JP5057762B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire (hereinafter, also simply referred to as “tire”), and more particularly, to a pneumatic tire for a passenger car that has excellent steering stability and suppresses a change in performance before and after traveling.

  Generally, a pneumatic tire has a carcass extending in a toroidal shape between a pair of bead portions as a skeleton, and a belt layer made of rubberized steel cord is disposed as a reinforcing layer on the outer side in the tire radial direction. . Further, tread rubber is disposed outside the belt layer in the tire radial direction to form a tread surface portion.

  In recent years, in order to improve the safety of vehicles, it has been required to increase the friction coefficient (μ) on both the dry road surface and the wet road surface of the tire to simultaneously improve the dry performance and wet performance of the tire. Various techniques have been developed to meet the demand for improvement in dry performance and wet performance. For example, in the development of a tire tread rubber composition that directly contributes to the dry performance and wet performance of a tire, the loss tangent (tan δ) near 0 ° C. and the loss tangent (tan δ) near 30 ° C. are used as indices. It is generally effective, and specifically, by using a rubber composition having a high tan δ at around 0 ° C. for the tread, the coefficient of friction (μ) on the wet road surface of the tire is increased to improve the wet performance. On the other hand, by using a rubber composition having a high tan δ at around 30 ° C. for the tread, the friction coefficient (μ) on the dry road surface of the tire can be increased and the dry performance can be improved. .

  In addition, demands for reducing fuel consumption of automobiles are also increasing in connection with the movement of global carbon dioxide emission regulations accompanying the recent increase in interest in environmental problems. In order to meet such demands, reduction of rolling resistance is also demanded for tire performance.

  In contrast, silica is known as a filler that can achieve both low heat build-up and grip on wet road surfaces, and by using silica as a tread rubber filler, heat generation of the tire is suppressed. It is possible to reduce rolling resistance and improve grip performance on wet road surfaces (see, for example, Patent Document 1).

  On the other hand, with respect to the steel cord used for the belt layer, various studies have been made from the viewpoint of improving the handling stability and the riding comfort. For example, Patent Document 2 discloses a thin wire diameter. (Element diameter 0.06 to 0.10 mm) A technique for improving maneuverability and stability during cornering by using a specific steel cord is described. Patent Document 3 discloses a tire in which a steel cord is defined by bending resistance and tensile elongation. Patent Documents 4 to 6 disclose a belt layer, a cord diameter, the number of filaments in one cord, and driving of the belt layer. Tires defined by a relational expression with the number of cords are disclosed respectively.

Further, Patent Document 7 discloses a tire that is a steel cord made of a predetermined steel filament and that prescribes a predetermined range of values defined by belt bending rigidity, cord strength, and gap amount of the belt cord. Documents 8 to 10 disclose a steel cord for reinforcing tires having a predetermined twist structure and predetermining a range of values defined by cord strength, cord break elongation and cord bending rigidity. Further, Patent Document 11 discloses a tire in which a belt is defined by a belt cord twisted structure and wire diameter and the number of belt cords driven, and Patent Document 12 discloses a twisted structure, a bending rigidity / cord strength ratio, a cord strength. Patent Document 13 discloses a tire in which a belt cord structure and a belt ply with a predetermined number of drivings are arranged via a buffer rubber, respectively. .
JP 2002-097309 A (Claims etc.) JP 59-38102 A (Claims etc.) JP-A-60-185602 (Claims) JP 63-2702 (Claims etc.) JP 63-2703 (Claims etc.) JP 63-2704 A (Claims etc.) JP-A 64-855381 (Claims etc.) JP-A 64-85382 (Claims etc.) JP-A 64-85383 (Claims etc.) JP-A 64-85384 (Claims etc.) JP-A-1-141103 (Claims etc.) JP-A-3-74206 (Claims etc.) JP-A-3-143703 (Claims etc.)

  As described above, by blending silica as a filler, it is possible to obtain a tread rubber excellent in fuel efficiency and driving stability performance on a wet road surface. However, the silica blended tread rubber has a problem that the performance change (sag) accompanying running is large, and has a problem that a large amount cannot be used for blending a high performance tire. Therefore, it has been desired to establish a technique for solving such a problem and realizing a tire that is excellent in tire performance such as low fuel consumption and steering stability and has little change in physical properties before and after traveling.

  Accordingly, an object of the present invention is to provide a high-performance pneumatic tire that solves the above-described problems, has excellent fuel efficiency and steering stability, and has little performance change before and after traveling.

  As a result of intensive studies, the present inventor has found that the above problem can be solved by combining a tread rubber with a low fuel consumption system and a predetermined belt structure, and has completed the present invention.

That is, the pneumatic tire of the present invention has a carcass extending in a toroidal shape between a pair of bead portions as a skeleton, and at least two crossing belt layers formed by rubberizing a steel cord on the outer side in the radial direction of the crown portion of the carcass. And the tread rubber are sequentially arranged, the steel cord has a single twist structure or a core-single layer sheath structure composed of 6 to 10 steel strands having a strand diameter of 0.10 to 0.20 mm. And the number of driven steel cords is 40/50 mm or more, the distance between the steel cords adjacent in the belt layer is 0.3 mm or more, and the tread rubber is dynamically stored at 30 ° C. The elastic modulus E ′ (MPa) and the loss tangent tan δ at 30 ° C. are respectively expressed by
10 ≦ E '
0.300 ≦ tan δ ≦ 0.700
It is characterized by satisfying the relationship represented by

In the present invention, in the tread rubber, it is preferable that 20 to 120 parts by weight of a white filler is blended with respect to 100 parts by weight of the rubber component, and the tread rubber has the following formula (I),
HOOC—CH═CH—COO—R ¹ —CO—CH═CH—COOH (I)
Wherein R ¹ is a group represented by the formula —R ² O—, a group represented by the formula — (R ³ O) _S —, a group represented by the formula —CH ₂ CH (OH) CH ₂ O—, or A group represented by the formula — (R ⁴ O—COR ⁵ —COO—) _t R ⁴ O—, wherein R ² is an alkylene group having ² to 36 carbon atoms, an alkenylene group or a divalent aromatic hydrocarbon group; ³ is an alkylene group having 2 to 4 carbon atoms, s is a number from 1 to 60 indicating the average number of moles added of the oxyalkylene group, R ⁴ is an alkylene group having 2 to 18 carbon atoms, an alkenylene group, a divalent aromatic carbonization A hydrogen group or — (R ⁶ O) _u R ⁶ — (R ⁶ is an alkylene group having 2 to 4 carbon atoms, u is a 1 to 30 number indicating the average number of moles added of the oxyalkylene group), and R ⁵ is a carbon number 2-18 alkylene group, alkenylene group or divalent aromatic hydrocarbon group, t is an average value of 1-3 It is also preferred to include a number.) A compound having a structure represented by.

  Further, in the present invention, the steel cord preferably has a structure formed by twisting so as to have a gap into which rubber can enter between at least one pair of adjacent steel strands located in the outermost layer of the cord, It is also preferable that the cross-sectional shape of the steel cord is flat and the major axis direction of the flat cross-section is arranged along the width direction of the belt layer. In particular, the steel cord has two steel strands arranged in parallel without being twisted together as a core, and the remaining steel strands around at least one pair of adjacent steel strands around the core. It has a core-single layer sheath structure that is twisted so as to have a gap that allows rubber to enter between the wires. Still preferably, the number of steel cords to be driven is 40 to 60/50 mm, and the distance between adjacent steel cords in the belt layer is 0.4 to 1.0 mm.

  According to the present invention, the above configuration makes it possible to realize a high-performance pneumatic tire that has excellent fuel efficiency and steering stability and has little performance change before and after traveling.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In FIG. 1, the schematic sectional drawing of an example of the pneumatic radial tire of this invention is shown. As shown in the figure, the tire according to the present invention has a carcass 1 extending in a toroidal shape between a pair of bead portions 11 as a skeleton, and at least two layers of cross belts formed by rubberizing a steel cord on the outer side in the radial direction of the crown portion. The layer 2 (2a, 2b) and the tread rubber 3 are sequentially arranged.

In the present invention, as the tread rubber 3, the dynamic storage elastic modulus E ′ (MPa) at 30 ° C. and the loss tangent tan δ at 30 ° C. are respectively expressed by the following equations:
10 ≦ E '
0.300 ≦ tan δ ≦ 0.700
The one satisfying the relationship represented by is used. Thereby, while ensuring low fuel consumption, the steering stability and HSP property on a wet road surface can be improved.

When the dynamic storage elastic modulus E ′ at 30 ° C. is less than 10.0 MPa, the effect of improving the steering stability on the dry road surface becomes insufficient. This dynamic storage modulus E ′ is preferably further represented by the following formula:
13 ≦ E '
Shall be satisfied. On the other hand, if the loss tangent tan δ at 30 ° C. is less than 0.300, steering stability on a wet road surface is insufficient. On the other hand, if it exceeds 0.700, the HSP property (high speed: durability) is deteriorated.

  Further, in the tire of the present invention, the cross belt layer 2 has a predetermined belt structure to be described later, so that it exhibits high circumferential tensile rigidity and in-plane bending rigidity, and has low out-of-plane bending rigidity. Have.

  Since the belt layer has a high tensile rigidity in the circumferential direction, the belt member bears the tension due to the internal pressure and can exert its effect, and since it has a high in-plane bending rigidity, it can be used during cornering. Since the in-plane bending deformation is reduced, a large cornering force can be generated and good steering stability can be exhibited.

  Further, the belt layer is subjected to a large in-plane bending deformation in the vicinity of the cornering limit point, and due to this deformation, the belt layer is subjected to a large compressive deformation inside the bending deformation, and buckling occurs. However, in the present invention, by reducing the out-of-plane bending rigidity of the two-layer belt layer, the out-of-plane deformation pressure accompanying compression is reduced, and buckling deformation can be suppressed by the tire internal pressure, resulting in ground contact. It is possible to improve the ground contact by suppressing the pressure drop and to make the ground pressure distribution uniform in the tread. Thereby, the input applied to the tread rubber can be made uniform, and an effect of suppressing physical property changes before and after traveling can be obtained. As mentioned above, tread rubber with silica compound has a large performance change (sag) due to running, and there is a problem that a large amount cannot be used for high performance compound, but it should be used in combination with such a belt layer. This eliminates this problem and enables application to high-performance tires containing high silica.

  In the present invention, the steel cord of the belt layer 2 has a single-stranded structure or core comprising 6 to 10 steel strands having a strand diameter of 0.10 to 0.20 mm, preferably 0.15 to 0.20 mm. It has a single layer sheath structure.

  The reason why the strand diameter is set to 0.10 to 0.20 mm is that when the strand diameter exceeds 0.20 mm, the bending rigidity of the cord increases and it becomes difficult to reduce the out-of-plane bending rigidity of the belt layer. It is. On the other hand, when the strand diameter is less than 0.10 mm, it becomes difficult to obtain high circumferential tensile rigidity under the conditions of the number of strands and the distance between adjacent cords suitable for the present invention, and the cost is high. Become.

  Also, if the number of strands is large, the bending rigidity increases due to interference between strands when the cord is bent. However, in the present invention, the number of strands is as small as 10 or less, so bending of interference between strands is difficult. The effect on rigidity is small. On the other hand, when the number of strands is less than 6, it is difficult to obtain a high circumferential tensile rigidity under the conditions of the number of strands and the distance between adjacent cords suitable for the present invention.

  Furthermore, in the present invention, the steel cord has a single twist structure or a core-single-layer sheath structure composed of 6 to 10 steel strands, and has a simple twist structure that limits the maximum number of strands. Is easy to secure. In particular, it is preferable that the steel cord has an open structure in which rubber is twisted so as to have a gap into which rubber can enter between at least one pair of adjacent steel strands located in the outermost layer of the cord. Thereby, the merit that productivity is high compared with a double twisted cord, and cost reduction is possible is also acquired.

  In the present invention, the number of steel cords to be driven is 40/50 mm or more, preferably 40 to 60/50 mm. The reason why the number of driving is set to 40/50 mm or more is that (1) it is necessary to secure the minimum necessary steel occupation ratio in order to obtain the necessary circumferential tensile rigidity and circumferential tensile rigidity. ) Due to the fact that the circumferential tensile stiffness and circumferential tensile stiffness of the crossing belt layer are the same steel occupancy ratio, the steel cord formed by the upper and lower belt layers has a smaller mesh and a higher number. Is.

  Here, it is preferable that the smaller the strand diameter and the smaller the number of strands, the greater the number of driven wires, and particularly effective use of the effect (2) above. It is important that the distance between the cords is 0.3 mm or more. If the distance between adjacent steel cords in the belt layer is less than 0.3 mm, fine cracks generated at the ends of the steel cords grow between adjacent steel cords, and then between the belt laminations. This leads to rapid expansion and the crack growth rate leading to belt separation becomes much faster. The distance between the adjacent steel cords is preferably about 0.4 to 1.0 mm.

  Preferably, the cross-sectional shape of the steel cord is flat, and the major axis direction of the flat cross-section is arranged along the width direction of the belt layer, so that higher in-plane bending rigidity and lower out-of-plane bending rigidity are obtained. Obtainable. It is also effective for ensuring rubber penetrability.

  The steel cord structure with a flat cross-sectional shape has a single twist structure in which the spiral shape of the strands is crushed in one direction, or two steel strands arranged in parallel without being twisted together, and the core A structure in which a sheath is formed by twisting steel strands around the periphery can be applied. In particular, two steel strands such as 2 parallels +4 to 7 are arranged in parallel without being twisted with each other as a core, and the remaining steel strands around at least one pair of adjacent steel strands. Applying a steel cord with a core-single-layer sheath structure that is twisted so that there is a gap through which rubber can enter, results in higher in-plane bending stiffness, lower out-of-plane bending stiffness, and good rubber penetrability Is particularly preferable.

  As the tread rubber 3 used in the present invention, specifically, one containing 20 to 120 parts by mass of a white filler with respect to 100 parts by mass of the rubber component can be suitably used. If the number of parts of the white filler is less than 20 parts by mass, the effect of improving the steering stability on the wet road surface is insufficient. It becomes.

  Specific examples of the rubber component of the tread rubber 3 include styrene / butadiene copolymer rubber (SBR), natural rubber (NR), styrene / isoprene copolymer rubber (SIR), and polyisoprene rubber (IR). And synthetic rubbers such as polybutadiene rubber (BR), butyl rubber (IIR), and ethylene / propylene copolymer.

  Examples of the white filler include silica and aluminum hydroxide, and among these, silica is preferable. Examples of the silica include, but are not limited to, wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like. Wet silica is preferred because it is excellent in the effect of achieving both grip properties and low rolling resistance. In addition, when using a silica as a white filler, it is preferable to add a silane coupling agent at the time of a mixing | blending from a viewpoint of further improving the reinforcement. Such silane coupling agents include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilyl). Ethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltri Methoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarba Yl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate Monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, dimethoxy Methylsilylpropylbenzothiazole tetrasulfide, and the like. Among these, bis (3 Triethoxysilylpropyl) tetrasulfide and 3-trimethoxysilylpropyl benzothiazole tetrasulfide are preferable. These silane coupling agents may be used alone or in combination of two or more.

Further, the tread rubber 3 preferably has the following formula (I),
HOOC—CH═CH—COO—R ¹ —CO—CH═CH—COOH (I)
Wherein R ¹ is a group represented by the formula —R ² O—, a group represented by the formula — (R ³ O) _S —, a group represented by the formula —CH ₂ CH (OH) CH ₂ O—, or A group represented by the formula — (R ⁴ O—COR ⁵ —COO—) _t R ⁴ O—, wherein R ² is an alkylene group, an alkenylene group or a divalent aromatic hydrocarbon group having ² to 36 carbon atoms. Preferably, it is an alkylene group having 2 to 18 carbon atoms or a phenylene group, more preferably an alkylene group having 4 to 12 carbon atoms, and R ³ is an alkylene group having 2 to 4 carbon atoms, preferably an ethylene group or A propylene group, and s is a number of 1 to 60 indicating the average number of moles added of the oxyalkylene group, preferably 2 to 40, more preferably 4 to 30. R ⁴ has 2 to 18 carbon atoms. Alkylene group, alkenylene group, divalent aromatic A hydrocarbon group or — (R ⁶ O) _u R ⁶ — (R ⁶ is an alkylene group having 2 to 4 carbon atoms, u is a number of 1 to 30 indicating the average number of added moles of an oxyalkylene group, preferably And R ⁵ is an alkylene group, alkenylene group or divalent aromatic hydrocarbon group having 2 to 18 carbon atoms, preferably 2 to 2 carbon atoms. 12 is an alkylene group or phenylene group, more preferably an alkylene group having 2 to 8 carbon atoms, t is an average value of 1 to 30, preferably 1 to 20, and more preferably 1 to 15. Contains a compound having the structure represented. By blending the compound of the above formula (I) with the tread rubber 3, sagging associated with running can be suppressed and performance change can be prevented. Specific examples of the compound represented by the formula (I) include dimaleates of alkylene diols such as glycerine dimaleate, 1,4-butanediol dimaleate, 1,6-hexanediol dimaleate, 1,6- Dialkylate of alkylene diol such as hexanediol difumarate, dimaleate of polyoxyalkylene glycol such as PEG200 dimaleate, PEG600 dimaleate (herein, PEG200 and PEG600 are polyethylene glycol having an average molecular weight of 200 or 600, respectively), at both ends A polybutylene maleate having a carboxyl group, a poly (PEG200) maleate having a carboxyl group at both ends, a polyalkylene glycol / maleic acid polyester having both ends, a carboxyl group at both ends Polybutylene adipate maleate, polyoxyalkylene glycol difumarate such as PEG600 difumarate, polybutylene fumarate having carboxyl groups at both ends, poly (PEG200) fumarate having carboxyl groups at both ends, etc. Examples include alkylene glycol / fumaric acid polyester. This compound preferably has a molecular weight of 250 or more, more preferably in the range of 250 to 5000, and particularly preferably in the range of 250 to 3000. Within this range, the flash point is high, which is desirable not only from the viewpoint of safety, but also from the viewpoint of the working environment because it produces less smoke. In the present invention, such compounds may be used alone or in combination of two or more. The blending amount is preferably in the range of 1.0 to 4.0 parts by mass with respect to 100 parts by mass of the rubber component. If the blending amount is less than 1.0 part by mass, the effect of suppressing sagging cannot be obtained.

  In addition to the above, carbon black can be blended in the tread rubber 3 as a filler. Such carbon black is not particularly limited, and those of FEF, SRF, HAF, ISAF, SAF grade, etc. can be used. Particularly, the iodine adsorption amount (IA) is 60 mg / g or more and A dibutyl phthalate (DBP) oil absorption of 80 mL / 100 g or more is preferred. By compounding carbon black, various physical properties of the rubber composition can be improved, but from the viewpoint of improving the wear resistance, those of HAF, ISAF, and SAF grades are more preferable. As a compounding quantity of carbon black, it is the range of 30-90 mass parts suitably with respect to 100 mass parts of rubber components. If the blending amount of the carbon black is less than 30 parts by mass, the processability is inferior in heat transfer properties and the like, whereas if it exceeds 90 parts by mass, the merit of steering stability on a wet road surface decreases.

  Moreover, the tread rubber 3 may contain a softening agent, and the blending amount thereof is in the range of 0 to 30 parts by mass with respect to 100 parts by mass of the rubber component. When the blending amount of the softening agent exceeds 30 parts by mass, the tensile strength and low heat build-up property of the vulcanized rubber tend to deteriorate. As the softener, process oil or the like can be used, and specific examples of the process oil include paraffin oil, naphthenic oil, aroma oil, and the like. Among these, an aroma oil is preferable from the viewpoint of tensile strength and wear resistance, and naphthenic oil and paraffin oil are preferable from the viewpoint of hysteresis loss and low-temperature characteristics.

  As the tread rubber 3, a general rubber crosslinking system can be used, and it is preferable to use a combination of a crosslinking agent and a vulcanization accelerator. As the cross-linking agent, sulfur or the like can be used, and the amount used thereof is preferably 0.1 to 10 parts by mass, more preferably 1 to 5 parts by mass as the sulfur content with respect to 100 parts by mass of the rubber component. preferable. When the compounding amount of the crosslinking agent is less than 0.1 parts by mass as the sulfur content with respect to 100 parts by mass of the rubber component, the fracture strength, wear resistance and low heat build-up of the vulcanized rubber are lowered, while exceeding 10 parts by mass And rubber elasticity is lost. The vulcanization accelerator is not particularly limited, but 2-mercaptobenzothiazole (M), dibenzothiazyl disulfide (DM), N-cyclohexyl-2-benzothiazylsulfenamide (CZ). And thiazole vulcanization accelerators such as Nt-butyl-2-benzothiazolylsulfenamide (NS), and guanidine vulcanization accelerators such as diphenylguanidine (DPG). As a usage-amount of a vulcanization accelerator, the range of 0.1-5 mass parts is preferable with respect to 100 mass parts of rubber components, and the range of 0.2-3 mass parts is more preferable. These vulcanization accelerators may be used alone or in combination of two or more.

  In addition to the above, for the tread rubber 3, for example, additives commonly used in the rubber industry such as anti-aging agent, zinc oxide, stearic acid, antioxidant, ozone deterioration preventing agent, and the like do not impair the purpose of the present invention. It can select suitably and mix | blend it.

  In the present invention, a desired effect can be obtained by satisfying the conditions relating to the tread rubber 3 and the belt layer 2, and the structure and material of the other members other than the above are particularly limited. It is not something. For example, as shown in the figure, a bead core 4 is embedded in each of the pair of bead portions 11 of the tire of the present invention, and the carcass 1 is folded around the bead core 4 from the inside of the tire to the outside and locked. A tread portion 12 made of a tread rubber 3 is disposed on the outer periphery of the crown portion of the belt layer 2, and a sidewall portion 13 is disposed on the side portion of the carcass 1. Furthermore, as a gas filled in the tire, an inert gas such as nitrogen, argon, helium, or the like can be used in addition to normal air or air whose oxygen partial pressure is adjusted.

Hereinafter, the present invention will be described in more detail with reference to examples.
As shown in FIG. 1, a pneumatic radial tire including two cross belt layers 2 a and 2 b formed by rubber-drawing steel cords and a tread rubber 3 in the radial direction of the crown portion of the carcass 1 was manufactured. As the belt layer of each example and comparative example, those satisfying the conditions according to the following Tables 2 and 3 were used. The tire size was 225 / 45R17, and the angles of the intersecting belt layers 2a and 2b were ± 63 ° with respect to the tire width direction. The composition of the tread rubber used is shown in Table 1 below.

  Each of the obtained test tires was evaluated according to the following. The results are shown together in Table 3 below together with the measured values of the dynamic storage elastic modulus E ′ at 30 ° C. and the loss tangent tan δ at 30 ° C. of the tread rubber.

(Measurement of E ′ and tan δ)
The dynamic storage elastic modulus (E ′) at 30 ° C. and the loss tangent (tan δ) at 30 ° C. were measured under the conditions of a frequency of 15 Hz and a strain of 5% using a rheometrics viscoelasticity measuring device.

(Maneuvering stability)
Each test tire was mounted on an actual vehicle, and the steering stability was evaluated by the driver's feeling running on a dry (dry) and wet (wet) circuit. The results are shown on a 10-point scale. The larger the value, the better the steering stability and the better. Steering stability on the dry road surface was evaluated again after the actual traveling of 50000 km (late driving period), and the difference from the initial driving was calculated. Regarding dry steering stability, the difference of 0.5 points is large in performance, and is a level at which a general driver can recognize the performance difference.

(HSP property (high-speed durability))
Evaluation of HSP property was performed according to the following.
A drum test was performed on each test tire, the speed was increased by 10 km / h, and the HSP property was evaluated based on the speed at the time of failure. The level that could withstand practical use was marked with ◯, and the level that could not withstand was marked with ×.

(Processability)
The workability was evaluated according to the following.
After unvulcanized rubber was seated on a sheeting roll, it was punched into a 10 cm × 2 cm × 2 mm mold, and after 24 hours of standing, the shrinkage change after punching was measured. The case where the amount of shrinkage was 40% or less was evaluated as ◯ (good), the case where it exceeded 40% and 60% or less was evaluated as Δ, and the case where it exceeded 60% was evaluated as ×.

＊１）シリカ（白色充填剤）のゴム成分１００質量部に対する部数（質量部）を示す。
＊２）式（Ｉ）において、Ｒ^１が−（Ｒ^４Ｏ−ＣＯＲ^５−ＣＯＯ−）_ｔＲ^４Ｏ−で示される基であり、Ｒ^４が−（Ｒ^６Ｏ）_ｕＲ^６−（Ｒ^６がエチレン基、ｕ＝３．５）であり、Ｒ^５が−ＣＨ＝ＣＨ−、ｔ＝４の化合物である。

* 1) The number of parts (parts by mass) relative to 100 parts by mass of the rubber component of silica (white filler).
* 2) In the formula (I), R ¹ is a group represented by — (R ⁴ O—COR ⁵ —COO—) _t R ⁴ O—, and R ⁴ is — (R ⁶ O) _u R ⁶ — ( R ⁶ is an ethylene group, u = 3.5), R ⁵ is a compound of —CH═CH—, t = 4.

  As shown in Table 3 above, in the pneumatic tires of the examples using the belt layer steel cords and tread rubbers that satisfy the predetermined conditions according to the present invention, excellent fuel economy and driving stability are realized. In addition, it was confirmed that it was possible to suppress the performance change before and after traveling.

1 is a schematic cross-sectional view showing a pneumatic tire according to an embodiment of the present invention.

Explanation of symbols

1 Carcass 2 (2a, 2b) Crossing belt layer 3 Tread rubber 4 Bead core 11 Bead portion 12 Tread portion 13 Side wall portion

Claims (8)

A pneumatic structure in which a carcass extending in a toroidal shape between a pair of bead portions is used as a skeleton, and at least two layers of crossing belt layers formed by rubber-drawing steel cords and a tread rubber are sequentially arranged outside the crown portion of the carcass in the radial direction. In the tire,
The steel cord has a single twist structure or a core-single layer sheath structure composed of 6 to 10 steel strands having a strand diameter of 0.10 to 0.20 mm, and the number of driven steel cords is 40/50 mm. The distance between the steel cords adjacent in the belt layer is 0.3 mm or more, and
The dynamic storage elastic modulus E ′ (MPa) at 30 ° C. and the loss tangent tan δ at 30 ° C. of the tread rubber are respectively expressed by the following equations:
10 ≦ E '
0.300 ≦ tan δ ≦ 0.700
A pneumatic tire characterized by satisfying the relationship expressed by:   The pneumatic tire according to claim 1, wherein in the tread rubber, 20 to 120 parts by mass of a white filler is blended with 100 parts by mass of the rubber component. The tread rubber has the following formula (I),
HOOC—CH═CH—COO—R ¹ —CO—CH═CH—COOH (I)
Wherein R ¹ is a group represented by the formula —R ² O—, a group represented by the formula — (R ³ O) _S —, a group represented by the formula —CH ₂ CH (OH) CH ₂ O—, or A group represented by the formula — (R ⁴ O—COR ⁵ —COO—) _t R ⁴ O—, wherein R ² is an alkylene group having ² to 36 carbon atoms, an alkenylene group or a divalent aromatic hydrocarbon group; ³ is an alkylene group having 2 to 4 carbon atoms, s is a number from 1 to 60 indicating the average number of moles added of the oxyalkylene group, R ⁴ is an alkylene group having 2 to 18 carbon atoms, an alkenylene group, a divalent aromatic carbonization A hydrogen group or — (R ⁶ O) _u R ⁶ — (R ⁶ is an alkylene group having 2 to 4 carbon atoms, u is a 1 to 30 number indicating the average number of moles added of the oxyalkylene group), and R ⁵ is a carbon number 2-18 alkylene group, alkenylene group or divalent aromatic hydrocarbon group, t is an average value of 1-3 Is a number.) The pneumatic tire according to claim 1 or 2, wherein it contains a compound having a structure represented by.   The said steel cord has a structure formed by twisting so that the rubber | gum can penetrate | invade between the at least 1 set of adjacent steel strands located in a cord outermost layer. The described pneumatic tire.   The pneumatic tire according to any one of claims 1 to 4, wherein a cross-sectional shape of the steel cord is flat, and a major axis direction of the flat cross-section is arranged along a width direction of the belt layer. .   The steel cord has two steel strands arranged in parallel without being twisted with each other as a core, and the remaining steel strands are disposed between at least one pair of adjacent steel strands around the core. The pneumatic tire according to claim 5, which has a core-single layer sheath structure in which rubber is twisted so as to have a gap into which rubber can enter.   The pneumatic tire according to any one of claims 1 to 6, wherein the number of driven steel cords is 40 to 60/50 mm.   The pneumatic tire according to any one of claims 1 to 7, wherein a distance between adjacent steel cords in the belt layer is 0.4 to 1.0 mm.

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