Heavy load tire

Abstract

To provide a heavy load tire in which wet grip performance is improved.SOLUTION: A heavy load tire includes a tread part. The tread part includes one or more circumferential main grooves continuously extending in a tire circumferential direction and consists of rubber composition containing rubber constituent and silica. When a groove depth of the deepest part of the circumferential main groove is H1 (mm), and the content of the silica relative to the rubber constituent 100 pts.mass of the rubber composition is D (pts.mass), H1 is 15.0 or less and H1×D is 250 or more. When the tread part is abrased along a tread radius so that the groove depth of the deepest part of the circumferential main groove becomes 75% thereof when it is new, a land ratio R at a contact area of the tread part is 0.90 or more.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In recent years, as the demand for environmental considerations has increased, electric vehicles have become more and more popular. Electric vehicles also have the weight of batteries, so there is a tendency for heavy loads to be applied to the tires of electric vehicles.

[0003] One method for improving the wet grip performance of heavy-duty tires is, for example, to form a shallow bottom portion of a predetermined size at the inner end of the lug groove (Patent Document 1).

[0004] In addition, a technique for finely dividing or highly structuring carbon black is known as a method for improving the wear resistance of truck and bus tires (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-5411 [Patent Document 2] Japanese Patent Application Publication No. 6-279624 Summary of the Invention [Problem to be solved by the invention]

[0006] Providing many lug grooves in the tread reduces the land ratio, which reduces the rigidity of the land area, causing the tread to heat up and reducing the wear resistance of the tire.

[0007] Furthermore, in the above-mentioned methods of finely dividing or highly structuring carbon black, the processability deteriorates due to the finely divided carbon black, which in turn may result in a deterioration in the dispersibility of the carbon black, which may in turn result in a deterioration in the abrasion resistance of the tire. For this reason, there has been a limit to the performance improvement methods based on the conventional improvement of carbon black.

[0008] An object of the present invention is to provide a heavy duty tire having improved wet grip performance. [Means for solving the problem]

[0009] The tire according to one embodiment of the present invention is A heavy-duty tire having a tread portion, The tread portion has one or more circumferential main grooves extending continuously in the tire circumferential direction, the tread portion is made of a rubber composition containing a rubber component and silica, The groove depth of the deepest part of the circumferential main groove is H1 (mm), When the content of silica per 100 parts by mass of the rubber component of the rubber composition is D (parts by mass), H1 is 15.0 or less, and H1×D is 250 or more, This is a heavy-duty tire in which the land ratio R at the contact surface of the tread portion is 0.90 or more 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. Effect of the Invention

[0010] According to the present invention, a heavy duty tire having improved wet grip performance is provided. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a portion of a heavy duty tire according to one embodiment of the present invention. [Diagram 2] 1 is a development view of a tread portion of a heavy duty tire according to one embodiment of the present invention. [Diagram 3]1 is a cross-sectional view showing a circumferential narrow groove in a tread portion of a heavy duty tire according to one embodiment of the present invention. [Figure 4] 1 is a cross-sectional view showing a circumferential narrow groove in a tread portion of a heavy duty tire according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] One embodiment of the present invention relates to a heavy-duty tire having a tread portion, the tread portion having one or more circumferential main grooves extending continuously in the circumferential direction of the tire, the tread portion being composed of a rubber composition containing a rubber component and silica, and wherein, when the groove depth at the deepest part of the circumferential main groove is H1 (mm) and the content of silica in the rubber composition per 100 parts by mass of the rubber component is D (parts by mass), H1 is 15.0 or less and H1×D is 250 or more, and 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.

[0013] Although it is not intended to be bound by theory, the mechanism by which wet grip performance is improved in the present invention is thought to be, for example, as follows.

[0014] First, (1) the groove depth H1 of the deepest part of the circumferential main groove is 15.0 mm or less, and the land ratio R of the ground contact surface of the tread part after the tread part is worn along the tread radius so that the groove depth of the deepest part of the circumferential main groove is 75% of that of a new product is 0.90 or more, so that the ground contact area of ​​the tire increases after the middle stage of wear, improving the road contact property of the tire. By improving the road contact property of the tire, it is possible to reduce the thickness of the tread part, and deformation due to shear of the tread part can be suppressed. On the other hand, when the deformation of the tread part is suppressed, heat generation of the tread part is also suppressed. In such a situation, the contribution of hysteresis friction (tan δ) to the wet grip performance of the tire becomes smaller. Therefore, the followability of the tread part to a wet road surface becomes more important for wet grip performance. Therefore, (2) the flexibility of the rubber composition constituting the tread part is increased by blending silica into the rubber composition, and the followability of the tread part to a wet road surface can be improved. Furthermore, (3) by making H1×D 250 or more, the silica content increases even when H1 is thin, which synergistically improves the road contact properties of the tire and the road following properties of the tread portion. And, it is believed that the above (1) to (3) achieve a remarkable effect of providing a heavy-duty tire with improved wet grip performance.

[0015] It is preferable that the D / R is 30 or more. By compounding a certain amount of silica relative to the land ratio, the silica content can be secured as the road-following ability increases, which is thought to further improve wet grip performance even under heavy loads.

[0016] The content of styrene butadiene rubber in the rubber component is S. C (mass%), S C It is preferable that / D is 0.60 or more. By increasing the content of styrene-butadiene rubber as the content of silica increases, it becomes possible to improve the dispersibility of silica, and it is considered that the flexibility of the rubber composition in the small deformation region is improved, and the wet grip performance is further improved.

[0017] When the total amount of styrene in the rubber component is S (mass%), S / D is preferably 0.130 or more. By increasing the total amount of styrene as the silica content increases, it becomes possible to improve the dispersibility of silica by the styrene group, which is thought to improve the flexibility of the rubber composition in the small deformation region and further improve the wet grip performance.

[0018] The tread portion preferably has 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, and the crown land portion preferably has one or more circumferential narrow grooves extending continuously in the tire circumferential direction. By adopting such a structure, it is believed that the pattern rigidity can be ensured and heat generation can be suppressed, and the wet grip performance can be further improved.

[0019] The crown land portion has sipes extending in the tire width direction, and when the depth of the deepest part of the sipe is H2 (mm), it is preferable that H2 / H1 is 0.25 or more. It is considered that by setting H2 / H1 in the above range, it is possible to suppress the deterioration of wet grip performance after the middle stage of wear due to the high rigidity of the tread portion.

[0020] It is preferable that the pair of shoulder land portions have no lug grooves. By providing no lug grooves in the shoulder land portions, it is possible to improve the rigidity of the shoulder land portions and suppress heat generation, and it is considered that the wear resistance of the shoulder land portions is improved.

[0021] When the thickness of the tread portion when new is T (mm), it is preferable that T×D is equal to or greater than 320. Even when the tread portion is thin, by increasing the silica content, the flexibility of the rubber composition constituting the tread portion can be increased and the ability of the tread portion to conform to wet road surfaces can be improved, which is believed to further improve wet grip performance.

[0022] 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.

[0023] 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.

[0024] The complex modulus of elasticity of the rubber composition at 0° C. (0° C.E*) is preferably 8.5 MPa or more and 13.0 MPa or less. When the 0° C.E* is in the above range, the rubber composition can easily conform to the unevenness of a wet road surface, which is considered to further improve the wet grip performance.

[0025] The tan δ of the rubber composition at 0° C. (0° C. tan δ) is preferably 0.15 or more and 0.25 or less. When the 0° C. tan δ is in the above range, the energy loss required for gripping can be secured, which is considered to further improve the wet grip performance.

[0026] <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.

[0027] "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 Tire 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 standard, it refers to the rim that can be assembled to the rim and can hold internal pressure, that is, the rim with the smallest rim diameter and the next narrowest rim width among the rims that do not leak air from between the rim and tire.

[0028] "Regular internal pressure" refers to the air pressure set 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 rim", it refers to JATMA, ETRTO, TRA in that order and follows those standards. For tires not specified in the standard, it refers to the regular internal pressure (250kPa or more) of another tire size (specified in the standard) that is specified with the regular rim as the standard rim. Note that if multiple regular internal pressures of 250kPa or more are specified, it refers to the smallest value among them.

[0029] "Normal condition" refers to an unloaded condition in which the tire is mounted on a normal rim and inflated to normal internal pressure.

[0030] "Normal load" refers to the load that is determined for each tire by the standard system that includes the standard on which the tire is based. For example, 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 the case of normal rims and normal internal pressures, JATMA, ETRTO, and TRA should be referenced in that order, and if there is an applicable size at the time of reference, that standard should be followed. For tires not specified in the above standards, the normal load W is calculated as follows: L V is the virtual volume of the tire (mm 3 ), Dt is the outer diameter of the tire (mm), Ht is the section height of the tire (mm), and Wt is the section width of the tire (mm). In this specification, the term "maximum load capacity" is synonymous with the normal load. TIFF2025041359000001.tif1484

[0031] 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.

[0032] 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 3 and 4) that is 2.0% or less of the tread width TW when the tire is new.

[0033] "Sipe" means a notch extending in the tire width direction and having a width of less than 1.5 mm perpendicular to the longitudinal direction of the groove when the tire is new. "Lug groove" means a groove extending in the tire width direction and having a width of 1.5 mm or more perpendicular to the longitudinal direction of the groove when the tire is new.

[0034] "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.

[0035] "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.

[0036] 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 ink to the tread surface, and pressing it against cardboard under a load of maximum load capacity (camber angle is 0°) to transfer the shape to the paper. The tire is then rotated 72° in circumferential directions, and the shape is transferred at five locations. In other words, five contact shapes are obtained. The actual contact area is calculated as the average area of ​​the ink parts at five locations.

[0037] The "thickness T (mm) of the tread portion when new" is the thickness of the tread portion on the center line of the tire, measured by cutting a new tire at a plane including the tire rotation axis and holding it 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 radially outermost layer of the tire. When the tire has a circumferential groove on the equatorial plane of the tire, the entire tread thickness is measured assuming that the groove is filled. 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 contact 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 contact 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 contact 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] A "lug groove" is a groove-like body that extends in the tire width direction and has a groove width perpendicular to the longitudinal direction of the groove of 1.5 mm or more when the tire is new.

[0042] "Total styrene content S (mass%) in the rubber component" refers to the total content (mass%) of styrene moieties contained in 100% by mass of the rubber component, and is calculated by Σ(styrene content (mass%) of each styrene-containing rubber × content (mass%) of each styrene-containing rubber in the rubber component / 100). For example, when the rubber component is composed of 30% by mass of a first SBR (styrene content 25% by mass), 60% by mass of a second SBR (styrene content 27.5% by mass), and 10% by mass of BR, the total styrene content (S) in 100% by mass of the rubber component is 24.0% by mass (=25×30 / 100+27.5×60 / 100). The styrene content of the styrene-containing rubber is 1 It is calculated by H-NMR measurement.

[0043] The "vinyl content (mol %) of the rubber component" is calculated by multiplying the vinyl butadiene unit content derived from 1,2-butadiene bonds of each rubber constituting the entire rubber component (100 mass %) by its content in the entire rubber component, and then adding up all the results.

[0044] The "rubber component of the rubber composition" refers to a component that contributes to crosslinking in the rubber composition, and generally has a weight average molecular weight (Mw) of 10,000 or more.

[0045] <Measurement method> "Rubber hardness" is a value measured by cutting out a sample for hardness measurement from the tread portion that forms the contact surface with the tire so that the thickness direction is in the radial direction of the tire, and pressing a Type A durometer against the sample from the contact surface side at 23°C in accordance with JIS K 6253.

[0046] The "glass transition temperature of the rubber composition" is determined by measuring a temperature distribution curve of tan δ using a dynamic viscoelasticity measuring device (e.g., Iplexer series manufactured by GABO) under the conditions of a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±0.5%, and a heating rate of 2°C / min, and determining the temperature corresponding to the largest tan δ value in the obtained temperature distribution curve (tan δ peak temperature). The measurement sample is a vulcanized rubber composition having a length of 20 mm, a width of 4 mm, and a thickness of 1 mm. When the sample is cut out from the tread portion of a tire, the length direction is the circumferential direction of the tire.

[0047] The "complex modulus at 0°C (0°CE*)" is a complex modulus measured using a dynamic viscoelasticity measuring device (e.g., Iplexer series manufactured by GABO) 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. The measurement sample is prepared in the same manner as in the case of the glass transition temperature of the rubber composition.

[0048] "Tan δ at 0°C (0°C tan δ)" is a loss tangent (tan δ) measured using a dynamic viscoelasticity measuring device (e.g., Iplexer series manufactured by GABO) under the conditions of temperature 0°C, frequency 10Hz, initial strain 10%, dynamic strain ±2.5%, and elongation mode. A sample for measuring the loss tangent is prepared in the same manner as in the case of the glass transition temperature of the rubber composition.

[0049] "Styrene content" is 1 It is a value calculated by H-NMR measurement, and is applied to rubber components having repeating units derived from styrene, such as SBR. "Vinyl content (amount of 1,2-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017, and is applied to rubber components having repeating units derived from butadiene, such as SBR and BR. "Cis content (amount of cis-1,4-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017, and is applied to rubber components having repeating units derived from butadiene, such as BR.

[0050] The "average primary particle size" is calculated by photographing particles with a transmission or scanning electron microscope and taking the arithmetic average of the particle sizes of 400 particles. If the particle shape is nearly circular, the diameter of the circle is used as the particle size, if it is needle-like or rod-like, the short diameter is used as the particle size, and in other cases, the equivalent circle diameter is calculated from the electron microscope image. The equivalent circle diameter is calculated as "4 x (particle area) / positive square root of π". The average primary particle size is applied to silica, carbon black, etc.

[0051] The "nitrogen adsorption specific surface area (N2SA) of silica" is measured by the BET method in accordance with ASTM D 3037-93. The "nitrogen adsorption specific surface area (N2SA) of carbon black" is measured in accordance with JIS K 6217-2:2017.

[0052] 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.

[0053] <Tires> 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, the shape of the heavy duty tire 1 is symmetrical with respect to the tire equator CL, except for the tread pattern.

[0054] 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 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 contact surface 2.

[0055] 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.

[0056] The carcass 16 is made of a carcass ply 26. The carcass ply 26 is laid between the bead portions 14 on both sides and extends along the tread portion 3 and the sidewall portion 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 and a topping rubber arranged in parallel. The carcass 16 may be formed of two or more carcass plies 26.

[0057] 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.

[0058] 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.

[0059] In FIG. 1, the tread portion 3 comprises a cap rubber layer 4 and a base rubber layer 5, the outer surface of the cap rubber layer 4 constitutes the tread contact surface 2, and the base rubber layer 5 is adjacent to the cap rubber layer 4 on the radially inner side of the tire, but is not limited to such an embodiment, and as long as the effects of the present invention are achieved, the tread portion may be a single rubber layer, or may further have one or more rubber layers between the base rubber layer 5 and the belt layer 6.

[0060] The tread thickness T of a new tire is preferably 23.0 mm or less, more preferably 21.0 mm or less, and even more preferably 20.0 mm or less from the viewpoint of suppressing deformation due to shear in the tread portion, and is preferably 15.0 mm or more, more preferably 17.0 mm or more, and even more preferably 18.0 mm or more from the viewpoint of fuel efficiency.

[0061] From the viewpoint of wet grip performance, T×D is preferably 320 or more, more preferably 370 or more, and even more preferably 420 or more. Moreover, T×D is preferably 1000 or less, more preferably 950 or less, and even more preferably 900 or less. Here, D is the content (parts by mass) of silica per 100 parts by mass of the rubber component of the rubber composition constituting the tread portion, and a preferable range will be described later.

[0062] The thickness t1 of the cap rubber layer is preferably 11.5 mm or more, more preferably 13.5 mm or more, and even more preferably 14.5 mm or more, while t1 is preferably 19.5 mm or less, more preferably 17.5 mm or less, and even more preferably 16.5 mm or less.

[0063] From the viewpoint of the effects of the present invention, t1 / T is preferably 0.76 or more, more preferably 0.79 or more, and even more preferably 0.80 or more. On the other hand, the upper limit of t1 / T is not particularly limited and may be 1.0, but is preferably less than 1.0, more preferably 0.85 or less, and even more preferably 0.83 or less.

[0064] "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, preferably 0.91 or more, and more preferably 0.92 or more. From the viewpoint of the effects of the present invention, R is preferably 0.98 or less, more preferably 0.97 or less, even more preferably 0.96 or less, and particularly preferably 0.95 or less.

[0065] The groove depth H1 of the deepest part of the circumferential main groove 8 is determined by the distance between the tread contact surface 2 and the deepest part of the groove bottom of the circumferential main groove. The groove depth H1 of the deepest part of the circumferential main groove is 15.0 mm or less, more preferably 14.6 mm or less, and even more preferably 14.2 mm or less. H1 is preferably 10.0 mm or more, more preferably 11.0 mm or more, and even more preferably 12.0 mm or more.

[0066] H1×D is 250 or more, preferably 280 or more, more preferably 300 or more, even more preferably 350 or more, even more preferably 400 or more, even more preferably 450 or more, even more preferably 500 or more, even more preferably 600 or more, and particularly preferably 800 or more. From the viewpoint of the effects of the present invention, H1×D is preferably 1200 or less, more preferably 1100 or less, and even more preferably 1000 or less. D is the content (parts by mass) of silica relative to 100 parts by mass of the rubber component of the rubber composition constituting the tread portion, and a preferred range will be described later.

[0067] D / R is preferably 20 or more, more preferably 22 or more, even more preferably 25 or more, still more preferably 30 or more, still more preferably 40 or more, and particularly preferably 50 or more. The upper limit of D / R is not particularly limited, but can be, for example, 100 or less, 95 or less, or 80 or less.

[0068] Fig. 2 is a development view of a tread portion of a heavy-duty tire according to an embodiment of the present invention. In Fig. 2, the tread portion has two circumferential main grooves 8 extending continuously in the tire circumferential direction, a pair of shoulder land portions 18 separated by the circumferential main grooves 8 and the ground contact edge Te, and a crown land portion 19 located between the pair of shoulder land portions 18, and the crown land portion 19 has one circumferential narrow groove 9 extending continuously in the tire circumferential direction. In Fig. 2, the crown land portion 19 has one circumferential narrow groove 9 extending continuously in the tire circumferential direction, but is not limited to such an embodiment, and the crown land portion 19 may have multiple circumferential narrow grooves 9.

[0069] The crown land portion 19 preferably has sipes inclined in the tire circumferential direction or the tire width direction. 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 course from one end to the other end in the tire width direction W, but is not limited to this form and may be parallel to the tire width direction, for example.

[0070] The depth H2 (mm) of the deepest part of the center sipe 10 is determined by the distance between the tread contact surface and the deepest part of the sipe. The depth H2 of the deepest part of the sipe is preferably 15.0 mm or less, more preferably 14.0 mm or less, and even more preferably 13.0 mm or less. H2 is preferably 2.5 mm or more, more preferably 3.0 mm or more, and even more preferably 3.5 mm or more.

[0071] H2 / H1 is preferably 0.25 or more, more preferably 0.30 or more, and even more preferably 0.33 or more. By setting H2 / H1 in the above range, it is believed 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, more preferably 0.95 or less, and even more preferably 0.90 or less.

[0072] 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 believed that the rigidity of the shoulder land portion can be improved and heat generation can be suppressed, thereby improving the wear resistance of the shoulder land portion.

[0073] FIG. 3 shows an enlarged view of a circumferential narrow groove in the tread portion of a heavy-duty tire according to one embodiment of the present invention. In FIG. 3, the circumferential narrow groove 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. In FIG. 3, the groove width of the neck portion is fixed and constant at its minimum groove width W1, but the neck portion 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 portion may be a straight line as shown in FIG. 3, or may be a zigzag shape. Here, the zigzag shape has the same meaning as above. In one preferred embodiment, the groove width of the neck portion is constant at its minimum groove width.

[0074] 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.

[0075] The minimum groove width W1 of the neck is preferably 0.5 mm or more, more preferably 0.7 mm or more, and even more preferably 0.9 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, and even more preferably 1.8 mm or less. By setting W1 in the above range, when a load is applied to the tread portion in the early stage of wear, the neck portion is easily closed by ground pressure, and the rigidity of the tread portion in the tire axial direction is increased. In addition, the rubber volume of the tread portion is easily ensured. This improves the wear resistance of the heavy-duty tire.

[0076] 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 circumferential narrow groove 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, and even more preferably 10.0 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.

[0077] 4 shows a modified example of the circumferential narrow groove. For the modified example, the configuration of the circumferential narrow groove described above can be adopted for the portions not described below.

[0078] In FIG. 4, the circumferential narrow groove includes an opening 13 (tapered portion) arranged radially outward of the neck portion of the tire, where the groove width expands in a tapered shape. The tapered portion increases the volume of the circumferential narrow groove in the early stage of wear. The tapered portion also increases the amount of water flowing from the neck portion to the body portion. This improves the drainage performance of the tread portion.

[0079] The 0°C E* of the rubber composition constituting the tread portion according to the present embodiment is preferably 8.5 MPa or more, more preferably 9.0 MPa or more, even more preferably 10.0 MPa or more, and particularly preferably 11.0 MPa or more. Also, the 0°C E* is preferably 15.0 MPa or less, more preferably 13.0 MPa or less, and even more preferably 12.5 MPa or less.

[0080] The 0°C tan δ of the rubber composition constituting the tread portion according to the present embodiment is preferably 0.10 or more, more preferably 0.15 or more, even more preferably 0.17 or more, still more preferably 0.19 or more, and particularly preferably 0.20 or more. Also, the 0°C tan δ is preferably 0.40 or less, more preferably 0.30 or less, and still more preferably 0.25 or less.

[0081] The 0°C E* and 0°C tan δ can be appropriately adjusted by the types and amounts of the rubber components, fillers, softeners, etc. described below. For example, the 0°C E* can be increased by increasing the amount of the filler in the rubber composition or decreasing the content of the softener. Therefore, a person skilled in the art can appropriately adjust the 0°C E* and 0°C tan δ of the rubber composition.

[0082] The glass transition temperature (Tg) of the rubber composition constituting the tread portion according to the present embodiment is preferably -70°C or higher, more preferably -60°C or higher, and even more preferably -50°C or higher. The Tg is preferably -20°C or lower, more preferably -30°C or lower, and even more preferably -35°C or lower. The Tg of the rubber composition can be appropriately adjusted by the types and amounts of the rubber components, fillers, softeners, etc. described below. Therefore, those skilled in the art can adjust the Tg of the rubber composition as appropriate.

[0083] The rubber hardness Hs of the rubber composition constituting the tread portion according to the present embodiment is, from the viewpoint of ride comfort performance, preferably more than 65, more preferably more than 66, and even more preferably more than 67. Moreover, from the viewpoint of the effects of the present invention, the rubber hardness Hs is preferably less than 75, more preferably less than 74, and even more preferably less than 73.

[0084] The rubber hardness of the rubber composition can be adjusted as appropriate by the types and amounts of the rubber components, fillers, softeners, etc. described below. For example, the rubber hardness can be lowered by increasing the oil content, and conversely, the rubber hardness can be increased by decreasing the oil content. Therefore, those skilled in the art can adjust the rubber hardness as appropriate.

[0085] When the tread portion includes two or more rubber layers, it is sufficient that any one of the rubber layers satisfies each physical property value, such as 0°C E*, of the rubber composition constituting the tread portion. However, it is preferable that the cap rubber layer satisfies each physical property value.

[0086] [Rubber composition] The rubber composition constituting the tread portion of the heavy duty tire according to the present embodiment (hereinafter referred to as the rubber composition according to the present embodiment) can be produced using the raw materials described below. Unless otherwise specified, it is applicable to any rubber layer of the tread portion.

[0087] <Rubber component> In the rubber composition according to the present 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), and acrylonitrile butadiene rubber (NBR). These rubber components may be used alone or in combination of two or more. The rubber composition according to the present embodiment preferably contains an isoprene rubber, and more preferably contains an isoprene rubber and a BR.

[0088] (Isoprene rubber) As the isoprene-based rubber, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. In addition to unmodified natural rubber (NR), natural rubber also includes modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), highly purified natural rubber (UPNR), and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

[0089] The NR is not particularly limited, and any NR commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0090] The content of the isoprene-based rubber in the rubber component is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more. The content is preferably 99% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and particularly preferably 85% by mass or less. Since the molecular weight of the isoprene-based rubber is larger than that of other rubber components, it is believed that the strength of the polymer is improved and the durability performance is improved by having the content of the isoprene-based rubber in the above range.

[0091] (BR) The BR is not particularly limited, and can be, for example, one commonly used in the tire industry, such as 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 butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high cis modified BR, low cis modified BR), etc., and it is preferable to include modified BR. These BRs may be used alone or in combination of two or more.

[0092] As the high-cis BR, for example, those commercially available from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. By containing high-cis BR, low-temperature properties and wear resistance can be improved. The cis content of the high-cis BR is preferably 95 mol % or more, more preferably 96 mol % or more, even more preferably 97 mol % or more, and particularly preferably 98 mol % or more. The cis content is measured by the above-mentioned measurement method.

[0093] As the modified BR, a modified butadiene rubber (modified BR) in which the terminals and / or the main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen and oxygen is preferably used.

[0094] 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 terminals of the modified BR molecule bonded with tin-carbon bonds (tin-modified BR), etc. The modified BR may be either non-hydrogenated or hydrogenated.

[0095] When BR is contained, the content in the rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more, from the viewpoint of the effects of the present invention. On the other hand, from the viewpoint of wet grip performance, the content is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0096] (SBR) There is no particular limitation on the SBR, and examples thereof include unmodified solution-polymerized SBR (S-SBR) and emulsion-polymerized SBR (E-SBR), as well as modified SBRs (modified S-SBR, modified E-SBR) thereof. Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Among these, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR), etc. can also be used. Among these, S-SBR is preferably used from the viewpoint of improving wet grip performance and grip performance on ice in a well-balanced manner.

[0097] The SBRs listed above may 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, Zeon Corporation, ZS Elastomers Co., Ltd., etc. may be used.

[0098] From the viewpoints of wet grip performance and abrasion resistance, the styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. From the viewpoints of temperature dependency of grip performance and blow resistance, the styrene content is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. In this specification, the styrene content of SBR is measured by the above-mentioned measurement method.

[0099] Content of SBR in rubber component C From the viewpoint of wet grip performance, the content S of the SBR in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, and particularly preferably 20% by mass or more. C The upper limit is not particularly limited, and can be, for example, 50% by mass or less, 40% by mass or less, 30% by mass or less, or 20% by mass or less.

[0100] S CFrom the viewpoint of the effects of the present invention, S is preferably 0.20 or more, more preferably 0.30 or more, even more preferably 0.40 or more, still more preferably 0.50 or more, and particularly preferably 0.60 or more. C The upper limit of / D is not particularly limited, but can be, for example, less than 1.00 or less than 0.80. D is the content (parts by mass) of silica relative to 100 parts by mass of the rubber component of the rubber composition constituting the tread portion, and a preferred range will be described later.

[0101] In the rubber component according to the present embodiment, the total styrene content S in the rubber component is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, even more preferably 7.0% by mass or more, and particularly preferably 10.0% by mass or more, from the viewpoint of the effects of the present invention. The upper limit of the total styrene content S in the rubber component is not particularly limited, but may be, for example, less than 18.0% by mass, less than 15.0% by mass, or less than 12.0% by mass.

[0102] From the viewpoint of the effects of the present invention, S / D is preferably 0.050 or more, more preferably 0.080 or more, even more preferably 0.100 or more, and particularly preferably 0.130 or more. The upper limit of S / D is not particularly limited, but may be, for example, 0.250 or less, 0.200 or less. D is the content (parts by mass) of silica relative to 100 parts by mass of the rubber component of the rubber composition constituting the tread portion, and a preferred range will be described later.

[0103] (Other rubber components) The rubber component according to the present embodiment may contain diene rubber other than the isoprene rubber, BR, and SBR, and rubber components other than diene rubber. As the rubber component other than diene rubber, a crosslinkable rubber component generally used in the tire industry may be used, for example, butyl rubber (IIR), halogenated butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, etc. These other rubber components may be used alone or in combination of two or more. The rubber component according to the present embodiment preferably contains 80% by mass or more of diene rubber, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more, and may be a rubber component consisting of only diene rubber.

[0104] <Filler> The rubber composition according to the present embodiment preferably contains silica as a filler, and further contains carbon black. Alternatively, the filler may be composed of only silica and carbon black.

[0105] (silica) 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), or other silica commonly used in the tire industry. Among them, hydrated silica prepared by a wet method is preferred because it has a large number of silanol groups. In addition to the above silica, silica made from biomass materials such as rice husks may be used as appropriate. These silicas may be used alone or in combination of two or more.

[0106] From the viewpoint of wear resistance and elongation at break, the nitrogen adsorption specific surface area (N2SA) of silica is 100m 2 / g or more is preferable, and 120m 2 / g or more is more preferable, and 140m 2 / g or more is more preferable, and 160m 2From the viewpoint of heat generation and processability, it is particularly preferable that the tensile strength is 350 m 2 / g or less is preferable, and 300m 2 / g or less is more preferable, and 250m 2 / g or less is more preferable. The N2SA of silica is measured by the above-mentioned measuring method.

[0107] The average primary particle size of silica is preferably less than 25nm, more preferably less than 22nm, and even more preferably less than 20nm.The lower limit of the average primary particle size is not particularly limited, but is preferably more than 1nm, more preferably more than 3nm, and even more preferably more than 5nm.The average primary particle size can be determined by the above-mentioned method.

[0108] The silica content D per 100 parts by mass of the rubber component can be appropriately set so that H1×D satisfies the above range, but from the viewpoint of the effects of the present invention, it is preferably 17 parts by mass or more, more preferably 18 parts by mass or more, even more preferably 20 parts by mass or more, still more preferably 30 parts by mass or more, even 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, from the viewpoint of tire strength, D is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 75 parts by mass or less.

[0109] (Carbon Black) The carbon black is not particularly limited, and GPF, FEF, HAF, ISAF, SAF, and other carbon blacks commonly used in the tire industry can be used. Specifically, N110, N115, N120, N125, N134, N135, N219, N220, N231, N234, N293, N299, N326, N330, N339, N343, N347, N351, N356, N358, N375, N539, N550, N582, N630, N642, N650, N660, N683, N754, N762, N765, N772, N774, N787, N907, N908, N990, N991, and the like can be suitably used. In addition to these, in-house synthesized products and the like can also be suitably used. These may be used alone or in combination of two or more.

[0110] From the perspective of reinforcement, the nitrogen adsorption specific surface area (N2SA) of carbon black is 20m 2 / g or more is preferable, and 50m 2 / g or more is more preferable, and 80m 2 / g or more is more preferable, and 100m 2 From the viewpoints of fuel economy and processability, it is particularly preferable that the tensile strength is 250 m 2 / g or less is preferable, and 200m 2 / g or less is more preferable, and 150m 2 The N2SA of carbon black is measured by the above-mentioned measuring method.

[0111] The average primary particle size of carbon black is preferably less than 30 nm, more preferably less than 26 nm, even more preferably less than 23 nm, and particularly preferably 22 nm or less. The lower limit of the average primary particle size is not particularly limited, but is preferably more than 5 nm, more preferably more than 8 nm, and even more preferably more than 10 nm. The average primary particle size can be determined by the above-mentioned method.

[0112] (Other fillers) Fillers other than silica and carbon black may include aluminum hydroxide, calcium carbonate, alumina, clay, talc, etc., which have been commonly used in the tire industry. Biochar may also be used.

[0113] In the rubber composition according to the present embodiment, the total amount of the filler per 100 parts by mass of the rubber component is preferably more than 30 parts by mass, more preferably more than 40 parts by mass, even more preferably more than 50 parts by mass, and particularly preferably more than 55 parts by mass, from the viewpoint of the effects of the present invention. The upper limit of the total amount of the filler per 100 parts by mass of the rubber component is preferably less than 100 parts by mass, more preferably less than 80 parts by mass, and even more preferably less than 70 parts by mass.

[0114] (Silane coupling agent) 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 has been used in combination with silica in the tire industry can be used. For example, mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide and bis(3-triethoxysilylpropyl)tetrasulfide; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane; Examples of the silane coupling agent include thioester-based silane coupling agents such as silane, vinyl triethoxysilane, vinyl trimethoxysilane, and the like; amino-based silane coupling agents such as 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, and 3-(2-aminoethyl) aminopropyl triethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyl triethoxysilane and γ-glycidoxypropyl trimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane; chloro-based silane coupling agents such as 3-chloropropyl trimethoxysilane and 3-chloropropyl triethoxysilane; and the like. Among these, 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, and the like can be used. The silane coupling agent may be used alone or in combination of two or more types.

[0115] The content of the silane coupling agent per 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 improving the dispersibility of silica, and 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 from the viewpoint of preventing a decrease in abrasion resistance.

[0116] The content of the silane coupling agent with respect to 100 parts by mass of silica is preferably 1.0 parts 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 improving the dispersibility of silica. Also, from the viewpoint of preventing the deterioration of abrasion resistance, 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.

[0117] <Softener> The rubber composition according to the present embodiment may contain a softener. Examples of the softener include a resin component, oil, liquid rubber, and an ester-based plasticizer. The softener also includes an extended oil, extended resin, or extended liquid rubber component of a rubber component that has been subjected to oil extension, resin extension, or liquid rubber extension. These softeners may be derived from petroleum or biomass. In addition, a low molecular weight hydrocarbon component obtained by pyrolyzing and extracting used tires or products containing various components may be used as a softener.

[0118] (Resin component) The resin component is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenol resins, etc. These resin components may be used alone or in combination of two or more.

[0119] (oil) 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, process oil with a low content of polycyclic aromatic compounds (PCA) compounds can be used as an environmental measure. Examples of the low PCA content process oil include light extract solvate (MES), treated distillate aromatic extract (TDAE), and heavy naphthenic oil. In addition to the above oils, from the viewpoint of life cycle assessment, used lubricating oil after being used in rubber mixers and engines, and waste edible oil used in restaurants that has been appropriately refined may be used.

[0120] (Liquid Rubber) The rubber composition according to the present embodiment preferably contains a liquid rubber. The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used alone or in combination of two or more.

[0121] (Ester plasticizer) Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), and trixylenyl phosphate (TXP). Among these, dioctyl sebacate (DOS) is preferably used. These ester-based plasticizers may be used alone or in combination of two or more.

[0122] When a softener is contained, the total content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 5 parts by mass, and even more preferably more than 8 parts by mass from the viewpoint of processability, and is preferably less than 100 parts by mass, more preferably less than 80 parts by mass, and even more preferably less than 60 parts by mass from the viewpoint of abrasion resistance.

[0123] <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 wax, processing aids, antioxidants, stearic acid, zinc oxide, crosslinking agents, vulcanization accelerators, etc.

[0124] When the wax is contained, the content thereof per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably 1.5 parts by mass or more, from the viewpoint of weather resistance of the rubber, and is preferably less than 10 parts by mass, more preferably less than 7.0 parts by mass, and even more preferably less than 5.0 parts by mass, from the viewpoint of preventing whitening of the tire due to bloom.

[0125] When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably more than 1.0 part by mass, more preferably more than 2.0 parts by mass, and even more preferably more than 2.5 parts by mass from the viewpoint of processability, and is preferably less than 10 parts by mass, more preferably less than 8.0 parts by mass, and even more preferably less than 5.0 parts by mass from the viewpoint of abrasion resistance.

[0126] When stearic acid is contained, the content per 100 parts by mass of the rubber component is preferably more than 1.0 part by mass, more preferably more than 2.0 parts by mass, and even more preferably more than 2.5 parts by mass from the viewpoint of processability, and is preferably less than 10 parts by mass, more preferably less than 8.0 parts by mass, and even more preferably less than 5.0 parts by mass from the viewpoint of vulcanization speed.

[0127] The antiaging agent is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and carbamic acid metal salts, and the like. Phenylenediamine-based antiaging 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 antiaging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred, and amine-based antiaging agents are more preferred. These antiaging agents may be used alone or in combination of two or more.

[0128] (Crosslinking agent) As the crosslinking agent, sulfur is preferably used. As the sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, etc. can be used.

[0129] In the case where sulfur is contained, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more from the viewpoint of ensuring a sufficient vulcanization reaction, and is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and particularly preferably 2.5 parts by mass or less from the viewpoint of preventing deterioration.

[0130] The vulcanization accelerator is not particularly limited, but examples thereof include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. Among these, sulfenamide-based vulcanization accelerators and / or guanidine-based vulcanization accelerators are preferred, since the desired effects can be more suitably obtained, and it is more preferable to use two of these types in combination.

[0131] When a vulcanization accelerator is contained, the total content per 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 even more preferably 2.0 parts by mass or more. The content of the vulcanization accelerator per 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 even more preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be secured.

[0132] <Application> The heavy-duty tires in this embodiment are tires that are intended to be mounted on automobiles that run on four wheels, and include tires for not only large trucks and buses, but also small trucks, buses, vans, etc., and are tires with a standard load of more than 1,000 kg. EXAMPLES

[0133] In the following, examples (embodiments) that are considered to be preferable for carrying out the present invention will be shown, but the scope of the present invention is not limited to the examples.

[0134] Using various chemicals shown below, a heavy-duty tire (size: 275 / 70R22.5, rim: 22.5×7.50) having the basic structure shown in FIG. 1, the tread pattern shown in FIG. 2, and the circumferential narrow grooves shown in FIG. 3 was examined, and the results calculated based on the evaluation method described below are shown in Tables 1 and 2. NR:RSS#3 SBR: C2525 manufactured by Versalis (styrene content: 25% by mass, vinyl content: 25% by mole, Tg: -52°C) BR: BUNA CB24 manufactured by ARLANXEO (BR synthesized using a Nd-based catalyst, cis content: 96 mol%, vinyl content: 0.7 mol%, Mw: 500,000) Carbon black: Show Black N134 (N2SA: 148m) manufactured by Cabot Japan Co., Ltd. 2 / g, average primary particle diameter: 18nm) Silica: Ultrasil 9100GR (N2SA235m) manufactured by Evonik Degussa 2 / g, average primary particle diameter: 15nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Beads of stearic acid camellia manufactured by NOF Corporation Anti-aging agent: Nocrac 6C (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. (Powdered sulfur containing 5% oil) Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccelaer D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0135] Examples and Comparative Examples According to the compounding recipes shown in Tables 1 and 2, chemicals other than sulfur and vulcanization accelerator are kneaded for 1 to 10 minutes using a 1.7 L closed Banbury mixer until the discharge temperature reaches 150 to 160°C, to obtain a kneaded product. Next, sulfur and vulcanization accelerator are added to the kneaded product obtained using a two-axis open roll, and the mixture is kneaded for 4 minutes until the temperature reaches 105°C, to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition is extruded into the shape of the tread part using an extruder equipped with a die of a predetermined shape, and is bonded together with other tire components to prepare an unvulcanized tire, and each test tire is produced by press-vulcanizing the tire at 150°C for 30 minutes.

[0136] <Rubber hardness measurement> A sample for hardness measurement is cut out from the tread of each test tire with a length of 20 mm, width of 4 mm, and thickness of 1 mm, so that the long side is in the tire circumferential direction and the thickness direction is in the tire radial direction. For the sample for hardness measurement, a type A durometer is pressed against the sample from the contact surface side of the tread in accordance with JIS K 6253 to measure the rubber hardness at 25°C.

[0137] <Measurement of 0℃ tan δ, 0℃ E* and glass transition temperature (Tg)> A test tire is cut from the tread of each test tire to a length of 20 mm, width of 4 mm, and thickness of 1 mm, with the long side in the tire circumferential direction and the thickness direction in the tire radial direction. For each rubber test piece, a dynamic viscoelasticity measuring device (Iplexer series manufactured by GABO) is used to measure the loss tangent (tan δ) and complex modulus of elasticity (E*) under the conditions of temperature 0°C, frequency 10Hz, initial strain 10%, and dynamic strain 2.5%. Furthermore, a temperature distribution curve of tan δ from -60 to 40°C is measured under the conditions of temperature 70°C, frequency 10Hz, initial strain 1%, amplitude ±0.1%, and heating rate 3°C / min, and the temperature corresponding to the largest tan δ value in the obtained temperature distribution curve (tan δ peak temperature) is taken as the glass transition temperature (Tg).

[0138] <Wet grip performance> Each test tire is assembled on a rim, and this is attached to the rear wheel of a bus, which is a test vehicle. The braking distance from an initial speed of 100 km / h on a wet asphalt road surface is obtained using this test vehicle. The result of the reference comparative example (Comparative Example 9) is set to 100 and expressed as an index. The higher 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

[0139] [Table 1]

[0140] [Table 2]

[0141] <Embodiment> The following are preferred embodiments.

[0142] [1] A heavy-duty tire having a tread portion, The tread portion has one or more circumferential main grooves extending continuously in the tire circumferential direction, the tread portion is made of a rubber composition containing a rubber component and silica, The groove depth of the deepest part of the circumferential main groove is H1 (mm), When the content of silica per 100 parts by mass of the rubber component of the rubber composition is D (parts by mass), H1 is 15.0 or less, and H1×D is 250 or more, A heavy-duty tire having a land ratio R of 0.90 or more 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. [2] The heavy-duty tire according to the above [1], having a D / R of 30 or more. [3] The content of styrene butadiene rubber in the rubber component is S C (mass%), S CThe heavy-duty tire according to the above [1] or [2], wherein / D is 0.60 or more. [4] The heavy duty tire according to any one of the above [1] to [3], wherein, when the total amount of styrene in the rubber component is S (mass %), S / D is 0.130 or more. [5] The tread portion has two circumferential main grooves extending continuously in the 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 heavy load tire according to any one of the above [1] to [4], wherein the crown land portion has one or more circumferential narrow grooves extending continuously in the tire circumferential direction. [6] The heavy-duty tire according to any one of the above [1] to [5], wherein the crown land portion has a sipe extending in the tire width direction, and when the groove depth of the deepest part of the sipe is H2 (mm), H2 / H1 is 0.25 or more. [7] The heavy duty tire according to any one of the above [1] to [6], wherein the pair of shoulder land portions have no lug grooves. [8] The heavy duty tire according to any one of the above [1] to [7], wherein H1×D is 350 or more. [9] The heavy duty tire according to any one of the above [1] to [8], having a D / R of 50 or more.

[10] The heavy duty tire according to any one of the above [1] to [9], wherein T×D is 320 or more, where T (mm) is the thickness of the tread portion when new.

[11] The heavy-duty tire according to any one of the above [1] to

[10] , 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.

[12] The heavy duty tire according to any one of the above [1] to

[11] , wherein the rubber composition has a complex modulus at 0° C. (0° C.E*) of 8.5 MPa or more and 13.0 MPa or less.

[13] The heavy duty tire according to any one of the above [1] to

[12] , wherein the tan δ at 0° C. (0° C. tan δ) of the rubber composition is 0.15 or more and 0.25 or less. [Explanation of symbols]

[0143] 1. Heavy duty tires 2 Tread (contact 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 Center sipe 11 Neck 12 Torso 13 Opening (tapered part) 14 Bead section 15 Inner Liner 16 Carcass 18 Shoulder Land Section 19 Crown Land Division 22 Bead core 24 Bead Apex 26 Carcass ply CL Tire Equator T Tread thickness H1 circumferential main groove depth at deepest point Depth of deepest part of H2 sipe W Tire width direction Te Tread Edge TW tread width

Claims

1. A heavy-duty tire having a tread portion, The tread portion has one or more circumferential main grooves extending continuously in the tire circumferential direction, the tread portion is made of a rubber composition containing a rubber component and silica, The groove depth of the deepest part of the circumferential main groove is H 1 (mm), When the content of silica per 100 parts by mass of the rubber component of the rubber composition is D (parts by mass), H 1 is 15.0 or less, and H 1 ×D is 250 or more, A heavy-duty tire having a land ratio R of 0.90 or more at a contact surface of the tread portion after the tread portion is worn along a tread radius so that a groove depth at the deepest part of the circumferential main groove is 75% of that at a new product.

2. 2. The heavy duty tire according to claim 1, wherein D / R is 30 or more.

3. The content of styrene butadiene rubber in the rubber component is S C (mass%), S C 3. The heavy duty tire according to claim 1, wherein / D is 0.60 or more.

4. 3. The heavy duty tire according to claim 1, wherein when a total amount of styrene in the rubber component is S (mass %), S / D is 0.130 or more.

5. 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 heavy duty tire according to claim 1 or 2, wherein the crown land portion has one or more circumferential narrow grooves extending continuously in the tire circumferential direction.

6. The crown land portion has a sipe extending in the tire width direction, and the groove depth of the deepest part of the sipe is H 2 (mm), H 2 / H 1 6. The heavy load turbine according to claim 5, wherein No.

7. The heavy duty tire according to claim 5 , wherein the pair of shoulder land portions have no lug grooves.

8. H 1 3. The heavy duty tire according to claim 1, wherein xD is 350 or more.

9. 3. The heavy duty tire according to claim 1, wherein D / R is 50 or more.

10. 3. The heavy duty tire according to claim 1, wherein T×D is 320 or more, where T (mm) is a thickness of the tread portion when new.

11. 6. The heavy-duty tire according to claim 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.

12. The heavy duty tire according to claim 1 or 2, wherein the rubber composition has a complex modulus of elasticity at 0° C. (0° C. E*) of 8.5 MPa or more and 13.0 MPa or less.

13. The heavy duty tire according to claim 1 or 2, wherein the rubber composition has a tan δ at 0° C. (0° C. tan δ) of 0.15 or more and 0.25 or less.

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