Pneumatic tires

Abstract

To provide a pneumatic tire which is sufficiently improved in an anti-crack performance and in a durability performance.SOLUTION: A pneumatic tire has a tread with grooves formed in a surface. The tread comprises a first rubber composition forming a groove bottom, and a second rubber composition further inside than the groove bottom in a radial direction of the tire and adjacent to the first rubber composition. If E1 mass% is an acetone extractable content of the first rubber composition and E2 mass% is the acetone extractable content of the second rubber composition, then (E1-E2)<20 is satisfied. If Wt (mm) is a cross-sectional width of the tire, Dt (mm) is an outer diameter of the tire and V (mm3) is virtual volume that is volume of a space occupied by the tire when the tire is mounted on a standard rim and has an internal pressure of 250 kPa, then the tire satisfies (Formula 1), 1700≤(Dt2×π / 4) / Wt≤2827.4, and (Formula 2), [(V+1.5×107) / Wt]≤2.88×105.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In recent years, there has been a growing demand for automobiles to have lower fuel consumption due to growing concerns about environmental issues and economic reasons, and there is also a strong demand for improved fuel efficiency in pneumatic tires (hereinafter simply referred to as "tires") that are fitted to automobiles.

[0003] The fuel efficiency of a tire can be evaluated by its rolling resistance, and it is known that the smaller the rolling resistance, the more fuel efficient the tire.

[0004] Therefore, it has been proposed to reduce the rolling resistance by devising the shape of the tire or the compounding of the rubber composition constituting the tire tread portion (for example, Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-178034 A [Patent Document 2] JP 2019-089911 A [Patent Document 3] WO2018 / 186367 publication [Patent Document 4] JP 2019-206643 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, tires manufactured using the above-mentioned conventional technology are susceptible to cracks occurring at the bottoms (groove bottoms) of the grooves (circumferential grooves and lateral grooves) formed in the tread, and their durability is also insufficient.

[0007] Therefore, an object of the present invention is to provide a pneumatic tire having sufficiently improved crack resistance and durability. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into solving the above problems, and have found that the above problems can be solved by the invention described below, thereby completing the present invention.

[0009] The invention described in claim 1 is A pneumatic tire having a tread portion with grooves formed on the surface thereof, the tread portion is formed with a first rubber composition constituting a groove bottom portion, and a second rubber composition adjacent to the first rubber composition on the inner side in the tire radial direction than the groove bottom portion, The first rubber composition and the second rubber composition each contain 60% by mass or more of SBR and 5% by mass or more of BR, When the acetone extractable content of the first rubber composition is E1% by mass and the acetone extractable content of the second rubber composition is E2% by mass, (E1-E2)<20; When the tire is mounted on a regular rim and the internal pressure is 250 kPa, the cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is the virtual volume V (mm 3 ), the pneumatic tire is characterized by satisfying the following (Formula 1) and (Formula 2). 1700≦(Dt 2 ×π / 4) / Wt≦2827.4 (Formula 1) [(V+1.5×10 7 ) / Wt]≦2.88×10 5 ...(Formula 2) The invention described in claim 2 is as follows: A pneumatic tire having a tread portion with grooves formed on the surface thereof, the tread portion is formed with a first rubber composition constituting a groove bottom portion, and a second rubber composition adjacent to the first rubber composition on the inner side in the tire radial direction than the groove bottom portion, The first rubber composition and the second rubber composition each contain 90% by mass or more of a diene-based rubber, and the diene-based rubber contains at least one of SBR, BR, and NR, When the acetone extractable content of the first rubber composition is E1% by mass and the acetone extractable content of the second rubber composition is E2% by mass, (E1-E2)<20; When the tire is mounted on a regular rim and the internal pressure is 250 kPa, the cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is the virtual volume V (mm 3 ), the pneumatic tire is characterized by satisfying the following (Formula 1) and (Formula 2). 1700≦(Dt 2 ×π / 4) / Wt≦2827.4 (Formula 1) [(V+1.5×10 7 ) / Wt]≦2.88×10 5 ...(Formula 2)

[0010] Claim 3 The invention described in The present invention is characterized in that the following formula (3) is satisfied: Or claim 2 The pneumatic tire is as described above. [(V+2.0×10 7 ) / Wt]≦2.88×10 5 ...(Formula 3)

[0011] Claim 4 The invention described in The present invention is characterized in that the following formula (4) is satisfied: 3 The pneumatic tire is as described above. [(V+2.5×10 7 ) / Wt]≦2.88×10 5 ·····(Formula 4)

[0012] Claim 5 The invention described in Claims 1 to 5, characterized in that, when the tire is mounted on a regular rim and the internal pressure is 250 kPa, the outer diameter of the tire is Dt (mm) and the cross-sectional height of the tire is Ht (mm), (Dt-2×Ht) is 470 (mm) or more. 4 13. The pneumatic tire according to claim 12,

[0013] Claim 6 The invention described in 10. The loss tangent (0°C tan δ) of the first rubber composition measured under conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain rate of 2.5% is 0.72 or more. 5 13. The pneumatic tire according to claim 12,

[0014] Claim 7 The invention described in 0°C tan δ is 0.75 or more. 6 The pneumatic tire is as described above.

[0015] Claim 8 The invention described in Claims 1 to 5, characterized in that the aspect ratio is 40% or more. 7 13. The pneumatic tire according to claim 12,

[0016] Claim 9 The invention described in The aspect ratio is 45% or more. 8 The pneumatic tire is as described above.

[0017] Claim 10 The invention described in The aspect ratio is 47.5% or more. 9 The pneumatic tire is as described above.

[0018] Claim 11 The invention described in Claims 1 to 5, wherein E1, E2 and Wt satisfy the following formula 5: 10 13. The pneumatic tire according to claim 12, (E1-E2)×Wt<5×10 3 ··············(Formula 5)

[0019] Claim 12 The invention described in The present invention is characterized in that the following formula (6) is satisfied: 11 The pneumatic tire is as described above. (E1-E2)×Wt<4×10 3 ·············(Formula 6)

[0020] Claim 13 The invention described in The present invention is characterized in that the following formula (7) is satisfied: 12 The pneumatic tire is as described above. (E1-E2)×Wt<3×10 3 ··············(Formula 7)

[0021] Claim 14 The invention described in The tire has a plurality of circumferential grooves in the tread portion, the circumferential grooves extending continuously in the tire circumferential direction. 10. The tire according to claim 1, wherein the total cross-sectional area of ​​the plurality of circumferential grooves is 10 to 30% of the cross-sectional area of ​​the tread portion. 13 13. The pneumatic tire according to claim 12,

[0022] Claim 15 The invention described in The tire has a plurality of axially extending lateral grooves in the tread portion, 10. The tire according to claim 1, wherein the total volume of the plurality of lateral grooves is 2.0 to 5.0% of the volume of the tread portion. 14 13. The pneumatic tire according to claim 12,

[0023] Claim 16 The invention described in Claims 1 to 5, characterized in that when the outer diameter of the tire is Dt (mm) when the tire is mounted on a regular rim and the internal pressure is 250 kPa, Dt is less than 685 (mm). 15 13. The pneumatic tire according to claim 12,

[0024] Claim 17 The invention described in 1 to 3, characterized in that the cross-sectional width Wt (mm) is less than 205 mm. 16 13. The pneumatic tire according to claim 12,

[0025] Claim 18 The invention described in 3. The cross-sectional width Wt (mm) is less than 200 mm. 17 The pneumatic tire is as described above.

[0026] Claim19 The invention described in 10. The present invention relates to a tire according to claim 1, wherein the ratio (0°C tan δ / Gd) of the loss tangent (0°C tan δ) of the first rubber composition to the thickness Gd (mm) of the groove bottom portion measured under conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain rate of 2.5% is 0.16 or less. 18 13. The pneumatic tire according to claim 12,

[0027] Claim 20 The invention described in 0°C tan δ / Gd is 0.14 or less. 19 The pneumatic tire is as described above. Effect of the Invention

[0028] According to the present invention, it is possible to provide a pneumatic tire having sufficiently improved crack resistance and durability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] [1] Characteristics of the tire according to the present invention First, the features of the tire according to the present invention will be described.

[0030] 1. Overview The tire according to the present invention has a tread portion having grooves formed on the surface thereof, and the tread portion is formed with a first rubber composition constituting a groove bottom portion and a second rubber composition adjacent to the first rubber composition on the inner side in the tire radial direction than the groove bottom portion. The first rubber composition and the second rubber composition each contain 60% by mass or more of SBR and 5% by mass or more of BR, or each contain 90% by mass or more of a diene rubber and contain at least one of SBR, BR and NR as the diene rubber. It is characterized by the presence of

[0031] The rubber composition is also characterized in that, when the acetone extractable content of the first rubber composition is E1 mass % and the acetone extractable content of the second rubber composition is E2 mass %, (E1-E2)<20.

[0032] Furthermore, the tire according to the present invention is mounted on a regular rim and the internal pressure is set to 250 kPa. The cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is a virtual volume V (mm 3 ), it is also characterized in that the following (Equation 1) and (Equation 2) are satisfied. 1700≦(Dt 2 ×π / 4) / Wt≦2827.4 (Formula 1) [(V+1.5×10 7 ) / Wt]≦2.88×10 5 ...(Formula 2)

[0033] By providing these characteristics, it is possible to provide a tire with substantially improved crack resistance and durability.

[0034] In the above description, the term "genuine rim" refers to a rim that is specified for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Manufacturers Association), it is the standard rim for the applicable size listed in the "JATMA YEAR BOOK", and in the case of ETRTO (The European Tyre and Rim Manufacturers Association), it is the standard rim for the applicable size listed in the "JATMA YEAR BOOK". For tires not specified by a standard, it refers to the rim with the smallest rim diameter and the next narrowest rim width that can be mounted on a rim and can hold internal pressure, that is, that does not cause air leakage between the rim and tire.

[0035] In addition, the outer diameter Dt of a tire is the outer diameter of the tire when it is mounted on a standard rim, with the internal pressure set to 250 kPa and no load applied, and the cross-sectional width Wt of a tire is the width obtained by excluding the patterns, letters, etc. on the side of the tire from the straight-line distance between the sidewalls (total width of the tire) including all patterns, letters, etc. on the side of the tire when the tire is mounted on a standard rim, with the internal pressure set to 250 kPa and no load applied.

[0036] In addition, the virtual volume of the tire V (mm 3 Specifically, the tire cross-sectional width (Wt) can be calculated by the following formula based on the tire outer diameter Dt (mm), tire cross-sectional height (the distance from the bottom of the bead to the outermost surface of the tread, which is half the difference between the tire outer diameter and the nominal rim diameter) Ht (mm), and tire cross-sectional width Wt (mm) when the tire is mounted on a regular rim and the internal pressure is set to 250 kPa with no load applied. V = [(Dt / 2) 2 -{(Dt / 2)-Ht} 2 ]×π×Wt

[0037] 2. Mechanism of effect manifestation in the tire according to the present invention The mechanism by which the tire according to the present invention exhibits its effects, that is, the mechanism by which the crack resistance and durability are sufficiently improved, is presumed to be as follows.

[0038] (1) Tire shape As described above, in the present invention, the tire cross-sectional width Wt (mm) and the outer diameter Dt (mm) are in the range of 1700≦(Dt 2 ×π / 4) / Wt≦2827.4 (Equation 1) is satisfied.

[0039] The above formula (1) is the area of ​​the tire when viewed from the side with respect to the cross-sectional width Wt [(Dt / 2) 2 ×π)=(Dt 2 × π / 4) so ​​as to satisfy the numerical range defined in Equation 1, it is believed that the heat dissipation properties of the side portion can be improved, and durability and low rolling resistance can be improved.

[0040] However, such tires experience large centrifugal forces when rolling, which causes the tire radius to grow significantly while rolling, potentially leading to cracks at the bottoms of the grooves (groove bottoms) formed in the tread portion.

[0041] Therefore, in the present invention, the virtual volume V (mm 3 ) and cross-sectional width Wt (mm) are [(V+1.5×10 7 ) / Wt]≦2.88×10 5 It is designed to satisfy (Equation 2).

[0042] In this way, by reducing the virtual volume V of the tire in accordance with the reduction in the cross-sectional width Wt of the tire and reducing the volume of the tire itself, the outer diameter growth rate due to centrifugal force can be reduced, and therefore the occurrence of cracks at the groove bottom can be suppressed. Note that in the present invention, the groove refers to all grooves provided on the tread surface, such as circumferential grooves and lateral grooves.

[0043] In this case, [(V+2.0×10 7 ) / Wt]≦2.88×10 5 It is more preferable that (Formula 3) is [(V+2.5×10 7 ) / Wt]≦2.88×10 5 It is more preferable that the formula is (Formula 4).

[0044] (2) Rubber composition forming the tread portion As described above, the tire according to the present invention has a tread portion including a first rubber composition constituting a groove bottom and a second rubber composition adjacent to the first rubber composition and radially inward of the groove bottom, and there is a relationship between the acetone extractable portion E1 (mass%) of the first rubber composition and the acetone extractable portion E2 (mass%) of the second rubber composition such that (E1-E2)<20.

[0045] This acetone extractable content can be considered as an index showing the amount of easily migrating components, such as softeners, in the rubber composition. If the difference (E1-E2) between the acetone extractable content (AE content) of the first rubber composition and the second rubber composition is small, the migration of easily migrating components from the first rubber composition to the second rubber composition is small, regardless of the type of rubber composition. In other words, by making (E1-E2) small, such as less than 20, the migration of softeners and the like at the bottom of the grooves is suppressed, regardless of the type of rubber composition, and it is believed that the occurrence of cracks can be suppressed.

[0046] The difference in acetone extractable content (AE amount) between the first rubber composition and the second rubber composition is preferably (E1-E2)<19, more preferably (E1-E2)<18, and further preferably (E1-E2)<17. The lower limit of (E1-E2) is not particularly limited, but is usually (E1-E2)>-40. The acetone extractable content of the rubber composition can be measured in accordance with JIS K 6229:2015 (extraction time: 10 hours).

[0047] The ground contact surface of the tread is preferably formed of a first rubber composition having the same composition as the groove bottom, and the specific configuration of the tread can be, for example, a combination of the first rubber composition as a cap rubber layer and the second rubber composition as a base rubber layer. The specific AE amounts in the first rubber composition and the second rubber composition are not particularly limited as long as the above-mentioned (E1-E2)<20, preferably (E1-E2)<19, more preferably (E1-E2)<18, and even more preferably (E1-E2)<17 is satisfied, but for both E1 and E2, it is 0 or more, preferably 3 or more, and more preferably 5 or more. For both E1 and E2, it is usually 40 or less, preferably 37 or less, and more preferably 35 or less.

[0048] [2] More preferred embodiments of the tire according to the present invention The tire according to the present invention can achieve even greater effects by adopting the following features.

[0049] 1. Flatness The tire according to the present invention preferably has an aspect ratio of 40% or more, which allows the area of ​​the side portion to be increased, which is believed to improve the heat dissipation properties of the entire tire and suppress a decrease in rigidity in the tread portion and side portion, thereby improving the durability of the tire.

[0050] The above aspect ratio (%) can be calculated by the following formula using the tire section height Ht (mm) and section width Wt (mm) when the internal pressure is set to 250 kPa. (Ht / Wt) x 100(%)

[0051] The above-mentioned aspect ratio is more preferably 45% or more, and even more preferably 47.5% or more. It is even more preferably 50% or more, particularly preferably 52.5% or more, and most preferably 55% or more. There is no particular upper limit, but it is, for example, 100% or less.

[0052] 2. Relationship between AE volume and cross-sectional width Wt (mm) As described above, the AE amount is an index that indicates the amount of easily migrating components, such as softeners, in the components of a rubber composition. By reducing the difference (E1-E2) in the AE amount between the first rubber composition and the second rubber composition, migration between the two rubber compositions can be suppressed, thereby suppressing the occurrence of cracks.

[0053] On the other hand, the larger the cross-sectional width Wt of a tire is, the greater the difference in the growth of the outer shape between the tread center portion and the shoulder portion becomes, which increases distortion in the groove portion and makes the tire more susceptible to cracking.

[0054] Therefore, we specifically examined the relationship between the difference in AE amount (E1-E2) and the cross-sectional width Wt, and found that (E1-E2)×Wt<5×10 3 It is preferable that (E1-E2)×Wt<4×10 3 It is more preferable that (E1-E2)×Wt<3×103 It has been found that it is more preferable that

[0055] 3. Tread grooves The tire according to the present invention has a circumferential groove in the tread portion that extends continuously in the tire circumferential direction, and the groove width L of the circumferential groove in the contact surface of the tread portion is 0 Groove width L at 80% of the maximum depth of the circumferential groove 80 Ratio (L 80 / L 0 ) is preferably 0.3 to 0.7. This makes it possible to suppress the movement of the entire land portion at the bottom surface of the land portion of the tread portion, and is believed to suppress chipping of the tread portion and improve durability. It is more preferably 0.35 to 0.65, even more preferably 0.40 to 0.60, and particularly preferably 0.45 to 0.55.

[0056] The above L 0 and L 80 is the linear distance (L) between the ends of the circumferential grooves on the tread surface of a tire mounted on a regular rim, with an internal pressure of 250 kPa and no load applied. 0 ), and the minimum distance of the groove wall at 80% of the groove depth (L 80 ) and can be calculated simply by cutting a section of the tire 2 to 4 cm wide in the radial direction and pressing the space between the beads to match the width of the rim.

[0057] It is preferable that the tread portion has a plurality of circumferential grooves, and the total cross-sectional area of ​​the plurality of circumferential grooves is 10 to 30% of the cross-sectional area of ​​the tread portion. This is believed to suppress movement of the tread portion and suppress chipping of the tread portion, thereby improving durability. It is more preferable that it is 15 to 27%, even more preferable that it is 18 to 25%, and particularly preferable that it is 21 to 23%.

[0058] The cross-sectional area of ​​the circumferential grooves mentioned above refers to the total area defined by the straight line connecting the ends of the tread circumferential grooves and the groove walls when the tire is mounted on a regular rim, the internal pressure is 250 kPa, and the tire is in an unloaded state. In simple terms, the cross-sectional area can be determined by cutting the tire in a radial direction with a width of 2 to 4 cm and pressing the space between the bead portions to match the width of the rim.

[0059] In addition, it is preferable that the tread portion has a plurality of lateral grooves extending in the tire axial direction, and the total volume of the plurality of lateral grooves is 2.0 to 5.0% of the volume of the tread portion. This is believed to suppress the movement of the tread portion and suppress chipping of the tread portion, thereby improving durability. It is more preferable that it is 2.2 to 4.0%, even more preferable that it is 2.5 to 3.5%, and particularly preferable that it is 2.7 to 3.0%.

[0060] The volume of the lateral grooves mentioned above refers to the total volume of the surfaces connecting the ends of the lateral grooves and the groove walls in a tire mounted on a regular rim with an internal pressure of 250 kPa and no load, and can be calculated simply by calculating the volume of each lateral groove in a state where the tire is cut out in a radial direction with a width of 2 to 4 cm and pressed down between the beads to match the rim width, and multiplying the volume by the number of grooves. The volume of the tread portion can be calculated by calculating the area of ​​the part of the tread portion not including the lateral grooves from the section, multiplying it by the outer diameter, and calculating the difference between the volume of the lateral grooves.

[0061] In order to suppress chipping of the tread portion and further improve durability, it is preferable that these lateral grooves include lateral grooves having a ratio (Gw / Gd) of groove width Gw to groove depth Gd of 0.50 to 0.80, more preferably 0.53 to 0.77, even more preferably 0.55 to 0.75, and particularly preferably 0.60 to 0.70.

[0062] The groove width and groove depth of the lateral grooves mentioned above refer to the maximum straight line connecting the tread surface ends of the lateral grooves that is perpendicular to the groove direction and the maximum depth of the lateral grooves when the tire is under no load and the internal pressure is 250 kPa. Simply put, these can be calculated from the state in which the space between the bead portions of a section 2 to 4 cm wide cut out of the tire in the radial direction is pressed down to match the rim width.

[0063] 4. Tire shape In the tire according to the present invention, when the tire is mounted on a regular rim and the internal pressure is set to 250 kPa, the specific outer diameter Dt (mm) is, for example, preferably 515 mm or more, more preferably 558 mm or more, even more preferably 585 mm or more, particularly preferably 658 mm or more, and most preferably 673 mm or more. On the other hand, it is preferably less than 843 mm, more preferably less than 725 mm, even more preferably less than 707 mm, particularly preferably less than 685 mm, and most preferably less than 655 mm.

[0064] The specific cross-sectional width Wt (mm) is, for example, preferably 115 mm or more, more preferably 130 mm or more, even more preferably 150 mm or more, even more preferably 170 mm or more, particularly preferably 185 mm or more, and most preferably 193 mm or more. On the other hand, it is preferably less than 305 mm, more preferably less than 245 mm, even more preferably less than 210 mm, particularly preferably less than 205 mm, and most preferably less than 200 mm.

[0065] Specifically, the cross-sectional height Ht (mm) is, for example, preferably 37 mm or more, more preferably 87 mm or more, and even more preferably 95 mm or more, while it is preferably less than 180 mm, more preferably less than 112 mm, and even more preferably less than 101 mm.

[0066] A specific virtual volume V is, for example, 13,000,000 mm3 It is preferable that the length is 29,000,000 mm or more. 3 More preferably, it is 36,000,000 mm or more. 3 More preferably, the thickness is 66,000,000 mm or more. 3 Preferably less than 44,000,000 mm 3 Preferably less than 38,800,000 mm 3 It is even more preferable that it is less than 1000 .mu.m.

[0067] In the present invention, in consideration of the stability of the ride comfort during running, (Dt-2×Ht) is preferably 450 (mm) or more, more preferably 470 (mm) or more, and even more preferably 480 (mm) or more. On the other hand, in consideration of the deformation of the tread portion, it is preferably less than 560 (mm), more preferably less than 530 (mm), and even more preferably less than 510 (mm).

[0068] 5. Loss tangent of the first rubber composition In the present invention, the first rubber composition constituting the groove bottom preferably has a loss tangent (0°C tan δ) of 0.72 or more measured under the conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain rate of 2.5%. This allows the effect of the present invention, namely, improved crack resistance and durability, to be fully exhibited. It is more preferable that the loss tangent is 0.75 or more, and even more preferable that the loss tangent is 0.78 or more.

[0069] The loss tangent (0° C. tan δ) can be measured, for example, by using a viscoelasticity measuring device, “IPLEXER (registered trademark)” manufactured by GABO.

[0070] The ratio 0°C tan δ / Gd of 0°C tan δ to the thickness of the groove bottom (the distance from the groove bottom surface to the cord layer in the tire radial direction) Gd (mm) is preferably 0.16 or less. This allows the effect of the present invention, namely, improved crack resistance and durability, to be fully exhibited. It is more preferable that the ratio is 0.14 or less, and even more preferable that the ratio is 0.12 or less.

[0071] The groove bottom referred to here may be the groove bottom of any circumferential groove, but it is preferable that at least the groove bottom of the circumferential groove having the largest groove bottom width (length in the tire width direction) satisfies the above relationship, and it is more preferable that the groove bottoms of all circumferential grooves satisfy the above relationship.

[0072] [3] Implementation form Hereinafter, the present invention will be described in detail based on the embodiments.

[0073] 1. Rubber composition The rubber composition forming the tread portion of the tire according to the present invention can be obtained by appropriately adjusting the types and amounts of various compounding materials such as the rubber component, filler, softener, vulcanizing agent, and vulcanization accelerator described below. In particular, by appropriately adjusting the softener and resin component, a rubber composition having the above-mentioned AE amount can be obtained.

[0074] (1) Rubber component In the present embodiment, the rubber component may be a rubber (polymer) that is generally used in tire manufacturing, such as styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene-based rubber (IR) including natural rubber (NR), nitrile rubber (NBR), etc. If these rubbers (polymers) are used, the crack resistance and durability of the pneumatic tire can be improved by satisfying (E1-E2)<20, preferably (E1-E2)<19, more preferably (E1-E2)<18, and even more preferably (E1-E2)<17, and further satisfying (Formula 1) and (Formula 2), regardless of the type of rubber component. Among them, it is preferable to use a rubber component containing diene rubber as the main component (90 mass% or more) for both the first rubber composition and the second rubber composition. Here, examples of diene rubber include IR including natural rubber (NR), SBR, BR, NBR, and modified versions of these. One selected from these may be used alone, or a blend of two or more may be used. Among the diene rubbers, it is particularly preferable to use SBR and BR.

[0075] (a) SBR The amount of SBR in 100 parts by mass of the rubber component is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more, while it is preferably 100 parts by mass or less, and more preferably 95 parts by mass or less.

[0076] The weight average molecular weight of SBR is, for example, more than 100,000 and less than 2,000,000. The styrene content of SBR is 5% by mass or more, particularly 8% by mass or more. Also, it is preferably less than 35% by mass, more preferably less than 25% by mass, and even more preferably less than 15% by mass. The vinyl bond amount (amount of 1,2-bonded butadiene units) of SBR is, for example, more than 5% by mass and less than 70% by mass. The structure of SBR (measurement of styrene content and vinyl bond amount) can be performed using, for example, a JNM-ECA series device manufactured by JEOL Ltd.

[0077] There are no particular limitations on the SBR, and examples of the SBR that can be used include emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. The SBR may be either unmodified SBR or modified SBR, which may be used alone or in combination of two or more kinds.

[0078] The modified SBR may be any SBR having a functional group that interacts with a filler such as silica, and examples thereof include terminal-modified SBR in which at least one end of SBR has been modified with a compound (modifying agent) having the above-mentioned functional group (terminal-modified SBR having the above-mentioned functional group at the end), main-chain-modified SBR in which the main chain has the above-mentioned functional group, main-chain-terminal-modified SBR in which the main chain and at least one end are modified with the above-mentioned modifier, and terminal-modified SBR modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or epoxy group introduced therein.

[0079] Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, etc. These functional groups may have a substituent.

[0080] Furthermore, as the modified SBR, for example, SBR modified with a compound (modifying agent) represented by the following formula can be used.

[0081] [ka]

[0082] In the formula, R 1 , R 2 and R 3 R may be the same or different and represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (-COOH), a mercapto group (-SH), or a derivative thereof. 4 and R 5 R may be the same or different and represents a hydrogen atom or an alkyl group. 4 and R 5may bond to form a ring structure together with the nitrogen atom, and n represents an integer.

[0083] As the modified SBR modified with a compound (modifying agent) represented by the above formula, SBR whose polymerization terminals (active terminals) have been modified with a compound represented by the above formula can be used.

[0084] R 1 , R 2 and R 3 R is preferably an alkoxy group, more preferably an alkoxy group having 1 to 8 carbon atoms, and further preferably an alkoxy group having 1 to 4 carbon atoms. 4 and R 5 is preferably an alkyl group, more preferably an alkyl group having 1 to 3 carbon atoms. n is preferably 1 to 5, more preferably 2 to 4, and further preferably 3. In addition, R 4 and R 5 When the nitrogen atom and the nitrogen atom are bonded to each other to form a ring structure, the ring is preferably a 4- to 8-membered ring. The alkoxy group also includes a cycloalkoxy group (such as a cyclohexyloxy group) and an aryloxy group (such as a phenoxy group and a benzyloxy group).

[0085] Specific examples of the modifying agent include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, etc. These may be used alone or in combination of two or more.

[0086] In addition, modified SBR modified with the following compounds (modifiers) can also be used as the modified SBR. Examples of the modifiers include polyglycidyl ethers of polyhydric alcohols such as ethylene glycol diglycidyl ether, glycerin triglycidyl ether, trimethylolethane triglycidyl ether, and trimethylolpropane triglycidyl ether; polyglycidyl ethers of aromatic compounds having two or more phenol groups such as diglycidylated bisphenol A; polyepoxy compounds such as 1,4-diglycidylbenzene, 1,3,5-triglycidylbenzene, and polyepoxidized liquid polybutadiene; epoxy group-containing tertiary amines such as 4,4'-diglycidyl-diphenylmethylamine and 4,4'-diglycidyl-dibenzylmethylamine; diglycidylaniline, N,N'-diglycidyl-4-glycidyloxyaniline, Diglycidyl amino compounds such as diglycidyl orthotoluidine, tetraglycidyl meta-xylylenediamine, tetraglycidyl aminodiphenylmethane, tetraglycidyl-p-phenylenediamine, diglycidyl aminomethylcyclohexane, and tetraglycidyl-1,3-bisaminomethylcyclohexane; amino group-containing acid chlorides such as bis-(1-methylpropyl)carbamic acid chloride, 4-morpholinecarbonyl chloride, 1-pyrrolidinecarbonyl chloride, N,N-dimethylcarbamic acid chloride, and N,N-diethylcarbamic acid chloride; epoxy group-containing silane compounds such as 1,3-bis-(glycidyloxypropyl)-tetramethyldisiloxane and (3-glycidyloxypropyl)-pentamethyldisiloxane;(Trimethylsilyl)[3-(trimethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(triethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(trippropoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(tributoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(methyldimethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(methyldiethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(methyldipropoxy sulfide group-containing silane compounds such as (trimethylsilyl)[3-(methyldibutoxysilyl)propyl]sulfide and (trimethylsilyl)[3-(methyldibutoxysilyl)propyl]sulfide; N-substituted aziridine compounds such as ethyleneimine and propyleneimine; methyltriethoxysilane, N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)-3-aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminoethyltrimethoxysilane, N,N-bis(trimethylsilyl)aminoethyltrimethoxysilane, Alkoxysilanes such as thyltriethoxysilane; (thio)benzophenone compounds having amino groups and / or substituted amino groups, such as 4-N,N-dimethylaminobenzophenone, 4-N,N-di-t-butylaminobenzophenone, 4-N,N-diphenylaminobenzophenone, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(diphenylamino)benzophenone, and N,N,N',N'-bis-(tetraethylamino)benzophenone; Benzaldehyde compounds having an amino group and / or a substituted amino group, such as dimethylaminobenzaldehyde, 4-N,N-diphenylaminobenzaldehyde, 4-N,N-divinylaminobenzaldehyde, etc.; N-substituted pyrrolidones, such as N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, Nt-butyl-2-pyrrolidone, N-methyl-5-methyl-2-pyrrolidone, etc.; N-substituted piperidones, such as N-methyl-2-piperidone, N-vinyl-2-piperidone, N-phenyl-2-piperidone, etc.;N-substituted lactams such as N-methyl-ε-caprolactam, N-phenyl-ε-caprolactam, N-methyl-ω-laurylolactam, N-vinyl-ω-laurylolactam, N-methyl-β-propiolactam, and N-phenyl-β-propiolactam, as well as N,N-bis-(2,3-epoxypropoxy)-aniline, 4,4-methylene-bis-(N,N-glycidylaniline), and tris-(2,3-epoxypropyl)-1,3,5-triazine-2,4,6-trione , N,N-diethylacetamide, N-methylmaleimide, N,N-diethylurea, 1,3-dimethylethyleneurea, 1,3-divinylethyleneurea, 1,3-diethyl-2-imidazolidinone, 1-methyl-3-ethyl-2-imidazolidinone, 4-N,N-dimethylaminoacetophene, 4-N,N-diethylaminoacetophenone, 1,3-bis(diphenylamino)-2-propanone, 1,7-bis(methylethylamino)-4-heptanone, etc. Modification with the above compounds (modifiers) can be carried out by known methods.

[0087] As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. may be used. The SBR may be used alone or in combination of two or more kinds.

[0088] (b)BR The amount of BR in 100 parts by mass of the rubber component is preferably 5 parts by mass or more and 15 parts by mass or less.

[0089] The weight average molecular weight of the BR is, for example, more than 100,000 and less than 2,000,000. The vinyl bond amount of the BR is, for example, more than 1 mass% and less than 30 mass%. The cis content of the BR is, for example, more than 1 mass% and less than 98 mass%. The trans content of the BR is, for example, more than 1 mass% and less than 60 mass%. The cis content can be measured by infrared absorption spectroscopy.

[0090] The BR is not particularly limited, and BR with a high cis content (cis content of 90% or more), BR with a low cis content, BR containing syndiotactic polybutadiene crystals, etc. can be used. The BR may be either unmodified BR or modified BR, and the modified BR may be modified BR into which the above-mentioned functional groups have been introduced. These may be used alone or in combination of two or more. The cis content can be measured by infrared absorption spectroscopy.

[0091] As the BR, for example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used.

[0092] (c) Other rubber components In this embodiment, as described above, the other rubber components may include rubbers (polymers) that are generally used in the manufacture of tires, such as isoprene-based rubber (IR) and nitrile rubber (NBR).

[0093] (2) Compounding materials other than rubber components (a) Filler In the present embodiment, the rubber composition preferably contains a filler. Specific examples of the filler include silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. Among these, silica and carbon black are preferably used as reinforcing agents. When silica is used, it is preferable to use it in combination with a silane coupling agent.

[0094] (a) Silica The rubber composition preferably contains silica as a reinforcing filler. The BET specific surface area of ​​the silica is 140 m from the viewpoint of obtaining good durability. 2 / g or more is preferable, and 160m 2 On the other hand, from the viewpoint of obtaining good rolling resistance during high-speed driving, a tire having a rolling resistance of 250 m 2 / g or less is preferable, and 220m 2The BET specific surface area is preferably less than N / g. 2 This is the SA value.

[0095] When silica is used as a reinforcing filler, the content of the silica in the first rubber composition is preferably 40 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 80 parts by mass or more, per 100 parts by mass of the rubber component. On the other hand, it is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 120 parts by mass or less. In the case of the second rubber composition, the AE amount increases or decreases inversely to the increase or decrease in the silica content, so the content is appropriately adjusted according to the desired AE amount.

[0096] Examples of silica include dry process silica (anhydrous silica), wet process silica (hydrated silica), etc. Among these, wet process silica is preferred because it has a large number of silanol groups.

[0097] As the silica, for example, products manufactured by Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Corporation, etc. can be used.

[0098] (b) Silane coupling agent The rubber composition preferably contains a silane coupling agent together with silica. The silane coupling agent is not particularly limited, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl silane, and the like. Examples of the silane include sulfide-based silanes such as rubamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide, mercapto-based silanes such as 3-mercaptopropyl trimethoxysilane, 2-mercaptoethyl triethoxysilane, and NXT and NXT-Z manufactured by Momentive, vinyl-based silanes such as vinyl triethoxysilane and vinyl trimethoxysilane, amino-based silanes such as 3-aminopropyl triethoxysilane and 3-aminopropyl trimethoxysilane, glycidoxy-based silanes such as γ-glycidoxypropyl triethoxysilane and γ-glycidoxypropyl trimethoxysilane, nitro-based silanes such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane, and chloro-based silanes such as 3-chloropropyl trimethoxysilane and 3-chloropropyl triethoxysilane. These may be used alone or in combination of two or more.

[0099] As the silane coupling agent, for example, products available from Degussa, Momentive, Shin-Etsu Silicones, Tokyo Chemical Industry, Azumax, Dow Corning Toray, etc. can be used.

[0100] The content of the silane coupling agent is, for example, more than 3 parts by mass and less than 25 parts by mass relative to 100 parts by mass of silica.

[0101] (c) Carbon black The rubber composition preferably contains carbon black. The content of carbon black in the first rubber composition is, for example, more than 1 part by mass and less than 200 parts by mass per 100 parts by mass of the rubber component. In the case of the second rubber composition, the AE amount increases or decreases inversely to the increase or decrease in the carbon black content, so the content is appropriately adjusted according to the desired AE amount.

[0102] The carbon black is not particularly limited, and examples thereof include furnace black (furnace carbon black) such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF and ECF; acetylene black (acetylene carbon black); thermal black (thermal carbon black) such as FT and MT; channel black (channel carbon black) such as EPC, MPC and CC; graphite, etc. These may be used alone or in combination of two or more.

[0103] The nitrogen adsorption specific surface area of ​​carbon black (N 2 SA) is, for example, 30m 2 / g over 250m 2 The carbon black has a dibutyl phthalate (DBP) absorption of, for example, more than 50 ml / 100 g and less than 250 ml / 100 g. The nitrogen adsorption specific surface area of ​​the carbon black is measured according to ASTM D4820-93, and the DBP absorption is measured according to ASTM D2414-93.

[0104] Specific carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Co., Ltd., Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These may be used alone or in combination of two or more kinds.

[0105] (D) Other fillers In addition to the above-mentioned carbon black and silica, the rubber composition may further contain fillers commonly used in the tire industry, such as calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, etc. The content of these fillers is, for example, more than 0.1 parts by mass and less than 200 parts by mass per 100 parts by mass of the rubber component.

[0106] (b) Softener The rubber composition may contain oil (including extender oil) or liquid rubber as a softener. In the case of the first rubber composition, the total content of these is, for example, preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 25 parts by mass or more, per 100 parts by mass of the rubber component. Also, it is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less. The oil content includes the amount of oil contained in the rubber (oil-extended rubber). In the case of the second rubber composition, the AE amount increases or decreases according to the increase or decrease in the softener content, so the content is appropriately adjusted according to the desired AE amount.

[0107] Examples of oils include mineral oils (generally referred to as process oils), vegetable oils, and mixtures thereof. Examples of mineral oils (process oils) that can be used include paraffin-based process oils, aromatic process oils, and naphthenic process oils. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil.

[0108] Specific examples of process oils (mineral oils) that can be used include products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Co., Ltd., Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., and the like.

[0109] The liquid rubbers mentioned as softeners are polymers that are in a liquid state at room temperature (25° C.) and contain the same monomers as solid rubbers. Examples of liquid rubbers include farnesene-based polymers, liquid diene-based polymers, and hydrogenated products thereof.

[0110] Farnesene polymers are polymers obtained by polymerizing farnesene and contain structural units based on farnesene. Farnesene has isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene).

[0111] The farnesene-based polymer may be a homopolymer of farnesene (farnesene homopolymer) or a copolymer of farnesene and a vinyl monomer (farnesene-vinyl monomer copolymer).

[0112] Examples of liquid diene polymers include liquid styrene-butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), and liquid styrene-isoprene copolymer (liquid SIR).

[0113] The liquid diene polymer has a weight average molecular weight (Mw) of, for example, 1.0×10 3 Super, 2.0×10 5 In this specification, the Mw of the liquid diene polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0114] The amount of the liquid polymer (total amount of the liquid farnesene polymer, liquid diene polymer, etc.) is, for example, more than 1 part by mass and less than 100 parts by mass per 100 parts by mass of the rubber component.

[0115] As the liquid rubber, for example, products of Kuraray Co., Ltd., Cray Valley Co., Ltd., etc. can be used.

[0116] (c) Resin component The rubber composition preferably contains a resin component as necessary. The resin component may be solid or liquid at room temperature. Specific examples of the resin component include styrene resin, coumarone resin, terpene resin, C5 resin, C9 resin, C5C9 resin, and acrylic resin, and two or more of them may be used in combination. In the case of the first rubber composition, the content of the resin component is, for example, preferably more than 20 parts by mass, more preferably more than 30 parts by mass, relative to 100 parts by mass of the rubber component. Also, it is preferably less than 70 parts by mass, more preferably less than 50 parts by mass. In the case of the second rubber composition, the AE amount increases or decreases according to the increase or decrease in the content of the resin component, so the content is appropriately adjusted according to the desired AE amount.

[0117] The styrene resin is a polymer using a styrene monomer as a constituent monomer, and examples thereof include polymers polymerized with a styrene monomer as the main component (50% by mass or more).Specific examples thereof include homopolymers obtained by polymerizing each of the styrene monomers (styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.) alone, copolymers obtained by copolymerizing two or more kinds of styrene monomers, and copolymers of a styrene monomer and another monomer that can be copolymerized therewith.

[0118] Examples of the other monomer include acrylonitriles such as acrylonitrile and methacrylonitrile, unsaturated carboxylic acids such as acrylics and methacrylic acid, unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate, dienes such as chloroprene and butadiene-isoprene, olefins such as 1-butene and 1-pentene, α,β-unsaturated carboxylic acids such as maleic anhydride, or acid anhydrides thereof.

[0119] Among the coumarone resins, coumarone-indene resins are preferred. Coumarone-indene resins are resins that contain coumarone and indene as monomer components that constitute the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

[0120] The amount of the coumarone-indene resin per 100 parts by mass of the rubber component is, for example, more than 1.0 part by mass and less than 50.0 parts by mass.

[0121] The hydroxyl value (OH value) of the coumarone-indene resin is, for example, more than 15 mgKOH / g and less than 150 mgKOH / g. The OH value is the amount of potassium hydroxide required to neutralize acetic acid bonded to hydroxyl groups when acetylating 1 g of the resin, expressed in milligrams, and is a value measured by potentiometric titration (JIS K 0070:1992).

[0122] The softening point of the coumarone-indene resin is, for example, more than 30° C. and less than 160° C. The softening point is the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

[0123] Terpene resins include polyterpene, terpene phenol, and aromatic modified terpene resins. Polyterpenes are resins obtained by polymerizing terpene compounds and their hydrogenated products. Terpene compounds are (C 5 H 8 ) n The hydrocarbons and their oxygen-containing derivatives are represented by the following composition: Monoterpenes (C 10 H 16 ), sesquiterpenes (C 15 H 24 ), diterpenes (C 20 H 32 ), and examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol.

[0124] Examples of polyterpenes include terpene resins such as α-pinene resin, β-pinene resin, limonene resin, dipentene resin, and β-pinene / limonene resin, which are made from the above-mentioned terpene compounds, as well as hydrogenated terpene resins obtained by hydrogenating the terpene resins. Examples of terpene phenols include resins obtained by copolymerizing the above-mentioned terpene compounds with phenolic compounds, and resins obtained by hydrogenating the above-mentioned resins, and specifically include resins obtained by condensing the above-mentioned terpene compounds, phenolic compounds, and formalin. Examples of phenolic compounds include, for example, phenol, bisphenol A, cresol, and xylenol. Examples of aromatic modified terpene resins include resins obtained by modifying terpene resins with aromatic compounds, and resins obtained by hydrogenating the above-mentioned resins. The aromatic compound is not particularly limited as long as it is a compound having an aromatic ring, and examples thereof include phenolic compounds such as phenol, alkylphenols, alkoxyphenols, and phenols containing an unsaturated hydrocarbon group; naphthol compounds such as naphthol, alkylnaphthols, alkoxynaphthols, and naphthols containing an unsaturated hydrocarbon group; styrene derivatives such as styrene, alkylstyrenes, alkoxystyrenes, and styrenes containing an unsaturated hydrocarbon group; coumarone, indene, and the like.

[0125] "C5 resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. As a C5 petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0126] The term "C9 resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a resin obtained by hydrogenating or modifying the resin. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of suitable resins include coumarone-indene resins, coumarone resins, indene resins, and aromatic vinyl resins. As aromatic vinyl resins, homopolymers of α-methylstyrene or styrene or copolymers of α-methylstyrene and styrene are preferred, and copolymers of α-methylstyrene and styrene are more preferred, because they are economical, easy to process, and have excellent heat generation properties. As aromatic vinyl resins, for example, those commercially available from Kraton, Eastman Chemical, etc. can be used.

[0127] The term "C5C9 resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions. As the C5C9 resin, for example, those commercially available from Tosoh Corporation, LUHUA, etc. can be used.

[0128] The acrylic resin is not particularly limited, but for example, a solventless acrylic resin can be used.

[0129] Examples of the solvent-free acrylic resin include (meth)acrylic resins (polymers) synthesized by high-temperature continuous polymerization (high-temperature continuous bulk polymerization) (methods described in U.S. Pat. No. 4,414,370, JP-A-59-6207, JP-B-5-58005, JP-A-1-313522, U.S. Pat. No. 5,010,166, and Toa Gosei Kenkyuu Nenpo TREND 2000 Vol. 3, p. 42-45, etc.) using as little secondary raw material as possible, such as polymerization initiators, chain transfer agents, and organic solvents. In the present invention, (meth)acrylic means methacryl and acrylic.

[0130] Examples of monomer components constituting the acrylic resin include (meth)acrylic acid, (meth)acrylic acid esters (alkyl esters, aryl esters, aralkyl esters, etc.), (meth)acrylamide, and (meth)acrylic acid derivatives such as (meth)acrylamide derivatives.

[0131] In addition, aromatic vinyls such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, and divinylnaphthalene may be used together with (meth)acrylic acid or a (meth)acrylic acid derivative as a monomer component constituting the acrylic resin.

[0132] The acrylic resin may be a resin composed only of a (meth)acrylic component, or a resin containing components other than the (meth)acrylic component as constituent elements. The acrylic resin may have a hydroxyl group, a carboxyl group, a silanol group, or the like.

[0133] Examples of the resin component that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JX Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

[0134] (d) Antioxidants The rubber composition preferably contains an antioxidant. The content of the antioxidant is, for example, more than 1 part by mass and less than 10 parts by mass per 100 parts by mass of the rubber component.

[0135] Examples of the antioxidant include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine. p-phenylenediamine-based antioxidants such as quinolinone, quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline, monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol, and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. These may be used alone or in combination of two or more.

[0136] As the antioxidant, for example, products available from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., Flexis, etc. can be used.

[0137] (e) Stearic acid The rubber composition may contain stearic acid. The content of stearic acid is, for example, more than 0.5 parts by mass and less than 10.0 parts by mass with respect to 100 parts by mass of the rubber component. As the stearic acid, a conventionally known product can be used, for example, a product from NOF Corporation, NOF Corporation, Kao Corporation, FUJIFILM Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc. can be used.

[0138] (f) Zinc oxide The rubber composition may contain zinc oxide. The content of zinc oxide is, for example, more than 0.5 parts by mass and less than 10 parts by mass with respect to 100 parts by mass of the rubber component. As the zinc oxide, a conventionally known product can be used, for example, a product of Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

[0139] (g) Wax Each rubber composition preferably contains a wax. The wax content is, for example, 0.5 to 20 parts by mass, preferably 1.5 to 15 parts by mass, and more preferably 3.0 to 10.0 parts by mass, per 100 parts by mass of the rubber component.

[0140] The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax, natural waxes such as vegetable wax and animal wax, synthetic waxes such as ethylene and propylene polymers, etc. These may be used alone or in combination of two or more kinds.

[0141] As the wax, for example, products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used.

[0142] (h) Crosslinking agents and vulcanization accelerators The rubber composition preferably contains a crosslinking agent such as sulfur, etc. The content of the crosslinking agent is, for example, more than 0.1 parts by mass and less than 10.0 parts by mass per 100 parts by mass of the rubber component.

[0143] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. These may be used alone or in combination of two or more kinds.

[0144] As sulfur, for example, products from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanritsu Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used.

[0145] Examples of crosslinking agents other than sulfur include vulcanizing agents containing sulfur atoms, such as TACKIROL V200 manufactured by Taoka Chemical Co., Ltd., DURALINK HTS (sodium 1,6-hexamethylenedithiosulfate dihydrate) manufactured by Flexsys, and KA9188 (1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane) manufactured by LANXESS, as well as organic peroxides such as dicumyl peroxide.

[0146] The rubber composition preferably contains a vulcanization accelerator. The content of the vulcanization accelerator is, for example, more than 0.3 parts by mass and less than 10.0 parts by mass per 100 parts by mass of the rubber component.

[0147] Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, Nt-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenyl guanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more kinds.

[0148] (i) Other In addition to the above components, the rubber composition may further contain additives commonly used in the tire industry, such as fatty acid metal salts, carboxylate metal salts, organic peroxides, etc. The content of these additives is, for example, more than 0.1 parts by mass and less than 200 parts by mass per 100 parts by mass of the rubber component.

[0149] 2. Preparation of tread rubber composition The rubber composition is produced by a general method, for example, a manufacturing method including a base kneading step of kneading a rubber component with a filler such as silica or carbon black, and a finish kneading step of kneading the kneaded product obtained in the base kneading step with a crosslinking agent.

[0150] The kneading can be carried out using a known (internal) kneading machine such as a Banbury mixer, a kneader, or an open roll.

[0151] The kneading temperature in the base kneading step is, for example, more than 50° C. and less than 200° C., and the kneading time is, for example, more than 30 seconds and less than 30 minutes. In the base kneading step, in addition to the above-mentioned components, compounding agents conventionally used in the rubber industry, for example, softeners such as oil, stearic acid, zinc oxide, antioxidants, waxes, vulcanization accelerators, etc. may be appropriately added and kneaded as necessary.

[0152] In the final kneading step, the kneaded product obtained in the base kneading step is kneaded with a crosslinking agent. The kneading temperature in the final kneading step is, for example, higher than room temperature and lower than 80° C., and the kneading time is, for example, longer than 1 minute and shorter than 15 minutes. In the final kneading step, in addition to the above components, a vulcanization accelerator, zinc oxide, etc. may be appropriately added and kneaded as necessary.

[0153] As described above, in this kneading operation, the contents of the softener and the resin component can be adjusted to obtain the first rubber composition or the second rubber composition.

[0154] 3. Tire manufacturing The tire of the present invention is manufactured by a normal method using the unvulcanized rubber composition obtained through the above-mentioned finish mixing process. Specifically, for example, the first rubber composition is molded as a cap rubber constituting the bottom of the groove, and the second rubber composition is molded adjacent to the cap rubber on the radially inner side of the tire as a base rubber to obtain a tread.

[0155] Next, the tire is molded together with other tire components in a normal manner on a tire building machine to produce an unvulcanized tire. Specifically, an inner liner as a component for ensuring airtightness of the tire, a carcass as a component for enduring the load, impact, and filling air pressure received by the tire, and a belt as a component for tightening the carcass and increasing the rigidity of the tread are wound around a molding drum, both ends of the carcass are fixed to both side edges, and bead portions as components for fixing the tire to the rim are arranged to mold the tire into a toroidal shape, and then a tread is attached to the center of the outer periphery, and a sidewall portion as a component for protecting the carcass and enduring bending is attached to the radially outer side to produce an unvulcanized tire.

[0156] In this embodiment, it is preferable to provide an inclined belt layer extending at an angle of 15° to 30° with respect to the tire circumferential direction as the belt, which ensures the durability of the tire and can sufficiently maintain the rigidity of the tread. In addition, since the tire can be restrained in the circumferential direction, it is easy to suppress the growth of the outer diameter.

[0157] The unvulcanized tire thus produced is then heated and pressurized in a vulcanizer to obtain a tire. The vulcanization step can be carried out by applying a known vulcanization method. The vulcanization temperature is, for example, more than 120°C and less than 200°C, and the vulcanization time is, for example, more than 5 minutes and less than 15 minutes.

[0158] At this time, the tire is molded into a shape that satisfies the above-mentioned (Equation 1) and (Equation 2) when mounted on a regular rim and the internal pressure is set to 250 kPa. When a sealing material layer, sponge material, or electronic parts such as sensors, which will be described later, are provided inside the tire, it is preferable to attach these to the inner surface of the vulcanized tire.

[0159] Specific examples of tires that can satisfy the above (Formula 1) and (Formula 2) include tires with size descriptions such as 145 / 60R18, 145 / 60R19, 155 / 55R18, 155 / 55R19, 155 / 70R17, 155 / 70R19, 165 / 55R20, 165 / 55R21, 165 / 60R19, 165 / 65R19, 165 / 70R18, 175 / 55R19, 175 / 55R20, 175 / 55R22, 175 / 60R18, 185 / 55R19, 185 / 60R20, 195 / 50R20, and 195 / 55R20.

[0160] In this embodiment, among tires that can satisfy (Formula 1) and (Formula 2), it is preferable to apply the present invention to pneumatic tires for passenger cars, and by satisfying (Formula 1) and (Formula 2), it is possible to more suitably contribute to solving the problem of the present invention, which is to provide a pneumatic tire that not only has low rolling resistance and excellent fuel efficiency performance, but also has sufficiently improved crack resistance and durability performance. Note that the passenger car tire referred to here is a tire that is mounted on a vehicle that runs on four wheels and has a maximum load capacity of 1000 kg or less. The pneumatic tire of the present invention may have a sealant layer for preventing punctures on the inner peripheral surface of the tread portion, and may further have a sponge material bonded to the inner peripheral surface of the sealant layer. Furthermore, the pneumatic tire may be provided with electronic components such as sensors inside. EXAMPLES

[0161] The present invention will be described in more detail below with reference to examples. In the following, a two-layer tread is produced using a first rubber composition as a cap rubber and a second rubber composition as a base rubber, and the AE amount is changed by changing the compounding of the second rubber composition relative to the compounding of the first rubber composition, but this does not prevent other embodiments from being adopted.

[0162] [Production of rubber composition for tread 1] Prior to the manufacture of each test tire to be evaluated in the following Experiments 1 to 4, first, a rubber composition for tread to be used in the manufacture of each test tire was manufactured.

[0163] (1) Compounding materials First, as compounding materials for the first rubber composition, 90 parts by mass of SBR (JSR1502 manufactured by JSR Corporation), 10 parts by mass of BR (UBEPOL BR150B manufactured by Ube Industries, Ltd.), 30 parts by mass of oil (Process Oil A / OMIX manufactured by Sankyo Yuka Kogyo Co., Ltd.), 5 parts by mass of carbon black (Showblack N134 manufactured by Cabot Japan Co., Ltd.), 100 parts by mass of silica (Ultrasil 9100GR manufactured by Evonik Corporation), 9 parts by mass of silane coupling agent (Si363 manufactured by Degussa Corporation), 40 parts by mass of resin (α-methylstyrene resin manufactured by Kraton Corporation), 1.5 parts by mass of wax (Ozoace 0355 manufactured by Nippon Seiro Co., Ltd.), 2 parts by mass of stearic acid (Camellia stearic acid manufactured by NOF Corporation), 2 parts by mass of zinc oxide (Zinc oxide No. 1 manufactured by Mitsui Mining and Smelting Co., Ltd.), and antioxidant (Nocrac manufactured by Ouchi Shinko Chemical Industry Co., Ltd.). Prepared were 1 part by mass of a vulcanization accelerator (Noccela CZ-G (CZ) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 1 part by mass of a vulcanization accelerator (Noccela D (DPG) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), and 2 parts by mass of sulfur (powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.).

[0164] On the other hand, the same compounding materials as the first rubber composition were prepared as compounding materials for the second rubber composition, except that the compounding amounts of oil, resin, silica, and carbon black were adjusted so that the AE amount was different from that of the first rubber composition.

[0165] (2) Production of Rubber Composition The compounding materials for the above-mentioned first rubber composition and second rubber composition were kneaded for 5 minutes at 150°C using a Banbury mixer, except for the sulfur and vulcanization accelerator, to obtain a kneaded mixture. Thereafter, sulfur and the vulcanization accelerator were added, and the mixture was kneaded for 5 minutes at 80°C using an open roll to obtain the first rubber composition and the second rubber composition.

[0166] [Experiment 1] In this experiment, a tire of size 175 was produced and evaluated.

[0167] 1. Tire manufacturing Of the first and second rubber compositions obtained above, the first rubber composition was used as a cap rubber and the second rubber composition was used as a base rubber to produce a two-layer tread. This was then laminated together with other tire components to form an unvulcanized tire, which was then press-vulcanized for 10 minutes under a condition of 170°C to produce each test tire of size 175 type (Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5).

[0168] In addition, for each test tire, the above-mentioned (L 80 / L 0 ) was 0.5, the total cross-sectional area of ​​the circumferential grooves was 22% of the cross-sectional area of ​​the tread, and the total volume of the lateral grooves, including the lateral grooves with a groove width / groove depth ratio of 0.65, was 3.5% of the volume of the tread. The thickness Gd of the groove bottom was 5.5 mm.

[0169] 2. Calculation of parameters After that, the outer diameter Dt (mm), section width Wt (mm), section height Ht (mm), and aspect ratio (%) of each test tire were obtained, and the virtual volume V (mm 3 ) was sought.

[0170] Additionally, test pieces were cut out from both the cap layer and base layer of the tread of each test tire, and the AE amount (E1, E2) of each test piece was measured in accordance with JIS K 6229: 2015 to calculate (E1 - E2) (E1: 26 mass%). The results are shown in Tables 1 and 2.

[0171] In addition, the loss tangent (0°C tan δ) of each test piece cut out from the cap layer was measured using a GABO Corporation “IPLEXER (registered trademark)” viscoelasticity measuring device under conditions of temperature 0°C, frequency 10 Hz, initial strain 10%, and dynamic strain rate 2.5%, and was found to be 0.76 (0°C tan δ / Gd = 0.138).

[0172] And then, (Dt-2×Ht), (Dt 2 ×π / 4) / Wt, (V+1.5×10 7 ) / Wt, (V+2.0×10 7 ) / Wt, (V+2.5×10 7 ) / Wt and (E1-E2) x Wt were calculated. The results are shown in Tables 1 and 2.

[0173] 3.Performance evaluation test (1) Evaluation of crack resistance After subjecting each test tire to an ozone deterioration treatment by keeping it under an ozone atmosphere, the tire was fitted to all wheels of a vehicle (a domestic FF vehicle with an engine displacement of 2000cc), filled with air to an internal pressure of 250 kPa, and driven around a test course on a dry road surface for 10 km at a speed of 120 km / h. After that, cracks of 0.1 mm or more in length that had occurred in grooves within a specified range of the tread were measured, and the total length was calculated. The evaluation was made relative to the measurement results of Comparative Examples 1-5, indexed according to the following formula. The larger the value, the better the crack resistance. Crack resistance performance = (measurement results of Comparative Examples 1-5) / (measurement results of test tires) x 100

[0174] (2) Durability evaluation Each test tire was fitted to all wheels of a vehicle (domestic FF vehicle, 2000cc displacement) and filled with air to an internal pressure of 250kPa. The vehicle was then overloaded and driven around a test course on a dry road surface at a speed of 50km / h for 10 laps, and then repeatedly driven over uneven surfaces at a speed of 80km / h. The vehicle then went around again at a speed of 50km / h, and the speed was gradually increased, and the speed at which the driver felt something was wrong was measured.

[0175] Next, the results of Comparative Examples 1-5 were set to 100, and the durability was relatively evaluated by indexing it according to the following formula. A larger value indicates better durability. Durability = (measurement results of test tires) / (measurement results of comparative examples 1-5) x 100

[0176] (3) Overall evaluation The results of the evaluations (1) and (2) above were summed up to determine the overall evaluation.

[0177] (4) Evaluation results The results of each evaluation are shown in Tables 1 and 2.

[0178] [Table 1]

[0179] [Table 2]

[0180] [Experiment 2] In this experiment, a tire of size 195 was produced and evaluated.

[0181] In the same manner as in Experiment 1, each test tire of Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-5 shown in Tables 3 and 4 was manufactured, and each parameter was determined in the same manner. Then, a performance evaluation test was conducted and evaluated in the same manner. In this experiment, the result of Comparative Example 2-5 was set as 100 and the evaluation was performed. The results of each evaluation are shown in Tables 3 and 4.

[0182] [Table 3]

[0183] [Table 4]

[0184] [Experiment 3] In this experiment, a 225 size tire was produced and evaluated.

[0185] In the same manner as in Experiment 1, each test tire of Examples 3-1 to 3-5 and Comparative Examples 3-1 to 3-5 shown in Tables 5 and 6 was manufactured, and each parameter was determined in the same manner. Then, a performance evaluation test was conducted and evaluated in the same manner. In this experiment, the result of Comparative Example 3-5 was set as 100 and the evaluation was performed. The results of each evaluation are shown in Tables 5 and 6.

[0186] [Table 5]

[0187] [Table 6]

[0188] [Summary of Experiments 1-3] The results of Experiments 1 to 3 (Tables 1 to 6) show that, for any tire size, 175, 195, or 225, if (E1-E2)<20 and the above-mentioned (Equation 1) and (Equation 2) are satisfied, a pneumatic tire with sufficiently improved crack resistance and durability can be provided.

[0189] It has been found that by satisfying the requirements set forth in claim 2 and subsequent claims, a tire with further improved crack resistance and durability can be provided.

[0190] On the other hand, it was found that if either (Formula 1) or (Formula 2) is not satisfied, the crack resistance during high-speed driving cannot be sufficiently improved, and the durability performance cannot be sufficiently improved either.

[0191] [Experiment 4] Next, three types of tires (Example 4-1 to Example 4-3) that have no significant difference in the relationship between the virtual volume V and the cross-sectional width Wt were manufactured with the same compounding and evaluated in the same manner. In addition to the evaluation of the crack resistance and durability, the fuel economy performance was also evaluated.

[0192] Specifically, each test tire was fitted to all wheels of a vehicle (a domestically produced FF vehicle with a 2000cc engine) and filled with air to an internal pressure of 250kPa, after which the vehicle was driven around a test course on a dry road surface for 10km at a speed of 100km / h, and the accelerator was then released, and the distance from when the accelerator was turned off until the vehicle came to a stop was measured as the rolling resistance during high-speed driving.The higher the value, the longer the distance from when the accelerator was turned off until the vehicle came to a stop, indicating a smaller rolling resistance in a steady state.

[0193] Next, the result of Example 4-3 was set as 100, and the fuel economy was evaluated by indexing according to the following formula. The larger the value, the smaller the rolling resistance in the steady state and the better the fuel economy performance. The evaluation results are shown in Table 7. Fuel efficiency performance=[(measurement result of test tire) / (measurement result of Example 4-3)]×100

[0194] The results of each evaluation were then summed up to give an overall evaluation, similar to Experiments 1 to 3. The results of each evaluation are shown in Table 7.

[0195] [Table 7]

[0196] From Table 7, it can be seen that, when there is no significant difference in the relationship between the virtual volume V and the cross-sectional width Wt, as the cross-sectional width Wt becomes smaller, such as less than 205 mm and less than 200 mm, and as the flattening ratio increases, the crack resistance, durability, and fuel efficiency are all improved, resulting in a remarkable effect.

[0197] [Production of rubber composition for tread 2] The first rubber composition used to manufacture the test tires of Experiment 5 was obtained under the same conditions and in the same manner as in the manufacture of the rubber composition for tread 1, except that 60 parts by mass of SBR (JSR1502 manufactured by JSR Corporation), 20 parts by mass of NR (RSS#3), and 20 parts by mass of BR (UBEPOL BR150B manufactured by Ube Industries, Ltd.) were used instead of 90 parts by mass of SBR and 10 parts by mass of BR. In addition, a second rubber composition used in the manufacture of the test tires of Experiment 5 was obtained under the same conditions and in the same manner as in the manufacture of the rubber composition for tread 1, except that 100 parts by mass of NR (RSS#3) was used instead of 90 parts by mass of SBR and 10 parts by mass of BR, and the amounts of oil, resin, silica, and carbon black were adjusted so that the AE amount was different from that of the first rubber composition.

[0198] [Experiment 5] Using the first and second rubber compositions produced in the production 2 of rubber compositions for treads, test tires of Example 5 and Comparative Example 5 having sizes shown in Table 8 were produced in the same manner as in Experiment 1, and then each parameter was determined and a performance evaluation test was carried out in the same manner as in Experiment 1. In this experiment, the results of Comparative Example 5 were set as 100 and the evaluation was carried out. The results of each evaluation are shown in Table 8.

[0199] [Production of rubber composition for tread 3] The first rubber composition used in the manufacture of the test tires of Experiment 6 was obtained under the same conditions and in the same manner as in the manufacture of the rubber composition for tread 1, except that 50 parts by mass of NR (RSS#3) and 50 parts by mass of BR (UBEPOL BR150B manufactured by Ube Industries, Ltd.) were used instead of 90 parts by mass of SBR and 10 parts by mass of BR. In addition, a second rubber composition used in the manufacture of the test tires of Experiment 6 was obtained under the same conditions and in the same manner as in the manufacture of the rubber composition for tread 1, except that 50 parts by mass of NR (RSS#3) and 50 parts by mass of SBR (JSR1502 manufactured by JSR Corporation) were used instead of 90 parts by mass of SBR and 10 parts by mass of BR, and the amounts of oil, resin, silica, and carbon black were adjusted so that the AE amount was different from that of the first rubber composition.

[0200] [Experiment 6] Using the first and second rubber compositions produced in Production 3 of rubber compositions for treads, test tires of Example 6 and Comparative Example 6 having sizes shown in Table 8 were produced in the same manner as in Experiment 1, and then each parameter was determined and a performance evaluation test was carried out in the same manner as in Experiment 1. In this experiment, the results of Comparative Example 6 were set as 100 and the evaluation was carried out. The results of each evaluation are shown in Table 8.

[0201] [Table 8]

[0202] Table 8 shows that even when the first rubber composition and the second rubber composition are rubber compositions other than SBR and BR, if (E1-E2)<20 and the above-mentioned (Formula 1) and (Formula 2) are satisfied, both the crack resistance and durability are improved, and the object of the present invention is achieved.

[0203] Although the present invention has been described above based on the embodiment, the present invention is not limited to the above embodiment. Various modifications can be made to the above embodiment within the same and equivalent scope of the present invention.

Claims

1. A pneumatic tire having a tread portion with grooves formed on the surface thereof, the tread portion is formed with a first rubber composition constituting a groove bottom portion, and a second rubber composition adjacent to the first rubber composition on a radially inner side of the groove bottom portion, The first rubber composition and the second rubber composition each contain 60% by mass or more of SBR and 5% by mass or more of BR, When the acetone extractable content of the first rubber composition is E1 mass % and the acetone extractable content of the second rubber composition is E2 mass %, (E1-E2)<20; When the tire is mounted on a regular rim and the internal pressure is set to 250 kPa, the cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is the virtual volume V (mm ３ ), the following (Formula 1) and (Formula 2) are satisfied: 1700≦(Dt ２ ×π / 4) / Wt≦2827.4 ……………………………………(Formula 1) [(V+1.5×10 ７ ) / Wt]≦2.88×10 ５ ・・・・・・(Formula 2)

2. A pneumatic tire having a tread portion with grooves formed on the surface, the tread portion is formed with a first rubber composition constituting a groove bottom portion, and a second rubber composition adjacent to the first rubber composition on a radially inner side of the groove bottom portion, The first rubber composition and the second rubber composition each contain 90% by mass or more of a diene-based rubber, and the diene-based rubber contains at least one of SBR, BR, and NR, When the acetone extractable content of the first rubber composition is E1 mass % and the acetone extractable content of the second rubber composition is E2 mass %, (E1-E2)<20; A pneumatic tire characterized by satisfying the following (Equation 1) and (Equation 2), where the cross-sectional width of the tire when mounted on a regular rim and the internal pressure is 250 kPa is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is a virtual volume V (mm3). 1700≦(Dt 2 ×π / 4) / Wt≦2827.4 (Formula 1) [(V+1.5×10 7 ) / Wt]≦2.88×10 5 (Formula 2)

3. 3. The pneumatic tire according to claim 1, wherein the following formula (3) is satisfied: [(V+2.0×10 ７ ) / Wt]≦2.88×10 ５ …… ...

4. 4. The pneumatic tire according to claim 3, wherein the following formula 4 is satisfied: [(V+2.5×10 ７ ) / Wt]≦2.88×10 ５ ・・・・・・(Formula 4)

5. The pneumatic tire according to any one of claims 1 to 4, characterized in that, when the outer diameter of the tire is Dt (mm) and the cross-sectional height of the tire is Ht (mm) when the tire is mounted on a regular rim and the internal pressure is 250 kPa, (Dt - 2 x Ht) is 470 (mm) or more.

6. 6. The pneumatic tire according to claim 1, wherein the loss tangent (0° C. tan δ) of the first rubber composition measured under conditions of a temperature of 0° C., a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain rate of 2.5% is 0.72 or more.

7. The pneumatic tire according to claim 6, wherein the 0° C. tan δ is 0.75 or more.

8. 8. The pneumatic tire according to claim 1, wherein an aspect ratio is 40% or more.

9. 9. The pneumatic tire according to claim 8, wherein the aspect ratio is 45% or more.

10. 10. The pneumatic tire according to claim 9, wherein the aspect ratio is 47.5% or more.

11. The pneumatic tire according to any one of claims 1 to 10, wherein E1, E2, and Wt satisfy the following (Formula 5). (E1-E2)×Wt<5×10 ３ ・・・・・・・・・・・・・・・・(Formula 5)

12. The pneumatic tire according to claim 11, characterized in that the following (Formula 6) is satisfied. (E1-E2)×Wt<4×10 ３ ・・・・・・・・・・・・・・・・(Formula 6)

13. 13. The pneumatic tire according to claim 12, wherein the following formula (7) is satisfied: (E1-E2)×Wt<3×10 ３ ・・・・・・・・・・・・・・・・(Formula 7)

14. The tire has a plurality of circumferential grooves in the tread portion, the circumferential grooves extending continuously in the tire circumferential direction.

14. The pneumatic tire according to claim 1, wherein a total cross-sectional area of ​​the plurality of circumferential grooves is 10 to 30% of a cross-sectional area of ​​the tread portion.

15. The tire has a plurality of axially extending lateral grooves in the tread portion, 15. The pneumatic tire according to claim 1, wherein a total volume of the plurality of lateral grooves is 2.0 to 5.0% of a volume of the tread portion.

16. 16. The pneumatic tire according to claim 1, wherein when the outer diameter of the tire is Dt (mm) when mounted on a regular rim and the internal pressure is set to 250 kPa, Dt is less than 685 (mm).

17. 17. The pneumatic tire according to claim 1, wherein the cross-sectional width Wt (mm) is less than 205 mm.

18. 18. The pneumatic tire according to claim 17, wherein the cross-sectional width Wt (mm) is less than 200 mm.

19. 19. The pneumatic tire according to claim 1, wherein the ratio 0°C tan δ / Gd of the loss tangent (0°C tan δ) of the first rubber composition measured under conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain rate of 2.5% to the thickness Gd (mm) of the groove bottom is 0.16 or less.

20. The pneumatic tire according to claim 19, wherein the 0° C. tan δ / Gd is 0.14 or less.

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