JP2006298216A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire making driveability, riding comfortability and road noise performance highly compatible with one another. <P>SOLUTION: A high hardness and high damping rubber layer 30 constituted of a rubber component containing a block copolymer A made of a block of polyisoprene containing a vinylisoprene unit and a block of polystyrene and a diene system rubber B at a weight rate of A:B=20:80 to 50:50 is provided between carcass layers 22 at end parts in the cross direction of a belt layer 24. The block copolymer A is a triblock copolymer having the block of polyisoprene between at least two of the polystyrene blocks, and it is favorable that the content of the vinylisoprene unit is 40 weight% or more and a glass transition point is -20°C or higher. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire capable of achieving both a high level of road noise performance, riding comfort, and steering stability.

  In recent years, weight reduction as a tire has been regarded as important as automobiles are becoming more fuel-efficient. In general, when a tire is lightened, road noise deteriorates and rigidity deteriorates and steering stability deteriorates. There is a problem of doing.

  Conventionally, as a technique for improving the deterioration of road noise, a rubber layer made of a low hardness rubber or a rubber having a high loss coefficient (tan δ) may be disposed on a tread portion, a sidewall portion, a bead portion, or the like. (For example, refer to Patent Documents 1 and 2 below). In particular, Patent Document 2 discloses a technique for reducing high-frequency road noise by providing attenuation layers made of high-attenuation rubber at both ends of a belt layer.

  However, when a rubber layer having a low hardness is provided, the rigidity of the tire is lowered, and therefore steering stability is deteriorated. On the other hand, rubber with a high tan δ uses, for example, a polymer with a high glass transition point, reduces the particle size of carbon black as a reinforcing filler, increases the amount of carbon black, or adds a large amount of resin. However, when the conventional high tan δ rubber is disposed on a tire, there is a problem that the rolling resistance deteriorates due to an increase in the heat generation amount of the rubber, the durability deteriorates, and the steering stability deteriorates. is there.

  On the other hand, as a technique for improving steering stability, Patent Document 3 below includes a vinylon short fiber provided with a triangular pad between the end of the belt layer and the carcass layer, and fibrillating the triangular pad. A technique of forming a rubber composition is disclosed. In this technology, by providing a triangular pad made of oriented rubber at the specified position, driving stability can be improved without sacrificing riding comfort, but road noise performance is improved. Not.

As described above, the conventional technology is not always satisfactory in achieving a high degree of compatibility between road noise performance, riding comfort, and steering stability.
JP 2002-205515 A Japanese Patent Laid-Open No. 9-300911 JP 2004-58970 A

  The present invention has been made in view of the above points, and is difficult to achieve with the prior art by using a specific rubber having a high hardness and a high loss factor (tan δ) for a specific part. An object of the present invention is to provide a pneumatic tire that can achieve a high level of handling stability, riding comfort, and road noise performance.

  As a result of diligent studies to solve the above-mentioned problems, the present inventor specified a specific isoprene-styrene block copolymer as a polymer component in a diene rubber that is usually used in a rubber composition for tires. The rubber composition having a high hardness and a high loss factor can be obtained by blending at a ratio of 5%, and by disposing it at the end of the belt layer as a tire member, the steering stability, riding comfort, road noise can be obtained. The present inventors have found that the performance can be made highly compatible and have completed the present invention.

  That is, a pneumatic tire according to the present invention includes a pair of annular bead cores, a carcass layer whose end side is locked by the bead core, and a belt layer disposed on the tread portion on the radially outer side of the carcass layer. In the pneumatic tire provided, a block copolymer (A) composed of a polyisoprene block containing a vinylisoprene unit and a polystyrene block at a width direction end of the belt layer, and a diene rubber (B), The rubber layer which consists of a rubber composition contained by the weight ratio of A: B = 20: 80-50: 50 is provided.

  In the pneumatic tire of the present invention, the rubber layer may be provided between or on the belt layers at the end in the width direction of the belt layer composed of a plurality of belts, but preferably in the width direction of the belt layer. It is to be provided between the carcass layer at the end, and by arranging the belt between the belt layer and the carcass layer, the above characteristics can be made more highly compatible.

  In the pneumatic tire of the present invention, the block copolymer (A) is preferably a triblock copolymer having the polyisoprene block between at least two polystyrene blocks. The block copolymer (A) preferably has a vinyl isoprene unit content of 40% by weight or more and a glass transition point of −20 ° C. or more.

  In the pneumatic tire of the present invention, the rubber layer has a hardness at 23 ° C. (spring hardness test type A of JIS K 6253) of 55 to 70 ° C. and a peak temperature of tan δ of 0 to 40 ° C. It is preferable that tan δ at 23 ° C. is 0.4 to 1.0.

  According to the pneumatic tire of the present invention, by using a rubber composition that has a higher hardness and a higher loss factor than ever before, this is applied to the end of the belt layer, preferably below the end of the belt layer. By providing as a rubber layer, steering stability, riding comfort, and road noise performance can be made highly compatible.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  The rubber composition used in the present invention contains a polymer component composed of 20 to 50% by weight of the block copolymer (A) and 20 to 50% by weight of the diene rubber (B). When the block copolymer (A) is less than 20% by weight, the increase in hardness and loss factor (tan δ) is insufficient, and the object of the present invention is to achieve both steering stability, riding comfort and road noise performance. Cannot be achieved. On the other hand, if the block copolymer (A) exceeds 50% by weight, the hardness becomes too high and the effect of reducing road noise is not recognized. A more preferable blending ratio is A: B = 25: 75 to 45:55.

  The block copolymer (A) 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. Soft blocks may be formed only with vinyl isoprene units, but usually also contain 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 (A) 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 (A) 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 (A) becomes low. Moreover, it is preferable that the glass transition temperature Tg of this block copolymer (A) is -20 degreeC or more, More preferably, it is -10 degreeC or more. If the glass transition temperature is less than −20 ° C., tan δ at room temperature becomes small and it becomes difficult to reduce road noise.

  More specifically, the block copolymer (A) 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. When the content of styrene units exceeds 30% by weight, the block copolymer (A) becomes too hard and adversely affects road noise performance. Moreover, since the glass transition temperature Tg will become low when the content rate of 1, 4- bond isoprene exceeds 40 weight%, it becomes difficult to acquire the effect with respect to road noise.

  As the diene rubber (B), 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.

  Various additives commonly used in tire rubber compositions, such as fillers such as carbon black, vulcanizing agents such as sulfur, vulcanization accelerators, anti-aging agents, zinc white, and stearic acid, are included in the rubber composition. An agent can be blended.

  Although it does not specifically limit as said carbon black, The iodine adsorption amount of 30-90 mg / g is used preferably, Specifically, GPF, FEF, and HAF are mentioned as a preferable thing. Carbon black is preferably blended in an amount of 30 to 70 parts by weight with respect to 100 parts by weight of the total amount of the block copolymer (A) and the diene rubber (B).

  Next, an embodiment of the pneumatic tire of the present invention will be described with reference to the drawings.

  FIG. 1 is a half cross-sectional view of a pneumatic tire 10 according to an embodiment. The tire 10 includes a pair of left and right bead portions 12 and sidewall portions 14, and a tread portion 16 that spans between the sidewall portions 14. Configured.

  The bead portion 12 is provided with an annular bead core 18, and is formed by at least one layer of a carcass ply formed by extending a plurality of cords arranged at right angles to the tire circumferential direction between the pair of left and right bead cores 18. A carcass layer 22 is provided. Both ends of the carcass layer 22 are locked by being folded back by the left and right bead cores 18 respectively.

  A belt layer 24 is disposed outside the carcass layer 22 in the tread portion 16 in the radial direction. The belt layer 24 is provided so as to overlap the radial outer peripheral surface of the crown portion of the carcass layer 22, and is formed by arranging at least two non-extensible belt cords such as steel cords at a shallow angle with respect to the tire circumferential direction. The belts are overlapped so that the belt cords intersect with each other, and in this embodiment, the belt is composed of an inner first belt 24a and an outer second belt 24b. Among them, the inner first belt 24a adjacent to the carcass layer 22 is wider, that is, the first belt 24a is the maximum width belt.

  In the structure as described above, a rubber layer 30 of a high damping rubber made of the above rubber composition is provided between the lower surface side at the end in the width direction of the belt layer 24, that is, between the carcass layer 22. .

  More specifically, the rubber layer 30 is interposed between the end portion in the width direction of the first belt 24 a having the maximum width and the carcass layer 22 so as to be sandwiched between the two, and the belt extends along the upper surface of the carcass layer 22. The end 24e (the end in the width direction of the maximum width belt 24a) extends outward in the tire width direction, that is, the outer end 30a in the width direction is positioned outside the belt end 24e. Further, the inner end 30b in the width direction of the rubber layer 30 is located on the inner side than the end 24f in the width direction of the second belt 24b. The width of the rubber layer 30 is not particularly limited, but is preferably 5 to 20% with respect to the width of the maximum width belt 24a.

  Moreover, it is preferable that the thickness (average thickness in the width direction) of the rubber layer 30 is 0.5 to 2.0 mm. If the thickness is less than 0.5 mm, the above-described effects of the present invention are not sufficiently obtained. Conversely, if the thickness is more than 2.0 mm, the road noise performance is excellent, but the balance is lost and the ride quality and the handling stability are reduced. There is a risk of damage.

  The rubber layer 30 has a hardness at 23 ° C. (spring type hardness test type A of JIS K 6253) of 55 to 70 degrees, and tan δ (static strain 5%, dynamic strain 1.0%, frequency 10 Hz) It is made of a rubber having a high hardness and a high damping with a peak temperature of 0 to 40 ° C. and a tan δ at 23 ° C. of 0.4 to 1.0. If the hardness is less than 55 degrees, it is difficult to ensure steering stability. On the other hand, when the hardness exceeds 70 degrees, it becomes difficult to improve road noise performance and riding comfort. If tan δ is less than 0.4, it is difficult to reduce road noise.

  The rubber layer 30 is formed by bonding an unvulcanized belt-like rubber sheet made of the rubber composition to a predetermined position of the carcass layer 22 and molding the belt layer 24 thereon when molding a tire according to a conventional method. By vulcanization molding, the above-described configuration can be formed.

  In the pneumatic tire 10 of the present embodiment obtained as described above, the rubber layer 30 having high hardness and high damping made of the specific rubber composition described above is provided on the lower surface side of the end portion of the belt layer 24. As a result, the driving stability can be improved and road noise in the 160 to 250 Hz band can be reduced without impairing riding comfort.

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

(Preparation of rubber composition)
Using a Banbury mixer, rubber compositions of Formulations I to VII shown in Table 1 below were prepared according to a general method. Each compounding agent in the table is as follows.

Block copolymer (A)
HYBRAR 5125 (trade name): polystyrene / vinyl isoprene triblock copolymer manufactured by Kuraray Co., Ltd. (content of styrene unit = 20% by weight, content of 1,4-linked isoprene unit = 36% by weight, vinyl isoprene unit) Content = 44 wt%, glass transition point Tg = −17 ° C.)
HYBRAR 5127 (trade name): polystyrene / vinyl isoprene triblock copolymer manufactured by Kuraray (content of styrene units = 20% by weight, content of 1,4-linked isoprene units = 24% by weight, vinyl isoprene units) Content = 56 wt%, glass transition point Tg = 8 ° C.).

Diene rubber (B)
・ Natural rubber: RSS # 3
NS116 (trade name): a styrene-butadiene copolymer rubber (glass transition point Tg = −20 ° C.) manufactured by Zeon Corporation.

Carbon Black / FEF: “Seast SO” manufactured by Tokai Carbon Co., Ltd.

  In addition, for compounding, as a common compounding agent, 3 parts by weight of zinc oxide (“Zinc oxide 3 types” manufactured by Mitsui Kinzoku Mining Co., Ltd.), 2 parts by weight of stearic acid (“Lunac S-25” manufactured by Kao Corporation), anti-aging agent ("Santflex 6C" manufactured by Flexis) 1 part by weight, 1 part by weight of a vulcanization accelerator ("Noxeller NS-P" manufactured by Ouchi Shinsei Chemical), and sulfur ("Sanfel EX" manufactured by Sanshin Chemical Industry Co., Ltd.) 3 parts by weight were blended respectively.

(Physical properties of vulcanized rubber)
Each rubber composition was vulcanized at 160 ° C. for 15 minutes to produce a test piece of a predetermined shape, and the hardness and dynamic modulus (loss factor) were measured by the following method using the obtained test piece. did. 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 Co., Ltd., with a static strain of 5%, a dynamic strain of 1.0%, and a frequency of 10 Hz, and within a temperature range of -60 to 60 ° C. The loss factor tan δ was measured in increments of 1 ° C. to determine the peak temperature of tan δ, and tan δ at a temperature of 23 ° C. was determined.

(Tire actual vehicle running test)
Using the rubber composition of each rubber composition shown in Table 2, a rubber sheet having a thickness shown in Table 2 (all width was 25 mm) was extruded by an extruder, and this was used as the rubber layer 30 shown in FIG. Tire size: 205 / 55R16 tires were produced according to a conventional method. The prepared tire was mounted on a test car, and road noise, riding comfort and steering stability were evaluated by the following methods. The results are shown in Table 2.

Road noise: Measure the noise level in the vehicle when the test vehicle travels on a specific road surface at 60 km / h, and the noise level in a specific frequency band (250 Hz), using the tire of Comparative Example 1 as a control, Evaluation was made in comparison with this. It means that the “+” side is inferior to the same performance, and the “−” side is excellent in the same performance. However, at +0.2 to -0.2 dB, it is determined to be substantially equivalent to the control.

Riding comfort / steering stability: This is a sensory evaluation when the driver in charge of the test vehicle runs and runs the above test car. The tire of Comparative Example 1 is used as a control, and the equivalent is “± 0”. The excellent one was evaluated as “+1”, the excellent one as “+2”, the slightly inferior one as “−1”, and the inferior one as “−2”.

  As shown in Table 2, in the pneumatic tires of Examples 1 to 4 according to the present invention, a rubber layer made of rubber having a high hardness and a high loss factor was provided on the lower belt end side of the belt layer. As a result, road noise was reduced and steering stability was improved without impairing riding comfort, as compared with Comparative Example 1 (control) in which a rubber layer that was not highly damped rubber was disposed. On the other hand, in Comparative Example 2, since a rubber layer made of a rubber composition with a small amount of the block copolymer (A) was provided, the effect of improving the above characteristics was not recognized. Moreover, in comparative example 3, since there were too many compounding quantities of the said block copolymer (A), riding comfort deteriorated and the road noise reduction effect was also inadequate. Further, in Comparative Example 4 using a conventional high-damping rubber composition not containing the block copolymer (A), a sufficient improvement effect of the above characteristics was not recognized.

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

Explanation of symbols

10 …… Pneumatic tire 18 …… Bead core 22 …… Carcass layer 24 …… Belt layer 30 …… High damping rubber rubber layer

Claims (5)

In a pneumatic tire comprising a pair of annular bead cores, a carcass layer whose end side is locked by the bead core, and a belt layer disposed on a radially outer side of the carcass layer in a tread portion,
A block copolymer (A) composed of a polyisoprene block containing a vinylisoprene unit and a polystyrene block and a diene rubber (B) at the end in the width direction of the belt layer, A: B = 20: A pneumatic tire comprising a rubber layer made of a rubber composition contained at a weight ratio of 80 to 50:50.   The pneumatic tire according to claim 1, wherein the rubber layer is provided between the rubber layer and the carcass layer at an end portion in the width direction of the belt layer.   The pneumatic tire according to claim 1, wherein the block copolymer (A) is a triblock copolymer having the polyisoprene block between at least two polystyrene blocks.   The block copolymer (A) has a vinyl isoprene unit content of 40% by weight or more and a glass transition point of -20 ° C or more. The described pneumatic tire. The rubber layer has a hardness at 23 ° C. (JIS K 6253 spring-type hardness test type A) of 55 to 70 degrees, a peak temperature of tan δ of 0 to 40 ° C., and a tan δ at 23 ° C. of 0. The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire is 4 to 1.0.

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