JP2008239746A - Elastomer composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an elastomer composite material useful as a deformation sensor material capable of detecting deformation or load in a wide range of members and portions. <P>SOLUTION: The elastomer composite material has an elastomer and a carbon based filler having a graphene layered structure. Onto a surface of the carbon based filler, a crosslinkable functional group is previously introduced by a ligand exchange reaction using a metallocene derivative having the crosslinkable functional group. By co-crosslinking of the crosslinkable functional group on the surface of the carbon based filler and the elastomer, the carbon based filler and the elastomer are fixed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an elastomer composite material used as, for example, a deformation sensor material capable of detecting deformation of a member.

For example, sensors using piezoelectric ceramics or piezoelectric polymers such as PVdF (polyvinylidene fluoride) have been proposed as means for detecting deformation and deformation of members and the magnitude and distribution of loads acting on the members. Patent Document 1 introduces a pressure-sensitive conductive elastomer whose electric resistance decreases with respect to deformation such as compression and expansion.
JP-A-4-349301

  The pressure-sensitive conductive elastomer described in Patent Document 1 is configured by dispersing a conductive filler or the like in the elastomer. This pressure-sensitive conductive elastomer has a characteristic that electric resistance decreases when it is deformed. That is, in the non-compressed state before deformation, the electric resistance of the pressure-sensitive conductive elastomer is large, and when compressed, it conducts by contact with the conductive filler in the elastomer and the electric resistance decreases. Therefore, when the conductive filler is brought into a certain contact state due to compression, the change in electrical resistance is reduced. For this reason, a deformation sensor using a pressure-sensitive conductive elastomer has a narrow measurement range. Further, the sensitivity varies greatly depending on the blending ratio of the conductive filler and the like. Furthermore, since the elastomer thermally expands at high temperatures, the behavior of decreasing electrical resistance against deformation changes, and the desired response sensitivity cannot be obtained. That is, in the case of a deformation sensor using a pressure-sensitive conductive elastomer, the operable temperature range is limited.

  This invention is made | formed in view of such a situation, and makes it a subject to provide an elastomer composite material useful as a deformation | transformation sensor material etc. which can detect the deformation | transformation and load in the wide range of a member and a site | part.

  As a result of intensive studies on materials that can be used for deformation sensors, the present inventor has developed a very unique elastomer composite material in which the electrical resistance increases as the amount of elastic deformation increases. Here, “elastic deformation” includes all deformation due to compression, extension, bending, and the like. The developed elastomer composite material is formed by filling an elastomer with a conductive filler in a predetermined state. According to the elastomer composite material, a three-dimensional conductive path is formed by contact between the conductive fillers via the elastomer component. For this reason, the elastomer composite material has high conductivity in a state in which no load is applied (hereinafter, referred to as “no-load state” as appropriate), in other words, in a natural state that is not deformed.

  As described above, in the conventional pressure-sensitive conductive elastomer, the electric resistance is large in the non-compressed state, and the electric resistance is reduced when deformed by compression. This can be explained as follows from the structure of the pressure-sensitive conductive elastomer. That is, since the filling rate of the conductive filler in the elastomer is low, the conductive fillers are separated from each other in a no-load state. Therefore, in the no-load state, the electric resistance of the pressure-sensitive conductive elastomer is large. On the other hand, when a load is applied and the pressure-sensitive conductive elastomer is deformed, the conductive fillers come into contact with each other, and a one-dimensional conductive path is formed. This reduces the electrical resistance.

  On the other hand, the above-mentioned elastomer composite material developed by the present inventors increases in electrical resistance as the amount of elastic deformation increases. The reason is considered as follows. FIG. 1 and FIG. 2 show changes in the conductive path of the elastomer composite material before and after applying a load as a model. However, what is shown in FIG. 1 and FIG. 2 is an example of the elastomer composite material, and does not limit the filling state and shape of the conductive filler at all.

  As shown in FIG. 1, in the elastomer composite material 100, most of the conductive fillers 102 exist in the state of primary particles (substantially in a single state) in the elastomer 101. Moreover, the filling rate of the conductive filler 102 is high, and it is blended in a state close to closest packing. Thereby, in the no-load state, the elastomer composite material 100 is formed with a three-dimensional conductive path P by the conductive filler 102. Therefore, in the no-load state, the electrical resistance of the elastomer composite material 100 is small. On the other hand, as shown in FIG. 2, when a load is applied to the elastomer composite material 100, the elastomer composite material 100 is elastically deformed (the dotted line frame in FIG. 2 indicates the no-load state of FIG. 1). . Here, since the conductive filler 102 is blended in a state close to closest packing, there is almost no space where the conductive filler 102 can move. Therefore, when the elastomer composite material 100 is elastically deformed, the conductive fillers 102 repel each other, and the contact state between the conductive fillers 102 changes. As a result, the three-dimensional conductive path P collapses and the electrical resistance increases.

  Thus, although the said elastomer composite material is a novel material that electrical resistance increases as the amount of elastic deformation increases, as a result of further studies, the following problems have been clarified. That is, since the elastomer is thermally expanded at a high temperature, the interval between the conductive fillers is increased. For this reason, it becomes difficult to form a three-dimensional conductive path of the conductive filler in a no-load state. As a result, the conductivity of the elastomer composite material in a no-load state is reduced. Further, since the three-dimensional conductive path is reduced, it is difficult to obtain a desired increase in electric resistance with respect to deformation, and the response sensitivity is lowered. Furthermore, when the adhesiveness between the two is not sufficient due to the combination of the elastomer and the conductive filler, the conductive filler moves from the initial position and gradually aggregates by repeating elastic deformation. As a result, the three-dimensional conductive path formed in the initial state is broken, and the conductivity in a no-load state is lowered. In addition, mechanical properties such as tensile strength of the elastomer composite material may be reduced due to aggregation of the conductive filler.

  Therefore, the elastomer composite material of the present invention made to solve these problems has an elastomer and a carbon-based filler having a graphene layer structure, and the surface of the carbon-based filler has a crosslinkable functional group. The crosslinkable functional group is previously introduced by a ligand exchange reaction using a metallocene derivative having a group, and the crosslinkable functional group on the surface of the carbon filler and the elastomer are co-crosslinked. It is characterized by.

  “Elastomer” in the present invention includes rubber and thermoplastic elastomer. Usually, for the purpose of reinforcing the elastomer, carbon black or the like having a relatively low graphitization degree (crystallinity), a large specific surface area, and a large number of functional groups on the surface is used. Carbon black is considered to have a graphene layered structure in which several layers (graphene sheets) bonded with a carbon six-membered ring and spread in a net shape are stacked.

  On the other hand, a carbon-based filler with a developed graphene layer structure, a relatively high degree of graphitization (crystallinity), and a small number of functional groups on the surface is poor in reinforcement to the elastomer, but is excellent in performance to impart conductivity to the elastomer. . Since the surface of the carbon-based filler having a high degree of graphitization (crystallinity) has few functional groups, it is difficult to introduce new functional groups or polymers on the surface of the carbon-based filler using the functional groups as a foothold. Therefore, it is difficult to improve the surface state of the carbon-based filler for the purpose of improving the reinforcing property for the elastomer.

  In this regard, on the surface of the carbon-based filler having a graphene layer structure included in the elastomer composite material of the present invention, the crosslinkable functional group is previously formed by a ligand exchange reaction using a metallocene derivative having a crosslinkable functional group. Has been introduced. That is, by replacing the ligand of the metallocene derivative with a carbon six-membered ring on the surface of the carbon-based filler, a crosslinkable functional group capable of co-crosslinking with the elastomer is formed on the surface of the carbon-based filler regardless of the functional group. It has been introduced. The introduced crosslinkable functional group and the elastomer are chemically bonded by co-crosslinking.

  FIG. 3 shows a model of the bonding state between the elastomer and the carbon-based filler in the elastomer composite material of the present invention. As shown in FIG. 3, a crosslinkable functional group 12 is introduced on the surface of the carbon-based filler 10 by a metallocene derivative. The crosslinkable functional group 12 and the elastomer 11 are co-crosslinked and chemically bonded. That is, the carbon filler 10 is fixed to the elastomer 11.

  As described above, since the adhesiveness between the elastomer and the carbon-based filler is good, that is, both are difficult to separate, the elastomer composite material of the present invention is excellent in mechanical properties such as tensile strength. As will be described in detail later, when the carbon-based filler is filled in a predetermined state in the elastomer, the electrical resistance of the elastomer composite material of the present invention increases as the amount of elastic deformation increases. Here, the elastomer is fixed to a carbon-based filler that hardly thermally expands. For this reason, even if the temperature rises, the expansion of the elastomer is suppressed. Therefore, a decrease in conductivity in a no-load state at a high temperature is suppressed. Further, since the reduction of the three-dimensional conductive path due to the expansion of the elastomer is suppressed, the desired response sensitivity can be maintained even at high temperatures. Furthermore, since the adhesiveness between the elastomer and the carbon-based filler is good, the carbon-based filler hardly aggregates even when elastic deformation is repeated. For this reason, even if it is used repeatedly, the initial three-dimensional conductive path can be maintained. Therefore, the elastomer composite material of the present invention is excellent in durability.

  Hereinafter, embodiments of the elastomer composite material of the present invention will be described. The elastomer composite material of the present invention is not limited to the following embodiments, and can be implemented in various forms that have been modified or improved by those skilled in the art without departing from the scope of the present invention. be able to.

  In the elastomer composite material of the present invention, the elastomer may be appropriately selected from rubber and thermoplastic elastomer. For example, when the elastomer composite material of the present invention is used as a deformation sensor material, the elastomer is desirably insulating. In order to develop the characteristic that the electrical resistance increases as the amount of elastic deformation increases, it is desirable to select in consideration of the relationship with the carbon-based filler described later.

  For example, when a mixture of an elastomer and a carbon-based filler (elastomer composition) is prepared, it is desirable to use one having a saturated volume fraction (φs) in a percolation curve of 35 vol% or more. When an electrically conductive carbon-based filler is mixed with an insulating elastomer to form an elastomer composition, the electrical resistance of the elastomer composition varies depending on the amount of the carbon-based filler. FIG. 4 schematically shows the relationship between the blending amount of the carbon-based filler and the electrical resistance in the elastomer composition.

  As shown in FIG. 4, when the carbon-based filler 103 is mixed with the elastomer 101, the electrical resistance of the elastomer composition is almost the same as the electrical resistance of the elastomer 101 at the beginning. However, when the blending amount of the carbon-based filler 103 reaches a certain volume fraction, the electrical resistance rapidly decreases and an insulator-conductor transition occurs (first inflection point). The blending amount of the carbon-based filler 103 at the first inflection point is referred to as a critical volume fraction (φc). Further, when the carbon-based filler 103 is further mixed, from a certain volume fraction, the change in electric resistance is reduced and the change in electric resistance is saturated (second inflection point). The blending amount of the carbon-based filler 103 at the second inflection point is referred to as a saturated volume fraction (φs). Such a change in electrical resistance is called a percolation curve and is considered to be due to the formation of a conductive path P1 by the carbon-based filler 103 in the elastomer 101.

  For example, when the carbon filler is agglomerated and formed into an aggregate due to the small particle size of the carbon filler or poor compatibility between the carbon filler and the elastomer, one-dimensional conductive A path is easily formed. In such a case, the critical volume fraction (φc) of the elastomer composition is relatively small, such as about 20 vol%. Similarly, the saturated volume fraction (φs) is also relatively small. In other words, when the critical volume fraction (φc) and the saturated volume fraction (φs) are small, the carbon-based filler is unlikely to exist as primary particles, and secondary particles (aggregates) are easily formed. Therefore, in this case, it is difficult to blend a large amount of the carbon-based filler in the elastomer. That is, it is difficult to mix the carbon-based filler in a state close to closest packing. In addition, when a large amount of a carbon-based filler having a small particle diameter is blended, the aggregate structure grows three-dimensionally, so that the change in electrical resistance against deformation becomes poor.

  Here, when the saturated volume fraction (φs) of the elastomer composition is 35 vol% or more, the carbon-based filler can be stably present in a substantially single particle state in the elastomer. Therefore, a carbon-type filler can be mix | blended with high filling rate in an elastomer. A three-dimensional conductive path is formed in the elastomer composite material of the present invention by blending the elastomer with a carbon filler in a substantially single particle state and at a high filling rate. That is, the elastomer composite material of the present invention has high conductivity in a no-load state. Further, the electrical resistance increases as the amount of elastic deformation increases. In the present specification, the “substantially single particle state” means that 50% by weight or more when the total weight of the carbon-based filler is 100% by weight is not an aggregated secondary particle but a single primary particle. It means that it exists in a state. Further, “high filling rate” means that the carbon-based filler is blended in a state close to closest packing.

  In the region of the saturated volume fraction (φs) or more, the electrical resistance of the elastomer composite material of the present invention is low, and stable conductivity is expressed. Therefore, when the saturated volume fraction (φs) is 35 vol% or more, the range of change in electrical resistance from the conductor to the insulator when deformed is widened. It is more preferable to use a saturated volume fraction (φs) of 40 vol% or more.

  Specific examples of elastomers include, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), acrylonitrile-butadiene copolymer rubber (NBR), styrene-butadiene copolymer rubber (SBR), Ethylene-propylene copolymer rubber [ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), etc.], butyl rubber (IIR), halogenated butyl rubber (Cl-IIR, Br-IIR, etc.) ), Hydrogenated nitrile rubber (H-NBR), chloroprene rubber (CR), acrylic rubber (AR), chlorosulfonated polyethylene rubber (CSM), hydrin rubber, silicone rubber, fluorine rubber, urethane rubber, synthetic latex and the like. . Examples of the thermoplastic elastomer include various thermoplastic elastomers such as styrene, olefin, urethane, polyester, polyamide, and fluorine, and derivatives thereof. Of these, one kind may be used alone, or two or more kinds may be used in combination. Among these, EPDM is preferable because it has extremely good compatibility with the carbon-based filler. NBR and silicone rubber having good compatibility with the carbon-based filler are also suitable.

  In the elastomer composite material of the present invention, the type of carbon-based filler is not particularly limited as long as it is a particle having a graphene layered structure. For example, carbon beads, carbon black, carbon nanotubes (CNT), mesocarbon microbeads (MCMB), vapor grown carbon fibers (VGCF), etc., produced by carbonizing a thermosetting resin can be used. Of these, one can be used alone, or two or more can be used in combination.

  In addition, the shape of the carbon-based filler is not particularly limited, such as a spherical shape, a needle shape, a prismatic shape, a scale shape, and the like. For example, when the elastomer composite material of the present invention exhibits the characteristic that the electrical resistance increases as the amount of elastic deformation increases, the aspect ratio of the carbon-based filler (the ratio of the long side to the short side) is 1 or more. A range of 2 or less is desirable. This is because when the aspect ratio is larger than 2, a one-dimensional conductive path is easily formed by contact between the carbon-based fillers. In this case, the saturated volume fraction (φs) may be less than 35 vol%. Further, from the viewpoint of bringing the filling state of the carbon-based filler in the elastomer closer to the close-packed filling state, it is preferable to employ particles having a true sphere or a shape very close to a true sphere (substantially spherical) as the carbon-based filler.

  Further, it is desirable that the carbon-based filler is present in the form of primary particles without being aggregated as much as possible. Therefore, when selecting the carbon-based filler, it is preferable to consider the average particle diameter, compatibility with the elastomer, and the like. For example, when a substantially spherical carbon-based filler is employed, the average particle size (primary particles) of the carbon-based filler is desirably 0.05 μm or more and 100 μm or less. If it is less than 0.05 μm, it tends to aggregate and form secondary particles. Moreover, there exists a possibility that the said saturated volume fraction ((phi) s) may be less than 35 vol%. Preferably it is 0.5 micrometer or more, More preferably, it is 1 micrometer or more. On the other hand, when the thickness exceeds 100 μm, the translational motion (parallel motion) of the carbon-based filler due to elastic deformation becomes relatively smaller than the particle diameter, and the change in electric resistance against the elastic deformation of the elastomer composite material becomes slow. Preferably it is 60 micrometers or less, More preferably, it is 30 micrometers or less. In addition, the critical volume fraction (φc) and the saturated volume fraction (φs) are within the desired ranges by appropriately adjusting the combination of the carbon-based filler and the elastomer, the average particle diameter of the carbon-based filler, and the like. Can be adjusted.

  In addition, the value of D90 / D10 in the particle size distribution of the carbon-based filler is desirably 1 or more and 30 or less. Here, D90 is the particle diameter at which the cumulative weight is 90% in the cumulative particle size curve, and D10 is the particle diameter at which the cumulative weight is 10%. When the value of D90 / D10 exceeds 30, since the particle size distribution becomes broad, the increase behavior of the electric resistance against the elastic deformation of the elastomer composite material becomes unstable. Thereby, the reproducibility of detection may be reduced. It is more preferable that the value of D90 / D10 is 10 or less. In addition, when using 2 or more types of particle | grains as a carbon-type filler, the value of D90 / D10 should just be 100 or less.

  As such a carbon-based filler, for example, various carbon beads are suitable. Specifically, Osaka Gas Chemical Co., Ltd. mesocarbon micro beads [MCMB6-28 (average particle size of about 6 μm), MCMB10-28 (average particle size of about 10 μm), MCMB25-28 (average particle size of about 25 μm)], Carbon micro beads manufactured by Nippon Carbon Co., Ltd .: Nika beads (registered trademark) ICB, Nika beads PC, Nika beads MC, Nika beads MSB [ICB 0320 (average particle size of about 3 μm), ICB 0520 (average particle size of about 5 μm), ICB 1020 (average particle size of about 10 μm) ), PC0720 (average particle diameter of about 7 μm), MC0520 (average particle diameter of about 5 μm)], Nisshinbo carbon beads (average particle diameter of about 10 μm), and the like.

  Moreover, in order to express desired conductivity in the elastomer composite material of the present invention, it is desirable that the carbon-based filler is blended at a ratio equal to or higher than the critical volume fraction (φc) in the percolation curve. Here, from the viewpoint of blending the carbon-based filler in a substantially single particle state with a high filling rate, the critical volume fraction (φc) is desirably 30 vol% or more. It is more preferable that it is 35 vol% or more. That is, in other words, the filling rate of the carbon-based filler is desirably 30 vol% or more when the total volume of the elastomer composite material is 100 vol%. In the case of less than 30 vol%, the carbon-based filler is not blended in a state close to the closest packing, so that desired conductivity is not exhibited. In addition, the change in electric resistance with respect to elastic deformation of the elastomer composite material becomes slow, and it becomes difficult to control the increase behavior of the electric resistance. It is more preferable that it is 35 vol% or more. On the other hand, the filling rate of the carbon-based filler is desirably 65 vol% or less when the total volume of the elastomer composite material is 100 vol%. When it exceeds 65 vol%, mixing with an elastomer becomes difficult and molding processability is lowered. In addition, the elastomer composite material is less likely to be elastically deformed. It is more preferable that it is 55 vol% or less.

  On the surface of the carbon filler, a crosslinkable functional group capable of co-crosslinking with the elastomer is introduced in advance. The crosslinkable functional group may be at least one selected from a vinyl group, an amino group, an epoxy group, a carboxy group, and a hydroxyl group. The crosslinkable functional group is introduced onto the surface of the carbon-based filler by a ligand exchange reaction using a metallocene derivative. Here, the metallocene is an organometallic compound in which two cyclopentadienyl anions are coordinated to a metal ion such as iron, cobalt, or nickel. The metallocene derivative should just have one or more crosslinkable functional groups in one of the cyclopentadienyl rings. Further, from the viewpoint of not impairing the conductivity of the carbon-based filler, it is desirable that the molecular weight of the metallocene derivative having a crosslinkable functional group is small. For example, those having a molecular weight of 200 or more and 2000 or less are suitable. From the viewpoint that various derivatives are easily available, ferrocene derivatives may be used. For example, vinyl ferrocene, ferrocene carboxylic acid, ferrocene acetic acid, amino ferrocene, ferrocene methanol and the like are suitable.

  The ligand exchange reaction can be performed, for example, by dispersing a carbon-based filler and a metallocene derivative in a solvent and heating and stirring at a predetermined temperature in the presence of aluminum and aluminum chloride. The solvent may be appropriately selected depending on the type of metallocene derivative, the reaction temperature, and the like. For example, dioxane, tetrahydrofuran, cyclohexane, decalin and the like can be used. Ligand exchange reaction, that is, one cyclopentadienyl ring of the metallocene derivative is replaced with a carbon six-membered ring on the surface of the carbon filler, whereby a crosslinkable functional group is introduced on the surface of the carbon filler. The introduced crosslinkable functional group co-crosslinks with the elastomer during vulcanization in the production of the elastomer composite material of the present invention.

The introduction rate of the crosslinkable functional group is desirably less than 15% from the viewpoint of not impairing the conductivity of the carbon-based filler, for example. Here, the introduction rate of the crosslinkable functional group is a value calculated by the following formula (1).
Crosslinkable functional group introduction rate (%) = Wf / (Wc + Wf) × 100 (1)
[In formula (1), Wf is the weight of the metallocene derivative having a crosslinkable functional group. Wc is the weight of the carbon-based filler. ]

  The elastomer composite material of the present invention may contain various additives in addition to the elastomer and the carbon-based filler. Examples of the additive include a crosslinking agent, a vulcanization accelerator, a vulcanization aid, an antiaging agent, a plasticizer, a softening agent, and a colorant.

  The elastomer composite material of the present invention can be produced, for example, as follows. First, additives such as a vulcanization aid and a softening agent are added to the elastomer and kneaded. Subsequently, after adding and kneading a carbon-based filler having a crosslinkable functional group introduced therein, a crosslinker and a vulcanization accelerator are further added and kneaded to obtain an elastomer composition. Next, the elastomer composition is formed into a predetermined shape, filled in a mold, and press vulcanized under predetermined conditions.

  Hereinafter, the elastomer composite material of the present invention will be described in more detail with reference to examples.

(1) Production of elastomer composite material First, a carbon-based filler having a crosslinkable functional group introduced therein was produced. 5 g of carbon beads (“Nika Beads ICB0520” manufactured by Nippon Carbon Co., Ltd., average particle diameter of about 5 μm, D90 / D10 = 3.2 in the particle size distribution), 0.2 g of vinylferrocene (Aldrich), and aluminum powder (Wako Pure Chemical Industries, Ltd.) (Industry Co., Ltd.) 0.003 g, aluminum chloride (Wako Pure Chemical Industries, Ltd.) 0.058 g, and 1,4-dioxane (Aldrich Co., Ltd.) 50 ml were charged into a flask, and the temperature was 90 ° C. in an oil bath. And stirred for 12 hours. Thereafter, unreacted vinyl ferrocene, aluminum powder and aluminum chloride were separated and purified, and dried to obtain carbon beads into which vinyl groups were introduced (hereinafter referred to as “vinyl group-introduced carbon beads”).

  Next, an elastomer composite material was produced using the produced vinyl group-introduced carbon beads. First, 80 parts by weight of EPDM (“Esplen (registered trademark) 301” manufactured by Sumitomo Chemical Co., Ltd.) (80 g) and 40 parts of oil-extended EPDM (“Esprene 400” manufactured by Sumitomo Chemical Co., Ltd.) ( 40 g), 5 parts (5 g) of zinc oxide (manufactured by Hakusui Chemical Co., Ltd.), 0.5 part (0.5 g) of stearic acid ("Lunac (registered trademark) S30" manufactured by Kao Corporation), and paraffinic process oil (Idemitsu Kosan "Diana (registered trademark) process oil PW-380") and 26 parts (26 g) were kneaded with a roll kneader. Next, 280 parts (280 g) of vinyl group-introduced carbon beads were added and mixed and dispersed with a roll kneader. Furthermore, as a crosslinking agent, 14 parts (14 g) of dicumyl peroxide (Nippon Yushi Co., Ltd. “Park Mill (registered trademark) D-40”) and ethylene glycol dimethacrylate (Seiko Chemical Co., Ltd. “Hicross ED-P”) 6 parts (6 g) was added and mixed and dispersed with a roll kneader to prepare an elastomer composition. The volume fraction of the vinyl group-introduced carbon beads in the prepared elastomer composition was about 50 vol% when the volume of the entire elastomer composition was 100 vol%.

  Next, the elastomer composition was formed into a sheet having a length of 40 mm, a width of 40 mm, and a thickness of 2 mm. It was filled in a mold and press vulcanized at 170 ° C. for 20 minutes to obtain an elastomer composite material. The obtained elastomer composite material was used as the elastomer composite material of the example. The filling rate of the vinyl group-introduced carbon beads in the elastomer composite material of the example was about 50 vol% when the volume of the elastomer composite material was 100 vol%.

(2) Evaluation of mechanical properties A dumbbell-shaped No. 7 test piece according to JIS K6251 was prepared from the elastomer composite material of the example, and a tensile test was performed according to the same JIS. The results are shown in FIG. In FIG. 5, as a comparative example, an elastomer composite material produced in the same manner as described above using carbon beads into which vinyl groups have not been introduced (“Nika Beads ICB0520” manufactured by Nippon Carbon Co., Ltd., the same in the following examples). The results are also shown.

  As shown in FIG. 5, according to the elastomer composite material of the example, no yield point appeared. On the other hand, in the elastomer composite material of the comparative example, the yield point appeared when the elongation reached about 50%. The yield point is believed to be caused by the separation of the carbon beads from the matrix EPDM. From this, it can be seen that, in the elastomer composite material of the example, the adhesion between the two is improved by co-crosslinking of EPDM and vinyl group-introduced carbon beads. Moreover, the elastomer composite material of an Example reached about twice the tensile stress at the time of a cutting | disconnection compared with the elastomer composite material of a comparative example. From the above, it was confirmed that the tensile strength was improved in the elastomer composite material of the example.

(3) Evaluation of durability In order to evaluate the durability when the elastomer composite material of the above example was used as a deformation sensor material, the following vibration test was performed.

(A) Production of sample for sensor In the production of the elastomer composite material of the above example, the prepared elastomer composition was molded into a long plate shape having a length of 100 mm, a width of 5 mm, and a thickness of 2 mm to obtain a molded body. The molded body was filled in a mold, a pair of electrodes were arranged at both ends in the longitudinal direction, and press vulcanized at 170 ° C. for 20 minutes to obtain a sensor element. A restraint plate was fixed to one surface of the obtained sensor element to obtain a sensor sample of the example. FIG. 6 shows a front view of the produced sensor sample. As shown in FIG. 6, the sensor sample 2 includes a sensor element 20 and a restraint plate 22. The restraint plate 22 is made of polyimide and has a strip shape of 120 mm in length, 10 mm in width, and 0.4 mm in thickness. The sensor element 20 is fixed to the surface of the restraining plate 22. Electrodes 21a and 21b are fixed to both ends of the sensor element 20, respectively. The electrodes 21a and 21b both have a strip shape, and are interposed between the sensor element 20 and the restraining plate 22. Conductive wires (not shown) are connected to the electrodes 21a and 21b, respectively.

(B) Test apparatus and test method FIG. 7 shows a schematic diagram of the test apparatus. As shown in FIG. 7, the test apparatus 4 includes an upper end holder 40, a lower end holder 41, and a vibration jig 42. The upper end holder 40 is immovable and holds one end (upper end) of the sensor sample 2 in the longitudinal direction. The lower end holder 41 is arranged to be spaced downward with respect to the upper end holder 40. The lower end holder 41 is fixed to the vibration jig 42. The vibration jig 42 can be repeatedly moved in the vertical direction. The lower end holder 41 holds the other end (lower end) of the sensor sample 2 in the longitudinal direction.

  When the vibration jig 42 is moved in the vertical direction, the interval between the upper end holder 40 and the lower end holder 41 contracts and expands. Thereby, the sensor sample 2 is curved and deformed. The electrical resistance value of the sensor element 20 is output to an external circuit (not shown) from the electrodes 21a, 21b and the like. “No distortion → curvature deformation → no distortion” with respect to the sensor sample 2 was taken as one cycle, and the amount of change in electrical resistance in one cycle was measured every predetermined cycle. The excitation frequency at the time of measuring electrical resistance was 10 mm / 1 Hz, and the other excitation frequencies were 10 mm / 5 Hz.

(C) Test result The result of the said vibration test is shown in FIG. FIG. 8 shows the ratio [ΔR _n / ΔR ₀ × 100 (%)] of the electric resistance change amount (ΔR _n ) in each cycle (1000th time and 10000th time) to the initial electric resistance change amount (ΔR ₀ ). Show. In addition, in FIG. 8, the result of the sample for sensors produced from the elastomer composite material using the carbon bead which has not introduce | transduced the vinyl group is also shown as a comparative example.

  As shown in FIG. 8, according to the sensor sample of the example, even if the number of cycles is repeated, that is, repeatedly curved and deformed, the amount of change in electrical resistance is reduced as compared with the sensor sample of the comparative example. Became smaller. The reason is considered as follows. That is, according to the elastomer composite material of the example, the adhesion between the EPDM and the vinyl group-introduced carbon beads is good, and therefore the vinyl group-introduced carbon beads are less likely to aggregate even if the curved deformation is repeated. For this reason, the initial three-dimensional conductive path is maintained even when the curved deformation is repeated. From the above, it was confirmed that the elastomer composite material of the example can maintain the initial increase in electrical resistance even after repeated elastic deformation and is excellent in durability.

(4) Evaluation of temperature dependence In order to evaluate temperature dependence at the time of using the elastomer composite material of the said Example as a deformation | transformation sensor material, the following tests were done.

(A) Production of Sensor Element In the production of the elastomer composite material of the above examples, the prepared elastomer composition was molded into a sheet having a length of 40 mm, a width of 40 mm, and a thickness of 5 mm to obtain a molded body. The molded body was filled in a mold, a pair of electrodes were disposed at both ends in the thickness direction, and press vulcanized at 170 ° C. for 20 minutes. This was cut into a 10 mm square, and used as the sensor element of the example.

(B) Test apparatus and test method FIG. 9 shows a schematic diagram of the test apparatus. As shown in FIG. 9, the test apparatus 5 includes a housing 50 and a pressing jig 51. The inside of the housing 50 can be controlled to a predetermined temperature. The sensor element 52 includes a sensor main body 520 and a pair of electrodes 521a and 521b disposed at both ends in the thickness direction (vertical direction) of the sensor main body 520. The sensor element 52 is fixed to the bottom wall of the housing 50 with the electrode 521b facing down. The electrode 521b and the bottom wall of the housing 50 are insulated. The electrodes 521a and 521b are connected to an external impedance analyzer 53 (manufactured by Solartron). The pressing jig 51 is disposed above the sensor element 52. The pressing jig 51 is disposed through the top wall of the housing 50 and can reciprocate in the vertical direction.

  The pressing jig 51 compresses the sensor element 52 by a predetermined amount from the electrode 521a side. The pressing jig 51 and the electrode 521a are insulated. Thereby, the sensor element 52 is compressed and deformed. The amount of deformation of the sensor element 52 is measured by a micrometer 54 that is integrated with the pressing jig 51. The electric resistance value of the sensor element 52 is measured by the impedance analyzer 53. Thus, the impedance (frequency 0.1 kHz) with respect to the deformation amount of the sensor element 52 under each temperature of 20 ° C., 80 ° C., and 120 ° C. was measured.

(C) Test result The result of the said test is shown in FIG. FIG. 11 shows a test result of a sensor element manufactured from an elastomer composite material using carbon beads into which a vinyl group is not introduced as a comparative example. First, as shown in FIG. 11, in the case of the sensor element of the comparative example, the impedance in the no-load state (deformation amount 0 μm) increased as the temperature increased as indicated by the dotted arrow in FIG. That is, according to the sensor element of the comparative example, it can be seen that the electrical conductivity in the no-load state is lowered at high temperatures. The impedance behavior with respect to the deformation amount increased at 20 ° C., but at 80 ° C. and 120 ° C., it showed an unstable behavior of increasing once after decreasing.

  On the other hand, in the case of the sensor element of the example, as shown in FIG. 10, the impedance in the no-load state (deformation amount 0 μm) is low in the range of 100 to 1000Ω at any temperature. Value. That is, according to the sensor element of the example, it can be seen that the conductivity in the no-load state is high regardless of the temperature. At any temperature, the impedance increased as the deformation amount increased. In the sensor element of the example, EPDM and vinyl group-introduced carbon beads that are difficult to thermally expand are fixed by co-crosslinking. For this reason, even if it becomes high temperature, it is thought that expansion of EPDM was suppressed and the fall of the electroconductivity in a no-load state was suppressed. In addition, since the decrease in the three-dimensional conductive path due to the expansion of EPDM is suppressed, it is considered that the desired increase in electrical resistance was obtained even at high temperatures.

  As described above, according to the elastomer composite material of the present invention, for example, based on an increase in electrical resistance, a target member, a load acting on the part, and various deformations of the member and the part can be detected. . Therefore, the elastomer composite material of the present invention is useful as a deformation sensor material. In addition, since an elastically deformable elastomer is used as a base material, various deformations such as compression, expansion, bending, etc. occurring in members and parts can be detected. Elastomers are excellent in processability and have a high degree of freedom in shape design. Therefore, it is possible to detect loads and deformations in a wide range of members and parts. Moreover, the electrical resistance value in a no-load state can be set within a predetermined range by adjusting the type of elastomer, the filling state and filling rate of the carbon-based filler, and the like. For this reason, the range of detectable load and elastic deformation amount, that is, the detection range can be increased. In addition, since the increase behavior of the electrical resistance with respect to the elastic deformation amount can be adjusted, a desired response sensitivity can be realized.

It is a schematic diagram which shows the electroconductive path before the load application of an elastomer composite material. It is a schematic diagram which shows the conductive path after the load application of the same elastomer composite material. It is a schematic diagram which shows the coupling | bonding state of the elastomer and carbonaceous filler in the elastomer composite material of this invention. It is a schematic diagram of the percolation curve in an elastomer composition. It is a graph which shows the result of the tension test in an Example. It is a front view of the sample for sensors used in the vibration test in an Example. It is a schematic diagram of the testing apparatus of the same vibration test. It is a graph which shows the result of the same vibration test. It is a schematic diagram of the testing apparatus of the temperature dependence evaluation test in an Example. It is a graph which shows the result of the same temperature dependence evaluation test (Example). It is a graph which shows the result of the same temperature dependence evaluation test (comparative example).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Carbon-type filler 11: Elastomer 12: Crosslinkable functional group 2: Sensor sample 20: Sensor element 21a, 21b: Electrode 22: Restraint plate 4: Test apparatus 40: Upper end holder 41: Lower end holder 42: Excitation jig 5 : Test apparatus 50: Housing 51: Pressing jig 52: Sensor element 520: Sensor body 521a, 521b: Electrode 53: Impedance analyzer 54: Micrometer 100: Elastomer composite material 101: Elastomer 102: Conductive filler 103: Carbon filler P : Conductive path P1: Conductive path

Claims (9)

Having an elastomer and a carbon-based filler having a graphene layer structure,
On the surface of the carbon-based filler, the crosslinkable functional group is introduced in advance by a ligand exchange reaction using a metallocene derivative having a crosslinkable functional group,
An elastomer composite material, wherein the crosslinkable functional group on the surface of the carbon filler and the elastomer are co-crosslinked.   The elastomer composite material according to claim 1, wherein the crosslinkable functional group includes one or more selected from a vinyl group, an amino group, an epoxy group, a carboxy group, and a hydroxyl group.   The elastomer composite material according to claim 1 or 2, wherein the metallocene derivative having a crosslinkable functional group has a molecular weight of 200 or more and 2000 or less.   The carbon-based filler includes one or more selected from carbon beads, carbon black, carbon nanotubes, mesocarbon microbeads, and vapor-grown carbon fibers produced by carbonizing a thermosetting resin. The elastomer composite material according to any one of the above.   The elastomer composite material according to any one of claims 1 to 4, wherein the carbon-based filler has a substantially spherical shape, and an average particle size of the carbon-based filler is 0.05 µm or more and 100 µm or less.   6. The elastomer according to claim 1, wherein the elastomer includes one or more selected from silicone rubber, ethylene-propylene copolymer rubber, natural rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, and acrylic rubber. The elastomer composite material described in 1. The carbon-based filler has a substantially spherical shape, and is blended in the elastomer in a substantially single particle state with a high filling rate,
The elastomer composite material according to any one of claims 1 to 6, wherein the elastomer composite material is elastically deformable and increases in electrical resistance as the amount of elastic deformation increases.   In the percolation curve representing the relationship between the blending amount of the carbon-based filler and the electric resistance of the elastomer composition having the elastomer and the carbon-based filler, the carbon-based filler at the second inflection point where the electric resistance change is saturated. The elastomer composite material according to claim 7, wherein the blending amount (saturated volume fraction: φs) is 35 vol% or more.   9. The elastomer composite material according to claim 7, wherein a filling rate of the carbon-based filler is 30 vol% or more and 65 vol% or less when the volume of the entire elastomer composite material is 100 vol%.

Images