Heavy load tire

Abstract

To provide a heavy load tire capable of improving wet grip performance.SOLUTION: Provided is a heavy load tire with a tread part, the tread part having a plurality of circumferential main grooves continuously extending in a tire circumferential direction, a pair of shoulder land parts partitioned by the circumferential main grooves and a ground contact end, and crown land parts located between the pair of shoulder land parts, the crown land parts having one or more circumferential fine grooves continuously extending in the tire circumferential direction, and the tread part being composed of a rubber composition containing a rubber component and a filler. When the groove width of the circumferential main groove is Ws (mm), the groove width of the circumferential fine groove is Wc (mm), and the tanδ of the rubber composition at 0°C is 0°C tanδ, the 0°C tanδ is 0.28 or greater, and 0°C tanδ / (Wc / Ws) is more than 1.0.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Due to recent environmental problems, the popularity of electric vehicles (EVs) is increasing even in large vehicles such as trucks and buses. Since EVs have an increased vehicle weight compared to conventional engine vehicles and also have an increased torque due to motor drive, high wear resistance performance is required for the tires of large EVs. In addition, due to the influence of recent environmental regulations, the requirements for low fuel consumption performance, wet grip performance, etc. in truck and bus tires are also increasing.

[0003] As a method for improving the wear resistance performance of truck and bus tires, for example, a technique for making carbon black into fine particles or high structuring is known (Patent Document 1). Further, as a method for improving the wet grip performance of heavy-duty tires, for example, a technique for forming a shallow bottom portion of a predetermined size at the inner end portion of a lug groove is known (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] If many lug grooves or the like are provided in the tread portion, the actual contact area ratio (land ratio) decreases, and thus the rigidity of the land portion tends to decrease. As a result, there is a problem that the tread portion easily generates heat and the wear resistance performance of the tire further decreases.

[0006] In addition, the methods of micronizing or highly structuring the above carbon black are not sufficient for improving the low fuel consumption performance of tires. Further, due to the deterioration of processability associated with micronization, the dispersibility of carbon black also deteriorates, and conversely, the wear resistance of the tire may deteriorate. Therefore, there are limitations to the conventional methods of improving performance by modifying carbon black.

[0007] An object of the present invention is to provide a heavy-duty tire capable of improving wet grip performance.

Means for Solving the Problems

[0008] The present invention is a heavy-duty tire having a tread portion, wherein the tread portion has a plurality of circumferential main grooves continuously extending in the tire circumferential direction, a pair of shoulder land portions partitioned by the circumferential main grooves and the grounding end, and a crown land portion located between the pair of shoulder land portions. The crown land portion has one or more circumferential fine grooves continuously extending in the tire circumferential direction. The tread portion is composed of a rubber composition containing a rubber component and a filler. When the groove width of the circumferential main groove is Ws (mm), the groove width of the circumferential fine groove is Wc (mm), and the tanδ at 0°C of the rubber composition is 0°C tanδ, 0°C tanδ is 0.28 or more, and 0°C tanδ / (Wc / Ws) is more than 1.0. The present invention relates to a heavy-duty tire.

Effects of the Invention

[0009] According to the present invention, a heavy-duty tire capable of improving wet grip performance is provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0011] A heavy-duty tire according to an embodiment of the present invention is a heavy-duty tire having a tread portion, wherein the tread portion has a plurality of circumferential main grooves continuously extending in the tire circumferential direction, a pair of shoulder land portions partitioned by the circumferential main grooves and the grounding ends, and a crown land portion located between the pair of shoulder land portions, the crown land portion has one or more circumferential grooves continuously extending in the tire circumferential direction, the tread portion is composed of a rubber composition containing a rubber component and a filler, when the groove width of the circumferential main groove is Ws (mm), the groove width of the circumferential groove is Wc (mm), and the tanδ at 0°C of the rubber composition is 0°C tanδ, 0°C tanδ is 0.28 or more, and 0°C tanδ / (Wc / Ws) is more than 1.0.

[0012] Although not intended to be bound by theory, the mechanism by which the wet grip performance is improved in the heavy-duty tire of the present invention is considered as follows, for example.

[0013] By setting the 0°C tanδ of the rubber composition constituting the tread portion within the above range, it is considered that energy loss on the tread portion surface is likely to occur even on a wet road surface.

[0014] Also, by having a groove with a groove width narrower than that of the circumferential main groove in the crown portion, it is considered that the crown portion is likely to come into contact with the road surface when the tire rolls, and it becomes possible to further enhance the wet grip performance.

[0015] Furthermore, by setting the ratio of 0 °C tan δ to Wc / Ws within the above range, when Wc / Ws is large, the actual contact area ratio at the crown portion becomes small. Therefore, it is considered that by increasing 0 °C tan δ, it becomes easier to improve the wet grip performance. On the other hand, when 0 °C tan δ is relatively small, it is considered that even if Wc / Ws is reduced, it is possible to improve the ground contact property.

[0016] And it is considered that by the cooperation of these, a remarkable effect that the wet grip performance of the heavy load tire is significantly improved is achieved.

[0017] The filler preferably contains silica having an average primary particle diameter of 17 nm or less.

[0018] Since the rubber composition constituting the tread portion (hereinafter also referred to as tread rubber) contains such fine silica, it is considered that it becomes easier to increase the heat generation property (tan δ) at a low temperature near 0 °C and it becomes easier to improve the wet grip performance.

[0019] The rubber component preferably contains styrene-butadiene rubber.

[0020] Since the rubber component contains styrene-butadiene rubber, it becomes possible to form fine domains of the styrene portion in the tread rubber and obtain the friction at the periphery of the domain portion and the scraping effect by the domain portion. Therefore, it is considered that it becomes easier to improve the wet grip performance.

[0021] The content of silica in the filler is preferably more than 50% by mass.

[0022] When the filler contains more than 50% by mass of silica, it is considered that the hydrophilicity of the silica surface can be improved, making it easier to obtain the followability of the tread rubber to the road surface, and also making it easier to increase the heat generation property (tanδ) of the tread rubber near 0°C. These work together, and it is considered that the wet grip performance is further improved.

[0023] Preferably, the circumferential fine groove includes a neck portion with a narrow groove width and a body portion disposed radially inward of the tire than the neck portion and having a groove width larger than the maximum groove width of the neck portion.

[0024] By providing a groove with a larger space in the radial direction inside the tire, the tread land portion is more likely to deform, and it is easier to improve the ground contact property of the tread rubber. Therefore, it is considered that the wet grip performance is further improved.

[0025] The heavy-duty tire according to the present embodiment preferably has a jointless band.

[0026] By providing a jointless band, the circumferential rigidity of the tread portion can be increased, and it is easier to generate a reaction force during braking. Therefore, it is considered that the wet grip performance is further improved.

[0027] From the viewpoint of ensuring wet grip performance, Wc / Ws is preferably 0.09 or more.

[0028] When the total styrene amount in the rubber component is S (% by mass) and the content of silica relative to 100 parts by mass of the rubber component of the rubber composition is D (parts by mass), S / D is preferably 0.13 or more.

[0029] As the content of silica in the rubber composition increases, by also increasing the total styrene amount in the rubber component, the dispersibility of silica can be improved by styrene groups, and the flexibility of the rubber composition in the micro-deformation region is improved. Therefore, it is considered that the wet grip performance is further improved.

[0030] The complex elastic modulus (0℃E*) of the rubber composition at 0°C is preferably 8.5 MPa or more and 16.0 MPa or less.

[0031] By setting 0℃E* within the above range, it is considered that the road surface followability of the tread is improved and the wet grip performance can be ensured.

[0032] It is preferable that the pair of shoulder lands do not have lug grooves.

[0033] By not providing lug grooves in the shoulder lands, the road surface contact area of the tire increases, and the wet grip performance of the rubber can be exhibited.

[0034] From the viewpoint of the road surface contact property of the tire, the groove depth H1 at the deepest part of the circumferential main groove is preferably 15.0 mm or less.

[0035] When the crown land has sipes extending in the tire width direction and the depth of the deepest part of the sipes is H2 (mm), it is preferable that H2 / H1 is 0.25 or more.

[0036] By setting H2 / H1 within the above range, it is considered that it is possible to suppress the decrease in wet grip performance after the middle stage of wear due to the high rigidity of the tread part.

[0037] When the content of silica with respect to 100 parts by mass of the rubber component of the rubber composition is D (parts by mass), it is preferable that H1×D is 250 or more.

[0038] By setting the product of H1 and D within the above range and increasing the silica content as H1 decreases, it is considered that the road surface contact property of the tire and the road surface followability of the tread part are synergistically improved.

[0039] When the tread contact width is TW (mm), it is preferable that Wc / TW is 0.003 or more and 0.020 or less, and Ws / TW is more than 0.020 and 0.060 or less.

[0040] By setting Wc / TW and Ws / TW within the above ranges, it is considered that wet grip performance can be ensured.

[0041] <Definition> The "tread portion" is the portion that forms the ground contact surface of the tire. In the radial cross-section of the tire, when it includes members that form the tire skeleton with steel or textile materials such as belt layers and carcass layers, it is the member outside these in the radial direction of the tire.

[0042] The "belt layer" is the layer provided outside the carcass layer in the radial direction of the tire.

[0043] The "normal state" is a no-load state where the tire is mounted on a normal rim and filled with air at normal internal pressure.

[0044] The "dimensions of each part of the tire" are, unless otherwise specified, values specified in the normal state for those appearing on the outer surface of the tire, and for those inside the tire or on the tire cut surface, they are values specified in the state where the cut tire piece is held within the rim width of the normal rim with the tire cut by a plane including the tire rotation axis.

[0045] The "regular rim" is the rim defined for each tire in a standard system that includes the standards on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Association), it refers to the "standard rim" in the applicable sizes described in the "Jatma Year Book"; in the case of ETRTO (The European Tyre and Rim Technical Organisation), it refers to the "Measuring Rim" described in the "STANDARDS MANUAL"; and in the case of TRA (The Tire and Rim Association, Inc.), it refers to the "Design Rim" described in the "YEAR BOOK". Refer to JATMA, ETRTO, and TRA in this order, and follow the relevant standard if there is an applicable size during the reference. In the case of a tire not defined in the above standards, it refers to the rim with the narrowest width among the minimum-diameter rims that can be assembled with the tire and can maintain the internal pressure (i.e., does not cause air leakage between the rim and the tire).

[0046] The "regular internal pressure" is the air pressure defined for each tire in a standard system that includes the standards on which the tire is based. For example, in the case of JATMA, it refers to the "maximum air pressure"; in the case of ETRTO, it refers to the "INFLATION PRESSURE"; and in the case of TRA, it refers to the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". Similar to the case of the regular rim, refer to JATMA, ETRTO, and TRA in this order, and follow the relevant standard if there is an applicable size during the reference. In the case of a tire not defined in the above standards, it refers to the regular internal pressure (but not less than 250 kPa) of another tire size described with the regular rim as the standard rim (however, it must be defined in the standard), and if there are multiple regular internal pressures not less than 250 kPa, it refers to the minimum value among them.

[0047] The "normal load" refers to the load defined for each tire in a standard system including the standards on which the tire is based. For example, in the case of JATMA, it is the "maximum load capacity"; in the case of ETRTO, it is the "LOAD CAPACITY"; in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". Refer to JATMA, ETRTO, and TRA in this order as in the case of the normal rim and normal internal pressure. If there is an applicable size during reference, follow the standards. In the case of a tire not defined in the above standards, the maximum load capacity W L calculated separately is taken as the normal load.

[0048] The "maximum load capacity W L " is calculated by the following formula. "V" is the virtual volume of the tire (mm 3 ), "Dt" is the outer diameter of the tire in the normal state (mm), "Ht" is the cross-sectional height of the tire in the cross-section of the tire by the plane including the tire rotation axis, in the tire radial direction (mm), and "Wt" is the cross-sectional width of the tire in the normal state (mm). When the rim diameter of the tire is R, Ht can be obtained by (Dt - R) / 2. When there are patterns or characters on the tire sidewall, Wt is the value obtained after excluding them.

[0049]

Equation

[0050] The "tread ground end Te" refers to the outermost ground position in the tire width direction when a normal load is applied to a tire in the normal state and it contacts the plane at a camber angle of 0 degrees. The "tread ground width TW" refers to the distance in the tire width direction between the tread ground ends Te.

[0051] The "circumferential main groove" means a groove that extends continuously in the tire circumferential direction and, when the tire is new, the maximum value of the groove width perpendicular to the longitudinal direction is more than 2.0% of the tread contact width TW. The "circumferential fine groove" means a groove that extends continuously in the tire circumferential direction and, when the tire is new, the groove width perpendicular to the longitudinal direction of the groove is 2.0% or less of the tread contact width TW.

[0052] A "siping" means a cut-like body that extends in the tire width direction and, when the tire is new, the width perpendicular to the longitudinal direction of the groove is less than 1.5 mm. A "lug groove" means a groove-like body that extends in the tire width direction and, when the tire is new, the groove width perpendicular to the longitudinal direction of the groove is 1.5 mm or more.

[0053] The "groove width" is the width (W1 in Fig. 6) at the opening of each of the circumferential main groove, circumferential fine groove, siping, and lug groove. When the groove width changes in the longitudinal direction of the groove, it refers to the maximum value of the groove width perpendicular to the longitudinal direction when the tire is new. In addition, as shown in Fig. 7, when a taper portion is provided at the opening of the groove, unless otherwise specified, the intersection of the extension line of the groove wall surface and the extension line of the land surface contour is virtually regarded as an edge, and the groove width at the opening is obtained (W1 in Fig. 7).

[0054] The "tread thickness" is the thickness of the tread portion on the tire center line measured in a state where the tire is cut by a plane including the tire rotation axis and held on a standard rim. Note that the inner end in the tire radial direction of the entire tread thickness is the inner interface of the rubber composition constituting the tread portion. When the tire is provided with a belt reinforcing layer, a belt layer, and a carcass layer, the outermost part of the outermost layer in the tire radial direction among these is the inner interface in the tire radial direction. When there is a circumferential groove on the tire equator plane, the groove is assumed to be filled and the total thickness of the tread is measured. For example, in Fig. 1, G corresponds to the tread thickness. The thickness t1 of the cap rubber layer and the thickness of other rubber layers constituting the tread portion are measured in the same way.

[0055] "The groove depth H1 at the deepest part of the circumferential main groove" is obtained by the distance between the tread surface and the deepest part of the groove bottom of the circumferential main groove. Note that the deepest part of the groove bottom of the circumferential main groove is the deepest part of the groove bottom of the circumferential main groove having the maximum groove depth among the circumferential main grooves adjacent to the crown land part.

[0056] "The depth H2 at the deepest part of the sipe" is obtained by the distance between the tread surface and the deepest part of the sipe. Note that the deepest part of the sipe is the deepest part of the sipe having the maximum depth among the sipers existing in the crown land part.

[0057] "The groove depth H3 at the deepest part of the circumferential fine groove" is obtained by the distance between the tread surface and the deepest part of the groove bottom of the circumferential fine groove. Note that the deepest part of the groove bottom of the circumferential fine groove is the deepest part of the groove bottom of the circumferential fine groove having the maximum groove depth among the circumferential fine grooves existing in the crown land part.

[0058] "The softening agent" is a material that imparts plasticity to the rubber component and is a component extracted from the rubber composition using acetone. The softening agent includes a softening agent that is liquid (liquid state) at 25°C and a softening agent that is solid at 25°C. However, wax and stearic acid commonly used in the tire industry are not included.

[0059] "The content of the softening agent" also includes the amount of the softening agent contained in the stretched rubber component stretched in advance by a softening agent such as oil, resin component, liquid rubber component, etc. The same applies to the content of oil, the content of resin component, and the content of liquid rubber. For example, when the stretching component is oil, the stretched oil is included in the content of oil.

[0060] <Measurement method> "0℃ tanδ" is the loss tangent measured under the conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±2.5%, and an elongation mode using a dynamic viscoelasticity measuring device (for example, the Implex series manufactured by GABO). The sample for 0℃ tanδ measurement is a vulcanized rubber composition with a length of 20 mm × width of 4 mm × thickness of 1 mm. When produced by cutting out from a tire, it is cut out from the tread part of the tire such that the circumferential direction of the tire is the long side and the radial direction of the tire is the thickness direction.

[0061] "0℃ E*" is the complex elastic modulus measured under the conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±2.5%, and an elongation mode using a dynamic viscoelasticity measuring device (for example, the Implex series manufactured by GABO). The sample for this measurement is produced in the same manner as in the case of 0℃ tanδ.

[0062] "Styrene content" is 1 a value calculated by 1H-NMR measurement and is applicable to rubber components having repeating units derived from styrene such as SBR.

[0063] "Vinyl content (amount of 1,2-bonded butadiene units)" is a value calculated by infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017 and is applicable to rubber components having repeating units derived from butadiene such as SBR and BR.

[0064] "Cis content (amount of cis-1,4-bonded butadiene units)" is a value calculated by infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017 and is applicable to rubber components having repeating units derived from butadiene such as BR.

[0065] "The total styrene content in the rubber component" refers to the total content (% by mass) of styrene units contained in 100% by mass of the rubber component. For each rubber component, a value obtained by multiplying the styrene content (% by mass) by the mass fraction in the rubber component is calculated, and the sum of these values is the result. Specifically, it is calculated by Σ (styrene content (% by mass) of each rubber containing styrene units × content (% by mass) of each rubber containing styrene units in the rubber component / 100).

[0066] "The weight-average molecular weight (Mw)" can be determined by standard polystyrene conversion based on the measured values obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSK gel SuperMultipore HZ-M manufactured by Tosoh Corporation). For example, it is applicable to SBR, BR, etc.

[0067] "The nitrogen adsorption specific surface area (N 2 SA) of carbon black" is measured in accordance with JIS K 6217-2:2017.

[0068] "The nitrogen adsorption specific surface area (N 2 SA) of silica" is measured by the BET method in accordance with ASTM D3037-93.

[0069] "The average primary particle size" is a value obtained by photographing particles with a transmission or scanning electron microscope and calculating the arithmetic mean of the particle sizes of 400 particles. When the shape of the particles is spherical, the diameter of the sphere is taken as the particle size; when the shape is other than spherical, the equivalent circle diameter ({the positive square root of 4 × (the area of the particle) / π}) is calculated from the microscope image as the particle size. The average primary particle size is applicable to silica, carbon black, etc.

[0070] "The softening point of the resin component" is measured with a ring and ball softening point measuring device in accordance with the softening point specified in JIS K 6220-1:2015 7.7, and it is the temperature at which the ball drops.

[0071] A tire according to an embodiment of the present invention will be described below with reference to the drawings as appropriate. However, the drawings used are merely illustrative of one embodiment, and the present invention is not limited by these drawings.

[0072] <Tire> FIG. 1 is a cross-sectional view showing a part of a heavy-duty tire according to an embodiment of the present invention. In FIG. 1, the vertical direction is the radial direction of the heavy-duty tire 1, the horizontal direction is the tire width direction of the heavy-duty tire 1, and the direction perpendicular to the paper surface is the circumferential direction of the heavy-duty tire 1. In FIG. 1, the shape of the heavy-duty tire 1 is symmetric with respect to the tire equator CL except for the tread pattern.

[0073] The heavy-duty tire 1 includes a tread portion 3, a belt layer 6, a sidewall portion 7, a bead portion 14, an inner liner 15, and a carcass 16. The inner liner 15 is located inside the carcass 16. The tread portion 3 forms a tread contact surface 2 that contacts the road surface. Two circumferential main grooves 8 and circumferential fine grooves 9 that continuously extend in the tire circumferential direction are formed in the tread contact surface 2.

[0074] The bead portion 14 includes a bead core 22 and an apex 24 that extends radially outward from the bead core 22. The bead core 22 is ring-shaped and includes a wound non-stretchable wire. The apex 24 tapers radially outward of the tire.

[0075] The carcass 16 is composed of a carcass ply 26. The carcass ply 26 is spanned between the bead portions 14 on both sides and extends along the tread portion 3 and the sidewall 7. The carcass ply 26 is folded around the bead core 22 from the inner side to the outer side in the tire width direction. The carcass ply 26 is composed of a large number of parallel cords and topping rubber. The carcass 16 may be formed of two or more carcass plies 26.

[0076] The belt layer 6 extends in the tire width direction. The belt layer 6 is located inside the tread portion 3 in the tire radial direction. The belt layer 6 is located outside the carcass 16 in the tire radial direction and reinforces the carcass 16.

[0077] The belt layer 6 is formed of four belt plies including a first belt layer 6a, a second belt layer 6b, a third belt layer 6c, and a fourth belt layer 6d laminated in order from the inner side in the tire radial direction. The first belt layer 6a is laminated on the carcass 16. In FIG. 1, in the tire rotation axis direction, the second belt layer 6b has the largest width among the four layers, and the fourth belt layer 6d has the smallest width among the four layers, but it is not limited to such a mode.

[0078] In FIG. 1, the tread portion 3 includes a cap rubber layer 4 whose outer surface constitutes the tread contact surface 2, and a base rubber layer 4 existing between the cap rubber layer 4 and the belt layer 6, but it is not limited to such a mode. As long as the effects of the present invention are achieved, the tread portion 3 may be a single rubber layer or may be formed of three or more rubber layers. When there are two or more rubber layers between the cap rubber layer 4 and the belt layer 6, among the layers closest to the belt layer 6, a layer having a thickness of 1 mm or more is defined as the base rubber layer.

[0079] The cap rubber layer 4 extends to both outer ends in the tire rotation axis direction of the tread portion 3. The covering rubber 20 covers each end of the second belt layer 6b and the third belt layer 6c.

[0080] The thickness G of the tread portion is preferably 15.0 mm or more, more preferably 16.0 mm or more, still more preferably 17.0 mm or more, and particularly preferably 18.0 mm or more. On the other hand, G is preferably 23.0 mm or less, more preferably 22.0 mm or less, still more preferably 21.0 mm or less, and particularly preferably 20.0 mm or less.

[0081] The thickness t1 of the cap rubber layer is preferably 11.5 mm or more, more preferably 12.5 mm or more, still more preferably 13.5 mm or more, and particularly preferably 14.5 mm or more. On the other hand, t1 is preferably 19.5 mm or less, more preferably 18.5 mm or less, still more preferably 17.5 mm or less, and particularly preferably 16.5 mm or less.

[0082] From the viewpoint of the effects of the present invention, t1 / G is preferably 0.65 or more, more preferably 0.70 or more, still more preferably 0.73 or more, further more preferably 0.76 or more, further more preferably 0.79 or more, and particularly preferably 0.80 or more. On the other hand, the upper limit value of t1 / G is not particularly limited and may be 1.0, but is preferably less than 1.0, more preferably 0.95 or less, still more preferably 0.90 or less, further more preferably 0.85 or less, and particularly preferably 0.83 or less.

[0083] FIG. 2 is a modified example of the heavy load tire according to the present embodiment. For the parts not described below regarding the modified example, the configuration of the above-described heavy load tire can be adopted.

[0084] In FIG. 2, a jointless band 17 is disposed between the second belt layer 6b and the third belt layer 6c. The second belt layer 6b and the third belt layer 6c have a width wider than that of the jointless band 17. That is, the plurality of belt plies constituting the belt layer 6 includes two belt plies having a width wider than the width of the full band 17, and the jointless band 17 is sandwiched between the two belt plies having this wide width.

[0085] FIG. 3 illustrates a ribbon 28 that constitutes the jointless band 17. The ribbon 28 has two cords 30 and a topping rubber 32, but is not limited to such an embodiment. The number of cords 30 in the ribbon 28 may be one or three or more. The jointless band 17 is formed by winding the ribbon 28 spirally in the circumferential direction. The jointless band 17 has a so-called jointless structure. Each cord 30 extends substantially in the circumferential direction. The angle of the cord 30 with respect to the circumferential direction is preferably 5° or less, more preferably 2° or less.

[0086] FIG. 4 shows an example of a developed view in which the tread pattern of the heavy load tire according to the present embodiment is developed on a plane.

[0087] The tread portion 3 has land portions partitioned by two circumferential grooves 8 that continuously extend in the tire circumferential direction in the tire width direction W. The shoulder land portions 18 are a pair of land portions formed between the circumferential main groove 8 and the tread grounding end Te. The crown land portion 19 is a land portion formed between the pair of shoulder land portions 18.

[0088] The circumferential main groove 8 extends in a zigzag shape while the center line in the width direction of each circumferential main groove sways horizontally. Here, extending in a zigzag shape means that the center in the width direction of the circumferential main groove extends in the tire circumferential direction while swaying in the tire width direction. Therefore, in addition to the form in which a straight groove repeatedly bends, the form in which a curved groove repeatedly curves in a wave shape is also included. Note that the circumferential main groove 8 may be straight in addition to being zigzag.

[0089] The groove depth H1 at the deepest part of the circumferential main groove 8 is 15.0 mm or less, preferably 14.8 mm or less, more preferably 14.6 mm or less, further preferably 14.4 mm or less, and particularly preferably 14.2 mm or less from the viewpoint of the effects of the present invention. On the other hand, H1 is preferably 10.0 mm or more, more preferably 11.0 mm or more, and further preferably 12.0 mm or more.

[0090] From the perspective of the effects of the present invention, H1 / G is preferably 0.60 or more, more preferably 0.62 or more, and even more preferably 0.64 or more. On the other hand, H1 / G is preferably 0.80 or less, more preferably 0.78 or less, even more preferably 0.76 or less, and particularly preferably 0.74 or less.

[0091] The groove width Ws of the circumferential main groove is preferably 8.0 mm or more, more preferably 8.2 mm or more, and even more preferably 8.4 mm or more. On the other hand, Ws is preferably 15.0 mm or less, more preferably 14.5 mm or less, and even more preferably 14.0 mm or less.

[0092] When the tread contact width is TW (mm), Ws / TW is more than 0.020, preferably more than 0.025, more preferably 0.030 or more, and even more preferably 0.035 or more. On the other hand, Ws / TW is preferably 0.060 or less, more preferably 0.055 or less, and even more preferably 0.050 or less.

[0093] In FIG. 4, the crown land portion 19 has one circumferential fine groove 9 extending continuously in the tire circumferential direction, but is not limited to such a mode, and the crown land portion 19 may have a plurality of circumferential fine grooves 9. Further, the circumferential fine groove 9 may be zigzag like the circumferential main groove 8 or may be linear.

[0094] The groove width Wc of the circumferential fine groove is preferably 0.5 mm or more, more preferably 0.7 mm or more, even more preferably 0.9 mm or more, and particularly preferably 1.0 mm or more. On the other hand, Wc is preferably 2.0 mm or less, more preferably 1.9 mm or less, even more preferably 1.8 mm or less, and particularly preferably 1.7 mm or less.

[0095] Wc / TW is 0.020 or less, preferably 0.018 or less, more preferably 0.015 or less, and even more preferably 0.012 or less. On the other hand, Wc / TW is preferably 0.003 or more, and more preferably 0.004 or more.

[0096] Wc / Ws is preferably 0.03 or more, more preferably 0.06 or more, and even more preferably 0.09 or more. On the other hand, Wc / Ws is preferably 0.28 or less, more preferably 0.25 or less, even more preferably 0.20 or less, and particularly preferably 0.15 or less.

[0097] The crown land portion 19 has sipes inclined in the tire circumferential direction or the tire width direction. Specifically, the sipes inclined in the tire circumferential direction or the tire width direction are bent or curved and extend in the process of advancing in the width direction.

[0098] In FIG. 4, the crown land portion 19 is provided with a plurality of center sipes 10 that communicate with the circumferential main grooves 8 and the circumferential fine grooves 9 and are bent in the process of extending from one end in the width direction to the other end. The center sipes 10 are bent so that the extending direction changes at the central portion in the width direction. Specifically, the center sipes 10 are inclined so as to shift toward one side in the tire circumferential direction as they go from one end in the width direction of the center sipes 10 toward the central portion in the width direction. Then, the center sipes 10 are bent at the central portion in the width direction and are inclined in the reverse direction so as to shift toward the other side in the tire circumferential direction as they go from the central portion in the width direction of the center sipes 10 to the other end. By providing the sipes inclined in the tire circumferential direction or the tire width direction on the crown land portion 19 in this way, it is possible to improve the wet grip performance due to the increase in the sipe length, and since the blocks can support each other not only in the front-rear direction but also in the lateral direction, it is considered that not only the rigidity in the tire circumferential direction can be improved but also the rigidity in the tire width direction can be improved, so that the wear resistance performance can also be improved.

[0099] When the depth of the deepest part of the crown sipe 10 is H2 (mm), H2 / H1 is preferably 0.25 or more, more preferably 0.30 or more, even more preferably 0.33 or more, and particularly preferably 0.40 or more. By setting H2 / H1 within the above range, it is considered that it is possible to suppress the decrease in the wet grip performance after the middle stage of wear due to the high rigidity of the tread portion. On the other hand, H2 / H1 is preferably 1.0 or less, and more preferably 0.95 or less.

[0100] In FIG. 4, no lug grooves and sipes are provided on the shoulder land portion 18. By not providing lug grooves on the shoulder land portion, it is considered that the road surface contact area of the tire increases, making it easier to exhibit wet grip performance.

[0101] FIG. 5 shows a cross-sectional view taken along line C-C of the crown sipe 10 shown in FIG. 4. As shown in FIG. 4, the crown sipe 10 has an opening portion with a groove width that gradually decreases toward the inner side in the tire radial direction, and a sipe portion 30 on the inner side in the tire radial direction thereof, but is not limited to such a mode.

[0102] FIG. 6 shows an enlarged view of the circumferential fine groove 9. In FIG. 5, the cross-section of the circumferential fine groove 9 has a flask shape. Specifically, the circumferential fine groove 9 has a neck portion 11 and a body portion 12 that is disposed on the inner side in the tire radial direction than the neck portion and has a groove width larger than the maximum groove width of the neck portion. Due to such a cross-sectional shape, even when a large load is applied to the tread portion 2, the stress applied to the side wall of the land portion is relaxed.

[0103] In the present embodiment, when it is a new tire or in the initial stage of wear of the tread portion 3, the portion of the circumferential fine groove 9 that appears on the tread surface is the neck portion 11. Since the neck portion can be closed by the load applied to the tread portion 3, the rigidity in the tire axial direction of the tread portion 3 is increased. On the other hand, as the wear of the tread portion 3 progresses, the tread surface moves inward in the tire radial direction, and the opening of the circumferential fine groove 9 shifts from the neck portion to the body portion. Therefore, as the wear progresses, the width of the circumferential fine groove 9 expands, and the drainage performance of the tread portion 3 after the mid-stage of wear is maintained high.

[0104] In FIG. 6, the groove width of the head portion is fixed at its minimum groove width W1 and is constant. However, as long as the effects of the present invention are exhibited, the head portion may have a portion with a groove width larger than W1. Therefore, the cross-sectional shape of the head portion may be linear as shown in FIG. 6, or may be zigzag. Here, the zigzag shape has the same meaning as described above. As a preferred embodiment, the groove width of the head portion is constant at its minimum groove width.

[0105] Further, the body portion 12 has a portion with a groove width larger than the maximum groove width of the head portion. Here, "having a portion with a groove width larger than the maximum groove width of the head portion" means that the body portion is configured to be wider than the maximum groove width of the head portion so that the effects of the present invention can be achieved. Therefore, the groove width of the body portion is not particularly limited as long as it includes a portion larger than the maximum groove width of the head portion so that the effects of the present invention can be achieved. For example, a part of the groove width of the body portion may have a portion narrower than the maximum groove width of the head portion, or the groove width of the body portion may be configured to consist only of a portion larger than the groove width of the head portion. In FIG. 5, since the groove width of the head portion 11 is fixed at its minimum groove width W1, the body portion 12 is composed only of a portion with a groove width larger than the groove width of the head portion 11.

[0106] The minimum groove width W1 of the head portion is preferably 0.5 mm or more, more preferably 0.7 mm or more, still more preferably 0.9 mm or more, and particularly preferably 1.0 mm or more. By setting W1 within the above range, water can easily flow from the head portion to the body portion during wet running, and sufficient drainage performance can be easily ensured. On the other hand, W1 is preferably 2.0 mm or less, more preferably 1.9 mm or less, still more preferably 1.8 mm or less, and particularly preferably 1.7 mm or less. By setting W1 within the above range, when a load is applied to the tread portion 3 at the initial stage of wear, the head portion is likely to be blocked by the contact pressure, and the rigidity of the tread portion 3 in the tire axial direction is increased. Also, the rubber volume of the tread portion 3 can be easily ensured. Thereby, the wear resistance performance of the heavy-duty tire 1 is improved.

[0107] The maximum groove width W2 of the carcass is preferably 2.0 mm or more, more preferably 3.0 mm or more, and even more preferably 4.0 mm or more. By setting W2 within the above range, even at the end of wear, the width of the flask-shaped circumferential groove 9 can be easily ensured, and sufficient drainage performance can be easily ensured. On the other hand, W2 is preferably 12.0 mm or less, more preferably 11.0 mm or less, even more preferably 10.0 mm or less, even more preferably 9.0 mm or less, and particularly preferably 8.0 mm or less. By setting W2 within the above range, the rubber volume of the tread portion 3 can be easily ensured. Thereby, the wear resistance of the heavy-duty tire 1 is improved.

[0108] W2 / W1 is preferably 2.0 or more, more preferably 2.5 or more, even more preferably 3.0 or more, and particularly preferably 3.5 or more. By setting W2 / W1 within the above range, even at the end of wear, the width of the flask-shaped circumferential groove 9 can be easily ensured, and sufficient drainage performance can be easily ensured. On the other hand, W2 / W1 is preferably 8.0 or less, more preferably 7.5 or less, even more preferably 7.0 or less, and particularly preferably 6.5 or less. By setting W2 / W1 within the above range, the rubber volume of the tread portion 3 can be easily ensured. Thereby, the wear resistance of the heavy-duty tire 1 is improved.

[0109] When the groove depth H3 (mm) at the deepest part of the circumferential fine groove 9 and the minimum length in the tire radial direction from the groove bottom to the neck of the circumferential fine groove 9 is H4 (mm), H4 / H3 is preferably 0.25 or more, more preferably 0.33 or more, and even more preferably 0.40 or more. By setting H4 / H3 within the above range, the groove volume of the carcass can be easily ensured, and sufficient drainage performance at the end of wear can be easily ensured. Also, H4 / H3 is preferably 0.75 or less, more preferably 0.73 or less. By setting H4 / H3 within the above range, at the initial stage of wear, the rigidity of the tread portion 3 in the tire axial direction is increased. Also, the rubber volume of the tread portion 3 can be easily ensured. Thereby, the wear resistance of the heavy-duty tire 1 is improved.

[0110] FIG. 7 shows a modified example of the circumferential groove 9. For parts not described below regarding this modified example, the configuration of the circumferential groove described above may be adopted.

[0111] In FIG. 7, the circumferential groove includes an opening (tapered portion) 13 where the groove width expands in a tapered shape arranged on the outer side in the tire radial direction of the head portion. By the tapered portion 13, the volume of the circumferential groove 9 in the initial stage of wear increases. Also, by the tapered portion 13, the amount of water flowing from the head portion into the tread portion increases. Thereby, the drainage performance of the tread portion 3 is enhanced.

[0112] It is preferable that the maximum groove width W2 of the tread portion is larger than the maximum groove width W3 of the tapered portion. Thereby, the groove volume of the circumferential groove 9 in the tread portion can be easily ensured, and it becomes possible to easily ensure sufficient drainage performance at the end stage of wear of the tread portion 3.

[0113] The tanδ (tanδ at 0°C) of the rubber composition constituting the tread portion is 0.28 or more, preferably 0.29 or more, and more preferably 0.30 or more. On the other hand, from the viewpoint of suppressing heat generation, tanδ at 0°C is preferably 0.35 or less, more preferably 0.34 or less, and even more preferably 0.33 or less. When the tread portion is composed of two or more rubber layers, the tanδ at 0°C refers to the tanδ at 0°C of the rubber composition constituting the cap rubber layer.

[0114] From the viewpoint of wet grip performance, the complex elastic modulus (E* at 0°C) of the rubber composition constituting the tread portion is preferably 7.5 MPa or more, more preferably 8.0 MPa or more, even more preferably 8.5 MPa or more, and particularly preferably 9.0 MPa or more. On the other hand, from the viewpoint of wet grip performance, E* at 0°C is preferably 17.0 MPa or less, more preferably 16.5 MPa or less, and even more preferably 16.0 MPa or less. When the tread portion is composed of two or more rubber layers, the E* at 0°C refers to the E* at 0°C of the rubber composition constituting the cap rubber layer.

[0115] 0 °C E* and 0 °C tanδ can be appropriately adjusted according to the types and blending amounts of the rubber component, filler, softener, etc. described below.

[0116] 0 °C tanδ / (Wc / Ws) is greater than 1.0, preferably greater than 1.4, more preferably greater than 1.8, still more preferably greater than 2.2, and particularly preferably greater than 2.6. On the other hand, the upper limit value of 0 °C tanδ / (Wc / Ws) is not particularly limited, but preferably less than 3.5, more preferably less than 3.25, and still more preferably less than 3.0.

[0117] When the content of silica is D (parts by mass) with respect to 100 parts by mass of the rubber component of the rubber composition constituting the tread portion, H1 × D is preferably 250 or more, more preferably 300 or more, still more preferably 350 or more, still more preferably 400 or more, still more preferably 450 or more, and particularly preferably 500 or more. Also, the upper limit value of H1 × D is not particularly limited, but preferably 1200 or less, more preferably 1000 or less, and still more preferably 800 or less.

[0118] [Rubber Composition] The rubber composition (hereinafter referred to as the rubber composition according to the present embodiment) constituting the tread portion of the heavy-duty tire according to the present embodiment contains a rubber component and a filler, and all can be manufactured using the raw materials described below. When the tread portion is composed of two or more rubber layers, it is applicable to the rubber composition constituting any rubber layer of the tread portion unless otherwise specified, but it is preferably applied to the rubber composition constituting the cap rubber layer.

[0119] [Rubber Component] In the rubber composition according to this embodiment, a diene rubber is preferably used as the rubber component. Examples of the diene rubber include isoprene rubber, butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene rubber (SIR), styrene-isoprene-butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and the like. These diene rubbers may be modified rubbers treated with a modifying group capable of interacting with a filler such as carbon black or silica, or may be hydrogenated rubbers in which a part of the unsaturated bonds is hydrogenated. The diene rubber may be used alone or in combination of two or more. Further, as the diene rubber, an extended rubber preliminarily extended using a softening agent described later may be used.

[0120] The content of the diene rubber in the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more. Further, a rubber component composed only of a diene rubber may be used.

[0121] As the diene rubber component, at least one selected from the group consisting of isoprene rubber, SBR, and BR is preferably used. The diene rubber component preferably contains isoprene rubber, more preferably contains isoprene rubber and SBR and / or BR, still more preferably contains isoprene rubber and SBR, and particularly preferably contains isoprene rubber, BR, and SBR.

[0122] (Isoprene rubber) As the isoprene rubber, for example, those commonly used in the tire industry such as isoprene rubber (IR) and natural rubber can be used. Natural rubber includes, in addition to unmodified natural rubber (NR), modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene rubbers may be used alone or in combination of two or more.

[0123] NR is not particularly limited, and those commonly used in the tire industry can be used. For example, SIR20, RSS#3, TSR20, etc. can be mentioned.

[0124] From the viewpoint of the effects of the present invention, the content of isoprene rubber in the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, still more preferably 40% by mass or more, still more preferably 50% by mass or more, and particularly preferably 55% by mass or more. Further, the content is preferably 99% by mass or less, more preferably 95% by mass or less, still more preferably 90% by mass or less, and particularly preferably 85% by mass or less.

[0125] (BR) BR is not particularly limited. For example, BR with a cis content of less than 50 mol% (low-cis BR), BR with a cis content of 90 mol% or more (high-cis BR), rare-earth-based butadiene rubber synthesized using a rare-earth element-based catalyst (rare-earth-based BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc., which are common in the tire industry, can be used. These BRs can be used alone or in combination of two or more.

[0126] As the high-cis BR, for example, those commercially available from Nippon Zeon Co., Ltd., UBE Industries, Ltd., JSR Corporation, etc. can be used. By containing high-cis BR, the wear resistance performance can be improved. The cis content of the high-cis BR is preferably 95 mol% or more, more preferably 96 mol% or more, and still more preferably 97 mol% or more. The cis content of BR is measured by the above measurement method.

[0127] As the modified BR, a modified butadiene rubber (modified BR) modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen in the terminal and / or main chain is preferably used.

[0128] Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and further having the ends of the modified BR molecules bonded by tin-carbon bonds (tin-modified BR), etc. The modified BR may be either unhydrogenated or hydrogenated.

[0129] From the viewpoint of the effects of the present invention, the content of BR in the rubber component is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less, still more preferably 30% by mass or less, and particularly preferably 25% by mass or less. The lower limit of the content is not particularly limited, but can be, for example, 1% by mass or more, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more.

[0130] (SBR) There is no particular limitation on SBR, and examples include unmodified solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR), etc. Modified SBRs include those with modified ends and / or main chains, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, those having a branched structure, etc.). Among them, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) can also be used. These SBRs can be used alone or in combination of two or more.

[0131] The SBRs listed above can be used alone or in combination of two or more. As the SBRs listed above, for example, those commercially available from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., ZS Elastomer Co., Ltd., etc. can be used.

[0132] The styrene content of the SBR can be appropriately selected so that the total amount of styrene S in the rubber component satisfies the following range, but it is preferably 40% by mass or less, more preferably 36% by mass or less, still more preferably 32% by mass or less, and particularly preferably 28% by mass or less. Also, the styrene content of the SBR is preferably 5% by mass or more, more preferably 7% by mass or more, still more preferably 10% by mass or more, and particularly preferably 12% by mass or more. The styrene content of the SBR is measured by the above measurement method.

[0133] From the viewpoints of ensuring reactivity with silica and abrasion resistance performance, the vinyl content of the SBR is preferably 5 mol% or more, more preferably 10 mol% or more, and still more preferably 15 mol% or more. Also, from the viewpoints of elongation at break and abrasion resistance performance, the vinyl content of the SBR is preferably 45 mol% or less, more preferably 40 mol% or less, and still more preferably 35 mol% or less. The vinyl content of the SBR is measured by the above measurement method.

[0134] From the viewpoint of the effects of the present invention, the weight average molecular weight (Mw) of the SBR is preferably 100,000 or more, more preferably 200,000 or more, and still more preferably 300,000 or more. Also, from the viewpoint of crosslinking uniformity, the weight average molecular weight is preferably 2,000,000 or less, more preferably 1,800,000 or less, and still more preferably 1,500,000 or less. The weight average molecular weight of the SBR is measured by the above measurement method.

[0135] The content of SBR in the rubber component can be appropriately selected so that the total amount of styrene in the rubber component satisfies the following range, but it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 15 parts by mass or more. Also, the content is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less, and particularly preferably 40% by mass or less.

[0136] (Other rubber components) The rubber component may contain other rubber components other than diene rubbers as long as the effects of the present invention are not affected. As other rubber components other than diene rubbers, crosslinkable rubber components generally used in the tire industry can be used. For example, non-diene rubbers such as butyl rubber (IIR), halogenated butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber can be mentioned. These other rubber components may be used alone or in combination of two or more. Further, in addition to the above rubber components, a known thermoplastic elastomer may or may not be contained.

[0137] From the viewpoint of the effects of the present invention, the total styrene amount S in the rubber component is preferably 30% by mass or less, more preferably 27% by mass or less, still more preferably 25% by mass or less, and particularly preferably 22% by mass or less. Further, the lower limit value of the total styrene amount S in the rubber component is not particularly limited, but is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and particularly preferably 7% by mass or more.

[0138] When the content of silica relative to 100 parts by mass of the rubber component is D (parts by mass), S / D is preferably 0.050 or more, more preferably 0.080 or more, still more preferably 0.10 or more, and particularly preferably 0.13 or more from the viewpoint of the effects of the present invention. Further, the upper limit value of S / D is not particularly limited, but can be, for example, 2.00 or less, 1.50 or less, 1.00 or less, 0.80 or less, 0.60 or less, 0.50 or less.

[0139] <Filler> The rubber composition according to the present embodiment preferably contains silica as a filler, and more preferably contains silica and carbon black. Further, it may be a filler consisting only of silica and carbon black.

[0140] (Silica) The silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., which are common in the tire industry, can be used. Among them, hydrous silica prepared by a wet method is preferred because it has many silanol groups. In addition to the above-mentioned silica, silica made from biomass materials such as rice husks may be appropriately used as raw materials. These silicas may be used alone or in combination of two or more.

[0141] The nitrogen adsorption specific surface area (N 2 SA) of the silica is preferably 100 m 2 / g or more, more preferably 120 m 2 / g or more, still more preferably 140 m 2 / g or more, particularly preferably 160 m 2 / g or more, from the viewpoints of abrasion resistance performance and elongation at break. Also, from the viewpoints of heat generation property and processability, it is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, still more preferably 250 m 2 / g or less. The N 2 SA of the silica is measured by the above-mentioned measurement method.

[0142] The average primary particle diameter of the silica is preferably 20 nm or less, more preferably 18 nm or less, still more preferably 17 nm or less, particularly preferably 16 nm or less. The lower limit value of the average primary particle diameter is not particularly limited, but from the viewpoint of the dispersibility of the silica, it is preferably 1 nm or more, more preferably 3 nm or more, still more preferably 5 nm or more. The average primary particle diameter of the silica is measured by the above-mentioned measurement method.

[0143] The content D of silica relative to 100 parts by mass of the rubber component can be appropriately set so that, for example, H1×D satisfies the above range. However, it is preferably 17 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 22 parts by mass or more, and particularly preferably 25 parts by mass or more. Also, from the viewpoint of reducing the specific gravity of the rubber and achieving weight reduction, it is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, still more preferably 75 parts by mass or less, and particularly preferably 60 parts by mass or less.

[0144] (Carbon black) The carbon black is not particularly limited. For example, those commonly used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. These carbon blacks may be used alone or in combination of two or more.

[0145] The nitrogen adsorption specific surface area (N 2 SA) of the carbon black is preferably 20 m 2 / g or more, more preferably 50 m 2 / g or more, still more preferably 80 m 2 / g or more, and particularly preferably 100 m 2 / g or more from the viewpoint of reinforcing property. Also, from the viewpoints of low fuel consumption performance and processability, it is preferably 250 m 2 / g or less, more preferably 200 m 2 / g or less, still more preferably 150 m 2 / g or less. The N 2 SA of the carbon black is measured by the above measurement method.

[0146] The average primary particle diameter of the carbon black is preferably 30 nm or less, more preferably 26 nm or less, still more preferably 23 nm or less, and particularly preferably 20 nm or less. The lower limit of the average primary particle diameter is not particularly limited, but is preferably 5 nm or more, more preferably 8 nm or more, and still more preferably 10 nm or more. The average primary particle diameter of the carbon black is measured by the above measurement method.

[0147] (Other fillers) Fillers other than silica and carbon black are not particularly limited, and for example, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, biochar, etc., which have been conventionally used in the tire industry, can be blended. These other fillers may be used alone or in combination of two or more.

[0148] From the viewpoint of the effects of the present invention, the total content of the filler with respect to 100 parts by mass of the rubber component is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, still more preferably 50 parts by mass or more, and particularly preferably 55 parts by mass or more. Also, the content is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, still more preferably 80 parts by mass or less, and particularly preferably 70 parts by mass or less.

[0149] The content of silica in the filler is preferably more than 40% by mass, more preferably more than 50% by mass, still more preferably more than 60% by mass, still more preferably more than 70% by mass, and particularly preferably more than 80% by mass. On the other hand, the upper limit value of the content is not particularly limited, and for example, it can be less than 99% by mass, less than 95% by mass, or less than 90% by mass.

[0150] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and in the tire industry, any silane coupling agent conventionally used in combination with silica can be used. For example, mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide, bis(3-triethoxysilylpropyl)tetrasulfide; thioester-based silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane; vinyl-based silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane; chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane; etc. Among them, it is preferable to contain a sulfide-based silane coupling agent and / or a mercapto-based silane coupling agent. As the silane coupling agent, for example, those commercially available from Evonik Degussa, Momentive, etc. can be used. The silane coupling agent may be used alone or in combination of two or more.

[0151] The content of the silane coupling agent with respect to 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more from the viewpoint of enhancing the dispersibility of silica. Further, from the viewpoint of preventing a decrease in wear resistance performance, it is preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8.0 parts by mass or less.

[0152] The content of the silane coupling agent with respect to 100 parts by mass of silica is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more from the viewpoint of enhancing the dispersibility of silica. Further, from the viewpoint of preventing a decrease in wear resistance performance, it is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

[0153] <Softening agent> The rubber composition according to this embodiment preferably contains a softening agent. Examples of the softening agent include a resin component, an oil, a liquid rubber, etc. The softening agent also includes an extended oil, an extended resin, and an extended liquid rubber component of a rubber component that has been subjected to oil extension, resin extension, or liquid rubber extension. These softening agents may be derived from petroleum or may be derived from biomass. Further, a low molecular weight hydrocarbon component obtained by thermally decomposing and extracting a used tire or a product containing various components may be used as the softening agent.

[0154] (Resin component) The resin component is not particularly limited, and examples thereof include petroleum resins, terpene resins, rosin resins, and phenolic resins commonly used in the tire industry. These resin components may be used alone or in combination of two or more.

[0155] Examples of the petroleum resin include C5-based petroleum resins, aromatic petroleum resins, and C5C9-based petroleum resins.

[0156] As used herein, the term "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction, which may be hydrogenated or modified. Examples of the C5 fraction include petroleum fractions corresponding to 4 to 5 carbon atoms such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5 petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0157] As used herein, the term "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, which may be hydrogenated or modified. Examples of the C9 fraction include petroleum fractions corresponding to 8 to 10 carbon atoms such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of the aromatic petroleum resin include, for example, coumarone-indene resin, coumarone resin, indene resin, and aromatic vinyl resin. As the aromatic vinyl resin, due to economic reasons, ease of processing, and excellent heat generation properties, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred. As the aromatic vinyl resin, for example, those commercially available from companies such as Crayton and Eastman Chemical can be used.

[0158] As used herein, the term "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, which may be hydrogenated or modified. Examples of the C5 fraction and the C9 fraction include the above-mentioned petroleum fractions. As the C5C9 petroleum resin, for example, those commercially available from Tosoh Corporation, LUHUA, etc. can be used.

[0159] Examples of terpene resins include polyterpene resins composed of at least one terpene compound selected from terpene compounds such as α-pinene, β-pinene, limonene, and dipentene; aromatic-modified terpene resins containing the terpene compound and an aromatic compound as monomer components; terpene phenol resins containing a terpene compound and a phenolic compound as monomer components; and those obtained by subjecting these terpene resins to a hydrogenation treatment (hydrogenated terpene resins). Examples of the aromatic compound serving as a monomer component of the aromatic-modified terpene resin include styrene, α-methylstyrene, vinyltoluene, divinyltoluene, and the like. Examples of the phenolic compound serving as a monomer component of the terpene phenol resin include phenol, bisphenol A, cresol, xylenol, and the like.

[0160] The rosin resin is not particularly limited, and examples thereof include natural resin rosin and rosin-modified resins obtained by modifying it by hydrogenation, disproportionation, dimerization, esterification, or the like.

[0161] The phenolic resin is not particularly limited, and examples thereof include phenol formaldehyde resins, alkylphenol formaldehyde resins, alkylphenol acetylene resins, and oil-modified phenol formaldehyde resins.

[0162] From the viewpoint of grip performance, the softening point of the resin component is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher. From the viewpoints of processability and improvement of the dispersibility of the rubber component and the filler, it is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. The softening point of the resin component is measured by the above measurement method.

[0163] From the viewpoint of the effects of the present invention, the content of the resin component relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. From the viewpoint of suppressing heat generation, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less.

[0164] (Oil) Examples of the oil include process oil, vegetable oil, etc. Examples of the process oil include paraffinic process oil (mineral oil), naphthenic process oil, aromatic process oil, etc. Specific examples of the process oil include, for example, MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), RAE (Residual Aromatic Extract), etc. Also, a process oil with a low content of polycyclic aromatic (PCA) compounds can be used for environmental measures. Examples of the low-PCA-content process oil include MES, TDAE, heavy naphthenic oil, etc. Also, from the perspective of life cycle assessment, it may be possible to use waste oil after being used in a rubber mixer or an engine, or refined waste cooking oil used in a restaurant.

[0165] When containing oil, the content relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more from the perspective of processability. Also, from the perspective of improving wear resistance performance, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less.

[0166] (Liquid rubber) The liquid rubber is not particularly limited as long as it is a polymer in a liquid state at normal temperature (25°C). Examples include liquid butadiene polymer (liquid BR), liquid isoprene rubber polymer (liquid IR), liquid styrene-butadiene copolymer (liquid SBR), liquid styrene-isoprene copolymer (liquid SIR), polymers containing myrcene or farnesene as monomer components, etc. These liquid rubbers may be used alone or in combination of two or more.

[0167] When containing a liquid polymer, the content relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more. Also, the content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 30 parts by mass or less.

[0168] From the viewpoint of the effects of the present invention, the content of the softening agent relative to 100 parts by mass of the rubber component (the total amount of all when using a plurality of softening agents in combination) is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more. Also, the content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 60 parts by mass or less, and particularly preferably 40 parts by mass or less.

[0169] <Other compounding agents> In addition to the above components, the rubber composition according to the present embodiment may appropriately contain compounding agents generally used in the conventional tire industry, such as wax, anti-aging agent, stearic acid, zinc oxide, vulcanizing agent, vulcanization accelerator, etc.

[0170] The wax is not particularly limited, and any of those usually used in the tire industry can be preferably used. For example, petroleum wax, mineral wax, synthetic wax, etc. can be mentioned, and petroleum wax is preferred. Examples of petroleum wax include paraffin wax, microcrystalline wax, and their selected special waxes, etc., and paraffin wax is preferred. Note that the wax according to the present embodiment does not contain stearic acid. As the wax, for example, those commercially available from Ouchi Shinsei Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Paramelt Co., etc. can be used. These waxes may be used alone or in combination of two or more.

[0171] When contained, the content relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and still more preferably 1.5 part by mass or more from the viewpoint of the weather resistance of the rubber. Further, from the viewpoint of preventing the whitening of the tire due to blooming, it is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0172] The anti-aging agent is not particularly limited, and examples thereof include anti-aging agents such as amine-based, quinoline-based, quinone-based, phenol-based, imidazole-based compounds, and metal carbamates. Among them, phenylenediamine-based anti-aging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine; and quinoline-based anti-aging agents such as poly(2,2,4-trimethyl-1,2-dihydroquinoline) and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferable. These anti-aging agents may be used alone or in combination of two or more.

[0173] When contained, the content relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and still more preferably 1.5 part by mass or more from the viewpoint of the ozone crack resistance of the rubber. Further, from the viewpoints of abrasion resistance performance and wet grip performance, it is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0174] When contained, the content relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and still more preferably 1.5 part by mass or more from the viewpoint of processability. Further, from the viewpoint of vulcanization rate, it is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0175] When zinc oxide is contained, the content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, and still more preferably 1.5 part by mass or more from the viewpoint of processability. Further, from the viewpoint of abrasion resistance performance, it is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0176] Sulfur is preferably used as the vulcanizing agent. As sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, etc. can be used.

[0177] When sulfur is contained as the vulcanizing agent, the content based on 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and still more preferably 0.5 part by mass or more from the viewpoint of ensuring a sufficient vulcanization reaction. Further, from the viewpoint of deterioration prevention, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, still more preferably 3.0 parts by mass or less, and particularly preferably 2.5 parts by mass or less.

[0178] Examples of vulcanizing agents other than sulfur include alkylphenol sulfur chloride condensates, sodium 1,6-hexamethylene-dithiolsulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. As these vulcanizing agents other than sulfur, those commercially available from Tago Chemical Industry Co., Ltd., Rancess Co., Ltd., Flexsys Co., etc. can be used.

[0179] Examples of vulcanization accelerators include sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiuram-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, caprolactam disulfide, etc. These vulcanization accelerators may be used alone or in combination of two or more. Among them, from the viewpoint that the desired effect can be more preferably obtained, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, and guanidine-based vulcanization accelerators are preferred, and it is more preferred to use sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators in combination.

[0180] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), and the like. Among them, TBBS and CBS are preferred.

[0181] Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole (MBT) or its salts, di-2-benzothiazolyldisulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, 2-(2,6-diethyl-4-morpholinothio)benzothiazole, and the like. Among them, MBTS and MBT are preferred, and MBTS is more preferred.

[0182] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, and the like. Among them, DPG is preferred.

[0183] When a vulcanization accelerator is contained, the total content with respect to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and still more preferably 2.0 parts by mass or more. Also, the content of the vulcanization accelerator with respect to 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and still more preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, the breaking strength and elongation tend to be ensured.

[0184] [Manufacture of Rubber Composition and Tire] The rubber composition according to this embodiment can be produced by a known method. For example, it can be produced by kneading each of the above components using a rubber kneading device such as an open roll, a closed kneader (Banbury mixer, kneader, etc.).

[0185] The kneading process includes, for example, a base kneading process of kneading compounding agents and additives other than the vulcanizing agent and the vulcanization accelerator, and a final kneading (F kneading) process of adding the vulcanizing agent and the vulcanization accelerator to the kneaded product obtained in the base kneading process and kneading them. Further, the base kneading process can be divided into a plurality of processes if desired.

[0186] The kneading conditions are not particularly limited. For example, in the base kneading process, kneading is performed at a discharge temperature of 150 to 170°C for 3 to 10 minutes, and in the final kneading process, kneading is performed at 70 to 110°C for 1 to 5 minutes. The vulcanization conditions are not particularly limited, and for example, a method of vulcanizing at 150 to 200°C for 10 to 30 minutes can be mentioned.

[0187] The tire of the present invention provided with a tread composed of the rubber composition can be produced by a normal method. That is, an unvulcanized rubber composition in which the above components are blended with the rubber component as needed is extruded according to the shape of the tread, bonded together with other tire members on a tire molding machine, and molded by a normal method to form an unvulcanized tire, and this unvulcanized tire is heated and pressurized in a vulcanizer to produce a tire. The vulcanization conditions are not particularly limited, and for example, a method of vulcanizing at 150 to 200°C for 10 to 30 minutes can be mentioned.

[0188] [Use of tire] The heavy-load tire according to this embodiment can be preferably used as a truck and bus tire, and can also be used as a tire for these electric vehicles (EVs). Note that the heavy-load tire is a tire assumed to be mounted on a four-wheel automobile, and refers to a tire having a maximum load capacity of 1000 kg or more. The maximum load capacity of the heavy-load tire is preferably 1200 kg or more, and more preferably 1400 kg or more.

Example

[0189] Hereinafter, examples (examples) considered to be preferable in implementation are shown, but the scope of the present invention is not limited to the examples.

[0190] Hereinafter, various chemicals used in the examples and comparative examples are summarized and shown. NR: RSS#3 SBR: EUROPRENE (registered trademark) SOL R C2525 manufactured by Versalis (styrene content: 26% by mass, vinyl content: 24 mol%, Mw: 600,000, non-oil exhibit) BR: BUNA CB24 manufactured by ARLANXEO (BR synthesized using a Nd-based catalyst, cis content: 96 mol%, Mw: 500,000) Carbon black: SHOW BLACK N134 (N manufactured by Cabot Japan Ltd.) 2 SA: 148m 2 / g, average primary particle diameter: 18 nm) Silica 1: ULTRASIL (registered trademark) VN3 (N manufactured by Evonik Degussa GmbH) 2 SA: 175m 2 / g, average primary particle diameter: 17 nm) Silica 2: ULTRASIL (registered trademark) 9100GR (N manufactured by Evonik Degussa GmbH) 2 SA 235m 2 / g, average primary particle diameter: 15 nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa GmbH Resin component: YS resin PX800 (terpene resin containing β-pinene as a monomer component, softening point: 80 °C) manufactured by Yasuhara Chemical Co., Ltd. Anti-aging agent: Nocrack 6C (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. Stearic acid: Bead stearic acid Tsubaki manufactured by NOF Corporation Zinc oxide: Zinc white No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur (5% oil-containing powder sulfur) manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Nocceler NS-P (N-tert-butyl-2-benzothiazolylsulfenamide (TBBS)) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. Vulcanization accelerator 2: Nocceler D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

[0191] (Examples and Comparative Examples) According to the formulation shown in Table 1, using a 1.7 L closed Banbury mixer, the chemicals other than sulfur and vulcanization accelerators are kneaded for 1 to 10 minutes until the discharge temperature reaches 150 to 160 °C to obtain a kneaded product. Next, using a twin-screw open roll, sulfur and vulcanization accelerators are added to the obtained kneaded product and kneaded for 4 minutes until the temperature reaches 105 °C to obtain an unvulcanized rubber composition. Using this unvulcanized rubber composition, it is extruded into the shape of the tread cap rubber layer using an extruder equipped with a die of a predetermined shape, and laminated together with the base rubber layer and other tire members to produce an unvulcanized tire, and press-vulcanized at 170 °C for 12 minutes to obtain each test tire described in Table 1.

[0192] A heavy-duty tire (size: 275 / 70R22.5, rim: 22.5×7.50, internal pressure: 900 kPa) with a tread portion made of a rubber composition having the basic structure shown in FIG. 1, having the tread pattern of FIG. 4, and obtained by changing the formulation according to Table 1 is examined, and the results calculated based on the following evaluation method are shown in Table 1. In addition, W1 of the circumferential fine groove is 1.0 mm, W2 is 4.0 mm, H3 is 14.0 mm, H4 is 10 mm; the groove width W4 of the circumferential main groove is 9.0 mm; the tread contact width TW is 228 mm; the thickness G of the tread portion is 19.0 mm; the thickness t1 of the cap rubber layer is 15.5 mm. Note that FIG. 8 is a cross-sectional view of a circumferential fine groove having no carcass portion and a constant groove width W1 in the tire radial direction.

[0193] <Measurement of 0°C tanδ and 0°C E> From the tread portion of each test tire, specimens are cut out with a length of 20 mm × width of 4 mm × thickness of 1 mm such that the tire circumferential direction is the long side and the tire radial direction is the thickness direction. For each rubber test piece, using a dynamic viscoelasticity measuring device (Iplexer series manufactured by GABO), the loss tangent (tanδ) and the complex elastic modulus (E*) are measured under the conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±2.5%, and an elongation mode.

[0194] <Wet grip performance> Each test tire is mounted on a rim and this is mounted on the rear wheel of a bus which is a test vehicle. On this test vehicle, the braking distance from an initial speed of 100 km / h is determined on a wet asphalt road surface. The result of the reference comparative example (Comparative Example 1) is expressed as an index with 100. The larger the index, the better the wet grip performance. (Wet grip performance index) = (Braking distance of the reference comparative example) / (Braking distance of each test tire) × 100

[0195]

Table 1

[0196] <Embodiment> Examples of embodiments of the present invention are shown below.

[0197] 〔1〕A heavy-duty tire having a tread portion, wherein the tread portion has a plurality of circumferential main grooves continuously extending in the tire circumferential direction, a pair of shoulder land portions partitioned by the circumferential main grooves and a ground contact end, and a crown land portion located between the pair of shoulder land portions. The crown land portion has one or more circumferential fine grooves continuously extending in the tire circumferential direction. The tread portion is composed of a rubber composition containing a rubber component and a filler. When the groove width of the circumferential main groove is Ws (mm), the groove width of the circumferential fine groove is Wc (mm), and the tanδ at 0°C of the rubber composition is 0°C tanδ, 0°C tanδ is 0.28 or more, and 0°C tanδ / (Wc / Ws) is more than 1.0. A heavy-duty tire. 〔2〕The heavy-duty tire according to the above 〔1〕, wherein the filler contains silica having an average primary particle diameter of 17 nm or less. 〔3〕The heavy-duty tire according to the above 〔1〕 or 〔2〕, wherein the rubber component contains styrene-butadiene rubber. 〔4〕The heavy-duty tire according to any one of the above 〔1〕 to 〔3〕, wherein the silica content in the filler is more than 50% by mass. 〔5〕The heavy-duty tire according to any one of the above 〔1〕 to 〔4〕, wherein the circumferential fine groove includes a neck portion with a narrow groove width and a body portion disposed inside the neck portion in the tire radial direction and having a groove width larger than the maximum groove width of the neck portion. 〔6〕The heavy-duty tire according to any one of the above 〔1〕 to 〔5〕, having a jointless band. 〔7〕The heavy-duty tire according to any one of the above 〔1〕 to 〔6〕, wherein Wc / Ws is 0.09 or more. 〔8〕When the total styrene amount in the rubber component is S (% by mass) and the silica content per 100 parts by mass of the rubber component of the rubber composition is D (parts by mass), S / D is 0.13 or more. The heavy-duty tire according to any one of the above 〔1〕 to 〔7〕. 〔9〕The heavy-duty tire according to any one of the above 〔1〕 to 〔8〕, wherein the complex elastic modulus (0°C E*) at 0°C of the rubber composition is 8.0 MPa or more and 16.0 MPa or less. 〔10〕The heavy load tire according to any one of the above items 〔1〕 to 〔9〕, wherein the pair of shoulder land portions do not have lug grooves. 〔11〕The heavy load tire according to any one of the above items 〔1〕 to 〔10〕, wherein the groove depth H1 at the deepest part of the circumferential main groove is 15.0 mm or less. 〔12〕The heavy load tire according to item 〔11〕 above, wherein the crown land portion has sipes extending in the tire width direction, and when the depth of the deepest part of the sipes is H2 (mm), H2 / H1 is 0.25 or more. 〔13〕The heavy load tire according to item 〔11〕 or 〔12〕 above, wherein when the content of silica with respect to 100 parts by mass of the rubber component of the rubber composition is D (parts by mass), H1 × D is 250 or more. 〔14〕The heavy load tire according to any one of the above items 〔1〕 to 〔13〕, wherein when the tread contact width is TW (mm), Wc / TW is 0.003 or more and 0.020 or less, and Ws / TW is more than 0.020 and 0.060 or less.

Explanation of reference numerals

[0198] 1 Heavy load tire 2 Tread surface 3 Tread portion 4 Cap rubber layer 5 Base rubber layer 6 Belt layer 7 Sidewall 8 Circumferential main groove 9 Circumferential fine groove 10 Crown sipe 11 Head portion 12 Body portion 13 Taper portion 14 Bead portion 15 Inner liner 16 Carcass 17 Jointless band 18 Shoulder land portion 19 Crown land portion 20 Capping rubber 22 Bead core 24 Apex 26 Carcass ply 28 Ribbon 30 Cord 32 Topping Rubber CL Tire Equator W Tire Width Direction Te Tread Grounding End TW Tread Grounding Width E Maximum Thickness of Shoulder Land L Maximum Thickness Line of Shoulder Land W1 Minimum Groove Width at the Head W2 Maximum Groove Width at the Body W3 Maximum Groove Width at the Taper Part H1 Groove Depth at the Deepest Part of the Circumferential Main Groove H2 Depth at the Deepest Part of the Sipes H3 Depth of the Flask-Shaped Circumferential Groove H4 Distance from the Bottom of the Flask-Shaped Circumferential Groove to the Head

Claims

1. A heavy-duty tire having a tread portion, wherein the tread portion has a plurality of circumferential main grooves continuously extending in the tire circumferential direction, a pair of shoulder land portions partitioned by the circumferential main grooves and a ground contact end, and a crown land portion located between the pair of shoulder land portions; the crown land portion has one or more circumferential narrow grooves continuously extending in the tire circumferential direction; the tread portion is composed of a rubber composition containing a rubber component and a filler; when the groove width of the circumferential main groove is Ws (mm), the groove width of the circumferential narrow groove is Wc (mm), and the tanδ at 0°C of the rubber composition is 0°C tanδ, a heavy-duty tire in which 0°C tanδ is 0.28 or more and 0°C tanδ / (Wc / Ws) is more than 1.

0.

2. The heavy-duty tire according to claim 1, wherein the filler contains silica having an average primary particle diameter of 17 nm or less.

3. The heavy-duty tire according to claim 1 or 2, wherein the rubber component contains styrene-butadiene rubber.

4. The heavy-duty tire according to claim 1 or 2, wherein the silica content in the filler is more than 50% by mass.

5. The heavy-duty tire according to claim 1 or 2, wherein the circumferential narrow groove includes a neck portion having a narrow groove width and a body portion disposed inside the neck portion in the tire radial direction and having a groove width larger than the maximum groove width of the neck portion.

6. The heavy-duty tire according to claim 1 or 2, having a jointless band.

7. The heavy-duty tire according to claim 1 or 2, wherein Wc / Ws is 0.09 or more.

8. The heavy-duty tire according to claim 1 or 2, wherein when the total styrene amount in the rubber component is S (% by mass) and the silica content in the rubber composition is D (parts by mass) with respect to 100 parts by mass of the rubber component, S / D is 0.13 or more.

9. The heavy-duty tire according to claim 1 or 2, wherein the complex elastic modulus (0°C E*) at 0°C of the rubber composition is 8.0 MPa or more and 16.0 MPa or less.

10. The heavy-duty tire according to claim 1 or 2, wherein the pair of shoulder land portions do not have lug grooves.

11. The heavy-duty tire according to claim 1 or 2, wherein the groove depth H1 at the deepest part of the circumferential main groove is 15.0 mm or less.

12. The crown land portion has sipes extending in the tire width direction. When the depth of the deepest part of the sipes is H2 (mm), the heavy-duty tire according to claim 11, wherein H2 / H1 is 0.25 or more.

13. The heavy-duty tire according to claim 11, wherein when the content of silica relative to 100 parts by mass of the rubber component of the rubber composition is D (parts by mass), H1×D is 250 or more.

14. The heavy-duty tire according to claim 1 or 2, wherein when the tread contact width is TW (mm), Wc / TW is 0.003 or more and 0.020 or less, and Ws / TW is more than 0.020 and 0.060 or less.

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