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 an acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45 mass% in an amount of 80 mass% or more, the carbon black has a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of 110 m2 / g or more, and the contained amount of the carbon black is 50 pts.mass or more for 100 pts.mass of the rubber component.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] A rubber actuator (so-called McKibben type) is known that has a rubber tube that expands and contracts using a working fluid and a sleeve (braided reinforcement structure) that covers the outer periphery of the rubber tube. It is known that for rubber products that repeatedly deform, such as the rubber tube of the rubber actuator, the amount of deformation of the rubber member can be measured from the electrical resistance value of the rubber member (see Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-037906 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the technology described in the above Patent Document 1, 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 a crack has occurred in the rubber member. For rubber actuators, which are filled with oil or other liquids, if a crack occurs in the rubber tube, it may lead to the tube bursting or the rubber actuator becoming unusable, so it is important to detect cracks in the rubber tube at an early stage. The inventors have conducted research and found that when the rubber actuator is expanded and contracted in 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 in one cycle changes due to distortion caused by cracks before the crack occurs, in the early stage of the crack, and in the advanced state (Figure 1). However, with typical conductive rubber, it is difficult to capture such changes in the electrical resistance waveform caused by distortion caused by cracks, and it is difficult to confirm the early stage of crack occurrence by only monitoring the electrical resistance. In contrast, by using a conductive rubber composition for sensing that has good responsiveness to changes in electrical resistance value with respect to distortion, it is possible to accurately detect the occurrence of cracks.

[0005] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a conductive rubber composition for sensing that has good responsiveness in terms of changes in electrical resistance to strain and can accurately detect the occurrence of cracks. [Means for solving the problem]

[0006] The gist of the present invention for solving the above problems is as follows.

[0007] The conductive rubber composition for sensing of the present invention contains a rubber component and carbon black, The rubber component contains 80% by mass or more of an acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45% by mass, The carbon black has a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​110 m 2 / g or more, The rubber composition is characterized in that the content of the carbon black is 50 parts by mass or more based on 100 parts by mass of the rubber component. The conductive rubber composition for sensing of the present invention has good responsiveness in terms of change in electrical resistance value to strain.

[0008] In the conductive rubber composition for sensing of the present invention, the rubber component preferably consists of only acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45 mass %, which further improves the oil resistance of the conductive rubber composition for sensing.

[0009] In the conductive rubber composition for sensing of the present invention, the carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption of 90 mL / 100 g or more, which further improves the responsiveness of the change in electrical resistance value to strain.

[0010] In a preferred embodiment of the conductive rubber composition for sensing of the present invention, the content of the carbon black is 55 parts by mass or more and 75 parts by mass or less per 100 parts by mass of the rubber component. In this case, it becomes possible to detect a change in electrical resistance value due to strain without delay and with high sensitivity. Effect of the Invention

[0011] According to the present invention, it is possible to provide a conductive rubber composition for sensing which has good responsiveness in terms of change in electrical resistance value in response to strain and is capable of detecting the occurrence of cracks with high accuracy. [Brief description of the drawings]

[0012] [Figure 1] 1 is a graph showing an electrical resistance waveform for one cycle for an example rubber actuator. [Diagram 2] FIG. 2 is a side view of an example of a rubber actuator. [Diagram 3] FIG. 2 is a partially exploded perspective view of an example of a rubber actuator. [Figure 4] FIG. 2 is a partial cross-sectional view of an example of a tube rubber. [Diagram 5] 11 is a graph showing an example of change in electrical resistance value when there is responsiveness and when there is no responsiveness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The conductive rubber composition for sensing of the present invention will be illustrated in detail below based on embodiments thereof.

[0014] <Conductive rubber composition for sensing> The conductive rubber composition for sensing of the present invention includes a rubber component and carbon black. Here, in the conductive rubber composition for sensing of the present invention, the rubber component includes 80 mass % or more of acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45 mass %, and the carbon black has a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​110 m 2 / g or more, and the content of the carbon black is 50 parts by mass or more per 100 parts by mass of the rubber component.

[0015] The CTAB adsorption specific surface area of ​​the carbon black is an index of the particle size of the carbon black. The larger the CTAB adsorption specific surface area, the smaller the particle size of the carbon black and the lower the electrical resistance value of the rubber composition. Also, the higher the carbon black content, the lower the electrical resistance value of the rubber composition. In the present invention, when 80 mass % or more of the rubber component is acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45 mass %, the CTAB adsorption specific surface area of ​​the carbon black is 110 m 2 / g or more and the carbon black content is 50 parts by mass or more per 100 parts by mass of the rubber component, the electrical resistance value of the rubber composition becomes sufficiently low, and further, the electrical resistance value changes reproducibly when strain is applied and reversibly returns to its original state when the strain is removed, thereby improving the responsiveness of the change in the electrical resistance value to strain.

[0016] As described above, the conductive rubber composition for sensing of the present invention has good responsiveness in terms of changes in electrical resistance value to strain. Therefore, by combining the conductive rubber composition for sensing of the present invention with AI learning using electrical resistance value as input, it becomes possible to detect the occurrence of cracks (AI sensing) from the dynamic behavior of changes in electrical resistance value. In addition, the conductive rubber composition for sensing of the present invention is an acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45% by mass, of which 80% by mass or more of the rubber component is high in 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 tube rubber for rubber actuators.

[0017] (Rubber component) The conductive rubber composition for sensing of the present invention contains a rubber component, and the rubber component provides rubber elasticity to the composition, enabling the rubber composition to expand and contract. The rubber component of the conductive rubber composition for sensing of the present invention contains 80% by mass or more, preferably 90% by mass or more, of acrylonitrile-butadiene rubber (NBR) having an acrylonitrile unit content of more than 45% by mass. In addition, the rubber component is preferably made only of acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45% by mass. Since acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45% by mass has excellent oil resistance, the conductive rubber composition for sensing of the present invention in which 80% by mass or more of the rubber component is acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45% by mass has high oil resistance and is suitable for applications requiring oil resistance, such as tube rubber for rubber actuators. In addition, when the rubber component is made only of acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45% by mass, the oil resistance is further improved.

[0018] The content of acrylonitrile units in the acrylonitrile-butadiene rubber (NBR) is more than 45% by mass, and if it exceeds 45% by mass, it is preferable from the viewpoint of oil resistance. Also, the content of acrylonitrile units in the acrylonitrile-butadiene rubber (NBR) is preferably 50% by mass or less from the viewpoint of fatigue resistance and crack extension resistance. The content of acrylonitrile units (bound acrylonitrile amount) of the acrylonitrile-butadiene rubber (NBR) can be measured by the Kjeldahl method in accordance with JIS K6384.

[0019] The rubber component may further contain other rubber components. As such other rubber components, various rubber components that impart rubber elasticity to the composition can be used. Examples of the other rubber components include acrylonitrile-butadiene rubber (NBR) having an acrylonitrile unit content of 45 mass% or less, natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), and chloroprene rubber (CR). The rubber components used may be one type or two or more types.

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

[0021] The carbon black has a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​110 m 2 / g or more. The CTAB adsorption specific surface area of ​​carbon black is 110m 2 When the carbon black has a particle size of 100 μm or more, the particle size is sufficiently small and the electrical resistance is sufficiently low, making it easy to detect changes in the electrical resistance and improving responsiveness. The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​the carbon black is set to 120 m from the viewpoint of making it easier to detect the change in the electrical resistance value. 2 / g or more is more preferable, and from the viewpoint of workability, 160m 2 / g or less is preferable. In this specification, the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area 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 carbon black.

[0022] The carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption of 90 mL / 100 g or more. The 24M4DBP absorption of carbon black is a physical property related to the structure of carbon black, and the larger the 24M4DBP absorption, the lower the electrical resistance of the rubber composition. The 24M4DBP absorption of carbon black is also an index of high strain loss and is related to the amount of friction between carbon blacks at high strain. At high strain, the greater the amount of friction between carbon blacks, the greater the change in electrical resistance due to expansion and contraction (high strain) during use, and the better the responsiveness of the change in electrical resistance to strain. When the 24M4DBP absorption of carbon black is 90 mL / 100 g or more, the electrical resistance of the rubber composition is sufficiently low, and the responsiveness of the change in electrical resistance to strain is further improved. The compressed dibutyl phthalate (24M4DBP) absorption amount of the carbon black is more preferably 100 mL / 100 g or more from the viewpoint of making it easier to detect changes in electrical resistance value, and is preferably 130 mL / 100 g or less from the viewpoint of suppressing variations due to kneading. In this specification, the compressed dibutyl phthalate (24M4DBP) absorption of carbon black is a value obtained by measuring the DBP (dibutyl phthalate) absorption after repeatedly applying a pressure of 24,000 psi four times in accordance with ISO 6894. The 24M4DBP absorption is used to determine the DBP absorption based on the non-destructive true structural form (primary structure) while excluding the DBP absorption due to the deformable and destructive structural form (secondary structure) caused by so-called van der Waals forces, and is an index for evaluating the skeletal structure of carbon black mainly composed of the primary structure.

[0023] The content of the carbon black is 50 parts by mass or more, preferably 55 parts by mass or more and 75 parts by mass or less, and more preferably 60 parts by mass or more and 70 parts by mass or less, relative to 100 parts by mass of the rubber component. When the content of the carbon black is less than 50 parts by mass relative to 100 parts by mass of the rubber component, the responsiveness of the change in the electrical resistance value to the strain is insufficient. On the other hand, when the content of the carbon black is 55 parts by mass or more relative to 100 parts by mass of the rubber component, the electrical resistance value of the rubber composition becomes sufficiently low (electricity flows sufficiently), and the change in the electrical resistance value becomes easier to detect. When the content of the carbon black is 75 parts by mass or less relative to 100 parts by mass of the rubber component, the electrical resistance value of the rubber composition becomes sufficiently high (electricity does not flow too much), and the change in the electrical resistance value becomes easier to detect, and the hardness of the rubber composition becomes low, and for example, the hardness becomes suitable for application to the tube rubber of a rubber actuator. If the electrical resistance is sufficiently high, electricity does not flow too much, so that the electrical resistance changes when the rubber is strained, and the change occurs immediately without delay, making it suitable for use in detecting cracks. If the electrical resistance is sufficiently low, electricity flows sufficiently and conducts electricity, making it suitable for use in detecting cracks. If the carbon black content is in the range of 55 parts by mass to 75 parts by mass per 100 parts by mass of the rubber component, it becomes possible to detect the change in electrical resistance due to strain without delay and with high sensitivity.

[0024] The carbon black is not particularly limited as long as it satisfies the above conditions, 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.

[0025] (Carbon Nanotubes) The conductive rubber composition for sensing of the present invention may further contain carbon nanotubes, which have the effect of improving the electrical conductivity of the composition.

[0026] When the conductive rubber composition for sensing of the present invention contains carbon nanotubes, the content of the carbon nanotubes is preferably less than 2 parts by mass, more preferably less than 1 part by mass, per 100 parts by mass of the rubber component. When the content of the carbon nanotubes is less than 2 parts by mass, per 100 parts by mass of the rubber component, the electrical resistance value of the rubber composition becomes sufficiently high (electricity does not flow too much), making it easier to detect changes in the electrical resistance value.

[0027] 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 have a length of 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.

[0028] The carbon nanotubes can be synthesized by plasma CVD (chemical vapor deposition), thermal CVD, surface decomposition, flow gas phase synthesis, arc discharge, etc., and commercially available products can also be used. Examples of commercially available carbon nanotubes include carbon nanotubes manufactured by KUMHO, 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.

[0029] <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 the rubber component with carbon black, and optionally further compound carbon nanotubes, and then kneading the mixture, followed by heating and extrusion, etc.

[0030] In addition to the above-mentioned components, the conductive rubber composition for sensing may contain 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.

[0031] <Applications of conductive rubber composition for sensing> The conductive rubber composition for sensing of the present invention described above has good responsiveness of the change in electrical resistance value to strain, and can therefore be used for sensing (detecting, detecting, sensing) the amount of strain. The conductive rubber composition for sensing can be used in various rubber products, and can be particularly suitably used for the tube rubber of a rubber actuator. In addition to rubber actuators, the conductive rubber composition can be appropriately used for any rubber member that generates strain during use, such as tires, anti-vibration rubber, vibration-isolating rubber, conveyor belts, crawlers, gloves, etc., and its uses are not limited to the above examples and can be widely applied.

[0032] (Rubber Actuator) A rubber actuator of a preferred embodiment using the conductive rubber composition for sensing of the present invention is shown in Fig. 2. The rubber actuator 10 shown in Fig. 2 includes an actuator body 100 composed of a cylindrical tube rubber 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 rubber 110, and the above-mentioned conductive rubber composition for sensing of the present invention is used for the tube rubber 110.

[0033] Fig. 2 is a side view of the rubber actuator 10 according to this embodiment. As shown in Fig. 2, the rubber actuator 10 includes an actuator body 100, a sealing mechanism 200, and a sealing mechanism 300. Furthermore, a connecting portion 20 is provided on each end of the rubber actuator 10. Furthermore, a resistance value measuring device 30 is connected to each connecting portion 20.

[0034] The actuator body 100 is composed of a tube rubber 110 and a sleeve 120. A working fluid flows into the actuator body 100 through a fitting 400 and a passage hole 410. Here, the rubber actuator 10 is operated by fluid pressure and may be of a pneumatic or hydraulic type. When a liquid is used as the working fluid, the liquid may be oil, water, or the like. When the rubber actuator is of a hydraulic type, the working fluid may be hydraulic oil that has been conventionally used in hydraulic drive systems.

[0035] When the working fluid flows into the rubber tube 110, the actuator body 100 moves in the axial direction D AX contracts in the radial direction D R In addition, the actuator body 100 expands in the axial direction D of the actuator body 100 as the working fluid flows out of the tube rubber 110. AX and expands in the radial direction D R This change in shape of the actuator body 100 allows the rubber actuator 10 to function as an actuator. Moreover, such a rubber actuator 10 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). The connecting part 20 is connected to the members that make up the limb. In this embodiment, the resistance value measuring device 30 is connected to the connecting part 20, but the connection point of the resistance value measuring device 30 is not limited thereto, and it may be directly connected to both ends of the tube rubber 110, for example.

[0036] The sealing mechanism 200 and the sealing mechanism 300 are AX The sealing mechanism 200 seals both ends of the actuator body 100 in the axial direction D. Specifically, the sealing mechanism 200 includes a sealing member 210 and a crimping member 230. The sealing member 210 seals both ends of the actuator body 100 in the axial direction D. AXThe crimping member 230 crimps the actuator body 100 together with the sealing member 210. An indentation 231 is formed on the outer circumferential surface of the crimping member 230, which is a mark caused by the crimping member 230 being crimped by a jig.

[0037] 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 10, 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 the passage hole 410 and flows into the inside of the actuator body 100, specifically, into the inside of the tube rubber 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 10. When the working fluid is injected into the rubber actuator 10 at the beginning of the operation of the rubber actuator 10, the gas originally present inside the rubber actuator 10 is discharged from the fitting 500 through the passage hole 510.

[0038] 3 is a partially exploded perspective view of the rubber actuator 10. As shown in FIG. As described above, the actuator body 100 is composed of the tube rubber 110 and the sleeve 120.

[0039] The tube rubber 110 is a cylindrical body that expands and contracts due to fluid pressure. The tube rubber 110 repeatedly contracts and expands due to the working fluid, and the above-mentioned conductive rubber composition for sensing of the present invention is applied to the tube rubber 110.

[0040] The sleeve 120 is cylindrical and covers the outer circumferential surface of the tube rubber 110. The sleeve 120 is a structure in which cords oriented in a predetermined direction are woven, and diamond shapes are repeated by crossing the oriented cords. By having such a shape, the sleeve 120 undergoes pantograph deformation and follows the contraction and expansion of the tube rubber 110 while regulating it.

[0041] In FIG. 3, the sealing mechanism 200 is disposed in the axial direction D of the actuator body 100. AX The sealing mechanism 200 is composed of a sealing member 210, a locking ring 220, and a crimping member 230.

[0042] 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.

[0043] The body portion 211 has a cylindrical shape, and a through hole 215 through which the working fluid passes is formed in the body portion 211. The through hole 215 communicates with the through hole 410 (see FIG. 2). The tube rubber 110 is inserted into the body portion 211.

[0044] The flange portion 212 is connected to the body portion 211 and is spaced apart from the body portion 211 in the axial direction D of the actuator 10. AX The flange portion 212 is located on the end side of the body portion 211 in the radial direction D. R The flange portion 212 engages the tube rubber 110 and the engaging ring 220 that are inserted into the body portion 211.

[0045] 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 rubber 110 inserted into the body portion 211. It is preferable that the uneven portion 213 is formed to have three or more convex portions. Further, at a position closer to flange portion 212 of body portion 211, small diameter portion 214 having an outer diameter smaller than that of body portion 211 is formed.

[0046] The locking ring 220 locks the sleeve 120. Specifically, the sleeve 120 is rotated in the radial direction D via the locking ring 220. R It is folded back on 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. That is, the locking ring 220 is arranged in the radial direction D of the body portion 211. R The sleeve 120 is locked at a position on the outside, 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. 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 .

[0047] The crimping member 230 crimps the actuator body 100 together with the sealing member 210. Metals such as aluminum alloys, brass, and iron can be used as the crimping member 230. When the crimping member 230 is crimped by a crimping jig, an indentation 231 as shown in FIG.

[0048] FIG. 4 is a partial cross-sectional view of one embodiment of the tube rubber 110. The tube rubber 110 shown in FIG. 4 has an inner layer rubber 111 located on the inner surface side of the tube rubber, and a radial direction D R Adjacent to the outside, an outer layer rubber 112 is positioned on the outer surface side of the tube rubber 110, forming a two-layer structure.

[0049] The conductive rubber composition for sensing of the present invention 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 into the gap between the inner layer rubber 111 and the outer layer rubber 112, which may reduce the durability of the tube rubber 110. However, by applying the conductive rubber composition for sensing of the present invention described above to the inner layer rubber 111, cracks in the inner layer rubber 111 can be found early, and the infiltration of the working fluid can be prevented. By replacing the tube rubber 110 at an appropriate time, the rubber actuator can be prevented from stopping functioning.

[0050] On the other hand, since the outer rubber layer 112 comes into contact with the sleeve 120, it is preferable to use a rubber composition that is excellent in crack resistance, abrasion resistance, sliding properties, etc., and can withstand the load from the sleeve 120 side.

[0051] The tube rubber 110 is not limited to a two-layer structure, and may have a one-layer structure or a laminated structure of three or more layers. When the tube rubber 110 has a laminated structure of three or more layers, it is preferable to apply the above-mentioned conductive rubber composition for sensing of the present invention to the innermost layer.

[0052] As described above, the tube rubber 110 repeatedly contracts and expands due to the working fluid, and the conductive rubber composition for sensing of the present invention is applied to it. Here, when the contraction rate of the actuator body 100 becomes high, the electrical resistance value of the actuator body 100 (tube rubber 110) becomes low. This is because the actuator body 100 is compressed in the axial direction D AX When the tube rubber 110 is contracted, the tube rubber 110 moves in the radial direction D within a predetermined range restricted by the sleeve 120. R When the tube rubber 110 expands, the thickness of the tube rubber 110 becomes thinner, and the distance between the carbon black particles contained in the tube rubber 110 becomes narrower. Specifically, when the actuator body 100 contracts, the tube rubber 110 expands, reducing the thickness of the tube rubber 110. As a result, the dimension (distance) of the carbon black in the thickness direction becomes narrower, and the carbon black comes 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 particles decreases, so that the conductivity of the tube rubber 110 increases, in other words, the electrical resistance value of the tube rubber 110 decreases.

[0053] Furthermore, cracks may occur in the tube rubber 110 due to repeated contraction and expansion by the working fluid, but the pattern of change in electrical resistance is different at each stage: no cracks, early cracking, and cracks, as shown in Figure 1. Here, by analyzing the dynamic behavior of the change in electrical resistance caused by distortion due to the occurrence of cracks in the tube rubber 110 using a statistical method or having an AI learn the dynamic behavior of the change in electrical resistance, 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

[0054] 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 in any way.

[0055] <Preparation of Rubber Composition> A rubber composition having the composition shown in Table 1 was prepared by kneading in a conventional manner. The type, physical properties and compounding amount of the carbon black used are shown in Table 2.

[0056] [Table 1]

[0057] *1 NBR: Acrylonitrile-butadiene rubber, acrylonitrile unit content = 48% by mass, manufactured by JSR Corporation, product name "N215SL" *2 Carbon black: The type, properties and amount of carbon black used are shown in Table 2. *3 Ester oil: Hallstar Company, product name "TP-95" *4 Hydrogenated fatty acid: New Japan Chemical Co., Ltd., product name "Stearic acid 50S" *5 Antioxidant: 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 type 2 granulated product" *7 Vulcanization accelerator A: N-cyclohexyl-2-benzothiazolylsulfenamide, Sanshin Chemical Industry Co., Ltd., product name "Suncerer CM-G" *8 Vulcanization accelerator B: Tetrakis(2-ethylhexyl)thiuram disulfide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela TOT" *9 Sulfur: Manufactured by Hosoi Chemical Industry Co., Ltd., product name "HK200-5", shown as the amount of sulfur content in Table 1

[0058] <Tests on vulcanized rubber> A rubber sheet having a thickness of 1 mm was prepared from the obtained rubber composition and vulcanized at 155°C for 45 minutes to prepare a vulcanized rubber sheet. A rectangular test piece having a size of 4.7 mm x 40 mm was prepared from the vulcanized rubber sheet. The test piece was evaluated for the presence or absence of strain response by the following method.

[0059] (1) Strain response test The prepared test specimen was stretched 10 times to 70% at room temperature with a chuck distance of 20 mm (after repeating the cycle of 0% → 70% stretch → 0% 10 times), and then dynamic electrical measurements were performed at a tensile speed of 6 mm / sec using a tensile tester (K18003) manufactured by System One. The electrical resistance was measured by sampling at DC 10 V and 200 Hz. The electrical resistance value varies reproducibly depending on the strain, and the ratio of the signal value (S), which is the difference between the minimum and maximum electrical resistance values ​​in the region of 10% stretch → 70% stretch → 10% stretch, to the standard deviation (n) of the electrical resistance value in the region of 0% to 10% stretch was evaluated according to the following criteria. ○: S / n ratio 9 or more, distortion response ×: S / n ratio less than 9, no distortion response An example of the strain dependency of electrical resistance is shown in Figure 5. As shown in Figure 5, rubber with a sufficiently large S / n ratio has a large change in electrical resistance due to strain and is responsive to strain, whereas rubber with a small S / n ratio has a small change in electrical resistance due to strain and has no response to strain. The results of the above tests are shown in Table 2.

[0060] <Testing with rubber actuator> The rubber compositions of Example 7 and Comparative Example 8 were applied to the inner layer rubber of a tube rubber having a two-layer structure of an inner layer rubber and an outer layer rubber as shown in FIG. 4 to prepare a cylindrical tube rubber.

[0061] Two aramid fibers of 2200 dtex were used as raw yarns, and the fibers were first twisted 12 times / 10 cm and then second twisted 12 times / 10 cm to produce an aramid fiber cord with a diameter of 0.7 mm. A mesh-like sleeve was prepared by weaving 64 of the aramid fiber cords. This sleeve was a mesh-like tubular body in which 64 aramid fiber cords were observed on the circumference in the cross section. Specifically, this sleeve was a mesh-like tubular body in which 32 aramid fiber cords arranged in parallel and spirally at equal intervals were alternately weaved with another 32 aramid fiber cords arranged in parallel and spirally at equal intervals, and the angle of each cord with respect to the axial direction of the sleeve was 25 degrees.

[0062] Using the tube rubber and the mesh sleeve, a rubber actuator having the structure shown in Figures 2 and 3 was produced. The length between sealing mechanism 200 and sealing mechanism 300 was 250 mm. UF46 manufactured by Cosmo Super Epoch Co., Ltd. was used as the hydraulic oil for the tube rubber.

[0063] (2) Crack detection test Hydraulic oil was injected into the rubber tube, and the air in the rubber tube was thoroughly replaced with hydraulic oil. Hydraulic oil was injected so that the pressure of the hydraulic oil in the rubber tube alternated between 0 MPa and 5 MPa every 3 seconds, and the tube was repeatedly stretched and contracted until a crack appeared in the tube, which then propagated until the actuator could no longer function. At this time, the electrical resistance value was monitored to attempt to detect the occurrence of cracks, and the occurrence of cracks was successfully detected using AI for the rubber actuator using the rubber sample of Example 7, which was evaluated as having "strain responsiveness," as the tube rubber. On the other hand, the occurrence of cracks could not be detected for the rubber actuator using the rubber sample of Comparative Example 8, which was evaluated as having "no strain responsiveness," as the tube rubber.

[0064] [Table 2]

[0065] *10 CB1: CTAB adsorption specific surface area=112m 2 / g, 24M4DBP absorption capacity = 100mL / 100g, Tokai Carbon Co., Ltd., product name "Seast 6" *11 CB2: CTAB adsorption specific surface area=123m 2 / g, 24M4DBP absorption capacity = 100mL / 100g, Asahi Carbon Co., Ltd., product name "Asahi #78" *12 CB3: CTAB adsorption specific surface area=83m 2 / g, 24M4DBP absorption capacity = 72mL / 100g, Asahi Carbon Co., Ltd., product name "Asahi #70L" *13 CB4: CTAB adsorption specific surface area=74m 2 / g, 24M4DBP absorption capacity = 90mL / 100g, Asahi Carbon Co., Ltd., product name "Asahi #70K"

[0066] From the results shown in Table 2, when 80% by mass or more of the rubber component is acrylonitrile-butadiene rubber with an acrylonitrile unit content of more than 45% by mass, the CTAB adsorption specific surface area A of carbon black is 110 m 2 / g or more and the carbon black content is 50 parts by mass or more per 100 parts by mass of the rubber component, the responsiveness of the change in electrical resistance value to strain is improved, and the occurrence of cracks can be detected. [Industrial Applicability]

[0067] The conductive rubber composition for sensing of the present invention has good responsiveness in terms of changes in electrical resistance to strain, and as an example, when applied to the tube rubber of a rubber actuator, it can be used to detect the occurrence of cracks from changes in electrical resistance. [Explanation of symbols]

[0068] 10: rubber actuator, 20: connection part, 30: resistance value measuring device, 100: actuator body, 110: tube rubber, 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: passage hole, 220: locking ring, 230: crimping member, 231: indentation, 300: sealing mechanism, 400, 500: fitting, 410, 510: passage hole, D AX :Axial direction, D R : Radial direction

Claims

1. The rubber composition includes a rubber component and carbon black, The rubber component contains 80% by mass or more of acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45% by mass, The carbon black has a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​110 m ２ / g or more, A conductive rubber composition for sensing, characterized in that the content of the carbon black is 50 parts by mass or more per 100 parts by mass of the rubber component.

2. The conductive rubber composition for sensing according to claim 1, wherein the rubber component consists solely of acrylonitrile-butadiene rubber having an acrylonitrile unit content of more than 45 mass%.

3. The conductive rubber composition for sensing according to claim 1 or 2, wherein the carbon black has a compressed dibutyl phthalate (24M4DBP) absorption of 90 mL / 100 g or more.

4. The conductive rubber composition for sensing according to any one of claims 1 to 3, wherein the content of the carbon black is 55 parts by mass or more and 75 parts by mass or less per 100 parts by mass of the rubber component.

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