TIRE

Abstract

A tire having a tread portion which can improve wear resistance performance when running on uneven ground, wherein the cap rubber layer forming the tread portion contains styrene-butadiene rubber (SBR), isoprene-based rubber, and silica; the content of the styrene-butadiene rubber (SBR) in 100 parts by mass of the rubber component is 40 parts by mass or more and 60 parts by mass or less, and the styrene content of the styrene-butadiene rubber (SBR) is 25% by mass or less; the content of the isoprene-based rubber in 100 parts by mass of the rubber component is more than 30 parts by mass; the content of the silica with respect to 100 parts by mass of the rubber component is 60 parts by mass or less; and the thickness of the tread portion is 9.4 mm or less.

Claims

1. A tire having a tread portion, wherein the cap rubber layer forming the tread portion contains styrene-butadiene rubber (SBR), isoprene-based rubber, and silica; the content of the styrene-butadiene rubber (SBR) in 100 parts by mass of the rubber component is 40 parts by mass or more and 60 parts by mass or less, and the styrene content of the styrene-butadiene rubber (SBR) is 25% by mass or less; the content of the isoprene-based rubber in 100 parts by mass of the rubber component is more than 30 parts by mass; the content of the silica with respect to 100 parts by mass of the rubber component is 60 parts by mass or less; and the thickness of the tread portion is 9.4 mm or less.

2. The tire according to claim 1, wherein the styrene-butadiene rubber (SBR) in the cap rubber layer has a styrene content of 20% by mass or less.

3. The tire according to claim 1, wherein the cap rubber layer contains parts by mass or more of butadiene rubber (BR) in 100 parts by mass of the rubber component.

4. The tire according to claim 1, wherein the cap rubber layer contains silica in an amount of 50 parts by mass or less with respect to 100 parts by mass of the rubber component.

5. The tire according to claim 1, wherein the silica contained in the cap rubber layer has an average primary particle size of 18 nm or less.

6. The tire according to claim 1, wherein the styrene content (% by mass) in the styrene-butadiene rubber (SBR) per the thickness G (mm) of the tread portion is 2.32 or more.

7. The tire according to claim 1, wherein the cap rubber layer has a loss tangent (30 C. tan ) of 0.13 or less measured under the conditions of temperature of 30 C., frequency of 10 Hz, initial strain of 5%, dynamic strain rate of 1%, and deformation mode: tensile.

8. The tire according to claim 7, wherein the cap rubber layer has the tan of 0.11 or less.

9. The tire according to claim 7, wherein the product of the 30 C. tan and the thickness G (mm) of the tread portion (30 C. tan G) is 1.40 or less.

10. The tire according to claim 1, wherein the thickness of the tread portion is 9.0 mm or less.

11. The tire according to claim 1, wherein the land ratio of the tread portion is 40% or more.

12. The tire according to claim 11, wherein the product of the land ratio (%) in the tread portion and the content (parts by mass) of styrene-butadiene rubber (SBR) in 100 parts by mass of the rubber component of the cap rubber layer (the land ratiothe content of SBR) is 3000 or more.

13. The tire according to claim 1, wherein the aspect ratio is 40% or more.

14. The tire according to claim 13, wherein the ratio of the silica content (parts by mass) with respect to 100 parts by mass of the rubber component to the aspect ratio (%) (the silica content/the aspect ratio) is 1.0 or less.

Description

EXAMPLE

[0247] Examples considered to be preferable when implementing the present invention are shown below, but the scope of the present invention is not limited to these examples. In the examples, a pneumatic tire (tire size: 215165R17 (Aspect ratio: 65%, land ratio: 68%)) made from a composition obtained by using various chemicals mentioned below and changing the formulation according to each Table were evaluated. The results calculated based on the following evaluation methods are shown in Tables 2 to 4. [0248] 1. Rubber composition forming cap rubber layer [0249] (1) Compounding material [0250] (a) Rubber component [0251] (a-1) NR: TSR20 [0252] (a-2) SBR-1: HPR840 (S-SBR) manufactured by ENEOS Material Co., Ltd. (Styrene content: 10% by mass, vinyl content: 42% by mass) [0253] (a-3) SBR-2: Modified S-SBR obtained by the method shown in the next paragraph (Styrene content: 25% by mass, vinyl content: 25% by mass) [0254] (a-4) BR: Ubepol BR150B (Hi-cis BR) from Ube Industries, Ltd. (cis content 97% by mass, trans content 2% by mass, vinyl content 1% by mass)

[0255] (Manufacture of SBR-2)

[0256] The above SBR-2 is produced according to the following procedure. First, two autoclaves having an internal volume of 10 L, having an inlet at the bottom and an outlet at the top, equipped with a stirrer and a jacket, were connected in series as reactors. Butadiene, styrene, and cyclohexane were each mixed in a predetermined ratio. This mixed solution is passed through a dehydration column filled with activated alumina, mixed with n-butyllithium in a static mixer to remove impurities. Then, it is continuously supplied from the bottom of the first reactor, further 2,2-bis(2-oxolanyl)propane as a polar substance and n-butyllithium as a polymerization initiator are continuously supplied at a predetermined rate from the bottom of the first reactor, and the internal temperature of the reactor is kept at 95 C. The polymer solution is continuously withdrawn from the top of the first reactor and supplied to the second reactor. The temperature of the second reactor is kept at 95 C., and a mixture of tetraglycidyl-1,3-bisaminomethylcyclohexane (monomer) as a modifier and an oligomer component is continuously added, as a 1000-fold dilution of cyclohexane, at a predetermined rate to carry out the denaturation reaction. This polymer solution is continuously withdrawn from the reactor, an antioxidant is added continuously by a static mixer, and the solvent is removed to obtain the desired modified diene polymer (SBR-2).

[0257] The vinyl content (unit: mass %) of the SBR-2 is determined by infrared spectroscopy from the absorption intensity near 910 cm.sup.1, which is the absorption peak of the vinyl group. Also, the styrene content (unit: % by mass) is determined from the refractive index according to JIS K6383: [0258] (b) Compounding materials other than rubber components [0259] (b-1) Carbon black (CB): VULCAN101-1 manufactured by Cabot Japan Co., Ltd. (N134, N.sub.2SA: 144 m.sup.2/g) [0260] (b-2) Silica: Ultrasil VN3 manufactured by Evonik Industries (N.sub.2SA: 175 m.sup.2/g, average primary particle size: 18 nm) [0261] (b-3) Silane coupling agent: Si266 manufactured by Evonik Industries (bis (3-triethoxysilylpropyl) disulfide) [0262] (b-4) Oil: VivaTec400 (TDAE oil) manufactured by H&R Co., Ltd. [0263] (b-5) Wax: Ozoace 0355 (special paraffin wax) manufactured by Nippon Seiro Co., Ltd. [0264] (b-6) Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd. (N-(1,3-dimethylbutyl)-Nphenyl-p-phenylenediamine) [0265] (b-7) Stearic acid: bead stearic acid Tsubaki manufactured by NOF Corporation [0266] (b-8) Zinc oxide: zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. [0267] (b-9) Sulfur: powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. [0268] (b-10) Vulcanization Accelerator-1: Nocceler CZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-cyclohexyl-2-benzothiazylsulfenamide (CBS)) [0269] (b-11) Vulcanization accelerator-1: Nocceler D manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N,N-diphenylguanidine) [0270] (2) Rubber composition forming cap rubber layer

[0271] Using a Banbury mixer, materials other than sulfur and a vulcanization accelerator are kneaded at 150 C. for 5 minutes according to the formulations shown in Tables 2 to 4 to obtain a kneaded product. Note that, each compounding quantity is a mass part.

[0272] Next, sulfur and a vulcanization accelerator are added to the kneaded product, and kneaded at 80 C. for 5 minutes using an open roll to obtain a rubber composition forming a cap rubber layer.

[0273] 2. Rubber Composition Forming Base Rubber Layer

[0274] In parallel, a rubber composition for forming the base rubber layer is obtained based on the formulation shown in Table 1 in the same manner as the rubber composition for forming the cap rubber layer.

TABLE-US-00001 TABLE 1 Compounding amount Compounding material (parts by mass) NR (TSR20) 70 BR (UBEPOL-BR150B manufactured by 30 Ube Industries. Ltd.) Carbon black (Show Black N330T 35 manufactured by Cabot Japan Co., Ltd.) Stearic acid (Tsubaki stearic 2 acid manufactured by NOF Corporation) Zinc oxide (Zinc white No. 1 4 manufactured by Mitsui Mining & Smelting Co., Ltd.) Wax (Sannok wax manufactured by 2 Ouchi Shinko Chemical Co., Ltd.) Antiaging agent (Nocrac 6C manufactured 3 by Ouchi Shinko Chemical Industry Co., Ltd) Antiaging agent (Antage RD manufactured 1 by Kawaguchi Chemical Industry Co., Ltd.) Sulfur (powder sulfur manufactured by 1.7 Tsurumi Chemical Industry Co., Ltd.) Vulcanization accelerator (Nocceler 1.2 CZ-G manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0275] 3. Pneumatic Tire

[0276] Using each rubber composition, the rubber composition is extruded in a predetermined shape so that (thickness of cap rubber layer (mm)/thickness of base rubber layer (mm)) is 90/10 to form the tread portion having the total thickness G (mm) shown in Tables 2 to 4.

[0277] After that, an unvulcanized tire was formed by pasting the tread portion together with other tire members, press vulcanized for 10 minutes at 170 C., and each pneumatic tire (test tire) of Examples 1 to 10 and Comparative examples 1 to 5 shown in Tables 2 to 4 is manufactured.

[0278] 4. Calculation of Parameters

[0279] The following parameters are then determined for each test tire.

[0280] (1) 30 C. Tan

[0281] From the cap rubber layer of the tread portion of each test tire, a rubber test piece for viscoelasticity measurement is prepared by cutting a size of 20 mm in length4 mm in width2 mm in thickness so that the tire circumferential direction is the long side. For each of the rubber test piece, 30 C. tan is measured using Eplexor series manufactured by GABO under the conditions of frequency of 10 Hz, initial strain of 5%, dynamic strain of 1%, and deformation mode: tensile, at a measurement temperature of 30 C. The 30 C. tan of the base rubber layer is 0.07.

[0282] Then, 30 C. tan G is calculated.

[0283] (2) Other Parameters

[0284] In addition, based on the specifications and formulated contents of each test tire, (styrene content in SBR/G), (SBR contentland ratio), and (silica content/aspect ratio) are calculated.

[0285] 5. Performance Evaluation (Uneven Ground Wear Resistance Performance)

[0286] Each test tire is installed on a standardized rim and inflated to a standardized internal pressure (250 kPa), then mounted on all wheels of a test vehicle (displacement 2000 cc, front-wheel drive vehicle) and run on uneven ground at 50 km/h for 4 hours. After that, the groove depth of the tread portion is measured to obtain the degree of reduction. Then, the running distance corresponding to the 1 mm decrease in the groove depth is calculated.

[0287] Assuming that the result in Comparative Example 3 is 100, the results are indexed based on the following formula to evaluate the wear resistance performance during running on uneven ground. The larger the numerical value, the better the wear resistance performance in running on uneven ground (uneven ground wear resistance performance).

Uneven ground wear resistance performance=[(result of each test tire)/(result of Comparative Example 3)]100

TABLE-US-00002 TABLE 2 EXAMPLE 1 2 3 4 5 6 7 8 9 10 Formulation of cap rubber layer NR 40 35 35 35 35 50 50 50 51 46 SBR-1 10 15 15 15 15 5 5 5 0 5 SBR-2 40 40 40 40 40 40 40 40 44 44 BR 10 10 10 10 10 5 5 5 5 5 CB 10 10 10 10 10 10 10 10 10 10 Silica 60 45 50 45 60 50 45 60 50 45 Coupling agent 4.8 3.6 4 3.6 4.8 4 3.6 4.8 4 3.6 Oil 20 20 20 20 20 20 20 20 21 21 Wax 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent 2 2 2 2 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 accelerator- 1 Vulcanization 2 2 2 2 2 2 2 2 2 2 accelerator-2 Parameter SBR content 50 55 55 55 55 45 45 45 44 49 (parts by mass) Amount of styrene in 21 21 21 21 21 23 23 23 25 23 SBR (% by mass) 30 C. tan 0.140 0.105 0.114 0.105 0.126 0.105 0.094 0.127 0.129 0.112 Tread thickness G (mm) 9.4 9.4 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 30 C. tan G 1.32 0.99 1.03 0.95 1.13 0.94 0.85 1.14 1.16 1.01 Amount of styrene in 2.34 2.22 2.32 2.32 2.32 2.59 2.59 2.59 2.78 2.61 SBR/G SBR content land ratio 3400 3740 3740 3740 3740 3060 3060 3060 2992 3332 Silica content 3900 2925 3250 2925 3900 3250 2925 3900 3250 2925 Aspect ratio Silica content/ 0.92 0.69 0.77 0.69 0.92 0.77 0.69 0.92 0.77 0.69 Aspect ratio Performance evaluation Uneven ground wear 116 123 125 119 131 138 131 144 150 144 resistance performance

TABLE-US-00003 TABLE 3 EXAMPLE 11 12 13 14 15 Formulation of cap rubber layer NR 50 35 31 31 35 SBR-1 4 20 29 45.6 17 SBR-2 36 40 30.4 13.6 40 BR 10 5 9.6 9.8 8 CB 10 10 10 10 10 Silica 60 60 60 60 60 Coupling agent 4.8 4.8 4.8 4.8 4.8 Oil 19 20 17.6 13.4 20 Wax 1.5 1.5 1.5 1.5 1.5 Anti-aging agent 2 2 2 2 2 Stearic acid 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 Sulfur 1.5 1.5 1.5 1.5 1.5 Vulcanization accelerator-1 2.5 2.5 2.5 2.5 2.5 Vulcanization accelerator-2 2 2 2 2 2 Parameter SBR content (parts by mass) 40 60 59.4 59.2 57 Amount of styrene in SBR 23.5 20.0 17.7 13.4 20.5 (% by mass) 30 C. tan 0.15 0.135 0.132 0.130 0.136 Tread thickness G (mm) 9 9 9 9 9 30 C. tan G 1.35 1.21 1.19 1.17 1.22 Amount of styrene in SBR/G 2.61 2.22 1.96 1.49 2.28 SBR content Land ratio 2720 4080 4039 4026 3879 Silica content Aspect ratio 3900 3900 3900 3900 3900 Silica content/Aspect ratio 0.92 0.92 0.92 0.92 0.92 Performance evaluation Uneven ground wear resistance 138 131 125 119 131 performance

TABLE-US-00004 TABLE 4 COMPARATIVE EXAMPLE 1 2 3 4 5 6 Formulation of cap rubber layer NR 30 30 30 40 30 25 SBR-1 19 24 19 19 19 42 SBR-2 16 16 16 16 16 28 BR 35 30 35 25 35 5 CB 10 10 10 10 10 10 Silica 80 80 60 80 80 80 Coupling agent 6.4 6.4 4.8 6.4 6.4 6.4 Oil 14 14 14 14 10 17 Wax 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization 2.5 2.5 2.5 2.5 2.5 2.5 accelerator-1 Vulcanization 2 2 2 2 2 2 accelerator-2 Parameter SBR content 35 40 35 35 35 70 (parts by mass) Amount of 17 16 17 17 17 16 styrene in SBR (% by mass) 30 C. tan 0.200 0.196 0.145 0.201 0.200 0.173 Tread thickness 9.6 9.6 9.6 9.6 9.0 9.6 G (mm) 30 C. tan G 1.92 1.88 1.39 1.93 1.80 1.66 Amount of 1.76 1.67 1.76 1.76 1.87 1.67 styrene in SBR/G SBR content 2380 2720 2380 2380 2380 4760 land ratio Silica content 5200 5200 3900 5200 5200 5200 Aspect ratio Silica content/ 1.23 1.23 0.92 1.23 1.23 1.23 Aspect ratio Performance evaluation Uneven ground 88 94 100 100 94 94 wear resistance performance

[0288] 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 embodiment within the same and equivalent scope of the present invention.

[0289] The present invention (1) is [0290] a tire having a tread portion, wherein [0291] the cap rubber layer forming the tread portion contains styrene-butadiene rubber (SBR), isoprene-based rubber, and silica; [0292] the content of the styrene-butadiene rubber (SBR) in 100 parts by mass of the rubber component is 40 parts by mass or more and 60 parts by mass or less, and the styrene content of the styrene-butadiene rubber (SBR) is 25% by mass or less; [0293] the content of the isoprene-based rubber in 100 parts by mass of the rubber component is more than 30 parts by mass; [0294] the content of the silica with respect to 100 parts by mass of the rubber component is 60 parts by mass or less; and [0295] the thickness of the tread portion is 9.4 mm or less.

[0296] The present invention (2) is [0297] the tire according to the present invention (1), wherein the styrene-butadiene rubber (SBR) in the cap rubber layer has a styrene content of 20% by mass or less.

[0298] The present invention (3) is [0299] the tire according to the present invention (1) or (2), wherein the cap rubber layer contains 5 parts by mass or more of butadiene rubber (BR) in 100 parts by mass of the rubber component.

[0300] The present invention (4) is [0301] the tire of any combination of the present inventions (1) to (3), wherein the cap rubber layer contains silica in an amount of 50 parts by mass or less with respect to 100 parts by mass of the rubber component.

[0302] The present invention (5) is [0303] the tire of any combination of the present inventions (1) to (4), wherein the silica contained in the cap rubber layer has an average primary particle size of 18 nm or less.

[0304] The present invention (6) is [0305] the tire of any combination of the present inventions (1) to (5), wherein the styrene content (% by mass) in the styrene-butadiene rubber (SBR) per the thickness G (mm) of the tread portion is 2.32 or more.

[0306] The present invention (7) is [0307] the tire of any combination of the present inventions (1) to (6), wherein the cap rubber layer has a loss tangent (30 C. tan ) of 0.13 or less measured under the conditions of temperature of 30 C., frequency of 10 Hz, initial strain of 5%, dynamic strain rate of 1%, and deformation mode: tensile.

[0308] The present invention (8) is [0309] the tire according to the present invention (7), wherein the cap rubber layer has the 30 C. tan of 0.11 or less.

[0310] The present invention (9) is [0311] the tire according to the present invention (7) or (8), wherein the product of the 30 C. tan and the thickness G (mm) of the tread portion (30 C. tan G) is 1.40 or less.

[0312] The present invention (10) is [0313] the tire of any combination of the present inventions (1) to (9), wherein the thickness of the tread portion is 9.0 mm or less.

[0314] The present invention (11) is [0315] the tire of any combination of the present inventions (1) to (10), wherein the land ratio of the tread portion is 40% or more.

[0316] The present invention (12) is [0317] the tire according to the present invention (11), wherein the product of the land ratio (%) in the tread portion and the content (parts by mass) of styrene-butadiene rubber (SBR) in 100 parts by mass of the rubber component of the cap rubber layer is 3000 or more.

[0318] The present invention (13) is [0319] the tire of any combination of the present inventions (1) to (12), wherein the aspect ratio is 40% or more.

[0320] The present invention (14) is [0321] the tire of any combination of the present inventions (1) to (13), wherein the ratio of the silica content (parts by mass) with respect to 100 parts by mass of the rubber component to the aspect ratio (%) is 1.0 or less.