Tire

Abstract

The present invention improves wet grip performance after high-speed driving. A tire having a tread portion is provided. The crown rubber layer forming the tread portion is formed of a rubber composition in which 60 to 80 parts by mass of the 100 parts by mass of the rubber component are composed of a styrene-butadiene rubber (SBR) having a styrene content of 25 mass% or less. The rubber composition contains 100 parts by mass or more of silica per 100 parts by mass of the rubber component. The rubber composition has a loss tangent (30 DEG C tan [delta]) of less than 0.27 when measured in a tensile deformation mode at a temperature of 30 DEG C, a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain rate of 1%. The thickness of the tread portion is 13 mm or less.

Description

Technical Field

[0001] The present invention relates to tires. Background Art

[0002] From the viewpoint of safety, tires are required to have high braking performance (grip performance), and various techniques for improving grip performance have been proposed (e.g., Patent Documents 1 to 3).

[0003] [Prior art literature]

[0004] [Patent Document]

[0005] [Patent Document 1] JP 2011-93386A

[0006] [Patent Document 2] JP 2013-79017A

[0007] [Patent Document 3] JP 2016-37100A Summary of the invention

[0008] [Problems to be solved by the invention]

[0009] However, with the construction of new expressways in recent years, people often travel long distances on these roads. After driving at high speeds, the heat generated by contact with the road surface may cause the rubber in the tire to deteriorate and may easily lead to a decrease in wet grip performance.

[0010] Therefore, an object of the present invention is to improve the wet grip performance after high-speed running.

[0011] [Methods used to solve the problem]

[0012] The present invention is a tire having a tread portion, wherein:

[0013] a cap rubber layer forming the tread portion containing 60 parts by mass or more and 80 parts by mass or less of styrene-butadiene rubber (SBR) having a styrene content of 25% by mass or less per 100 parts by mass of the rubber component, and containing 100 parts by mass or more of silica relative to 100 parts by mass of the rubber component; and

[0014] The crown rubber layer is formed of a rubber composition having a loss tangent (30°C tanδ) less than 0.27 measured in a tensile deformation mode under the conditions of a temperature of 30°C, a frequency of 10 Hz, an initial strain of 5% and a dynamic strain rate of 1%; and

[0015] The thickness of the tread portion is 13 mm or less.

[0016] [Effects of the Invention]

[0017] According to the present invention, wet grip performance after high-speed running can be improved. DETAILED DESCRIPTION

[0018] [1] Features of the tire of the present invention

[0019] First, the features of the tire of the present invention will be described.

[0020] 1. Overview

[0021] The tire of the present invention includes the following components: a carcass that is mounted between one and the other of a pair of bead portions that fit with a rim and forms a skeleton of the tire; a fiber material (such as a belt layer and a belt reinforcement layer); and a tread portion that is radially disposed outwardly on these components. The tread portion includes a crown rubber layer that is radially disposed outwardly on the tire and forms a ground contact surface, and a base rubber layer that is radially disposed inwardly on the crown rubber layer as necessary.

[0022] A cap rubber layer forming a tread portion is formed from a rubber composition comprising 60 parts by mass or more and 80 parts by mass or less of styrene-butadiene rubber (SBR) having a styrene content of 25% by mass or less per 100 parts by mass of a rubber component, and comprising 100 parts by mass or more of silica relative to 100 parts by mass of the rubber component.

[0023] The rubber composition has a loss tangent (30°C tanδ) measured in a tensile deformation mode under the conditions of a temperature of 30°C, a frequency of 10 Hz, an initial strain of 5% and a dynamic strain rate of 1% and is less than 0.27.

[0024] The thickness of the tread portion is 13 mm or less.

[0025] The cap rubber layer described herein is not limited to the rubber layer forming the outermost layer of the tread portion, and when there are two or more layers within 5 mm inward from the tread surface, at least one of these layers must satisfy the above-mentioned requirements for the rubber composition.

[0026] As will be described below, these features enable improved wet grip performance after high-speed running.

[0027] 2. Mechanism of the Effect of the Tire of the Present Invention

[0028] It is believed that the mechanism by which the above-mentioned effects are exhibited in the tire of the present invention is as follows.

[0029] As described above, the cap rubber layer of the tire of the present invention is formed of a rubber composition containing 60 parts by mass or more and 80 parts by mass or less of SBR having a styrene content of 25% by mass or less per 100 parts by mass of the rubber component.

[0030] By including 60 parts by mass or more and 80 parts by mass or less of SBR having a small amount of styrene (specifically, 25% by mass or less) in 100 parts by mass of the rubber component, minute styrene domains can be formed in the rubber matrix. It is believed that these minute styrene domains can be easily formed by setting the SBR content in 100 parts by mass of the rubber component to 60 parts by mass or more and 80 parts by mass or less and reducing the content of the diene rubber component other than SBR to less than half.

[0031] By forming these minute styrene areas, even when the tread portion contacts the road surface during high-speed running, heat generation can be sufficiently suppressed, thereby suppressing thermal degradation of the tread portion. It is therefore believed that sufficient wet grip performance can be maintained without losing road compliance even after high-speed running.

[0032] In the present invention, the tire contains 100 parts by mass or more of silica relative to 100 parts by mass of the rubber component, which is the same as or exceeds the content of the rubber component. It is believed that the inclusion of such a large amount of silica strengthens the reinforcing properties of the rubber by silica, and can sufficiently suppress the influence of heat (thermal degradation) during high-speed running.

[0033] In the present invention, the rubber composition forming the cap rubber layer has a loss tangent (30°C tanδ) less than 0.27 measured in a tensile deformation mode under the conditions of temperature 30°C, frequency 10 Hz, initial strain 5% and dynamic strain rate 1%.

[0034] The loss tangent tanδ is a viscoelastic parameter indicating energy absorption performance, that is, the performance of absorbing energy from the road surface and converting it into heat. The larger the value, the more energy can be absorbed and converted into heat. Therefore, if the loss tangent tanδ is large, the tread portion heats up, the rubber deteriorates, and the wet grip performance is likely to decrease.

[0035] Therefore, in the present invention, as described above, 30° C. tan δ is set to be less than 0.27, which is considered to suppress excessive heat generation in the tread portion and suppress deterioration of wet grip performance.

[0036] Furthermore, in the present invention, the thickness of the tread portion is set to 13 mm or less to reduce the volume of the tread portion, which is considered to suppress heat generation in the tread portion and suppress heat accumulation (heat storage), thereby sufficiently suppressing deterioration of wet grip performance.

[0037] As described above, in the tire of the present invention, the tire contains an appropriate amount of SBR with a small amount of styrene to form a microscopic styrene region, and contains silica in an amount equal to or greater than the rubber component to ensure reinforcement of the rubber, thereby suppressing thermal degradation of the tread during high-speed running. In addition, by appropriately controlling 30°C tanδ and the thickness of the tread, heat generation and heat storage in the tread are suppressed.

[0038] It is believed that these effects work together to enable the tire of the present invention to have improved wet grip performance after high speed running.

[0039] In the present invention, the styrene content is preferably 20% by mass or less, more preferably 15% by mass or less, and the lower limit is preferably 3% by mass or more, more preferably 5% by mass or more, and further preferably 8% by mass or more.

[0040] The phrase "80 parts by mass or more of SBR having a styrene content of 25% by mass or less is contained in 100 parts by mass of the rubber component" means that the amount of SBR per 100 parts by mass of the rubber component is 80 parts by mass or more and the amount of styrene in the entire SBR is 25% by mass or less.

[0041] In other words, when the rubber component contains only one styrene-containing polymer (SBR), this indicates that the styrene amount is 25% by mass or less; when the rubber component contains multiple styrene-containing polymers (SBR), this indicates that the styrene amount calculated by the sum of the products of the styrene amount (mass %) in each polymer and the mixing amount (mass parts) of the polymer in every 100 parts by mass of the rubber component is 25% by mass or less.

[0042] More specifically, when SBR1 (X1 parts by mass) having a styrene amount of S1% by mass and SBR2 (X2 parts by mass) having a styrene amount of S2% by mass are contained per 100 parts by mass of the rubber component, the amount of styrene calculated by the formula {(S1×X1)+(S2×X2)} / (X1+X2) is 25% by mass or less.

[0043] Furthermore, in the vulcanized rubber composition, the amount of styrene can also be calculated by measuring the amount of styrene contained in the rubber composition after acetone extraction using solid-state nuclear magnetic resonance (solid-state NMR) or Fourier transform infrared spectrometer (FTIR).

[0044] In this invention, the content of silica is more preferably 110 parts by mass or more, and even more preferably 120 parts by mass or more relative to 100 parts by mass of the rubber component. In view of the kneading processability of the rubber composition, the upper limit is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, and further preferably 130 parts by mass or less.

[0045] In the present invention, tanδ at 30°C is more preferably 0.25 or less, further preferably 0.23 or less, further preferably 0.22 or less, and particularly preferably 0.21 or less. The lower limit is not particularly limited, but is preferably 0.15 or more, more preferably 0.17 or more, further preferably 0.19 or more, and further preferably 0.20 or more.

[0046] Here, the “loss tangent (tan δ)” can be measured using a viscoelasticity measuring device (for example, “Eplexor (registered trademark)” manufactured by GABO Corporation).

[0047] The above 30°C tanδ can be appropriately adjusted by changing the mixing amount of each mixed material described later. Specifically, 30°C tanδ can be increased by increasing the SBR content in the rubber component, increasing the styrene content in the SBR component, increasing the amount of fillers (such as silica and carbon black), increasing the content of the resin component, etc. On the contrary, 30°C tanδ can be reduced by reducing the SBR content in the rubber component, reducing the styrene content in the SBR component, reducing the amount of fillers (such as silica and carbon black), reducing the content of the resin component, etc.

[0048] Furthermore, in the present invention, the thickness of the tread portion is more preferably 12 mm or less, further preferably 10 mm or less, and further preferably 7 mm or less. The lower limit is preferably 5 mm or more, and more preferably 6 mm or more.

[0049] In the present invention, the tread portion refers to a region forming a contact surface of the tire, and is a radially outward portion of components including a fiber material such as a carcass, a belt layer, and a belt reinforcing layer.

[0050] The thickness of the tread portion refers to the thickness of the tread portion on the tire equatorial plane in the tire radial cross section, and when the tread portion is formed of a single rubber composition, it refers to the thickness of the rubber composition; and when the tread portion is formed of a laminated structure of multiple rubber compositions as described later, it refers to the total thickness of these layers. When the tire has grooves on the equatorial plane, it refers to the thickness from the intersection of the straight line connecting the outermost end points of the grooves in the tire radial direction and the tire equatorial plane to the interface of the innermost part of the tread portion in the tire radial direction.

[0051] The thickness of the tread portion can be measured by taking a cross section in the tire radial direction and aligning the bead portion with the standardized rim width.

[0052] In the above description, the "standardized rim" is a rim specified 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 a standard rim of applicable size described in the "JATMA YEAR BOOK"; in the case of ETRTO (The European Tire and Rim Technical Organization), it is a "Measuring Rim" described in the "STANDARDS MANUAL"; in the case of TRA (The Tire and Rim Association, Inc.), it is a "Design Rim" described in the "YEAR BOOK". JATMA, ETRTO, and TRA are referred to in sequence, and if there is an applicable size when referring, the standard is followed. In the case of tires not specified in the standard, it refers to a rim that can be assembled and maintain internal pressure (i.e., a rim that does not cause air leakage from between the rim and the tire) and has the smallest rim diameter and the narrowest rim width.

[0053] [2] More preferred embodiments of the tire of the present invention

[0054] The tire of the present invention can achieve better effects by adopting the following aspects.

[0055] 1. Loss tangent of crown rubber layer (tanδ)

[0056] As described above, in the present invention, tan δ at 30° C. is set to be less than 0.27.

[0057] Generally, the greater the tanδ on the low temperature side of the crown rubber layer (e.g., tanδ at 0°C (0°C tanδ)), the better the wet grip performance. However, when the 0°C tanδ is increased by adjusting the formulation of the rubber composition, the tanδ on the high temperature side is generally inevitably increased. Also, when the 30°C tanδ is 0.27 or more, it is difficult to suppress excessive heat generation in the tread portion, and the deterioration of the wet grip performance cannot be sufficiently suppressed.

[0058] On the other hand, since tanδ is also an indicator of the degree of phase difference between the input and response of the rubber, if tanδ is large, the time required for the friction generated on the rubber surface to be transmitted to the inside of the tire and the reaction force to be transmitted to the road surface will be longer, which may lead to a decrease in wet grip performance. In addition, if the difference between 0℃ tanδ and 30℃ tanδ becomes large, there is a concern that the energy loss between 0℃ and 30℃ will increase, which may worsen the heat generation during driving.

[0059] Based on the above considerations, it is believed that the preferred relationship between 30°C tan δ and 0°C tan δ is such that 30°C tan δ can be maintained less than 0.27 while 0°C tan δ is as large as possible.

[0060] Specifically, if the relationship of (0°C tan δ≦-7×30°C tan δ+2.5) is satisfied, it is believed that sufficient wet grip performance can be maintained even after high-speed running. It is more preferred to satisfy the relationship of (0°C tan δ≦-7×30°C tan δ+2.3), and it is further preferred to satisfy the relationship of (0°C tan δ≦-7×30°C tan δ+2.1).

[0061] In addition, 0°C tanδ can be adjusted by various compounding materials in the same manner as the above 30°C tanδ. The above relationship between 0°C tanδ and 30°C tanδ can be more easily satisfied by reducing the SBR content, reducing the styrene content in the SBR component, reducing the content of the resin component, etc.

[0062] 2. Multi-layer tread

[0063] In the present invention, the tread portion may be formed of only one crown rubber layer disposed on the outer side in the tire radial direction, or may be formed of two layers by disposing the base rubber layer on the inner side of the crown rubber layer in the tire radial direction, or may be formed of three layers, four layers or more layers. In this case, the thickness of the crown rubber layer in the entire tread portion is preferably 10% or more. Even after high-speed driving, sufficient friction can be generated between the tread portion surface and the road surface and the friction force can be fully transmitted to the inside of the tire, thereby further improving the wet grip performance. More preferably, the thickness is 70% or more.

[0064] As described above, in the case of a laminated structure of multiple rubber compositions, the "thickness of the tread portion" refers to the total thickness of the laminated layers. In the case of a tire having grooves on the equatorial plane of the tire, the "thickness of the tread portion" refers to the thickness from the intersection of the straight line connecting the outermost end points of the grooves in the tire radial direction and the equatorial plane of the tire to the innermost interface of the tread portion in the tire radial direction.

[0065] The “thickness of the crown rubber layer” refers to the thickness of the crown rubber layer on the tire equatorial plane in the tire radial cross section, and when the tire has grooves on the equatorial plane, it refers to the thickness from the intersection of the straight line connecting the outermost end points of the grooves in the tire radial direction and the tire equatorial plane to the interface with the base rubber layer at the innermost part of the tread in the tire radial direction. The “thickness of the base rubber layer” refers to the thickness from the interface with the crown rubber layer to the innermost part of the tread in the tire radial direction.

[0066] As described above, the thickness of the crown rubber layer and the thickness of the base rubber layer can be calculated by measuring the thickness of the crown rubber layer and the thickness of the base rubber layer in the thickness of the tread portion. When there are grooves on the equatorial plane of the tire, the thickness of the crown rubber layer and the thickness of the base rubber layer can be calculated at the center of the land portion of the tread portion closest to the equatorial plane, thereby calculating the thickness of the crown rubber layer and the thickness of the base rubber layer.

[0067] In the case of a multi-layer tread portion, it is preferred that the 30°C tanδ (30°C tanδB) of the base rubber layer is less than the 30°C tanδ (30°C tanδC) of the cap rubber layer, that is, (30°C tanδB / 30°C tanδC) <1. This reduces the phase difference until the response inside the tire matches the wet grip performance produced by the cap rubber layer, increases the response speed, and it is believed that the wet grip performance is further improved. In addition, the specific (30°C tanδB / 30°C tanδC) is not particularly limited as long as it is less than 1, but the upper limit is preferably less than 0.40, more preferably less than 0.35, and the lower limit is, for example, preferably greater than 0.15, more preferably greater than 0.20.

[0068] 3. Particle size of silica contained in the crown rubber layer

[0069] In the present invention, from the viewpoint of improving the reinforcing property, the particle diameter (average primary particle diameter) of silica contained in the cap rubber layer is preferably 17 nm or less.

[0070] The average primary particle size can be calculated by directly observing silica particles extracted from a rubber composition cut out from a tire using a transmission electron microscope (TEM) or the like, calculating an equivalent cross-sectional diameter from the area of ​​each silica particle obtained, and calculating an average value.

[0071] 4. Resin component content in the crown rubber layer

[0072] In the present invention, the rubber composition forming the cap rubber layer preferably contains a resin component.

[0073] It is believed that by including the resin component in the rubber composition, the adhesion of the resin component ensures grip to the road surface even during high-speed running, thereby further improving the handling stability during high-speed running.

[0074] Preferred resin components include rosin resins, styrene resins, coumarone resins, terpene resins, C5 resins, C9 resins, C5C9 resins and acrylic resins, which will be described later, and among these resins, styrene resins (e.g., α-methylstyrene) are more preferred. The content per 100 parts by mass of the rubber component is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, further preferably 25 parts by mass or more, and further preferably 35 parts by mass or more. In consideration of the softening of the rubber, the upper limit is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and further preferably 40 parts by mass or less.

[0075] 5. Acetone extract of the tire crown rubber layer (AE)

[0076] In the present invention, from the viewpoint of exhibiting wet grip performance, the acetone extract (AE) of the cap rubber layer is preferably 18.7% by mass or more, more preferably 19% by mass or more, further preferably 20% by mass or more, further preferably 20.1% by mass or more, further preferably 20.8% by mass or more, further preferably 21% by mass or more, and further preferably 21.2% by mass or more. On the other hand, the upper limit is not particularly limited, but is preferably 24% by mass or less, more preferably 23% by mass or less, and further preferably 22% by mass or less.

[0077] The acetone extract (AE) can be regarded as an index showing the content of the softener and the like in the rubber composition, and can also be regarded as an index showing the flexibility of the rubber composition. Therefore, it is believed that by appropriately controlling the amount of AE in the cap rubber layer, the contact area between the tire and the road surface can be sufficiently ensured, and wet grip performance can be stably exhibited.

[0078] The acetone extract (AE) can be measured in accordance with JIS K 6229: 2015. Specifically, a vulcanized rubber specimen cut out from a measurement site is immersed in acetone for a certain period of time and the mass loss rate (%) of the specimen is measured, thereby obtaining AE (mass %).

[0079] More specifically, each vulcanized rubber specimen was immersed in acetone at room temperature and pressure for 72 hours to extract soluble components, the mass of each specimen before and after the extraction was measured, and the acetone extract (AE) could be calculated according to the following formula.

[0080] Acetone extract (%) = {(mass of rubber sample before extraction - mass of rubber sample after extraction) / (mass of rubber sample before extraction)} × 100

[0081] The acetone extract content can be appropriately changed by changing the compounding ratio of the plasticizer in the rubber composition.

[0082] 6. Landing rate

[0083] In the tire of the present invention, when mounted on a standardized rim and under a standardized internal pressure, the ground contact ratio of the tread portion of the tire is preferably 55% or more, more preferably 60% or more, further preferably 63% or more, and further preferably 65% ​​or more.

[0084] The "ground contact ratio" is the ratio of the actual contact area to the hypothetical contact area that fills all the grooves on the tread surface. A larger ground contact ratio means a larger contact area with the road surface, which results in sufficient and stable grip performance and excellent handling stability.

[0085] The upper limit of the ground contact rate is not particularly limited, but is preferably 85% or less, more preferably 80% or less, further preferably 75% or less, and further preferably 70% or less.

[0086] In addition, the product of the content (parts by mass) of styrene-butadiene rubber (SBR) having a styrene content of 25% by mass or less in 100 parts by mass of the rubber component of the crown rubber layer and the ground contact ratio (%) of the tread portion (SBR content x ground contact ratio) is preferably 7500 or less, more preferably 7200 or less, further preferably 7000 or less, further preferably 6900 or less, further preferably 6400 or less, further preferably 6000 or less, and further preferably 5900 or less. The lower limit is not particularly limited, but is preferably 3500 or more, more preferably 3700 or more, further preferably 3900 or more, further preferably 4000 or more, further preferably 4300 or more, further preferably 4550 or more, further preferably 4900 or more, and further preferably 5200 or more. Thus, the wear resistance during high-speed running is further improved due to the effect of the network of the styrene region acting together.

[0087] The ground contact ratio can be determined from the ground contact shape under standardized rim, standardized internal pressure and standardized load conditions.

[0088] Specifically, the tire is mounted on a standardized wheel hub, a standardized internal pressure is applied, and the tire is left at rest at 25°C for 24 hours. Then, the ink is applied to the tire tread surface, a standardized load is applied and pressed on a cardboard (camber angle is 0°), and the contact shape is transferred to the cardboard. The tire is rotated 72° in the circumferential direction, and the contact shape is transferred to 5 places. That is, 5 contact shapes are obtained. At this time, the 5 contact shapes are smoothly connected at the part interrupted by the groove in the outline of the contact shape, and the obtained shape is called a virtual contact surface.

[0089] The contact rate can be calculated as follows: (average area of ​​5 contact shapes (black parts) transferred to the cardboard / average area of ​​the virtual contact surface obtained from the 5 contact shapes)×100 (%).

[0090] "Standard internal pressure" refers to the air pressure specified for each tire in each standard of the standard system including the standards on which the above-mentioned tires are based. In the case of JATMA, it refers to the maximum air pressure; in the case of ETRTO, it refers to the "INFLATION PRESSURE" table; in the case of TRA, it refers to the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table. As in the case of "standardized rim", it refers to referring to JATMA, ETRTO and TRA in sequence and following these standards. In the case of a tire not specified in the standard, it refers to the standardized internal pressure (above 250 KPa) of another tire size (specified in the standard) that specifies the standardized rim as a standard rim. In the case where multiple standard internal pressures of 250 KPa or more are specified, it refers to the minimum value among them.

[0091] The "standardized load" is a load specified for each tire by each standard in the standard system including the standards on which the tire is based, and refers to the maximum mass that can be loaded on the tire. In the case of JATMA, it refers to the maximum load capacity, in the case of ETRTO, it refers to the "LOAD CAPACITY", and in the case of TRA, it refers to the maximum value described in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table. As in the case of the above-mentioned "standardized rim" and "standard internal pressure", refer to JATMA, ETRTO and TRA in sequence and follow their standards. In the case of a tire not specified by the standard, the standardized load W is calculated as follows L .

[0092] V = {(Dt / 2) 2 -(Dt / 2-Ht) 2}×π×Wt

[0093] W L＝ 0.000011×V+175

[0094] W L :Standardized load (kg)

[0095] V: Imaginary volume of the tire (mm 3 )

[0096] Dt: Tire outer diameter Dt (mm)

[0097] Ht: Tire section height (mm)

[0098] Wt: tire section width (mm)

[0099] 7. Flatness

[0100] The aspect ratio is the ratio of the section height to the section width of the tire, and the smaller the ratio, the smaller the proportion of the portion deformed in the tire width direction relative to the friction received by the tread portion, and the easier it is to transmit force, which is considered to improve wet grip performance. On the other hand, if the aspect ratio is small, the amount of bending of the side portion is small, which may lead to deterioration of ride comfort.

[0101] In consideration of these points, in the tire of the present invention, the specific aspect ratio is preferably 30% or more and 60% or less.

[0102] In addition, the product of the silica content (parts by mass) and the flatness (%) of the rubber component of the crown rubber layer relative to 100 parts by mass (silica content × flatness) is preferably 12,000 or less, more preferably 11,000 or less, further preferably 10,000 or less, further preferably 9,000 or less, further preferably 8,000 or less, further preferably 7,500 or less, further preferably 7,000 or less, and further preferably 6,600 or less. The lower limit is not particularly limited, but is preferably 1,000 or more, more preferably 3,000 or more, further preferably 3,500 or more, further preferably 4,000 or more, further preferably 4,500 or more, further preferably 5,000 or more, and further preferably 5,500 or more. Thus, the effect of the silica network works together, thereby further improving the wear resistance during high-speed running.

[0103] The aspect ratio (%) can be calculated by the following formula using the tire cross-sectional height Ht (mm), tire cross-sectional width Wt (mm), tire outer diameter Dt (mm) and rim radius R (mm) when the internal pressure is 250 kPa.

[0104] Flatness (%) = (Ht / Wt) × 100 (%)

[0105] Ht=(Dt-R) / 2

[0106] [3] Implementation Method

[0107] Hereinafter, the present invention will be described in detail according to embodiments.

[0108] 1. Rubber composition

[0109] In the tire of the present invention, the rubber composition forming the cap rubber layer can be obtained by appropriately adjusting the kinds and contents of various compounding materials (eg, rubber component, filler, plasticizer, vulcanizing agent and vulcanization accelerator described below).

[0110] (1) Mixed materials

[0111] (a) Rubber component

[0112] In the present invention, the rubber component contains styrene-butadiene rubber (SBR) from the perspective of containing styrene in the rubber component. Styrene polymers other than SBR (such as styrene-butadiene-styrene block copolymer (SBS) and styrene-butadiene block copolymer (SB)) may also be contained.

[0113] In addition, rubber (polymer) commonly used in the production of tires such as diene rubber (e.g., isoprene rubber, butadiene rubber (BR) and nitrile rubber (NBR)) and butyl rubber (e.g., butyl rubber) can be used in combination with the above-mentioned styrene polymers. For example, a combination of SBR and BR, or a combination of SBR, BR and isoprene rubber is preferred.

[0114] (i) SBR

[0115] The weight average molecular weight of SBR is, for example, greater than 100,000 and less than 2,000,000. In the present invention, as described above, the amount of styrene in the SBR component is less than 25% by mass. The vinyl content (1,2-bonded butadiene content) of SBR is, for example, greater than 5% by mass and less than 70% by mass. The vinyl content of SBR refers to the 1,2-bonded butadiene content relative to the total butadiene part in the SBR component. The structural identification of SBR (the determination of the amount of styrene and the vinyl content) can be carried out using, for example, the JNM-ECA series equipment manufactured by JEOL.

[0116] In the present invention, as described above, the amount of SBR per 100 parts by mass of the rubber component is 60 parts by mass or more and 80 parts by mass or less, and more preferably 65 parts by mass or more and 75 parts by mass or less.

[0117] SBR is not particularly limited, and for example, emulsion polymerization styrene-butadiene rubber (E-SBR), solution polymerization styrene-butadiene rubber (S-SBR) etc. can be used. SBR can be unmodified SBR or modified SBR. In addition, hydrogenated SBR obtained by hydrogenating the butadiene part of SBR. Hydrogenated SBR can be obtained by subsequently hydrogenating the BR part of SBR, or a similar structure can be obtained by copolymerizing styrene, ethylene and butadiene.

[0118] The modified SBR may be any SBR having a functional group that interacts with a filler (e.g., silica), and examples thereof include a terminal-modified SBR in which at least one end of the SBR is modified with a compound (modifier) ​​having a functional group (terminal-modified SBR having a functional group at the terminal); a main chain-modified SBR having a functional group in the main chain; a main chain-terminal-modified SBR having a functional group in the main chain and at least one terminal (e.g., an SBR having a functional group in the main chain and at least one terminal modified by a modifier); and a terminal-modified SBR modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and into which a hydroxyl group or an epoxy group is introduced.

[0119] 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 thioether group, a disulfide group, a sulfone group, a sulfoxide 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 a substituent.

[0120] As the modified SBR, for example, SBR modified with a compound (modifier) ​​represented by the following formula can be used.

[0121]

[0122] In the formula, R 1 , R 2 and R 3 are the same or different and represent an alkyl group, an alkoxy group, a silyl group, an acetal group, a carboxyl group (-COOH), a mercapto group (-SH) or a derivative thereof. 4 and R 5 are the same or different and represent a hydrogen atom or an alkyl group. 4 and R 5 May bond to form a ring structure together with the nitrogen atom. "n" represents an integer.

[0123] As the SBR modified with the compound (modifier) ​​represented by the above formula, SBR whose polymerization end (active end) of solution-polymerized styrene-butadiene rubber (S-SBR) has been modified with the compound represented by the above formula (for example, modified SBR described in JP-A-2010-111753) can be used.

[0124] R 1 , R 2 and R 3 Preferably it is an alkoxy group (preferably an alkoxy group having 1 to 8 carbon atoms, more preferably an alkoxy group having 1 to 4 carbon atoms). 4 and R 5 It is preferably an alkyl group (preferably an alkyl group having 1 to 3 carbon atoms). "n" is preferably 1 to 5, more preferably 2 to 4, and further preferably 3. 4 and R 5 When combined to form a ring structure together with a nitrogen atom, a 4- to 8-membered ring is preferred. The alkoxy group also includes a cycloalkoxy group (cyclohexyloxy group, etc.) and an aryloxy group (phenoxy group, benzyloxy group, etc.).

[0125] Specific examples of the modifier include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane and 3-diethylaminopropyltriethoxysilane. These can be used alone or in combination of two or more.

[0126] As the modified SBR, a modified SBR modified by the following compounds (modifiers) can also be used. Examples of the modifier include: polyglycidyl ethers of polyols, such as ethylene glycol diglycidyl ether, glycerol triglycidyl ether, trimethylolethane triglycidyl ether, and trimethylolpropane triglycidyl ether; polyglycidyl ethers of aromatic compounds having two or more phenolic groups, such as diglycidyl bisphenol A; polyepoxides, such as 1,4-diglycidylbenzene, 1,3,5-triglycidylbenzene, and polyepoxidized liquid polybutadiene; tertiary amines containing epoxy groups, such as 4,4'-diglycidyl-diphenylmethylamine and 4,4'-diglycidyl-dibenzylmethylamine; diglycidylamino compounds, such as diglycidyl Oleyl aniline, N,N'-diglycidyl-4-glycidyloxyaniline, diglycidyl o-toluidine, tetraglycidyl m-phenylenediamine, tetraglycidylaminodiphenylmethane, tetraglycidyl-p-phenylenediamine, diglycidylaminomethylcyclohexane and tetraglycidyl-1,3-bisaminomethylcyclohexane; amino group-containing acid chlorides, such as bis(1-methylpropyl)carbamoyl chloride, 4-morpholinylphosgene, 1-pyrrolidinylphosgene, N,N-dimethylcarbamoyl chloride and N,N-diethylcarbamoyl chloride; epoxy group-containing silane compounds, such as 1,3-bis-(glycidyloxypropyl)-tetramethyl Silane compounds containing thioether groups, such as (trimethylsilyl)[3-(trimethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(triethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(tripropoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(tributoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(methyldimethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(methyldiethoxysilyl)propyl]sulfide, ] sulfide, (trimethylsilyl) [3- (methyldipropoxysilyl) propyl] sulfide and (trimethylsilyl) [3- (methyldibutoxysilyl) propyl] sulfide; N-substituted aziridine compounds such as ethyleneimine and propyleneimine; alkoxysilanes such as methyltriethoxysilane, N,N-bis (trimethylsilyl) -3-aminopropyltrimethoxysilane, N,N-bis (trimethylsilyl) -3-aminopropyltriethoxysilane, N,N-bis (trimethylsilyl) aminoethyltrimethoxysilane and N,N-bis (trimethylsilyl) aminoethyltriethoxysilane;(Thio)benzophenone compounds having an amino group and / or a substituted amino group, such as 4-N,N-dimethylaminobenzophenone, 4-N,N-di-tert-butylaminobenzophenone, 4-N,N-diphenylaminobenzophenone, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(diphenylamino)benzophenone and N,N,N',N'-bis-(tetraethylamino)benzophenone; (thio)benzophenone compounds having an amino group and / or a substituted amino group, such as 4-N,N-dimethylaminobenzophenone, 4-N,N-di-tert-butylaminobenzophenone, 4-N,N-diphenylaminobenzophenone, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(diphenylamino)benzophenone and N,N,N',N'-bis-(tetraethylamino)benzophenone; N-substituted benzaldehyde compounds, such as 4-N,N-dimethylaminobenzaldehyde, 4-N,N-diphenylaminobenzaldehyde and 4-N,N-divinylaminobenzaldehyde; N-substituted pyrrolidones, such as N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, N-tert-butyl-2-pyrrolidone and N-methyl-5-methyl-2-pyrrolidone; N-substituted piperidones, such as N-methyl-2-piperidone, N-vinyl-2- piperidone and N-phenyl-2-piperidone; lactams such as N-methyl-ε-caprolactam, N-phenyl-ε-caprolactam, N-methyl-ω-laurolactam, N-vinyl-ω-laurolactam, N-methyl-β-propiolactam and N-phenyl-β-propiolactam; and N,N-bis-(2,3-epoxypropoxy)-aniline, 4,4-methylene-bis-(N,N-glycidylaniline), tris-(2,3-epoxypropyl)-1,3,5-triazine -2,4,6-triones, N,N-diethylacetamide, N-methylmaleimide, N,N-diethylurea, 1,3-dimethylethyleneurea, 1,3-divinylethyleneurea, 1,3-diethyl-2-imidazolidinone, 1-methyl-3-ethyl-2-imidazolidinone, 4-N,N-dimethylaminoacetophenone, 4-N,N-diethylaminoacetophenone, 1,3-bis(diphenylamino)-2-propanone, 1,7-bis(methylethylamino)-4-heptanone, etc. The modification using the above compounds (modifiers) can be carried out by known methods. ;

[0127] As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., ENEOS Materials Co., Ltd., Asahi Kasei Corporation, Nippon Zeon Corporation, etc. can be used. The SBR can be used alone or in combination of two or more.

[0128] (ii) BR

[0129] In the present invention, the rubber composition may contain BR as required. In this case, the BR content in 100 parts by mass of the rubber component is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and further preferably 20 parts by mass or more. On the other hand, it is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and further preferably 25 parts by mass or less.

[0130] The weight average molecular weight of BR is, for example, greater than 100,000 and less than 2,000,000. The vinyl content of BR is, for example, greater than 1% by mass and less than 30% by mass. The cis content of BR is, for example, greater than 1% by mass and less than 98% by mass. The trans content of BR is, for example, greater than 1% by mass and less than 60% by mass.

[0131] BR is not particularly limited, and may be BR with a high cis content (90% or more cis content), BR with a low cis content, or BR containing syndiotactic polybutadiene crystals. BR may be unmodified or modified, and modified BR includes modified BR having the above-mentioned functional groups introduced therein. These may be used alone or in combination of two or more. The cis content may be measured by infrared absorption spectroscopy.

[0132] As BR, for example, products of Ube Industries, Ltd., ENEOS Materials Co., Ltd., Asahi Kasei Corporation, Nippon Zeon Corporation, etc. can be used.

[0133] (iii) Isoprene rubber

[0134] In the present invention, the rubber composition may contain isoprene rubber as required. In this case, the content of isoprene rubber in 100 parts by mass of the rubber component is preferably 3 parts by mass or more, more preferably 5 parts by mass or more. On the other hand, it is preferably 20 parts by mass or less, more preferably less than 10 parts by mass.

[0135] Examples of the isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR.

[0136] As NR, for example, SIR20, RSS#3, TSR20, SVR-L, etc., which are generally used in the tire industry, can be used. As IR, there is no particular limitation, and for example, IR2200, which is generally used in the tire industry, etc. can be used. As modified NR, deproteinized natural rubber (DPNR), high purity natural rubber (UPNR), etc. can be mentioned; as modified NR, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. can be mentioned; as modified IR, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. can be mentioned. These can be used alone or in combination of two or more.

[0137] (iv) Other rubber components

[0138] Furthermore, as a rubber component other than the above-mentioned rubber components, a rubber (polymer) generally used for manufacturing tires, such as nitrile rubber (NBR), may be contained.

[0139] (b) Compounding materials other than rubber components

[0140] (i) Filling

[0141] In the present invention, as described above, the rubber composition contains silica as a filler, but may contain other fillers. Specific examples of fillers other than silica include carbon black, graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica.

[0142] (i-1) Silicon dioxide

[0143] In the present invention, the content of silica is 100 parts by mass or more relative to 100 parts by mass of the rubber component. As described above, the content is more preferably 110 parts by mass or more, and even more preferably 120 parts by mass or more. The upper limit is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, and even more preferably 130 parts by mass or less.

[0144] In the present invention, from the viewpoint of obtaining good durability performance, the BET specific surface area of ​​silica contained in the rubber composition is preferably greater than 140 m 2 / g, more preferably greater than 160m 2 / g, and more preferably greater than 180m 2 On the other hand, from the perspective of obtaining good rolling resistance during high-speed running, it is preferably less than 250 m 2 / g, more preferably less than 230m 2 / g, and more preferably less than 220m 2 / g. The BET specific surface area is the value of N2 SA measured by the BET method according to ASTM D3037-93.

[0145] In the present invention, as described above, in the rubber composition, it is preferred to use silica having a particle size of 17 nm or less, and by using silica having a smaller particle size, the contact frequency with the polymer (styrene region) can be increased, thereby improving the reinforcement. The lower limit is not particularly limited, but from the perspective of dispersibility during mixing, it is preferably 10 nm or more.

[0146] Examples of silicon dioxide include dry silicon dioxide (anhydrous silicon dioxide) and wet silicon dioxide (hydrated silicon dioxide). Among them, wet silicon dioxide is preferred because it has a large number of silanol groups. In addition, silicon dioxide made from hydrated glass or silicon dioxide made from biomass materials (such as rice husks) can also be used.

[0147] As silica, for example, products of Evonik Industries, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Co., Ltd., and the like can be used.

[0148] (i-2) Silane coupling agent

[0149] The rubber composition of the present invention preferably contains a silane coupling agent together with silica.

[0150] The silane coupling agent is not particularly limited. Specific examples of the silane coupling agent include sulfide-based silane coupling agents such as 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)tetrasulfide, 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 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and NXT and NXT-Z manufactured by Momentive; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino The silane coupling agents include amino-based silane coupling agents such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chlorine-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. These silanes may be used alone or in combination of two or more.

[0151] As the silane coupling agent, for example, products available from Evonik Industries, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., AZmax Co., Ltd., Dow Corning Toray Corporation, etc. can be used.

[0152] The content of the silane coupling agent is, for example, greater than 3 parts by mass and less than 25 parts by mass relative to 100 parts by mass of silica.

[0153] (i-3) Carbon black

[0154] In the present invention, the rubber composition preferably contains carbon black from the viewpoint of reinforcement.

[0155] The specific content ratio of carbon black is preferably 2 parts by mass or more, and more preferably 4 parts by mass or more, while it is preferably 10 parts by mass or less, and more preferably 6 parts by mass or less, relative to 100 parts by mass of the rubber component.

[0156] Carbon black is not particularly limited, and examples thereof include furnace blacks (furnace blacks), such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF, and ECF; acetylene black (acetylene carbon black); thermal blacks (thermal blacks), such as FT and MT; and channel blacks (channel blacks), such as EPC, MPC, and CC. These may be used alone or in combination of two or more.

[0157] The CTAB specific surface area (cetyltrimethylammonium bromide) of carbon black is preferably 130 m 2 / g or more, more preferably 160m 2 / g or more, and more preferably 170 m 2 / g or more, on the other hand, it is preferably 250m 2 / g or less, and more preferably 200m 2 The CTAB specific surface area is a value measured according to ASTM D3765-92.

[0158] Specific carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available products include, for example, products of Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Tanso Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Co., Ltd., Nippon Steel Carbon Co., Ltd., Columbia Carbon Co., Ltd., etc. These may be used alone or in combination of two or more.

[0159] (i-4) Other fillers

[0160] In addition to the above-mentioned silica and carbon black, the rubber composition may contain fillers commonly used in the tire industry, such as graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, etc., as required. The content of these fillers is, for example, greater than 0.1 parts by mass and less than 200 parts by mass per 100 parts by mass of the rubber component.

[0161] (ii) Plasticizer component

[0162] Rubber composition can comprise oil (comprising filler oil), liquid rubber and resin as the plasticizer component of softening rubber.Plasticizer component is the component that can be extracted with acetone from vulcanized rubber.Relative to the rubber component of 100 mass parts, the total content of plasticizer component is preferably more than 55 mass parts, more preferably more than 60 mass parts, and further preferably more than 65 mass parts.On the other hand, it is preferably less than 80 mass parts, more preferably less than 75 mass parts, and further preferably less than 70 mass parts.When rubber component is oil-filled rubber component, the amount of filler oil is included in oil content.

[0163] (ii-1) Oil

[0164] The oil may be, for example, a mineral oil, a synthetic oil, a vegetable oil, an animal oil or a mixture thereof.

[0165] Examples of available mineral oils include paraffinic process oils, aromatic process oils, and naphthenic process oils. For example, products manufactured by Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Co., Ltd., OLISOY Co., Ltd., H&R Co., Ltd., Toyokuni Oil Refining Co., Ltd., Showa Shell Sekiyu Co., Ltd., Fuji Kosan Co., Ltd., etc. can be used. These can be used alone or in combination of two or more.

[0166] From the perspective of life cycle analysis, it can be used as mixers for rubber kneading machines, lubricants for engines, waste cooking oil for restaurants, etc. after appropriate purification.

[0167] Examples of the vegetable oil include 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 oil, peanut oil, grapeseed oil, and wood wax.

[0168] In addition, examples of vegetable oils include refined oils (e.g., salad oils) obtained by refining the above-mentioned oils, esterified oils obtained by ester exchange, hardened oils obtained by hydrogenation, thermally polymerized oils obtained by thermal polymerization, oxidatively polymerized oils obtained by oxidation, and waste edible oils obtained by recovering oils that have been used as edible oils, etc. Vegetable oils may be liquid or solid at room temperature (25° C.). These oils may be used alone or in combination of two or more.

[0169] As the vegetable oil, acylglycerol is preferred, and triacylglycerol is more preferred. Acylglycerol refers to a compound in which a hydroxyl group of glycerol is bonded to a carboxylic acid through an ester bond. Acylglycerol is not particularly limited, and may be 1-monoacylglycerol, 2-monoacylglycerol, 1,2-diacylglycerol, 1,3-diacylglycerol or triacylglycerol. In addition, acylglycerol may be a monomer, a dimer or a polymer of a trimer or more. Acylglycerols of dimers or more can be obtained by thermal polymerization, oxidative polymerization, etc. In addition, acylglycerol may be liquid or solid at room temperature (25°C).

[0170] The method for confirming whether or not the rubber composition contains acylglycerols is not particularly limited, but can be performed by 1 For example, a rubber composition containing triacylglycerol is immersed in deuterated chloroform at room temperature (25° C.) for 24 hours to remove the rubber composition, and then the triacylglycerol is measured at room temperature. 1 H-NMR. When the signal of tetramethylsilane (TMS) was set to 0.00 ppm, signals were observed near 5.26 ppm, near 4.28 ppm, and near 4.15 ppm. These signals are presumed to be signals from hydrogen atoms bonded to carbon atoms adjacent to the oxygen atom of the ester group, and thus it can be confirmed that acylglycerol is contained. Here, "nearby" means a range of ±0.10 ppm.

[0171] The carboxylic acid is not particularly limited and may be an unsaturated fatty acid or a saturated fatty acid. Examples of unsaturated fatty acids include monounsaturated fatty acids (eg, oleic acid) and polyunsaturated fatty acids (eg, linoleic acid and linolenic acid).

[0172] As the vegetable oil, for example, oil commercially available from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Co., Ltd., Olisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Manufacturing Co., Ltd., Fuji Kosan Co., Ltd., Nissin Oilliyo Group Ltd., etc. can be used.

[0173] (ii-2) Liquid rubber

[0174] The liquid rubber mentioned as the plasticizer is a polymer which is liquid at room temperature (25°C) and is a rubber component which can be extracted with acetone from a vulcanized tire. Examples of the liquid rubber include farnesene polymers, liquid diene polymers and hydrogenated products thereof.

[0175] Farnesene polymers are polymers obtained by polymerizing farnesene and have a farnesene-based structural unit. Farnesene includes isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodetetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene).

[0176] 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).

[0177] Examples of the liquid diene-based polymer include liquid styrene-butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), and the like.

[0178] The weight average molecular weight (Mw) of the liquid diene polymer measured by gel permeation chromatography (GPC) in terms of polystyrene is, for example, greater than 1.0×10 3 And less than 2.0×10 5 In this specification, the Mw of the liquid diene polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0179] The content of the liquid rubber (the total content of the liquid farnesene polymer, the liquid diene polymer, etc.) relative to 100 parts by mass of the rubber component is, for example, more than 1 part by mass and less than 100 parts by mass.

[0180] As the liquid rubber, for example, products of Kuraray Co., Ltd. and Cray Valley Corporation can be used.

[0181] (ii-3) Resin component

[0182] The resin component also acts as a tackifier and can be solid or liquid at room temperature. Specific examples of the resin component include resins such as rosin resins, styrene resins, coumarone resins, terpene resins, C5 resins, C9 resins, C5C9 resins, acrylic resins, and two or more thereof can also be used in combination. Relative to 100 parts by mass of the rubber component, the content of the resin component is preferably greater than 2 parts by mass and less than 45 parts by mass. The resin component may have a modified group capable of reacting with silica or the like as required.

[0183] Rosin resin is a resin whose main component is rosin acid obtained by processing rosin. These rosin resins (rosins) can be classified according to whether they are modified, and can be classified into unmodified rosin (non-modified rosin) and modified rosin (rosin derivative). The example of unmodified rosin includes tall oil rosin (also known as tall oil rosin), gum rosin, wood rosin, disproportionated rosin, polymerized rosin, hydrogenated rosin, other chemically modified rosins, etc. Modified rosin is a modified substance of unmodified rosin, and the example of such modified rosin includes rosin ester, unsaturated carboxylic acid modified rosin, unsaturated carboxylic acid modified rosin ester, rosin amide compound and rosin amine salt.

[0184] The styrene resin is a polymer using a styrene monomer as a constituent monomer, and examples thereof include polymers obtained by polymerizing a styrene monomer as a main component (50% by mass or more), etc. Specifically, it includes homopolymers obtained by polymerizing a styrene monomer (styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.) alone, copolymers obtained by copolymerizing two or more styrene monomers, and further, copolymers obtained by copolymerizing a styrene monomer with other monomers copolymerizable with the styrene monomer.

[0185] Examples of other monomers include acrylonitriles such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid and methacrylic acid; unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate; dienes such as chloroprene, butadiene and isoprene; olefins such as 1-butene and 1-pentene; and α,β-unsaturated carboxylic acids and anhydrides thereof such as maleic anhydride and the like.

[0186] As the benzofuran resin, benzofuran-indene resin is preferably used. Benzene-indene resin is a resin containing benzofuran and indene as monomer components constituting the backbone (main chain) of the resin. Examples of monomer components other than benzofuran and indene contained in the backbone include styrene, α-methylstyrene, methylindene and vinyltoluene, etc.

[0187] The content of the coumarone-based resin is, for example, greater than 1.0 part by mass and less than 50.0 parts by mass relative to 100 parts by mass of the rubber component.

[0188] The hydroxyl value (OH value) of the coumarone-indene resin is, for example, greater than 15 mgKOH / g and less than 150 mgKOH / g. The OH value is the amount of potassium hydroxide required to neutralize acetic acid bonded to the hydroxyl group when 1 g of the resin is acetylated, and is expressed in milligrams. It is a value measured by potentiometric titration (JIS K 0070: 1992).

[0189] The softening point of the coumarone-indene resin is, for example, higher than 30° C. and lower than 160° C. The softening point is a temperature at which a ball falls when the softening point specified in JIS K 6220-1:2001 is measured by a ring and ball softening point measuring apparatus.

[0190] Examples of terpene resins include polyterpene, terpene phenol, and aromatic modified terpene resins. Polyterpene is a resin obtained by polymerizing a terpene compound and its hydrogenate. A terpene compound is a terpene having (C5H8) n A hydrocarbon or an oxygen-containing derivative thereof, which is classified as a monoterpene (C 10 H 16), sesquiterpenes (C 15 H 24 ), diterpenes (C 20 H 32 ) as a basic skeleton. Examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol.

[0191] Examples of polyterpenes include terpene resins made from the above-mentioned terpene compounds, such as α-pinene resin, β-pinene resin, limonene resin, dipentene resin and β-pinene / limonene resin, and hydrogenated terpene resins obtained by hydrogenating the terpene resin. Examples of terpene phenols include resins obtained by copolymerizing the above-mentioned terpene compounds with phenolic compounds, and resins obtained by hydrogenating the above-mentioned resins, specifically, resins formed by condensing the above-mentioned terpene compounds, phenolic compounds and formaldehyde. Examples of phenolic compounds include phenol, bisphenol A, cresol and xylenol, etc. Examples of aromatic modified terpene resins include resins obtained by modifying terpene resins with aromatic compounds, and resins obtained by hydrogenating the above-mentioned resins. The aromatic compound is not particularly limited as long as it is a compound having an aromatic ring, and examples thereof include phenol compounds such as phenol, alkylphenol, alkoxyphenol and phenol containing an unsaturated hydrocarbon group; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol and naphthol containing an unsaturated hydrocarbon group; styrene derivatives such as styrene, alkylstyrene, alkoxystyrene and styrene containing an unsaturated hydrocarbon group; benzofuran; and indene.

[0192] C5 resin refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5-based petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0193] C9 resin refers to a resin obtained by polymerizing a C9 fraction, and it can be hydrogenated or modified. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyl toluene, alkyl styrene, indene, methyl indene. As a specific example, it is preferred to use, for example, benzofuran-indene resin, benzofuran resin, indene resin and aromatic vinyl resin. As aromatic vinyl resin, preferably α-methylstyrene or a homopolymer of styrene or a copolymer of α-methylstyrene and styrene, because it is economical, easy to process and excellent in terms of heat generation. More preferably, a copolymer of α-methylstyrene and styrene. As aromatic vinyl resin, aromatic vinyl resins such as those commercially available from Clayton Company, Eastman Chemical Company, etc. can be used.

[0194] C5C9 resin refers to a resin obtained by copolymerizing the above-mentioned C5 fraction and the above-mentioned C9 fraction, and it may be hydrogenated or modified. Examples of C5 fraction and C9 fraction include the above-mentioned petroleum fraction. As C5C9 resin, for example, resins commercially available from Tosoh Corporation, LUHUA Corporation, etc. may be used.

[0195] The acrylic resin is not particularly limited, but for example, a solvent-free type acrylic resin may be used.

[0196] As the solvent-free acrylic resin, there can be mentioned a (meth)acrylic resin (polymer) synthesized by a high temperature continuous polymerization method (high temperature continuous bulk polymerization method, which is a method described in US 4414370 B, JP 84-6207A, JP 93-58805B, JP 89-313522A, US 5010166 B, ToaSynthetic Research Annual Report TREND2000 No.3p42-45, etc.), and a polymerization initiator, a chain transfer agent, an organic solvent, etc. are not used as auxiliary raw materials as much as possible. In the present invention, (meth)acrylic acid refers to methacrylic acid and acrylic acid.

[0197] Examples of monomer components constituting the acrylic resin include (meth)acrylic acid and (meth)acrylic acid derivatives such as (meth)acrylic acid esters (alkyl esters, aryl esters, aralkyl esters, etc.), (meth)acrylamide, (meth)acrylamide derivatives, and the like.

[0198] In addition, as a monomer component constituting the above acrylic resin, an aromatic vinyl compound such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, divinylnaphthalene may be used together with (meth)acrylic acid or a (meth)acrylic acid derivative.

[0199] The acrylic resin may be a resin composed of only a (meth)acrylic component or a resin further having a component other than the (meth)acrylic component. In addition, the acrylic resin may have a hydroxyl group, a carboxyl group, a silanol group, or the like.

[0200] Specific examples of usable resin components include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF Corporation, Arizona Chemical Co., Ltd., Nippon Paint Chemicals Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Co., Ltd., Arakawa Chemical Industries, Ltd., Taoka Chemical Industries, Ltd., and the like.

[0201] (iii) Stearic acid

[0202] In the present invention, the rubber composition preferably contains stearic acid. For every 100 parts by mass of the rubber component, the content of stearic acid is, for example, greater than 0.5 parts by mass and less than 10.0 parts by mass. As stearic acid, conventionally known products can be used. For example, products such as NOF Corporation, NOF Corporation, Kao Corporation, Fujifilm Co., Ltd., Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc. can be used.

[0203] (iv) Anti-aging agents

[0204] In the present invention, the rubber composition preferably contains an antioxidant in an amount of, for example, more than 0.5 parts by mass and less than 10 parts by mass, and more preferably 1 part by mass or more, relative to 100 parts by mass of the rubber component.

[0205] Examples of anti-aging agents include naphthylamine anti-aging agents, such as phenyl-α-naphthylamine; diphenylamine anti-aging agents, such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; p-phenylenediamine anti-aging agents, such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and N,N'-di-2-naphthyl-p-phenylenediamine; quinoline anti-aging agents, such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol anti-aging agents, such as 2,6-di-tert-butyl-4-methylphenol, styrenated phenol; bisphenol, triphenol, polyphenol anti-aging agents, such as tetrakis-[methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane. These can be used alone or in combination of two or more.

[0206] As the anti-aging agent, for example, products of Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., Flexis Corporation, etc. can be used.

[0207] (v) Wax

[0208] In the present invention, the rubber composition preferably contains wax. The content of the wax is, for example, preferably 0.5 to 20 parts by mass, more preferably 1.0 to 15 parts by mass, and further preferably 1.5 to 10 parts by mass relative to 100 parts by mass of the rubber component.

[0209] The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax, natural waxes such as vegetable wax and animal wax, synthetic waxes such as polymers of ethylene, propylene, etc. These may be used alone or in combination of two or more.

[0210] As the wax, products available from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., and the like can be used.

[0211] (vi) Zinc oxide

[0212] In the present invention, the rubber composition may contain zinc oxide. The content of zinc oxide is, for example, greater than 0.5 parts by mass and less than 10 parts by mass relative to 100 parts by mass of the rubber component. As zinc oxide, conventionally known products can be used, for example, products of Mitsui Mining and Smelting Co., Ltd., Toho Zinc Co., Ltd., HAKUSUI TECH Co., Ltd., Shodo Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

[0213] (vii) Cross-linking agent and vulcanization accelerator

[0214] In the present invention, the rubber composition preferably contains a crosslinking agent (such as sulfur). The content of the crosslinking agent is, for example, greater than 0.1 parts by mass and less than 10.0 parts by mass relative to 100 parts by mass of the rubber component.

[0215] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur commonly used in the rubber industry. These may be used alone or in combination of two or more.

[0216] As sulfur, products available from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanryu Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., and the like can be used.

[0217] Crosslinking agents other than sulfur include vulcanizing agents containing sulfur atoms, such as Tackirol V200 manufactured by Taoka Chemical Industry Co., Ltd. and KA9188 (1,6-bis(N,N′-dibenzylthiocarbamoyldisulfide)hexane) manufactured by LANXESS, and organic peroxides such as dicumyl peroxide.

[0218] The rubber composition preferably contains a vulcanization accelerator to promote crosslinking. The content of the vulcanization accelerator is, for example, greater than 0.3 parts by mass and less than 10.0 parts by mass relative to 100 parts by mass of the rubber component.

[0219] Examples of the vulcanization accelerator include thiazole vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazolyl sulfenamide; thiuram vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, N-tert-butyl-2-benzothiazole sulfenamide, N-ethylene oxide-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine vulcanization accelerators such as diphenylguanidine, di-o-tolylguanidine, and o-tolylbiguanide. These may be used alone or in combination of two or more.

[0220] (viii) Others

[0221] In addition to the above components, the rubber composition may contain additives commonly used in the tire industry, such as fatty acid metal salts, carboxylic acid metal salts, organic peroxides, reversion inhibitors, etc. The content of these additives is, for example, greater than 0.1 parts by mass and less than 50 parts by mass relative to 100 parts by mass of the rubber component.

[0222] (2) Preparation of rubber composition

[0223] The rubber composition forming the crown rubber layer is prepared by appropriately adjusting the various mixing materials mentioned above and using conventional methods, for example, a manufacturing method including the following steps: a basic mixing step of mixing the rubber component with a filler (such as silica), and a refined mixing step of mixing the mixed product obtained in the basic mixing step with a cross-linking agent.

[0224] The kneading can be carried out using a known (closed type) mixer such as a Banbury mixer, a kneader or an open roll mill.

[0225] The mixing temperature of the basic mixing process is, for example, greater than 50° C. and less than 200° C., and the mixing time is, for example, greater than 30 seconds and less than 30 minutes. In the basic mixing process, in addition to the above-mentioned components, compounding agents commonly used in the rubber industry, such as plasticizer components (such as oil), zinc oxide, anti-aging agents, waxes, vulcanization accelerators, etc., may also be appropriately added as needed and mixed. The order of adding materials during mixing is not particularly limited, and the rubber component may be crushed in a mixer and then fillers and softeners may be added, or the fillers and softeners may be mixed in advance in a mixer and then the rubber component may be added.

[0226] In the refining and kneading step, the kneaded product obtained in the basic kneading step is kneaded with a crosslinking agent. The kneading temperature in the refining and kneading step is, for example, greater than room temperature and less than 80° C., and the kneading time is, for example, greater than 1 minute and less than 15 minutes. In the refining and kneading step, in addition to the above components, a vulcanization accelerator, zinc oxide, etc. may be appropriately added as needed and kneaded.

[0227] 2. Tire manufacturing

[0228] The tire of the present embodiment can be manufactured as an unvulcanized tire by molding the rubber composition obtained as described above into a tread rubber of a predetermined shape as a cap rubber layer, and then molding it together with other tire components on a tire molding machine in a conventional manner.

[0229] In the case where the tread portion has a multilayer structure provided with a base rubber layer, the rubber composition for forming the base rubber layer can be obtained by kneading the above-mentioned rubber component and compounding materials in the same manner while appropriately changing the compounding amount. Then, the rubber composition for forming the base rubber layer is extruded together with the crown rubber layer to form a tread rubber of a predetermined shape, and then molded on a tire molding machine in a conventional manner together with other tire components to produce an unvulcanized tire.

[0230] Specifically, the inner liner as a component for ensuring the airtightness of the tire, the carcass as a component for bearing the load, impact and filling pressure of the tire, and the belt layer component as a component for clamping the carcass to increase the rigidity of the tread are wound on the forming drum, and the two ends of the carcass are fixed to the edges on both sides, and the bead part as a component for fixing the tire on the rim is arranged and formed into a ring shape. Then, the tread is attached to the central part of the outer circumference, and the sidewall is attached to the radially outer side to form the side portion, thereby producing an unvulcanized tire.

[0231] Then, the unvulcanized tire thus produced is heated and pressurized in a vulcanizer to obtain a tire. The vulcanization step can be performed by applying known vulcanization means. The vulcanization temperature is, for example, greater than 120° C. and less than 200° C., and the vulcanization time is, for example, greater than 5 minutes and less than 15 minutes.

[0232] As described above, the obtained tire contains an appropriate amount of SBR with a small amount of styrene to form a minute styrene region, and contains silica in an amount equal to or greater than the rubber component to ensure reinforcement of the rubber, thereby suppressing thermal degradation of the tread portion during high-speed running. In addition, by appropriately controlling 30°C tanδ and the thickness of the tread, heat generation and heat storage in the tread are suppressed. These effects work together, thereby being able to maintain sufficient wet grip performance even after high-speed running.

[0233] The tire of the present invention is not particularly limited in type and can be used as a passenger car tire, a tire for a heavy-duty vehicle (such as a truck and a bus), a tire for a two-wheeled vehicle, a run-flat tire, a non-pneumatic tire, etc., but is preferably used as a passenger car tire. In addition, it is preferably a pneumatic tire.

[0234] [Example]

[0235] Examples (embodiments) considered to be preferred in carrying out the present invention are shown below, but the scope of the present invention is not limited to these examples. In the examples, pneumatic tires (tire size 205 / 55R16, aspect ratio: 55%) having a crown rubber layer made of a composition obtained by changing the formulation according to each table using various chemicals and having a ground contact ratio shown in each table were examined. The results calculated based on the following evaluation method are shown in Tables 2 to 4.

[0236] 1. Rubber composition for forming a crown rubber layer

[0237] (1) Mixed materials

[0238] (a) Rubber component

[0239] (i) NR: TSR20

[0240] (ii) SBR-1: SLR6430 (S-SBR) manufactured by Trinseo

[0241] (Styrene content: 40% by mass, vinyl content: 24% by mass)

[0242] (iii) SBR-2: Modified S-SBR obtained by the method shown in the next paragraph

[0243] (Styrene content: 25% by mass, vinyl content: 27% by mass)

[0244] (iii) SBR-3: HPR840 (S-SBR) manufactured by ENEOS Materials Co., Ltd.

[0245] (Styrene content: 10% by mass, vinyl content: 42% by mass)

[0246] (iv) BR: Ubepol BR150B (Hicis BR) manufactured by Ube Industries, Ltd.

[0247] (cis content 97 mass%, trans content 2 mass%, vinyl content 1 mass%)

[0248] (Production of SBR-2)

[0249] SBR-2 was prepared according to the following process. First, two autoclaves with an internal volume of 10L, an inlet at the bottom and an outlet at the top, and equipped with a stirrer and a jacket were connected in series as reactors, and butadiene, styrene and cyclohexane were mixed in a predetermined ratio. The mixed solution was passed through a dehydration column filled with activated alumina and mixed with n-butyl lithium in a static mixer to remove impurities. Then, the solution was continuously fed from the bottom of the first reactor. In addition, 2,2-bis(2-oxolane)propane as a polar substance and n-butyl lithium as a polymerization initiator were continuously fed from the bottom of the first reactor at a predetermined rate, respectively, and the temperature inside the reactor was maintained at 95°C. The polymer solution was continuously taken out from the reactor head and fed into the second reactor. The temperature of the second reactor was maintained at 95°C, and a mixture of tetraglycidyl-1,3-bisaminomethylcyclohexane (monomer) and monomer components as a modifier was continuously added at a predetermined rate as a 1000-fold diluted cyclohexane solution to carry out a modification reaction. The polymer solution was continuously taken out from the reactor, and an antioxidant was continuously added using a static mixer, after which the solvent was removed to obtain SBR-2.

[0250] The vinyl content of SBR-2 (unit: mass %) was determined by infrared spectroscopy from about 910 cm -1 The absorption intensity at 100 μm (absorption peak of vinyl group) was measured. The styrene content (unit: mass %) was measured from the refractive index according to JIS K6383 (1995).

[0251] (b) Compounding materials other than rubber components

[0252] (i) Carbon black: Diablack N220 (N2 SA: 115 m 2 / g)

[0253] (ii) Silica: Ultrasil VN3 (N2SA: 175 m 2 / g, average primary particle size: 15nm)

[0254] (iii) Oil: H&R VIVATEC 500 (TDAE oil)

[0255] (iv) Silane coupling agent-1: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Industries

[0256] (v) Silane coupling agent-2: NXT (3-octanoylthiopropyltriethoxysilane) manufactured by Momentive

[0257] (vi) Resin: SYLVATRAXX4401 (α-methylstyrene resin) manufactured by Kraton

[0258] (vii) Zinc oxide: Type 2 zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd.

[0259] (viii) Stearic acid: Bead stearic acid "Tsubaki" manufactured by NOF Corporation

[0260] (ix) Wax: Sannok N (specially selected wax) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0261] (x) Antiaging agent-1: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.

[0262] (xi) Antiaging agent-2: Antigen RD (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Sumitomo Chemical Co., Ltd.

[0263] (xii) Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Co., Ltd. (containing 5% oil)

[0264] (xiii) Vulcanization accelerator-1: Nocceler CZ (N-cyclohexyl-2-benzothiazole sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0265] (xiv) Vulcanization accelerator-2: Soxinol D (N,N'-diphenylguanidine (DPG) manufactured by Sumitomo Chemical Co., Ltd.)

[0266] (2) Rubber composition for forming a crown rubber layer

[0267] According to each formulation shown in Table 2 to Table 4, materials other than sulfur and vulcanization accelerator were kneaded at 150° C. for 5 minutes using a Banbury mixer to obtain a kneaded mixture. Each compounding amount is expressed in parts by mass, and the amount of the extender oil in the rubber is included in the total amount of "oil".

[0268] Next, sulfur and a vulcanization accelerator were added to the kneaded product obtained above, and the mixture was kneaded using an open roll mill under the condition of 80° C. for 5 minutes to obtain a rubber composition for forming a cap rubber layer.

[0269] 2. Rubber composition for forming base rubber layer

[0270] Meanwhile, a rubber composition for forming a base rubber layer was obtained based on the formulation shown in Table 1 in the same manner as in the production of the rubber composition for forming a cap rubber layer.

[0271] [Table 1]

[0272]

[0273] 3. Manufacturing of pneumatic tires

[0274] Each of the rubber compositions obtained above was extruded in a predetermined shape so that the ratio of (cap rubber layer / base rubber layer) was 70 / 30 to form a tread portion having a thickness shown in Tables 2 to 4.

[0275] Thereafter, the tire was bonded together with other tire components to form an unvulcanized tire, and then press-vulcanized at 170° C. for 10 minutes to produce each of the pneumatic tires (test tires) of Examples 1 to 13 and Comparative Examples 1 to 7 shown in Tables 2 to 4.

[0276] 4. Calculation of parameters

[0277] The following parameters of each test tire were then determined.

[0278] (1) tanδ at 30℃

[0279] A rubber sample for viscoelasticity measurement was prepared by cutting a piece of rubber having a length of 20 mm, a width of 4 mm, and a thickness of 2 mm (where the long side is in the tire circumferential direction) from the crown rubber layer of the tread portion of each test tire. The 30°C tanδ of each rubber sample was then measured using the "Eplexor" series manufactured by GABO under the conditions of a measurement temperature of 30°C, a frequency of 10 Hz, an initial strain of 5%, a dynamic strain rate of 1%, and a tensile deformation mode. The 30°C tanδ (30°C tanδB) of the base rubber layer was set to 0.07.

[0280] The resulting 30°C tan δ (30°C tan δC) was then used to calculate (-7 x 30°C tan δ + 2.5), (-7 x 30°C tan δ + 2.3), (-7 x 30°C tan δ + 2.1), and (30°C tan δB / 30°C tan δC).

[0281] (2) tanδ at 0℃

[0282] The 0°C tan δ of the cap rubber layer was measured under the same conditions as above except that the temperature was changed to 0°C.

[0283] (4)AE

[0284] A vulcanized rubber test piece was prepared by cutting out from the cap rubber layer of the tread portion of each test tire, and AE (mass %) was measured in accordance with JIS K 6229:2015.

[0285] (4) SBR content (mass) × ground contact rate (%)

[0286] The product of the content (parts by mass) of styrene-butadiene rubber (SBR) having a styrene content of 25% by mass or less in 100 parts by mass of the rubber component of the cap rubber layer of the tread portion of each test tire and the ground contact ratio (%) of the tread portion was calculated.

[0287] (5) Silica content (mass fraction) × flatness (%)

[0288] The product of the silica content (parts by mass) and the aspect ratio (%) relative to 100 parts by mass of the rubber component of the cap rubber layer of the tread portion of each test tire was calculated.

[0289] 5. Performance evaluation test (wet grip performance after high-speed driving)

[0290] Each test tire was mounted on all wheels of a vehicle (a domestic front-engine front-drive vehicle with a displacement of 2000cc), and the tire was filled with air so that the internal pressure was 250kPa. The vehicle was driven on a test track with a dry road surface at 100km / h for 50km, and then on a test track with a wet road surface at 80km / h, and for the grip performance during driving (wet grip performance), 20 drivers each performed a sensory evaluation on a 5-point scale (the higher the number, the better). The total score evaluated by the 20 drivers was then calculated.

[0291] Next, the result of Comparative Example 1 was set to 100 and indexed according to the following formula to evaluate the wet grip performance after high-speed running. A larger value indicates better wet grip performance after high-speed running.

[0292] Wet grip performance after high-speed running==[(result of test tire) / (result of Comparative Example 1)]×100 [Table 2]

[0293]

[0294] [Table 3]

[0295]

[0296] [Table 4]

[0297]

[0298] Although the present invention has been described based on the above embodiment, the present invention is not limited to the above embodiment. Various modifications can be made to the above embodiment within the scope of the same and equivalent to the present invention.

[0299] The present invention (1) is a tire having a tread portion, wherein:

[0300] a cap rubber layer forming the tread portion containing 60 parts by mass or more and 80 parts by mass or less of styrene-butadiene rubber (SBR) having a styrene content of 25% by mass or less per 100 parts by mass of the rubber component, and containing 100 parts by mass or more of silica relative to 100 parts by mass of the rubber component; and

[0301] The crown rubber layer is formed of a rubber composition having a loss tangent (30°C tanδ) less than 0.27 measured in a tensile deformation mode under the conditions of a temperature of 30°C, a frequency of 10 Hz, an initial strain of 5% and a dynamic strain rate of 1%; and

[0302] The thickness of the tread portion is 13 mm or less.

[0303] The present invention (2) is the tire according to the present invention (1), wherein the styrene content in the styrene-butadiene rubber (SBR) is 20% by mass or less.

[0304] The present invention (3) is the tire according to the present invention (2), wherein the styrene content in the styrene-butadiene rubber (SBR) is 15% by mass or less.

[0305] The present invention (4) is the tire according to any combination of the present inventions (1) to (3), wherein the content of the silica is 110 parts by mass or more per 100 parts by mass of the rubber component.

[0306] The present invention (5) is a tire according to any combination of the present inventions (1) to (4), wherein the 30°C tan δ is 0.21 or less.

[0307] The present invention (6) is a tire according to any combination of the present inventions (1) to (5), wherein the thickness of the tread portion is 7 mm or less.

[0308] The present invention (7) is a tire according to any combination of the present inventions (1) to (6), wherein the loss tangent (0°C tanδ) of the crown rubber layer measured in a tensile deformation mode under the conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 5% and a dynamic strain rate of 1% and the 30°C tanδ of the crown rubber layer satisfy the following formula (1):

[0309] 0℃tanδ≦-7×30℃tanδ+2.5(1).

[0310] The present invention (8) is a tire as described in any combination of the present inventions (1) to (7), wherein the tread portion is made multi-layered by arranging a base rubber layer inside the crown rubber layer, and the thickness of the crown rubber layer accounts for more than 70% of the entire tread portion.

[0311] The present invention (9) is the tire according to any combination of the present inventions (1) to (8), wherein the particle size (average primary particle size) of the silica is 17 nm or less.

[0312] The present invention (10) is a tire as described in any combination of the present inventions (1) to (9), wherein the crown rubber layer contains a resin component selected from the group consisting of rosin resins, styrene resins, furan resins, terpene resins, C5 resins, C9 resins, C5C9 resins and acrylic resins.

[0313] The present invention (11) is a tire according to any combination of the present inventions (1) to (10), wherein the acetone extract (AE) of the cap rubber layer is 21% by mass or more.

[0314] The present invention (12) is a tire according to any combination of the present inventions (1) to (11), wherein the ground contact ratio of the tread portion is 63% or more.

[0315] The present invention (13) is a tire as described in any combination of the present inventions (1) to (12), wherein the product of the content (mass parts) of styrene-butadiene rubber (SBR) having a styrene content of less than 25 mass% in the rubber component in 100 mass parts of the crown rubber layer and the ground contact rate (%) of the tread portion (SBR content×ground contact rate) is less than 7200.

[0316] The present invention (14) is a tire as described in any combination of the present inventions (1) to (13), wherein the product of the silica content (parts by mass) of the crown rubber layer relative to 100 parts by mass of the rubber component and the aspect ratio (%) of the tire is less than 11,000.

[0317] The present invention (15) is a tire as described in any combination of the present inventions (1) to (14), wherein the tread portion is multi-layered by providing a base rubber layer inside the crown rubber layer, and the thickness of the tread portion is 13 mm or less; and

[0318] The loss tangent (30°C tanδ) of the base rubber layer measured in a tensile deformation mode under the conditions of temperature 30°C, frequency 10 Hz, initial strain 5% and dynamic strain rate 1% is smaller than 30°C tanδ of the crown rubber layer.

Claims

1. A tire having a tread portion, wherein: a cap rubber layer forming the tread portion containing 60 parts by mass or more and 80 parts by mass or less of styrene-butadiene rubber (SBR) having a styrene content of 25% by mass or less per 100 parts by mass of the rubber component, and containing 100 parts by mass or more of silica relative to 100 parts by mass of the rubber component; and The crown rubber layer is formed of a rubber composition having a loss tangent (30°C tanδ) less than 0.27 measured in a tensile deformation mode under the conditions of a temperature of 30°C, a frequency of 10 Hz, an initial strain of 5% and a dynamic strain rate of 1%; and The thickness of the tread portion is 13 mm or less.

2. The tire according to claim 1, wherein: The styrene content in the styrene-butadiene rubber (SBR) is 20% by mass or less.

3. The tire according to claim 2, wherein: The styrene content in the styrene-butadiene rubber (SBR) is 15% by mass or less.

4. The tire according to any one of claims 1 to 3, wherein: The content of the silica is 110 parts by mass or more relative to 100 parts by mass of the rubber component.

5. The tire according to any one of claims 1 to 4, wherein: The 30°C tanδ is 0.21 or less.

6. The tire according to any one of claims 1 to 5, wherein: The tread portion has a thickness of 7 mm or less.

7. The tire according to any one of claims 1 to 6, wherein: The loss tangent (0°C tanδ) of the crown rubber layer measured in a tensile deformation mode under the conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 5% and a dynamic strain rate of 1% and the 30°C tanδ of the crown rubber layer satisfy the following formula (1): 0℃tanδ≦-7×30℃tanδ+2.5(1).

8. The tire according to any one of claims 1 to 7, wherein: The tread portion is multi-layered by providing a base rubber layer inside the cap rubber layer, and the thickness of the cap rubber layer accounts for more than 70% of the entire tread portion.

9. The tire according to any one of claims 1 to 8, wherein: The particle size (average primary particle size) of the silica is 17 nm or less.

10. The tire according to any one of claims 1 to 9, wherein: The cap rubber layer includes a resin component selected from the group consisting of rosin-based resins, styrene-based resins, coumarone-based resins, terpene-based resins, C5 resins, C9 resins, C5C9 resins, and acrylic resins.

11. The tire according to any one of claims 1 to 10, wherein: The acetone extract (AE) of the tread cap rubber layer is 21% by mass or more.

12. The tire according to any one of claims 1 to 11, wherein: The ground contact ratio of the tread portion is 63% or more.

13. The tire according to any one of claims 1 to 12, wherein: The product of the content (parts by mass) of styrene-butadiene rubber (SBR) having a styrene content of 25% by mass or less in 100 parts by mass of the rubber component in the cap rubber layer and the ground contact ratio (%) of the tread portion (SBR content×ground contact ratio) is 7200 or less.

14. The tire according to any one of claims 1 to 13, wherein: The product of the silica content (parts by mass) of the cap rubber layer relative to 100 parts by mass of the rubber component and the aspect ratio (%) of the tire is 11000 or less.

15. The tire according to any one of claims 1 to 14, wherein: The tread portion is multi-layered by providing a base rubber layer inside the crown rubber layer, and the thickness of the tread portion is 13 mm or less; and The loss tangent (30°C tanδ) of the base rubber layer measured in a tensile deformation mode under the conditions of temperature 30°C, frequency 10 Hz, initial strain 5% and dynamic strain rate 1% is smaller than 30°C tanδ of the crown rubber layer.

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