tire

Abstract

Provided is a tire which improves plunger strength and belt edge separation resistance while reducing rolling resistance, and in which these properties are achieved. The present invention relates to a pneumatic tire which comprises a tread section 1, side wall sections 2, and bead sections 3, and in which a belt layer 7 is arranged on the outer circumferential side of a carcass layer 4 in the tread section 1. A tread gauge GT is set to be 10 mm or less. A belt cord is configured from a steel cord having a cord diameter of 0.62-0.72 mm, a tensile elastic modulus of 175 GPa or greater under a load of 5-30 N, and a breaking stress of 3400 MPa or greater. The thickness of the belt layer at the tire equator CL is set to be 0.90-1.05 mm. In addition, in a tread rubber, the blending amount Ms of silica and the blending amount Mc of carbon black are set so as to satisfy Ms / (Ms + Mc) > 0.50, and the breaking strength TB and tanδ60℃ of the tread rubber are set so as to satisfy TB / tanδ60℃ > 70.

Description

tire

[0001] This invention relates to a tire that includes a belt layer made of steel cords.

[0002] In recent years, from the perspective of improving fuel efficiency during vehicle operation, measures have been taken to lighten tires by reducing the rubber thickness of the tread, for example, and to reduce rolling resistance by increasing the amount of silica in the rubber composition that makes up the tread (see, for example, Patent Document 1). However, there is a concern that plunger strength will decrease in such tires. "Plunger strength" refers to the strength measured in a plunger energy test, which measures the fracture energy when a plunger of a predetermined size is pressed against the center of the tread and the tire breaks. It is an indicator of the durability of a pneumatic tire against fracture energy when it overcomes bumps on uneven road surfaces (fracture durability of the tread against bump input). For example, it is expected that the decrease in plunger strength can be suppressed if a high-strength belt is used in the above tire, but there is a concern that belt edge separation may occur due to a decrease in adhesion during driving if a high-strength belt is simply used. Therefore, measures are needed to reduce rolling resistance while preventing a decrease in plunger strength and the occurrence of belt edge separation.

[0003] Japanese Patent Application Publication No. 2023-002855

[0004] The objective of the present invention is to provide a tire that improves plunger strength and belt edge separation resistance while reducing rolling resistance, thereby achieving both of these performance characteristics.

[0005] The present invention, for achieving the above objective, comprises a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of these sidewall portions, with a carcass layer mounted between these pair of bead portions, and a plurality of belt layers including belt cords inclined with respect to the circumferential direction of the tire arranged on the outer circumference side of the carcass layer in the tread portion, wherein the rubber gauge of the tread portion is 10 mm or less, and the belt cords have a cord diameter of 0.62 mm to 0.72 mm and a tensile modulus of elasticity at a load of 5 N to 30 N The tread consists of steel cords with a strength of 175 GPa or more and a breaking stress of 3400 MPa or more, the thickness of each layer of the belt layer at the tire equator is 0.90 mm to 1.05 mm, the tread rubber constituting the tread portion consists of a rubber composition in which silica and carbon black are compounded with diene rubber, the amount of silica compounded per 100 parts by mass of the diene rubber is Ms [unit: parts by mass], the amount of carbon black compounded per 100 parts by mass of the diene rubber is Mc [unit: parts by mass], the breaking strength of the tread rubber at room temperature is TB [unit: MPa], and the loss loss tangent of the tread rubber at 60°C is tanδ 60℃ In this case, the tread rubber is characterized by satisfying the following equations (1) and (2): Ms / (Ms+Mc)>0.50 ... (1) TB / tanδ 60℃ >70 ... (2)

[0006] In this invention, the rubber gauge in the tread portion is sufficiently small, and the tread rubber has the above-described compound and physical properties, thus reducing rolling resistance. On the other hand, since the belt cord has the above-described characteristics and the thickness of the belt layer is within the above-described appropriate range, rolling resistance can be reduced while improving plunger strength and resistance to belt edge separation. Specifically, since the cord diameter and belt layer thickness of the belt cord are within the above-described appropriate range, rolling resistance can be reduced while ensuring plunger strength. The elastic modulus of the belt cord (steel cord) is sufficiently large as described above, which prevents a decrease in adhesion during driving and improves resistance to belt edge separation. The breaking stress of the belt cord (steel cord) is sufficiently large as described above, which improves plunger strength. Through the cooperation of these factors, it is possible to reduce rolling resistance while improving plunger strength and resistance to belt edge separation, achieving a good balance between these performances.

[0007] In this invention, the cross-sectional area S [mm²] of the belt cord 2 It is preferable that the amount of steel cord A, calculated as the product of [number of strands / 50mm] and the number of strands E [strands / 50mm] driven into the belt cord per 50mm in the direction perpendicular to the extension direction of the belt cord, be between 7.5 and 9.5. Setting the amount of steel cord A in this way is advantageous for achieving both a reduction in rolling resistance and an improvement in plunger strength.

[0008] In the present invention, the rubber composition constituting the tread rubber preferably contains 5 parts by mass or more of resin per 100 parts by mass of diene rubber, and the resin is preferably at least one selected from the group consisting of C5 / C9 petroleum resins, C9 petroleum resins, dicyclopentadiene resins, dicyclopentadiene / C9 resins, hydrogenated resins thereof, and terpene resins. By incorporating such a resin, the physical properties of the tread rubber are improved, which is advantageous in reducing rolling resistance.

[0009] In the present invention, it is preferable that the belt cord has a 1x2 structure. A belt cord with such a structure has good adhesion to the covering rubber and is less prone to peeling during driving, which is advantageous for improving resistance to belt edge separation.

[0010] In this invention, the tensile modulus of elasticity [unit: GPa] of the belt cord (steel cord) under a load of 5N to 30N is determined by performing a tensile test on a belt cord (steel cord) taken from a tire, in accordance with "Breaking load and total elongation at breaking" (section 6.4) of JIS G 3510:1992 "Test method for steel tire cord," with a test length of 250 mm and a tensile speed of 5 mm / min. The resulting slope of the load-strain curve in the load range of 5N to 30N is then divided by the sum of the cross-sectional areas of the strands constituting the cord. The breaking stress [unit: MPa] of a belt cord (steel cord) is a value obtained by dividing the stress at which the cord breaks, measured by performing a tensile test on a belt cord (steel cord) taken from a tire, in accordance with "Breaking load and total elongation at break" (section 6.4) of JIS G 3510:1992 "Test method for steel tire cords" under the conditions of a test length of 250 mm and a tensile speed of 5 mm / min, by the sum of the cross-sectional areas of the strands constituting the cord.

[0011] In this invention, the tensile strength TB [unit: MPa] of the tread rubber is the stress at fracture measured in accordance with JIS K 6251:2017 "Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties" by punching out a JIS No. 3 dumbbell-shaped test piece (thickness 2 mm) and measuring under conditions of room temperature (temperature 20°C) and a tensile speed of 500 mm / min. The loss tangent tanδ of the tread rubber. 60℃ These values ​​were measured using a viscoelastic spectrometer in accordance with JIS K 6394:2007 "Vulcanized rubber and thermoplastic rubber - Method for determining dynamic properties - General guidelines," under the conditions of a tensile deformation strain of 10% ± 2%, a frequency of 20 Hz, and a temperature of 60°C.

[0012] Figure 1 is a meridian cross-sectional view of a tire according to an embodiment of the present invention.

[0013] The configuration of the present invention will be described in detail below with reference to the attached drawings.

[0014] The tire of the present invention, when it is a pneumatic tire as shown in Figure 1, comprises a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged on the radially inner side of the sidewall portions 2. In Figure 1, the symbol CL indicates the tire equator. Although not depicted in Figure 1 because it is a meridian cross-sectional view, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the circumferential direction of the tire and form an annular shape, thereby forming the basic toroidal structure of the pneumatic tire. The following explanation using Figure 1 is basically based on the illustrated meridian cross-sectional shape, but each tire component extends in the circumferential direction of the tire and forms an annular shape.

[0015] A carcass layer 4, including multiple reinforcing cords (carcass cords) extending in the tire diameter direction, is mounted between a pair of left and right bead sections 3. A bead core 5 is embedded in each bead section 3, and a bead filler 6 with a roughly triangular cross-section is arranged on the outer circumference of the bead core 5. The carcass layer 4 is folded back around the bead core 5 from the inside to the outside in the tire width direction. As a result, the bead core 5 and bead filler 6 are enclosed by the main body portion of the carcass layer 4 (the portion extending from the tread section 1 through each sidewall section 2 to each bead section 3) and the folded portion (the portion that is folded back around the bead core 5 in each bead section 3 and extends toward each sidewall section 2).

[0016] Multiple belt layers (two in Figure 1) are embedded on the outer periphery of the carcass layer 4 in the tread section 1. Each belt layer 7 includes multiple reinforcing cords (belt cords) inclined with respect to the tire's circumferential direction, and the belt cords are arranged so as to intersect each other between layers. In these belt layers 7, the inclination angle of the belt cords with respect to the tire's circumferential direction is set to, for example, a range of 10° to 40°. Steel cords, as described later, are used as the belt cords constituting the belt layers 7.

[0017] To improve high-speed durability, at least one belt cover layer 8 may be provided on the outer circumference of the belt layer 7. The belt cover layer 8 includes reinforcing cords (belt cover cords) oriented in the circumferential direction of the tire. In the belt cover layer 8, the angle of the belt cover cords with respect to the circumferential direction of the tire is set to, for example, 0° to 5°. For example, organic fiber cords can be used as the belt cover cords that make up the belt cover layer 8. The belt cover layer 8 can be a full cover layer 8a that covers the entire width of the belt layer 7, or a pair of edge cover layers 8b that locally cover both ends of the belt layer 7 in the tire width direction, either individually or in combination (in the illustrated example, both the full cover layer 8a and the edge cover layers 8b are provided). The belt cover layer 8 is preferably constructed by spirally winding a strip material, in which at least one belt cover cord is covered with coated rubber, in the circumferential direction of the tire, and a jointless structure is particularly preferred.

[0018] In the tread portion 1, a tread rubber layer 10 is arranged on the outer circumference side of the above-mentioned tire components (carcass layer 4, belt layer 7, belt cover layer 8). The tread rubber layer 10 may be a single-layer structure made of one type of rubber, or it may be a laminated structure in which two types of rubber with different physical properties (a cap tread layer 11 exposed on the tread surface and an under tread layer 12 arranged on its inner circumference) are laminated in the tire diameter direction. In the sidewall portion 2, a side rubber layer 20 is arranged on the outer circumference side (outer side in the tire width direction) of the carcass layer 4, and in the bead portion 3, a rim cushion rubber layer 30 is arranged on the outer circumference side (outer side in the tire width direction) of the carcass layer 4.

[0019] Since this invention primarily relates to the belt layer 7 and tread rubber layer 10 described above, the basic internal structure (cross-sectional structure) of the tire, excluding these, is not limited to the general structure described above.

[0020] In the present invention, the belt cord constituting the belt layer 7 is made of steel cord as described above. In particular, the belt cord used is a steel cord having a cord diameter of 0.62 mm to 0.72 mm, preferably 0.62 mm to 0.68 mm, a tensile modulus of elasticity of 175 GPa or more, preferably 180 GPa to 250 GPa, under a load of 5 N to 30 N, and a breaking stress of 3400 MPa or more, preferably 3500 MPa to 3900 MPa. Such a steel cord has a moderately large cord diameter and a sufficiently large breaking stress, thus ensuring excellent plunger strength. Furthermore, because such a steel cord has a sufficiently large tensile modulus, peeling during operation is less likely to occur, improving resistance to belt edge separation.

[0021] If the cord diameter of the belt cord is less than 0.62 mm, sufficient cord strength cannot be ensured, and the effect of improving plunger strength will be limited. If the cord diameter of the belt cord exceeds 0.72 mm, the thickness of the belt layer 7 increases, and the effect of reducing rolling resistance will be limited. If the breaking stress of the belt cord is less than 3400 MPa, sufficient cord strength cannot be ensured, and the effect of improving plunger strength will be limited. If the tensile modulus of the belt cord under a load of 5 N to 30 N is less than 175 GPa, the deterioration of adhesion during running cannot be sufficiently suppressed, and the effect of improving resistance to belt edge separation will be limited.

[0022] The thickness of the belt layer 7 using the above-mentioned belt cord at the tire equator CL (the total thickness of the belt layer 7 including the coating rubber in the pneumatic tire after vulcanization) is measured by the belt gauge G B Therefore, belt gauge G B The thickness of the belt layer 7 (belt gauge G) is 0.90 mm to 1.05 mm, preferably 0.95 mm to 1.00 mm. B The smaller the thickness, the lower the rolling resistance, and the larger the thickness, the more plunger strength can be ensured. By setting this thickness within an appropriate range, rolling resistance can be reduced while ensuring plunger strength. The thickness of the belt layer 7 at the tire equator CL (belt gauge G) B), if it is less than 0.90 mm, the effect of securing plunger strength will be limited. The thickness of the belt layer 7 at the tire equator CL (belt gauge G B ) exceeds 1.05 mm, the effect of reducing rolling resistance will be limited.

[0023] The structure of the belt cord (steel cord) is not particularly limited, but it preferably has a 1×N structure obtained by twisting N (N=2 to 6) strands together. In particular, a 1×2 structure can be suitably employed. A steel cord having such a structure is excellent in adhesiveness with the coating rubber, which is advantageous for preventing belt edge separation. Further, by adopting the 1×N structure (particularly the 1×2 structure), it becomes easy to secure physical properties such as the aforementioned tensile elastic modulus and breaking stress.

[0024] Let the cross-sectional area of the belt cord be S [mm 2 per cord], and let E [cords / 50mm] be the number of driven belt cords per 50 mm in the direction orthogonal to the extending direction of the belt cords in the belt layer 7. When the product of these is defined as the steel cord amount A (=S×E), the steel cord amount A is preferably 7.5 to 9.5, more preferably 7.5 to 8.8. Setting the steel cord amount A in this manner is advantageous for achieving both reduction in rolling resistance and improvement in plunger strength. If the steel cord amount A is less than 7.5, the effect of securing plunger strength will be limited. If the steel cord amount A exceeds 9.5, the effect of reducing rolling resistance will be limited. Note that the cross-sectional area S of the belt cord [mm 2 per cord] and the individual values of the driven number E [cords / 50mm] are not particularly limited as long as the above steel cord amount A is satisfied, but for example, the cross-sectional area S can be set to 0.15 to 0.21, and the driven number E can be set to 43 to 60, for example.

[0025] In the present invention, the rubber gauge in the tread portion 1 (tread gauge G T ) is 10 mm or less, preferably 9.5 mm or less. The rubber gauge in the tread portion 1 (tread gauge G TThe tread gauge (tread gauge G) is the thickness of the tread rubber layer 10 provided on the outer circumference of the tire components (carcass layer 4, belt layer 7, belt cover layer 8) in the tread section 1. As shown in Figure 1, it is the rubber thickness from the tread surface of the tread section 1 to the outermost component in the tire direction. If the tread rubber layer 10 has a laminated structure of a cap tread layer 11 and an under tread layer 12, it is the total thickness of these layers. As a result, even at the thickest point of the rubber gauge in the tread section 1, it does not exceed 10 mm, thus reducing the amount of rubber used in the tread section 1, reducing tire weight, and lowering rolling resistance. T If the diameter exceeds 10 mm, the effect of reducing rolling resistance becomes limited.

[0026] The rubber constituting the tread rubber layer 10 (tread rubber) consists of a rubber composition in which at least silica and carbon black are compounded with a diene-based rubber as the main component. When the amount of silica compounded per 100 parts by mass of diene-based rubber is Ms [unit: parts by mass] and the amount of carbon black compounded per 100 parts by mass of diene-based rubber is Mc [unit: parts by mass], these compounding amounts satisfy the relationship Ms / (Ms+Mc) > 0.50, preferably 0.60 ≤ Ms / (Ms+Mc) ≤ 0.99. Furthermore, the breaking strength of the tread rubber at room temperature is TB [unit: MPa], and the loss tangent of the tread rubber at 60°C is tanδ 60℃ When these are TB / tanδ 60℃ >70, preferably TB / tanδ 60℃ The relationship ≥ 75 is satisfied. Because the tread rubber has such a compound and physical properties, it can effectively reduce rolling resistance.

[0027] If the compounding amounts Ms and Mc do not satisfy the above relationship, sufficient silica will not be incorporated into the tread rubber, resulting in a limited effect in reducing rolling resistance. (Breaking strength TB and loss tangent tanδ) 60℃If the above relationship is not satisfied, the effect of improving abrasion resistance will be limited. Although the individual ranges of the blending amounts Ms and Mc are not limited, the blending amount Ms of silica relative to 100 parts by mass of diene rubber can be set, for example, from 40 parts by mass to 100 parts by mass, and the blending amount Mc of carbon black relative to 100 parts by mass of diene rubber can be set, for example, from 5 parts by mass to 40 parts by mass. Similarly, the breaking strength TB and loss tangent tanδ 60℃ Although the individual ranges of are not limited, the breaking strength TB is, for example, 15 MPa to 30 MPa, and the loss tangent tanδ 60℃ can be set to 0.09 to 0.31, for example.

[0028] As silica, those commonly used in rubber compositions for tires can be used. Examples include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These may be used alone or in combination of two or more. As carbon black, those commonly used in rubber compositions for tires can be used. For example, carbon blacks such as furnace black, acetylene black, thermal black, channel black, and graphite may be blended. Among these, furnace black is preferred, and specific examples thereof include SAF, ISAF, ISAF-HS, ISAF-LS, IISAF, IISAF-HS, HAF, HAF-HS, HAF-LS, FEF, and the like.

[0029] The above rubber composition may be blended with fillers other than silica and carbon black. Examples of other fillers include materials generally used in rubber compositions for tires, such as clay, talc, calcium carbonate, mica, and aluminum hydroxide.

[0030] When blending silica as described above, a silane coupling agent may also be blended. By blending a silane coupling agent, the dispersibility of silica in a rubber component (diene rubber) can be improved. Examples of the silane coupling agent include bis-(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, γ-mercaptopropyl triethoxysilane, and 3-octanoylthiopropyl triethoxysilane. The blending amount of the silane coupling agent is preferably 3.0% by mass to 10.0% by mass, more preferably 4.0% by mass to 9.0% by mass, relative to the blending amount of silica. If the blending amount of the silane coupling agent is less than 3.0% by mass of the blending amount of silica, the blending amount is too small, so the effect resulting from blending the silane coupling agent cannot be sufficiently expected. If the blending amount of the silane coupling agent exceeds 10% by mass of the blending amount of silica, the silane coupling agents will condense with each other, which may adversely affect the hardness and strength.

[0031] In addition to the above-mentioned silica and carbon black, the resin described below can also be blended into the rubber composition constituting the tread rubber. The blending amount of the resin is preferably 5 parts by mass or more, more preferably 10 parts by mass to 50 parts by mass, per 100 parts by mass of the diene rubber. Examples of the resin include at least one selected from the group consisting of C5 / C9 petroleum resins, C9 petroleum resins, dicyclopentadiene resins (DCPD resins), dicyclopentadiene / C9 resins (DCPD / C9 resins), hydrogenated resins thereof, and terpene resins. Blending such a resin improves the physical properties of the tread rubber and is advantageous for reducing rolling resistance. If the blending amount of the resin is less than 5 parts by mass, the additional effect resulting from blending the resin will be limited.

[0032] Other compounding agents besides those mentioned above may be added to the rubber composition constituting the tread rubber. Examples of other compounding agents include vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, liquid polymers, and various other compounding agents commonly used in tire rubber compositions. The amounts of these compounding agents can be the conventional amounts, as long as they do not contradict the objectives of the present invention. As for the mixing machine, ordinary rubber mixing machines such as Banbury mixers, kneaders, and rolls can be used.

[0033] The present invention addresses, among the various conditions described above, the rubber gauge (tread gauge G) in at least the tread portion 1. T The width of the belt (steel cord) is 10 mm or less, the cord diameter of the belt cord is 0.62 mm to 0.72 mm, the tensile modulus of elasticity under a load of 5 N to 30 N is 175 GPa or more, the breaking stress is 3400 MPa or more, and the thickness of the belt layer 7 at the tire equator (belt gauge G) B The thickness is 0.90 mm to 1.05 mm, the tread rubber constituting the tread portion 1 is made of a rubber composition in which silica and carbon black are compounded with diene rubber, the amount of silica Ms [unit: parts by mass] and the amount of carbon black Mc [unit: parts by mass] per 100 parts by mass of diene rubber satisfy the relationship Ms / (Ms+Mc) > 0.50, and the breaking strength TB [unit: MPa] of the tread rubber at room temperature and the loss tangent tanδ at 60°C 60℃ toga TB / tanδ 60℃ The relationship >70 is satisfied. Through the combined effects of the above-mentioned effects based on each of these conditions, the present invention can reduce rolling resistance while improving plunger strength and resistance to belt edge separation, achieving a good balance between these performances. Furthermore, by appropriately combining other conditions, effects based on those conditions are added, thereby effectively achieving a reduction in rolling resistance and an improvement in plunger strength and resistance to belt edge separation.

[0034] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples.

[0035] The tire size is 275 / 45R20, and it has the internal structure (cross-sectional structure) illustrated in Figure 1. Regarding the tread portion (tread rubber layer), the rubber gauge (tread gauge) in the tread portion, the type of tread rubber, the breaking strength TB of the tread rubber at room temperature, and the loss tangent tanδ of the tread rubber at 60°C are specified. 60℃ The ratio TB / tanδ 60℃ The ratio of silica content Ms to the total amount of carbon black Mc [unit: parts by mass] in the tread rubber (Ms / (Ms+Mc)), and the amount of resin [unit: parts by mass] in the tread rubber are set as shown in Tables 1 and 2. Furthermore, for the belt layer (belt cord), the wire structure, cord diameter, tensile modulus under loads of 5N to 30N, breaking stress, thickness of the belt layer at the tire equator (belt gauge), and cross-sectional area S [mm²] of the belt cord are set. 2 Conventional examples, comparative examples 1 to 11, and examples 1 to 12 (test tires) were manufactured with the amount of steel cord A, calculated as the product of the number of belt cords per 50 mm in the direction perpendicular to the extension direction of the belt cord E [cords / 50 mm], set as shown in Tables 1 to 2.

[0036] In the "Type of Tread Rubber" column of Tables 1 and 2, the number (A to E) of which of the tread rubbers A to E, consisting of the formulations shown in Table 3, was used is indicated. 60℃ Regarding the section marked "", the tread rubber's breaking strength TB [unit: MPa] was measured in accordance with JIS K 6251:2017 "Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties" by punching out a JIS No. 3 dumbbell-shaped test piece (thickness 2 mm) at room temperature (temperature 20°C) and a tensile speed of 500 mm / min. The tread rubber's loss tangent tanδ 60℃The tensile modulus was measured using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) in accordance with JIS K 6394:2007 "Vulcanized rubber and thermoplastic rubber - Method for determining dynamic properties - General guidelines," under the conditions of a tensile deformation strain of 10% ± 2%, a vibration frequency of 20 Hz, and a temperature of 60°C. The "tensile modulus" in Tables 1 and 2 was calculated by performing a tensile test on a belt cord (steel cord) taken from a tire, in accordance with "Breaking load and total elongation at breaking" (section 6.4) of JIS G 3510:1992 "Test method for steel tire cord," with a test length of 250 mm and a tensile speed of 5 mm / min. The slope of the resulting load-strain curve in the load range of 5 N to 30 N was divided by the sum of the cross-sectional areas of the wires constituting the cord. The "breaking stress" in Tables 1 and 2 was calculated by dividing the stress at which the cord broke, measured by tensile testing of belt cords (steel cords) taken from tires, in accordance with "Breaking load and total elongation at break" (section 6.4) of JIS G 3510:1992 "Test method for steel tire cords" with a test length of 250 mm and a tensile speed of 5 mm / min, by the sum of the cross-sectional areas of the strands constituting the cord.

[0037] These test tires were evaluated for low rolling resistance, plunger strength, and belt separation durability using the evaluation methods described below, and the results are shown in Tables 1 and 2.

[0038] Each low-rolling-resistance test tire was mounted on a wheel with a rim size of 20 x 9J, inflated to an air pressure of 200 kPa, and measured while running at a speed of 80 km / h using an indoor drum testing machine (drum diameter: 1707 mm) with a load equivalent to 85% of the maximum load at the specified air pressure as described in the JATMA yearbook. The evaluation results were expressed as an index using the reciprocal of the measured value, with the conventional value set to 100. A larger index value indicates lower rolling resistance and superior low-rolling-resistance performance.

[0039] For each plunger strength test, the tires were mounted on a wheel with a rim size of 20 x 9J, the air pressure was set to 250 kPa, and a tire failure test (plunger failure test) was performed by pressing a plunger with a plunger diameter of 19 ± 1.6 mm against the center of the tread at a load speed (plunger indentation speed) of 50.0 ± 1.5 m / min, in accordance with JIS D4230:1998 "Automotive Tires". The tire strength (tire failure energy) was measured. The evaluation results are shown as an index with the measured value of Conventional Example 1 set to 100. A larger value indicates greater failure energy (plunger energy) and superior plunger strength.

[0040] For the belt separation durability test, each test tire was mounted on a wheel with a rim size of 20 x 9J. Each test tire was then sealed in oxygen at an internal pressure of 280 kPa and kept in a chamber maintained at room temperature of 70°C for two weeks. After this, the oxygen was released, and the tire was filled with air at an internal pressure of 170 kPa. The pre-treated test tires were then tested using a steel drum testing machine (1707 mm in diameter) with a smooth drum surface. The test was conducted at an ambient temperature of 38 ± 3°C, a running speed of 50 km / h, a slip angle of 0° ± 3°, and a load variation of 70% ± 40% of the JATMA maximum load. The load and slip angle were varied using a 0.083 Hz square wave for 100 hours, covering 5000 km. After the test, the tire was cut open, and the length of the widthwise separation (peeling) at the widthwise end of the belt layer was measured. The evaluation results were expressed as an index using the reciprocal of the measured value, with the conventional value set to 100. A higher index value indicates a smaller separation length and superior durability against belt edge separation.

[0041]

[0042]

[0043]

[0044] The types of raw materials used in Table 3 are shown below. • SBR: Styrene-butadiene rubber manufactured by the following method • BR: Butadiene rubber, Nipol BR1220 (polybutadiene rubber, glass transition temperature Tg = -107°C) manufactured by Zeon Corporation • Silica: ZEOSIL 1165MP (CTAB adsorption specific surface area: 1160 m²) manufactured by Solvay 2 / g) ・CB: Carbon black, manufactured by Tokai Carbon Co., Ltd. Seast 3 (HAF carbon black, nitrogen adsorption specific surface area (N2SA): 79m² 2 ( / g) ・Oil: Shell Lubricants Japan Extract No. 4 S ・Resin: Aromatic modified terpene resin, Yasuhara Chemical YS Resin TO-125 (glass transition temperature Tg = 78°C) ・Anti-aging agent: Flexis 6 PPD ・Wax: Ouchi Shinko Chemical Sunnock ・Silane coupling agent: Evonik Degussa Si69 ・Vulcanization accelerator 1: Ouchi Shinko Chemical Noxellar CZ-G (CZ) ・Vulcanization accelerator 2: Sumitomo Chemical Soxinol D-G (DPG) ・Sulfur: Tsurumi Chemical Industries Kinka brand oil-containing fine sulfur powder

[0045] Method for producing styrene-butadiene rubber First, as a polymerization step, cyclohexane 1000 g / h (hours), tetramethylethylenediamine 0.155 g / h, 1,3-butadiene 159.3 g / h, 1-butene 0.364 g / h, and styrene 42.9 g / h were charged into an autoclave with a stirrer under a nitrogen atmosphere. Then, n-butyllithium was continuously added at 1.43 mmol / h, and polymerization was started at 70°C. Once the polymerization was sufficiently stable, 1-(trimethoxysilyl)-4-vinylbenzene was added at 0.04 g / h, and the reaction was carried out with stirring. Next, as a modification step, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine was added at 0.17 g / h to the solution that flowed out of the reactor outlet, and the reaction was carried out with stirring. After that, methanol was added as a polymerization inhibitor to obtain a solution containing conjugated diene rubber. To the obtained solution, 1.142 parts by mass of Irganox 1520L (manufactured by BASF) was added as an antioxidant per 100 parts by mass of conjugated diene rubber. The solvent was then removed by steam stripping, and the mixture was vacuum-dried at 60°C for 24 hours to obtain solid conjugated diene rubber. The conjugated diene rubber obtained by polymerization is a reaction product of a conjugated diene polymer, which is a copolymer of butadiene, styrene, and a branching agent, and a modifying agent. It is a modified conjugated diene rubber having modifying groups containing nitrogen atoms, silicon atoms, and adjacent oxygen atoms derived from the modifying agent. The conjugated diene rubber (styrene-butadiene rubber) synthesized as described above has a weight-average molecular weight Mw = 3.15 × 10⁻⁵ 5 It has the following characteristics: (g / mol), styrene content St = 36%, vinyl content Vn = 27%, and glass transition temperature Tg = -54°C.

[0046] As is clear from Tables 1-2, the tires of Examples 1-12 maintained or improved low rolling resistance, plunger strength, and belt separation durability compared to the conventional example, achieving a good balance of these performance characteristics. On the other hand, Comparative Example 1 (an example in which plunger strength was improved by increasing the tread gauge in the conventional example) had a large tread gauge, a low tensile modulus of elasticity under loads of 5N to 30N, and a large belt gauge, resulting in reduced low rolling resistance and belt separation durability. Comparative Example 2 had a low tensile modulus of elasticity of the belt cord under loads of 5N to 30N, resulting in reduced belt separation durability. Comparative Example 3 had a low breaking strength of the belt cord, resulting in reduced plunger strength. Comparative Example 4 had a large tread gauge, resulting in reduced low rolling resistance. Comparative Example 5 had a small belt gauge, resulting in reduced belt separation durability. Comparative Example 6 had a large belt gauge, resulting in reduced low rolling resistance. Comparative Example 7 had a small cord diameter of the belt cord, resulting in reduced belt separation durability. Comparative Example 8 had a larger belt cord diameter, resulting in reduced rolling resistance. Comparative Example 9 used tread rubber B and TB / tanδ 60℃ Since both Ms / (Ms+Mc) were small, rolling resistance and plunger strength decreased. Comparative Example 10 used tread rubber C and TB / tanδ 60℃ Because the value was small, rolling resistance and plunger strength were reduced. Comparative Example 11 used tread rubber D, and because Ms / (Ms+Mc) was small, plunger strength was reduced.

[0047] 1. Tread section 2. Sidewall section 3. Bead section 4. Carcass layer 5. Bead core 6. Bead filler 7. Belt layer 8. Belt cover layer 10. Tread rubber layer 20. Side rubber layer 30. Rim cushion rubber layer CL Tire equator

Claims

1. A pneumatic tire comprising a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of these sidewall portions, with a carcass layer mounted between these pair of bead portions, and a plurality of belt layers including belt cords inclined with respect to the circumferential direction of the tire arranged on the outer circumference side of the carcass layer in the tread portion, wherein the rubber gauge of the tread portion is 10 mm or less, the belt cords consist of steel cords with a cord diameter of 0.62 mm to 0.72 mm, a tensile modulus of elasticity of 175 GPa or more under a load of 5 N to 30 N, and a breaking stress of 3400 MPa or more, and the thickness of each layer of the belt layer at the tire equator is 0.90 mm to 1.05 mm. The tread rubber constituting the tread portion consists of a rubber composition in which silica and carbon black are compounded with diene rubber, the amount of silica compounded with 100 parts by mass of diene rubber is Ms [unit: parts by mass], the amount of carbon black compounded with 100 parts by mass of diene rubber is Mc [unit: parts by mass], the breaking strength of the tread rubber at room temperature is TB [unit: MPa], and the loss tangent of the tread rubber at 60°C is tanδ 60℃ In this case, the tread rubber is a pneumatic tire characterized by satisfying the following equations (1) and (2): Ms / (Ms+Mc)>0.50 ... (1) TB / tanδ 60℃ >70 ... (2) 2. Cross-sectional area S of the belt cord [mm²] 2 The pneumatic tire according to claim 1, characterized in that the amount of steel cord A, calculated as the product of [number of strands / 50 mm] and the number of strands E [strands / 50 mm] driven into the belt cord per 50 mm in a direction perpendicular to the extension direction of the belt cord, is 7.5 to 9.

5.

3. The pneumatic tire according to claim 1 or 2, characterized in that the rubber composition constituting the tread rubber further comprises 5 parts by mass or more of resin per 100 parts by mass of the diene-based rubber, wherein the resin is at least one selected from the group consisting of C5 / C9 petroleum resin, C9 petroleum resin, dicyclopentadiene resin, dicyclopentadiene / C9 resin, and hydrogenated resins thereof, and terpene resins.

4. The pneumatic tire according to any one of claims 1 to 3, characterized in that the belt cord has a 1x2 structure.

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