Rubber molding

Abstract

To provide a rubber molded article which can retain excellent slidability even in a low-temperature atmosphere (for instance, a low temperature atmosphere at -40°C-5°C especially after long-term usage), and can obtain a desired allophone inhibitory effect in the low-temperature atmosphere.SOLUTION: A rubber composition with respect to a rubber molded article, having natural rubber (NR) and butadiene rubber (BR) as the main rubber components is such that: a ratio of the natural rubber (NR) to the butadiene rubber (BR) is 80 / 20-10 / 90 at NR / BR ratio; 20-70 pts.mass of paraffin wax having a melting point of 45-57°C is contained based on 100 pts.mass of the total rubber components; and the total content of the paraffin wax and fatty acid amide having a melting point of 35-85°C is 40-100 pts.mass.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber molded body, for example, a rubber molded body used to slide against other members such as metal, and particularly to a rubber molded body that can be applied to rubber molded products such as stabilizer bushings for automobiles, which have excellent noise suppression effects due to their ability to maintain good sliding properties even in low-temperature environments (for example, -40°C to 5°C) after long-term use. [Background technology]

[0002] Due to their flexibility and other characteristics, rubber molded articles are sometimes used to cushion objects from contact with one another. For example, when rubber molded articles are used in locations where components come into contact with one another, such as doors, they are placed between the contact surfaces of the components to prevent damage to the components due to the contact, thereby maintaining the desired functionality. However, rubber molded articles often have a high coefficient of friction, and friction between the rubber molded article and the application location (e.g., other components such as metal) can sometimes result in the generation of abnormal noise.

[0003] Furthermore, rubber molded articles for automobiles, such as stabilizer bushings and the like, which are fitted with metal parts, can generate abnormal noise due to a stick-slip phenomenon at the contact points with mounting hardware and the like when the automobile starts moving, brakes suddenly, turns left or right, etc., and measures to address this are needed. One approach to address this abnormal noise is to use a rubber composition containing a lubricant such as a fatty acid amide, and a self-lubricating rubber composition has been proposed that reduces the coefficient of friction by causing the lubricant to bloom on the surface of the rubber molded article (vulcanized rubber surface) (Patent Document 1).

[0004] Furthermore, as a rubber composition to be used for automobile stabilizer bushings and the like, it has been studied to significantly reduce the friction coefficient of the surface of a rubber molded article even under a wide range of temperature atmospheres (for example, 10°C to 50°C), and to suppress the generation of abnormal noise due to the stick-slip phenomenon under said wide temperature atmospheres. For example, in a rubber composition having a carbon number distribution with two peaks in the low molecular weight component region and the high molecular weight component region, if Cmax of the low molecular weight component region is C 24 ~C 29 , the Cmax of the high molecular weight component region is C 32 ~C 38 It has been proposed to blend 2 to 25 parts by weight of petroleum wax (Patent Document 2).

[0005] On the other hand, it is known that rubber compositions containing fatty acid amides as described above begin vulcanization quickly and are prone to scorching (premature vulcanization) during molding. Therefore, in order to make scorching less likely and reduce sliding resistance, it has been proposed to add an α-olefin wax having a double bond at the molecular chain end instead of adding fatty acid amides as described above (Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-100731 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-265691 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-206788 Summary of the Invention [Problem to be solved by the invention]

[0007] When a rubber molded article using the rubber composition as described above is used in sliding contact with another member (an other member such as a metal with which the rubber molded article can slide; hereinafter simply referred to as a sliding contact member), and is used in a low-temperature atmosphere such as -40°C to 5°C (particularly a low-temperature atmosphere after long-term use), there is a risk that the effect of suppressing the generation of abnormal noise due to stick-slip (hereinafter simply referred to as an abnormal noise suppression effect) may be insufficient.

[0008] For example, the rubber composition containing petroleum-based wax in Patent Document 2 does not consider the melting point of the wax, and the melting point of the microcrystalline wax used in the examples of Patent Document 2 is also 60°C or higher. Therefore, when used as a rubber composition for rubber molded products such as stabilizer bushings, there is a risk that the noise suppression effect at relatively low temperatures (for example, 5°C or lower) will be insufficient.

[0009] Although Patent Document 3 describes that the rubber composition uses an α-olefin wax having a double bond at the molecular chain terminal to adjust the scorch time, it does not consider adjusting the scorch time by changing the type or amount of vulcanization accelerator used. Furthermore, it does not consider the effect of preventing abnormal noise in low-temperature environments. Therefore, when used as a rubber composition for rubber molded products such as stabilizer bushings, there is a risk that the effect of preventing abnormal noise at relatively low temperatures will be insufficient.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a rubber molded article such as an automobile stabilizer bushing that can maintain excellent sliding properties even in a low-temperature atmosphere (for example, -40°C to 5°C, particularly in a low-temperature atmosphere after long-term use) and can achieve the desired noise suppression effect in the low-temperature atmosphere. [Means for solving the problem]

[0011] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that a rubber composition used in a rubber molded product contains natural rubber (NR) and butadiene rubber (BR) as the main rubber components, and when the total rubber components are taken as 100 parts by mass, the rubber composition contains a specific amount of paraffin wax with a relatively low melting point, and also contains specific amounts of both a fatty acid amide with a relatively low melting point and paraffin wax with a relatively low melting point, thereby obtaining a rubber molded product that can exhibit an abnormal noise suppression effect even when in sliding contact with a sliding contact object member in a low-temperature atmosphere, and have completed the present invention.

[0012] The following [1] to [5] are examples of aspects of the present invention.

[0013] [1] A rubber molding made using a rubber composition, the rubber composition containing natural rubber (NR) and butadiene rubber (BR) as main rubber components, and the natural rubber (NR) and the butadiene rubber (BR) are mixed in a ratio of natural rubber / butadiene rubber = 70 / 30~20 / 80 When the total rubber component is 100 parts by mass, the melting point 48~56℃ 20 to 300 ml of paraffin wax 60 parts by mass, and the paraffin wax and the melting point 75~81℃ The content of both fatty acid amides 40~90 A rubber molded article characterized by having a mass ratio of 1:1.

[0014] [2] The rubber composition comprises the natural rubber (NR) and the butadiene rubber (BR) in a mass ratio of natural rubber / butadiene rubber=40 / 60 to 20 / 80 and the butadiene rubber (BR) is contained in an amount of 50 to 85 parts by mass when the total rubber components are taken as 100 parts by mass, and the butadiene rubber (BR) has a cis-1,4-bond content of 90% or more.

[0015] [3] The rubber composition has a melting point of 100 parts by mass of the total rubber component. 75~81℃ The fatty acid amide content of 20~30 The rubber molded body according to [1], characterized in that it is parts by mass.

[0016] [4] The butadiene rubber (BR) has a Mooney viscosity (ML 1+4 ) is 50 to 75 R The rubber molded article according to [2],

[0017] [5] The rubber composition is a rubber molded article according to any one of [1] to [4], characterized in that it contains, as a vulcanization accelerator, at least one or more selected from the group consisting of tetrakis(2-ethylhexyl)thiuram disulfide, 2-(4'-morpholinodithio)benzothiazole, and 4,4'-dithiodimorpholine in an amount of 0.5 to 10 parts by mass, based on 100 parts by mass of the total rubber components. [Effects of the Invention]

[0018] According to the present invention, excellent sliding properties can be maintained even in low temperature atmospheres (for example, at -40°C to 5°C, particularly in low temperature atmospheres after long-term use), and the desired noise suppression effect can be obtained in such low temperature atmospheres. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a front view of a stabilizer bush used in the embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a stabilizer bushing used in the examples. [Figure 3] FIG. 1 is a schematic diagram of a Heydon friction and wear tester for explaining a method for measuring a friction coefficient used in Examples. [Figure 4] FIG. 2 is a perspective view illustrating an abnormal noise evaluation test method used in the examples. [Figure 5] FIG. 2 is a front view illustrating the abnormal noise evaluation test method used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0020] Matters relating to the implementation of the present invention will be described in detail below.

[0021] [Method for preparing rubber molded product] The rubber composition for the rubber molded article of the present invention can be prepared by kneading the essential materials, such as the rubber component, paraffin wax, and other materials, such as fatty acid amide, carbon black, vulcanization accelerator, vulcanizing agent, and vulcanization aid, using a kneading machine such as a pressure kneader, Banbury mixer, intermix mixer, or open roll.

[0022] The vulcanization conditions (vulcanization temperature and vulcanization time) for the rubber molded article of the present invention vary depending on the rubber composition and molding machine used. For example, a rubber molded article with the desired elasticity can be obtained by vulcanizing the rubber composition at a vulcanization temperature of 145 to 170°C for 3 to 60 minutes. Various molding machines can be used. For example, compression molding, in which rubber is charged into a mold and pressed under pressure, or a transfer molding machine or injection machine is used to inject the rubber composition into a mold and vulcanize it under pressure, can be used. Among these, injection molding is preferred because of its excellent productivity, such as its ability to shorten the vulcanization time.

[0023] The shape of the portion of the rubber molded article of the present invention that comes into sliding contact with a contact object (hereinafter referred to simply as the "contacted portion") also depends on the shape of the contact object. For example, if the contact object is a metal shaft, the contacted portion will have an insertion hole for inserting the metal shaft. The rubber molded article of the present invention can eliminate the deterioration of sliding properties caused by temperature environments and continuous use, and can effectively suppress an increase in frictional resistance between the contact object and the contact object. Therefore, when the contacted portion of the rubber molded article slides against the contact object, the generation of abnormal noise (stick-slip noise) due to the sliding can be suppressed, thereby eliminating problems such as a poor vehicle ride.

[0024] 1 and 2 show an example of a stabilizer bushing 1 as a rubber molded product made using the rubber composition of the present invention. As shown in the figures, the stabilizer bushing 1 is configured so that a stabilizer bar 4 is inserted and held in a hollow portion 2 having a circular cross section. Furthermore, a main body (rubber portion) 3 of the thick-walled cylindrical stabilizer bushing 1 is held in a substantially U-shaped bracket (not shown) and is configured so as to be fixed to the vehicle body via the bracket.

[0025] Because such a stabilizer bushing 1 is used by fitting a stabilizer bar 4, which is a metal part, rotational and rubbing forces are applied to the contact area between the stabilizer bar 4 and the surface of the inner hole of the stabilizer bushing 1 (the inner circumferential surface of the hollow portion 2) when the vehicle starts, brakes suddenly, turns left or right, etc., and abnormal noise is likely to occur due to the stick-slip phenomenon. Therefore, by forming the stabilizer bushing 1 from a lubricating rubber composition, which will be described in detail later, the lubricating component (paraffin wax, etc.) gradually precipitates on the surface (rubber surface) of the stabilizer bushing 1 and acts as a self-lubricant, improving the slipperiness when the stabilizer bar 4 and stabilizer bushing 1 rub against each other, thereby preventing the generation of abnormal noise.

[0026] When a general lubricating rubber composition is used, the self-lubricating component is less likely to precipitate on the rubber surface in a low-temperature atmosphere, which makes it more likely that abnormal noise will occur due to the stick-slip phenomenon. Particularly in a low-temperature atmosphere, if the self-lubricating component is scraped off by wear on the rubber surface, the self-lubricant on the rubber surface will be insufficient, making it more likely that abnormal noise will occur.

[0027] On the other hand, the rubber composition of the rubber molded product of the present invention (for example, anti-vibration rubber) can fully exhibit noise suppression effects even in low-temperature atmospheres by incorporating a relatively large amount of a specific low-melting-point wax, which is a self-lubricant. The reason why it is necessary to incorporate a large amount of the specific low-melting-point wax is unclear, but it is thought to be due to the appropriate deposition properties over a wide temperature range from -40°C to 5°C and the lubrication properties of the deposited components.

[0028] Next, each component of the rubber composition used in the rubber molded article of the present invention will be described.

[0029] [Rubber component] The rubber composition for the rubber molded product according to the present invention contains both natural rubber (NR) and butadiene rubber (BR) as the main rubber components. "Containing natural rubber (NR) and butadiene rubber (BR) as the main rubber components" means that 90% by mass or more of the total rubber components are made up of natural rubber (NR) and butadiene rubber (BR) (the total amount of natural rubber (NR) and butadiene rubber (BR) (NR + BR) is 90% by mass or more).

[0030] The ratio of natural rubber (NR) to butadiene rubber (BR) is 80 / 20 to 10 / 90 (mass ratio) in terms of natural rubber (NR) / butadiene rubber (BR) (hereinafter, natural rubber will be referred to as NR and butadiene rubber will be referred to as BR as appropriate).

[0031] When the NR / BR ratio is 80 / 20 to 10 / 90 (mass ratio), the surface deposition of low-melting-point paraffin wax (deposition on the surface of the rubber molded body) enhances the noise suppression effect in low-temperature environments. Furthermore, even if the wax that has bloomed on the surface of the rubber molded body is scraped off due to continuous friction, the wax is likely to gradually emerge from the rubber molded body to the surface in appropriate amounts, thereby maintaining the noise suppression effect. The content ratio of natural rubber (NR) to butadiene rubber (BR) is preferably NR / BR = 40 / 60 to 15 / 85 (mass ratio). As the BR ratio increases, rubber elasticity tends to be more easily maintained in low-temperature environments. However, if the NR content is too low, the kneadability (e.g., rubber kneading cohesion) may decrease during the preparation of the desired rubber composition, and the rubber strength may decrease, making it more susceptible to breakage due to repeated deformation, etc.

[0032] The rubber component may contain rubber components other than NR and BR, for example, at a ratio of 10% by mass of the total rubber components. Examples of rubber components other than NR and BR include high-styrene rubber for high hardness and reduced friction coefficient, and styrene-butadiene rubber (SBR) for improved processability. Furthermore, masterbatches containing vulcanization accelerators, sulfur, etc., can be used to improve the working environment and processability, and there is no problem even if the masterbatches contain small amounts of other rubber components such as EPDM.

[0033] The butadiene rubber (BR) used in the present invention preferably has a high cis 1,4-bond content from the viewpoint of low-temperature properties and durability (durability against repeated deformation). For example, it is preferable to use a high-cis BR having a cis 1,4-bond content of 90% or more, and more preferably a cis 1,4-bond content of 93% or more. When using this high-cis BR having a cis 1,4-bond content of 90% or more, the content can be set as appropriate, but it is preferable to set the content to 50 to 85 parts by mass, assuming that the total rubber components of the rubber composition are 100 parts by mass.

[0034] In addition, for BR with the same chemical composition, the Mooney viscosity (ML 1+4 The higher the Mooney viscosity (ML) at 100°C, the higher the molecular weight and the better the durability. 1+4 ) is preferably 50 or more. On the other hand, Mooney viscosity (ML 1+4 As the Mooney viscosity (ML 1+4 If the Mooney viscosity (ML) at 100°C is too high, the kneading processability and molding processability of the rubber composition may be easily reduced. 1+4 ) is preferably set to, for example, 75 or less. More preferably, the Mooney viscosity (ML 1+4 ) is set to 65 or less. 1+4 The content of the butadiene rubber (BR) having a molecular weight of 50 to 75 can be appropriately set, but it is preferable to set the content to 50 to 90 mass % with respect to the rubber composition.

[0035] Specific examples of such butadiene rubber include JSR BR730, JSR BR54, and JSR BR740 (all manufactured by JSR Corporation), Ubepol 390L (manufactured by Ube Industries, Ltd.), and BUNA CB21, CB22, and CB1221 (all manufactured by Arlanxeo).

[0036] [Wax component] The rubber composition for the rubber molded product of the present invention contains 20 to 70 parts by mass of paraffin wax having a melting point of 45 to 57° C. per 100 parts by mass of the total rubber components as described above. When the paraffin wax has a melting point within this range, it is highly effective in suppressing noise caused by stick-slip in a low-temperature atmosphere.

[0037] Furthermore, the total content of the paraffin wax having a melting point of 45 to 57°C and the fatty acid amide having a melting point of 35 to 85°C must be 30 to 100 parts by mass. That is, as the wax component, 30 to 70 parts by mass of paraffin wax having a melting point of 45 to 57°C may be used alone, or 30 to 100 parts by mass of a combined paraffin wax having a melting point of 45 to 57°C and a fatty acid amide having a melting point of 35 to 85°C may be used. Preferably, the total content of the paraffin wax having a melting point of 45 to 57°C and the fatty acid amide having a melting point of 35 to 85°C is 40 to 80 parts by mass.

[0038] The paraffin wax used in the present invention is not particularly limited as long as it has a melting point in the range of 45 to 57°C, but from the viewpoint of ease of handling, paraffin wax in a granular or particulate form is preferably used.

[0039] Examples of paraffin waxes having a melting point of 45 to 57°C include Paraffin Wax-115, Paraffin Wax-120, Paraffin Wax-125, and Paraffin Wax-130 (all manufactured by Nippon Seiro Co., Ltd.).

[0040] Paraffin wax is sometimes used in an amount of, for example, 5 parts by mass or less per 100 parts by mass of the total rubber component to improve the static ozone resistance of diene rubber. When paraffin wax is used to improve ozone resistance, even if it is used in an amount of 3 parts by mass or more (even when considering durability, it is used in an amount of 5 parts by mass or less), the expected improvement in ozone resistance is not achieved. When improving the ozone resistance of automotive anti-vibration rubber, taking into account the fact that it will be exposed to high-temperature atmospheres, paraffin wax with a melting point of 60°C or higher is usually used.

[0041] In the rubber composition for the rubber molded article of the present invention, paraffin wax having a melting point of more than 57° C. may also be used in an amount of, for example, 5 parts by mass or less for the purpose of improving ozone resistance.

[0042] As described above, the rubber composition for the rubber molded article of the present invention contains a total content of paraffin wax having a melting point of 45 to 57°C and fatty acid amide having a melting point of 35 to 85°C. 30 As described above, the wax component is a paraffin wax having a melting point of 45 to 57°C. 30 However, it is preferable to use a fatty acid amide together with the paraffin wax, since this facilitates the wax component to precipitate more quickly on the surface of the rubber molded article. The content of the fatty acid amide having a melting point of 35 to 85°C is preferably 10 to 30 parts by mass.

[0043] Fatty acid amides with a melting point of 35 to 85° C. are likely to precipitate on the surface of rubber molded articles even in low-temperature environments, and can sufficiently contribute to reducing friction even in the low-temperature range. The content of the fatty acid amides with a melting point of 35 to 85° C. can also be appropriately set, but it is preferable to set the content to 10 to 40 parts by mass, assuming that the total rubber components of the rubber composition are 100 parts by mass.

[0044] Examples of fatty acid amides having a melting point of 35 to 85°C include N-oleyl oleamide (melting point 35°C), oleamide (melting point 75°C), erucamide (melting point 81°C), N-stearyl oleamide (melting point 67°C), and N-stearyl erucamide (melting point 74°C). A melting point of 50 to 85°C is preferred. If the melting point is lower than 50°C, there is a risk of lumps of fatty acid amide forming, for example, during transportation. Among these, oleamide (melting point 75°C) and erucamide (melting point 81°C) are preferred because they tend to precipitate in a relatively low-temperature atmosphere.

[0045] Furthermore, the rubber composition for the rubber molded article of the present invention may contain a fatty acid amide having a melting point exceeding 85° C., for the purpose of improving the durability of sliding when exposed to a high-temperature atmosphere for a long period of time. Examples of fatty acid amides having a melting point exceeding 85° C. include lauric acid amide (melting point 87° C.), palmitic acid amide (melting point 100° C.), stearic acid amide (melting point 101° C.), hydroxystearic acid amide (melting point 107° C.), N-stearylstearic acid amide (melting point 95° C.), ethylene bisoleic acid amide (melting point 119° C.), ethylene biserucic acid amide (melting point 120° C.), hexamethylene bisoleic acid amide (melting point 110° C.), N,N'-dioleyl adipamide (melting point 118° C.), and N,N'-dioleyl sebacate amide (melting point 113° C.). Examples of fatty acid amides with relatively high melting points include methylene bisstearic acid amide (melting point 142°C), ethylene bislauric acid amide (melting point 157°C), ethylene bisstearic acid amide (melting point 145°C), ethylene bishydroxystearic acid amide (melting point 145°C), ethylene bisbehenic acid amide (melting point 142°C), hexamethylene bisstearic acid amide (melting point 140°C), hexamethylene bisbehenic acid amide (melting point 142°C), hexamethylene bishydroxystearic acid amide (melting point 135°C), and N,N'-distearyl adipamide (melting point 141°C). The content of these fatty acid amides with relatively high melting points is set, for example, to 10 parts by mass or less per 100 parts by mass of the total rubber component. Adding these fatty acid amides in amounts exceeding 10 parts by mass is undesirable because the effect of improving sliding properties remains almost unchanged and may actually lead to increased material costs.

[0046] [Wax components other than fatty acid amides and paraffin wax] In addition to the wax components described above, the rubber composition of the rubber molded article of the present invention may contain up to 5 parts by mass of, for example, microcrystalline wax or polyethylene wax. Microcrystalline wax is a wax that is sometimes mixed with paraffin wax to improve the ozone resistance and processability of diene rubbers, but it is known to have a relatively higher melting point than paraffin wax. Microcrystalline wax is primarily composed of isoparaffin wax with small amounts of normal paraffin and naphthene, but is classified differently from paraffin wax due to differences in its manufacturing method and melting point.

[0047] [Vulcanization chemicals (vulcanizing agents, vulcanization accelerators, and vulcanization retarders)] The vulcanization chemicals described in the description of the rubber composition of the rubber molded article of the present invention refer to all chemicals that contribute to the vulcanization reaction, such as vulcanizing agents, vulcanization accelerators, and vulcanization retarders (retarders). Some substances classified as vulcanization accelerators also act as vulcanizing agents, making it difficult to distinguish between vulcanization accelerators and vulcanizing agents. For this reason, in the following description, for convenience, vulcanization accelerators and vulcanizing agents may be simply referred to as vulcanization chemicals.

[0048] As the vulcanizing agent used in the rubber composition of the rubber molded article of the present invention, known vulcanizing agents can be used, and vulcanization methods that can be used include vulcanization with sulfur or sulfur-based compounds, resin vulcanization, quinoid vulcanization, bismaleimide vulcanization, organic peroxide vulcanization, etc. Among these, vulcanization using sulfur or sulfur-based compounds is sometimes preferred because it provides excellent durability to the vibration-proof rubber.

[0049] Specific examples of sulfur or sulfur-based compounds include sulfur, sulfur chloride, 2-(4'-morpholinodithio)benzothiazole, 4,4'-dithiodimorpholine, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetrabenzylthiuram disulfide, and dipentamethylenethiuram tetrasulfide. Among these, sulfur is preferably contained in an amount of 0.1 to 0.8 parts by mass. It is known that sulfur vulcanization of rubber is excellent in durability, but a high sulfur content results in poor heat resistance. Therefore, when considering both heat resistance and durability, the sulfur content is preferably in the range of 0.1 to 0.8 parts by mass.

[0050] As the vulcanization chemicals, at least one or more selected from the group consisting of tetrakis(2-ethylhexyl)thiuram disulfide, 2-(4'-morpholinodithio)benzothiazole, and 4,4'-dithiodimorpholine are preferably contained in an amount of 0.5 to 10 parts by mass, more preferably 1 to 10 parts by mass.

[0051] The "0.5 to 10 parts by mass of one or more selected from the group consisting of tetrakis(2-ethylhexyl)thiuram disulfide, 2-(4'-morpholinodithio)benzothiazole, and 4,4'-dithiodimorpholine" means that the total amount of tetrakis(2-ethylhexyl)thiuram disulfide, 2-(4'-morpholinodithio)benzothiazole, and 4,4'-dithiodimorpholine is 0.5 to 10 parts by mass. As described above, the rubber composition of the present invention contains a total amount of fatty acid amide of 10 parts by mass or more per 100 parts by mass of the rubber component. Such a rubber composition containing a relatively large amount of fatty acid amide tends to have a faster vulcanization rate and a shorter scorch time.

[0052] When the total amount of tetrakis(2-ethylhexyl)thiuram disulfide, 2-(4'-morpholinodithio)benzothiazole and 4,4'-dithiodimorpholine is 0.5 to 10 parts by mass, a rubber composition having excellent heat resistance and excellent scorch resistance (less susceptible to scorch) can be easily obtained, which is preferable.

[0053] When a sulfur compound is used as a vulcanizing agent, it is preferable to use a vulcanization accelerator in combination. Specific examples of the vulcanization accelerator include sulfenamide compounds such as N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and N,N-diisopropyl-2-benzothiazole sulfenamide, thiazole compounds such as 2-mercaptobenzothiazole, 2-(2,4-dinitrophenyl)mercaptobenzothiazole, 2-(2,6-diethyl-4-morpholinothio)benzothiazole, and dibenzothiazyl disulfide, and diphenylguanidine compounds such as methyl ... Examples of the thiuram compounds include guanidine compounds such as thiuram nitrile, triphenylguanidine, diorthonitrile guanidine, orthonitrile biguanide, and diphenylguanidine phthalate, and thiuram compounds such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetrabenzylthiuram disulfide, and dipentamethylenethiuram tetrasulfide.

[0054] Furthermore, in order to adjust the vulcanization rate, vulcanization retarders (scorch inhibitors) such as N-cyclohexylthiophthalimide and N-phenyl-N-(trichloromethylthio)benzenesulfonamide can be preferably used.

[0055] [Carbon black] There are no particular limitations on the carbon black used in the rubber composition for the rubber molded product of the present invention, and for example, commercially available carbon black can be used. 2The carbon black having a specific surface area of ​​38 to 90 parts by mass is preferably contained. The nitrogen adsorption specific surface area is an index of the particle size of carbon black, and a large nitrogen adsorption specific surface area indicates a small particle size. When carbon black within this range is used, it becomes easier to obtain a rubber molded article (with little deformation) with good reinforcement (durability), low friction, and low compression set. Examples of such carbon black include carbon blacks known as rubber furnace blacks, such as ISAF grade, ISAF-HS grade, ISAF-LS grade, HAF grade, HAF-HS grade, HAF-LS grade, MAF grade, MAF-HS grade, and FEF grade. Furthermore, carbon black for coloring and conductive carbon blacks with a nitrogen adsorption specific surface area of ​​38 to 120 m are also available. 2 / g, can be used without any problems. Examples include Toka Black #7360SB, Toka Black #7270SB, Toka Black #4500 (all manufactured by Tokai Carbon Co., Ltd.), MA8, MA230, MA220 (all manufactured by Mitsubishi Chemical Corporation), SB735, SBSB285, SB335, SB605, SB625 (all manufactured by Asahi Carbon Co., Ltd.), etc.

[0056] In addition to the carbon black, a carbon black with a nitrogen adsorption specific surface area of ​​38m is also used for the purpose of adjusting hardness and processability. 2 It is possible to use carbon black with a nitrogen adsorption specific surface area of ​​38 m / g. 2 The carbon black having a molecular weight of less than 1 / g is preferably used in an amount of, for example, 20 parts by mass or less per 100 parts by mass of the rubber component.

[0057] [Vulcanization aid] When a sulfur compound is used as a vulcanizing agent, it is preferable to use it in combination with a vulcanization aid such as zinc oxide (ZnO), zinc oxide complex, stearic acid, zinc stearate, etc. These vulcanization aids may be used alone or in combination of two or more kinds.

[0058] Here, composite zinc oxide is known to have a layer of zinc oxide (zinc oxide) on the surface and an inorganic metal salt inside as a core component, and examples include the META-Z L series (META-Z L40, L50, L60) manufactured by Inoue Lime Industry Co., Ltd.

[0059] The amount of zinc oxide or composite zinc white is, for example, 3 parts by mass or more and 15 parts by mass or less per 100 parts by mass of the rubber component.

[0060] The amount of stearic acid or zinc stearate is preferably 0.1 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the rubber component.

[0061] [Anti-aging agent] The rubber composition for the rubber molded article of the present invention preferably contains an antioxidant. The diene rubber (natural rubber, butadiene rubber) used in the present invention does not have high ozone resistance or heat resistance as a rubber component, so it is preferable to appropriately improve it with a known antioxidant. Examples of antioxidants include carbamate-based antioxidants, phenylenediamine-based antioxidants, phenol-based antioxidants, diphenylamine-based antioxidants, quinoline-based antioxidants, imidazole-based antioxidants, and waxes. These can be used alone or in combination of two or more types.

[0062] The content of the antioxidant is preferably in the range of 1 to 15 parts by mass, more preferably 3 to 10 parts by mass, per 100 parts by mass of the rubber component.

[0063] [Filler] The rubber composition for the rubber molded article of the present invention may contain a filler for the purpose of adjusting hardness and improving processability. Fillers that are commonly used in rubber compositions, such as silica (wet silica, dry silica, colloidal silica, etc.), calcium carbonate, clay, and talc, can be used as the filler. These fillers can be used alone or in combination of two or more.

[0064] [Process oil] The rubber composition for the rubber molded article of the present invention may contain a process oil for the purpose of adjusting hardness and improving processability. Examples of process oils include naphthenic oils, paraffinic oils, and aromatic oils. These may be used alone or in combination of two or more.

[0065] [Processing aids] The rubber composition for the rubber molded article of the present invention may contain a processing aid for the purpose of improving processability.

[0066] The processing aid can be a compound that is commonly used in rubber processing. Specific examples include higher fatty acids such as ricinoleic acid, stearic acid, palmitic acid, and lauric acid, salts of higher fatty acids such as barium stearate, zinc stearate, and calcium stearate, and esters of higher fatty acids such as ricinoleic acid, stearic acid, palmitic acid, and lauric acid. These can be used alone or in combination of two or more.

[0067] [Coupling agent] In the rubber composition of the rubber molded article of the present invention, a coupling agent for carbon black or a silane coupling agent can be used to adjust vibration characteristics. Examples of coupling agents for carbon black include hydrazide compound coupling agents, sulfide compound coupling agents, and pyrazolone compound coupling agents. Examples of silane coupling agents include mercapto silane coupling agents, sulfide silane coupling agents, amine silane coupling agents, epoxy silane coupling agents, and vinyl silane coupling agents. These can be used alone or in combination of two or more. Among the silane coupling agents, mercapto silane coupling agents and sulfide silane coupling agents are particularly preferred. These can be used alone or in combination of two or more. [Example]

[0068] Examples of the present invention (Examples 1 to 10) are shown below, but the present invention is not limited to these examples.

[0069] <Creating rubber molded products> The rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8 shown in Tables 1 and 2 below were molded (vulcanized for 8 minutes at a temperature of 160°C) into the shape of the stabilizer bushing 1 shown in Figure 1 using an injection molding machine with a clamping force of 50 tons (approximately 490 kN), thereby obtaining rubber molded products for evaluation (stabilizer bushings; hereinafter referred to as evaluation molded products) in Tables 3 and 4 below.

[0070] <Preparation of rubber composition> The rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8 were prepared by blending and kneading various materials in the proportions shown in Tables 1 and 2. The kneading was carried out by first kneading the materials other than the vulcanizing agent and vulcanization accelerator for 5 minutes using a Banbury mixer to obtain a kneaded mixture. Next, the vulcanizing agent and vulcanization accelerator were added to the kneaded mixture while cooling it using an open roll (cooling was carried out by setting the cooling water temperature in the open roll to about 20°C), and kneading was carried out for 5 minutes to obtain each rubber composition.

[0071] [Table 1]

[0072] [Table 2]

[0073] The various materials listed in Tables 1 and 2 are as follows: Natural rubber: SVR CV60 Butadiene rubber-1; cis 1,4-bond content 96, Mooney viscosity (ML 1+4 )63, ARLANXEO Co., Ltd. "BUNA-CB21" Butadiene rubber-2; cis 1,4-bond content 96, Mooney viscosity (ML 1+4 )44, JSR Corporation "BR-01" Paraffin wax-1; melting point 48, "Paraffin Wax-115" manufactured by Nippon Seiro Co., Ltd. Paraffin wax-2; melting point 53, "Paraffin Wax-125" manufactured by Nippon Seiro Co., Ltd. Paraffin wax-3; melting point 56, "Paraffin Wax-130" manufactured by Nippon Seiro Co., Ltd. Paraffin wax-4, melting point 65, "Ozoace-0100" manufactured by Nippon Seiro Co., Ltd. Microcrystalline wax; melting point 75, Nippon Seiro Co., Ltd. "Hi-Mic-1070" Fatty acid amide-1: oleic acid amide, melting point 75°C, "Diamid O-200" manufactured by Mitsubishi Chemical Corporation Fatty acid amide-2: Erucic acid amide, melting point 81°C, Mitsubishi Chemical Corporation "Diamid L-200" Fatty acid amide-3; stearic acid amide, melting point 101°C, "Diamid 200" manufactured by Mitsubishi Chemical Corporation Zinc oxide: Sakai Chemical Industry Co., Ltd. "Zinc oxide type 2" Stearic acid: "Camellia Stearate" manufactured by Nippon Oil & Fats Co., Ltd. Antioxidant-1: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, "Vulkanox 4020" manufactured by LANXESS Anti-aging agent - 2;2-mercaptobenzimidazole, "Nocrac MB" manufactured by Ouchiko Co., Ltd. Carbon black-1; nitrogen adsorption specific surface area 75m 2 / g (HAF grade), "VULCAN 3D" manufactured by Cabot Japan Co., Ltd. Carbon black-2; nitrogen adsorption specific surface area 47m 2 / g (MAF grade), "Niteron #10" manufactured by Nippon Steel Carbon Co., Ltd. Oil: ENEOS Corporation's "Crisef Oil H56" Vulcanization chemicals-1: Sulfur, Tsurumi Chemical Industry Co., Ltd. "Kinka Brand Fine Sulfur 200 Mesh" Vulcanization chemicals: 2, 2-(4'-morpholinodithio)benzothiazole, "Noccela MDB-P" manufactured by Ouchiko Chemical Co., Ltd. Vulcanization chemicals - 3;4,4'-dithiodimorpholine, "Actor R" manufactured by Kawaguchi Chemical Co., Ltd. Vulcanization chemicals-4: Tetrakis(2-ethylhexyl)thiuram disulfide, "Noccela TOT-N" manufactured by Ouchi Shinko Chemical Co., Ltd. Vulcanization chemicals-5: Tetramethylthiuram disulfide, "Noccela TT-P" manufactured by Ouchi Shinko Chemical Co., Ltd. Vulcanization chemicals-6: N-cyclohexyl-2-benzothiazolylsulfenamide, "Noccela CZ-G" manufactured by Ouchiko Chemical Co., Ltd. Vulcanization chemicals - 7; 1,3-diphenylguanidine, "Noccela D" manufactured by Ouchiko Chemical Co., Ltd. <<Creating vulcanized rubber sheets for measuring rubber properties>> The rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8 shown in Tables 1 and 2 were subjected to compression molding using a 2 mm sheet mold with a cavity having a thickness of 2 mm, and vulcanization molding was carried out at 160°C for a vulcanization time of (ct90+5) to obtain vulcanized rubber sheets having a thickness of 2 mm (hereinafter simply referred to as evaluation rubber sheets).

[0074] Using the rubber compositions, evaluation rubber sheets, and evaluation molded articles of Examples 1 to 10 and Comparative Examples 1 to 8 obtained as described above, the properties were evaluated according to the following criteria, and the results are shown in Tables 3 and 4 below. The evaluation methods for each evaluation item of Examples 1 to 10 and Comparative Examples 1 to 8 are as follows.

[0075] ≪Workability≫ The kneadability (so-called rubber kneading cohesiveness, etc.) during preparation was observed and evaluated for the rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8. In the evaluation and judgment of this processability (◯ and × in Tables 3 and 4), the kneadability of each rubber composition was compared, and ◯ was indicated when the kneadability was relatively high, and × was indicated when the kneadability was relatively low.

[0076] <<Vulcanization characteristic test - Measurement of vulcanization speed (unvulcanized test)>> For the rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8, a vulcanization curve was drawn for 20 minutes using a V-type Curelastometer in accordance with JIS K6300-2 at a measurement temperature of 150°C, an amplitude angle of ±1°, and a frequency of 100 cpm, and the tC(10) and tC(90) values ​​were calculated from the vulcanization curve.

[0077] <Moony Scoach Time (Moony Scoach Exam)> For the rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8, a Mooney viscometer was used in accordance with JIS K 6300-1 using an L-type rotor. The minimum Mooney viscosity at a measurement temperature of 125°C was defined as Vm, and the time t5 required for the viscosity to rise by 5M from Vm was measured, and this t5 was defined as the Mooney scorch time.

[0078] In the evaluation and judgment of this Mooney scorch test, when the Mooney scorch time was shorter than 12 minutes, it was deemed that there was a risk of early vulcanization and that there was concern about a decrease in productivity as a rubber molded product (a bushing for preventing abnormal noise) (determined as unsuitable) and was rated as ×. On the other hand, when the Mooney scorch time was 12 minutes or more, it was determined that the material was suitable for a rubber molded product and was rated as ○.

[0079] <Vulcanized rubber hardness> Each of the evaluation rubber sheets obtained using the rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8 was cut into a predetermined shape to prepare a sample (vulcanized rubber), and the hardness HA was measured using a Type A durometer in accordance with JIS K 6253-3.

[0080] <Tensile properties (tensile test)> Each evaluation rubber sheet obtained using the rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8 was punched out with a JIS No. 3 dumbbell, and the tensile strength at break (Tb) and elongation at break (Eb) were measured in accordance with JIS K 6251.

[0081] In the evaluation of this tensile test, a breaking strength (Tb) of 14 MPa or more was rated as "Good." On the other hand, if it was less than 14 MPa, it was deemed that the rubber strength was low and that the molded rubber product would be prone to breaking when a strong force was applied (determined to be non-compliant), and was rated as "Poor."

[0082] <Friction coefficient> Each evaluation rubber sheet obtained using the rubber compositions of Examples 1 to 10 and Comparative Examples 1 to 8 was cut into a 50 mm x 10 mm piece to prepare sample S. After leaving the sample S in an atmosphere at 23°C for 24 hours, the friction coefficient was measured using a Heidon friction and wear tester 6 shown in FIG. 4. Specifically, sample S, measuring 50 mm in the moving direction, 10 mm in width, and 2 mm in thickness, was attached to a movable stage 61 that could move on a fixed stage 60 as shown in FIG. 4. When the movable stage 61 was moved 16.7 mm in the planar direction (the direction of the black arrow in the figure) at a speed of 16.7 mm per second, the force (F) applied to a counter member 63 that was fixed to the load cell 62 and could not move was measured using the load cell 62. Reference numeral 64 denotes an operating lever that adjusts the position of the counter member 63 with the fulcrum between the load cell 62 and the counter member 63 as the fulcrum, and reference numeral 65 denotes a balancer attached between the load cell 62 and the fulcrum.

[0083] Here, the counter member 63 used was made of stainless steel with a contact surface of 10 mm x 10 mm and a surface roughness (Rmax) of 5 to 10 μm. A load (weight) W of 100 g was placed on the counter member 63. The friction coefficient μ is calculated by the formula F = μM. The peak friction coefficient obtained first after the movable base 61 started to move was defined as the static friction coefficient (μs), and the average friction coefficient obtained over the subsequent 16.7 mm movement was defined as the kinetic friction coefficient (μd).

[0084] <Rubber molded product (stabilizer bush) evaluation (noise evaluation test)> [Evaluation of abnormal noise during initial product development] As shown in Figures 1 and 2, the molded evaluation product of stabilizer bushing 1 (outer dimensions 43 mm) having a hollow portion 2 (diameter 18 mm) was measured for the presence or absence of abnormal noise by simulating the initial state of the product using the method described below.

[0085] First, as shown in Figures 4 and 5, a 19 mm diameter iron bar 4 with an electrocoating (cation coating) surface was inserted into the hollow portion 2 provided in the main body 3 of the stabilizer bush 1 (molded product for evaluation), and then the stabilizer bush 1 was fixed to a fixed base 50 in a state where it was compressed radially through the hollow portion 2 (in the direction perpendicular to the axis indicated by the arrow in Figure 5) using an approximately U-shaped bracket 5.

[0086] Next, the iron bar 4 was rotated (input) axially in the torsional direction (the torsional direction indicated by the arrow in Fig. 5) by ±15° at a frequency of 1 Hz. This axial rotation was performed for 5 minutes in a low-temperature atmosphere (in this example, temperatures of 0°C, -10°C, -20°C, -30°C, and -40°C), and the presence or absence of abnormal noise was measured.

[0087] In judging the abnormal noise evaluation simulating the initial stage of the product, if no abnormal noise was generated within 5 minutes from the start of the shaft rotation, it was marked as ◯, and if abnormal noise was generated, it was marked as ×.

[0088] [Evaluation of abnormal noise after product durability] When the result of the measurement of the above item [evaluation of abnormal noise in the initial stage of the product] was judged to be good, the presence or absence of abnormal noise was measured by simulating the product after endurance using the method described below.

[0089] First, immediately after measuring the above item [initial product noise evaluation], the iron bar 4 was rotated axially for 168 hours under the same axial rotation conditions as in the previous measurement (torsion direction ±15°, frequency 1 Hz, low temperature atmosphere). After that, water was injected into the gap between the hollow portion 2 and the iron bar 4, and the iron bar 4 was rotated axially for another 5 minutes, and the presence or absence of abnormal noise was measured.

[0090] The evaluation of abnormal noise simulating the endurance of the product is the same as the above item (evaluation of abnormal noise in the initial stage of the product).

[0091] <Overall Judgment> When all the evaluation items were judged as ◯, the overall evaluation was ◯, and when even one evaluation included an ×, the overall evaluation was ×.

[0092] [Table 3]

[0093] [Table 4]

[0094] From the compounding ratios of each rubber composition shown in Tables 1 and 2 and the results shown in Tables 3 and 4, the following can be said.

[0095] First, in Examples 1 to 10, the rubber compositions used had a natural rubber (NR) / butadiene rubber (BR) ratio of 80 / 20 to 10 / 90, contained 20 to 70 parts by mass of paraffin wax with a melting point of 45 to 57°C, and contained 30 to 100 parts by mass of the combined content of paraffin wax with a melting point of 45 to 57°C and fatty acid amide with a melting point of 35 to 85°C (hereinafter referred to as the present invention category). All evaluation items for Examples 1 to 10 were rated as good, and the overall rating was good.

[0096] On the other hand, when a rubber composition outside the scope of the present invention was used, that is, in Comparative Examples 1 to 8, at least one of the evaluation items was marked "x", resulting in an overall rating of "x".

[0097] Specifically, Comparative Examples 1 and 2, in which the rubber compositions used contained only fatty acid amide-2 without paraffin wax, had low friction coefficients at room temperature, but generated abnormal noise in the abnormal noise evaluation test at low temperatures either at the initial stage of production or after product durability. If abnormal noise was generated in the abnormal noise evaluation test at the initial stage of production, the molded rubber product was deemed unsuitable, and the abnormal noise evaluation test after product durability was not conducted (the same applies below).

[0098] In addition, Comparative Example 3, in which the total amount of paraffin wax and fatty acid amide in the rubber composition used was less than 30 parts by mass, generated abnormal noise in an abnormal noise evaluation test conducted under a low-temperature atmosphere in the initial stage of the product. Comparative Examples 4 and 5, in which the rubber composition used contained high-melting-point paraffin wax-4 or microcrystalline wax, and Comparative Example 6, in which the rubber composition used contained a combination of high-melting-point fatty acid amide and paraffin wax-2, generated abnormal noise in an abnormal noise evaluation test conducted under a low-temperature atmosphere in the initial stage of the product. Comparative Example 7, in which the rubber composition used did not contain natural rubber (NR) but only butadiene rubber (BR) in the rubber component, had poor rubber kneading processability and, further, low rubber strength in a tensile test, and was determined to be unsuitable for use as a rubber molded product (for this reason, an abnormal noise evaluation test was not conducted for Comparative Example 7). Comparative Example 8, in which the rubber composition used did not contain butadiene rubber (BR), generated abnormal noise in an abnormal noise evaluation test conducted under a low-temperature atmosphere in the initial stage of the product.

[0099] In Example 5, in which the wax component of the rubber composition used contained only 50 parts by mass of paraffin wax, and in Example 6, in which the ratio of natural rubber (NR) to butadiene rubber (BR) in the rubber composition used was NR / BR = 70 / 30, good results were obtained in all evaluation items, and although there was a tendency for the friction coefficient to be slightly higher at room temperature, there was no particular problem. In addition, the Mooney viscosity (ML 1+4 Example 6, which is 44, obtained good results in all evaluation items, and although the rubber strength tends to be slightly lower than that of Example 1, there is no particular problem.

[0100] Therefore, as in the rubber composition for the rubber molded article of the present invention, which uses natural rubber (NR) and butadiene rubber (BR) as the main rubber components, and the ratio of natural rubber (NR) to butadiene rubber (BR) is 80 / 20 to 10 / 90 in terms of NR / BR ratio, and contains 20 to 70 parts by mass of paraffin wax having a melting point of 45 to 57°C per 100 parts by mass of the total rubber components, and the total content of the paraffin wax and fatty acid amide having a melting point of 35 to 85°C is within the range of 40 to 100 parts by mass, it is possible to obtain a rubber molded article that has excellent noise suppression effects even when used in a low-temperature atmosphere (especially a low-temperature atmosphere after long-term use).

[0101] In comparison with rubber molded articles made using conventional rubber compositions (e.g., rubber compositions as disclosed in Patent Documents 1 to 3), the rubber molded article of the present invention can exhibit excellent noise suppression effects even when used in low-temperature environments where noise due to friction is likely to occur, and can maintain excellent noise suppression effects even in low-temperature environments after long-term use or after repeated friction. [Industrial Applicability]

[0102] The rubber molded article according to the present invention has excellent sliding properties even when contact or rubbing occurs between the rubber portion and a sliding contact object, and is less likely to generate abnormal noise during contact or rubbing, particularly in a low-temperature atmosphere, even after long-term sliding, making it less likely to generate abnormal noise due to rubbing.

[0103] For example, rubber molded products that are often exposed to the outside air, such as stabilizer bushings, are sometimes used in cold regions or in winter in low-temperature environments, such as -40° C. to 5° C. Therefore, the rubber molded article according to the present invention can be suitably used as automotive rubber molded products that may be subject to friction for a long period of time and that can be used in low-temperature environments, such as stabilizer bushings. [Explanation of symbols]

[0104] 1...Stabilizer bush 2...Hollow part 3...Main body (rubber part) 4...Stabilizer bar 5...Bracket

Claims

1. A rubber molded article made using a rubber composition, the rubber composition having natural rubber (NR) and butadiene rubber (BR) as main rubber components, and containing the natural rubber (NR) and the butadiene rubber (BR) in a mass ratio of natural rubber / butadiene rubber = 70 / 30 to 20 / 80, and containing 20 to 60 parts by mass of paraffin wax having a melting point of 48 to 56°C, and containing 40 to 90 parts by mass of both the paraffin wax and a fatty acid amide having a melting point of 75 to 81°C, when the total rubber component is taken as 100 parts by mass.

2. The rubber composition contains the natural rubber (NR) and the butadiene rubber (BR) in a mass ratio of natural rubber / butadiene rubber = 40 / 60 to 20 / 80, and contains 50 to 85 parts by mass of the butadiene rubber (BR) when the total rubber component is 100 parts by mass, and the butadiene rubber (BR) has a cis-1,4-bond content of 90% or more.

3. The rubber molded article according to claim 1, characterized in that the rubber composition contains 20 to 30 parts by mass of the fatty acid amide having a melting point of 75 to 81°C when the total rubber component is 100 parts by mass.

4. The butadiene rubber (BR) has a Mooney viscosity (ML １＋４ 3. The rubber molded article according to claim 2, wherein the modulus of elasticity is 50 to 75.

5. The rubber composition of any one of claims 1 to 4, characterized in that it contains, when the total rubber component is taken as 100 parts by mass, 0.5 to 10 parts by mass of at least one vulcanization accelerator selected from the group consisting of tetrakis(2-ethylhexyl)thiuram disulfide, 2-(4'-morpholinodithio)benzothiazole, and 4,4'-dithiodimorpholine.

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