PNEUMATIC TIRE

Abstract

To provide a pneumatic tire excellent in steering stability and fuel efficiency at high-speed driving, it is provided a pneumatic tire having a tread portion with a circumferential groove and a belt layer, wherein a monofilament cord is used as a reinforcing cord for the belt layer; the number of arrangements e (lines/5 cm) of the monofilament cords arranged per 5 cm in the tire width direction in the tire radial cross section of the belt layer is 50/5 cm or more; and the distance G (mm) from the surface of the land portion closest to the equatorial plane among land portions separated by the circumferential groove to the monofilament cord, and the loss tangent (30° C. tan δ) when the rubber composition constituting the surface of the tread portion is measured under conditions of temperature: 30° C., initial strain: 5%, dynamic strain: ±1%, frequency: 10 Hz, and deformation mode: tensile, satisfy 30° C. tan δ×G<1.5.

Claims

1. A pneumatic tire having a tread portion with a circumferential groove and a belt layer, wherein a monofilament cord is used as a reinforcing cord for the belt layer; the number of arrangements e (lines/5 cm) of the monofilament cords arranged per 5 cm in the tire width direction in the tire radial cross section of the belt layer is 50/5 cm or more; and the distance G (mm) from the surface of the land portion closest to the equatorial plane among land portions separated by the circumferential groove to the monofilament cord, and the loss tangent (30° C. tan δ) when the rubber composition constituting the surface of the tread portion is measured under conditions of temperature: 30° C., initial strain: 5%, dynamic strain: ±1%, frequency: 10 Hz, and deformation mode: tensile, satisfy the following formula 1.
30° C. tan δ×G<1.5  formula 1

2. The pneumatic tire according to claim 1, wherein the following formula 2 is satisfied.
30° C. tan δ×G<1.0  formula 2

3. The pneumatic tire according to claim 1, wherein the number of arrangements e (lines/5 cm) of the monofilament cord and the outer diameter r (mm) of the monofilament cord satisfy the following formula 3.
e×r.sup.2/4×π>4.0  formula 3

4. The pneumatic tire according to claim 3, wherein the following formula 4 is satisfied.
e×r.sup.2/4×π>5.0  formula 4

5. The pneumatic tire according to claim 1, wherein the loss tangent (0° C. tan δ) when the rubber composition constituting the surface of the tread portion is measured under conditions of temperature: 0° C., initial strain: 5%, dynamic strain: ±0.25%, frequency: 10 Hz, and deformation mode: tensile, is 0.5 or more.

6. The pneumatic tire according to claim 5, wherein the loss tangent (0° C. tan δ) is 0.7 or more.

7. The pneumatic tire according to claim 1, wherein the loss tangent (0° C. tan δ) and the distance G (mm) satisfy the following formula 5.
0° C. tan δ/G<0.14  formula 5

8. The pneumatic tire according to claim 7, wherein the following formula 6 is satisfied.
0° C. tan δ/G<0.10  formula 6

9. The pneumatic tire according to claim 1, wherein the angle formed by the monofilament cord and the straight line parallel to the tire circumferential direction is 10° or more and 35° or less.

10. The pneumatic tire according to claim 1, wherein the outer diameter r (mm) of the monofilament cord is 0.1 mm or more and 0.5 mm or less.

11. The pneumatic tire according to claim 1, wherein at least two layers of the belt layer are provided, and at least one set of belt layers adjacent to each other in the radial direction of the tire is arranged at a distance of 0.1 mm or more and 0.8 mm or less.

12. The pneumatic tire according to claim 1, wherein the tread portion has a plurality of circumferential grooves extending continuously in the tire circumferential direction, and the total cross-sectional area of the plurality of circumferential grooves is 10% or more and 30% or less of the cross-sectional area of the tread portion.

13. The pneumatic tire according to claim 1, wherein the tread portion has a plurality of circumferential grooves extending continuously in the tire circumferential direction, and the ratio (L.sub.80/L.sub.0) of the groove width L.sub.80 at a depth of 80% of the maximum depth of the circumferential groove to the groove width L.sub.0 of the circumferential groove on the ground contact surface of the tread portion is 0.3 or more and 0.7 or less.

14. The pneumatic tire according to claim 1, wherein the tread portion further 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% or more and 5.0% or less of the volume of the tread portion.

Description

EXAMPLES

[0209] Hereinafter, the present invention will be described in more detail with reference to Examples. In the following, tires having a tire size of 195/65R15 were manufactured.

1. Manufacture of tread components

[0210] First, the tread member was manufactured.

(1) Compounding Material

[0211] First, each compounding material shown below was prepared.

(A) Rubber component

(B) NR: TSR20

[0212] (B) SBR: HPR850 manufactured by JSR Corporation (Solution polymerization SBR) (Styrene content: 27.5% by mass, vinyl bond amount: 58.5% by mass)
(C) BR: UBEPOL BR150B manufactured by Ube Industries, Ltd. [0213] (cis content: 97% by mass, trans content: 2% by mass)
(b) Compounding materials other than rubber components
(A) Carbon Black: Show Black N220 manufactured by Cabot Japan Co., Ltd. [0214] (N.sub.2SA: 111 m.sup.2/g)
(B) Silica: Ultrasil VN3 manufactured by Evonik Industries, Inc. [0215] (BET specific surface area: 165 m.sup.2/g)
(C) Silane coupling agent: NXT manufactured by Momentive [0216] (3-Octanoylthiopropyltriethoxysilane)
(D) Oil: VIVATEC NC500 manufactured by H & R (Aroma process oil)
(E) Resin: Terpene styrene resin TO125 manufactured by Yasuhara Chemical Co., Ltd. (Aromatic modified terpene resin)
(F) Zinc oxide: Zinc Oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd.
(G) Anti-aging agent-1: Nocrack 6C manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. (N-Phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine)
(H) Anti-aging agent-2: Antage RD manufactured by Kawaguchi Chemical Industry Co., Ltd. (2,2,4-trimethyl-1,2-dihydroquinoline)
(I) Wax: Ozo Ace 0355 manufactured by Nippon Seiro Co., Ltd.
(J) Stearic acid: Stearic acid “Tsubaki” manufactured by NOF CORPORATION
(K) Cross-linking agent and vulcanization accelerator

[0217] Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0218] Vulcanization accelerator-1: Noxeller CZ-G (CZ) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. [0219] (N-cyclohexyl-2-benzothiazolyl sulfeneamide)

[0220] Vulcanization accelerator-2: Noxeller D (DPG) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. 1,3-Diphenylguanidine)

(2) Production of Rubber Composition

[0221] Next, materials other than sulfur and the vulcanization accelerator were kneaded under the condition of 150° C. for 5 minutes using a Banbury mixer according to the respective compounding contents shown in Tables 1 and 2, to obtain a kneaded product.

[0222] Then, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded using an open roll for 5 minutes under the condition of 80° C. to obtain a tread rubber composition.

(3) Fabrication of Tread Member

[0223] Next, the obtained tread rubber composition was molded into a predetermined shape to prepare a tread member.

2. Fabrication of Belt Members

[0224] Separately, a belt member was manufactured. Specifically, after arranging the steel cords having the configurations and outer diameters shown in Tables 1 and 2 with the ends (lines/5 cm) shown in Tables 1 and 2, a known belt layer rubber composition was coated on both sides thereof so that the average distance between the steel cords of the two belt layers becomes the distance D shown in Tables 1 and 2 to produce a belt member having a two-layer structure.

3. Manufacture of Tire

[0225] After that, together with other tire members, two layers are pasted together to form an unvulcanized tire so that the steel cord in the belt member intersects a straight line parallel to the tire circumferential direction at the angles shown in Tables 1 and 2; and the formed unvulcanized tire was press vulcanized for 10 minutes under conditions at 170° C. to produce tires for each test of size 195/65R15 (Examples 1 to 5 and Comparative Examples 1 to 5). The weight of each test tire was 7.5±0.1 kg.

[0226] In each test tire, the above-mentioned (L.sub.80/L.sub.0) is 0.5, the total cross-sectional area of the circumferential groove is 22% of the cross-sectional area of the tread portion, and the total volume of the lateral grooves, including a lateral groove in which the groove width/groove depth is 0.65, was 3.5% of the volume of the tread portion.

4. Parameter Calculation

[0227] Then, the distance G (mm) from the outermost surface of the tread portion of each test tire to the outermost surface of the belt layer was measured. At the same time, rubber was cut out from the rubber layer on the surface of the tread portion of each test tire to prepare a rubber test piece for viscoelasticity measurement having a length of 40 mm and a width of 4 mm. Then, 30° C. tan δ was measured using Iplexer series manufactured by GABO under conditions of temperature: 30° C., initial strain: 5%, dynamic strain: ±1%, frequency: 10 Hz, deformation mode: tensile. Further, 0. tan δ was measured under the conditions of temperature: 0° C., initial strain: 5%, dynamic strain: ±0.25%, frequency: 10 Hz, and deformation mode: tensile. The results are shown in Tables 1 and 2.

[0228] Thereafter, based on the results, “30° C. tan δ×G”, “e×r.sup.2/4×n” and “0° C. tan δ×G” were calculated. The results are shown in Tables 1 and 2.

5. Performance Evaluation Test

(1) Evaluation of Steering Stability During High-Speed Driving

[0229] Each test tire was mounted to all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc), filled with air so that the internal pressure became 250 kPa, and then driven at 120 km/h on the test course on a dry road surface. The handling property at that time was evaluated by the driver sensually on a scale of 5 from 1 to 5. Then, the total score of the evaluation by 20 drivers was calculated.

[0230] Next, the result in Comparative Example 3 was set to 100 and the results were indexed based on the following equation to evaluate the steering stability during high-speed driving. The larger the value, the better the steering stability at high-speed driving.

[0231] Steering Stability=[(Result of test tire)/(Result of Comparative Example 3)]×100

(2) Evaluation of Low Fuel Consumption During High-Speed Driving

[0232] Each test tire was mounted to all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc), filled with air so that the internal pressure became 250 kPa, and then driven on the test course on the dry road surface at a speed of 80 km/h. After going around the course for 10 km, the accelerator was released, and the distance from when the accelerator was turned off until the vehicle stopped was measured.

[0233] Next, the result in Comparative Example 2 was set to 100, and the results were indexed based on the following equation to relatively evaluate the low rolling resistance and to evaluate the fuel efficiency at high-speed driving. The larger the value, the longer the distance from the timing when the accelerator is turned off until the vehicle stops, the smaller the rolling resistance in the steady state, showing excellent low rolling resistance and excellent fuel efficiency.

Fuel efficiency=[(Result of test tire)/(Result of Comparative Example 2)]×100

(3) Comprehensive Evaluation

[0234] The evaluation results of (1) and (2) above were totaled to form a comprehensive evaluation.

[0235] The evaluation results are shown in Tables 1 and 2. In Tables 1 and 2, “1×1” in the cord configuration indicates a monofilament, and “1×2” indicates a twisted cord in which two filaments are twisted together.

TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 (Mixing) NR 10 10 10 10 10 10 SBR 80 80 80 80 85 85 BR 10 10 10 10 5 5 Carbon black 5 5 5 5 5 5 Silica 60 60 50 50 50 50 Silane coupling agent 6 6 5 5 5 5 Oil 15 15 15 15 15 15 Resin 3 3 8 8 13 13 Zinc oxide 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-1 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-2 1 1 1 1 1 1 Wax 1 1 1 1 1 1 Stearic acid 1 1 1 1 1 1 Sulfur 1.7 1.7 1.7 1.7 1.7 1.7 Vulcanization accelerator-1 2.5 2.5 2.5 2.5 2.5 2.5 Vulcanization accelerator-2 2.5 2.5 2.5 2.5 2.5 2.5 (Code) Cord configuration 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 Outer diameter (mm) 0.3 0.3 0.3 0.3 0.3 0.3 Ends e (book/5 cm) 60 75 75 75 75 90 (Belt layer) Average distance between cords D (mm) 0.45 0.45 0.45 0.45 0.45 0.45 Angle (°) 28 28 23 23 23 23 (Parameter) 30° C. tanδ 0.16 0.16 0.11 0.11 0.11 0.11 0° C. tanδ 0.65 0.65 0.65 0.65 0.72 0.72 Distance G (mm) from the tread surface 8.5 8.5 8.5 7.2 7 7 30° C. tanδ × G 1.36 1.36 0.94 0.79 0.77 0.77 e × r.sup.2/4 × π 4.24 5.30 5.30 5.30 5.30 6.36 0° C. tanδ/G 0.08 0.08 0.08 0.09 0.10 0.10 (Evaluation results) Steering stability at high-speed 109 117 126 132 134 140 driving Low fuel consumption during 105 103 109 115 118 116 high-speed driving Comprehensive evaluation 214 220 235 247 252 256

TABLE-US-00002 TABLE 2 Comparative Example 1 2 3 4 5 (Mixing) NR 10 10 10 10 10 SBR 80 80 80 80 85 BR 10 10 10 10 5 Carbon black 5 5 5 5 5 Silica 60 60 60 50 50 Silane coupling agent 6 6 6 5 5 Oil 10 10 15 15 15 Resin 45 45 3 8 13 Zinc oxide 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-1 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-2 1 1 1 1 1 Wax 1 1 1 1 1 Stearic acid 1 1 1 1 1 Sulfur 1.7 1.7 1.7 1.7 1.7 Vulcanization accelerator-1 2.5 2.5 2.5 2.5 2.5 Vulcanization accelerator-2 2.5 2.5 2.5 2.5 2.5 (Code) Cord configuration 1 × 2 1 × 1 1 × 2 1 × 2 1 × 2 Outer diameter (mm) 0.59 0.3 0.59 0.59 0.59 Ends e (book/5 cm) 42 42 60 42 42 (Belt layer) Average distance between cords D (mm) 0.45 0.45 0.45 0.45 0.45 Angle (°) 28 28 28 28 28 (Parameter) 30° C. tanδ 0.21 0.21 0.16 0.11 0.11 0° C. tanδ 1.23 1.23 0.65 0.65 0.72 Distance G (mm) from the 8.5 8.5 8.5 6.5 6.5 tread surface 30° C. tanδ× G 1.79 1.79 1.36 0.72 0.72 e × r.sup.2/4 × π 11.48 2.97 16.40 11.48 11.48 0° C. tanδ/G 0.14 0.14 0.08 0.10 0.11 (Evaluation results) Steering stability at high speed 88 85 100 95 90 Low rolling resistance (fuel efficiency) 85 100 90 90 95 Comprehensive evaluation 173 185 190 185 185

[0236] The results in Tables 1 and 2 shows that, when the reinforcing cord is a monofilament, the end e is 50 (lines/5 cm) or more, and the product of the distance G from the land surface closest to the equatorial plane to the monofilament and 30° C. tan δ of the rubber layer constituting the surface of the tread portion is less than 1.5, that is, (formula 1) is satisfied, a pneumatic tire having excellent steering stability and fuel efficiency at high-speed driving can be provided.

[0237] Then, it can be seen that, by control of (formula 2) to (formula 6), by appropriate control of 0° C. tan δ of the rubber layer constituting the surface of the tread portion, the angle of the cord and outer diameter, or the like, it is possible to provide pneumatic tires with even better steering stability and fuel efficiency.

[0238] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiments within the same and equivalent scope as the present invention.