tire

Abstract

This tire has a tread comprising: a first layer constituting a tread surface; and a second layer adjacent to the radially inner side of the first layer, wherein the first layer and the second layer are formed of a rubber composition containing a rubber component and a thermoplastic elastomer.

Description

[Technical Field]

[0001] The present invention relates to a tire having an improved balance between grip performance and durability. [Background technology]

[0002] A technique for improving grip performance by compounding a thermoplastic elastomer into tread rubber is known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-210937 Summary of the Invention [Problem to be solved by the invention]

[0004] Thermoplastic elastomers are softer at room temperature than resins, and when added to rubber, they suppress an increase in the hardness of the rubber composition. Furthermore, when heat is applied, the intermolecular forces between the hard segments weaken, allowing energy loss to occur, which is thought to improve grip performance at the beginning of driving.

[0005] On the other hand, when considering the vulcanization adhesion with other tire components made of a rubber composition that does not contain a thermoplastic elastomer, there is a concern that the thermoplastic elastomer will concentrate at the adhesive interface due to the heat and concentration gradient during vulcanization, reducing the adhesion between the rubber components and resulting in a deterioration in durability.

[0006] An object of the present invention is to provide a tire that has an improved balance between grip performance and durability. [Means for solving the problem]

[0007] As a result of extensive research, the inventors have found that when a thermoplastic elastomer is compounded in a first rubber layer (typically a cap tread) constituting the tread surface, a tire with a well-balanced improvement in grip performance and durability can be obtained by interposing a rubber layer compounded with a thermoplastic elastomer under specified conditions between the first rubber layer and the belt layer, and have thus completed the present invention.

[0008] That is, the present invention is [1] A tire having a tread including a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer, wherein the first layer and the second layer are made of a rubber composition containing a rubber component and a thermoplastic elastomer; [2] The tire according to the above [1], wherein the rubber composition constituting the first layer contains 5 to 50 parts by mass of a thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer. [3] The tire according to [1] or [2] above, wherein the rubber composition constituting the second layer contains 3 to 30 parts by mass of a thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer. [4] The tire according to any one of the above [1] to [3], wherein the value of parts by mass of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer is greater than the value of parts by mass of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer. [5] The tire according to any one of the above [1] to [4], wherein the rubber components constituting the first layer and the second layer contain styrene-butadiene rubber. [6] The tire according to any one of [1] to [5] above, wherein the thermoplastic elastomer has a styrene block at a polymer terminal. [7] The tire according to any one of the above [1] to [6], further comprising one or more rubber layers between the second layer and the belt layer. [8] The tire according to any one of the above [1] to [7], further comprising a third layer between the second layer and the belt layer, the third layer being composed of a rubber composition containing a rubber component and sulfur, and the value of parts by mass of sulfur per 100 parts by mass of the rubber component constituting the third layer being greater than the value of parts by mass of sulfur per 100 parts by mass of the rubber component constituting the second layer. [9] The tire according to any one of the above [1] to [8], wherein at least one of the rubber composition constituting the first layer and the rubber composition constituting the second layer contains a thiuram vulcanization accelerator.

[10] The tire according to any one of the above [1] to [9], wherein the product of the content (parts by mass) of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer and the thickness t1 (mm) of the first layer is 120 or more.

[11] The tire according to any one of the above [1] to

[10] , wherein the product of the content (parts by mass) of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer and the thickness t2 (mm) of the second layer is 6 or more. [Effects of the Invention]

[0009] According to the present invention, when a thermoplastic elastomer is compounded in a first rubber layer (typically a cap tread) constituting the tread surface, a rubber layer compounded with a thermoplastic elastomer under predetermined conditions is interposed between the first rubber layer and the belt layer, thereby providing a tire with an improved balance of grip performance and durability. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an enlarged cross-sectional view of a portion of a tread of a tire according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] A tire according to one embodiment of the present disclosure has a tread including a first layer constituting a tread surface and a second layer adjacent to and radially inward of the first layer, the first layer and the second layer being formed of a rubber composition containing a thermoplastic elastomer, and it is preferable that the content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer is greater than the content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer.

[0012] While not intending to be bound by theory, it is believed that the tire disclosed herein achieves a balanced improvement in grip performance and durability through the following mechanism: By interposing a rubber layer containing a thermoplastic elastomer between the tread surface layer and the belt layer, adhesion is achieved between the tread surface layer and the adjacent second layer through vulcanization adhesion and intermolecular forces of the thermoplastic elastomer, and adhesion is ensured between the second layer and the belt topping rubber through vulcanization adhesion between the diene rubbers. Therefore, even if the content of the thermoplastic elastomer in the entire tread portion is increased, adhesion between adjacent rubber members is ensured, durability performance is maintained, and grip performance is also improved.

[0013] A procedure for producing a tire, including the production of a rubber composition according to an embodiment of the present disclosure, will be described in detail below. However, the following description is merely an example for explaining the present disclosure, and is not intended to limit the technical scope of the present invention to the described range. In this specification, when a numerical range is indicated using "to" it is intended to include both ends of the range.

[0014] In this disclosure, unless otherwise specified, the dimensions and angles of each component of a tire are measured when the tire is mounted on a standard rim and inflated to the standard internal pressure, with no load being applied to the tire.

[0015] "Genuine rim" is the rim specified for each tire by the standard system that includes the standard on which the tire is based, such as "standard rim" for JATMA, "design rim" for TRA, and "measuring rim" for ETRTO. For tire sizes that are not specified in the above standard systems, it refers to the narrowest rim among the smallest diameter rims that can be mounted on the tire and do not cause air leakage between the rim and tire.

[0016] "Normal internal pressure" is the air pressure specified for each tire by each standard, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE." For tire sizes not specified in the above standard systems, the normal internal pressure is 250 kPa.

[0017] Fig. 1 is an enlarged cross-sectional view showing a portion of the tread of a tire according to the present disclosure. Fig. 1 shows an enlarged view of a portion of the tread according to the present disclosure in which no grooves are formed on the tread surface. In Fig. 1, the up-down direction is the radial direction of the tire, the left-right direction is the axial direction of the tire, and the direction perpendicular to the paper surface is the circumferential direction of the tire.

[0018] As shown in the figure, the tread portion of the tire of the present disclosure includes a first layer and a second layer, with the outer surface of the first layer constituting the tread surface and the second layer adjacent to the radially inner side of the first layer. The first layer typically corresponds to a cap tread. Furthermore, as long as the objectives of the present disclosure are achieved, one or more rubber layers may be further provided between the second layer and the belt layer.

[0019] Furthermore, a rubber layer for imparting adhesiveness during molding may be provided between the belt layer and the innermost layer in the radial direction among the rubber layers constituting the tread portion.

[0020] In Figure 1, the double arrow t1 indicates the thickness of the first layer, the double arrow t2 indicates the thickness of the second layer, and the double arrow t3 indicates the thickness of the third layer. In Figure 1, an arbitrary point on the tread surface where no grooves are formed is indicated by the symbol P. The line indicated by the symbol N is a line (normal) that passes through point P and is perpendicular to the tangent plane at point P. In this specification, the thicknesses t1, t2, and t3 are measured along the normal N drawn from point P, with point P being the tire equatorial plane when no grooves are present on the tire equatorial plane, or the center in the tire width direction of the land portion closest to the tire equatorial plane when grooves are present on the tire equatorial plane.

[0021] In the present disclosure, the thickness t1 of the first layer is not particularly limited, but from the viewpoint of grip performance, it is preferably 2.0 mm or more, more preferably 3.0 mm or more, and even more preferably 4.0 mm or more, while from the viewpoint of heat buildup, it is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[0022] In the present disclosure, the thickness t2 of the second layer is not particularly limited, but is preferably 1.0 mm or more, more preferably 1.5 mm or more, and even more preferably 2.0 mm or more. t2 is preferably 5.0 mm or less, more preferably 4.0 mm or less, and even more preferably 3.0 mm or less.

[0023] In the present disclosure, the thickness t3 of the third layer is not particularly limited, but is preferably 0.5 mm or more, more preferably 1.0 mm or more, and is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less.

[0024] The thickness t1 of the first layer relative to the thickness of the entire tread portion is preferably 30 to 95%, more preferably 40 to 90%, even more preferably 45 to 85%, and particularly preferably 50 to 80%. Note that the thickness of the entire tread portion in the present disclosure means the total thickness of the rubber layers that constitute the tread portion, and is determined by the shortest distance from the tread surface to the belt layer.

[0025] The product of the content (parts by mass) of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer and the thickness t1 (mm) of the first layer is preferably 120 or more, more preferably 130 or more, even more preferably 140 or more, and particularly preferably 150 or more. By setting the product of the content of the thermoplastic elastomer in the first layer and the thickness of the first layer within the above range, it is believed that the grip performance of the first layer can be improved, making it easier to obtain excellent initial grip performance while maintaining durability. Furthermore, the product of the content (parts by mass) of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer and the thickness t1 (mm) of the first layer is preferably 400 or less, more preferably 300 or less, even more preferably 250 or less, and particularly preferably 200 or less.

[0026] The product of the thermoplastic elastomer content (parts by mass) per 100 parts by mass of the rubber component constituting the second layer and the thickness t2 (mm) of the second layer is preferably 6 or more, more preferably 9 or more, even more preferably 12 or more, and particularly preferably 15 or more. By setting the product of the thermoplastic elastomer content in the second layer and the thickness of the second layer within the above range, the second layer can maintain good adhesion to the first layer and exhibit good heat buildup within the second layer, which is thought to facilitate obtaining excellent initial grip performance while maintaining durability. Furthermore, the product of the thermoplastic elastomer content (parts by mass) per 100 parts by mass of the rubber component constituting the second layer and the thickness t2 (mm) of the second layer is preferably 150 or less, more preferably 100 or less, even more preferably 75 or less, and particularly preferably 50 or less.

[0027] [First tread layer] As described above, the first tread layer is made of a rubber composition containing a rubber component and a thermoplastic elastomer.

[0028] <Rubber component> The rubber composition constituting the first layer preferably contains at least one rubber component selected from the group consisting of styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene-based rubber, and more preferably contains styrene-butadiene rubber (SBR). The rubber component may also consist solely of SBR.

[0029] (SBR) The SBR is not particularly limited, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Among these, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) can also be used. These SBRs may be used alone or in combination of two or more.

[0030] Examples of S-SBR that can be used in the present disclosure include S-SBR manufactured and sold by JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomers Co., Ltd., and the like.

[0031] From the viewpoints of grip performance and abrasion resistance, the styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. From the viewpoints of temperature dependency of grip performance and blow resistance, it is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. In this specification, the styrene content of SBR is 1 It is calculated by H-NMR measurement.

[0032] The vinyl bond content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, from the viewpoints of ensuring reactivity with silica and improving rubber strength and abrasion resistance. Furthermore, the vinyl bond content of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, and even more preferably 60 mol% or less, from the viewpoints of preventing an increase in temperature dependency, grip performance, elongation at break, and abrasion resistance. In this specification, the vinyl bond content of SBR (amount of 1,2-bonded butadiene units) is measured by infrared absorption spectroscopy.

[0033] From the viewpoint of grip performance, the content of SBR in 100% by mass of the rubber component constituting the first layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and particularly preferably 70% by mass or more. There is no particular upper limit for the content of SBR in the rubber component, and it may be 100% by mass.

[0034] (BR) The BR is not particularly limited, and examples thereof include those commonly used in the tire industry, such as BR with a cis content (cis-1,4 bond content) of less than 50% (low-cis BR), BR with a cis content of 90% or more (high-cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR). These BRs are commercially available from Ube Industries, Ltd., Sumitomo Chemical Co., Ltd., JSR Corporation, Lanxess KK, and the like. These BRs may be used alone or in combination.

[0035] The rare earth BR may be any catalyst commonly used in the tire industry. Known rare earth catalysts may be used in the synthesis (polymerization) of the rare earth BR, including catalysts containing lanthanum series rare earth compounds, organoaluminum compounds, aluminoxanes, halogen-containing compounds, and, if necessary, Lewis bases. Among these, neodymium (Nd)-based catalysts using Nd-containing compounds as the lanthanum series rare earth compound are preferred, from the viewpoint of obtaining a BR with a high cis content and a low vinyl content.

[0036] In the SPB-containing BR, 1,2-syndiotactic polybutadiene crystals are not simply dispersed in the BR, but are dispersed after being chemically bonded to the BR.

[0037] Modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and examples thereof include tin-modified BR, in which the terminals of the modified BR molecule are bonded with tin-carbon bonds, and butadiene rubber having a condensed alkoxysilane compound at the active terminal of the butadiene rubber (silica-modified BR).

[0038] When BR is contained, the content thereof in 100% by mass of the rubber component is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less, from the viewpoint of grip performance. Furthermore, when BR is contained, the lower limit of the content is not particularly limited, and can be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more.

[0039] (Isoprene rubber) Examples of isoprene-based rubbers that can be used include those commonly used in the tire industry, such as isoprene rubber (IR) and natural rubber. Natural rubber includes unmodified natural rubber (NR) as well as modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), highly purified natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

[0040] The NR is not particularly limited, and those commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0041] When an isoprene-based rubber (preferably natural rubber, more preferably unmodified natural rubber (NR)) is contained, the content thereof in 100% by mass of the rubber component is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less, from the viewpoint of grip performance. Furthermore, when an isoprene-based rubber is contained, the content thereof is not particularly limited to a lower limit, but can be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more.

[0042] (Other rubber components) The rubber component according to the present disclosure may contain rubber components other than the isoprene-based rubber, SBR, and BR. Examples of other rubber components that can be used include crosslinkable rubber components commonly used in the tire industry, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used alone or in combination of two or more.

[0043] <Thermoplastic elastomer> The rubber composition constituting the first layer contains a thermoplastic elastomer from the viewpoint of improving grip performance.

[0044] As used herein, the term "thermoplastic elastomer" refers to a polymeric compound having elasticity, a thermoplastic resin material composed of a copolymer having a polymer that constitutes a crystalline hard segment with a high melting point and a polymer that constitutes an amorphous soft segment with a low glass transition temperature. The crystalline hard segments of a thermoplastic elastomer, with a high melting point, act as pseudo-crosslinking points, thereby exhibiting elasticity. Rubber, on the other hand, contains double bonds in its molecular chain, and when crosslinked (vulcanized) by adding sulfur or the like, generates a three-dimensional network structure, thereby exhibiting elasticity. Therefore, when a thermoplastic elastomer is heated, the hard segments melt, and when cooled, the pseudo-crosslinking points are regenerated, making it reusable. On the other hand, when rubber is crosslinked (vulcanized), it generates a three-dimensional network structure, losing fluidity and making it difficult to reuse, even when heated. The thermoplastic elastomer of the present disclosure does not contain the rubber component.

[0045] The thermoplastic elastomer usable in the present disclosure is not particularly limited, but examples thereof include styrene-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, olefin-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, etc., with styrene-based thermoplastic elastomers and polyurethane-based thermoplastic elastomers being preferred. These thermoplastic elastomers may be used alone or in combination of two or more.

[0046] The styrene-based thermoplastic elastomer is a copolymer having at least one styrene block (hard segment) and at least one elastomer block (soft segment). The molecular structure of the styrene-based thermoplastic elastomer is not particularly limited, but a molecular structure having a styrene block at one or both ends and an elastomer block elsewhere is preferred. Having a styrene block at at least one end tends to provide better grip performance. Furthermore, it is more preferred that the styrene-based thermoplastic elastomer has a structure that does not have a styrene block in the main chain portion other than the end. This structure tends to prevent the rubber from becoming too hard at room temperature, providing better grip performance, as well as better fracture properties and abrasion resistance.

[0047] Examples of the elastomer block include vinyl-polydiene, polyisoprene, polybutadiene, polyethylene, polychloroprene, poly-2,3-dimethylbutadiene, etc. Furthermore, the elastomer block may also be a hydrogenated version of the above elastomer block.

[0048] Examples of styrene-based thermoplastic elastomers include styrene-isobutylene block copolymer (SIB), styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butylene block copolymer (SEB), styrene-ethylene-propylene block copolymer (SEP), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-butylene-ethylene block copolymer (SEBC), hydrogenated styrene-butadiene copolymer (HSBR), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), and styrene-butadiene-butylene-styrene block copolymer (SBBS).

[0049] The styrene unit content (styrene content) of the styrene-based thermoplastic elastomer is preferably 5% by mass or more, more preferably 10% by mass or more, from the viewpoint of grip performance, and is preferably 30% by mass or less, more preferably 20% by mass or less, from the viewpoint of suppressing heat buildup.

[0050] The polyurethane-based thermoplastic elastomer is not particularly limited, but for example, one prepared from a polyol and a diisocyanate can be suitably used. Examples of polyols include polyester-based polyols, polyester ether-based polyols, polycarbonate-based polyols, and polyether-based polyols. Examples of diisocyanates include tolylene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI).

[0051] Examples of olefin-based thermoplastic elastomers include ethylene-α-olefin copolymers such as ethylene-propylene copolymer (EPR), ethylene-butene copolymer (EBR), ethylene-hexene copolymer (EHR), and ethylene-octene copolymer (EOR); and ethylene-α-olefin-diene terpolymers such as ethylene-propylene-ethylidenenorbornene copolymer, ethylene-propylene-butadiene copolymer, and ethylene-propylene-isoprene copolymer.

[0052] The content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more, from the viewpoint of grip performance, and is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, even more preferably 40 parts by mass or less, even more preferably 35 parts by mass or less, and particularly preferably 30 parts by mass or less, from the viewpoint of abrasion resistance.

[0053] <Filler> The rubber composition constituting the first layer preferably contains carbon black and / or silica as a filler, and the filler may contain carbon black or may consist of carbon black only.

[0054] (carbon black) As the carbon black, any carbon black commonly used in the tire industry can be used as appropriate, such as GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks may be used alone or in combination of two or more.

[0055] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m from the viewpoint of elongation at break. 2 / g or more is preferable, and 70m 2 / g or more is more preferable. From the viewpoint of fuel efficiency and processability, 200m 2 / g or less is preferable, and 150m 2 The N2SA of carbon black is a value measured in accordance with JIS K 6217-2 "Fundamental properties of carbon black for rubber - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method."

[0056] From the viewpoint of reinforcing properties, the dibutyl phthalate (DBP) oil absorption of carbon black is preferably 50 mL / 100 g or more, more preferably 70 mL / 100 g or more, and even more preferably 90 mL / 100 g or more. From the viewpoints of fuel economy and processability, the DBP oil absorption is preferably 400 mL / 100 g or less, more preferably 350 mL / 100 g or less. The DBP oil absorption of carbon black is a value measured in accordance with JIS K 6221.

[0057] The content of carbon black per 100 parts by mass of the rubber component constituting the first layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, and particularly preferably 40 parts by mass or more, from the viewpoint of grip performance. There is no particular upper limit to the content of carbon black, but from the viewpoint of fuel economy and wear resistance, it is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 110 parts by mass or less.

[0058] (silica) The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica) or silica prepared by a wet method (hydrated silica), which are commonly used in the tire industry. Among them, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. Silica can be used alone or in combination of two or more types.

[0059] The nitrogen adsorption specific surface area (N2SA) of silica is 140m from the viewpoint of fuel efficiency and wear resistance. 2 / g or more is preferable, and 170m 2 / g or more is more preferable, and 200m 2 / g or more is more preferable. From the viewpoint of fuel efficiency and processability, 2 / g or less is preferable, and 300m 2 / g or less is more preferable, and 250m 2 / g or less is more preferable. In this specification, the N2SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0060] The average primary particle size of silica is preferably 20 nm or less, more preferably 18 nm or less, and even more preferably 16 nm or less. There is no particular restriction on the lower limit of the average primary particle size, but it is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. When the average primary particle size of silica is within the above range, the dispersibility of silica can be further improved, and the reinforcement properties, fracture properties, and abrasion resistance can be further improved. The average primary particle size of silica can be determined by observing with a transmission or scanning electron microscope, measuring 400 or more primary silica particles observed within the field of view, and averaging the results.

[0061] When silica is contained, the content per 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more from the viewpoint of wet grip performance, and is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 95 parts by mass or less from the viewpoint of abrasion resistance.

[0062] The total content of silica and carbon black per 100 parts by mass of the rubber component constituting the first layer is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more from the viewpoint of abrasion resistance, and is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, and even more preferably 140 parts by mass or less from the viewpoint of fuel economy and elongation at break.

[0063] Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent that has conventionally been used in combination with silica in the tire industry can be used. Specific examples of the silane coupling agent include silane coupling agents having a sulfide group, such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; silane coupling agents having a mercapto group, such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, NXT-Z30, NXT-Z45, NXT-Z60, and NXT-Z100 manufactured by Momentive, and Si363 manufactured by Evonik Degussa; and silane coupling agents having a mercapto group, such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. Examples of suitable silane coupling agents include silane coupling agents having a thioester group; silane coupling agents having a vinyl group such as vinyltriethoxysilane and vinyltrimethoxysilane; silane coupling agents having an amino group such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; silane coupling agents having a glycidoxy group such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; silane coupling agents having a nitro group such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and silane coupling agents having a chloro group such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, silane coupling agents having a sulfide group, silane coupling agents having a mercapto group, and silane coupling agents having a thioester group are preferred, with silane coupling agents having a mercapto group being more preferred. These silane coupling agents may be used alone or in combination of two or more.

[0064] When a silane coupling agent is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more, from the viewpoint of improving the dispersibility of silica, and is preferably 20 parts by mass or less, more preferably 12 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 9.0 parts by mass or less, from the viewpoint of preventing a decrease in abrasion resistance.

[0065] As the filler, in addition to carbon black and silica, other fillers may also be used. Such fillers are not particularly limited, and any fillers commonly used in this field, such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, etc., may be used. These fillers may be used alone or in combination of two or more.

[0066] <Softener> The rubber composition constituting the first layer preferably contains a softener to improve grip performance, such as a resin component, oil, or liquid rubber.

[0067] The rubber composition constituting the first layer may contain a resin component for the purpose of improving adhesion to adjacent rubber members. Examples of the resin component include, but are not limited to, petroleum resins, terpene resins, rosin resins, and phenolic resins commonly used in the tire industry. These resin components may be used alone or in combination of two or more.

[0068] As used herein, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as the C5 petroleum resin.

[0069] As used herein, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified version of the resin. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that are suitable for use include coumarone-indene resins, coumarone resins, indene resins, and aromatic vinyl resins. Preferred aromatic vinyl resins are homopolymers of α-methylstyrene or styrene, or copolymers of α-methylstyrene and styrene, with copolymers of α-methylstyrene and styrene being more preferred, due to their economical efficiency, ease of processing, and excellent heat generation properties. Examples of aromatic vinyl resins that can be used include commercially available products from Kraton, Eastman Chemical Company, and the like.

[0070] As used herein, the term "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions described above. As the C5C9 petroleum resin, for example, commercially available products from Tosoh Corporation, LUHUA, etc. can be used.

[0071] Examples of terpene resins include polyterpene resins made of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, and the like; aromatic modified terpene resins made from the terpene compound and an aromatic compound; terpene phenolic resins made from a terpene compound and a phenolic compound; and those obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol.

[0072] The rosin-based resin is not particularly limited, but examples thereof include natural resin rosin and rosin-modified resins obtained by modifying rosin by hydrogenation, disproportionation, dimerization, esterification, etc.

[0073] The phenolic resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

[0074] The softening point of the resin component is preferably 60°C or higher, more preferably 65°C or higher, from the viewpoint of grip performance. Furthermore, from the viewpoint of processability and improving the dispersibility of the rubber component and the filler, the softening point is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. In this specification, the softening point may be defined as the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

[0075] When a resin component is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 12 parts by mass or more, from the viewpoint of grip performance, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less, from the viewpoint of suppressing heat buildup.

[0076] Examples of oils include process oil, vegetable oils, and animal fats. Examples of the process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. Furthermore, as an environmental measure, process oil with a low content of polycyclic aromatic compounds (PCA) can also be used. Examples of the low-PCA process oil include mild extract solvates (MES), treated distillate aromatic extracts (TDAE), and heavy naphthenic oil.

[0077] When oil is contained, the content per 100 parts by mass of the rubber component is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, from the viewpoint of processability. Also, from the viewpoint of abrasion resistance, the content is preferably 120 parts by mass or less, more preferably 110 parts by mass or less, and even more preferably 100 parts by mass or less. In this specification, the oil content includes the amount of oil contained in the oil-extended rubber.

[0078] The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used alone or in combination of two or more.

[0079] When a liquid rubber is contained, the content thereof per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. The content of the liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

[0080] When a softener is contained, the content per 100 parts by mass of the rubber component (the total amount when multiple softeners are used in combination) is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, and particularly preferably 50 parts by mass or more from the viewpoint of grip performance. Also, from the viewpoint of processability, the content is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 100 parts by mass or less.

[0081] <Other compounding agents> In addition to the above-mentioned components, the rubber composition constituting the first layer may contain, as appropriate, compounding agents commonly used in the tire industry, such as wax, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents such as sulfur, vulcanization accelerators, etc.

[0082] When wax is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of weather resistance of the rubber, and is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, from the viewpoint of preventing whitening of the tire due to bloom.

[0083] Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. These processing aids may be used alone or in combination of two or more. Examples of processing aids that can be used include those commercially available from Schill + Seilacher, Performance Additives, etc.

[0084] When a processing aid is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of improving processability, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, from the viewpoint of abrasion resistance and breaking strength.

[0085] The antioxidant is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and carbamic acid metal salts, and examples thereof include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N,N'-bis(1-methylheptyl)-p-phenylenediamine, N,N'-bis(1,4-dimethylbutyl) ...-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N,N'-bis(1-methylheptyl)-p-phenylenediamine, N,N'-bis(1,4 Phenylenediamine-based antioxidants such as N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, N-4-methyl-2-pentyl-N'-phenyl-p-phenylenediamine, N,N'-diaryl-p-phenylenediamine, hindered diaryl-p-phenylenediamine, phenylhexyl-p-phenylenediamine, and phenyloctyl-p-phenylenediamine, as well as quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, are preferred. These antioxidants may be used alone or in combination of two or more.

[0086] When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of ozone crack resistance of the rubber, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance and wet grip performance.

[0087] When stearic acid is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of vulcanization rate.

[0088] When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance.

[0089] As the vulcanizing agent, sulfur is preferably used, and examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0090] When sulfur is contained as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, the content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur contained in the oil-containing sulfur.

[0091] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Co., Ltd., Lanxess K.K., Flexis, etc.

[0092] The vulcanization accelerator is not particularly limited, but examples thereof include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamate-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. Among these, sulfenamide-based and thiuram-based vulcanization accelerators are preferred because they more suitably achieve the desired effects. It is believed that the rubber composition according to the present disclosure is prone to inhibition of the vulcanization reaction by the thermoplastic elastomer, but the use of a highly reactive thiuram-based vulcanization accelerator makes it easier to obtain vulcanization adhesion between adjacent rubber layers, thereby improving durability.

[0093] Examples of sulfenamide vulcanization accelerators include N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N-(tert-butyl)-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolylsulfenamide, N,N'-diisopropyl-2-benzothiazolylsulfenamide, and N,N-dicyclohexyl-2-benzothiazolylsulfenamide. Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole and dibenzothiazolyl disulfide. Examples of thiuram vulcanization accelerators include tetramethylthiuram monosulfide. Examples of the guanidine vulcanization accelerators include diphenyl guanidine (DPG), di-orthotolyl guanidine, and orthotolyl biguanidine. Examples of the dithiocarbamate vulcanization accelerators include zinc dibutyldithiocarbamate, zinc dibenzyldithiocarbamate, sodium dibutyldithiocarbamate, copper dimethyldithiocarbamate, ferric dimethyldithiocarbamate, and tellurium diethyldithiocarbamate. These vulcanization accelerators may be used alone or in combination of two or more.

[0094] When a vulcanization accelerator is contained, the content thereof per 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, even more preferably 2.0 parts by mass or more, particularly preferably 2.5 parts by mass or more, and is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 6.0 parts by mass or less.

[0095] At least one of the rubber composition constituting the first layer and the rubber composition constituting the second layer preferably contains a thiuram vulcanization accelerator. When a thiuram vulcanization accelerator is contained, the amount per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more. The amount is preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less.

[0096] [Second tread layer] As described above, the second tread layer is made of a rubber composition containing a rubber component and a thermoplastic elastomer.

[0097] <Rubber component> The rubber composition constituting the second layer preferably contains at least one rubber component selected from the group consisting of styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene-based rubber, and more preferably styrene-butadiene rubber (SBR). The rubber component may contain SBR and isoprene-based rubber, may consist of SBR alone, or may consist of SBR and isoprene-based rubber alone.

[0098] As the SBR, BR, isoprene-based rubber, and other rubber components, the same rubber components as those in the rubber composition constituting the first layer can be suitably used in the same manner.

[0099] <Thermoplastic elastomer> The rubber composition constituting the second layer contains a thermoplastic elastomer. The same thermoplastic elastomer as the rubber composition constituting the first layer can be suitably used in the same manner. From the viewpoint of grip performance, the content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer is preferably greater than the content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer.

[0100] The content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more from the viewpoint of grip performance, and is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 15 parts by mass or less from the viewpoint of abrasion resistance.

[0101] <Filler> The rubber composition constituting the second layer preferably contains carbon black and / or silica as a filler, more preferably carbon black. If silica is contained, it is preferable to also contain a silane coupling agent. The carbon black, silica, silane coupling agent, and other fillers can be the same as those in the rubber composition constituting the first layer, and can be used in the same manner.

[0102] The amount of carbon black per 100 parts by mass of the rubber component constituting the second layer is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 60 parts by mass or more, from the viewpoint of durability. The upper limit of the amount of carbon black is not particularly limited, but is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 110 parts by mass or less, from the viewpoint of fuel economy and abrasion resistance.

[0103] <Softener> The rubber composition constituting the second layer preferably contains a softener. Examples of softeners include resin components, oils, and liquid rubbers. The same softeners as those in the rubber composition constituting the first layer can be suitably used in the same manner.

[0104] <Other compounding agents> In addition to the above-mentioned components, the rubber composition constituting the second layer may contain, as appropriate, compounding agents commonly used in the tire industry, such as wax, processing aids, antioxidants, vulcanizing agents such as stearic acid, zinc oxide, and sulfur, vulcanization accelerators, etc. The compounding agents may be the same as those in the rubber composition constituting the first layer and may be used in the same manner.

[0105] As described above, the tread portion of the tire of the present disclosure may further have one or more rubber layers between the second layer and the belt layer, as long as the object of the present disclosure is achieved. The tread portion preferably has a third layer between the second layer and the belt layer, which is composed of a rubber composition containing a rubber component and sulfur.

[0106] The rubber composition constituting the rubber layer that can be present between the second layer and the belt layer preferably contains at least one rubber component selected from the group consisting of styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene-based rubber, and more preferably contains styrene-butadiene rubber (SBR). The rubber component may contain SBR and isoprene-based rubber, may consist of SBR alone, or may consist of SBR and isoprene-based rubber alone.

[0107] As the SBR, BR, isoprene-based rubber, and other rubber components, the same rubber components as those in the rubber composition constituting the first layer can be suitably used in the same manner.

[0108] The rubber composition constituting the rubber layer that can be present between the second layer and the belt layer may contain a thermoplastic elastomer. The same thermoplastic elastomer as the rubber composition constituting the first layer can be suitably used in the same manner. From the viewpoint of grip performance, the content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the rubber layer (preferably the third layer) that can be present between the second layer and the belt layer is preferably less than the content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer. The content of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the rubber layer (preferably the third layer) that can be present between the second layer and the belt layer is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

[0109] The rubber composition constituting the rubber layer that can be present between the second layer and the belt layer preferably contains carbon black and / or silica as a filler. If silica is contained, it is preferable to also contain a silane coupling agent. The carbon black, silica, silane coupling agent, and other fillers that are the same as those in the rubber composition constituting the first layer can be suitably used in the same manner.

[0110] The rubber composition constituting the rubber layer that can be present between the second layer and the belt layer preferably contains a softener. Examples of the softener include resin components, oil, and liquid rubber. The softener may be the same as that of the rubber composition constituting the first layer, and may be used in the same manner.

[0111] The rubber composition constituting the rubber layer that can be present between the second layer and the belt layer may contain, in addition to the above-mentioned components, compounding agents that are conventionally commonly used in the tire industry, such as wax, processing aids, antioxidants, vulcanizing agents such as stearic acid, zinc oxide, and sulfur, vulcanization accelerators, etc. The compounding agents may be the same as those in the rubber composition constituting the first layer and may be suitably used in the same manner.

[0112] When the tread portion has a three-layer structure, the sulfur content per 100 parts by mass of the rubber component constituting the third layer is preferably greater than the sulfur content per 100 parts by mass of the rubber component constituting the second layer, from the viewpoint of further improving adhesion to the adjacent belt topping rubber. The sulfur content per 100 parts by mass of the rubber component constituting the third layer is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 1.8 parts by mass or more. From the viewpoint of preventing deterioration, the sulfur content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less.

[0113] The rubber composition according to the present disclosure can be produced by a known method. For example, it can be produced by a method in which the components other than the vulcanizing agent and vulcanization accelerator are kneaded in a known kneading machine commonly used in the tire industry, such as a Banbury mixer, kneader, or open roll, and then the vulcanizing agent and vulcanization accelerator are added and further kneaded, followed by vulcanization. For example, in the kneading step, the mixture is kneaded at 80°C to 170°C for 1 minute to 30 minutes, and in the vulcanization step, the mixture is vulcanized at 130°C to 190°C for 3 minutes to 20 minutes.

[0114] [tire] The tire according to the present disclosure has a tread including the first and second layers, and may be a pneumatic tire or a non-pneumatic tire. Examples of pneumatic tires include tires for passenger cars, trucks and buses, motorcycles, and high-performance tires. The high-performance tire in this specification refers to a tire with particularly excellent grip performance, and is a concept that also includes racing tires used on racing vehicles.

[0115] A tire having a tread including the first and second layers can be manufactured by a conventional method using the rubber composition described above. That is, an unvulcanized rubber composition obtained by blending the above components with a rubber component as needed is extruded to match the shape of the tread, laminated together with other tire components in a tire building machine, and molded by a conventional method to form an unvulcanized tire, and the unvulcanized tire is then heated and pressurized in a vulcanizer to manufacture the tire. [Example]

[0116] The present disclosure will be described based on examples, but the present disclosure is not limited to only the examples.

[0117] The various chemicals used in the examples and comparative examples are listed below. SBR1: Tufuden 4850 manufactured by Asahi Kasei Corporation (unmodified S-SBR, styrene content: 40% by mass, vinyl bond content: 46% by mass, contains 50 parts by mass of oil per 100 parts by mass of rubber solids) SBR2: Tufuden 3830 manufactured by Asahi Kasei Corporation (unmodified S-SBR, styrene content: 33% by mass, vinyl bond content: 34%, contains 37.5 parts by mass of oil per 100 parts by mass of rubber solids) NR:TSR20 Carbon black 1: Seast 9SAF (N2SA: 142 ml) manufactured by Tokai Carbon Co., Ltd. 2 / g, DBP oil absorption: 115mL / 100g) Carbon black 2: Cabot Japan Co., Ltd. Show Black N330 (N2SA: 75m 2 / g, DBP oil supply amount: 102mL / 100g) Silica: ULTRASIL (registered trademark) 9100GR (N2SA: 235 ml) manufactured by Evonik Degussa 2 / g, average primary particle diameter: 15nm) Thermoplastic elastomer 1: Dynaron 4600P (styrene-ethylene-butylene-ethylene block copolymer (SEBC), styrene content: 20%) manufactured by JSR Corporation Thermoplastic elastomer 2: Hybrar 5125 (styrene-isoprene-styrene block copolymer (SIS), styrene content: 20%) manufactured by Kuraray Co., Ltd. Thermoplastic elastomer 3: Miractran P22M (polyurethane-based thermoplastic elastomer) manufactured by Nippon Miractran Co., Ltd. Resin component: Tosoh Corporation's PetroTack 100V (C5C9 petroleum resin, softening point: 96°C, Mw: 3800, SP value: 8.3) Oil: H&R VivaTec 500 (TDAE oil) Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Wax: Sunnock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: NOF Corporation's "Tsubaki" stearic acid Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Sancerer TBZTD (tetrabenzyl thiuram disulfide) manufactured by Sanshin Chemical Industry Co., Ltd. Vulcanization accelerator 3: Sancerer NS-G (N-(tert-butyl)-2-benzothiazolyl sulfenamide) manufactured by Sanshin Chemical Industry Co., Ltd.

[0118] Examples and Comparative Examples According to the compounding recipes shown in Tables 1 to 3, chemicals other than sulfur and vulcanization accelerators were kneaded using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd. Next, sulfur and vulcanization accelerators were added to the resulting kneaded mixture and kneaded using an open roll to obtain an unvulcanized rubber composition. The resulting unvulcanized rubber composition was molded to match the shapes of the first, second, and third layers of the tread, and then laminated together with other tire components to produce an unvulcanized tire. The tire was then vulcanized at 170°C to obtain a test tire (205 / 65R15).

[0119] <Adhesion test> According to the configuration shown in Table 4, the unvulcanized rubber compositions constituting the first, second, and third layers of the tread were stacked and press-vulcanized at 170°C for 15 minutes to obtain vulcanization-bonded rubber compositions. During vulcanization, cellophane was sandwiched approximately 60 mm from the edge to provide a gripping margin for the testing machine. The vulcanization-bonded rubber compositions were subjected to adhesion performance tests in accordance with JIS K 6256-1, "Vulcanized and Thermoplastic Rubber—Determination of Adhesion—Part 1: Peel Strength from Fabric." Specifically, rubber sheets of the vulcanization-bonded rubber compositions were cut to 25 mm widths to prepare test pieces, which were then peeled at a rate of 50 mm / min. The adhesion between the first and second layers was expressed as an index, with the peel strengths of Comparative Examples 3 and 11, the second and third layers as compared to Comparative Examples 6 and 14, and the innermost tread layer and belt layer as compared to Comparative Examples 1 and 9, all of which were set to 100. A higher adhesion performance index indicates better adhesion. The innermost tread layer refers to the first layer when the tread has one layer, the second layer when the tread has two layers, and the third layer when the tread has three layers.

[0120] <Durability performance test> Using a drum testing machine, the running time until peeling damage occurred in the tread rubber was measured at a speed of 230 km / h on the drum under conditions of a standard rim (6.0 J), internal pressure (260 kPa), load (4.56 kN), and road temperature of 80°C. The results were expressed as an index, with the reference comparative example (Comparative Example 7 in Table 4, Comparative Example 15 in Table 5) being set at 100. A higher index indicates better durability at high temperatures and when running at high speeds.

[0121] <Initial grip performance test> Each test tire was mounted on all wheels of a 2000cc domestically produced 4WD vehicle, and the vehicle was driven for 15 laps on a test course with a dry asphalt surface and a lap length of 3km. The time for each lap was measured, and the reciprocal of the difference between the lap time on the second lap and the best lap was expressed as an index, with the reference comparative example (Comparative Example 7 in Table 4, Comparative Example 15 in Table 5) set at 100. The higher the index, the smaller the difference between the lap time on the second lap and the best lap, and the higher the grip performance at the start of the run.

[0122] <Grip stability performance test> Each test tire was fitted to all wheels of a 2000cc domestically produced 4WD vehicle, and the vehicle was driven for 15 laps on a test course with a dry asphalt surface and a circumference of 3km. The best lap time and the average lap time from laps 10 to 15 were measured, and the reciprocal of the difference in time was expressed as an index, with the reference comparative example (Comparative Example 7 in Table 4, Comparative Example 15 in Table 5) set at 100. The higher the value, the higher the grip stability.

[0123] Tables 4 and 5 also show the overall performance index (the sum of the durability performance index, initial grip performance index, and grip stability performance index).

[0124] [Table 1]

[0125] [Table 2]

[0126] [Table 3]

[0127] [Table 4]

[0128] [Table 5]

[0129] The results in Tables 1 to 5 show that the tires of the present disclosure, in which the first layer and the second layer of the tread are composed of a rubber composition containing a rubber component and a thermoplastic elastomer, have a well-balanced improvement in grip performance and durability. [Explanation of symbols]

[0130] 1. Tread surface 2...first layer 3...Second layer 4...Third layer

Claims

1. A tire having a tread including a first layer constituting a tread surface and a second layer adjacent to and radially inward of the first layer, wherein the first layer and the second layer are made of a rubber composition containing a rubber component and a thermoplastic elastomer, a value of parts by mass of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer is larger than a value of parts by mass of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer, the rubber composition constituting the first layer contains 5 to 35 parts by mass of a thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer, The tire wherein the rubber composition constituting the second layer contains 3 to 15 parts by mass of a thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer.

2. The tire according to claim 1 , wherein the rubber component constituting the first layer and the second layer comprises a styrene-butadiene rubber.

3. 3. The tire according to claim 1, wherein the thermoplastic elastomer has styrene blocks at the polymer ends.

4. The tire according to any one of claims 1 to 3, further comprising one or more rubber layers between the second layer and the belt layer.

5. 5. The tire according to claim 1, further comprising a third layer between the second layer and the belt layer, the third layer being composed of a rubber composition containing a rubber component and sulfur, wherein a value of parts by mass of sulfur per 100 parts by mass of the rubber component constituting the third layer is larger than a value of parts by mass of sulfur per 100 parts by mass of the rubber component constituting the second layer.

6. The tire according to any one of claims 1 to 5, wherein at least one of the rubber composition constituting the first layer and the rubber composition constituting the second layer contains a thiuram vulcanization accelerator.

7. The tire according to any one of claims 1 to 6, wherein the product of the content (parts by mass) of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the first layer and the thickness t1 (mm) of the first layer is 120 or more.

8. The tire according to any one of claims 1 to 7, wherein a product of a content (parts by mass) of the thermoplastic elastomer per 100 parts by mass of the rubber component constituting the second layer and a thickness t2 (mm) of the second layer is 6 or greater.

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