Rubber composition for rim cushion

Abstract

The present invention provides a rubber composition for rim cushions, the rubber composition being improved in terms of low possibility of heat generation, while maintaining good hardness, elongation at break and wear resistance and achieving a good balance among these properties at high levels. According to the present invention, silica having a CTAB adsorption specific surface area of 60 m2 / g to 100 m2 / g, carbon black having a CTAB adsorption specific surface area of 60 m2 / g to 160 m2 / g, and a sulfur-containing silane coupling agent are added to a diene rubber that contains 35% by mass to 65% by mass of an isoprene rubber and 35% by mass to 65% by mass of a butadiene rubber; at least one terminally modified butadiene rubber for silica is used as the butadiene rubber; the addition amount of the silica relative to 100 parts by mass of the diene rubber is set to 10 parts by mass or more; the total addition amount of the silica and the carbon black relative to 100 parts by mass of the diene rubber is set to more than 50 parts by mass; and the product of the stress M100 at 100% elongation and the hardness is set to 150 or more.

Description

Technical Field

[0001] The present invention relates to a rubber composition for rim cushioning mainly intended for use in a rim cushioning rubber layer of a tire.

Background Art

[0002] In pneumatic tires, it is required to improve fuel consumption performance during running in order to reduce the environmental load. Therefore, heat generation of the rubber composition constituting each part of the pneumatic tire is suppressed. In recent years, in order to further improve fuel consumption performance, for example, it has also been required to suppress heat generation of the rubber composition constituting the rim cushioning rubber layer of a pneumatic tire.

[0003] As an index of the heat generation property of a rubber composition, generally, tan δ at 60°C (hereinafter referred to as "tan δ(60°C)") measured by dynamic viscoelasticity measurement is used, and the smaller the tan δ(60°C) of the rubber composition, the smaller the heat generation property. And, as a method of reducing tan δ(60°C) of the rubber composition, for example, reducing the blending amount of a filler such as carbon black or increasing the particle size of carbon black can be mentioned. Alternatively, it has also been proposed to blend silica having a large particle size (for example, Patent Document 1 teaches that low heat generation is achieved by blending silica having a large particle size in a rubber composition for a sidewall). However, with these methods, sufficient rubber hardness is not always obtained, and there are concerns about the effects on the elongation at break and abrasion resistance required for the rubber composition for rim cushioning. Therefore, in the rubber composition for rim cushioning, further measures are required to improve low heat generation property (tan δ(60°C)) while maintaining good elongation at break and abrasion resistance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a rubber composition for a rim cushion that improves low heat generation while maintaining good elongation at break and abrasion resistance, and enables these performances to be highly balanced and compatible with each other.

Means for Solving the Problems

[0006] The rubber composition for a rim cushion of the present invention that achieves the above object is a diene rubber containing 35% to 65% by mass of an isoprene rubber and 35% to 65% by mass of a butadiene rubber, and has a CTAB adsorption specific surface area of 60 m 2 / g to 100 m 2 / g of silica, carbon black having a CTAB adsorption specific surface area of 60 m 2 / g to 160 m 2 / g, and a sulfur-containing silane coupling agent are compounded. The butadiene rubber contains at least one terminal-modified butadiene rubber for silica. The compounding amount of the silica with respect to 100 parts by mass of the diene rubber is 10 parts by mass or more, and the total compounding amount of the silica and the carbon black with respect to 100 parts by mass of the diene rubber exceeds 50 parts by mass, and the product of the stress M100 [unit: MPa] at 100% elongation at room temperature and the hardness at room temperature is 150 or more.

Effects of the Invention

[0007] The rubber composition for a rim cushion of the present invention has the above-mentioned composition, and since the stress M100 at 100% elongation and the hardness satisfy the above-mentioned relationship, it improves low heat generation while maintaining good elongation at break and abrasion resistance, and these performances can be highly balanced and compatible with each other. In particular, the CTAB adsorption specific surface area is 60 m 2 / g to 100 m 2By using silica with a large particle size, which is / g, the elongation at break can be improved. While using a terminal-modified butadiene rubber for silica, the elongation at break can be maintained well, and the low heat build-up property can be made excellent. By these synergistic effects, the low heat build-up property (tanδ at 60°C) can be improved while maintaining good elongation at break and abrasion resistance. Also, when the product of the stress M100 at 100% elongation and the hardness is 150 or more, it becomes possible to well exhibit the physical properties required for a rim cushion rubber such as abrasion resistance.

[0008] In the present invention, the proportion of the terminal-modified butadiene rubber for silica contained in the butadiene rubber is preferably 15% by mass to 100% by mass. The total blending amount of silica and carbon black with respect to 100 parts by mass of the diene rubber is preferably 80 parts by mass or less. Further, sulfur and a vulcanization accelerator are blended with respect to the diene rubber, and the total blending amount of sulfur and the vulcanization accelerator with respect to 100 parts by mass of the diene rubber is preferably 3.5 parts by mass or more.

[0009] The rubber composition for a rim cushion rubber of the present invention can be suitably used for the rim cushion rubber layer of a tire. A tire provided with a rim cushion rubber layer made of the rubber composition for a rim cushion of the present invention can reduce the rolling resistance and improve the low fuel consumption performance while well exhibiting the elongation at break and abrasion resistance required for a rim cushion rubber due to the excellent physical properties of the rubber composition for a rim cushion rubber of the present invention.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

[0012] As shown in Fig. 1, a pneumatic tire in which the rubber composition for a rim cushion of the present invention is used includes a tread portion 1, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3 disposed on the inner side in the tire radial direction of the sidewall portion 2. In Fig. 1, reference symbol CL indicates the tire equator. Although not depicted because Fig. 1 is a meridian cross-sectional view, the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction to form an annular shape, thereby constituting the toroidal basic structure of the pneumatic tire. Hereinafter, the description using Fig. 1 is basically based on the illustrated meridian cross-sectional shape, but each tire component member extends in the tire circumferential direction to form an annular shape.

[0013] A carcass layer 4 is mounted between the pair of left and right bead portions 3. This carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the vehicle inner side to the outer side around a bead core 5 disposed in each bead portion 3. Further, a bead filler 6 is disposed on the outer periphery of the bead core 5, and this bead filler 6 is wrapped by the main body portion and the folded-back portion of the carcass layer 4. On the other hand, a plurality of layers (two layers in Fig. 1) of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range of, for example, 10° to 40°. Further, a belt reinforcing layer 8 (two layers of a full cover 8a covering the entire width of the belt layer 7 and an edge cover 8b locally covering the end portion of the belt layer 7) is provided on the outer peripheral side of the belt layer 7. The belt reinforcing layer 8 includes an organic fiber cord oriented in the tire circumferential direction. In the belt reinforcing layer 8, the angle of the organic fiber cord with respect to the tire circumferential direction is set in the range of, for example, 0° to 5°.

[0014] A tread rubber layer 10 is disposed on the outer peripheral side of the carcass layer 4 in the tread portion 1, a side rubber layer 20 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and a rim cushion rubber layer 30 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the bead portion 3. The rubber composition for rim cushion of the present invention is used for such a rim cushion rubber layer 30 of a tire. Therefore, the basic structure of other parts is not limited to the above structure. Incidentally, although the rim cushion rubber layer 30 is a layer adjacent to the side rubber layer 20, unlike the side rubber layer 20 which constitutes the sidewall portion 2 where the bending during running is the largest in the tire and thus requires, for example, flex fatigue resistance, etc., it is a member that comes into contact with a rim (not shown) and is likely to wear due to friction with the rim, and thus is a layer that is required to have high hardness and excellent wear resistance.

[0015] The tire in which the rubber composition for rim cushion of the present invention is used is preferably a pneumatic tire as described above (a tire filled with an inert gas such as air, nitrogen or other gas inside), but may also be a non-pneumatic tire. In the case of a non-pneumatic tire, the rubber composition for rim cushion of the present invention is used for the portion that contacts the rim when mounted on the rim (the portion corresponding to the rim cushion rubber layer 30 in a pneumatic tire).

[0016] In the rubber composition for rim cushion of the present invention, the rubber component is a diene rubber and necessarily includes an isoprene rubber and a butadiene rubber. Further, the butadiene rubber includes at least one kind of silica-terminated modified butadiene rubber. By thus using an isoprene rubber and a butadiene rubber (silica-terminated modified butadiene rubber), it is advantageous for improving low heat build-up while maintaining good elongation at break and wear resistance.

[0017] Examples of isoprene rubbers include various natural rubbers, epoxidized natural rubbers, and various synthetic polyisoprene rubbers. Among these isoprene rubbers, natural rubber can be particularly preferably used. The compounding amount of the isoprene rubber is 35% to 65% by mass, preferably 40% to 60% by mass, in 100% by mass of the diene rubber. By compounding such an amount of the isoprene rubber, the elongation at break, low heat build-up property, and abrasion resistance can be improved in a well-balanced manner. When the compounding amount of the isoprene rubber is less than 35% by mass, the elongation at break decreases. When the compounding amount of the isoprene rubber exceeds 65% by mass, the abrasion resistance and low heat build-up property deteriorate.

[0018] The terminal-modified butadiene rubber for silica is a butadiene rubber in which both or one of its molecular terminals is modified with a functional group having reactivity with a silanol group on the silica surface. Examples of the functional group that reacts with the silanol group include at least one selected from a polyorganosiloxane group, a polyorganosiloxane structure containing a hydroxyl group, an alkoxysilyl group, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, an imino group, an epoxy group, an amide group, a thiol group, and an ether group. Among these, a polyorganosiloxane group, a polyorganosiloxane structure containing a hydroxyl group, an alkoxysilyl group, a hydroxyl group, and an amino group are preferable. Also, a combination of a plurality of these functional groups (for example, two types such as an amino group and an alkoxysilyl group) may be used. By including at least one kind of terminal-modified butadiene rubber for silica as the butadiene rubber, the affinity with the large-particle-size silica described later becomes good, and it is advantageous for improving the low heat build-up property while maintaining good elongation at break and abrasion resistance. Incidentally, the type of butadiene rubber other than the terminal-modified butadiene rubber for silica is not particularly limited, and rubbers generally used in tire rubber compositions can be used.

[0019] For the terminal-modified butadiene rubber for silica, from the viewpoint of improving abrasion resistance, it is preferable to use one having a glass transition temperature Tg of preferably -110°C to -70°C. By having such a low glass transition temperature, the abrasion resistance can be improved. Incidentally, the glass transition temperature can be measured by differential scanning calorimetry (DSC).

[0020] The compounding amount of the butadiene rubber is 35% by mass to 65% by mass, preferably 40% by mass to 60% by mass in 100% by mass of the diene rubber. By compounding an appropriate amount of the butadiene rubber in this way, it is advantageous for improving the elongation at break, low heat build-up property, and abrasion resistance in a well-balanced manner. If the compounding amount of the butadiene rubber is less than 35% by mass, the abrasion resistance and low heat build-up property deteriorate. If the compounding amount of the butadiene rubber exceeds 65% by mass, the elongation at break decreases.

[0021] As described above, the butadiene rubber necessarily contains at least one kind of terminal-modified butadiene rubber for silica. When the total amount of the butadiene rubber contained in the rubber composition for rim cushion of the present invention is 100% by mass, the proportion of the terminal-modified butadiene rubber for silica is preferably 15% by mass to 100% by mass, more preferably 40% by mass to 70% by mass. By containing a sufficient amount of the terminal-modified butadiene rubber for silica in this way, the affinity with the large-particle-size silica described later becomes good, and it is advantageous for improving the low heat build-up property while maintaining good elongation at break and abrasion resistance.

[0022] The rubber composition for rim cushion of the present invention can contain other diene rubbers in addition to the above-mentioned isoprene-based rubber and butadiene rubber. As the other diene rubbers, rubbers that can be generally used in tire rubber compositions can be used. For example, styrene-butadiene rubber and the like can be exemplified. These other diene rubbers can be used alone or as an arbitrary blend.

[0023] In the present invention, silica and carbon black are always compounded as fillers with respect to the above-mentioned diene rubber. When compounding these fillers, the compounding amount of silica is 10 parts by mass or more, preferably 20 parts by mass to 70 parts by mass, with respect to 100 parts by mass of the above-mentioned diene rubber. Further, the total compounding amount of silica and carbon black is more than 50 parts by mass, preferably 80 parts by mass or less, more preferably 55 parts by mass to 70 parts by mass, with respect to 100 parts by mass of the diene rubber. By compounding silica and carbon black in appropriate amounts in this way, the elongation at break, low heat build-up property, and abrasion resistance can be improved in a well-balanced manner. When the compounding amount of silica is less than 10 parts by mass, the elongation at break decreases. When the total compounding amount of silica and carbon black is 50 parts by mass or less, the abrasion resistance decreases. The compounding amount of carbon black alone is not particularly limited, but it is preferably 0 parts by mass to 60 parts by mass, more preferably 5 parts by mass to 50 parts by mass.

[0024] As the silica used in the present invention, for example, silica commonly used in rubber compositions for tires such as wet-process silica, dry-process silica, or surface-treated silica can be used. However, silica having a CTAB adsorption specific surface area of 60 m 2 / g to 100 m 2 / g, preferably 65 m 2 / g to 95 m 2 / g must be used. By using silica having a large particle size in this way, the low heat build-up property can be improved. When the CTAB adsorption specific surface area of silica is less than 60 m 2 / g, the elongation at break and abrasion resistance decrease. When the CTAB adsorption specific surface area of silica exceeds 100 m 2 / g, the low heat build-up property decreases. As long as the silica satisfies the above conditions, it may be appropriately selected from commercially available products and used, or silica obtained by a normal production method may also be used.

[0025] As the carbon black used in the present invention, carbon black commonly used in rubber compositions for tires can be used. However, carbon black having a CTAB adsorption specific surface area of 60 m 2 / g to 160 m 2 / g, preferably 80 m 2 / g to 135 m 2 / g of carbon black must be used. By using such carbon black, it is advantageous for improving elongation at break, low heat generation property, and abrasion resistance in a well-balanced manner. When the CTAB adsorption specific surface area of the carbon black is less than 60 m 2 / g, the elongation at break and abrasion resistance decrease. When the CTAB adsorption specific surface area of the carbon black exceeds 160 m 2 / g, the low heat generation property deteriorates.

[0026] The rubber composition of the present invention can be blended with other fillers other than silica and carbon black. Examples of other fillers include materials generally used in tire rubber compositions such as clay, talc, calcium carbonate, mica, aluminum hydroxide, and the like.

[0027] In the rubber composition for a rim cushion of the present invention, when blending the above-mentioned silica, a sulfur-containing silane coupling agent must be blended. By blending a silane coupling agent, the dispersibility of silica in a diene-based rubber can be improved. Examples of the sulfur-containing silane coupling agent include bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and the like. Among these, those having a tetrasulfide bond in the molecule can be preferably used. The blending amount of the silane coupling agent is preferably less than 10% by mass, more preferably 3% to 9% by mass, based on the blending amount of silica. When the blending amount of the silane coupling agent is 10% by mass or more of the silica blending amount, the silane coupling agents condense with each other, and the desired hardness and strength in the rubber composition cannot be obtained.

[0028] It is preferable to further compound sulfur and a vulcanization accelerator into the rubber composition for rim cushions of the present invention. When sulfur and a vulcanization accelerator are compounded, the total amount of the compounding is preferably 3.5 parts by mass or more, more preferably 4 parts by mass to 7.5 parts by mass, based on 100 parts by mass of the diene rubber. By compounding a sufficient amount of sulfur and a vulcanization accelerator in this way, the hardness, the stress M100 at 100% elongation at room temperature, and the low heat generation property can be improved in a well-balanced manner. When the total amount of sulfur and a vulcanization accelerator is less than 3.5 parts by mass, the balance of the hardness, the stress M100 at 100% elongation at room temperature, and the low heat generation property deteriorates. Incidentally, the individual compounding amounts of sulfur and a vulcanization accelerator are not particularly limited, but for sulfur, it is preferably 1.5 parts by mass to 5 parts by mass, more preferably 2 parts by mass to 4 parts by mass, and for the vulcanization accelerator, it is preferably 1.5 parts by mass to 4 parts by mass, more preferably 2 parts by mass to 3.5 parts by mass.

[0029] As the vulcanization accelerator, those generally used in rubber compositions for tires can be used. For example, sulfenamide-based vulcanization accelerators, guanidine-based vulcanization accelerators, and thiuram-based vulcanization accelerators can be exemplified. Examples of sulfenamide-based vulcanization accelerators include N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide (DZ), N-cyclohexyl-2-benzothiazole sulfenamide (CZ), N-oxydiethylene-2-benzothiazole sulfenamide (OBS), N-(tert-butyl)benzothiazole-2-sulfenamide (NS), etc. Examples of guanidine-based vulcanization accelerators include diphenylguanidine (DPG), diorthotolylguanidine, etc. Examples of thiuram-based vulcanization accelerators include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetrabenzylthiuram disulfide, etc. Among these, particularly N-cyclohexyl-2-benzothiazole sulfenamide (CZ), N-(tert-butyl)benzothiazole-2-sulfenamide (NS), and diphenylguanidine (DPG) can be preferably used. Also, among these, it is preferable to blend a sulfenamide-based one and optionally use either a guanidine-based or a thiuram-based one in combination. In particular, it is preferable to use two kinds, a sulfenamide-based and a guanidine-based, in combination.

[0030] Other compounding agents other than the above can be added to the rubber composition for rim cushions of the present invention. Examples of other compounding agents include various compounding agents generally used in rubber compositions for tires, such as vulcanizing or crosslinking agents other than sulfur, anti-aging agents, liquid polymers, etc. The compounding amounts of these compounding agents can be conventional general compounding amounts as long as they do not go against the purpose of the present invention. Also, as the kneader, ordinary rubber kneading machines, such as Banbury mixers, kneaders, rolls, etc. can be used.

[0031] In addition to being composed of the above-described formulation, the rubber composition for rim cushions of the present invention is set such that the product of the stress M100 [unit: MPa] at 100% elongation at room temperature and the hardness at room temperature is 150 or more, preferably 200 to 400. By having such characteristics, suitable rubber physical properties (for example, hardness, elongation at break, abrasion resistance) as rim cushion rubber can be obtained. When the above product is less than 150, the abrasion resistance decreases. This product can be adjusted, for example, by the blending amount of the above-described filler and the total amount of sulfur and vulcanization accelerator. The stress M100 at 100% elongation at room temperature is a value measured under the conditions of a tensile speed of 500 mm / min and room temperature (20°C) using a No. 3 dumbbell test piece in accordance with JIS K6251. The hardness at room temperature is measured at room temperature (temperature 20°C) using a Type A durometer in accordance with JIS K6253. If the product of the stress M100 and the hardness satisfies the above relationship, the individual values are not particularly limited, but the stress M100 at 100% elongation at room temperature can be set, for example, to 1.0 MPa to 10.0 MPa, and the hardness at room temperature can be set, for example, to 50 to 80, preferably 60 to 75.

[0032] Hereinafter, the present invention will be further described by way of examples, but the scope of the present invention is not limited to these examples.

Examples

[0033] In preparing 22 types of rubber compositions for rim cushions (standard example 1, comparative examples 1 to 10, and examples 1 to 11) having the formulations shown in Tables 1 to 2, the compounding components excluding the vulcanization accelerator and sulfur were weighed respectively, kneaded for 5 minutes in a 1.8 L closed Banbury mixer, and the masterbatch was discharged and cooled to room temperature. Thereafter, this masterbatch was fed into a 1.8 L closed Banbury mixer, the vulcanization accelerator and sulfur were added, and mixed for 2 minutes to obtain each rubber composition for rim cushions.

[0034] Using the obtained rubber composition for rim cushions, vulcanization was carried out at 170 °C for 10 minutes using a mold of a predetermined shape to prepare vulcanized rubber test pieces. The hardness of this vulcanized rubber test piece was measured under the condition of a temperature of 20 °C using a type A durometer in accordance with JIS K6253. Further, from the obtained vulcanized rubber test piece, a JIS No. 3 dumbbell-shaped test piece was cut out in accordance with JIS K6251, and the stress M100 at 100% elongation at room temperature was measured at a tensile speed of 500 mm / min and room temperature (20 °C). Using these hardness and M100 values, the product of the stress M100 [unit: MPa] at 100% elongation at room temperature and the hardness at room temperature was calculated and described in the column of "M100 × hardness" in Tables 1 to 2. In addition, in Tables 1 to 2, the total amount of carbon black and silica (the total of "CB + silica" in the table) was also described.

[0035] Using each of the above-mentioned rubber compositions for rim cushions (vulcanized rubber test pieces), the evaluation of the elongation at break (EB), tanδ at 60 °C, and abrasion resistance was carried out by the method shown below.

[0036] Elongation at break (EB) Using each rubber composition for rim cushions (vulcanized rubber test piece), a JIS No. 3 dumbbell-shaped test piece was cut out in accordance with JIS K6251, and a tensile test was carried out at a tensile speed of 500 mm / min at room temperature (20 °C), and the tensile break elongation at the time of break was measured. The obtained results were shown as an index with the value of Standard Example 1 being 100. The larger this index value, the larger the tensile break elongation. If the index value is "95" or more, it means that good tensile break elongation comparable to that of Standard Example 1 was maintained.

[0037] tanδ at 60 °C For each rubber composition for rim cushions (vulcanized rubber test piece), tanδ at 60 °C was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of an initial strain of 10%, an amplitude of ±2%, a frequency of 20 Hz, and a temperature of 60 °C. The evaluation results were shown in the column of "tanδ(60 °C)" in Tables 1 to 2 as an index with the value of Standard Example 1 being 100. The smaller this value, the more excellent the low heat generation property.

[0038] Wear resistance For each rubber composition for each rim cushion (vulcanized rubber test piece), the wear amount was measured using a pico wear tester in accordance with ASTM-D2228. The evaluation results were shown by an index in which the reciprocal of the measured value of Standard Example 1 was set to 100. The larger this index, the better the wear resistance. Incidentally, if this index value is "98" or more, it means that the wear resistance has been maintained at a sufficient level while maintaining the conventional level.

[0039] [Table 1]

[0040] [Table 2]

[0041] The types of raw materials used in Tables 1 to 2 are shown below. · NR: Natural rubber, STR20 · BR1: Butadiene rubber, Nipol BR1220 manufactured by Zeon Corporation, Japan · BR2: End-modified butadiene rubber for silica, BR511 manufactured by JSR Corporation · CB1: Carbon black (grade: ISAF), Showblack N234 manufactured by Cabot Japan Ltd. (CTAB adsorption specific surface area: 115 m 2 / g) · CB2: Carbon black (grade: FEF), Showblack N550 manufactured by Cabot Japan Ltd. (CTAB adsorption specific surface area: 40 m 2 / g) · Silica 1: 1085GR manufactured by Solvay (CTAB adsorption specific surface area: 85 m 2 / g) · Silica 2: 115GR manufactured by Solvay (CTAB adsorption specific surface area: 115 m 2 / g) · Silane coupling agent: Si69 manufactured by Evonik Degussa Japan Ltd. · Aromatic oil: Extract No. 4S manufactured by Showa Shell Sekiyu KK · Anti-aging agent 1: Santoflex 6PPD manufactured by Flexsys · Anti-aging agent 2: Nocrack 224 manufactured by Ouchi Shinko Chemical Industry Co., Ltd. · Wax: Paraffin wax manufactured by Ouchi Shinko Chemical Industry Co., Ltd. · Stearic acid: Bead stearic acid manufactured by NOF Corporation · Zinc oxide: Zinc oxide No. 3 manufactured by Shoindo Chemical Industry Co., Ltd. · Insoluble sulfur: Micron OT-20 manufactured by Shikoku Chemicals Corporation · Vulcanization accelerator 1: Sulfenamide-based vulcanization accelerator, Nocceler NS-P manufactured by Ouchi Shinko Chemical Industry Co., Ltd. · Vulcanization accelerator 2: Guanidine-based vulcanization accelerator, Perkacit DPG manufactured by Flexsys · Vulcanization accelerator 3: Thiuram-based vulcanization accelerator, tetrabenzylthiuram disulfide, Perkacit TBzTD pdr-d manufactured by Performance Additives

[0042] As is clear from Tables 1 to 2, Examples 1 to 11 maintained and improved hardness, elongation at break, and abrasion resistance while improving low heat generation (tanδ at 60°C) compared to Standard Example 1, and achieved a good balance of these performances.

[0043] On the one hand, in Comparative Example 1, the CTAB adsorption specific surface area of carbon black was small, the total amount of carbon black and silica was small, and the product of M100×hardness was small, so the wear resistance could not be maintained. In Comparative Example 2, the CTAB adsorption specific surface area of carbon black was small and the product of M100×hardness was small, so the wear resistance could not be maintained. In Comparative Example 3, the CTAB adsorption specific surface area of carbon black was small, the total amount of carbon black and silica was small, and the product of M100×hardness was small, so the wear resistance could not be maintained. In Comparative Example 4, the CTAB adsorption specific surface area of carbon black was small and the product of M100×hardness was small, so the wear resistance could not be maintained. In Comparative Example 5, the amount of natural rubber was small while the amount of butadiene rubber was large, carbon black was not compounded, the total amount of carbon black and silica was small, and the product of M100×hardness was small, so the wear resistance could not be maintained. In Comparative Example 6, the amount of natural rubber was small while the amount of butadiene rubber was large, and the CTAB adsorption specific surface area of carbon black was small, so the wear resistance could not be maintained. In Comparative Example 7, the amount of natural rubber was small while the amount of butadiene rubber was large, so the wear resistance could not be maintained and the effect of improving low heat build-up could not be obtained either. In Comparative Example 8, carbon black was not compounded and the total amount of carbon black and silica was small, so the wear resistance could not be maintained. In Comparative Example 9, the CTAB adsorption specific surface area of silica was large, so the elongation at break deteriorated and the effect of improving low heat build-up could not be obtained either. In Comparative Example 10, silica was not compounded, so the effect of improving low heat build-up could not be obtained either.

[0044] The present disclosure includes the following inventions. Invention [1]: With respect to a diene rubber containing 35% by mass to 65% by mass of an isoprene rubber and 35% by mass to 65% by mass of a butadiene rubber, silica having a CTAB adsorption specific surface area of 60 m 2 / g to 100 m 2 / g, and carbon black having a CTAB adsorption specific surface area of 60 m 2 / g to 160 m 2A rubber composition for a rim cushion, which is compounded with carbon black having a specific gravity of / g and a sulfur-containing silane coupling agent, wherein the butadiene rubber contains at least one terminal-modified butadiene rubber for silica, the compounding amount of the silica with respect to 100 parts by mass of the diene rubber is 10 parts by mass or more, and the total compounding amount of the silica and the carbon black with respect to 100 parts by mass of the diene rubber exceeds 50 parts by mass, and the product of the stress M100 [unit: MPa] at 100% elongation at room temperature and the hardness at room temperature is 150 or more. A rubber composition for a rim cushion characterized by the above. The rubber composition for a rim cushion according to Invention [1], characterized in that the proportion of the terminal-modified butadiene rubber for silica contained in the butadiene rubber is 15% by mass to 100% by mass. The rubber composition for a rim cushion according to Invention [1] or [2], characterized in that the total compounding amount of the silica and the carbon black with respect to 100 parts by mass of the diene rubber is 80 parts by mass or less. The rubber composition for a rim cushion according to any one of Inventions [1] to [3], characterized in that sulfur and a vulcanization accelerator are compounded with respect to the diene rubber, and the total compounding amount of the sulfur and the vulcanization accelerator with respect to 100 parts by mass of the diene rubber is 3.5 parts by mass or more. A tire comprising a rim cushion rubber layer made of the rubber composition for a rim cushion according to any one of Inventions [1] to [4].

Explanation of symbols

[0045] 1 Tread part 2 Sidewall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cover layer 10 Tread rubber layer 20 Side rubber layer 30 Rim cushion rubber layer CL Tire equator

Claims

1. A rubber composition for a rim cushion, comprising 35 to 65% by mass of an isoprene rubber and 35 to 65% by mass of a butadiene rubber, and containing silica having a CTAB adsorption specific surface area of 60 m 2 / g to 100 m 2 / g, carbon black having a CTAB adsorption specific surface area of 60 m 2 / g to 160 m 2 / g, and a sulfur-containing silane coupling agent, wherein the butadiene rubber contains at least one terminal-modified butadiene rubber for silica, the compounding amount of the silica with respect to 100 parts by mass of the diene rubber is 10 parts by mass or more, and the total compounding amount of the silica and the carbon black with respect to 100 parts by mass of the diene rubber exceeds 50 parts by mass, and the product of the stress M100 [unit: MPa] at 100% elongation at room temperature and the hardness at room temperature is 150 or more. A rubber composition for a rim cushion characterized by that.

2. The rubber composition for a rim cushion according to claim 1, characterized in that the proportion of the terminal-modified butadiene rubber for silica contained in the butadiene rubber is 15% by mass to 100% by mass.

3. The rubber composition for a rim cushion according to claim 1 or 2, characterized in that the total amount of the silica and the carbon black compounded with respect to 100 parts by mass of the diene rubber is 80 parts by mass or less.

4. The rubber composition for a rim cushion according to claim 1 or 2, characterized in that sulfur and a vulcanization accelerator are compounded with the diene rubber, and the total amount of the sulfur and the vulcanization accelerator compounded with respect to 100 parts by mass of the diene rubber is 3.5 parts by mass or more.

5. A tire comprising a rim cushion rubber layer made of the rubber composition for a rim cushion according to claim 1 or 2.

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