Conductive rubber composition for sensing

Abstract

To provide a conductive rubber composition for sensing that has good responsiveness in change of electrical resistance value to strain and can accurately detect crack occurrence.SOLUTION: Provided is a conductive rubber composition for sensing that contains a rubber component and a carbon black and is characterized in that the rubber component contains acrylonitrile-butadiene rubber in an amount of 80 mass% or more, the product (A×B×C) of cetyltrimethylammonium bromide (CTAB) adsorption specific surface area A (m2 / g) of the carbon black, compressed dibutyl phthalate (24M4DBP) absorption amount B (mL / 100 g) of the carbon black, and the contained amount C (pts.mass) of the carbon black per 100 pts.mass of the rubber component is 600,000 or more, and the carbon black has a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area A of 110 m2 / g or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a conductive rubber composition for sensing. [Background technology]

[0002] A rubber actuator (so-called McKibben type) is known, which has a rubber tube that expands and contracts using a working fluid, and a sleeve (mesh reinforcement structure) that covers the outer surface of the rubber tube. For rubber products that undergo repeated deformation, such as the rubber tube of this rubber actuator, it is possible to measure the amount of deformation of the rubber member from the electrical resistance value of the rubber member (see Patent Document 1 below). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-037906 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] According to the technology described in Patent Document 1 above, the amount of deformation of a rubber member can be determined by measuring the electrical resistance of the rubber member. However, it is not possible to detect whether or not cracks have occurred in the rubber member. In the case of rubber actuators, which are filled with liquids such as oil, if cracks occur in the rubber tube, it may lead to the tube rupturing or rendering the rubber actuator unusable. Therefore, early detection of cracks in the rubber tube at its initial stage is considered important. The inventors investigated and found that when the expansion and contraction of a rubber actuator is considered one cycle, and the electrical resistance of the tube rubber is monitored in real time during the expansion and contraction, the waveform of the electrical resistance changes in one cycle due to strain caused by cracks, before cracks occur, in the initial stages of crack occurrence, and in the advanced stages (Figure 1). However, with general conductive rubber, it is difficult to capture such changes in the waveform of electrical resistance caused by strain due to cracks, and it is difficult to confirm the initial stages of crack occurrence by monitoring electrical resistance alone. In contrast, by using a sensing conductive rubber composition that has good responsiveness to changes in electrical resistance in response to strain, it becomes possible to detect the occurrence of cracks with high accuracy.

[0005] Therefore, the present invention aims to solve the problems of the above-mentioned prior art and provide a conductive rubber composition for sensing that has good responsiveness to changes in electrical resistance with respect to strain and can accurately detect the occurrence of cracks. [Means for solving the problem]

[0006] The gist of the present invention, which solves the above problems, is as follows.

[0007] The conductive rubber composition for sensing of the present invention comprises a rubber component and carbon black. The aforementioned rubber component contains 80% by mass or more of acrylonitrile-butadiene rubber. Adsorption specific surface area A(m²) of the carbon black for cetyltrimethylammonium bromide (CTAB) 2 The product (A × B × C) of the amount of compressed dibutyl phthalate (24M4DBP) absorbed by the carbon black (mL / 100g), the amount of carbon black (C) per 100 parts by mass of the rubber component, is 600,000 or more. The specific surface area A of the carbon black adsorbing cetyltrimethylammonium bromide (CTAB) is 110 m². 2 It is characterized by being 1 / g or more. The conductive rubber composition for sensing of the present invention has good responsiveness to changes in electrical resistance with respect to strain.

[0008] In the conductive rubber composition for sensing of the present invention, it is preferable that the rubber component consists only of acrylonitrile-butadiene rubber having an acrylonitrile unit content of 34% by mass or more. In this case, the oil resistance of the conductive rubber composition for sensing is further improved.

[0009] In a preferred example of the conductive rubber composition for sensing of the present invention, the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area A (m 2 / g) of the carbon black, the compression dibutyl phthalate (24M4DBP) absorption amount B (mL / 100 g) of the carbon black, and the content C (parts by mass) of the carbon black with respect to 100 parts by mass of the rubber component are such that the product (A × B × C) is 650,000 or more and 900,000 or less. In this case, the responsiveness to changes in electrical resistance with respect to strain is improved, and it has a suitable hardness for application to the tube rubber of a rubber actuator.

[0010] In another preferred example of the conductive rubber composition for sensing of the present invention, the content C of the carbon black with respect to 100 parts by mass of the rubber component is 45 parts by mass or more and 75 parts by mass or less. In this case, it is possible to detect changes in electrical resistance due to strain without delay and with high sensitivity.

Effects of the Invention

[0011] According to the present invention, it is possible to provide a conductive rubber composition for sensing that has good responsiveness to changes in electrical resistance with respect to strain and can accurately detect the occurrence of cracks.

Brief Description of the Drawings

[0012] [Figure 1] It is a graph showing an electrical resistance waveform for one cycle with respect to an example of a rubber actuator. [Figure 2] It is a side view of an example of a rubber actuator. [Figure 3] It is a partial exploded perspective view of an example of a rubber actuator. [Figure 4] It is a partial cross-sectional view of an example of a tube rubber. [Figure 5] It is a graph showing examples of changes in the electrical resistance values in the cases with and without responsiveness.

Mode for Carrying Out the Invention

[0013] Hereinafter, the conductive rubber composition for sensing of the present invention will be specifically illustrated and described based on its embodiments.

[0014] <Conductive Rubber Composition for Sensing> The conductive rubber composition for sensing of the present invention contains a rubber component and carbon black. Here, in the conductive rubber composition for sensing of the present invention, the rubber component contains 80% by mass or more of acrylonitrile-butadiene rubber, and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area A (m 2 / g), the compression dibutyl phthalate (24M4DBP) absorption amount B (mL / 100 g) of the carbon black, and the content C (parts by mass) of the carbon black with respect to 100 parts by mass of the rubber component, the product (A × B × C) is 600,000 or more, and the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area A of the carbon black is 110 m 2 / g or more.

[0015] The CTAB adsorption specific surface area A of the carbon black is an indicator of the particle size of the carbon black. The larger the CTAB adsorption specific surface area A, the smaller the particle size of the carbon black and the lower the electrical resistance of the rubber composition. Furthermore, the 24M4DBP absorption amount B of the carbon black is a physical property related to the structure of the carbon black, and the larger the 24M4DBP absorption amount B, the lower the electrical resistance of the rubber composition. The 24M4DBP absorption amount B of the carbon black is also an indicator of high strain loss and is related to the amount of friction between carbon black particles under high strain. Under high strain, a greater amount of friction between carbon black particles leads to a greater change in electrical resistance due to expansion and contraction (high strain) during use, and improves the responsiveness of the change in electrical resistance to strain. In addition, the higher the content C of the carbon black per 100 parts by mass of the rubber component, the lower the electrical resistance of the rubber composition. Furthermore, in the present invention, when 80% by mass or more of the rubber component is acrylonitrile-butadiene rubber, the product (A × B × C) is 600,000 or more, and the CTAB adsorption specific surface area A of carbon black is 110 m². 2 When the value is above / g, the electrical resistance of the rubber composition becomes sufficiently low, and furthermore, when strain is applied, the electrical resistance changes in a reproducible manner, and when the strain is removed, the electrical resistance returns to its reversible state, resulting in improved responsiveness to changes in electrical resistance in response to strain.

[0016] As described above, the conductive rubber composition for sensing of the present invention has improved responsiveness to changes in electrical resistance in response to strain. Therefore, by combining the conductive rubber composition for sensing of the present invention with AI learning that uses electrical resistance as input, it becomes possible to detect the occurrence of cracks (AI sensing) from the dynamic behavior of changes in electrical resistance. Furthermore, the conductive rubber composition for sensing of the present invention has 80% by mass or more of its rubber component as acrylonitrile-butadiene rubber, and this acrylonitrile-butadiene rubber has high oil resistance. Therefore, the conductive rubber composition for sensing of the present invention has high oil resistance and is suitable for applications requiring oil resistance, such as the rubber tubing of rubber actuators.

[0017] (Rubber component) The conductive rubber composition for sensing according to the present invention contains a rubber component, which provides rubber elasticity to the composition and enables the expansion and contraction of the rubber composition. The conductive rubber composition for sensing according to the present invention contains 80% by mass or more of acrylonitrile-butadiene rubber (NBR), preferably 90% by mass or more. Furthermore, it is preferable that the rubber component contains 80% by mass or more of acrylonitrile-butadiene rubber having an acrylonitrile unit content of 34% by mass or more, and it is even more preferable that it consists solely of acrylonitrile-butadiene rubber having an acrylonitrile unit content of 34% by mass or more. Since acrylonitrile-butadiene rubber has excellent oil resistance, the conductive rubber composition for sensing according to the present invention, in which 80% by mass or more of the rubber component is acrylonitrile-butadiene rubber, has high oil resistance and is suitable for applications requiring oil resistance, such as the tubing of rubber actuators. Furthermore, if the rubber component consists solely of acrylonitrile-butadiene rubber having an acrylonitrile unit content of 34% by mass or more, the oil resistance is further improved.

[0018] The acrylonitrile unit content of the acrylonitrile-butadiene rubber (NBR) is preferably 34% by mass or more, more preferably 45% by mass or more, from the viewpoint of oil resistance, and preferably 50% by mass or less from the viewpoint of fatigue resistance and crack propagation resistance. The acrylonitrile unit content (amount of bound acrylonitrile) of the aforementioned acrylonitrile-butadiene rubber (NBR) can be measured by the Kjeldahl method in accordance with JIS K6384.

[0019] The aforementioned rubber component may further contain other rubber components. Various rubber components that provide rubber elasticity to the composition can be used as such other rubber components. Examples of such other rubber components include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), and the like. Furthermore, one or more rubber components may be used.

[0020] (Carbon black) The conductive rubber composition for sensing of the present invention contains carbon black, and the carbon black provides conductivity to the composition, enabling the sensing of the rubber composition.

[0021] The product (A × B × C) of the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area A (m 2 / g) of the carbon black, the dibutyl phthalate (24M4DBP) absorption amount B (mL / 100 g) of the carbon black, and the content C (parts by mass) of the carbon black with respect to 100 parts by mass of the rubber component is 600,000 or more, and preferably 650,000 or more and 900,000 or less. When the product (A × B × C) of the CTAB adsorption specific surface area A, the 24M4DBP absorption amount B, and the carbon black content C is less than 600,000, the responsiveness of the change in the electrical resistance value to strain is insufficient. On the other hand, when the product (A × B × C) of the CTAB adsorption specific surface area A, the 24M4DBP absorption amount B, and the carbon black content C is 650,000 or more, the responsiveness of the change in the electrical resistance value to strain is improved, and when it is 900,000 or less, the hardness of the rubber composition becomes low, for example, it becomes a suitable hardness for application to the tube rubber of a rubber actuator.

[0022] The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area A of the carbon black is 110 m 2 / g or more. When the CTAB adsorption specific surface area of the carbon black is 110 m 2 / g or more, the particle size of the carbon black is sufficiently small, the electrical resistance value is sufficiently low, it becomes easy to detect the change in the electrical resistance value, and the responsiveness is improved. The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of the carbon black is preferably 120 m 2 / g or more from the viewpoint of further facilitating the detection of the change in the electrical resistance value, and preferably 160 m 2 / g or less from the viewpoint of workability. In this specification, the specific surface area of ​​carbon black adsorbed with cetyltrimethylammonium bromide (CTAB) is a value measured in accordance with JIS K6217-3, and represents the external surface area of ​​carbon black excluding micropores, as the specific surface area when CTAB (cetyltrimethylammonium bromide) is adsorbed onto the carbon black.

[0023] The amount of compressed dibutyl phthalate (24M4DBP) absorbed by the carbon black, B, is preferably 90 mL / 100 g or more, from the viewpoint of making it easier to detect changes in electrical resistance with respect to strain, and preferably 130 mL / 100 g or less, from the viewpoint of suppressing variations due to mixing. In this specification, the compressed dibutyl phthalate (24M4DBP) absorption of carbon black is measured in accordance with ISO 6894, after applying pressure to 24,000 psi four times. This 24M4DBP absorption is used to determine the DBP absorption based on the non-destructive true structural form (primary structure), excluding the DBP absorption due to deformable and destructive structural forms (secondary structure) caused by van der Waals forces. It is an index for evaluating the skeletal structure of carbon black, which is mainly composed of the primary structure.

[0024] The carbon black content C per 100 parts by mass of the rubber component is preferably 45 parts by mass or more and 75 parts by mass or less, and more preferably 55 parts by mass or more and 70 parts by mass or less. When the carbon black content is 45 parts by mass or more per 100 parts by mass of the rubber component, the electrical resistance of the rubber composition becomes sufficiently low (electricity flows sufficiently), making it easier to detect changes in electrical resistance. When the carbon black content is 75 parts by mass or less per 100 parts by mass of the rubber component, the electrical resistance of the rubber composition becomes sufficiently high (electricity does not flow too much), making it easier to detect changes in electrical resistance, and the hardness of the rubber composition becomes lower, resulting in a hardness suitable for application, for example, to the rubber tube of a rubber actuator. Furthermore, if the electrical resistance is sufficiently high, electricity will not flow too much, and by applying strain to the rubber, the electrical resistance will change, and since this change is immediate without delay, it is suitable for use in crack detection. Conversely, if the electrical resistance is sufficiently low, electricity will flow sufficiently and conduction will occur, making it suitable for use in crack detection. Moreover, if the carbon black content is in the range of 45 parts by mass to 75 parts by mass per 100 parts by mass of rubber component, it becomes possible to detect changes in electrical resistance due to strain without delay and with high sensitivity.

[0025] The carbon black mentioned above is not particularly limited as long as it meets the above conditions, and examples include ISAF and SAF grade carbon black. These carbon blacks may be used individually or in combination of two or more types.

[0026] (Carbon nanotubes) The conductive rubber composition for sensing according to the present invention may further contain carbon nanotubes. These carbon nanotubes have the effect of improving the conductivity of the composition.

[0027] When the conductive rubber composition for sensing of the present invention contains carbon nanotubes, the carbon nanotube content is preferably less than 2 parts by mass, and more preferably less than 1 part by mass, per 100 parts by mass of the rubber component. When the carbon nanotube content is less than 2 parts by mass per 100 parts by mass of the rubber component, the electrical resistance of the rubber composition becomes sufficiently high (electricity does not flow too much), making it easier to detect changes in electrical resistance.

[0028] The carbon nanotubes (CNTs) are structures composed of carbon atoms with a diameter of several nanometers to tens of nanometers, and have an extremely fine tubular structure. The carbon nanotubes may be single-walled nanotubes or multi-walled nanotubes. The carbon nanotubes are preferably 0.1 μm to 30 μm in length, and more preferably 0.1 μm to 10 μm in length. Furthermore, the carbon nanotubes are preferably those with a diameter of 10 nm to 300 nm, and more preferably those with a diameter of 100 nm to 250 nm.

[0029] The aforementioned carbon nanotubes can be synthesized by methods such as plasma CVD (chemical vapor deposition), thermal CVD, surface decomposition, fluid vapor phase synthesis, and arc discharge, and commercially available products can also be used. Examples of commercially available carbon nanotubes include carbon nanotubes manufactured by KUMHO Corporation, VGCF (registered trademark) vapor phase carbon fiber manufactured by Showa Denko Corporation, and carbon nanotubes manufactured by Materials Technologies Research (MTR) Corporation in the United States.

[0030] <Method for producing a conductive rubber composition for sensing> The rubber composition of the present invention can be manufactured, for example, by mixing carbon black with a rubber component using a Banbury mixer or roll, and optionally further mixing in carbon nanotubes, then kneading, followed by heating, extrusion, etc.

[0031] In addition to the components described above, the conductive rubber composition for sensing may also contain softeners, stearic acid, antioxidants, zinc oxide (zinc oxide), vulcanization accelerators, vulcanizing agents, etc., selected as appropriate within a range that does not impair the purpose of the present invention. Commercially available products can be suitably used as these compounding agents.

[0032] <Applications of conductive rubber compositions for sensing> The conductive rubber composition for sensing according to the present invention, as described above, exhibits good responsiveness to changes in electrical resistance in response to strain, and can therefore be used for sensing (detecting, identifying, and sensing) amounts of strain. This conductive rubber composition for sensing can be used in various rubber products, and is particularly suitable for use in the rubber tubes of rubber actuators. In addition to rubber actuators, it can be appropriately adapted for use in any rubber component that experiences strain during use, such as tires, vibration damping rubber, vibration isolation rubber, conveyor belts, crawlers, gloves, etc., and it goes without saying that its applications are not limited to the examples given above and are broadly applicable.

[0033] (Rubber actuator) Figure 2 shows a preferred embodiment of a rubber actuator using the sensing conductive rubber composition of the present invention. The rubber actuator 10 shown in Figure 2 comprises an actuator body 100 composed of a cylindrical tube rubber 110 that expands and contracts by fluid pressure, and a sleeve 120 which is a cylindrical structure made of cords oriented in a predetermined direction and covers the outer surface of the tube rubber 110. The above-described sensing conductive rubber composition of the present invention is used for the tube rubber 110.

[0034] Figure 2 is a side view of the rubber actuator 10 according to this embodiment. As shown in Figure 2, the rubber actuator 10 comprises an actuator body 100, a sealing mechanism 200, and a sealing mechanism 300. Connecting parts 20 are provided at both ends of the rubber actuator 10. A resistance value measuring device 30 is connected to each connecting part 20.

[0035] The actuator body 100 is composed of a rubber tube 110 and a sleeve 120. Working fluid flows into the actuator body 100 through a fitting 400 and a through hole 410. The rubber actuator 10 operates by fluid pressure and may be pneumatic or hydraulic. When a liquid is used as the working fluid, examples of such liquids include oil and water. If the rubber actuator is hydraulic, the working fluid can be the hydraulic oil conventionally used in hydraulic drive systems.

[0036] The actuator body 100 is affected by the flow of working fluid into the rubber tube 110, which causes the actuator body 100 to move in the axial direction D AX It contracts in the radial direction D R It expands. Also, the actuator body 100 expands due to the outflow of working fluid from the tube rubber 110, and the axial D of the actuator body 100 AX It expands in the radial direction D RIt contracts. Through this change in the shape of the actuator body 100, the rubber actuator 10 performs its function as an actuator. Furthermore, this type of rubber actuator 10 is a so-called McKibben type and can be applied not only to artificial muscles but also to robot limbs (upper limbs, lower limbs, etc.) that require higher capacity (contraction force). The connecting portion 20 is connected to the components that make up the limb. In this embodiment, a resistance value measuring device 30 is connected to the connecting portion 20, but the connection point of the resistance value measuring device 30 is not limited to this, and for example, it may be directly connected to both ends of the rubber tube 110.

[0037] The sealing mechanism 200 and the sealing mechanism 300 are located in the axial direction D AX The actuator body portion 100 is sealed at both ends. Specifically, the sealing mechanism 200 includes a sealing member 210 and a crimping member 230. The sealing member 210 is located in the axial direction D of the actuator body portion 100. AX The end is sealed. The crimping member 230 also crimps the actuator body 100 together with the sealing member 210. An indentation 231 is formed on the outer surface of the crimping member 230, which is the mark left by the crimping of the crimping member 230 by the jig.

[0038] The difference between sealing mechanism 200 and sealing mechanism 300 lies in the different roles of fittings 400, 500 (and through holes 410, 510). The fitting 400 provided in the sealing mechanism 200 protrudes so that a hose (pipeline) connected to the drive pressure source of the rubber actuator 10, specifically a compressor for the working fluid, can be attached. The working fluid that flows in through the fitting 400 passes through the through hole 410 and flows into the inside of the actuator body 100, specifically into the inside of the rubber tube 110. On the other hand, the fitting 500 provided in the sealing mechanism 300 protrudes so that it can be used as a gas vent when injecting working fluid into the rubber actuator 10. When working fluid is injected into the rubber actuator 10 during the initial operation of the rubber actuator 10, any gas that was originally present inside the rubber actuator 10 is discharged from the fitting 500 through the through hole 510.

[0039] Figure 3 is an exploded perspective view of the rubber actuator 10. As shown in Figure 3, the rubber actuator 10 comprises an actuator body 100 and a sealing mechanism 200. As described above, the actuator body 100 is composed of a rubber tube 110 and a sleeve 120.

[0040] The tube rubber 110 is a cylindrical body that expands and contracts due to fluid pressure. The tube rubber 110 repeatedly expands and contracts due to the working fluid, and the conductive rubber composition for sensing of the present invention described above is applied to it.

[0041] The sleeve 120 is cylindrical and covers the outer surface of the tube rubber 110. The sleeve 120 is a structure woven from cords oriented in a predetermined direction, and the intersection of the oriented cords creates a repeating rhombus shape. Due to this shape, the sleeve 120 deforms like a pantograph, following the contraction and expansion of the tube rubber 110 while restricting it.

[0042] In Figure 3, the sealing mechanism 200 is located in the axial direction D of the actuator body 100. AX The end portion is sealed. The sealing mechanism 200 consists of a sealing member 210, a locking ring 220, and a crimping member 230.

[0043] The sealing member 210 has a body portion 211 and a flange portion 212. While metals such as stainless steel can be suitably used as the sealing member 210, it is not limited to such metals, and hard plastic materials or the like may also be used.

[0044] The body portion 211 is cylindrical, and a through hole 215 is formed in the body portion 211 through which the working fluid passes. The through hole 215 communicates with a through hole 410 (see Figure 2). A tube rubber 110 is inserted through the body portion 211.

[0045] The flange portion 212 is connected to the body portion 211, and is located in the axial direction D of the actuator 10, which is greater than the body portion 211. AX It is located on the end side. The flange portion 212 is radially D greater than the body portion 211. R The outer diameter is large along the curve. The flange portion 212 locks the rubber tube 110 and the locking ring 220, which are inserted into the body portion 211.

[0046] The outer surface of the body portion 211 has irregularities 213 formed on it. The irregularities 213 contribute to suppressing slippage of the tube rubber 110 inserted through the body portion 211. It is preferable that three or more protrusions are formed by the irregularities 213. Furthermore, a small-diameter portion 214, which has a smaller outer diameter than the body portion 211, is formed near the flange portion 212 of the body portion 211.

[0047] The locking ring 220 locks the sleeve 120. Specifically, the sleeve 120 is moved radially D through the locking ring 220. R It is folded over to the outside. 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 is located in the radial direction D of the body portion 211. R The sleeve 120 is locked on the outside, at a position adjacent to the flange portion 212. In this embodiment, the locking ring 220 is designed to lock onto the smaller diameter portion 214, which is smaller than the body portion 211, and therefore has a two-part shape. However, the locking ring 220 is not limited to two parts; it may be divided into more parts, or some of the divided parts may be rotatably connected. The locking ring 220 can be made of the same metal or hard plastic material as the sealing member 210.

[0048] The crimping member 230 crimps the actuator body 100 together with the sealing member 210. The crimping member 230 can be made of a metal such as aluminum alloy, brass, or iron. When the crimping member 230 is crimped using a crimping jig, an indentation 231 is formed on the crimping member 230 as shown in Figure 2.

[0049] Figure 4 is a partial cross-sectional view of one embodiment of the tube rubber 110. The tube rubber 110 shown in Figure 4 consists of an inner layer rubber 111 located on the inner surface side of the tube rubber, and the inner layer rubber 111 in the radial direction D R It has a two-layer structure consisting of an outer layer rubber 112 located adjacent to the outside of the tube rubber 110 and on the outer surface side.

[0050] The conductive rubber composition for sensing according to the present invention, as described above, has excellent oil resistance and can therefore be suitably applied to the inner layer rubber 111 that comes into contact with the working fluid. If the oil resistance of the inner layer rubber 111 is insufficient, the working fluid may penetrate between the inner layer rubber 111 and the outer layer rubber 112, potentially reducing the durability of the tube rubber 110. However, by applying the conductive rubber composition for sensing according to the present invention, as described above, to the inner layer rubber 111, cracks in the inner layer rubber 111 can be detected early, preventing the intrusion of the working fluid and allowing the tube rubber 110 to be replaced at an appropriate time, thereby preventing the rubber actuator from malfunctioning.

[0051] On the other hand, since the outer layer rubber 112 is in contact with the sleeve 120, it is preferable to use a rubber composition that has excellent crack resistance, abrasion resistance, sliding properties, etc., and can withstand loads from the sleeve 120 side.

[0052] Furthermore, the tube rubber 110 is not limited to a two-layer structure; it may also have a single-layer structure or a laminated structure of three or more layers. In the case where the tube rubber 110 has a laminated structure of three or more layers, it is preferable to apply the conductive rubber composition for sensing of the present invention described above to the innermost layer.

[0053] As described above, the tube rubber 110 undergoes repeated contraction and expansion due to the working fluid, and the conductive rubber composition for sensing of the present invention is applied to it. Here, as the contraction rate of the actuator body 100 increases, the electrical resistance value of the actuator body 100 (tube rubber 110) decreases. This is because fluid flows into the actuator body 100 and the actuator body 100 moves in the axial direction D AX When it contracts, the tube rubber 110 moves radially D within a predetermined range restricted by the sleeve 120. R As it expands, the thickness of the tube rubber 110 decreases, which in turn narrows the distance between the carbon black particles contained in the tube rubber 110. Specifically, when the actuator body 100 contracts, the tube rubber 110 expands, causing the thickness of the tube rubber 110 to decrease. As a result, the distance between the carbon black particles in the thickness direction decreases, bringing the carbon black particles closer together. In other words, as the contraction rate of the actuator body 100 increases and its length decreases, the distance between the carbon blacks becomes narrower, which increases the conductivity of the tube rubber 110, or in other words, decreases the electrical resistance of the tube rubber 110.

[0054] Furthermore, repeated contraction and expansion by the working fluid can cause cracks to form in the tube rubber 110. As shown in Figure 1, the pattern of change in electrical resistance differs at each stage: no cracks, initial crack formation, and cracks present. By analyzing the dynamic behavior of the change in electrical resistance caused by strain due to crack formation in the tube rubber 110 using statistical methods, or by training an AI with this data, it becomes possible to detect the occurrence of cracks in the tube rubber 110 from the dynamic behavior of the change in electrical resistance. [Examples]

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0056] <Preparation of rubber composition> The rubber compositions shown in Table 1 were prepared by kneading using conventional methods. The acrylonitrile unit content and amount of acrylonitrile in the acrylonitrile-butadiene rubber used, as well as the type, properties, and amount of carbon black, are shown in Table 2.

[0057] [Table 1]

[0058] *1 NBR: Table 2 shows the acrylonitrile unit content and blending amount of the acrylonitrile-butadiene rubber used. *2 Carbon black: The type, properties, and amount of carbon black used are shown in Table 2. *3 Ester oil: Manufactured by Hallstar Company, product name "TP-95" *4 Hydrogenated fatty acid: Manufactured by Shin Nippon Rika Co., Ltd., product name "Stearic Acid 50S" *5 Anti-aging agent: 2,2,4-trimethyl-1,2-dihydroquinoline polymer, manufactured by Seiko Chemical Co., Ltd., product name "Nonflex RD" *6 Zinc oxide: Manufactured by Hakusui Tech Co., Ltd., product name "Zinc Oxide 2 Types Granulated Product" *7 Sulfurization accelerator A: N-cyclohexyl-2-benzothiazolyl sulfenamide, manufactured by Sanshin Chemical Co., Ltd., trade name "Sunceller CM-G" *8 Sulfurization accelerator B: Tetrakis(2-ethylhexyl)thiuram disulfide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noxellar TOT" *9 Sulfur: Manufactured by Hosoi Chemical Industry Co., Ltd., product name "HK200-5", shown as the amount of sulfur component in Table 1.

[0059] <Testing with vulcanized rubber> A 1 mm thick rubber sheet was prepared from the obtained rubber composition and vulcanized at 155°C for 45 minutes to produce a vulcanized rubber sheet. A 4.7 mm × 40 mm strip-shaped test piece was prepared from the vulcanized rubber sheet. The presence or absence of strain response was evaluated for the test piece using the following method.

[0060] (1) Strain response test The prepared test specimens were stretched 70% 10 times at room temperature with a tensile testing machine (K18003) and a chuck distance of 20 mm. (After repeating the cycle of 0% → 70% stretch → 0% 10 times), dynamic electrical measurements were performed at a tensile speed of 6 mm / sec. Electrical resistance values ​​were sampled at DC 10V, 200 Hz. The electrical resistance values ​​varied reproducibly with strain, and the ratio of the signal value (S), which is the difference between the minimum and maximum electrical resistance values ​​in the 10% stretch → 70% stretch → 10% stretch region, to the standard deviation (n) of the electrical resistance values ​​in the 0% to 10% stretch region was evaluated according to the following criteria to determine if it was sufficient. ○: S / N ratio of 9 or higher, with strain response. ×: S / N ratio less than 9, no strain response An example of the strain dependence of electrical resistance is shown in Figure 5. As shown in Figure 5, rubber with a sufficiently large signal-to-noise ratio shows a large change in electrical resistance due to strain and exhibits strain responsiveness, while rubber with a small signal-to-noise ratio shows a small change in electrical resistance due to strain and lacks strain responsiveness. The results of the above test are shown in Table 2.

[0061] <Testing with a rubber actuator> A cylindrical tube rubber was fabricated by applying the rubber compositions of Example 13 and Comparative Example 16 to the inner layer rubber of a two-layer tube rubber structure, which consists of an inner layer rubber and an outer layer rubber, as shown in Figure 4.

[0062] Two strands of 2200 dtex aramid fiber were used as the raw material. An aramid fiber cord with a diameter of 0.7 mm was produced by applying a 12-turn / 10 cm under-twist and then a 12-turn / 10 cm over-twist. A mesh-like sleeve was prepared by weaving together 64 of these aramid fiber cords. This sleeve was a mesh-like tubular body in which 64 aramid fiber cords could be observed around the circumference in a cross-section. Specifically, this sleeve was a mesh-like tubular body in which 32 aramid fiber cords arranged at equal intervals, parallel and spirally were alternately woven together with another 32 aramid fiber cords arranged at equal intervals, parallel and spirally, and obliquely intersecting these 32 aramid fiber cords. The angle of each cord with respect to the axial direction of the sleeve was 25 degrees.

[0063] Using the aforementioned rubber tube and mesh-like sleeve, a rubber actuator with the structure shown in Figures 2 and 3 was fabricated. The length between sealing mechanism 200 and sealing mechanism 300 is 250 mm. UF46 manufactured by Cosmo Super Epoch Co., Ltd. was used as the hydraulic fluid for the rubber tube.

[0064] (2) Crack detection test Hydraulic fluid was injected into the rubber tube to completely replace the air inside the tube. The hydraulic fluid injection operation was repeated so that the pressure of the hydraulic fluid inside the rubber tube alternated between 0 MPa and 5 MPa every 3 seconds, and the tube was repeatedly expanded and contracted until a crack formed in the tube, the crack extended, and the actuator could no longer function. In this experiment, we attempted to detect the occurrence of cracks by monitoring the electrical resistance. For the rubber actuator using the rubber sample from Example 13, which was evaluated as having "strain responsiveness," we successfully detected crack occurrence using AI. On the other hand, for the rubber actuator using the rubber sample from Comparative Example 16, which was evaluated as having "no strain responsiveness," we were unable to detect crack occurrence.

[0065] [Table 2]

[0066] *10 NBR1: Acrylonitrile-butadiene rubber, acrylonitrile unit content = 35% by mass, manufactured by JSR Corporation, product name "N230S" *11 NBR2: Acrylonitrile-butadiene rubber, acrylonitrile unit content = 41.5% by mass, manufactured by JSR Corporation, product name "N220S" *12 NBR3: Acrylonitrile-butadiene rubber, acrylonitrile unit content = 48% by mass, manufactured by JSR Corporation, product name "N215SL" *13 CB1: CTAB adsorption specific surface area=112m 2 / g, 24M4DBP absorption rate = 100mL / 100g, manufactured by Tokai Carbon Co., Ltd., product name "Seast 6" *14 CB2: CTAB adsorption specific surface area=123m 2 / g, 24M4DBP absorption rate = 100mL / 100g, manufactured by Asahi Carbon Co., Ltd., product name "Asahi #78" *15 CB3: CTAB adsorption specific surface area=83m 2 / g, 24M4DBP absorption rate = 72mL / 100g, manufactured by Asahi Carbon Co., Ltd., product name "Asahi #70L" *16 CB4: CTAB adsorption specific surface area=74m 2 / g, 24M4DBP absorption rate = 90mL / 100g, manufactured by Asahi Carbon Co., Ltd., product name "Asahi #70K"

[0067] The results shown in Table 2 indicate that when 80% or more of the rubber component is acrylonitrile-butadiene rubber, the product of the CTAB adsorption specific surface area A of carbon black, the 24M4DBP absorption amount B, and the content C (A × B × C) is 600,000 or more, and the CTAB adsorption specific surface area A is 110 m². 2 When the value is above / g, the responsiveness of the change in electrical resistance to strain improves, making it possible to detect the occurrence of cracks. [Industrial applicability]

[0068] The conductive rubber composition for sensing according to the present invention exhibits good responsiveness to changes in electrical resistance in response to strain. For example, when applied to the rubber tube of a rubber actuator, it can be used to detect the occurrence of cracks from changes in electrical resistance. [Explanation of Symbols]

[0069] 10: Rubber actuator, 20: Connecting part, 30: Resistance value measuring device, 100: Actuator body, 110: Rubber tube, 111: Inner layer rubber, 112: Outer layer rubber, 120: Sleeve, 200: Sealing mechanism, 210: Sealing member, 211: Body part, 212: Flange part, 213: Uneven part, 214: Small diameter part, 215: Through hole, 220: Locking ring, 230: Crimping member, 231: Indentation, 300: Sealing mechanism, 400, 500: Fitting, 410, 510: Through hole, D AX :Axial direction, D R Radial direction

Claims

1. It contains rubber components and carbon black. The rubber component contains 80% by mass or more of acrylonitrile-butadiene rubber. Adsorption specific surface area A (m²) of the carbon black cetyltrimethylammonium bromide (CTAB) ２ The product (A × B × C) of the amount of compressed dibutyl phthalate (24M4DBP) absorbed by the carbon black (mL / 100g), the amount of carbon black (mL / g), and the amount of carbon black (parts by mass) per 100 parts by mass of the rubber component (C) is 600,000 or more. The specific surface area A of the carbon black adsorbing cetyltrimethylammonium bromide (CTAB) is 110 m². ２ A conductive rubber composition characterized by having a density of 1 / g or more, used for sensing the amount of strain from the change in electrical resistance value in response to strain.

2. The conductive rubber composition according to claim 1, wherein the rubber component consists solely of acrylonitrile-butadiene rubber having an acrylonitrile unit content of 34% by mass or more.

3. Adsorption specific surface area A (m²) of the carbon black cetyltrimethylammonium bromide (CTAB) ２ The conductive rubber composition according to claim 1 or 2, wherein the product of (A × B × C) of the amount of compressed dibutyl phthalate (24M4DBP) absorbed by the carbon black (mL / 100g), the amount of carbon black contained in 100 parts by mass of the rubber component (C in parts by mass) is 650,000 or more and 900,000 or less.

4. The conductive rubber composition according to any one of claims 1 to 3, wherein the content C of the carbon black relative to 100 parts by mass of the rubber component is 45 parts by mass or more and 75 parts by mass or less.

5. A method for using the conductive rubber composition according to any one of claims 1 to 4 to sense the amount of strain from the change in electrical resistance value in response to strain.

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