JP2019048913A - Rubber composition for oil seal and oil seal - Google Patents

Abstract

To provide a rubber composition for oil seal having hydrolysis resistance for suitable use even in an engine oil environment in which moisture is mixed, while having heat resistance and oil resistance comparable to those of an acrylic rubber, and further excellent in cold resistance and compression set, and an oil seal.SOLUTION: There are provided a rubber composition for oil seal constituted by a polymer consisting of a polyamine crosslinkable hydrogenated nitrile rubber, and a plasticizer of 5 to 25 pts.wt. per 100 pts.wt. of the polymer, with nitrile content of the polymer of 20 to 30 wt.%, and an oil seal constituted by a crosslinked body by polyamine crosslinking the rubber composition for oil seal.SELECTED DRAWING: None

Description

  The present invention relates to a rubber composition for oil sealing and an oil seal, and more specifically, a hydrolysis resistance suitably used in an engine oil environment mixed with water while having heat resistance and oil resistance comparable to acrylic rubber. The present invention relates to a rubber composition for oil seal and oil seal which are excellent in cold resistance and compression set.

  Conventionally, acrylic rubber (ACM) which is excellent in heat resistance and oil resistance has been widely used as an oil seal.

  On the other hand, the applicant has so far disclosed a rubber composition for fuel seal (Patent Documents 1 and 2). In these Patent Documents 1 and 2, a plasticizer is contained in the rubber composition in order to impart resistance to the polycyclic aromatic compound contained in the fuel to the fuel seal (rubber).

WO 2013/175877 (Fuel seal) WO 2013/175878 (Fuel seal)

  In conventional oil seals, acrylic rubber is hydrolyzed and resinified and hardened in engine oil mixed with water generated by fuel combustion or in a bad oil environment containing a large amount of water, so the sealing function is stable. There is room for further improvement in terms of maintaining the

  Since acrylic rubber causes hydrolysis in an acid or alkaline environment due to its molecular structure, we examined the material change to hydrogenated nitrile rubber (HNBR) which is also excellent in heat resistance and oil resistance as a countermeasure.

  However, it has been found that conventional peroxide cross-linked HNBR does not have heat resistance comparable to acrylic rubber. There is also a room for improvement in the hydrolysis resistance, particularly in engine oil contaminated with water.

  Also, with the globalization of the market, the rubber materials used for engine oil seal members are not only heat resistant in consideration of the engine use environment, but also for ensuring sealability when the engine stops in a cold region. Cold resistance is also required. However, in HNBR, a method for improving cold resistance without deteriorating compression set has not been sufficiently established.

  Therefore, the object of the present invention is to have hydrolysis resistance comparable to that of acrylic rubber, which is suitably used even in engine oil environment mixed with water while having heat resistance and oil resistance, and further has cold resistance and compression set. It is an object of the present invention to provide an oil seal rubber composition and an oil seal which are excellent.

  Further, other objects of the present invention will become clear by the following description.

  The above problems are solved by the following inventions.

(Claim 1)
A polymer comprising a polyamine crosslinkable hydrogenated nitrile rubber and 5 to 25 parts by weight of a plasticizer per 100 parts by weight of the polymer, wherein the nitrile content of the polymer is 20 to 30% by weight Rubber composition for oil seal.
(Claim 2)
An oil seal comprising a crosslinked product obtained by polyamine crosslinking the rubber composition for oil seal according to claim 1.

  According to the present invention, while having heat resistance and oil resistance comparable to acrylic rubber, it has hydrolysis resistance suitably used even in an engine oil environment mixed with water, and furthermore, cold resistance and compression set. The rubber composition for oil seal and the oil seal which are excellent also can be provided.

  Hereinafter, embodiments of the present invention will be described in detail.

1. Composition for oil seal The composition for oil seal of the present invention comprises a polymer comprising a polyamine crosslinkable hydrogenated nitrile rubber (hereinafter also referred to as HNBR), and 5 to 25 parts by weight of a plasticizer per 100 parts by weight of the polymer The nitrile content of the polymer is 20-30% by weight.

  The crosslinked product obtained by polyamine crosslinking the composition for oil seal of the present invention exhibits significantly superior hydrolysis resistance as compared with acrylic rubber (Comparative Example 7). In addition, even when compared with peroxide-crosslinked HNBR (comparative example 6), it is particularly resistant to contact with engine oil mixed with water for a long time (at least 2000 hours) under high temperature (at least 150 ° C.) Excellent in hydrolyzability. Thereby, it was found that the crosslinked body according to the present invention is suitably used as an oil seal.

  In addition, the crosslinked product according to the present invention exhibits heat resistance and oil resistance which are significantly superior to peroxide-crosslinked HNBR. It has been demonstrated that this heat resistance, oil resistance is comparable to, and preferably exceeds acrylic rubber. Therefore, the characteristics required for the oil seal are suitably satisfied also with respect to the points other than the above-mentioned hydrolysis resistance.

  Furthermore, according to the present invention, an effect excellent in cold resistance (properties excellent in compression set at low temperature) is also exhibited, and sealability at the time of engine stop in a cold region can be favorably secured. In particular, by simultaneously achieving heat resistance and cold resistance, an oil seal that can be used in various regions regardless of the climate etc. can be realized, and the market can be favorably coped with globalization. Moreover, according to the present invention, since cold resistance can be improved while maintaining excellent compression set, excellent sealability can be exhibited at low temperatures.

2. HNBR (polymer)
As the polyamine crosslinkable HNBR, those comprising an α, β-ethylenically unsaturated nitrile monomer unit, a diene monomer unit and an α, β-ethylenically unsaturated dicarboxylic acid monoester monomer unit (3 An original system can be preferably used.

  In addition, as the polyamine crosslinkable HNBR, an α, β-ethylenically unsaturated nitrile monomer unit, a diene monomer unit, an α, β-ethylenically unsaturated dicarboxylic acid monoester monomer unit, and α The thing (quaternary system) which consists of (alpha), (beta)-ethylenic unsaturated carboxylic acid ester monomer units other than (beta)-ethylenic unsaturated dicarboxylic acid monoester monomer units can also be used preferably.

  Furthermore, the two types of HNBR described above may be blended and used as a polymer.

  Below, each monomer unit which comprises HNBR is demonstrated.

(1) α, β-ethylenically unsaturated nitrile monomer unit α, β-ethylenically unsaturated nitrile monomer unit is particularly limited if it is an α, β-ethylenically unsaturated compound having a nitrile group And, for example, acrylonitrile, α-halogenoacrylonitrile in which the α-position is a chloro group, and a bromo group, methacrylonitrile in which the α-position is an alkyl group, and the like, and preferably acrylonitrile or methacrylonitrile.

  In the present invention, the content of the α, β-ethylenically unsaturated nitrile monomer unit (also referred to as nitrile content or CN content) in the polymer is 20 to 30% by weight.

(2) Diene-based monomer unit The diene-based monomer unit is 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, 1 And C ₄ -C ₁₂ conjugated or non-conjugated diene monomers such as 4-hexadiene, preferably derived from conjugated diene monomers, more preferably 1,3-butadiene.

These diene monomer units are, for example, C _{2 to} C ₁₂ α-olefin monomer units such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene. May be used in combination with

  When the diene monomer unit is used without being used in combination with the α-olefin monomer unit, the content of the diene monomer unit in the polymer is not particularly limited, but may be, for example, 20 to 80% by weight it can.

  When a diene monomer unit is used in combination with an α-olefin monomer unit, the total content of the diene monomer unit and the α-olefin monomer unit in the polymer is not particularly limited. It can be 20 to 80% by weight.

(3) α, β-ethylenically unsaturated dicarboxylic acid monoester monomer unit As the α, β-ethylenically unsaturated dicarboxylic acid monoester monomer unit, maleic acid, fumaric acid, citraconic acid, itaconic acid, etc. C _{1 to} C ₁₀ , preferably C _{2 to} C ₆ monoalkyl ester, C _{5 to} C ₁₂ , preferably C _{6 to} C ₁₀ monocycloalkyl ester, C _{6 to} C ₁₂ , preferably C _{7 to} C ₁₀ mono (alkyl substituted cycloalkyl) esters and the like are mentioned, more preferably monopropyl ester or mono n-butyl ester of maleic acid, fumaric acid or citraconic acid, particularly preferably mono n-butyl maleate Is used.

  The content of the α, β-ethylenically unsaturated dicarboxylic acid monoester monomer unit in the polymer is not particularly limited, but can be, for example, 0.1 to 20% by weight.

(4) Other α, β-ethylenically unsaturated carboxylic acid ester monomer units HNBR, together with the above monomer units, is not an α, β-ethylenically unsaturated dicarboxylic acid monoester monomer unit It may have an α, β-ethylenically unsaturated carboxylic acid ester monomer unit.

As such an α, β-ethylenically unsaturated carboxylic acid ester monomer unit, a (meth) acrylic acid alkyl ester monomer unit having a C _{1 to} C ₈ alkyl group and a C _{2 to} C ₈ alkoxyalkyl group Examples thereof include at least one of (meth) acrylic acid alkoxyalkyl ester monomer units and diester monomer units corresponding to the α, β-ethylenically unsaturated dicarboxylic acid monoester monomer.

  When other α, β-ethylenically unsaturated carboxylic acid ester monomer units are used, the content of the other α, β-ethylenically unsaturated carboxylic acid ester monomer units in the polymer is not particularly limited. It can be 0.1 to 30% by weight.

(5) Others The iodine value of the polymer is not particularly limited, but can be, for example, 120 or less, 80 or less, 25 or less, or 15 or less.

  The HNBR described above is also available as a commercial product. Examples of commercially available products include "Zetpol 3610" (CN content: 20.5% by weight), "Zetpol 3710" (CN content: 23.6% by weight) and the like manufactured by Zeon Corporation of Japan.

  As a polymer, one type of HNBR may be used alone, or two or more types of HNBR may be used in combination. When two or more HNBRs are used in combination, the nitrile content of the polymer is determined as the nitrile content in a blend composed of two or more HNBRs.

  The blending amount of the polymer in the oil seal rubber composition is not particularly limited, but is preferably 30 to 90% by weight, more preferably 40 to 80% by weight, and further preferably 50 to 70% by weight. Most preferred.

3. Polyamine Crosslinks The polymers comprising HNBR described above are polyamine crosslinkable and polyamine cross-linked in oil seals. For polyamine crosslinking, a polyamine compound is used as a crosslinking agent.

  Examples of polyamine compounds include hexamethylenediamine, its carbamate, benzoate or cinnamaldehyde adduct, aliphatic diamine such as diamino-modified siloxane, 4,4'-methylenebiscyclohexylamine or its cinnamaldehyde adduct, bis (4-amino-) Alicyclic diamines such as 3-methyldicyclohexyl) methane, 4,4'-methylenedianiline, p, p'-ethylenedianiline, m- or p-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4 '-Diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-(m- or p-phenylenediisopropylidene) dianiline, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophen) Noxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 4,4'-bis (4-aminophenoxy) biphenol, bis [4 4- (4-Aminophenoxy) phenyl] ether, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis Aromatic diamines such as (4-aminophenoxy) benzene can be mentioned, preferably aromatic diamines, more preferably p-substituted aromatic diamines and the like.

  The crosslinking agent comprising a polyamine compound can be used, for example, in a proportion of about 0.1 to 15 parts by weight, preferably about 0.2 to 4 parts by weight, per 100 parts by weight of the polymer.

  In addition, a crosslinking system may be configured by using a crosslinking agent comprising a polyamine compound and a crosslinking accelerator comprising a guanidine compound such as 1,3-di-o-tolylguanidine etc. in combination.

4. Plasticizer The composition for oil seal contains a plasticizer as a compounding agent.

  The plasticizer is not particularly limited, and examples thereof include aliphatic carboxylic acid diester compounds of polyalkylene glycol represented by the following general formula (1).

R ¹ COO (C _n H _{2 n} O) _m COR ² (1)
[In formula (1), R ¹ and R ² each independently represent a C _{1 to} C ₁₄ alkyl group or alkenyl group, n is an integer of 2 to 4 and m is an integer of 2 to 30] . ]

  Such aliphatic carboxylic acid diester compounds of polyalkylene glycol are also available as commercial products. As a commercial item, the polyetherester plasticizer "RS700" (PEG (MW300) di-2-ethyl hexanoate) by Adeka company etc. are mentioned, for example.

  In the present invention, the blending amount of the plasticizer is 5 to 25 parts by weight, preferably 7 to 22 parts by weight, and more preferably 10 to 20 parts by weight per 100 parts by weight of the polymer.

  In the present invention, excellent heat resistance and cold resistance are exhibited when the nitrile content in the polymer is 20 to 30% by weight and the blending amount of the plasticizer is in the above range. In particular, by combining the above-mentioned specific amount of plasticizer with a polymer having a specific nitrile content, it is possible to achieve both excellent compression set and excellent cold resistance in an oil seal, and excellent in adaptability to globalization. This is completely different from Patent Documents 1 and 2 in which the fuel seal is made resistant to polycyclic aromatic compounds by a plasticizer.

  Further, by combining the above-mentioned specific amount of the plasticizer with the polymer having the specific nitrile content, the kneadability of the material (rubber composition for oil seal) is also improved, and the production efficiency is improved. Therefore, it can respond suitably to mass production, and it is excellent in the adaptation to globalization mentioned above also in this viewpoint.

5. Other Compounding Agents In addition to the above-described plasticizer, compounding agents such as, for example, a filler, a processing aid, an anti-aging agent, a lubricant and the like can be appropriately blended in the composition for oil sealing.

6. Method of Producing Oil Seal In an example of a method of producing an oil seal, first, a composition (rubber composition for oil seal) obtained by appropriately adding the above-described compounding agent to the above-described polymer is kneaded using a kneader or the like. .

  Next, a crosslinking agent (or a crosslinking system) comprising the above-described polyamine compound is added to the composition, and the mixture is kneaded using an open roll. Then, press crosslinking is performed at about 100 to 200 ° C., preferably about 130 to 200 ° C., more preferably about 150 to 200 ° C., for about 30 seconds to 5 hours, preferably about 3 to 10 minutes. Thereafter, if necessary, oven crosslinking (secondary crosslinking) may be performed at about 150 to 200 ° C. for about 0.5 to 24 hours. Thus, the oil seal of the present invention is obtained.

  According to the present invention, the nitrile content in the polymer in the rubber composition for oil sealing is 20 to 30% by weight, and the blending amount of the plasticizer is 5 to 25 parts by weight per 100 parts by weight of the polymer. As described above, the kneadability of the dough is also improved, and the production efficiency is improved. Therefore, it can respond suitably to mass production, and it is excellent in the adaptation to globalization mentioned above also in this viewpoint.

7. The oil seal according to the present invention is a seal member (sealing device) provided to be in contact with engine oil in various engines and for sealing the engine oil, for example, an annular structure such as an O-ring or the like. It can have. In addition, the oil seal of the present invention can be applied to the case where the oil contains water in addition to the engine.

  The oil seal of the present invention maintains a good sealing function even in an engine oil mixed with water generated by the combustion of fuel or in a rough oil environment containing a large amount of water.

  Examples of the present invention will be described below, but the present invention is not limited by these examples.

Example 1
Polyamine crosslinkable hydrogenated nitrile rubber ("Zetpol 3610" manufactured by Nippon Zeon, CN content 20.5% by weight) 100 parts by weight, silica ("Nipsil E75" manufactured by Tosoh Silica Corporation), BET specific surface area 30 to 60 m ² / g: Filler 50 parts by weight, polyoxyethylene alkyl ether phosphoric acid ester (Toho Chemical Co., Ltd. "Phosfanol RL-210"; processing aid) 1 part by weight Polyetherester plasticizer (Adeka) 15 parts by weight of RS 700 ′ ′) and 2 parts by weight of 4,4 ′-(α, α′-dimethylbenzoyl) diphenylamine (antiaging agent) were kneaded with a kneader to obtain an uncrosslinked fabric.

  The obtained uncrosslinked fabric is transferred to an open roll, and 2.5 parts by weight of hexamethylenediamine carbamate (crosslinking agent) and 1.6 parts by weight of 1,3-di-o-tolyl guanidine (crosslinking accelerator) are added. After kneading, press-crosslinking at 170.degree. C. for 20 minutes and oven crosslinking (secondary crosslinking) at 170.degree. C. for 4 hours were carried out to obtain a test strip-like crosslinked product.

(Example 2)
In Example 1, a polyamine-crosslinkable hydrogenated nitrile rubber having a CN content of 23.6% by weight is used instead of a polyamine-crosslinkable hydrogenated nitrile rubber having a CN content of 20.5% by weight as a polymer In the same manner as in Example 1 except that Zetpol 3710 ′ ′) was used, a cross-linked product in the form of a test piece was obtained.

(Example 3)
In Example 1, a polyamine-crosslinkable hydrogenated nitrile rubber having a CN content of 20.5% is replaced with a polyamine-crosslinkable hydrogenated nitrile rubber having a CN content of 23.6% as a polymer (Zetpol 3710 manufactured by Nippon Zeon Co., Ltd.) ) 50 parts by weight in combination with a polyamine-crosslinkable hydrogenated nitrile rubber having a CN content of 35.2% (“Zetpol 2510” manufactured by Zeon Corporation) (CN content of blended polymer is 29.4% by weight) A crosslinked test piece was obtained in the same manner as in Example 1 except for the above.

(Comparative example 1)
In Example 1, a polyamine-crosslinkable hydrogenated nitrile rubber having a CN content of 35.2% by weight is used instead of a polyamine-crosslinkable hydrogenated nitrile rubber having a CN content of 20.5% by weight as a polymer In the same manner as in Example 1 except that Zetpol 2510 ′ ′) was used, a cross-linked product in the form of a test piece was obtained.

(Comparative example 2)
A crosslinked test piece was obtained in the same manner as in Example 1 except that the blending of the plasticizer was omitted in Example 1.

(Comparative example 3)
A crosslinked test strip was obtained in the same manner as in Example 1 except that the blending amount of the plasticizer was changed to 30 parts by weight in Example 1.

(Comparative example 4)
In Comparative Example 1, a crosslinked test piece was obtained in the same manner as Comparative Example 1 except that the blending of the plasticizer was omitted.

(Comparative example 5)
In Comparative Example 1, a crosslinked test piece was obtained in the same manner as Comparative Example 1 except that the blending amount of the plasticizer was changed to 30 parts by weight.

(Comparative example 6)
Peroxide crosslinkable hydrogenated nitrile rubber ("Zetpol 2000" manufactured by Nippon Zeon Co., Ltd., CN content 36.2% by weight) 100 parts by weight, FEF carbon ("Seat S0" manufactured by Tokai Carbon Co., Ltd.) 50 parts by weight, zinc oxide 5 An uncrosslinked fabric was obtained by kneading, with a kneader, 5 parts by weight of a weight part, 1 part by weight of stearic acid, and a polyether ester plasticizer ("RS 700" manufactured by Adeka Co., Ltd.).

  The uncrosslinked material obtained is transferred to an open roll, and 3 parts by weight of 1,4-bis [1- (tert-butylperoxy) -1-methylethyl] benzene (crosslinking agent) is added and kneaded, and then 170 ° C., Press-crosslinking for 20 minutes and oven-crosslinking (secondary crosslinking) at 170 ° C. for 4 hours were performed to obtain a test strip-like crosslinked product.

(Comparative example 7)
100 parts by weight of acrylic rubber (ACM) (“PA-212” manufactured by Unimatec), 60 parts by weight of FEF carbon (“Seat S0” manufactured by Tokai Carbon Co., Ltd.), 1 part by weight of stearic acid, processing aid (Strak manufactured by Schill & Seilacher) Toll WB 212 ′ ′) 2 parts by weight, sodium stearate (“NS Soap” manufactured by Kao Corporation) 3 parts by weight, and 4 parts of 4,4 ′-(α, α′-dimethylbenzoyl) diphenylamine (antiaging agent) The mixture was kneaded with a kneader to obtain an uncrosslinked fabric.

  The obtained uncrosslinked fabric is transferred to an open roll, kneaded with 2,4,6-trimercapto-s-triazine (a sulfur-based crosslinking agent), and then press-crosslinked at 180 ° C. for 8 minutes; The oven crosslinking (secondary crosslinking) for 4 hours at ° C. was performed to obtain a cross-linked product in the form of a test piece.

<Evaluation method>
1. Kneadability After kneading the blend except for the crosslinking accelerator, the dischargeability of the dough from the kneader was evaluated based on the following criteria.
〔Evaluation criteria〕
○: There is no dough remaining or dirt in the kneader after discharging the dough ×: If the dough remaining or dirt is noticeable in the kneader after discharging the dough, it takes time to clean

2. Compression set in oil (CS) (hydrolysis resistance evaluation)
According to JIS K6258 and JIS K6262, JIS No. 1 to which 1000 ppm of water is added. In three oils, the values after standing at 150 ° C. for 240 hours and 2000 hours were measured with a P14 O ring. At the time of opening, the test jig was cooled to room temperature and then opened. The heat resistance was evaluated by setting the limit value of sealability to a point at which the compression set rate became 80%, 場合 below that, and x above.

3. Compression set (CS @ 240 h) (heat resistance evaluation)
In accordance with JIS K6262, the value after leaving at 150 ° C. for 240 hours was measured with a P14 O-ring. However, in order to ensure consistency with the above-described compression-in-oil set test, the test jig was cooled to room temperature and then opened. The heat resistance was evaluated by setting the limit value of sealability to a point at which the compression set rate became 80%, 場合 below that, and x above.

4. Compression set (CS @ 72 h) (heat resistance evaluation)
In accordance with JIS K6262, the value after leaving at 150 ° C. for 72 hours was measured with a G25 O-ring. The heat resistance was evaluated based on the following evaluation criteria based on the calculated compression set rate.
〔Evaluation criteria〕
:: The compression set rate is less than 12% ○: The compression set rate is 12% or more and less than 15% Δ: The compression set rate is 15% or more and less than 20% x: The compression set rate Is 20% or more

5. Low temperature property In accordance with JIS K6261, the TR-10 value by a low temperature elastic recovery tester was used as an index of low temperature property. Based on the measured TR-10 value, the low temperature property was evaluated by the following evaluation criteria.
〔Evaluation criteria〕
◎: TR-10 value is less than -39 ° C ○: TR-10 value is -39 ° C or more and less than -29 ° C Δ: TR-10 value is -29 ° C or more and less than -19 ° C × : TR-10 value is -19 ° C or more

  The above results are shown in Table 1.

<Evaluation>
From Table 1, the cross-linked products of Examples 1 to 3 have heat resistance comparable to, and exceeding that of the acrylic rubber (ACM) of Comparative Example 7, and sufficient hydrolysis resistance that can not be achieved with acrylic rubber (ACM). It turns out that it has degradability. Moreover, although peroxide-crosslinked HNBR shown to the comparative example 6 is excellent in hydrolysis resistance compared with the acrylic rubber (ACM) of the comparative example 7, it turns out that heat resistance is inadequate.

  From the above, while having the heat resistance and oil resistance comparable to acrylic rubber, the cross-linked products of Examples 1 to 3 have hydrolysis resistance suitably used even in an engine oil environment mixed with water. I understand.

  Further, it is understood from Table 1 that all of the polyamine crosslinked HNBRs shown in Examples 1 to 3 are excellent in the kneadability, the heat resistance and the low temperature property.

  On the other hand, as shown in Comparative Example 1, when the amount of nitrile exceeds 30 wt%, sufficient cold resistance is obtained by using a plasticizer in a compounding amount within a range that does not deteriorate the kneadability and compression set property. It turns out that it can not be obtained.

  In Comparative Examples 2 and 3 in which a polymer having a small amount of nitrile was used, when a plasticizer was not contained (Comparative Example 2), excellent compression set distortion was exhibited but low temperature properties were insufficient, and a large amount of plasticizer was compounded. In the case (Comparative Example 3), although the low temperature property is particularly excellent, the kneadability and the compression set are inferior.

  In Comparative Examples 4 and 5 in which a polymer having a large amount of nitrile was used, when the plasticizer was not contained (Comparative Example 4), a particularly excellent compression set property was exhibited, but the low temperature property was significantly insufficient, and a large amount of plasticizer was used. When compounded (comparative example 5), although low temperature property is excellent, it is inferior to kneadability and compression set.

  Furthermore, it turns out that the composition which concerns on Examples 1-3 is also favorable in kneadability.

Claims (2)

  A polymer comprising a polyamine crosslinkable hydrogenated nitrile rubber and 5 to 25 parts by weight of a plasticizer per 100 parts by weight of the polymer, wherein the nitrile content of the polymer is 20 to 30% by weight Rubber composition for oil seal.   An oil seal comprising a crosslinked product obtained by polyamine crosslinking the rubber composition for oil seal according to claim 1.