JP2020132809A - Rubber composition and crosslinked body thereof - Google Patents

Abstract

To provide a rubber composition that has sufficiently high tear strength, and has excellent removability when removed from a die, and has a low specific gravity.SOLUTION: A rubber composition has an ethylene/C3-20 α-olefin/nonconjugated polyene copolymer (A), hydrophilic silica (B), and a crosslinker (C).SELECTED DRAWING: None

Description

The present invention relates to a rubber composition and a crosslinked product thereof.

Ethylene propylene / diene copolymer rubber (EPDM) has excellent heat aging resistance, weather resistance, and ozone resistance compared to general-purpose conjugated diene rubber because it does not have an unsaturated bond in the main chain of its molecular structure. It is widely used in various applications such as parts for electric wires, materials for electric wires, electrical / electronic parts, building civil engineering materials, and industrial material parts.

EPDM is often used in the form of a rubber composition containing a reinforcing material such as carbon black, and is used for producing a rubber crosslinked product. The rubber composition containing EPDM and the like is subjected to molding and cross-linking in a form further containing a cross-linking agent, and is guided to a rubber cross-linked body.

Here, when molding such a rubber crosslinked body using a mold, it is necessary to remove the molded body from the mold, but from the viewpoint of improving work efficiency, it is required to perform the mold removal at a high temperature. There is. However, in order to enable demolding at a high temperature, the obtained rubber crosslinked body must have sufficient tearing characteristics at a high temperature. Therefore, various attempts have been made to obtain a rubber crosslinked body having a high tear strength. For example, Patent Document 1 describes an EPDM-based rubber mold material containing EPDM having a specific Mooney viscosity, a specific antioxidant, a filler, and the like in a specific ratio as a rubber composition that gives such a rubber crosslinked product. Is disclosed. Further, Patent Document 1 also describes that this EPDM-based rubber mold material has excellent heat aging characteristics and tear strength at high temperatures.

On the other hand, a wristwatch-type wearable terminal is an information terminal having a form similar to a wristwatch, and is usually used in a state of being worn on the wrist like a wristwatch. For this reason, the wristwatch-type wearable terminal has a configuration having a main body portion that has an essential function as an information terminal and a band for fixing the main body portion to the wrist. The field of wristwatch-type wearable terminals has grown remarkably for sports, and in recent years, wristwatch-type wearable terminals equipped with a pulse rate monitor have been put on the market. Further growth is expected in the field of wristwatch-type wearable terminals.

Japanese Unexamined Patent Publication No. 2004-256715

As described in Patent Document 1, various attempts have been made to improve the demoldability when obtaining a rubber crosslinked product from a rubber composition containing EPDM or the like. However, even in the case of a rubber composition containing EPDM or the like, the conventional rubber composition still has a low tear strength when it is removed from the mold after being converted into a rubber crosslinked body, depending on the reinforcing material used. It may tear and the demoldability may decrease. Therefore, further improvement in demoldability when obtaining a rubber crosslinked product from a rubber composition containing EPDM or the like is desired.

On the other hand, in a wristwatch-type wearable terminal equipped with a pulse rate monitor, it is necessary to press the terminal against the skin when measuring the pulse. Therefore, such a wristwatch-type wearable terminal is used in a state where a tensile force is continuously applied to the band, and the band itself is required to have a sufficiently high tear strength. The band is also required to be lightweight so that the terminal does not shift during pulse measurement.

Therefore, the present invention can provide a rubber crosslinked body having a sufficiently high tear strength, is excellent in demolding property when demolding from the mold when molding and crosslinking using the mold, and An object of the present invention is to provide a rubber composition having a low specific gravity.

In producing a rubber crosslinked product using a rubber composition containing EPDM and a reinforcing material, the present inventors adopt hydrophilic silica as a reinforcing material, and when molding and cross-linking are performed using a mold, gold is used. We have found that it is excellent in mold removal from the mold, and have completed the present invention.

The present invention relates to the following [1] to [8].
[1]
Ethylene / α-olefin / non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms and
Hydrophilic silica (B) and
A rubber composition containing a cross-linking agent (C).

[2]
The rubber composition according to the above [1], wherein the hydrophilic silica (B) does not have a hydrophobic group.
[3]
The above [1] containing 30 to 80 parts by mass of the hydrophilic silica (B) with respect to 100 parts by mass of the ethylene / α-olefin / non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms. ] Or the rubber composition according to [2].

[4]
The ethylene / α-olefin / non-conjugated polyene copolymer copolymer (A) having 3 to 20 carbon atoms is
The copolymer weight of the first ethylene / α-olefin / non-conjugated polyene copolymer having 3 to 20 carbon atoms and an ethylene content of 50.7 to 56.3% by mass and a non-conjugated polyene content of 6.8 to 8.4% by mass. Combined (A1) 10 to 90% by mass,
Ethylene content of 61.7 to 67.3% by mass and non-conjugated polyene content of 3.7 to 5.3% by mass of second ethylene / α-olefin / non-conjugated polyene copolymer with 3 to 20 carbon atoms The rubber composition according to any one of the above [1] to [3], which comprises 10 to 90% by mass of the coalesced (A2).

[5]
The rubber composition according to any one of [1] to [4] above, wherein the cross-linking agent (C) is sulfur.
[6]
The rubber composition according to any one of [1] to [5] above, which is used for a wristwatch-type wearable terminal band.

[7]
A rubber crosslinked body obtained by cross-linking the rubber composition according to any one of [1] to [6].
[8]
A wristwatch-type wearable terminal band including the rubber crosslinked body according to the above [7].

According to the present invention, it is possible to provide a rubber crosslinked body having a sufficiently high tear strength, and it is excellent in demolding property when demolding from a mold when molding and crosslinking using a mold. A rubber composition having a low specific gravity can be provided.

[Rubber composition]
The rubber composition according to the present invention
Ethylene / α-olefin / non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms and
Hydrophilic silica (B) and
Includes a cross-linking agent (C).

Here, in the present specification, the mass part of each component with respect to 100 parts by mass of the ethylene / α-olefin / non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms may be referred to as “phr”. In addition, the expression "phr" is sometimes used for the amount of oil spread in the oil spread rubber. In that case, the amount of oil blended with respect to 100 parts by mass of the constituent rubber in the oil spread rubber is used. Represent.

Hereinafter, the rubber composition of the present invention and each component constituting the rubber composition of the present invention will be described in detail.
<Ethylene / α-olefin / non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms>
Ethylene, α-olefin, non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms constituting the rubber composition of the present invention (in the present specification, it may be simply referred to as "copolymer (A)". There is) is a copolymer of ethylene, an α-olefin having 3 to 20 carbon atoms, and a non-conjugated polyene. That is, the copolymer (A) contains a structural unit derived from ethylene, a structural unit derived from an α-olefin having 3 to 20 carbon atoms, and a structural unit derived from a non-conjugated polyene. In the rubber composition of the present invention, the copolymer (A) functions as a rubber main agent.

Here, in the present specification, the term "ethylene-derived structural unit" means a structural unit corresponding to ethylene, that is, a structural unit represented by −CH ₂ −CH ₂ −. “Structural units derived from α-olefins having 3 to 20 carbon atoms” and “structural units derived from non-conjugated polyenes” are also interpreted in the same manner, and structural units corresponding to α-olefins having 3 to 20 carbon atoms, respectively. , And the structural unit corresponding to the non-conjugated polyene.

The copolymer (A) used in the present invention is a rubber component, and may be a random copolymer or a block copolymer. The copolymer (A) is preferable because it is excellent in weather resistance, vulcanization property and the like.

Here, as the α-olefin having 3 to 20 carbon atoms, specifically, propylene, 1-butene, 4-methylpentene-1,1-hexene, 1-hexene, 1-octene, 1-nonene , 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-nonadecene, 1-eicosene, 9-methyldecene-1,11-methyldodecene -1 and 12-ethyltetradecene-1 and the like can be mentioned. Of these, propylene, 1-butene, 4-methylpentene-1, 1-hexene and 1-octene are preferable, and propylene is particularly preferable. These α-olefins may be used alone or in combination of two or more.

Also, as a specific example of non-conjugated polyene,
1,4-Hexadiene, 3-methyl-1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 4,5-dimethyl-1,4-hexadiene, 7- Chain non-conjugated diene such as methyl-1,6-octadiene, 8-methyl-4-ethylidene-1,7-nonadien, 4-ethylidene-1,7-undecadien;
Norbornene, 5-methylene-2-norbornene, 5-vinyl-2-norbornene (VNB), 5-isopropenyl-2-norbornene, 5- (2-propenyl) -2-norbornene, 5-isobutenyl-2-norbornene, 5- (3-butenyl) -2-norbornene, 5- (1-methyl-2-propenyl) -2-norbornene, 5- (4-pentenyl) -2-norbornene, 5- (1-methyl-3-butenyl) ) -2-Norbornene, 5- (5-hexenyl) -2-Norbornene, 5- (1-methyl-4-pentenyl) -2-Norbornene, 5- (2,3-dimethyl-3-butenyl) -2- Norbornene, 5- (2-ethyl-3-butenyl) -2-norbornene, 5- (6-heptenyl) -2-norbornene, 5- (3-methyl-5-hexenyl) -2-norbornene, 5- (3) , 4-Dimethyl-4-pentenyl) -2-norbornene, 5- (3-ethyl-4-pentenyl) -2-norbornene, 5- (7-octenyl) -2-norbornene, 5- (2-methyl-6) -Heptenyl) -2-norbornene, 5- (1,2-dimethyl-5-hexenyl) -2-norbornene, 5- (5-ethyl-5-hexenyl) -2-norbornene, 5- (1,2,3 Unsaturated norbornene derivatives such as −trimethyl-4-pentenyl) -2-norbornene, 5-vinylidene-2-norbornene, 5-ethylidene-2-norbornene (ENB), 5-isopropylidene-2-norbornene, methyltetrahydroinden, And cyclic non-conjugated diene, such as dicyclopentadiene;
2,3-Diisopropylidene-5-norbornene, 2-ethylidene-3-isopropylidene-5-norbornene, 2-propenyl-2,2-norbornene, 4-ethylidene-8-methyl-1,7-nonadien, etc. Trien and the like can be mentioned. Of these non-conjugated polyenes, VNB and ENB are preferred.
These non-conjugated polyenes may be used alone or in combination of two or more.

Specific examples of the copolymer (A) include ethylene / propylene / 5-ethylidene-2-norbornene random copolymer, ethylene / propylene / 5-vinyl-2-norbornene random copolymer, and ethylene / propylene / 5-ethylidene. Examples thereof include -2-norbornene and 5-vinyl-2-norbornene random copolymers.

The copolymer (A) contains a structural unit derived from ethylene, preferably 40 to 80% by mass, more preferably 45 to 75% by mass, and further preferably 50 to 70% by mass. Further, the structural unit derived from the non-conjugated polyene is preferably contained in an amount of 2 to 15% by mass, more preferably 2 to 10% by mass, still more preferably 3 to 8% by mass. In the present specification, the content of the ethylene-derived structural unit in the copolymer (A) may be referred to as "ethylene content", and the content of the non-conjugated polyene-derived structural unit in the copolymer (A). The content is sometimes referred to as the "non-conjugated polyene content".

Further, in the above-mentioned copolymer (A), the mass ratio of the structural unit derived from ethylene to the structural unit derived from α-olefin having 3 to 20 carbon atoms is 90/10 to 40/60, preferably 60/40 to 60. It is 70/30. When this mass ratio is within the above range, a material having good mechanical strength can be obtained.

The ethylene / α-olefin / non-conjugated polyene copolymer having 3 to 20 carbon atoms constituting the copolymer (A) may be used alone or in combination of two or more. Is also good. However, in the present invention, the copolymer (A) is
First ethylene / α-olefin / non-conjugated polyene copolymer (A1) having an ethylene content of 50.7 to 56.3% by mass and a non-conjugated polyene content of 6.8 to 8.4% by mass and having 3 to 20 carbon atoms. ) (Hereinafter, it may also be referred to as "copolymer (A1)".)
A second ethylene-α-olefin-non-conjugated polyene copolymer (A2) having an ethylene content of 61.7 to 67.3% by mass and a non-conjugated polyene content of 3.7 to 5.3% by mass and having 3 to 20 carbon atoms. ) (Hereinafter, it may also be referred to as "copolymer (A2)"). When the copolymer (A) contains such a copolymer (A1) and a copolymer (A2), it is preferable because a well-processable uncrosslinked rubber composition can be obtained and the mechanical strength is excellent.

Here, as an example of the copolymer (A1), X-4010M (manufactured by Mitsui Chemicals) and the like can be mentioned. The proportion of the copolymer (A1) in the copolymer (A) is usually 10% by mass or more, preferably 40% by mass or more, more preferably 60% by mass, from the viewpoint that improvement in processability and crosslinkability can be expected. That is all. On the other hand, the copolymer (A1) tends to have a lower ethylene content than the copolymer (A2) and a lower mechanical strength at room temperature than the copolymer (A2). Therefore, from the viewpoint of sufficiently maintaining the mechanical strength at room temperature, the proportion of the copolymer (A1) in the copolymer (A) is usually 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass. % Or less.

Further, as an example of the copolymer (A2), 3062EM (manufactured by Mitsui Chemicals) and the like can be mentioned. The proportion of the copolymer (A2) in the copolymer (A) is usually 10% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more from the viewpoint of improving the mechanical strength at room temperature. On the other hand, the copolymer (A2) tends to have a higher molecular weight than the copolymer (A1), and the processability tends to be inferior to that of the copolymer (A1). Therefore, from the viewpoint of ensuring a certain level of processability, the proportion of the copolymer (A2) in the copolymer (A) is usually 60% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. is there.

Such a copolymer (A) typically consists only of the copolymer (A1) and the copolymer (A2). However, the copolymer (A) is not limited to an embodiment consisting only of the copolymer (A1) and the copolymer (A2), and for example, the copolymer (A1) and the copolymer (A2). ) May contain 60% by mass or less of an ethylene / α-olefin / non-conjugated polyene copolymer (A3) having 3 to 20 carbon atoms.

In the present invention, each copolymer that can constitute the copolymer (A) such as the copolymer (A1) and the copolymer (A2) is in the form of an oil-extended rubber obtained by adding oil. Alternatively, it may be in the form of non-oil-extended rubber.

However, when a polymer (A) in the form of oil-extended rubber is used, the "parts by mass" and "% by mass" of the copolymer (A) are both unless otherwise specified. , The total mass of the oil-extended rubber minus the mass of the oil contained in the oil-extended rubber is used as a reference. For example, a copolymer consisting of only X (g) of non-oil-extended rubber as a copolymer (A1) and Y (g) of oil-expanded rubber having an oil spreading amount of a (phr) as a copolymer (A2). In the case of (A), the mass of the copolymer (A), which is the reference of the “part by mass”, is X + Y × 100 / (100 + a) (g). At this time, the contents of the copolymer (A1) and the copolymer (A2) in the copolymer (A) are X / (X + Y × 100 / (100 + a)) × 100 (mass%) and (% by mass), respectively. It becomes Y × 100 / (100 + a)) / (X + Y × 100 / (100 + a)) × 100 (mass%).

<Hydrophilic silica (B)>
The rubber composition of the present invention contains hydrophilic silica (B). In the present invention, the hydrophilic silica (B) is used as an essential component when hydrophilic silica is used as the reinforcing material of the rubber composition, as compared with the case where a reinforcing material other than silica or hydrophobic silica is used. It is based on the fact that a rubber crosslinked body having high tear strength can be provided, and that the mold can be removed from the mold when it is molded and crosslinked using the mold. Further, when hydrophilic silica is used as a reinforcing material of the rubber composition, a rubber crosslinked body having a low specific density can be provided. Therefore, for example, if a band obtained by using the rubber composition of the present invention is adopted as a band of a wearable terminal for a wristwatch, a wearable terminal for a wristwatch that is comfortable to wear can be obtained, and a pulse rate monitor is mounted. In the case of a wearable terminal for a wristwatch, the terminal is less likely to shift during pulse measurement.

Here, the hydrophilic silica means silica having no hydrophobic group on the surface, and examples thereof include known dry silica and wet silica usually used in the rubber industry. In the present invention, the hydrophilic silica (B) is a silica having a large amount of silanol groups because it has an effect of increasing the amount of bound rubber, which is known to contribute to the improvement of strength in the uncrosslinked rubber composition. It is preferable to have. Examples of such preferable hydrophilic silica include Aerosil (registered trademark) 200 (manufactured by Nippon Aerosil Co., Ltd.).
The blending amount of the hydrophilic silica (B) can be appropriately selected depending on the intended use, but is usually 30 to 80 parts by mass, preferably 40 to 70 parts by mass with respect to 100 parts by mass of the copolymer (A).

<Crosslinking agent (C)>
The cross-linking agent (C) constituting the rubber composition of the present invention is not particularly limited as long as the copolymer (A) can be cross-linked, and is usually used in the field of rubber such as sulfur compounds and peroxide-based cross-linking agents. It may be of various types used.

In the present invention, a sulfur-based compound (C1) can be mentioned as a suitable cross-linking agent (C). By cross-linking the rubber composition with the sulfur-based compound (C1), much superior flexibility and mechanical properties can be imparted as compared with the case where a peroxide-based cross-linking agent such as dicumyl peroxide is used. Can be done.

Examples of the type of the sulfur compound (C1) include sulfur, sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, tetramethylthiuram disulfide, selenium dithiocarbamate and the like. Of these, sulfur and tetramethylthiuram disulfide are preferable.

On the other hand, a peroxide-based cross-linking agent (C2) can also be used as the cross-linking agent (C).
As a peroxide-based cross-linking agent (C2),
1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis (t-butylperoxy) octane, Peroxyketals such as 1,1-bis (t-butylperoxy) cyclododecane, as well as
Di-t-butyl peroxide, t-butyl cumyl peroxide, dicumyl peroxide, α, α'-bis (t-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (T-Butylperoxy) Hexane-3, t-Butylperoxy-2-ethylhexanoate, t-Butylperoxy-3,5,5-trimethylhexanoate, 2,5-dimethyl-2,5 -Dialkyl peroxides such as di (benzoyl peroxy) hexane can be mentioned.

The content of the cross-linking agent (C) in the rubber composition of the present invention is 0.01 to 10 parts by mass, preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the copolymer (A). is there.
Here, when the sulfur-based compound (C1) is used as the cross-linking agent (C), the content thereof is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the copolymer (A). ..
On the other hand, when the peroxide-based cross-linking agent (C2) is used as the cross-linking agent (C), the content thereof shall be 0.5 to 5 parts by mass with respect to 100 parts by mass of the copolymer (A). Is preferable.

<Other ingredients>
The rubber composition of the present invention contains the above-mentioned copolymer (A), hydrophilic silica (B), and cross-linking agent (C), and may further contain other components depending on the intended use.

Other components that can be contained in the rubber composition of the present invention include reinforcing materials other than hydrophilic silica (B) (hereinafter, "reinforcing material (B')"), plasticizers, vulcanization accelerators, co-crosslinking agents, and additions. Examples thereof include various additives such as vulcanization aids, processing aids, antiaging agents, activators, hygroscopic agents, foaming agents, and foaming aids. Further, if necessary, known colorants, dispersants, flame retardants and the like can be used as other components.

Reinforcing material (B')
In order to enhance mechanical properties such as tensile strength, tear strength, and abrasion resistance when the rubber composition of the present invention is formed into a crosslinked product, in addition to the above hydrophilic silica (B), hydrophilic silica ( A reinforcing material (B') other than B) may be contained.

Examples of the type of reinforcing material (B') include carbon black, activated calcium carbonate, light calcium carbonate, heavy calcium carbonate, talc, clay and the like. These reinforcing materials may be used alone or in combination of two or more.

Among these, carbon black is preferable as the reinforcing material (B') from the viewpoint of uniform dispersibility in the rubber matrix, excellent reinforcing property, and versatility (cost).
The type of carbon black is not particularly limited, and examples thereof include known types usually used in the rubber industry, such as furnace black (classified by ASTM D 1765), channel black, thermal black, and acetylene black, depending on the purpose of use. ..

Here, carbon black may be used by surface-treating it with a silane coupling agent or the like.
Further, as the heavy calcium carbonate, commercially available "Whiten SB" (trade name; Shiraishi Calcium Co., Ltd.) or the like can be used.

The type and blending amount of the reinforcing material (B') can be appropriately selected depending on the intended use, but is usually 10 to 300 parts by mass, preferably 10 to 200 parts by mass with respect to 100 parts by mass of the copolymer (A). ..

Plasticizer The rubber composition of the present invention may further contain a known plasticizer commonly used as a softener in the field of rubber, depending on its use.

Specific examples of such plasticizers include process oil (for example, "Diana Process Oil PS-430" (trade name; manufactured by Idemitsu Kosan Co., Ltd.)), lubricating oil, paraffin oil, liquid paraffin, petroleum asphalt, and Petroleum-based softeners such as vaseline; hydrocarbon-based softeners such as coal tar and coal tar pitch; fatty oil-based softeners such as paraffin oil, flaxseed oil, rapeseed oil, soybean oil, and palm oil; beeswax, carnauba wax, And waxes such as lanolin; fatty acids such as ricinolic acid, palmitic acid, stearic acid, barium stearate, calcium stearate, and zinc laurate or salts thereof; naphthenic acid, pine oil, and rosin or derivatives thereof; terpenic acid, petroleum Synthetic polymer substances such as resins, atactic polypropylene, and kumaron inden resins; ester-based softeners such as dioctyl phthalate, dioctyl adipate, and dioctyl sebacate; other microcrystallin wax, liquid polybutadiene, modified liquid polybutadiene, liquid thiocol , Hydrocarbon-based synthetic lubricating oil, tall oil, and sub (factis). Of these, petroleum-based softeners are preferable. Among the petroleum-based softeners, petroleum-based process oils are preferable, and among them, paraffin-based process oils, naphthen-based process oils, aroma-based process oils and the like are more preferable.

Here, the content of the plasticizer can be appropriately selected depending on the intended use, and is usually up to 200 parts by mass, preferably up to 150 parts by mass, and more preferably up to 130 parts by mass with respect to 100 parts by mass of the copolymer (A). The mass part is desirable.

Vulcanization Accelerator The rubber composition according to the present invention may further contain a vulcanization accelerator in addition to the above-mentioned copolymer (A), hydrophilic silica (B) and cross-linking agent (C).

Here, in the rubber composition according to the present invention, the content of the vulcanization accelerator is preferably 0.1 to 15 parts by mass, more preferably 0, with respect to 100 parts by mass of the copolymer (A). It is 5 to 10 parts by mass. When the vulcanization accelerator is contained in the rubber composition at such a content, the rubber composition has excellent cross-linking properties, and the generation of bloom in the obtained rubber cross-linked body can be further reduced.

Specific examples of the sulfide accelerator include N-cyclohexyl-2-benzothiazole sulfenamide (for example, "Sunceller CM" (trade name; manufactured by Sanshin Chemical Industry Co., Ltd.)), N-oxydiethylene-2- Benzothiazole sulfenamide, N, N'-diisopropyl-2-benzothiazole sulfenamide, 2-mercaptobenzothiazole (for example, "Suncella M" (trade name; manufactured by Sanshin Chemical Industry Co., Ltd.)), 2- (4-morpholinodithio) penzothiazole (for example, "Noxeller MDB-P" (trade name; manufactured by Sanshin Chemical Industry Co., Ltd.)), 2- (2,4-dinitrophenyl) mercaptobenzothiazole, 2- (4) 2,6-diethyl-4-morpholinothio) Thiazoles such as benzothiazole and dibenzothiadyldisulfide; guanidines such as diphenylguanidine, triphenylguanidine and diorsotrilguanidine; acetaldehyde-aniline condensate, butylaldehyde-aniline Condensate, aldehyde amine type; imidazoline type such as 2-mercaptoimidazolin; thiourea type such as diethyl thiourea and dibutyl thiourea; tetramethyl thiuram monosulfide, tetramethyl thiuram disulfide (for example, "Suncella TT" (trade name; Sanshin Kagaku) (Manufactured by Kogyo Co., Ltd.), etc.), tetraethylthiuram disulfide (for example, "Sunceller TET" (trade name; manufactured by Sanshin Kagaku Kogyo Co., Ltd.), etc.) and other thiuram-based; Dithioate systems such as zinc (for example, "Suncella BZ" (trade name; manufactured by Sanshin Chemical Industry Co., Ltd.)), telluryl diethyldithiocarbamate, etc .; ethylenethiourea (for example, "Suncella 22-C" (trade name; Sanshin Chemical Industry Co., Ltd.) (Manufactured by Shinkagaku Kogyo Co., Ltd.), etc.), Thiourea type such as N, N'-diethylthiourea; Zantate type such as zinc dibutylxatogenate; Other zinc flower (for example, "META-Z102" (trade name; Inoue Lime Industry Co., Ltd.) Zinc oxide) such as)) and the like.

Co-crosslinking agent When a peroxide-based cross-linking agent (C2) is used as the cross-linking agent (C), the copolymer (A), the reinforcing material (B) and the cross-linking are used in the rubber composition according to the present invention. In addition to the agent (C), an appropriate co-crosslinking agent can be further contained, if necessary, for the purpose of improving physical properties and vulcanization rate.

Examples of co-crosslinking agents are polyethylene glycol dimethacrylate (PEGDM) such as Blemmer PDE-100 (trade name manufactured by Nippon Kasei Co., Ltd.), diallyl phthalate (DAP), and triallyl such as Tyke (trade name manufactured by Nippon Kasei Co., Ltd.). Triallyl cyanurate (TAC) such as isocyanurate (TAIC), Tuck (trade name manufactured by Musashino Chemical Laboratory Co., Ltd.), tetrahydrofurfuryl methacrylate (THMMA) such as acrylic ester THF (trade name manufactured by Mitsubishi Rayon Co., Ltd.) , Sunester EG (trade name manufactured by Sanshin Kagaku Kogyo Co., Ltd.) and Acryester ED (trade name manufactured by Mitsubishi Rayon Co., Ltd.), ethylene dimethacrylate (EDMA), Acryester BD (trade name manufactured by Mitsubishi Rayon Co., Ltd.) Dimethacrylic acid 1,3-butylene (BDMA), Sun Ester TMPMA (trade name manufactured by Sanshin Chemical Industry Co., Ltd.), Acryester TMP (trade name manufactured by Mitsubishi Rayon Co., Ltd.) and Hicross M (Seiko Kagaku Co., Ltd.) Examples thereof include trimethylol propanyl methacrylate (TMPMA) such as (trade name).

The amount of the copolymer (A) added is appropriately about 1 to 10 parts by mass with respect to 100 parts by mass of the copolymer (A).
Further, in the rubber composition of this embodiment, vulcanization aids such as methacrylic ester and triallyl isocyanurate (TAIC) such as Tyke (Nihon Kasei Co., Ltd.) during vulcanization using a peroxide-based cross-linking agent. It may be further added as an agent.

Vulcanization Auxiliary Agent The rubber composition according to the present invention may further contain a vulcanization auxiliary agent in addition to the above-mentioned copolymer (A), hydrophilic silica (B) and cross-linking agent (C).

Specific examples of the vulcanization aid include magnesium oxide and zinc oxide (for example, zinc oxide such as "META-Z102" (trade name; manufactured by Inoue Lime Industry Co., Ltd.)). The content is usually 1 to 20 parts by mass with respect to 100 parts by mass of the copolymer (A).

Processing aid The rubber composition according to the present invention may further contain a processing aid in addition to the above-mentioned copolymer (A), hydrophilic silica (B) and cross-linking agent (C).

As the processing aid, a compound used for ordinary rubber processing can be used. Specifically, higher fatty acids such as ricinolic acid, stearic acid, partiminic acid, and lauric acid; salts of higher fatty acids such as barium stearate, zinc stearate, and calcium stearate; ricinolic acid, stearic acid, partimic acid, lauric acid, etc. Examples of higher fatty acid esters of.

Such a processing aid is usually used in a ratio of 10 parts by mass or less, preferably 5 parts by mass or less with respect to 100 parts by mass of the copolymer (A), but is appropriately used depending on the required physical property values. It is desirable to determine the optimum amount.

Anti-aging agent The rubber product produced from the rubber composition according to the present invention may contain an anti-aging agent in order to further extend the product life. In addition, examples of the anti-aging agent include conventionally known anti-aging agents such as amine-based anti-aging agents, phenol-based anti-aging agents, and sulfur-based anti-aging agents.

Specifically, aromatic secondary amine-based antiaging agents such as phenylbutylamine, N, N-di-2-naphthyl-p-phenylenediamine, dibutylhydroxytoluene, tetrakis- [methylene-3- (3', 3',). 5'-di-t-butyl-4'-hydroxyphenyl) propionate] Phenolic anti-aging agents such as methane; bis [2-methyl-4- (3-n-alkylthiopropionyloxy) -5-t-butylphenyl ] Thioether-based anti-aging agents such as sulfide; Dithiocarbamate-based anti-aging agents such as nickel dibutyldithiocarbamate; 2-mercaptobenzoylimidazole, zinc salt of 2-mercaptobenzoimidazole, dilaurylthiodipropionate, distearylthiodipro Examples thereof include sulfur-based anti-aging agents such as pionate.

These antioxidants can be used alone or in combination of two or more, and the content of such antioxidants is usually 0, based on 100 parts by mass of the copolymer (A). It is 3 to 10 parts by mass, preferably 0.5 to 7.0 parts by mass, and more preferably 0.7 to 5.0 parts by mass. When the content of the anti-aging agent is within the above range, the inhibition of vulcanization at the time of cross-linking of the rubber composition can be reduced, and the generation of bloom in the obtained cross-linked rubber body can be reduced.

<Manufacturing method of rubber composition>
The rubber composition of the present invention is generally composed of the above-mentioned predetermined parts by mass of the copolymer (A), the hydrophilic silica (B) and the cross-linking agent (C), and the above-mentioned "other components" to be blended as necessary. It can be prepared by the same method as that for preparing a rubber compound.

For example, using an internal mixer such as a Banbury mixer, a kneader, or an intermix, each of the above-mentioned components is preferably prepared at a temperature of 80 to 190 ° C., more preferably 80 to 170 ° C., preferably for 2 to 20 minutes. , More preferably after kneading for 3 to 10 minutes, kneading at a roll temperature of 40 to 80 ° C. for 3 to 30 minutes using a roll such as an open roll or a kneader, and then extruding / dispensing the kneaded product. Can be prepared. Further, when the kneading temperature in the internal mixers is low, a vulcanization accelerator or a vulcanization aid may be kneaded at the same time. Further, the kneading using the internal mixers may be performed by using rolls instead of the internal mixers depending on the kneading temperature and the like.

<Rubber crosslinked body>
The rubber composition of the present invention can be used as a raw material for a rubber crosslinked product. The rubber crosslinked body of the present invention is obtained by crosslinking the above-mentioned rubber composition. The rubber crosslinked product of the present invention has high tear strength and a low specific gravity. Therefore, it is very useful as a rubber product in various fields requiring light weight and high strength.

Here, the rubber crosslinked product of the present invention can be obtained by cross-linking the above-mentioned rubber composition. In order to produce a crosslinked product from the composition of the present invention, an unvulcanized rubber composition is prepared by the method as described above in the same manner as in the case of vulcanizing general rubber, and then this rubber composition is prepared. May be vulcanized after being formed into the intended shape.

The unvulcanized rubber composition prepared as described above can be molded and vulcanized by various molding methods. However, the rubber composition of the present invention is excellent in demoldability when molded and crosslinked using a mold. Therefore, the rubber composition of the present invention can most effectively exhibit its characteristics when it is molded and vulcanized by mold molding such as compression molding, injection molding, and injection molding.

Compression molding can be performed, for example, by placing a pre-weighed unvulcanized rubber composition in a mold, closing the mold, and then heating at a temperature of 120 to 270 ° C. for 30 seconds to 120 minutes. Then, by performing demolding, the desired crosslinked product is obtained.

Injection molding can be performed, for example, as follows. First, a ribbon-shaped or pellet-shaped rubber composition is supplied to the pot in a preset amount by a screw. Subsequently, the preheated rubber composition is fed into the mold by a plunger in 1 to 20 seconds. After injecting the rubber composition, it is heated at a temperature of 120 to 270 ° C. for 30 seconds to 120 minutes. Then, by performing demolding, the desired crosslinked product is obtained.

Injection molding can be performed, for example, as follows. First, the pre-weighed rubber composition is placed in a pot and injected into a mold by a piston in 1 to 20 seconds. After injecting the rubber composition, it is heated at a temperature of 120 to 270 ° C. for 30 seconds to 120 minutes. Then, by performing demolding, the desired crosslinked product is obtained.

Applications of the rubber crosslinked body of the present invention thus obtained include, for example, a wristwatch-type wearable terminal band, rubber boots, rubber gloves, and the like. Here, when the rubber crosslinked body of the present invention is used for a wristwatch-type wearable terminal band, the wristwatch-type wearable terminal provided with this band has a main body portion that has an essential function as an information terminal and the main body portion on the arm. A band for fixing is included, and the band includes the rubber crosslinked body of the present invention.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. The measurement method of each physical property is as follows.

<Evaluation of unvulcanized rubber physical properties>
(Moony viscosity (ML (1 + 4) 125 ° C.), minimum viscosity (Vm))
The Mooney viscosity (ML (1 + 4) 125 ° C.) at 125 ° C. was measured under the condition of 125 ° C. using a Mooney viscometer (SMV202 type manufactured by Shimadzu Corporation) in accordance with JIS K6300. At this time, the minimum viscosity (Vm (125 ° C.)) from the start of measurement was determined.

(Vulcanization rate)
By using the rubber composition in the examples and comparative examples, measurement device: by MDR2000P (ALPHA TECHNOLOGIES Co. MDR (Moving Die Rheometer)), perform cure meter _{test, S 'Max -S' Min,} tc10, tc20, tc50 And tc90 were measured as follows.

The sample was set in a measuring device, and the torque change obtained under the conditions of a constant temperature and a constant shear rate was measured to obtain a vulcanization curve. The vulcanization curve determining the minimum value S _'Min and maximum value S' _Max torque from the torque based on the time of measurement start _{(S 'Max -S' Min)} × 0.1, (S 'Max -S' _{min) × 0.2, (S '} Max -S' min) × 0.5 and _{(S 'Max -S' min)} × 0.9 and made up to the time (min) respectively tc10, tc20, tc50 and It was set to tk90. Here, this tc10 means a vulcanization start point, and tc90 means an optimum vulcanization point. In the present invention, this tc90 was used as the vulcanization rate.

Further, the time from the minimum value of the torque to the increase of the torque by 1 point (1 dNm) was defined as the vulcanization induction time (TS1; minutes).
The maximum slope of the vulcanization curve was MCR (dNm / min).

<Evaluation of vulcanized rubber physical properties>
(Tensile breaking point stress, tensile breaking point elongation)
The tensile breaking point stress and the tensile breaking point elongation of the sheet made of the rubber crosslinked body were measured by the following methods.

A sheet made of a rubber crosslinked body is punched out to prepare a No. 3 dumbbell test piece described in JIS K 6251 (2017), and this test piece is used to measure a measurement temperature 23 according to the method specified in JIS K 6251. Tensile tests were conducted under the conditions of ° C., relative humidity of 50%, and tensile speed of 500 mm / min. Tensile stress (25% modulus (M25)) when the elongation rate was 25%, and tensile strength when the elongation rate was 50%. Stress (50% modulus (M50)), tensile stress when elongation is 100% (100% modulus (M100)), tensile stress when elongation is 200% (200% modulus (M200)), Tensile stress (300% modulus (M300)), tensile breaking point stress (TB) and tensile breaking point elongation (EB) when the elongation rate was 300% were measured.
Further, the same measurement was performed when the measurement temperature was changed to 180 ° C.

(Tear strength)
The tear strength (TR-B) was measured according to "Test method B-Procedure (a): Method using a non-cut angle type test piece" specified in JIS-K6252-1.

(Durometer A hardness)
According to JIS K 6253, the hardness of the sheet (type A durometer, HA) was measured by stacking flat portions to a thickness of about 12 mm using six 2 mm sheet-shaped rubber molded products having a smooth surface. However, the test pieces containing foreign matter, air bubbles, and scratches were not used. The size of the measurement surface of the test piece was set so that the tip of the push needle could be measured at a position 12 mm or more away from the end of the test piece.

(specific gravity)
Measured according to JIS L1013 (2010).
<Regarding the components used in Examples and Comparative Examples>
In the examples and comparative examples, the following were used as ethylene / propylene / non-conjugated polyene copolymers:
EPDM1: Ethylene / propylene / ENB copolymer (trade name: Mitsui EPT (trademark) X-4010M (manufactured by Mitsui Chemicals, Inc.)), ML (1 + 4) 100 ° C. (ASTM D 1646): 8, ethylene content (ASTM) D 3900): 54 wt%, ENB content (ASTM D 6047): 7.6 wt%, [η]: 1.03 dl / g, specific gravity: 0.87;
EPDM2: Ethylene / propylene / ENB copolymer (trade name: Mitsui EPT (trademark) 3062EM (manufactured by Mitsui Chemicals, Inc.)), ML (1 + 4) 125 ° C (ASTM D 1646): 43, ethylene content (ASTM D 3900) ): 65 wt%, ENB content (ASTM D 6047): 4.5 wt%, [η]: 2.72 dl / g, specific gravity: 0.87, oil spread: 20 phr.

In addition, the following silica was used:
Hydrophilic silica 1: Fumed silica without surface modification (trade name: Aerosil (registered trademark) 200 (manufactured by Nippon Aerosil Co., Ltd.)), specific gravity: 1.06;
Hydrophobic silica 1: Fumed silica surface-modified with a trimethylsilyl group (trade name: Aerosil (registered trademark) RX200 (manufactured by Nippon Aerosil Co., Ltd.)).

[Example 1]
As a first step, using MIXTRON BB MIXER (manufactured by Kobe Steel Co., Ltd., BB-4 type, volume 2.95 L, rotor 4 WH), 70 parts by mass of EPDM1 and 36 parts by mass of EPDM2 as the copolymer (A). (Equivalent to 30 parts by mass as the amount of copolymer component), 167 parts by mass of the above-mentioned hydrophilic silica as hydrophilic silica (B), and active zinc flower as a vulcanization aid (trade name: META-Z 102, Inoue lime). (Manufactured by Kogyo Co., Ltd.) 5 parts by mass, 2 parts by mass of stearic acid as a processing aid, and paraffin-based process oil as a plasticizer (trade name: Diana Process Oil PS-430, manufactured by Idemitsu Kosan Co., Ltd.) 44 parts by mass And were kneaded to obtain a compound. The kneading conditions were a rotor rotation speed of 50 rpm, a floating weight pressure of 3 kg / cm ² , and a kneading time of 5 minutes, and the kneading discharge temperature was 120 ° C.

The composition of the formulation obtained in the first step is shown in Table 1. Here, regarding the blending amount of EPDM2, the value shown in the upper row represents the total amount of the oil-extended rubber, and the value indicated by the brackets in the lower row is the amount of the copolymer component (that is, the oil-extended rubber). The remaining amount obtained by subtracting the amount of oil contained in the oil-extended rubber from the total amount of the rubber).

The specific gravity of the compound obtained in the first step was measured by the method described in the section of "specific gravity" in the above "evaluation of vulcanized rubber physical properties". The results are shown in Table 2-1.
Next, as the second step, 2-mercaptobenzothiazole (Suncellor M: Sanshin Chemical Industry Co., Ltd.) was used as a vulcanization accelerator in the rubber composition using an 8-inch roll for the formulation obtained in the first step. ) 0.5 parts by mass, tetramethylthiuram disulfide (Sunseller TT: manufactured by Sanshin Chemical Industry Co., Ltd.) 0.5 parts by mass, tetraethyltiuram disulfide (Sunseller TET: manufactured by Sanshin Chemical Industry Co., Ltd.) 0. 5 parts by mass, 1.5 parts by mass of zinc dibutyldithiocarbamate (Suncella BZ: manufactured by Sanshin Chemical Industry Co., Ltd.) and 0.8 parts by mass of sulfur as a cross-linking agent (C) were added and kneaded, and not yet kneaded. A crosslinked rubber composition was obtained. The kneading conditions were such that the roll temperature was front roll / rear roll: 50 ° C./50 ° C., the roll rotation speed was front roll / rear roll: 18 rpm / 15 rpm, and the roll gap was 2 mm, and the kneading time was 8 minutes. The composition of the uncrosslinked rubber composition is shown in Table 1.

The physical properties of the obtained uncrosslinked rubber composition (unvulcanized rubber physical properties) were measured based on the above-mentioned "evaluation of unvulcanized rubber physical properties". Here, the cure meter test was performed under measurement conditions of a temperature of 180 ° C. and a time of 20 minutes. The results are shown in Table 2-1.

Further, this uncrosslinked rubber composition was crosslinked by pressing at 180 ° C. for 10 minutes using a press molding machine to prepare a rubber sheet having a thickness of 2 mm as a rubber crosslinked body. The physical properties of the obtained rubber sheet (vulcanized rubber physical properties) were measured based on the above-mentioned "evaluation of vulcanized rubber physical properties". Specifically, the durometer A hardness of the obtained rubber sheet, the tensile stress (M25, M50, M100, M200, M300) at 23 ° C. and 180 ° C., the breaking point strength TB (MPa), and the breaking point. Elongation EB (%) and tear strength (TR-B) were measured, respectively. The results are shown in Table 2-2 below.

The demoldability was evaluated as follows. First, the uncrosslinked rubber composition was molded and crosslinked by pressing in a mold at 180 ° C. for 10 minutes using a press molding machine. The dies used at this time are a pair of dies that form a cavity having a size capable of forming a rubber sheet having a width of 150 mm, a depth of 150 mm, and a thickness of 2 mm when combined with each other for molding. It has a cutting groove around it, and has a structure in which excess rubber composition can be discharged from the cavity through the cutting groove. That is, by the molding and cross-linking, a vulcanized molded product having a main body portion to be a vulcanized rubber sheet and a biting portion corresponding to the cutting groove is obtained, and the cutting portion is around the main body portion. Will be.

After completing this molding and cross-linking, the vulcanized molded product was removed from the mold, and the appearance of the obtained vulcanized molded product was visually observed to see if the cut-out portion could be removed without tearing. Was evaluated. In this evaluation, the vulcanized molded product was scored according to the following criteria.
〇: None of the four sides of the sheet is torn.
Δ: One to three of the four sides of the sheet are torn.
X: 4 out of 4 sides of the sheet are torn.
The results are shown in Table 2-2 below.

[Comparative Example 1]
Examples except that 67 parts by mass of carbon black (SRF) (trade name: Asahi # 50G, manufactured by Asahi Carbon Co., Ltd.) was used instead of the above-mentioned hydrophilic silica 1 used as the hydrophilic silica (B). The procedure was the same as in 1. Here, the cure meter test for the uncrosslinked rubber composition is carried out under the measurement conditions shown in Table 2-1 and the press temperature and time for producing the rubber crosslinked body used for measuring the physical properties of the vulcanized rubber. 2-2 is shown in Table 2-2.

The composition of the uncrosslinked rubber composition is shown in Table 1, and the results on the specific gravity, unvulcanized rubber physical properties, vulcanized rubber physical properties and demolding properties of the formulation obtained in the first step are shown in Table 2-1 and Shown in 2-2.

[Comparative Example 2]
Instead of the hydrophilic silica 1 used as the hydrophilic silica (B), 15 parts by mass of the hydrophobic silica 1 and 45 parts by mass of carbon black (SRF) (trade name: Asahi # 50G, manufactured by Asahi Carbon Co., Ltd.) Was used, and the same procedure as in Example 1 was carried out. Here, the cure meter test for the uncrosslinked rubber composition is carried out under the measurement conditions shown in Table 2-1 and the press temperature and time for producing the rubber crosslinked body used for measuring the physical properties of the vulcanized rubber. 2-2 is shown in Table 2-2.

The composition of the uncrosslinked rubber composition is shown in Table 1, and the results on the specific gravity, unvulcanized rubber physical properties, vulcanized rubber physical properties and demolding properties of the formulation obtained in the first step are shown in Table 2-1 and Shown in 2-2.

[Comparative Example 3]
Examples except that the same amount of carbon black (FEF) (trade name: Asahi # 60G, manufactured by Asahi Carbon Co., Ltd.) was used in place of the above-mentioned hydrophilic silica 1 used as the hydrophilic silica (B). The procedure was the same as in 1. Here, the cure meter test for the uncrosslinked rubber composition is carried out under the measurement conditions shown in Table 2-1 and the press temperature and time for producing the rubber crosslinked body used for measuring the physical properties of the vulcanized rubber. 2-2 is shown in Table 2-2.

The composition of the uncrosslinked rubber composition is shown in Table 1, and the results on the specific gravity, unvulcanized rubber physical properties, vulcanized rubber physical properties and demolding properties of the formulation obtained in the first step are shown in Table 2-1 and Shown in 2-2.

[Comparative Example 4]
Same as Example 1 except that the same amount of clay (trade name: Dixie Clay (trademark), manufactured by Vanderbilt Chemicals Co., Ltd.) was used in place of the hydrophilic silica 1 used as the hydrophilic silica (B). I went to. Here, the cure meter test for the uncrosslinked rubber composition is carried out under the measurement conditions shown in Table 2-1 and the press temperature and time for producing the rubber crosslinked body used for measuring the physical properties of the vulcanized rubber. 2-2 is shown in Table 2-2.

The composition of the uncrosslinked rubber composition is shown in Table 1, and the results on the specific gravity, unvulcanized rubber physical properties, vulcanized rubber physical properties and demolding properties of the formulation obtained in the first step are shown in Table 2-1 and Shown in 2-2.

[Comparative Example 5]
Except that the same amount of talc (trade name: MISTRON VAPOR, manufactured by Imerys Specialties Japan Co., Ltd.) was used in place of the above-mentioned hydrophilic silica 1 used as the hydrophilic silica (B). This was done in the same manner as in Example 1. Here, the cure meter test for the uncrosslinked rubber composition is carried out under the measurement conditions shown in Table 2-1 and the press temperature and time for producing the rubber crosslinked body used for measuring the physical properties of the vulcanized rubber. 2-2 is shown in Table 2-2.

The composition of the uncrosslinked rubber composition is shown in Table 1, and the results on the specific gravity, unvulcanized rubber physical properties, vulcanized rubber physical properties and demolding properties of the formulation obtained in the first step are shown in Table 2-1 and Shown in 2-2.

[Comparative Example 6]
The same procedure as in Example 1 was carried out except that the same amount of the hydrophobic silica 1 was used in place of the hydrophilic silica 1 used as the hydrophilic silica (B). Here, the cure meter test for the uncrosslinked rubber composition is carried out under the measurement conditions shown in Table 2-1 and the press temperature and time for producing the rubber crosslinked body used for measuring the physical properties of the vulcanized rubber. 2-2 is shown in Table 2-2.

The composition of the uncrosslinked rubber composition is shown in Table 1, and the results on the specific gravity, unvulcanized rubber physical properties, vulcanized rubber physical properties and demolding properties of the formulation obtained in the first step are shown in Table 2-1 and Shown in 2-2.

Claims (8)

Ethylene / α-olefin / non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms and
Hydrophilic silica (B) and
A rubber composition containing a cross-linking agent (C). The rubber composition according to claim 1, wherein the hydrophilic silica (B) does not have a hydrophobic group. According to claim 1 or 2, the hydrophilic silica (B) is contained in an amount of 30 to 80 parts by mass with respect to 100 parts by mass of the α-olefin / non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms. The rubber composition described. The ethylene / α-olefin / non-conjugated polyene copolymer (A) having 3 to 20 carbon atoms is
The copolymer weight of the first ethylene / α-olefin / non-conjugated polyene copolymer having 3 to 20 carbon atoms and an ethylene content of 50.7 to 56.3% by mass and a non-conjugated polyene content of 6.8 to 8.4% by mass. Combined (A1) 10 to 90% by mass,
Ethylene content of 61.7 to 67.3% by mass and non-conjugated polyene content of 3.7 to 5.3% by mass of second ethylene / α-olefin / non-conjugated polyene copolymer with 3 to 20 carbon atoms The rubber composition according to any one of claims 1 to 3, which comprises 10 to 90% by mass of the coalesced (A2). The rubber composition according to any one of claims 1 to 4, wherein the cross-linking agent (C) is sulfur. The rubber composition according to any one of claims 1 to 5, which is used for a wristwatch-type wearable terminal band. A rubber crosslinked body obtained by crosslinking the rubber composition according to any one of claims 1 to 6. A wristwatch-type wearable terminal band including the rubber crosslinked body according to claim 7.