Heavy load duty tire

Abstract

To provide a heavy load duty tire capable of improving abrasion resistance.SOLUTION: This heavy load duty tire comprises a tread. The tread includes two circumferential-direction main groves continuously extending in a tire circumferential direction, a pair of shoulder lands partitioned by the circumferential-direction main groves and a ground end, and a crown land positioned between the pair of shoulder lands. The crown land includes one or more circumferential-direction thin groves continuously extending in the tire circumferential direction. When H1 (mm) denotes the groove depth of the deepest part of the circumferential-direction main groves, E (mm) denotes the maximum thickness of the shoulder lands measured in a normal direction to a tire inner cavity surface, and 70°Ctanδ denotes tanδ of a rubber composition constituting the tread at 70°C, H1 is 15.0 or less, and E×70°Ctanδ is 7.5 or less, .SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Due to recent environmental issues, electric vehicles (EVs) are becoming more common among large vehicles such as trucks and buses. EVs are heavier than conventional engine vehicles, and because they are motor-driven, the torque also increases, so tires for large EVs require high levels of wear resistance.

[0003] As a method for improving the wear resistance of truck and bus tires, a technique for microparticulating or highly structuring carbon black is known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-279624 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned methods of finely dividing or highly structuring carbon black are not sufficient to improve the fuel economy of tires. In addition, the deterioration of processability associated with finely dividing carbon black can also deteriorate the dispersibility of carbon black, which can in turn deteriorate the abrasion resistance of tires. For this reason, there are limitations to the performance improvement methods based on the conventional improvement of carbon black.

[0006] An object of the present invention is to provide a heavy duty tire that is capable of improving wear resistance. [Means for solving the problem]

[0007] The present invention relates to a heavy-duty tire having a tread portion, the tread portion having two circumferential main grooves extending continuously in the tire circumferential direction, a pair of shoulder land portions separated by the circumferential main grooves and ground contact edges, and a crown land portion located between the pair of shoulder land portions, the crown land portion having one or more circumferential narrow grooves extending continuously in the tire circumferential direction, and in which, when the groove depth of the deepest part of the circumferential main groove is H1 (mm), the maximum thickness of the shoulder land portions measured in the normal direction to the tire cavity surface is E (mm), and the tan δ at 70°C of a rubber composition constituting the tread portion is 70°C tan δ, H1 is 15.0 or less and E × 70°C tan δ is 7.5 or less. Effect of the Invention

[0008] According to the present invention, a heavy duty tire capable of improving wear resistance is provided. [Brief description of the drawings]

[0009] [Figure 1] 1 is a meridian cross-sectional view of a heavy duty tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a development view of a tread portion of the tire of FIG. 1. [Diagram 3] 3 is a cross-sectional view taken along line CC in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view showing a circumferential narrow groove. [Diagram 5] 11A and 11B are cross-sectional views showing modified examples of the circumferential narrow grooves. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] One embodiment of the present invention relates to a tire for heavy loads having a tread portion, the tread portion having two circumferential main grooves extending continuously in the tire circumferential direction, a pair of shoulder land portions separated by the circumferential main grooves and the ground contact edge, and a crown land portion located between the pair of shoulder land portions, the crown land portion having one or more circumferential narrow grooves extending continuously in the tire circumferential direction, the groove depth of the deepest part of the circumferential main grooves being H1 (mm), the maximum thickness of the shoulder land portions measured in the normal direction to the tire cavity surface being E (mm), and the tan δ at 70°C of the rubber composition constituting the tread portion being 70°C tan δ, H1 is 15.0 or less, and E × 70°C tan δ is 7.5 or less.

[0011] The reason why the uneven wear resistance of the tire of the present invention is improved is thought to be as follows, without intending to be bound by theory.

[0012] It is believed that by providing two circumferential main grooves and setting the depth of the deepest part of the circumferential main groove to 15.0 mm or less, it is possible to ensure the pattern rigidity and suppress heat generation. It is also believed that by providing circumferential narrow grooves in the crown land portion, it is possible to disperse the ground pressure of the tread portion. Furthermore, it is believed that by suppressing the product of the maximum thickness of the shoulder land portion and the 70°C tan δ of the tread rubber to a certain value or less, it is possible to suppress heat generation in the shoulder land portion and the entire tread portion including the crown land portion.

[0013] Furthermore, these features working together enable each land portion to absorb local deformation from the road surface and suppress softening of the tread rubber due to heat generation, which is thought to improve wear resistance in land portions where deformation is greater when the tread rubber comes into contact with the ground.

[0014] From the viewpoint of ensuring the rigidity of the tread portion after wear, it is preferable that the land ratio R at the contact surface of the tread portion after the tread portion is worn along the tread radius so that the groove depth at the deepest part of the circumferential main groove is 75% of that of a new tire, is 0.90 or more.

[0015] The complex modulus at 70° C. (70° C. E*) of the rubber composition constituting the tread portion is preferably 6.8 MPa or more, from the viewpoint of ensuring the rigidity of the tread portion.

[0016] It is preferable that the pair of shoulder land portions have no lug grooves.

[0017] By not providing lug grooves in the shoulder land portion, it is possible to improve the rigidity of the shoulder land portion and suppress heat generation, and it is believed that the wear resistance of the shoulder land portion is improved.

[0018] It is preferable that the crown land portion has a sipe extending in the tire width direction, and when the depth of the deepest part of the sipe is H2 (mm), H2 / H1 is 0.25 or more.

[0019] By setting H2 / H1 within the above range, it is believed that it is possible to suppress the deterioration of wet grip performance in the middle and subsequent stages of wear that is otherwise caused by increasing the rigidity of the tread portion.

[0020] It is preferable that the circumferential narrow groove includes a neck portion having a narrow groove width, and a body portion that is disposed radially inward of the neck portion in the tire radial direction and has a portion with a groove width larger than the maximum groove width of the neck portion.

[0021] It is believed that the provision of a neck portion and a body portion that overlap the circumferential narrow grooves makes it possible to suppress the deterioration of wet grip performance from the middle stage of wear onward, which is caused by increasing the rigidity of the tread portion.

[0022] The 70° C. tan δ of the rubber composition constituting the tread portion is preferably 0.15 or less from the viewpoint of suppressing softening of the rubber due to an increase in temperature of the tread rubber.

[0023] The ratio of 70° C. tan δ to the land ratio R in the contact area of ​​the tread portion (70° C. tan δ / R) is preferably less than 0.15.

[0024] It is believed that by setting 70°C tan δ / R in the above range and increasing the land ratio R as the 70°C tan δ of the tread rubber increases, deformation of the tread portion is reduced and heat generation is suppressed. As a result, it is believed that softening of the tread portion (especially the cap rubber layer) is reduced and wear resistance is improved.

[0025] <Definition> The "tread portion" refers to the portion that forms the contact surface of the tire, and in the case where the tire includes components that form the tire skeleton made of steel or textile materials, such as a belt layer, a belt reinforcing layer, and a carcass layer, in the radial cross section of the tire, the component that is radially outward of these components.

[0026] "Genuine rim" refers to the rim that is specified for each tire by the standard system that includes the standard on which the tire is based, for example, "Standard rim" in the applicable size listed in the "Jatma Year Book" for JATMA (Japan Automobile Tire Manufacturers Association), "Measuring Rim" in the "STANDARDS MANUAL" for ETRTO (The European Tyre and Rim Technical Organisation), and "Design Rim" in the "YEAR BOOK" for TRA (The Tire and Rim Association, Inc.). Refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. In the case of a tire not specified in the above standards, it refers to the narrowest rim among the smallest diameter rims that can be assembled with the tire and can hold internal pressure (i.e., no air leakage from between the rim and tire).

[0027] "Regular internal pressure" refers to the air pressure specified for each tire by each standard in the standard system including the standard on which the tire is based. For JATMA, it refers to the "Maximum Air Pressure", for ETRTO, it refers to the "INFLATION PRESSURE", and for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". As with regular rims, refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. In the case of tires not specified in the above standards, it refers to the regular internal pressure (250kPa or more) of another tire size (defined in the standard) for which the regular rim is specified as the standard rim, and if multiple regular internal pressures of 250kPa or more are specified, it refers to the smallest value among them.

[0028] "Normal condition" refers to a state in which a tire is mounted on a normal rim, inflated to normal internal pressure, and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are measured in the normal condition.

[0029] "Normal load" is the load that each standard specifies for each tire in the standard system that includes the standard on which the tire is based. For JATMA, it is "Maximum Load Capacity", for ETRTO, it is "LOAD CAPACITY", and for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". As with normal rims and normal internal pressures, refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. For tires that are not specified in the above standards, the normal load W is calculated as follows: L In this specification, the term "maximum load capacity" is synonymous with the normal load. V = {(Dt / 2) 2 -(Dt / 2-Ht) 2}×π×Wt W L =0.000011×V+175 V: Virtual volume of the tire (mm 3) Dt: Outer diameter of the tire (mm) Ht: Section height of the tire (mm) Wt: tire section width (mm)

[0030] The "tread edge Te" is the outermost contact point in the tire width direction when a normal tire is loaded with a normal load and contacts a flat surface with a camber angle of 0 degrees. The "tread width TW" is the distance in the tire width direction between the tread edges Te.

[0031] A "circumferential main groove" refers to a groove that extends continuously in the circumferential direction of the tire and has a maximum groove width W4 perpendicular to the longitudinal direction that exceeds 2.0% of the tread width TW when the tire is new. A "circumferential narrow groove" refers to a groove that extends continuously in the circumferential direction of the tire and has a groove width perpendicular to the longitudinal direction (minimum groove width W1 at the neck in Figures 4 and 5) that is 2.0% or less of the tread width TW when the tire is new.

[0032] "Sipe" means a cut-like body that extends in the tire width direction and has a width perpendicular to the longitudinal direction of the tire of less than 1.5 mm when the tire is new. "Lug groove" means a groove-like body that extends in the tire width direction and has a width perpendicular to the longitudinal direction of the tire of 1.5 mm or more when the tire is new.

[0033] "Tread radius" means the radius of curvature of the circular arc formed by the tread surface from the intersection of the tire equatorial plane and the tread surface to the outer side in the tire width direction in a meridian cross section of the tire in a normal state.

[0034] "The land ratio R of the contact surface of the tread portion after the tread portion is worn along the tread radius so that the groove depth at the deepest part of the circumferential main groove is 75% of that at a new product" is the ratio of the total area of ​​the contact surface to the total surface area of ​​the tread surface (i.e., the area obtained by the outer contour in the contact shape of the tread portion) in a state in which all grooves are assumed to be filled, when the tread portion is worn along the tread radius so that the groove depth at the deepest part of the circumferential main groove is 75% of that at a new product, a normal load is applied to a tire in a normal state, and the tire contacts a flat surface with a camber angle of 0 degrees. Here, "all grooves" includes the circumferential main grooves, circumferential narrow grooves, lug grooves, and sipes.

[0035] The "total area of ​​the contact patch" is calculated from the tire's contact shape. The contact shape is obtained by mounting the tire on a standard rim, applying standard internal pressure, and leaving it at 25°C for 24 hours, then applying standard load and pressing it against cardboard (camber angle is 0°) to transfer the shape to the paper. The tire is then rotated 72° in circumferential directions and transferred to five locations. In other words, five contact shapes are obtained. The actual contact area is calculated as the average area of ​​the five ink-filled locations.

[0036] "The maximum thickness E of the shoulder land portion measured in the normal direction to the tire cavity surface" means the distance from the tread ground contact edge Te to the tire cavity surface 17, and is obtained by a straight line (maximum thickness line L) that passes through the tread ground contact edge Te and is perpendicular to the tire cavity surface 17. Note that E includes the belt layer, the carcass, and the inner liner.

[0037] The "thickness of the tread portion" is the thickness of the tread portion on the center line of the tire, measured when the tire is cut at a plane including the tire rotation axis and held on a regular rim. The radially inner end of the entire tread portion is the radially inner interface of the rubber composition constituting the tread portion, and when the tire has a belt reinforcing layer, a belt layer, and a carcass layer, it is the thickness of the entire rubber layer radially outer than the outermost layer in the tire radial direction among these. When the tire has a circumferential groove on the equatorial plane of the tire, the thickness of the entire tread is measured assuming that the groove is filled. For example, in FIG. 1, G corresponds to the thickness of the tread portion. The thickness t1 of the cap rubber layer constituting the tread portion and the thickness of the other rubber layers are measured in the same manner.

[0038] The "groove depth H1 of the deepest part of the circumferential main groove" is determined by the distance between the tread surface and the deepest part of the groove bottom of the circumferential main groove. 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 that has the greatest groove depth among the circumferential main grooves adjacent to the crown land portion.

[0039] The "depth H2 of the deepest part of the sipe" is determined by the distance between the tread surface and the deepest part of the sipe. The deepest part of the sipe is the deepest part of the sipe that has the greatest depth among the sipes present in the crown land portion.

[0040] The "groove depth H3 of the deepest part of the circumferential narrow groove" is determined by the distance between the tread surface and the deepest part of the groove bottom of the circumferential narrow groove. The deepest part of the groove bottom of the circumferential narrow groove is the deepest part of the groove bottom of the circumferential narrow groove that has the largest groove depth among the circumferential narrow grooves present in the crown land portion.

[0041] "Softener" is a material that imparts plasticity to the rubber component, and is a component that is extracted from the rubber composition using acetone. Softeners include softeners that are liquid (liquid state) at 25°C and softeners that are solid at 25°C. However, this does not include wax and stearic acid that are commonly used in the tire industry.

[0042] <Measurement method> "70°C tan δ" is the loss tangent measured using a dynamic viscoelasticity measuring device (e.g., Iplexer series manufactured by GABO) under the conditions of temperature 70°C, frequency 10Hz, initial strain 10%, dynamic strain ±1%, and elongation mode. The sample for 70°C tan δ measurement is a vulcanized rubber composition having a length of 20mm x width 4mm x thickness 1mm. When cutting out from a tire, the sample is cut out from the tread portion of the tire so that the long side is in the tire circumferential direction and the thickness direction is in the tire radial direction.

[0043] "70℃E*" is the complex modulus measured using a dynamic viscoelasticity measuring device (e.g., Iplexer series manufactured by GABO) under the conditions of temperature 70℃, frequency 10Hz, initial strain 10%, dynamic strain ±1%, and extension mode. The measurement sample is prepared in the same manner as for 70℃ tan δ.

[0044] 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 to these drawings.

[0045] [tire] Fig. 1 is a cross-sectional view showing a portion of a heavy duty tire according to one embodiment of the present invention. In Fig. 1, the up-down direction is the radial direction of the heavy duty tire 1, the left-right 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, CL represents the tire equator (tire center line) of the heavy duty tire 1. The shape of this heavy duty tire 1 is symmetrical with respect to CL, except for the tread pattern.

[0046] This heavy-duty tire 1 includes a tread portion 3, a belt layer 6, a sidewall 7, beads 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 surface 2 that comes into contact with the road surface. Two circumferential main grooves 8 and a circumferential narrow groove 9 that extend continuously in the circumferential direction of the tire are formed in the tread surface 2.

[0047] The bead 14 includes a bead core 22 and an apex 24 extending 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.

[0048] The carcass 16 is made of a carcass ply 26. The carcass ply 26 is laid between the beads 14 on both sides and extends along the tread portion 3 and the sidewall 7. The carcass ply 26 is folded back around the bead core 22 from the inner side to the outer side in the tire width direction. The carcass ply 26 is made of a large number of cords arranged in parallel and a topping rubber. The carcass 16 may be formed of two or more carcass plies 26.

[0049] The belt layer 6 extends in the tire width direction. The belt layer 6 is located on the inner side of the tread portion 3 in the tire radial direction. The belt layer 6 is located on the outer side of the carcass 16 in the tire radial direction and reinforces the carcass 16.

[0050] 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, which are laminated in this order from the inner side in the radial direction of the tire. The first belt layer 6a is laminated on a carcass 16. In FIG. 1, the second belt layer 6b has the largest width of the above four layers in the tire rotation axis direction, and the fourth belt layer 6d has the smallest width of the above four layers, but is not limited to such an embodiment.

[0051] The tread portion 3 includes a cap rubber layer 4 and a base rubber layer 5, with the outer surface of the cap rubber layer 4 forming the tread surface 2 and the base rubber layer 5 adjacent to the inner side in the tire radial direction of the cap rubber layer 4. In addition, one or more rubber layers may be further provided between the base rubber layer 5 and the belt layer 6 as long as the effects of the present invention are achieved.

[0052] The cap rubber layer 4 extends to both outer ends in the tire rotational 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.

[0053] The thickness G of the tread portion is preferably 15.0 mm or more, more preferably 16.0 mm or more, even 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, even more preferably 21.0 mm or less, and particularly preferably 20.0 mm or less.

[0054] The thickness t1 of the cap rubber layer is preferably 11.5 mm or more, more preferably 12.5 mm or more, even more preferably 13.5 mm or more, and particularly preferably 14.5 mm or more, while t1 is preferably 19.5 mm or less, more preferably 18.5 mm or less, even more preferably 17.5 mm or less, and particularly preferably 16.5 mm or less.

[0055] From the viewpoint of the effect of the present invention, t1 / G is preferably 0.65 or more, more preferably 0.70 or more, even more preferably 0.73 or more, even more preferably 0.76 or more, even more preferably 0.79 or more, and particularly preferably 0.80 or more. On the other hand, the upper limit 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, even more preferably 0.90 or less, even more preferably 0.85 or less, and particularly preferably 0.83 or less.

[0056] FIG. 2 shows an example of a development view of a tread pattern of a heavy duty tire according to one embodiment of the present invention, which is developed on a plane.

[0057] The tread portion 3 has land portions separated by two circumferential grooves 8 that extend continuously 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 grooves 8 and the tread ground contact edge Te. The crown land portion 19 is a land portion formed between the pair of shoulder land portions 18.

[0058] The circumferential main grooves 8 extend in a zigzag shape with the widthwise centerline of each circumferential main groove deflecting laterally. Here, extending in a zigzag shape means that the widthwise center of the circumferential main groove extends in the tire circumferential direction while deflecting in the tire width direction. Therefore, in addition to a form in which a straight groove is repeatedly bent, a form in which a curved groove is repeatedly curved in a wave shape is also included. Note that the circumferential main grooves 8 may be straight instead of zigzag.

[0059] From the viewpoint of the effects of the present invention, the groove depth H1 of the deepest portion 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, even more preferably 14.4 mm or less, and particularly preferably 14.2 mm or less. On the other hand, H1 is preferably 10.0 mm or more, more preferably 11.0 mm or more, and even more preferably 12.0 mm or more.

[0060] From the viewpoint 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 even more preferably 0.74 or less.

[0061] The maximum groove width W4 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, while W4 is preferably 15.0 mm or less, more preferably 14.5 mm or less, and even more preferably 14.0 mm or less.

[0062] 2, the crown land portion 19 has one circumferential narrow groove 9 that extends continuously in the tire circumferential direction, but is not limited to this embodiment, and the crown land portion 19 may have a plurality of circumferential narrow grooves 9. The circumferential narrow groove 9 may be zigzag like the circumferential main groove 8, or may be linear.

[0063] 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 extend while being bent or curved as they proceed in the tire width direction.

[0064] In FIG. 2, the crown land portion 19 is provided with a plurality of center sipes 10 that are connected to the circumferential main groove 8 and the circumferential narrow groove 9 and bent in the process from one end to the other end in the width direction. The center sipes 10 are bent so that the extension direction changes at the center in the width direction. Specifically, the center sipes 10 are inclined so as to shift to one side in the circumferential direction of the tire as they move from one end in the width direction of the center sipes 10 toward the center in the width direction. The center sipes 10 are bent at the center in the width direction, and are inclined in the opposite direction so as to shift to the other side in the circumferential direction of the tire as they move from the center in the width direction of the center sipes 10 toward the other end. In this way, by providing the crown land portion 19 with sipes inclined in the tire circumferential direction or the tire width direction, the blocks can support each other not only in the front-rear direction but also in the lateral direction, which contributes to improving not only the rigidity in the tire circumferential direction but also the rigidity in the tire width direction, and it is considered that the wear resistance can be improved.

[0065] 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, and more preferably 0.33 or more. By setting H2 / H1 in the above range, it is considered that the deterioration of wet grip performance after the middle stage of wear due to the high rigidity of the tread portion can be suppressed. On the other hand, H2 / H1 is preferably 1.0 or less, and more preferably 0.95 or less.

[0066] In Fig. 2, no lug grooves or sipes are provided in the shoulder land portion 18. By not providing lug grooves in the shoulder land portion, it is possible to improve the rigidity of the shoulder land portion and suppress heat generation, which is thought to improve the wear resistance of the shoulder land portion.

[0067] Fig. 3 shows a cross-sectional view of the crown sipe 10 shown in Fig. 2 taken along line CC. As shown in Fig. 3, the crown sipe 10 has an opening portion whose groove width gradually decreases toward the inside in the tire radial direction, and a sipe portion 30 on the inside in the tire radial direction, but is not limited to this embodiment.

[0068] Fig. 4 shows an enlarged view of the circumferential narrow groove 9. In Fig. 3, the cross section of the circumferential narrow groove 9 has a flask shape. Specifically, the circumferential narrow groove 9 has a neck portion 11 and a body portion 12 that is disposed radially inward of the neck portion and has a portion with 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 3, the stress applied to the side wall of the land portion is mitigated.

[0069] In this embodiment, when the tire is new or in the early stage of wear of the tread portion 3, the portion of the circumferential narrow groove 9 that appears on the tread surface is the neck portion 11. This neck portion can be closed by the load applied to the tread portion 3, so the rigidity of the tread portion 3 in the tire axial direction 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 narrow groove 9 moves from the neck portion to the body portion. Therefore, as the wear progresses, the width of the circumferential narrow groove 9 increases, and the drainage performance of the tread portion 3 from the middle stage of wear onwards is maintained at a high level.

[0070] In Fig. 4, the groove width of the neck is fixed and constant at its minimum groove width W1, but the neck may have a portion with a groove width larger than W1 as long as the effect of the present invention is exhibited. Therefore, the cross-sectional shape of the neck may be straight as shown in Fig. 3, or may be zigzag. Here, zigzag has the same meaning as above. In one preferred embodiment, the groove width of the neck is constant at its minimum groove width.

[0071] Moreover, the body 12 has a portion with a groove width larger than the maximum groove width of the neck. Here, "having a portion with a groove width larger than the maximum groove width of the neck" means that the body is configured to be wider than the maximum groove width of the neck so as to achieve the effects of the present invention. Therefore, the groove width of the body is not particularly limited as long as it includes a portion larger than the maximum groove width of the neck so as to achieve the effects of the present invention. For example, a part of the groove width of the body may have a portion narrower than the maximum groove width of the neck, and the body may be configured to have only a portion with a groove width larger than the groove width of the neck. In FIG. 3, the groove width of the neck 11 is fixed at its minimum groove width W1, so the body 12 is configured only with a portion with a groove width larger than the groove width of the neck 11.

[0072] The minimum groove width W1 of the neck 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. By setting W1 in the above range, water can easily flow from the neck to the body during wet driving, 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, even more preferably 1.8 mm or less, and particularly preferably 1.7 mm or less. By setting W1 in the above range, when a load is applied to the tread portion 3 in the early stage of wear, the neck is easily closed by ground pressure, and the rigidity of the tread portion 3 in the tire axial direction is increased. In addition, the rubber volume of the tread portion 3 is easily ensured. This improves the wear resistance of the heavy-duty tire 1.

[0073] The maximum groove width W2 of the body 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 in the above range, the width of the flask-shaped circumferential groove 9 can be easily ensured even at the end of the wear stage, 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 in the above range, the rubber volume of the tread portion 3 can be easily ensured. This improves the wear resistance of the heavy-duty tire 1.

[0074] 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 in the above range, the width of the flask-shaped circumferential groove 9 can be easily ensured even at the end of the wear stage, 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 in the above range, the rubber volume of the tread portion 3 can be easily ensured. This improves the wear resistance of the heavy-duty tire 1.

[0075] When the groove depth H3 (mm) of the deepest part of the circumferential narrow groove 9 and the minimum length in the tire radial direction from the groove bottom to the neck of the circumferential narrow groove 9 are 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 in the above range, the groove volume of the body part can be easily ensured, and it is possible to easily ensure sufficient drainage performance at the end of the wear stage. In addition, H4 / H3 is preferably 0.75 or less, more preferably 0.73 or less. By setting H4 / H3 in the above range, the rigidity of the tread portion 3 in the tire axial direction is increased in the early wear stage. In addition, the rubber volume of the tread portion 3 is easily ensured. This improves the wear resistance of the heavy load tire 1.

[0076] 5 shows a modified example of the circumferential narrow groove 9. For the portions of this modified example that are not described below, the configuration of the circumferential narrow groove described above can be adopted.

[0077] In Fig. 5, the circumferential narrow groove includes an opening (tapered portion) 13 arranged on the radially outer side of the neck portion of the tire, where the groove width expands in a tapered shape. The tapered portion 13 increases the volume of the circumferential narrow groove 9 in the early stage of wear. The tapered portion 13 also increases the amount of water flowing from the neck portion to the body portion. This improves the drainage performance of the tread portion 3.

[0078] The maximum groove width W2 of the body portion is preferably larger than the maximum groove width W3 of the tapered portion, which makes it easy to ensure the groove volume of the circumferential narrow groove 9 in the body portion, and therefore makes it easy to ensure sufficient drainage performance of the tread portion 3 at the final stage of wear.

[0079] After the tread portion is worn along the tread radius so that the depth of the deepest part of the circumferential main groove is 75% of that of a new tire, the land ratio R at the contact surface of the tread portion is preferably 0.85 or more, more preferably 0.87 or more, and even more preferably 0.90 or more, from the viewpoint of the effects of the present invention. Moreover, the land ratio R is preferably 0.98 or less, more preferably 0.97 or less, and even more preferably 0.96 or less.

[0080] The maximum thickness E of the shoulder land portion measured in the normal direction to the tire cavity surface 17 is preferably 32.0 mm or more, more preferably 33.0 mm or more, and even more preferably 34.0 mm or more. On the other hand, E is preferably 45.0 mm or less, more preferably 44.0 mm or less, and even more preferably 43.0 mm or less.

[0081] The tan δ at 70°C (70°C tan δ) of the rubber composition constituting the tread portion is preferably 0.19 or less, more preferably 0.17 or less, even more preferably 0.16 or less, even more preferably 0.15 or less, and particularly preferably 0.14 or less, from the viewpoint of suppressing softening of the rubber due to temperature rise in the tread portion. On the other hand, from the viewpoint of absorbing deformation from the road surface, it is preferably 0.08 or more, more preferably 0.09 or more, and even more preferably 0.10 or more. However, when the tread portion is composed of two or more rubber layers, the 70°C tan δ refers to the 70°C tan δ of the rubber composition constituting the cap rubber layer.

[0082] The 70° C. tan δ of the rubber composition can be appropriately adjusted by the types and amounts of the rubber component, filler, and softener described below.

[0083] From the viewpoint of the effects of the present invention, the product of E and 70°C tan δ (E×70°C tan δ) is 7.5 or less, preferably 7.0 or less, more preferably 6.5 or less, and even more preferably 6.0 or less. In addition, the lower limit of E×70°C tan δ is not particularly limited, but is preferably 2.5 or more, more preferably 3.0 or more, even more preferably 3.5 or more, and particularly preferably 4.0 or more.

[0084] The complex modulus of elasticity at 70°C (70°C E*) of the rubber composition constituting the tread portion is preferably 6.0 MPa or more, more preferably 6.4 MPa or more, even more preferably 6.8 MPa or more, even more preferably 7.0 MPa or more, and particularly preferably 7.2 MPa or more, from the viewpoint of ensuring the rigidity of the tread portion. On the other hand, from the viewpoint of the effects of the present invention, 70°C E* is preferably 10.0 MPa or less, more preferably 9.5 MPa or less, and even more preferably 9.0 MPa or less. However, when the tread portion is composed of two or more rubber layers, the 70°C E* refers to the 70°C E* of the rubber composition constituting the cap rubber layer.

[0085] The 70° C. E* of the rubber composition can be appropriately adjusted by the types and amounts of the rubber component, filler, softener, etc., which will be described later.

[0086] 70°C tan δ / R is preferably less than 0.19, more preferably less than 0.17, even more preferably less than 0.15, and particularly preferably less than 0.14. It is believed that by setting 70°C tan δ / R in the above range and increasing the land ratio R as the 70°C tan δ of the tread rubber increases, deformation of the tread portion is reduced and heat generation is suppressed. On the other hand, the lower limit of 70°C tan δ / R is not particularly limited, but is preferably 0.030 or more, more preferably 0.040 or more, even more preferably 0.050 or more, and particularly preferably 0.060 or more.

[0087] [Rubber composition] The rubber composition constituting the tread portion according to this embodiment will be described below, but unless otherwise specified, it can be applied to any of the rubber layers in the tread portion.

[0088] The rubber component usable in this embodiment is not particularly limited, and crosslinkable rubber components generally used in the tire industry can be used, such as diene rubbers such as natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), styrene isoprene rubber (SIR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR); and 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. These rubber components may be used alone or in combination of two or more.

[0089] <Filler> In the rubber composition according to the present embodiment, a filler containing carbon black and / or silica is suitably used.

[0090] The carbon black is not particularly limited, and any carbon black commonly used in the tire industry can be appropriately used, such as GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks may be used alone or in combination of two or more kinds.

[0091] The amount of carbon black per 100 parts by mass of the rubber component is not particularly limited, and can be, for example, 1 to 150 parts by mass, 5 to 120 parts by mass, or 10 to 100 parts by mass depending on the purpose of compounding.

[0092] The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrated silica), etc. These silicas can be used alone or in combination of two or more kinds.

[0093] The content of silica per 100 parts by mass of the rubber component is not particularly limited, and can be, for example, 1 to 150 parts by mass, 5 to 120 parts by mass, or 10 to 100 parts by mass depending on the purpose of compounding.

[0094] Fillers other than silica and carbon black are not particularly limited, and may be those that have been commonly used in the tire industry, such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, biochar, etc. These other fillers may be used alone or in combination of two or more.

[0095] Silica is preferably used in combination with a silane coupling agent.The silane coupling agent is not particularly limited, and any silane coupling agent that is conventionally used in combination with silica in the tire industry can be used.Such silane coupling agents include, for example, sulfide-based silane coupling agents, mercapto-based silane coupling agents, thioester-based silane coupling agents, amino-based silane coupling agents, glycidoxy-based silane coupling agents, etc.

[0096] <Other compounding agents> In addition to the above-mentioned components, the rubber composition according to the present embodiment may appropriately contain compounding agents that are generally used in the tire industry, such as a softener, wax, stearic acid, zinc oxide, an antioxidant, a vulcanizing agent, and a vulcanization accelerator.

[0097] Examples of the softener include a resin component, oil, and liquid polymer.

[0098] The resin component is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenol resins, etc. commonly used in the tire industry, and may be hydrogenated versions of these. Examples of petroleum resins include C5 petroleum resins, aromatic petroleum resins, C5C9 petroleum resins, etc. These resin components may be used alone or in combination of two or more.

[0099] Examples of the oil include process oil, vegetable oil, and animal oil. Examples of the process oil include paraffin-based process oil, naphthenic process oil, and aromatic process oil. In addition, as an environmental measure, process oil with a low content of polycyclic aromatic compound (PCA) compounds can be used. Examples of the low PCA content process oil include light extract solvate (MES), treated distillate aromatic extract (TDAE), and heavy naphthenic oil.

[0100] The liquid polymer is not particularly limited as long as it is a polymer in a liquid state at room temperature (25°C), and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc., which may be hydrogenated, or may be modified liquid polymers (preferably terminally modified liquid polymers) in which the main chain and / or terminals of these are modified with modifying groups. These liquid polymers may be used alone or in combination of two or more.

[0101] The content of the softener per 100 parts by mass of the rubber component is not particularly limited, and can be, for example, 1 to 100 parts by mass, 5 to 75 parts by mass, or 10 to 50 parts by mass depending on the purpose of compounding.

[0102] As the vulcanizing agent, sulfur is preferably used, and examples of the sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0103] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, sodium 1,6-hexamethylene-dithiosulfate dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane.

[0104] Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiuram-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, caprolactam disulfide, etc. These vulcanization accelerators may be used alone or in combination of two or more.

[0105] [Production of rubber composition and tire] The rubber composition according to the present embodiment can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or a kneader).

[0106] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and the vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and the vulcanization accelerator are added to the kneaded product obtained in the base kneading step and kneaded. Furthermore, the base kneading step can be divided into a plurality of steps as desired.

[0107] The kneading conditions are not particularly limited, but examples thereof include a method in which in the base kneading step, kneading is performed for 3 to 10 minutes at a discharge temperature of 150 to 170° C., and in the final kneading step, kneading is performed for 1 to 5 minutes at 70 to 110° C. The vulcanization conditions are not particularly limited, but examples thereof include a method in which vulcanization is performed for 10 to 30 minutes at 150 to 200° C.

[0108] A tire having a tread portion can be manufactured by a normal method using the above-mentioned rubber composition. That is, an unvulcanized rubber composition obtained by blending each of the above-mentioned components with a rubber component as necessary is extruded into the shape of each rubber layer of the tread portion using an extruder equipped with a die of a predetermined shape, and is laminated together with other tire components on a tire building machine and molded by a normal method to form an unvulcanized tire, and the unvulcanized tire is heated and pressurized in a vulcanizer to manufacture a tire. The vulcanization conditions are not particularly limited, and examples thereof include a method of vulcanizing at 150 to 200°C for 10 to 30 minutes.

[0109] [Tire Uses] The tire according to the present embodiment can be suitably used as a heavy-duty tire. Note that a heavy-duty tire is a tire that is intended to be mounted on a vehicle that runs on four wheels, and has a maximum load capacity of 1000 kg or more. The maximum load capacity of a heavy-duty tire is preferably 1200 kg or more, and more preferably 1400 kg or more. EXAMPLES

[0110] In the following, examples (embodiments) that are considered to be preferable for implementation are shown, but the scope of the present invention is not limited to the embodiments. A heavy-duty tire (size: 275 / 70R22.5, rim: 22.5×7.50, internal pressure: 900 kPa) having the basic structure shown in FIG. 1, the tread pattern shown in FIG. 2, and the circumferential narrow groove shown in FIG. 4 was examined, and the results calculated based on the following evaluation method are shown in Table 1. Note that the W1 of the circumferential narrow groove is 1.0 mm, W2 is 4.0 mm, H3 is 14.0 mm, and H4 is 10 mm; the maximum groove width W4 of the circumferential main groove is 9.0 mm; the tread ground width TW is 228 mm; the thickness G of the tread portion is 19.0 mm; and the thickness t1 of the cap rubber layer is 15.5 mm.

[0111] <Wear resistance> Each test tire is assembled onto a rim, which is then attached to the rear wheel of a bus, which is a test vehicle. A test driver drives this test vehicle 10,000 km on public roads, and the amount of wear after the drive is measured. The reciprocal value of the amount of wear is expressed as an index (wear resistance performance index), with Comparative Example 1 being set at 100. The higher the index, the more excellent the wear resistance performance. (Wear resistance performance index)=(Wear amount of tire of Comparative Example 4) / (Wear amount of each test tire)×100

[0112] [Table 1]

[0113] <Embodiment> Examples of embodiments of the present invention are given below.

[0114] [1] A heavy-duty tire having a tread portion, the tread portion having two circumferential main grooves extending continuously in the tire circumferential direction, a pair of shoulder land portions separated by the circumferential main grooves and the ground contact edge, and a crown land portion located between the pair of shoulder land portions, the crown land portion having one or more circumferential narrow grooves extending continuously in the tire circumferential direction, the groove depth of the deepest part of the circumferential main grooves being H1 (mm), the maximum thickness of the shoulder land portions measured in the normal direction to the tire inner cavity surface being E (mm), and the tan δ at 70°C of the rubber composition constituting the tread portion being 70°C tan δ, H1 is 15.0 or less, and E × 70°C tan δ is 7.5 or less. [2] The heavy-duty tire according to [1] above, wherein after the tread portion is worn along the tread radius so that the groove depth at the deepest part of the circumferential main groove is 75% of that at a new product, the land ratio R at the contact surface of the tread portion is 0.90 or more. [3] The heavy-duty tire according to the above [1] or [2], wherein the rubber composition constituting the tread portion has a complex modulus at 70°C (70°C E*) of 6.8 MPa or more. [4] The heavy duty tire according to any one of the above [1] to [3], wherein the pair of shoulder land portions have no lug grooves. [5] The heavy-duty tire according to any one of the above [1] to [4], wherein the crown land portion has a sipe extending in the tire width direction, and when the depth of the deepest part of the sipe is H2 (mm), H2 / H1 is 0.25 or more. [6] The heavy-duty tire according to any one of the above [1] to [5], wherein the circumferential narrow groove includes a neck portion having a narrow groove width, and a body portion arranged radially inward of the neck portion and having a portion having a groove width larger than the maximum groove width of the neck portion. [7] The heavy duty tire according to any one of the above [1] to [6], having a 70° C. tan δ of 0.15 or less. [8] The heavy duty tire according to any one of the above [2] to [7], having a 70° C. tan δ / R of less than 0.15. [Explanation of symbols]

[0115] 1. Heavy duty tires 2 Tread surface 3 Tread section 4 Cap rubber layer 5 Base rubber layer 6 Belt Layer 7 Sidewall 8 Circumferential main groove 9 Circumferential thin groove 10 Crown sipes 11 Neck 12 Torso 13 Tapered section 14 Bead 15 Inner Liner 16 Carcass 17 Tire inner cavity surface 18 Shoulder Land Section 19 Crown Land Division 20 Covering rubber 22 Bead core 24 Apex 26 Carcass ply 30 Sipe section CL Tire Equator W Tire width direction Te Tread Edge TW tread width E Maximum thickness of shoulder land L Shoulder land maximum thickness line W1 Minimum groove width at neck W2 Maximum groove width of the body W3 Maximum groove width of tapered section H1: Depth of the deepest part of the circumferential main groove H2 Crown sipe deepest point H3 Depth of flask-shaped circumferential groove H4 Distance from the bottom of the flask-shaped circumferential groove to the neck

Claims

1. A heavy-duty tire having a tread portion, The tread portion has two circumferential main grooves extending continuously in a tire circumferential direction, a pair of shoulder land portions separated by the circumferential main grooves and a ground contact edge, and a crown land portion located between the pair of shoulder land portions, The crown land portion has one or more circumferential narrow grooves extending continuously in the tire circumferential direction, When the groove depth of the deepest portion of the circumferential main groove is H1 (mm), the maximum thickness of the shoulder land portion measured in a normal direction to the tire cavity surface is E (mm), and the tan δ at 70° C. of the rubber composition constituting the tread portion is 70° C. tan δ, A heavy-duty tire having H1 of 15.0 or less and E×70° C. tan δ of 7.5 or less.

2. 2. The heavy-duty tire according to claim 1, wherein a land ratio R at a contact surface of the tread portion is 0.90 or more after the tread portion is worn along a tread radius so that a groove depth at the deepest portion of the circumferential main groove is 75% of that at a new product.

3. 3. The heavy duty tire according to claim 1, wherein the rubber composition constituting the tread portion has a complex modulus of elasticity at 70° C. (70° C. E*) of 6.8 MPa or more.

4. The heavy duty tire according to claim 1 or 2, wherein the pair of shoulder land portions have no lug grooves.

5. 3. The heavy load tire according to claim 1, wherein the crown land portion has a sipe extending in the tire width direction, and when a depth of a deepest portion of the sipe is H2 (mm), H2 / H1 is 0.25 or more.

6. 3. The heavy-duty tire according to claim 1, wherein the circumferential narrow groove includes a neck portion having a narrow groove width, and a body portion arranged radially inward of the neck portion and having a portion having a groove width larger than a maximum groove width of the neck portion.

7. 3. The heavy duty tire according to claim 1, wherein 70° C. tan δ is 0.15 or less.

8. 3. The heavy duty tire according to claim 2, wherein 70° C. tan δ / R is less than 0.15.

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