Tire

Abstract

The present invention provides a tire comprising a tread having a rubber composition containing a rubber component, wherein the tread has at least one circumferential main groove running continuously in the circumferential direction of the tire, the circumferential main groove runs in the circumferential direction of the tire in a winding manner such that the centerline of the circumferential main groove is shifted in the tire width direction at a plurality of bend sections or such that the extension direction of the centerline of the circumferential main groove changes before and after the bend sections, and the rubber composition has a tan δ at 20 °C (20 °C tan δ) of 0.30 or less and also has a rupture strength TB (MPa) at 175 °C and a rupture strength EB (%) at 175 °C that satisfy the relationship TB × EB / 2 ≥ 600.

Description

Technical Field

[0001] The present disclosure relates to a tire having improved chipping resistance performance when traveling at high speed on a rough road.

Background Art

[0002] For the tread portion of trucks, SUVs, etc. traveling on rough roads, a tread pattern having zigzag circumferential main grooves is often adopted from the viewpoint of ensuring handling stability, etc. However, since damage such as chips (chip cuts) where the damage generated in the tread expands and becomes small and chipped easily occur, it is necessary to ensure the durability performance (chip resistance performance) against chip cuts.

[0003] Patent Document 1 describes that a tire in which a rubber component containing butadiene rubber and natural rubber and carbon black are compounded in tread rubber has improved abrasion resistance and cut resistance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, there is a problem that when the compounding amount of carbon black is increased, the heat generation property increases.

[0006] An object of the present disclosure is to provide a tire having improved chipping resistance performance when traveling at high speed on a rough road.

Means for Solving the Problems

[0007] As a result of intensive studies, it has been found that in a tire having a circumferential main groove with a bent portion in the tread portion, by setting the loss tangent tanδ, breaking strength, and elongation at break of the rubber composition constituting the tread within a predetermined range, the chipping resistance performance when driving at high speed on a rough road is improved.

[0008] That is, the present disclosure relates to a tire including a tread constituted by a rubber composition containing a rubber component, the tread having at least one circumferential main groove continuously extending in the tire circumferential direction, the circumferential main groove being bent at a plurality of bent portions such that the center line of the circumferential main groove is displaced in the tire width direction, or the extending direction of the center line of the circumferential main groove changes before and after the bent portion, and extending in the tire circumferential direction, and the rubber composition having a tanδ (tanδ at 20°C) of 0.30 or less at 20°C, and a breaking strength TB (MPa) at 175°C and a breaking Time elongation EB (%) at 175°C satisfying the relational expression TB × EB / 2 ≥ 600.

Advantages of the Invention

[0009] According to the present disclosure, even in a tire having a circumferential main groove with a bent portion in the tread portion where chip cuts are likely to occur, by setting the tanδ, breaking strength, and elongation at break of the rubber composition constituting the tread within a predetermined range, a tire with improved chipping resistance performance when driving at high speed on a rough road can be obtained.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0011] A tire according to an embodiment of the present disclosure is a tire provided with a tread composed of a rubber composition containing a rubber component, wherein the tread has at least one circumferential main groove continuously extending in the tire circumferential direction, and the circumferential main groove is bent at a plurality of bent portions so that the center line of the circumferential main groove is displaced in the tire width direction, or the extending direction of the center line of the circumferential main groove changes before and after the bent portion, and extends in the tire circumferential direction, and the rubber composition has a tanδ (20°C tanδ) of 0.30 or less (preferably 0.25 or less, more preferably 0.20 or less, still more preferably 0.18 or less) at 20°C, and the breaking strength TB (MPa) at 175°C and the breaking Time elongation EB (%) satisfy the relational expression TB × EB / 2 ≥ 600 (preferably TB × EB / 2 ≥ 625, more preferably TB × EB / 2 ≥ 650).

[0012] Although not intending to be bound by theory, the reason why the tire of the present disclosure is excellent in chipping resistance performance when traveling at high speed on a rough road is considered as follows. When a tire having a circumferential main groove with a bent portion travels on a rough road, foreign objects such as small stones are less likely to escape from the main groove. When traveling at high speed in that state, the tread rubber surface near the foreign object is fixed by the foreign object, and a strong force is instantaneously applied during grounding, causing the temperature to rise to a high temperature. On the other hand, since the inside of the tread rubber is less affected by foreign objects, it generates heat and softens as in normal driving. As a result of these, an instantaneous difference in change and stress occurs between the tread rubber surface and the inside, and chipping is likely to occur. Therefore, by improving the tensile properties of the tread rubber at high temperatures and reducing the heat generation at normal temperatures, the chipping resistance performance is improved synergistically.

[0013] The manufacturing procedure of a tire including a rubber composition for a tread which is an embodiment of the present disclosure will be described in detail below. However, the following description is an exemplification for explaining the present disclosure, and is not intended to limit the technical scope of the present disclosure only to this description scope. In this specification, when a numerical range is indicated using "~", both end values thereof are included.

[0014] [Rubber composition for tread] As described above, the rubber composition (rubber composition for tread) constituting the tread contains a rubber component.

[0015] The rubber composition for tread according to the present disclosure preferably contains silica having an average particle diameter of 17 nm or less (preferably 16 nm or less, more preferably 15 nm or less) (preferably 25 parts by mass or more, more preferably 35 to 120 parts by mass, still more preferably 50 to 100 parts by mass, particularly preferably 60 to 90 parts by mass).

[0016] The rubber composition for tread according to the present disclosure preferably contains 10% by mass or more of isoprene rubber in the rubber component; more preferably contains 10% by mass or more of isoprene rubber and 20% by mass or more of styrene-butadiene rubber; still more preferably contains 10 to 80% by mass of isoprene rubber and 20 to 80% by mass or more of styrene-butadiene rubber; still more preferably contains 12 to 75% by mass of isoprene rubber and 25 to 75% by mass of styrene-butadiene rubber; particularly preferably contains 15 to 70% by mass of isoprene rubber and 30 to 70% by mass of styrene-butadiene rubber.

[0017] [Rubber component] The rubber composition for tread according to the present disclosure preferably contains isoprene rubber as the rubber component, and more preferably contains at least one of isoprene rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR). The rubber component may be a rubber component containing isoprene rubber, SBR, and BR, may be a rubber component consisting only of isoprene rubber, SBR, and BR, or may be a rubber component consisting only of isoprene rubber and SBR.

[0018] [Isoprene rubber] As the isoprene rubber, for example, general ones in the tire industry such as isoprene rubber (IR) and natural rubber can be used. Natural rubber includes, in addition to unmodified natural rubber (NR), modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene rubbers may be used alone or in combination of two or more.

[0019] NR is not particularly limited, and general ones in the tire industry can be used. For example, SIR20, RSS#3, TSR20, etc. can be mentioned.

[0020] When containing isoprene rubber, the content in the rubber component is preferably 10% by mass or more, more preferably 12% by mass or more, and further preferably 15% by mass or more from the viewpoint of chipping resistance performance (TB and EB). On the other hand, from the viewpoint of wet grip performance, it is preferably 80% by mass or less, more preferably 75% by mass or less, further preferably 70% by mass or less, and particularly preferably 65% by mass or less.

[0021] (SBR) SBR is not particularly limited, and examples include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Examples of modified SBR include SBR with modified terminals and / or main chains, and modified SBR coupled with tin, silicon compounds, etc. (condensates, those having a branched structure, etc.). Among them, E-SBR is preferred because it can improve heat generation and wear resistance performance well. These SBRs may be used alone or in combination of two or more.

[0022] From the viewpoints of wet grip performance and abrasion resistance performance, the styrene content of SBR is preferably 5% by mass or more, more preferably 15% by mass or more, and still more preferably 20% by mass or more. Also, from the viewpoints of the temperature dependence of grip performance and abrasion resistance performance, it is preferably 60% by mass or less, more preferably 50% by mass or less. In the present specification, the styrene content of SBR is 1 calculated by H-NMR measurement.

[0023] From the viewpoints of ensuring reactivity with silica, rubber strength, and abrasion resistance performance, the vinyl content of SBR is preferably 10 mol% or more, more preferably 13 mol% or more, and still more preferably 16 mol% or more. Also, from the viewpoints of preventing an increase in temperature dependence, wet grip performance, elongation at break, and abrasion resistance performance, the vinyl bond amount of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, and still more preferably 60 mol% or less. In the present specification, the vinyl content (amount of 1,2-bonded butadiene units) of SBR is measured by infrared absorption spectroscopy.

[0024] From the viewpoint of abrasion resistance performance, the weight average molecular weight (Mw) of SBR is preferably 150,000 or more, more preferably 200,000 or more, and still more preferably 250,000 or more. Also, from the viewpoints of crosslinking uniformity and the like, Mw is preferably 2,500,000 or less, more preferably 2,000,000 or less. Note that Mw can be determined by standard polystyrene conversion based on the measured values by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0025] From the viewpoint of chipping resistance performance (TB and EB), the content in the rubber component when containing SBR is preferably 20% by mass or more, more preferably 25% by mass or more, still more preferably 30% by mass or more, and particularly preferably 35% by mass or more. Also, from the viewpoint of abrasion resistance performance, it is preferably 80% by mass or less, more preferably 75% by mass or less, still more preferably 70% by mass or less, and particularly preferably 65% by mass or less.

[0026] (BR) BR is not particularly limited. For example, BR with a cis content (amount of cis-1,4-bonded butadiene units) of less than 50% (low-cis BR), BR with a cis content of 90% or more (high-cis BR), rare-earth butadiene rubber synthesized using a rare-earth element-based catalyst (rare-earth 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. Commercially available products from Ube Industries, Ltd., Sumitomo Chemical Co., Ltd., JSR Corporation, Lanxess Corporation, etc. can be used. These BRs can be used alone or in combination of two or more.

[0027] For the rare-earth BR, those generally used in the tire industry can be used. As the rare-earth element-based catalyst used for the synthesis (polymerization) of rare-earth BR, known catalysts can be used, for example, lanthanum series rare-earth element compounds, organoaluminum compounds, aluminoxane, halogen-containing compounds, and catalysts containing a Lewis base as required. Among them, an Nd-based catalyst using a neodymium (Nd)-containing compound as the lanthanum series rare-earth element compound is preferable from the viewpoint of obtaining BR with a high cis content and a low vinyl content.

[0028] Examples of the SPB-containing BR include those in which the 1,2-syndiotactic polybutadiene crystals are not simply dispersed in BR but are dispersed after being chemically bonded to BR.

[0029] Examples of the modified BR include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the ends of the modified BR molecules are bonded by tin-carbon bonds (tin-modified BR), and butadiene rubber having a condensed alkoxysilane compound at the active ends of the butadiene rubber (modified BR for silica), etc.

[0030] The weight average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more from the viewpoints of abrasion resistance and grip performance. Further, from the viewpoints of crosslinking uniformity and the like, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. Note that Mw can be determined by standard polystyrene conversion based on the measured value by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0031] From the viewpoint of abrasion resistance performance, the content in the rubber component when containing BR is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more. Further, from the viewpoint of wet grip performance, it is preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, and particularly preferably 45% by mass or less.

[0032] (Other rubber components) As the rubber component according to the present disclosure, the rubber component other than the above-mentioned isoprene rubber, SBR, and BR may be contained. As other rubber components, crosslinkable rubber components generally used in the tire industry can be used. For example, 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), hydrin rubber, etc. can be mentioned. These other rubber components may be used alone or in combination of two or more.

[0033] <Filler> The rubber composition for treads according to the present disclosure preferably contains carbon black and / or silica as fillers. Further, the filler may be a filler consisting only of carbon black and silica.

[0034] (Silica) The 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 preferable because it has many silanol groups. These silicas may be used alone or in combination of two or more.

[0035] The average primary particle diameter of the silica is preferably 19 nm or less, more preferably 18 nm or less, further preferably 17 nm or less, still further preferably 16 nm or less, and particularly preferably 15 nm or less. The lower limit of the average primary particle diameter is not particularly limited, but is preferably 1 nm or more, more preferably 3 nm or more, and further preferably 5 nm or more. By setting the average primary particle diameter of the silica within the above range, the dispersibility of the silica can be further improved, and the effects of improving heat generation and chipping resistance performance are enhanced. As a result, even if the blending amount of silica is reduced, the chipping resistance performance (TB and EB) can be effectively improved, and the increase in heat generation (20°C tanδ) accompanying the increase in the blending amount can be suppressed. The average primary particle diameter of the silica can be observed by a transmission or scanning electron microscope, and measured for 400 or more primary particles of the silica observed in the visual field, and obtained by averaging.

[0036] The nitrogen adsorption specific surface area (N2SA) of the silica is preferably 170 m 2 / g or more, more preferably 180 m 2 / g or more, further preferably 190 m 2 / g or more, and particularly preferably 200 m 2 / g or more from the viewpoints of heat generation (20°C tanδ) and chipping resistance performance. Also, from the viewpoint of processability, it is preferably 350 m 2 / g or less, preferably 300 m 2250 m / g or less is more preferable, and 250 m / g or less is even more preferable. The N2SA of the silica in this specification is a value measured by the BET method in accordance with ASTM D3037-93. 2 / g or less is even more preferable. The N2SA of the silica in this specification is a value measured by the BET method in accordance with ASTM D3037-93.

[0037] From the viewpoint of chipping resistance performance (TB and EB), the content of silica relative to 100 parts by mass of the rubber component is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, even more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, even more preferably 50 parts by mass or more, even more preferably 55 parts by mass or more, and particularly preferably 60 parts by mass or more. Also, from the viewpoint of heat generation (20 °C tan δ), it is preferably 120 parts by mass or less, more preferably 110 parts by mass or less, even more preferably 100 parts by mass or less, even more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, even more preferably 75 parts by mass or less, even more preferably 70 parts by mass or less, and particularly preferably 65 parts by mass or less.

[0038] (Carbon black) The carbon black is not particularly limited, and those commonly used in the tire industry such as GPF, FEF, HAF, ISAF, SAF, etc. can be used. 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. 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.

[0039] From the viewpoints of weather resistance and reinforcement, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 50 m 2 / g or more, more preferably 80 m 2 / g or more, and even more preferably 100 m 2More preferably, it is above / g. Further, from the viewpoints of dispersibility, heat generation property, fracture characteristics, and durability, it is preferably 250 m 2 / g or less, more preferably 220 m 2 / g or less. The N2SA of the carbon black in this specification is a value measured in accordance with Method A of JIS K 6217-2 "Basic properties of carbon black for rubber - Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0040] When containing carbon black, the content with respect to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, further preferably 8 parts by mass or more, and particularly preferably 10 parts by mass or more from the viewpoint of chipping resistance performance (TB and EB). Further, from the viewpoint of heat generation property (20°C tanδ), it is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, further preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less.

[0041] (Other fillers) As fillers other than silica and carbon black, those commonly used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, talc, etc., can be blended.

[0042] The content of silica in the total 100% by mass of silica and carbon black is preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, and particularly preferably 65% by mass or more. Also, the content of the silica is preferably 99% by mass or less, more preferably 95% by mass or less, further preferably 90% by mass or less, and particularly preferably 85% by mass or less.

[0043] From the perspective of chipping resistance performance, the total content of silica and carbon black relative to 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, still more preferably 55 parts by mass or more, still more preferably 60 parts by mass or more, still more preferably 65 parts by mass or more, and particularly preferably 70 parts by mass or more. From the perspective of heat generation, it is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, still more preferably 110 parts by mass or less, still more preferably 100 parts by mass or less, still more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0044] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited. For example, 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, etc. are mentioned, and sulfide-based silane coupling agents are preferred. These silane coupling agents may be used alone or in combination of two or more.

[0045] When containing a silane coupling agent, the content relative to 100 parts by mass of silica is preferably 5 parts by mass or more, more preferably 6 parts by mass or more, still more preferably 7 parts by mass or more, and particularly preferably 8 parts by mass or more from the viewpoint of enhancing the dispersibility of silica. Further, from the viewpoint of preventing a decrease in wear resistance performance, it is preferably 18 parts by mass or less, more preferably 16 parts by mass or less, still more preferably 14 parts by mass or less, and particularly preferably 12 parts by mass or less.

[0046] <Softening agent> The rubber composition for a tread according to the present disclosure preferably contains a softening agent. Examples of the softening agent include a resin component, an oil, a liquid rubber, and the like. The 20°C tanδ, TB, and EB of the rubber composition can be appropriately adjusted by the blending amount of the above softening agent.

[0047] The resin component is not particularly limited, and examples thereof include 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.

[0048] In this specification, the "C5-based petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of the C5 fraction include petroleum fractions corresponding to 4 to 5 carbon atoms such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5-based petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0049] In this specification, the "aromatic-based petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and those obtained by hydrogenating or modifying them may also be used. Examples of the C9 fraction include petroleum fractions corresponding to 8 to 10 carbon atoms such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of the aromatic-based petroleum resin include, for example, Coumarone-indene resins, coumarone resins, indene resins, and aromatic vinyl resins are preferably used. As the aromatic vinyl resin, due to economic reasons, easy processing, and excellent heat generation properties, a homopolymer of α-methylstyrene or styrene, or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred. As the aromatic vinyl resin, for example, those commercially available from companies such as Kreton and Eastman Chemical can be used.

[0050] In this specification, "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and it may be hydrogenated or modified. Examples of the C5 fraction and the C9 fraction include the above-mentioned petroleum fractions. As the C5C9 petroleum resin, for example, those commercially available from Tosoh Corporation, LUHUA, etc. can be used.

[0051] As the terpene resin, a polyterpene resin composed of at least one selected from terpene compounds such as α-pinene, β-pinene, limonene, and dipentene; an aromatic-modified terpene resin using the terpene compound and an aromatic compound as raw materials; a terpene phenol resin using the terpene compound and a phenolic compound as raw materials; and those obtained by subjecting these terpene resins to a hydrogenation treatment (hydrogenated terpene resins) can be mentioned. Examples of the aromatic compound used as a raw material for the aromatic-modified terpene resin include styrene, α-methylstyrene, vinyltoluene, divinyltoluene, etc. Examples of the phenolic compound used as a raw material for the terpene phenol resin include phenol, bisphenol A, cresol, xylenol, etc.

[0052] The rosin resin is not particularly limited, and examples include natural resin rosin, rosin-modified resins obtained by modifying it by hydrogenation, disproportionation, dimerization, esterification, etc.

[0053] The phenolic resin is not particularly limited, and examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, oil-modified phenol formaldehyde resin, and the like.

[0054] From the viewpoint of grip performance, the softening point of the resin component is preferably 60°C or higher, more preferably 65°C or higher. Further, from the viewpoints of processability and improvement of the dispersibility of the rubber component and the filler, it is preferably 150°C or lower, more preferably 140°C or lower, and still more preferably 130°C or lower. In the present specification, the softening point can be defined as the temperature at which the sphere drops when measured with a ring and ball softening point measuring device in accordance with the softening point defined in JIS K 6220-1:2001.

[0055] From the viewpoint of chipping resistance performance, the content of the resin component relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, still more preferably 10 parts by mass or more, and particularly preferably 12 parts by mass or more. Further, from the viewpoint of suppressing heat generation, it is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0056] Examples of the oil include process oil, vegetable oil, animal oil, and the like. Examples of the process oil include paraffinic process oil, naphthenic process oil, aromatic process oil, and the like. Further, a process oil having a low content of polycyclic aromatic compound (PCA) can also be used for environmental measures. Examples of the low-PCA content process oil include mildly extracted solvent solvate (MES), treated distillate aromatic extract (TDAE), heavy naphthenic oil, and the like. These oils may be used alone or in combination of two or more.

[0057] When contained, the content relative to 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 still more preferably 20 parts by mass or more from the viewpoint of chipping resistance. Further, from the viewpoint of abrasion resistance performance, it is preferably 120 parts by mass or less, more preferably 110 parts by mass or less, still more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, still more preferably 60 parts by mass or less, and particularly preferably 50 parts by mass or less. In the present specification, the oil content includes the oil amount contained in the oil-extended rubber.

[0058] The liquid rubber is not particularly limited as long as it is a polymer in a liquid state at normal temperature (25°C). 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, and the like. These liquid rubbers may be used alone or in combination of two or more.

[0059] When contained, the content relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, still more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. Further, the content of the liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 20 parts by mass or less.

[0060] The content of the softening agent relative to 100 parts by mass of the rubber component (the total amount of all when a plurality of softening agents are used in combination) 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 from the viewpoint of grip performance. Further, from the viewpoint of processability, it is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, still more preferably 110 parts by mass or less, still more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, still more preferably 70 parts by mass or less, and particularly preferably 60 parts by mass or less.

[0061] <Other compounding agents> In addition to the above components, the rubber composition for treads according to the present disclosure may appropriately contain compounding agents generally used in the conventional tire industry, such as wax, processing aids, anti-aging agents, stearic acid, zinc oxide, vulcanizing agents, vulcanization accelerators, and the like.

[0062] When wax is contained, the content per 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 weather resistance of the rubber. Also, from the viewpoint of preventing the whitening of the tire due to blooming, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0063] Examples of the 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, mixtures of fatty acid metal salts and fatty acid amides, etc. Processing aids containing fatty acid metal salts are preferred. These processing aids may be used alone or in combination of two or more. As the processing aids, for example, those commercially available from Schill+Seilacher, Performance Additives, etc. can be used.

[0064] When the processing aid is contained, the content per 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, still more preferably 1.5 part by mass or more, particularly preferably 2.0 part by mass or more, from the viewpoint of exerting the effect of improving processability. Also, from the viewpoints of abrasion resistance and breaking strength, it is preferably 10 parts by mass or less, more preferably 8.0 parts by mass or less, still more preferably 6.0 parts by mass or less, particularly preferably 4.0 parts by mass or less.

[0065] The anti-aging agent is not particularly limited. For example, anti-aging agents such as amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and metal carbamates can be mentioned. p-Phenylenediamine-based anti-aging agents such as 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, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred. These anti-aging agents may be used alone or in combination of two or more.

[0066] When containing an anti-aging agent, the content relative to 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, further preferably 1.5 part by mass or more, still further preferably 2.0 part by mass or more, still further preferably 2.5 part by mass or more, and particularly preferably 3.1 part by mass or more from the viewpoint of ozone crack resistance of the rubber. Also, from the viewpoints of abrasion resistance performance and wet grip performance, it is preferably 10 parts by mass or less, more preferably 8.0 parts by mass or less, and further preferably 5.0 parts by mass or less.

[0067] When containing stearic acid, the content relative to 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 vulcanization rate, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0068] When containing zinc oxide, the content relative to 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.

[0069] Sulfur is preferably used as the vulcanizing agent. As sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, etc. can be used.

[0070] When sulfur is contained as the vulcanizing agent, the content based on 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and still more preferably 0.5 part by mass or more from the viewpoint of ensuring a sufficient vulcanization reaction. Also, from the viewpoint of preventing deterioration, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and still more preferably 3.0 parts by mass or less. In addition, when oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of the pure sulfur component contained in the oil-containing sulfur.

[0071] Examples of vulcanizing agents other than sulfur include alkylphenol sulfur chloride condensates, sodium 1,6-hexamethylene-dithiolsulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane), etc. As these vulcanizing agents other than sulfur, those commercially available from Tago Chemical Industry Co., Ltd., Rancess Co., Ltd., Flexsys Co., etc. can be used.

[0072] The vulcanization accelerator is not particularly limited. For example, sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamate-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, xanthate-based vulcanization accelerators can be mentioned. Among them, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred from the viewpoint that the desired effects can be obtained more suitably.

[0073] 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, N,N-dicyclohexyl-2-benzothiazolylsulfenamide, etc. Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole, dibenzothiazolyl disulfide, etc. Examples of guanidine vulcanization accelerators include diphenylguanidine (DPG), diorthotolylguanidine, orthotolylbiguanidine, etc. These vulcanization accelerators may be used alone or in combination of two or more.

[0074] When contained, the content of the vulcanization accelerator 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. Also, the content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, the breaking strength and elongation tend to be ensured.

[0075] The rubber composition according to the present disclosure can be produced by a known method. For example, using a known kneader used in the general tire 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 vulcanized. For example, in the kneading step, kneading is performed at 80°C to 170°C for 1 minute to 30 minutes, and in the vulcanization step, vulcanization is performed at 130°C to 190°C for 3 minutes to 20 minutes.

[0076] In this specification, the tanδ at 20°C is used as an index correlated with heat generation. The tanδ at 20°C in this specification indicates the loss tangent tanδ measured under the conditions of a temperature of 20°C, an initial strain of 2%, a dynamic strain of 1%, and a frequency of 50 Hz. From the perspective of heat generation, the tanδ at 20°C of the rubber composition according to the present disclosure is 0.30 or less, preferably 0.25 or less, more preferably 0.20 or less, and even more preferably 0.18 or less. On the other hand, from the perspective of wet grip performance, it is preferably 0.08 or more, and more preferably 0.10 or more.

[0077] The TB in this specification indicates the breaking strength (tensile strength at break) measured in accordance with JIS K 6251 under the condition of a tensile speed of 8.3 mm / second in an atmosphere of 175°C. The breaking strength TB indicates the force (MPa) required to pull the sample to break, and the larger the value of TB, the better the fracture resistance.

[0078] From the perspective of chipping resistance performance, the TB of the rubber composition according to the present disclosure is preferably 5.5 MPa or more, more preferably 5.9 MPa or more, and even more preferably 6.3 MPa or more. Also, the upper limit value of TB is not particularly limited.

[0079] In addition, the EB in this specification indicates the elongation at break (elongation at cut) measured in accordance with JIS K 6251 under the condition of a tensile speed of 8.3 mm / second in an atmosphere of 175°C. The elongation at break EB indicates the elongation rate (%) when the sample is pulled to break, and the larger the value of EB, the better the fatigue resistance characteristics.

[0080] From the perspective of chipping resistance performance, the EB of the rubber composition according to the present disclosure is preferably 190% or more, more preferably 200% or more, and even more preferably 205% or more. Also, the upper limit of EB is not particularly limited.

[0081] In this specification, the relational expression TB×EB / 2 is used as an index correlated with chipping resistance performance. As a result of intensive studies in the present disclosure, it has been found that the product of TB and EB measured at a high temperature of 175°C strongly correlates with the chipping resistance performance of a tire having a circumferential main groove with a bent portion in the tread portion, and good chipping resistance performance is ensured if TB×EB / 2 is within a specific range. TB×EB / 2 is 600 or more, preferably 625, and more preferably 650 or more. By setting TB×EB / 2 within the above range, sufficient chipping resistance performance can be obtained. Further, the upper limit of TB×EB is not particularly limited.

[0082] [Tire] The tire according to the present disclosure includes a tread composed of the above tread rubber composition, and the category is not particularly limited, and it can be used as a passenger car tire, an SUV tire, a heavy load vehicle tire such as a truck or a bus, a two-wheeled vehicle tire, a run-flat tire, a non-pneumatic tire, etc., but it is preferably a heavy load vehicle tire. Further, since the tire according to the present disclosure has excellent chipping resistance performance, it is suitable for running on a rough road surface (unpaved and rough road surface).

[0083] A tire provided with a tread composed of the above tread rubber composition can be manufactured by a normal method using the above tread rubber composition. That is, an unvulcanized rubber composition in which each of the above components is blended as necessary with respect to the rubber component is extruded according to the shape of the tread, 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.

[0084] FIG. 1 shows an example of a developed view in which the tread pattern of a tire according to an embodiment of the present disclosure is developed in a plane, but the present disclosure is not limited thereto. A tread pattern in which the mounting direction to the vehicle is specified is formed on the tread 2. The tread pattern of the tread portion 2 is formed in an asymmetric shape with respect to the tire equator C.

[0085] The tread 2 has an outer tread end To and an inner tread end Ti. The outer tread end To is located on the outer side (right side in FIG. 1) of the vehicle when the tire is mounted on the vehicle. The inner tread end Ti is located on the inner side (left side in FIG. 1) of the vehicle when the tire is mounted on the vehicle.

[0086] Each tread end To, Ti is the grounding position on the outermost side in the tire width direction W (the left-right direction in FIG. 1; hereinafter simply referred to as the width direction W) when a normal load is applied to the tire in a normal state and the tire is grounded on a plane with a camber angle of 0 degrees. The normal state means that the tire is mounted on a normal rim and filled with a normal internal pressure, and moreover, it is in an unloaded state. In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are values measured in the above normal state. In the normal state, the distance in the width direction W between the outer tread end To and the inner tread end Ti is defined as the tread width TW.

[0087] The "normal rim" is the rim defined for each tire in the standard system including the standard on which the tire is based. 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".

[0088] The "normal internal pressure" is the air pressure defined for each tire in the standard system including the standard on which the tire is based. 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".

[0089] The "normal load" is the load defined for each tire in the standard system including the standard on which the tire is based. In the case of JATMA, it is the "maximum load capacity"; 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 "LOAD CAPACITY".

[0090] The tread 2 has a pair of circumferential main grooves 3A and 3B that continuously extend in the tire circumferential direction on both sides in the tire width direction of the tire equator C. In FIG. 1, the circumferential main grooves 3A and 3B are zigzag-shaped with an amplitude in the tire width direction. A total of four circumferential main grooves 3A and 3B are provided. However, the number of circumferential main grooves is not particularly limited, and for example, it can be 2 to 5, preferably 3 to 5, and more preferably 4.

[0091] In FIG. 1, a center main groove 3A and a pair of shoulder main grooves 3B that continuously extend in the tire circumferential direction on the outer side in the tire width direction of the center main groove 3A are provided. Also, a plurality of middle cross grooves 5A that connect between the center main groove 3A and the shoulder main grooves 3B, and a plurality of shoulder cross grooves 5B that connect between the shoulder main grooves 3B and the tread ends To and Ti are provided. Thereby, in the tread portion 2 of the present disclosure, a center land portion 7 divided between a pair of center main grooves 3A and 3, a plurality of middle blocks 8 divided by the center main groove 3A, the shoulder main grooves 3B, and the middle cross grooves 5A are provided at intervals in the tire circumferential direction, a pair of middle block rows 8R, and a plurality of shoulder blocks 9 divided by the shoulder main grooves 3B, the ground contact end Te, and the shoulder cross grooves 5B are provided at intervals in the tire circumferential direction, and a pair of shoulder block rows 9R are arranged.

[0092] The groove width of each of the circumferential main grooves 3A and 3B can be arbitrarily determined according to the convention. In order to provide sufficient drainage performance while maintaining the pattern rigidity of the tread 2, the groove width W1 (see FIG. 2) of each of the circumferential main grooves 3A and 3B is preferably about 2.5% to 5% of the tread width TW, for example. From the viewpoint of the effect of the present disclosure, the groove depth of each of the circumferential main grooves 3A and 3B is preferably 6.0 to 12.0 mm, more preferably 7.0 to 11.0 mm, and even more preferably 8.5 to 10.5 mm.

[0093] FIG. 2 shows an enlarged view of the center main groove 3A on the right side of FIG. 1. As shown in FIG. 2, the center main groove 3A of the present disclosure includes a center inner portion 10a that linearly extends in the tire circumferential direction on the inner side in the tire width direction, a center outer portion 10b that linearly extends in the tire circumferential direction on the outer side in the tire width direction than the center inner portion 10a, and a center joint portion 11 that joins the center inner portion 10a and the center outer portion 10b, and has a zigzag shape. Such a center main groove 3A includes an edge component in the tire width direction, thereby enhancing the braking force. Further, the center main groove 3A having the center inner portion 10a and the center outer portion 10b includes a large edge component in the tire circumferential direction, thereby improving the turning performance. Note that the zigzag shape is not limited to the above, and for example, it may be a zigzag shape in which a plurality of long side portions inclined to one side with respect to the tire circumferential direction, a short side portion that joins between adjacent long side portions in the tire circumferential direction and has a length smaller than that of the long side portion in the tire circumferential direction are alternately arranged.

[0094] The center main groove 3A has an inner groove edge 3i that extends in the tire circumferential direction on the inner side in the tire width direction and an outer groove edge 3o that extends in the tire circumferential direction on the outer side in the tire width direction. The inner groove edge 3i includes an inner inner edge 3a that extends along the tire circumferential direction at the innermost side in the tire width direction and an inner outer edge 3b that extends along the tire circumferential direction at the outermost side in the tire width direction. Further, the outer groove edge 3o includes an outer inner edge 3c that extends along the tire circumferential direction at the innermost side in the tire width direction and an outer outer edge 3d that extends along the tire circumferential direction at the outermost side in the tire width direction.

[0095] In the present disclosure, the center inner portion 10a refers to a groove formed by the inner inner edge 3a and the outer inner edge 3c. Further, the center outer portion 10b refers to a groove formed by the inner outer edge 3b and the outer outer edge 3d.

[0096] In addition, the center joint part 11 includes a first center part 11a in which the groove center line 12a (indicated by the dashed-dotted line) is inclined toward one side in the tire width direction (inclined upward to the left in FIG. 2), and a second center part 11b in which the groove center line 12b is inclined toward the other side in the tire width direction (inclined upward to the right in FIG. 2). Thus, the center main groove 3A of the present disclosure is formed by continuously connecting the center inner part 10a, the first center part 11a, the center outer part 10b, and the second center part 11b on one side in the tire circumferential direction. In FIG. 2, the center inner part 10a, the first center part 11a, the center outer part 10b, and the second center part 11b are indicated by virtual lines.

[0097] The groove center line 12 of the center main groove 3A is formed by a straight line successively connecting the intermediate point s1 between one end a1 of the inner inner edge 3a and one end a2 of the outer inner edge 3c, the intermediate point s2 between the other end a3 of the inner outer edge 3b and the other end a4 of the outer outer edge 3d, the intermediate point s3 between one end a5 of the inner outer edge 3b and one end a6 of the outer outer edge 3d, and the intermediate point s4 between the other end a7 of the inner inner edge 3a and the other end a8 of the outer inner edge 3c.

[0098] As shown in FIG. 2, the groove center line 12 of the center main groove 3A has an amplitude λ1. The amplitude λ1 is the peak-to-peak amplitude in the tire width direction of the groove center line 12. The amplitude λ1 is preferably 2.0 mm or more, more preferably 2.5 mm or more, further preferably 3.0 mm or more, and particularly preferably 3.5 mm or more. Also, the amplitude λ1 is preferably 20.0 mm or less, more preferably 15.0 mm or less, further preferably 10.0 mm or less, still further preferably 8.0 mm or less, still further preferably 6.0 mm or less, still further preferably 5.0 mm or less, and particularly preferably 4.5 mm or less. By setting the amplitude λ1 of the groove center line within the above range, a large edge component in the tire width direction can be obtained, and the braking force is improved.

[0099] The ratio of TB×EB to the amplitude λ1 of the groove center line (TB×EB / λ1) is preferably 50 or more, more preferably 100 or more, still more preferably 150 or more, still more preferably 200 or more, still more preferably 250 or more, and particularly preferably 300 or more. By improving the tensile properties of the tread rubber as λ1 increases, the chipping resistance performance and the handling stability can be improved in a well-balanced manner. On the other hand, the upper limit value of TB×EB / λ1 is not particularly limited, but for example, it can be 1000 or less, 900 or less, 800 or less, 700 or less, 600 or less.

[0100] The value obtained by multiplying the 20°C tanδ of the rubber composition according to the present disclosure by the amplitude λ1 of the groove center line (20°C tanδ×λ1) is preferably 4.0 or less, more preferably 2.5 or less, still more preferably 2.0 or less, still more preferably 1.5 or less, still more preferably 1.2 or less, and particularly preferably 0.90 or less. By decreasing the 20°C tanδ as λ1 increases, the chipping resistance performance can be further improved. On the other hand, from the viewpoints of wet grip performance and handling stability, 20°C tanδ×λ1 is preferably 0.20 or more, more preferably 0.25 or more, still more preferably 0.30 or more, still more preferably 0.35 or more, still more preferably 0.40 or more, and particularly preferably 0.45 or more.

[0101] In order to more effectively exhibit the above-described effects, as shown in FIG. 2, the length L1 in the tire circumferential direction of the center inner portion 10a is preferably 80 to 120% of the length L2 in the tire circumferential direction of the center outer portion 10b.

[0102] When the length L5 in the tire circumferential direction of the center joint portion 11 is large, there is a possibility that the snow column shear force becomes small. When the length L5 of the center joint portion 11 is small, there is a possibility that the snow removal performance of the center main groove 3A deteriorates. For this reason, the length L5 of the center joint portion 11 is preferably 10 to 40% of the length L1 of the center inner portion 10a.

[0103] The shoulder block 9 may be provided with shoulder grooves 22 extending in the tire circumferential direction. As a result, the shoulder block 9 is divided into an outer piece 9A disposed between the shoulder groove 22 and the tread ends To, Ti, and an inner piece 9B disposed closer to the tire equator C than the outer piece 9A.

[0104] By providing such shoulder grooves 22, the edge component in the tire circumferential direction is increased, improving the turning performance. Also, since the rigidity in the tire circumferential direction of the outer piece 9A and the inner piece 9B is ensured to be large, the running performance on a dry road is improved. Note that the shoulder grooves 22 extend linearly, but are not limited to such a form. For example, they may extend in a wave shape, a sine wave shape, or a zigzag shape. The groove width W2 of the shoulder grooves 22 is preferably, for example, 1.0% to 2.0% of the tread width TW. The groove depth of the shoulder grooves 22 is preferably, for example, 0.40 to 0.60 times the deepest groove depth of the circumferential main grooves 3A, 3B.

[0105] The center land 7, the middle block 8, the outer piece 9A, and the inner piece 9B may be provided with sipes 25 having one or both ends opening into the circumferential main grooves 3A, 3B or the shoulder grooves 22 and extending at an angle of 0 to 30° with respect to the tire width direction. In particular, by providing the sipes 25 in the center land 7, when the block edge in the tire circumferential direction of the center land 7 comes into contact with the ground, it deforms in a direction to close the width, so that the wall surfaces of adjacent sipes come into close contact with each other and support each other, suppressing a decrease in the rigidity of the land. Therefore, the sipes 25 enhance the drainage performance and the uneven wear resistance performance in a well-balanced manner in the center land 7 where high ground pressure acts and drainage is difficult. Note that the sipes 25 extend linearly, but are not limited to such a form. For example, they may extend in a wave shape, a sine wave shape, or a zigzag shape. In this specification, a "sipe" refers to a narrow cut having a width of 2.0 mm or less, preferably 0.5 to 1.5 mm.

[0106] In the circumferential main groove of the present disclosure, at a plurality of bent portions 4, the center line of the circumferential main groove is displaced in the tire width direction (see FIGS. 2 and 3), or the extending direction of the center line of the circumferential main groove changes before and after the bent portion 4 (see FIG. 4), and it may be bent so as to extend in the tire circumferential direction, and is not limited to the zigzag shape of FIG. 1. In the present disclosure, the bent portion refers to a predetermined region that is bent at an acute angle or curved so as to change the extending direction of the center line of the circumferential main groove extending in the circumferential direction. The bent portion 4 may be an intersection portion with a transverse groove that crosses the circumferential main groove in the width direction. When the bent portion 4 is an intersection portion of the circumferential main groove and the transverse groove, the transverse groove may extend obliquely with respect to the width direction. Also, the groove width of the circumferential main groove may be wider, narrower, or the same width as the intersecting transverse groove. The circumferential main groove of the present disclosure communicates throughout the entire tire circumferential direction, but when an arbitrary virtual line (see the two-dot chain line in FIGS. 2 to 4) extending linearly along the circumferential direction is assumed, portions where it is interrupted repeatedly exist.

[0107] FIGS. 3 and 4 show enlarged views of other circumferential main grooves according to the present disclosure. In FIG. 3, the circumferential main groove 3 does not extend linearly along the tire circumferential direction, but extends linearly while being inclined with respect to the tire circumferential direction, and at the bent portion 4 of the circumferential main groove 3, the transverse groove 5 intersects and extends to the circumferential main groove 3. In FIG. 4, the circumferential main groove 3 extends while being curved in a sine wave shape with respect to the tire circumferential direction. In any case, when an arbitrary virtual line extending linearly along the circumferential direction is assumed, portions where it is interrupted repeatedly exist.

Example

[0108] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited only to these examples.

[0109] Hereinafter, various chemicals used in the examples and comparative examples are collectively shown. NR: TSR20 SBR: Modified solution-polymerized SBR produced in Production Example 1 described below (styrene content: 30% by mass, vinyl content: 52 mol%, Mw: 250,000, non-oil product) BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (cis content: 97%, Mw: 440,000) Carbon black: Diablack N220 (N2SA: 115 m 2 / g) manufactured by Mitsubishi Chemical Corporation Silica 1: ULTRASIL (registered trademark) VN3 (N2SA: 175 m 2 / g, average primary particle size: 18 nm) manufactured by Evonik Degussa Silica 2: Zeosil (registered trademark) 1115MP (N2SA: 115 m 2 / g, average primary particle size: 25 nm) manufactured by Solvay Silica 3: ULTRASIL (registered trademark) 9100GR (N2SA: 230 m 2 / g, average primary particle size: 15 nm) manufactured by Evonik Degussa Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Oil: VivaTec 400 (TDAE oil) manufactured by H&R Resin component: Petrothene 100V (C5C9-based petroleum resin, softening point: 96°C) manufactured by Tosoh Corporation Wax: Oz Ace 0355 manufactured by Nippon Seiro Co., Ltd. Antioxidant 1: No Crack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. Antioxidant 2: No Crack RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. Stearic acid: Bead Stearic Acid Tsubaki manufactured by NOF Corporation Zinc oxide: Zinc White No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Processing aid 1: Ultra-Flow (registered trademark) 440 (natural fatty acid zinc / metal soap) manufactured by Performance Additives Processing aid 2: Struktol WB16 (mixture of fatty acid ester and fatty acid metal salt) manufactured by Schill+Seilacher Sulfur: HK-200-5 (5% oil-containing powdered sulfur) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Sanseler NS-G (N-(tert-butyl)-2-benzothiazolylsulfenamide (TBBS)) manufactured by Sanshin Chemical Industry Co., Ltd. Vulcanization accelerator 2: Nocceler D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0110] Production Example 1: Synthesis of modified solution-polymerized SBR Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-substituted autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium was added to initiate polymerization. Polymerization was carried out under adiabatic conditions, and the maximum temperature reached 85°C. When the polymerization conversion rate reached 99%, 1,3-butadiene was added, and polymerization was continued for another 5 minutes. Then, N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane was added as a modifier to carry out the reaction. After the polymerization reaction was completed, 2,6-di-tert-butyl-p-cresol was added. Next, solvent was removed by steam stripping and dried with a hot roll adjusted to 110°C to obtain modified solution-polymerized SBR.

[0111] (Examples and Comparative Examples) According to the formulation shown in Table 1, using a 1.7 L sealed Banbury mixer, chemicals other than sulfur and vulcanization accelerators were kneaded for 1 to 10 minutes until the discharge temperature reached 150 to 160°C to obtain a kneaded product. Next, using a twin-screw open roll, sulfur and vulcanization accelerators 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.

[0112] Further, the obtained unvulcanized rubber composition was extruded into the shape of a 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 a test tire (size: 195 / 65R15 91V, rim: 15×6.0J, internal pressure: 240 kPa). Each test tire had the tread pattern shown in FIG. 1.

[0113] The following evaluations were performed on the obtained test rubber compositions and test tires. The evaluation results are shown in Table 1.

[0114] <Viscoelasticity test> A strip-shaped test piece with a width of 4 mm, a length of 20 mm, and a thickness of 2 mm was punched out from the sheet-shaped vulcanized rubber composition and used for the test. Using a spectrometer manufactured by Ueshima Seisakusho Co., Ltd., tanδ (tanδ at 20 °C) at 20 °C was measured under the conditions of an initial strain of 2%, a dynamic strain of 1%, and a frequency of 50 Hz.

[0115] <Tensile test> Dumbbell-shaped No. 3 test pieces made of each vulcanized rubber composition were prepared, and a tensile test was carried out under the conditions of a tensile speed of 8.3 mm / sec in an atmosphere of 175 °C in accordance with JIS K 6251:2017 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Tensile Test Properties", and the breaking strength TB (MPa) and the elongation at break EB (%) were measured.

[0116] <Chipping resistance performance> Each test tire was incorporated into a standard rim, filled with air up to the standard internal pressure, then mounted on a vehicle and driven on an uneven road at a speed of 60 km / h for 4 hours. After driving, for all the cracks generated on the tire surface, the circumferential length was measured, and the maximum value of the circumferential length was determined for each tire. The results were expressed as an index with Comparative Example 3 set to 100 according to the following formula. The larger the index, the smaller the crack, indicating better chipping resistance performance when driving at high speed on a rough road. The index was calculated by the following formula. (Chipping resistance performance index) = (circumferential length of the crack in Comparative Example 3) / (circumferential length of the crack in each formulation example) × 100

[0117] By performing each of the above tests based on the composition content of Table 1, each index or a value close thereto can be obtained.

[0118] [Table 1]

[0119] From the results of Table 1, it can be seen that the tire of the present disclosure having a circumferential main groove with a bent portion in the tread portion and having the loss tangent tanδ, breaking strength, and elongation at break of the rubber composition constituting the tread within a predetermined range has improved chipping resistance performance when driving at high speed on rough roads.

[0120] <Embodiment> Examples of the embodiments of the present disclosure are shown below.

[0121] 〔1〕A tire provided with a tread composed of a rubber composition containing a rubber component, wherein the tread has at least one circumferential main groove continuously extending in the tire circumferential direction, and the circumferential main groove is bent at a plurality of bent portions so that the center line of the circumferential main groove is displaced in the tire width direction, or the extending direction of the center line of the circumferential main groove changes before and after the bent portion, and extends in the tire circumferential direction, and the rubber composition has a tanδ (20°C tanδ) of 0.30 or less at 20°C, and the breaking strength TB (MPa) at 175°C and the breaking Time elongation EB (%) at 175°C satisfy the relational expression: TB × EB / 2 ≥ 600. 〔2〕The tire according to the above 〔1〕, wherein the circumferential main groove is zigzag-shaped having an amplitude in the tire width direction. 〔3〕The tire according to the above 〔1〕 or 〔2〕, wherein the depth of the circumferential main groove is 6.0 to 12.0 mm (preferably 7.0 to 11.0 mm, more preferably 8.5 to 10.5 mm). 〔4〕The amplitude λ1 of the peak-to-peak in the tire width direction of the groove center line of the circumferential main groove is 2.0 to 20.0 mm (preferably 2.5 to 5.0 mm, preferably 3.0 to 5.0 mm, particularly preferably 3.5 to 4.5 mm), and the tire according to any one of the above 〔1〕 to 〔3〕. 〔5〕TB × EB / λ1 ≥ 50 (preferably TB × EB / λ1 ≥ 100, more preferably TB × EB / λ1 ≥ 150, still more preferably TB × EB / λ1 ≥ 200, still more preferably TB × EB / λ1 ≥ 250, particularly preferably TB × EB / λ1 ≥ 300), and the tire according to 〔4〕 above. 〔6〕20 °C tanδ × λ1 ≤ 4.0 (preferably 20 °C tanδ × λ1 ≤ 2.5, more preferably 20 °C tanδ × λ1 ≤ 2.0, still more preferably 20 °C tanδ × λ1 ≤ 1.5, still more preferably 20 °C tanδ × λ1 ≤ 1.2, particularly preferably 20 °C tanδ × λ1 ≤ 0.90), and the tire according to 〔4〕 or 〔5〕 above. 〔7〕The tread has 3 to 5 circumferential main grooves, and the tire according to any one of the above 〔1〕 to 〔6〕. 〔8〕The 20 °C tanδ of the rubber composition is 0.25 or less, and the tire according to any one of the above 〔1〕 to 〔7〕. 〔9〕The 20 °C tanδ of the rubber composition is 0.20 or less, and the tire according to any one of the above 〔1〕 to 〔8〕. 〔10〕TB × EB / 2 ≥ 625, and the tire according to any one of the above 〔1〕 to 〔9〕. 〔11〕TB × EB / 2 ≥ 650, and the tire according to any one of the above 〔1〕 to 〔10〕. 〔12〕The rubber composition contains silica having an average particle diameter of 17 nm or less (preferably 16 nm or less, more preferably 15 nm or less), and the tire according to any one of the above 〔1〕 to 〔11〕. 〔13〕The rubber composition contains 10% by mass or more of isoprene rubber in the rubber component, and the tire according to any one of the above 〔1〕 to 〔12〕. 〔14〕The rubber composition contains 10% by mass or more (preferably 10 to 80% by mass, more preferably 12 to 75% by mass, still more preferably 15 to 70% by mass) of an isoprene-based rubber and 20% by mass or more (preferably 20 to 80% by mass, more preferably 25 to 75% by mass, still more preferably 30 to 70% by mass) of a styrene-butadiene rubber per 100 mass parts of the rubber component. part and contains 25 parts by mass or more (preferably 35 to 120 parts by mass, more preferably 50 to 100 parts by mass, still more preferably 60 to 90 parts by mass) of silica having an average particle diameter of 17 nm or less (preferably 16 nm or less, more preferably 15 nm or less), the tire according to any one of the above [1] to

[13] .

Explanation of Symbols

[0122] 2 Tread 3 Circumferential main groove 3A Center main groove 3B Shoulder main groove 4 Bend 5 Transverse groove 5A Middle transverse groove 5B Shoulder transverse groove 7 Center land 8 Middle block 8R Middle block row 9 Shoulder block 9R Shoulder block row 9A Outer piece 9B Inner piece 22 Shoulder fine groove 25 Siping C Tire circumferential direction To Outer tread end Ti Inner tread end TW Tread width W Tire width direction

Claims

1. A tire comprising a tread made of a rubber composition containing a rubber component, The tread has at least one circumferential main groove continuously extending in the circumferential direction of the tire, The circumferential main groove is bent at a plurality of bent portions so that the center line of the circumferential main groove is displaced in the tire width direction, or the extending direction of the center line of the circumferential main groove changes before and after the bent portion, and extends in the circumferential direction of the tire, The rubber composition has a tanδ (tanδ at 20°C) of 0.30 or less at 20°C, and the breaking strength TB (MPa) at 175°C and the elongation at break EB (%) at 175°C satisfy the relational expression, TB × EB / 2 ≥ 600 and, Here, the tanδ at 20°C of the rubber composition is measured under the conditions of a temperature of 20°C, an initial strain of 2%, a dynamic strain of 1%, and a frequency of 50 Hz. The breaking strength TB (MPa) at 175°C and the elongation at break EB (%) at 175°C of the rubber composition are measured under the conditions of a tensile speed of 8.3 mm / second in a 175°C atmosphere in accordance with JIS K 6251.

2. The tire according to claim 1, wherein the circumferential main groove is zigzag-shaped having an amplitude in the tire width direction.

3. The tire according to claim 1 or 2, wherein the depth of the circumferential main groove is 6.0 to 12.0 mm.

4. The tire according to any one of claims 1 to 3, wherein the peak-to-peak amplitude λ1 in the tire width direction of the groove center line of the circumferential main groove is 2.0 to 20.0 mm.

5. The tire according to claim 4, wherein TB × EB / λ1 ≥ 50.

6. The tire according to claim 4 or 5, wherein 20°C tanδ × λ1 ≤ 4.

0.

7. The tire according to any one of claims 1 to 6, wherein the tread has 3 to 5 circumferential main grooves.

8. The tire according to any one of claims 1 to 7, wherein the 20°C tanδ of the rubber composition is 0.25 or less.

9. The tire according to any one of claims 1 to 8, wherein the 20°C tanδ of the rubber composition is 0.20 or less.

10. The tire according to any one of claims 1 to 9, wherein TB × EB / 2 ≥ 625.

11. The tire according to any one of claims 1 to 10, wherein TB × EB / 2 ≥ 650.

12. The tire according to any one of claims 1 to 11, wherein the rubber composition contains silica having an average particle diameter of 17 nm or less.

13. The tire according to any one of claims 1 to 12, wherein the rubber composition contains 10% by mass or more of isoprene rubber in the rubber component.

14. The tire according to any one of claims 1 to 13, wherein the rubber composition contains 25 to 120 parts by mass of silica having an average particle diameter of 17 nm or less with respect to 100 parts by mass of a rubber component containing 10 to 80% by mass of isoprene rubber and 20 to 80% by mass of styrene-butadiene rubber.

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