Forward and reverse rotation oil seal

Abstract

To provide a forward and reverse rotation oil seal capable of continuing excellently sealing even during forward and reverse rotation.SOLUTION: The forward and reverse rotation oil seal of the present invention is applied to a forward and reverse rotation oil seal 1 in which a seal lip 2a of an elastomeric portion 2 slides on a rotary shaft 5 that rotates in both forward and reverse directions. As the material for the elastomeric portion 2, a rubber composition is used in which 0.5 to 6 pts.mass, preferably 0.8 to 3 pts.mass of peroxide is blended with 100 pts.mass of a ternary fluororubber.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an oil seal, and more particularly to a forward / reverse rotation oil seal that can accommodate both forward and reverse rotation of a rotating shaft. [Background technology]

[0002] Generally, in automobiles equipped with gasoline engines, the engine rotation is switched from forward to reverse using a gear to back up the vehicle, so the oil seals used in the engines are standard oil seals that only work in one direction, forward.

[0003] Conventionally, as a material for such oil seals for gasoline engines, for example, Patent Document 1 proposes a silicone rubber composition obtained by compounding 0.5 to 30 parts by weight of magnesium oxide with 100 parts by weight of organopolysiloxane. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2899208 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the trend towards electrification has been accelerating in the automobile industry. In this case, electric vehicles driven by a motor do not have a reverse gear, and the direction of motor rotation is switched from forward to reverse to move the vehicle in reverse, so a bidirectional oil seal that can rotate in both forward and reverse directions is required.

[0006] When the rubber composition of Patent Document 1 is used as the material for such a forward / reverse rotation oil seal, repeated forward and reverse rotation causes deterioration of the oil (e.g., hydrocarbon oil in a reduction gearbox), which leads to depolymerization of the organopolysiloxane in the main chain, causing deterioration of the rubber and resulting in oil leakage. [Means for solving the problem]

[0007] In order to avoid such problems, the inventors conducted extensive research and discovered that by using a rubber composition obtained by compounding a suitable amount of peroxide with a ternary fluororubber as the material for forward and reverse rotation oil seals, oil leakage caused by deterioration of rubber due to oil deterioration can be avoided, leading to the completion of the present invention.

[0008] That is, the present invention is a forward / reverse rotating oil seal in which the seal lip of the elastic body part is in sliding contact with a rotating shaft that rotates in both forward and reverse directions, and is characterized in that the material for the elastic body part is a rubber composition in which 100 parts by weight of ternary fluororubber is blended with 0.5 to 6 parts by weight of peroxide. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a forward / reverse rotation oil seal that can continue to seal oil well in both forward and reverse rotation operations. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a vertical cross-sectional view of one side of a forward and reverse rotation oil seal according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to this embodiment.

[0012] As shown in Figure 1, a forward / reverse rotation oil seal 1 according to the present invention (hereinafter simply referred to as oil seal) is composed of an elastic body 2 and a reinforcing ring 3. The elastic body 2 is made of a rubber material and is bonded to and integrated with the reinforcing ring 3 made of a metal material.

[0013] The oil seal 1 configured in this manner is fitted and fixed to a housing (not shown) at the outer peripheral surface 2b of the elastic body portion 2, and the seal lip 2a formed on the inner peripheral side of the elastic body portion 2 slides against the rotating shaft 5 with the required pressure (tension force), thereby sealing in the oil. Here, the rotating shaft 5 is, for example, the drive shaft of a motor, which is rotated in both forward and reverse directions.

[0014] In addition, a garter spring 4 is fitted to the outer periphery of the seal lip 2a in the elastic body portion 2, which assists the tension of the seal lip 2a against the rotary shaft 5, thereby ensuring a more reliable seal in the oil.

[0015] Such an oil seal 1 is molded using a mold, and in the molding process, the elastic body portion 2 is formed by crosslinking (vulcanizing) a rubber material. There are no particular restrictions on the hardness of the rubber material, but in the case of oil seals, rubber with a hardness in the range of 60 to 90 (Type A: JISK 6253-3) is mainly used due to its relationship with tension force, etc.

[0016] In the present invention, the rubber material (rubber composition) used for the elastic body portion 2 uses fluororubber (FKM) as the base rubber, and in particular, in the present invention, a ternary fluororubber (a ternary copolymer of vinylidene fluoride, propylene hexafluoride, and ethylene tetrafluoride) is applied.

[0017] Examples of ternary fluororubbers include Viton GBL-200S, GBL-600S, GF-200S, and GF-600S (all trade names manufactured by Chemours Inc.), Dyneon FPO3730 and FLS2650 (all trade names manufactured by 3M Japan Ltd.), Daiel G-901, G-902, G-912, G-922, G-925, and G-952 (all trade names manufactured by Daikin Industries, Ltd.), Tecnoflon P457, P757, P459, and P959 (all trade names manufactured by Solvay (Italy)), and Fluonox KR320P, KR340P, KR520P, KR545P, KR565P, and KR525LP (all trade names manufactured by Gujarat Fluorochemicals (India)).

[0018] The peroxide compounded in the ternary fluoroelastomer is one of the essential components of the present invention, and is compounded in an amount of about 0.5 to 6 parts by weight of a peroxide such as 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, which is used in combination with about 2 to 8 parts by weight of a co-crosslinking agent such as triallyl isocyanurate (Taic). In this crosslinking system, the peroxide decomposes under heat, and the resulting methyl radicals react with Taic, which abstracts halogens from the fluoroelastomer polymer and forms crosslinking points; this is also called triazine crosslinking.

[0019] As the peroxide, peroxyketals and dialkyl peroxides can be used. Examples of peroxyketals include 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, such as Perhexa 3M and its 40% content product, Perhexa 3M-40 (trade name, manufactured by Nippon Oil & Fats Co., Ltd.), and n-butyl-4,4-bis(t-butylperoxy)valerate, such as Perhexa V and its 40% content product, Perhexa V-40 (trade name, manufactured by Nippon Oil & Fats Co., Ltd.). Dialkyl peroxides can be used. Examples of peroxides include dicumyl peroxides such as Percumyl D and Percumyl D-40 (trade name, manufactured by Nippon Oil & Fats Co., Ltd.), which contains 40% Percumyl peroxide; α,α'-bis(t-butylperoxy-m-isopropyl)benzenes such as Perbutyl P and Peroximon F-40 (trade name, manufactured by Nippon Oil & Fats Co., Ltd.), which contains 40% Perbutyl P; and 2,5-dimethyl-2,5-di(t-butylperoxy)hexanes such as Perhexa 25B and Perhexa 25B-40 (trade name, manufactured by Nippon Oil & Fats Co., Ltd.), which contains 40% Perbutyl P.

[0020] The amount of peroxide to be compounded is 0.5 to 6 parts by weight, preferably 0.8 to 3 parts by weight, per 100 parts by weight of ternary fluororubber. If the amount is less than this, an appropriate crosslinked product cannot be obtained, while if the amount is too much, there is no effect of increasing the weight, and in addition, gas generated by decomposition of the peroxide can cause problems such as bubbles in the rubber, which is undesirable.

[0021] When α,α'-bis(t-butylperoxy-m-isopropyl)benzene is used as a crosslinking agent, blooming may occur. In such cases, it is advisable to use 0.5 to 1 part by weight of polyethylene glycol such as PEG4000S (trade name manufactured by Sanyo Chemical Industries, Ltd.) in combination.

[0022] The co-crosslinking agent is blended in an amount of about 0.5 to 8 parts by weight per 100 parts by weight of ternary fluororubber, and may be polyethylene glycol dimethacrylate (PEGDM) such as Blemmer PDE-100 (trade name, manufactured by Nippon Oil & Fats Co., Ltd.), diallyl phthalate (DAP), triallyl isocyanurate (TAIC) such as Taik (trade name, manufactured by Nippon Kasei Co., Ltd.), triallyl cyanurate (TAC) such as Tack (trade name, manufactured by Musashino Chemical Laboratory Co., Ltd.), tetrahydrofurfuryl methacrylate (TFA) such as Acrylate THF (trade name, manufactured by Mitsubishi Rayon Co., Ltd.), or the like. HFMA), ethylene dimethacrylate (EDMA) such as Sunester EG (trade name, manufactured by Sanshin Chemical Industry Co., Ltd.) and Acryester ED (trade name, manufactured by Mitsubishi Rayon Co., Ltd.), 1,3-butylene dimethacrylate (BDMA) such as Acryester BD (trade name, manufactured by Mitsubishi Rayon Co., Ltd.), and trimethylolpropane trimethacrylate (TMPMA) such as Sunester TMPMA (trade name, manufactured by Sanshin Chemical Industry Co., Ltd.), Acryester TMP (trade name, manufactured by Mitsubishi Rayon Co., Ltd.), and Hicross M (trade name, manufactured by Seiko Chemical Co., Ltd.).

[0023] To obtain a crosslinked product with an appropriate level of strength, 0 to 60 parts by weight, preferably 10 to 30 parts by weight of a reinforcing filler is added to the rubber composition as needed, relative to 100 parts by weight of the base rubber.

[0024] Carbon black is a common reinforcing filler, and examples of such carbon black include HAF carbon (ASTM N330) such as Showblack N330 (trade name, manufactured by Showa Cabot Corporation), MAF carbon such as Seast 116 (trade name, manufactured by Tokai Carbon Co., Ltd.), FEF carbon (ASTM N550) such as Asahi #60 (trade name, manufactured by Asahi Carbon Co., Ltd.) and Seast SO (trade name, manufactured by Tokai Carbon Co., Ltd.), GPF carbon (ASTM N660) such as Asahi #55 (trade name, manufactured by Asahi Carbon Co., Ltd.), SRF carbon (ASTM N774) such as Asahi #50 (trade name, manufactured by Asahi Carbon Co., Ltd.), and MT carbon (ASTM N990) such as Asahi Thermal (trade name, manufactured by Asahi Carbon Co., Ltd.), HTC #20 (trade name, manufactured by Chubu Carbon Co., Ltd.), and Tharmax MT (trade name, manufactured by R.T. Vanderbilt (USA)).

[0025] In addition to carbon black, inorganic reinforcing agents can be used alone or in combination as reinforcing fillers. Examples of such reinforcing agents include fumed silica such as Aerosil 130, 200, 300, 380, OX50, TT600, MOX80, MOX170, COX84, R972, and R974 (all of which are trade names manufactured by Nippon Aerosil Co., Ltd.) and Reolosil QS13, QS30, QS38, and QS102 (all of which are trade names manufactured by Tokuyama Corporation), carbon black, and the like. Rex #67, #80, #100, #1120, XR, 22S, CS-5, CS-7 (all trade names of Shionogi Pharmaceutical Co., Ltd.), Silton A, R-2 (all trade names of Mizusawa Industrial Chemical Co., Ltd.), Tokusil AL-1, Gu, U, UR, US (all trade names of Tokuyama Corporation), Nipsil AQ, ER, LP, NA, NP, NS-K, VN-3 (all trade names of Nippon Silica Co., Ltd.), Ultrasil VN3 (trade name of Degussa (Germany)), Hi-Sil 233 (PPG wet silica such as Hakuenka CC, DD, O, U (all trade names manufactured by Shiraishi Kogyo Co., Ltd.), activated calcium carbonate such as Hakuenka A, AA (all trade names manufactured by Shiraishi Kogyo Co., Ltd.), special calcium carbonate such as Mistron Vapor (trade name manufactured by Japan Mistron Co., Ltd.), magnesium silicate such as Hitron, Hitron A, Microlite, US-100, US-150S, US-150SS, Hilac, Hilac SS (all trade names manufactured by Takehara Chemical Industry Co., Ltd.), Winner Clay A (hard clay: trade name manufactured by Kawashige Co., Ltd.), hard top clay, soft clay, crown clay, etc. clay (aluminum silicate) such as Silcanite, NN clay, Special Kaolin clay, Hard Bright, No. 5 clay, SPMA clay, Union Clay RC-1, Glomax LL, and Hydrite PX (all of which are product names of Takehara Chemical Industry Co., Ltd.), JP-100 kaolin, 5M kaolin, NN kaolin, Hard Sil, ST kaolin, and Cartabo (all of which are product names of Tsuchiya Kaolin Industry Co., Ltd.), ST-100, ST-200, and ST-301 (all of which are product names of Shiraishi Calcium Co., Ltd.), and Nulok321, Nucap100, Nucap190, Nucap200, and Nucap390 (all of which are JMExamples include silane-modified clays such as Huber (USA) (trade name) and Burgess KE, CB, 5178, 2211 (both trade names manufactured by Burgess Pigment (USA)).

[0026] Furthermore, diatomaceous earth is added to the rubber composition as needed to maintain an oil film as an oil seal.

[0027] Examples of diatomaceous earth include Celite 503, 535, 545, and SSC (all trade names manufactured by Johns-Manville, USA), Radiolite #100, #200, #300, #500, #500S, #600, #700, #800, #800-S, and #900, Fine Flow A, Fine Flow B, and Microfine (all trade names manufactured by Showa Chemical Industry Co., Ltd.), which are added in an amount of 3 to 18 parts by weight per 100 parts by weight of base rubber. Less than 3 parts by weight is ineffective, while more than 18 parts by weight is undesirable because it reduces abrasion resistance and therefore sealing performance.

[0028] Furthermore, to maintain the wear resistance required for an oil seal, a metal oxide is added to the rubber composition as needed. Examples of metal oxides include red iron oxide (iron sesquioxide), red iron oxide (iron tetraoxide), and chromium oxide, with red iron oxide being particularly preferred.

[0029] Examples of red iron oxide (iron sesquioxide) include TAROX R-110P (trade name, manufactured by Titanium Kogyo Co., Ltd.), EP-15W, and Tensho-in (all trade names, manufactured by Nippon Bengara Kogyo Co., Ltd.), Shippo-in and Senju-in (all trade names, manufactured by Morishita Bengara Kogyo Co., Ltd.), Todacolor 100ED, 120ED, 130ED, and 200 (all trade names, manufactured by Toda Kogyo Co., Ltd.), and Bayferrox 110M, 120M, 120NM, and 130M (all trade names, manufactured by Lanxess AG). Less than 5 parts by weight is ineffective, while more than 30 parts by weight is undesirable because the physical properties of the rubber deteriorate.

[0030] Furthermore, for the purpose of achieving dimensional stability and low cost, an extender filler is added to the rubber composition in an amount of 0 to 60 parts by weight, preferably 5 to 30 parts by weight, per 100 parts by weight of the base rubber, if necessary.

[0031] Examples of extender fillers include light calcium carbonate such as Green Ball (trade name manufactured by Inoue Lime Industry Co., Ltd.), Tama Pearl TP-121, TP-121R, TP222H, TP-222HS, TP-123, and TP-123CS (all of which are trade names manufactured by Okutama Kogyo Co., Ltd.), and Silver W (trade name manufactured by Shiraishi Kogyo Co., Ltd.), Whiteron SSB, SB, and S (all of which are trade names manufactured by Shiraishi Calcium Co., Ltd.), Sunlight #100, #300, #700, #800, #1000, #1500, #2000, #2200, and #2500 (all of which are trade names manufactured by Takehara Chemical Industry Co., Ltd.), and NS#100, NS#200, NS#400, NS#600, NS#1000, NS#2300, NS#2500, NS#2700, and NS#30. Heavy calcium carbonate such as 00, SS#30, SS#80, NN#200, NN#500 (all of which are product names of Nitto Funka Kogyo Co., Ltd.) and Super S, SS, SSS, 4S, #1500, #1700, #2000 (all of which are product names of Maruo Calcium Co., Ltd.), talc (talc) such as JET-S (product name of Asada Flour Milling Co., Ltd.), Talc GTA, CTA1, CTA2, and Fine Talc (all of which are product names of Kunimine Kogyo Co., Ltd.), and MS, MS-P, MS-A, ND, SW, SW-E, SWA, SWB, SSS, SS, and S (all of which are product names of Nippon Talc Co., Ltd.), Crystallite AA, VX-S, VX-S-2, and VX-SR (all of which are product names of Tatsumori Co., Ltd.) and Min-U-Sil Examples include quartz powder such as 5, 10, 15, 30 (all trade names manufactured by US Silica, USA) and Imsil A-10, A-15, A-25, A-108 (all trade names manufactured by Illinois Minerals, USA); wollastonite (calcium metasilicate) such as JA-30W, 325M (all trade names manufactured by Asada Flour Milling Co., Ltd.), Hicon A-60, S-4 (all trade names manufactured by Tsuchiya Kaolin Kogyo Co., Ltd.), and NYAD325, 400, 1250, G (all trade names manufactured by NYCO, USA); zinc oxide such as Zinc Oxide No. 1 (trade name manufactured by Sakai Chemical Industry Co., Ltd.), aluminum sulfate, barium sulfate, calcium sulfate, titanium oxide, molybdenum disulfide, and the like, and usually one to several types are used in combination with the reinforcing filler.

[0032] Furthermore, to improve the rubber kneadability and extrusion properties, the rubber composition may contain about 0.3 to 5 parts by weight of a lubricant or internal mold release agent per 100 parts by weight of the base rubber, if necessary. However, adding too much can cause blooming, bleeding, poor fusion, etc., so although it depends on the type, about 0.5 to 3 parts by weight is usually added.

[0033] Examples of lubricants and internal release agents include low molecular weight polyethylene such as Mitsui Hiwax 100P, 110P, 200P, 210P, 220P, 320P, and 420P (all trade names manufactured by Mitsui Petrochemical Industries, Ltd.), carnauba wax, and montan wax.

[0034] In this embodiment, the oil seal 1 shown in Fig. 1 is produced by crosslinking the rubber composition using a mold of a predetermined structure. Here, the elastic body 2 made of the rubber composition is crosslinked and bonded integrally to a metal reinforcing ring 3 in the mold. In this case, by applying an adhesive to the reinforcing ring 3 in advance, the elastic body 2 and the reinforcing ring 3 are firmly bonded by the adhesive at the same time as the crosslinking molding.

[0035] The choice of adhesive used to bond the elastic body portion 2 and the metallic reinforcing ring 3 is crucial, and care must be taken in combining it with the type of rubber. A silane adhesive is preferably used as this adhesive, which is obtained by dissolving a silane coupling agent in an organic solvent such as methanol at a concentration of about 1 to 20% by weight.

[0036] Examples of silane adhesives include Chemlok 5150, 607, 608, 7701, AP131, AP132, AP133, AP134, AP1751, Y1520A, Y1530, Y1540, KP1001, KP1002, Y4310, and Y5323 (all of which are trade names manufactured by Lord Far East, Inc.), Metalok S-2, S-5, S-7, and S-10A (all of which are trade names manufactured by Toyo Kagaku Kenkyusho Co., Ltd.), Sixon AN-187, 304, and 305 (all of which are trade names manufactured by Morton International Co., Ltd.), Vislock #150, #170, #180, #181, and #200 (all of which are trade names manufactured by Nichiei Chemical Co., Ltd.), and Monicas Examples include CF-5M, QZR-48, and 100 (all trade names manufactured by Yokohama Polymer Research Institute Co., Ltd.).

[0037] The adhesive is applied first to the metal reinforcing ring 3 in the cross-linking molding process for the oil seal 1 shown in Figure 1. At this time, the surface of the reinforcing ring 3 is activated in advance by sandblasting or the like, or a phosphate treatment film is formed on the reinforcing ring 3, and then the adhesive is applied to the reinforcing ring 3 after it has been degreased with methylene chloride or the like, and if necessary, the reinforcing ring 3 is baked at 80 to 190°C for about 10 to 120 minutes before use.

[0038] Next, more specific examples of the oil seal according to the embodiment of the present invention will be described below, but the present invention is not limited to these.

[0039] Example 1 The rubber composition for forming the elastic body 2 of the oil seal 1 of this embodiment was prepared by weighing out 100 parts by weight of Tecnoflon P757 (fluorine content 67%: product name of Solvay S.A., Italy), a ternary fluororubber and peroxide crosslinking, 15 parts by weight of Tharmax MT (product name of RTVanderbilt Co., Ltd., USA), as carbon black, 15 parts by weight of Radiolite Microfine (product name of Showa Chemical Industry Co., Ltd.), as diatomaceous earth, 10 parts by weight of Bayferrox 120M (product name of Lanxess AG), as red iron oxide, 4 parts by weight of Taik (product name of Nippon Kasei Co., Ltd.), as triallyl isocyanurate, and 2 parts by weight of Perhexa 25B-40 (product name of Nippon Oil & Fats Co., Ltd.), a peroxide containing 40% 2,5-dimethyl-2,5-di(t-butylperoxy)hexane. These components were kneaded together in a known rubber roll to prepare an uncrosslinked rubber.

[0040] The rubber was then cross-linked and molded using a mold of a predetermined structure to produce an oil seal (inner diameter: 30 mm, outer diameter: 47 mm, thickness: 7 mm) as shown in Figure 1. Similarly, a test piece with a thickness of 2 mm was also produced, and its rubber hardness was measured, finding it to be 77 degrees (JIS A, after 3 seconds).

[0041] Example 2 Oil seals and test pieces were prepared using the same composition as in Example 1, except that the base fluororubber was changed to a peroxide-crosslinked ternary fluororubber, Viton GBL600S (fluorine content 68%: product name, manufactured by Chemours, Inc., USA). The rubber hardness in this case was 75 degrees (JIS A, after 3 seconds).

[0042] Example 3 Oil seals and test pieces were prepared using the same composition as in Example 1, except that the fluororubber base rubber was changed to Daiel G-901 (fluorine content 71%: product name of Daikin Industries, Ltd.), a peroxide-crosslinked ternary fluororubber. The rubber hardness in this case was 75 degrees (JIS A, after 3 seconds).

[0043] Comparative Example 1 For comparison with the above examples, the base rubber fluororubber was changed from the formulation of Example 1 to Dyneon FC-2170 (fluorine content 66%: product name of 3M Japan Ltd.), a binary fluororubber made of vinylidene fluoride and hexafluoropropylene, which is crosslinked with polyol. The triallyl isocyanurate and peroxide were changed to 3 parts by weight of Kyowamag M-150 (product name of Kyowa Chemical Industry Co., Ltd.) as highly active magnesium oxide and 6 parts by weight of Carbit (product name manufactured by Omi Chemical Industry Co., Ltd.) as calcium hydroxide, respectively. Oil seals and test pieces were prepared using the same composition. The rubber hardness in this case was 78 degrees (JIS A, after 3 seconds).

[0044] Comparative Example 2 For comparison with the above-mentioned Examples, the fluororubber base rubber was changed to Technoflon FOR7380K (fluorine content 68%: product name of Solvay (Italy)), a ternary fluororubber crosslinked with polyol, from the formulation of Comparative Example 1, and oil seals and test pieces were prepared using the same composition. The rubber hardness in this case was 77 degrees (JIS A, after 3 seconds).

[0045] Comparative Example 3 For comparison with the previous examples, the fluororubber base rubber was changed to Viton GAL200S (fluorine content 66%: product name of Chemours, Inc. (USA), a binary fluororubber, which is peroxide crosslinked) from the formulation of Example 1, but the rest of the composition was the same as that of Example 1. An oil seal and a test piece were produced using the same composition. The rubber hardness in this case was 76 degrees (JIS A, after 3 seconds).

[0046] Comparative Example 4 For comparison with the above examples, the fluororubber base rubber was changed from the formulation of Example 1 to AFLAS 600S (fluorine content 57%, product name of AGC Corporation), a peroxide-crosslinked binary fluororubber (FEPM) made from tetrafluoroethylene and propylene, except that the same composition was prepared and an oil seal and test piece were produced. The rubber hardness in this case was 74 degrees (JIS A, after 3 seconds).

[0047] Then, for the above Examples 1 to 3 and Comparative Examples 1 to 4, performance tests and normal state physical property tests of the oil seals were carried out.

[0048] For the performance test, the oil seal was attached to a high-speed rotation test machine and a rotation test was conducted at room temperature in forward rotation at 16,000 rpm, followed by a rotation test in reverse rotation at 2,000 rpm, after which the presence or absence of oil leakage was visually confirmed.

[0049] Next, a rotation test was conducted in a low-temperature environment of -30°C at 5,000 rpm in the forward direction, and the presence or absence of oil leakage was visually confirmed.

[0050] The normal state physical property tests were conducted in accordance with JIS K6251 and JIS K6253, and hardness, tensile strength, and elongation were evaluated using 2 mm thick test pieces.

[0051] Next, for immersion test 1, a sealed container (pressure cooker) was prepared, and a 2 mm thick test piece was placed inside it along with a mixture of MOBIL EV COOL DRIVE 303 (trade name of ExxonMobil, USA), a lubricant for reduction gearboxes in electric vehicles, with 0.5% distilled water added. After heating at 150°C for 500 hours, the rubber hardness of the fluororubber was measured.

[0052] For comparison, in immersion test 2, a sealed container was prepared, and only MOBIL EV COOL DRIVE 303 (trade name of ExxonMobil (USA)), a lubricating oil for reduction gearboxes in electric vehicles, and a 2 mm thick test piece were placed in it. After heating at 150°C under normal pressure for 500 hours, the rubber hardness of the fluororubber was measured.

[0053] The test results are shown in Table 1. [Table 1]

[0054] As is clear from the test results shown in Table 1, no oil leakage was observed in the oil seals of all examples according to the present invention during either forward or reverse rotation, demonstrating that they have good sealing properties.

[0055] In contrast, in the oil seals of Comparative Examples 1 to 3, oil leakage was observed during both forward and reverse rotation, and it was found that they were unable to keep the oil sealed in well.

[0056] Furthermore, the oil seal of Comparative Example 4 maintained its sealing ability during forward and reverse rotation at room temperature, but oil leakage was observed at low temperatures, and it was found that it could not continue to seal oil well.

[0057] In Immersion Test 1, the rubber hardened and deteriorated, and an increase in rubber hardness was observed in Comparative Examples 1 to 3. In contrast, in Immersion Test 2, almost no change in rubber hardness was observed in any of the Examples and Comparative Examples.

[0058] This shows that the hardening of rubber due to the deterioration of hydrocarbon oil can be reproduced under the conditions of Immersion Test 1, and that this coincides well with the leakage phenomenon observed in the oil seal rotation test. The reaction mechanism by which the hardening and deterioration of fluororubber is accelerated in Immersion Test 1 is thought to be as follows.

[0059] Hydrocarbon oils, such as lubricants for electric vehicle reduction gearboxes, usually contain two types of additives. One type (amine compound) causes hardening and deterioration of fluororubber. The other type (phosphite compound) generates a strong acid when it reacts with moisture. Based on the above, it is thought that the lubricant used in the immersion test reacted with moisture in a sealed container, generating an acidic component, which accelerated deterioration. It is speculated that this reacted with the fluororubber together with the amine compound, accelerating the hardening and deterioration of the rubber.

[0060] Phosphite compounds as additives are susceptible to undesirable hydrolysis upon exposure to even trace amounts of moisture or water during storage or handling. Initially, hydrolysis of the phosphite produces acidic P-OH and PH=O protons, which are good reducing agents that react directly with oxygen or hydroperoxides. However, if hydrolysis continues beyond this initial stage, stronger acids are formed that greatly promote the formation of oxidation products. It is believed that the acidic substances generated by this hydrolysis accelerate the hardening and deterioration of the fluororubber.

[0061] In Immersion Test 1, the addition of a small amount of water and a sealed container are essential conditions, and in Immersion Test 2, where no small amount of water was added, no hardening or deterioration of the fluororubber progressed. Also, when an immersion test was carried out without using a sealed container and with a small amount of water added at normal pressure (open system) (results not shown in the table), the water that was added initially volatilized, so hydrolysis did not occur in the lubricating oil and acidic substances were not generated, and therefore hardening and deterioration of the fluororubber was not accelerated.

[0062] From the above results, the inventors discovered that by using the rubber composition of the above formulation as the material for the elastic body portion 2 of the oil seal 1, it is possible to prevent hardening and deterioration of the rubber due to acidic substances produced by deteriorated lubricating oil, and to continue to seal the oil well in both forward and reverse rotational operation, which led to the completion of the present invention.

[0063] Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment and can be modified as necessary. [Explanation of symbols]

[0064] 1 Oil seal 2 Elastic body part 2a Seal lip 5 Rotation Axis

Claims

[Claim 1] In a forward and reverse rotation oil seal in which the seal lip of the elastic body portion is in sliding contact with the rotating shaft that rotates in both forward and reverse directions, The material of the elastic body portion is A forward and reverse rotation oil seal characterized by using a rubber composition in which 0.5 to 6 parts by weight of peroxide is compounded with 100 parts by weight of ternary fluororubber.

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