Rubber composition for side treads

Abstract

Provided is a rubber composition for a side tread, whereby it becomes possible to improve low heat-generating properties while retaining elongation at break and cut resistance at satisfactory levels and it also becomes possible to achieve all of these properties at high levels and in a good balance. 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 20 m2 / g to 60 m2 / g, and a sulfur-containing silane coupling agent are mixed with a diene-based rubber comprising 35% by mass to 65% by mass of an isoprene-based rubber and 35% by mass to 65% by mass of a butadiene-based rubber synthesized with a neodymium-based catalyst, in which the addition amount of silica is set at 2 parts by mass to 25 parts by mass and the total addition amount of silica and carbon black is set at 55 parts by mass or less per 100 parts by mass of the diene-based rubber, the ratio of the addition amount Ms of silica to the addition amount Mc of carbon black, i.e., Ms / Mc, is set as 0.8 or less, and the ratio of the addition amount of the sulfur-containing silane coupling agent to the addition amount of silica is set at less than 10% by mass.

Description

[Technical Field]

[0001] The present invention relates primarily to a rubber composition for side treads, intended for use in the side tread layer of tires. [Background technology]

[0002] In pneumatic tires, there is a need to improve fuel efficiency during driving in order to reduce environmental impact. Therefore, efforts are being made to suppress heat generation in the rubber compositions that make up each part of the pneumatic tire. In recent years, to further improve fuel efficiency, for example, efforts are being made to suppress heat generation in the rubber composition that makes up the side tread rubber layer of pneumatic tires (side tread rubber composition).

[0003] Generally, the tanδ (hereinafter referred to as "tanδ(60°C)") measured at 60°C by dynamic viscoelasticity measurement is used as an indicator of the heat generation of rubber compositions, and the smaller the tanδ(60°C) of the rubber composition, the lower the heat generation. Methods to reduce the tanδ(60°C) of a rubber composition include, for example, reducing the amount of filler such as carbon black or increasing the particle size of carbon black. Alternatively, it has been proposed to incorporate butadiene rubber polymerized using a neodymium-based catalyst (see, for example, Patent Document 1). However, with these methods, there was a risk that the break elongation and cut resistance required for rubber compositions for side treads would not be sufficiently obtained. Therefore, further measures are needed to improve low heat generation (tanδ(60°C)) in rubber compositions for side treads while maintaining good break elongation and cut resistance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2011-074332 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide a rubber composition for side treads that improves low heat generation while maintaining good elongation at break and cut resistance, thereby achieving a high level of balance between these performance characteristics. [Means for solving the problem]

[0006] The rubber composition for side treads of the present invention, which achieves the above objective, is an isoprene-based rubber 35% by mass~ 55 For a diene rubber containing mass% and 45 mass% to 65 mass% of butadiene rubber synthesized with a neodymium-based catalyst, the CTAB adsorption specific surface area is 60 m². 2 / g~100m 2 Silica with a specific surface area of ​​CTAB adsorption of 20 m² / g. 2 / g~60m 2 A rubber composition for side treads comprising carbon black in a quantity of / g and a sulfur-containing silane coupling agent, characterized in that the amount of silica blended per 100 parts by mass of the diene rubber is 2 to 25 parts by mass, the total amount of silica and carbon black blended is 55 parts by mass or less, the ratio of the amount of silica blended to the amount of carbon black blended Mc Ms / Mc is 0.8 or less, and the ratio of the amount of sulfur-containing silane coupling agent blended to the amount of silica blended is less than 10% by mass. [Effects of the Invention]

[0007] The rubber composition for side treads of the present invention, by having the above-described formulation, improves low heat generation while maintaining good elongation at break and cut resistance, and achieves a high level of balance between these performances. Specifically, it is possible to reduce heat generation by using butadiene rubber polymerized with a neodymium-based catalyst, but there are concerns about a decrease in elongation at break and cut resistance. Therefore, the CTAB adsorption specific surface area is 60 m². 2 / g~100m 2By using large-particle-size silica with a specific surface area of 100 m² / g or more in combination, the degradation of these properties can be suppressed. On the other hand, although there is concern about the deterioration of tanδ(60°C) when using large-particle-size silica, regarding this, since the blending ratio of large-particle-size silica and carbon black is set as described above, tanδ(60°C) can be maintained well. Through the cooperation of these, while maintaining good elongation at break and cut resistance, the low heat generation property (tanδ at 60°C) can be improved, and it becomes possible to exhibit well the physical properties required for the side tread rubber layer.

[0008] In the present invention, it is preferable that sulfur and a vulcanization accelerator are blended in a total amount of 2.5 parts by mass or more with respect to 100 parts by mass of the diene rubber. By blending an appropriate amount of sulfur and a vulcanization accelerator in this way, it is advantageous for improving the low heat generation property.

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

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a meridian cross-sectional view showing an example of a pneumatic tire using the rubber composition for a side tread of the present invention.

Modes for Carrying Out the Invention

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

[0012] As shown in FIG. 1, a pneumatic tire in which the rubber composition for side tread 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, the symbol CL indicates the tire equator. Although not depicted because FIG. 1 is a meridian 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 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 inner side to the outer side in the tire width direction 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 is arranged such that the reinforcing cords cross 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 arranged on the outer circumference of the carcass layer 4 in the tread section 1, a side tread rubber layer 20 is arranged on the outer circumference (outer side in the tire width direction) of the carcass layer 4 in the sidewall section 2, and a rim cushion rubber layer 30 is arranged on the outer circumference (outer side in the tire width direction) of the carcass layer 4 in the bead section 3. The rubber composition for side treads of the present invention is used in the side tread rubber layer 20 of such a tire. Therefore, the basic structure of other parts is not limited to the structure described above. In addition, the side tread rubber layer 20 is different from the tread rubber layer 10 that contacts the road surface and the rim cushion rubber layer 30 that contacts the rim (not shown), as it is the part of the tire that bends the most during driving, and therefore it is required to have excellent elongation at break (resistance to bending fatigue). Furthermore, it is required to have excellent cut resistance as it tends to be frequently subjected to external damage.

[0015] The tire using the rubber side tread composition of the present invention is preferably a pneumatic tire (a tire in which air, nitrogen, or other inert gas is filled inside), but it may also be a non-pneumatic tire. In the case of a non-pneumatic tire, the rubber side tread composition of the present invention can be used in the portion located between the portion that contacts the road surface (the portion corresponding to the tread rubber layer 10 in a pneumatic tire) and 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 side treads of the present invention, the rubber component is a diene-based rubber, and always contains isoprene-based rubber and butadiene rubber. Furthermore, as the butadiene rubber, butadiene rubber polymerized using a neodymium-based catalyst (hereinafter sometimes referred to as Nd-BR) is always used. Using isoprene-based rubber and butadiene rubber (Nd-BR) in this way is advantageous for improving low heat generation while maintaining good elongation at break and cut resistance.

[0017] Examples of isoprene-based rubbers include various types of natural rubber, epoxidized natural rubber, and various types of synthetic polyisoprene rubber. Among these isoprene-based rubbers, natural rubber is particularly suitable for use. The amount of isoprene-based rubber added is 35% to 65% by mass, preferably 40% to 60% by mass, and more preferably 40% to 55% by mass, based on 100% by mass of diene-based rubber. By adding such an amount of isoprene-based rubber, it is possible to improve the elongation at break, low heat generation, and abrasion resistance in a balanced manner. If the amount of isoprene-based rubber added is less than 35% by mass, the elongation at break decreases. If the amount of isoprene-based rubber added exceeds 65% by mass, the cut resistance deteriorates.

[0018] Butadiene rubber polymerized using neodymium-based catalysts (Nd-BR) is a known material. It is butadiene rubber polymerized using neodymium-based catalysts such as elemental neodymium, compounds of neodymium with other metals, or organoneodymium compounds. Butadiene rubber synthesized with these neodymium-based catalysts has the characteristics of high molecular weight and a sharp molecular weight distribution. Commercially available Nd-BR can also be used, such as Buna CB22 and Buna CB24 from Arlanxeo. By polymerizing butadiene rubber using a neodymium-based catalyst in this way, the low exothermic properties can be improved. It should be noted that if butadiene rubber polymerized with other catalysts (e.g., nickel or cobalt) is used, the desired low exothermic properties cannot be obtained.

[0019] In this invention, only one type of butadiene rubber (Nd-BR) is used, and two or more types of Nd-BR are not used in combination, nor is Nd-BR used in combination with other types of butadiene rubber. In this invention, by using only one type of Nd-BR and combining it with large-particle silica as described later, it is possible to improve low heat generation while maintaining good elongation at break and cut resistance. If two or more types of butadiene rubber are included, it is not possible to achieve a good balance of these properties.

[0020] The butadiene rubber used in this invention may be polymerized using a neodymium-based catalyst as described above, but it is preferable that the vinyl content in the butadiene rubber (Nd-BR) is 0.5% to 1.0% by mass, more preferably 0.5% to 0.8% by mass, and even more preferably 0.6% to 0.7% by mass. Such a low vinyl content is advantageous for improving the heat generation properties. If the vinyl content in the butadiene rubber (Nd-BR) is less than 0.5% by mass, the processability decreases. If the vinyl content in the butadiene rubber (Nd-BR) exceeds 1.0% by mass, the heat generation properties decrease. The vinyl content of the butadiene rubber (Nd-BR) shall be measured by infrared spectroscopy (Hampton method). The increase or decrease in the vinyl content of the butadiene rubber can be appropriately adjusted by conventional methods, such as by changing the type of catalyst (specific type of neodymium-based catalyst as described above).

[0021] The amount of butadiene rubber (Nd-BR) added is 35% to 65% by mass, preferably 40% to 60% by mass, and more preferably 45% to 50% by mass, based on 100% by mass of the diene rubber. Adding an appropriate amount of butadiene rubber in this way is advantageous for balancing and improving elongation at break, low heat generation, and abrasion resistance. If the amount of butadiene rubber added is less than 35% by mass, the cut resistance deteriorates. If the amount of butadiene rubber added exceeds 65% by mass, the elongation at break decreases.

[0022] The rubber composition for side treads of the present invention may contain other diene rubbers in addition to the isoprene-based rubber and butadiene rubber (Nd-BR) described above. As the other diene rubbers, rubbers commonly used in tire rubber compositions can be used. For example, styrene-butadiene rubber can be used. These other diene rubbers can be used alone or in any blend.

[0023] In the present invention, silica and carbon black are always blended as fillers with respect to the above-mentioned diene rubber. 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, the CTAB adsorption specific surface area is 60 m 2 / g to 100 m 2 / g, preferably 70 m 2 / g to 90 m 2 / g, more preferably 75 m 2 / g to 85 m 2 / g. By using silica with such a large particle size, it is possible to suppress the decrease in elongation at break caused by using the above-mentioned Nd-BR. When the CTAB adsorption specific surface area of silica is less than 60 m 2 / g, the heat generation property decreases. When the CTAB adsorption specific surface area of silica exceeds 100 m 2 / g, the abrasion resistance decreases. As long as it is silica that 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.

[0024] The blending amount Ms of silica is 2 parts by mass to 25 parts by mass, preferably 2 parts by mass to 20 parts by mass, more preferably 5 parts by mass to 15 parts by mass with respect to 100 parts by mass of the above-mentioned diene rubber. By blending silica in an appropriate amount in this way, elongation at break, low heat generation property, and cut resistance can be improved in a balanced manner. When the blending amount of silica is less than 2 parts by mass, elongation at break and cut resistance decrease. When the blending amount of silica exceeds 25 parts by mass, the low heat generation property deteriorates.

[0025] As the carbon black used in the present invention, among the carbon blacks commonly used in rubber compositions for tires, the CTAB adsorption specific surface area is 20 m 2 / g to 60 m 2 / g, preferably 30 m 2 / g to 50 m 2 / g, more preferably 35 m 2 / g to 45 m 2Always use carbon black with a surface area of 2 less than 20 m 2 / g. By using such carbon black, it is advantageous for improving elongation at break, low heat generation property, and cut resistance in a well-balanced manner. When the CTAB adsorption specific surface area of carbon black is less than 20 m

[0026] In the present invention, silica and carbon black are always used in combination as described above. At this time, the total amount of silica and carbon black is 55 parts by mass or less, preferably 25 to 40 parts by mass, more preferably 20 to 30 parts by mass, based on 100 parts by mass of the above-mentioned diene rubber. By blending silica and carbon black in appropriate amounts in this way, elongation at break, cut resistance, and abrasion resistance can be improved in a well-balanced manner. When the total amount of silica and carbon black exceeds 55 parts by mass, the heat generation property deteriorates. Incidentally, the blending amount of carbon black alone is not particularly limited, but it is preferably 15 to 30 parts by mass, more preferably 15 to 30 parts by mass.

[0027] Furthermore, when silica and carbon black are used in combination, the ratio Ms / Mc of the blending amount Ms of silica to the blending amount Mc of carbon black is preferably 0.8 or less, more preferably 0.1 to 0.75, and even more preferably 0.25 to 0.7. By blending silica and carbon black in appropriate amounts in this way, particularly by keeping the amount of silica in the filler low, deterioration of tanδ(60°C) due to blending of large particle size silica can be suppressed, and elongation at break, low heat generation property, and cut resistance can be improved in a well-balanced manner. When the ratio Ms / Mc of the blending amount of silica to the blending amount of carbon black exceeds 0.8, tanδ(60°C) cannot be maintained well and the low heat generation property deteriorates.

[0028] The rubber composition of the present invention may contain fillers other than silica and carbon black. Examples of other fillers include materials commonly used in tire rubber compositions, such as clay, talc, calcium carbonate, mica, and aluminum hydroxide.

[0029] In the rubber composition for side treads of the present invention, a sulfur-containing silane coupling agent is always included when compounding the silica described above. By compounding the sulfur-containing silane coupling agent, the dispersibility of silica in diene-based rubber can be improved. Examples of sulfur-containing silane coupling agents include bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane. Among these, those having tetrasulfide bonds in the molecule can be used particularly suitably. The amount of silane coupling agent should preferably be less than 10% by mass, more preferably 3% to 9% by mass, relative to the amount of silica. If the amount of silane coupling agent is 10% by mass or more of the amount of silica, the silane coupling agents will condense with each other, and the desired hardness and strength in the rubber composition cannot be obtained.

[0030] The rubber composition for side treads of the present invention preferably further contains sulfur and a vulcanization accelerator. When sulfur and a vulcanization accelerator are added, the total amount is preferably 2.5 parts by mass or more, more preferably 2.5 to 3.0 parts by mass, per 100 parts by mass of diene rubber. By adding a sufficient amount of sulfur and a vulcanization accelerator in this way, the heat generation can be improved. If the total amount of sulfur and a vulcanization accelerator is less than 2.5 parts by mass, the heat generation will decrease. The individual amounts of sulfur and a vulcanization accelerator are not particularly limited, but for sulfur, it is preferably 1.0 to 2.0 parts by mass, more preferably 1.5 to 2.0 parts by mass, and for a vulcanization accelerator, it is preferably 0.5 to 1.5 parts by mass, more preferably 0.5 to 1.0 part by mass.

[0031] As vulcanization accelerators, those commonly used in tire rubber compositions can be used, for example, sulfenamide-based vulcanization accelerators, guanidine-based vulcanization accelerators, and thiram-based vulcanization accelerators. Examples of sulfenamide-based vulcanization accelerators include N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide (DZ), N-cyclohexyl-2-benzothiazolesulfenamide (CZ), N-oxydiethylene-2-benzothiazolesulfenamide (OBS), and N-(tert-butyl)benzothiazole-2-sulfenamide (NS). Examples of guanidine-based vulcanization accelerators include diphenylguanidine and dioltotolylguanidine. Examples of thiram-based vulcanization accelerators include tetramethylthiram monosulfide and tetramethylthiram disulfide.

[0032] Other compounding agents may be added to the rubber composition for side treads of the present invention. Examples of other compounding agents include vulcanizing or crosslinking agents other than sulfur, antioxidants, liquid polymers, and various other compounding agents commonly used in tire rubber compositions. The amounts of these compounding agents can be the conventional amounts, as long as they do not contradict the purpose of the present invention. As for the mixing machine, ordinary rubber mixing machines such as Banbury mixers, kneaders, and rolls can be used.

[0033] The rubber composition for side treads of the present invention can be mixed using conventional methods, but in order to more effectively reduce heat generation, it is preferable to mix isoprene rubber, butadiene rubber synthesized with a neodymium catalyst, carbon black, and silica in a step before mixing in vulcanizing compounding agents (sulfur, vulcanization accelerator, etc.). In particular, in this step, it is preferable to first mix the entire amount of isoprene rubber with carbon black and silica in a first mixing step, and then add and mix the butadiene rubber synthesized with a neodymium catalyst to the mixture obtained in the first mixing step in a second mixing step. By mixing in this order, including the first and second mixing steps, the butadiene rubber synthesized with a neodymium catalyst is added and mixed after the isoprene rubber, carbon black, and silica, so it is possible to control the carbon black to be preferentially incorporated into the isoprene rubber that was added first, thereby improving cut resistance while achieving reduced heat generation.

[0034] In addition to having the above-described compound, the rubber composition for side treads of the present invention preferably has a tanδ of 0.06 or less, more preferably 0.05 or less, at 60°C. Having such characteristics allows the rubber composition for side treads to generate a sufficiently low amount of heat. If the tanδ at 60°C exceeds 0.06, the low heat generation performance deteriorates. The "tanδ at 60°C" was measured using a viscoelastic spectrometer under the conditions of initial strain of 10%, amplitude of ±2%, frequency of 20Hz, and temperature of 60°C.

[0035] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. [Examples]

[0036] Twenty different rubber compositions for side treads (Reference Example 1, Comparative Examples 1-8, Examples 1-11) were prepared using the formulations shown in Tables 1-2. For each composition, the components excluding the vulcanization accelerator and sulfur were weighed and mixed in a 1.8 L sealed Banbury mixer for 5 minutes. The masterbatch was then released and allowed to cool to room temperature. Subsequently, this masterbatch was placed in a 1.8 L sealed Banbury mixer, the vulcanization accelerator and sulfur were added, and the mixture was mixed for 2 minutes to obtain each rubber composition for side treads.

[0037] Note that in Tables 1 and 2, the "Mc+Ms" column represents the sum of the amounts of carbon black and silica. The "Ms / Mc" column represents the ratio of silica to carbon black. The "Sulfur + Vulcanization Accelerator" column represents the sum of the amounts of sulfur and vulcanization accelerator. Tables 1 and 2 show the timing of adding butadiene rubber (any of BR1 to BR3) in the process before adding vulcanizing compounding agents (sulfur and vulcanization accelerators). "Simultaneous" indicates when butadiene rubber is added together with isoprene rubber, carbon black, silica, etc. (i.e., when all components except vulcanizing compounding agents are added simultaneously in one process), and "Later addition" indicates when butadiene rubber is added after isoprene rubber, carbon black, silica, etc. (i.e., when the process of adding all components except vulcanizing compounding agents includes the first and second kneading processes, and butadiene rubber is added in the second kneading process).

[0038] Each of the obtained rubber compositions for side treads was evaluated for elongation at break, tanδ at 60°C, and cut resistance using the method described below.

[0039] Elongation at break Each side tread rubber composition was vulcanized in a mold of a predetermined shape at 170°C for 10 minutes to prepare vulcanized rubber test specimens. Using these vulcanized rubber test specimens, JIS No. 3 dumbbell-shaped test specimens were cut out in accordance with JIS K6251, and tensile tests were performed at room temperature (20°C) at a tensile speed of 500 mm / min to measure the tensile elongation at fracture. The obtained results are shown in the "Elongation at Fracture" column of Tables 1 and 2, with the value of Standard Example 1 set to 100. A larger index value indicates a larger tensile elongation at fracture.

[0040] tanδ at 60℃ Each side tread rubber composition was vulcanized in a mold of a predetermined shape at 170°C for 10 minutes to prepare vulcanized rubber test specimens. For these vulcanized rubber test specimens, the tanδ at 60°C was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., under the conditions of initial strain of 10%, amplitude of ±2%, frequency of 20Hz, and temperature of 60°C. The evaluation results are shown in the "tanδ(60°C)" column of Tables 1-2, using the reciprocal of the measured value as an index with the value of Standard Example 1 set to 100. A larger value indicates superior low heat generation.

[0041] Cut resistance A test tire (tire size: 245 / 45R19) was manufactured, having a side tread layer made of each rubber composition for the side tread, and possessing the basic structure shown in Figure 1. Each test tire was mounted on a 19-inch rim wheel, inflated to 270 kPa, and mounted on a test vehicle. The vehicle was driven at a speed of 10 km / h at a 30° angle to a 110 mm high curb, and the degree of damage (pinch cut) to the sidewall (side tread layer) when it crossed the curb (length and depth of damage) was evaluated. The evaluation results were expressed as an index using the reciprocal of the measured value, with the value of Standard Example 1 set to 100. A larger index value indicates smaller damage length and depth, and better cut resistance.

[0042] [Table 1]

[0043] [Table 2]

[0044] The types of raw materials used in Tables 1 and 2 are shown below. • NR: Natural rubber, NUSIRA • BR1: Butadiene rubber synthesized using a cobalt catalyst, manufactured by Nippon Zeon Corporation, Nipol BR1220 (cis-1,4-bond content: 98 mol%, glass transition temperature Tg = -106°C, weight-average molecular weight Mw = 4.5) • BR2: Butadiene rubber synthesized using a neodymium catalyst, manufactured by ARLANXEO, Buna CB22 (cis-1,4-bond content: 98 mol%, glass transition temperature Tg = -106°C, weight-average molecular weight Mw = 7.5) • BR2: Butadiene rubber synthesized using a neodymium catalyst, manufactured by ARLANXEO, Buna CB24 (cis-1,4-bond content: 97 mol%, glass transition temperature Tg = -106°C, weight-average molecular weight Mw = 6.2) • CB1: Carbon black, manufactured by Shin-Nippon Carbon Co., Ltd. Nitelon #55S (CTAB adsorption specific surface area: 30m²) 2 / g, nitrogen adsorption specific surface area N2SA: 30m 2 / g) • CB2: Carbon black, manufactured by Asahi Carbon Co., Ltd. Asahi #70K (CTAB adsorption specific surface area: 75m²) 2 / g, nitrogen adsorption specific surface area N2SA:71m 2 / g) • Silica 1: SOLVAY Zeosil 1085GR (CTAB adsorption specific surface area: 80 m²) 2 / g, BET specific surface area: 90m 2 / g) ·Silica 2: Evonik ULTRASIL VN3GR (CTAB adsorption specific surface area: 160m 2 / g, nitrogen adsorption specific surface area N2SA: 220m 2 / g) • Silane coupling agent: KBE-846, manufactured by Shin-Etsu Chemical Co., Ltd. • Zinc oxide: ZM Silesia ZINC OXIDE • Stearic acid: Lunac S-25 manufactured by Kao Corporation • Sulfur: MIDAS-105 manufactured by Bigensha • Vulcanization accelerator: Bayer Vulkacit NZ / EG

[0045] As is clear from Tables 1-2, Examples 1-11 maintained and improved the break elongation and cut resistance well compared to Standard Example 1, while also improving low heat generation (tanδ at 60°C), achieving a good balance of these performance characteristics. Although Examples 1 and 11 share the same formulation, differing only in the "stage of adding BR," Example 11, in which butadiene rubber (BR2) synthesized with a neodymium catalyst was added and kneaded after isoprene-based rubber, carbon black, and silica, showed even greater cut resistance than Example 1, in which these materials were added simultaneously.

[0046] On the other hand, in Comparative Example 1, although butadiene rubber (Nd-BR) synthesized with a neodymium catalyst was used, the amount of natural rubber was low and the amount of butadiene rubber (Nd-BR) was high, resulting in reduced elongation at break. In Comparative Example 2, although butadiene rubber (Nd-BR) synthesized with a neodymium catalyst was used, the amount of natural rubber was high and the amount of butadiene rubber (Nd-BR) was low, resulting in reduced cut resistance. In Comparative Example 3, the amount of silica was low, resulting in reduced elongation at break and reduced cut resistance. In Comparative Example 4, the amount of silica was high, resulting in poor low heat generation. In Comparative Example 5, the specific surface area of ​​silica adsorbing CTAB was large, resulting in poor low heat generation. In Comparative Example 6, the specific surface area of ​​carbon black adsorbing CTAB was large, resulting in reduced elongation at break, reduced cut resistance, and poor low heat generation. In Comparative Example 7, the amount of silica was excessive relative to the amount of carbon black, resulting in reduced cut resistance and poor low heat generation. Comparative Example 8, lacking a silane coupling agent, exhibited reduced elongation at break and worsened low-exothermic properties.

[0047] This disclosure encompasses the following inventions: Invention [1] A diene rubber containing 35% to 65% by mass of isoprene rubber and 35% to 65% by mass of butadiene rubber synthesized with a neodymium catalyst, wherein the CTAB adsorption specific surface area is 60 m². 2 / g~100m 2 Silica with a specific surface area of ​​CTAB adsorption of 20 m² / g. 2 / g~60m 2 A rubber composition for side treads comprising carbon black in a quantity of / g and a sulfur-containing silane coupling agent, wherein the amount of silica blended per 100 parts by mass of the diene rubber is 2 to 25 parts by mass, the total amount of silica and carbon black blended is 55 parts by mass or less, the ratio of the amount of silica blended to the amount of carbon black blended Mc Ms / Mc is 0.8 or less, and the ratio of the amount of sulfur-containing silane coupling agent blended to the amount of silica blended is less than 10% by mass. Invention [2] The rubber composition for side treads according to Invention [1], characterized in that a total of 2.5 parts by mass or more of sulfur and a vulcanization accelerator are blended with 100 parts by mass of the diene rubber. Invention [3] A tire characterized by comprising a side tread rubber layer made of the side tread rubber composition described in claim [1] or [2]. [Explanation of Symbols]

[0048] 1. Tread section 2 Sidewall section 3. Bead section 4. Carcass layer 5 Bead core 6. Bead Filler 7 Belt layer 8 Belt cover layer 10 Tread rubber layer 20 Side tread rubber layer 30 Rim cushion rubber layer CL Tire Equator

Claims

1. A diene rubber containing 35% to 55% by mass of isoprene rubber and 45% to 65% by mass of butadiene rubber synthesized with a neodymium catalyst has a CTAB adsorption specific surface area of ​​60 m². ２ / g to 100m ２ Silica at / g, with a CTAB adsorption specific surface area of ​​20 m². ２ / g ~ 60m ２ A rubber composition for side treads comprising carbon black in a quantity of 1 / g and a sulfur-containing silane coupling agent, wherein the amount of silica blended per 100 parts by mass of the diene rubber is 2 to 25 parts by mass, the total amount of silica and carbon black blended is 55 parts by mass or less, the ratio of the amount of silica blended to the amount of carbon black blended Mc Ms / Mc is 0.8 or less, and the ratio of the amount of sulfur-containing silane coupling agent blended to the amount of silica blended is less than 10% by mass.

2. The rubber composition for side treads according to claim 1, characterized in that sulfur and a vulcanization accelerator are blended in a total of 2.5 parts by mass or more per 100 parts by mass of the diene rubber.

3. A tire characterized by comprising a side tread rubber layer made of the side tread rubber composition described in claim 1 or 2.

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