Crosslinked rubber composition

Abstract

This invention provides a tough crosslinked rubber composition using an acid-modified ethylene-α-olefin elastomer. [Solution] The crosslinked rubber composition is obtained by crosslinking an uncrosslinked rubber composition containing an acid-modified ethylene-α-olefin elastomer, magnesium oxide, and an α,β-unsaturated carboxylic acid metal salt. The magnesium oxide content in the uncrosslinked rubber composition is 4 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification. The α,β-unsaturated carboxylic acid metal salt content in the uncrosslinked rubber composition is 40 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification.

Description

Technical Field

[0001] The present invention relates to a crosslinked rubber composition.

Background Art

[0002] As a crosslinked rubber composition used for rubber products, those having an acid-modified product of an ethylene-α-olefin elastomer as a rubber component are known. For example, Patent Document 1 discloses a crosslinked product of an uncrosslinked rubber composition containing a maleic anhydride-modified product of ethylene propylene diene monomer and carbodiimide as a crosslinked rubber composition used for a rubber product of a rubber fiber composite.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a tough crosslinked rubber composition using an acid-modified product of an ethylene-α-olefin elastomer.

Means for Solving the Problems

[0005] The present invention is a crosslinked rubber composition obtained by crosslinking an uncrosslinked rubber composition containing an acid-modified product of an ethylene-α-olefin elastomer, magnesium oxide, and an α,β-unsaturated carboxylic acid metal salt, wherein the content of magnesium oxide in the uncrosslinked rubber composition is 4 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the ethylene-α-olefin elastomer before acid modification, and the content of the α,β-unsaturated carboxylic acid metal salt in the uncrosslinked rubber composition is 40 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the ethylene-α-olefin elastomer before acid modification.

Effects of the Invention

[0006] According to the present invention, a tough crosslinked rubber composition using an acid-modified ethylene-α-olefin elastomer can be obtained by having an uncrosslinked rubber composition before crosslinking that contains an acid-modified ethylene-α-olefin elastomer, magnesium oxide, and an α,β-unsaturated carboxylic acid metal salt, wherein the magnesium oxide content in the uncrosslinked rubber composition is 4 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification, and the α,β-unsaturated carboxylic acid metal salt content in the uncrosslinked rubber composition is 40 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification. [Modes for carrying out the invention]

[0007] The embodiments will be described in detail below.

[0008] The crosslinked rubber composition X according to the embodiment is obtained by crosslinking an uncrosslinked rubber composition X' containing an acid-modified ethylene-α-olefin elastomer, magnesium oxide, and an α,β-unsaturated carboxylic acid metal salt. The magnesium oxide content in the uncrosslinked rubber composition X' is 4 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification, and the α,β-unsaturated carboxylic acid metal salt content in the uncrosslinked rubber composition X' is 40 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification.

[0009] According to this embodiment of crosslinked rubber composition X, the uncrosslinked rubber composition X' before crosslinking contains an acid-modified ethylene-α-olefin elastomer, magnesium oxide, and an α,β-unsaturated carboxylic acid metal salt. The magnesium oxide content in the uncrosslinked rubber composition X' is 4 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification, and the α,β-unsaturated carboxylic acid metal salt content in the uncrosslinked rubber composition X' is 40 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification. This makes it possible to obtain a tough crosslinked rubber composition X using an acid-modified ethylene-α-olefin elastomer. Specifically, normally, a large elongation at break Eb and a high storage longitudinal modulus E' are inversely related, but with crosslinked rubber composition X, it is possible to obtain the characteristics of a large elongation at break Eb and a high longitudinal modulus E'. Furthermore, with the crosslinked rubber composition X, the difference between the elastic modulus E' at room temperature and the elastic modulus E' at high temperature is small, thus providing excellent temperature stability of the elastic modulus E'.

[0010] The acid-modified ethylene-α-olefin elastomer contained in the uncrosslinked rubber composition X' is the main component of the rubber. From the viewpoint of obtaining a tough crosslinked rubber composition X, the content of the acid-modified ethylene-α-olefin elastomer in the rubber component is preferably 90% by mass or more, more preferably 100% by mass. The uncrosslinked rubber composition X' may also contain other rubber components besides the acid-modified ethylene-α-olefin elastomer, such as un-acid-modified ethylene-α-olefin elastomer, chloroprene rubber (CR), hydrogenated nitrile rubber (H-NBR), etc.

[0011] Examples of ethylene-α-olefin elastomers before acid modification include ethylene propylene diene monomer (EPDM), ethylene propylene copolymer (EPM), ethylene butene diene monomer (EBDM), ethylene butene copolymer (EBM), and ethylene octene copolymer (EOM). The ethylene-α-olefin elastomer preferably contains one or more of these, and more preferably contains EPDM from the viewpoint of obtaining a tough crosslinked rubber composition X.

[0012] From the viewpoint of obtaining a tough crosslinked rubber composition X, the ethylene content of the ethylene-α-olefin elastomer is preferably 45% by mass or more and 55% by mass or less, more preferably 50% by mass or more and 53% by mass or less.

[0013] When the ethylene-α-olefin elastomer contains a non-conjugated diene component, examples of such non-conjugated diene components include 5-ethylidene-2-norbornene (ENB), 5-vinyl-2-norbornene (VNB), dicyclopentadiene, and 1,4-hexadiene. From the viewpoint of obtaining a tough crosslinked rubber composition X, ENB is preferred among these non-conjugated diene components. When the ethylene-α-olefin elastomer contains ENB as a non-conjugated diene component, the diene content (ENB content) is preferably 4% by mass or more and 12% by mass or less, and more preferably 7.5% by mass or more and 8.5% by mass or less, from the same viewpoint.

[0014] Examples of acids in the acid-modified product include maleic anhydride, maleic acid, itaconic anhydride, itaconic acid, fumaric acid, methacrylic acid, acrylic acid, and acids having a mercapto group. Examples of acids having a mercapto group include mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptosuccinic acid, thiosalicylic acid, and thiocyanuric acid. The acid in the acid-modified product preferably contains one or more of these acids, and from the viewpoint of obtaining a tough crosslinked rubber composition X, it is more preferable to contain an acid having a mercapto group, and even more preferable to contain 3-mercaptopropionic acid.

[0015] Acid-modified ethylene-α-olefin elastomers can be prepared by kneading ethylene-α-olefin elastomer, an acid, and a reaction initiator using a closed-type kneader such as a kneader or Banbury mixer. The kneading temperature is, for example, 140°C to 160°C. The kneading time is, for example, 2 minutes to 10 minutes.

[0016] At this time, the amount of acid added is preferably 0.3 parts by mass or more and 5 parts by mass or less, and more preferably 0.5 parts by mass or more and 1.5 parts by mass or less, per 100 parts by mass of ethylene-α-olefin elastomer before acid modification, from the viewpoint of obtaining excellent kneading processability.

[0017] A reaction initiator is a substance that forms a radical at the reaction site where an acid grafts onto the ethylene-α-olefin elastomer polymer. Examples of reaction initiators include organic peroxides.

[0018] Examples of organic peroxides used as reaction initiators include dialkyl peroxides. Examples of organic peroxides of dialkyl peroxides include dicumyl peroxide and 1,3-bis-(t-butylperoxyisopropyl)benzene. From the viewpoint of obtaining excellent kneadability, the organic peroxide used as a reaction initiator preferably contains dialkyl peroxides, and more preferably contains dicumyl peroxide.

[0019] From the viewpoint of appropriately modifying the ethylene-α-olefin elastomer, the amount of organic peroxide used as a reaction initiator is preferably 0.03 parts by mass or more and 0.2 parts by mass or less, and more preferably 0.05 parts by mass or more and 0.15 parts by mass or less, per 100 parts by mass of ethylene-α-olefin elastomer before acid modification.

[0020] The magnesium oxide content in the uncrosslinked rubber composition X' is 4 to 50 parts by mass per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification, but from the viewpoint of obtaining a tough crosslinked rubber composition X, it is preferably 10 to 35 parts by mass, and more preferably 9 to 25 parts by mass.

[0021] Examples of α,β-unsaturated carboxylate metal salts include metal diacrylate and metal dimethacrylate. Examples of metal diacrylate include zinc diacrylate and magnesium diacrylate. Examples of metal dimethacrylate include zinc dimethacrylate and magnesium dimethacrylate. The α,β-unsaturated carboxylate metal salt preferably contains one or more of these, and from the viewpoint of obtaining a tough crosslinked rubber composition X, it is more preferable to include a metal dimethacrylate, and even more preferable to include zinc dimethacrylate.

[0022] The content of α,β-unsaturated carboxylic acid metal salts in the uncrosslinked rubber composition X' is 40 parts by mass or more and 100 parts by mass or less per 100 parts by mass of ethylene-α-olefin elastomer before acid modification, but from the viewpoint of obtaining a tough crosslinked rubber composition X, it is preferably 46 parts by mass or more and 90 parts by mass or less, and more preferably 47 parts by mass or more and 60 parts by mass or less. From the same viewpoint, the content of α,β-unsaturated carboxylic acid metal salts in the uncrosslinked rubber composition X' is preferably greater than the content of magnesium oxide. From the same viewpoint, the mass ratio of the content of α,β-unsaturated carboxylic acid metal salts in the uncrosslinked rubber composition X' to the content of magnesium oxide is preferably 1.2 or more and 15 or less, and more preferably 2 or more and 5 or less.

[0023] The unvulcanized rubber composition X' may contain carbon black. Examples of the carbon black include channel black, furnace black, thermal black, acetylene black, and the like. Examples of the furnace black include SAF, ISAF, N-339, HAF, N-351, MAF, FEF, SRF, GPF, ECF, N-234, and the like. Examples of the thermal black include FT, MT, and the like. The carbon black preferably contains one or more of these, and from the viewpoint of obtaining a tough vulcanized rubber composition X, it preferably contains furnace black, and more preferably contains ISAF.

[0024] From the viewpoint of obtaining a tough vulcanized rubber composition X, the content of the carbon black in the unvulcanized rubber composition X' is preferably 20 parts by mass or more and 60 parts by mass or less, more preferably 35 parts by mass or more and 45 parts by mass or less, based on 100 parts by mass of the ethylene-α-olefin elastomer before acid modification.

[0025] The uncrosslinked rubber composition X’ contains a crosslinking agent. Examples of the crosslinking agent include sulfur and organic peroxides. Examples of the organic peroxides as the crosslinking agent include dialkyl peroxides, peroxycarbonates, ketone peroxides, diacyl peroxides, peroxyketals, alkyl peresters, etc. Examples of the dialkyl peroxides include dicumyl peroxide, α,α'-di(t-butylperoxy)diisopropylbenzene, etc. Examples of the peroxycarbonates include di(4-t-butylcyclohexyl) peroxydicarbonate, bis(4-t-butylcyclohexyl) peroxydicarbonate, diisopropyl peroxydicarbonate, di-3-methoxybutyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, di(3-methyl-3-methoxybutyl) peroxydicarbonate, etc. Examples of the ketone peroxides include methyl ethyl ketone peroxide, acetylacetone peroxide, etc. Examples of the diacyl peroxides include benzoyl peroxide, etc. Examples of the peroxyketals include t-butyl peroxybenzoate, 1,1-di-t-butylperoxycyclohexane, etc. Examples of the alkyl peresters include α-cumyl peroxyneodecanoate, t-butyl peroxyneodecanoate, etc. The organic peroxide as the crosslinking agent preferably contains one or more of these. From the viewpoint of obtaining excellent kneading processability, it is more preferable to contain dialkyl peroxides, and it is even more preferable to contain α,α'-di(t-butylperoxy)diisopropylbenzene.

[0026] The crosslinking agent contains sulfur and / or an organic peroxide, and from the viewpoint of obtaining a tough crosslinked rubber composition X, it is preferable to contain both sulfur and an organic peroxide. In that case, the sulfur content in the uncrosslinked rubber composition X' is, for example, 0.3 parts by mass or more and 1 part by mass or less per 100 parts by mass of ethylene-α-olefin elastomer before acid modification. The organic peroxide content in the uncrosslinked rubber composition X' is, for example, 2 parts by mass or more and 4 parts by mass or less per 100 parts by mass of ethylene-α-olefin elastomer before acid modification.

[0027] The uncrosslinked rubber composition X' may also contain rubber compounding agents such as processing aids, vulcanization accelerators, vulcanization accelerators, and anti-aging agents.

[0028] The elongation at break Eb(23°C) in the grain direction of the crosslinked rubber composition X according to the embodiment is preferably 100% or more, more preferably 130% or more. This elongation at break Eb(23°C) is determined from the tensile properties measured at a test temperature of 23°C in accordance with JIS K6251:2023.

[0029] The storage modulus of elasticity E'(23°C) in the grain direction of the crosslinked rubber composition X according to the embodiment is preferably 60 MPa or more, more preferably 65 MPa or more. This storage modulus of elasticity E'(23°C) is measured by a tensile method using a strip-shaped test piece of the crosslinked rubber composition X with the grain direction as the length direction, based on JIS K6394:2007, with the mean strain being the strain when a load 1.3 times the load at 1% strain is applied, the strain amplitude being 1%, the frequency being 10 Hz, and the test temperature being 23°C.

[0030] The value obtained by dividing the product of the elongation at break in the grain direction Eb(23°C) and the storage modulus of elasticity in the grain direction E'(23°C) at 23°C by 100 for the crosslinked rubber composition X according to the embodiment is preferably 100 MPa or more, and more preferably 110 MPa or more. This value is an indicator of the toughness of the crosslinked rubber composition X.

[0031] The ratio of the storage modulus E'(120°C) in the grain direction of the crosslinked rubber composition X according to the embodiment to the storage modulus E'(23°C) in the grain direction of the crosslinked rubber composition X is preferably 0.7 or higher, more preferably 0.75 or higher. This ratio is an indicator of the temperature stability of the storage modulus E'.

[0032] The crosslinked rubber composition X according to the above embodiment can be obtained by kneading a rubber component containing an acid-modified ethylene-α-olefin elastomer using a rubber kneader such as a kneader, Banbury mixer, or open roll, adding a rubber compounding agent containing magnesium oxide and an α,β-unsaturated carboxylic acid metal salt and kneading it to prepare an uncrosslinked rubber composition X', and then crosslinking the uncrosslinked rubber composition X' at a predetermined temperature and pressure.

[0033] The crosslinked rubber composition X according to this embodiment is suitable for forming the product body of a rubber product, specifically, for example, for forming the belt body of a power transmission belt, and the effect of the crosslinked rubber composition X's high storage modulus in the longitudinal direction can be effectively obtained in the rubber product. [Examples]

[0034] (Crosslinked rubber composition) Sheet-like crosslinked rubber compositions were prepared according to Examples 1-6 and Comparative Examples 1-8. The respective formulations are also shown in Table 1.

[0035] <Example 1> EPDM (EP33, manufactured by ENEOS Material Co., Ltd., ethylene content: 52% by mass, diene content (ENB content): 8.1% by mass) was placed in a closed-type kneader and kneaded. Then, 1 part by mass of 3-mercaptopropionic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.1 parts by mass of dicumyl peroxide (Perkmyl D, manufactured by NOF Corporation), an organic peroxide acting as a reaction initiator, were added to 100 parts by mass of the EPDM and kneaded at a temperature of 100°C to prepare a 3-mercaptopropionic acid modified EPDM. Next, to the 3-mercaptopropionic acid modified EPDM, an uncrosslinked rubber composition was prepared by kneading the following: 40 parts by mass of ISAF carbon black (Seasto 6, manufactured by Tokai Carbon Co., Ltd.), 10 parts by mass of paraffinic process oil (Sampa 2280, manufactured by Nippon Sun Oil Co., Ltd.), 12 parts by mass of magnesium oxide (Kyowa Mag 150, manufactured by Kyowa Chemical Industry Co., Ltd.), 0.5 parts by mass of stearic acid (Stearic Acid S50, manufactured by Shin Nippon Rika Co., Ltd.) as a processing aid, 0.5 parts by mass of sulfur (Seimi OT, manufactured by Tsurumi Chemical Industry Co., Ltd.) as a crosslinking agent, 7 parts by mass of an organic peroxide-containing material (Peroximon F-40, manufactured by NOF Corporation) containing 40% by mass of α,α'-di(t-butylperoxy)diisopropylbenzene (organic peroxide: 2.8 parts by mass), and 50 parts by mass of zinc dimethacrylate (Actor ZMA, manufactured by Kawaguchi Chemical Industry Co., Ltd.) as a co-crosslinking agent. Then, a sheet-like crosslinked rubber composition was obtained by press molding this uncrosslinked rubber composition. The obtained sheet-like crosslinked rubber composition was designated as Example 1.

[0036] <Examples 2-6 and Comparative Examples 1-8> Examples 2, 3, and 4 were crosslinked rubber compositions identical to those in Example 1, except that the amount of magnesium oxide added was 22 parts by mass, 4 parts by mass, and 35 parts by mass, respectively, per 100 parts by mass of EPDM.

[0037] Examples 5 and 6 were crosslinked rubber compositions identical to those in Example 1, except that the amount of zinc dimethacrylate was 46 parts by mass and 90 parts by mass, respectively, per 100 parts by mass of EPDM.

[0038] Comparative Examples 1 and 2 were crosslinked rubber compositions identical to those in Examples 1 and 2, except that EPDM was used instead of 3-mercaptopropionic acid modified EPDM, and the amount of zinc dimethacrylate was 30 parts by mass per 100 parts by mass of EPDM.

[0039] Comparative Examples 3 and 4 were crosslinked rubber compositions with the same configuration as Examples 1 and 2, except that EPDM was used instead of 3-mercaptopropionic acid modified EPDM.

[0040] Comparative Examples 5 and 6 were crosslinked rubber compositions identical to those in Examples 1 and 2, except that the amount of zinc dimethacrylate was 30 parts by mass per 100 parts by mass of EPDM.

[0041] Comparative Example 7 was a crosslinked rubber composition with the same configuration as Example 1, except that zinc oxide (three types of zinc oxide, manufactured by Sakai Chemical Industry Co., Ltd.) was used instead of magnesium oxide.

[0042] Comparative Example 8 was a crosslinked rubber composition with the same configuration as Example 1, except that magnesium carbonate (manufactured by Kinsei Kamishima Chemical Industry Co., Ltd.) was used instead of magnesium oxide.

[0043] [Table 1]

[0044] (Test methods and results) The sheet-like crosslinked rubber compositions of Examples 1-6 and Comparative Examples 1-8 were subjected to the following tests. The results are shown in Table 2.

[0045] <Elongation at severance Eb> For the sheet-like crosslinked rubber compositions of Examples 1-6 and Comparative Examples 1-8, dumbbell-shaped test pieces were cut out with the grain direction as the length direction, and the tensile properties were measured at a test temperature of 23°C according to JIS K6251:2023, from which the elongation at break Eb(23°C) was determined.

[0046] <Storage modulus of elasticity E'> For the sheet-like crosslinked rubber compositions of Examples 1-6 and Comparative Examples 1-8, strip-shaped test pieces were cut out with the grain direction as the length direction. Based on JIS K6394:2007, the average strain was defined as the strain when a load 1.3 times the load at 1% strain was applied, and the storage modulus of elasticity E'(23°C) was measured by tensile testing with a strain amplitude of 1%, a frequency of 10Hz, and a test temperature of 23°C. The value obtained by dividing the product of the elongation at break Eb(23°C) and the storage modulus of elasticity E'(23°C) by 100 was calculated. Furthermore, the storage modulus of elasticity E'(120°C) was measured in the same manner at a test temperature of 120°C, and the ratio of the storage modulus of elasticity E'(120°C) to the storage modulus of elasticity E'(23°C) was calculated.

[0047] [Table 2] [Industrial applicability]

[0048] This invention is useful in the field of crosslinked rubber compositions.

Claims

1. A crosslinked rubber composition is formed by crosslinking an uncrosslinked rubber composition containing an acid-modified ethylene-α-olefin elastomer, magnesium oxide, and an α,β-unsaturated carboxylic acid metal salt. A crosslinked rubber composition wherein the content of magnesium oxide in the uncrosslinked rubber composition is 4 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification, and the content of the α,β-unsaturated carboxylic acid metal salt in the uncrosslinked rubber composition is 40 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the ethylene-α-olefin elastomer before acid modification.

2. In the crosslinked rubber composition described in claim 1, The ethylene-α-olefin elastomer is a crosslinked rubber composition containing ethylene propylene diene monomer.

3. In the crosslinked rubber composition described in claim 1, The crosslinked rubber composition contains an acid having a mercapto group as the acid in the acid-modified product.

4. In the crosslinked rubber composition described in claim 1, The crosslinked rubber composition in which the α,β-unsaturated carboxylate metal salt comprises a dimethacrylate metal salt.

5. In the crosslinked rubber composition described in claim 1, The aforementioned uncrosslinked rubber composition is a crosslinked rubber composition containing sulfur and an organic peroxide.

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