JP2007119582A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which can achieve a shortened braking distance on a wet road surface without any adverse influence on rolling resistance and steering stability. <P>SOLUTION: The pneumatic tire is provided with a tread rubber part 18 comprising a cap rubber layer 22 and a base rubber layer 20, wherein the base rubber layer 20 is formed from a rubber composition containing a polymer component comprising 85 to 60 wt.% diene rubber and 15 to 40 wt.% block copolymer composed of blocks of polyisoprene containing vinylisoprene units and blocks of polystyrene. More particularly, of the center region 20a and the shoulder region 20b of the base rubber layer 20, the shoulder region 20b is formed from the above rubber composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire.

  In recent years, with the progress of high performance and low fuel consumption of automobiles, there is a demand for steering stability of tires, reduction of braking distance on wet road surfaces, and reduction of rolling resistance. However, steering stability, braking performance on a wet road surface, and reduction of rolling resistance are contradictory to each other, and it is an important issue to achieve both of them.

  In particular, in order to achieve both rolling resistance and braking performance (grip property) on a wet road surface, conventionally, a rubber composition containing silica is used in a cap rubber layer of a tread. In addition, in order to reduce rolling resistance, there are also methods such as reducing the filling amount of carbon black or using silica together in the base rubber layer of the tread.

  However, if a large amount of silica is added to the cap rubber layer or the base rubber layer, the processability of the unvulcanized rubber deteriorates and the electrical resistance of the rubber increases, which may cause radio noise while driving. There is. In addition, when the carbon black filling amount is reduced in the base rubber layer, the strength of the rubber is reduced, which may cause separation of the tread rubber portion during running.

  By the way, in Patent Document 1 below, in order to reduce rolling resistance and improve steering stability, in the base rubber layer of the tread, a high hardness rubber layer in the center region and a low heat generation rubber layer in the shoulder region It has been proposed to properly arrange.

  In Patent Document 2 below, in order to achieve both handling stability and ride comfort, the tread base rubber layer has a lower dynamic elastic modulus at room temperature than the cap rubber layer, and a dynamic elastic modulus at 80 ° C. More specifically, the base rubber layer is composed of natural rubber, a polymer alloy comprising a highly crystalline syndiotactic-1,2-bonded polybutadiene resin and a cis-1,4-bonded polybutadiene rubber. It has been proposed to form a rubber composition comprising

  As described above, Patent Documents 1 and 2 propose that the rubber composition for forming the base rubber layer of the tread achieves both the steering stability and the contradiction of the rubber composition of the base rubber layer. There is no disclosure of improving the braking performance on wet road surfaces by blending.

Patent Document 3 below discloses a tire rubber composition comprising a block copolymer composed of a polyisoprene block containing a vinylisoprene unit and a polystyrene block and a diene rubber. In order to achieve both steering stability and road noise reduction, the rubber layer made of the rubber composition is disposed outside the carcass layer in the side wall portion. The effect of is not disclosed.
JP 2000-198319 A JP 2004-114878 A Japanese Patent Laid-Open No. 2005-194397

  An object of this invention is to provide the pneumatic tire which can reduce the braking distance on a wet road surface, without deteriorating rolling resistance or steering stability.

  The present inventor has found that the braking distance on a wet road surface can be reduced by using a rubber having a high loss coefficient (tan δ) for the base rubber layer of the tread. And, as a rubber with such a high loss factor, by using a blend using a specific polyisoprene and polystyrene block copolymer, it is possible to brake on a wet road surface without deteriorating rolling resistance and steering stability. It has been found that the distance can be reduced, and the present invention has been completed.

  That is, the pneumatic tire according to the present invention is a pneumatic tire provided with a tread rubber portion composed of a cap rubber layer and a base rubber layer, wherein the base rubber layer comprises 85 to 60% by weight of diene rubber and vinyl isoprene. It consists of a rubber composition containing a polymer component consisting of 15 to 40% by weight of a block copolymer comprising a polyisoprene block containing units and a polystyrene block.

  The improvement in braking performance on a wet road surface is particularly effective when the rubber composition is disposed in the shoulder region of the base rubber layer. Therefore, in this invention, it is preferable that the shoulder region of the said base rubber layer consists of the said rubber composition.

  According to the present invention, a rubber composition having a high loss factor is obtained by blending a specific polyisoprene and polystyrene block copolymer as a polymer component with a diene rubber usually used in a rubber composition for tires. By using this for the base rubber layer of the tread rubber portion, the braking distance on the wet road surface can be reduced without impairing rolling resistance (that is, low fuel consumption) and steering stability.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a half sectional view of the pneumatic tire according to the first embodiment. The tire is formed of a pair of left and right annular bead cores 12 and at least one layer of a carcass ply formed by extending a plurality of cords arranged at right angles to the circumferential direction of the tire. A carcass layer 14, a belt layer 16 in which a non-extensible belt cord such as a steel cord is inclined at a shallow angle with respect to the tire circumferential direction, and is disposed on the outer periphery of the crown portion of the carcass layer 14. And a tread rubber portion 18 disposed on the outer side in the tire radial direction. The tread rubber portion 18 is composed of two layers of a base rubber layer 20 on the inner side in the tire radial direction and a cap rubber layer 22 on the outer side in the tire radial direction that serves as a ground contact surface.

  The rubber composition for base constituting the base rubber layer 20 includes, as polymer components, a diene rubber (A), a block copolymer (B) composed of a polyisoprene block containing a vinylisoprene unit and a polystyrene block. Is used. By using the high-damping rubber composition having a high loss coefficient obtained by blending such a specific block copolymer (B) for the base rubber layer 20, the wet road surface without impairing rolling resistance or steering stability. The braking performance can be improved. On the other hand, for example, in a rubber composition in which the loss coefficient is increased by simply increasing the amount of carbon black, the rolling resistance is deteriorated.

  As the diene rubber (A), various diene rubbers generally used as a rubber composition for tires can be used. For example, natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer A combined rubber or the like can be used alone or in combination of two or more.

  The block copolymer (B) is a block copolymer composed of a soft block composed of a polymer portion of isoprene and a hard block composed of a polymer portion of styrene, and in the isoprene unit constituting the soft block. Contain vinyl isoprene units. Here, the vinyl isoprene unit refers to a portion where isoprene forms at least one of a 1,2-bond and a 3,4-bond instead of a normal 1,4-bond. The soft block may be formed only with vinyl isoprene units, but usually also contains 1,4-linked isoprene units, which may be randomly linked within the soft block, or alternatively vinyl. The polymer portion of the isoprene unit and the polymer portion of the 1,4-bonded isoprene unit may be combined in a block manner.

  The block copolymer (B) is preferably a triblock copolymer having a polyisoprene soft block between at least two polystyrene hard blocks. More specifically, a hard block-soft block-hard block-soft block, hard block-soft block-hard block-soft block-hard block, as long as it has a triblock structure of hard block-soft block-hard block. The structure may be as follows.

The block copolymer (B) preferably contains 40% by weight or more of vinyl isoprene units. When the weight ratio of the vinyl isoprene unit is less than 40% by weight, the glass transition point of the block copolymer (B) is lowered. Moreover, it is preferable that the glass transition temperature Tg of this block copolymer (B) is -20 degreeC or more, More preferably, it is -10 degreeC or more. If the glass transition temperature is less than −20 ° C., it becomes difficult to improve the braking performance on wet road surfaces. More specifically, the block copolymer (B) contains 10 to 30% by weight of styrene units, 40 to 80% by weight of vinyl isoprene units, and 0 to 40% by weight of 1,4-linked isoprene units. It is preferable. In addition, the content rate of each of these units is measured using an infrared method by ¹ H-NMR, and the glass transition temperature is measured according to JIS K7121.

  In the rubber composition for base, the polymer component is composed of 85 to 60% by weight of the diene rubber (A) and 15 to 40% by weight of the block copolymer (B). When the block copolymer (B) is less than 15% by weight, the effect of improving the braking performance on a wet road surface is insufficient. On the other hand, if the block copolymer (B) exceeds 40% by weight, the rolling resistance deteriorates.

  The above rubber composition for bases is generally used for rubber compositions for tires, such as fillers such as carbon black, vulcanizing agents such as sulfur, vulcanization accelerators, anti-aging agents, zinc white, and stearic acid. Various additives can be blended. The carbon black is preferably blended in an amount of 30 to 60 parts by weight with respect to 100 parts by weight of the polymer component.

  As a rubber composition which comprises the cap rubber layer 22, various rubber compositions for tread caps can be used, and it is not specifically limited. For example, a styrene-butadiene rubber alone or a blend rubber of 50% by weight or more of styrene-butadiene rubber and 50% by weight or less of another diene rubber can be used as the polymer component. Other diene rubbers are not particularly limited, and include natural rubber, and diene synthetic rubbers such as isoprene rubber and butadiene rubber. These may be used alone or in combination of two or more. Such cap rubber compositions are generally used in tire rubber compositions such as oils, zinc white, stearic acid, anti-aging agents, vulcanizing agents, and vulcanization accelerators in addition to fillers such as carbon black and silica. Various additives can be blended.

  FIG. 2 is a half sectional view of the pneumatic tire according to the second embodiment. In this embodiment, the base rubber layer 20 is composed of a center region 20a including the tire equator line CL and a shoulder region 20b disposed adjacent to the outer side in the width direction, and the regions 20a and 20b are blended differently. It differs from the said 1st Embodiment by the point currently formed with the rubber composition.

  The shoulder region 20b is formed of the base rubber composition, while the center region 20a is formed of various tread base rubber compositions not containing the block copolymer (B). The shoulder region 20b is particularly effective in reducing the braking distance on the wet road surface, and its contribution is small in the center region 20a. On the other hand, since the block copolymer (B) has a high loss factor, it inherently tends to deteriorate the rolling resistance. For this reason, the block copolymer (B) is limited to the shoulder region 20b without being blended with the block copolymer (B) in the center region 20a having a small contribution to the braking performance on wet road surfaces. Thus, the braking distance on the wet road surface can be reduced while further suppressing the deterioration of the rolling resistance.

  The rubber composition constituting the center region 20a is not particularly limited, and polymer components such as natural rubber, butadiene rubber, styrene-butadiene rubber, carbon black, oil, zinc white, stearic acid, anti-aging agent, What mixed suitably additives, such as a vulcanizing agent and a vulcanization accelerator, is used. More specifically, a blend rubber of natural rubber and butadiene rubber is used as the polymer component. Alternatively, natural rubber, a highly crystalline syndiotactic-1,2-bonded polybutadiene resin, and a cis-1,4-bonded polybutadiene are used. It is preferable to use a blend of a polymer alloy made of rubber. Moreover, it is preferable to mix | blend 20-80 weight part of carbon black with respect to 100 weight part of said polymer components, and in addition to carbon black as a filler, you may use a silica together.

  In the base rubber layer 20, the ratio between the center region 20a and the shoulder region 20b is preferably set as follows. That is, the distance from the tire equator line CL to the tread ground contact E (the outer end of the tread rubber portion 18 in contact with the road surface when a standard load (75% of the maximum load specified by JATMA) is applied to the tire) is represented by x. The boundary line R between the center region 20a and the shoulder region 20b is preferably set within a range of 0.2x to 0.8x from the tire equator line CL, more preferably a range of 0.4x to 0.7x. Is to be set within. This boundary line R is preferably set at a position deviated from the main groove 24 extending in the tire circumferential direction. This is because in the main groove 24, the base rubber layer 20 is thin, and therefore, if the boundary line R is set in this portion, the strain concentrates and cracking is likely to occur.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

1. Preparation of Rubber Composition for Base Using a Banbury mixer, rubber compositions of Formulations I to IV shown in Table 1 below were prepared according to a general method. As shown in Table 1, the blends I and III were varied in carbon black, oil and the like in order to make the hardness almost the same as the blends II and IV, respectively. The detail of each component of Table 1 is as follows.

・ Natural rubber: RSS # 3,
VCR: “UBEPOL-VCR617” manufactured by Ube Industries, Ltd. (polymer alloy composed of highly crystalline syndiotactic-1,2 bond polybutadiene resin and cis-1,4 bond polybutadiene rubber).

Block copolymer 1: “Hybler 5125” (manufactured by Kuraray Co., Ltd.) (triblock copolymer in which polystyrene and vinylisoprene are bonded. Content of styrene unit = 20% by weight, content of 1,4-bonded isoprene unit = 36 % By weight, vinyl isoprene unit content = 44% by weight, glass transition point Tg = −17 ° C.)
Block copolymer 2: “Hibler 5127” manufactured by Kuraray Co., Ltd. (Triblock copolymer in which polystyrene and vinylisoprene are bonded. Content of styrene units = 20% by weight, content of 1,4-bonded isoprene units = 24 % By weight, vinyl isoprene unit content = 56% by weight, glass transition point Tg = 8 ° C.).

・ Carbon black: “Seast SO” manufactured by Tokai Carbon Co., Ltd.
-Oil: “JOMO Process X-140” manufactured by Japan Energy,
・ Zinc oxide: "Zinc oxide 3 types" manufactured by Mitsui Mining & Smelting Co., Ltd.
・ Stearic acid: “Lunac S-25” manufactured by Kao Corporation
Anti-aging agent: “Sant Flex 6C” manufactured by Flexis,
・ Vulcanization accelerator CBS: “Noxeller NS-P” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Sulfur: “Sanfer EX” manufactured by Sanshin Chemical Industry Co., Ltd.

2. Vulcanized rubber properties of base rubber composition About each rubber composition obtained above, vulcanized at 160 ° C for 15 minutes to prepare a test piece of a predetermined shape, and using the obtained test piece, hardness The dynamic elastic modulus (loss coefficient) was measured by the following method. The results are shown in Table 1.

Hardness: Measured at a temperature of 23 ° C. using a spring type hardness test type A according to JIS K 6253.

-Dynamic elastic modulus: Using a dynamic viscoelasticity measuring device manufactured by UBM, the loss coefficient tanδ was measured at an initial elongation of 10%, an amplitude of 5%, and a frequency of 10 Hz at temperatures of 25 ° C and 60 ° C. .

3. Preparation of rubber composition for cap A rubber composition for cap was prepared according to a general method using a Banbury mixer. The composition of the rubber composition for cap is 96.25 parts by weight of styrene butadiene rubber (“TUF3330” manufactured by Asahi Kasei Chemicals), 30 parts by weight of butadiene rubber (“BR01” manufactured by JSR), carbon black (“Dia Black N339” manufactured by Mitsubishi Chemical). ) 40 parts by weight, 40 parts by weight of silica (“Nippal AQ” manufactured by Tosoh Silica), 4 parts by weight of a silane coupling agent (“Si69” manufactured by Degussa), aroma oil (“JOMO Process X-140” manufactured by Japan Energy) 10 Part by weight, 3 parts by weight of zinc oxide (“Zinc oxide 3 types” manufactured by Mitsui Mining & Smelting), 2 parts by weight of stearic acid (“Lunac S-25” manufactured by Kao), anti-aging agent (“Santflex 6C” manufactured by Flexis) 2 Parts by weight, 2 parts by weight of wax (“OZOACE0355” manufactured by Nippon Seiki), vulcanization accelerator D (“Socino” manufactured by Sumitomo Chemical) D ") 1 part by weight, vulcanization accelerator CZ (manufactured by Sumitomo Chemical Co." Soxinol CZ ") 2 parts by weight sulfur (Tsurumi Chemical Co." powdery sulfur ") was 2 parts by weight.

4). Production and evaluation of pneumatic tire And 3. A pneumatic radial tire having a tire size of 215 / 60R16 was produced by vulcanization molding according to a conventional method using the rubber composition obtained in the above. The rubber composition used in the base rubber layer 20 is as shown in Table 2 below. In Examples 1 and 2 and Comparative Examples 1 and 2, as shown in FIG. In Example 3 and Comparative Example 3, as shown in FIG. 2, the center region 20a and the shoulder region 20b of the base rubber layer 20 have different rubber blends. At that time, the distance from the tire equator line CL to the boundary line R between the regions 20a and 20b was set to 0.7x, where x is the distance from the tire equator line CL to the tread ground contact edge E.

  About each produced radial tire, rolling resistance, the braking distance on wet road surface, and steering stability were evaluated in accordance with the following method. The results are shown in Table 2.

-Rolling resistance (low fuel consumption): Rolling when running at 23 ° C and 80 km / h on a rolling resistance measurement drum with tires mounted with a rim of 16 x 6 1/2 JJ, air pressure of 230 kPa and load of 450 kgf Resistance was measured. The results are expressed as an index in which the value of Comparative Example 1 is set to 100 for Example 1 and the values of Comparative Example 2 are set to 100 for Examples 2 and 3 and Comparative Example 3, and the rolling resistance decreases as the index decreases. It is small and thus shows excellent fuel efficiency.

-Braking distance on wet road surface: The rim used was 16 x 6 1/2 JJ, mounted on a 2500cc test vehicle, and the distance from braking at 80 km / h on a wet asphalt road surface was measured. The results are expressed as an index in which the value of Comparative Example 1 is set to 100 for Example 1, and the values of Comparative Example 2 are set to 100 for Examples 2, 3 and Comparative Example 3, and the braking distance is shorter as the index is larger. It shows excellent braking performance.

Steering stability: The rim used was 16 × 6 1/2 JJ, mounted on a 2500cc test car, and the steering stability was evaluated by sensory evaluation with a test driver. Comparative Example 1 for Example 1 and Comparative Example 2 for Examples 2 and 3 and Comparative Example 3 were used as controls, respectively, equivalent to ± 0, slightly inferior to -1, and inferior to- 2. Slightly superior one is +1, and excellent one is +2.

  As shown in Table 2, in the pneumatic tires of Examples 1 to 3 according to the present invention, the braking distance on the wet road surface was reduced without substantially impairing rolling resistance and steering stability. Further, as is clear from the comparison between Examples 2 and 3 and Comparative Examples 2 and 3, the effect of reducing the braking distance on the wet road surface is larger in the shoulder region 20b than in the center region 20a. As described above, by using the rubber composition containing the block copolymer (B) only in the shoulder region 20b, the wet road surface is slightly improved without impairing rolling resistance at all and slightly improving the steering stability. The braking distance at can be reduced.

  The present invention can improve braking performance on wet road surfaces without deteriorating fuel efficiency and steering stability, and can be used for various pneumatic tires including radial tires for passenger cars.

1 is a half sectional view of a pneumatic tire according to a first embodiment of the present invention. It is a half sectional view of a pneumatic tire according to a second embodiment of the present invention.

Explanation of symbols

18 ... tread rubber portion 20 ... base rubber layer 20a ... center region 20b ... shoulder region 22 ... cap rubber layer

Claims (3)

  A pneumatic tire having a tread rubber portion comprising a cap rubber layer and a base rubber layer, wherein the base rubber layer comprises 85 to 60% by weight of a diene rubber, a polyisoprene block containing a vinylisoprene unit, and a polystyrene block. A pneumatic tire comprising a rubber composition containing a polymer component comprising 15 to 40% by weight of a block copolymer comprising:   The pneumatic tire according to claim 1, wherein a shoulder region of the base rubber layer is made of the rubber composition. The block copolymer is a triblock copolymer having the polyisoprene block between at least two polystyrene blocks, the vinyl isoprene unit content is 40% by weight or more, and glass The pneumatic tire according to claim 1, wherein the transition point is −20 ° C. or higher.

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