Rubber composition for tire tread and tire

Abstract

To provide a rubber composition for a tire tread having good chipping resistance, tear resistance, abrasion resistance and low rolling resistance.SOLUTION: A rubber composition for a tire tread according to an embodiment includes rubber components including a natural rubber and a styrene-butadiene rubber, and silica having a CTAB adsorption specific surface area of less than 200m2 / g. The amount of the natural rubber in 100 parts by mass of the rubber component is more than 40 parts by mass and less than 75 parts by mass. The amount of styrene in the rubber component other than the natural rubber is 21% by mass or less. The amount of the silica is more than 55 parts by mass and less than 90 parts by mass per 100 parts by mass of the rubber component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition for a tire tread and a tire using the same. [Background technology]

[0002] Various proposals have been made to improve the chipping resistance of tires. Here, chipping refers to the occurrence of chips on the land of blocks or the like provided on the tread surface, and there is a need to suppress such chipping.

[0003] For example, Patent Document 1 discloses a rubber composition that improves chipping resistance without impairing handling stability by blending a diene rubber containing natural rubber with a thermoplastic resin obtained by copolymerizing styrene, indene, and dicyclopentadiene together with specific carbon black.

[0004] Patent Document 2 discloses a rubber composition that improves the abrasion resistance of tires and improves their cut resistance and chipping resistance by blending a rubber additive containing a specific sulfur-containing hydrocarbon polymer with a rubber component that contains 50% by mass or more of isoprene-based rubber and has a glass transition temperature of −90°C or higher and lower than −50°C.

[0005] Patent Document 3 discloses that chipping resistance can be improved by incorporating 40 to 60 parts by mass of styrene-butadiene rubber with a styrene content of 25% by mass or less per 100 parts by mass of the rubber component, as well as 30 parts by mass or less of an isoprene-based rubber, and further incorporating 100 parts by mass or less of silica as a filler per 100 parts by mass of the rubber component. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-070778 [Patent Document 2] Japanese Patent Application Publication No. 2024-027437 [Patent Document 3] Japanese Patent Application Publication No. 2024-002911 Summary of the Invention [Problem to be solved by the invention]

[0007] For example, off-road tires require chipping resistance and tear resistance, but it has traditionally been difficult to ensure these properties while also maintaining wear resistance and low rolling resistance (fuel economy).

[0008] In view of the above, an object of an embodiment of the present invention is to provide a rubber composition for a tire tread that has good chipping resistance, tear resistance, abrasion resistance, and low rolling resistance, and a tire using the same. [Means for solving the problem]

[0009] The present invention includes the embodiments shown below. [1] Rubber components including natural rubber and styrene butadiene rubber, and a CTAB adsorption specific surface area of ​​200 m 2 / g or less of silica, wherein the amount of the natural rubber in 100 parts by mass of the rubber component is more than 40 parts by mass and less than 75 parts by mass, the amount of styrene in the rubber component other than the natural rubber is 21% by mass or less, and the amount of the silica is more than 55 parts by mass and less than 90 parts by mass per 100 parts by mass of the rubber component. [2] The rubber composition for a tire tread according to [1], wherein 100 parts by mass of the rubber component contains more than 40 parts by mass and not more than 60 parts by mass of the natural rubber, 15 parts by mass or more and less than 60 parts by mass of the styrene-butadiene rubber, and 0 parts by mass or more and less than 45 parts by mass of butadiene rubber. [3] The rubber composition for a tire tread according to [1] or [2], wherein the styrene-butadiene rubber comprises a modified styrene-butadiene rubber. [4] The rubber composition for a tire tread according to any one of [1] to [3], wherein the amount of the silica is 60 to 75 parts by mass per 100 parts by mass of the rubber component. [5] A tire having a tread formed from the rubber composition for a tire tread according to any one of [1] to [4]. [Effects of the Invention]

[0010] According to an embodiment of the present invention, it is possible to provide a rubber composition for a tire tread that has good chipping resistance, tear resistance, abrasion resistance, and low rolling resistance, and a tire using the same. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the rubber composition for tire tread according to this embodiment (hereinafter also simply referred to as "rubber composition"), the rubber component contains natural rubber (NR) and styrene-butadiene rubber (SBR).

[0012] The natural rubber is not particularly limited and examples thereof include ribbed smoked sheet (RSS), technically graded rubber (TSR), and natural rubber latex. Modified versions of these, such as epoxidized natural rubber, may also be used. Modified and unmodified natural rubbers may also be used in combination.

[0013] The styrene butadiene rubber may be solution-polymerized styrene butadiene rubber (SSBR) or emulsion-polymerized styrene butadiene rubber (ESBR). The styrene butadiene rubber may be modified styrene butadiene rubber (modified SBR) whose ends or main chain have been modified, unmodified styrene butadiene rubber (unmodified SBR), or a combination of modified SBR and unmodified SBR. Preferably, the styrene butadiene rubber contains modified SBR, more preferably modified solution-polymerized styrene butadiene rubber (modified SSBR). In this case, the modified SBR (preferably modified SSBR) is preferably contained in 100% by mass of SBR at 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more, and may be 100% by mass.

[0014] The modified SBR is one that has been modified by introducing a functional group into the terminal and / or main chain. The functional group preferably contains an oxygen atom and / or a nitrogen atom, and examples thereof include at least one selected from the group consisting of an amino group, a hydroxy group, an alkoxy group, an alkoxysilyl group, an epoxy group, and a carboxy group. The use of a modified SBR containing such a functional group can enhance the effect of improving the dispersibility of silica.

[0015] In this embodiment, the rubber component contains more than 40% by mass and less than 75% by mass of natural rubber. That is, the amount of natural rubber per 100 parts by mass of the rubber component is more than 40 parts by mass and less than 75 parts by mass. Furthermore, the amount of styrene (bound styrene amount) in the rubber components other than natural rubber is 21% by mass or less. By including a relatively large amount of natural rubber in the rubber component, chipping resistance and tear resistance can be improved. Furthermore, by having a styrene amount of 21% by mass or less in the rubber component other than natural rubber (hereinafter also referred to as "other rubber component X"), the balance between abrasion resistance and low rolling resistance can be improved. While the reason for this is not intended to be limited to this, it is believed that a low styrene amount enhances compatibility between the other rubber component X and natural rubber, thereby improving low rolling resistance and abrasion resistance while maintaining chipping resistance and tear resistance.

[0016] As described above, the other rubber component X contains a styrene-butadiene rubber. Therefore, the other rubber component X contains a styrene unit. In this embodiment, the other rubber component X is formed by combining one or more rubbers so that the styrene content in the other rubber component X is 21% by mass or less. The styrene content in the other rubber component X is preferably 1 to 21% by mass, more preferably 2 to 20% by mass, and even more preferably 5 to 18% by mass.

[0017] The amount of styrene in the other rubber component X is the total content (mass%) of styrene units contained in the total amount of the other rubber component X, and Σ(each rubber X A Content (mass%) x each rubber X A The amount of styrene in each rubber (mass%) is calculated by dividing the total by 100. A The content (mass%) of each rubber X constituting the other rubber component X in 100 mass% of the other rubber component X is A The mass ratio of each rubber X A The amount of styrene in (mass%) is 1 Determined by H-NMR.

[0018] The other rubber component X may be composed of only styrene-butadiene rubber, or may contain other diene rubbers together with styrene-butadiene rubber. The diene rubber refers to a rubber having repeating units corresponding to diene monomers having conjugated double bonds, and containing carbon-carbon double bonds in the polymer main chain.

[0019] Specific examples of other diene rubbers include synthetic isoprene rubber (IR), butadiene rubber (BR), nitrile rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, etc. Among these, butadiene rubber is preferred as the other diene rubber, and therefore the rubber component may contain natural rubber, styrene-butadiene rubber, and butadiene rubber.

[0020] In one embodiment, 100 parts by mass of the rubber component may include more than 40 parts by mass and less than 75 parts by mass of natural rubber, 15 to less than 60 parts by mass of styrene-butadiene rubber, and 0 to less than 45 parts by mass of butadiene rubber. Here, the butadiene rubber is an optional component. Preferably, 100 parts by mass of the rubber component includes more than 40 to 60 parts by mass of natural rubber, 15 to less than 60 parts by mass of styrene-butadiene rubber, and 0 to less than 45 parts by mass of butadiene rubber. More preferably, 100 parts by mass of the rubber component includes 42 to 60 parts by mass of natural rubber, 16 to 58 parts by mass of styrene-butadiene rubber, and 0 to 42 parts by mass of butadiene rubber. 100 parts by mass of the rubber component may include 42 to 60 parts by mass of natural rubber, 20 to 48 parts by mass of styrene-butadiene rubber, and 0 to 30 parts by mass of butadiene rubber. 100 parts by mass of the rubber component may contain 10 parts by mass or more of butadiene rubber.

[0021] The total amount of natural rubber and styrene-butadiene rubber in 100 parts by mass of the rubber component is preferably 55 parts by mass, more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more.

[0022] The rubber composition according to this embodiment has a CTAB adsorption specific surface area of ​​200 m 2 / g。By blending silica with such a small CTAB adsorption specific surface area, it is possible to improve low rolling resistance and tear resistance. Examples of silica include wet silica and dry silica, and it is preferable to use wet silica such as wet precipitation silica and wet gelation silica.

[0023] The lower limit of the CTAB adsorption specific surface area of ​​silica is not particularly limited, but for example, from the viewpoint of increasing the rigidity when used in off-road tires, it is set to 100 m 2 The CTAB adsorption specific surface area of ​​silica is preferably 105 to 190 m / g or more. 2 / g, and more preferably 150 to 180m 2 / g, and more preferably 160 to 170m 2 The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area of ​​silica is measured in accordance with JIS K6430:2008, Appendix G.

[0024] The amount of silica in the rubber composition is more than 55 parts by mass and less than 90 parts by mass per 100 parts by mass of the rubber component. When the amount of silica exceeds 55 parts by mass, it is possible to improve abrasion resistance and tear resistance. When the amount of silica is less than 90 parts by mass, it is possible to improve abrasion resistance and low rolling resistance. The amount of silica is preferably 60 to 85 parts by mass, more preferably 60 to 80 parts by mass, and even more preferably 60 to 75 parts by mass per 100 parts by mass of the rubber component.

[0025] The rubber composition according to the present embodiment may contain a silane coupling agent. Examples of the silane coupling agent include a sulfide silane coupling agent and a mercapto silane coupling agent. The content of the silane coupling agent is not particularly limited, and may be, for example, 5 to 20 parts by mass or 5 to 15 parts by mass per 100 parts by mass of silica.

[0026] In the rubber composition according to the present embodiment, the filler may be silica alone, or other fillers may be blended together with silica. Carbon black is preferably used as the other filler. The proportion of silica in the filler is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0027] When the rubber composition contains carbon black, the content of carbon black is not particularly limited, but is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 3 to 15 parts by mass, and may be 3 to 10 parts by mass, per 100 parts by mass of the rubber component.

[0028] The rubber composition according to the present embodiment may further contain a thermoplastic resin. The thermoplastic resin blended into the rubber composition is also called a tackifying resin, and can enhance the effect of improving chipping resistance and tear resistance. The thermoplastic resin is not particularly limited, but preferably has a softening point of 50 to 150°C, more preferably 70 to 120°C. The softening point of the resin is measured using a ring and ball softening point tester in accordance with JIS K6220-1:2015.

[0029] Specific examples of thermoplastic resins include petroleum resins (e.g., C5 petroleum resins, C9 petroleum resins, C5 / C9 petroleum resins), styrene resins, terpene resins (e.g., polyterpene resins, terpene phenol resins), coumarone resins (e.g., coumarone resins, coumarone-indene resins), and rosin resins (e.g., natural resin rosin, rosin-modified maleic acid resins), and any one or more of these may be used in combination.

[0030] The content of the thermoplastic resin is not particularly limited, and may be 0.5 to 20 parts by mass, 1 to 15 parts by mass, 2 to 10 parts by mass, or 2 to 7 parts by mass per 100 parts by mass of the rubber component.

[0031] In addition to the above components, the rubber composition according to the present embodiment may contain various additives that are generally used in rubber compositions, such as oil, zinc oxide, stearic acid, antioxidants, wax, vulcanizing agents, and vulcanization accelerators.

[0032] Examples of oils include mineral oils such as paraffinic oil, naphthenic oil, and aromatic oil, and vegetable oils such as linseed oil, safflower oil, soybean oil, corn oil, castor oil, rapeseed oil, and cottonseed oil. These oils can be used alone or in combination of two or more. The content of the oil is not particularly limited, and may be, for example, 0 to 100 parts by mass, 10 to 50 parts by mass, or 15 to 35 parts by mass per 100 parts by mass of the rubber component.

[0033] The content of zinc oxide is not particularly limited, and may be, for example, 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass relative to 100 parts by mass of the rubber component.

[0034] The content of stearic acid is not particularly limited, and may be, for example, 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass relative to 100 parts by mass of the rubber component.

[0035] Examples of the antioxidant include various antioxidants such as amine-ketone, aromatic secondary amine, monophenol, bisphenol, and benzimidazole antioxidants, and any one of them can be used alone or in combination of two or more. The content of the antioxidant is not particularly limited, and may be, for example, 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass per 100 parts by mass of the rubber component.

[0036] The content of the wax is not particularly limited, and may be, for example, 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass per 100 parts by mass of the rubber component.

[0037] As the vulcanizing agent, sulfur is preferably used. The content of the vulcanizing agent is not particularly limited, and may be 0.1 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 3 parts by mass per 100 parts by mass of the rubber component.

[0038] Examples of the vulcanization accelerator include various vulcanization accelerators such as sulfenamide-based, guanidine-based, thiuram-based, and thiazole-based accelerators, and any one of them can be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and may be 0.1 to 10 parts by mass, 1 to 7 parts by mass, or 2 to 5 parts by mass per 100 parts by mass of the rubber component.

[0039] The rubber composition according to the present embodiment can be prepared by kneading in a conventional manner using a commonly used mixer such as a Banbury mixer, kneader, roll, etc. That is, for example, in a first mixing stage, additives other than the vulcanizing agent and vulcanization accelerator are added and mixed with the rubber component, and then in a final mixing stage, the vulcanizing agent and vulcanization accelerator are added and mixed with the resulting mixture to prepare the rubber composition.

[0040] The rubber composition according to the present embodiment can be used in tire treads. Examples of tires include pneumatic tires of various sizes and for various uses, such as tires for passenger cars and large tires for trucks and buses. The rubber composition is preferably used in the treads of off-road tires such as mud-terrain (M / T) and all-terrain (A / T) tires.

[0041] A tire according to one embodiment includes a tread made using the rubber composition. That is, the tire according to one embodiment includes a tread rubber formed from the rubber composition. The tread rubber of the tire may have a two-layer structure of a cap rubber and a base rubber, or a single-layer structure in which the two are integrated. In the single-layer structure, the tread rubber may be formed from the rubber composition. In the two-layer structure, the outer cap rubber that comes into contact with the road surface is preferably formed from the rubber composition, but the base rubber disposed inside the cap rubber may also be formed from the rubber composition, or both the cap rubber and the base rubber may be formed from the rubber composition.

[0042] The method for manufacturing a tire is not particularly limited. For example, the rubber composition is extruded into a predetermined shape according to a conventional method to obtain an unvulcanized tread rubber component. The tread rubber component is combined with other tire components to produce an unvulcanized tire (green tire). Thereafter, the tire can be manufactured by vulcanizing and molding at, for example, 140°C to 180°C. [Example]

[0043] Examples of the present invention will be shown below, but the present invention is not limited to these examples.

[0044] The components used in the examples and comparative examples are as follows. ·NR:RSS#3 SBR-1: Unmodified ESBR, styrene content = 23.5% by mass, "SBR1502" manufactured by ENEOS Material Corporation SBR-2: Terminally modified SSBR, styrene content = 20.5% by mass, "HPR350" manufactured by ENEOS Material Corporation SBR-3: Terminally modified SSBR, styrene content = 10% by mass, "HPR840" manufactured by ENEOS Material Corporation BR: UBE Corporation "BR150B"

[0045] Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. Silica-1: Ultrasil VN3 manufactured by Evonik Industries, CTAB=167m 2 / g Silica-2: Evonik Industries "Ultrasil 9100GR", CTAB=200m 2 / g Silica-3: Evonik Industries "Ultrasil 5000GR", CTAB=110m 2 / g Silane coupling agent: Evonik Industries "Si69"

[0046] Oil: ENEOS Corporation "Process NC-140" Zinc oxide: "Zinc oxide type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Wax: Nippon Seiro Co., Ltd. "OZOACE0355" Resin: C5 / C9 petroleum resin (aliphatic / aromatic copolymer hydrocarbon resin), Tosoh Corporation's "Petrotack 90", softening point = 95°C

[0047] Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator CZ: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd. Vulcanization accelerator DPG: "Noccela D" manufactured by Ouchi Shinko Chemical Co., Ltd.

[0048] Using a Banbury mixer, rubber compositions were prepared according to the formulations (parts by mass) shown in Tables 1 to 3 below. Specifically, in the first mixing stage, compounding ingredients excluding sulfur and vulcanization accelerator were added to the rubber component and kneaded (discharge temperature = 155°C). Next, in the final mixing stage, sulfur and vulcanization accelerator were added to the resulting kneaded mixture and kneaded (discharge temperature = 90°C) to prepare the rubber composition. Note that "St (%) in X" in the tables refers to the amount of styrene (% by mass) in the other rubber component X.

[0049] Each of the rubber compositions thus obtained was evaluated for low rolling resistance, abrasion resistance, chipping resistance, and tear resistance, using the following evaluation methods.

[0050] [Low rolling resistance performance] Using the rubber composition as tread rubber, a test pneumatic radial tire (tire size: 215 / 45ZR17) was produced by vulcanization molding according to a conventional method. The rolling resistance of the obtained test tire was measured using a rolling resistance measurement drum tester under conditions of an air pressure of 230 kPa, a load of 450 kgf (4.4 kN), a temperature of 23°C, and a speed of 80 km / h. The reciprocal of the rolling resistance was expressed as an index, with the value of Comparative Example 1 being set at 100. A larger index indicates lower rolling resistance and better low rolling resistance performance (fuel economy).

[0051] [Wear resistance] The rubber composition was vulcanized at 160°C for 30 minutes to prepare a rubber sample. The abrasion loss of the rubber sample was measured using a Lambourn abrasion tester in accordance with JIS K6264-2:2005 under conditions of a load of 3 kg, a slip ratio of 24%, a temperature of 23°C, and a sand dropping rate of 20 g / min. The reciprocal of the abrasion loss was expressed as an index, with the value for Comparative Example 1 set to 100. A larger index indicates a smaller abrasion loss and better abrasion resistance.

[0052] [Chipping resistance] A tensile test was conducted in accordance with JIS K6251:2017 to determine the tensile product. Specifically, the rubber composition was vulcanized at 160°C for 30 minutes to prepare a rubber sample (dumbbell-shaped No. 3, thickness 2.0 mm). A tensile test (speed: 500 mm / min) was conducted on the rubber sample to measure the elongation at break Eb (%) and tensile strength T (MPa). The tensile product, which is the product of the elongation at break and the tensile strength (Eb x T), was determined and expressed as an index, with the value for Comparative Example 1 set to 100. A larger index indicates a larger tensile product and better chipping resistance.

[0053] [Tear resistance] Tear strength was measured in accordance with JIS K6252-1:2015. Specifically, the rubber composition was vulcanized at 160°C for 30 minutes to prepare a rubber sample (crescent shape, thickness 2.0 mm). A tensile test (speed: 500 mm / min) was conducted on the rubber sample to determine tear strength, which was expressed as an index with the value of Comparative Example 1 set to 100. A larger index indicates greater tear strength and better tear resistance.

[0054] [Table 1]

[0055] [Table 2]

[0056] [Table 3]

[0057] The results are shown in Tables 1 to 3. In Comparative Example 1, the amount of natural rubber was near the lower limit and satisfied the specified range, but the amount of styrene in the other rubber component X was greater than 21% by mass, resulting in poor low rolling resistance and wear resistance. In Comparative Example 2, the styrene butadiene rubber in Comparative Example 1 was replaced with butadiene rubber, and although wear resistance was improved, chipping resistance and tear resistance were deteriorated.

[0058] In Comparative Example 3, the amount of natural rubber was increased to 60 parts by mass compared to Comparative Example 1, which improved chipping resistance and tear resistance. However, as in Comparative Example 1, the amount of styrene in the other rubber component X was greater than 21% by mass, so the abrasion resistance was poor.

[0059] In Comparative Example 4, the amount of silica exceeded the upper limit, resulting in poor abrasion resistance and chipping resistance. In Comparative Example 5, a thermoplastic resin was added to Comparative Example 4, and chipping resistance was improved somewhat but not satisfactorily, and the abrasion resistance and low rolling resistance were also poor.

[0060] In Comparative Example 6, the amount of styrene in the other rubber component X was 21% by mass or less, but the amount of natural rubber was less than the specified amount, so chipping resistance was inferior to that of Comparative Example 1.

[0061] In Comparative Example 7, chipping resistance and tear resistance were superior to Comparative Example 1, but the amount of natural rubber exceeded the specified amount, so the effect of improving low rolling resistance was not obtained and the abrasion resistance was inferior. In Comparative Example 8, a thermoplastic resin was added to Comparative Example 7, but the effect of improving low rolling resistance and abrasion resistance was not observed.

[0062] In Comparative Example 9, the amount of silica was less than the specified amount, so no improvement in abrasion resistance was achieved and tear resistance was inferior to Comparative Example 1. In Comparative Example 10, silica with a CTAB adsorption specific surface area larger than the specified amount was used, and the tire was inferior to Comparative Example 1 in low rolling resistance and tear resistance.

[0063] In contrast, Examples 1 to 13 were improved over Comparative Example 1 in all of low rolling resistance, wear resistance, chipping resistance, and tear resistance, and were excellent in these performances.

[0064] Specifically, Examples 1 to 4 are examples in which the amount of natural rubber was kept constant compared to Comparative Example 1, while the amount of styrene in the other rubber component X was reduced. In Examples 1 to 4, the lower the amount of styrene in the other rubber component X, the more improved the compatibility with natural rubber, thereby improving the effects of improving abrasion resistance, tear resistance, and chipping resistance. Low rolling resistance was also significantly improved compared to Comparative Example 1, but the improvement leveled off at a styrene amount of about 15% by mass, and Example 4 showed a smaller improvement in low rolling resistance compared to Example 2.

[0065] Examples 5 to 7 are examples in which the amount of natural rubber was kept constant while the amount of styrene in the other rubber component X was reduced compared to Comparative Example 3. In Examples 5 to 7, the reduction in the amount of styrene in the other rubber component X improved compatibility with natural rubber, and compared to Comparative Example 3, the chipping resistance and tear resistance were maintained or improved, while the abrasion resistance and low rolling resistance were significantly improved.

[0066] Examples 8 and 9 are examples in which the amount of silica was reduced to 80 parts by mass while the amount of natural rubber was kept constant compared to Comparative Examples 4 and 5. Examples 8 and 9 showed significant improvements in low rolling resistance, abrasion resistance, and chipping resistance compared to Comparative Examples 4 and 5, and all four performances, including tear resistance, were good.

[0067] In Examples 10 to 12, the mass ratio of NR / SBR / BR was set to 50 / 35 / 15, and the amount of silica was changed within the specified range. Regardless of the silica amount, the tires exhibited excellent low rolling resistance, abrasion resistance, chipping resistance, and tear resistance.

[0068] Example 13 is an example in which silica was replaced with a material having a small CTAB adsorption specific surface area compared to Example 1, and similar to Example 1, it had excellent low rolling resistance, wear resistance, chipping resistance, and tear resistance.

[0069] The various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

Claims

1. Rubber components including natural rubber and styrene butadiene rubber, and a CTAB adsorption specific surface area of ​​200 m ２ and less than 1 / g of silica, the amount of the natural rubber is more than 40 parts by mass and less than 75 parts by mass per 100 parts by mass of the rubber component, the amount of styrene in the rubber component other than the natural rubber is 21% by mass or less, The amount of the silica is more than 55 parts by mass and less than 90 parts by mass per 100 parts by mass of the rubber component. A rubber composition for tire treads.

2. 2. The rubber composition for a tire tread according to claim 1, wherein 100 parts by mass of the rubber component comprises more than 40 parts by mass and not more than 60 parts by mass of the natural rubber, 15 parts by mass or more and less than 60 parts by mass of the styrene-butadiene rubber, and 0 part by mass or more and less than 45 parts by mass of the butadiene rubber.

3. The rubber composition for a tire tread according to claim 1 , wherein the styrene-butadiene rubber comprises a modified styrene-butadiene rubber.

4. 2. The rubber composition for a tire tread according to claim 1, wherein the amount of the silica is 60 to 75 parts by mass per 100 parts by mass of the rubber component.

5. A tire having a tread formed from the rubber composition for a tire tread according to any one of claims 1 to 4.

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