Tire for heavy load

Abstract

To provide a tire 2 for a heavy load that can suppress wet performance from deteriorating due to abrasion, while reducing rolling resistance.SOLUTION: A tire 2 comprises a tread 4 constituted of rubber compositions including rubber constituents including styrene-butadiene rubber and filler including silica. The tread 4 has a plurality of circumferential main grooves 10. The plurality of circumferential main grooves 10 constitute a pair of crown land parts 20, in the tread 4. The crown land part 20 has a crown narrow groove 24. A crown narrow land part 34 constituted of the crown narrow groove 24 has crown sipes 40. Contents CSB of the styrene-butadiene rubber, contents BS of the silica, a groove depth DGs of the crown sipe 40, and a grown depth DGg of the crown narrow groove 24 satisfy the following relational expression of (CSB+BS) / (DGg-DGs)≥5.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heavy-duty tire.

Background Art

[0002] In tires, from the viewpoints of environmental consideration and safety, reduction of rolling resistance and improvement of running performance on a wet road surface (hereinafter referred to as wet performance) are required. For example, in Patent Document 1, by providing ridge portions protruding in opposite directions from adjacent land portions sandwiching a circumferential groove, reduction of rolling resistance is achieved. An outer groove space is provided on the outer peripheral side of the ridge portion, an inner groove space is provided on the inner peripheral side, and a communication recess for communicating the two is provided, thereby improving wet performance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a heavy-duty tire that can suppress a decrease in wet performance due to wear while reducing rolling resistance.

Means for Solving the Problems

[0005] The heavy-duty tire according to one aspect of the present invention includes a tread composed of a rubber composition containing a rubber component including styrene-butadiene rubber and a filler including silica, and the tread has a tread surface that contacts the road surface. The tread has a plurality of circumferential main grooves extending continuously in the circumferential direction. The plurality of circumferential main grooves include a crown circumferential main groove located on the equatorial plane and a pair of shoulder circumferential main grooves located on the outermost side in the axial direction. The plurality of circumferential main grooves form a plurality of land portions on the tread. The plurality of land portions include a pair of crown land portions closest to the equatorial plane and a pair of shoulder land portions including the ends of the tread surface. Each of the crown land portions has crown fine grooves extending continuously in the circumferential direction. The crown fine grooves form two crown fine land portions on the crown land portion. Each of the crown fine land portions has a crown sipe that crosses the crown fine land portion. The crown fine grooves include a carcass main body and an enlarged portion located radially inside the carcass main body. Due to the deformation of the tread, the opposing wall surfaces of the carcass main body contact each other. The groove width of the enlarged portion is wider than the groove width of the carcass main body. The groove depth DGs of the crown sipe is shallower than the groove depth DGg of the crown fine grooves. The content CSB of the styrene-butadiene rubber in 100 parts by mass of the rubber component is 10 parts by mass or more. The content BS of the silica with respect to 100 parts by mass of the rubber component is 15 parts by mass or more. The content CSB of the styrene-butadiene rubber, the content BS of the silica, the groove depth DGs (mm) of the crown sipe, and the groove depth DGg (mm) of the crown fine grooves satisfy the following relational expression. (CSB + BS) / (DGg - DGs) ≥ 5

Effect of the Invention

[0006] The present invention can provide a heavy-duty tire that can suppress a decrease in wet performance due to wear while reducing rolling resistance.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

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Figure 9

Mode for Carrying Out the Invention

[0008] The tire of the present invention is assembled to a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire assembled to the rim is also called a tire-rim assembly. The tire-rim assembly includes a rim and a tire assembled to this rim.

[0009] In the present invention, a state where the tire is assembled to a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to this tire is referred to as a standard state.

[0010] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the standard state. The dimensions and angles of each part in the meridian cross-section of the tire that cannot be measured in the state where the tire is assembled to the standard rim are measured on the cut surface of the tire obtained by cutting the tire along a plane including the rotation axis. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in the tire assembled to the standard rim. Note that the configuration of the tire that cannot be confirmed in the state where the tire is assembled to the standard rim is confirmed on the aforementioned cut surface.

[0011] The standard rim means the rim defined in the standard on which the tire depends. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are standard rims.

[0012] The standard internal pressure means the internal pressure defined in the standard on which the tire depends. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are standard internal pressures.

[0013] The standard load means the load defined in the standard on which the tire depends. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are standard loads.

[0014] In the present invention, the tread portion of the tire is the portion of the tire that contacts the road surface. The bead portion is the portion of the tire that is fitted to the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. The tire includes, as parts, a tread portion, a pair of bead portions, and a pair of sidewall portions. The central portion of the tread portion is also called the crown portion. The end portion of the tread portion is also called the shoulder portion.

[0015] [Findings on which the present invention is based] The fine grooves that allow the wall surfaces to support each other due to the deformation of the tread can effectively suppress the deformation of the tread. There is a prospect that these fine grooves can contribute to the reduction of rolling resistance. However, since the rigidity of the tread seemingly increases, there is a concern that the wet performance will deteriorate. Therefore, by providing sipes, the deterioration of wet performance is suppressed. By providing such fine grooves and sipes, it is expected that the tire can reduce rolling resistance while suppressing a decrease in wet performance at the initial stage of wear. The tread wears. As a result, the volume of the grooves cut in the tread decreases. When the groove volume decreases, the drainage performance deteriorates. Therefore, there is a concern that the wet performance deteriorates as the tread wears. Therefore, in order for the fine grooves to contribute to suppressing a decrease in wet performance in the middle stage of wear, the radially inner portion of the fine grooves is configured by an enlarged portion with an enlarged groove width, in other words, adopting a fine groove having a flask-like cross-sectional shape has been considered. As the tread wears, its volume decreases. Therefore, the rigidity of the tread appears to increase. The increase in rigidity works favorably for rolling resistance but unfavorably for wet performance. Therefore, in the later stage of wear where the sipes disappear, there is a risk that the decrease in wet performance cannot be suppressed only by the exposed enlarged portion. Therefore, the inventors focused on the amounts of styrene-butadiene rubber and silica contained in the rubber composition constituting the tread (specifically, the cap portion), and the depths of the fine grooves and sipes, and have conducted studies to complete the invention described below.

[0016] [Details of Embodiments of the Present Invention] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0017] The present invention relates to a tire having a tread composed of a rubber composition containing a rubber component including a styrene-butadiene rubber and a filler including silica, the tread having a tread surface that comes into contact with a road surface, the tread having a plurality of circumferential main grooves extending continuously in a circumferential direction, the plurality of circumferential main grooves including a crown circumferential main groove located on an equatorial plane and a pair of shoulder circumferential main grooves located on the axially outermost sides, the plurality of circumferential main grooves constituting a plurality of land portions in the tread, the plurality of land portions including a pair of crown land portions closest to the equatorial plane and a pair of shoulder land portions including ends of the tread surface, each of the crown land portions having a crown narrow groove extending continuously in the circumferential direction, the crown narrow groove constituting two crown narrow land portions in the crown land portion, each of the crown narrow land portions being a groove depth DGs of the crown narrow groove is shallower than a groove depth DGg of the crown narrow groove; a styrene-butadiene rubber content CSB in 100 parts by mass of the rubber component is 10 parts by mass or more; a silica content BS relative to 100 parts by mass of the rubber component is 15 parts by mass or more; and the styrene-butadiene rubber content CSB and the silica content BS, as well as the groove depth DGs of the crown sipes and the groove depth DGg of the crown narrow groove satisfy the following relational expression: (CSB+BS) / (DGg-DGs)≧5

[0018] The tread of a tire wears with use. The tire of the present invention can suppress the deterioration of wet performance due to wear while reducing rolling resistance not only in the early stage of wear but also in the later stage of wear when the crown sipes disappear. The mechanism by which such an effect is achieved has not been clarified, but is presumed to be as follows.

[0019] When the tread surface comes into contact with the road surface, the tread deforms. Due to this deformation, the wall surfaces of the crown grooves come into contact with each other in the carcass body. The crown land portions located on both sides of the crown grooves support each other. The deformation of the crown land is suppressed. The carcass body can contribute to reducing the rolling resistance. The rigidity of the crown land seemingly increases. There is concern about a decrease in wet performance. However, the crown sipe suppresses the decrease in wet performance. In the initial stage of wear, it is presumed that in this way, the tire can suppress the decrease in wet performance due to wear while reducing the rolling resistance. As the wear of the tread progresses, the groove volume such as the circumferential main groove decreases. There is concern about a decrease in wet performance. However, on the radially inner side of the carcass body, there is an enlarged portion having a groove width wider than the groove width of the carcass body. When the carcass body disappears, the enlarged portion is exposed. The enlarged portion can contribute to suppressing the decrease in wet performance. The volume of the tread decreases due to wear. Since the deformation allowance of the tread becomes smaller, the rigidity of the tread seemingly increases. The increase in rigidity can contribute to reducing the rolling resistance. In the middle stage of wear, it is presumed that in this way, the tire can suppress the decrease in wet performance due to wear while reducing the rolling resistance. As the wear of the tread further progresses, the volume of the tread further decreases. The rigidity of the tread seemingly further increases. The increase in rigidity works favorably for the rolling resistance but unfavorably for the wet performance. In the late stage of wear when the crown sipe disappears, although the enlarged portion remains, there is a risk that the tire may not be able to suppress the decrease in wet performance. However, the rubber composition constituting the tread of this tire contains styrene-butadiene rubber and silica. As the glass transition temperature (Tg) of the rubber component increases, the road surface followability in the micro-deformation region improves. Regardless of the wear stage, the tread can contribute to the improvement of wet performance. In particular, since the content of styrene-butadiene rubber, the content of silica, and the respective groove depths of the crown fine grooves and the crown sipe are set to satisfy the above-mentioned relational expressions, even in the later stage of wear, due to the synergistic effect of styrene-butadiene rubber and silica, the decrease in wet performance is suppressed. This tire can suppress the decrease in wet performance while maintaining low rolling resistance from the start of use until replacement becomes necessary. According to the present invention, a tire can be obtained that suppresses the decrease in wet performance due to wear while reducing rolling resistance.

[0020] The rubber component further contains natural rubber and butadiene rubber, and it is preferable that the content CSB of the styrene-butadiene rubber, the content CN of the natural rubber, and the content CB of the butadiene rubber in 100 parts by mass of the rubber component satisfy the following relational expression. CN≧CSB+CB

[0021] By further containing natural rubber (hereinafter, NR) and butadiene rubber (hereinafter, BR) in the rubber component so as to satisfy the above-mentioned relational expression, it is presumed that the dispersibility of silica in the rubber composition is enhanced while maintaining the durability of the tread. In this case, it is presumed that this tire can suppress the decrease in wet performance due to wear while reducing rolling resistance.

[0022] The content CS of the silica in 100 parts by mass of the filler is preferably 40 parts by mass or more. This is because the tread can further enhance the road surface followability in the micro-deformation region, and the tire can improve the wet performance regardless of the wear stage.

[0023] The silica preferably includes silica made from biomass materials. This is because such silica can contribute to the reduction of environmental load.

[0024] The filler preferably contains silica with an average primary particle diameter of 16 nm or less. This is because such silica can contribute to the improvement of abrasion resistance and durability.

[0025] The filler further contains carbon black, and preferably the carbon black contains recycled carbon black. Recycled carbon black can contribute to the reduction of environmental load, and there is a possibility that it can reduce the friction between its surface and the rubber molecular chain and suppress heat generation.

[0026] The filler further contains carbon black, and preferably the carbon black contains carbon black with an average primary particle diameter of 19 nm or less. This is because such carbon black can contribute to the improvement of abrasion resistance and durability.

[0027] The rubber composition preferably further contains a resin component. This is because the resin component can contribute to the improvement of wet performance.

[0028] The land ratio defined below is preferably 80% or more. In this case, the land portions can easily support each other, and the rigidity of the tread can be effectively increased. The tire can effectively reduce rolling resistance and can also improve abrasion resistance. In particular, when the filler contains silica, there is a concern that the rigidity of the tread may decrease compared to the case where the entire amount of the filler is composed of carbon black. However, by setting the land ratio to 80% or more, the tread can maintain the required rigidity. Land ratio: The ratio of the total area value of the contact surfaces of a plurality of land portions included in the contact surface to the area value of the entire contact surface, obtained by mounting the tire on a standard rim, adjusting the internal pressure to the standard internal pressure, applying a load of 100% of the standard load with a camber angle of 0 degrees, and grounding the tire on a flat road surface.

[0029] The crown sipe preferably extends in a zigzag pattern in its longitudinal and depth directions. This way, when the tread deforms and the walls of the crown sipe come into close contact with each other, the walls restrain each other, effectively increasing the rigidity of the tread. The tire can effectively reduce rolling resistance and also improve wear resistance. Also in this case, especially when the filler contains silica, there is a concern that the rigidity of the tread may decrease compared to the case where the entire amount of the filler is composed of carbon black. However, by forming the crown sipe as a three-dimensional sipe that extends in a zigzag pattern in its longitudinal and depth directions, the tread can maintain the required level of rigidity.

[0030] The crown groove includes an inner crown groove close to the equatorial plane, an outer crown groove close to the edge of the tread surface, and a connecting crown groove connecting the inner crown groove and the outer crown groove. It is preferable that the inner crown groove and the outer crown groove are alternately arranged in the circumferential direction. As described above, when a force acts on the tread and the tread deforms, the walls of the crown groove come into contact with each other in the body part. Since the crown groove extends in the circumferential direction while meandering, the walls effectively mesh with each other. The crown land parts located on both sides of the crown groove restrain each other. The apparent rigidity of the crown land part increases. The deformation of the crown land part is effectively suppressed. The tire can effectively reduce rolling resistance and also improve wear resistance. Also in this case, especially when the filler contains silica, there is a concern that the rigidity of the tread may decrease compared to the case where the entire amount of the filler is composed of carbon black. However, by forming the crown groove with an inner crown groove, an outer crown groove, and a connecting crown groove, and arranging the inner crown groove and the outer crown groove alternately in the circumferential direction, the tread can maintain the required level of rigidity.

[0031] Thus, the heavy-duty tire of the present invention can suppress a decrease in wet performance due to wear while reducing rolling resistance.

[0032] [Rubber composition] The tread is composed of a rubber composition. The tread is a cross-linked product of the rubber composition. The rubber composition for this tread is described below. The rubber composition includes a rubber component and a filler.

[0033] [Rubber component] The rubber component includes styrene-butadiene rubber (hereinafter referred to as SBR). The rubber component may include SBR and further other rubber components, or may consist only of SBR.

[0034] [SBR] There is no particular limitation on SBR, and examples include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), modified SBRs of these (modified S-SBR, modified E-SBR), etc. Examples of modified SBR include SBR with modified terminals and / or main chains, modified SBR coupled with tin, silicon compounds, etc. (condensates, those having a branched structure, etc.). Among these, the SBR contained in the rubber component is preferably S-SBR and modified SBR. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) etc. can also be used as SBR in this rubber composition. One type is selected from these SBRs and may be used alone, or two or more types are selected and used in combination.

[0035] SBR is excellent in viscoelastic properties in a region highly correlated with wet performance (specifically, grip performance on a wet road surface), and is excellent in compatibility and reactivity with silica described later. SBR is considered to be able to contribute to the improvement of wet performance and abrasion resistance.

[0036] From the viewpoint of contributing to the improvement of wet performance and abrasion resistance, the styrene content of SBR is preferably 5% by mass or more, more preferably 7% by mass or more, still more preferably 9% by mass or more. The styrene content of SBR is preferably 24% by mass or less, more preferably 18% by mass or less, still more preferably 16% by mass or less. The styrene content of SBR is 1 Calculated by 1H-NMR measurement.

[0037] The vinyl content of the SBR is 26 mol% or more. If the vinyl content is less than 26 mol%, it is difficult to improve the wet performance and abrasion resistance to the extent required for tire performance. This vinyl content is preferably 27 mol% or more, more preferably 28 mol% or more, still more preferably 29 mol% or more, and particularly preferably 30 mol% or more. The vinyl content of the SBR is preferably 45 mol% or less, more preferably 44 mol% or less, still more preferably 43 mol% or less, and particularly preferably 42 mol% or less. The vinyl content (amount of 1,2-bonded butadiene units) of the SBR is measured by infrared absorption spectroscopy.

[0038] From the viewpoint of improving wet performance, the glass transition temperature (Tg) of the SBR is preferably -80°C or higher, more preferably -70°C or higher, and still more preferably -65°C or higher. From the viewpoint of reducing rolling resistance, the Tg of the SBR is preferably -40°C or lower, more preferably -45°C or lower, still more preferably -50°C or lower, and particularly preferably -55°C or lower. The Tg of the SBR is determined by performing differential scanning calorimetry (DSC) in accordance with JIS K7121 on the "pure SBR content" obtained by removing the extender oil using acetone in accordance with JIS K6229.

[0039] From the viewpoint of improving abrasion resistance, the weight average molecular weight (Mw) of the SBR is preferably 100,000 or more, more preferably 150,000 or more, and still more preferably 190,000 or more. From the viewpoints of crosslinking uniformity, etc., the Mw of the SBR is preferably 2.5 million or less, more preferably 2 million or less, and still more preferably 1 million or less. The Mw of the SBR can be determined by standard polystyrene conversion based on the measured values by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0040] As described above, the content CSB of SBR in 100 parts by mass of the rubber component is 10 parts by mass or more. SBR can effectively contribute to the improvement of abrasion resistance and wet performance. From this perspective, the content CSB is preferably 15 parts by mass or more, more preferably 17 parts by mass or more, and still more preferably 19 parts by mass or more. From the perspective of maintaining good abrasion resistance, the content CSB is preferably 60 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 25 parts by mass or less.

[0041] As described above, the rubber component can include other rubber components other than SBR. As other rubber components other than SBR, crosslinkable rubber components generally used in the tire industry can be used. Examples of such rubber components include isoprene rubber, butadiene rubber (BR), styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene-propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, etc. One of these other rubber components can be selected and used alone, or two or more can be selected and used in combination.

[0042] The rubber component of the rubber composition for the tread preferably includes isoprene rubber and BR as rubber components other than SBR.

[0043] [Isoprene rubber] Examples of isoprene rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, denatured NR, denatured IR, etc. As NR, for example, those commonly used in the tire industry such as SIR20, RSS#3, TSR20, etc. can be used. As IR, although not particularly limited, for example, those commonly used in the tire industry such as IR2200, etc. can be used. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc. Examples of denatured NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Examples of denatured IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These may be used alone or in combination of two or more. Among these, NR is preferred. The rubber component of the rubber composition for the tread preferably contains NR and BR as rubber components other than SBR.

[0044] When the rubber component contains NR, from the viewpoint of increasing the strength of the tread and improving the abrasion resistance, the content CN of NR in 100 parts by mass of the rubber component is preferably 30 parts by mass or more, more preferably 45 parts by mass or more, still more preferably 55 parts by mass or more. This content CN is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, still more preferably 65 parts by mass or less.

[0045] [Butadiene Rubber] The butadiene rubber (BR) is not particularly limited. For example, BR with a cis content of less than 50% by mass (low-cis BR), BR with a cis content of 90% by mass or more (high-cis BR), rare-earth-based butadiene rubber synthesized using a rare-earth element-based catalyst (rare-earth-based BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc., which are common in the tire industry, can be used. These may be used alone or in combination of two or more. The cis content of BR is a value calculated by infrared absorption spectrum analysis.

[0046] When the rubber component contains BR, from the viewpoint of improving abrasion resistance, the content CB of BR in 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 15 parts by mass or more. The content CB of BR is preferably 40 parts by mass or less, more preferably 25 parts by mass or less.

[0047] When the rubber component further contains NR and BR in addition to SBR, as described above, the content CN of NR is preferably the same as the total of the content CSB of SBR and the content CB of BR, or more than the total of the content CSB of SBR and the content CB of BR. This is because the dispersibility of silica in the rubber composition can be enhanced while maintaining the durability of the tread. In this case, it is presumed that the tire can suppress the deterioration of wet performance due to wear while reducing rolling resistance. From this viewpoint, it is more preferable that the content CN of NR is more than the total of the content CSB of SBR and the content CB of BR. In other words, it is more preferable that the content CN of NR, the content CSB of SBR, and the content CB of BR satisfy the following relational expression. CN>CSB+CB

[0048] [Filler] As described above, the rubber composition for the tread contains a filler, and this filler contains silica. In other words, this rubber composition contains silica as a filler. More preferably, the filler contains carbon black and silica, and it may contain only carbon black and silica. In other words, it is more preferable that the rubber composition contains carbon black and silica as fillers, and it may be a filler consisting of only carbon black and silica.

[0049] [Silica] The silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., which are common in the tire industry, can be used. Further, from the perspective of environmental load, as described above, silica made from biomass materials (for example, amorphous silica refined from rice husks) may be used. Among them, hydrous silica prepared by a wet method is preferred because it has many silanol groups. These silicas may be used alone or in combination of two or more.

[0050] Silica made from biomass materials can be obtained, for example, by extracting silicate from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and reacting the silicate with sulfuric acid in the same manner as conventional wet silica to precipitate silicon dioxide, followed by filtration, washing with water, drying, and pulverization. Note that when silica crystallizes, it does not dissolve in water and the silicic acid that is its component cannot be utilized. By controlling the combustion temperature and combustion time, the crystallization of silica in rice husk ash is suppressed (see, for example, Japanese Patent Application Laid-Open No. 2009-2594, Akita Prefectural University Web Journal B / 2019, vol. 6, p. 216-222, etc.). And the amorphous silica extracted from rice husks may be commercially available from companies such as Wilmar.

[0051] From the perspective of improving abrasion resistance and durability, the average primary particle size of the silica is preferably 22 nm or less, more preferably 19 nm or less, and even more preferably 16 nm or less. This average primary particle size is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more.

[0052] The average primary particle size of the silica can be determined by observing the silica with a transmission or scanning electron microscope, measuring the outer diameters of 400 or more primary particles of the silica observed in the field of view, and taking the average.

[0053] From the perspective of improving abrasion resistance and durability, the nitrogen adsorption specific surface area (N2SA) of the silica is preferably 100 m 2 / g or more, preferably 110 m2 More preferably, it is 120 m 2 / g or more, and even more preferably 120 m 2 / g or more. This nitrogen adsorption specific surface area is preferably 500 m 2 / g or less, more preferably 350 m 2 / g or less, and even more preferably 250 m The nitrogen adsorption specific surface area (N2SA) of silica is measured by the BET method in accordance with ASTM D3037-93.

[0054] The content BS of silica with respect to 100 parts by mass of the rubber component is 15 parts by mass or more. Silica can effectively reinforce the tread. Since the rigidity of the tread increases, the abrasion resistance and durability are improved. From this viewpoint, the content BS of silica is preferably 17 parts by mass or more, more preferably 19 parts by mass or more, and even more preferably 20 parts by mass or more. From the viewpoint of obtaining flexibility and relaxing stress, the content BS of silica is preferably 70 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 35 parts by mass or less.

[0055] [Carbon black] The carbon black is not particularly limited. For example, those commonly used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. Further, from the viewpoint of reducing the environmental load and reducing the friction between the carbon black surface and the rubber molecular chain and suppressing the heat generation property, this tire can also use recycled carbon black (rCB) obtained from the thermal decomposition of used tires. These carbon blacks may be used alone or in combination of two or more. In the present invention, for the purpose of distinguishing from recycled carbon black (rCB), the above-mentioned carbon black commonly used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF is also called standard carbon black (sCB).

[0056] Recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires as described above. For example, European Patent Application Publication No. 3427975 refers to "Rubber Chemistry and Technology", Vol. 85, No. 3, pages 408 - 449 (2012), particularly pages 438, 440, 442, and describes that it can be obtained by pyrolysis of organic materials at 550 - 800 °C with oxygen excluded or by vacuum pyrolysis at relatively low temperatures (

[0027] ). The carbon black obtained from such a pyrolysis process usually lacks functional groups on its surface, as mentioned in

[0004] of Patent No. 6856781 (Comparison of the surface morphology and chemistry of pyrolytic carbon black and commercially available carbon black, Powder Technology 160 (2005) 190 - 193).

[0057] Recycled carbon black may lack functional groups on its surface or may be treated to contain functional groups on its surface. The treatment to make the surface of recycled carbon black contain functional groups can be carried out by conventional methods. For example, in European Patent Application Publication No. 3173251, carbon black obtained from a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. Also, in Patent No. 6856781, carbon black obtained from a pyrolysis process is treated with an amino acid compound containing at least one thiol group or disulfide group to obtain carbon black with an activated surface. The recycled carbon black according to this embodiment also includes carbon black treated to contain functional groups on its surface. As the recycled carbon black, those commercially available from Strebl Green Carbon, LDCarbon, etc. can be used.

[0058] From the viewpoint of improving abrasion resistance and durability, the average primary particle diameter of carbon black is preferably 25 nm or less, more preferably 22 nm or less, and even more preferably 19 nm or less. This average primary particle diameter is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more.

[0059] The average primary particle diameter of carbon black can be determined by observing carbon black with a transmission or scanning electron microscope, measuring the outer diameters of 400 or more primary particles of carbon black observed in the field of view, and taking the average.

[0060] From the viewpoint of improving abrasion resistance and durability, the nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 10 m 2 / g or more, more preferably 20 m 2 / g or more, and even more preferably 30 m 2 / g or more. The nitrogen adsorption specific surface area (N2SA) is preferably 250 m 2 / g or less, more preferably 200 m 2 / g or less, and even more preferably 150 m 2 / g or less. The nitrogen adsorption specific surface area (N2SA) of carbon black is measured in accordance with JIS K6217-2:2017.

[0061] When the rubber composition contains carbon black, the content BC of carbon black with respect to 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 25 parts by mass or more from the viewpoints of exerting a reinforcing effect and preventing deterioration by ultraviolet rays. From the viewpoint of the tread obtaining flexibility and being able to relieve stress, it is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less.

[0062] The content of recycled carbon black in 100 parts by mass of carbon black is not particularly limited, and can be, for example, more than 1 part by mass, more than 5 parts by mass, more than 10 parts by mass, more than 20 parts by mass, more than 25 parts by mass, more than 30 parts by mass. From the viewpoint of exerting the reinforcing effect of carbon black, less than 95 parts by mass is preferable, less than 90 parts by mass is more preferable, and less than 85 parts by mass is even more preferable.

[0063] [Other fillers] As fillers other than silica and carbon black, those conventionally generally used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, talc, etc., can be compounded.

[0064] From the viewpoint that the tread can further improve the road surface followability in the micro-deformation region and the tire can improve the wet performance regardless of the wear stage, the content CS of silica in 100 parts by mass of the filler is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more. This content CS is preferably 95 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 65 parts by mass or less.

[0065] From the viewpoint of improving abrasion resistance and durability, the total content of the filler with respect to 100 parts by mass of the rubber component is preferably 45 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 55 parts by mass or more. From the viewpoint that the tread can obtain flexibility and relieve stress, 80 parts by mass or less is preferable, 70 parts by mass or less is more preferable, and 65 parts by mass or less is even more preferable.

[0066] [Silane coupling agent] As described above, the rubber composition contains silica as a filler. It is preferable to use silica in combination with a silane coupling agent. The silane coupling agent is not particularly limited, but in the tire industry, any silane coupling agent conventionally used in combination with silica can be used. Examples of the silane coupling agent include mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, NXT-Z100, NXT-Z45, and NXT manufactured by Momentive; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide and bis(3-triethoxysilylpropyl)tetrasulfide; thioester-based silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane; and the like. Among these, sulfide-based silane coupling agents and / or mercapto-based silane coupling agents are preferable, and sulfide-based silane coupling agents are more preferable. These silane coupling agents may be used alone or in combination of two or more.

[0067] From the perspective of enhancing the dispersibility of silica, the content of the silane coupling agent relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, still more preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more. From the perspective of suppressing the reduction in abrasion resistance, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and still more preferably 10 parts by mass or less.

[0068] From the perspective of enhancing the dispersibility of silica, the content of the silane coupling agent relative to 100 parts by mass of silica is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 8 parts by mass or more. From the perspectives of cost reduction and improvement in processability, it is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and still more preferably 16 parts by mass or less.

[0069] [Other compounding agents] In addition to the above components, the rubber composition according to the present embodiment can appropriately contain compounding agents generally used in the conventional tire industry, such as softeners, waxes, stearic acid, zinc oxide, anti-aging agents, vulcanizing agents, vulcanization accelerators, and the like.

[0070] Examples of the softener include resin components, oils, liquid rubbers, and the like.

[0071] The resin component that can be used in the present embodiment is not particularly limited, but resins commonly used in the tire industry can be used. For example, tackifying resins such as C9-based resins, C5-based resins, C5C9-based resins, dicyclopentadiene-based resins, aromatic vinyl-based resins, coumarone-based resins, indene-based resins, terpene-based resins, rosin-based resins, and phenol-based resins can be mentioned. These resin components may be used alone or in combination of two or more.

[0072] C9 resins refer to resins obtained by polymerizing C9 fractions. It can be a polymer of the C9 fraction alone or a copolymer of the C9 fraction and other components. For example, a resin obtained by copolymerizing dicyclopentadiene (DCPD) and a C9 fraction is called a DCPD / C9 resin. Also, those that are hydrogenated or modified may be used. Examples of C9 fractions include petroleum fractions corresponding to 8 to 10 carbon atoms such as vinyltoluene, alkylstyrene, coumarone, indene, methylindene, and dicyclopentadiene. These C9 resins may be used alone or in combination of two or more.

[0073] C5 resins refer to resins obtained by polymerizing C5 fractions, and those that are hydrogenated or modified may be used. Examples of C5 fractions other than dicyclopentadiene include petroleum fractions corresponding to 4 to 5 carbon atoms such as cyclopentadiene, isoprene, pentane, isopentane, neopentane, pentene, and pentadiene. These C5 resins may be used alone or in combination of two or more.

[0074] C5C9 resins refer to resins obtained by copolymerizing the C5 fraction and the C9 fraction, and those that are hydrogenated or modified may be used. As C5C9 petroleum resins, for example, those commercially available from Tosoh Corporation, LUHUA Co., Ltd., etc. can be used. These C5C9 resins may be used alone or in combination of two or more.

[0075] The dicyclopentadiene-based resin refers to a resin containing cyclopentadiene (CPD) or dicyclopentadiene (DCPD) as a monomer component, which may be hydrogenated or modified. Examples of the dicyclopentadiene-based resin include DCPD / C9 resins containing dicyclopentadiene and the C9 fraction as monomer components (the DCPD / C9 resin may be hydrogenated or modified), and DCPD / C9 resins containing dicyclopentadiene and styrene as monomer components are preferred, and DCPD / C9 resins containing dicyclopentadiene, styrene, and indene as monomer components are particularly preferred. As the dicyclopentadiene-based resin, for example, those commercially available from ExxonMobil, ENEOS Corporation, Nippon Zeon Co., Ltd., Maruzen Petrochemical Co., Ltd., etc. can be used. These dicyclopentadiene-based resins may be used alone or in combination of two or more.

[0076] The aromatic vinyl-based resin refers to a resin containing aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, p-chlorostyrene, etc. as the monomer component with the highest content, which may be hydrogenated or modified. As the aromatic vinyl-based resin, due to economic reasons, easy processing, and excellent heat generation properties, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred. As the aromatic vinyl-based resin, for example, those commercially available from Crayton, Eastman Chemical, Mitsui Chemicals, etc. can be used. These aromatic vinyl-based resins may be used alone or in combination of two or more.

[0077] The coumarone resin refers to a resin containing coumarone as a monomer component, and it may be hydrogenated or modified. Examples of coumarone resins include coumarone-indene resins containing coumarone and indene as monomer components, coumarone-indene-styrene resins containing coumarone, indene, and styrene as monomer components, and the like. These coumarone resins may be used alone or in combination of two or more.

[0078] The indene resin refers to a resin containing indene as a monomer component, and it may be hydrogenated or modified. Examples of indene resins include coumarone-indene resins containing coumarone and indene as monomer components, coumarone-indene-styrene resins containing coumarone, indene, and styrene as monomer components, and the like. These indene resins may be used alone or in combination of two or more.

[0079] The terpene resin refers to a resin containing a terpene compound such as α-pinene, β-pinene, limonene, or dipentene as the monomer component with the highest content, and it may be hydrogenated or modified. Specific examples of terpene resins include, for example, polyterpene resins containing only one or more of the above terpene compounds as monomer components; aromatic-modified terpene resins containing the terpene compound and an aromatic compound as monomer components; terpene phenol resins containing the terpene compound and a phenolic compound as monomer components, and the like. Examples of aromatic compounds that are monomer components of aromatic-modified terpene resins include styrene, α-methylstyrene, vinyltoluene, divinyltoluene, and the like. Examples of phenolic compounds that are monomer components of terpene phenol resins include phenol, bisphenol A, cresol, xylenol, and the like. These terpene resins may be used alone or in combination of two or more.

[0080] The rosin-based resin refers to a resin containing rosin acid compounds such as abietic acid, neoabietic acid, palustric acid, isopimaric acid, etc., and those which are hydrogenated or modified may also be used. The rosin-based resin is not particularly limited, and examples thereof include natural resin rosin, rosin-modified resins obtained by modifying it by hydrogenation, disproportionation, dimerization, esterification, etc. These rosin-based resins may be used alone or in combination of two or more.

[0081] The phenolic resin refers to a resin containing a phenolic compound such as phenol or cresol as the monomer component with the highest content. The phenolic resin is not particularly limited, and examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, oil-modified phenol formaldehyde resin, etc. These phenolic resins may be used alone or in combination of two or more.

[0082] From the viewpoint of wet performance, the softening point of the resin component is preferably 80°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher. From the viewpoints of processability and improvement of the dispersibility of the rubber component and the filler, it is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. The softening point of the resin is the temperature at which the ball drops when measured with a ring and ball softening point measuring device according to the softening point defined in JIS K 6220-1:2015 7.7.

[0083] When the rubber composition contains a resin component, the content of the resin component relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoint of wet performance. From the viewpoint of suppressing heat generation, the content of the resin component is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0084] Examples of the oil include process oil, vegetable oil, animal oil, etc. Examples of the process oil include paraffinic process oil, naphthenic process oil, aromatic process oil, etc. It is also possible to use a process oil with a low content of polycyclic aromatic compounds (PCA) considering the impact on the environment. Examples of the low-PCA-content process oil include mildly extracted solvent solvate (MES), treated distillate aromatic extract (TDAE), heavy naphthenic oil, etc.

[0085] When the rubber composition contains an oil, the content of the oil relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoint of improving processability. From the viewpoint of improving abrasion resistance, the content of the oil is preferably 90 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0086] The liquid rubber is not particularly limited as long as it is a polymer in a liquid state at normal temperature (25°C). Examples thereof include liquid butadiene rubber (liquid BR), liquid styrene-butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene-isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used alone or in combination of two or more.

[0087] When the rubber composition contains a liquid rubber, the content of the liquid rubber relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. The content of the liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

[0088] The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; synthetic waxes such as polymers of ethylene, propylene, etc. As commercially available products, products of Ouchi Shinsei Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

[0089] When the rubber composition contains wax, the content of wax relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and still more preferably 1.5 part by mass or more from the viewpoint of the weather resistance of the rubber. The content of wax is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less from the viewpoint of preventing whitening of the tire due to bloom.

[0090] The anti-aging agent is not particularly limited, and examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, imidazole-based compounds, and anti-aging agents such as metal carbamates. Phenylenediamine-based anti-aging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred. These anti-aging agents may be used alone or in combination of two or more.

[0091] When the rubber composition contains an anti-aging agent, the content of the anti-aging agent relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and still more preferably 1.5 part by mass or more from the viewpoint of the ozone crack resistance of the rubber. The content of the anti-aging agent is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less from the viewpoints of wear resistance performance and wet grip performance.

[0092] As the stearic acid, those conventionally known can be used, and as commercially available products, products of NOF Corporation, Kao Corporation, FUJIFILM Wako Pure Chemical Corporation, Chiba Fatty Acids Co., Ltd. etc. can be used. These may be used alone or two or more of them may be used in combination.

[0093] When the rubber composition contains stearic acid, the content of stearic acid with respect to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and still more preferably 1.5 part by mass or more from the viewpoint of processability. The content of stearic acid is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less from the viewpoint of vulcanization rate.

[0094] As the zinc oxide, those conventionally known can be used, and as commercially available products, products of Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Sho-doh Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd. etc. can be used. These may be used alone or two or more of them may be used in combination.

[0095] When the rubber composition contains zinc oxide, the content of zinc oxide with respect to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and still more preferably 1.5 part by mass or more from the viewpoint of processability. The content of zinc oxide is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less from the viewpoint of abrasion resistance performance.

[0096] Sulfur is preferably used as the vulcanizing agent. As the sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly-dispersed sulfur etc. can be used.

[0097] When the rubber composition contains sulfur as a vulcanizing agent, from the viewpoint of ensuring a sufficient vulcanization reaction, the sulfur content per 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and even more preferably 1.0 part by mass or more. From the viewpoint of preventing deterioration, the sulfur content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.5 parts by mass or less. In addition, when using oil-containing sulfur as the vulcanizing agent, the content of the vulcanizing agent is represented by the amount of pure sulfur contained in the oil-containing sulfur.

[0098] Examples of vulcanizing agents other than sulfur include alkylphenol sulfur chloride condensates, sodium 1,6-hexamethylenedithiolsulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, and the like. As these vulcanizing agents other than sulfur, commercially available products from companies such as Taoka Chemical Co., Ltd., Rancess Co., Ltd., and Flexsys can be used.

[0099] Examples of vulcanization accelerators include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, or xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among these, from the viewpoint of more suitably obtaining the desired effect, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are preferred, and sulfenamide-based vulcanization accelerators are more preferred.

[0100] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), and the like. Among these, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS) and N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) are preferred.

[0101] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, and the like. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0102] Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyldisulfide, and the like. Among these, 2-mercaptobenzothiazole is preferred.

[0103] When the rubber composition contains a vulcanization accelerator, the content of the vulcanization accelerator relative to 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 1.5 part by mass or more, and still more preferably 2.0 part by mass or more. The content of the vulcanization accelerator is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, still more preferably 6.0 parts by mass or less, and particularly preferably 5.0 parts by mass or less. By setting the content of the vulcanization accelerator within such a range, it tends to be possible to ensure the breaking strength and elongation.

[0104] The rubber composition is produced, for example, by kneading the above-mentioned respective components using a rubber kneading apparatus such as an open roll or a Banbury mixer. As the kneading conditions, in the base kneading step of kneading additives other than the vulcanizing agent and the vulcanization accelerator, the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finishing kneading step of kneading the vulcanizing agent and the vulcanization accelerator, the kneading temperature is usually 120°C or lower, preferably 85 to 110°C.

[0105] The manufactured rubber composition is processed into a predetermined shape using an extruder or the like. In a molding machine, a green tire (a tire in an unvulcanized state) is prepared in combination with a sidewall or the like. By vulcanizing the green tire in a mold incorporated in a vulcanizer, a tire is obtained. The tire is a crosslinked product of the green tire. The vulcanization temperature is usually 140 to 190 °C, preferably 150 to 185 °C. The vulcanization time is usually 5 to 15 minutes.

[0106] The rubber composition described above is used for the tread of a tire (specifically, the cap portion that contacts the road surface during driving). Next, a tire having a tread formed using this rubber composition will be described.

[0107] [Tire] FIG. 1 is a plan view showing a part of the tread 4 of a tire 2 according to an embodiment of the present invention. This tire 2 is mounted on a vehicle such as a truck or a bus. This tire 2 is a heavy-duty tire. In FIG. 1, the direction indicated by the double-headed arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis of the tire 2. The direction indicated by the double-headed arrow CD is the circumferential direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the radial direction of the tire 2. The one-dot chain line CL extending in the circumferential direction in FIG. 1 represents the equatorial plane of the tire 2. In FIG. 1, the side indicated by the arrow CD1 is the first circumferential direction side of the tire 2, and the side indicated by the arrow CD2 is the second circumferential direction side of the tire 2.

[0108] FIG. 1 shows the tread pattern formed on the tread 4. Taking the tread pattern shown in FIG. 1 as an example, the tread pattern of the present invention will be described below. In the present invention, the internal structure of the tire 2 is not particularly limited. Although not described in detail, this tire 2 has a general internal structure as the internal structure of a heavy-duty tire.

[0109] The tread 4 is located on the radially outer side of the tire 2 and extends in the circumferential direction. The outer peripheral surface of the tread 4 is the tread surface 6. The tire 2 contacts the road surface at the tread surface 6. The tread 4 has the tread surface 6 that contacts the road surface. The tread 4 is made of crosslinked rubber. The tread 4 is a crosslinked product of the rubber composition described above. Grooves 8 are engraved in the tread 4. Thereby, a tread pattern is constituted.

[0110] The intersection of the tread surface 6 and the equatorial plane is the equator. As shown in FIG. 1, when the groove 8 is located on the equatorial plane, the equator is specified based on the virtual outer surface obtained by assuming that there is no groove 8 on the equatorial plane.

[0111] The two-dot chain line indicated by the symbol TE represents the end of the tread surface 6. In the tire, when the end of the tread surface is indistinguishable in appearance, a normal load is applied to the tire in the normal state, the camber angle is set to 0°, and the tire is brought into contact with a plane. The position on the outer surface of the tire corresponding to the axially outer end of the contact surface obtained is used as the end of the tread surface.

[0112] In the tread surface 6 shown in FIG. 1, the end TE (not shown) of the tread surface 6 located on the left side of the equatorial plane is the first end TE1. The end TE located on the right side of the equatorial plane is the second end TE2.

[0113] The length indicated by the symbol TW in FIG. 1 is the width of the tread surface 6. The width TW of the tread surface 6 is the axial distance from the first end TE1 to the second end TE2 of the tread surface 6. The width TW of the tread surface 6 is represented by the length measured along the tread surface 6.

[0114] FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1. FIG. 2 shows the cross section of the groove 8, specifically, the center circumferential main groove described later. Based on FIG. 2, the main configuration of the groove 8 is described. In FIG. 2, the direction indicated by the double arrow RD is the radial direction of the tire 2. The side indicated by the arrow RD1 is the outer side in the radial direction of the tire 2, and the side indicated by the arrow RD2 is the inner side in the radial direction of the tire 2. In the present invention, the cross section of the groove 8 is represented by a cross section along a plane perpendicular to the length direction of the groove 8.

[0115] The groove 8 has a pair of wall surfaces 8W including the groove opening 8M and a bottom surface 8B including the groove bottom 8T. The groove width of the groove 8 is represented by the distance between the first wall surface 8W and the second wall surface 8W, which are a pair of wall surfaces 8W, that is, the distance between the wall surfaces. In FIG. 2, the length indicated by the double arrow WG is the groove width of the groove 8 at the groove opening 8M. The groove width WG is represented by the shortest distance between a pair of edges 8E constituting the groove opening 8M. When the portion of the groove opening 8M of the groove 8 is processed in a tapered manner, the groove width at the groove opening 8M of the groove 8 is represented based on a virtual edge obtained by assuming that it is not processed in a tapered manner. The length indicated by the double arrow DG is the groove depth of the groove 8. The groove depth DG of the groove 8 is represented by the shortest distance from the line segment connecting the left and right edges 8E to the groove bottom 8T of the groove 8. The position of the groove 8, the groove width WG, and the groove depth DG are appropriately determined according to the specifications of the tire 2.

[0116] The groove bottom 8T is the deepest position in the cross section of the groove 8. Along the normal line of the line segment connecting the left and right edges 8E constituting the groove opening 8M, the distance from this line segment to the bottom surface 8B is measured. The position where the distance from this line segment to the bottom surface 8B is the maximum is the groove bottom 8T. The bottom surface 8B shown in FIG. 2 is a curved surface. The bottom surface 8B may include a plane, and this plane may include the groove bottom 8T. In this case, the width center of the plane is used as the groove bottom 8T.

[0117] A groove 8 having a groove width WG of less than 1.0 mm at the groove opening 8M is also called a sipe. Grooves 8 other than sipes are also called normal grooves and have a groove width WG of 1.0 mm or more at their groove openings 8M. The sipe may include a portion having a groove width of 1.0 mm or more between the groove opening 8M and the groove bottom 8T (hereinafter referred to as a portion corresponding to a normal groove). In this case, as the tread 4 wears and the portion corresponding to the normal groove is exposed, the sipe switches to a normal groove. The normal groove may include a portion having a groove width of less than 1.0 mm (a portion corresponding to a sipe) between the groove opening 8M and the groove bottom 8T. In this case, as the tread 4 wears and the portion corresponding to the sipe is exposed, the normal groove switches to a sipe. Even a normal groove that has a narrow groove width and whose pair of wall surfaces can contact each other when the tire contacts the road surface is also called a narrow groove. A normal groove that has a wide groove width and whose pair of wall surfaces do not contact each other even when the tire contacts the road surface is also called a main groove.

[0118] As shown in FIG. 1, a plurality of circumferential main grooves 10 arranged in the axial direction are engraved in the tread 4 of this tire 2. Each circumferential main groove 10 extends continuously in the circumferential direction. The circumferential main groove 10 is the aforementioned main groove. The tread 4 has a plurality of circumferential main grooves 10 arranged in the axial direction and extending continuously in the circumferential direction.

[0119] The groove depth of the circumferential main groove 10 is, for example, 10 mm or more and 21 mm or less. From the viewpoint that the tire 2 can exhibit good wet performance, the groove depth is preferably 13 mm or more and 18 mm or less.

[0120] The tread 4 shown in FIG. 1 has three circumferential main grooves 10 arranged in the axial direction. Among the three circumferential main grooves 10, the circumferential main groove 10 located outermost in the axial direction is the shoulder circumferential main groove 12. The circumferential main groove 10 located on the equatorial plane is the crown circumferential main groove 14. The plurality of circumferential main grooves 10 engraved in this tread 4 include the crown circumferential main groove 14 and a pair of shoulder circumferential main grooves 12. In addition, when a circumferential main groove is further provided between the crown circumferential main groove 14 and the shoulder circumferential main groove 12, this circumferential main groove is also called a middle circumferential main groove.

[0121] In FIG. 1, the length indicated by the double arrow WGc is the groove width at the groove opening of the crown circumferential main groove 14. The length indicated by the double arrow WGh is the groove width at the groove opening of the shoulder circumferential main groove 12.

[0122] The ratio (WGc / TW) of the groove width WGc of the crown circumferential main groove 14 to the width TW of the tread surface 6 exceeds 2.0%. Specifically, the ratio (WGc / TW) is preferably 4.0% or more and 10% or less. As shown in FIG. 1, the groove width WGh of the shoulder circumferential main groove 12 is wider than the groove width WGc of the crown circumferential main groove 14. The ratio (WGh / TW) of the groove width WGh of the shoulder circumferential main groove 12 to the width TW of the tread surface 6 is preferably 5.0% or more and 11% or less.

[0123] As shown in FIG. 1, on the bottom surface of the crown circumferential main groove 14, protrusions 16 protruding from the bottom surface are provided. A plurality of protrusions 16 are arranged at predetermined intervals in the circumferential direction. The protrusions 16 prevent stones from biting into the crown circumferential main groove 14.

[0124] As described above, the tread 4 has a plurality of circumferential main grooves 10. The plurality of circumferential main grooves 10 form a plurality of land portions 18 on the tread 4.

[0125] In the tread 4 shown in FIG. 1, by cutting three circumferential main grooves 10, four land portions 18 are formed. Among the four land portions 18, the land portion 18 closest to the equatorial plane is the crown land portion 20. In other words, the land portions 18 located on both sides of the crown circumferential main groove 14 are the crown land portions 20. The land portion 18 located most outward in the axial direction is the shoulder land portion 22. The shoulder land portion 22 is located outside the axial direction of the shoulder circumferential main groove 12 and includes the end TE of the tread surface 6. The plurality of land portions 18 formed on this tread 4 include a pair of crown land portions 20 and a pair of shoulder land portions 22. In addition, when a land portion is further provided between the crown land portion 20 and the shoulder land portion 22, this land portion is also called a middle land portion.

[0126] In FIG. 1, the length indicated by the double arrow WLS is the maximum width of the shoulder land portion 22. In the shoulder land portion 22 of this tire 2, the ratio (WLS / TW) of the maximum width WLS to the width TW of the tread surface 6 is 15% or more and 25% or less.

[0127] The shoulder land portion 22 has a shoulder lateral groove 62. The shoulder lateral groove 62 crosses the shoulder land portion 22. The shoulder lateral groove 62 is shallower than the crown siping 40 described later. The shoulder lateral groove 62 includes an inner shoulder lateral groove 64 located on the equatorial plane side and an outer shoulder lateral groove 66 located on the end side of the tread surface 6. The shoulder land portion 22 further has shoulder fine grooves 68 extending continuously in the circumferential direction. The shoulder fine grooves 68 intersect the shoulder lateral groove 62 at the boundary between the inner shoulder lateral groove 64 and the outer shoulder lateral groove 66. The shoulder fine grooves 68 are shallower than the crown siping 40 described later.

[0128] FIG. 3 shows a part of the tread surface 6 shown in FIG. 1. FIG. 3 shows the crown land portion 20. Each of the two crown land portions 20 provided on the tread 4 of this tire 2 has crown fine grooves 24 extending continuously in the circumferential direction.

[0129] At least one crown fine groove 24 is engraved in the crown land portion 20. One crown fine groove 24 is engraved in the crown land portion 20 shown in FIG. 3.

[0130] In FIG. 3, the length indicated by the double arrow WLC is the maximum width of the crown land portion 20. In the crown land portion 20 of this tire 2, the ratio (WLC / TW) of the maximum width WLC to the width TW of the tread surface 6 is 17% or more and 27% or less. In FIG. 3, the dashed-dotted line LCM is the center line of the maximum width of the crown land portion 20. The crown fine groove 24 is located on the center line LCM of the maximum width. In other words, the crown fine groove 24 is arranged so as to overlap with this center line LCM of the maximum width in the radial direction.

[0131] Figure 4 is a cross-sectional view of the crown groove 24 along line IV-IV in Figure 3. Figure 4 shows a cross-section of the crown groove 24 along a plane perpendicular to the length direction of the crown groove 24. The crown groove 24 includes a body portion 26 and an enlarged portion 28. The body portion 26 of the crown groove 24 shown in Figure 4 includes a tapered portion 30 and a body portion main body 32. The crown groove 24 is the groove described above. When the tire 2 contacts the road surface and the tread 4 deforms, a pair of opposing wall surfaces 24W of the crown groove 24 contact each other at the body portion main body 32.

[0132] The tapered portion 30 includes the groove opening 24M of the crown groove 24. The tapered portion 30 tapers inward from the groove opening 24M. The contour of the wall surface of the tapered portion 30 shown in Figure 4 is represented by a straight line. This contour may be represented by a curve. The length indicated by the double arrow WT in Figure 4 is the groove width at the groove opening 24M of the tapered portion 30. The groove width WT of the tapered portion 30 is preferably 0.15 times or more and 0.35 times or less of the groove width WGc of the crown circumferential direction main groove 14.

[0133] The body portion main body 32 is located radially inside the tapered portion 30. The body portion main body 32 is continuous with the tapered portion 30. The body portion main body 32 extends straight in the depth direction of the crown groove 24. The contour of the wall surface of the body portion main body 32 is represented by a straight line. The body portion main body 32 has a uniform groove width in the depth direction of the crown groove 24.

[0134] The position indicated by the symbol PU in Figure 4 is the boundary between the tapered portion 30 and the body portion main body 32. The boundary PU is represented by the intersection of the wall surface contour line of the tapered portion 30 and the wall surface contour line of the body portion main body 32. As shown in Figure 4, when the boundary portion between the tapered portion 30 and the body portion main body 32 is rounded, the boundary PU is represented by the intersection of the extension line of the wall surface contour line of the tapered portion 30 and the extension line of the wall surface contour line of the body portion main body 32.

[0135] The tapered portion 30 may not be provided in the crown groove 24. In this case, the body portion 26 is composed of only the body portion main body 32. From the viewpoint that the tire 2 can effectively suppress the concentration of strain on the groove opening 24M of the crown fine groove 24 while securing the groove volume of the crown fine groove 24, as shown in FIG. 4, it is preferable that the crown fine groove 24 is provided with a tapered portion 30.

[0136] In FIG. 4, the length indicated by the double-headed arrow WD is the groove width of the carcass main body 32. The portion of the groove opening 24M of the crown fine groove 24 is processed in a tapered manner. The groove width of the crown fine groove 24 is represented by the groove width at a virtual groove opening obtained by assuming that the tapered portion 30 is not provided. The groove width at this virtual groove opening is equal to the groove width WD of the carcass main body 32.

[0137] The enlarged width portion 28 is located radially inside the carcass 26, specifically, the carcass main body 32. The enlarged width portion 28 is continuous with the carcass main body 32. The enlarged width portion 28 has a groove width wider than the groove width WD of the carcass main body 32. The enlarged width portion 28 includes the groove bottom 24T of the crown fine groove 24.

[0138] In FIG. 4, the position indicated by the reference sign PS is the boundary between the carcass main body 32 and the enlarged width portion 28. As described above, in the cross section of the crown fine groove 24, the wall contour line of the carcass main body 32 is a straight line. In the present invention, the position where the wall contour line of the enlarged width portion 28 converges to the wall contour line of the carcass main body 32 is the boundary PS between the carcass main body 32 and the enlarged width portion 28. Specifically, in the groove width from the carcass main body 32 to the enlarged width portion 28, the position showing a groove width 1.1 times the groove width WD of the carcass main body 32 is represented as the boundary PS between the carcass main body 32 and the enlarged width portion 28.

[0139] In FIG. 4, the length indicated by the double-headed arrow WM is the maximum groove width of the enlarged width portion 28. In FIG. 4, the position indicated by the reference sign PM is the position where the enlarged width portion 28 shows the maximum groove width WM. The enlarged width portion 28 tapers outward from the portion showing the maximum groove width WM. In the portion from the maximum groove width position PM to the boundary PS, the enlarged width portion 28 curves so as to be recessed inward from its outer side. The widened portion 28 tapers inward from the portion indicating the maximum groove width WM. In the portion from the maximum groove width position PM to the groove bottom 24T, the widened portion 28 has a rounded contour. In this portion, the widened portion 28 curves so as to bulge outward from its inner side. In the widened portion 28, the boundary between the portion that curves so as to be recessed inward from its outer side and the portion that curves so as to bulge outward from its inner side is located radially outside the maximum groove width position PM.

[0140] The widened portion 28 includes an inflection portion 82 and a bottom portion 84. The inflection portion 82 is located radially inside the body main body 32. The bottom portion 84 is located radially inside the inflection portion 82.

[0141] The inflection portion 82 connects between the body main body 32 and the bottom portion 84. The groove width of the inflection portion 82 gradually increases from the body main body 32 side toward the bottom portion 84 side. The inflection portion 82 curves so as to be recessed inward from its outer side. In this tire 2, the contour of the inflection portion 82 is represented by an arc. In FIG. 4, the arrow Rc is the radius of the arc representing the contour of the inflection portion 82.

[0142] The bottom portion 84 includes the groove bottom 24T. The bottom portion 84 has a rounded contour. The bottom portion 84 curves so as to bulge outward from its inner side. The contour of the bottom portion 84 of the crown narrow groove 24 shown in FIG. 4 is represented by an arc. In FIG. 4, the arrow Rt is the radius of the arc representing the contour of the bottom portion 84. The radius Rt of this arc is, for example, 1.5 mm or more and 3.5 mm or less.

[0143] The position indicated by the symbol PR is the boundary between the inflection portion 82 and the bottom portion 84. The arc representing the contour of the inflection portion 82 and the arc representing the contour of the bottom portion 84 are in contact with each other at the boundary PR. As shown in FIG. 4, the maximum groove width position PM of the widened portion 28 is included in the bottom portion 84. In other words, the maximum groove width position PM is located radially inside the boundary PR. The maximum groove width WM of the widened portion 28 is equal to twice the radius Rt of the arc representing the contour of the bottom portion 84. In this tire 2, the radius Rc of the arc representing the contour of the inflection portion 82 is larger than the radius Rt of the arc representing the contour of the bottom portion 84. Thereby, the crown fine groove 24 can fully exhibit its function. From this viewpoint, the ratio Rc / Rt of the radius Rc of the arc representing the contour of the inflection portion 82 to the radius Rt of the arc representing the contour of the bottom portion 84 is preferably 1.5 or more and 20 or less. By setting the ratio Rc / Rt to 1.5 or more, the tire 2 can suppress the occurrence of uneven wear due to a sudden change in rigidity. From this viewpoint, the ratio Rc / Rt is more preferably 2.0 or more. By setting the ratio Rc / Rt to 20 or less, the widened portion 28 can effectively contribute to suppressing the deterioration of wet performance. From this viewpoint, the ratio Rc / Rt is more preferably 15 or less.

[0144] As described above, the widened portion 28 has a groove width wider than the groove width WD of the carcass main body 32. From the viewpoint of maintaining wet performance, the maximum groove width WM of the widened portion 28 is preferably 2 times or more, and more preferably 3 times or more, the groove width WD of the carcass main body 32. From the viewpoint of suppressing the influence on the rigidity of the crown land portion 20 and enabling the tire 2 to maintain good uneven wear resistance, the maximum groove width WM of the widened portion 28 is preferably 8 times or less, and more preferably 7 times or less, the groove width WD of the carcass main body 32.

[0145] In FIG. 4, the length indicated by the double-headed arrow DGg is the groove depth of the crown fine groove 24. The length indicated by the double-headed arrow HH is the groove depth of the carcass 26. The length indicated by the double-headed arrow HT is the groove depth of the taper portion 30.

[0146] From the viewpoint that the tire 2 can effectively suppress the concentration of strain on the groove opening 24M of the crown fine groove 24 while ensuring the groove volume of the crown fine groove 24, the ratio (HT / DGg) of the groove depth HT of the taper portion 30 to the groove depth DGg of the crown fine groove 24 is preferably 0.12 or more and 0.14 or less.

[0147] As described above, the crown land portion 20 has a crown groove 24 (specifically, one crown groove 24). The crown groove 24 forms two crown land portions 34 on the crown land portion 20. Of the two crown land portions 34, the crown land portion 34 closer to the equatorial plane is the inner crown land portion 36, and the crown land portion 34 closer to the tread surface 6 end TE is the outer crown land portion 38.

[0148] Each of the two crown land portions 34 has a plurality of crown sipes 40 that cross the crown land portion 34. The plurality of crown sipes 40 form a plurality of crown blocks 42 on the crown land portion 34. The crown sipes 40 are shallower than the crown circumferential main groove 14.

[0149] The crown sipes 40 provided in the inner crown land portion 36 are also called inner crown sipes 44. The crown blocks 42 of the inner crown land portion 36 are also called inner crown blocks 46. The crown sipes 40 provided in the outer crown land portion 38 are also called outer crown sipes 48. The crown blocks 42 of the outer crown land portion 38 are also called outer crown blocks 50.

[0150] FIG. 5 is a cross-sectional view of the crown sipes 40, specifically, the inner crown sipes 44, along the line V-V of FIG. 3. FIG. 5 shows a cross-section of the inner crown sipes 44 along a plane perpendicular to the longitudinal direction of the inner crown sipes 44. The cross-sectional shape of the outer crown sipes 48 is the same as that of the inner crown sipes 44. Taking the inner crown sipes 44 as an example, the cross-sectional shape of the crown sipes 40 is described.

[0151] The crown sipes 40 extend straight in their depth direction. The crown sipes 40 have a pair of wall surfaces 40W including a groove opening 40M and a bottom surface 40B including a groove bottom 40T. In FIG. 5, the double-headed arrow WGs is the groove width at the groove opening 40M of the crown sipes 40. The double-headed arrow DGs is the groove depth of the crown sipes 40. The groove width WGs of the crown side 40 of this tire 2 is less than 1.0 mm. When a load acts on the crown land portion 34 and the crown land portion 34 deforms, the wall surfaces 40W of the crown side 40 come into contact with each other and support each other. The groove depth DGs of the crown side 40 is shallower than the groove depth DGg of the crown fine groove 24. When the tread 4 wears, the crown side 40 disappears earlier than the crown fine groove 24.

[0152] The crown fine groove 24 of this tire 2 has a carcass body 32 with a narrow groove width. When the tread surface 6 contacts the road surface, the tread 4 deforms. Due to this deformation, in the carcass body 32 of the crown fine groove 24, the opposing wall surfaces 24W of the crown fine groove 24 come into contact with each other. The crown land portions 34 located on both sides of the crown fine groove 24 support each other. The deformation of the crown land portion 20 is suppressed. The crown fine groove 24 can contribute to reducing the rolling resistance. On the other hand, since the rigidity of the crown land portion 20 seemingly increases, there is a concern about the deterioration of wet performance. However, the crown land portion 34 is provided with a crown side 40 that crosses the crown land portion 34. The crown side 40 can function as an edge component that scratches the road surface. The crown side 40 suppresses the deterioration of wet performance. In the initial stage of wear, it is presumed that in this way, the tire 2 can suppress the deterioration of wet performance due to wear while reducing the rolling resistance.

[0153] As the wear of the tread 4 progresses, the groove volume of the circumferential main groove 10 and the like decreases. There is a concern about the deterioration of wet performance. However, on the radially inner side of the carcass body 32 of the crown fine groove 24, there is a widened portion 28. When the carcass body 32 disappears, the widened portion 28 is exposed. The widened portion 28 has a groove width wider than the groove width of the carcass body 32. The widened portion 28 can contribute to suppressing the deterioration of wet performance. On the other hand, the volume of the tread 4 decreases due to wear. Since the deformation allowance of the tread 4 becomes smaller, the rigidity of the tread 4 seemingly increases. The increase in rigidity can contribute to reducing the rolling resistance. In the middle stage of wear, it is presumed that in this way, the tire 2 can suppress the deterioration of wet performance due to wear while reducing the rolling resistance.

[0154] As the wear of the tread 4 further progresses, the volume of the tread 4 further decreases. Since the crown side groove 40 is shallower than the crown groove 24, the crown side groove 40 disappears earlier than the crown groove 24. The apparent rigidity of the tread 4 further increases. The increase in rigidity works favorably for the rolling resistance but unfavorably for the wet performance. In the later stage of wear when the crown side groove 40 disappears, the enlarged portion 28 remains, but the tire 2 may not be able to suppress the deterioration of the wet performance. However, the rubber composition constituting the tread 4 of this tire 2 contains styrene-butadiene rubber and silica. As the glass transition temperature (Tg) of the rubber component increases, the road surface followability in the micro-deformation region improves. Regardless of the wear stage, the tread 4 can contribute to the improvement of the wet performance. In particular, since the content CSB of styrene-butadiene rubber, the content BS of silica, the groove depth DGg of the crown groove 24, and the groove depth DGs of the crown side groove 40 are set to satisfy the above-mentioned relational expression, even in the later stage of wear, the synergistic effect of styrene-butadiene rubber and silica suppresses the deterioration of the wet performance.

[0155] The tread 4 of the tire 2 wears due to use. This tire 2 can suppress the deterioration of the wet performance due to wear while reducing the rolling resistance, not only in the initial stage of wear but also in the later stage of wear when the crown side groove 40 disappears. In other words, this tire 2 can suppress the deterioration of the wet performance while maintaining a low rolling resistance from the start of use until replacement becomes necessary.

[0156] As described above, the crown side groove 40 is shallower than the crown groove 24. In other words, the crown groove 24 is deeper than the crown side groove 40. Specifically, it is preferable that the groove depth DGg (mm) of the crown groove 24 and the groove depth DGs (mm) of the crown side groove 40 satisfy the following relational expression. 2.0 ≦ (DGg - DGs) ≦ 10.0 After the crown sipe 40 disappears, the crown groove 24 remains, but the influence on the rolling resistance and the influence on the wet performance due to the rigidity of the tread 4 after the disappearance of the crown sipe 40 are suppressed to a small extent. Even in the later stage of wear, this tire 2 can suppress the deterioration of the wet performance while maintaining a low rolling resistance. From this perspective, it is more preferable that the groove depth DGg (mm) of the crown groove 24 and the groove depth DGs (mm) of the crown sipe 40 satisfy the following relational expression. 3.0 ≦ (DGg - DGs) ≦ 7.0

[0157] In FIG. 4, the length indicated by the double arrow HN is the groove depth from the groove opening 24M of the crown groove 24 to the maximum groove width position PM. From the perspective that the enlarged portion 28 can effectively contribute to suppressing the deterioration of the wet performance, the ratio (HN / DGg) of the groove depth HN from the groove opening 24M to the maximum groove width position PM of the crown groove 24 to the groove depth DGg of the crown groove 24 is preferably 0.75 or more and 0.95 or less.

[0158] The land ratio of this tire 2 is preferably 80% or more. Thereby, as a whole, the land portions 18 can easily support each other, and the rigidity of the tread 4 can be effectively increased. The tire 2 can effectively reduce the rolling resistance and can also improve the wear resistance. As described above, the rubber composition of this tread 4 contains silica as a filler. Therefore, there is a concern that the rigidity of the tread 4 may decrease compared to the case where the entire amount of the filler is composed of carbon black. However, by setting the land ratio to 80% or more, the tread 4 can maintain the required rigidity. In this tire 2, the crown groove 24 and the crown sipe 40 can fully exhibit their functions. This tire 2 can suppress the deterioration of the wet performance due to wear while reducing the rolling resistance. From this perspective, the land ratio is more preferably 85% or more. From the perspective of maintaining good wet performance, the land ratio is preferably 95% or less.

[0159] As shown in FIG. 3, the crown circumferential main groove 14 of this tire 2 includes a first apex 14a near the first end TE1 (not shown) of the tread surface 6 and a second apex 14b near the second end TE2 of the tread surface 6. The crown circumferential main groove 14 extends in a zigzag manner while alternately passing through the first apex 14a and the second apex 14b in the circumferential direction. As described above, the crown circumferential main groove 14 is located on the equatorial plane. In many cases, the crown circumferential main groove 14 is included in the ground contact surface. The pair of edges 14E constituting the groove opening 14M of the crown circumferential main groove 14 each extend in a zigzag manner in the circumferential direction. The crown circumferential main groove 14 can function as an edge component even in the later stage of wear. The crown circumferential main groove 14 can contribute to suppressing the deterioration of wet performance due to wear. From this viewpoint, it is preferable that the crown circumferential main groove 14 includes a first apex 14a near the first end TE1 of the tread surface 6 and a second apex 14b near the second end TE2 of the tread surface 6, and extends in a zigzag manner while alternately passing through the first apex 14a and the second apex 14b in the circumferential direction.

[0160] As shown in FIG. 3, the crown fine grooves 24 extend in the circumferential direction while meandering rather than being straight. In particular, the crown fine grooves 24 of this tire 2 include inner crown fine grooves 56 near the equatorial plane, outer crown fine grooves 58 near the end TE of the tread surface 6, and connecting crown fine grooves 60 connecting the inner crown fine grooves 56 and the outer crown fine grooves 58. Among the connecting crown fine grooves 60, the connecting crown fine groove 60 connecting the inner crown fine groove 56 located on the first circumferential direction side and the outer crown fine groove 58 located on the second circumferential direction side is also called the first connecting crown fine groove 60a. The connecting crown fine groove 60 connecting the outer crown fine groove 58 located on the first circumferential direction side and the inner crown fine groove 56 located on the second circumferential direction side is also called the second connecting crown fine groove 60b. When a unit formed by connecting an inner crown groove 56, a first connecting crown groove 60a, an outer crown groove 58, and a second connecting crown groove 60b in this order is defined as a groove unit, a plurality of these groove units are connected in the circumferential direction to form a crown groove 24. The inner crown groove 56 and the outer crown groove 58 are alternately arranged in the circumferential direction.

[0161] When a force acts on the crown land portion 20 and the crown land portion 20 deforms, the crown groove 24 has its wall surfaces in contact with each other in the body main portion 32. Since the crown groove 24 extends in the circumferential direction while meandering, the wall surfaces effectively mesh with each other. The crown groove land portions 34 located on both sides of the crown groove 24 restrain each other. The apparent rigidity of the crown land portion 20 increases. The deformation of the crown land portion 20 is effectively suppressed. This tire 2 can effectively reduce rolling resistance and can also improve wear resistance. As described above, the rubber composition of this tread 4 contains silica as a filler. Therefore, although there is a concern that the rigidity of the tread may decrease compared to the case where the entire amount of the filler is composed of carbon black, by configuring the crown groove with an inner crown groove, an outer crown groove, and a connecting crown groove, and alternately arranging the inner crown groove and the outer crown groove in the circumferential direction, the tread can maintain the required rigidity. From this perspective, the crown groove 24 preferably includes an inner crown groove 56, an outer crown groove 58, and a connecting crown groove 60 that connects the inner crown groove 56 and the outer crown groove 58, and the inner crown groove 56 and the outer crown groove 58 are alternately arranged in the circumferential direction.

[0162] The groove depth DGg of the crown groove 24 of this tire 2 is the same as or shallower than the groove depth DGc of the crown circumferential main groove 14. As described above, the crown groove 24 has an enlarged portion 28 on the groove bottom 24T side. The enlarged portion 28 of the crown groove 24 can effectively contribute to compensating for the reduced groove volume in the later stage of wear. This tire 2 can effectively suppress the deterioration of wet performance due to wear. From this perspective, the groove depth DGg of the crown fine groove 24 is preferably the same as the groove depth DGc of the crown circumferential main groove 14, or the crown fine groove 24 is shallower than the crown circumferential main groove 14. In other words, the ratio (DGg / DGc) of the groove depth DGg of the crown fine groove 24 to the groove depth DGc of the crown circumferential main groove 14 is preferably 1.0 or less. In the later stage of wear, from the perspective that the entire crown fine groove 24 can effectively contribute to compensating for the reduced groove volume of the enlarged portion 28 without disappearing, the ratio (DGg / DGc) is preferably 0.75 or more.

[0163] The ratio (HH / DGg) of the groove depth HH of the body portion 26 of the crown fine groove 24 to the groove depth DGg of the crown fine groove 24 is preferably 0.20 or more and 0.50 or less. By setting the ratio (HH / DGg) to 0.20 or more, the tire 2 can effectively suppress the influence of the enlarged portion 28 on the rigidity of the crown land portion 20. The crown fine groove 24 can effectively contribute to apparently increasing the rigidity of the crown land portion 20. The tire 2 can further reduce the rolling resistance. From this perspective, the ratio (HH / DGg) is more preferably 0.25 or more. By setting the ratio (HH / DGg) to 0.50 or less, the enlarged portion 28 can effectively contribute to compensating for the groove volume reduced by wear. From this perspective, the ratio (HH / DGg) is more preferably 0.45 or less.

[0164] The body main part 32 of the crown fine groove 24 has a groove width WD that is narrower than the groove width WGc at the groove opening of the crown circumferential main groove 14. As described above, when the tire 2 contacts the road surface and the tread 4 deforms, the pair of opposing wall surfaces 24W of the crown fine groove 24 come into contact with each other at the body main part 32. The crown fine land parts 34 adjacent to each other across the crown fine groove 24 support each other. The crown fine land parts 34 are formed in the crown part of the tread part. By the adjacent crown fine land parts 34 supporting each other, apparently, the rigidity of the crown part is increased and the deformation of the crown part is suppressed. This tire 2 can reduce the rolling resistance and effectively suppress the occurrence of wear in the crown part. This tire 2 can also improve the resistance to uneven wear. From this viewpoint, the ratio (WD / WGc) of the groove width WD of the body main part 32 of the crown fine groove 24 to the groove width WGc of the crown circumferential main groove 14 is preferably 0.35 or less, and more preferably 0.20 or less. From the viewpoint that the crown fine groove 24 can contribute to drainage and the tire 2 can maintain good wet performance, the ratio (WD / WGc) is preferably 0.01 or more, and more preferably 0.05 or more.

[0165] As described above, since the crown sipe 40 is shallower than the crown fine groove 24, the crown sipe 40 disappears earlier than the crown fine groove 24. From the viewpoint of suppressing the influence on the rolling resistance and the influence on the wet performance due to the switching from the crown sipe 40 to the enlarged part 28 of the crown fine groove 24, the ratio (DGs / DGg) of the groove depth DGs of the crown sipe 40 to the groove depth DGg of the crown fine groove 24 is preferably 0.30 or more, and more preferably 0.50 or more. From the same viewpoint, this ratio (DGs / DGg) is preferably 0.85 or less.

[0166] In this tire 2, it is preferable that the crown width 40 is deeper than the carcass portion 26 of the crown groove 24. In other words, the ratio (DGs / DGg) of the groove depth DGs of the crown width 40 to the groove depth DGg of the crown groove 24 is preferably larger than the ratio (HH / DGg) of the groove depth HH of the carcass portion 26 of the crown groove 24 to the groove depth DGg of the crown groove 24. Thereby, this tire 2 can suppress the influence on the rolling resistance and the influence on the wet performance due to the switching from the crown width 40 to the enlarged portion 28 of the crown groove 24 to a small extent. From this viewpoint, the ratio (DGs / DGg) is larger than the ratio (HH / DGg), the ratio (HH / DGg) is 0.20 or more and 0.50 or less, and the ratio (DGs / DGg) is more preferably 0.30 or more and 0.85 or less.

[0167] In this tire 2, it is preferable that the groove bottom 40T of the crown width 40 is located radially outside the maximum groove width position PM of the enlarged portion 28. Thereby, this tire 2 can suppress the influence on the rolling resistance and the influence on the wet performance due to the switching from the crown width 40 to the enlarged portion 28 of the crown groove 24 to a smaller extent. Even in the later stage of wear, this tire 2 can suppress the decrease in wet performance while maintaining a low rolling resistance. As described above, it is preferable that the crown width 40 is deeper than the carcass portion 26 of the crown groove 24. In other words, it is preferable that the groove bottom 40T of the crown width 40 is located radially inside the carcass portion 26. Even in the later stage of wear, from the viewpoint that this tire 2 can suppress the decrease in wet performance while maintaining a low rolling resistance, it is more preferable that the groove bottom 40T of the crown width 40 is located radially inside the carcass portion 26 and radially outside the maximum groove width position PM of the enlarged portion 28.

[0168] As shown in FIG. 3, the inner crown side rib 44 of this tire 2 connects between the second apex 14b of the crown circumferential main groove 14 and the outer crown fine groove 58 of the crown fine groove 24. The outer crown side rib 48 connects between the shoulder circumferential main groove 12 and the inner crown fine groove 56 of the crown fine groove 24. As described above, the inner crown fine grooves 56 and the outer crown fine grooves 58 are alternately arranged in the circumferential direction. The inner crown side rib 44 and the outer crown side rib 48 are alternately arranged in the circumferential direction.

[0169] The inner crown side rib 44 shown in FIG. 3 is inclined with respect to the axial direction. The outer crown side rib 48 is also inclined with respect to the axial direction. The crown side rib 40 is inclined with respect to the axial direction. The crown side rib 40 may extend in the axial direction. The crown side rib 40 that extends in the axial direction or is inclined with respect to the axial direction can function effectively as an edge component. This tire 2 can improve wet performance. From this viewpoint, the crown side rib 40 preferably extends in the axial direction or is inclined with respect to the axial direction. The crown side rib 40 is more preferably inclined with respect to the axial direction.

[0170] In FIG. 3, the angle θuc represents the angle formed by the inner crown side rib 44 with respect to the axial direction. The angle θuc is also called the inclination angle of the inner crown side rib 44. The angle θsc represents the angle formed by the outer crown side rib 48 with respect to the axial direction. The angle θsc is also called the inclination angle of the outer crown side rib 48. From the viewpoint that the inner crown side rib 44 can function effectively as an edge component, the inclination angle θuc of the inner crown side rib 44 is preferably 0 degrees or more, and more preferably 5 degrees or more. From the same viewpoint, the inclination angle θuc is preferably 45 degrees or less. From the viewpoint that the outer crown side rib 48 can function effectively as an edge component, the inclination angle θsc of the outer crown side rib 48 is preferably 0 degrees or more, and more preferably 5 degrees or more. From the same viewpoint, the inclination angle θsc is preferably 45 degrees or less.

[0171] As shown in FIG. 3, the end on the tread surface 6 side of the end TE of the inner crown side 44 is located on the second direction side in the circumferential direction rather than the end on the equatorial plane side of the inner crown side 44. The end on the tread surface 6 side of the end TE of the outer crown side 48 is located on the first direction side in the circumferential direction rather than the end on the equatorial plane side of the outer crown side 48. The direction of inclination of the inner crown side 44 is opposite to that of the outer crown side 48. In this tire 2, when a force acts on the crown land portion 20 from the equatorial plane side toward the end TE of the tread surface 6, the wall surfaces contact each other and support each other in the outer crown side 48. The outer crown thin land portion 38 can effectively restrain the movement of the inner crown thin land portion 36. As a result, the rigidity of the crown land portion 20 seemingly increases. When a force acts on the crown land portion 20 from the end TE side of the tread surface 6 toward the equatorial plane, the wall surfaces contact each other and support each other in the inner crown side 44. The inner crown thin land portion 36 can effectively restrain the movement of the outer crown thin land portion 38. Also in this case, the rigidity of the crown land portion 20 seemingly increases. In either case, the deformation of the crown land portion 20 is effectively suppressed. This tire 2 can further reduce the rolling resistance. From this viewpoint, it is preferable that the direction of inclination of the crown side 40 in the inner crown thin land portion 36 is opposite to the direction of inclination of the crown side 40 in the outer crown thin land portion 38.

[0172] From the viewpoint of effectively suppressing a decrease in wet performance due to wear while reducing the rolling resistance, the crown sides 40 provided on each of the two crown thin land portions 34 are inclined with respect to the axial direction, the direction of inclination of the inner crown side 44 is opposite to the direction of inclination of the outer crown side 48, the inner crown side 44 connects between the second apex 14b of the crown circumferential main groove 14 and the outer crown thin groove 58 of the crown thin groove 24, and it is more preferable that the outer crown side 48 connects between the inner crown thin groove 56 of the crown thin groove 24 and the shoulder circumferential main groove 12.

[0173] FIGS. 6 and 7 show a modified example of the crown side 40. FIG. 7 represents a cross section of the crown side 40 along the line VII-VII in FIG. 6. As shown in FIG. 6, the crown sipe 40 extends in a zigzag pattern in its longitudinal direction. As shown in FIG. 7, this crown sipe 40 also extends in a zigzag pattern in its depth direction. This crown sipe 40 extends in a zigzag pattern in both its longitudinal direction and depth direction. The amplitude of the zigzag is preferably, for example, 0.5 mm or more and 3.0 mm or less.

[0174] This crown sipe 40 is a three-dimensional sipe. When the tread deforms and the walls of the crown sipe come into close contact with each other, the walls restrain each other, and the rigidity of the tread is effectively increased. The tire can effectively reduce the rolling resistance and can also improve the wear resistance. As described above, the rubber composition of this tread 4 contains silica as a filler. Therefore, there is a concern that the rigidity of the tread may decrease compared to the case where the entire amount of the filler is composed of carbon black. However, by configuring the crown sipe 40 as a three-dimensional sipe that extends in a zigzag pattern in both its longitudinal direction and depth direction, the tread 4 can maintain the required rigidity. From this perspective, it is preferable that the crown sipe 40 extends in a zigzag pattern in both its longitudinal direction and depth direction.

[0175] FIG. 8 shows another modification of the crown sipe 40. This crown sipe 40 has a sipe body 72 and a tubular portion 74. The sipe body 72 includes the groove opening 40M of the crown sipe 40. The tubular portion 74 includes the groove bottom 40T of the crown sipe 40.

[0176] Although not shown, the sipe body 72 extends straight in the longitudinal direction of the crown sipe 40 in the same manner as the crown sipe 40 shown in FIG. 3. As shown in FIG. 8, the sipe body 72 extends straight in the depth direction of the crown sipe 40. The length indicated by the double arrow Wp in FIG. 8 is the groove width of the sipe body 72. The groove width Wp of the sipe body 72 is also the groove width WGs at the groove opening 40M of this crown sipe 40. The tubular portion 74 is located radially inside the sipe body 72. The tubular portion 74 extends in the longitudinal direction of the crown sipe 40.

[0177] In FIG. 8, the solid line LF is the boundary line between the sipe body 72 and the tubular portion 74. The length indicated by the double arrow WF is the groove width of the crown sipe 40 measured along this boundary line LF. The boundary line LF is set at a position where the groove width WF becomes 1.0 mm. The outer portion of the boundary line LF, that is, the groove width Wp of the sipe body 72 is less than 1.0 mm. The inner portion of this boundary line LF, that is, the groove width of the tubular portion 74 is 1.0 mm or more. The groove width of the tubular portion 74 is wider than the groove width of the sipe body 72.

[0178] The tubular portion 74 extends inward from the position of the boundary line LF. The length indicated by the double arrow WX in FIG. 8 is the maximum groove width of the tubular portion 74. The position indicated by the reference sign PX in FIG. 8 is the position where the tubular portion 74 exhibits the maximum groove width WX. The tubular portion 74 tapers outward from the portion showing the maximum groove width WX. The tubular portion 74 tapers inward from the portion showing the maximum groove width WX.

[0179] The cross-sectional shape of the tubular portion 74 may be circular or elliptical. This cross-sectional shape may be a shape in which the portion showing the maximum groove width WX is represented by a straight line, and the sipe body 72 side and the groove bottom 40T side of the straight line portion are represented by arcs (hereinafter, this shape is also called a track shape).

[0180] The sipe body 72 can function as an edge component. The sipe body 72 can contribute to suppressing the deterioration of wet performance. As described above, the groove width Wp of the sipe body 72 is less than 1.0 mm. When a load acts on the crown land portion 34 and the crown land portion 34 deforms, the wall surfaces 40W of the crown sipe 40 come into contact with each other and support each other. The sipe body 72 can also contribute to reducing the rolling resistance. The tubular portion 74 is exposed when the sipe body 72 disappears. The tubular portion 74 has a wide groove width. After the sipe body 72 disappears, this tubular portion 74 can contribute to maintaining the wet performance.

[0181] The maximum groove width WX of the tubular portion 74 is preferably 4 times or more, more preferably 5 times or more, the groove width Wp of the sipe body 72. Thereby, the tubular portion 74 can contribute to maintaining the wet performance. The maximum groove width WX of the tubular portion 74 is preferably 13 times or less, more preferably 12 times or less, the groove width Wp of the sipe body 72. Thereby, the size of the tubular portion 74 is appropriately maintained. The reduction in rigidity of the crown land portion 34 is suppressed.

[0182] As described above, the tubular portion 74 includes a bottom surface 40B including the groove bottom 40T of the crown sipe 40. In the cross section shown in FIG. 8, the contour of the bottom surface 40B of the tubular portion 74 is represented by an arc passing through the groove bottom 40T. The arrow Rb in FIG. 8 is the radius of this arc.

[0183] The radius Rb of the arc representing the contour of the bottom surface 40B of the tubular portion 74 is preferably 1.5 mm or more and 3.5 mm or less. By setting the radius Rb to 1.5 mm or more, the generation of cracks at the groove bottom 40T is effectively suppressed. From this viewpoint, the radius Rb is more preferably 2.0 mm or more. By setting the radius Rb to 3.5 mm or less, the reduction in rigidity of the crown block 42 due to providing the tubular portion 74 in the crown sipe 40 is suppressed. The rigidity of the crown block 42 is appropriately maintained. The tire 2 can improve the resistance to uneven wear. From this viewpoint, the radius Rb is more preferably 3.0 mm or less.

[0184] The length indicated by the double arrow DC in FIG. 8 is the groove depth of the sipe body 72. The groove depth DC, in other words, the position of the boundary line LF, is appropriately determined in consideration of the specifications of the tire 2.

[0185] The ratio (DC / DGs) of the groove depth DC of the sipe body 72 of the crown sipe 40 to the groove depth DGs of the crown sipe 40 is preferably 0.35 or more and 0.80 or less. By setting the ratio (DC / DGs) to 0.35 or more, the tire 2 can expose the tubular portion 74 at an appropriate timing. While maintaining the rigidity of the crown block 42, the tire 2 can cause the tread 4 to wear. The tire 2 can maintain good uneven wear resistance. From this perspective, the ratio (DC / DGs) is more preferably 0.40 or more. By setting the ratio (DC / DGs) to 0.80 or less, the tubular portion 74 can effectively contribute to the improvement of the appearance quality and the exhibition of the traction performance. From this perspective, the ratio (DC / DGs) is more preferably 0.75 or less.

[0186] FIG. 9 shows still another modification of the crown side 40. As shown in this FIG. 9, the side main body 72 shown in FIG. 8 may be composed of a three-dimensional side as in the crown side 40 shown in FIG. 7. In this case, when the crown land portion 34 is deformed and the wall surfaces 40W of the crown side 40 come into contact with each other, both wall surfaces 40W adhere sufficiently. The deformation of the crown land portion 34 is effectively suppressed.

[0187] As is clear from the above description, according to the present invention, a heavy-duty tire can be obtained that can suppress a decrease in wet performance due to wear while reducing rolling resistance.

Example

[0188] Hereinafter, the present invention will be described in more detail by way of examples and the like, but the present invention is not limited only to such examples.

[0189] Various chemicals used in the examples and comparative examples are described. NR: TSR20 SBR: HPR840 (S-SBR, styrene content: 10% by mass, vinyl content: 42 mol%, Tg: -60 ° C, Mw: 190,000) manufactured by JSR Corporation BR: UBEPOL BR (registered trademark) 150B (cis content: 97 mol%) manufactured by Ube Industries, Ltd. Carbon black 1: Dia Black N134 manufactured by Mitsubishi Chemical Corporation (N2SA: 148 m 2 / g) Carbon black 2: SS550 manufactured by Strebl Green Carbon (carbon black obtained from the thermal decomposition process of tires) Silica 1: Ultrasil 9100GR manufactured by Evonik Degussa (N2SA: 230 m 2 / g, average primary particle size: 15 nm) Silica 2: K185 manufactured by Wilmar (amorphous silica refined from rice husks) Silane coupling agent: Si266 manufactured by Evonik Degussa (bis(3-triethoxysilylpropyl) disulfide) Resin component: Oppera PR-383 manufactured by Exxon Mobil (hydrogenated DCPD / C9 resin, resin containing dicyclopentadiene, styrene, and indene as monomer components, softening point: 103 °C) Wax: Oz Ace 0355 manufactured by Nippon Seiro Co., Ltd. Antioxidant 1: No Crack 6C manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) Antioxidant 2: No Crack RD manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) Stearic acid: Tsubaki Bead Stearic Acid manufactured by NOF Corporation Zinc oxide: Zinc White No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 manufactured by Hosoi Chemical Industry Co., Ltd. (5% oil-containing powdered sulfur) Vulcanization accelerator: Nocceler NS manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-t-butyl-2-benzothiazolesulfenamide)

[0190] [Examples and Comparative Examples] According to the compounding ingredients shown in Table 1-3, using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd., materials other than sulfur and vulcanization accelerators are kneaded at 150 °C for 5 minutes to obtain a kneaded product. Next, sulfur and vulcanization accelerators are added to the obtained kneaded product, and it is kneaded at 80 °C for 5 minutes using an open roll to obtain a rubber composition (unvulcanized rubber composition). The obtained rubber composition is used to form a tread, which is bonded together with other parts such as sidewalls to form an unvulcanized tire. The unvulcanized tire is press-vulcanized at 150 °C for 12 minutes to manufacture a test tire (size: 315 / 70R22.5, for trucks and buses). The tread pattern shown in FIG. 1 is used for the tread pattern of the test tire.

[0191] [Preparation before evaluation] Buffing is performed on the tread of the test tire. Specifically, the tread is polished until the crown groove body and the crown sipe of the crown groove disappear and an enlarged portion remains on the tread surface. This reproduces the later stage of wear.

[0192] For the test tire in which the later stage of wear is reproduced by buffing, the calculation results based on the following evaluation method are shown in Table 1-3.

[0193] [Rolling resistance (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) is measured when the test tire in which the later stage of wear is reproduced runs on a drum at a speed of 80 km / h under the following conditions. The reciprocals of the measured values of Example 1 and Comparative Examples 1-2 are expressed as an index with Comparative Example 2 as 100. The reciprocals of the measured values of Examples 2-3 and Comparative Examples 3-4 are expressed as an index with Comparative Example 4 as 100. The reciprocals of the measured values of Examples 4-5 and Comparative Examples 5-6 are expressed as an index with Comparative Example 6 as 100. The results are shown in the column of "RRC" in Table 1-3 below. The larger the numerical value, the lower the rolling resistance. Rim: 9.00×22.5 Internal pressure: 900 kPa Vertical load: 33.35 kN

[0194] [WET Performance] Using the following test vehicle, a test for wet performance (wet braking performance) is conducted in accordance with R117-02 (ECE Regulation No. 117 Revision 2). Test tires that reproduce the later stage of wear are mounted on all wheels of the test vehicle. In this wet performance, on a water-sprinkled road surface, braking is started from the specified initial speed, and the braking distance until stopping is measured. Test Vehicle: 10-ton truck (2-D vehicle) Load: 75% of the standard loading capacity Wet Road Surface: Water depth 0.5 - 2 mm Speed: 65 km / h The measured values of Example 1 and Comparative Examples 1-2 are expressed as an index with Comparative Example 2 set to 100 using the following formula. (Wet Performance Index) = (Braking Distance of the Tire in Comparative Example 2) / (Braking Distance of Each Test Tire) × 100 The measured values of Examples 2-3 and Comparative Examples 3-4 are expressed as an index with Comparative Example 4 set to 100 using the following formula. (Wet Performance Index) = (Braking Distance of the Tire in Comparative Example 4) / (Braking Distance of Each Test Tire) × 100 The measured values of Examples 4-5 and Comparative Examples 5-6 are expressed as an index with Comparative Example 6 set to 100 using the following formula. (Wet Performance Index) = (Braking Distance of the Tire in Comparative Example 6) / (Braking Distance of Each Test Tire) × 100 The results are shown in the "WET" column of Table 1-3 below. The larger the numerical value, the better the wet performance.

[0195] [Table 1]

[0196] [Table 2]

[0197] [Table 3] [Industrial Applicability]

[0198] The technology described above, which can reduce rolling resistance while suppressing a decrease in wet performance due to wear, can be applied to various tires.

[0199] [Appendix] The present invention includes the following aspects.

[0200] [1] A tire comprising a tread composed of a rubber composition containing a rubber component containing styrene-butadiene rubber and a filler containing silica, the tread having a tread surface that contacts the road surface, the tread having a plurality of circumferential main grooves extending continuously in the circumferential direction, the plurality of circumferential main grooves including a crown circumferential main groove located on the equatorial plane and a pair of shoulder circumferential main grooves located at the outermost axial positions, the plurality of circumferential main grooves forming a plurality of land portions on the tread, the plurality of land portions including a pair of crown land portions closest to the equatorial plane and a pair of shoulder land portions including the ends of the tread surface, each of the crown land portions having crown fine grooves extending continuously in the circumferential direction, the crown fine grooves forming two crown fine land portions on the crown land portion, each of the crown fine land portions having a crown siped that crosses the crown fine land portion, the crown fine grooves comprising a carcass body and an enlarged portion located radially inside the carcass body, due to deformation of the tread, opposing wall surfaces of the carcass body contact each other, the groove width of the enlarged portion being wider than the groove width of the carcass body, the groove depth DGs of the crown siped being shallower than the groove depth DGg of the crown fine grooves, the content CSB of the styrene-butadiene rubber in 100 parts by mass of the rubber component being 10 parts by mass or more, The content BS of the silica with respect to 100 parts by mass of the rubber component is 15 parts by mass or more, A heavy-duty tire in which the content CSB of the styrene-butadiene rubber, the content BS of the silica, the groove depth DGs (mm) of the crown sipe, and the groove depth DGg (mm) of the crown fine groove satisfy the following relational expression. (CSB + BS) / (DGg - DGs) ≥ 5 [2] The rubber component further contains natural rubber and butadiene rubber, A heavy-duty tire according to the above [1], wherein the content CSB of the styrene-butadiene rubber, the content CN of the natural rubber, and the content CB of the butadiene rubber in 100 parts by mass of the rubber component satisfy the following relational expression. CN ≥ CSB + CB [3] A heavy-duty tire according to the above [1] or [2], wherein the content CS of the silica in 100 parts by mass of the filler is 40 parts by mass or more. [4] A heavy-duty tire according to any one of the above [1] to [3], wherein the silica contains silica made from a biomass material as a raw material. [5] A heavy-duty tire according to any one of the above [1] to [4], wherein the filler contains silica having an average primary particle diameter of 16 nm or less. [6] A heavy-duty tire according to any one of the above [1] to [5], wherein the filler further contains carbon black, and the carbon black contains recycled carbon black. [7] The filler further contains carbon black, A heavy-duty tire according to any one of the above [1] to [6], wherein the carbon black contains carbon black having an average primary particle diameter of 19 nm or less. [8] A heavy-duty tire according to any one of the above [1] to [7], wherein the rubber composition further contains a resin component. [9] A heavy-duty tire according to any one of the above [1] to [8], wherein the land ratio defined below is 80% or more. Land ratio: The ratio of the total area value of the contact surfaces of a plurality of land parts included in the contact surface to the area value of the entire contact surface, obtained by mounting the tire on a regular rim, adjusting the internal pressure to the regular internal pressure, applying a load of 100% of the regular load with a camber angle of 0 degrees, and bringing the tire into contact with a flat road surface.

[10] The heavy-duty tire according to any one of [1] to [9], wherein the crown sidewall extends in a zigzag pattern in its longitudinal direction and depth direction.

[11] The crown groove includes an inner crown groove close to the equatorial plane, an outer crown groove close to the edge of the tread surface, and a connecting crown groove connecting the inner crown groove and the outer crown groove. The heavy-duty tire according to any one of the above [1] to

[10] , wherein the inner crown groove and the outer crown groove are alternately arranged in the circumferential direction.

Explanation of reference numerals

[0201] 2 ··· Tire 4 ··· Tread 6 ··· Tread surface 10 ··· Circumferential main groove 12 ··· Shoulder circumferential main groove 14 ··· Crown circumferential main groove 18 ··· Land part 20 ··· Crown land part 22 ··· Shoulder land part 24 ··· Crown groove 26 ··· Body part of crown groove 24 28 ··· Enlarged part of crown groove 24 30 ··· Tapered part of body part 26 32 ··· Body main body of body part 26 34 ··· Crown land 36 ··· Inner crown land 38 ··· Outer crown land 40 ··· Crown sidewall 42 ··· Crown block 44 ··· Inner crown sidewall 48 ··· Outer crown sidewall 56... Inner crown fine groove 58... Outer crown fine groove

Claims

1. A tire having a tread composed of a rubber composition including a rubber component including a styrene-butadiene rubber and a filler including silica, the tread having a tread surface that comes into contact with a road surface, The tread has a plurality of circumferential main grooves extending continuously in a circumferential direction, The plurality of circumferential main grooves include a crown circumferential main groove located on an equatorial plane and a pair of shoulder circumferential main grooves located on the axially outermost sides, A plurality of the circumferential main grooves define a plurality of land portions in the tread, The plurality of land portions include a pair of crown land portions closest to the equatorial plane and a pair of shoulder land portions including edges of the tread surface, Each of the crown land portions has a crown narrow groove extending continuously in a circumferential direction, The crown narrow groove constitutes two crown narrow land portions in the crown land portion, Each of the crown narrow land portions has a crown sipe that crosses the crown narrow land portion, The crown narrow groove includes a body body and an expanded width portion located radially inward of the body body, The deformation of the tread causes opposing wall surfaces of the body to come into contact with each other, The groove width of the expanded width portion is wider than the groove width of the trunk body, The groove depth DGs of the crown sipe is shallower than the groove depth DGg of the crown narrow groove, The content (CSB) of the styrene-butadiene rubber in 100 parts by mass of the rubber component is 10 parts by mass or more, A content BS of the silica relative to 100 parts by mass of the rubber component is 15 parts by mass or more, The styrene butadiene rubber content CSB, the silica content BS, the crown sipe groove depth DGs (mm), and the crown narrow groove groove depth DGg (mm) satisfy the following relationship: Heavy duty tires. (CSB+BS) / (DGg-DGs)≧5

2. The rubber component further comprises natural rubber and butadiene rubber, the content CSB of the styrene-butadiene rubber, the content CN of the natural rubber, and the content CB of the butadiene rubber in 100 parts by mass of the rubber component satisfy the following relational formula:

2. A heavy duty tire according to claim 1. CN≧CSB+CB

3. The content CS of the silica in 100 parts by mass of the filler is 40 parts by mass or more; 2. A heavy duty tire according to claim 1.

4. The silica includes silica made from a biomass material.

2. A heavy duty tire according to claim 1.

5. The filler contains silica having an average primary particle size of 16 nm or less.

2. A heavy duty tire according to claim 1.

6. the filler further comprises carbon black; The carbon black comprises recycled carbon black.

2. A heavy duty tire according to claim 1.

7. the filler further comprises carbon black; The carbon black contains carbon black having an average primary particle size of 19 nm or less.

2. A heavy duty tire according to claim 1.

8. The rubber composition further contains a resin component.

2. A heavy duty tire according to claim 1.

9. The land ratio, as defined below, is 80% or more.

2. A heavy duty tire according to claim 1. Land ratio: The ratio of the total area of ​​the contact surface of a plurality of land portions included in the contact surface to the area of ​​the entire contact surface, obtained by mounting the tire on a regular rim, adjusting the internal pressure to the regular internal pressure, and applying a load of 100% of the regular load with a camber angle of 0 degrees to the tire on a flat road surface.

10. The crown sipe extends in a zigzag pattern in its length and depth directions.

2. A heavy duty tire according to claim 1.

11. the crown narrow groove comprises an inner crown narrow groove close to the equatorial plane, an outer crown narrow groove close to an edge of the tread surface, and a connecting crown narrow groove connecting the inner crown narrow groove and the outer crown narrow groove, The inner crown narrow grooves and the outer crown narrow grooves are alternately arranged in the circumferential direction. A heavy duty tire according to any one of claims 1 to 10.

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