JP4740764B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire.

  Recently, globalization has progressed, and tire destinations are being developed in various regions from low to high temperatures. For this reason, the number of cases used under harsher conditions increases, which causes cracks at the groove bottom of the tread.

  As a conventional method for reducing cracks at the bottom of the tread groove, there is a method of increasing the amount of an anti-aging agent and weathering wax in the rubber composition forming the tread. However, an increase in the anti-aging agent and the wax leads to a deterioration in fuel efficiency, and the steering stability is lowered due to a decrease in tire rigidity.

  There is also a method of using an anti-aging agent that is effective for a long time, but the use of such an anti-aging agent increases the cost. Furthermore, although there is a method of using weather resistant rubber as the rubber component of the rubber composition for tread, the weather resistant rubber has a problem in fracture characteristics, which causes a decrease in wear resistance and cut / chip property, In addition, low fuel consumption and grip properties are deteriorated. In addition, there is a method of reducing local distortion at the bottom of the tread groove during traveling, but such distortion reduction is greatly influenced by the tire structure (shape) and is not versatile.

  By the way, in Patent Document 1 below, in order to improve the durability and crack resistance of the side portion and / or tread portion of a pneumatic tire, and reduce rolling resistance, a halogen is produced by reacting isoolefin with paramethylstyrene. It has been proposed to coat the outer surface of the side part or tread part of a tire with a thin layer of a rubber composition containing a rubber and a diene rubber. However, with this technique, it is considered that the stress cannot be sufficiently absorbed with respect to the crack at the bottom of the groove that is greatly affected by the stress concentration, and thus is insufficient for suppressing the crack at the bottom of the groove that is the subject of the present invention. Moreover, the improvement effect of steering stability cannot be obtained.

  In Patent Document 2 below, in order to obtain a high-performance pneumatic tire excellent in handling stability and wear resistance, a rubber layer having a hardness higher than that of the central portion may be provided around the blocks and ribs. Proposed. Patent Document 3 below proposes that the side wall surface and the bottom surface of the main groove have higher hardness than the tread in order to improve the steering stability without reducing the pattern noise reduction performance and the performance on snow and ice. Yes. However, these documents 2 and 3 do not suppress cracks at the bottom of the groove, and do not disclose the configuration of the present invention to be described later and the special effects.

Patent Document 4 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, a rubber layer made of the above rubber composition is embedded on the outer side in the tire axial direction of the bead filler. The effect is not disclosed.
JP-A-11-254904 JP-A-2-246808 JP 2004-114994 A JP 2005-194398 A

  An object of the present invention is to provide a pneumatic tire in which cracks at a groove bottom portion of a tread in a long-term use are reduced without deteriorating fuel efficiency and grip performance.

  The pneumatic tire according to the present invention is a pneumatic tire having grooves on a tread surface, and a block copolymer comprising 80 to 50% by weight of a diene rubber, a polyisoprene block containing a vinylisoprene unit, and a polystyrene block. A rubber film layer made of a rubber composition containing 20 to 70 parts by weight of a filler with respect to 100 parts by weight of a polymer component consisting of 20 to 50% by weight is provided at the bottom of the groove. is there.

  According to the present invention, a weather resistant rubber composition is obtained by blending a specific polyisoprene and polystyrene block copolymer with a diene rubber usually used in a tire rubber composition as a polymer component. By providing a rubber film layer at the bottom of the tread groove, it is possible to reduce cracks at the bottom of the groove during long-term use without deteriorating fuel efficiency and gripping properties.

  The rubber film layer is preferably provided on the bottom and side walls of the groove, thereby improving steering stability and reducing cracks in the groove during long-term use without deteriorating fuel economy and gripping properties. can do.

  As described above, according to the present invention, it is possible to reduce the cracks in the groove bottom portion during long-term use without deteriorating the fuel efficiency and grip performance.

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

  FIG. 1 is a half cross-sectional view of a pneumatic tire according to an 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 18 disposed on the outer side in the tire radial direction. A plurality of main grooves 20 extending in the tire circumferential direction are provided on the tread surface which is the surface of the tread 18. A thin rubber film layer 22 is provided on the wall surface in the main groove 20.

  As shown in FIG. 2 in an enlarged manner, the rubber film layer 22 is provided so as to cover the surfaces of the bottom 20A and the side walls 20B and 20B of the main groove 20 in this embodiment. The height H of the rubber film layer 22 provided on the side wall 20B is preferably 50% or more of the height h of the side wall 20B. The rubber film layer 22 may be provided only on the bottom portion 20A of the main groove 20, but it is preferable that the rubber film layer 22 is also provided on the side wall 20B in order to improve steering stability. Further, when provided also on the side wall 20B, as shown in FIG. 3, it may be provided so as to extend to the shoulder 20C of the main groove 20, that is, a part of the rubber film layer 22 reaches the tread surface. . Further, although not shown, the rubber film layer 22 may be provided on the entire surface of the tread 18 including the inside of the main groove 20. This is because the rubber film layer 22 exposed to the outside from the main groove 20 is a thin film, and therefore disappears due to wear at the beginning of running of the tire, and thus does not affect the subsequent running. Further, when a lateral groove (not shown) extending so as to intersect the main groove 20 is provided, the rubber film layer may be similarly provided on the wall surface in the lateral groove.

  The rubber film layer 22 preferably has a thickness of 0.2 to 1 mm. If the thickness of the rubber film layer 22 is smaller than 0.2 mm, it is difficult to obtain an effect of improving steering stability and a crack reducing effect of the groove portion in a long-term use. On the other hand, if it exceeds 1 mm, fuel efficiency tends to deteriorate and steering stability tends to be impaired. Here, the above-mentioned thickness of the rubber film layer 22 is the thickness at the bottom 20A, and a rubber sheet of 0.2 to 1 mm is attached to the main groove position on the surface of the unvulcanized tread, and the main groove is formed by the vulcanization mold. By molding 20, the rubber film layer 22 having the same thickness is formed at the groove bottom.

  The rubber composition constituting the rubber film layer 22 uses, as a polymer component, a diene rubber (A) and a block copolymer (B) composed of a polyisoprene block containing a vinylisoprene unit and a polystyrene block. It was. By blending such a specific block copolymer (B), a rubber composition having a high hardness, a high loss factor, and excellent weather resistance can be obtained.

  As the diene rubber (A), various diene rubbers generally used as tire rubber compositions can be used, such as natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene rubber, and 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. In addition, the block copolymer (B) preferably has a glass transition point Tg of −20 ° C. or higher from the viewpoint of ensuring good grip properties. In addition, although the upper limit of a glass transition point is not specifically limited, Usually, it is 60 degrees C or less, More preferably, it is 20 degrees C or less. 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 to do. In addition, the content rate of these each unit is measured using an infrared method by < ¹ > H-NMR, and a glass transition point is measured based on JISK7121.

  In the rubber composition, the polymer component is composed of 80 to 50% by weight of the diene rubber (A) and 20 to 50% by weight of the block copolymer (B). When the block copolymer (B) is less than 20% by weight, it is difficult to obtain an effect of improving the steering stability and an effect of reducing the cracks in the groove part in long-term use. On the other hand, if the block copolymer (B) exceeds 50% by weight, the fuel efficiency tends to deteriorate and the steering stability tends to be impaired.

  The filler is blended in an amount of 20 to 70 parts by weight per 100 parts by weight of the polymer component. When the blending amount of the filler is less than 20 parts by weight, sufficient reinforcement cannot be obtained as compared with the tread rubber blending. On the other hand, if it exceeds 70 parts by weight, it is difficult to produce a thin sheet, and even if it can be produced, the working efficiency deteriorates and the fuel efficiency deteriorates.

Examples of the filler include carbon black and silica, which may be used alone or in combination. The filler preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 40 to 200 m ² / g. Here, the nitrogen adsorption specific surface area is measured according to JIS K6217.

  The rubber composition may contain various additives generally used in tire rubber compositions such as vulcanizing agents such as sulfur, vulcanization accelerators, anti-aging agents, zinc oxide, and stearic acid. .

  The rubber composition composed of the above is formed into a sheet according to a conventional method, and then attached to the unvulcanized tread surface according to the position of the main groove, and vulcanized and molded in a tire mold. The rubber film layer 22 is formed on the wall surface in the main groove 20 together with the molding of the main groove 20.

  In addition, as a rubber composition which comprises the tread 18, various rubber compositions for tread 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 tread rubber compositions are generally used in rubber compositions for tire treads, such as oil, zinc oxide, stearic acid, anti-aging agents, vulcanizing agents, vulcanization accelerators, in addition to fillers such as carbon black and silica. Various additives can be blended.

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

1. Rubber composition constituting rubber film layer 22 Using a Banbury mixer, rubber compositions of Formulations I to VII shown in Table 1 below were prepared according to a general method. The detail of each component of Table 1 is as follows.

SBR: Styrene-butadiene rubber “SBR1712” manufactured by JSR,
EPDM: JSR ethylene-propylene-diene copolymer rubber “EP33”,
Halogenated rubber: “EXXPRO90-10” manufactured by EXXON (a polymer obtained by brominating a copolymer of isobutylene and paramethylstyrene).

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: “Dia Black N330” (N ₂ SA = 79 m ² / g) manufactured by Mitsubishi Chemical Corporation
Oil: “JOMO Process NC-140” manufactured by Japan Energy.

  In each rubber composition, as a common compound, 3 parts by weight of zinc oxide (“Zinc oxide type 3” manufactured by Mitsui Kinzoku Mining Co., Ltd.) and stearic acid (“Lunac S-25” manufactured by Kao Co., Ltd.) per 100 parts by weight of the polymer component. ) 2 parts by weight, 1 part by weight of an anti-aging agent (“Santflex 6C” manufactured by Flexis), 1 part by weight of a vulcanization accelerator CBS (“Soxinol CZ” manufactured by Sumitomo Chemical Co., Ltd.), sulfur (“Sanfel manufactured by Sanshin Chemical Industry Co., Ltd.) EX ") 3 parts by weight were blended.

  About each obtained rubber composition, it vulcanizes | cures at 160 degreeC x 15 minutes, and produces the test piece of a predetermined shape, Hardness and a dynamic elastic modulus (loss coefficient) are used for the following test piece. Measured by the 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 Co., Ltd., the loss coefficient tan δ at 25 ° C. and 60 ° C. was measured at an initial elongation of 10%, an amplitude of 5%, and a frequency of 10 Hz. .

2. Production and Evaluation of Pneumatic Tire According to the rubber film layer configuration shown in Table 2 below, the sheet made of the rubber composition (thickness 0.2 mm or 0.5 mm) is placed at the position of the main groove with respect to the unvulcanized tread surface. A pneumatic radial tire having a rubber film layer 22 on the wall surface in the main groove 20 as shown in FIGS. 1 and 2 (tire size: 215 / 60R16) was molded. Comparative Example 1 is a control in which a tire was molded without providing the rubber film layer 22.

  As the rubber composition of the tread body, 96.25 parts by weight of styrene-butadiene rubber (“Toughden 2830” manufactured by Asahi Kasei Chemicals), 30 parts by weight of natural rubber (RSS # 3), silica (“Nip Seal AQ” manufactured by Tosoh Silica) 60 parts by weight, carbon black ("Dia Black N330" manufactured by Mitsubishi Chemical Corporation) 10 parts by weight, oil ("JOMO Process NC-140" manufactured by Japan Energy Co., Ltd.) 3.75 parts by weight, silane coupling agent ("Si75" manufactured by Degussa) ) 4.8 parts by weight, 3 parts by weight of zinc oxide (“Zinc Oxide 3 types” manufactured by Mitsui Mining & Mining), 2 parts by weight of stearic acid (“Lunac S-25” manufactured by Kao), anti-aging agent (“Sant” manufactured by Flexis) Flex 6C ") 2 parts by weight, Wax (" OZOACE0355 "manufactured by Nippon Seiki), Vulcanization Accelerator D (Ouchi Shinsei Chemical Industry) Nocceler D ") 2.0 parts by weight, vulcanization accelerator CBS (manufactured by Sumitomo Chemical Co." Soxinol CZ ") 1.8 parts by weight, and a sulfur (available from Sanshin Chemical Industry Ltd.," Sanferu EX ") 1.5 parts by weight.

  For each of the produced radial tires, rolling resistance, braking distance on a wet road surface, steering stability, and tread groove bottom crack were evaluated according to the following methods. 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 with the value of Comparative Example 1 being 100, and the smaller the index, the smaller the rolling resistance, and thus the better the fuel efficiency.

-Braking distance (grip property) on a wet road surface: The rim used was 16 × 6 1 / 2JJ mounted on a 2500 cc test vehicle, and the distance from a speed of 80 km / h on a wet asphalt road surface to braking was measured. The results are expressed as an index with the value of Comparative Example 1 being 100, and the larger the index, the shorter the braking distance and the better the grip.

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. In the evaluation, Comparative Example 1 was used as a control, and the equivalent of this was set to ± 0, slightly inferior to −1, inferior to −2, slightly superior to +1, and superior to +2.

-Tread groove bottom crack: After the tire was heat-aged at 80 ° C. for 4 weeks, it was run for 10,000 km on a drum with an air pressure of 230 kPa and a load of 450 kgf, and then the presence or absence of cracks in the main groove was confirmed.

  As shown in Table 2, when the pneumatic tires of Examples 1 to 4 according to the present invention are compared to Comparative Example 1 as a control, the grip performance is improved while suppressing the deterioration of fuel efficiency as much as possible. In addition, the handling stability was improved and the occurrence of cracks in the tread groove was suppressed. On the other hand, in Comparative Examples 2 and 3 where the block copolymer (B) is not used for the rubber film layer 22 (where Comparative Example 3 uses the same halogenated rubber as in Patent Document 1), There was no effect of improving steering stability, and cracks occurred at the bottom of the tread groove.

  The present invention can improve steering stability without reducing fuel economy and gripping properties, and can reduce the occurrence of cracks in grooves during long-term use. Therefore, it can be applied to various pneumatic tires including radial tires for passenger cars. Can be used.

1 is a half sectional view of a pneumatic tire according to an embodiment of the present invention. It is sectional drawing to which the main groove was expanded. It is sectional drawing to which the main groove which concerns on the example of a change was expanded.

Explanation of symbols

  18 ... tread, 20 ... main groove, 20A ... bottom, 20B ... side wall, 22 ... rubber film layer

Claims (4)

  In a pneumatic tire having a groove on the tread surface, a polymer comprising 80 to 50% by weight of a diene rubber and 20 to 50% by weight of a block copolymer composed of a polyisoprene block containing a vinylisoprene unit and a polystyrene block. A pneumatic tire characterized in that a rubber film layer made of a rubber composition in which 20 to 70 parts by weight of a filler is blended with 100 parts by weight of a component is provided at the bottom of the groove.   The pneumatic tire according to claim 1, wherein the rubber film layer is provided on a bottom portion and a side wall of the groove.   The pneumatic tire according to claim 1 or 2, wherein the rubber film layer has a thickness of 0.2 to 1 mm. 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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