Crosslinked rubber composition

Abstract

To achieve excellent physical properties in a crosslinked rubber composition comprising an ethylene-α-olefin elastomer crosslinked with an organic peroxide.SOLUTION: The present invention provides a crosslinked rubber composition crosslinked with an organic peroxide. The crosslinked rubber composition contains an ethylene-α-olefin elastomer, a silane coupling agent with a mercapto group, and silica.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Crosslinked rubber compositions containing a silane coupling agent are known. For example, Patent Document 1 discloses a crosslinked rubber composition for shoes containing butadiene rubber, styrene-butadiene rubber, silica, and a silane coupling agent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6035453 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to obtain high physical properties in a crosslinked rubber composition of an ethylene-α-olefin elastomer crosslinked with an organic peroxide. [Means for solving the problem]

[0005] The present invention relates to a crosslinked rubber composition which contains an ethylene-α-olefin elastomer, a silane coupling agent having a mercapto group, and silica, and which is crosslinked with an organic peroxide. Effect of the Invention

[0006] According to the present invention, in a crosslinked rubber composition of an ethylene-α-olefin elastomer crosslinked with an organic peroxide, excellent physical properties can be obtained by containing a silane coupling agent having a mercapto group and silica. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0008] The crosslinked rubber composition according to the embodiment contains an ethylene-α-olefin elastomer, a silane coupling agent having a mercapto group, and silica, and is crosslinked with an organic peroxide.

[0009] According to the crosslinked rubber composition of the embodiment, in the crosslinked rubber composition of an ethylene-α-olefin elastomer crosslinked by an organic peroxide, excellent physical properties can be obtained by containing a silane coupling agent having a mercapto group and silica.

[0010] Here, the ethylene-α-olefin elastomer constitutes a rubber component in the crosslinked rubber composition. The ethylene-α-olefin elastomer is preferably a main component in the rubber component. The content of the ethylene-α-olefin elastomer in the rubber component is preferably 70 mass% or more, more preferably 90 mass% or more, and even more preferably 100 mass%.

[0011] Examples of ethylene-α-olefin elastomers include ethylene-propylene copolymer (EPR), ethylene-propylene-diene terpolymer (hereinafter referred to as "EPDM"), ethylene-octene copolymer, ethylene-butene copolymer, etc. The ethylene-α-olefin elastomer preferably contains one or more of these, and more preferably contains EPDM from the viewpoint of versatility.

[0012] The ethylene content of the ethylene-α-olefin elastomer is preferably 45% by mass or more and 60% by mass or less, more preferably 50% by mass or more and 56% by mass or less, and even more preferably 51% by mass or more and 54% by mass or less, from the viewpoint of achieving a balance between high physical properties and roll processability. When the ethylene-α-olefin elastomer is EPDM, examples of the diene component include ethylidene nobornene (ENB), dicyclopentadiene, 1,4-hexadiene, and the like. From the viewpoint of versatility, the diene component preferably contains ethylidene nobornene among these. When the diene component of EPDM is ethylidene nobornene, the ENB content is preferably 2% by mass or more and 10% by mass or less, more preferably 2.5% by mass or more and 9% by mass or less, and even more preferably 7% by mass or more and 8% by mass or less, from the viewpoint of obtaining high physical properties.

[0013] As for the silane coupling agent having a mercapto group, since the ease of reaction between silica and the silane coupling agent depends on the bulkiness of the terminal functional group of the silane coupling agent, it is preferable to include a silane coupling agent having a bulky functional group such as a dimethoxysilane group, a diethoxysilane group, a trimethoxysilane group, or a triethoxysilane group, for example, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-mercaptopropyltriethoxysilane, etc. The silane coupling agent having a mercapto group preferably includes one or more of these, and from the viewpoint of obtaining high physical properties, it is more preferable to include 3-mercaptopropylmethyldimethoxysilane. In the case of a silane coupling agent having a mercapto group, unlike other silane coupling agents, it is presumed that high physical properties can be obtained because the chain transfer of radicals is high, the radicals are not easily deactivated even in reactions in air such as vulcanization, and the reaction efficiency with the polymer is high.

[0014] From the viewpoint of obtaining high physical properties, the content of the silane coupling agent having a mercapto group in the crosslinked rubber composition is preferably 0.1 to 40 parts by mass, more preferably 0.2 to 30 parts by mass, even more preferably 0.5 to 20 parts by mass, and even more preferably 1 to 2 parts by mass, relative to 100 parts by mass of the ethylene-α-olefin elastomer. Note that the content in the crosslinked rubber composition means the amount blended in the uncrosslinked rubber composition before crosslinking (hereinafter the same).

[0015] Examples of silica include synthetic silica. Examples of synthetic silica include wet silica and dry silica. Examples of wet silica include precipitated silica and gel silica. Examples of dry silica include calcined silica and arc silica. It is preferable that silica contains one or more of these, and from the viewpoint of obtaining high physical properties, it is preferable that silica contains wet silica, and it is more preferable that silica contains precipitated silica.

[0016] From the viewpoint of obtaining high physical properties, the content of silica in the crosslinked rubber composition is preferably 1 part by mass or more and 80 parts by mass or less, more preferably 20 parts by mass or more and 60 parts by mass or less, and even more preferably 30 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the ethylene-α-olefin elastomer. From the same viewpoint, the ratio of the content of silica in the crosslinked rubber composition to the content of the silane coupling agent having a mercapto group is preferably 10 to 40, more preferably 20 to 30.

[0017] The organic peroxide is preferably used for crosslinking because the radical chain transferability of the mercapto group inhibits the deactivation of the radical of the organic peroxide, and the crosslinking density increases, resulting in high physical properties. Examples of the organic peroxide used for crosslinking the crosslinked rubber composition according to the embodiment include dialkyl peroxide, peroxyketal, and peroxyester. Examples of the dialkyl peroxide include dicumyl peroxide, 1,3-di(t-butylperoxy)diisopropylbenzene, 1,4-di(t-butylperoxy)diisopropylbenzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane-3. Examples of the peroxyketal include 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, and n-butyl-4,4-di(t-butylperoxy)valerate. Examples of peroxyesters include 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-hexyl peroxybenzoate, t-butyl peroxybenzoate, etc. The organic peroxide preferably contains one or more of these, and preferably contains a dialkyl peroxide, more preferably contains dicumyl peroxide, because it has high hydrogen abstraction ability, is likely to cause a crosslinking reaction, and can provide high physical properties.

[0018] In order to obtain high physical properties, the amount of organic peroxide in the uncrosslinked rubber composition before crosslinking is preferably 0.05 parts by mass or more and 10 parts by mass or less, more preferably 0.5 parts by mass or more and 5 parts by mass or less, and even more preferably 1 part by mass or more and 2 parts by mass or less, relative to 100 parts by mass of the ethylene-α-olefin elastomer.

[0019] The crosslinked rubber composition according to the embodiment may contain carbon black, a processing aid, a vulcanization accelerator, a vulcanization acceleration aid, oil, an antioxidant, and other rubber compounding ingredients, as necessary.

[0020] The stress at 50% elongation S of the crosslinked rubber composition according to the embodiment at standard temperature 50 is preferably 1.3 MPa or more, more preferably 1.5 MPa or more. The tensile strength at break at standard temperature Tb is preferably 8 MPa or more, more preferably 10 MPa or more. The elongation at break at standard temperature Eb is preferably 700% or less, more preferably 300% or less. These tensile properties are measured based on JIS K6251:2017.

[0021] The vertical storage elastic modulus E' at 25°C and the vertical storage elastic modulus E' at 100°C of the crosslinked rubber composition according to the embodiment are both preferably 5 MPa or more and 15 MPa or less, more preferably 7 MPa or more and 12 MPa or less. The ratio of the vertical storage elastic modulus E' at 100°C to the vertical storage elastic modulus E' at 25°C is preferably 0.6 or more, more preferably 0.7 or more. Both tan δ at 25°C and tan δ at 100°C are preferably 0.07 or more and 0.13. These dynamic properties are measured based on JIS K6394:2007 with a dynamic strain of 1.0% and a frequency of 10 Hz.

[0022] The crosslinked rubber composition according to the embodiment has a toluene swelling ratio of preferably 200% or less, more preferably 150% or less after immersion in toluene at room temperature for 7 days. The toluene swelling ratio is expressed as a percentage of the increase in volume before and after immersion in toluene, with the volume before immersion in toluene being 100%, and is an index of the degree of crosslinking.

[0023] The crosslinked rubber composition according to the above embodiment can be obtained by kneading an ethylene-α-olefin elastomer, a silane coupling agent having a mercapto group, silica and an organic peroxide using a rubber kneading machine such as a kneader, a Banbury mixer or an open roll to prepare an uncrosslinked rubber composition, and then crosslinking the uncrosslinked rubber composition at a predetermined temperature and a predetermined pressure.

[0024] The crosslinked rubber composition according to the embodiment is suitable for forming the main body of a rubber product, and specifically, is suitable for forming the main body of a belt such as a transmission belt, which requires high physical properties. EXAMPLES

[0025] (Crosslinked Rubber Composition) The crosslinked rubber compositions were prepared in the following Examples 1 to 2 and Comparative Examples 1 to 3. The configurations of each are also shown in Table 1.

[0026] <Example 1> In a closed mixer, EPDM1 (T7241 manufactured by ENEOS Materials, ethylene content: 52% by mass, ENB content: 7.7% by mass) was mixed with 1.5 parts by mass of a silane coupling agent having a mercapto group, 3-mercaptopropylmethyldimethoxysilane (KBM-802 manufactured by Shin-Etsu Chemical Co., Ltd.), 40 parts by mass of precipitated silica (Ultrasil VN3 manufactured by Evonik Co., Ltd.), and 3 parts by mass of an organic peroxide, dicumyl peroxide (Percumyl D manufactured by Nippon Oil & Fats Co., Ltd.), for 100 parts by mass of this EPDM, to prepare an uncrosslinked rubber composition. Then, this uncrosslinked rubber composition was press-molded to prepare a sheet-shaped crosslinked rubber composition. The obtained sheet-shaped crosslinked rubber composition was designated as Example 1.

[0027] <Example 2> A sheet-shaped cross-linked rubber composition having the same composition as in Example 1 was prepared, except that EPDM2 (EP93 manufactured by ENEOS Materials, ethylene content: 55 mass%, ENB content: 2.7 mass%) was used instead of EPDM1, and this was designated as Example 2.

[0028] <Comparative Example 1> A sheet-shaped crosslinked rubber composition having the same composition as in Example 1 was prepared as Comparative Example 1, except that 3-mercaptopropylmethyldimethoxysilane, which is a silane coupling agent having a mercapto group, was not blended.

[0029] <Comparative Example 2> A sheet-shaped crosslinked rubber composition having the same composition as in Example 1 was prepared as Comparative Example 2, except that bis(3-(triethoxysilyl)propyl)tetrasulfide (Si69 LiuYang SanJi Chemical Co., Ltd.) was used instead of 3-mercaptopropylmethyldimethoxysilane, a silane coupling agent having a mercapto group.

[0030] <Comparative Example 3> A sheet-shaped crosslinked rubber composition having the same composition as in Example 2, except that 3-mercaptopropylmethyldimethoxysilane, a silane coupling agent having a mercapto group, was not blended, was prepared and used as Comparative Example 3.

[0031] [Table 1]

[0032] (Test Method) <Tensile properties> For each of Examples 1 to 2 and Comparative Examples 1 to 3, the stress at 50% elongation S at standard temperature was measured based on JIS K6251:2017. 50 The tensile strength at break Tb and the elongation at break Eb were measured.

[0033] <Dynamic properties> For each of Examples 1 and 2 and Comparative Examples 1 to 3, the storage vertical elastic modulus E' at 25°C and 100°C and tan δ at 25°C and 100°C were measured at a dynamic strain of 1.0% and a frequency of 10 Hz according to JIS K6394:2007.

[0034] <Toluene swelling ratio> For each of the small test pieces of Example 1 and Comparative Examples 1 and 2, the test pieces were immersed in toluene at room temperature for 7 days, and the increase in volume before and after immersion in toluene was calculated as the toluene swelling ratio, with the volume before immersion in toluene being 100%.

[0035] (Test Results) The test results are shown in Table 1. From Table 1, it can be seen that Example 1 has higher physical properties than Comparative Examples 1 and 2. It can also be seen that Example 2 has higher physical properties than Comparative Example 3. [Industrial Applicability]

[0036] The present invention is useful in the technical field of crosslinked rubber compositions.

Claims

1. A crosslinked rubber composition comprising an ethylene-α-olefin elastomer, a silane coupling agent having a mercapto group, and silica, and crosslinked with an organic peroxide.

2. The crosslinked rubber composition according to claim 1, The ethylene-α-olefin elastomer has an ethylene content of 45% by mass or more and 60% by mass or less.

3. The crosslinked rubber composition according to claim 1, The ethylene-α-olefin elastomer comprises an ethylene-propylene-diene terpolymer.

4. The crosslinked rubber composition according to claim 3, A crosslinked rubber composition, wherein the diene component of the ethylene-propylene-diene terpolymer is ethylidene nobornene, and the ENB content thereof is 2% by mass or more and 10% by mass or less.

5. The crosslinked rubber composition according to claim 1, The crosslinked rubber composition, wherein the silane coupling agent having a mercapto group contains 3-mercaptopropylmethyldimethoxysilane.

6. The crosslinked rubber composition according to claim 1, The crosslinked rubber composition, wherein the silica comprises wet silica.

7. The crosslinked rubber composition according to claim 1, The crosslinked rubber composition, wherein the organic peroxide comprises a dialkyl peroxide.

Images