Rubber composition for sealing and sealing member

Abstract

To provide a sealing member which has good heat resistance and hardly deteriorates in sealing performance even when used under a high-temperature environment.SOLUTION: A rubber composition for seal contains a carboxyl group-containing acrylic rubber, silica, and two or more kinds of inorganic fibers. The content of the silica is 25-100 pts.wt. based on 100 pts.wt. of the carboxyl group-containing acrylic rubber. The total content of the inorganic fibers is 35-100 pts.wt. based on 100 pts.wt. of the carboxyl group-containing acrylic rubber. The sealing member has a sliding part comprising a vulcanizate of the rubber composition for seal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rubber composition for sealing and a sealing member using the rubber composition for sealing.

Background Art

[0002] In automobiles, many oil seals are used, including oil seals for transmissions and differential gears. Automotive oil seals are required to have lower torque as well as oil sealing performance, along with the demand for lower fuel consumption.

[0003] As a method for reducing the torque of a sealing member, a method for reducing the friction of a rubber member that slides on a mating member has been proposed. Specifically, for example, Patent Document 1 proposes a sealing member using a rubber composition for sealing containing carboxyl-based acrylic rubber, artificial graphite, and a coupling agent. According to this sealing member, it is described that low friction can be achieved while maintaining good sealing performance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The above oil seal may be used in a high-temperature environment. According to the study by the present inventors, it has been clarified that the vulcanizate of the rubber composition for sealing in which artificial graphite and a coupling agent are blended with the carboxyl-based acrylic rubber proposed in Patent Document 1 is inferior in heat resistance to the vulcanizate of the rubber composition for sealing without blending artificial graphite. Therefore, when a seal member using a rubber composition containing artificial graphite is used in a high-temperature environment, its hardness may increase or its elongation at break may decrease during cutting. As a result, its followability to the mating member may decrease, leading to a decrease in sealing performance, or the sliding part may be easily damaged.

[0006] In view of such a situation, an object of the present invention is to provide a sealing member having good heat resistance and being less likely to have a decrease in sealing performance even when used in a high-temperature environment.

Means for Solving the Problems

[0007] The rubber composition for seals of the present invention contains a carboxyl group-containing acrylic rubber, silica, and two or more kinds of inorganic fibers. The content of the above silica is 25 to 100 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber. The total content of the above inorganic fibers is 35 to 100 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber.

[0008] The rubber composition for seals of the present invention has the specific composition described above. Therefore, by using a vulcanizate of the above rubber composition for seals in the sliding part of a sealing member, a sealing member having good heat resistance and a small sliding resistance can be provided.

[0009] In the above rubber composition for seals, it is preferable that the inorganic fibers are at least two kinds selected from the group consisting of glass fibers, carbon fibers, and calcium silicate fibers. In this case, it is more suitable for providing a sealing member with a small sliding resistance.

[0010] In the above rubber composition for seals, it is preferable that the inorganic fibers have an average fiber diameter of 5 to 20 μm and an average fiber length of 10 to 400 μm.

[0011] The above rubber composition for seals contains at least glass fibers and calcium silicate fibers as the inorganic fibers. It is preferable that the content of the glass fiber is 5 to 20 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber. In this case, it is more suitable for providing a sealing member having good heat resistance and low sliding resistance.

[0012] The rubber composition for sealing further contains carbon black, It is preferable that the content of the carbon black is 10 parts by weight or less with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber. In this case, the vulcanizate of the rubber composition for sealing has good heat resistance and is less likely to cause a change (deterioration) in physical properties due to heat.

[0013] The sealing member of the present invention has a sliding portion made of a vulcanizate of the rubber composition for sealing. Even when the sealing member is used in a high-temperature environment, the sealing performance is less likely to deteriorate. Further, the sliding portion has a low sliding resistance and is suitable for reducing the torque of the sealing member.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a sealing member having good heat resistance, less likely to deteriorate in sealing performance even when used in a high-temperature environment, and having a small sliding resistance.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0016] Hereinafter, a rubber composition for sealing according to an embodiment of the present invention and an oil seal which is an example of a sealing member according to an embodiment of the present invention using this rubber composition for sealing will be described. First, the oil seal will be described with reference to FIG. 1.

[0017] The oil seal 10 is formed in a ring shape, and the outer peripheral surface of its outer peripheral portion is fixed to, for example, the housing 35 of the transmission, etc., and the lip tip 24 of the inner peripheral portion is in sliding contact with the lip contact surface 36a of the shaft surface of the mating member such as the rotating shaft 36, and seals lubricating oil or the like enclosed in the space between the housing 35 and the rotating shaft 36. The oil seal 10 is formed by vulcanizing and bonding a metal ring 11 and an elastic member 12. The metal ring 11 is bent into an L-shaped cross section by a parallel portion 14 and a perpendicular portion 15 parallel to the axial direction. The elastic member 12 is adhered so as to cover the outer peripheral surface of the parallel portion 14 of the metal ring 11 and the axial one-side surface of the perpendicular portion 15, and includes a protective lip 19 and a lip head 18 having a lip tip 24 that serves as a sliding contact portion with the rotating shaft 36 on the radially inner side. A garter spring 13 for assisting the tightening force is provided on the outer peripheral surface of the lip head 18.

[0018] The protective lip 19 extends toward the rotating shaft 36 and blocks the passage of dust between it and the rotating shaft 36. Further, the protective lip 19 extends obliquely in a direction away from the lip head 18. The lip head 18 is disposed on the inner peripheral side of the parallel portion 14 of the metal ring 11 and has a spring groove 18a for fitting the garter spring 13 on its outer peripheral surface, and the inner peripheral surface has a tapered shape toward the radially inner side. Therefore, on the inner peripheral surface of the lip head 18, two lip side surfaces 20, 23 that are inclined in opposite directions to each other are formed on both axial sides with the tapered lip tip (boundary edge) 24 as a boundary.

[0019] One lip side surface 20 disposed away from the protective lip 19 is a lip sealing fluid side surface disposed on the sealed fluid side, and the other lip side surface 23 disposed on the protective lip 19 side is a lip atmosphere side surface. At the lip head 18, mainly the lip tip 24 is in sliding contact with the lip contact surface (surface of the shaft) 36a of the rotating shaft 36. Note that the lip head 18 is curved radially outward when the lip tip 24 contacts the lip contact surface 36a of the rotating shaft 36, and the deformed lip tip 24, the lip sealing fluid side surface 20 in its vicinity, and the lip atmosphere side surface 23 contact the lip contact surface 36a. However, in FIG. 1, the lip head 18 in a non-curved state is shown.

[0020] The elastic member 12 including the lip head 18 that serves as a sliding portion with the rotating shaft 36 is made of a vulcanizate of the rubber composition for sealing according to the embodiment of the present invention. The rubber composition for sealing includes a carboxyl group-containing acrylic rubber, silica, and two or more types of inorganic fibers. Since the oil seal 10 has the elastic member 12 made of the above vulcanizate, the sealing performance is less likely to deteriorate even when used in a high-temperature environment. Further, the oil seal 10 has a small sliding resistance and can achieve low torque.

[0021] Next, the above rubber composition for sealing (hereinafter, also simply referred to as rubber composition) will be described. The rubber composition includes an unvulcanized carboxyl group-containing acrylic rubber, silica, and two or more types of inorganic fibers. The carboxyl group-containing acrylic rubber is not particularly limited, and examples thereof include polymers represented by the following formula (1), which are copolymers of a carboxyl group-containing monomer and an acrylic monomer.

[0022]

Chemical formula

[0023] The carboxyl group-containing acrylic rubber represented by the above formula (1) has a unit having a carboxyl group serving as a crosslinking point and becomes a vulcanized rubber by heating in the coexistence of a vulcanizing agent. The carboxyl group-containing acrylic rubber may be a copolymer formed by reacting a carboxyl group-containing monomer, an acrylic monomer, and a third monomer. Examples of the third monomer include one or a combination of a plurality of species such as butoxyethyl acrylate, ethylene, and methyl acrylate.

[0024] As the carboxyl group-containing acrylic rubber, commercially available products can also be used. Examples of commercially available products of the carboxyl group-containing acrylic rubber include Nipol AR-14, Nipol AR12 (both manufactured by Zeon Corporation, Japan), NOXTITE PA-521, NOXTITE PA-522HF, NOXTITE PA-526, NOXTITE PA-524 (all manufactured by Unimatech Co., Ltd.), Lactester CH, Lactester CT, Lactester CUC (all manufactured by Osaka Soda Co., Ltd.), and the like. As the carboxyl group-containing acrylic rubber, one type of carboxyl group-containing acrylic rubber may be used, or two or more types of carboxyl group-containing acrylic rubbers may be used in combination.

[0025] The silica may be any that can be compounded in the rubber composition. The above-mentioned silica preferably has a pH of 8 or more and 12 or less, because it is suitable for reducing the torque of the oil seal.

[0026] In the present invention, the pH of the silica is a value obtained by measuring a water suspension containing 4 wt% of silica with a pH meter. The pH of the above-mentioned silica can be adjusted, for example, by adjusting the amount of acid added to the alkaline reaction solution during the production of the silica.

[0027] The shape of the above-mentioned silica is not particularly limited. For example, it may be spherical. When the shape of the above-mentioned silica is spherical, the particle diameter of the above-mentioned silica may be, for example, about 5 nm to 20 μm. The particle diameter of the above-mentioned silica is measured based on JIS Z 8825:2013 Particle Size Analysis - Laser Diffraction / Scattering Method.

[0028] The content of silica in the above rubber composition is 25 to 100 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber. When the content of the above-mentioned silica is less than 25 parts by weight, the hardness of the vulcanizate of the above rubber composition becomes low. Therefore, the sealing performance of the oil seal 10 having the elastic member 12 made of the above vulcanizate becomes insufficient. On the other hand, when the content of the above-mentioned silica exceeds 100 parts by weight, the hardness of the vulcanizate of the above rubber composition becomes excessive. Therefore, the oil seal 10 having the elastic member 12 made of the above vulcanizate has a reduced followability to the mating member and the sealing performance becomes insufficient. The content of the above-mentioned silica is preferably 30 to 70 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber.

[0029] The above rubber composition contains two or more kinds of inorganic fibers. By using a rubber composition containing two or more kinds of inorganic fibers, the surface of the elastic member 12 made of the vulcanizate of this rubber composition becomes a non-uniform rough surface. Therefore, the elastic member 12 made of the vulcanizate of the above rubber composition has a small sliding resistance to the mating member (rotating shaft 36).

[0030] The total content of the inorganic fibers in the rubber composition is 35 to 100 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber. When the total content of the inorganic fibers is less than 35 parts by weight, the elastic member 12 made of the vulcanizate of the rubber composition has a large sliding resistance. On the other hand, when the total content of the inorganic fibers exceeds 100 parts by weight, the vulcanizate of the rubber composition becomes too hard. Therefore, the elastic member 12 made of the vulcanizate has poor followability with respect to the mating member, and the oil seal 10 has insufficient sealing performance.

[0031] Examples of the inorganic fibers include glass fibers, carbon fibers, calcium silicate fibers, and the like. The rubber composition preferably contains at least two of these inorganic fibers. It is suitable for forming an elastic member 12 having good heat resistance and low sliding resistance.

[0032] The glass fiber may be glass wool (short fiber) or glass fiber (long fiber), but glass fiber is preferred.

[0033] The carbon fiber may be PAN-based carbon fiber or pitch-based carbon fiber.

[0034] The calcium silicate fiber may be a fibrous or needle-like material mainly composed of calcium silicate, and examples thereof include wollastonite. Here, the phrase "mainly composed of calcium silicate" means that the content rate of calcium silicate exceeds 50% by weight.

[0035] The average fiber diameter of the inorganic fibers is preferably 5 to 20 μm. Also, the average fiber length of the inorganic fibers is preferably 10 to 400 μm. The above rubber composition contains two or more types of inorganic fibers. The average fiber diameter and average fiber length of the above inorganic fibers are preferably within the above ranges for each type of inorganic fiber. For example, when the above rubber composition contains glass fiber and calcium silicate fiber as inorganic fibers, it is preferable that each of the glass fiber and the calcium silicate fiber has an average fiber diameter and an average fiber length within the above-mentioned ranges. Using inorganic fibers of such dimensions is suitable for reducing the sliding resistance of the elastic member 12 of the oil seal 10 made of the vulcanizate of the above rubber composition. In addition, the average aspect ratio of the above inorganic fibers is preferably 2 to 20.

[0036] The fiber length and fiber diameter of the above inorganic fibers are obtained by randomly selecting 100 pieces of the same type of inorganic fibers, observing the selected inorganic fibers with a microscope to measure the fiber length and fiber diameter of each inorganic fiber, and calculating the average value of the fiber length and fiber diameter for each type of inorganic fiber. At this time, as the microscope, an optical microscope, a scanning electron microscope, etc. can be used. The aspect ratio of the above inorganic fibers is the value obtained by dividing the above fiber length by the above fiber diameter.

[0037] The above rubber composition preferably contains at least glass fiber and calcium silicate fiber as the above inorganic fibers. This combination is particularly suitable as a combination for reducing the sliding resistance of the elastic member 12 made of the vulcanizate of the above rubber composition. In this case, as the above inorganic fibers, only two types of glass fiber and calcium silicate fiber may be contained, or other inorganic fibers may be contained in addition to the glass fiber and calcium silicate fiber.

[0038] When at least glass fiber and calcium silicate fiber are contained as the inorganic fiber, the content of the glass fiber is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber. If the content of the glass fiber is less than 5 parts by weight, the sliding resistance of the elastic member 12 made of the vulcanizate of the rubber composition may not be sufficiently reduced. On the other hand, if the content of the glass fiber exceeds 20 parts by weight, the vulcanizate of the rubber composition becomes hard, and the sealing performance of the elastic member 12 made of the vulcanizate may be lowered. Also, when at least glass fiber and calcium silicate fiber are contained as the inorganic fiber, the content of the calcium silicate fiber is preferably 30 to 70 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber.

[0039] The inorganic fiber may be surface-treated with a silane coupling agent. In this case, the tensile strength at break (Tb) and the elongation at break (Eb) of the vulcanizate constituting the elastic member 12 are improved, and the oil seal 10 is more suitable for maintaining low torque performance over a long period of time.

[0040] The rubber composition may further contain carbon black. By containing carbon black, the vulcanizate of the rubber composition can be colored black. Therefore, the elastic member 12 made of the vulcanizate is less likely to show dirt and the like prominently. The content of the carbon black is preferably 10 parts by weight or less with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber. If the content of the carbon black exceeds 10 parts by weight, the heat resistance of the vulcanizate of the rubber composition may be lowered. On the other hand, the lower limit of the content of carbon black is not particularly limited, and from the viewpoint of coloring the vulcanizate black, the content of carbon black may be 1 part by weight or more. The rubber composition may not contain carbon black.

[0041] The above rubber composition further contains a vulcanizing agent. The vulcanizing agent may be any one that can crosslink carboxyl group-containing acrylic rubber such as an amine-based vulcanizing agent. In addition, the above rubber composition may contain, if necessary, a vulcanization accelerator such as a guanidine compound, a sulfenamide compound, 1,8-diazabicyclo[5.4.0]undec-7-ene, a tertiary amine, a processing aid such as a saturated fatty acid (for example, stearic acid, etc.), microcrystalline wax, etc. Furthermore, it may contain other known additives such as an antioxidant, an ozone deterioration inhibitor, a plasticizer, etc. blended in the oil seal.

[0042] It is preferable that the above rubber composition does not contain graphite. This is because when graphite is contained, the vulcanizate of the above rubber composition becomes inferior in heat resistance.

[0043] The normal physical properties of the vulcanizate of the above rubber composition are preferably the following physical properties. Here, the normal physical properties are the physical properties measured after the above rubber composition is vulcanized and stored at room temperature for 24 hours.

[0044] The durometer A hardness of the vulcanizate of the above rubber composition is preferably A70 to A90. If the durometer A hardness of the above vulcanizate is less than A70, the tightening force of the elastic member 12 against the mating member (rotating shaft 36) may be insufficient and oil leakage may occur. On the other hand, if the durometer A hardness of the above vulcanizate exceeds A90, the followability of the elastic member 12 against the mating member becomes insufficient, and in this case, oil leakage may also occur. The durometer A hardness may be measured by a method conforming to JIS K 6253-3:2012.

[0045] The tensile strength at break (Tb) of the vulcanizate of the above rubber composition is preferably 8.0 MPa or more. Also, the elongation at break (Eb) of the vulcanizate of the above rubber composition is preferably 100% or more. When the vulcanized product satisfies these tensile properties, the elastic member 12 has sufficient mechanical strength and is suitable for ensuring the sealing performance as an oil seal over a long period of time. The above-mentioned tensile strength at break (Tb) and elongation at break (Eb) may be measured by a method conforming to JIS K 6251:2017.

[0046] The oil seal 10 according to the present embodiment can be manufactured, for example, through the following steps. (1) First, a rubber composition containing an unvulcanized carboxyl group-containing acrylic rubber, silica, two or more kinds of inorganic fibers, a vulcanizing agent, and further various additives such as a vulcanization accelerator and a processing aid to be blended as needed is prepared. This rubber composition may be prepared by previously weighing each compounding component and kneading them with a kneader such as a roll or a kneader.

[0047] (2) Next, the above rubber composition is poured into a mold and vulcanization-molded under predetermined conditions. In this step, when vulcanization-molding the above rubber composition, it is preferable to previously provide the metal ring 11 in the mold and vulcanization-bond the metal ring 11 and the elastic member 12. Thereby, the manufacturing man-hours can be reduced.

[0048] (3) Thereafter, the molded product is taken out of the mold, the garter spring 13 is fitted, and the oil seal 10 is completed.

[0049] (Other embodiments) The sealing member according to the embodiment of the present invention is not limited to an oil seal, and may be, for example, a dust seal or other seal members.

[0050] Since the sealing member according to the embodiment of the present invention is excellent in heat resistance, it can be suitably used, for example, as an oil seal used in a place where it may be exposed to a high temperature environment of about 150°C.

Examples

[0051] Hereinafter, the present invention will be described more specifically by way of examples. However, the embodiments of the present invention are not limited to the following examples. In each of the examples and comparative examples, a rubber composition was prepared, a seal made of a vulcanizate of each rubber composition was manufactured, and the physical properties of the obtained sheet were measured. The compounding compositions of the respective rubber compositions are shown in Table 1. Also, the measurement results of the physical properties are shown in Table 2.

[0052] In the examples and comparative examples, the compounding chemicals used for preparing the rubber composition are as follows. · Carboxyl group-containing acrylic rubber Nipol AR-14 (manufactured by Nippon Zeon Co., Ltd.) · Silica Nip Seal ER (manufactured by Tosoh Silica Corporation) · Inorganic fiber (glass fiber) MF06JB1-20 (manufactured by Asahi Fiber Glass Co., Ltd.), fiber diameter = 10 μm, fiber length = 63 μm · Inorganic fiber (calcium silicate fiber) NYAD 400 (manufactured by NYCO Minerals Inc.), fiber diameter = 7 μm, fiber length = 35 μm · Carbon black Seast SO (manufactured by Tokai Carbon Co., Ltd.) · Graphite Artificial graphite (manufactured by SFC Carbon Co., Ltd.), average particle diameter 6 μm · Others Processing aid: Stearic acid (TST) (manufactured by Miyoshi Oil & Fat Co., Ltd.) Antioxidant: Nonflex LAS-P (manufactured by Seiko Chemical Co., Ltd.) Ozone deterioration inhibitor: Santite S (manufactured by Seiko Chemical Co., Ltd.) Silane coupling agent: DOWSIL Z-6076 SILANE (manufactured by Toray Dow Corning Co., Ltd.) Plasticizer: Adeka Sizer RS-1000 (manufactured by ADEKA Corporation) Vulcanizing agent: Sunfel 6-MC (manufactured by Sanshin Chemical Industry Co., Ltd.) Vulcanization accelerator: Renogran XLA-60 (manufactured by LANXESS Co., Ltd.)

[0053] (Example 1) (1) 100 parts by weight of carboxyl group-containing acrylic rubber, 55 parts by weight of silica, 5 parts by weight of glass fiber, 35 parts by weight of calcium silicate fiber, 5 parts by weight of carbon black, 2 parts by weight of processing aid, 2 parts by weight of antioxidant, 3 parts by weight of ozone deterioration inhibitor, 1 part by weight of silane coupling agent, 10 parts by weight of plasticizer, 0.6 parts by weight of vulcanizing agent, and 2 parts by weight of vulcanization accelerator were kneaded with a roll to obtain a rubber composition.

[0054] (2) After casting the rubber composition obtained in (1) above into a mold, primary vulcanization was carried out under the conditions of 170 °C for 3 minutes, and further, secondary vulcanization was carried out under the conditions of 190 °C for 1 hour to produce a 2 mm thick sheet made of the vulcanizate of the above rubber composition.

[0055] (Example 2) A sheet was produced in the same manner as in Example 1 except that the blending amount of the glass fiber was changed to 10 parts by weight.

[0056] (Example 3) A sheet was produced in the same manner as in Example 2 except that the blending amount of the calcium silicate fiber was changed to 45 parts by weight.

[0057] (Example 4) A sheet was produced in the same manner as in Example 2 except that the blending amount of the calcium silicate fiber was changed to 65 parts by weight.

[0058] (Example 5) A sheet was produced in the same manner as in Example 1 except that the blending amount of the glass fiber was changed to 20 parts by weight.

[0059] (Example 6) A sheet was produced in the same manner as in Example 1 except that the blending amount of the glass fiber was changed to 40 parts by weight.

[0060] (Comparative Example 1) A sheet was produced in the same manner as in Example 1 except that glass fiber and calcium silicate fiber were not blended.

[0061] (Comparative Example 2) A sheet was produced in the same manner as in Example 1, except that glass fibers were not compounded.

[0062] (Comparative Example 3) A sheet was produced in the same manner as in Example 1, except that the compounding amount of glass fibers was 35 parts by weight and calcium silicate fibers were not compounded.

[0063] (Comparative Example 4) A sheet was produced in the same manner as in Comparative Example 2, except that 30 parts by weight of graphite was further compounded.

[0064] (Comparative Example 5) A sheet was produced in the same manner as in Comparative Example 2, except that the compounding amount of carbon black was changed to 15 parts by weight.

[0065]

Table 1

[0066] The physical properties of the sheets produced in each of the examples and comparative examples were measured by the following methods. (1) Evaluation of normal physical properties (1-1) Durometer A hardness: A sheet cut out to a size of 30×50 mm was used as a test piece. The durometer A hardness was measured using a type A durometer in accordance with the method specified in "JIS K 6253-3:2012". The measurement was carried out with three test pieces stacked.

[0067] (1-2) Tensile strength at break (Tb) and elongation at break (Eb): A dumbbell-shaped No. 3 test piece was cut out from the sheet. A tensile test was carried out in accordance with "JIS K 6251:2017". At this time, the tensile speed was 500 mm / min and the number of test pieces was 3.

[0068] (2) Evaluation after the aging test (2-1) Accelerated aging test (Method A): A sheet (test piece) cut out to a size of 30×50 mm and a dumbbell-shaped No. 3 test piece were used, and an accelerated aging test (Method A) was conducted in accordance with the method specified in "JIS K 6257:2017". A forced circulation type thermal aging tester (crosswind type) was used as the test apparatus. The test pieces were prepared in the same manner as in (1-1) and (1-2) above. The test conditions were 150 °C for 1008 hours.

[0069] (2-2) Physical properties after aging test: For the test pieces subjected to the above aging test, the durometer A hardness, tensile strength at break (Tb), and elongation at break (Eb) were measured in the same manner as in (1-1) and (1-2) above.

[0070] (3) Friction and wear test: A sheet cut out into a disc shape with a diameter of 46 mm was used as the test piece. Using this test piece, a friction and wear test was conducted to measure the coefficient of dynamic friction.

[0071] Figure 2 is a schematic diagram showing the test apparatus used for the friction and wear test. The friction and wear test apparatus 40 can measure the coefficient of friction when the test piece and the annular measuring jig are relatively rotated while being pressed against each other with a constant load. The friction and wear test apparatus 40 includes a holding portion 42 that holds the measuring jig 41 and a stage 44 that supports the test piece 43.

[0072] The holding portion 42 is configured to be able to apply a vertical load at a preset value in a state where the lower surface 41a of the measuring jig 41 is in contact with the upper surface 43a of the test piece 43. The test piece 43 is fixedly attached to the upper surface 44a of the stage 44 so as to be integrally rotatable. The stage 44 is rotatable around the central axis S of the measuring jig 41, and the test piece 43 and the measuring jig 41 in contact with each other are relatively rotated. As a result, the test piece 43 and the measuring jig 41 slide against each other.

[0073] The friction and wear test device 40 is configured to measure the frictional force generated between the test piece 43 and the measurement jig 41 when they are sliding. The friction and wear test device 40 converts the measured frictional force into a coefficient of friction and outputs it. The coefficient of friction is the value at the end of the test. The test conditions for the friction and wear test are shown below.

[0074] Test Conditions Test device: Friction and wear tester EFM-III-F (manufactured by Orientec Co., Ltd.) Measurement jig: Outer diameter 25.6 mm, inner diameter 20.0 mm, thickness 15.0 mm, material S45C, surface roughness Ra = 0.8 μm Vertical load: 5 kg Surface pressure: 0.24 MPa Rotation speed: 500 rpm Peripheral speed: 0.6 m / s Test time: 10 min Room temperature: 25 °C

[0075]

Table 2

[0076] As shown in Table 2, the vulcanizates (sheets) produced in Examples 1 to 6 had a smaller coefficient of friction than the vulcanizates produced in Comparative Examples 1 to 5. Also, the physical properties of the vulcanizates produced in Examples 1 to 6 were less likely to change compared to the vulcanizates produced in Comparative Examples 1 to 5 even after the accelerated aging test.

Explanation of Reference Numerals

[0077] 10 Oil seal 11 Metal ring 12 Elastic member 13 Garter spring 18 Seal head 19 Protection lip 20 Lip seal liquid side 23 Lip atmosphere side

Claims

1. A rubber composition for sealing, comprising a carboxyl group-containing acrylic rubber, silica, and two or more kinds of inorganic fibers, wherein the content of the silica is 25 to 100 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber, the total content of the inorganic fibers is 35 to 100 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber, and the inorganic fibers include at least glass fibers and calcium silicate fibers.

2. The rubber composition for sealing according to claim 1, wherein the inorganic fibers have an average fiber diameter of 5 to 20 μm and an average fiber length of 10 to 400 μm.

3. The rubber composition for sealing according to claim 1 or 2, wherein the content of the glass fibers is 5 to 20 parts by weight with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber.

4. Furthermore, it contains carbon black, and the content of the carbon black is 10 parts by weight or less with respect to 100 parts by weight of the carboxyl group-containing acrylic rubber. The rubber composition for sealing according to any one of claims 1 to 3.

5. A sealing member having a sliding portion made of a vulcanizate of the rubber composition for sealing according to any one of claims 1 to 4.

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