Heavy duty tire

Abstract

To provide a heavy duty tire 2 that can suppress a decrease in wet performance due to wear while reducing rolling resistance.SOLUTION: A tire 2 includes a tread 4 formed from a rubber composition containing a rubber component including a styrene butadiene rubber and a filler including silica. The tread 4 includes a main lateral groove 48 and a circumferential narrow groove 18. A content CSB of the styrene butadiene rubber, a content BS of the silica, a groove depth MH (mm) of a groove portion 82 of the main lateral groove 48, and a groove depth HB (mm) from a groove opening 18M of the circumferential narrow groove 18 to a width reference position PB satisfy the following relational expression: (CSB+BS) / (MH-HB)≥5.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] In terms of environmental considerations and safety, tires are required to have reduced rolling resistance and improved driving performance on wet roads (hereinafter referred to as wet performance). For example, in Patent Document 1, rolling resistance is reduced by providing protrusions that protrude toward each other from adjacent land portions sandwiching a circumferential groove, and WET performance is improved by providing an outer groove space on the outer periphery of the protrusions and an inner groove space on the inner periphery, and further providing a connecting recess that connects the two. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-94891 Summary of the Invention [Problem to be solved by the invention]

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

[0005] A heavy-duty tire according to one aspect of the present invention has a tread made of a rubber composition including a rubber component containing styrene-butadiene rubber and a filler containing silica. The tread has a tread surface that comes into contact with the road surface. The tread has a plurality of circumferential grooves extending continuously in the circumferential direction. The plurality of circumferential grooves form a plurality of land portions aligned in the axial direction in the tread. The plurality of land portions include a plurality of main land portions located between adjacent circumferential grooves. Each of the main land portions has a plurality of main lateral grooves connecting adjacent circumferential grooves. The plurality of main lateral grooves form a plurality of main blocks aligned in the circumferential direction in the main land portion. The main lateral groove has a groove portion and a sipe portion located radially inward of the groove portion and continuing to the groove portion. The groove width of the sipe portion is narrower than the groove width of the groove portion. The circumferential groove located between adjacent main land portions is a circumferential narrow groove. Among the multiple main land portions, the main land portion located outermost in the axial direction is an outer main land portion. The circumferential groove located axially outside each of the outer main land portions is a circumferential wide groove having a groove width wider than the groove width of the circumferential narrow groove. The circumferential narrow groove has a body portion and an expanded width portion located radially inside the body portion. The body portion includes a body portion main body to which the expanded width portion is continuous. Due to deformation of the tread, opposing wall surfaces of the circumferential narrow groove contact each other at the body portion main body. The maximum width of the expanded width portion is wider than the minimum width of the body portion main body. A position between the body portion main body and the position where the expanded width portion shows its maximum width, which shows a groove width 2.0 times the minimum width of the body portion main body, is a width reference position. The groove depth MH of the groove portion is shallower than the groove depth HB from the groove opening of the circumferential narrow groove to the width reference position. The content CSB of the styrene butadiene rubber per 100 parts by mass of the rubber component is 10 parts by mass or more. The silica content BS per 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 groove depth MH (mm) of the groove portion, and the groove depth HB (mm) from the groove opening of the circumferential narrow groove to the width reference position satisfy the following relationship: (CSB+BS) / (HB-MH)≧5 [Effects of the Invention]

[0006] The present invention can provide a heavy-duty tire that can suppress deterioration of wet performance due to wear while reducing rolling resistance. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a development view showing a portion of a tread of a heavy duty tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a development view showing a part of FIG. [Figure 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2. [Figure 5] FIG. 3 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a cross-sectional view showing a modification of the transverse sipe of FIG. 6. [Figure 8] FIG. 2 is a cross-sectional view illustrating the arrangement of main lateral grooves, circumferential narrow grooves, and transverse sipes. [Figure 9] 10A and 10B are cross-sectional views illustrating modified arrangements of main lateral grooves, circumferential narrow grooves, and transverse sipes. [Figure 10] FIG. 10 is a cross-sectional view illustrating another modified example of the arrangement of the main lateral grooves, the circumferential narrow grooves, and the transverse sipes. DETAILED DESCRIPTION OF THE INVENTION

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

[0009] In the present invention, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the 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 a normal state. The dimensions and angles of each part of the tire's meridian cross section, which cannot be measured when the tire is mounted on a regular rim, are measured on a 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 of the tire mounted on a regular rim. Note that the tire configuration, which cannot be confirmed when the tire is mounted on a regular rim, is confirmed on the cut surface.

[0011] A genuine rim is a rim specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "design rim" in the TRA standard, and the "measuring rim" in the ETRTO standard are all genuine rims.

[0012] Normal tire pressure refers to the pressure specified in the standard on which the tire is based. The "maximum tire pressure" in the JATMA standard, the "maximum tire pressure" listed in the TRA standard's "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0013] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0014] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions. The center of the tread is also called the crown, and the edges of the tread are also called the shoulders.

[0015] [Findings that form the basis of the present invention] If the formulation of the rubber composition that makes up the tread is revised so that tan δ at 70°C is reduced, the rolling resistance of the tire will be reduced. However, in this case, tan δ at 0°C will also be reduced. To improve wet performance, the higher tan δ at 0°C is preferable. It is difficult to achieve both reduced rolling resistance and improved wet performance by revising the formulation of the rubber composition. The narrow grooves, whose wall surfaces can support each other when the tread deforms, can effectively suppress the deformation of the tread. By replacing the conventional circumferential main grooves with narrow grooves extending in the circumferential direction (hereinafter referred to as "circumferential narrow grooves") in the tread, it is possible to reduce rolling resistance without revising the rubber composition. However, in this case, the rigidity of the tread increases compared to conventional treads, raising concerns that wet performance may be reduced. Therefore, in order to suppress the deterioration of wet performance, the use of lateral grooves that cross the land areas in combination with the narrow grooves is being considered. The tread wears, which reduces the volume of the grooves cut into the tread. This reduction in groove volume reduces drainage. By providing circumferential narrow grooves and lateral grooves in the tread, tires can reduce rolling resistance while suppressing a decline in wet performance in the early stages of wear. However, there is concern that wet performance will decline from the middle stages of wear onwards. If the circumferential narrow grooves are provided with enlarged width sections in their radially inner parts, and the lateral grooves are provided with sipe sections in their radially inner parts, and the enlarged width sections and sipe sections are configured so that they are exposed from the middle stage of wear onwards, it is expected that the deterioration of wet performance from the middle stage of wear onwards can be suppressed. As the tread wears, its volume decreases. This causes the tread's apparent rigidity to increase. While increased rigidity is beneficial for reducing rolling resistance, it is detrimental to wet performance. Therefore, if the sipe portion is exposed first and the maximum width position of the expanded width portion is exposed later, the tire may not be able to sufficiently prevent a decrease in wet performance with just the sipe portion that is exposed first. Therefore, in order to achieve both reduced rolling resistance and improved wet performance, the inventors have provided the tread with circumferential narrow grooves having enlarged width portions and lateral grooves having sipe portions, and have conducted studies focusing on the amounts of styrene butadiene rubber and silica contained in the rubber composition that constitutes the tread (more specifically, the cap portion) and the timing at which the enlarged width portions and the tubular portion are exposed, and have completed the invention described below.

[0016] [Details of the embodiment 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 provides a tire having a tread made of a rubber composition including a rubber component containing styrene-butadiene rubber and a filler containing silica, the tread having a tread surface that comes into contact with a road surface, The tread has a plurality of circumferential grooves extending continuously in the circumferential direction, The plurality of circumferential grooves define a plurality of land portions arranged in the tread in the axial direction, the plurality of land portions include a plurality of main land portions located between adjacent ones of the circumferential grooves, Each of the main land portions has a plurality of main lateral grooves connecting adjacent ones of the circumferential grooves, the plurality of main lateral grooves define a plurality of main blocks arranged in the circumferential direction in the main land portion, The main lateral groove includes a groove portion and a sipe portion located radially inward of the groove portion and connected to the groove portion, The groove width of the sipe portion is narrower than the groove width of the groove portion, the circumferential groove located between the adjacent main land portions is a circumferential narrow groove, Among the plurality of main land portions, a main land portion located outermost in the axial direction is an outer main land portion, the circumferential groove located axially outward of each of the outer main land portions is a circumferential wide groove having a groove width wider than a groove width of the circumferential narrow groove, the circumferential narrow groove has a body portion and an enlarged width portion located radially inward of the body portion, The body portion includes a body main body to which the expanded width portion is connected, Due to deformation of the tread, opposing wall surfaces of the circumferential narrow groove come into contact with each other in the trunk body, The maximum width of the expanded width portion is wider than the minimum width of the trunk body, Between the body main body and the position where the expanded width portion has the maximum width, a position where the groove width is 2.0 times the minimum width of the body main body is a width reference position, A groove depth MH of the groove portion is shallower than a groove depth HB from the groove opening of the circumferential narrow groove to the width reference position, 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 relative to 100 parts by mass of the rubber component is 15 parts by mass or more, The heavy-duty tire is one in which the styrene-butadiene rubber content CSB, the silica content BS, the groove depth MH (mm) of the groove portion, and the groove depth HB (mm) from the groove opening of the circumferential narrow groove to the width reference position satisfy the following relational expressions: (CSB+BS) / (HB-MH)≧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 initial stage of wear but also in the middle stage of wear from when the sipe portions of the main lateral grooves are exposed until the width reference position of the expanded width portion of the circumferential narrow groove is exposed. The mechanism by which this 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. This deformation causes the wall surfaces of the circumferential narrow grooves to come into contact with each other at the body of the circumferential groove. The main land portions located on both sides of the circumferential narrow groove support each other. This suppresses tread deformation. The body of the circumferential groove can contribute to reducing rolling resistance. The rigidity of the tread appears to increase. There are concerns about a decrease in wet performance. However, the groove portions of the main lateral grooves that connect adjacent circumferential grooves suppress the decrease in wet performance. In this way, in the early stages of wear, it is presumed that the tire can suppress the decrease in wet performance due to wear while reducing rolling resistance. As tread wear progresses, the groove volume of the circumferential grooves and other grooves decreases, raising concerns about a decline in wet performance. However, an expanded width portion is located radially inward of the body portion. A sipe portion is located radially inward of the groove portion. When the body portion main body disappears, an expanded width portion with a groove width wider than the groove width of the body portion main body is exposed. When the groove portion disappears, a sipe portion with a groove width narrower than the groove width of the groove portion is exposed. The expanded width portion and sipe portion contribute to suppressing a decline in wet performance. Because the groove depth MH of the groove portion is shallower than the groove depth HB from the groove mouth of the circumferential narrow groove to the width reference position indicating a groove width 2.0 times the minimum width of the body portion main body, simultaneous exposure of the sipe portion and a portion with a groove width wider than 2.0 times the minimum width of the body portion main body is avoided. The occurrence of uneven wear due to sudden pattern changes is suppressed. The main lateral grooves and circumferential narrow grooves can each stably perform their respective functions. The volume of the tread decreases with wear. After the sipes are exposed, the area with a groove width greater than 2.0 times the minimum width of the body is exposed, but the tread's deformation margin is reduced, so the tread's rigidity appears to increase. This increased rigidity contributes to reduced rolling resistance. While increased rigidity is beneficial for reducing rolling resistance, it is detrimental to wet performance. However, the rubber composition constituting the tire tread contains styrene-butadiene rubber and silica. As the glass transition temperature (Tg) of the rubber component increases, road-holding performance in the small deformation region improves. The tread contributes to improved wet performance regardless of the stage of wear. In particular, the styrene-butadiene rubber content (CS), silica content (BS), groove depth (MH), and groove depth (HB) from the groove opening of the circumferential narrow groove to the width reference position representing a groove width 2.0 times the minimum width of the body are set to satisfy the aforementioned relationship. Therefore, even in the intermediate stage of wear, from the time the sipe portion of the main lateral groove is exposed until the width reference position of the expanded width portion of the circumferential narrow groove is exposed, the synergistic effect of the styrene-butadiene rubber and silica suppresses deterioration of wet performance. This tire maintains low rolling resistance while suppressing deterioration of wet performance from the time of use until replacement is required. According to the present invention, a tire can be obtained that can suppress deterioration of wet performance due to wear while reducing rolling resistance.

[0020] It is preferable that the rubber component further contains natural rubber and butadiene rubber, and 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 relationship: CN≧CSB+CB

[0021] It is believed that the rubber component further containing natural rubber (hereinafter, NR) and butadiene rubber (hereinafter, BR) so as to satisfy the above-mentioned relationship can improve the dispersibility of silica in the rubber composition while maintaining the durability of the tread. In this case, it is believed that the tire can suppress the deterioration of 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, because this allows the tread to further improve its road-following ability in the small deformation region, thereby improving the wet performance of the tire regardless of the stage of wear.

[0023] The silica preferably contains silica made from biomass materials, because such silica can contribute to reducing the environmental load.

[0024] The filler preferably contains silica having an average primary particle size of 16 nm or less, because such silica can contribute to improving abrasion resistance and durability.

[0025] The filler further contains carbon black, and the carbon black preferably contains recycled carbon black, because recycled carbon black can contribute to reducing environmental impact and is expected to reduce friction between its surface and rubber molecular chains, thereby suppressing heat buildup.

[0026] The filler further contains carbon black, and the carbon black preferably has an average primary particle size of 19 nm or less, because such carbon black can contribute to improving abrasion resistance and durability.

[0027] The rubber composition preferably further contains a resin component, because the resin component can contribute to improving wet performance.

[0028] The land ratio, as defined below, is preferably 75% or more. In this case, the land portions easily support each other, effectively increasing the rigidity of the tread. This effectively reduces the rolling resistance of the tire and also improves its wear resistance. Land ratio: The ratio of the total area of ​​the contact area of ​​the multiple land areas included in the contact area to the area of ​​the entire contact area, obtained by placing a tire mounted on a standard rim, adjusted to the standard internal pressure, on a flat road surface with a camber angle of 0 degrees and a load of 100% of the standard load.

[0029] Each of the plurality of main blocks has a transverse sipe that crosses the main block, The transverse sipe has a sipe body and a tubular portion located radially inward of the sipe body, It is preferable that the groove width of the tubular portion is wider than the groove width of the sipe body. This allows the sipe body to function as an edge component. Good wet performance is maintained. Furthermore, as the tread deforms and the wall surfaces of the sipe body come into close contact with each other, the wall surfaces constrain each other, effectively increasing the rigidity of the tread. In the early stages of wear, the sipe body can effectively contribute to maintaining wet performance and reducing rolling resistance. When the sipe body disappears, the tubular portion is exposed. After the sipe body disappears, the exposed tubular portion can contribute to suppressing a decline in wet performance.

[0030] It is more preferable that the groove bottom of the groove portion or the width reference position is located between the radially outer end and the radially inner end of the tubular portion. As a result, the tubular portion is exposed for a period from when the grooves disappear until the portion with a groove width greater than 2.0 times the minimum width of the body is exposed. During this period, the pattern changes significantly, but good wet performance is maintained.

[0031] the plurality of main land portions include inner main land portions located between adjacent ones of the circumferential narrow grooves, It is preferable that the sipe body of the transverse sipe included in the main block of the inner main land portion extends in a zigzag pattern in the length direction and depth direction. This effectively increases the rigidity of the tread when the tread deforms and the wall surfaces of the sipe bodies come into close contact with each other, effectively reducing rolling resistance and improving wear resistance while maintaining wet performance.

[0032] The circumferential narrow groove preferably includes a first narrow groove near a first end, which is one end of the tread surface, a second narrow groove near a second end, which is the other end of the tread surface, and a connecting narrow groove connecting the first narrow groove and the second narrow groove, and the first narrow groove and the second narrow groove are alternately arranged in the circumferential direction. As described above, when a force is applied to the tread and the tread deforms, the wall surfaces of the circumferential narrow grooves come into contact with each other at their body portions. The circumferential narrow grooves extend in a meandering manner in the circumferential direction, so the wall surfaces effectively mesh with each other. The main land portions located on both sides of the circumferential narrow groove restrain each other. The rigidity of the tread is apparently increased. Tread deformation is effectively suppressed. The tire can effectively reduce rolling resistance and also improve wear resistance.

[0033] In this way, the heavy duty tire of the present invention can suppress deterioration of wet performance due to wear while reducing rolling resistance.

[0034] [Rubber composition] The tread is made of a rubber composition. The tread is a crosslinked product of the rubber composition. The rubber composition for the tread will be described below. The rubber composition includes a rubber component and a filler.

[0035] [Rubber component] The rubber component contains styrene butadiene rubber (hereinafter referred to as SBR). The rubber component contains SBR and may further contain other rubber components, or may consist of only SBR.

[0036] [SBR] The SBR is not particularly limited, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs whose terminals and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Among these, S-SBR and modified SBR are preferred as the SBR contained in the rubber component. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) and the like can also be used as the SBR in this rubber composition. One of these SBRs may be selected and used alone, or two or more may be selected and used in combination.

[0037] SBR has excellent viscoelastic properties in the area highly correlated with wet performance (specifically, grip performance on wet roads), and it also has excellent compatibility and reactivity with silica, which will be described later. SBR is thought to contribute to improving wet performance and abrasion resistance.

[0038] The styrene content of SBR is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 9% by mass or more, from the viewpoint of contributing to improvements in wet performance and abrasion resistance. The styrene content of SBR is preferably 24% by mass or less, more preferably 18% by mass or less, and even more preferably 16% by mass or less. The styrene content of SBR is 1 It is calculated by H-NMR measurement.

[0039] The vinyl content of SBR is 26 mol% or more. If the vinyl content is less than 26 mol%, it is difficult to improve 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, even more preferably 29 mol% or more, and particularly preferably 30 mol% or more. The vinyl content of SBR is preferably 45 mol% or less, more preferably 44 mol% or less, even more preferably 43 mol% or less, and particularly preferably 42 mol% or less. The vinyl content of SBR (amount of 1,2-bonded butadiene units) is measured by infrared absorption spectroscopy.

[0040] 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 even 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, even 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 a "pure SBR fraction" obtained by removing the extender oil with acetone in accordance with JIS K6229.

[0041] The weight-average molecular weight (Mw) of SBR is preferably 100,000 or more, more preferably 150,000 or more, and even more preferably 190,000 or more, from the viewpoint of improving abrasion resistance. From the viewpoint of crosslinking uniformity, etc., the Mw of SBR is preferably 2.5 million or less, more preferably 2 million or less, and even more preferably 1 million or less. The Mw of SBR can be determined in terms of standard polystyrene based on measurements obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0042] As described above, the content of SBR (CSB) per 100 parts by mass of the rubber component is 10 parts by mass or more. SBR can effectively contribute to improving abrasion resistance and wet performance. From this viewpoint, the content of CSB is preferably 15 parts by mass or more, more preferably 17 parts by mass or more, and even more preferably 19 parts by mass or more. From the viewpoint of maintaining good abrasion resistance, the content of CSB is preferably 60 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 25 parts by mass or less.

[0043] As mentioned above, the rubber component can contain rubber components other than SBR. Examples of rubber components other than SBR include crosslinkable rubber components commonly used in the tire industry. 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), and hydrin rubber. One of these other rubber components may be selected and used alone, or two or more may be selected and used in combination.

[0044] The rubber component of the rubber composition for the tread preferably contains an isoprene-based rubber and BR as rubber components other than SBR.

[0045] [Isoprene rubber] Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. Examples of NR include SIR20, RSS#3, and TSR20, which are commonly used in the tire industry. Examples of IR include, but are not limited to, IR2200, which are commonly used in the tire industry. Examples of modified NR include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. 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.

[0046] When the rubber component contains NR, from the viewpoint of increasing the tread strength and improving the abrasion resistance, the content CN of NR per 100 parts by mass of the rubber component is preferably 30 parts by mass or more, more preferably 45 parts by mass or more, and even 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, and even more preferably 65 parts by mass or less.

[0047] [Butadiene rubber] The butadiene rubber (BR) is not particularly limited, and examples thereof include those commonly used in the tire industry, such as 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 butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR). These may be used alone or in combination of two or more. The cis content of BR is a value calculated by infrared absorption spectroscopy.

[0048] When the rubber component contains BR, the BR content CB 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, and is preferably 40 parts by mass or less, more preferably 25 parts by mass or less, from the viewpoint of improving abrasion resistance.

[0049] When the rubber component further contains NR and BR in addition to SBR, as described above, the NR content CN is preferably equal to the sum of the SBR content CSB and the BR content CB, or greater than the sum of the SBR content CSB and the BR content CB. This is because the dispersibility of silica in the rubber composition is improved while maintaining the durability of the tread. In this case, it is presumed that the tire can suppress deterioration of wet performance due to wear while reducing rolling resistance. From this perspective, it is more preferable that the NR content CN is greater than the sum of the SBR content CSB and the BR content CB. In other words, it is more preferable that the NR content CN, the SBR content CSB, and the BR content CB satisfy the following relationship: CN>CBS+CB

[0050] [Filler] As previously mentioned, the rubber composition for the tread includes a filler, and the filler includes silica. In other words, the rubber composition includes silica as a filler. The filler more preferably contains carbon black and silica, or may contain only carbon black and silica. In other words, the rubber composition more preferably contains carbon black and silica as a filler, or may contain only carbon black and silica as a filler.

[0051] [silica] The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica) or silica prepared by a wet method (hydrated silica), which are commonly used in the tire industry. Furthermore, from the viewpoint of environmental impact, as mentioned above, silica made from biomass materials (e.g., amorphous silica purified from rice husks) can also be used. Among these, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. These silicas can be used alone or in combination of two or more.

[0052] 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 then reacting the silicate with sulfuric acid in the same manner as conventional wet-process silica to produce a silicon dioxide precipitate, which is then filtered, washed with water, dried, and pulverized. When silica crystallizes, it becomes insoluble in water, and its component, silicic acid, cannot be utilized. By controlling the combustion temperature and duration, the crystallization of silica in rice husk ash can be suppressed (see, for example, JP 2009-2594 A and Akita Prefectural University Web Journal B / 2019, vol. 6, pp. 216-222). The amorphous silica extracted from rice husks may be commercially available from Wilmar Co., Ltd., etc.

[0053] From the viewpoint of improving abrasion resistance and durability, the average primary particle size of silica is preferably 22 nm or less, more preferably 19 nm or less, and even more preferably 16 nm or less, and the average primary particle size is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more.

[0054] The average primary particle diameter of silica can be determined by observing silica with a transmission or scanning electron microscope, measuring the outer diameters of 400 or more primary silica particles observed within the field of view, and averaging the measured values.

[0055] From the viewpoint of improving wear resistance and durability, the nitrogen adsorption specific surface area (N2SA) of silica is 100m 2 / g or more is preferable, and 110m 2 / g or more is more preferable, and 120m 2 / g or more is more preferable. 2 / g or less is preferable, and 350m 2 / g or less is more preferable, and 250m 2 / g or less is more preferable. The nitrogen adsorption specific surface area (N2SA) of silica is measured by the BET method in accordance with ASTM D3037-93.

[0056] The silica content BS per 100 parts by mass of the rubber component is 15 parts by mass or more. Silica can effectively reinforce the tread. The rigidity of the tread is increased, thereby improving abrasion resistance and durability. From this viewpoint, the silica content BS 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 silica content BS 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.

[0057] [Carbon black] The carbon black is not particularly limited, and can be, for example, GPF, FEF, HAF, ISAF, SAF, or other carbon black commonly used in the tire industry. Furthermore, from the viewpoint of reducing the environmental impact and reducing friction between the carbon black surface and rubber molecular chains, thereby suppressing heat buildup, recycled carbon black (rCB) obtained by pyrolysis of used tires can also be used in this tire. These carbon blacks can be used alone or in combination of two or more types. In the present invention, the aforementioned carbon blacks commonly used in the tire industry, such as GPF, FEF, HAF, ISAF, and SAF, are also called standard carbon blacks (sCB) to distinguish them from recycled carbon black (rCB).

[0058] As mentioned above, recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, citing "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, describes that recycled carbon black can be obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (

[0027] ). Carbon black obtained from such pyrolysis processes typically lacks functional groups on its surface, as mentioned in

[0004] of Japanese Patent No. 6856781 (Comparison of the Surface Morphology and Chemistry of Pyrolytic Carbon Black with Commercial Carbon Black, Powder Technology 160 (2005) pp. 190-193).

[0059] Recycled carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. Treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, European Patent Application Publication No. 3,173,251 discloses that 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. Japanese Patent No. 6,856,781 also discloses that carbon black obtained from a pyrolysis process is treated with an amino acid compound containing at least one thiol or disulfide group to obtain surface-activated carbon black. The recycled carbon black of this embodiment also includes carbon black treated to include functional groups on its surface. As the recycled carbon black, commercially available products from Strable Green Carbon, LD Carbon, etc. can be used.

[0060] From the viewpoint of improving abrasion resistance and durability, the average primary particle size of carbon black is preferably 25 nm or less, more preferably 22 nm or less, and even more preferably 19 nm or less, and is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more.

[0061] 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 within the field of view, and averaging the measured values.

[0062] From the viewpoint of improving wear resistance and durability, the nitrogen adsorption specific surface area (N2SA) of carbon black is 10m 2 / g or more is preferable, and 20m 2 / g or more is more preferable, and 30m 2 / g or more is more preferable. The nitrogen adsorption specific surface area (N2SA) is 250m 2 / g or less is preferable, and 200m 2 / g or less is more preferable, and 150m 2 The nitrogen adsorption specific surface area (N2SA) of carbon black is measured in accordance with JIS K6217-2:2017.

[0063] When the rubber composition contains carbon black, the carbon black content BC per 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 viewpoint of exerting a reinforcing effect and preventing deterioration due to ultraviolet rays. From the viewpoint of imparting flexibility to the tread and alleviating 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.

[0064] The content of recycled carbon black in 100 parts by mass of carbon black is not particularly limited, but may 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, or more than 30 parts by mass. From the viewpoint of exerting the reinforcing effect of carbon black, the content is preferably less than 95 parts by mass, more preferably less than 90 parts by mass, and even more preferably less than 85 parts by mass.

[0065] [Other fillers] Fillers other than silica and carbon black that have been commonly used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, and talc, can be blended.

[0066] From the viewpoint of further improving the road surface following ability of the tread in the small deformation region and improving the wet performance of the tire regardless of the stage of wear, 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.

[0067] From the viewpoint of improving abrasion resistance and durability, the total content of the filler per 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 of providing flexibility to the tread and alleviating stress, the content is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 65 parts by mass or less.

[0068] [Silane coupling agents] 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, and any silane coupling agent conventionally used in combination with silica in the tire industry can be used. Examples of the silane coupling agent include mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane and Momentive's NXT-Z100, NXT-Z45, and NXT; 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; vinyltriethoxysilane and vinyltrimethoxysilane. Examples of suitable silane coupling agents include vinyl-based silane coupling agents such as silane; 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; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, sulfide-based silane coupling agents and / or mercapto-based silane coupling agents are preferred, and sulfide-based silane coupling agents are more preferred. These silane coupling agents may be used alone or in combination of two or more.

[0069] The content of the silane coupling agent per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more, from the viewpoint of improving the dispersibility of silica, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, from the viewpoint of suppressing a decrease in abrasion resistance.

[0070] 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, even more preferably 5 parts by mass or more, and particularly preferably 8 parts by mass or more, from the viewpoint of improving the dispersibility of silica. From the viewpoint of reducing costs and improving processability, it is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and even more preferably 16 parts by mass or less.

[0071] [Other compounding agents] In addition to the above components, the rubber composition according to the present embodiment may appropriately contain compounding agents that are generally used in the tire industry, such as a softener, wax, stearic acid, zinc oxide, an antioxidant, a vulcanizing agent, and a vulcanization accelerator.

[0072] Examples of the softener include resin components, oils, and liquid rubbers.

[0073] The resin component usable in this embodiment is not particularly limited, but may be a resin commonly used in the tire industry, such as a C9 resin, a C5 resin, a C5C9 resin, a dicyclopentadiene resin, an aromatic vinyl resin, a coumarone resin, an indene resin, a terpene resin, a rosin resin, or a phenol resin. These resin components may be used alone or in combination of two or more.

[0074] C9 resin refers to a resin obtained by polymerizing a C9 fraction. It may be a C9 fraction polymerized alone or a copolymer obtained by copolymerizing a C9 fraction with other components. For example, a resin obtained by copolymerizing dicyclopentadiene (DCPD) with a C9 fraction is called a DCPD / C9 resin. These resins may also be hydrogenated or modified. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, coumarone, indene, methylindene, and dicyclopentadiene. These C9 resins may be used alone or in combination.

[0075] The C5 resin refers to a resin obtained by polymerizing a C5 fraction, and may be a hydrogenated or modified C5 resin. Examples of C5 fractions other than dicyclopentadiene include petroleum fractions having 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.

[0076] The C5C9 resin refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. As the C5C9 petroleum resin, for example, commercially available products from Tosoh Corporation, LUHUA, etc. can be used. These C5C9 resins may be used alone or in combination of two or more.

[0077] Dicyclopentadiene-based resins refer to resins containing cyclopentadiene (CPD) or dicyclopentadiene (DCPD) as monomer components, and may be hydrogenated or modified. Examples of dicyclopentadiene-based resins include DCPD / C9 resins containing dicyclopentadiene and the C9 fraction as monomer components (the DCPD / C9 resins may be hydrogenated or modified). 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. Examples of dicyclopentadiene-based resins that can be used include those commercially available from ExxonMobil, ENEOS Corporation, Nippon Zeon Co., Ltd., Maruzen Petrochemical Co., Ltd., and the like. These dicyclopentadiene-based resins may be used alone or in combination.

[0078] The aromatic vinyl resin refers to a resin containing an aromatic vinyl compound such as styrene, α-methylstyrene, vinyltoluene, or p-chlorostyrene as the monomer component with the largest content, and may be a hydrogenated or modified version of such a compound. As the aromatic vinyl resin, 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, because they are economical, easy to process, and have excellent heat generation properties. As the aromatic vinyl resin, for example, commercially available products from Kraton, Eastman Chemical Company, Mitsui Chemicals, Inc., etc. can be used. These aromatic vinyl resins may be used alone or in combination of two or more.

[0079] Coumarone resins refer to resins containing coumarone as a monomer component, and may be hydrogenated or modified. Examples of coumarone resins include coumarone-indene resins containing coumarone and indene as monomer components, and coumarone-indene-styrene resins containing coumarone, indene, and styrene as monomer components. These coumarone resins may be used alone or in combination of two or more.

[0080] Indene resins refer to resins containing indene as a monomer component, and may be hydrogenated or modified. Examples of indene resins include coumarone-indene resins containing coumarone and indene as monomer components, and coumarone-indene-styrene resins containing coumarone, indene, and styrene as monomer components. These indene resins may be used alone or in combination.

[0081] Terpene resins refer to resins containing terpene compounds such as α-pinene, β-pinene, limonene, and dipentene as the most abundant monomer component, and may be hydrogenated or modified. Specific examples of terpene resins include polyterpene resins containing only one or more of the terpene compounds as monomer components; aromatic-modified terpene resins containing the terpene compound and an aromatic compound as monomer components; and terpene phenolic resins containing the terpene compound and a phenolic compound as monomer components. Examples of aromatic compounds that serve as monomer components for aromatic-modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds that serve as monomer components for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol. These terpene resins may be used alone or in combination.

[0082] The rosin-based resin refers to a resin containing a rosin acid compound such as abietic acid, neoabietic acid, palustric acid, or isopimaric acid, and may be a hydrogenated or modified version of such a resin. The rosin-based resin is not particularly limited, but examples thereof include natural rosin resin and rosin-modified resins obtained by modifying rosin through hydrogenation, disproportionation, dimerization, esterification, or the like. These rosin-based resins may be used alone or in combination of two or more.

[0083] The phenolic resin refers to a resin that contains a phenolic compound such as phenol or cresol as the monomer component with the highest content. Examples of the phenolic resin include, but are not limited to, phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin. These phenolic resins may be used alone or in combination of two or more.

[0084] 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 viewpoint of processability and improving the dispersibility of the rubber component and the filler, the softening point is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. The softening point of the resin is the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2015 7.7 is measured using a ring and ball softening point tester.

[0085] When the rubber composition contains a resin component, the content of the resin component per 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 buildup, 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.

[0086] Examples of oils include process oil, vegetable oils and fats, and animal fats and oils. Examples of process oils include paraffinic process oil, naphthenic process oil, and aromatic process oil. In consideration of environmental impact, process oil with a low content of polycyclic aromatic compounds (PCA) can also be used. Examples of low-PCA process oils include mild extract solvates (MES), treated distillate aromatic extracts (TDAE), and heavy naphthenic oil.

[0087] When the rubber composition contains oil, the amount of oil per 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 amount of 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.

[0088] The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used alone or in combination of two or more.

[0089] When the rubber composition contains a liquid rubber, the content of the liquid rubber per 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, and 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.

[0090] The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; and synthetic waxes such as polymers of ethylene, propylene, etc. Commercially available products that can be used include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. These may be used alone or in combination of two or more.

[0091] When the rubber composition contains wax, the content of the wax per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of weather resistance of the rubber. The content of the 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.

[0092] The antioxidant is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamates. Phenylenediamine-based antioxidants, such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based antioxidants, such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, are preferred. These antioxidants may be used alone or in combination.

[0093] When the rubber composition contains an antioxidant, the content of the antioxidant per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of ozone crack resistance of the rubber. The content of the antioxidant is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, from the viewpoint of abrasion resistance and wet grip performance.

[0094] As the stearic acid, conventionally known ones can be used, and commercially available products that can be used include products from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

[0095] When the rubber composition contains stearic acid, the content of stearic acid per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, from the viewpoint of vulcanization rate.

[0096] As the zinc oxide, conventionally known ones can be used, and commercially available products include those available from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

[0097] When the rubber composition contains zinc oxide, the content of zinc oxide per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less from the viewpoint of abrasion resistance.

[0098] As the vulcanizing agent, sulfur is preferably used, and examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0099] When the rubber composition contains sulfur as a vulcanizing agent, the sulfur content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. 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. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is expressed as the amount of pure sulfur contained in the oil-containing sulfur.

[0100] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylenedithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Co., Ltd., Lanxess K.K., Flexis, etc.

[0101] 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, and xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among these, 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, in terms of more suitably achieving the desired effects.

[0102] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), etc. Among these, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS) and N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) are preferred.

[0103] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0104] Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, etc. Among these, 2-mercaptobenzothiazole is preferred.

[0105] When the rubber composition contains a vulcanization accelerator, the content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts 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, even 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 this range, it tends to be possible to ensure breaking strength and elongation.

[0106] The rubber composition is produced, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or a Banbury mixer. As for the kneading conditions, in the base kneading step in which additives other than the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish kneading step in which the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 120°C or lower, preferably 85 to 110°C.

[0107] The produced rubber composition is processed into a predetermined shape using an extruder or the like. In a molding machine, the rubber composition is combined with sidewalls and the like to prepare a green tire (a tire in an uncrosslinked state). The green tire is vulcanized in a mold incorporated in a vulcanizer to obtain a tire. 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.

[0108] The rubber composition described above is used in the tread of a tire (specifically, the cap portion that comes into contact with the road surface during driving). Next, a tire having a tread formed using this rubber composition will be described.

[0109] [tire] 1 is a plan view showing a part of a tread 4 of a tire 2 according to one embodiment of the present invention in which the tire 2 is developed. The tire 2 is mounted on vehicles such as trucks and buses. The tire 2 is a heavy-duty tire. In FIG. 1, the direction indicated by the double 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 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. In FIG. 1, a dashed line CL extending in the circumferential direction represents the equatorial plane of the tire 2. A tire 2 traveling on a road surface makes contact with the road surface from the side indicated by arrow CD1 to the side indicated by arrow CD2. The CD1 side is the leading side of the tire 2, and the CD2 side is the trailing side of the tire 2.

[0110] Fig. 1 shows an example of a tread pattern configured on a tread 4. The tread pattern of the present invention will be described below using the tread pattern shown in Fig. 1 as an example. In the present invention, the internal structure of the tire 2 is not particularly important. Although not described in detail, this tire 2 has a general internal structure as the internal structure of a heavy-duty tire. FIG. 2 shows a portion of the tread pattern shown in FIG.

[0111] 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 a tread surface 6. The tire 2 comes into contact with the road surface at the tread surface 6. The tread 4 has the tread surface 6 that comes into contact with the road surface. The tread 4 is made of crosslinked rubber. The tread 4 is a crosslinked product of the above-mentioned rubber composition. Grooves 8 are cut into the tread 4. This forms a tread pattern.

[0112] The intersection of the tread surface 6 and the equatorial plane is the equator. Although not shown, when the grooves 8 are located on the equatorial plane, the equator is identified based on a virtual outer surface obtained by assuming that the grooves 8 are not on the equatorial plane.

[0113] The position indicated by the symbol TE represents the edge of the tread surface 6 . In a tire, if the edge of the tread surface cannot be identified visually, the position on the outer surface of the tire corresponding to the axially outer edge of the contact patch obtained by applying a normal load to a tire in a normal state, setting the camber angle to 0°, and contacting the tire with a flat surface is used as the edge of the tread surface.

[0114] 1, one end TE of the tread surface 6 located on the left side of the equatorial plane is called a first end TE1, and the other end TE located on the right side of the equatorial plane is called a second end TE2.

[0115] 1 is the width of the tread surface 6. The width TW of the tread surface 6 is the axial distance from a first end TE1 to a second end TE2 of the tread surface 6. The width TW of the tread surface 6 is expressed as the length measured along the tread surface 6.

[0116] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1. Fig. 3 shows a cross-section of a groove 8, more specifically, a shoulder circumferential groove, which will be described later. The main configuration of the groove 8 will be described based on Fig. 3.

[0117] The groove 8 has a pair of wall surfaces 8W including a groove mouth 8M and a bottom surface 8B including a groove bottom 8T. The groove width of the groove 8 is expressed as the distance between the pair of wall surfaces 8W, that is, the distance between the wall surfaces. The length indicated by the double-headed arrow WG in Figure 3 is the groove width of the groove 8 at the groove opening 8M. The groove width WG is expressed as the shortest distance between a pair of edges 8E that form the groove opening 8M. If the groove opening 8M of the groove 8 is tapered, the groove width at the groove opening 8M of the groove 8 is expressed based on a virtual edge obtained by assuming that the groove is not tapered. The length indicated by the double-headed arrow DG is the depth of the groove 8. The depth DG of the groove 8 is expressed as 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, groove width WG, and groove depth DG of the groove 8 are determined appropriately according to the specifications of the tire 2.

[0118] The groove bottom 8T is the deepest position in the cross section of the groove 8. The distance from the line segment connecting the left and right edges 8E that make up the groove opening 8M to the bottom surface 8B is measured along the normal to this line segment. The position where the distance from this line segment to the bottom surface 8B is the longest is the groove bottom 8T. 3 is a curved surface. The bottom surface 8B may include a flat surface, and this flat surface may include the groove bottom 8T. In this case, the width center of the flat surface is used as the groove bottom 8T.

[0119] A groove 8 having a groove width WG of less than 1.0 mm at its groove mouth 8M is also called a sipe. A groove 8 other than a sipe is also called a normal groove, and has a groove width WG of 1.0 mm or more at its groove mouth 8M. The sipe may include a portion having a groove width of 1.0 mm or more between the groove mouth 8M and the groove bottom 8T (hereinafter referred to as a portion equivalent to a normal groove). In this case, as the tread 4 wears and the portion equivalent to a normal groove becomes exposed, the sipe changes into a normal groove. The normal groove may include a portion (a portion corresponding to a sipe) having a groove width of less than 1.0 mm between the groove mouth 8M and the groove bottom 8T. In this case, the normal groove changes into a sipe when the tread 4 wears and the portion corresponding to the sipe becomes exposed. Even among ordinary grooves, those with a narrow groove width that allows opposing walls to come into contact with each other when the tire touches the road surface are also called narrow grooves, while those with a wide groove width that prevents opposing walls from coming into contact with each other when the tire touches the road surface are also called wide grooves.

[0120] 3, the length indicated by the double-headed arrow DGC is the groove depth of the circumferential groove 10. The groove depth DGC of the circumferential groove 10 is, for example, 10 mm or more and 21 mm or less. From the viewpoint of enabling the tire 2 to exhibit good wet performance, the groove depth DGC is preferably 13 mm or more and 18 mm or less.

[0121] The tread 4 of this tire 2 is formed with circumferential grooves 10 that extend continuously in the circumferential direction. The tread 4 is formed with a plurality of circumferential grooves 10, which define a plurality of land portions 12 aligned in the axial direction. In other words, the tread 4 has a plurality of circumferential grooves 10. The plurality of circumferential grooves 10 define a plurality of land portions 12 in the tread 4.

[0122] In the present invention, the circumferential groove located outermost in the axial direction among the multiple circumferential grooves cut in the tread is also referred to as a shoulder circumferential groove. A circumferential groove located on the equatorial plane is also referred to as a center circumferential groove. When no circumferential groove is provided on the equatorial plane, the circumferential groove closest to the equatorial plane is also referred to as a center circumferential groove. When a circumferential groove is located between the center circumferential groove and the shoulder circumferential groove, this circumferential groove is also referred to as a middle circumferential groove.

[0123] The tread 4 shown in Fig. 1 has four circumferential grooves 10 aligned in the axial direction. Of the four circumferential grooves 10, the circumferential groove 10 located outermost in the axial direction is a shoulder circumferential groove 16. The circumferential groove 10 closest to the equatorial plane is a center circumferential groove 14. 1, the length indicated by the double-headed arrow WGCc is the groove width at the groove opening of the center circumferential groove 14. The length indicated by the double-headed arrow WGCs is the groove width at the groove opening of the shoulder circumferential groove 16.

[0124] The ratio (WGCc / TW) of the groove width WGCc of the central circumferential groove 14 to the width TW of the tread surface 6 is 2.0% or less. 1, the groove width WGCs of the shoulder circumferential groove 16 is wider than the groove width WGCc of the center circumferential groove 14. The ratio (WGCs / TW) of the groove width WGCs of the shoulder circumferential groove 16 to the width TW of the tread surface 6 exceeds 2.0%. Specifically, the ratio (WGCs / TW) is preferably 4.0% or more and 10% or less.

[0125] The shoulder circumferential groove 16 of this tire 2 includes an outer vertex 16s close to the edge TE of the tread surface 6 and an inner vertex 16u close to the equatorial plane. The outer vertices 16s and the inner vertices 16u are arranged alternately in the circumferential direction. The shoulder circumferential groove 16 extends in the circumferential direction, alternately passing through the outer vertices 16s and the inner vertices 16u. The shoulder circumferential groove 16 extends in a zigzag manner in the circumferential direction. The shoulder circumferential groove 16 may also extend straight in the circumferential direction.

[0126] As will be described later, the center circumferential groove 14 is a narrow groove whose opposing wall surfaces can come into contact with each other when the tire 2 comes into contact with the road surface. The shoulder circumferential grooves 16 are wide grooves whose opposing wall surfaces do not come into contact with each other even when the tire 2 comes into contact with the road surface. The center circumferential groove 14 of this tire 2 is a narrow circumferential groove 18 , and the shoulder circumferential grooves 16 are wide circumferential grooves 20 . The four circumferential grooves 10 formed in the tread 4 of this tire 2 are composed of a pair of circumferential narrow grooves 18 and a pair of circumferential wide grooves 20. The circumferential wide grooves 20 have a groove width WGCs wider than the groove width WGCc of the circumferential narrow grooves 18.

[0127] In the present invention, among the multiple land portions configured in the tread, the land portion located outermost in the axial direction is also called a shoulder land portion. A land portion located on the equatorial plane is also called a center land portion. When no land portion is provided on the equatorial plane, the land portion closest to the equatorial plane is also called a center land portion. A land portion located between the center land portion and the shoulder land portion is also called a middle land portion.

[0128] The tread 4 has five land portions 12 aligned in the axial direction. Of the five land portions 12, the land portion 12 located outermost in the axial direction is a shoulder land portion 22. The land portion 12 located on the equatorial plane is a center land portion 24. The land portion 12 located between the center land portion 24 and the shoulder land portion 22 is a middle land portion 26. Although not described in detail, the width of each land portion 12 is determined appropriately according to the specifications of the tire 2.

[0129] In the present invention, among the plurality of land portions formed in the tread, the land portion between adjacent circumferential grooves is also called a main land portion.

[0130] As shown in Fig. 2, the center land portion 24 of this tire 2 is located between two center circumferential grooves 14. The middle land portion 26 is located between the center circumferential groove 14 and the shoulder circumferential groove 16. The center land portion 24 and the middle land portion 26 are each the land portion 12 between adjacent circumferential grooves 10. In this tread 4, the center land portion 24 and the middle land portion 26 are main land portions 28. The five land portions 12 formed in the tread 4 include three main land portions 28 located between adjacent circumferential grooves 10. The tread 4 of this tire 2 is configured with a plurality of land portions 12 aligned in the axial direction, and the plurality of land portions 12 includes a plurality of main land portions 28 positioned between adjacent circumferential grooves 10.

[0131] In the present invention, among the plurality of main land portions, the main land portion located outermost in the axial direction is also referred to as an outer main land portion. In this tire 2, of the main land portions 28, that is, the center land portion 24 and the pair of middle land portions 26, the main land portion 28 located outermost in the axial direction is the middle land portion 26. The middle land portion 26 is an outer main land portion 28s. The main land portion 28 located between the left and right outer main land portions 28s is also called the inner main land portion 28u. In this tire 2, the center land portion 24 is the inner main land portion 28u. Circumferential narrow grooves 18 are located on both sides of the inner main land portion 28u. The main land portion 28 located between adjacent circumferential narrow grooves 18 is the inner main land portion 28u.

[0132] The shoulder circumferential groove 16 is located axially outward of the middle land portion 26. As described above, the shoulder circumferential groove 16 is the wide circumferential groove 20. The circumferential groove 10 located axially outward of the outer main land portion 28s is the wide circumferential groove 20 having a groove width wider than the groove width of the narrow circumferential groove 18.

[0133] The shoulder land portion 22 is located axially outward of the shoulder circumferential groove 16 and includes the edge TE of the tread surface 6. The shoulder land portion 22 is located further outward of the shoulder circumferential groove 16 that is located outermost in the axial direction. The shoulder land portion 22 is not a main land portion 28.

[0134] In this tire 2, a land portion 12 may be further provided between the shoulder land portion 22 and the middle land portion 26. In this case, the land portion 12 located between the shoulder land portion 22 and the middle land portion 26 has circumferential grooves 10 located on both sides thereof, and therefore is a main land portion 28. A plurality of land portions 12 may be further provided between the shoulder land portion 22 and the middle land portion 26.

[0135] In this tire 2, a plurality of lateral grooves 32 that cross the land portions 12 are formed in all of the land portions 12 that are formed in the tread 4. As a result, a plurality of blocks 34 that are arranged in the circumferential direction are formed in each land portion 12. The tread pattern of this tire 2 is a block pattern.

[0136] The lateral grooves 32 cut in the central land portion 24 are also called central lateral grooves 36. The central lateral grooves 36 connect the central circumferential groove 14 on the first end TE1 side of the tread surface 6 (hereinafter referred to as the first central circumferential groove 141) and the central circumferential groove 14 on the second end TE2 side (hereinafter referred to as the second central circumferential groove 142). The blocks 34 formed in the center land portion 24 are also called center blocks 38. The plurality of center lateral grooves 36 form the plurality of center blocks 38 in the center land portion 24.

[0137] The lateral grooves 32 formed in the middle land portion 26 are also called middle lateral grooves 40. The middle lateral grooves 40 connect the shoulder circumferential grooves 16 and the center circumferential groove 14. The blocks 34 formed in the middle land portion 26 are also called middle blocks 42. The plurality of middle lateral grooves 40 form the plurality of middle blocks 42 in the middle land portion 26.

[0138] The lateral grooves 32 cut in the shoulder land portions 22 are also called shoulder lateral grooves 44. The shoulder lateral grooves 44 connect the edge TE of the tread surface 6 and the outer apex 16s of the shoulder circumferential groove 16. The blocks 34 formed in the shoulder land portion 22 are also called shoulder blocks 46. The shoulder lateral grooves 44 form the shoulder blocks 46 in the shoulder land portion 22.

[0139] The shoulder lateral grooves 44 have deep bottom portions 44d on the shoulder circumferential groove 16 side and shallow bottom portions 44s on the end TE side of the tread surface 6. Shoulder sipes 44p are formed in the shallow bottom portions 44s. The shoulder blocks 46 are formed with shoulder narrow grooves 46g that connect the deep bottom portions 44d on the leading side and the shallow bottom portions 44s on the trailing side.

[0140] In the present invention, the lateral grooves 32 that cross the main land portions 28 are also called main lateral grooves 48 . As described above, the center land portion 24 and the middle land portion 26 are the main land portion 28. Therefore, the center lateral groove 36 cut in the center land portion 24 and the middle lateral groove 40 cut in the middle land portion 26 are the main lateral grooves 48. The tread 4 is formed with a plurality of main land portions 28, and each main land portion 28 has a plurality of main lateral grooves 48 connecting adjacent circumferential grooves 10.

[0141] In the present invention, the blocks 34 formed by cutting a plurality of main lateral grooves 48 into the main land portion 28 are also called main blocks 50 . The center block 38 formed by carving the center lateral groove 36 in the center land portion 24 and the middle block 42 formed by carving the middle lateral groove 40 in the middle land portion 26 constitute the main block 50. The plurality of main lateral grooves 48 cut in the main land portion 28 constitute a plurality of main blocks 50 arranged in the circumferential direction in the main land portion 28.

[0142] As mentioned above, among the multiple main land portions 28, the main land portion 28 located outermost in the axial direction is the outer main land portion 28s, and the main land portion 28 located between the left and right outer main land portions 28s is the inner main land portion 28u. The main lateral grooves 48 cut in the outer main land portion 28s are also called outer main lateral grooves 78, and the main blocks 50 formed in the outer main land portion 28s are also called outer main blocks 50s. The main lateral grooves 48 cut in the inner main land portion 28u are also called inner main lateral grooves 80, and the main blocks 50 formed in the inner main land portion 28u are also called inner main blocks 50u.

[0143] As described above, the shoulder land portion 22 is not a main land portion 28. The shoulder lateral grooves 44 cut in the shoulder land portion 22 are not main lateral grooves 48. The shoulder blocks 46 formed by cutting the shoulder lateral grooves 44 in the shoulder land portion 22 are not main blocks 50.

[0144] The main blocks 50 of the tire 2 are provided with transverse sipes 52 that cross the main blocks 50 . The transverse sipes 52 of this tire 2 are provided in the center blocks 38 and the middle blocks 42, which are the main blocks 50. The transverse sipes 52 may be provided only in the center blocks 38. The transverse sipes 52 may be provided only in the middle blocks 42. In other words, in this tire 2, in at least one main land portion 28, each of the multiple main blocks 50 has a transverse sipe 52 that crosses the main block 50.

[0145] Fig. 4 is a cross-sectional view of the inner main lateral groove 80 taken along line IV-IV in Fig. 2. Fig. 4 shows a cross-section of the inner main lateral groove 80 taken along a plane perpendicular to the longitudinal direction of the inner main lateral groove 80. In this tire 2, the cross-sectional shape of the outer main lateral groove 78 is the same as that of the inner main lateral groove 80. A description of the cross-sectional shape of the outer main lateral groove 78 will be omitted. 4 shows the cross-sectional shape of the main lateral groove 48. The cross-sectional shape of the main lateral groove 48 will be described based on this FIG.

[0146] The main lateral groove 48 includes a groove portion 82 and a sipe portion 84. The groove portion 82 includes the groove mouth 48M of the main lateral groove 48. The groove width of the groove portion 82 is 1.0 mm or more. The groove portion 82 is not a sipe. The sipe portion 84 includes the groove bottom 48T of the main lateral groove 48. The groove width of the sipe portion 84 is narrower than the groove width of the groove portion 82. Specifically, the groove width of the sipe portion 84 is less than 1.0 mm. The sipe portion 84 is a sipe.

[0147] The groove 82 comprises a tapered portion 86 and a body main body 88. The tapered portion 86 includes the groove opening 48M mentioned above. The tapered portion 86 tapers inward from the groove opening 48M. The body main body 88 is located radially inside the tapered portion 86. The body main body 88 is continuous with the tapered portion 86. The boundary between the body main body 88 and the tapered portion 86 is the groove opening 88M of the body main body 88. The body main body 88 tapers inward from the groove opening 88M. The body main body 88 includes the groove bottom 82T of the groove 82. The groove width of the body main body 88 is wider than the groove width of the sipe portion 84.

[0148] The grooves 82 may not be provided with the tapered portions 86. In this case, the wall surfaces of the body body 88 shown in Fig. 4 are expanded outward, and the cross-sectional shape of the grooves 82 is adjusted so that the intersections of the extensions of the wall surfaces and the extensions of the tread surface 6 become the groove openings of the main lateral grooves 48. From the viewpoint of effectively suppressing the concentration of strain on the edges of the main blocks 50 while ensuring the groove volume of the main lateral grooves 48 in the tire 2, it is preferable that the groove portions 82 of the main lateral grooves 48 be provided with tapered portions 86 as shown in FIG. 4.

[0149] The sipe portion 84 is located radially inward of the groove portion 82. The sipe portion 84 is cut into the groove bottom 82T of the groove portion 82. The sipe portion 84 extends further inward from the groove bottom 82T of the groove portion 82. The sipe portion 84 is shaped by a blade made of a flat plate. The wall surface of the sipe portion 84 is made up of a flat surface.

[0150] 4, the length indicated by the double arrow MY is the groove depth of the main lateral groove 48. The length indicated by the double arrow MH is the groove depth of the groove portion 82. The length indicated by the double arrow MT is the groove depth of the tapered portion 86.

[0151] The groove depth MY of the main lateral grooves 48 is the same as the groove depth DGC of the circumferential grooves 10, or the main lateral grooves 48 are shallower than the circumferential grooves 10. Specifically, the groove depth MY of the main lateral grooves is preferably 0.80 to 1.00 times the groove depth DGC of the shoulder circumferential grooves 16.

[0152] From the viewpoint that the tire 2 can effectively suppress the concentration of strain on the edges of the main blocks 50 while ensuring the groove volume of the main lateral grooves 48, it is preferable that the ratio (MT / MY) of the groove depth MT of the tapered portion 86 to the groove depth MY of the main lateral grooves 48 be 0.12 or more and 0.14 or less.

[0153] Fig. 5 is a cross-sectional view of the center circumferential groove 14 taken along line VV in Fig. 2. Fig. 5 shows a cross-section of the center circumferential groove 14 taken along a plane perpendicular to the length direction of the center circumferential groove 14. As described above, the center circumferential groove 14 is the circumferential narrow groove 18. FIG.

[0154] The circumferential narrow groove 18 includes a body portion 58 and an enlarged width portion 60. The body portion 58 includes a groove mouth 18M of the circumferential narrow groove 18. The enlarged width portion 60 is located radially inward of the body portion 58. The enlarged width portion 60 includes a groove bottom 18T of the circumferential narrow groove 18.

[0155] The body portion 58 of this tire 2 includes a tapered portion 62 and a body portion main body 64. The groove opening 18M of this circumferential narrow groove 18 is processed to have a tapered shape.

[0156] The tapered portion 62 includes the groove opening 18M of the circumferential narrow groove 18. The tapered portion 62 tapers inward from the groove opening 18M. The contour of the wall surface of the tapered portion 62 shown in Fig. 5 is represented by a straight line. This contour may also be represented by a curved line. 5 is the groove width at the groove mouth 18M of the tapered portion 62. The groove width WA of the tapered portion 62 is preferably 0.15 to 0.45 times the groove width WGCs of the shoulder circumferential groove 16.

[0157] The barrel body 64 is located radially inside the tapered portion 62. The barrel body 64 is continuous with the tapered portion 62. The barrel body 64 extends straight in the depth direction of the circumferential narrow groove 18. In the cross section shown in FIG. 5, the outline of the wall surface of the barrel body 64 is represented by a straight line. The length indicated by the double arrow WD in FIG. 5 is the minimum width of the barrel body 64. The barrel body 64 has a uniform groove width WD in the depth direction of the circumferential narrow groove 18. As described above, when the groove opening 8M of the groove 8 is tapered, the groove width at the groove opening 8M of the groove 8 is expressed based on the virtual edge obtained assuming that the groove is not tapered. The groove width at the groove opening 18M of the circumferential narrow groove 18 is expressed as the groove width WD of the trunk main body 64.

[0158] The position indicated by the symbol PU in Figure 5 is the boundary between the tapered portion 62 and the barrel main body 64. The boundary PU is represented by the intersection of the wall surface contour line of the tapered portion 62 and the wall surface contour line of the barrel main body 64. As shown in Figure 5, when the boundary between the tapered portion 62 and the barrel main body 64 is rounded, the boundary PU is represented by the intersection of the extension of the wall surface contour line of the tapered portion 62 and the extension of the wall surface contour line of the barrel main body 64.

[0159] The expanded width portion 60 is located radially inward of the barrel main body 64. The expanded width portion 60 is continuous with the barrel main body 64. The expanded width portion 60 has a groove width wider than the groove width WD of the barrel main body 64. 5, the length indicated by the double-headed arrow WN is the maximum width of the expanded width portion 60. The position indicated by the symbol PN is the position where the expanded width portion 60 has the maximum width WN (hereinafter referred to as the maximum width position PN). The portion of the circumferential narrow groove 18 excluding the body portion 58, i.e., the expanded width portion 60 of the circumferential narrow groove 18, tapers outward from the maximum width position PN and tapers inward from the maximum width position PN.

[0160] The expanded width portion 60 includes an inflection portion 94 and a bottom portion 96. The inflection portion 94 is located radially inward of the barrel main body 64. The bottom portion 96 is located radially inward of the inflection portion 94.

[0161] The inflection portion 94 connects the trunk portion main body 64 and the bottom portion 96. The groove width of the inflection portion 94 gradually increases from the trunk portion main body 64 side toward the bottom portion 96 side. The inflection portion 94 curves so as to recess inward from its outer side. In this tire 2, the outline of the inflection portion 94 is represented by an arc. In FIG. 5, arrow Rc indicates the radius of the arc representing the outline of the inflection portion 94.

[0162] The position indicated by the symbol PS in Figure 5 is the boundary between the barrel main body 64 and the expanded width portion 60. As described above, in the cross section of the circumferential narrow groove 18, the wall surface contour line of the barrel main body 64 is a straight line. In the present invention, the position where the wall surface contour line of the expanded width portion 60 converges to the wall surface contour line of the barrel main body 64 (in the circumferential narrow groove 18 shown in Figure 5, this is the boundary between the straight line representing the contour of the barrel main body 64 and the arc representing the contour of the inflection portion 94) is the boundary PS between the barrel main body 64 and the expanded width portion 60. When the boundary PS cannot be identified based on differences in contour, the position showing a groove width that is 1.1 times the groove width WD of the barrel main body 64 in the groove width from the barrel main body 64 to the expanded width portion 60 is represented as the boundary PS between the barrel main body 64 and the expanded width portion 60.

[0163] The bottom portion 96 includes the groove bottom 18T. The bottom portion 96 has a rounded contour. The bottom portion 96 is curved so as to bulge outward from its inner side. The contour of the bottom portion 96 of the circumferential narrow groove 18 shown in FIG. 5 is represented by a circular arc. In FIG. 5, an arrow Rt indicates the radius of the circular arc representing the contour of the bottom portion 96. The radius Rt of this circular arc is, for example, not less than 1.5 mm and not more than 3.5 mm.

[0164] The position indicated by the symbol PR is the boundary between the inflection portion 94 and the bottom portion 96. The arc representing the contour of the inflection portion 94 and the arc representing the contour of the bottom portion 96 are in contact at the boundary PR. 5, the maximum width position PN of the expanded width portion 60 is included in the bottom portion 96. In other words, the maximum width position PN is located radially inward of the boundary PR. The maximum width WN of the expanded width portion 60 is equal to twice the radius Rt of the circular arc that defines the outline of the bottom portion 96. In the tire 2, the radius Rc of the arc that defines the outline of the inflection portion 94 is larger than the radius Rt of the arc that defines the outline of the bottom portion 96. This allows the circumferential narrow groove 18 to fully exhibit its function. From this viewpoint, it is preferable that the ratio Rc / Rt of the radius Rc of the arc that defines the outline of the inflection portion 94 to the radius Rt of the arc that defines the outline of the bottom portion 96 be 1.5 or greater and 20 or less. Setting the ratio Rc / Rt to 1.5 or greater can suppress the occurrence of uneven wear due to a sudden change in rigidity in the tire 2. From this viewpoint, the ratio Rc / Rt is more preferably 2.0 or greater. Setting the ratio Rc / Rt to be equal to or less than 20 can suppress deterioration in wet performance of the tire 2. From this viewpoint, the ratio Rc / Rt is more preferably equal to or less than 15.

[0165] As described above, the expanded width portion 60 has a groove width wider than the groove width WD of the body main body 64. From the viewpoint of maintaining wet performance, the maximum width WN of the expanded width portion 60 is preferably at least two times, and more preferably at least three times, the minimum width WD of the body main body 64. From the viewpoint of suppressing the effect on the rigidity of the crown portion of the tread 4 and enabling the tire 2 to maintain good uneven wear resistance, the maximum width WN of the expanded width portion 60 is preferably no more than eight times, and more preferably no more than seven times, the minimum width WD of the body main body 64.

[0166] The tapered portion 62 may not be provided in the circumferential narrow groove 18. In other words, the body portion 58 may be composed of only the body portion main body 64. In this case, the cross-sectional shape of the circumferential narrow groove 18 is adjusted so that the wall surface of the body portion main body 64 shown in Fig. 5 extends outward and the intersection of the extension of the wall surface and the extension of the tread surface 6 corresponds to the groove opening of the body portion main body 64, i.e., the groove opening 18M of the circumferential narrow groove 18. From the viewpoint of effectively suppressing the concentration of strain on the edges of the main blocks 50 while ensuring the groove volume of the circumferential narrow grooves 18 in the tire 2, it is preferable that the circumferential narrow grooves 18 be provided with tapered portions 62 as shown in FIG. 5.

[0167] 5, the length indicated by the double-headed arrow HM is the groove depth of the circumferential narrow groove 18. The length indicated by the double-headed arrow HH is the groove depth of the trunk portion 58. The length indicated by the double-headed arrow HT is the groove depth of the tapered portion 62.

[0168] The groove depth HM of the circumferential narrow groove 18 of this tire 2 is approximately the same as the groove depth DGC of the circumferential groove 10. Specifically, the groove depth HM of the circumferential narrow groove 18 is 0.95 to 1.05 times the groove depth DGCs of the shoulder circumferential groove 16.

[0169] 5 is the width reference position of the circumferential narrow groove 18. The width reference position PB is a position between the body main body 64 of the circumferential narrow groove 18 and the maximum width position PN of the expanded width portion 60, and indicates a groove width that is 2.0 times the minimum width WD of the body main body 64. When the exposed position of the circumferential narrow groove 18 passes through the width reference position PB, the expanded width portion 60 of the circumferential narrow groove 18 can effectively contribute to suppressing a deterioration in wet performance. In FIG. 5, the length indicated by the double-headed arrow HB is the groove depth from the groove opening 18M of the circumferential narrow groove 18 to the width reference position PB.

[0170] From the viewpoint that the tire 2 can effectively suppress the concentration of strain on the edges of the main blocks 50 while ensuring the groove volume of the circumferential narrow grooves 18, it is preferable that the ratio (HT / HM) of the groove depth HT of the tapered portion 62 to the groove depth HM of the circumferential narrow grooves 18 is 0.12 or more and 0.14 or less.

[0171] As described above, the circumferential narrow groove 18 of this tire 2 has a barrel body 64 with a narrow groove width WD. When the tread surface 6 comes into contact with the road surface, the tread 4 deforms. In this tire 2, the groove width WD of the barrel body 64 is adjusted so that the opposing wall surfaces 18W of the circumferential narrow groove 18 come into contact with each other at the barrel body 64 due to the deformation of the tread 4.

[0172] The circumferential narrow groove 18 is formed between the center land portion 24 and the middle land portion 26. As described above, the circumferential narrow groove 18 is the circumferential groove 10, and the center land portion 24 and the middle land portion 26 are the main land portion 28. In this tire 2, the circumferential groove 10 located between adjacent main land portions 28 is the circumferential narrow groove 18.

[0173] When the tread surface 6 comes into contact with the road surface and the tread 4 deforms, the opposing wall surfaces 18W of the circumferential narrow grooves 18 come into contact with each other in the trunk body 64. The main land portions 28 (more specifically, the main blocks 50) located on both sides of the circumferential narrow grooves 18 support each other. Deformation of the tread 4 is suppressed. The circumferential narrow grooves 18 can contribute to reducing rolling resistance. On the other hand, the rigidity of the tread 4 appears to increase, which raises concerns about a decrease in wet performance. However, the groove portions 82 of the main lateral grooves 48 suppress the decrease in wet performance. In this way, in the early stages of wear, it is presumed that the tire 2 can suppress the decrease in wet performance due to wear while reducing rolling resistance.

[0174] As the wear of the tread 4 progresses, the groove volume of the circumferential grooves 10 and the like decreases. This raises concerns about a decline in wet performance. However, an expanded width portion 60 having a groove width wider than the groove width of the body portion main body 64 is located radially inward of the body portion 58 of the circumferential narrow groove 18. Furthermore, a sipe portion 84 having a narrower groove width than the groove portion 82 is located radially inward of the groove portion 82 of the main lateral groove 48. In the circumferential narrow groove 18, when the body portion main body 64 disappears, the expanded width portion 60 is exposed. In the main lateral groove 48, when the groove portion 82 disappears, the sipe portion 84 is exposed. The expanded width portion 60 and the sipe portion 84 can contribute to suppressing a decline in wet performance. In this tire 2, the groove depth MH of the groove portion 82 is shallower than the groove depth HB from the groove mouth 18M of the circumferential narrow groove 18 to the width reference position PB. This prevents the sipe portion 84 and a portion having a groove width greater than 2.0 times the minimum width of the trunk body 64 from being exposed simultaneously. This prevents the occurrence of uneven wear due to sudden pattern changes. The main lateral grooves 48 and the circumferential narrow grooves 18 can each stably perform their respective functions.

[0175] Wear reduces the volume of the tread 4. After the sipe portion 84 is exposed, a portion having a groove width greater than 2.0 times the minimum width of the trunk body 64 is exposed, but the deformation allowance of the tread 4 is reduced, so the rigidity of the tread 4 appears to increase. The increased rigidity can contribute to a reduction in rolling resistance. While increased rigidity is advantageous for reducing rolling resistance, it is detrimental to 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, road-holding performance in the small deformation region improves. The tread 4 of this tire 2 can contribute to improved wet performance regardless of the stage of wear. In particular, the styrene-butadiene rubber content CS, the silica content BS, the groove depth MH of the groove portion 82, and the groove depth HB from the groove opening 18M of the circumferential narrow groove 18 to the width reference position PB are set to satisfy the aforementioned relationship. Therefore, even in the middle stage of wear, from when the sipe portion 84 of the main lateral groove 48 is exposed until the width reference position PB of the expanded width portion 60 of the circumferential narrow groove 18 is exposed, the synergistic effect of the styrene-butadiene rubber and silica suppresses deterioration of wet performance.

[0176] This tire 2 can suppress deterioration of wet performance while maintaining low rolling resistance from the time it starts to be used until it needs to be replaced. The tire 2 can suppress deterioration of wet performance due to wear while reducing rolling resistance.

[0177] As described above, the groove depth MH of the groove portion 82 is shallower than the groove depth HB from the groove opening 18M of the circumferential narrow groove 18 to the width reference position PB. In other words, the groove depth HB from the groove opening 18M of the circumferential narrow groove 18 to the width reference position PB is deeper than the groove depth MH of the groove portion 82. Specifically, it is preferable that the groove depth HB (mm) from the groove opening 18M of the circumferential narrow groove 18 to the width reference position PB and the groove depth MH (mm) of the groove portion 82 satisfy the following relationship. 0<(HB-MH)≦5.0 Since the width reference position PB of the enlarged width portion 60 of the circumferential narrow groove 18 is exposed at an appropriate timing after the groove portion 82 of the main lateral groove 48 disappears, the occurrence of uneven wear due to a sudden pattern change is suppressed. The main lateral groove 48 and the circumferential narrow groove 18 can stably perform their respective functions. From this perspective, it is more preferable that the groove depth HB (mm) from the groove opening 18M of the circumferential narrow groove 18 to the width reference position PB and the groove depth MH (mm) of the groove portion 82 satisfy the following relationship: 1.0≦(HB-MH)≦4.0

[0178] The land ratio of this tire 2 is preferably 75% or more. In this case, the land portions 12 easily support each other, effectively increasing the rigidity of the tread 4. The tire 2 can effectively reduce rolling resistance and also improve 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 will be reduced compared to when the entire filler is composed of carbon black. However, by setting the land ratio to 75% or more, the tread 4 can maintain a necessary level of rigidity. In this tire 2, the circumferential narrow grooves 18 and the main lateral grooves 48 can fully perform their functions. The tire 2 can suppress deterioration of wet performance due to wear while reducing rolling resistance. From this perspective, a land ratio of 78% or more is more preferable. From the perspective of maintaining good wet performance, a land ratio of 90% or less is preferable.

[0179] The ratio (HH / HM) of the groove depth HH of the body portion 58 to the groove depth HM of the circumferential narrow groove 18 is preferably 0.30 or more and 0.70 or less. By setting the ratio (HH / HM) to 0.30 or greater, the tire 2 can effectively suppress the effect of the expanded width portion 60 on the rigidity of the main blocks 50. The tire 2 can allow wear of the tread 4 to progress while maintaining the rigidity of the main blocks 50. The tire 2 can maintain good resistance to uneven wear. From this viewpoint, it is more preferable that the ratio (HH / HM) be 0.35 or greater. By setting the ratio (HH / HM) to 0.70 or less, the width reference position PB of the expanded width portion 60 of the circumferential narrow groove 18 can be exposed at an appropriate timing after the sipe portion 84 of the main lateral groove 48 is exposed. Even in this case, the tire 2 can allow the wear of the tread 4 to progress while maintaining the rigidity of the main blocks 50, and can maintain good uneven wear resistance. From this viewpoint, it is more preferable that the ratio (HH / HM) be 0.65 or less.

[0180] The ratio (MH / HM) of the groove depth MH of the groove portion 82 of the main lateral groove 48 to the groove depth HM of the circumferential narrow groove 18 is preferably 0.30 or greater and 0.60 or less. By setting the ratio (MH / HM) to 0.30 or greater, the tire 2 can eliminate the groove portions 82 at an appropriate timing. The tire 2 can maintain good appearance quality and traction performance. From this viewpoint, the ratio (MH / HM) is more preferably 0.35 or greater. By setting the ratio (MH / HM) to 0.60 or less, the tire 2 can effectively suppress the effect of the groove portions 82 on the rigidity of the main blocks 50. The tire 2 can allow the wear of the tread 4 to progress while maintaining the rigidity of the main blocks 50. The tire 2 can effectively suppress the occurrence of center wear, thereby maintaining good uneven wear resistance. From this perspective, it is more preferable that the ratio (MH / HM) be 0.55 or less.

[0181] The body portion main body 64 of the circumferential narrow groove 18 has a groove width WD narrower than the groove width WGCs at the groove opening of the shoulder circumferential groove 16. As described above, in this circumferential narrow groove 18, when the tire 2 comes into contact with the road surface, a pair of wall surfaces in this body portion main body 64 come into contact with each other. Adjacent main land portions 28 sandwiching the circumferential narrow groove 18 support each other. The main land portion 28 is configured in the crown portion of the tread portion. The adjacent main land portions 28 supporting each other apparently increase the rigidity of the crown portion, and deformation of the crown portion is suppressed. This tire 2 can effectively suppress the occurrence of wear in the crown portion. This tire 2 can improve uneven wear resistance. From this viewpoint, the ratio (WD / WGCs) of the groove width WD of the body main body 64 of the circumferential narrow groove 18 to the groove width WGCs of the shoulder circumferential groove 16 is preferably equal to or less than 0.35, and more preferably equal to or less than 0.20. From the viewpoint that the circumferential narrow grooves 18 can contribute to drainage and the tire 2 can maintain good wet performance, the ratio (WD / WGCs) is preferably equal to or greater than 0.01, and more preferably equal to or greater than 0.05.

[0182] The length indicated by the double-headed arrow HN in FIG. 5 is the groove depth from the groove opening 18M of the circumferential narrow groove 18 to the maximum width position PN. From the viewpoint that the expanded width portion 60 can effectively contribute to suppressing a deterioration in wet performance, it is preferable that the ratio (HN / HM) of the groove depth HN from the groove mouth 18M of the circumferential narrow groove 18 to the groove depth HM of the circumferential narrow groove 18 be 0.75 or more and 0.95 or less.

[0183] 2, the circumferential narrow grooves 18 extend in a circumferential direction in a meandering manner rather than in a straight line. In particular, the circumferential narrow grooves 18 of the tire 2 include a first narrow groove 66 close to a first end TE1 of the tread surface 6, a second narrow groove 68 close to a second end TE2 of the tread surface 6, and a connecting narrow groove 70 connecting the first narrow groove 66 and the second narrow groove 68. Of the connecting narrow grooves 70, the connecting narrow groove 70 that connects the first narrow groove 66 located on the leading side and the second narrow groove 68 located on the trailing side is also called a first connecting narrow groove 70a. The connecting narrow groove 70 that connects the second narrow groove 68 located on the leading side and the first narrow groove 66 located on the trailing side is also called a second connecting narrow groove 70b. When a groove unit is formed by connecting the first narrow groove 66, the first connecting narrow groove 70a, the second narrow groove 68, and the second connecting narrow groove 70b in this order, the circumferential narrow groove 18 is formed by connecting a plurality of such groove units in the circumferential direction. The first narrow grooves 66 and the second narrow grooves 68 are arranged alternately in the circumferential direction.

[0184] When the tread surface 6 comes into contact with the road surface and the tread 4 deforms, the opposing wall surfaces 18W of the circumferential narrow grooves 18 come into contact with each other in the trunk body 64. The circumferential narrow grooves 18 extend circumferentially in a serpentine manner, so the wall surfaces effectively mesh with each other. The main land portions 28 located on both sides of the circumferential narrow grooves 18 constrain each other. The apparent rigidity of the main land portions 28 is increased. Deformation of the main land portions 28 is effectively suppressed. This tire 2 can effectively reduce rolling resistance and also improve wear resistance. As described above, the rubber composition of the tread 4 contains silica as a filler. Therefore, there is a concern that the rigidity of the tread will decrease compared to when the filler is entirely composed of carbon black. However, by configuring the circumferential narrow grooves 18 with first narrow grooves 66, second narrow grooves 68, and connecting narrow grooves 70 and arranging the first narrow grooves 66 and second narrow grooves 68 alternately in the circumferential direction, the tread 4 can maintain a required level of rigidity. From this viewpoint, it is preferable that the circumferential narrow groove 18 comprises a first narrow groove 66, a second narrow groove 68, and a connecting narrow groove 70 connecting the first narrow groove 66 and the second narrow groove 68, and that the first narrow groove 66 and the second narrow groove 68 are arranged alternately in the circumferential direction.

[0185] The tire 2 includes a pair of central circumferential grooves 14, that is, a first central circumferential groove 141 and a second central circumferential groove 142, disposed on either side of the equatorial plane. As described above, the central circumferential groove 14 of this tire 2 is the circumferential narrow groove 18. The first central circumferential groove 141 is a first circumferential narrow groove 181 , and the second central circumferential groove 142 is a second circumferential narrow groove 182 .

[0186] The first narrow groove 66 and the second narrow groove 68 of the circumferential narrow groove 18 extend in the circumferential direction. The first narrow groove 66 and the second narrow groove 68 have a constant length in the circumferential direction. The second narrow groove 68 of the second circumferential narrow groove 182 has the same length as the first narrow groove 66 of the first circumferential narrow groove, and the first narrow groove 66 of the second circumferential narrow groove 182 has the same length as the second narrow groove 68 of the first circumferential narrow groove 181. The first narrow groove 66 of the first circumferential narrow groove 181 and the second narrow groove 68 of the second circumferential narrow groove 182 are located on the end TE side of the tread surface 6, and the second narrow groove 68 of the first circumferential narrow groove 181 and the first narrow groove 66 of the second circumferential narrow groove 182 are located on the equatorial plane side. For ease of explanation, the second narrow groove 68 of the first circumferential narrow groove 181 and the first narrow groove 66 of the second circumferential narrow groove 182 will be referred to as the inner narrow groove 72, and the first narrow groove 66 of the first circumferential narrow groove 181 and the second narrow groove 68 of the second circumferential narrow groove 182 will be referred to as the outer narrow groove 74. The first connecting narrow groove 70a of the first circumferential narrow groove 181 and the second connecting narrow groove 70b of the second circumferential narrow groove 182 will be referred to as the outer connecting groove 76s. The outer connecting groove 76s connects the outer narrow groove 74 on the leading side and the inner narrow groove 72 on the trailing side. The second connecting narrow groove 70b of the first circumferential narrow groove 181 and the first connecting narrow groove 70a of the second circumferential narrow groove 182 will be referred to as the inner connecting groove 76u. The inner connecting groove 76u connects the inner narrow groove 72 on the leading side and the outer narrow groove 74 on the trailing side.

[0187] The inner narrow groove 72 of the first circumferential narrow groove 181 (hereinafter referred to as the first inner narrow groove 721) is located further rearward than the inner narrow groove 72 of the second circumferential narrow groove 182 (hereinafter referred to as the second inner narrow groove 722), but the first inner narrow groove 721 and the second inner narrow groove 722 partially overlap with each other in the axial direction. The outer narrow groove 74 of the first circumferential narrow groove 181 (hereinafter referred to as the first outer narrow groove 741) is located further rearward than the outer narrow groove 74 of the second circumferential narrow groove 182 (hereinafter referred to as the second outer narrow groove 742), but the first outer narrow groove 741 and the second outer narrow groove 742 partially overlap with each other in the axial direction.

[0188] 1, the length indicated by the double arrow LS is the circumferential length of the inner narrow groove 72. The length indicated by the double arrow LL is the circumferential length of the outer narrow groove 74. In this tire 2, the outer narrow groove 74 is longer than the inner narrow groove 72. Specifically, the circumferential length LL of the outer narrow groove 74 is preferably 1.1 to 1.5 times the circumferential length LS of the inner narrow groove 72.

[0189] The first circumferential narrow groove 181 and the second circumferential narrow groove 182 approach each other where the first inner narrow groove 721 and the second inner narrow groove 722 face each other, and separate from each other where the first outer narrow groove 741 and the second outer narrow groove 742 face each other. The axial distance between the first circumferential narrow groove 181 and the second circumferential narrow groove 182 varies in the circumferential direction. This axial distance is short between the first inner narrow groove 721 and the second inner narrow groove 722, and is long between the first outer narrow groove 741 and the second outer narrow groove 742. The inner main lateral grooves 80 formed in the inner main land portion 28u connect the first inner narrow groove 721 and the second inner narrow groove 722, which have a short axial distance between them. The inner main lateral grooves 80 are disposed in portions where adjacent circumferential narrow grooves 18 are close to each other. As described above, the first outer narrow groove 741 is located further rearward than the second outer narrow groove 742. The end of the inner main lateral groove 80 located on the first end TE1 side of the tread surface 6 is located further rearward than the end of the inner main lateral groove 80 located on the second end TE2 side. In other words, the inner main lateral groove 80 is inclined with respect to the axial direction.

[0190] The inner main block 50u formed between the first circumferential narrow groove 181 and the second circumferential narrow groove 182 is located circumferentially between the leading-side inner main lateral groove 80 and the trailing-side inner main lateral groove 80, and is axially located between the first outer narrow groove 741 and the second outer narrow groove 742. Moreover, the outer narrow groove 74 is longer than the inner narrow groove 72, and the axial distance between the first outer narrow groove 741 and the second outer narrow groove 742 is longer than the axial distance between the first inner narrow groove 721 and the second inner narrow groove 722. An inner main block 50u formed between adjacent circumferential narrow grooves 18 is surrounded by two inner main lateral grooves 80 arranged in a portion where the adjacent circumferential narrow grooves 18 are close to each other, and two outer narrow grooves 74 as elements of the circumferential narrow grooves 18. This inner block 50u has an octagonal shape. This tire 2 can suppress an increase in ground pressure at the edges of the inner main block 50u. This tire 2 can improve uneven wear resistance. From this perspective, it is preferable that the inner main lateral groove 80 bridging between adjacent circumferential narrow grooves 18 be arranged in a portion where the adjacent circumferential narrow grooves 18 are close to each other.

[0191] The inner vertices 16u of the shoulder circumferential grooves 16 serving as the wide circumferential grooves 20 include a first inner vertex 16uu that overlaps with the inner narrow groove 72 of the circumferential narrow groove 18 in the axial direction, and a second inner vertex 16us that overlaps with the outer narrow groove 74. The first inner vertices 16uu and the second inner vertices 16us are alternately arranged in the circumferential direction, with the outer vertex 16s sandwiched between them. The outer vertices 16s of the shoulder circumferential groove 16 include a first outer vertex 16sa that overlaps with the shoulder lateral groove 44 and a second outer vertex 16sb that overlaps with the shoulder block 46. The first outer vertices 16sa and the second outer vertices 16sb are arranged alternately in the circumferential direction with the inner vertex 16u sandwiched therebetween. While the circumferential narrow groove 18 oscillates once, the shoulder circumferential groove 16, i.e., the circumferential wide groove 20 oscillates twice. When the tire 2 runs on a wet road surface, water easily flows through the circumferential wide groove 20. This circumferential wide groove 20 can contribute to improving wet performance.

[0192] The axial distance between the circumferential wide groove 20 and the circumferential narrow groove 18 varies in the circumferential direction. In the circumferential wide groove 20 on the first end TE1 side of the tread surface 6, this axial distance is short between the second inner apex 16us and the outer narrow groove 74 and long between the first outer apex 16sa and the inner narrow groove 72. In the circumferential wide groove 20 on the second end TE2 side of the tread surface 6, this axial distance is short between the second inner apex 16us and the outer narrow groove 74 and long between the second outer apex 16sb and the inner narrow groove 72. The outer main lateral grooves 78 formed in the outer main land portion 28s connect the second inner apex 16us of the circumferential wide groove 20, which has the short axial distance, to the outer narrow groove 74. The outer main lateral grooves 78 are disposed in the portions where the circumferential wide groove 20 and the circumferential narrow groove 18 are close to each other.

[0193] As shown in FIG. 2 , in the outer main land portion 28s, the outer main lateral grooves 78 are inclined with respect to the axial direction. The axially inner ends of the outer main lateral grooves 78 are located earlier than the axially outer ends. When the tire 2 travels, the axially inner ends of the outer main lateral grooves 78 contact the road surface earlier than the axially outer ends. The outer main lateral grooves 78 extend axially outward from their axially inner ends. When the tire 2 travels on a wet road surface, the outer main lateral grooves 78 can effectively drain water present between the tire 2 and the road surface from the contact patch. This tire 2 can improve wet performance. From this perspective, in the outer main land portion 28s, it is preferable that the outer main lateral grooves 78 be inclined with respect to the axial direction, and that the axially inner ends of the outer main lateral grooves 78 contact the road surface earlier than the axially outer ends.

[0194] Fig. 6 is a cross-sectional view taken along line VI-VI in Fig. 2. Fig. 6 shows a cross-section of the transverse sipe 52. Fig. 6 shows a cross-section of the transverse sipe 52 taken along a plane perpendicular to the longitudinal direction of the transverse sipe 52.

[0195] 6 shows a cross section of the transverse sipe 52 provided in the center block 38. As described above, the transverse sipe 52 is also provided in the middle block 42. The cross-sectional shape of the transverse sipes 52 of the middle block 42 may be the same as or different from that of the transverse sipes 52 of the center block 38 . 2 is the same as the cross-sectional shape of the transverse sipes 52 of the middle block 42 in the center block 38. A description of the cross-sectional shape of the transverse sipes 52 of the middle block 42 will be omitted.

[0196] The transverse sipe 52 has a sipe body 54 and a tubular portion 56. The sipe body 54 includes a groove mouth 52M of the transverse sipe 52. The tubular portion 56 includes a groove bottom 52T of the transverse sipe 52. The tubular portion 56 is located radially inward of the sipe body 54. The tubular portion 56 extends in the length direction of the transverse sipe 52.

[0197] As shown in Fig. 2, the sipe body 54 extends in a zigzag pattern in the length direction of the transverse sipe 52, and as shown in Fig. 6, it extends in a zigzag pattern in the depth direction of the transverse sipe 52. This sipe body 54 is a three-dimensional sipe. As shown in Fig. 7, the sipe body 54 may be a two-dimensional sipe that spreads like a flat plate. In this case, the sipe body 54 extends straight in the length direction and straight in the depth direction.

[0198] 6, the solid line LM is the boundary line between the sipe body 54 and the tubular portion 56. The length indicated by the double arrow WM is the groove width of the transverse sipe 52 measured along this boundary line LM. The boundary line LM is set at a position where the groove width WM is 1.0 mm. The transverse sipe 52 has a groove width Wp of less than 1.0 mm at its groove mouth 52M. The groove width of the portion outside the boundary line LM, i.e., the sipe body 54, is less than 1.0 mm. The sipe body 54 is a sipe. The groove width of the portion inside this boundary line LM, i.e., the tubular portion 56, is 1.0 mm or more. The groove width of the tubular portion 56 is wider than the groove width of the sipe body 54.

[0199] The tubular portion 56 extends inward from the position of the boundary line LM. The length indicated by the double arrow WT in FIG. 6 is the maximum groove width of the tubular portion 56. The position indicated by the symbol PT is the position where the tubular portion 56 shows the maximum groove width WT. The tubular portion 56 tapers outward from the portion showing the maximum groove width WT. The tubular portion 56 tapers inward from the portion showing the maximum groove width WT.

[0200] The cross-sectional shape of the tubular portion 56 may be circular or elliptical. This cross-sectional shape may be a shape in which the portion indicating the maximum groove width WT is represented by a straight line, and the sipe body 54 side and the groove bottom 52T side of this straight line are represented by arcs (hereinafter, this shape is also referred to as a track shape).

[0201] The sipe body 54 can function as an edge component. The sipe body 54 can contribute to suppressing deterioration of wet performance in the early stages of wear. The tubular portion 56 suppresses reduction in groove volume due to wear. The tubular portion 56 can contribute to suppressing deterioration of wet performance after the sipe body 54 has disappeared. From this perspective, it is preferable that each of the multiple main blocks 50 provided in the tread 4 has a transverse sipe 52 that crosses the main block 50, that the transverse sipe 52 has a sipe body 54 and a tubular portion 56 located radially inward of the sipe body 54, and that the groove width of the tubular portion 56 is wider than the groove width of the sipe body 54.

[0202] 6, the position indicated by the symbol PG is the radially outer end of the tubular portion 56. The position indicated by the symbol PA is the radially inner end of the tubular portion 56. This radially inner end PA is also the bottom 52T of the transverse sipe 52.

[0203] The pattern configuration changes significantly during the period from when the grooves 82 disappear until the portions of the circumferential narrow grooves 18 having a groove width greater than 2.0 times the minimum width WD of the trunk body 64 are exposed. During this period, there is a concern that wet performance may deteriorate. However, in this tire 2, as shown in FIG. 8, the width reference position PB of the circumferential narrow groove 18 is located between the radially outer end PG and the radially inner end PA of the tubular portion 56. The tubular portion 56 is exposed while the pattern configuration changes significantly. The exposed tubular portion 56 can contribute to suppressing a decrease in wet performance. Even while the pattern configuration changes significantly, this tire 2 can maintain good wet performance. For ease of explanation, the position of the groove bottom 82T of the groove portion 82 of the lateral groove 48 is indicated by a two-dot chain line LT. 9, the transverse sipes 52 may be configured so that the groove bottoms 82T of the groove portions 82 of the main lateral grooves 48 are located between the radially outer ends PG and the radially inner ends PA of the tubular portions 56. In this case as well, the exposed tubular portions 56 can contribute to suppressing deterioration in wet performance, so that the tire 2 can maintain good wet performance even while the pattern configuration changes significantly. 10 , the transverse sipes 52 may be configured so that both the width reference position PB of the circumferential narrow groove 18 and the groove bottoms 82T of the groove portions 82 of the main lateral grooves 48 are located between the radially outer end PG and the radially inner end PA of the tubular portion 56. In this case as well, the exposed tubular portion 56 can contribute to suppressing deterioration in wet performance, so that the tire 2 can maintain good wet performance even when the pattern configuration changes significantly. From the viewpoint of enabling the tire 2 to maintain good wet performance even while the pattern configuration changes significantly, it is preferable that the groove bottom 82T of the groove portion 82 of the main lateral groove 48 and the width reference position PB of the circumferential narrow groove 18, or both the groove bottom 82T of the groove portion 82 of the main lateral groove 48 and the width reference position PB of the circumferential narrow groove 18, are located between the radial outer end PG and the radial inner end PA of the tubular portion 56.

[0204] As described above, the center land portion 24 of the tire 2 is the inner main land portion 28u. As shown in Fig. 2, the inner main land portion 28u is located between two circumferential narrow grooves 18. The multiple main land portions 28 provided in the tread 4 of the tire 2 include the inner main land portion 28u located between adjacent circumferential narrow grooves 18. The inner main land portion 28u has multiple inner main blocks 50u.

[0205] Each of the inner main blocks 50u has a transverse sipe 52. A sipe body 54 of the transverse sipe 52 is a three-dimensional sipe. The sipe body 54 may also be a two-dimensional sipe.

[0206] In the sipe body 54, the wall surfaces contact and support each other when the tire 2 is running. If the sipe body 54 is a three-dimensional sipe, when the tread 4 deforms and the wall surfaces of the sipe body 54 come into close contact with each other, the wall surfaces constrain each other, effectively increasing the rigidity of the tread 4. The tire 2 can effectively reduce rolling resistance and also improve wear resistance. As described above, the rubber composition of the tread 4 contains silica as a filler. Therefore, there is a concern that the rigidity of the tread 4 will be reduced compared to when the filler is composed entirely of carbon black. However, by configuring the sipe body 54 as a three-dimensional sipe extending in a zigzag pattern in the length and depth directions, the tread 4 can maintain a required level of rigidity. From this perspective, it is preferable that the sipe body 54 of the transverse sipe 52 extend in a zigzag pattern in the length and depth directions.

[0207] In this tire 2, the sipe bodies 54 of the transverse sipes 52 of the main blocks 50 of the outer main land portion 28s also extend in a zigzag pattern in the length and depth directions. Even in the outer main land portion 28s, when the tread 4 deforms and the wall surfaces of the sipe bodies 54 come into close contact with each other, the wall surfaces constrain each other, effectively increasing the rigidity of the tread 4. The tire 2 can effectively reduce rolling resistance while maintaining wet performance, and can also improve wear resistance. From this perspective, it is more preferable that the sipe bodies 54 of the transverse sipes 52 of the main blocks 50 of the outer main land portion 28s, in addition to the sipe bodies 54 of the transverse sipes 52 of the main blocks 50 provided in the inner main land portion 28u, extend in a zigzag pattern in the length and depth directions.

[0208] 6, the length indicated by the double arrow DA is the groove depth of the transverse sipe 52. The length indicated by the double arrow DC is the groove depth of the sipe main body . In the tire 2, the groove depth DA of the transverse sipes 52 is the same as the groove depth DGC of the circumferential grooves 10, or the transverse sipes 52 are shallower than the circumferential grooves 10. Specifically, the groove depth DA of the transverse sipes 52 is 0.80 to 1.00 times the groove depth DGCs of the shoulder circumferential grooves 16, which are the wide circumferential grooves 20.

[0209] The ratio (DC / DA) of the groove depth DC of the sipe body 54 of the transverse sipe 52 to the groove depth DA of the transverse sipe 52 is preferably 0.35 or greater and 0.80 or less. By setting the ratio (DC / DA) to 0.35 or greater, the tire 2 can expose the tubular portion 56 at an appropriate timing. The tire 2 can allow the wear of the tread 4 to progress while maintaining the rigidity of the main blocks 50. The tire 2 can maintain good uneven wear resistance. From this viewpoint, the ratio (DC / DA) is more preferably 0.40 or greater. By setting the ratio (DC / DA) to 0.80 or less, the tubular portion 56 can effectively contribute to improving the appearance quality and exhibiting traction performance. From this viewpoint, the ratio (DC / DA) is more preferably 0.75 or less.

[0210] As described above, the groove width of the tubular portion 56 is wider than the groove width of the sipe body 54. Specifically, the maximum groove width WT of the tubular portion 56 is preferably four times or more, and more preferably five times or more, the groove width of the sipe body 54 at the groove mouth 52M, in other words, the groove width Wp of the transverse sipe 52. This allows the tubular portion 56 to contribute to maintaining wet performance. The maximum groove width WT of the tubular portion 56 is preferably 13 times or less, and more preferably 12 times or less, the groove width Wp of the transverse sipe 52. This allows the size of the tubular portion 56 to be maintained appropriately. A decrease in the rigidity of the main block 50 is suppressed.

[0211] As described above, the tubular portion 56 has a bottom surface that includes the groove bottom 52T of the transverse sipe 52. In the cross section shown in Figure 6, the contour of the bottom surface of the tubular portion 56 is represented by an arc that passes through the groove bottom 52T. The arrow Rb in Figure 6 indicates the radius of this arc.

[0212] The radius Rb of the arc that defines the contour of the bottom surface of the tubular portion 56 is preferably 1.5 mm or more and 3.5 mm or less. Setting the radius Rb to be equal to or greater than 1.5 mm effectively suppresses the occurrence of cracks at the groove bottom 52T. From this viewpoint, it is more preferable that the radius Rb be equal to or greater than 2.0 mm. By setting the radius Rb to 3.5 mm or less, a decrease in the rigidity of the main blocks 50 caused by providing the tubular portions 56 in the transverse sipes 52 is suppressed. The rigidity of the main blocks 50 is appropriately maintained. The tire 2 can have improved uneven wear resistance. From this viewpoint, it is more preferable that the radius Rb be 3.0 mm or less.

[0213] As is clear from the above description, the present invention provides a heavy-duty tire that can suppress deterioration of wet performance due to wear while reducing rolling resistance. [Example]

[0214] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0215] Various chemicals used in the examples and comparative examples are explained. NR:TSR20 SBR: HPR840 manufactured by JSR Corporation (S-SBR, styrene content: 10% by mass, vinyl content: 42% by mole, Tg -60°C, Mw 190,000) BR: UBEPOL BR (registered trademark) 150B (cis content: 97 mol%) manufactured by Ube Industries, Ltd. Carbon black 1: Diablack N134 (N2SA:148m) manufactured by Mitsubishi Chemical Corporation 2 / g) Carbon Black 2: SS550 manufactured by Streble Green Carbon (carbon black obtained from the tire pyrolysis process) Silica 1: Ultrasil 9100GR (N2SA: 230 ml) manufactured by Evonik Degussa 2 / g, average primary particle diameter: 15nm) Silica 2: Wilmar K185 (amorphous silica purified from rice husks) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Resin component: Exxon Mobil's Oppera PR-383 (hydrogenated DCPD / C9 resin, containing dicyclopentadiene, styrene, and indene as monomer components, softening point: 103°C) Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Antioxidant 1: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Antioxidant 2: Nocrac RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Camellia stearic acid beads manufactured by NOF Corporation Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (powdered sulfur containing 5% oil) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela NS (Nt-butyl-2-benzothiazole sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0216] [Examples and Comparative Examples] According to the formulation shown in Table 1, materials other than sulfur and vulcanization accelerator were kneaded for 5 minutes at 150°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded mixture. Next, sulfur and vulcanization accelerator were added to the obtained kneaded mixture, and the mixture was kneaded for 5 minutes at 80°C using an open roll to obtain a rubber composition (uncrosslinked rubber composition). The obtained rubber composition was molded into a tread, which was then bonded together with other parts such as sidewalls to form an unvulcanized tire. The unvulcanized tire was press-vulcanized for 12 minutes at 150°C to produce a test tire (size: 315 / 70R22.5, truck and bus tires). The tread pattern of the test tire used was the tread pattern shown in Figure 1.

[0217] [Preparation before evaluation] The tread of the test tire is buffed. Specifically, the tread is buffed until the groove portions of the main lateral grooves and the body portions of the circumferential narrow grooves disappear, while taking care not to expose the width reference positions of the expanded width portions of the circumferential narrow grooves. The sipe portions of the main lateral grooves and the inflection portions of the circumferential narrow grooves are exposed on the tread surface. This reproduces the middle stage of wear.

[0218] For test tires in which the middle stage of wear was reproduced by buffing, the calculation results based on the evaluation method shown below are shown in Table 1-3.

[0219] [Rolling resistance (RRC)] Using a rolling resistance tester, test tires simulating the middle stage of wear are measured for rolling resistance coefficient (RRC) when they run on a drum at a speed of 80 km / h under the following conditions: The reciprocals of the measured values ​​for Example 1 and Comparative Examples 1-2 are expressed as an index with Comparative Example 2 set to 100; The reciprocals of the measured values ​​for Examples 2-3 and Comparative Examples 3-4 are expressed as an index with Comparative Example 4 set to 100; and The reciprocals of the measured values ​​for Examples 4-5 and Comparative Examples 5-6 are expressed as an index with Comparative Example 6 set to 100. The results are shown in the "RRC" column in Table 1-3 below. The higher the value, the lower the rolling resistance. Rim: 8.25 x 22.5 Internal pressure: 900kPa Vertical load: 31.25kN

[0220] [Wet performance (WET)] Wet performance (wet braking performance) tests are conducted in accordance with R117-02 (ECE Regulation No. 117 Revision 2) using the test vehicle listed below. Test tires that replicate the mid-stage of wear are mounted on all wheels of the test vehicle. For this wet performance test, braking is initiated from a specified initial speed on a water-sprayed road surface, and the braking distance is measured. Test vehicle: 10-ton truck (2-D vehicle) Load capacity: 75% of standard load capacity Wet road surface: Water depth 0.5 to 2 mm Speed: 65km / h The measured values ​​of Example 1 and Comparative Examples 1 and 2 are expressed as indexes using the following formula, with Comparative Example 2 being set at 100. (Wet performance index) = (braking distance of tire of 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 indexes using the following formula, with Comparative Example 4 being set at 100. (Wet performance index) = (braking distance of tire of 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 indexes using the following formula, with Comparative Example 6 being set at 100. (Wet performance index) = (braking distance of tire of Comparative Example 6) / (braking distance of each test tire) × 100 The results are shown in the "WET" column in Table 1-3 below. The higher the value, the better the wet performance.

[0221] [Table 1]

[0222] [Table 2]

[0223] [Table 3] [Industrial Applicability]

[0224] The above-described technology that can suppress deterioration of wet performance due to wear while reducing rolling resistance can be applied to various tires.

[0225] [Note] The present invention includes the following aspects.

[0226] [1] A tire having a tread made of a rubber composition including a rubber component containing styrene-butadiene rubber and a filler containing silica, the tread having a tread surface that comes into contact with a road surface, The tread has a plurality of circumferential grooves extending continuously in the circumferential direction, The plurality of circumferential grooves define a plurality of land portions arranged in the tread in the axial direction, the plurality of land portions include a plurality of main land portions located between adjacent ones of the circumferential grooves, Each of the main land portions has a plurality of main lateral grooves connecting adjacent ones of the circumferential grooves, the plurality of main lateral grooves define a plurality of main blocks arranged in the circumferential direction in the main land portion, The main lateral groove includes a groove portion and a sipe portion located radially inward of the groove portion and connected to the groove portion, The groove width of the sipe portion is narrower than the groove width of the groove portion, the circumferential groove located between the adjacent main land portions is a circumferential narrow groove, Among the plurality of main land portions, a main land portion located outermost in the axial direction is an outer main land portion, the circumferential groove located axially outward of each of the outer main land portions is a circumferential wide groove having a groove width wider than a groove width of the circumferential narrow groove, the circumferential narrow groove has a body portion and an enlarged width portion located radially inward of the body portion, The body portion includes a body main body to which the expanded width portion is connected, Due to deformation of the tread, opposing wall surfaces of the circumferential narrow groove come into contact with each other in the trunk body, The maximum width of the expanded width portion is wider than the minimum width of the trunk body, Between the body main body and the position where the expanded width portion has the maximum width, a position where the groove width is 2.0 times the minimum width of the body main body is a width reference position, A groove depth MH of the groove portion is shallower than a groove depth HB from the groove opening of the circumferential narrow groove to the width reference position, 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 relative to 100 parts by mass of the rubber component is 15 parts by mass or more, A heavy-duty tire, wherein the styrene-butadiene rubber content CSB, the silica content BS, the groove depth MH (mm) of the groove portion, and the groove depth HB (mm) from the groove opening of the circumferential narrow groove to the width reference position satisfy the following relational expressions: (CSB+BS) / (HB-MH)≧5 [2] The rubber component further contains natural rubber and butadiene rubber, The heavy-duty tire according to the above-mentioned [1], wherein a content CSB of the styrene-butadiene rubber, a content CN of the natural rubber, and a content CB of the butadiene rubber in 100 parts by mass of the rubber component satisfy the following relational expression: CN≧CSB+CB [3] The 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] The silica includes silica made from biomass material. A heavy-duty tire according to any one of [1] to [3] above. [5] The heavy-duty tire according to any one of [1] to [4] above, wherein the filler contains silica having an average primary particle diameter of 16 nm or less. [6] The filler further comprises carbon black; The carbon black comprises recycled carbon black. A heavy-duty tire according to any one of [1] to [5] above. [7] The filler further comprises carbon black; The heavy-duty tire according to any one of [1] to [6] above, wherein the carbon black contains carbon black having an average primary particle diameter of 19 nm or less. [8] The heavy-duty tire according to any one of [1] to [7] above, wherein the rubber composition further contains a resin component. [9] The land ratio, as defined below, is 75% or more; A heavy-duty tire according to any one of [1] to [8] above. Land ratio: The ratio of the total area of ​​the contact area of ​​the multiple land portions included in the contact area to the area of ​​the entire contact area, 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 and bringing the tire into contact with a flat road surface.

[10] Each of the plurality of main blocks has a transverse sipe that crosses the main block, The transverse sipe has a sipe body and a tubular portion located radially inward of the sipe body, The heavy-duty tire according to any one of the above [1] to [9], wherein the groove width of the tubular portion is wider than the groove width of the sipe main body.

[11] The heavy-duty tire according to the above-mentioned

[10] , wherein the groove bottom of the groove portion or the width reference position is located between the radially outer end and the radially inner end of the tubular portion.

[12] The plurality of main land portions include inner main land portions located between adjacent ones of the circumferential narrow grooves, The heavy-duty tire according to the above-mentioned

[10] or

[11] , wherein the sipe body of the transverse sipe of the main block of the inner main land portion extends in a zigzag pattern in the length direction and the depth direction.

[13] The circumferential narrow groove comprises a first narrow groove near a first end which is one end of the tread surface, a second narrow groove near a second end which is the other end of the tread surface, and a connecting narrow groove connecting the first narrow groove and the second narrow groove, The first narrow grooves and the second narrow grooves are alternately arranged in the circumferential direction. The heavy-duty tire according to any one of [1] to

[12] above. [Explanation of symbols]

[0227] 2. Tires 4. Tread 6. Tread surface 10...Circumferential groove 12... Rikubu 28, 28s, 28u...Main land area 32 Yokomizo 48, 78, 80... Main lateral groove 50, 50s, 50u... Main block 52 Transverse sipe 54···Sipe body 56...Tubular part 58 Torso 60....Expanded width section 62 Tapered section 64 Body 66...first narrow groove 68...Second narrow groove 70...Connected narrow groove 82 Groove 84···Sipe section 86 Tapered section 88... Body 94...inflection section 96...bottom

Claims

1. A tire having a tread made of a rubber composition including a rubber component containing styrene-butadiene rubber and a filler containing silica, the tread having a tread surface that comes into contact with a road surface, The tread has a plurality of circumferential grooves extending continuously in the circumferential direction, The plurality of circumferential grooves define a plurality of land portions arranged in the tread in the axial direction, the plurality of land portions include a plurality of main land portions located between adjacent ones of the circumferential grooves, Each of the main land portions has a plurality of main lateral grooves connecting adjacent ones of the circumferential grooves, the plurality of main lateral grooves define a plurality of main blocks arranged in the circumferential direction in the main land portion, The main lateral groove includes a groove portion and a sipe portion located radially inward of the groove portion and connected to the groove portion, The groove width of the sipe portion is narrower than the groove width of the groove portion, the circumferential groove located between the adjacent main land portions is a circumferential narrow groove, Among the plurality of main land portions, a main land portion located outermost in the axial direction is an outer main land portion, the circumferential groove located axially outward of each of the outer main land portions is a circumferential wide groove having a groove width wider than a groove width of the circumferential narrow groove, the circumferential narrow groove has a body portion and an enlarged width portion located radially inward of the body portion, The body portion includes a body main body to which the expanded width portion is connected, Due to deformation of the tread, opposing wall surfaces of the circumferential narrow groove come into contact with each other in the trunk body, The maximum width of the expanded width portion is wider than the minimum width of the trunk body, Between the body main body and the position where the expanded width portion has the maximum width, a position where the groove width is 2.0 times the minimum width of the body main body is a width reference position, A groove depth MH of the groove portion is shallower than a groove depth HB from the groove opening of the circumferential narrow groove to the width reference position, 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 groove depth MH (mm) of the groove portion, and the groove depth HB (mm) from the groove opening of the circumferential narrow groove to the width reference position satisfy the following relational formula: Heavy duty tires. (CSB+BS) / (HB-MH)≧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 expression:

2. The 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. The heavy duty tire according to claim 1.

4. The silica includes silica made from biomass material.

2. The heavy duty tire according to claim 1.

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

2. The heavy duty tire according to claim 1.

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

2. The 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 diameter of 19 nm or less.

2. The heavy duty tire according to claim 1.

8. The rubber composition further contains a resin component.

2. The heavy duty tire according to claim 1.

9. The land ratio, as defined below, is 75% or more.

2. The heavy duty tire according to claim 1. Land ratio: The ratio of the total area of ​​the contact area of ​​the plurality of land portions included in the contact area to the area of ​​the entire contact area, 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 contacting a flat road surface.

10. Each of the plurality of main blocks has a transverse sipe that crosses the main block, The transverse sipe has a sipe body and a tubular portion located radially inward of the sipe body, The groove width of the tubular portion is wider than the groove width of the sipe body.

2. The heavy duty tire according to claim 1.

11. The groove bottom of the groove portion or the width reference position is located between a radially outer end and a radially inner end of the tubular portion.

11. A heavy duty tire according to claim 10.

12. the plurality of main land portions include inner main land portions located between adjacent ones of the circumferential narrow grooves, The sipe body of the transverse sipe included in the main block of the inner main land portion extends in a zigzag pattern in the length direction and the depth direction.

11. A heavy duty tire according to claim 10.

13. the circumferential narrow groove comprises a first narrow groove near a first end which is one end of the tread surface, a second narrow groove near a second end which is the other end of the tread surface, and a connecting narrow groove connecting the first narrow groove and the second narrow groove, The first narrow grooves and the second narrow grooves are alternately arranged in the circumferential direction. A heavy duty tire according to any one of claims 1 to 12.

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