JP7488150B2 - Conductive rubber composition for sensing - Google Patents

Description

The present invention relates to a conductive rubber composition for sensing.

There are cases where it is required to measure the amount of deformation of rubber products such as tires. However, general rubber that does not contain conductive materials does not have a sensing function to detect the amount of deformation of the rubber. Therefore, to detect the amount of deformation of a general rubber product, it is necessary to install a separate sensor (strain sensor, acceleration sensor, position detection sensor, angle sensor, etc.) on the outside of the rubber product.

JP 2007-525357 A

However, if a separate sensor is installed outside the rubber product (for example, installing a laser oscillator and a reflector to measure the distance between two points, or installing an ultrasonic transmitter and a reflector to measure the distance between two points, etc.), the structure of the rubber product will become more complex, its weight will increase, and the cost will inevitably become higher.
In addition, for example, a sensor that has a laser oscillator and a reflector and measures the distance between two points, or a sensor that has an ultrasonic transmitter and a reflector and measures the distance between two points, has the problem that it cannot measure the distance between two points and cannot measure the amount of deformation unless the object to be measured deforms linearly.
Under such circumstances, the inventors discovered that by compounding a conductive material into rubber to impart conductivity, the resistance value changes when the rubber deforms, and there is a correlation between the amount of deformation of the rubber and the resistance value. The inventors then came up with the idea of predicting the amount of deformation of the rubber from the change in the resistance value of the rubber. However, after further investigation, the inventors discovered that rubber that has simply been made conductive does not have a sufficient sensing function for detecting the amount of deformation of the rubber, and also consumes a large amount of power, making it difficult to use it as a sensor.

The present invention aims to solve the problems of the conventional technology and provide a conductive rubber composition for sensing that is suitable for use in sensing components that detect deformation.

The gist of the present invention, which solves the above problems, is as follows:

The conductive rubber composition for sensing of the present invention is characterized by containing a rubber component, carbon black, and carbon nanotubes.
The conductive rubber composition for sensing of the present invention has a small resistance value and can be suitably used for a sensing member for detecting deformation.

In a preferred embodiment of the conductive rubber composition for sensing of the present invention, the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of the carbon black is 3000 or more, and the volume fraction of the carbon black is 20 volume% or more. In this case, the volume resistivity of the rubber composition is easily adjusted to 1.0× ¹⁰⁸ Ω·cm or less.

In another preferred embodiment of the conductive rubber composition for sensing of the present invention, the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of the carbon black is 1250 or more, and the volume fraction of the carbon black is 20 volume% or more. In this case, it is easy to make the volume resistivity of the rubber composition 1.0× ¹⁰⁸ Ω·cm or less.

In another preferred embodiment of the conductive rubber composition for sensing of the present invention, the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of the carbon black is 900 or more, and the volume fraction of the carbon black is 20 volume% or more. In this case, it is easy to make the volume resistivity of the rubber composition 1.0× ¹⁰⁸ Ω·cm or less.

In another preferred embodiment of the conductive rubber composition for sensing of the present invention, the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of the carbon black is 310 or more, and the volume fraction of the carbon black is 20 volume% or more. In this case, it is easy to make the volume resistivity of the rubber composition 1.0× ¹⁰⁸ Ω·cm or less.

Another conductive rubber composition for sensing according to the present invention includes a rubber component and carbon black,
The rubber composition is characterized in that the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B (m ² /g) of the carbon black is 3,000 or more.
Such another conductive rubber composition for sensing of the present invention also has a small resistance value and can be suitably used for a sensing member for detecting deformation.

In the conductive rubber composition for sensing of the present invention, it is preferable that the rubber component contains a diene rubber. In this case, a vulcanized rubber suitable as a sensing member can be produced from the conductive rubber composition for sensing.

Here, it is preferable that the diene rubber is at least one selected from the group consisting of natural rubber, synthetic isoprene rubber, butadiene rubber, styrene butadiene rubber, and acrylonitrile butadiene rubber. In this case, it is easy to obtain a rubber composition (vulcanized rubber) with excellent physical properties (breaking strength, breaking elongation, etc.).

In the conductive rubber composition for sensing of the present invention, it is also preferable that the rubber component contains a non-diene rubber. In this case, too, a rubber composition suitable as a sensing member can be produced from the conductive rubber composition for sensing.

Here, it is preferable that the non-diene rubber is at least one selected from the group consisting of urethane rubber, ethylene propylene diene rubber, and bromobutyl rubber. In this case, it is easy to obtain a rubber composition having excellent physical properties (breaking strength, breaking elongation, etc.).

The present invention provides a conductive rubber composition suitable for use in sensing components that detect deformation.

1 is a schematic diagram of one embodiment of a deformation detection sensor using the conductive rubber composition for sensing of the present invention. 1 is a cross-sectional view of one embodiment of a tire using the conductive rubber composition for sensing of the present invention. FIG. 1 is a side view of one embodiment of a rubber actuator using the conductive rubber composition for sensing of the present invention. FIG. 1 is a partially exploded perspective view of one embodiment of a rubber actuator using the conductive rubber composition for sensing of the present invention. 1 is a graph showing the relationship between the product (A×B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black, and the volume resistivity, in examples and comparative examples containing carbon black and carbon nanotubes. 1 is a graph showing the relationship between the product (A×B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black, and the volume resistivity, in examples and comparative examples that contain carbon black but not carbon nanotubes.

The conductive rubber composition for sensing of the present invention will be described in detail below with reference to an embodiment.

<Conductive rubber composition for sensing according to the first embodiment>
The conductive rubber composition for sensing according to the first embodiment of the present invention is characterized by including a rubber component, carbon black, and carbon nanotubes.

The conductive rubber composition for sensing according to the first embodiment of the present invention contains carbon nanotubes in addition to carbon black, and the carbon black and the carbon nanotubes provide the rubber composition with excellent electrical conductivity, thereby enabling the resistance value of the rubber composition to be reduced. Therefore, the conductive rubber composition for sensing according to the first embodiment of the present invention can be suitably used for a sensing member that detects the amount of deformation.
The conductive rubber composition for sensing according to the first embodiment of the present invention contains carbon black and carbon nanotubes, and by appropriately selecting their contents and surface areas, it is easy to achieve a volume resistivity (electrical resistance value) of 1.0×10 ⁸ Ω·cm or less.

(Rubber component)
As the rubber component, various rubber components that impart rubber elasticity to the composition can be used, and are not particularly limited. The rubber component used may be one type or two or more types.

The rubber component preferably contains a diene rubber. When the rubber component contains a diene rubber, the vulcanized rubber can be easily prepared and can be suitably used for various rubber products. In addition, by appropriately selecting the diene rubber to be used and the vulcanizing system such as a vulcanizing agent and a vulcanization accelerator, a vulcanized rubber suitable for use as a sensing member can be prepared.
Examples of the diene rubber include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR).

Here, it is preferable that the diene rubber is at least one selected from the group consisting of natural rubber, synthetic isoprene rubber, butadiene rubber, styrene butadiene rubber, and acrylonitrile butadiene rubber. In this case, there is an advantage that the raw diene rubber (rubber component) is easy to obtain, and it is easy to obtain a rubber composition (vulcanized rubber) with excellent physical properties (breaking strength, breaking elongation, etc.).

The rubber component may contain a non-diene rubber. Even when the rubber component contains a non-diene rubber, a rubber composition suitable for use as a sensing member can be produced.
Examples of the non-diene rubber include silicone rubber, fluororubber, urethane rubber, ethylene propylene diene rubber (EPDM), and bromobutyl rubber.

Here, it is preferable that the non-diene rubber is at least one selected from the group consisting of urethane rubber, ethylene propylene diene rubber, and bromobutyl rubber. In this case, it is easy to obtain a rubber composition having excellent physical properties (breaking strength, breaking elongation, etc.).

In the present invention, "diene rubber" means a rubber in which the ratio of units derived from diene monomers among the monomer units constituting the diene rubber is 5 mol % or more, and "non-diene rubber" means a rubber in which the ratio of units derived from diene monomers among the monomer units constituting the non-diene rubber is less than 5 mol %. Here, examples of diene monomers include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, ethylidenenorbornene, dicyclopentadiene, 1,4-hexadiene, etc.

(Carbon black)
The carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, SAF grade carbon black, etc. These carbon blacks may be used alone or in combination of two or more kinds.

From the viewpoint of improving the electrical conductivity of the rubber composition and reducing the resistance value, the carbon black preferably has a large cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B (m ² /g) (in other words, a small particle size is preferable). For example, when the volume resistivity of the rubber composition is to be a certain value (for example, 1.0×10 ⁸ Ω·cm) or less, the target volume resistivity can be achieved even if the carbon black content A (parts by mass) is reduced by using a carbon black having a large cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B (m ² /g). Here, the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B of the carbon black is preferably appropriately adjusted depending on the carbon black content and the carbon nanotube content described later, and in one embodiment, it is preferably 20 m ² /g or more, more preferably 30 m ² /g or more, and preferably 200 m ² /g or less. When the CTAB adsorption specific surface area of the carbon black is 20 m ² /g or more, the electrical conductivity of the rubber composition is improved, and when it is 200 m ² /g or less, the workability in kneading the rubber composition is good.

The carbon black content is preferably adjusted appropriately depending on the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black itself and the content of carbon nanotubes described below, and in one embodiment, the content is preferably in the range of 5 to 100 parts by mass, and more preferably in the range of 10 to 50 parts by mass, per 100 parts by mass of the rubber component. When the carbon black content is 5 parts by mass or more per 100 parts by mass of the rubber component, the conductivity of the rubber composition is improved, and when it is 100 parts by mass or less, the workability in kneading the rubber composition is good and an increase in hardness of the rubber composition can be suppressed.

(carbon nanotube)
The carbon nanotube (CNT) is a structure made of carbon atoms with a diameter of about several nm to several tens of nm, and has an extremely fine tube-like structure.
The carbon nanotubes may be single-walled or multi-walled nanotubes.
The carbon nanotubes preferably have a length of 0.1 μm to 30 μm, and more preferably 0.1 μm to 10 μm.
The carbon nanotubes preferably have a diameter of 10 nm to 300 nm, and more preferably have a diameter of 100 nm to 250 nm.

The carbon nanotubes can be synthesized by plasma CVD (chemical vapor deposition), thermal CVD, surface decomposition, flow gas synthesis, arc discharge, etc., and commercially available products can also be used. Examples of commercially available carbon nanotubes that can be used include carbon nanotubes manufactured by Kumuho Corporation, vapor grown carbon fiber VGCF (registered trademark) manufactured by Showa Denko KK, and carbon nanotubes manufactured by Materials Technologies Research (MTR) of the United States.

The content of the carbon nanotubes is preferably adjusted appropriately depending on the content A (parts by mass) of the carbon black and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black, and in one embodiment, is preferably in the range of 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the rubber component. If the content of the carbon nanotubes is 0.1 part by mass or more per 100 parts by mass of the rubber component, the conductivity of the rubber composition is improved, and if it is 20 parts by mass or less, the workability in kneading the rubber composition is improved, an increase in hardness of the rubber composition can be suppressed, and further, the raw material cost of the rubber composition can be reduced.

(Preferable Relationship Between CTAB Adsorption Specific Surface Area and Carbon Black Content)
In the conductive rubber composition for sensing according to the first embodiment of the present invention, the product (A×B) of the carbon black content A (parts by mass) relative to 100 parts by mass of the rubber component, the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B (m ² /g) of the carbon black, and the volume fraction of the carbon black satisfy a specific relationship, so that the conductive rubber composition can be particularly suitably used for a sensing member for detecting deformation. Examples of these suitable relationships are shown below, but the conductive rubber composition for sensing according to the first embodiment of the present invention is not limited thereto. The following suitable relationships are not particularly limited, but are derived from the relationship between the product (A×B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B (m ² /g) of many rubber compositions and the volume fraction of the carbon black from the viewpoint of making the volume resistivity (electrical resistance value) of the rubber composition 1.0× ^{10 8} Ω·cm or less.

In this specification, the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of carbon black is a value measured in accordance with JIS K6217-3, and is the external surface area of carbon black excluding micropores, expressed as the specific surface area when CTAB (cetyltrimethylammonium bromide) is adsorbed onto the carbon black.
In addition, when the rubber composition contains two or more types of carbon black, the "product (A × B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black" refers to the sum ( _A1 × _B1 , _A2 × B2, ...) of the products of the carbon black contents _A1 , _{A2 ,} ... (parts by mass) and the CTAB adsorption specific surface areas _B1 , _{B2 ,} ... ( ^m2 _{/ g} ) of _each carbon black.
The volume fraction of carbon black can be calculated by dividing the volume of carbon black, which is calculated from the content and specific gravity of carbon black, by the total volume of the rubber composition. In this specification, carbon nanotubes are not counted as carbon black and are not included in the calculation as a numerator.

In a preferred example (1) of the conductive rubber composition for sensing according to the first embodiment of the present invention, the product (A×B) of the carbon black content A (parts by mass) relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of the carbon black is 3000 or more, and the volume fraction of the carbon black is 20 volume% or more. In this case, the volume resistivity of the rubber composition is easily adjusted to 1.0× ¹⁰⁸ Ω·cm or less.

In a preferred example (2) of the conductive rubber composition for sensing according to the first embodiment of the present invention, the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of the carbon black is 1250 or more, and the volume fraction of the carbon black is 20 volume% or more. In this case as well, it is easy to make the volume resistivity of the rubber composition 1.0× ¹⁰⁸ Ω·cm or less.

In a preferred example (3) of the conductive rubber composition for sensing according to the first embodiment of the present invention, the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of the carbon black is 900 or more, and the volume fraction of the carbon black is 20 volume% or more. In this case as well, it is easy to make the volume resistivity of the rubber composition 1.0× ¹⁰⁸ Ω·cm or less.

In a preferred example (4) of the conductive rubber composition for sensing according to the first embodiment of the present invention, the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B ( ^m2 /g) of the carbon black is 310 or more, and the volume fraction of the carbon black is 20 volume% or more. In this case as well, it is easy to make the volume resistivity of the rubber composition 1.0× ¹⁰⁸ Ω·cm or less.

<Conductive rubber composition for sensing according to the second embodiment>
The conductive rubber composition for sensing according to the second embodiment of the present invention includes a rubber component and carbon black,
The rubber composition is characterized in that the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B (m ² /g) of the carbon black is 3,000 or more.

The conductive rubber composition for sensing of the second embodiment of the present invention does not need to contain carbon nanotubes, but since the product (A x B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black is 3000 or more (i.e., the carbon black has a fine particle size (large surface area) or a high carbon black content), it has excellent conductivity, a low resistance value, and is easy to make the volume resistivity of the rubber composition 1.0 x ¹⁰⁸ Ω-cm or less. Therefore, the conductive rubber composition for sensing of the second embodiment of the present invention can also be suitably used in a sensing component that detects deformation.

In the conductive rubber composition for sensing of the second embodiment of the present invention, the rubber component is the same as the rubber component of the conductive rubber composition for sensing of the first embodiment described above, and the preferred rubber component is also the same.

In the conductive rubber composition for sensing of the second embodiment of the present invention, the carbon black is the same as that in the conductive rubber composition for sensing of the above-mentioned first embodiment. Note that in the conductive rubber composition for sensing of the second embodiment of the present invention, it is necessary to appropriately select the carbon black content A (parts by mass) and the product (A×B) of the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black so that it is 3000 or more.

<Method for producing conductive rubber composition for sensing>
The rubber composition of the present invention can be produced, for example, by using a Banbury mixer, a roll or the like to compound and knead specific amounts of carbon black and carbon nanotubes, or carbon black satisfying a specific relationship, with a rubber component, followed by heating and extrusion, etc.

The conductive rubber composition for sensing according to the first and second embodiments of the present invention described above may contain, in addition to the above-mentioned components, a conductive polymer, a softener, stearic acid, an antioxidant, zinc oxide (zinc oxide), a vulcanization accelerator, a vulcanizing agent, etc., which may be appropriately selected and blended within a range that does not impair the object of the present invention. Commercially available products can be suitably used as these blending agents.

<Applications of the conductive rubber composition for sensing>
The above-mentioned conductive rubber composition for sensing of the present invention is used for sensing (detecting, detecting, sensing) the amount of displacement, and can be used for sensing the amount of deformation of various rubber products, such as tires, rubber actuators, vibration-proof rubber, vibration-isolating rubber, rubber crawlers, conveyor belts, rubber hoses, various shoe soles, sporting goods, etc.

FIG. 1 shows a deformation detection sensor according to a preferred embodiment using the conductive rubber composition for sensing of the present invention.
The deformation amount detection sensor 1 shown in FIG. 1 includes a sensing rubber member 2 and a resistance value measuring device 3. The resistance value measuring device 3 is connected to both ends of the sensing rubber member 2, and the sensing rubber member 2 is made of the above-mentioned conductive rubber composition for sensing of the present invention. The sensing rubber member 2 may be incorporated in the rubber product as a part of the rubber product exemplified above, or may be separately attached to the rubber product. The sensing rubber member 2 shown in FIG. 1 is strip-shaped, but the shape is not particularly limited and can be appropriately changed depending on the shape of the measurement target, etc.

For example, a sensing rubber member made of the above-mentioned conductive rubber composition for sensing of the present invention can be incorporated into a part of a tire (inner liner, tread rubber, side rubber, etc.) and the resistance value of the sensing rubber member can be measured (monitored) using a resistance measuring device, thereby measuring (monitoring) the amount of deformation of the tire. In addition, by measuring (monitoring) the amount of deformation of the tire, information such as the road surface condition, the tire contact condition, and the degree of tire wear can be continuously obtained.

The sensing rubber member is made of the above-mentioned conductive rubber composition for sensing of the present invention and has excellent conductivity, so it has the advantage of consuming little power even when a voltage is continuously applied. In addition, because the sensing rubber member consumes little power, the amount of deformation can be easily measured using a small (portable) resistance value measuring device.

The sensing rubber member (conductive rubber composition for sensing) preferably has a volume resistivity of 1.0× ¹⁰ Ω·cm or less, and more preferably 1.0× ¹⁰ Ω·cm or more. If the volume resistivity of the sensing rubber member is 1.0× ¹⁰ Ω·cm or less, power consumption is small, and if the volume resistivity is 1.0× ¹⁰ Ω·cm or more, the change in resistance value according to the amount of deformation is large, improving measurement accuracy.

Conventional general deformation measurement sensors, such as sensors consisting of a laser oscillator and a reflector that measure the distance between two points, or sensors consisting of an ultrasonic transmitter and a reflector that measure the distance between two points, cannot measure the distance between two points and cannot measure the amount of deformation unless the measurement target deforms linearly. In contrast, the sensing rubber member made of the conductive rubber composition for sensing of the present invention has a high degree of freedom in deformation and can be deformed into complex shapes. In addition, the sensing rubber member has the advantage that the amount of deformation can be predicted from the resistance value even if it does not deform linearly.

(tire)
A preferred embodiment of a tire using the conductive rubber composition for sensing of the present invention is shown in Fig. 2. A tire 10 of one preferred embodiment includes a pair of bead portions 11, a pair of sidewall portions 12, a tread portion 13, and a carcass 15 reinforcing these portions, and further includes a sensing rubber member 17 on the tire inner surface side of the carcass 15.

The tire 10 shown in FIG. 2 comprises a pair of bead portions 11, a pair of sidewall portions 12, a tread portion 13, and a carcass 15 extending in a toroidal shape between bead cores 14 embedded in the bead portions 11. The tire further comprises a belt 16 consisting of two reinforcing layers 16a, 16b arranged in the tread portion 13 on the radially inner side of the tread surface and on the radially outer side of the crown portion of the carcass 15, and a sensing rubber member 17 arranged on the inner side of the carcass 15. Resistance measuring devices 18 are connected to both ends of the sensing rubber member 17.

In the tire 10 shown in FIG. 2, the carcass 15 is composed of one carcass ply, and is composed of a main body portion extending in a toroidal shape between a pair of bead cores 14 each embedded in the bead portion 11, and a folded portion wound up radially outward from the inside to the outside in the tire width direction around each bead core 14, but the number of plies and the structure of the carcass 15 are not limited to this. From the viewpoint of tire durability, a radial carcass is preferable as the carcass. Here, the carcass ply constituting the carcass 15 is composed of multiple reinforcing cords covered with a coating rubber, and the reinforcing cords may be organic fiber cords such as polyethylene terephthalate cords, nylon cords, rayon cords, etc., or steel cords.

The belt 16 of the tire 10 shown in FIG. 2 is made up of two reinforcing layers 16a and 16b, each of which is usually a rubberized layer of cords extending at an angle to the tire equatorial plane, preferably a rubberized layer of steel cords, and the two reinforcing layers are laminated so that the cords constituting the reinforcing layers cross each other with the tire equatorial plane in between to form the belt 16. Note that while the belt 16 in the figure is made up of two reinforcing layers, the number of reinforcing layers constituting the belt 16 is not limited to one and may be one or more.

2 includes a sensing rubber member 17 on the innermost surface of the tire, which is the tire inner surface side of the carcass 15. The sensing rubber member 17 may be provided as a substitute for an inner liner that is normally provided to ensure airtightness of the tire (i.e., it may have air impermeability in addition to a sensing function), or it may be separately attached to the tire inner surface side of the inner liner.
Here, the sensing rubber member 17 is made of the above-mentioned conductive rubber composition for sensing of the present invention. Furthermore, a resistance value measuring device 18 is connected to both ends of the sensing rubber member 17, and the amount of deformation of the tire 10 can be measured (monitored) by measuring (monitoring) the resistance value of the sensing rubber member 17 with the resistance value measuring device 18. Furthermore, by measuring (monitoring) the amount of deformation of the tire 10, information such as the road surface condition, the tire contact condition, and the degree of tire wear can be continuously obtained.

(Rubber actuator)
A rubber actuator of a preferred embodiment using the conductive rubber composition for sensing of the present invention is shown in Fig. 3. The rubber actuator 20 of one preferred embodiment includes an actuator body 100 including a cylindrical tube 110 that expands and contracts due to fluid pressure, and a sleeve 120 that is a cylindrical structure in which cords oriented in a predetermined direction are woven and covers the outer circumferential surface of the tube 110, and the tube 110 is made of the conductive rubber composition for sensing of the present invention described above.

Figure 3 is a side view of the rubber actuator 20 according to this embodiment. As shown in Figure 3, the rubber actuator 20 includes an actuator body 100, a sealing mechanism 200, and a sealing mechanism 300. Furthermore, a connecting portion 30 is provided on each end of the rubber actuator 20. Furthermore, a resistance value measuring device 40 is connected to each connecting portion 30.

The actuator body 100 is composed of a tube 110 and a sleeve 120. A working fluid flows into the actuator body 100 through a fitting 400 and a through hole 410. Here, the rubber actuator 20 is operated by fluid pressure and may be pneumatic or hydraulic. When a liquid is used as the working fluid, examples of the liquid include oil and water. When the rubber actuator is hydraulic, the working fluid may be hydraulic oil that has been used in hydraulic drive systems.

When the working fluid flows into the tube 110, the actuator body 100 contracts in the axial direction D _AX of the actuator body 100 and expands in the radial direction D _R. When the working fluid flows out of the tube 110, the actuator body 100 expands in the axial direction D _AX of the actuator body 100 and contracts in the radial direction D _R. This change in shape of the actuator body 100 allows the rubber actuator 20 to function as an actuator.
Furthermore, such a rubber actuator 20 is a so-called McKibben type, and can be used not only as an artificial muscle, but also as a robot limb (upper limb, lower limb, etc.) that requires higher performance (contractile force). Members constituting the limb are connected to the connecting part 30. In this embodiment, the resistance value measuring device 40 is connected to the connecting part 30, but the connection point of the resistance value measuring device 40 is not limited thereto, and may be directly connected to both ends of the tube 110, for example.

The sealing mechanism 200 and the sealing mechanism 300 seal both ends of the actuator body 100 in the axial direction D _AX . Specifically, the sealing mechanism 200 includes a sealing member 210 and a crimping member 230. The sealing member 210 seals the end of the actuator body 100 in the axial direction D _AX . The crimping member 230 crimps the actuator body 100 together with the sealing member 210. An indentation 231, which is a mark caused by the crimping member 230 being crimped by a jig, is formed on the outer circumferential surface of the crimping member 230.

The difference between the sealing mechanism 200 and the sealing mechanism 300 is that the roles of the fittings 400 and 500 (and the passage holes 410 and 510) are different.
The fitting 400 provided on the sealing mechanism 200 protrudes so that a drive pressure source for the rubber actuator 20, specifically a hose (pipe) connected to a compressor for the working fluid, can be attached. The working fluid that flows in through the fitting 400 passes through a passage hole 410 and flows into the inside of the actuator body 100, specifically into the inside of the tube 110.
On the other hand, the fitting 500 provided on the sealing mechanism 300 protrudes so as to be used as a gas vent when injecting the working fluid into the rubber actuator 20. When the working fluid is injected into the rubber actuator 20 at the beginning of the operation of the rubber actuator 20, the gas originally present inside the rubber actuator is discharged from the fitting 500 through the passage hole 510.

4 is a partially exploded perspective view of the rubber actuator 20. As shown in FIG. 4, the rubber actuator 20 includes an actuator body 100 and a sealing mechanism 200.
As described above, the actuator body 100 is composed of the tube 110 and the sleeve 120 .

The tube 110 is a cylindrical body that expands and contracts due to fluid pressure. The tube 110 repeatedly contracts and expands due to the working fluid, and is made of the above-mentioned conductive rubber composition for sensing of the present invention.

The sleeve 120 is cylindrical and covers the outer surface of the tube 110. The sleeve 120 is a structure made by weaving cords oriented in a specific direction, and the oriented cords cross to form a repeated diamond shape. By having such a shape, the sleeve 120 undergoes pantograph deformation and follows the contraction and expansion of the tube 110 while regulating it.

4, the sealing mechanism 200 seals the end portion in the axial direction D _AX of the actuator body 100. The sealing mechanism 200 is composed of a sealing member 210, a locking ring 220, and a crimping member 230.

The sealing member 210 has a body portion 211 and a flange portion 212. The sealing member 210 is preferably made of a metal such as stainless steel, but is not limited to such a metal and may be made of a hard plastic material or the like.

The body portion 211 is tubular, and has a through hole 215 through which the working fluid passes. The through hole 215 communicates with the through hole 410 (see FIG. 3). The tube 110 is inserted into the body portion 211.

The flange portion 212 is connected to the body portion 211 and is located closer to the end portion in the axial direction D _AX of the actuator 10 than the body portion 211. The flange portion 212 has a larger outer diameter in the radial direction D _R than the body portion 211. The flange portion 212 locks the tube 110 and the locking ring 220 inserted into the body portion 211.

An uneven portion 213 is formed on the outer circumferential surface of the body portion 211. The uneven portion 213 contributes to preventing slippage of the tube 110 inserted into the body portion 211. It is preferable that the uneven portion 213 is formed with three or more convex portions.
Further, a small diameter portion 214 having an outer diameter smaller than that of the body portion 211 is formed at a position closer to the flange portion 212 of the body portion 211 .

The locking ring 220 locks the sleeve 120. Specifically, the sleeve 120 is folded back outward in the radial direction D _R via the locking ring 220.
The outer diameter of the locking ring 220 is larger than the outer diameter of the body portion 211. The locking ring 220 locks the sleeve 120 at the position of the small diameter portion 214 of the body portion 211. In other words, the locking ring 220 locks the sleeve 120 at a position that is on the outer side of the body portion 211 in the radial direction D _R and adjacent to the flange portion 212.
In this embodiment, the locking ring 220 is divided into two parts so that it can be locked to the small diameter portion 214 that is smaller than the body portion 211. Note that the locking ring 220 is not limited to being divided into two parts, and may be divided into more parts, or some of the divided parts may be connected to each other so as to be rotatable.
The locking ring 220 can be made of the same metal or hard plastic material as the sealing member 210 .

The crimping member 230 crimps the actuator body 100 together with the sealing member 210. The crimping member 230 may be made of a metal such as an aluminum alloy, brass, or iron. When the crimping member 230 is crimped by a crimping jig, an indentation 231 as shown in FIG. 3 is formed on the crimping member 230.

As described above, the tube 110 is repeatedly contracted and expanded by the working fluid, and is made of the conductive rubber composition for sensing of the present invention.
Here, as the contraction rate of the actuator body 100 increases, the electrical resistance value of the actuator body 100 (tube 110) decreases. This is because, when a fluid flows into the actuator body 100 and the actuator body 100 contracts in the axial direction D _AX , the tube 110 expands in the radial direction D _R within a predetermined range restricted by the sleeve 120, and the thickness of the tube 110 becomes thinner, narrowing the distance between the carbon black and/or carbon nanotubes contained in the tube 110.
Specifically, when the actuator body 100 contracts, the tube 110 expands, reducing the thickness of the tube 110. As a result, the dimension (distance) of the carbon black and/or carbon nanotubes in the thickness direction becomes narrower, and the carbon black and/or carbon nanotubes come closer to each other.
That is, when the contraction rate of the actuator body 100 increases and the length decreases, the distance between the carbon black and/or carbon nanotubes decreases, so that the conductivity of the tube 110 increases, in other words, the electrical resistance value of the tube 110 decreases. Then, by measuring the resistance value with the resistance value measuring device 40 connected to each connecting portion 30, the amount of deformation of the tube 110 can be measured.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

<Preparation of Rubber Composition>
Rubber compositions having the formulations shown in Tables 1 to 6 were prepared by kneading in a normal manner. The first kneading stage was carried out at 140° C., and the second kneading stage was carried out at 100° C. The volume resistivity of the obtained rubber compositions was measured by the following method.

(1) Measurement method of volume resistivity The obtained rubber composition was vulcanized at 155°C for 50 minutes to prepare a test piece having a size of 80 mm (width) x 80 mm (length) x 2 mm (thickness), and the volume resistivity of the test piece was measured according to JIS K6911 using Advantest Corp. R8340A (high resistance measuring device). The results are shown in Tables 1 to 6.
Figure 5 shows the relationship between the product (A x B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black, and the volume resistivity, when carbon nanotubes are contained, and Figure 6 shows the relationship between the product (A x B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black, and the volume resistivity, when carbon nanotubes are not contained.

*1 NR: Natural rubber *2 BR: Butadiene rubber, manufactured by Ube Industries, product name "UBEPOL-BR150L"
*3 Carbon black 1: Asahi Carbon Co., Ltd., product name "Asahi NPG", CTAB adsorption specific surface area = 31 m ² /g
*4 Carbon black 2: Asahi Carbon Co., Ltd., product name "Asahi Sharp 70L", CTAB adsorption specific surface area = 71 m ² /g
*5 Carbon black 3: Asahi Carbon Co., Ltd., product name "Asahi Sharp 70K", CTAB adsorption specific surface area = 70 m ² /g
*6 Carbon black 4: manufactured by Tokai Carbon Co., Ltd., product name "Seast 6", CTAB adsorption specific surface area = 112 m ² /g
*7 Carbon black 5: manufactured by Tokai Carbon Co., Ltd., product name "Seat 600P", CTAB adsorption specific surface area = 134 m ² /g
*8 Carbon nanotubes: Manufactured by Kumuho Corporation, product name "Durobeads K-Nanos 100P Mitsubishi Corporation"
*9 Hydrogenated fatty acid: New Japan Chemical Co., Ltd., product name "Stearic acid 50S"
*10 Zinc oxide: Manufactured by Hakusui Tech Co., Ltd., product name "Zinc oxide type 2 granulated product"
*11 Anti-aging agent 1: Nippon Seiro Co., Ltd., product name "Ozoace-0280"
*12 Antiaging agent 2: Sumitomo Chemical Co., Ltd., trade name "Antigen 6C"
*13 Vulcanization accelerator 1: Sanshin Chemical Industry Co., Ltd., product name "Suncerer NS-G"
*14 Sulfur: Hosoi Chemical Industry Co., Ltd., product name "HK200-5"

*15 Bromobutyl rubber: manufactured by Japan Butyl Co., Ltd., product name "JSR BROMOBUTYL 2222"
*16 Process oil: JXTG Energy Corporation, product name "Super Oil Y22"
*17 Vulcanization accelerator 2: Product name "Noccela DM-P" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

From Tables 1 to 6 and Figures 5 and 6, it can be seen that as the product (A x B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black increases, the resistance value decreases, and a rubber composition suitable for use as a sensing component can be obtained.

In particular, a rubber composition containing both carbon black and carbon nanotubes is
(1) The product (A×B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B (m ² /g) of the carbon black is 3,000 or more, and the volume fraction of the carbon black is 20 volume% or more.
(2) The product (A×B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B (m ² /g) of the carbon black is 1250 or more, and the volume fraction of the carbon black is 20 volume% or more.
(3) The product (A×B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B (m ² /g) of the carbon black is 900 or more, and the volume fraction of the carbon black is 20 volume% or more.
(4) The product (A×B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B (m ² /g) of the carbon black is 310 or more, and the volume fraction of the carbon black is 20 volume% or more.
The volume resistivity is 1.0×10 ⁸ (Ω·cm) or less, which is particularly suitable as a rubber composition for sensing.

In addition, a rubber composition containing carbon black but not carbon nanotubes is
It can be seen that when the product (A x B) of the carbon black content A (parts by mass) and the CTAB adsorption specific surface area B ( ^m2 /g) of the carbon black is 3000 or more, the volume resistivity is 1.0 x ¹⁰⁸ (Ω·cm) or less, making it particularly suitable as a rubber composition for sensing.

The conductive rubber composition for sensing of the present invention can be used as a sensor that predicts the amount of deformation of rubber from changes in the resistance value of the rubber.

1: deformation amount detection sensor; 2: sensing rubber member; 3: resistance value measuring device;
REFERENCE SIGNS LIST 10: tire, 11: bead portion, 12: sidewall portion, 13: tread portion, 14: bead core, 15: carcass, 16: belt, 16a, 16b: reinforcing layer, 17: sensing rubber member, 18: resistance value measuring device,
20: Rubber actuator, 30: Connection portion, 40: Resistance measuring device, 100: Actuator body, 110: Tube, 120: Sleeve, 200: Sealing mechanism, 210: Sealing member, 211: Body portion, 212: Flange portion, 213: Concave and recessed portion, 214: Small diameter portion, 215: Passing hole, 220: Locking ring, 230: Crimping member, 231: Indentation, 300: Sealing mechanism, 400, 500: Fitting, 410, 510: Passing hole, D _AX : Axial direction, D _R : Radial direction

Claims (5)

The rubber composition includes a rubber component, carbon black, and carbon nanotubes,
the product (A×B) of the content A (parts by mass) of the carbon black relative to 100 parts by mass of the rubber component and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area B (m ² /g) of the carbon black is 310 or more; and
A conductive rubber composition for sensing, characterized in that the volume fraction of the carbon black is 20 volume % or more . The conductive rubber composition for sensing according to claim 1 , wherein the rubber component includes a diene rubber. The conductive rubber composition for sensing according to claim 2 , wherein the diene rubber is at least one selected from the group consisting of natural rubber, synthetic isoprene rubber, butadiene rubber, styrene butadiene rubber, and acrylonitrile butadiene rubber. The conductive rubber composition for sensing according to claim 1 , wherein the rubber component includes a non-diene rubber. The conductive rubber composition for sensing according to claim 4 , wherein the non-diene rubber is at least one selected from the group consisting of urethane rubber, ethylene propylene diene rubber, and bromobutyl rubber.

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