JP2019194282A - Tire rubber composition and pneumatic tire - Google Patents

Abstract

To provide a tire rubber composition that has improved wet performance and wear resistant performance, both performances to be achieved in a balanced manner, and a pneumatic tire.SOLUTION: The present invention provides a tire rubber composition constituting a tread part of a pneumatic tire. The tire rubber composition contains a filler containing silica and carbon black of 55 pts.mass or more 80 pts.mass or less, relative to a diene rubber 100 pts.mass containing natural rubber and polybutadiene rubber with the polybutadiene rubber of 35 pts.mass or more 70 pts.mass or less; the content of the silica is 10 mass% or more and 50 mass% or less of the total amount of the filler; and a tanδ at 20°C is 0.18 or more and 0.28 or less, and a JIS-A hardness at 20°C is 66 or more and 76 or less.SELECTED DRAWING: Figure 2

Description

  TECHNICAL FIELD The present invention relates to a tire rubber composition part intended to be used mainly in a tread part of a heavy duty pneumatic tire and a pneumatic tire using the same.

  Pneumatic tires are mainly formed with a large number of grooves on the tread surface to ensure drainage and to ensure traction performance on the wet road surface (hereinafter referred to as wet performance). On the other hand, if the number of grooves is increased too much, the rigidity of the land portion tends to decrease and the wear resistance tends to decrease. Therefore, some conventional pneumatic tires attempt to improve these contradictory performances by devising the arrangement and shape of the grooves (see, for example, Patent Document 1). However, there is a limit to achieving both wet performance and wear resistance performance only by the groove mode, and these contradictory performances are improved by the characteristics of the rubber composition for tires constituting the tread portion. Measures to achieve both are required.

JP 2017-124773 A

  An object of the present invention is to provide a rubber composition for a tire and a pneumatic tire that improve both wet performance and wear resistance performance and make it possible to achieve a balance between these performances.

  The rubber composition for a tire of the present invention that achieves the above object comprises silica and carbon black with respect to 100 parts by mass of a diene rubber comprising natural rubber and polybutadiene rubber and containing 35 to 70 parts by mass of the polybutadiene rubber. The filler to be contained is blended in an amount of 55 parts by weight or more and 80 parts by weight or less, the blending amount of the silica is 10% by weight or more and 50% by weight or less of the total amount of the fillers, and tan δ at 20 ° C. is 0.18 or more and 0 .28 or less, and the JIS-A hardness at 20 ° C. is 66 or more and 76 or less.

  The rubber composition for tires of the present invention has the above-mentioned composition, and tan δ and hardness at 20 ° C. are set in the above-mentioned range, so that wet performance and wear resistance performance are improved, and these performances are balanced. You can balance well. The JIS-A hardness at 20 ° C. is a hardness measured using a type A durometer at 20 ° C. in accordance with a durometer hardness test specified in JIS K6253. Further, tan δ at 20 ° C. is a value measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of a frequency of 20 Hz, an initial strain of 10%, and a dynamic strain of ± 2% in an atmosphere of 20 ° C. . Both tan δ and hardness can be measured using a rubber piece taken from a vulcanized pneumatic tire.

  In the tire rubber composition of the present invention, the volume fraction of the filler with respect to all the compounding agents in the rubber composition is preferably 19% or more and 28% or less. Moreover, it is preferable that the volume fraction of the silica with respect to all the compounding agents in a rubber composition is 2% or more and 14% or less.

  In the pneumatic tire of the present invention using the tire rubber composition described above for the tread portion, a plurality of circumferential grooves extending along the tire circumferential direction on the surface of the tread portion, and extending along the tire width direction. A plurality of lug grooves, and a plurality of blocks are defined by the circumferential grooves and the lug grooves, and a plurality of center blocks arranged on the tire equator are arranged over the entire circumference of the tire. The center block row includes a center block row, and when the center region is within a range of 50% of the tread deployment width centered on the tire equator, the center is adjacent in the tire circumferential direction with respect to the total area of all the grooves in the center region. It is preferable that the ratio of the total area of the lug groove located between blocks is 20% to 50%. As a result, in the center region that contributes to wet performance, the center lug groove and other grooves that have a particularly large effect on wet performance are well balanced, and it is advantageous to achieve both high wear resistance and wet performance. become.

  In the pneumatic tire of the present invention, the ratio of the total area of the lug grooves in the center region to the total area of all the grooves in the center region is preferably 30% to 60%. As a result, in the center region contributing to the wet performance, the balance between the circumferential groove and the lug groove is improved, which is advantageous in achieving both high wear resistance and wet performance.

  In the pneumatic tire according to the present invention, the total length of the widthwise groove component obtained by projecting the contour lines on the tread surfaces of a plurality of blocks toward the projection plane perpendicular to the tire equator is La, and toward the projection plane parallel to the tire equator. When the total length of the projected circumferential groove component is Lb, and the length in the tire width direction in the range that abuts against the road surface when the normal internal pressure is filled and 20% of the normal load is applied is TW ′, The length preferably satisfies the relationship of 40 ≦ La / TW ′ ≦ 50 and 65 ≦ Lb / TW ′ ≦ 75. As a result, the balance between the ground contact width TW ′ in the low load state and the width direction component and the circumferential direction component of the groove on the entire tread surface is improved, which is advantageous for achieving both high wear resistance and wet performance. .

  In the pneumatic tire of the present invention, when the range of 10% of the length in the tire width direction of the center block centering on the tire equator is the equator region, the area of the block tread in the equator region relative to the total area of the equator region is The ratio is preferably 30% to 70%. Thereby, the balance between the groove and the land portion in the equator region having a great influence on the wet performance is improved, which is advantageous in achieving both high wear resistance performance and wet performance.

  In the pneumatic tire of the present invention, it is preferable that a narrow groove extending along the tire width direction and having both ends opened in the circumferential groove is formed on the tread surface of the center block. Thereby, the groove component of the narrow groove can be added without significantly reducing the block rigidity, and the wet performance can be improved while maintaining the wear resistance performance.

  In the present invention, the “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim for JATMA and a “TRAM” for TRA. “Design Rim” or “Measuring Rim” for ETRTO. “Regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA, and the table “TIRE ROAD LIMITS AT VARIOUS” is TRA. The maximum value described in “COLD INFRATION PRESURES”, “INFLATION PRESSURE” in the case of ETRTO, is 180 kPa when the tire is for passenger cars. “Regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is JATMA, and the table “TIRE ROAD LIMITS AT VARIOUS” is TRA. The maximum value described in “COLD INFORMATION PRESURES”, “LOAD CAPACITY” if it is ETRTO, but if the tire is for a passenger car, the load is equivalent to 88% of the load.

1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. It is a front view showing typically an example of a tread part of a pneumatic tire of the present invention. It is a front view which shows typically another example of the tread part of the pneumatic tire of this invention. It is explanatory drawing which expands and shows the center block of this invention.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  In the rubber composition for tires of the present invention, the rubber component is a diene rubber, and specifically comprises two kinds of natural rubber and polybutadiene rubber. By using natural rubber and polybutadiene rubber as the diene rubber, the wear resistance of the rubber composition can be improved. As natural rubber or polybutadiene rubber, those usually used in rubber compositions for treads of pneumatic tires may be used.

  The polybutadiene rubber is necessarily contained in an amount of 35 to 70 parts by mass, preferably 35 to 55 parts by mass, in 100 parts by mass of the diene rubber. The blending amount of the natural rubber is preferably 30 parts by mass or more and 65 parts by mass or less, more preferably 45 parts by mass to 65 parts by mass with respect to 100 parts by mass of the diene rubber. Abrasion resistance falls that the compounding quantity of polybutadiene rubber is less than 35 mass parts. When the blending amount of the polybutadiene rubber exceeds 70 parts by mass, the wet performance is deteriorated.

  The rubber composition for tires of the present invention always contains a filler containing silica and carbon black. By mix | blending these fillers, the intensity | strength of the rubber composition for tires can be raised. The blending amount of the filler is 55 parts by mass or more and 80 parts by mass or less, preferably 56 parts by mass to 70 parts by mass with respect to 100 parts by mass of the diene rubber described above. Among these fillers, the compounding amount of silica is 10% by mass or more and 50% by mass or less, preferably 11% by mass to 33% by mass, based on the total amount of the fillers. Thus, wet performance can be made favorable, improving abrasion resistance by including only a suitable quantity of silica in a filler. When the blending amount of the filler is less than 55 parts by mass, the wet performance is deteriorated. When the blending amount of the filler exceeds 80 parts by mass, the wear resistance performance decreases. When the blending amount of silica is less than 10% by mass of the total amount of the filler, the wet performance is lowered. When the compounding amount of silica exceeds 50% by mass of the total amount of the filler, the wear resistance performance decreases.

  The compounding amount of silica may satisfy the ratio with respect to the total amount of the filler described above, but is preferably 6 parts by mass to 30 parts by mass, more preferably 7 parts by mass to 23 parts with respect to 100 parts by mass of the diene rubber. It is good to make it a mass part.

CTAB adsorption specific surface area of silica is not particularly limited, preferably 140m ² / g~230m ² / g, may more preferably at 150m ² / g~180m ² / g.

  As silica, silica usually used in a rubber composition for tires, for example, wet method silica, dry method silica, or surface-treated silica can be used. Silica can be used by appropriately selecting from commercially available products. Moreover, the silica obtained by the normal manufacturing method can be used.

  As described above, the filler necessarily contains carbon black, and the blending amount of carbon black is preferably 70% by mass to 94% by mass, and more preferably 77% by mass to 93% by mass with respect to the total amount of the filler. Moreover, it is preferable to mix | blend 35 mass parts-65 mass parts with respect to 100 mass parts of the above-mentioned diene rubbers, More preferably 45 mass parts-55 mass parts. As described above, by containing an appropriate amount of carbon black in the filler, the strength of the rubber composition can be increased and the wear resistance can be increased.

As carbon black, it is preferable to use carbon black whose grade classified according to ASTM D1765 is, for example, SAF or ISAF grade. Nitrogen adsorption specific surface area N ₂ SA of carbon black is not particularly limited, and may and preferably from 90m ² / g~150m ² / g, more preferably 110m ² / g~145m ² / g.

  Furthermore, in the present invention, the volume fraction of the above-mentioned filler with respect to all the compounding agents in the rubber composition is preferably 19% or more and 28% or less, more preferably 20% to 25%. Thus, wear resistance can be made favorable by setting the volume fraction of a filler. When the volume fraction of the filler is less than 19%, the effect of improving wet performance and wear resistance performance is limited. When the volume fraction of the filler exceeds 28%, it becomes difficult to sufficiently secure the effect of improving the wear resistance.

  Further, the volume fraction of silica with respect to all the compounding agents in the rubber composition is preferably 2% or more and 14% or less, more preferably 3% to 10%. Thus, by setting the volume fraction of silica, wet performance can be improved while improving or maintaining the wear resistance. When the volume fraction of silica is less than 2%, the effect of improving wet performance and wear resistance is limited. When the volume fraction of silica exceeds 14%, it is difficult to sufficiently secure the effect of improving the wear resistance. The volume fraction of the filler and silica is the compound volume obtained by dividing the compounded weight in the compound of carbon and silica by the specific gravity of each raw material as A, and dividing the total weight of the compound by the specific gravity of the compound. Where B is the ratio of volume A to volume B (A / B).

  In the rubber composition for a tread of the present invention, a silane coupling agent may be blended with silica in order to improve the dispersibility of silica and enhance the reinforcement with the diene rubber. The amount of the silane coupling agent is preferably 6% by mass to 16% by mass, and more preferably 8% by mass to 12% by mass with respect to the amount of silica. If the blending amount of the silane coupling agent is less than 6% by mass of the blending amount of silica, the effect of improving the dispersibility of silica cannot be obtained sufficiently. On the other hand, when the silane coupling agent exceeds 16% by mass, the silane coupling agents are polymerized, and the desired effect cannot be obtained.

  Other compounding agents other than those described above can be added to the rubber composition for tires of the present invention. Other ingredients include fillers other than silica and carbon black, vulcanizing agents or crosslinking agents, vulcanization accelerators, anti-aging agents, liquid polymers, thermosetting resins, thermoplastic resins, etc. Various compounding agents used for the tire rubber composition can be exemplified. The compounding amounts of these compounding agents can be conventional conventional compounding amounts as long as they do not contradict the purpose of the present invention. Moreover, as a kneading machine, a normal rubber kneading machine, for example, a Banbury mixer, a kneader, a roll or the like can be used.

  The tire rubber composition of the present invention constituted by the above-mentioned composition further has a tan δ at 20 ° C. of 0.18 to 0.28, preferably 0.19 to 0.24, and is JIS- at 20 ° C. A hardness is 66-76, Preferably it is 67-74. By having such physical properties, wear resistance performance and wet performance can be improved. If tan δ at 20 ° C. is less than 0.18, it is difficult to sufficiently ensure the effect of improving the wear resistance and wet performance. When tan δ at 20 ° C. exceeds 0.28, it is difficult to sufficiently ensure the effect of improving the wear resistance. If the JIS-A hardness at 20 ° C. is less than 66, it is difficult to sufficiently ensure the effect of improving the wear resistance. When the JIS-A hardness at 20 ° C. exceeds 76, it is difficult to sufficiently secure the effect of improving the wear resistance.

  The rubber composition for tires of the present invention can improve wet performance and wear resistance performance and balance these performances in a well-balanced manner by the above blending and physical properties. Therefore, it can be suitably used for a tread portion of a pneumatic tire (particularly, a heavy duty pneumatic tire). The structure of the pneumatic tire to which the rubber composition for tires of the present invention is applied is not particularly limited, but depending on the rubber composition as long as the tire achieves both wet performance and wear resistance performance by the shape and arrangement of the grooves. The synergistic effect of the performance and the performance of the tire structure makes it possible to achieve both wet performance and wear resistance performance at a higher level. For example, the pneumatic tire shown in FIGS. 1 to 3 is excellent in wet performance and wear resistance as described later, and the rubber composition for tires of the present invention can be suitably used.

  As shown in FIG. 1, the pneumatic tire of the present invention is disposed on a tread portion 1, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and on the tire radial direction inner side of the sidewall portion 2. And a pair of bead portions 3. Although FIG. 1 is a meridian cross-sectional view and is not depicted, the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction to form an annular shape. The toroidal basic structure is constructed. Other tire constituent members depicted in the meridian cross-sectional view also extend in the tire circumferential direction to form an annular shape unless otherwise specified.

  A carcass layer 4 is mounted between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back around the bead core 5 disposed in each bead portion 3 from the vehicle inner side to the outer side. A bead filler 6 is disposed on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4. On the other hand, a plurality of layers (four layers in FIG. 1) of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and is disposed so that the reinforcing cords cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. Although not adopted in the tire of FIG. 1, in the present invention, a belt reinforcing layer (not shown) can be further provided on the outer peripheral side of the belt layer 7. When the belt reinforcing layer is provided, the belt reinforcing layer includes, for example, an organic fiber cord oriented in the tire circumferential direction, and the angle of the organic fiber cord with respect to the tire circumferential direction can be set to, for example, 0 ° to 5 °.

  A tread rubber layer R1 is disposed on the outer peripheral side of the carcass layer 4 in the tread portion 1, and a side rubber layer R2 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2. A rim cushion rubber layer R3 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4. The tread rubber layer R1 may have a structure in which two types of rubber layers (cap tread rubber layer and under tread rubber layer) having different physical properties are laminated in the tire radial direction. The tire rubber composition of the present invention is used for the tread rubber layer R1 among these rubber layers.

  As shown in FIG. 2, a plurality of circumferential grooves 10 extending in the tire circumferential direction and a plurality of lug grooves 20 extending in the tire width direction are provided on the outer surface of the tread portion 1. A plurality of blocks 30 are defined by the circumferential grooves 10 and the lug grooves 20.

  As the circumferential grooves 10, a pair of inner circumferential grooves 11 disposed on both sides of the tire equatorial plane CL, and a pair of outer circumferential lines disposed on the outer sides in the tire width direction of the pair of inner circumferential grooves 11, respectively. Directional grooves 12 are provided. The inner circumferential groove 11 and the outer circumferential groove 12 extend over the entire circumference of the tire while being bent in a zigzag shape along the tire circumferential direction.

  The inner circumferential groove 11 has a groove width of, for example, 6 mm to 15 mm and a groove depth of, for example, 10 mm to 18 mm. The outer circumferential groove 12 has a groove width of, for example, 4 mm to 12 mm, and a groove depth. For example, it is 6 mm or more and 18 mm or less. The groove width W1 of the inner circumferential groove 11 is set to be larger than the groove width W2 of the outer circumferential groove 12, and the groove width ratio W2 / W1 satisfies the relationship of 0.5 to 0.9, for example. Yes.

  As the lug groove 20, a center lug groove 21 provided between the pair of inner circumferential grooves 11 and having both ends communicating with the inner circumferential groove 11, and an inner circumferential groove 11 adjacent in the tire width direction, It is provided between the outer circumferential groove 12, one end communicates with the inner circumferential groove 11, and the other end intersects the outer circumferential groove 12 in the land portion on the outer side in the tire width direction of the outer circumferential groove 12. An intermediate lug groove 22 that terminates and an outer circumferential groove 12 that is provided on the outer side in the tire width direction, one end of which intersects the outer circumferential groove 12 and between the inner circumferential groove 11 and the outer circumferential groove 12. A shoulder lug groove 23 is provided which terminates in the section and is open at the other end toward the grounding end. A plurality of these center lug grooves 21, intermediate lug grooves 22, and shoulder lug grooves 23 are provided, and are arranged at intervals in the tire circumferential direction.

  The center lug groove 21 has a groove width of, for example, 4 mm to 9 mm and a groove depth of, for example, 9 mm to 18 mm. The intermediate lug groove 22 has a groove width of, for example, 4 mm to 9 mm, and a groove depth of, for example, 2 mm. The shoulder lug groove 23 has a groove width of, for example, 4 mm or more and 16 mm or less, and a groove depth of, for example, 2 mm or more and 16 mm or less.

  The center lug groove 21 and the intermediate lug groove 22 are connected to the common inner circumferential groove 11, but the positions of the portions connected to the inner circumferential groove 11 in the tire circumferential direction are the center lug groove 21 and the intermediate lug 21. It differs from the groove 22. Similarly, the intermediate lug groove 22 and the shoulder lug groove 23 are connected to the common outer circumferential groove 12, but the position of the portion connected to the outer circumferential groove 12 in the tire circumferential direction is the intermediate lug groove 22. And the shoulder lug groove 23 are different.

  The block 30 formed in the tread portion 1 includes a center block 31 defined by a pair of inner circumferential grooves 11 and a center lug groove 21 adjacent in the tire circumferential direction, and an inner circumferential groove 11 adjacent in the tire width direction. And an intermediate block 32 defined by the outer circumferential groove 12 and the intermediate lug groove 22 adjacent in the tire circumferential direction, and a shoulder lug groove 23 adjacent in the tire circumferential direction outside the outer circumferential groove 12 in the tire width direction. The shoulder block 33 is included. The center block 31, the intermediate block 32, and the shoulder block 33 are arranged along the tire circumferential direction.

  The center lug groove 21 has a circumferentially extending portion 21a extending in the tire circumferential direction and a widthwise extending portion 21b extending in the tire width direction by bending at a plurality of positions. Specifically, one center lug groove 21 includes a pair of width-direction extending portions 21b whose one ends communicate with the inner circumferential groove 11 and a circumference connecting the other ends of the pair of width-direction extending portions 21b. It is comprised with the direction extension part 21a. The circumferentially extending portion 21a is at least partially on the tire equator CL, and is inclined within a range of, for example, 0 ° to 15 ° with respect to the tire circumferential direction.

  On the tread surface of the center block 31, as shown in the example of FIG. 3, it is possible to provide a narrow groove 40 that extends along the tire width direction and has both ends opened to a circumferential groove. The narrow groove 40 is a groove having a groove width and a groove depth smaller than those of the various lug grooves 20 described above, and the groove width is, for example, 0.5 mm to 5.0 mm, and the groove depth is, for example, 0.5 mm to 5.0 mm. can do. The narrow groove 40 can be bent at a plurality of positions as shown. By providing such a narrow groove 40, the groove component can be increased without significantly reducing the block rigidity, so that the wet performance can be enhanced while maintaining the wear resistance performance.

  In such a structure, when the center region is within 50% of the tread deployment width TW centering on the tire equator, all the grooves in the center region (inner circumferential grooves 11, center lug grooves 21, intermediate lugs) Ratio of the total area A2 of the lug groove (center lug groove 21) located between the center blocks 31 adjacent in the tire circumferential direction to the total area A1 of a part of the groove 22 and the narrow groove 40) (A2 / A1 × 100%) ) Is preferably 20% to 50%, more preferably 26% to 40%. By setting the groove area in this way, the center lug groove 21 which has a particularly large influence on the wet performance and the other grooves are well balanced in the center region contributing to the wet performance, and the wear resistance performance and the wet performance are improved. It is advantageous to achieve both at the same time. If the above-mentioned ratio (A2 / A1 × 100%) is less than 20%, further improvement in wet performance due to the tread structure cannot be sufficiently expected. If the above-mentioned ratio (A2 / A1 × 100%) exceeds 50%, further improvement in wear resistance performance due to the tread structure cannot be fully expected.

  Furthermore, the lug groove (center lug groove 21, center lug groove 21) in the center area with respect to the total area A1 of all the grooves in the center area (inner circumferential groove 11, center lug groove 21, part of intermediate lug groove 22, narrow groove 40) The ratio (A3 / A1 × 100%) of the total area A3 of a part of the intermediate lug groove 22 is preferably 30% to 60%, more preferably 37% to 51%. By setting the groove area in this manner, the balance between the circumferential groove 10 and the lug groove 20 is improved in the center region contributing to the wet performance, and the wear resistance performance and the wet performance are both highly compatible. Will be advantageous. If the above-mentioned ratio (A3 / A1 × 100%) is less than 30%, further improvement in wet performance due to the tread structure cannot be sufficiently expected. If the above-mentioned ratio (A2 / A1 × 100%) exceeds 60%, further improvement of the wear resistance performance by the tread structure cannot be sufficiently expected.

  In the structure of the tread portion 1 described above, the total length of the widthwise groove component obtained by projecting the contour lines on the tread of the block 30 (center block 31, intermediate block 32, shoulder block 33) toward the projection plane perpendicular to the tire equator CL, respectively. La is the total length of the circumferential groove component projected toward the projection plane parallel to the tire equator CL, and Lb is in contact with the road surface when the normal internal pressure is filled and 20% of the normal load is applied. When the length in the tire width direction of the range is TW ′, these lengths preferably satisfy the relationship of 40 ≦ La / TW ′ ≦ 50 and 65 ≦ Lb / TW ′ ≦ 75. As a result, the contact width TW 'in the low load state and the groove shape of the entire tread surface (balance between the width direction component and the circumferential direction component of each groove) are improved, and both wear resistance performance and wet performance are highly compatible. To be advantageous. When La / TW ′ is less than 40, further improvement in wet performance due to the tread structure cannot be sufficiently expected. If La / TW ′ exceeds 50, further improvement in wear resistance due to the tread structure cannot be fully expected. If Lb / TW ′ is less than 65, further improvement in wet performance due to the tread structure cannot be sufficiently expected. If Lb / TW ′ exceeds 75, further improvement in wear resistance due to the tread structure cannot be sufficiently expected.

  The lengths La and Lb are projected toward the projection plane perpendicular to the tire equator CL and the projection plane parallel to the tire equator CL with respect to the contour lines (each side) on the tread surface of the block 30 as shown in FIG. Then, it is decomposed into a width direction component and a circumferential direction component, the length (La ′) of each width direction component and the length (Lb ′) of the circumferential direction component are obtained, and the sum is calculated (La: Sum of La ′, Lb: Sum of Lb ′). In FIG. 4, the center block 31 has been described as an example, but each component is obtained by the same method for the other blocks 30 (intermediate block 32 and shoulder block 33).

  In the structure of the tread portion 1 described above, when the range of 10% of the tire width direction length w of the center block 31 centering on the tire equator CL is defined as the equator region, the equator region is within the equator region with respect to the total area A4 of the equator region. The ratio (A5 / A4 × 100%) of the area A5 of the block tread (land) is preferably 30% to 70%, more preferably 35% to 50%. By setting the groove area in this way, the balance between the groove and the land in the equator region, which has a great influence on the wet performance, is improved, and it is advantageous for achieving both high wear resistance and wet performance. . When the above-mentioned ratio (A5 / A4 × 100%) is less than 30%, further improvement of wet performance due to the tread structure cannot be sufficiently expected. If the above-mentioned ratio (A5 / A4 × 100%) exceeds 70%, further improvement in wear resistance performance by the tread structure cannot be sufficiently expected.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  31 types of rubber compositions for treads (Comparative Examples 1 to 6 and Examples 1 to 25) each having the composition shown in Tables 1 to 3 were weighed for the composition components except the vulcanization accelerator and sulfur, and 1.7 L. The mixture was kneaded for 5 minutes with a closed Banbury mixer, and the master batch was discharged at a temperature of 150 ° C. and cooled at room temperature. Then, this master batch was subjected to the same 1.7 L closed Banbury mixer, and a vulcanization accelerator and sulfur were added and mixed for 2 minutes to prepare a tire rubber composition.

  In Tables 1-3, for each rubber composition for tires, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho, in an atmosphere at a temperature of 20 ° C., a frequency of 20 Hz, an initial strain of 10%, and a dynamic strain of ± 2%. The value of tan δ measured at 20 ° C. under the conditions and the value of hardness measured using a type A durometer under the conditions of 20 ° C. in accordance with the durometer hardness test prescribed in JIS K6253 are shown together.

  Further, each tread rubber composition is used in the tread portion, the tire size is 275 / 80R22.5, has the basic structure shown in FIG. 1, and has the tread pattern shown in FIG. Ratio of the total area of lug grooves located between adjacent center blocks in the tire circumferential direction to the total area of all grooves (A2 / A1 × 100%), within the center area with respect to the total area of all grooves in the center area The ratio of the total area of the lug grooves (A3 / A1 × 100%), the contour line on the tread surface of each block to the projection length perpendicular to the tire equator, and the total length La of the circumferential groove component and the tire equator Tire width direction length TW ′ in the range of contact with the road surface when the total length Lb of the circumferential groove component projected toward the parallel projection surface and the normal internal pressure is filled and 20% of the normal load is applied La / TW ′ and Lb / TW ′, and the ratio of the area of the block tread in the equator region to the total area of the equator region (A5 / A4 × 100%) as set forth in Tables 1 to 3 The wet performance and wear resistance performance were evaluated by the methods shown below.

Wet performance Each test tire is assembled to a wheel with a rim size of 151 / 148J, and the air pressure is set to 900 kPa. On a wet surface with a water depth of 1 mm on the road surface, acceleration was performed with a full accelerator from a stopped state under the condition of no traction control operation (diff lock), and an average tire slip rate from 6 km / h to 21 km / h was measured. The evaluation result was shown by the index | exponent which sets the value of the comparative example 1 to 100 using the reciprocal number of the measured value. The larger the index value, the smaller the slip ratio, which means that the traction property (wet performance) on the wet road surface is excellent.

Wear resistance performance Each test tire is mounted on a wheel with a rim size of 151 / 148J, and the air pressure is 900 kPa. The remaining groove (groove depth) after the same travel distance was measured. The evaluation results are shown as an index with the value of Comparative Example 1 as 100. The larger the index value, the larger the remaining groove (groove depth), which means superior wear resistance.

The types of raw materials used in Tables 1 to 3 are shown below.
・ Natural rubber: STR20
・ Butadiene rubber: NIPOL BR 1220 manufactured by Nippon Zeon
Carbon black: Show black N110 manufactured by Cabot Japan
-Silica: ULTRASIL VN3GR manufactured by EVONIK
Silane coupling agent: Si69 manufactured by Degussa
Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical
・ Wax: Sannok manufactured by Ouchi Shinsei Chemical Co., Ltd. ・ Zinc flower: Zinc oxide manufactured by Shodo Chemical Co., Ltd. : SANTOCURE TBBS manufactured by FLEXSYS

  As is clear from Tables 1 to 3, the pneumatic tires of Examples 1 to 25 improved the wet performance and the wear resistance performance with respect to the pneumatic tire of Comparative Example 1, and balanced these performances in a well-balanced manner.

  On the other hand, the pneumatic tire of Comparative Example 2 deteriorated in wet performance because the tire rubber composition did not contain silica. Since the pneumatic tire of Comparative Example 3 contained a small amount of filler in the tire rubber composition, wet performance deteriorated. Since the pneumatic tire of Comparative Example 4 contained too much butadiene rubber in the tire rubber composition, wet performance deteriorated. In the pneumatic tire of Comparative Example 5, since the ratio of the amount of silica to the total amount of the filler in the tire rubber composition was too large, the wear resistance performance deteriorated. In the pneumatic tire of Comparative Example 6, the wear resistance deteriorated because the amount of the filler in the tire rubber composition was too large.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 10 Circumferential groove 11 Inner circumferential groove 12 Outer circumferential groove 20 Lug groove 21 Center lug groove 22 Intermediate lug groove 23 Shoulder lug groove 30 block 31 center block 32 intermediate block 33 shoulder block 40 narrow groove R1 tread rubber layer R2 side rubber layer R3 rim cushion rubber layer CL tire equator

Claims (8)

  Filler containing silica and carbon black is blended in an amount of 55 parts by weight or more and 80 parts by weight or less with respect to 100 parts by weight of diene rubber composed of natural rubber and polybutadiene rubber and containing 35 parts by weight or more and 70 parts by weight or less of the polybutadiene rubber. The blending amount of the silica is 10% by mass or more and 50% by mass or less of the total amount of the filler, tan δ at 20 ° C. is 0.18 or more and 0.28 or less, and the JIS-A hardness at 20 ° C. is 66. A tire rubber composition characterized by being 76 or less.   2. The tire rubber composition according to claim 1, wherein a volume fraction of the filler with respect to all compounding agents in the rubber composition is 19% or more and 28% or less.   3. The tire rubber composition according to claim 2, wherein a volume fraction of the silica with respect to all compounding agents in the rubber composition is 2% or more and 14% or less. A pneumatic tire using the tire rubber composition according to any one of claims 1 to 3 in a tread portion,
The surface of the tread portion includes a plurality of circumferential grooves extending along the tire circumferential direction, and a plurality of lug grooves extending along the tire width direction, the circumferential groove and the lug grooves, A plurality of blocks are partitioned by, and the plurality of blocks includes a center block row configured by arranging a plurality of center blocks arranged on the tire equator over the entire circumference of the tire,
Lug groove located between the center blocks adjacent to each other in the tire circumferential direction with respect to the total area of all the grooves in the center region when the center region is within a range of 50% of the tread development width centered on the tire equator A pneumatic tire characterized in that the ratio of the total area of the tire is 20% to 50%.   The pneumatic tire according to claim 4, wherein a ratio of a total area of the lug grooves in the center region to a total area of all the grooves in the center region is 30% to 60%.   The total length of the widthwise groove component obtained by projecting the contour lines on the treads of the plurality of blocks toward the projection surface perpendicular to the tire equator is La, and the circumferential groove component projected toward the projection surface parallel to the tire equator When the total length is Lb, and the length in the tire width direction in a range that contacts the road surface when 20% of the normal load is loaded with the normal internal pressure and TW ′ is assumed, these lengths are 40 ≦ La. The pneumatic tire according to claim 4 or 5, wherein a relationship of / TW'≤50 and 65≤Lb / TW'≤75 is satisfied.   When the range of 10% of the length in the tire width direction of the center block centering on the tire equator is defined as the equator region, the ratio of the area of the block tread in the equator region to the total area of the equator region is 30% to It is 70%, The pneumatic tire in any one of Claims 4-6 characterized by the above-mentioned.   The pneumatic tire according to any one of claims 4 to 7, wherein a narrow groove extending along the tire width direction and having both ends opened to the circumferential groove is formed on a tread surface of the center block. .

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