubber composition.
The "Hansen solubility parameter distance Ra1 between rubber and poor solvent" can be calculated using the following formula (1).
Ra1 = {4 × (δ _d1- δ _d2 ) ² + (δ _p1- δ _p2 ) ² + (δ _h1- δ _h2 ) ² } ^1/2 ... (1)
δ _d1 : Rubber dispersion term δ _d2 : Poor solvent dispersion term δ _p1 : Rubber polarity term δ _p2 : Poor solvent polarity term δ _h1 : Rubber hydrogen bond term δ _h2 : Poor solvent hydrogen bond term

The Hansen solubility parameter distance Ra2 between the fibrous carbon nanostructure and the poor solvent is preferably 8.0 or more, more preferably 9.0 or more, and preferably 15.0 or less. , 14.0 or less is more preferable. When Ra2 is within the above range, the bundle structure of the fibrous carbon nanostructures can be defibrated satisfactorily, and the fibrous carbon nanostructures can be more satisfactorily dispersed in the rubber composition.
The "Hansen solubility parameter distance Ra2 between the fibrous carbon nanostructure and the poor solvent" can be calculated using the following formula (2).
Ra2 = {4 × (δ _{d3 −} δ _d2 ) ² + (δ _{p3 −} δ _p2 ) ² + (δ _{h3 −} δ _h2 ) ² } ^1/2 ... (2)
δ _d2 : Dispersion term of poor solvent δ _d3 : Dispersion term of fibrous carbon nanostructures δ _p2 : Polarity term of poor solvent δ _p3 : Polarity term of fibrous carbon nanostructures δ _h2 : Hydrogen bond term of poor solvent δ _h3 : Hydrogen bond term of fibrous carbon nanostructure

The definition and calculation method of the Hansen solubility parameter are described in the following documents. Charles M. Hansen, "Hansen Solubility Parameters: A Users Handbook", CRC Press, 2007.

Further, for a substance whose document value of the Hansen solubility parameter is unknown, the Hansen solubility parameter can be easily estimated from the chemical structure by using computer software (Hansen Solubility Parameters in Practice (HSPiP)).
Specifically, for example, HSPiP version 3 may be used, the value may be used for the poor solvent registered in the database, and the estimated value may be used for the poor solvent not registered.

Here, when ethylene tetrafluoride-perfluoromethyl vinyl ether-based rubber (FFKM) is used as the rubber type of the rubber particles, cyclohexane, water, alcohols (isopropyl alcohol, methanol, etc.) and ketones are used as the poor solvent. Classes (methyl ethyl ketone, acetone, etc.) and the like can be used. When vinylidene fluoride rubber (FKM) is used as the rubber type of the rubber particles, cyclohexane, water, or the like can be used as the poor solvent.

The total concentration of the rubber particles and the fibrous carbon nanostructures in the mixture is preferably 1% by mass or more, more preferably 3% by mass or more, and 5% by mass in the mixture (100% by mass). % Or more, more preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less. When the total concentration of the rubber particles and the fibrous carbon nanostructures is at least the above lower limit value, the fibrous carbon nanostructures can be satisfactorily dispersed when the dispersion treatment is performed. Further, when the total concentration of the rubber particles and the fibrous carbon nanostructures is not more than the above upper limit value, the fibrous carbon nanostructures can be satisfactorily dispersed.

[Additive]
Examples of the additive that can be arbitrarily blended in the mixed solution include, without particular limitation, a known additive such as a dispersant.
Here, as the dispersant, a known dispersant that can assist the dispersion of the fibrous carbon nanostructures can be used. Specifically, examples of the dispersant include surfactants, polysaccharides, π-conjugated polymers, and polymers having an ethylene chain as a main chain. Of these, surfactants are more preferred.

From the viewpoint of suppressing deterioration of the performance of the rubber composition, the blending amount of the additive is preferably 1 part by mass or less per 100 parts by mass of the rubber particles, and is 0 parts by mass (that is,). It is more preferable that the mixed solution and the dispersion liquid do not contain additives).

[Mixing method]
The method for mixing the above-mentioned rubber particles, the fibrous carbon nanostructures, the poor solvent for the rubber particles, and any additive is not particularly limited, and a known mixing method is used. Can be done. Above all, from the viewpoint of suppressing the occurrence of damage to the fibrous carbon nanostructures, it is preferable to mix the above-mentioned components using a stirrer under no pressure.

The order in which the above-mentioned components are 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. May be good. Above all, from the viewpoint of preparing a mixed solution by a simple operation, it is preferable to mix all the components at once.

<Dispersion process>
In the dispersion step, the mixture obtained in the above mixing step is supplied to the disperser, and the mixture is subjected to a dispersion treatment to obtain a dispersion.

[Disperser]
Here, the disperser is not particularly limited, and a rotary disperser, a media stirring type disperser, or the like can be used.
The rotary disperser miniaturizes the processing target by the shearing force, the collision force, and the cavitation generated in the vicinity of the rotating rotating body. Examples of the rotary disperser include a homogenizer such as a rotary homogenizer (for example, M-Technique's Claremix), an in-line rotor / stator type mixer (for example, Pacific Kiko's Cavitron, Sharp Flow Mill, and Matsubo's Milder). , Primix Corporation's fill mix) and other medialess dispersers that can perform distributed processing without using distributed media.
In the media stirring type disperser, the media filled in the mill is made to flow by stirring or the like to disperse the processing target. The degree of dispersion during the dispersion treatment can be adjusted by adjusting the particle size and filling rate of the media, the stirring peripheral speed of the media mill, the supply speed, and the like. Examples of the media stirring type disperser include bead mills, ball mills, sand mills, etc., for example, Nanomill of Asada Iron Works, Star Mill of Ashizawa Finetech, Dyno Mill of Simmal Enterprises, Visco Mill of Imex, Nippon Coke Industries. The company's attritor etc. can be mentioned.
Above all, from the viewpoint of further improving the tensile strength of the rubber composition and further reducing the volume resistivity, the disperser preferably uses a medium, and more preferably a bead mill.

[Dispersion]
The dispersion obtained in the above-mentioned dispersion step contains rubber particles derived from the above-mentioned predetermined rubber particles, fibrous carbon nanostructures, a poor solvent for the rubber particles, and an arbitrary additive. ..
The ratio of each component contained in the dispersion liquid is usually the same as the ratio of each component contained in the mixed liquid.
The rubber particles described above may be crushed by a dispersion treatment by a disperser and may exist as rubber particles having a smaller average particle size in the dispersion liquid.

<Dispersion medium removal process>
In the dispersion medium removing step, the poor solvent used as the dispersion medium is removed from the dispersion liquid obtained in the above dispersion step to obtain a rubber composition.

Here, the method for removing the poor solvent from the dispersion liquid is not particularly limited, and a known method such as drying or filtration can be used. Above all, as a method for removing the poor solvent of the rubber particles, 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. ..

The rubber composition obtained as described above may be used as it is as a rubber material or a composite material, or may be granulated by an arbitrary method such as pulverization or flaking.
Further, the obtained rubber composition is further mixed with an arbitrary compounding agent for rubber, for example, a cross-linking agent, a co-cross-linking agent, a reinforcing material, an antioxidant, an organic peroxide, etc., and kneaded, and molded and cross-linked. Can also be performed to obtain a desired molded product. Kneading, molding and cross-linking can be performed using known methods and equipment.

The rubber composition containing the rubber and the fibrous carbon nanostructures obtained by the method for producing the rubber composition of the present invention is subjected to molding processing and cross-linking because the fibrous carbon nanostructures are well dispersed. As a result, it is possible to obtain a molded product having excellent tensile strength and low volume resistance.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, the elastic modulus G'' of rubber, the average particle size of rubber particles, and the tensile strength and volumetric modulus of the rubber composition were measured or evaluated using the following methods. ..

<Loss modulus G''>
Using a rubber process analyzer (model: RPA2000) manufactured by Alpha Technologies, dynamic viscoelasticity was measured at 70 ° C., 1 Hz, and a strain of 0.5% to determine the loss elastic modulus G''.
The loss elastic modulus G ″ represents the viscosity of the rubber, and the smaller the value, the more difficult it is for the rubber particles to aggregate with each other, indicating that the stability of the particles is excellent.
<Average particle size>
The particle size distribution (number basis) of the obtained rubber particles was measured using a vacuum suction type sieving machine (manufactured by Hosokawa Micron, product name "Air Jet Sheave e200LS"). Then, the median diameter (D50) of the obtained particle size distribution (number basis) was taken as the average particle size of the rubber particles.
<Tensile strength>
The obtained crosslinked rubber sheet was punched into a dumbbell test piece (JIS No. 3) to prepare a test piece. The prepared test piece was subjected to a tensile tester (Strograph VG manufactured by Toyo Seiki Co., Ltd.) under the conditions of a test temperature of 23 ° C., a test humidity of 50%, and a tensile speed of 500 ± 50 mm / min in accordance with JIS K6251: 2010. A tensile test was performed below, and the tensile strength TS (the value obtained by dividing the maximum tensile force recorded when the test piece was pulled until it was cut by the initial cross-sectional area of the test piece) was measured. The larger the value, the better the tensile strength.
<Volume resistivity>
Using a resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd., product name "Loresta-GX MCP-T700", probe: LSP), the volume resistivity of the obtained crosslinked rubber sheet is measured at 10 points at different measurement points. Then, the average value was obtained from the measured values at 10 points, and the average value was taken as the volume resistivity of the rubber composition. The smaller the volume resistivity value, the better the conductivity.

(Example 1)
A lump of FFKM as rubber (manufactured by Asahi Glass Co., Ltd., "Afras PM-1100", Hansen solubility parameter (δ _d1 = 12.8, δ _p1 = 0.9, δ _h1 = 1.0)) is crushed at a low temperature (Toho). FFKM particles having an average particle size of 0.07 mm were obtained by throwing them into a crushing temperature: -80 ° C, crushing frequency: 3 times) and crushing them, and then passing them through a sieve of 150 μm. ..
In a 10 L SUS can, 200 g (100 parts by mass) of the obtained FFKM particles having an average particle size of 0.07 mm and cyclohexane as a poor solvent for the FFKM particles (Hansen solubility parameter (δ _d2 = 16.8, δ _p2)). = 0, δ _h2 = 0.2)) and 4000 g of single-walled carbon nanotubes as fibrous carbon nanostructures (manufactured by Nippon Zeon Corporation, product name “ZEONANO SG101”, specific gravity: 1.7, average diameter: 3 .5 nm, average length: 350 μm, BET specific surface area: 1350 m ² / g, G / D ratio: 3.5, t-plot: convex upward, Hansen solubility parameter (δ _d3 = 19.4, δ _p3 = 6) .0, δ _h3 = 4.5)) 8.0 g (4 parts by mass) was charged (mixing step). Then, using a Cavitron (manufactured by Pacific Kiko Co., Ltd., product name "CD1000", rotor / stator: slit type, slit width 1 mm) as a disperser, dispersion processing is performed at a temperature of 20 ° C. and a rotation speed of 200 Hz for 60 minutes. A slurry-like dispersion liquid containing FFKM particles and single-walled carbon nanotubes was obtained (dispersion step).
Then, the obtained dispersion was air-dried to remove the poor solvent (cyclohexane). Then, it was vacuum-dried at a temperature of 80 ° C. for 12 hours in a vacuum dryer (manufactured by Yamato Scientific Co., Ltd.) to obtain a composite rubber material (rubber composition) in which FFKM and single-walled carbon nanotubes were composited.
The distance R1 of the Hansen solubility parameter between FFKM and cyclohexane is 8.1, the distance R2 of the Hansen solubility parameter between single-walled carbon nanotubes and cyclohexane is 9.0, and the absolute value of the difference between R1 and R2 is 0.9. there were.
104 g of the obtained composite rubber material (FFKM 100 parts by mass / single layer CNT 4 parts by mass) was used as a high temperature kneader using a lab plast mill (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name "10C100", capacity: 60 ml, 50 rpm). After kneading at a kneading temperature of 150 ° C. for 5 minutes, 5 g (5 parts by mass) of triallyl isocyanurate (manufactured by Nippon Kasei Co., Ltd., product name "TAIC (registered trademark)") is added, and the kneading temperature is 150. Further kneading was performed at ° C. for 5 minutes (preliminary kneading step).
Next, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (2,5-dimethyl-2,5-di (t-butylperoxy) hexane (as an organic peroxide) was added to 109 parts by mass of the pre-kneaded product (FFKM 100 parts by mass / single layer CNT 4 parts by mass / TAIC 5 parts by mass). (Manufactured by Nichiyu Co., Ltd., product name "Perhexa 25B40") 2.5 parts by mass are rolled and mixed, and after undergoing primary vulcanization (170 ° C., 20 minutes) and secondary vulcanization (200 ° C., 4 hours), the thickness is 2 mm. A crosslinked rubber sheet was obtained.
The tensile strength and volume resistivity were measured using the obtained crosslinked rubber sheet. The results are shown in Table 1.

(Example 2)
Crosslinking was carried out in the same manner as in Example 1 except that isopropyl alcohol (Hansen solubility parameter (δ _d2 = 15.8, δ _p2 = 6.1, δ _{h2 = 16.4)) was used instead of cyclohexane as a poor solvent.} Obtained a rubber sheet. The Hansen solubility parameter distance R1 between FFKM and isopropyl alcohol is 17.3, the Hansen solubility parameter distance R2 between single-walled carbon nanotubes and isopropyl alcohol is 13.9, and the absolute value of the difference between R1 and R2 is 3. It was 4. The tensile strength and volume resistivity of the obtained crosslinked rubber sheet were measured. The results are shown in Table 1.

(Example 3)
As a disperser, a bead mill (manufactured by Asada Iron Works, trade name "Nanomill NM-G1.4L", media: zirconia beads, average diameter of dispersed media: 0.5 mm, filling rate of dispersed media: 48%) was used instead of Cavitron. A crosslinked rubber sheet was obtained in the same manner as in Example 1 except that the three-pass dispersion treatment was performed at a temperature of 40 ° C. (dispersion treatment conditions: peripheral speed 12.5 m / sec, discharge rate: 70 g / min). rice field. The tensile strength and volume resistivity of the obtained crosslinked rubber sheet were measured. The results are shown in Table 1.

(Example 4)
A crosslinked rubber sheet was obtained in the same manner as in Example 1 except that FKM (manufactured by The Chemours Company, product name "Viton GBL600S") was used instead of FFKM as the rubber. The average particle size of the FKM particles is 0.08 mm, the distance R1 of the Hansen solubility parameter between FKM and cyclohexane is 10.2, and the distance R2 of the Hansen solubility parameter between single-walled carbon nanotubes and cyclohexane is 9.0 and R1. The absolute value of the difference in R2 was 1.2. The tensile strength and volume resistivity of the obtained crosslinked rubber sheet were measured. The results are shown in Table 1.

(Comparative Example 1)
A crosslinked rubber sheet was obtained in the same manner as in Example 1 except that the FFKM particles remaining on the sieve having a thickness of 150 μm were used as the rubber particles. The average particle size of the FFKM particles was 0.16 mm. The tensile strength and volume resistivity of the obtained crosslinked rubber sheet were measured. The results are shown in Table 1.

(Comparative Example 2)
A crosslinked rubber sheet was obtained in the same manner as in Example 1 except that toluene (Hansen solubility parameter (δ _d2 = 18.0, δ _p2 = 1.4, δ _{h2 = 2.0)) was used instead of cyclohexane.} rice field. The distance R1 of the Hansen solubility parameter between FFKM and toluene is 10.5, the distance R2 of the Hansen solubility parameter between single-walled carbon nanotubes and toluene is 5.9, and the absolute value of the difference between R1 and R2 is 4.6. there were. The tensile strength and volume resistivity of the obtained crosslinked rubber sheet were measured. The results are shown in Table 1.

(Comparative Example 3)
The dispersion treatment was carried out under the same conditions as in Example 3 except that the number of times of crushing the FFKM mass when treated with the low temperature crusher was changed to one. The average particle size of the FFKM particles was 0.4 mm. Since the average particle size of the FFKM particles is close to the size of the dispersed media, the dispersed media and the FFKM particles could not be separated by the clearance of the gap separator of the bead mill device, and the dispersion treatment could not be performed.

(Comparative Example 4)
FEPM (manufactured by AGC, product name "Afras 100S") was used as the rubber instead of FFKM, and it was crushed at low temperature together with talc as a dusting agent (5 parts by mass with respect to 100 parts by mass of FEPM). Obtained a crosslinked rubber sheet in the same manner as in Example 1. The average particle size of FEPM particles is 0.08 mm, the distance R1 of the Hansen solubility parameter between FEPM and cyclohexane is 6.8, and the distance R2 of the Hansen solubility parameter between single-walled carbon nanotubes and cyclohexane is 9.0 and R1. The absolute value of the difference in R2 was 2.2. The tensile strength and volume resistivity of the obtained crosslinked rubber sheet were measured. The results are shown in Table 1.

From Table 1, in Examples 1 to 4 in which the dispersion treatment was performed using rubber particles having a predetermined average particle size and made of rubber having a predetermined loss elastic modulus, rubber having excellent tensile strength and low volume modulus. It can be seen that a crosslinked product can be obtained.
On the other hand, from Table 1, it can be seen that in Comparative Examples 1 and 3 in which the average particle size of the rubber particles is out of the predetermined range, the dispersibility of the carbon nanotubes becomes insufficient and the tensile strength decreases.
Further, from Table 1, in Comparative Example 2 in which the difference between the Hansen solubility parameter distances R1 and R2 is out of the predetermined range, the mixture of rubber and carbon nanotubes becomes non-uniform, so that the tensile strength decreases and the volume It can be seen that the resistivity increases.
Further, from Table 1, in Comparative Example 4 using rubber having a loss resistivity exceeding a predetermined upper limit, it is necessary to add a dusting agent because the rubber particles are likely to aggregate, and as a result, the tensile strength is lowered. Moreover, it can be seen that the volume resistivity becomes large.

According to the present invention, it is possible to produce a rubber composition having a high tensile strength and a low volume resistivity.

Claims (6)

A mixing step of mixing rubber particles, fibrous carbon nanostructures, and a poor solvent for the rubber particles to obtain a mixed solution.
A dispersion step of dispersing the mixed solution using a disperser to obtain a dispersion, and
A dispersion medium removing step of removing the poor solvent from the dispersion liquid,
Including
The rubber particles are made of rubber having a loss elastic modulus G ″ at 70 ° C. of 180 kPa or less, and have an average particle size of 0.01 mm or more and less than 0.1 mm.
The absolute value of the difference (Ra1-Ra2) between the Hansen solubility parameter distance Ra1 between the rubber and the poor solvent and the Hansen solubility parameter distance Ra2 between the fibrous carbon nanostructure and the poor solvent is 4 or less. Method for producing rubber composition. The method for producing a rubber composition according to claim 1, wherein the mixed solution contains the fibrous carbon nanostructures in a proportion of 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber particles. The rubber composition according to claim 1 or 2, wherein the rubber particles include at least one selected from the group consisting of fluororubber particles, silicone rubber particles, hydrogenated nitrile rubber particles, acrylic rubber particles and nitrile rubber particles. Production method. The method for producing a rubber composition according to any one of claims 1 to 3, further comprising a crushing step of crushing the rubber in the absence of a dusting agent to obtain the rubber particles before the mixing step. The method for producing a rubber composition according to claim 4, wherein the dusting agent is talc, barium sulfate, silica, calcium carbonate, clay or carbon black. The method for producing a rubber composition according to any one of claims 1 to 5, wherein the disperser uses media.