Conductive rubber composition for percolation formation observation and quality control method using the same

Abstract

To provide a conductive rubber composition which enables a percolation formation state of a conductive filler in rubber to be visually observed.SOLUTION: This conductive rubber composition for observing percolation formation of a conductive filler is configured such that at least one type of a conductive filler (B) selected from the group consisting of a carbon nanotube and a carbon black in which DBP oil absorption is 150 ml / 100 g to 1000 mL / 100 g is contained by 1-20 mass with respect to 100 mass of rubber (A), a content of a carbon black (C) in which DBP oil absorption is 20 ml / 100 g or more and less than 150 mL / 100 g is 90 mass or smaller, a content of a white filler (D) is 30 mass or smaller, and a content of a processing aid (E) is 3 mass or smaller.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive rubber composition for observing percolation formation and a quality control method using the same. [Background technology]

[0002] Rubber compositions containing conductive fillers are known. Patent Document 1 describes a conductive rubber composition that contains rubber, carbon nanotubes, and a colorant, with the carbon nanotubes contained in an amount of 0.45 to 4.5 parts by weight per 100 parts by weight of the rubber. This document claims to provide a conductive rubber composition that is both conductive and colorable, and a rubber molded article made of the composition. Patent Document 2 also describes a bearing seal member comprising a rubber molded article and a core metal; the rubber molded article is obtained by vulcanization molding of a rubber composition containing 100 parts by mass of rubber (A) containing acrylic ester as a main component, 1 to 30 parts by mass of a carbon material (B), and 10 to 100 parts by mass of carbon black (C) having a DBP oil absorption of 20 ml / 100 g or more and less than 150 ml / 100 g, the carbon material (B) being carbon nanotubes (B1) or carbon black (B2) having a DBP oil absorption of 150 ml / 100 g or more and 1000 ml / 100 g or less, and the volume resistivity of the rubber molded article being 1×10 6 The document describes a seal member characterized by a resistivity of Ω·cm or less. The resulting seal member has excellent conductivity, and it is said that bearings using this seal member can effectively suppress electromagnetic noise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-34650 [Patent Document 2] Japanese Patent Publication No. 2020-152796 Summary of the Invention [Problem to be solved by the invention]

[0004] It is common technical knowledge among those skilled in the art that it is difficult to visualize and observe the percolation formation state of conductive fillers in rubber in conductive rubber molded products such as those described in Patent Documents 1 and 2, and there has been a demand for a means to obtain images suitable for observation.

[0005] The present invention has been made to solve the above problems, and aims to provide a conductive rubber composition that allows the percolation formation state of conductive fillers in rubber to be visualized and observed. [Means for solving the problem]

[0006] The above problem can be solved by providing any one of the following [1] to [7]. [1] A conductive rubber composition for observing percolation formation of a conductive filler, a conductive rubber composition for observing percolation formation, comprising, per 100 parts by mass of rubber (A), 1 to 20 parts by mass of at least one conductive filler (B) selected from the group consisting of carbon nanotubes and carbon black having a DBP oil absorption of 150 mL / 100 g or more and 1000 mL / 100 g or less, the content of carbon black (C) having a DBP oil absorption of 20 mL / 100 g or more and less than 150 mL / 100 g being 90 parts by mass or less, the content of white filler (D) being 30 parts by mass or less, and the content of processing aid (E) being 3 parts by mass or less; [2] The conductive rubber composition for percolation formation observation according to [1], wherein the content of components other than the rubber (A), the conductive filler (B), the carbon black (C), the white filler (D), and the processing aid (E) is 20 parts by mass or less; [3] The conductive rubber composition for observing percolation formation according to [1] or [2], wherein the white filler (D) is at least one inorganic filler selected from the group consisting of silica, clay, calcium carbonate, diatomaceous earth, wollastonite, barium sulfate, and titanium oxide, or at least one organic filler selected from the group consisting of cellulose powder, reclaimed rubber, and powdered rubber; [4] The conductive rubber composition for observing percolation formation according to any one of [1] to [3], wherein the processing aid (E) is at least one selected from the group consisting of ester waxes, fatty acids, and hydrocarbons; [5] The volume resistivity of the rubber molding is 1×10 6 The conductive rubber composition for observing percolation formation according to any one of [1] to [4], which has a resistivity of Ω·cm or less; [6] A quality control method for a rubber molded product, which determines the amount of conductive filler (B) to be blended into the rubber molded product by visualizing and observing the percolation formation state of the conductive filler (B) using the conductive rubber composition for percolation formation observation according to any one of [1] to [5]; [7] A quality control method for rubber molded products, which uses the conductive rubber composition for observing percolation formation described in any one of [1] to [5] to visualize and observe the percolation formation state of the conductive filler (B), thereby selecting rubber molded products having conductive properties. [Effects of the Invention]

[0007] The present invention provides a conductive rubber composition that allows the percolation state of conductive fillers in rubber to be visualized and observed, thereby making it possible to determine the optimum amount of conductive filler to be blended into a rubber molded article and providing a suitable quality control method for selecting rubber molded articles that have conductive properties. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an SPM image obtained using the rubber sheet of Example 1. [Figure 2] 1 is an SPM image obtained using the rubber sheet of Example 2. [Figure 3] 1 is an SPM image obtained using the rubber sheet of Example 3. [Figure 4] 1 is an SPM image obtained using the rubber sheet of Example 6. [Figure 5]10 is an SPM image obtained using the rubber sheet of Example 7. [Figure 6] 1 is an SPM image obtained using the rubber sheet of Example 10. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention is a conductive rubber composition for observing the percolation formation of conductive fillers, characterized in that it contains 1 to 20 parts by mass of at least one conductive filler (B) selected from the group consisting of carbon nanotubes and carbon black having a DBP oil absorption of 150 mL / 100 g or more and 1000 mL / 100 g or less, per 100 parts by mass of rubber (A), the content of carbon black (C) having a DBP oil absorption of 20 mL / 100 g or more and less than 150 mL / 100 g is 90 parts by mass or less, the content of white filler (D) is 30 parts by mass or less, and the content of processing aid (E) is 3 parts by mass or less.

[0010] It is believed that rubber becomes conductive when a conductive filler is added to the rubber, resulting in percolation by the conductive filler. However, it has been difficult to visualize and observe the percolation state of the conductive filler in the rubber. As will be seen from the examples described below, when Comparative Example 1, in which the carbon black (C) content was 100 parts by mass, Comparative Example 2, in which the white filler (D) content was 50 parts by mass, Comparative Example 3, in which the processing aid (E) content was 5 parts by mass, and Comparative Example 4, in which the white filler (D) content was 40 parts by mass, per 100 parts by mass of rubber (A), observations were performed using a scanning probe microscope (SPM). Errors occurred, preventing SPM images from being obtained, making it impossible to observe the percolation state of the conductive filler. In contrast, by adjusting the contents of the conductive filler, carbon black with DBP oil absorption within a certain range, the white filler, and the processing aid within a certain range in the rubber, it became possible to visualize and observe the percolation state of the conductive filler in the rubber. This makes it possible to determine the optimum amount of conductive filler to be compounded in a rubber molded article, and also to provide a suitable quality control method for selecting rubber molded articles that have conductive properties. This fact was made clear by the inventors' investigations, and it is clear that there is great significance in adopting the configuration of the present invention.

[0011] Rubber The rubber (A) used in the present invention is not particularly limited, and examples thereof include acrylic rubbers such as acrylic rubber (ACM) and ethylene acrylic rubber (AEM); nitrile rubbers such as nitrile rubber (NBR) and hydrogenated nitrile rubber (HNBR); chloroprene rubber (CR); ethylene propylene rubber (EPDM); fluororubber (FKM); etc. Among these, at least one selected from the group consisting of acrylic rubber (ACM), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), ethylene acrylic rubber (AEM), chloroprene rubber (CR), ethylene propylene rubber (EPDM), and fluororubber (FKM) is preferred, and at least one selected from the group consisting of acrylic rubber (ACM), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), ethylene acrylic rubber (AEM), and ethylene propylene rubber (EPDM) is more preferred.

[0012] The acrylic rubber used for rubber (A) is not particularly limited, and may be any rubber containing an acrylic ester as the main component. Suitable examples of acrylic esters include methyl acrylate, ethyl acrylate, butyl acrylate, and methoxyethyl acrylate. Examples of monomers copolymerized with acrylic esters include acrylonitrile and ethylene. Specifically, suitable examples include acrylic rubber (ACM) obtained by copolymerizing two or more acrylic esters selected from methyl acrylate, ethyl acrylate, butyl acrylate, and methoxyethyl acrylate with a crosslinkable monomer, and acrylic rubber (AEM) obtained by copolymerizing methyl acrylate, ethylene, and a crosslinkable monomer. Examples of AEM available include DuPont's "VAMAC" (registered trademark). While structural units derived from other copolymerizable monomers may be included within the scope of the present invention, the content is typically 10% by mass or less, and preferably 5% by mass or less.

[0013] The nitrile rubber used for rubber (A) is not particularly limited, and a copolymer of acrylonitrile and 1,3-butadiene can be used. Hydrogenation of the double bonds remaining in the 1,3-butadiene units after polymerization is optional. Non-hydrogenated nitrile rubber (NBR) and hydrogenated nitrile rubber (HNBR) can be preferably used. The content of acrylonitrile units in the nitrile rubber is preferably 15 to 50% by mass. As long as the effects of the present invention are not impaired, structural units derived from other copolymerizable monomers may be contained, but the content is usually 10% by mass or less, and preferably 5% by mass or less.

[0014] The chloroprene rubber (CR) used in the rubber (A) is not particularly limited, and may be any rubber containing 2-chloro-1,3-butadiene as the main component. 2-Chloro-1,3-butadiene may be polymerized alone, or 2-chloro-1,3-butadiene may be copolymerized with other monomers. Suitable other monomers include acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and methoxyethyl acrylate. The content of the other monomers is usually 10% by mass or less, and preferably 5% by mass or less.

[0015] The ethylene propylene rubber (EPDM) used for rubber (A) is not particularly limited, and a copolymer of ethylene, propylene, and a diene compound can be used. Examples of diene compounds contained in EPDM include ethylidene norbornene (ENB), 1,4-hexadiene, and dicyclopentadiene. While structural units derived from other copolymerizable monomers may be contained within a range that does not impair the effects of the present invention, the content is usually 10% by mass or less, and preferably 5% by mass or less.

[0016] The fluororubber (FKM) used in the rubber (A) is not particularly limited, and examples thereof include copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), copolymers of VDF and trichlorofluoroethylene (CTFE), copolymers of VDF, HFP, and tetrafluoroethylene (TFE), copolymers of TFE and propylene, copolymers of TFE and fluorinated vinyl ether, and copolymers of hydrocarbon diene monomers and fluorinated monomers. Among these, ternary fluororubbers, which are copolymers of VDF, HFP, and tetrafluoroethylene (TFE), are preferably used. As long as the effects of the present invention are not impaired, structural units derived from other copolymerizable monomers may be contained, but the content is usually 10% by mass or less, preferably 5% by mass or less.

[0017] [Conductive filler (B)] The conductive filler (B) used in the present invention is at least one selected from the group consisting of carbon nanotubes (B1) and carbon black (B2) having a DBP oil absorption of 150 mL / 100 g or more and 1000 mL / 100 g or less. Examples of carbon nanotubes (B1) (hereinafter, carbon nanotubes may be abbreviated as CNT) include single-walled carbon nanotubes and multi-walled carbon nanotubes. Single-walled CNTs are preferred when conductivity is important, while multi-walled CNTs are preferred when cost is important. The average diameter of the CNTs (B1) is not particularly limited, but is preferably 1 nm or more. On the other hand, the average diameter is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 20 nm or less. The aspect ratio (average length / average diameter) is not particularly limited, but is preferably 100 to 100,000. Examples of single-walled CNTs include "ZEONANO SG101" manufactured by Zeon Corporation and "TUBALL" manufactured by Oxial Corporation, and examples of multi-walled CNTs include "FloTube 7000" and "FloTube 9000" manufactured by CNano, and "NC7000" manufactured by Nanosil.

[0018] Carbon black (B2) has a DBP oil absorption of 150 mL / 100 g or more and 1000 mL / 100 g or less. DBP oil absorption indicates the amount (mL) of dibutyl phthalate (DBP) that can be absorbed by 100 g of carbon black (based on JIS K6217-4). The more developed the aggregate and agglomerate structure in carbon black (B2), the higher the DBP oil absorption. Carbon materials with excellent electrical conductivity generally have a high DBP oil absorption.

[0019] If the DBP oil absorption of carbon black (B2) is less than 150 mL / 100 g, the conductivity of the molded rubber product will be insufficient. To obtain better conductivity, the DBP oil absorption of carbon black (B2) is preferably 180 mL / 100 g or more, and more preferably 200 mL / 100 g or more. On the other hand, if the DBP oil absorption exceeds 1000 mL / 100 g, the fluidity of the rubber composition may deteriorate. The DBP oil absorption is preferably 800 mL / 100 g or less.

[0020] The type of carbon black (B2) is not particularly limited, as long as it has a DBP oil absorption within the above range and the volume resistivity of the resulting rubber molded product is below a certain level. Examples include Lion Specialty Chemicals' "Ketjenblack EC300J" and "Ketjenblack EC600JD," Denka's "Acetylene Black," Cabot's "Vulcan XC-72," Columbian International's "Conductex 7055 Ultra," and Evonik Degussa's "Printex XE2 B." Carbon black has a highly developed aggregate and agglomerate structure, with hollow primary particles, making it possible to impart conductivity with a small amount of addition.

[0021] The content of the conductive filler (B) is 1 to 20 parts by mass per 100 parts by mass of the rubber (A). If the content of the conductive filler (B) is less than 1 part by mass, the conductivity of the rubber molded article will be insufficient, making it difficult to visualize the percolation state of the conductive filler in the rubber. The content of the conductive filler (B) is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 8 parts by mass or more, particularly preferably 10 parts by mass or more, and most preferably 12 parts by mass or more. On the other hand, if the content of the conductive filler (B) exceeds 20 parts by mass, the mold releasability will deteriorate. The content of the conductive filler (B) is preferably 18 parts by mass or less, more preferably 16 parts by mass or less.

[0022] [Carbon Black (C)] The carbon black (C) used in the present invention has a DBP oil absorption of 20 mL / 100 g or more and less than 150 mL / 100 g. The carbon black (C) does not have as developed an aggregate or agglomerate structure as the conductive filler (B). This includes most of the carbon blacks compounded in general rubber compositions. If the DBP oil absorption of the carbon black (C) is 150 mL / 100 g or more, the moldability of the rubber composition may deteriorate. The DBP oil absorption of the carbon black (C) is preferably 100 mL / 100 g or less, and more preferably 50 mL / 100 g or less. On the other hand, the DBP oil absorption of the carbon black (C) is preferably 22 mL / 100 g or more, and more preferably 25 mL / 100 g or more.

[0023] The type of carbon black (C) is not particularly limited, as long as the DBP oil absorption is within the above range. Specifically, MT, FT, SRF, GPF, FEF, MAF, HAF, ISAF, SAF, etc. can be used, and MT, FT, SRF, and GPF are preferred from the viewpoint of the balance between performance and cost. Two or more types of carbon black (C) may be used in combination.

[0024] The content of carbon black (C) is 90 parts by mass or less per 100 parts by mass of rubber (A). As will be seen from the examples described later, in Comparative Example 1, in which the content of carbon black (C) was 100 parts by mass per 100 parts by mass of rubber (A), observation using a scanning probe microscope (SPM) resulted in an error, preventing an SPM image from being obtained, and the percolation formation state of the conductive filler could not be observed. Therefore, it is important to satisfy the requirement that the content of carbon black (C) be 90 parts by mass or less per 100 parts by mass of rubber (A). The content of carbon black (C) is preferably 85 parts by mass or less, more preferably 75 parts by mass or less, even more preferably 65 parts by mass or less, particularly preferably 60 parts by mass or less, and most preferably 55 parts by mass or less. On the other hand, the content of carbon black (C) is preferably 0 parts by mass or more, more preferably 1 part by mass or more, even more preferably 5 parts by mass or more, particularly preferably 8 parts by mass or more, and most preferably 10 parts by mass or more.

[0025] [White filler (D)] The white filler (D) used in the present invention is not particularly limited, but is preferably at least one inorganic filler selected from the group consisting of silica, clay, calcium carbonate, diatomaceous earth, wollastonite, barium sulfate, and titanium oxide, or at least one organic filler selected from the group consisting of cellulose powder, reclaimed rubber, and powdered rubber. Among these, inorganic fillers are preferred, and at least one inorganic filler selected from the group consisting of silica, clay, calcium carbonate, and diatomaceous earth is more preferred. Two or more types of white fillers (D) may be used in combination.

[0026] The content of the white filler (D) is 30 parts by mass or less per 100 parts by mass of the rubber (A). As will be seen from the examples described below, in Comparative Example 2, in which the content of the white filler (D) was 50 parts by mass per 100 parts by mass of the rubber (A), and Comparative Example 4, in which the content of the white filler (D) was 40 parts by mass per 100 parts by mass of the rubber (A), observation using a scanning probe microscope (SPM) resulted in an error, preventing an SPM image from being obtained, and the percolation formation state of the conductive filler could not be observed. Therefore, it is important to satisfy the requirement that the content of the white filler (D) be 30 parts by mass or less per 100 parts by mass of the rubber (A). The content of the white filler (D) is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, particularly preferably 10 parts by mass or less, and most preferably 8 parts by mass or less. On the other hand, the content of the white filler (D) is preferably 0 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, particularly preferably 3 parts by mass or more, and most preferably 5 parts by mass or more.

[0027] [Processing aids (E)] The processing aid (E) used in the present invention is not particularly limited, but is preferably at least one selected from the group consisting of ester waxes, fatty acids, and hydrocarbons. Specifically, ester waxes such as fatty acid ester waxes and partial ester waxes of fatty acids and polyhydric alcohols; fatty acids such as stearic acid and oleic acid; and hydrocarbons such as paraffin wax and microcrystalline wax are preferably used.

[0028] The content of the processing aid (E) is 3 parts by mass or less per 100 parts by mass of the rubber (A). As will be seen from the examples described below, in Comparative Example 3, in which the content of the processing aid (E) was 5 parts by mass per 100 parts by mass of the rubber (A), observation using a scanning probe microscope (SPM) resulted in an error, preventing an SPM image from being obtained, and the percolation formation state of the conductive filler could not be observed. Therefore, it is important to satisfy the requirement that the content of the processing aid (E) be 3 parts by mass or less per 100 parts by mass of the rubber (A). The content of the processing aid (E) is preferably 2.5 parts by mass or less, more preferably 2 parts by mass or less, even more preferably 1.5 parts by mass or less, and particularly preferably 1.2 parts by mass or less. On the other hand, the content of the processing aid (E) is preferably 0 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.4 parts by mass or more, particularly preferably 0.6 parts by mass or more, and most preferably 0.8 parts by mass or more.

[0029] The conductive rubber composition for observing percolation formation of the present invention may contain components other than the rubber (A), conductive filler (B), carbon black (C), white filler (D), and processing aid (E) as long as the effects of the present invention are not impaired. Examples of other components include various additives such as vulcanizing agents and vulcanization accelerators (F), vulcanization aids, co-crosslinking agents, vulcanization retarders, adhesives, acid acceptors, colorants, fillers, plasticizers, antioxidants, coupling agents, corrosion inhibitors, and tackifiers. From the viewpoint of facilitating observation of the percolation formation state of the conductive filler in the rubber, a preferred embodiment is that the content of the components other than the rubber (A), conductive filler (B), carbon black (C), white filler (D), and processing aid (E) is 20 parts by mass or less. The content of the other components is more preferably 16 parts by mass or less, even more preferably 14 parts by mass or less, particularly preferably 12 parts by mass or less, and most preferably 10 parts by mass or less. On the other hand, the amount of the other components is preferably 0.1 parts by mass or more.

[0030] In the present invention, the volume resistivity of the rubber molded product obtained by vulcanizing and molding the rubber composition is 1×10 6 In a preferred embodiment, the resistivity is Ω·cm or less. Whether or not a rubber molded product has been given electrical conductivity can be confirmed by checking whether the volume resistivity is below a certain value. The volume resistivity is 1×10 5 It is preferable that the resistance is Ω·cm or less, and 1×10 4 It is more preferable that the resistance is Ω·cm or less, and 1×10 3 It is more preferable that the resistance is Ω·cm or less, and 1×10 2 It is particularly preferable that the volume resistivity is Ω·cm or less. The volume resistivity here is a value obtained by measurement in accordance with JIS K6271-2, Method 3.

[0031] The method for producing the conductive rubber composition for percolation formation observation of the present invention is not particularly limited, and it can be suitably obtained by kneading various components such as rubber (A), conductive filler (B), carbon black (C), white filler (D), and processing aid (E). The kneading method is not particularly limited, and kneading can be performed using an open roll, kneader, Banbury mixer, intermixer, extruder, etc. Among these, kneading using an open roll or kneader is preferred. The temperature during kneading is preferably 20 to 160°C.

[0032] The obtained conductive rubber composition for observing percolation formation can then be vulcanized to obtain a molded rubber article. Examples of methods for molding the rubber composition include injection molding, extrusion molding, compression molding, and roll molding. Among these, injection molding and compression molding are preferred. In this case, the composition may be vulcanized after pre-molding, or simultaneously with molding. Alternatively, the composition may be vulcanized simultaneously with molding, followed by secondary vulcanization. The vulcanization temperature is preferably typically 150 to 230°C. The vulcanization time is typically 0.1 to 60 minutes. Heating methods for vulcanization include heater heating, steam heating, oven heating, and hot air heating, which are commonly used for vulcanizing rubber.

[0033] Depending on the shape and dimensions of the rubber molded product, the interior may not be sufficiently vulcanized even if the surface is vulcanized, so secondary vulcanization may be carried out by further heating.

[0034] The vulcanization method is not particularly limited, and a vulcanization method suitable for the rubber (A) can be selected. Examples of vulcanization methods include sulfur vulcanization, peroxide vulcanization, and amine vulcanization. Sulfur or a sulfur-containing compound is used as a vulcanizing agent for sulfur vulcanization. Furthermore, an organic peroxide is used as a vulcanizing agent for peroxide vulcanization. The content of the vulcanizing agent and vulcanization accelerator (F) is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 1.5 parts by mass, per 100 parts by mass of the rubber (A).

[0035] While there is a problem in visualizing the percolation formation state of conductive filler in rubber, by using the conductive rubber composition for observing percolation formation of the present invention, it has become possible to visualize and observe the percolation formation state of conductive filler. Therefore, a preferred embodiment is a quality control method for rubber molded products in which the amount of conductive filler (B) to be blended into a rubber molded product is determined by visualizing and observing the percolation formation state of conductive filler (B) using the conductive rubber composition for observing percolation formation of the present invention. Another preferred embodiment is a quality control method for rubber molded products in which the percolation formation state of conductive filler (B) is visualized and observed using the conductive rubber composition for observing percolation formation of the present invention, thereby selecting rubber molded products with conductive performance. [Example]

[0036] The present invention will be explained in more detail below using examples. Rubber Acrylic rubber (ACM (A1)): "Nipol AR31" manufactured by Zeon Corporation Nitrile rubber (NBR(A2)): Krynac 4450 manufactured by LANXESS KK [Conductive filler (B)] Carbon material (B1): Cnano "FloTube 7000" Carbon material (B2): "Acetylene Black" manufactured by Denka Co., Ltd., DBP oil absorption 212 mL / 100 g [Carbon Black (C)] Carbon black (C): Asahi Thermal manufactured by Asahi Carbon Co., Ltd., DBP oil absorption 28 mL / 100 g [White filler (D)] Silica (D1): "Nipsil VN3" manufactured by Silica Corporation Clay (D2): R.T. Vanderbitt Company, Inc. "Dixie Clay" Calcium carbonate (D3): "Light Calcium Carbonate (Red Ball)" manufactured by Taiyo Chemical Industry Co., Ltd. [Processing aids (E)] Ester wax: NI Chemitech Co., Ltd. "Grec G-8205" [Vulcanizing agents and vulcanization accelerators (F)] Vulcanizing agent and vulcanization accelerator (F1): "Noccela TTFE" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanizing agent and vulcanization accelerator (F2): NOF Corporation "Perhexa 25B"

[0037] Example 1 A mixture or a partial master batch of the composition shown in Table 1 was kneaded using an open roll at a temperature of 40 to 70°C for 15 to 30 minutes to produce an unvulcanized rubber sheet 2.0 to 3.0 mm thick. The resulting unvulcanized rubber sheet was then press-vulcanized at 160 to 220°C for 2 to 20 minutes to obtain a vulcanized rubber sheet 150 mm long x 150 mm wide x 2 mm thick, which was then subjected to secondary vulcanization in an oven at 180°C for 2 to 5 hours to produce the rubber sheet of Example 1 (hereinafter sometimes abbreviated as rubber sheet).

[0038] [Volume resistivity measurement] The volume resistivity of the obtained rubber sheet was measured according to JIS K6271-2 Method 3. The results are shown in Table 1.

[0039] [Observation of percolation formation using a scanning probe microscope (SPM)] The rubber sheet was cut and frozen in liquid nitrogen, and then a microtome was used to prepare a cross section for measurement. A scanning probe microscope (SPM) was used to map the cross section at 10 μm square and 3.3 μm square. The force curves were fitted using the DMT (Derjaguin-Muller-Toporov) theory to calculate the elastic modulus. The dispersion state of the conductive filler on the surface of the rubber sheet was mapped using the obtained elastic modulus, and the percolation formation of the conductive filler (B) was observed. The resulting SPM image is shown in Figure 1. ◯: The percolation formation state of the conductive filler was visualized and could be observed. ×: An error occurred and an SPM image could not be obtained, making observation impossible.

[0040] Examples 2 to 11, Comparative Examples 1 to 4 Rubber sheets were produced in the same manner as in Example 1, except that the components were changed as shown in Table 1, and the volume resistivity was measured and percolation formation was observed. The results are shown in Table 1. SPM images obtained in Examples 2, 3, 6, 7, and 10 are shown in Figures 2 to 6, respectively.

[0041] [Table 1]

Claims

1. A conductive rubber composition for observing percolation formation of a conductive filler, comprising: A conductive rubber composition for observing percolation formation, characterized in that it contains 1 to 20 parts by mass of at least one conductive filler (B) selected from the group consisting of carbon nanotubes and carbon black having a DBP oil absorption of 150 mL / 100 g or more and 1000 mL / 100 g or less, per 100 parts by mass of rubber (A), the content of carbon black (C) having a DBP oil absorption of 20 mL / 100 g or more and less than 150 mL / 100 g is 90 parts by mass or less, the content of white filler (D) is 30 parts by mass or less, and the content of processing aid (E) is 3 parts by mass or less.

2. 2. The conductive rubber composition for observing percolation formation according to claim 1, wherein the content of components other than the rubber (A), the conductive filler (B), the carbon black (C), the white filler (D), and the processing aid (E) is 20 parts by mass or less.

3. 3. The conductive rubber composition for observing percolation formation according to claim 1 or 2, wherein the white filler (D) is at least one inorganic filler selected from the group consisting of silica, clay, calcium carbonate, diatomaceous earth, wollastonite, barium sulfate, and titanium oxide, or at least one organic filler selected from the group consisting of cellulose powder, reclaimed rubber, and powdered rubber.

4. 3. The conductive rubber composition for observing percolation formation according to claim 1, wherein the processing aid (E) is at least one selected from the group consisting of ester wax, fatty acids, and hydrocarbons.

5. The volume resistivity of the rubber molded product is 1 x 10 ６ The conductive rubber composition for observing percolation formation according to claim 1 or 2, which has a resistivity of Ω·cm or less.

6. A quality control method for rubber molded products, which determines the amount of conductive filler (B) to be blended into a rubber molded product by visualizing and observing the percolation formation state of the conductive filler (B) using the conductive rubber composition for percolation formation observation described in claim 1 or 2.

7. A quality control method for rubber molded products, which comprises visualizing and observing the percolation formation state of the conductive filler (B) using the conductive rubber composition for percolation formation observation according to claim 1 or 2, thereby selecting rubber molded products having conductive properties.

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