Tire

Abstract

To provide a tire that is excellent in integrated performance of fuel efficiency and abrasion resistance.SOLUTION: A tire comprises a cap tread including rubber components and sulfur. In the cap tread, a content of styrene in 100 mass% of the rubber components are below 20 mass%, a content Lc of styrene-butadiene rubber are 5 mass% or more and 100 mass% or less, a content Sc of the sulfur with respect to 100 parts by mass of the rubber component are 0.5 parts by mass or more and 1.5 parts by mass or less, and a thickness T of the cap tread is less than 10.5 mm. A ratio (SWELL / (Sc×T)) of SWELL (%) of the cap tread to the content Sc (mass parts) of sulfur with respect to the 100 parts by mass of the rubber components x the thickness T (mm) of the cap tread is 21 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] Recently, from the viewpoints such as environmental consideration, improvement in low fuel consumption, wear resistance, etc. has been desired for tires.

Summary of the Invention

Problems to be Solved by the Invention

[0003] However, since low fuel consumption and wear resistance are generally contradictory performances, it is difficult to improve them in a well-balanced manner.

[0004] An object of the present invention is to solve the above problems and provide a tire excellent in the comprehensive performance of low fuel consumption and wear resistance.

Means for Solving the Problems

[0005] The present invention is a tire provided with a cap tread containing a rubber component and sulfur, wherein the content Lc of styrene-butadiene rubber having a styrene content of 20% by mass or less in 100% by mass of the rubber component is 5% by mass or more and 100% by mass or less, and the content Sc of sulfur with respect to 100 parts by mass of the rubber component is 0.5 part by mass or more and 1.5 parts by mass or less, the thickness T of the cap tread is less than 10.5 mm, and the present invention relates to a tire in which the ratio (SWELL / (Sc×T)) of the SWELL (%) of the cap tread to the content Sc (parts by mass) of sulfur with respect to 100 parts by mass of the rubber component × the thickness T (mm) of the cap tread is 21 or more.

Effects of the Invention

[0006] The present invention relates to a tire provided with a cap tread containing a rubber component and sulfur, wherein the cap tread has a styrene-butadiene rubber content Lc of 5% by mass or more and 100% by mass or less with a styrene content of 20% by mass or less in 100% by mass of the rubber component, a sulfur content Sc of 0.5 part by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the rubber component, a thickness T of the cap tread of less than 10.5 mm, and a ratio (SWELL / (Sc×T)) of the SWELL (%) of the cap tread to the sulfur content Sc (parts by mass) × the thickness T (mm) of the cap tread with respect to 100 parts by mass of the rubber component of 21 or more. Therefore, it is possible to provide a tire excellent in the overall performance of low fuel consumption and wear resistance.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0008] The above tire is provided with a cap tread containing a rubber component and sulfur, and the cap tread has a styrene-butadiene rubber content Lc of 5% by mass or more and 100% by mass or less with a styrene content of 20% by mass or less in 100% by mass of the rubber component, a sulfur content Sc of 0.5 part by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the rubber component, a thickness T of the cap tread of less than 10.5 mm, and a ratio (SWELL / (Sc×T)) of the SWELL (%) of the cap tread to the sulfur content Sc (parts by mass) × the thickness T (mm) of the cap tread with respect to 100 parts by mass of the rubber component of 21 or more.

[0009] The reason why the above-described effects are obtained by the above tire is not necessarily clear, but it is presumed as follows. In a low fuel consumption formulation, a method of reducing the amount of filler is common, but the reinforcing property decreases and it is generally difficult to achieve both wear resistance. Even if the crosslink density is changed simply by changing the sulfur content, it is difficult to achieve both low fuel consumption and wear resistance. This is presumably because increasing sulfur increases the crosslink density and reduces energy loss, but elongation decreases and wear resistance deteriorates; while decreasing the sulfur content can ensure elongation, energy loss tends to increase and low fuel consumption deteriorates. The thinner the tread, the more beneficial it is for improving low fuel consumption through weight reduction. On the other hand, as the thickness is reduced, the tire life decreases, so it is necessary to combine with a formulation with good wear resistance. Similarly, it is difficult to achieve both low fuel consumption and wear resistance. In the above tire, in a formulation with a small amount of sulfur, for example, when peroxide is added, the polymer chains bind to each other, making it less likely for energy loss to occur compared to sulfur crosslinking, and it is considered that low fuel consumption is improved. Furthermore, by combining with a styrene-butadiene rubber with a low styrene content, that is, a low Tg styrene-butadiene rubber, the steric hindrance of the styrene unit is reduced and the crosslinking efficiency is increased, so the energy loss can be further reduced. Therefore, by combining a styrene-butadiene rubber with a low styrene content and a small amount of sulfur, it becomes possible to incorporate a large amount of filler, and it becomes possible to achieve both low fuel consumption and wear resistance. Therefore, it is speculated that by combining a styrene-butadiene rubber with a low styrene content and a small amount of sulfur, setting the thickness of the cap tread to a predetermined value or less, and setting the ratio of the SWELL of the cap tread to the product of the sulfur content Sc and the thickness T of the cap tread (SWELL / (Sc×T)) to a predetermined value or more, the comprehensive performance of low fuel consumption and wear resistance is improved.

[0010] Thus, the above tire solves the problem (objective) of improving the overall performance of low fuel consumption and wear resistance by having a configuration that satisfies the relationship of "SWELL / (Sc×T) ≥ 21". That is, the parameter of "SWELL / (Sc×T) ≥ 21" does not define the problem (objective). The problem of this application is to improve the overall performance of low fuel consumption and wear resistance, and as a solution means, it has a configuration that satisfies the said parameter.

[0011] The above tire has a cap tread. The cap tread is composed of a rubber composition for cap tread.

[0012] In this specification, the cap tread is a rubber layer that forms the outermost layer in the tire radial direction among the rubber layers constituting the tread. When the tread is a single-layer structure tread, it is the single-layer structure tread itself. When the tread is a two-layer structure tread of a cap tread and a base tread, it is the rubber layer that forms the surface layer. When the tread has a structure of three or more layers, it is the rubber layer that forms the outermost layer, which respectively corresponds to the cap tread.

[0013] Hereinafter, the chemicals that can be used in the rubber composition for cap tread will be described.

[0014] The rubber composition for cap tread contains a rubber component. Here, the rubber component is a component that contributes to crosslinking. Generally, a polymer with a weight average molecular weight (Mw) of 10,000 or more and a polymer component that is not extracted by acetone corresponds to the rubber component. The elastomer component is in a solid state at normal temperature (25°C).

[0015] The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, still more preferably 200,000 or more, particularly preferably 270,000 or more, and preferably 2,000,000 or less, more preferably 1,500,000 or less, still more preferably 1,000,000 or less. When within the above range, the effect tends to be obtained better.

[0016] In the present specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) can be determined by standard polystyrene conversion based on the measured values obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation). In the case of a polymer having a modifying group, since the modifying group and the silica gel of the column interact with each other and accurate Mw and Mn cannot be obtained, usually, Mw and Mn are measured before the modification treatment is carried out.

[0017] The rubber component that can be used in the rubber composition for a cap tread may be an unmodified rubber or a modified rubber. Examples of the modified rubber include rubbers having a functional group that interacts with a filler such as silica. For example, a terminal-modified rubber (a terminal-modified rubber having the above functional group at the terminal) in which at least one end of the rubber is modified with a compound (modifying agent) having the above functional group, a main-chain modified rubber having the above functional group in the main chain, a main-chain terminal-modified rubber having the above functional group in the main chain and at the terminal (for example, a main-chain terminal-modified rubber having the above functional group in the main chain and at least one end modified with the above modifying agent), and a terminal-modified rubber modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or an epoxy group introduced therein, and the like can be mentioned.

[0018] Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, etc. These functional groups may have substituents. Among them, an amino group (preferably an amino group in which a hydrogen atom of the amino group is substituted with an alkyl group having 1 to 6 carbon atoms), an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms), and an alkoxysilyl group (preferably an alkoxysilyl group having 1 to 6 carbon atoms) are preferred.

[0019] The rubber composition for a cap tread contains, as a rubber component, a styrene-butadiene rubber having a styrene content of 20% by mass or less.

[0020] The styrene-butadiene rubber that can be used as the styrene-butadiene rubber having a styrene content of 20% by mass or less (hereinafter also referred to as low-styrene-content SBR) is not particularly limited, and for example, an emulsion-polymerized styrene-butadiene rubber (E-SBR), a solution-polymerized styrene-butadiene rubber (S-SBR), etc. can be used.

[0021] The styrene content of the above low-styrene-content SBR is 20% by mass or less, preferably 15% by mass or less, more preferably 12% by mass or less, and particularly preferably 10% by mass or less. The lower limit of the styrene content is preferably 3% by mass or more, more preferably 5% by mass or more, and still more preferably 6% by mass or more. When within the above range, the effect tends to be obtained more favorably. In this specification, the styrene content is calculated by 1 1H-NMR measurement.

[0022] The vinyl content of the above low styrene content SBR is preferably 30% by mass or more, more preferably 35% by mass or more, still more preferably 40% by mass or more. The upper limit of the vinyl content is preferably 55% by mass or less, more preferably 52% by mass or less, still more preferably 50% by mass or less. When it is within the above range, the effect tends to be obtained more favorably. In addition, in this specification, the vinyl content (1,2-bonded butadiene unit amount) can be measured by infrared absorption spectrum analysis.

[0023] The weight average molecular weight (Mw) of the above low styrene content SBR is preferably 100,000 or more, more preferably 150,000 or more, still more preferably 200,000 or more. The above Mw is preferably 400,000 or less, more preferably 350,000 or less, still more preferably 300,000 or less. When it is within the above range, the effect tends to be obtained more favorably. In addition, in this specification, the weight average molecular weight (Mw) can be determined by standard polystyrene conversion based on the measured value by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation).

[0024] In the rubber composition for cap tread, the content Lc of the above low styrene content SBR in 100% by mass of the rubber component is 5% by mass or more and 100% by mass or less. The lower limit of Lc is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 75% by mass or more, and the upper limit is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0025] In the rubber composition for cap tread, a rubber component other than the above low styrene content SBR may be included. Examples of such rubber components include diene rubbers. Examples of diene rubbers include isoprene rubbers, butadiene rubber (BR), styrene butadiene rubbers (SBR) other than the above-mentioned SBR with a low styrene content, styrene isoprene butadiene rubbers (SIBR), ethylene propylene diene rubbers (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubbers (NBR), and the like. Further, examples of rubber components include butyl rubbers, fluororubbers, and the like. These may be used alone or in combination of two or more. Further, these rubber components may be subjected to modification treatment or hydrogenation treatment, and extended rubbers extended with oils, resins, liquid rubber components, etc. may also be used. Among them, it is preferable to contain at least one of isoprene rubbers and BR, and more preferably to contain BR.

[0026] Examples of isoprene rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. As NR, for example, those common in the rubber industry such as SIR20, RSS#3, TSR20, etc. can be used. IR is not particularly limited, and for example, those common in the rubber industry such as IR2200, etc. can be used. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc., examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc., and examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These may be used alone or in combination of two or more.

[0027] When the rubber composition for the cap tread contains an isoprene rubber, the content of the isoprene rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and is preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0028] BR is not particularly limited. For example, high-cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, BR synthesized using a rare-earth catalyst (rare-earth BR), etc. can be used. These may be used alone or in combination of two or more. Among them, BR preferably contains high-cis BR with a cis content of 90% by mass or more. The cis content is more preferably 95% by mass or more. The cis content can be measured by infrared absorption spectrometry.

[0029] When there is one type of BR, the cis amount of BR means the cis amount of that BR. When there are multiple types, it means the average cis amount. The average cis amount of BR can be calculated by {Σ(content of each BR × cis amount of each BR)} / total content of all BR. For example, in 100% by mass of the rubber component, if BR with a cis amount of 90% by mass is 20% by mass and BR with a cis amount of 40% by mass is 10% by mass, the average cis amount of BR is 73.3% by mass (=(20×90 + 10×40) / (20 + 10)).

[0030] Also, either non-modified BR or modified BR can be used for BR. Examples of modified BR include modified BR into which a functional group similar to that of a modified rubber is introduced. Also, hydrogenated butadiene polymer (hydrogenated BR) can be used for BR.

[0031] In the rubber composition for cap tread, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0032] In addition, the raw materials (monomers) of synthetic rubbers such as SBR and BR may be derived from petroleum or recycled from rubber products such as tires and non-rubber products such as polystyrene. The monomers obtained by recycling (recycled monomers) are not particularly limited, and examples include recycled butadiene and recycled aromatic vinyl. Examples of the butadiene include 1,2-butadiene and 1,3-butadiene. The aromatic vinyl is not particularly limited, and examples include styrene. Among them, it is preferable to use recycled butadiene (recycled butadiene) and / or recycled styrene (recycled styrene) as raw materials.

[0033] The method for producing recycled monomers is not particularly limited. For example, it can be synthesized from recycled naphtha obtained by decomposing rubber products such as tires. The method for producing recycled naphtha is not particularly limited. For example, rubber products such as tires may be decomposed under high temperature and high pressure, decomposed by microwaves, or extracted after mechanical pulverization.

[0034] Furthermore, the raw materials (monomers) of synthetic rubbers such as SBR and BR may be derived from biomass. The monomers derived from biomass (biomass monomers) are not particularly limited, and examples include biomass-derived butadiene and biomass-derived aromatic vinyl. Examples of the butadiene include 1,2-butadiene and 1,3-butadiene. The aromatic vinyl is not particularly limited, and examples include styrene. The method for producing biomass monomers is not particularly limited. For example, it can be obtained by biological and / or chemical and / or physical conversion of animals and plants. Fermentation by microorganisms is typical for biological conversion, and examples of chemical and / or physical conversion include those using catalysts, high heat, high pressure, electromagnetic waves, supercritical fluids, and combinations thereof. Examples of the biomass sources of these monomers include sugars, wood, plant residues after obtaining useful components, plant-derived ethanol, biomass naphtha, and the like.

[0035] The polymers synthesized from biomass monomer components (biomass polymers) are not particularly limited, and examples include polybutadiene rubber synthesized from biomass-derived butadiene, and aromatic vinyl / butadiene copolymers synthesized from biomass-derived butadiene and / or biomass-derived aromatic vinyl. Examples of the aromatic vinyl / butadiene copolymers include styrene-butadiene rubber synthesized from biomass-derived butadiene and / or biomass-derived styrene.

[0036] Whether the raw material of the polymer is derived from biomass can be determined by pMC (percent Modern Carbon) measured in accordance with ASTM D6866-10.

[0037] pMC is the ratio of the 14 C concentration of the sample to the 14 C concentration of the modern standard reference, and this value is used as an index indicating the biomass ratio of the compound (rubber). The significance of this value is described below.

[0038] In one mole (6.02×10 23 pieces) of carbon atoms, there are approximately 6.02×10 11 pieces of 14 C, which is about one trillionth of the normal carbon atoms. 14 14 C is called a radioactive isotope, and its half-life is 5730 years and it decreases regularly. It takes 226,000 years for all of these to decay. Therefore, in fossil fuels such as coal, oil, and natural gas, which are considered to have passed more than 226,000 years after carbon dioxide in the atmosphere was taken up and fixed by plants, etc., the 14 14 C element that was also contained in them at the time of fixation has all decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas do not contain 14 14 C element at all. Therefore, chemical substances produced from these fossil fuels as raw materials also do not contain 14 14 C element at all.

[0039] On the one hand, 14 C is constantly generated by nuclear reactions of cosmic rays in the atmosphere, and the balance between the continuous generation and the decrease due to radioactive decay results in a constant amount of 14 C in the Earth's atmospheric environment. Therefore, the 14 C concentration of substances derived from biomass resources that are cycling in the current environment is about 1×10 -12 mol% with respect to the total

[0040] This 14 C is generally measured as follows. Using accelerator mass spectrometry based on a tandem accelerator, 13 C concentration ( 13 C / 12 C), 14 C concentration ( 14 C / 12 C) is measured. In the measurement, 14 As the modern standard reference for the concentration of 14 C, the 14 C concentration in the circulating carbon in nature in 1950 is adopted. As a specific standard substance, the oxalic acid standard provided by NIST (National Institute of Standards and Technology) is used. The specific activity of carbon in this oxalic acid (the 13 C radioactive intensity per gram of carbon) is separated for each carbon isotope, 14 C is corrected to a constant value, and the value after applying the decay correction from 1950 AD to the measurement date is used as the standard

[0041] Therefore, if the rubber is made of a 100% biomass (natural) - derived material, although there are regional differences, it will show a value of approximately 110 pMC (currently, in the normal state, it often does not reach 100). On the other hand, for chemical substances derived from fossil fuels such as petroleum, when measuring the 14 C concentration, it will show almost 0 pMC (for example, 0.3 pMC). This value corresponds to the biomass ratio of 0% mentioned above.

[0042] From the above, using materials such as rubber with a high pMC value, that is, materials such as rubber with a high biomass ratio, in the rubber composition is suitable from the perspective of environmental protection.

[0043] The rubber composition for cap tread contains sulfur. In the rubber composition for cap tread, the sulfur content Sc is 0.5 parts by mass or more, preferably 0.6 parts by mass or more, more preferably 0.7 parts by mass or more, and still more preferably 0.8 parts by mass or more, based on 100 parts by mass of the rubber component. The content is 1.5 parts by mass or less, preferably 1.3 parts by mass or less, more preferably 1.1 parts by mass or less, and still more preferably 1.0 parts by mass or less. When within the above range, the effect tends to be obtained better.

[0044] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. As commercially available products, products of Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Kasei Kogyo Co., Ltd., Flexsys, Nippon Retorting Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used. These can be used alone or in combination of two or more.

[0045] From the perspective of obtaining better effects, the rubber composition for cap tread preferably contains an organic peroxide.

[0046] When an organic peroxide is included, the mechanism by which more effective results are obtained is not clear. However, since the polymer chains are bonded by the organic peroxide, energy loss is less likely to occur. Therefore, it is considered that the low fuel consumption property is improved and the overall performance with the wear resistance is improved.

[0047] Examples of the organic peroxide include, for example, the formula R 1 -O-O-R 2 (In the formula, R 1 and R 2 represent the same or different, hydrogen or an organic group.) and the like. The organic group is not particularly limited and may be a monovalent hydrocarbon group having a known substituent (linear, branched, cyclic hydrocarbon group (aliphatic hydrocarbon group, alicyclic hydrocarbon group, aromatic hydrocarbon group, etc.)) and the like. The number of carbon atoms of the organic group is preferably 4 or more, more preferably 5 or more, and is preferably 15 or less, more preferably 13 or less. The substituent is not particularly limited, and examples include an amino group, an amide group, a hydroxyl group, a sulfide group, an epoxy group, a tin-containing group, an alkoxysilyl group, a silanol group, a carbonyl group, a carboxyl group, a thiocarbonyl group, an ammonium group, a nitrile group, an imine group, and the like.

[0048] Examples of the organic peroxide include acyl peroxides such as benzoyl peroxide, dibenzoyl peroxide, p-chlorobenzoyl peroxide, peroxy esters such as 1-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl peroxyphtalate, ketone peroxides such as methyl ethyl ketone peroxide, alkyl peroxides such as di-t-butyl peroxybenzoate, 1,3-bis(1-butylperoxyisopropyl)benzene, hydroperoxides such as t-butyl hydroperoxide, dicumyl peroxide, t-butyl cumyl peroxide and the like. Among them, from the viewpoint of obtaining more effective results, dicumyl peroxide and t-butyl cumyl peroxide are preferable, and dicumyl peroxide is more preferable.

[0049] In the rubber composition for cap tread, the content of the organic peroxide is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, still more preferably 1.0 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 8.0 parts by mass or less, more preferably 5.0 parts by mass or less, still more preferably 3.0 parts by mass or less. When within the above range, the effect tends to be obtained more favorably. In addition, the content of dicumyl peroxide is also desirably in the same range.

[0050] The rubber composition for cap tread preferably contains a filler. The filler is not particularly limited, and materials known in the rubber field can be used. For example, inorganic fillers such as carbon black, silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, bio char (BIO CHAR); poorly dispersible fillers, etc. can be mentioned. Among them, from the viewpoint of obtaining more effects, carbon-derived fillers (carbon-containing fillers) such as carbon black and silica are preferable.

[0051] In the rubber composition for cap tread, the content Fc (total amount of fillers such as silica and carbon black) of the filler is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, still more preferably 90 parts by mass or more, particularly preferably 95 parts by mass or more, based on 100 parts by mass of the rubber component, and is preferably 250 parts by mass or less, more preferably 200 parts by mass or less, still more preferably 150 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0052] When the filler is contained in a predetermined amount or more, particularly when it is contained in 90 parts by mass or more, the mechanism by which more effects are obtained is not clear. However, by combining a styrene-butadiene rubber with a low styrene content and a small amount of sulfur, it is possible to reduce energy loss. Therefore, it is possible to increase elongation and improve abrasion resistance by blending a large amount of the filler. Accordingly, it is considered that the comprehensive performance of low fuel consumption and abrasion resistance is improved.

[0053] In the rubber composition for cap treads, carbon black that can be used is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc. As commercially available products, products of Asahi Carbon Co., Ltd., Cabot Japan Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin Nippon Carbon Co., Ltd., Columbian Carbon Co., etc. can be used. These may be used alone or in combination of two or more. In addition to carbon black made from conventional mineral oil and the like as raw materials, carbon black made from biomass materials such as lignin may also be used. Further, recycled carbon black obtained by decomposing rubber products, plastic products, etc. containing carbon black such as tires may be appropriately used in an equivalent substitution with the above carbon black.

[0054] In the rubber composition for cap treads, the content of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and preferably 15 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 8 parts by mass or less, based on 100 parts by mass of the rubber component. When within the above range, the effect tends to be obtained more favorably.

[0055] The nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 5 m 2 / g or more, more preferably 10 m 2 / g or more, still more preferably 15 m 2 / g or more. Also, the above N2SA is preferably 150 m 2 / g or less, more preferably 130 m 2 / g or less, still more preferably 120 m 2 / g or less. When within the above range, the effect tends to be obtained more favorably. Note that the nitrogen adsorption specific surface area of carbon black is determined according to JIS K6217-2:2001.

[0056] The dibutyl phthalate absorption (DBP) of carbon black is preferably 40 ml / 100 g or more, more preferably 60 ml / 100 g or more, and still more preferably 70 ml / 100 g or more. Also, when the above DBP is within the range of preferably 200 ml / 100 g or less, more preferably 150 ml / 100 g or less, and still more preferably 100 ml / 100 g or less, the effect tends to be obtained more favorably. Note that the DBP of carbon black is determined by the measurement method of JIS K6217-4:2001.

[0057] In the rubber composition for cap treads, the usable silica is not particularly limited. For example, silica prepared by the dry method (anhydrous silica), silica prepared by the wet method (hydrous silica), etc., which are common in the tire industry, can be used. The raw material of silica is not particularly limited. For example, it may be a raw material derived from minerals such as quartz, or a raw material derived from organisms such as rice husks (for example, silica using biomass materials such as rice husks as raw materials), or silica recycled from products containing silica may also be used. Among them, hydrous silica prepared by the wet method is preferred because it has many silanol groups. These silicas may be used alone or in combination of two or more.

[0058] Silica using biomass materials as raw materials can be obtained, for example, by extracting silicate from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and reacting the silicate with sulfuric acid in the same manner as conventional wet silica to precipitate silicon dioxide, followed by filtration, washing with water, drying, and pulverization.

[0059] Silica recycled from products containing silica can be used, for example, silica recovered from products containing silica such as electronic components such as semiconductors, tires, desiccants, and filter materials such as diatomaceous earth. Also, the recovery method is not particularly limited, and examples include pyrolysis and decomposition by electromagnetic waves. Among them, silica recovered from electronic components such as semiconductors or tires is preferred.

[0060] When silica crystallizes, it becomes insoluble in water and the silicic acid that is its component cannot be utilized. By controlling the combustion temperature and combustion time, crystallization of the silica in rice husk ash can be suppressed (see, for example, Japanese Patent Application Laid-Open No. 2009-2594, Akita Prefectural University Web Journal B / 2019, vol. 6, p. 216-222, etc.).

[0061] As the amorphous silica extracted from rice husks, those commercially available from Wilmar Co., Ltd. and others can be used.

[0062] In the rubber composition for cap treads, the content of silica is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, still more preferably 90 parts by mass or more, and preferably 200 parts by mass or less, more preferably 150 parts by mass or less, still more preferably 120 parts by mass or less, based on 100 parts by mass of the rubber component. When it is within the above range, the effect tends to be obtained more favorably.

[0063] When the silica is contained in a predetermined amount or more, particularly when it is contained in 80 parts by mass or more, the mechanism by which more effects are obtained is not clear. However, by combining a styrene-butadiene rubber with a low styrene content and a small amount of sulfur, it becomes possible to reduce the energy loss. Therefore, it becomes possible to increase elongation and improve wear resistance by blending a large amount of silica. Accordingly, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0064] The nitrogen adsorption specific surface area (N2SA) of the silica is preferably 50 m 2 / g or more, more preferably 100 m 2 / g or more, still more preferably 150 m 2 / g or more. Also, the upper limit of the N2SA of the silica is not particularly limited, but it is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, still more preferably 250 m 2 / g or less. When it is within the above range, the effect tends to be obtained more favorably. Note that the N2SA of the silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0065] Examples of the hardly dispersible filler include microfibrillated plant fibers, short fibrous cellulose, gel-like compounds, etc. Among them, microfibrillated plant fibers are preferred.

[0066] As the above-mentioned microfibrillated plant fibers, cellulose microfibrils are preferred in terms of obtaining good reinforcing properties. The cellulose microfibrils are not particularly limited as long as they are derived from natural products. For example, resource biomass such as fruits, grains, and root vegetables, wood, bamboo, hemp, jute, kenaf, and pulp, paper, cloth, agricultural crop residues, food waste, and waste biomass such as sewage sludge obtained from these as raw materials, unused biomass such as rice straw, wheat straw, and thinned wood, and cellulose produced by organisms such as jellyfish and acetic acid bacteria. These microfibrillated plant fibers may be used alone or in combination of two or more.

[0067] In this specification, cellulose microfibrils typically mean cellulose fibers having an average fiber diameter within the range of 10 μm or less, and more typically, cellulose fibers having a micro-structure with an average fiber diameter of 500 nm or less formed by an aggregation of cellulose molecules. A typical cellulose microfibril is formed as an aggregate of cellulose fibers having the above-mentioned average fiber diameter, for example.

[0068] When the rubber composition for cap tread contains a hardly dispersible filler, the content of the hardly dispersible filler is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit of the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0069] When the rubber composition for cap tread contains silica, it is preferably further contained with a silane coupling agent. The silane coupling agent is not particularly limited, and those known in the rubber field can be used. For example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, etc. of the sulfide series, 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, NXT, NXT-Z manufactured by Momentive, etc. of the mercapto series, vinyltriethoxysilane, vinyltrimethoxysilane, etc. of the vinyl series, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, etc. of the amino series, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, etc. of the glycidoxy series, 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane, etc. of the nitro series, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, etc. of the chloro series, etc. can be mentioned. As commercially available products, products of Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azmax Co., Ltd., Toray Dow Corning Co., Ltd., etc. can be used. These may be used alone or in combination of two or more kinds.Among them, from the viewpoint of obtaining more effects, mercapto-based silane coupling agents (such as silane coupling agents having a mercapto group, silane coupling agents in which the mercapto group is protected, etc.) are preferable.

[0070] In the rubber composition for cap tread, the content of the silane coupling agent is preferably 0.1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more with respect to 100 parts by mass of silica. The upper limit of the content is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, still more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably. In addition, the content of the mercapto-based silane coupling agent is also preferably in the same range.

[0071] The rubber composition for cap tread preferably contains a plasticizer. In this specification, the plasticizer is a material that imparts plasticity to the rubber component, and is a concept including both plasticizers that are liquid (liquid state) at normal temperature (25 °C) and plasticizers that are solid at normal temperature (25 °C). Examples of plasticizers include resin components, oils, liquid polymers, ester-based plasticizers, etc. These plasticizers may be derived from petroleum, may be derived from biomass, or may be derived from naphtha recycled from rubber products or non-rubber products. Also, low-molecular-weight hydrocarbon components obtained by thermally decomposing and extracting used tires and products containing various components may be used as plasticizers. These plasticizers may be used alone or in combination of two or more.

[0072] Specific examples of the above plasticizers include oils, liquid polymers, resins, etc. These may be used alone or in combination of two or more.

[0073] Examples of the oil include process oil, vegetable oil, animal oil, etc. Examples of the process oil include paraffinic process oil (mineral oil), naphthenic process oil, aromatic process oil, etc. Specific examples of the process oil include, for example, MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), RAE (Residual Aromatic Extract), etc. Also, a process oil with a low content of polycyclic aromatic (PCA) compounds can be used for environmental protection. Examples of the low-PCA-content process oil include MES, TDAE, heavy naphthenic oil, etc. Further, from the perspective of life cycle assessment, waste oil after being used in a rubber mixer or an engine, or refined waste cooking oil used in a restaurant may be used.

[0074] In this specification, the vegetable oil includes, for example, linseed oil, rapeseed oil, safflower oil, soybean oil, corn oil, cottonseed oil, rice oil, tall oil, sesame oil, perilla oil, castor oil, tung oil, pine oil, pine tar oil, sunflower oil, coconut oil, palm oil, palm kernel oil, olive oil, camellia oil, jojoba oil, macadamia nut oil, peanut oil, grape seed oil, wood wax, etc. Further, the vegetable oil includes refined oil (such as salad oil) obtained by refining the above oil, transesterified oil obtained by transesterifying the above oil, hydrogenated oil obtained by hydrogenating the above oil, thermally polymerized oil obtained by thermally polymerizing the above oil, oxidatively polymerized oil obtained by oxidizing the above oil, waste cooking oil recovered from those used as edible oil, etc. Note that the vegetable oil may be liquid or solid at room temperature (25°C). These vegetable oils may be used alone or in combination of two or more.

[0075] The vegetable oil according to this embodiment preferably contains acylglycerol, and more preferably contains triacylglycerol. In this specification, acylglycerol refers to a compound in which a hydroxy group of glycerin and a fatty acid are ester-bonded. The acylglycerol is not particularly limited, and may be 1-monoacylglycerol, 2-monoacylglycerol, 1,2-diacylglycerol, 1,3-diacylglycerol, or triacylglycerol. Further, the acylglycerol may be a monomer, a dimer, or a multimer of trimer or higher. Note that acylglycerols of dimer or higher can be obtained by thermal polymerization, oxidative polymerization, or the like. Also, the acylglycerol may be liquid or solid at normal temperature (25°C).

[0076] As a method for confirming whether the acylglycerol is contained in the rubber composition, it is not particularly limited, but 1 it can be confirmed by 1H-NMR measurement. For example, a rubber composition containing triacylglycerol is immersed in deuterated chloroform at normal temperature (25°C) for 24 hours. After removing the rubber composition, 1 1H-NMR is measured. When the signal of tetramethylsilane (TMS) is set to 0.00 ppm, signals are observed around 5.26 ppm, around 4.28 ppm, and around 4.15 ppm. These signals are presumed to be signals derived from hydrogen atoms bonded to carbon atoms adjacent to the oxygen atom of the ester group. In this paragraph, "around" means a range of ±0.10 ppm.

[0077] The fatty acid is not particularly limited and may be an unsaturated fatty acid or a saturated fatty acid. Examples of the unsaturated fatty acid include monounsaturated fatty acids such as oleic acid, and polyunsaturated fatty acids such as linoleic acid and linolenic acid. Examples of the saturated fatty acid include butyric acid and lauric acid.

[0078] Among these, as the fatty acid, it is desirable to contain a fatty acid with few double bonds, that is, a saturated fatty acid or a monounsaturated fatty acid, and oleic acid is preferred. As the vegetable oil containing such a fatty acid, for example, a vegetable oil containing a saturated fatty acid or a monounsaturated fatty acid may be used, or a vegetable oil subjected to modification such as transesterification may be used. Further, in order to produce a vegetable oil containing such a fatty acid, plants may be improved by variety improvement, genetic recombination, genome editing, etc.

[0079] As the oil, for example, those commercially available from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Co., Ltd., Orysoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Fuji Kogyo Co., Ltd., Nisshin Oillio Group Co., Ltd., etc. can be used.

[0080] Examples of the liquid polymer include a liquid diene polymer (liquid rubber) and a liquid farnesene polymer at 25°C. Examples of the liquid rubber include a liquid styrene-butadiene copolymer (liquid SBR), a liquid butadiene polymer (liquid BR), a liquid isoprene polymer (liquid IR), a liquid styrene-isoprene copolymer (liquid SIR), a liquid styrene-butadiene-styrene block copolymer (liquid SBS block polymer), a liquid styrene-isoprene-styrene block copolymer (liquid SIS block polymer), etc. These may have their terminals or main chains modified with polar groups. Also, hydrogenated products thereof can be used.

[0081] The weight average molecular weight (Mw) in terms of polystyrene measured by gel permeation chromatography (GPC) of the liquid diene polymer is preferably 1.0×10 3 ~5.0×10 4 and more preferably 3.0×10 3 ~1.5×10 4 Also, the lower limit or upper limit of Mw of the liquid diene polymer may be 4500 or 8500. In this specification, the Mw of the liquid diene polymer is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0082] As the above liquid diene polymer, for example, products of Sartomer Co., Kuraray Co., Ltd. etc. can be used.

[0083] As the above resin, as a tire compound, resins (resins) usually used can be used, and they may be liquid or solid at normal temperature (25°C). For example, aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenol resins, rosin resins, petroleum resins, terpene resins, acrylic resins, etc. can be mentioned. Further, the resin may be a hydrogenated resin (hydrogenated resin). These may be used alone or in combination of two or more. Also, the resin itself may be a copolymer of monomer components from a plurality of sources. Among them, aromatic vinyl polymers, petroleum resins, terpene resins, and hydrogenated resins thereof are desirable.

[0084] When using a resin that is solid at normal temperature as the above resin, the softening point is preferably 50°C or higher, more preferably 55°C or higher, still more preferably 60°C or higher, and particularly preferably 85°C or higher. Also, it is preferably 160°C or lower, more preferably 150°C or lower, still more preferably 140°C or lower, and particularly preferably 100°C or lower. When within the above range, the effect tends to be obtained more favorably. When the resin is liquid at normal temperature, the softening point is preferably 20°C or lower, preferably 10°C or lower, and preferably 0°C or lower. In the case of a hydrogenated resin, it is desirable that the softening point is the same as above. Note that the softening point of the above resin is measured with a ring and ball softening point measuring device for the softening point defined in JIS K6220-1:2001, and is the temperature at which the ball drops.

[0085] The above aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. For example, resins obtained by polymerizing α-methylstyrene and / or styrene can be mentioned. Specifically, homopolymers of styrene (styrene resins), homopolymers of α-methylstyrene (α-methylstyrene resins), copolymers of α-methylstyrene and styrene, copolymers of styrene and other monomers, etc. can be mentioned.

[0086] The above coumarone-indene resin is a resin containing coumarone and indene as main monomer components constituting the resin skeleton (main chain). As monomer components contained in the skeleton other than coumarone and indene, styrene, α-methylstyrene, methyl indene, vinyl toluene, etc. can be mentioned.

[0087] The above coumarone resin is a resin containing coumarone as the main monomer component constituting the resin skeleton (main chain).

[0088] The above indene resin is a resin containing indene as the main monomer component constituting the resin skeleton (main chain).

[0089] As the above phenolic resin, for example, known ones such as polymers obtained by reacting phenol with aldehydes such as formaldehyde, acetaldehyde, and furfural in the presence of an acid or alkali catalyst can be used. Among them, those obtained by reacting with an acid catalyst (such as novolak-type phenolic resins) are preferred.

[0090] Examples of the above rosin resin include rosin-based resins typified by natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

[0091] Examples of the above petroleum resin include C5-based resins, C9-based resins, C5 / C9-based resins, dicyclopentadiene (DCPD) resins, C9 / DCPD resins, and hydrogenated products thereof. Among them, DCPD resins, hydrogenated DCPD resins, C9 / DCPD resins, and C9 / hydrogenated DCPD resins are preferred.

[0092] The above terpene resin is a polymer containing terpenes as constituent units. For example, there are polyt terpene resins obtained by polymerizing terpene compounds, aromatic modified terpene resins obtained by polymerizing terpene compounds and aromatic compounds, and the like. Examples of aromatic modified terpene resins include terpene phenol resins using terpene compounds and phenolic compounds as raw materials, terpene styrene resins using terpene compounds and styrene compounds as raw materials, and terpene phenol styrene resins using terpene compounds, phenolic compounds and styrene compounds as raw materials. As terpene compounds, α-pinene, β-pinene, etc. can be mentioned; as phenolic compounds, phenol, bisphenol A, etc. can be mentioned; and as aromatic compounds, styrene compounds (styrene, α-methylstyrene, etc.) can be mentioned. Among them, aromatic modified terpene resins are preferred.

[0093] The above acrylic resin is a polymer containing acrylic monomers as constituent units. For example, there are styrene acrylic resins such as styrene acrylic resins obtained by copolymerizing an aromatic vinyl monomer component and an acrylic monomer component and having a carboxyl group. Among them, a solvent-free carboxyl group-containing styrene acrylic resin can be preferably used.

[0094] As the above resin, for example, products of Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, ExxonMobil, KRATON, Nippon Paint Co., Ltd., Nippon Catalyst Co., Ltd., ENEOS Co., Ltd., Arakawa Chemical Industries, Ltd., Tago Chemical Industry Co., Ltd., etc. can be used.

[0095] From the perspective of sustainability, it is desirable to use plant-derived plasticizers such as the above plant-derived oils and farnesene-based polymers as the above plasticizer.

[0096] The farnesene-based polymer is a polymer obtained by polymerizing farnesene and has a structural unit based on farnesene. Farnesene has isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene), but (E)-β-farnesene having the following structure is preferred.

Chemical formula

[0097] The farnesene-based polymer may be a homopolymer of farnesene (farnesene homopolymer) or a copolymer of farnesene and a vinyl monomer (farnesene-vinyl monomer copolymer). These may be used alone or in combination of two or more. Among them, a copolymer of farnesene and a vinyl monomer is preferred.

[0098] Examples of vinyl monomers include aromatic vinyl compounds such as styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, 5-t-butyl-2-methylstyrene, vinyl ethylbenzene, divinylbenzene, trivinylbenzene, divinylnaphthalene, tert-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl)dimethylaminoethyl ether, N,N-dimethylaminoethylstyrene, N,N-dimethylaminomethylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2-t-butylstyrene, 3-t-butylstyrene, 4-t-butylstyrene, vinylxylene, vinylnaphthalene, vinyltoluene, vinylpyridine, diphenylethylene, and tertiary amino group-containing diphenylethylene, and conjugated diene compounds such as butadiene and isoprene. These may be used alone or in combination of two or more. Among them, butadiene is preferred. That is, as the farnesene-vinyl monomer copolymer, a copolymer of farnesene and butadiene (farnesene-butadiene copolymer) is preferred.

[0099] In the farnesene-vinyl monomer copolymer, the copolymerization ratio by mass (farnesene / vinyl monomer) of farnesene and the vinyl monomer is preferably 40 / 60 to 90 / 10.

[0100] Farnesene-based polymers with a weight average molecular weight (Mw) of 3000 or more and 300,000 or less can be preferably used. The Mw of the farnesene-based polymer is preferably 8000 or more, more preferably 10,000 or more, and preferably 100,000 or less, more preferably 60,000 or less, and even more preferably 50,000 or less. When within the above range, the effects tend to be more preferably obtained.

[0101] The farnesene-based polymer may be in a liquid state or a solid state at room temperature (25°C). Among them, a liquid farnesene-based polymer in a liquid state at room temperature (25°C) is desirable.

[0102] In the rubber composition for cap tread, the content of the plasticizer (total amount of plasticizers) is preferably 20 parts by mass or more, more preferably 35 parts by mass or more, still more preferably 40 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, still more preferably 50 parts by mass or less. When within the above range, the effect tends to be obtained more favorably. Note that the content of the plasticizer includes the amount of oil and resin contained in the oil-extended rubber and resin-extended rubber.

[0103] When containing a predetermined amount or more of the plasticizer, particularly when containing 35 parts by mass or more, the mechanism by which more effects are obtained is not clear. However, by combining a styrene-butadiene rubber with a low styrene content and a small amount of sulfur, it becomes possible to reduce energy loss. Therefore, it is possible to increase elongation and improve abrasion resistance by blending a large amount of the plasticizer. Accordingly, it is considered that the comprehensive performance of low fuel consumption and abrasion resistance is improved.

[0104] In the rubber composition for cap tread, the content of the solid plasticizer in a solid state at room temperature (25 °C) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, still more preferably 20 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 30 parts by mass or less. When within the above range, the effect tends to be obtained more favorably. Note that the content of the above resin in a solid state at room temperature (25 °C) and the above aromatic vinyl polymer in a solid state at room temperature (25 °C) are preferably in the same range.

[0105] In the above rubber composition, the content of the liquid plasticizer in a liquid state at room temperature (25 °C) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, still more preferably 20 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 30 parts by mass or less. When within the above range, the effect tends to be obtained more favorably. Note that the content of the liquid plasticizer includes the amount of oil contained in the oil-extended rubber and the amount of the liquid resin of the resin-extended rubber extended with the liquid resin. The content of the oil in a liquid state at normal temperature (25 °C) is preferably in the same range.

[0106] From the viewpoints of crack resistance, ozone resistance, etc., the rubber composition for cap tread preferably contains an anti-aging agent.

[0107] The anti-aging agent is not particularly limited, but naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine, 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-ditolyl-p-phenylenediamine (DTPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), N,N'-di-2-naphthyl-p-phenylenediamine (DNPD) and other p-phenylenediamine-based anti-aging agents; quinoline-based anti-aging agents such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based anti-aging agents such as 2,6-di-t-butyl-4-methylphenol, styrenated phenol; bis, tris, polyphenol-based anti-aging agents such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, etc. Among them, p-phenylenediamine-based anti-aging agents and quinoline-based anti-aging agents are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and polymers of 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. As commercially available products, for example, products of Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinsei Chemical Industry Co., Ltd., Flexsys Co., Ltd., etc. can be used.

[0108] In the rubber composition for cap tread, the content of the anti-aging agent is preferably 0.2 parts by mass or more, more preferably 2.0 parts by mass or more, still more preferably 3.0 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, more preferably 5.0 parts by mass or less.

[0109] The rubber composition for cap tread preferably contains stearic acid. In the rubber composition for cap tread, the content of stearic acid is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0110] As the stearic acid, conventionally known ones can be used. For example, products of NOF Corporation, Kao Corporation, FUJIFILM Wako Pure Chemical Corporation, Chiba Fatty Acids Co., Ltd., etc. can be used.

[0111] The rubber composition for cap tread preferably contains zinc oxide. In the rubber composition for cap tread, the content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component, and is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less.

[0112] As the zinc oxide, conventionally known ones can be used. For example, products of Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Shoindo Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

[0113] The rubber composition for cap tread may be blended with wax. In the rubber composition for cap tread, the content of wax is preferably 1.0 parts by mass or more, more preferably 1.5 parts by mass or more, based on 100 parts by mass of the rubber component, and is preferably 10.0 parts by mass or less, more preferably 2.0 parts by mass or less.

[0114] The wax is not particularly limited, and any wax commonly used in the tire industry can be preferably used. For example, petroleum waxes, mineral waxes, synthetic waxes, plant-derived waxes, etc. can be mentioned. Among them, petroleum waxes and plant-derived waxes are preferred, and petroleum waxes are more preferred. Examples of plant-derived waxes include rice wax, carnauba wax, candelilla wax, etc. Examples of petroleum waxes include paraffin wax, microcrystalline wax, these selected special waxes, etc., and paraffin wax is preferred. Note that the wax according to this embodiment does not contain stearic acid. As the wax, for example, those commercially available from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Paramelt Co., etc. can be used. These waxes may be used alone or in combination of two or more.

[0115] The rubber composition for cap tread preferably contains a vulcanization accelerator. In the rubber composition for cap tread, the content of the vulcanization accelerator is not particularly limited and can be freely determined according to the desired vulcanization rate and crosslink density. However, based on 100 parts by mass of the rubber component, it is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and still more preferably 3.5 parts by mass or more. The upper limit is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, and still more preferably 6.0 parts by mass or less.

[0116] The type of the vulcanization accelerator is not particularly limited, and those commonly used can be used. Examples of the vulcanization accelerator include benzothiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyldisulfide, and N-cyclohexyl-2-benzothiazylsulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, N-t-butyl-2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine, and orthotolylbiguanidine. These may be used alone or in combination of two or more. Among them, sulfenamide-based, guanidine-based, and benzothiazole-based vulcanization accelerators are preferred.

[0117] In addition to the above components, the rubber composition for the cap tread may be appropriately blended with compounding agents generally used in the tire industry, such as materials such as mold release agents.

[0118] In this specification, various materials containing carbon atoms (such as rubber, oil, resin, vulcanization accelerator, anti-aging agent, surfactant, etc.) may be derived from carbon dioxide in the atmosphere. As a method for obtaining the above-mentioned formulation from carbon dioxide, carbon dioxide may be directly converted, or methane obtained through a methanation process of synthesizing methane from carbon dioxide may be converted.

[0119] The rubber composition for the cap tread is kneaded using a rubber kneading device such as an open roll or a Banbury mixer with the above components, and then a crosslinked rubber composition can be obtained by a method such as crosslinking.

[0120] As for the kneading conditions, in the base kneading step of kneading additives other than the crosslinking agent (vulcanizing agent) and the vulcanization accelerator, the kneading temperature is preferably 100 °C or higher, more preferably 120 °C or higher, and preferably 180 °C or lower, more preferably 170 °C or lower. In the finishing kneading step of kneading the vulcanizing agent and the vulcanization accelerator, the kneading temperature is preferably 80 °C or higher, and preferably 120 °C or lower, more preferably 110 °C or lower. Further, the composition kneaded with the vulcanizing agent and the vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. As the vulcanization temperature, it is preferably 140 °C or higher, more preferably 150 °C or higher, and preferably 190 °C or lower, more preferably 185 °C or lower.

[0121] The rubber composition for the cap tread is used for the cap tread of the tire member.

[0122] The above tire is manufactured by a usual method using the above rubber composition for the cap tread. That is, a composition blended with various additives as required is extruded into the shape of various tire members such as a cap tread at the unvulcanized stage, formed by a usual method on a tire molding machine, bonded together with other tire members to form an unvulcanized tire, and then heated and pressurized in a vulcanizer to manufacture the tire.

[0123] The above tire is not particularly limited, and examples thereof include pneumatic tires, solid tires, airless tires, etc. Among them, pneumatic tires are preferred.

[0124] The above tire is preferably used as a passenger car tire, a large passenger car tire, a large SUV tire, a truck / bus tire, a two-wheeler tire, a racing tire, a winter tire (a studless tire, a snow tire, a stud tire), an all-season tire, a run-flat tire, an aircraft tire, a mine tire, etc.

[0125] The above tire includes a cap tread made from the above rubber composition for the cap tread. The above tire has a ratio (SWELL / (Sc×T)) of the SWELL (%) of the cap tread (rubber composition for the cap tread after vulcanization) to the sulfur content Sc (parts by mass) per 100 parts by mass of the rubber component in the rubber composition for the cap tread × the thickness T (mm) of the cap tread (Sc×T) of 21 or more. SWELL / (Sc×T) is preferably 22 or more, more preferably 23 or more. The upper limit of SWELL / (Sc×T) is preferably 40 or less, more preferably 35 or less, and even more preferably 30 or less. When within the above range, the effect tends to be obtained more favorably.

[0126] When SWELL / (Sc×T) is adjusted to be a predetermined value or more, particularly 21 or more, the mechanism by which a more pronounced effect is obtained is not clear, but it is considered that the improvement in elongation due to a small sulfur content and the improvement in low fuel consumption due to the thin and lightweight cap tread act synergistically, improving the overall performance of low fuel consumption and abrasion resistance.

[0127] The SWELL of the cap tread (rubber composition for the cap tread after vulcanization) is preferably 250% or less, more preferably 235% or less, and even more preferably 228% or less. The lower limit of SWELL is preferably 200% or more, more preferably 210% or more, and even more preferably 215% or more. When within the above range, the effect tends to be obtained more favorably. Here, the smaller the value of SWELL, the higher the crosslink density. Note that SWELL is a value measured by the method described in the examples below.

[0128] The method for adjusting SWELL is not particularly limited. For example, it can be increased by methods such as reducing the amount of sulfur or vulcanization accelerator, increasing the amount of softening agent, reducing the amount of reinforcing agent, increasing the amount of plasticizer, increasing the iodine value of the plasticizer, etc., and can be decreased by methods such as increasing the amount of sulfur or vulcanization accelerator, reducing the amount of softening agent, increasing the amount of reinforcing agent, reducing the amount of plasticizer, reducing the iodine value of the plasticizer, etc.

[0129] In the above tire, the thickness T (mm) of the cap tread is less than 10.5 mm, preferably 10.0 mm or less, more preferably 9.7 mm or less, and still more preferably 9.5 mm or less. The lower limit of the thickness T of the cap tread is preferably 5.0 mm or more, more preferably 6.0 mm or more, and still more preferably 7.0 mm or more. Also, when within the above range, there is a tendency that the effect can be preferably obtained.

[0130] In this specification, the thickness T of the cap tread refers to the thickness of the cap tread on the tire equatorial plane in the tire radial cross-section, and in the tire radial cross-section, it is the straight-line distance from the tread surface (the surface of the cap tread) to the inner surface of the cap tread in the tire radial direction.

[0131] The thickness of the cap tread on the tire equatorial plane is a value measured along the tire equatorial plane from the outermost surface of the cap tread on the tire equatorial plane. When there is an energizing member or the like on the tire equatorial plane, it is a value measured along the tire equatorial plane from the straight line connecting the ends of the interface blocked by the energizing member. When there is a groove on the tire equatorial plane, it is the thickness measured at the center in the tire width direction of the land portion closest to the tire equatorial plane, and it is the thickness measured in the normal direction of the outer surface of the cap tread in the tire radial direction.

[0132] In the above tire, it is desirable that the ratio (Lc / T) of the content Lc (mass%) of styrene-butadiene rubber having a styrene content of 20 mass% or less in 100 mass% of the rubber component of the rubber composition for the cap tread to the thickness T (mm) of the cap tread is 8.0 or more. Lc / T is preferably 8.5 or more, more preferably 8.7 or more, and still more preferably 8.9 or more. Also, the upper limit of Lc / T is preferably 12.0 or less, more preferably 11.0 or less, and still more preferably 10.0 or less. When within the above range, there is a tendency that the effect can be obtained more favorably.

[0133] When Lc / T is adjusted to a predetermined value or more, particularly 8.5 or more, the mechanism by which more effects can be obtained is not clear. However, by including a sufficient amount of styrene-butadiene rubber with a low styrene content with respect to the thickness of the cap tread, the steric hindrance of the styrene unit is reduced and the crosslinking efficiency is increased, so that the energy loss can be further reduced. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0134] For the above tire, it is desirable that the ratio (Fc / T) of the content (parts by mass) of the filler Fc to 100 parts by mass of the rubber component of the rubber composition for the cap tread and the thickness T (mm) of the cap tread is 7.9 or more. Fc / T is preferably 9.0 or more, more preferably 9.5 or more, and still more preferably 10.0 or more. Also, the upper limit of Fc / T is preferably 15.0 or less, more preferably 14.0 or less, and still more preferably 13.0 or less. When within the above range, the effects tend to be obtained more favorably.

[0135] When Fc / T is adjusted to a predetermined value or more, particularly 9.0 or more, the mechanism by which more effects can be obtained is not clear. However, by blending a sufficient amount of the filler in a large amount with respect to the thickness of the cap tread, it is possible to increase the elongation and improve the wear resistance. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0136] In the above tire, the groove depth D (mm) of the circumferential groove formed in the tread is preferably 4.0 mm or more, more preferably 4.5 mm or more, still more preferably 5.0 mm or more, particularly preferably 5.5 mm or more, and is preferably 8.5 mm or less, more preferably 8.0 mm or less, still more preferably 7.5 mm or less. When within the above range, the effects tend to be obtained more favorably.

[0137] When the groove depth D of the circumferential groove formed in the tread is adjusted to a predetermined range, the mechanism by which more effects can be obtained is not clear. However, by adjusting the groove depth, the weight reduction and the maintenance of elongation are adjusted in a well-balanced manner, and as a result, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0138] In the above tire, it is desirable that the ratio (Lc / D) of the content Lc (mass%) of styrene-butadiene rubber having a styrene content of 20 mass% or less in 100 mass% of the rubber component to the groove depth D (mm) of the circumferential groove formed in the tread is 3.0 or more and 17.0 or less. Lc / D is preferably 8.0 or more, more preferably 9.0 or more, and still more preferably 10.0 or more. Also, the upper limit of Lc / D is preferably 15.0 or less, more preferably 14.0 or less, and still more preferably 13.0 or less. When within the above range, the effect tends to be obtained more favorably.

[0139] When Lc / D is adjusted to a predetermined range, the mechanism by which a more effective result is obtained is not clear. However, by adjusting the groove depth, weight reduction and elongation maintenance are balanced, and by containing a sufficient amount of styrene-butadiene rubber with a low styrene content, the steric hindrance of the styrene unit is reduced and the crosslinking efficiency is increased, so that the energy loss can be further reduced. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0140] In this specification, the groove depth D of the circumferential groove is measured along the normal line of the surface obtained by extending the surface forming the ground contact surface of the tread outermost surface, and means the distance from the surface obtained by extending the surface forming the ground contact surface to the deepest groove bottom, and refers to the maximum distance among the groove depths of the provided circumferential grooves.

[0141] In this specification, dimensions such as thickness are measured with the bead portion of the tire adjusted to the normal rim width. At the time of measurement, the tire is cut out in the tire radial direction, and both bead ends of the sample are fixed in a state where they are adjusted to the width of the normal rim.

[0142] In this specification, unless otherwise specified, the dimensions of each part of the tire are the values measured in the normal state. The "normal state" refers to the state where the tire is mounted on a standard rim and filled with the standard internal pressure, and is in a no-load state. Here, the "standard rim" is the rim defined for each tire in the standard system including the standard on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Association), it is the standard rim in the applicable size described in the "JATMA YEAR BOOK"; in the case of ETRTO (The European Tyre and Rim Technical Organisation), it is the "Measuring Rim" described in the "STANDARDS MANUAL"; in the case of TRA (The Tire and Rim Association, Inc.), it is the "Design Rim" described in the "YEAR BOOK". Refer to JATMA, ETRTO, and TRA in this order, and follow the relevant standard if there is an applicable size during the reference. In the case of a tire not defined in the standard, it refers to the rim with the smallest rim diameter and then the narrowest rim width among the rims that can be mounted with the tire and can hold the internal pressure, that is, the rim that does not cause air leakage between the rim / tire. Also, the "standard internal pressure" refers to 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 ETRTO, it is the "INFLATION PRESSURE"; in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". Refer to JATMA, ETRTO, and TRA in this order, and follow the relevant standard if there is an applicable size during the reference. In the case of a tire not defined in the standard, it refers to the standard internal pressure (however, 250 KPa or more) of another tire size (defined in the standard) with the above-mentioned standard rim described as the standard rim. In the case where multiple standard internal pressures of 250 KPa or more are described, it refers to the minimum value among them.

[0143] Hereinafter, an example of the above tire will be described with reference to the drawings, but it is not limited to such a form.

[0144] In FIG. 1, the vertical direction is the radial direction of the tire 2, the left - right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. The tire 2 is symmetric about the left - right axis. The tread 4 includes a cap layer 30 (cap tread) and a base layer 28 (base tread).

[0145] Note that in FIG. 1, an example of a two - layer structure tread 4 composed of a cap layer 30 and a base layer 28 is shown, but a single - layer structure tread or a tread having a structure of three or more layers may also be used.

[0146] In the tire 2 of FIG. 1, the cap layer 30 is made of the above rubber composition. The cap layer 30 contains a rubber component and sulfur. The content Lc of styrene - butadiene rubber with a styrene content of 20% by mass or less in 100% by mass of the rubber component is 5% by mass or more and 100% by mass or less. The content Sc of sulfur with respect to 100 parts by mass of the rubber component is 0.5 part by mass or more and 1.5 parts by mass or less, and the thickness T of the cap layer 30 is less than 9.0 mm. Also, the ratio (SWELL / (Sc×T)) of the SWELL (%) of the cap layer 30 to the product of the content Sc of sulfur with respect to 100 parts by mass of the rubber component in the cap layer 30 and the thickness T of the cap tread is 21 or more.

[0147] In the tire 2, each sidewall 6 extends substantially radially inward from the end of the tread 4. The outer radial portion of this sidewall 6 is joined to the tread 4. The inner radial portion of this sidewall 6 is joined to the clinch 10. This sidewall 6 can prevent damage to the carcass 14.

[0148] Each wing 8 in FIG. 1 is located between the tread 4 and the sidewall 6. The wing 8 is joined to each of the tread 4 and the sidewall 6.

[0149] Each clinch 10 is located substantially radially inside the sidewall 6 and has a portion in contact with the rim at at least one location.

[0150] The carcass 14 is provided with a carcass ply 36. In this tire 2, the carcass 14 consists of a single carcass ply 36, but it may be composed of two or more plies.

[0151] In this tire 2, the carcass ply 36 is spanned between the bead cores 32 on both sides and runs along the tread 4 and the sidewall 6. The carcass ply 36 is folded back from the axial inner side to the outer side around each bead core 32. Due to this folding, a main part 36a and a pair of folded parts 36b are formed on the carcass ply 36. That is, the carcass ply 36 is provided with a main part 36a and a pair of folded parts 36b.

[0152] Each bead core 32 is provided with a bead apex 34 that extends radially outward from this bead core 32. The bead core 32 is ring-shaped and preferably includes a wound non-stretchable wire. The bead apex 34 tapers radially outward.

[0153] Although not shown, the carcass ply 36 preferably consists of a number of parallel cords and topping rubber. The absolute value of the angle formed by each cord with respect to the equatorial plane CL is preferably from 75° to 90°. In other words, this carcass 14 preferably has a radial structure.

[0154] The belt layer 16 in FIG. 1 is located radially inside the tread 4. The belt layer 16 is laminated with the carcass 14. The belt layer 16 reinforces the carcass 14. In the tire 2 of FIG. 1, the belt layer 16 consists of an inner layer 38 and an outer layer 40. As is clear from FIG. 1, in the axial direction, it is desirable that the width of the inner layer 38 is slightly larger than the width of the outer layer 40. In this tire 2, the axial width of the belt layer 16 is preferably not less than 0.6 times and not more than 0.9 times the cross-sectional width of the tire 2.

[0155] Each of the inner layer 38 and the outer layer 40 preferably consists of a large number of parallel single-wire steel cords (steel monofilaments) and topping rubber (coating rubber). In other words, the belt layer 16 includes a large number of parallel steel monofilaments.

[0156] The band 18 in FIG. 1 is located radially outside the belt layer 16. In the axial direction, the band 18 has a width equal to the width of the belt layer 16. This band 18 may have a width larger than the width of this belt layer 16.

[0157] Although not shown, the band 18 preferably consists of a cord and topping rubber. The cord is wound in a spiral. This band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is preferably 5° or less, more preferably 2° or less. Since the belt layer 16 is restrained by this cord, lifting of the belt layer 16 is suppressed.

[0158] The belt layer 16 and the band 18 in FIG. 1 constitute a reinforcing layer. The reinforcing layer may be constituted only by the belt layer 16.

[0159] FIG. 2 is an enlarged view near the tread 4 in FIG. 1. The tire in FIG. 2 is a tire 2 having a groove 26 on the tire equatorial plane (CL). In this case, the thickness (T) of the cap tread is the thickness measured at the center in the tire width direction of the land portion closest to the groove 26 on the tire equatorial plane in the radial cross section of the tire, and is the thickness measured in the normal direction of the surface of the cap layer 30 (cap tread). Specifically, it refers to the linear distance in the normal direction from the outer surface of the cap layer 30 in the tire radial direction to the interface on the outermost surface side of the tire of the base layer 28.

[0160] The inner liner 20 is located inside the carcass 14. The inner liner 20 is joined to the inner surface of the carcass 14. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 retains the internal pressure of the tire 2.

[0161] Each chafer 22 is located near the bead 12. In this embodiment, it is desirable that the chafer 22 consists of cloth and rubber impregnated in this cloth. This chafer 22 may be integrated with the clinch 10.

[0162] In this tire 2, the tread 4 has main grooves 42 as grooves 26. As shown in FIG. 1, a plurality, specifically three main grooves 42 are engraved in this tread 4. These main grooves 42 are arranged at intervals in the axial direction. By engraving three main grooves 42 in this tread 4, four ribs 44 extending in the circumferential direction are formed. That is, the main groove 42 is between the ribs 44.

[0163] Each main groove 42 extends in the circumferential direction. The main groove 42 is continuous without interruption in the circumferential direction. The main groove 42 promotes the drainage of water existing between the road surface and the tire 2, for example, in rainy weather. For this reason, even when the road surface is wet, the tire 2 can come into sufficient contact with the road surface. D in FIG. 2 indicates the groove depth of the circumferential main groove 42 formed in the tread 4.

[0164] In the tire 2, regarding the sulfur content Sc (parts by mass) relative to 100 parts by mass of the rubber component of the cap layer 30, the styrene content in the rubber component of the cap layer 30 is 20% by mass or less, the content Lc (%) of styrene-butadiene rubber, the content Fc (parts by mass) of the filler relative to 100 parts by mass of the rubber component of the cap layer 30, the thickness T (mm) of the cap layer 30, and the groove depth D of the circumferential groove formed in the tread, it is desirable that Lc / T, Fc / T, Lc / D, T, and D are within the aforementioned ranges.

Example

[0165] Hereinafter, examples (Examples) considered preferable in implementation are shown, but the scope of the present disclosure is not limited to the examples.

[0166] Hereinafter, various chemicals used in the manufacture of tires will be collectively described. The chemicals are purified according to established methods as necessary. SBR1: Modified SBR (Manufacturing Example 1 below, styrene content: 35% by mass, vinyl content: 50% by mass, Mw: 700,000) SBR2: Modified SBR (Manufacturing Example 2 below, styrene content: 10% by mass, vinyl content: 40% by mass, Mw: 700,000) SBR3: Modified SBR (Manufacturing Example 3 below, styrene content: 20% by mass, vinyl content: 20% by mass, Mw: 700,000) BR: BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass) Silica: ULTRASIL VN3 manufactured by Degussa (N2SA: 175m 2 / g) Carbon black: N220 manufactured by Mitsubishi Chemical Corporation (N2SA: 114m 2 / g, DBP: 100 ml / 100 g) Silane coupling agent: NXT manufactured by Momentive (3-octanoylthio-1-propyltriethoxysilane) Resin: Sylvatraxx 4401 manufactured by Arizona Chemical (copolymer of α-methylstyrene and styrene, softening point: 85°C) Oil: NC300 manufactured by Japan Energy Corporation Zinc oxide: Ginrei R manufactured by Toho Zinc Co., Ltd. Antioxidant: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd. (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) Wax: Sannox Wax manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. Stearic acid: "Kir" stearic acid manufactured by NOF Corporation Sulfur: Powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Organic peroxide 1: Parkmill D (dicumyl peroxide manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) Organic peroxide 2: Peroyl TCP (bis(4-tert-butylcyclohexyl) peroxydicarbonate manufactured by NOF Corporation) Vulcanization accelerator CZ: Nocceler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator DPG: Nocceler D (N,N'-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator TBzTD: Sanseler TBzTD (tetrabenzylthiuram disulfide) manufactured by Sanshin Chemical Industry Co., Ltd.

[0167] (Production Example 1) Hexane, 1,3-butadiene, styrene, tetrahydrofuran, and ethylene glycol diethyl ether are charged into a nitrogen-substituted autoclave reactor. Next, bis(diethylamino)methylvinylsilane and n-butyllithium are charged as cyclohexane solution and n-hexane solution, respectively, to initiate polymerization. The stirring speed is set at 130 rpm and the temperature inside the reactor is set at 65°C. While continuously supplying the monomers into the reactor, copolymerization of 1,3-butadiene and styrene is carried out for 3 hours. Next, the obtained polymer solution is stirred at a stirring speed of 130 rpm, N-(3-dimethylaminopropyl)acrylamide is added, and the reaction is carried out for 15 minutes. After the polymerization reaction is completed, 2,6-di-tert-butyl-p-cresol is added. Then, the solvent is removed by steam stripping and dried with a hot roll adjusted to 110°C to obtain modified styrene-butadiene rubber (SBR1).

[0168] (Production Example 2) Charge a nitrogen-substituted autoclave reactor with cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene. Adjust the temperature of the reactor contents to 20 °C, and then add n-butyllithium to initiate polymerization. Polymerize under adiabatic conditions, and the maximum temperature reaches 85 °C. When the polymerization conversion rate reaches 99%, add butadiene, polymerize for an additional 5 minutes, and then add 3-dimethylaminopropyltrimethoxysilane as a modifier and react for 15 minutes. After the polymerization reaction is completed, add 2,6-di-tert-butyl-p-cresol. Then, perform solvent removal by steam stripping and dry with a hot roll adjusted to 110 °C to obtain modified styrene-butadiene rubber (SBR2).

[0169] (Production Example 3) Charge a nitrogen-substituted autoclave reactor with cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene. Adjust the temperature of the reactor contents, add n-butyllithium to initiate polymerization. Polymerize under adiabatic conditions, and when the polymerization conversion rate reaches 99%, add 1,3-butadiene, polymerize further, add N-(3-dimethylaminopropyl)acrylamide as a modifier and react. After the polymerization reaction is completed, add 2,6-di-tert-butyl-p-cresol. Then, perform solvent removal by steam stripping and dry with a hot roll to obtain modified styrene-butadiene rubber (SBR3).

[0170] <Preparation of Test Tires> According to the compounding contents shown in each table, use a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd. to knead the materials other than sulfur and vulcanization accelerators at 150 °C for 5 minutes to obtain a kneaded product. Add sulfur and vulcanization accelerators to the kneaded product, and knead using an open roll at 80 °C for 5 minutes to obtain an unvulcanized rubber composition. Mold the unvulcanized rubber composition for the cap tread into the shape of the cap tread, laminate it together with other tire members on a tire molding machine to form an unvulcanized tire, and vulcanize at 170 °C for 10 minutes to manufacture a test tire (size 205 / 70R15, passenger car tire).

[0171] Assuming test tires obtained from compositions with formulations and specifications changed according to each table, the results calculated based on the following evaluation method are shown in each table. The reference comparative examples are as follows. Table 1: For wear resistance, Comparative Example 7; for low fuel consumption, Comparative Example 8

[0172] <swell> Prepare each measurement sample (1×1 cm, thickness 2 mm) from the cap tread of the test tire. Immerse the sample in toluene at 25°C for 24 hours, and measure the volume change (SWELL (%)) before and after immersion. Based on SWELL, it is possible to evaluate the crosslink density of the entire measurement sample. The smaller the value, the higher the crosslink density.

[0173] <Low fuel consumption> Using a rolling resistance tester, measure the rolling resistance when the test tire is running at an internal pressure (230 kPa) and a speed (80 km / h), and display it as an index with the reference comparative example set to 100. The larger the numerical value, the better the low fuel consumption performance.

[0174] <Wear resistance> Mount the test tire on a vehicle and measure the groove depth of the tread after a driving distance of 8000 km. Then, calculate the driving distance when the groove depth decreases by 1 mm, and display it as an index according to the following formula. The larger the numerical value, the better the wear resistance. (Wear resistance index) = (Driving distance when the groove depth of each formulation decreases by 1 mm) / (Driving distance when the groove depth of the reference comparative example decreases by 1 mm) × 100

[0175]

Table 1

[0176] The present invention (1) is a tire provided with a cap tread containing a rubber component and sulfur, wherein the content Lc of styrene-butadiene rubber in the rubber component with a styrene content of 20% by mass or less in 100% by mass of the rubber component is 5% by mass or more and 100% by mass or less, and the content Sc of sulfur with respect to 100 parts by mass of the rubber component is 0.5 part by mass or more and 1.5 parts by mass, the thickness T of the cap tread is less than 10.5 mm, A tire in which the ratio (SWELL / (Sc×T)), where SWELL(%) of the cap tread and Sc (parts by mass) is the content of sulfur with respect to 100 parts by mass of the rubber component and T (mm) is the thickness of the cap tread, is 21 or more.

[0177] The present invention (2) is the tire according to the present invention (1), wherein the cap tread contains an organic peroxide.

[0178] The present invention (3) is the tire according to the present invention (1) or (2), wherein the content Fc of the filler with respect to 100 parts by mass of the rubber component in the cap tread is 90 parts by mass or more.

[0179] The present invention (4) is a tire in any combination with any one of the present inventions (1) to (3), wherein the content of silica with respect to 100 parts by mass of the rubber component in the cap tread is 80 parts by mass or more.

[0180] The present invention (5) is a tire in any combination with any one of the present inventions (1) to (4), wherein the content of the plasticizer with respect to 100 parts by mass of the rubber component in the cap tread is 35 parts by mass or more.

[0181] The present invention (6) is a tire in any combination with any one of the present inventions (1) to (5), wherein the ratio (Lc / T), where Lc(%) is the content of styrene-butadiene rubber with a styrene content of 20% by mass or less in 100% by mass of the rubber component and T (mm) is the thickness of the cap tread, is 8.5 or more.

[0182] The present invention (7) is a tire in any combination with any one of the present inventions (1) to (6), wherein the ratio (Fc / T), where Fc is the content (parts by mass) of the filler with respect to 100 parts by mass of the rubber component and T (mm) is the thickness of the cap tread, is 9.0 or more.

[0183] The present invention (8) is a tire in any combination with any one of the present inventions (1) to (7), wherein the groove depth D of the circumferential groove formed in the tread is 4.0 mm or more and 8.5 mm or less.

[0184] The tire of the present invention (9) is a tire in any combination with any one of the present inventions (1) to (8) in which the ratio (Lc / D) of the content Lc (mass%) of styrene-butadiene rubber having a styrene content of 20 mass% or less in 100 mass% of the rubber component to the groove depth D (mm) of the circumferential groove formed in the tread is 3.0 or more and 17.0 or less.

Explanation of Signs

[0185] 2 Tire 4 Tread 6 Sidewall 8 Wing 10 Clinch 12 Bead 14 Carcass 16 Belt layer 18 Band 20 Inner liner 22 Chafer 24 Tread surface 26 Groove 28 Base layer 30 Cap layer 32 Bead core 34 Bead apex 36 Carcass ply 36a Main part 36b Folded-back part 38 Inner layer 40 Outer layer 42 Main groove 44 Rib CL Equatorial plane of the tire T Thickness of the cap tread D Main groove depth of the circumferential main groove formed in the tread< / swell>

Claims

1. A tire having a cap tread containing a rubber component and sulfur, wherein the cap tread has a content Lc of styrene-butadiene rubber with a styrene content of 20% by mass or less in 100% by mass of the rubber component of 5% by mass or more and 100% by mass or less, and a content Sc of sulfur of 0.5 part by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the rubber component, wherein the thickness T of the cap tread is less than 10.5 mm, and a ratio (SWELL / (Sc×T)) of the SWELL (%) of the cap tread to the content Sc (parts by mass) of sulfur with respect to 100 parts by mass of the rubber component × the thickness T (mm) of the cap tread is 21 or more.

2. The tire according to claim 1, wherein the cap tread contains an organic peroxide.

3. The tire according to claim 1, wherein the cap tread has a filler content Fc of 90 parts by mass or more with respect to 100 parts by mass of the rubber component.

4. The tire according to claim 1, wherein the cap tread has a silica content of 80 parts by mass or more with respect to 100 parts by mass of the rubber component.

5. The tire according to claim 1, wherein the cap tread has a plasticizer content of 35 parts by mass or more with respect to 100 parts by mass of the rubber component.

6. The tire according to claim 1, wherein a ratio (Lc / T) of the content Lc (mass%) of styrene-butadiene rubber with a styrene content of 20% by mass or less in 100% by mass of the rubber component to the thickness T (mm) of the cap tread is 8.5 or more.

7. The tire according to claim 1, wherein a ratio (Fc / T) of the content (parts by mass) of the filler Fc with respect to 100 parts by mass of the rubber component to the thickness T (mm) of the cap tread is 9.0 or more.

8. The tire according to claim 1, wherein the groove depth D of the circumferential groove formed in the tread is 4.0 mm or more and 8.5 mm or less. **Claim 9** The ratio (Lc / D) of the content Lc (mass%) of styrene-butadiene rubber having a styrene content of 20 mass% or less in 100 mass% of the rubber component to the groove depth D (mm) of the circumferential groove formed in the tread is 3.0 or more and 17.0 or less. The tire according to claim 1.

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