JP4552478B2 - Nitrile group-containing copolymer rubber composition and rubber vulcanizate - Google Patents

Description

  The present invention relates to a nitrile group-containing copolymer rubber composition, and more particularly, to a nitrile group-containing copolymer rubber having good processability and giving a rubber vulcanizate having excellent mechanical strength.

A vulcanized product of a nitrile group-containing copolymer rubber obtained by hydrogenating a carbon-carbon unsaturated bond of an unsaturated nitrile-conjugated diene copolymer such as acrylonitrile-butadiene rubber is not only good in oil resistance but also in ozone resistance. Since it is remarkably excellent in heat resistance and heat aging resistance, it is used in gaskets, oil seals, automobile hoses, automobile belts and the like.
However, the nitrile group-containing copolymer rubber prepared to have a low Mooney viscosity in order to improve roll processability and extrusion processability does not necessarily have sufficient mechanical strength of the vulcanizate. Therefore, if you try to improve the mechanical strength of the vulcanizate by adding a large amount of vulcanizing agent or increasing the amount of reinforcing filler, the workability and productivity will decrease, and the elongation of the vulcanized product will also decrease. This causes the disadvantage of increased hardness. Therefore, there is a need for a nitrile group-containing copolymer rubber composition that provides a vulcanizate having a low Mooney viscosity, good processability, and high mechanical strength.

  An object of the present invention is to provide a nitrile group-containing copolymer rubber composition having good processability and capable of providing a vulcanizate having excellent mechanical strength.

As a result of earnest research to solve the above problems, the present inventors have found that the above object can be achieved by using a nitrile group-containing copolymer rubber having a specific iodine value, Mooney viscosity and gel, The present invention has been completed based on this finding.
Thus, according to the present invention, a nitrile group-containing copolymer rubber obtained by hydrogenating a carbon-carbon unsaturated bond of an unsaturated nitrile-conjugated diene copolymer and a nitrile group-containing copolymer containing a vulcanizing agent. A rubber composition comprising:
(1) unsaturated nitrile - conjugated diene copolymer, alpha, beta-ethylenically unsaturated nitrile monomer, obtained by copolymerizing及beauty co conjugated diene monomer, alpha, beta-ethylenically An unsaturated nitrile-conjugated diene copolymer having a content of the unsaturated nitrile monomer unit of 10 to 60 % by weight,
(2) A nitrile group-containing copolymer rubber obtained by hydrogenating a carbon-carbon unsaturated bond of the unsaturated nitrile-conjugated diene copolymer has an iodine value of 40 or less and Mooney viscosity (ML _{1 + 4} , 100 ° C.) Is a nitrile group-containing copolymer rubber composition, characterized in that it contains 50 to 100 and contains gel in a proportion of 3 to 20% by weight. Moreover, according to this invention, the vulcanizate formed by vulcanizing this rubber composition is provided.

  The nitrile group-containing copolymer rubber composition of the present invention can provide a vulcanizate having excellent processability and excellent mechanical strength.

The nitrile group-containing copolymer rubber used in the present invention is obtained by hydrogenating a carbon-carbon unsaturated bond of an unsaturated nitrile-conjugated diene copolymer, has an iodine value of 40 or less, and has a Mooney viscosity (ML _{1 + 4} , 100 ° C. ) Is 50 to 100 and contains 3 to 20% by weight of the gel.

  The unsaturated nitrile-conjugated diene copolymer (hereinafter sometimes referred to as “base nitrile rubber”), which is a polymer before hydrogenation of the nitrile group-containing copolymer rubber used in the present invention, is α, β-ethylene. It is a rubber obtained by copolymerizing a polymerizable unsaturated nitrile monomer and a conjugated diene monomer. The content of the α, β-ethylenically unsaturated nitrile monomer unit in the base nitrile rubber is usually 10 to 60% by weight, preferably 15 to 55% by weight, more preferably 20 to 50% by weight. If the content of the α, β-ethylenically unsaturated nitrile monomer unit is too small, the oil resistance may be poor, and conversely if too large, the cold resistance may be poor.

The α, β-ethylenically unsaturated nitrile monomer is not limited as long as it is an α, β-ethylenically unsaturated compound containing a nitrile group. For example, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, etc. Among them, acrylonitrile is preferable.
The conjugated diene monomer is not limited as long as it is a conjugated diene-containing compound copolymerizable with an α, β-ethylenically unsaturated nitrile monomer. For example, 1,3-butadiene, isoprene, 2,3 Preferred examples include conjugated diene-containing compounds having 4 to 12 carbon atoms such as dimethyl-1,3-butadiene and 1,3-pentadiene, and among these, 1,3-butadiene is preferred.

  The method for polymerizing the base nitrile rubber is not particularly limited, and may be a known emulsion polymerization method or solution polymerization method, but production by an emulsion polymerization method is preferred from the viewpoint of industrial productivity.

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the base nitrile rubber is preferably 10 to 300, more preferably 20 to 250, and particularly preferably 30 to 200. Outside this range, the Mooney viscosity of the nitrile group-containing copolymer rubber obtained by hydrogenation may become inappropriate. The Mooney viscosity of the base nitrile rubber can be adjusted by appropriately selecting conditions such as a polymerization reaction temperature and a polymerization initiator concentration.

The nitrile group-containing copolymer rubber used in the present invention is obtained by hydrogenating the carbon-carbon unsaturated bond of the base nitrile rubber, and has an iodine value of 40 or less. If the iodine value is too high, the heat aging resistance and ozone resistance of the vulcanizate may be reduced. By increasing the hydrogenation rate of the carbon-carbon unsaturated bond of the base nitrile rubber, the iodine value can be reduced.

  In the hydrogenation of the base nitrile rubber, if the nitrile group is hydrogenated, the oil resistance of the cross-linked product is lowered. Therefore, it is necessary to selectively hydrogenate only the carbon-carbon unsaturated bond. Such selective hydrogenation may be performed by a known method, such as an oil layer hydrogenation method in which hydrogen is supplied to a base nitrile rubber dissolved in an organic solvent in the presence of a hydrogenation catalyst, and a base in an aqueous latex state. There is an aqueous layer hydrogenation method in which nitrile rubber is hydrogenated. Furthermore, the aqueous layer hydrogenation method includes a direct hydrogenation method in which hydrogen is supplied to a reaction system in the presence of a hydrogenation catalyst, and a hydrogenation by reduction in the presence of an oxidizing agent, a reducing agent and an activator. Indirect hydrogen reduction method is known.

The organic solvent solution of base nitrile rubber in the oil layer hydrogenation method is obtained by solution polymerization of base nitrile rubber, and if necessary, the concentration is adjusted by dilution with an organic solvent, or the latex of base nitrile rubber obtained by emulsion polymerization is coagulated. After drying, it is prepared by dissolving in an organic solvent. The solid content concentration of the solution is 1 to 70% by weight, preferably 1 to 40% by weight.
The solvent is not limited as long as it is an organic liquid that dissolves the base nitrile rubber, but benzene, toluene, xylene, hexane, cyclohexane, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, cyclohexanone, acetone and the like are preferably used.

  As a catalyst for the oil layer hydrogenation method, any known selective hydrogenation catalyst can be used without limitation, and among the elements belonging to Group VIII of the periodic table, a platinum group such as ruthenium, rhodium, palladium, osmium, iridium, and platinum. Elements are preferred. Among these, palladium and rhodium are more preferable, and palladium is particularly preferable. Two or more of these may be used in combination, but in that case, palladium is preferably the main active ingredient.

Examples of palladium catalysts include: organic acid salts such as palladium acetate and paradium cyanide; halides such as palladium fluoride, palladium chloride, palladium bromide and palladium iodide; oxyacid salts such as palladium nitrate and palladium sulfate; oxidation Palladium; Palladium hydroxide; Dichlorocyclooctadiene palladium, Dichloronorbornadiene palladium, Tetrakis acetonitrile palladium tetrafluoroborate, Dichlorobisacetonitrile palladium, Dichlorobisethylenediamine palladium, Dichlorobistriethylphosphine palladium, Dichlorobis (dimethyl sulfide) palladium, Dibenzoyl sulfide And a complex salt or complex such as palladium.
Examples of rhodium catalysts include halides such as rhodium chloride, rhodium bromide, rhodium iodide; inorganic acid salts such as rhodium nitrate and rhodium sulfate; rhodium acetate, rhodium formate, rhodium propionate, rhodium butyrate, rhodium valerate, Organic acid salts such as rhodium naphthenate; rhodium oxide; rhodium trihydroxide; dichlorobis- (triphenylphosphine) rhodium, trichlorotris-pyridine rhodium, tetrarhodium dodecacarbonyl, dirhodium octacarbonyl, hexarhodium hexadecarbonyl, dicarbonyl And complex compounds such as rhodium acetylacetonate, tris (hexane-2,4-dione) rhodium, and tris (heptane-2,4-dione) rhodium.
These catalysts are usually used by being supported on a carrier. Examples of the carrier include silica, silica-alumina, alumina, diatomaceous earth, activated carbon and the like.

  The temperature of the oil layer hydrogenation reaction is usually 0 to 200 ° C, preferably 5 to 150 ° C, more preferably 10 to 100 ° C. If the reaction temperature is too high, the nitrile group may be hydrogenated or the reaction solvent may be hydrogenated. If the reaction temperature is too low, the reaction rate may decrease. The hydrogen pressure is usually 0.1-30 MPa, preferably 0.1-20 MPa, more preferably 0.5-10 MPa. Although reaction time is not specifically limited, Usually, it is 30 minutes-50 hours.

  In the water layer direct hydrogenation method, the solid content concentration of the base nitrile rubber latex is preferably 20% by weight or less in order to prevent agglomeration. The selective hydrogenation catalyst is not particularly limited as long as it is a compound that is difficult to decompose with water. Specific examples of the palladium catalyst include palladium salts of carboxylic acids such as formic acid, propionic acid, lauric acid, succinic acid, oleic acid, and phthalic acid; palladium chloride, dichloro (cyclooctadiene) palladium, dichloro (norbornadiene) palladium, Palladium chloride such as ammonium hexachloropalladium (IV); Iodide such as palladium iodide; Palladium sulfate dihydrate and the like. Of these, palladium salts of carboxylic acids, dichloro (norbornadiene) palladium, ammonium hexachloropalladium (IV), and the like are particularly preferable. The amount of the hydrogenation catalyst used may be appropriately determined, but is preferably 5 to 6,000 ppm, more preferably 10 to 4,000 ppm per weight of the base nitrile rubber.

  The reaction temperature of the aqueous layer direct hydrogenation method is usually 0 to 300 ° C, preferably 20 to 150 ° C, more preferably 30 to 100 ° C. If the reaction temperature is too low, the reaction rate may decrease. Conversely, if the reaction temperature is too high, side reactions such as hydrogenation of nitrile groups may occur. The hydrogen pressure is usually 0.1 to 30 MPa, preferably 0.5 to 20 MPa. The reaction time is selected in consideration of the reaction temperature, hydrogen pressure, target hydrogenation rate, and the like.

  After completion of the reaction of the aqueous layer direct hydrogenation method, the hydrogenation catalyst in the latex is removed. As the method, for example, an adsorbent such as activated carbon or ion exchange resin can be added to adsorb the hydrogenation catalyst with stirring, and then the latex can be filtered or centrifuged. It is also possible to leave it in the latex without removing the hydrogenation catalyst.

In the indirect hydrogen reduction method, the solid content concentration of the charged base nitrile rubber latex is 1 to 70% by weight, preferably 1 to 40% by weight.
As the oxidizing agent, oxygen, air, hydrogen peroxide, or the like is used. The molar ratio of the oxidizing agent to the carbon-carbon double bond is preferably 0.1: 1 to 100: 1, more preferably 0.8: 1 to 5: 1.
As the reducing agent, hydrazines such as hydrazine, hydrazine hydrate, hydrazine acetate, hydrazine sulfate, and hydrazine hydrochloride; or compounds that liberate hydrazine are used. The molar ratio of the reducing agent to the carbon-carbon double bond is preferably 0.1: 1 to 100: 1, more preferably 0.8: 1 to 5: 1.
As the activator, metal ions such as copper, iron, cobalt, lead, nickel, iron and tin are used. The use amount of the activator is such that the molar ratio to the carbon-carbon double bond is preferably 1: 1000 to 10: 1, more preferably 1:50 to 1: 2.
In the indirect hydrogen reduction method, the hydrogenation reaction is carried out by heating within the range from 0 ° C. to the reflux temperature. Such a heating range is usually 0 to 250 ° C, preferably 20 to 100 ° C, more preferably 40 to 80 ° C.

Nitrile group-containing copolymer rubber used in the present invention has a Mooney viscosity _{(ML 1 + 4, 100 ℃} ) is from 50 to 100, preferably from 50 to 8 0. If the Mooney viscosity is too low, the mechanical strength of the vulcanizate may be reduced. On the other hand, if the Mooney viscosity is too high, the workability may be reduced. The Mooney viscosity of the nitrile group-containing copolymer rubber is adjusted by the Mooney viscosity of the selected base nitrile rubber. Since the nitrile group-containing copolymer rubber used in the present invention has a relatively low Mooney viscosity, it has excellent processability in roll kneading, extrusion molding, injection molding, and the like.

The nitrile group-containing copolymer rubber used in the present invention contains 3 to 20% by weight of gel, preferably 3 to 15% by weight, and more preferably 5 to 10% by weight. Here, the gel is the weight ratio of the insoluble component after 200 mg of the rubber component is immersed in 100 ml of tetrahydrofuran (THF) and allowed to stand at 25 ° C. for 48 hours to the total rubber component before being immersed in THF. If the gel content is too low, the mechanical strength of the nitrile group-containing copolymer rubber vulcanizate may be insufficient. Conversely, if the gel content is too high, the dispersion of the filler added will deteriorate. However, workability may be reduced. Since the nitrile group-containing copolymer rubber of the present invention contains an appropriate amount of gel, the Mooney viscosity is relatively small as described above and the workability is good, and the resulting vulcanizate has sufficient mechanical strength. It will be big.

  As a method for adjusting the gel content of the nitrile group-containing copolymer rubber, (i) adjusting the degree of crosslinking of the polymer of the base nitrile rubber, (b) selecting reaction conditions for hydrogenating the base nitrile rubber, ( And c) blending a nitrile group-containing copolymer rubber containing no or a small amount of gel with a nitrile group-containing copolymer rubber containing a large amount of gel. The method (a) is performed by selecting the polymerization temperature, the kind and amount of the crosslinkable monomer, and the like. In the (b) method, gel is generated by the water layer indirect hydrogen reduction method, and therefore the amount of gel is adjusted by a reaction inhibitor or the like.

As the vulcanizing agent contained in the nitrile group-containing copolymer rubber composition of the present invention, a sulfur vulcanizing agent or an organic peroxide is usually used.
Examples of the sulfur-based vulcanizing agent include sulfur such as powdered sulfur and precipitated sulfur; and organic sulfur compounds such as 4,4′-dithiomorpholine, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and polymer polysulfide.

  Examples of the organic peroxide include dialkyl peroxides, diacyl peroxides, and peroxyesters. Dialkyl peroxides include dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) -3-hexyne, 1,3-bis (t- Butyl peroxyisopropyl) benzene and the like. Examples of the diacyl peroxide include dibenzoyl peroxide and diisobutyryl peroxide. Examples of peroxyesters include t-butyl peroxyisopropyl percarbonate).

  The vulcanizing agent content of the composition of the present invention varies depending on the type of the vulcanizing agent, but is usually 0.1 to 10 parts by weight, preferably 0.3, per 100 parts by weight of the nitrile group-containing copolymer rubber. -7 parts by weight, particularly preferably 0.5-5 parts by weight. If the amount of the vulcanizing agent used is too small, the vulcanizate may have a large compression set, and if too large, the rubber elasticity may be inferior.

  When a sulfur vulcanizing agent is used as the vulcanizing agent, a vulcanization accelerator is usually used in combination. Examples of the vulcanization accelerator include zinc oxide, sulfenamide vulcanization accelerator, guanidine vulcanization accelerator, thiazole vulcanization accelerator, thiuram vulcanization accelerator, and dithioate vulcanization accelerator. Can be mentioned. The amount of the vulcanization accelerator used is not particularly limited, and may be determined according to the use of the vulcanizate, the required performance, the type of sulfur vulcanizing agent, the type of vulcanizing accelerator, and the like.

  When an organic peroxide is used as a vulcanizing agent, a vulcanization aid is usually used in combination. Examples of the vulcanization aid include triallyl cyanurate, trimethylolpropane trimethacrylate, N, N′-m-phenylenebismaleimide and the like. These may be dispersed in clay, calcium carbonate, silica or the like to improve processability. The amount of vulcanization aid used is not particularly limited, and may be determined according to the use of the vulcanizate, the required performance, the type of vulcanization agent, the type of vulcanization aid, and the like.

  The nitrile group-containing copolymer rubber composition used in the present invention usually contains a vulcanization accelerator, a vulcanization aid, an anti-aging agent, a reinforcing agent (carbon black, silica, etc.), a filler (calcium carbonate) as necessary. , Talc, etc.), plasticizers, lubricants, adhesives, lubricants, flame retardants, antifungal agents, antistatic agents, colorants and the like.

  The method for preparing the nitrile group-containing copolymer rubber composition of the present invention is not limited. Usually, the components excluding the vulcanizing agent are first kneaded by a mixer such as a Banbury mixer, an intermixer, a kneader, and then rolled. Add the vulcanizing agent and knead the mixture.

  In order to obtain a molded product using the prepared rubber composition, in order to fix the shape by molding with a molding machine corresponding to the desired shape, such as an extruder, an injection molding machine, a compressor, a roll, etc. Use vulcanizate. It may be vulcanized after being molded in advance, or molding and vulcanization may be performed simultaneously. The molding temperature is usually 10 to 200 ° C, preferably 25 to 120 ° C. The vulcanization temperature is usually 100 to 200 ° C., preferably 130 to 190 ° C., and the vulcanization time is usually 1 to 5 hours, preferably 2 minutes to 1 hour.

  In addition, depending on the shape and size of the vulcanizate, the surface may be vulcanized, or the interior may not be sufficiently vulcanized, so secondary vulcanization may be performed by further heating. .

  When the nitrile group-containing copolymer rubber of the present invention is used, the viscosity of the kneaded product is low and the processability is good, and the vulcanized product of the present invention is generally a vulcanized product of the nitrile group-containing copolymer rubber. In addition to having excellent oil resistance, ozone resistance and heat aging resistance, it has high mechanical strength. As an application, it is suitably used as a material for industrial parts such as hoses, belts, seals and rolls. Specifically, it is suitable as a material for fuel hoses, timing belts, packings, oil seals, OA rolls, automobile interior members, fuel seals, gaskets and the like.

The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these examples. In the following, [part] and [%] are based on weight unless otherwise specified.
The test and evaluation were as follows.

(1) Copolymer composition The base nitrile rubber before hydrogenation was dissolved in deuterium chloroform, and the copolymer composition was calculated by NMR analysis.
(2) Iodine value The iodine value was measured according to JIS K 6235.
(3) Mooney viscosity Mooney viscosity (ML _{1 + 4} , 100 ° C.) was measured according to JIS K 6300.

(4) Gel content The gel content of the rubber component was determined by accurately weighing 200 mg of a rubber sample, immersing it in 100 ml of tetrahydrofuran, allowing it to stand at 25 ° C. for 24 hours, and then filtering with an 80 mesh stainless steel wire mesh. The solvent was volatilized with respect to the insoluble matter remaining in the swelling state and the weight after drying was precisely weighed, and the dry insoluble matter was determined as a ratio (% by weight) to the rubber sample before immersion.

(5) Tensile test (tensile strength, elongation, 50% tensile stress, 100% tensile stress)
The rubber composition was put into a mold having a length of 15 cm, a width of 15 cm, and a thickness of 0.2 cm, and press-molded at 160 ° C. for 30 minutes while applying pressure to obtain a sheet-like vulcanizate. The obtained sheet-like vulcanizate was punched with a No. 3 type dumbbell to prepare a test piece. Using these test pieces, the tensile strength, elongation, 50% tensile stress, and 100% tensile stress of the vulcanizate were measured according to JIS K 6251.

(6) Hardness About the vulcanizate obtained in the same manner as in (5) above, the hardness of the vulcanizate was measured using a durometer hardness tester type A according to JIS K 6253.

(7) Compression set The rubber composition was put into a mold having an inner diameter of 29 mm and a thickness of 12.5 mm, and vulcanized at 160 ° C. for 30 minutes at a press pressure of 10 MPa to obtain a test piece. The compression set was measured after the test piece was kept in a 25% compressed state at 135 ° C. for 72 hours in accordance with JIS K 6262.

(8) Extrusion test (swell, extruded skin)
The rubber composition was subjected to an extrusion test according to ASTM D 2230-77. The scoring method was evaluated in four stages according to the ASTM-A method. The larger the number, the better the surface smoothness of the molded product. In addition, the swell was calculated from the extruded sample.

Nitrile group-containing copolymer rubber production example 1
Using latex of base nitrile rubber (acrylonitrile monomer unit 45%, Mooney viscosity 70, gel content 0%) obtained by emulsion polymerization, hydrogenated by aqueous layer indirect hydrogen reduction method, added sodium chloride and coagulated After that, the crumb was separated by filtration, washed and dried to obtain a nitrile group-containing copolymer rubber 1. The nitrile group-containing copolymer rubber 1 had an acrylonitrile monomer unit of 45%, an iodine value of 28, a Mooney viscosity of 108, and a gel content of 65%.

Nitrile group-containing copolymer rubber production example 2
The same base nitrile rubber latex used in Production Example 1 of nitrile group-containing copolymer rubber was coagulated with sodium chloride, and then the crumb was filtered off, washed with water and dried to obtain a solid rubber obtained as methyl isobutyl ketone. Dissolved and hydrogenated by an oil layer hydrogenation method, poured into a large amount of methanol and precipitated, filtered, washed with methanol, dried and taken out as a solid rubber to obtain a nitrile group-containing copolymer rubber 2. The nitrile group-containing copolymer rubber 2 had an acrylonitrile monomer unit of 45%, an iodine value of 24, a Mooney viscosity of 78, and a gel content of 0%.

Example 1
25 parts of nitrile group-containing copolymer rubber 1 and 75 parts of nitrile group-containing copolymer rubber 2 were kneaded at 50 ° C. for 5 minutes with an open roll to obtain a rubber mixture. 100 parts of the rubber mixture, 1 part of an amine-based anti-aging agent (Nauguard 445, manufactured by Uniroyal) and 1 part of 2-mercaptobenzimidazole zinc (NOCRACK MBZ, manufactured by Ouchi Shinsei Chemical Co., Ltd.), reinforcing agent Carbon black (FEF carbon, Tokai Carbon Co., Ltd.) 50 parts, vulcanization accelerator 5 parts zinc oxide and stearic acid 1 part, and plasticizer trimellitic acid ester (Adekasizer C8, Asahi Denka Co., Ltd.) 5 After mixing with a Banbury mixer at 50 ° C., 1.5 parts of tetramethylthiuram disulfide (Noxeller TT, manufactured by Ouchi Shinsei Co., Ltd.), an open roll, and 2-mercaptobenzothiazole (Noxeller M, Ouchi) 0.5 parts (manufactured by Shinsei Co., Ltd.) was added and kneaded at 50 ° C. for 10 minutes to obtain a rubber composition. The iodine value, Mooney viscosity, gel content of a mixture of two nitrile group-containing copolymer rubbers; the Mooney viscosity of the rubber composition; and; the test for tensile test, hardness, compression set and extrusion test of the vulcanizate; The evaluation results are shown in Table 1.

Examples 2-3 and Comparative Examples 1-4
In Example 1, a rubber composition was obtained in the same manner as in Example 1 except that the components shown in Table 1 in the formulation were used in the number of parts shown in the table. Table 1 shows the results of tests and evaluations on the same items as in Example 1.

As shown in Table 1, when nitrile group-containing copolymer rubber obtained by mixing two nitrile group-containing copolymer rubbers and adjusting the gel amount defined in the present invention is used, tensile strength, elongation Further, the hardness was moderate, the compression set of the vulcanized product was small, and the physical properties were balanced. Moreover, the Mooney viscosity of the rubber composition was low, the processability of extrusion molding was good, the swell was small, and the skin of the molded product (vulcanized product) was smooth (Examples 1 to 3).
On the other hand, according to a rubber composition in which only the nitrile group-containing copolymer rubber 1 is used as the rubber and the gel content is extremely high and the Mooney viscosity is too high, the vulcanizate has reduced tensile strength and elongation, and the hardness is Increased, compression set increased. Moreover, the swell was large in extrusion molding, and the workability decreased (Comparative Example 1). Even when the Mooney viscosity was within the specified range, the same test results as in Comparative Example 1 were obtained when a rubber containing more gel than in the present invention was used (Comparative Example 2). According to the rubber composition using only the nitrile group-containing copolymer rubber 2 containing no gel, the tensile strength, elongation and 50% tensile stress were all good and the compression set was small, but the hardness became soft and the extrusion The skin of the molded product became rough (Comparative Example 3). Similarly, according to the rubber composition in which only the nitrile group-containing copolymer rubber 2 containing no gel is used and the carbon black is increased to make the hardness moderate, the Mooney viscosity is high, so the swell is small. Resulted in rough skin and poor processability (Comparative Example 4).

Claims (2)

A nitrile group-containing copolymer rubber obtained by hydrogenating a carbon-carbon unsaturated bond of an unsaturated nitrile-conjugated diene copolymer, and a nitrile group-containing copolymer rubber composition containing a vulcanizing agent,
(1) unsaturated nitrile - conjugated diene copolymer, alpha, beta-ethylenically unsaturated nitrile monomer, obtained by copolymerizing及beauty co conjugated diene monomer, alpha, beta-ethylenically An unsaturated nitrile-conjugated diene copolymer having a content of the unsaturated nitrile monomer unit of 10 to 60 % by weight,
(2) A nitrile group-containing copolymer rubber obtained by hydrogenating a carbon-carbon unsaturated bond of the unsaturated nitrile-conjugated diene copolymer has an iodine value of 40 or less and Mooney viscosity (ML _{1 + 4} , 100 ° C.) Is a nitrile group-containing copolymer rubber composition characterized in that it contains 50 to 100 and contains gel in a proportion of 3 to 20% by weight.   A rubber vulcanizate obtained by vulcanizing the rubber composition according to claim 1.