Rubber composition for sealing members of rolling bearings

Abstract

To provide a rubber composition for making a rolling bearing seal member that has excellent electrical conductivity and wear resistance, and to provide a rolling bearing seal member that is made from said rubber composition.SOLUTION: Provided is a rubber composition for rolling bearing seal member, which is a rubber composition for forming rolling bearing seal member, and in which, characterized, a rubber mainly composed of acrylic acid ester is contained by 100 pts.mass and a carbon black having a DBP oil absorption of 200 ml / 100 g or more and 500 ml / 100 g or less is contained by 20 to 40 pts.mass, and a carbon black having a DBP oil absorption of less than 200 ml / 100 g is not contained.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition for forming a sealing member for a rolling bearing, and a sealing member using the rubber composition. [Background technology]

[0002] In automotive components, such as bearings used in engine accessories (alternators, air conditioners, etc.) and suspension parts, sealing members are arranged in which the surface of a ring-shaped core is covered with a rubber molded product to prevent the intrusion of muddy water or dust, taking into account grease leakage and the intrusion of muddy water or dust during rain or on rough roads. For this sealing member, a conductive rubber molded product is used as a measure to prevent electrolytic corrosion and reduce electromagnetic noise (so-called radio noise).

[0003] Here, rubber molded products used as sealing members in rolling bearings are required to have physical properties that enable them to withstand harsh environments such as high temperatures and high humidity, where rubber is prone to deterioration. For example, a rubber molded article is prepared as a sealing member having excellent heat resistance and electrical conductivity and good releasability from a mold during production, the rubber molded article being obtained by vulcanization molding of a rubber composition containing 100 parts by mass of a rubber (A) mainly composed of an acrylic ester, 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 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 A sealing member characterized by a resistance of Ω·cm or less is known (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-152796 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the present inventors have discovered for the first time that rubber molded products containing carbon black having a DBP oil absorption of less than 200 ml / 100 g have the problem that they have insufficient resistance to wear caused by the rotation of rolling bearings (wear resistance).

[0006] Therefore, an object of the present invention is to provide a rubber composition for producing a sealing member for a rolling bearing having excellent electrical conductivity and wear resistance, and a sealing member for a rolling bearing produced from said rubber composition. [Means for solving the problem]

[0007] The present inventors conducted intensive research to solve the above problems and discovered that a sealing member for a rolling bearing having excellent electrical conductivity and wear resistance can be produced by blending a specific amount of carbon black having a specific DBP oil absorption instead of carbon black having a DBP oil absorption of less than 200 ml / 100 g, thereby completing the present invention.

[0008] That is, the gist of the present invention is [1] A rubber composition for forming a sealing member of a rolling bearing, A rubber composition for a sealing member of a rolling bearing, comprising 100 parts by mass of a rubber containing an acrylic ester as a main component, and 20 to 40 parts by mass of carbon black having a DBP oil absorption of 200 ml / 100 g or more and 500 ml / 100 g or less, and not containing any carbon black having a DBP oil absorption of less than 200 ml / 100 g. [2] The rubber composition for a sealing member of a rolling bearing according to [1] above, wherein the acrylic ester is an acrylic ester having a carboxyl group. [3] The rubber composition for a sealing member of a rolling bearing according to [1] or [2], further comprising 5 to 100 parts by mass of a white filler. [4] The rubber composition for a sealing member of a rolling bearing according to any one of [1] to [3] above, further comprising 0.1 to 5 parts by mass of a coupling agent. [5] A bearing seal member molded from the rubber composition according to any one of [1] to [4] above, A bearing seal member having a volume resistivity of 100 Ω·cm or less. Regarding. Effect of the Invention

[0009] By using the rubber composition for a sealing member of a rolling bearing of the present invention, a sealing member for a rolling bearing having excellent electrical conductivity and abrasion resistance can be produced. By disposing the rolling bearing seal member of the present invention in automobile parts, such as bearings used in engine auxiliaries (alternators, air conditioners, etc.) and suspension parts, the reliability of the rolling bearing can be maintained even when the automobile is used in harsh environments. [Brief description of the drawings]

[0010] [Figure 1] 1A and 1B are explanatory diagrams showing the configuration of a rolling bearing equipped with a sealing member for a rolling bearing according to an embodiment of the present invention, in which (a) is a cross-sectional view of the entire rolling bearing, and (b) is an enlarged cross-sectional view of a main portion. [Diagram 2] FIG. 2 is an explanatory diagram showing a method for carrying out an abrasion resistance test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in more detail below. Note that the present invention is not limited to the embodiments shown in the accompanying drawings, but includes all embodiments satisfying the requirements of the claims.

[0012] [Rolling bearings] Fig. 1 is an explanatory diagram showing the configuration of a rolling bearing equipped with a sealing member for a rolling bearing according to an embodiment of the present invention, showing a deep groove ball bearing as an example. Fig. 1(a) is a cross-sectional view of the entire rolling bearing 1, and Fig. 1(b) is an enlarged cross-sectional view of a main part.

[0013] In Fig. 1, a rolling bearing 1 has an inner ring 2 and an outer ring 3 that rotate relatively via rolling elements 5,... held by a cage 4, and grease 10 is filled between the inner ring 2 and the outer ring 3 as a lubricant. In addition, on the left and right of the rolling elements 5,... in the bearing width direction, there are provided sealing devices composed of a seal member 11 that is substantially annular in front view and a circumferential groove 6 formed on the outer peripheral surface of the inner ring 2, which closes an annular opening A between the inner ring 2 and the outer ring 3. The seal member 11 is attached to at least one of the annular openings A, A on the left and right in the bearing width direction between the inner ring 2 and the outer ring 3 of the rolling bearing 1. (Instead of a double shield type that seals both sides of the rolling bearing 1 as shown in Figure 1, a single shield type that seals only one side of the rolling bearing 1 may be used depending on the location of use.) And, as shown in Figure 1(b), the sealing member 11 is formed by coating the outer and inner peripheral portions of an annular core bar 12 made of a steel plate or the like with an elastomer 13 such as synthetic rubber by vulcanization bonding, and the tip of the elastomer 13 has a lip structure, and the lip structure consists of an inner main lip 14 and an outer dust lip 15 on the inner peripheral side (inner ring 2 side) and an outer diameter lip 16 on the outer peripheral side (outer ring 3 side). The main lip 14 is intended to prevent leakage of the grease 10 filled inside the bearing 1 and to prevent the intrusion of foreign matter from the outside, and the dust lip 15 is intended to reduce the intrusion of foreign matter from the outside by using a labyrinth seal effect. The outer lip 16 is fitted into the outer ring circumferential groove 7 formed on the inner peripheral surface of the outer ring 3 to position and fix the seal member 11 to the bearing 1 and to prevent the intrusion of foreign matter from the outer diameter part of the seal member 11. Furthermore, a recess 15A is formed in the dust lip 15, and the seal member 11 also has the function of facilitating the discharge of water or muddy water that has intruded between the dust lip 15 and the main lip 14.

[0014] [Rubber composition] The rubber composition of the present invention is a rubber composition for forming a sealing member of a rolling bearing, It is characterized by containing 100 parts by mass of rubber whose main component is an acrylic ester and 20 to 40 parts by mass of carbon black having a DBP oil absorption of 200 ml / 100 g or more and 500 ml / 100 g or less, and containing no carbon black having a DBP oil absorption of less than 200 ml / 100 g.

[0015] The rubber mainly composed of acrylic ester used in the rubber composition of the present invention may be a commercially available polymer or copolymer of acrylic ester having crosslinking points such as carboxyl group, active chlorine, and epoxy group, and any of these commercially available products can be used in the present invention. In addition, the rubber mainly composed of acrylic ester may be an ethylene-acrylic rubber (AEM) which is a copolymer with ethylene, or an acrylic rubber (ANM) containing an AN (acrylonitrile) composition. There is no particular limitation on the type of acrylic rubber. For example, in the "Nipol" (trade name) manufactured by Nippon Zeon Co., Ltd., the polymer or copolymer of acrylic ester having a carboxyl group is "AR12", the polymer or copolymer of acrylic ester having an epoxy group is "AR31", "AR42W", "AR54", and the polymer or copolymer of acrylic ester having an active chlorine group is "AR71", "AR72LS", and the like. As the AEM, DuPont's "VAMAC" (registered trademark) and the like can be used. Among these, acrylic acid ester copolymers having a carboxyl group are preferred because they have excellent heat resistance, water resistance, distortion resistance of the sealing member, and ability to prevent rust on the core metal portion to which the sealing member is fixed (metal rust prevention).

[0016] The DBP oil absorption of carbon black indicates the amount (mL) of dibutyl phthalate (DBP) that can be absorbed by 100 g of carbon black (based on JIS K 6217-4). The more the aggregate or agglomerate structure is developed in carbon black, the higher the DBP oil absorption. Carbon materials with excellent electrical conductivity generally have a large DBP oil absorption. The DBP oil absorption of the carbon black used in the present invention is 200 ml / 100 g or more, preferably 300 ml / 100 g or more, whereas if the DBP oil absorption exceeds 500 ml / 100 g, the fluidity of the rubber composition may deteriorate, so the DBP oil absorption is 500 ml / 100 g or less, preferably 400 ml / 100 g or less.

[0017] As carbon black having a DBP oil absorption of 200 ml / 100 g or more and 500 ml / 100 g or less, for example, "Ketjen Black EC300J" and "Ketjen Black EC600JD" manufactured by Lion Specialty Chemicals Co., Ltd. can be suitably used.

[0018] In the rubber composition of the present invention, the carbon black having a DBP oil absorption of 200 ml / 100 g or more and 500 ml / 100 g or less is contained in an amount of 20 to 40 parts by mass per 100 parts by mass of rubber mainly composed of acrylic acid ester, so that the sealing member can be made conductive. If the content is less than 20 parts by mass, the electrical conductivity is insufficient, which is undesirable in that electrical conductivity is deteriorated by rekneading, and if the content exceeds 40 parts by mass, the flowability of the rubber is reduced, which is undesirable in that molding defects of the bearing seal are easily caused.

[0019] The rubber composition of the present invention is also characterized in that it does not contain carbon black having a DBP oil absorption of less than 200 ml / 100 g. When a rolling bearing is manufactured using a rubber composition for a sealing member that contains carbon black having a DBP oil absorption of less than 200 ml / 100 g, the wear resistance is insufficient, as described in the comparative example below. In the present invention, the term "not containing" means that the substance is not substantially contained.

[0020] From the viewpoint of improving adhesion between the rubber molded article and the core metal, the rubber composition of the present invention may contain 5 to 100 parts by mass of a white filler per 100 parts by mass of rubber containing an acrylic ester as a main component.

[0021] The content of the white filler is more preferably 70 parts by mass or less.

[0022] The type of white filler is not particularly limited, and may be any filler that is normally used in rubber compositions. Examples of such fillers include inorganic fillers such as silica, clay, calcium carbonate, diatomaceous earth, wollastonite, barium sulfate, and titanium oxide, and organic fillers such as cellulose powder, regenerated rubber, and powdered rubber. Among these, inorganic fillers are preferably used, and from the viewpoint of improving adhesion, silica, clay, calcium carbonate, and diatomaceous earth are more preferably used. Two or more types of white fillers may be used in combination.

[0023] The rubber composition of the present invention may further contain 0.1 to 10 parts by mass of a coupling agent from the viewpoint of improving the reinforcement property of the rubber.

[0024] The content of the coupling agent is more preferably 0.1 parts by mass or more, and more preferably 5 parts by mass or less.

[0025] The coupling agent is not particularly limited as long as it is used as a coupling agent for acrylic rubber, and examples thereof include silane coupling agents such as vinyl-based silane coupling agents, amino-based silane coupling agents, epoxy-based silane coupling agents, and mercapto-based silane coupling agents, and zirconia-based silane coupling agents.

[0026] In addition to the above-mentioned components, the rubber composition of the present invention may usually further contain various additives such as crosslinking agents, vulcanizing agents, plasticizers, reinforcing agents, metal oxides, softening agents, antioxidants, processing aids, flame retardants, and ultraviolet absorbing agents in appropriate amounts within the range that does not impair the effects of the present invention.

[0027] The crosslinking agent is not particularly limited as long as it is for acrylic rubber, and a known crosslinking agent can be appropriately used. Examples of common crosslinking agents include diamine crosslinking agents such as hexamethylenediamine, sulfur, and organic peroxides.

[0028] In addition, when using the crosslinking agent, a crosslinking accelerator, a crosslinking assistant, etc., can also be used. Examples of the crosslinking accelerator include sulfenamide compounds such as N-cyclohexyl-2-benzothiazolylsulfenamide, N-oxydiethylene-2-benzothiazolylsulfenamide, and N,N-diisopropyl-2-benzothiazolylsulfenamide; thiazole compounds such as 2-mercaptobenzothiazole, 2-(2',4'-dinitrophenyl)mercaptobenzothiazole, 2-(4'-morpholinodithio)benzothiazole, and dibenzothiazyl disulfide; guanidine compounds such as diphenylguanidine, diorthotolylguanidine, diorthonitrileguanidine, orthonitrile biguanide, and diphenylguanidine phthalate; and acetaldehyde-aniline reaction products, butyraldehyde-aniline condensates, hexamethylenetetramine, and acetaldehyde ammonia. Examples of the compounds include aldehyde amine or aldehyde-ammonia compounds; imidazoline compounds such as 2-mercaptoimidazoline; thiourea compounds such as thiocarbanilide, diethylthiourea, dibutylthiourea, trimethylthiourea, and diorthotolylthiourea; thiuram compounds such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetraoctylthiuram disulfide, and pentamethylenethiuram tetrasulfide; dithioacid salt compounds such as ferric dimethyldithiocarbamate, sodium dimethyldithiocarbamate, selenium dimethyldithiocarbamate, and tellurium dimethyldithiocarbamate; xanthate compounds such as zinc dibutylxanthogenate; and zinc oxide.

[0029] Examples of the vulcanizing agent include aliphatic primary amines and aromatic primary amines. Examples of the aliphatic amine include hexamethylenediamine, hexamethylenediamine carbamate, tetramethylenepentamine, hexamethylenediamine-cinnamaldehyde adduct, and hexamethylenediamine-dibenzoate salt. Examples of the aromatic amine include 4,4'-methylenedianiline, 4,4'-oxyphenyldiphenylamine, m-phenylenediamine, p-phenylenediamine, and 4,4'-methylenebis(o-chloroaniline). Examples of the vulcanizing agent include zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc di-n-butyldithiocarbamate, zinc ethylphenyldithiocarbamate, and zinc butylphenyldithiocarbamate.

[0030] Examples of the plasticizer include phthalate esters such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl phthalate, dioctyl phthalate, butyloctyl phthalate, di-(2-ethylhexyl) phthalate, diisooctyl phthalate, and diisodecyl phthalate; dimethyl adipate, diisobutyl adipate, di-(2-ethylhexyl) adipate, diisooctyl adipate, diisodecyl adipate, octyldecyl adipate, di-(2-ethylhexyl) azelate, diisooctyl azelate, diisobutyl azelate, and dibutyl azelate; Examples of the fatty acid esters include fatty acid esters such as isodecyl trimellitate, octyl trimellitate, n-octyl trimellitate, and isononyl trimellitate, as well as di-(2-ethylhexyl) fumarate, diethylene glycol monooleate, glyceryl monoricinoleate, trilauryl phosphate, tristearyl phosphate, tri-(2-ethylhexyl) phosphate, epoxidized soybean oil, and polyether esters. These may be used alone or in combination of two or more.

[0031] Examples of metal oxides include zinc oxide, active zinc oxide, surface-treated zinc oxide, zinc carbonate, composite zinc oxide, composite active zinc oxide, surface-treated magnesium oxide, magnesium oxide, calcium hydroxide, ultrafine calcium hydroxide, lead monoxide, red lead, white lead, etc. These may be used alone or in combination of two or more.

[0032] Examples of the softener include petroleum-based softeners and vegetable oil-based softeners. Examples of the petroleum-based softeners include aromatic, naphthenic, and paraffinic softeners. Examples of the vegetable softeners include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, and wood wax. These may be used alone or in combination of two or more.

[0033] Examples of the antiaging agent include naphthylamine-based, diphenylamine-based, p-phenylenediamine-based, quinoline-based, hydroquinone derivative-based, mono-, bis-, tris-, polyphenol-based, thiobisphenol-based, hindered phenol-based, phosphite-based, imidazole-based, dithiocarbamic acid nickel salt-based, phosphoric acid-based antiaging agents, etc. These can be used alone or in combination of two or more kinds.

[0034] Examples of processing aids include stearic acid, oleic acid, lauric acid, zinc stearate, calcium stearate, potassium stearate, sodium stearate, stearylamine, etc. These may be used alone or in combination of two or more.

[0035] The method for producing the rubber composition of the present invention is not particularly limited. For example, the rubber mainly composed of the above acrylic acid ester, carbon black having a DBP oil absorption of 200ml / 100g or more and 500ml / 100g or less, and optionally a white filler, a coupling agent, other additives, etc. are combined and kneaded with a mixer such as a Banbury mixer, a Brabender mixer, an intermixer, or a kneader at preferably 10 to 200°C, more preferably 20 to 170°C, and then transferred to a roll or the like, and a vulcanizing agent or a vulcanizing aid that is unstable to heat is added, and the rubber composition can be produced by secondary kneading at preferably 10 to 80°C.

[0036] [Bearing seal member] A rubber molded article that will become a bearing seal member can be obtained by crosslinking the rubber composition of the present invention containing the above-mentioned components. Crosslinking can be performed, for example, by vulcanizing the rubber composition based on a known method, and then molding the composition into a sheet or the like to obtain a rubber molded article. The vulcanization treatment is preferably performed in two stages: primary vulcanization and secondary vulcanization. There is no particular limitation on the temperature conditions for the vulcanization treatment, but both the primary vulcanization and secondary vulcanization are preferably in the range of 140 to 180°C. There is no particular limitation on the vulcanization treatment time, but it is preferable to perform the primary vulcanization for 10 to 30 minutes and the secondary vulcanization for 1 to 10 hours.

[0037] The vulcanization means can be appropriately selected from general methods used for vulcanizing rubber, such as steam vulcanization, press vulcanization, and oven vulcanization.

[0038] The bearing seal member of the present invention is characterized in that it has a volume resistivity of 100 Ω·cm or less. The volume resistivity of 100 Ω·cm or less can effectively suppress electromagnetic noise. The volume resistivity is preferably 10 Ω·cm or less. The volume resistivity is a value obtained by measurement in accordance with JIS K6271-2, Method 3.

[0039] Among other things, the bearing seal member of the present invention has an advantage that the decrease in volume resistivity is small even when processing is performed during preforming, and therefore any surplus material that is generated can be remixed and reused.

[0040] The bearing seal member of the present invention obtained in the above manner has excellent electrical conductivity and wear resistance. EXAMPLES

[0041] The present invention will now be described with reference to examples, but the present invention is not limited to these examples in any way.

[0042] The components used in the examples and comparative examples described below are as follows. Acrylic acid ester copolymer (1): "AR12" (manufactured by Zeon Corporation, contains carboxyl groups) Acrylic acid ester copolymer (2): "ANM" (manufactured by Nippon Zeon, contains epoxy groups) Processing aid (1): Stearic acid, "Camellia Stearate" (NOF Corporation) Anti-aging agent: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, "Nocrac CD", Ouchi Shinko Chemical Industry Co., Ltd. Processing aid (2): Stearylamine, "Lipomin 18D", Lion Specialty Chemicals Carbon black (1): "Ketchin Black EC300-J", Lion Specialty Chemicals, DBP oil absorption 360ml / 100g Carbon black (2): "FT carbon" DBP oil absorption: 20ml / 100g or more, but less than 150ml / 100g White filler (1): Silicon dioxide "Nipseal ER", Tosoh Silica Corporation White filler (2): Diatomaceous earth "Celite #499", Tokyo Diatomaceous Earth Co., Ltd. White filler (3): Silicon dioxide and aluminum oxide "Sutington No. 5", BASF Coupling agent (1): γ-aminopropyltriethoxysilane, "A-1100" Nippon Unicar Coupling agent (2): γ-glycidoxypropyltrimethoxysilane, "A-187" Nippon Unicar Vulcanizing agent (1): Hexamethylenediamine carbamate, "Diak-1" DuPont Crosslinking accelerator (1): 1,3-di-O-tolylguanidine "Noccera-DT", Ouchi Shinko Chemical Industry Co., Ltd. Vulcanizing agent (2): Zinc dimethyldithiocarbamate "Noccera-PZ", Ouchi Shinko Chemical Industry Co., Ltd. Crosslinking accelerator (2): Ferric dimethyldithiocarbamate "Noccera-TTFE", Ouchi Shinko Chemical Industry Co., Ltd.

[0043] Example 1 The raw materials were pressed with a rolling mill roll and then mixed in an internal mixer to obtain the composition shown in Table 1, thereby preparing a rubber composition. Next, the obtained rubber composition was kneaded with a mixing roll, and then subjected to a primary vulcanization (150-180°C, 10-15 minutes) and a secondary vulcanization (150-180°C x 1-10 hours) to form it into a sheet, thereby obtaining a rubber sheet (rubber molded body) having a thickness of 2 m.

[0044] (Example 2 5, Reference example 1 , Comparative Examples 1 to 7) A rubber composition was prepared in the same manner as in Example 1, except that the raw materials were mixed so as to obtain the composition shown in Table 1, and then a rubber sheet (rubber molded article) was obtained.

[0045] The properties of each rubber composition and rubber sheet obtained as described above were evaluated according to the following evaluation methods. The results are shown in Table 1.

[0046] (Conductive) The rubber sheet was measured based on JIS-K6271-2 Method 2 to obtain the volume resistivity of the material. Next, the rubber composition was reprocessed (remixed) in an 8-inch roll machine at a roll temperature of 50°C, a rotation ratio of 12:10, and a roll gap of 1.0 mm. The volume resistivity of the material after each reprocessing was determined, and it was confirmed whether the electrical conductivity was maintained compared to before reprocessing.

[0047] (hardness)

[0048] The durometer hardness (Shore A hardness) of the rubber sheet was measured in accordance with JIS K6253.

[0049] (Strength) The tensile strength (Mpa) of No. 3 dumbbell test pieces of the rubber sheets was measured in accordance with JIS K6251.

[0050] (stretch) The elongation (%) of a No. 3 dumbbell test piece of the rubber sheet was measured in accordance with JIS K6251.

[0051] (heat resistance) A heat aging test was carried out. Specifically, in accordance with JIS K6257, a heat aging test was started on the rubber sheet at 170°C, and the hardness change (ΔHS) and elongation change rate (ΔEB) relative to the initial value 70 hours after the start were calculated. Judgment criteria ○: Amount of change ΔHS = within ±10 points, rate of change in elongation ΔEB within ±30%. Both are satisfactory. ×: Amount of change ΔHS=within ±10 points, and rate of change in elongation ΔEB within ±30%. Neither of these is satisfied.

[0052] (water resistance) In accordance with JIS K 6258, the rubber sheet was immersed in water and left at 100°C for 72 hours, after which the hardness change (ΔHS) and elongation change rate (ΔEB) were determined in the same manner as in the heat resistance test. In addition, the volume change rate was calculated from the volume after immersion at 100°C for 72 hours and the volume before immersion. Judgment criteria ○: Amount of change ΔHS = within ±10 points, elongation change rate ΔEB within ±30%, volume change rate within 8%. All are satisfied. ×: Amount of change ΔHS = within ±10 points, rate of change in elongation ΔEB within ±30%, rate of change in volume within 8%. None of the above is satisfied.

[0053] (Compression set) Measured according to JIS K 6262 at 150°C for 72 hours. Judgment criteria ○: Change is 50 or less. ×: Change is 50 or more.

[0054] (Wear resistance) Dummy seals (test pieces, n=4) were prepared using the rubber composition, and an abrasion resistance tester as shown in FIG. 2 was used to rotate the test pieces while applying a load from above with a friction plate, and the amount of wear (mm) was confirmed. Load: 400gf, Rotational speed: 5000rpm, 1 hour Judgment criteria ○: 0.02mm or less △: More than 0.02mm and less than 0.023mm ×: 0.03mm or more and less than 0.10mm ××: 0.10mm or more

[0055] (Metal rust evaluation) The rubber sheet was pressure-bonded to an SPCC steel plate (size: 20 mm×100 mm×2 mm). Next, the sheets were placed in an environment of 85°C for 24 hours with a relative humidity of 95% or higher, and the surfaces of the pressed SPCC steel sheets were visually inspected to evaluate whether they were free of rust as "good" or whether they had rust as "poor".

[0056] [Table 1]

[0057] From the results shown in Table 1, Examples 1 to 5 The rubber sheets obtained in the above step 1 have excellent electrical conductivity and abrasion resistance. the law of nature, It is also found to be excellent in heat resistance, water resistance, distortion resistance, and metal rust prevention properties of the core metal portion to which the rubber sheet is fixed. On the other hand, the rubber sheets obtained in Comparative Examples 1 to 4, which contain carbon black having a DBP oil absorption of less than 200 ml / 100 g, are 5 The abrasion resistance was inferior to that of the rubber sheet obtained in the step 1. In addition, the rubber sheets obtained in Comparative Examples 5 to 7, which have a low carbon black content with a DBP oil absorption of 200 ml / 100 g or more and 500 ml / 100 g or less, are 5 The electrical conductivity of the rubber sheet obtained was inferior to that of the rubber sheet obtained in 2. above, with the electrical conductivity decreasing with repeated use. [Explanation of symbols]

[0058] 1. Rolling bearings 2. Inner Circle 3 Outer ring 4 Cage 5 Rolling elements 6 Inner ring groove 7 Outer ring groove 10 Grease 11 Sealing material 12 Core wire 13 Elastic Body 14 Main Lip 15 Dust Trip 15A groove 16 Outer Lip A Annular opening

Claims

1. A rubber composition for forming a sealing member of a rolling bearing, comprising: The rubber composition comprises 100 parts by mass of a rubber mainly composed of an acrylic ester and 20 to 40 parts by mass of carbon black having a DBP oil absorption of 200 ml / 100 g or more and 500 ml / 100 g or less, the acrylic acid ester is an acrylic acid ester having a carboxyl group, and does not contain carbon black having a DBP oil absorption of less than 200 ml / 100 g.

2. The rubber composition for use as a sealing member of a rolling bearing according to claim 1, further comprising 5 to 100 parts by mass of a white filler.

3. The rubber composition for use as a sealing member of a rolling bearing according to claim 1 or 2, further comprising 0.1 to 5 parts by mass of a coupling agent.

4. A bearing seal member molded from the rubber composition according to any one of claims 1 to 3, A bearing seal member, characterized in that the volume resistivity is 100 Ω·cm or less.

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