Tire

Abstract

To provide a rubber composition for a tread which is excellent in balance between wet grip performance and chipping-resistant performance.SOLUTION: The rubber composition for a tread contains, based on 100 pts.mass of a rubber component containing 20 to 50 mass% of a butadiene rubber and 30 to 80 mass% of a styrene-butadiene rubber, 1 to 20 pts.mass of an ethylene-propylene-styrene copolymer and 60 pts.mass or more of a filler containing silica and has an elongation at break under a 180°C atmosphere based on JIS K 6251:2017 of 300% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition for a tread and a tire having a tread composed of this rubber composition.

Background Art

[0002] Patent Document 1 describes a tire having a tread composed of a rubber composition containing an ethylene-propylene-styrene copolymer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the blending amount of natural rubber in the rubber composition is increased to improve chipping resistance as in the rubber composition described in Patent Document 1, there is a problem that the wet grip performance deteriorates.

[0005] An object of the present invention is to provide a rubber composition for a tread having an excellent balance between wet grip performance and chipping resistance.

Means for Solving the Problems

[0006] The inventor of the present invention has found that a rubber composition for a tread containing a rubber component containing a predetermined amount of butadiene rubber and styrene-butadiene rubber, an ethylene-propylene-styrene copolymer, and a filler containing silica and having a breaking elongation within a predetermined range improves wet grip performance and chipping resistance in a well-balanced manner, and has completed the present invention.

Effects of the Invention

[0007] According to the present invention, it is possible to provide a tread rubber composition excellent in the balance between wet grip performance and chipping resistance performance, and a tire having a tread composed of the rubber composition.

Embodiment for Carrying Out the Invention

[0008] A rubber composition for a tire according to an embodiment of the present invention contains a rubber component including a predetermined amount of butadiene rubber and styrene-butadiene rubber, an ethylene-propylene-styrene copolymer, and a filler including silica, and is characterized by having a breaking elongation within a predetermined range. In the present specification, when a numerical range is indicated using "~", it includes the numerical values at both ends thereof.

[0009] In the present specification, the "normal rim" is a rim defined for each tire in a standard system including the standard on which the tire is based. For example, in the case of JATMA, it is the standard rim, in the case of TRA, it is the "Design Rim", and in the case of ETRTO, it is the "Measuring Rim".

[0010] In the present specification, the "normal internal pressure" is the air pressure defined for each tire by the above standard. In the case of JATMA, it is the maximum air pressure, in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, it is the "INFLATION PRESSURE".

[0011] The present invention includes a first invention to a third invention, and the first invention to the third invention will be described below.

[0012] [First Invention] The first invention is [1] Based on 100 parts by mass of a rubber component containing 20 to 50% by mass (preferably 22 to 45% by mass, more preferably 25 to 40% by mass) of butadiene rubber and 30 to 80% by mass (preferably 35 to 78% by mass, more preferably 40 to 75% by mass) of styrene-butadiene rubber, 1 to 20 parts by mass (preferably 2 to 15 parts by mass, more preferably 3 to 10 parts by mass) of an ethylene-propylene-styrene copolymer, and 60 parts by mass or more (preferably 60 to 150 parts by mass, more preferably 65 to 140 parts by mass) of a filler containing silica, a tread rubber composition having an elongation at break of 300% or more (preferably 325% or more, more preferably 350% or more) under an atmosphere of 180 °C based on JIS K 6251:2017, [2] The tread rubber composition according to [1], wherein the composition ratio of the ethylene-propylene-styrene copolymer is 10 to 60% by mass of ethylene, 10 to 60% by mass of propylene, and 5 to 40% by mass of styrene. [3] The tread rubber composition according to [1] or [2], wherein the rubber component contains 30 to 80% by mass (preferably 35 to 78% by mass, more preferably 40 to 75% by mass) of an emulsion-polymerized styrene-butadiene rubber. [4] The tread rubber composition according to any one of [1] to [3], containing 1 to 120 parts by mass (preferably 5 to 105 parts by mass, more preferably 10 to 90 parts by mass) of silica having a nitrogen adsorption specific surface area of 150 m 2 / g or more. [5] The tread rubber composition according to any one of [1] to [4], containing 20 to 120 parts by mass (preferably 25 to 100 parts by mass, more preferably 30 to 80 parts by mass) of carbon black having a nitrogen adsorption specific surface area of 100 m 2 / g or more. [6] Regarding a tire having a tread composed of the tread rubber composition according to any one of [1] to [5].

[0013] <Rubber component> The rubber component used in the first invention contains styrene-butadiene rubber (SBR) and butadiene rubber (BR). Also, within a range not impairing the effects of the present invention, isoprene-based rubbers such as natural rubber may be blended. Further, the rubber component may be a rubber component consisting only of SBR and BR, or may be a rubber component consisting only of isoprene-based rubber, SBR, and BR.

[0014] (SBR) There are no particular limitations on SBR, and examples include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), modified SBRs of these (modified S-SBR, modified E-SBR), etc., and it may or may not be oil-extended. Examples of modified SBR include SBR with modified terminals and / or main chains, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, those having a branched structure, etc.). Among them, E-SBR is preferred because of its excellent chipping resistance performance.

[0015] Examples of S-SBR that can be used in the first invention include S-SBR manufactured and sold by JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc.

[0016] From the viewpoints of grip performance and rubber strength, the styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. Also, from the viewpoint of low fuel consumption performance, the styrene content of SBR is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. Note that the styrene content of SBR in this specification is 1 a value calculated by 1H-NMR measurement.

[0017] From the viewpoint of chipping resistance performance, the content of SBR in the rubber component is 30% by mass or more, preferably 35% by mass or more, and more preferably 40% by mass or more. Also, from the viewpoint of abrasion resistance performance, it is 80% by mass or less, preferably 78% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0018] (BR) BR is not particularly limited. For example, BR with a cis-1,4 bond content of less than 50% (low-cis BR), BR with a cis-1,4 bond content of 90% or more (high-cis BR), rare-earth butadiene rubber synthesized using a rare-earth element-based catalyst (rare-earth-based BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc., which are common in the tire industry, can be used. Among these BRs, high-cis BR is preferred because of its excellent abrasion resistance performance.

[0019] Examples of high-cis BR include BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B, BR150B, BR150L manufactured by Ube Industries, Ltd., BR730 manufactured by JSR Corporation, etc. By containing high-cis BR, the low-temperature properties and abrasion resistance performance can be improved. Examples of rare-earth-based BR include BUNA-CB25 manufactured by Lanxess.

[0020] From the viewpoints of durability and abrasion resistance performance, the cis-1,4 bond content (cis content) of BR is preferably 90% by mass or more, more preferably 93% by mass or more, and still more preferably 95% by mass or more. When the cis content is higher, since the polymer chains are regularly arranged, the interaction between polymers becomes stronger, the rubber strength is improved, and the chipping resistance performance is considered to be improved.

[0021] The content in the rubber component of BR is 20% by mass or more, preferably 22% by mass or more, and more preferably 25% by mass or more. When it is less than 20% by mass, the effects of the present invention tend to be insufficient. Also, the content of BR is 50% by mass or less, preferably 45% by mass or less, and more preferably 40% by mass or less. When it exceeds 50% by mass, the chipping resistance performance decreases, and block chipping tends to occur easily.

[0022] (Isoprene rubber) As the isoprene rubber, for example, those commonly used in the tire industry such as isoprene rubber (IR) and natural rubber can be used. Natural rubber includes, in addition to non-modified natural rubber (NR), modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and grafted natural rubber. These rubbers may be used alone or in combination of two or more.

[0023] NR is not particularly limited, and those commonly used in the tire industry can be used. For example, SIR20, RSS#3, TSR20, etc. can be mentioned.

[0024] When containing isoprene rubber, the content in the rubber component is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more from the viewpoint of chipping resistance performance. Also, from the viewpoint of wet grip performance, it is preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less.

[0025] (Other rubber components) As the rubber component according to the first invention, rubber components other than the above-mentioned isoprene rubber, SBR, and BR may be contained. As other rubber components, crosslinkable rubber components commonly used in the rubber industry can be used. For example, diene rubbers such as styrene-isoprene-butadiene copolymer rubber (SIBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and butyl rubber can be mentioned. These other rubber components may be used alone or in combination of two or more.

[0026] <Ethylene-propylene-styrene copolymer> Ethylene-propylene-styrene copolymer is a copolymer of ethylene, propylene, and styrene, and has the property that the ethylene phase and the propylene phase are compatible with the rubber component, and the styrene phase is compatible with the filler. The rubber composition according to the first invention uses a rubber component containing SBR and BR, the copolymer, and a filler containing silica in combination, thereby improving the interaction between the polymer and the filler. Therefore, the dispersibility of the filler in the rubber component is improved and it is evenly dispersed, so it is considered that the wet grip performance and the anti-chipping performance are improved in a well-balanced manner.

[0027] From the viewpoint of low fuel consumption performance, the ethylene content in the ethylene-propylene-styrene copolymer is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more. From the viewpoint of wet grip performance, it is preferably 60% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less.

[0028] From the viewpoint of wet grip performance, the propylene content in the ethylene-propylene-styrene copolymer is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more. From the viewpoint of low fuel consumption performance, it is preferably 60% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less.

[0029] From the viewpoint of anti-chipping performance, the styrene content in the ethylene-propylene-styrene copolymer is preferably 5% by mass or more, more preferably 8% by mass or more, and still more preferably 10% by mass or more. From the viewpoint of low fuel consumption performance, it is preferably 40% by mass or less, more preferably 25% by mass or less, and still more preferably 20% by mass or less.

[0030] Examples of such ethylene-propylene-styrene copolymers include Promix 400 manufactured by Flow Polymers Inc.

[0031] The content by mass of the ethylene-propylene-styrene copolymer with respect to 100 parts by mass of the rubber component is 1 part by mass or more, preferably 2 parts by mass or more, and more preferably 3 parts by mass or more. When the content of the ethylene-propylene-styrene copolymer is less than 1 part by mass, the chipping resistance performance tends to decrease. Also, the content of the ethylene-propylene-styrene copolymer is 20 parts by mass or less, preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less. When the content of the ethylene-propylene-styrene copolymer exceeds 20 parts by mass, the wet grip performance tends to decrease.

[0032] <Filler> The filler used in the first invention is characterized by containing silica as an essential component. Also, silica is preferably used in combination with a silane coupling agent.

[0033] (Silica) Silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., which are common in the tire industry, can be used. Among them, hydrous silica prepared by a wet method is preferred because it has many silanol groups. Silica may be used alone or in combination of two or more.

[0034] The nitrogen adsorption specific surface area (N2SA) of silica is preferably 125 m 2 / g or more from the viewpoint of elongation at break, more preferably 150 m 2 / g or more, even more preferably 175 m 2 / g or more, particularly preferably 200 m 2 / g or more. Also, the N2SA of silica is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, from the viewpoints of low fuel consumption performance and processability, and even more preferably 250 m 2Less than / g is more preferable. It is considered that such small particles of silica are dispersed near the boundaries of each phase of the isoprene rubber, BR, and SBR, increasing the contact area between the rubber component and the silica and exerting the effect of improving the chipping resistance performance. The N2SA of silica in this specification is a value measured by the BET method in accordance with ASTM D3037-93.

[0035] From the viewpoint of wet grip performance, the content of silica is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. From the viewpoints of the dispersibility of silica and processability, it is preferably 120 parts by mass or less, more preferably 105 parts by mass or less, still more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0036] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica in the rubber industry can be used. Examples of such silane coupling agents include sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide and bis(3-triethoxysilylpropyl)tetrasulfide; mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, NXT-Z100, NXT-Z45, and NXT manufactured by Momentive; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane; and the like. These silane coupling agents may be used alone or in combination of two or more.

[0037] When containing a silane coupling agent, the content thereof per 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and further preferably 1 part by mass or more. Also, the content of the silane coupling agent per 100 parts by mass of the rubber component is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less.

[0038] (Other fillers) As the filler, other fillers may be used in addition to silica. Such fillers are not particularly limited, and for example, any fillers generally used in the rubber industry such as carbon black, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, talc, clay, etc. can be used. These fillers may be used alone or in combination of two or more. When using a filler other than silica, carbon black is preferred from the viewpoint of rubber strength. That is, the filler preferably contains silica and carbon black, and more preferably consists only of silica and carbon black.

[0039] As the carbon black, those generally used for rubber can be appropriately used. Examples of the carbon black include furnace black, acetylene black, thermal black, channel black, graphite, etc. Specifically, N110, N115, N120, N125, N134, N135, N219, N220, N231, N234, N293, N299, N326, N330, N339, N343, N347, N351, N356, N358, N375, N539, N550, N582, N630, N642, N650, N660, N683, N754, N762, N765, N772, N774, N787, N907, N908, N990, N991, etc. can be preferably used, and in addition, self-made synthetic products, etc. can also be preferably used. These carbon blacks may be used alone or in combination of two or more.

[0040] The nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 100 m 2 / g or more, more preferably 125 m 2 / g or more, even more preferably 135 m 2 / g or more, and particularly preferably 145 m 2 / g or more. Also, the upper limit of the N2SA of the carbon black is not particularly limited, but from the viewpoints of low fuel consumption performance, dispersibility, and processability, it is preferably 400 m 2 / g or less, and preferably 300 m2 It is more preferably 250 m 2 / g or less, and even more preferably 200 m 2 / g or less is particularly preferred. It is considered that such small-particle carbon black is dispersed near the boundary of each phase of isoprene rubber, BR, and SBR, increasing the contact area between the rubber component and carbon black and exerting the effect of improving chipping resistance performance. The N2SA of carbon black in this specification is a value measured according to JIS K 6217-2 "Basic characteristics of carbon black for rubber - Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single-point method".

[0041] The average primary particle diameter of carbon black is preferably 30 nm or less, preferably 25 nm or less, and even more preferably 20 nm or less. Also, from the viewpoint of processability, the average primary particle diameter of carbon black is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. When the particle diameter of carbon black is within the above range, it tends to be easier to achieve both wet grip performance and chipping resistance performance. In this specification, the average primary particle diameter of carbon black can be determined by observing with a transmission electron microscope and measuring 400 or more primary particles observed in the field of view and taking the average thereof.

[0042] From the viewpoints of weather resistance and reinforcement, the content of carbon black based on 100 parts by mass of the rubber component is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, and particularly preferably 35 parts by mass or more. Also, although the upper limit of the content of carbon black is not particularly limited, from the viewpoints of low fuel consumption performance and processability, it is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0043] From the perspective of better exerting the effects of the present invention, the content of the filler in 100 parts by mass of the rubber component of the entire filler is 60 parts by mass or more, preferably 65 parts by mass or more, and more preferably 70 parts by mass or more. Also, from the perspectives of the dispersibility of the filler and processability, it is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, still more preferably 130 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0044] From the perspective of wet grip performance, the content of silica in the filler is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and particularly preferably 12% by mass or more. Also, from the perspectives of weather resistance and reinforcement, it is preferably 95% by mass or less, more preferably 90% by mass or less, and still more preferably 85% by mass or less.

[0045] <Other components> In addition to the above rubber component, ethylene-propylene-styrene copolymer, and filler, the rubber composition according to the first invention may appropriately contain compounding agents and additives conventionally used in the tire industry, such as oil, wax, anti-aging agent, stearic acid, zinc oxide, vulcanizing agent, vulcanization accelerator, etc., as necessary.

[0046] From the perspective of ensuring good abrasion resistance performance, when containing oil, the content relative to 100 parts by mass of the rubber component is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and still more preferably 60 parts by mass or less. Also, from the perspective of processability, it is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more. In this specification, the content of oil also includes the amount of oil contained in oil-extended rubber.

[0047] From the perspective of the weather resistance of the rubber composition, when containing wax, the content relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, and more preferably 1 part by mass or more. Also, from the perspective of preventing the whitening of the tire due to blooming, it is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

[0048] The anti-aging agent is not particularly limited, and those used in the rubber industry can be used. For example, quinoline-based, quinone-based, phenol-based, phenylenediamine-based anti-aging agents, etc. can be mentioned.

[0049] When containing an anti-aging agent, the content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, from the viewpoint of the ozone crack resistance of the rubber composition. Also, from the viewpoints of abrasion resistance performance and grip performance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0050] When containing stearic acid, the content based on 100 parts by mass of the rubber component is preferably 0.2 part by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability. Also, from the viewpoint of vulcanization rate, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0051] When containing zinc oxide, the content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability. Also, from the viewpoint of abrasion resistance performance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0052] As the vulcanizing agent, sulfur is preferably used. As sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, etc. can be used.

[0053] When containing sulfur as the vulcanizing agent, the content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction and obtaining good grip performance and abrasion resistance performance. Also, from the viewpoint of deterioration prevention, it is preferably 3.0 parts by mass or less, more preferably 2.5 parts by mass or less.

[0054] Examples of vulcanizing agents other than sulfur include vulcanizing agents containing sulfur atoms such as Tackiol V200 manufactured by Taoka Chemical Industry Co., Ltd., DURALINK HTS (sodium 1,6 - hexamethylene - dithiolsulfate dihydrate) manufactured by Flexsys, KA9188 (1,6 - bis(N,N’ - dibenzylthiocarbamoyldithio)hexane) manufactured by Lanxess, and organic peroxides such as dicumyl peroxide.

[0055] Examples of vulcanization accelerators include sulfenamide - type, thiazole - type, thiuram - type, thiourea - type, guanidine - type, dithiocarbamic acid - type, aldehyde - amine - type or aldehyde - ammonia - type, imidazoline - type, and xanthate - type vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among them, sulfenamide - type vulcanization accelerators, thiazole - type vulcanization accelerators, and guanidine - type vulcanization accelerators are preferred, and sulfenamide - type vulcanization accelerators are more preferred.

[0056] Examples of sulfenamide - type vulcanization accelerators include N - tert - butyl - 2 - benzothiazolylsulfenamide (TBBS), N - cyclohexyl - 2 - benzothiazolylsulfenamide (CBS), N,N - dicyclohexyl - 2 - benzothiazolylsulfenamide (DCBS), etc. Among them, N - tert - butyl - 2 - benzothiazolylsulfenamide (TBBS) and N - cyclohexyl - 2 - benzothiazolylsulfenamide (CBS) are preferred.

[0057] When containing a vulcanization accelerator, the content relative to 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, from the viewpoint of vulcanization acceleration. From the viewpoint of processability, it is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

[0058] <Manufacture of Rubber Composition and Tire> The rubber composition according to the first invention can be produced by a known method. For example, using a known kneader used in the general rubber industry such as a Banbury mixer, a kneader, an open roll, etc., among the above components, after kneading the components other than the vulcanizing agent and the vulcanization accelerator, the vulcanizing agent and the vulcanization accelerator are added thereto and further kneaded, and then it can be produced by a method such as vulcanization.

[0059] Since the rubber composition according to the first invention is excellent in chipping resistance, it is preferably used for the tread of a tire.

[0060] The elongation at break (elongation at cut) EB (%) of the rubber composition according to the first invention is 300% or more, preferably 325% or more, and more preferably 350% or more. The elongation at break in this embodiment is measured by preparing a No. 3 dumbbell test piece made of the vulcanized rubber composition and performing a tensile test in an atmosphere of 180 °C in accordance with JIS K 6251:2017 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Tensile Test Properties".

[0061] A tire using the rubber composition according to the first invention can be produced by a normal method using the above rubber composition. That is, the rubber composition in which the above compounding agent is blended with the rubber component as necessary is extruded according to the shape of the tread, etc., and bonded together with other tire members on a tire molding machine and molded by a normal method to form an unvulcanized tire, and this unvulcanized tire is heated and pressurized in a vulcanizer to produce a tire.

[0062] [Second Invention] The second invention is [1] 1 to 20 parts by mass of an ethylene-propylene-styrene copolymer, 60 parts by mass or more of a filler containing silica, based on 100 parts by mass of a rubber component containing 0 to 20% by mass of an isoprene-based rubber, 30 to 50% by mass of a butadiene rubber, and 30 to 70% by mass of a styrene-butadiene rubber, and having an elongation at break of 300% or more in an atmosphere of 180 °C based on JIS K 6251:2017, a tread rubber composition 〔2〕The composition ratio of the ethylene-propylene-styrene copolymer is 10 to 60% by mass of ethylene, 10 to 60% by mass of propylene, and 5 to 40% by mass of styrene, and the tread rubber composition according to 〔1〕, 〔3〕The rubber component contains 30 to 70% by mass of an emulsion-polymerized styrene-butadiene rubber, and the tread rubber composition according to 〔1〕 or 〔2〕, 〔4〕The content of silica in the filler is 1 to 70% by mass, and the tread rubber composition according to any one of 〔1〕 to 〔3〕, 〔5〕The nitrogen adsorption specific surface area is 150 m 2 / g or more, and the tread rubber composition according to any one of 〔1〕 to 〔4〕 contains 1 to 100 parts by mass of silica, 〔6〕The nitrogen adsorption specific surface area is 100 m 2 / g or more, and the tread rubber composition according to any one of 〔1〕 to 〔5〕 contains 20 to 120 parts by mass of carbon black, 〔7〕Relates to a tire having a tread composed of the tread rubber composition according to any one of 〔1〕 to 〔6〕.

[0063] <Rubber component> The rubber component used in the second invention contains styrene-butadiene rubber (SBR) and butadiene rubber (BR). Also, within a range that does not impair the effects of the present invention, isoprene-based rubbers such as natural rubber and other rubber components may be blended. As SBR, BR, isoprene-based rubbers, and other rubber components, those similar to the rubber components in the first invention can be preferably used in a similar manner.

[0064] The content of SBR in the rubber component is 30% by mass or more from the viewpoint of chipping resistance performance, preferably 35% by mass or more, and more preferably 40% by mass or more. Also, from the viewpoint of abrasion resistance performance, it is 70% by mass or less, preferably 65% by mass or less, and more preferably 60% by mass or less.

[0065] The content in the rubber component of BR is 30% by mass or more, preferably 35% by mass or more, and more preferably 40% by mass or more. When it is less than 30% by mass, the effects of the present invention tend to be insufficient. Also, the content of BR is 50% by mass or less, preferably 45% by mass or less, and more preferably 40% by mass or less. When it exceeds 50% by mass, the chipping resistance performance deteriorates, and block chipping tends to occur.

[0066] When containing an isoprene rubber, the content in the rubber component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more from the viewpoint of chipping resistance performance. Also, the content of the isoprene rubber in the rubber component is 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less. When the content of the isoprene rubber in the rubber component exceeds 20% by mass, the wet grip performance tends to deteriorate.

[0067] <Ethylene-propylene-styrene copolymer> The rubber composition according to the second invention contains an ethylene-propylene-styrene copolymer. As the ethylene-propylene-styrene copolymer, the same ones as those in the rubber composition of the first invention can be preferably used in the same manner.

[0068] <Filler> The filler used in the second invention is characterized by containing silica as an essential component. Also, silica is preferably used in combination with a silane coupling agent. Further, carbon black or other fillers may be used as the filler. As the silica, silane coupling agent, carbon black, and other fillers, the same ones as those in the rubber composition of the first invention can be preferably used in the same manner.

[0069] From the perspective of wet grip performance, the silica content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. Also, from the perspectives of silica dispersibility and processability, it is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, still more preferably 40 parts by mass or less.

[0070] When containing a silane coupling agent, the content with respect to 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and still more preferably 1 part by mass or more. Also, the content of the silane coupling agent with respect to 100 parts by mass of the rubber component is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less.

[0071] When containing carbon black, the content with respect to 100 parts by mass of the rubber component is preferably 20 parts by mass or more, more preferably 35 parts by mass or more, still more preferably 50 parts by mass or more, and particularly preferably 60 parts by mass or more from the perspectives of weather resistance and reinforcement. Also, although the upper limit of the carbon black content is not particularly limited, from the perspectives of low fuel consumption performance and processability, it is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and still more preferably 90 parts by mass or less.

[0072] From the perspective of being able to more effectively exhibit the effects of the present invention, the content of the total filler with respect to 100 parts by mass of the rubber component is 60 parts by mass or more, preferably 65 parts by mass or more, and more preferably 70 parts by mass or more. Also, from the perspectives of filler dispersibility and processability, it is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, still more preferably 130 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0073] From the viewpoint of wet grip performance, the silica content in the filler is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and particularly preferably 12% by mass or more. From the viewpoints of weather resistance and reinforcement, it is preferably 70% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less, and particularly preferably 30% by mass or less.

[0074] <Other components> In addition to the above rubber component, ethylene-propylene-styrene copolymer, and filler, the rubber composition according to the second invention can also appropriately contain compounding agents and additives conventionally used in the tire industry, such as oil, wax, anti-aging agent, stearic acid, zinc oxide, vulcanizing agent, vulcanization accelerator, etc., as required. The above compounding agents and additives can be preferably used in the same manner as those in the rubber composition of the first invention.

[0075] <Manufacture of rubber composition and tire> The rubber composition according to the second invention can be produced by a known method. For example, using a known kneader used in the general rubber industry such as a Banbury mixer, kneader, or open roll, after kneading the components other than the vulcanizing agent and vulcanization accelerator among the above components, the vulcanizing agent and vulcanization accelerator are added thereto and further kneaded, and then it can be produced by a method such as vulcanization.

[0076] Since the rubber composition according to the second invention is excellent in chipping resistance, it is preferably used for the tread of a tire.

[0077] The elongation at break (elongation at cut) EB (%) of the rubber composition according to the second invention is 300% or more, preferably 325% or more, and more preferably 350% or more. The elongation at break in this embodiment is measured by preparing a No. 3 dumbbell test piece made of the vulcanized rubber composition and performing a tensile test in an atmosphere of 180°C in accordance with JIS K 6251:2017 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Tensile Test Characteristics".

[0078] The tire using the rubber composition according to the second invention can be manufactured by a normal method using the rubber composition. That is, the rubber composition in which the above-mentioned compounding agent is blended with the rubber component as necessary is extruded according to the shape of the tread or the like, bonded together with other tire members on a tire molding machine, and molded by a normal method to form an unvulcanized tire. The tire can be manufactured by heating and pressurizing this unvulcanized tire in a vulcanizer.

[0079] [Third Invention] The third invention is 〔1〕For 100 parts by mass of a rubber component containing 55 to 80% by mass of styrene-butadiene rubber and 20 to 45% by mass of butadiene rubber, 1 to 20 parts by mass of an ethylene-propylene-styrene copolymer and a filler containing 60 parts by mass or more of silica are contained, and the elongation at break in an atmosphere of 180 °C based on JIS K 6251:2017 is 300% or more. A rubber composition for tread, 〔2〕The rubber composition for tread according to 〔1〕, which contains 25 to 45 parts by mass of carbon black. 〔3〕The rubber composition for tread according to 〔1〕 or 〔2〕, wherein the composition ratio of the ethylene-propylene-styrene copolymer is 10 to 60% by mass of ethylene, 10 to 60% by mass of propylene, and 5 to 40% by mass of styrene. 〔4〕The rubber composition for tread according to any one of 〔1〕 to 〔3〕, wherein the rubber component contains 55 to 80% by mass of emulsion-polymerized styrene-butadiene rubber. 〔5〕The rubber composition for tread according to any one of 〔1〕 to 〔4〕, wherein the content of silica in the filler is 30 to 95% by mass. 〔6〕The rubber composition for tread according to any one of 〔1〕 to 〔5〕, which contains 20 to 120 parts by mass of silica having a nitrogen adsorption specific surface area of 150 m 2 / g or more. 〔7〕The rubber composition for tread according to any one of 〔1〕 to 〔6〕, which contains 25 to 45 parts by mass of carbon black having a nitrogen adsorption specific surface area of 100 m 2 / g or more. Relates to a tire having a tread composed of the tread rubber composition according to any one of [8], [1] to [7].

[0080] <Rubber component> The rubber component used in the third invention contains styrene-butadiene rubber (SBR) and butadiene rubber (BR). Also, within a range not impairing the effects of the present invention, isoprene-based rubbers such as natural rubber and other rubber components may be blended. As SBR, BR, isoprene-based rubbers, and other rubber components, those similar to the rubber components in the first invention can be preferably used in a similar manner.

[0081] The content in the rubber component of SBR is 55% by mass or more from the viewpoint of chipping resistance performance, preferably 57% by mass or more, and more preferably 60% by mass or more. Also, from the viewpoint of wear resistance performance, it is 80% by mass or less, preferably 78% by mass or less, and more preferably 75% by mass or less.

[0082] The content in the rubber component of BR is 20% by mass or more, preferably 22% by mass or more, and more preferably 25% by mass or more. When it is less than 20% by mass, the effects of the present invention tend to be insufficient. Also, the content of BR is 45% by mass or less, preferably 43% by mass or less, and more preferably 40% by mass or less. When it exceeds 45% by mass, the chipping resistance performance deteriorates, and block chipping tends to occur.

[0083] <Ethylene-propylene-styrene copolymer> The rubber composition according to the third invention contains an ethylene-propylene-styrene copolymer. As the ethylene-propylene-styrene copolymer, those similar to the rubber composition in the first invention can be preferably used in a similar manner.

[0084] <Filler> The filler used in the third invention is characterized by containing silica as an essential component. Further, it is preferable that the silica is used in combination with a silane coupling agent. Additionally, carbon black or other fillers may be used as the filler. As the silica, silane coupling agent, carbon black, and other fillers, those similar to those in the rubber composition of the first invention can be preferably used in a similar manner.

[0085] From the viewpoint of wet grip performance, the content of silica is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, still more preferably 40 parts by mass or more, and particularly preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. Further, from the viewpoints of the dispersibility of silica and processability, it is preferably 120 parts by mass or less, more preferably 105 parts by mass or less, still more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0086] When containing a silane coupling agent, the content with respect to 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and still more preferably 1 part by mass or more. Further, the content of the silane coupling agent with respect to 100 parts by mass of the rubber component is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less.

[0087] When containing carbon black, the content with respect to 100 parts by mass of the rubber component is preferably 25 parts by mass or more, more preferably 28 parts by mass or more, and still more preferably 30 parts by mass or more from the viewpoints of weather resistance and reinforcing property. Further, from the viewpoint of wet grip performance, it is preferably 45 parts by mass or less, more preferably 42 parts by mass or less, and still more preferably 40 parts by mass or less.

[0088] From the perspective of better demonstrating the effects of the present invention, the content of the filler in the rubber component of the whole filler is 60 parts by mass or more, preferably 65 parts by mass or more, and more preferably 70 parts by mass or more per 100 parts by mass of the rubber component. Also, from the perspective of the dispersibility of the filler and processability, it is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, still more preferably 130 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0089] From the perspective of wet grip performance, the silica content in the filler is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and particularly preferably 55% by mass or more. Also, from the perspectives of weather resistance and reinforcing properties, it is preferably 95% by mass or less, more preferably 90% by mass or less, and still more preferably 85% by mass or less.

[0090] <Other components> In addition to the above rubber component, ethylene-propylene-styrene copolymer, and filler, the rubber composition according to the third invention may also appropriately contain compounding agents and additives conventionally used in the tire industry, such as oil, wax, anti-aging agent, stearic acid, zinc oxide, vulcanizing agent, vulcanization accelerator, etc., as necessary. The above compounding agents and additives can be preferably used in the same manner as those in the rubber composition of the first invention.

[0091] <Manufacture of rubber composition and tire> The rubber composition according to the third invention can be manufactured by a known method. For example, using a known kneader used in the general rubber industry such as a Banbury mixer, kneader, or open roll, among the above components, after kneading the components other than the vulcanizing agent and vulcanization accelerator, the vulcanizing agent and vulcanization accelerator are added thereto and further kneaded, and then vulcanized.

[0092] Since the rubber composition according to the third invention has excellent chipping resistance, it is preferably used for the tread of a tire.

[0093] The elongation at break (elongation at cut) EB (%) of the rubber composition according to the third invention is 300% or more, preferably 325% or more, and more preferably 350% or more. The elongation at break in this embodiment is measured by preparing a No. 3 dumbbell test piece made of the vulcanized rubber composition and performing a tensile test in an atmosphere of 180°C in accordance with JIS K 6251:2017 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Tensile Test Properties".

[0094] The tire using the rubber composition according to the third invention can be manufactured by a normal method using the rubber composition. That is, the rubber composition in which the above-mentioned compounding agents are compounded as necessary with respect to the rubber component is extruded according to the shape of a tread or the like, bonded together with other tire members on a tire molding machine, and molded by a normal method to form an unvulcanized tire, and this unvulcanized tire is heated and pressurized in a vulcanizer to manufacture a tire.

Examples

[0095] The present invention will be specifically described based on examples, but the present invention is not construed as being limited only to these.

[0096] Various chemicals used in the examples and comparative examples will be described. NR: TSR20 SBR1: JSR1502 (E-SBR, styrene content: 23.5% by mass) manufactured by JSR Corporation SBR2: JSR0112 (E-SBR, styrene content: 37% by mass, containing 34% by mass of oil based on 100% by mass of rubber solids) manufactured by JSR Corporation BR: BR1220 (unmodified BR, cis content: 96% by mass) manufactured by Nippon Zeon Co., Ltd. Carbon black 1: Diablack I (N220) (N2SA: 114 m 2 / g, average primary particle diameter: 22 nm) manufactured by Mitsubishi Chemical Corporation Carbon black 2: Showblack N134 (N2SA: 148 m 2 / g, average primary particle diameter: 18 nm) manufactured by Cabot Japan Ltd. Silica 1: ULTRASIL® VN3 manufactured by Evonik Degussa (N2SA: 175 m 2 / g) Silica 2: Zeosil Premium 200 MP manufactured by Solvay (N2SA: 220 m 2 / g) Silane coupling agent 1: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa Silane coupling agent 2: NXT-Z45 (mercapto-based silane coupling agent) manufactured by Momentive Copolymer: Promix 400 manufactured by Flow Polymers Oil: VivaTec400 (TDAE oil) manufactured by H&R Wax: Oz Ace 355 manufactured by Nippon Seiro Co., Ltd. Antioxidant: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Stearic acid: Stearic acid "Tsubaki" manufactured by NOF Corporation Zinc oxide: Zinc white No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator: Nocceler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0097] (Examples and Comparative Examples) According to the formulation recipes shown in Tables 1 to 4, using a 1.7 L sealed Banbury mixer, chemicals other than sulfur and vulcanization accelerator were kneaded for 5 minutes until the discharge temperature reached 170 °C to obtain a kneaded product. Further, the obtained kneaded product was kneaded again (remilled) for 4 minutes at a discharge temperature of 150 °C using the Banbury mixer. Next, using a twin-screw open roll, sulfur and vulcanization accelerator were added to the obtained kneaded product and kneaded for 4 minutes until the temperature reached 105 °C to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized at 170 °C for 12 minutes to prepare a test rubber composition.

[0098] Further, the unvulcanized rubber composition was extruded into the shape of a tire tread using an extruder equipped with a die of a predetermined shape, and laminated together with other tire members to form an unvulcanized tire, which was then press-vulcanized at 170 °C for 12 minutes to produce and prepare a test tire (size: 180 / 55ZR17, rim: 5.5×17, internal pressure: 290 kPa).

[0099] The following evaluations were performed on the obtained test rubber compositions and test tires. The evaluation results are shown in Table 1.

[0100] <Elongation at break> A dumbbell No. 3 test piece made of each vulcanized rubber composition was prepared, and a tensile test was carried out in an atmosphere of 180 °C in accordance with JIS K 6251:2017 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Tensile Test Properties", and the elongation at break (elongation at break) EB (%) was measured. The larger the elongation at break, the better the chipping resistance performance of the rubber composition.

[0101] <Wet grip performance> Each test tire was mounted on all four wheels of a vehicle (domestic FF2000cc), and the braking distance from an initial speed of 100 km / h on a wet asphalt road surface was determined. The results were expressed as an index with the reference comparative example (Comparative Example 1 in Tables 1 and 2, Comparative Example 8 in Tables 3 and 4) set to 100 according to the following formula. The larger the index, the better the wet grip performance. The index was determined by the following formula. Note that 95 or more is the performance target value, 98 or more is preferable, and 101 or more is more preferable. (Wet grip performance index)= (Braking distance of reference comparative example) / (Braking distance of each formulation example)×100

[0102] <Chipping resistance performance> Each test tire was incorporated into a standard rim, filled with air up to the standard internal pressure, and then mounted on a vehicle and run on an uneven road at a speed of 50 km / h for 4 hours. After the run, for all the cracks generated on the tire surface, the circumferential length thereof was measured, and the maximum value of the circumferential length was determined for each tire. The results were expressed as an index with the reference comparative example (Comparative Example 1 in Tables 1 and 2, Comparative Example 8 in Tables 3 and 4) being 100 according to the following formula. The larger the index, the smaller the crack, indicating better chipping resistance. The index was determined by the following formula. Note that 95 or more is the performance target value, 98 or more is preferable, 101 or more is more preferable, and 105 or more is even more preferable. (Chipping resistance performance index) = (Circumferential length of crack in reference comparative example) / (Circumferential length of crack in each compounding example) × 100

[0103] The comprehensive performance of wet grip performance and chipping resistance performance (average value of wet grip performance index and chipping resistance performance index) has a performance target value of 103 or more, 105 or more is preferable, and 107 or more is more preferable.

[0104] [Table 1]

[0105] [Table 2]

[0106] [Table 3]

[0107] [Table 4]

[0108] From the results in Tables 1 to 4, it can be seen that the rubber composition for a tread of the present invention, which contains a rubber component containing a predetermined amount of butadiene rubber and styrene-butadiene rubber, an ethylene-propylene-styrene copolymer, and a filler containing silica and has a breaking elongation within a predetermined range, has its wet grip performance and chipping resistance improved in a well-balanced manner.

Claims

1. For 100 parts by mass of a rubber component containing 20 to 50% by mass of butadiene rubber and 30 to 80% by mass of styrene-butadiene rubber, 1 to 10 parts by mass of an ethylene-propylene-styrene copolymer and a filler containing silica and carbon black are contained in an amount of 60 parts by mass or more. A vulcanized rubber composition for a tread having an elongation at break of 300% or more in an atmosphere of 180 °C based on JIS K 6251:2017. A vulcanized rubber composition for a tread that satisfies either one or both of the following two conditions. Condition α: The content of the styrene-butadiene rubber is 60% by mass or more in 100% by mass of the rubber component. Condition β: The content of the carbon black is 60 parts by mass or more with respect to 100 parts by mass of the rubber component.

2. The vulcanized rubber composition for a tread according to claim 1, wherein the composition ratio of the ethylene-propylene-styrene copolymer is 10 to 60% by mass of ethylene, 10 to 60% by mass of propylene, and 5 to 40% by mass of styrene.

3. The vulcanized rubber composition for a tread according to claim 1 or 2, wherein the styrene-butadiene rubber is an emulsion-polymerized styrene-butadiene rubber.

4. The silica contained in the filler is silica having a nitrogen adsorption specific surface area of 150 m 2 / g or more, and its content is 1 to 120 parts by mass with respect to 100 parts by mass of the rubber component. The vulcanized rubber composition for a tread according to any one of claims 1 to 3.

5. The carbon black contained in the filler is carbon black having a nitrogen adsorption specific surface area of 100 m 2 / g or more, and its content is 20 to 120 parts by mass with respect to 100 parts by mass of the rubber component. The vulcanized rubber composition for a tread according to any one of claims 1 to 4.

6. A tire having a tread composed of the vulcanized rubber composition for a tread according to any one of claims 1 to 5.

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