JP5038637B2 - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which reduces a crack at a groove bottom part of a tread in the case of long term use without deteriorating low fuel consumption, grip performance, and driveability. <P>SOLUTION: In the pneumatic tire having grooves 20 on a tread surface, a bottom part 20A and a side wall 20B of the grooves are provided with a rubber film layer 22 composed of a rubber composition where 2-8 pts.wt. of short length fiber fibrillated during mixing and 20-70 pts.wt. of a filler are compound based on 100 pts.wt. of diene-based rubber, and a fibril generated by mixing is dispersed. The rubber film layer 22 is preferably provided in a state wherein the fibril generated during mixing is oriented perpendicular to the tire circumferential direction. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

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, a thin layer of a rubber composition containing a rubber obtained by reacting isoolefin with paramethylstyrene and halogenated and a diene rubber covers the outer surface of the tire side portion and tread portion. It has been proposed. This document is intended to improve the durability and crack resistance of the side portion and / or tread portion of a pneumatic tire, but the feature of the present invention is that a short fiber to be fibrillated is blended. Is not disclosed.

  Patent Document 2 below proposes that a fine body such as crystalline SPB resin or nylon short fiber is blended in the surface layer of the tread in order to improve the running performance on an icy and snowy road surface. However, in this document, the fine body is aimed at the scratch effect of icy and snowy roads and does not contribute to reducing cracks at the bottom of the tread groove.

  Patent Document 3 below discloses blending short fibers such as polyester fibers on the side wall surface and bottom surface of the main groove in order to improve steering stability without reducing pattern noise reduction performance and performance on ice and snow. Has been. However, this document aims to make the wall surface of the main groove harder than the tread by blending the above short fibers, and thereby to provide steering stability in a tire having a relatively soft tread. It does not suppress cracks at the bottom of the groove.

In addition, Patent Document 4 below discloses a rubber composition comprising 2 to 8 parts by weight of vinylon short fibers that are fibrillated during mixing with respect to 100 parts by weight of a rubber component. In order to achieve both steering stability and ride comfort, a triangular pad made of the rubber composition is provided between the end of the belt layer and the carcass layer. The effect of is not disclosed.
JP-A-11-254904 JP-A-8-156529 JP 2004-114994 A JP 2004-58970 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, grip performance, and steering stability.

The pneumatic tire manufacturing method according to the present invention is a manufacturing method of a pneumatic tire provided with a main groove extending in the tire circumferential direction on the tread surface, with respect to the diene rubber 100 parts by weight, the solvent wet cooling gel spinning A sheet made of a rubber composition containing 2 to 8 parts by weight of short fibers to be fibrillated during mixing and 20 to 70 parts by weight of filler is not added so that the train direction is perpendicular to the tire circumferential direction. A rubber film layer in which fibrils produced during mixing are oriented perpendicularly to the tire circumferential direction is provided at the bottom of the main groove by being attached to the surface of the sulfur tread and vulcanized.

  The short fibers are broken by the compressive stress acting during the mixing of the rubber composition to generate fibrils having a fresh surface, and the generated fibrils are dispersed in the rubber composition. By providing the rubber film layer made of the rubber composition thus obtained at the bottom of the groove of the tread, the crack resistance is improved by the fibrils dispersed in the rubber film layer.

Further, the rubber film layer is excellent in the crack suppressing effect at the groove bottom portion generated along the tire circumferential direction because the fibrils generated during mixing are oriented perpendicular to the tire circumferential direction. The rubber film layer is preferably provided on the bottom and side walls of the groove from the viewpoint of handling stability.

  According to the present invention, a high-strength rubber composition obtained by blending a short fiber to be fibrillated with a diene rubber usually used in a tire rubber composition is provided as a rubber film layer at the groove bottom of the tread. Therefore, it is possible to reduce cracks at the bottom of the groove during long-term use without deteriorating fuel efficiency, grip performance, and steering stability.

  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 20A of the main groove 20, but is preferably provided also on the side wall 20B. 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. When the thickness of the rubber film layer 22 is smaller than 0.2 mm, it is difficult to obtain the effect of reducing cracks in the groove portion in 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 is obtained by blending short fibers that fibrillate during mixing with the diene rubber. As the diene rubber that is a polymer component, various diene rubbers generally used as a rubber composition for tires can be used. For example, natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene rubber, etc. Can be used alone or in combination of two or more.

  The short fiber is not particularly limited as long as it is fibrillated by compressive stress acting during the mixing of the rubber composition, but preferably, easy fibrillated vinylon short fibers are used. Such vinylon short fibers are produced by solvent wet cooling gel spinning and have a uniform fiber structure, and are easily fibrillated, unlike ordinary vinylon fibers that are twisted and used for cords, fabrics, etc. It is. Here, the fibril is a slender fibrous structural element having a length of 100 to 6000 μm and a diameter of 0.1 to 100 μm, in which short fibers are subjected to compressive stress and broken along the fiber axis. The solvent wet cooling gel spinning method is a method in which a stock solution is discharged from a nozzle into a cooled solidification bath, and the whole is uniformly gelled to form a stable structure, and then the solvent is removed. Further, the size of the short fibers before fibrillation is not particularly limited, but the size is such that the short fibers are not entangled with each other during mixing.

  The said short fiber is mix | blended 2-8 weight part with respect to 100 weight part of diene rubbers. If it is less than 2 parts by weight, it is difficult to obtain the effect of reducing cracks in the groove during long-term use. Moreover, when it exceeds 8 weight part, there exists a tendency for low-fuel-consumption property to be impaired.

  The rubber composition obtained by fibrillating the short fibers is preferably prepared using a masterbatch obtained by blending and mixing a relatively large amount of the short fibers with a diene rubber. In this case, in the preparation of the masterbatch, increasing the blending ratio of the short fibers to the diene rubber increases the viscosity during mixing, and increases the shear force during mixing to fibrillate most of the short fibers. And the dispersibility of the fibrils in the final rubber film layer can be improved.

  When producing such a short fiber masterbatch, it is preferable to blend 20-50 parts by weight of the above short fibers with respect to 100 parts by weight of the diene rubber. In this case, in order to increase the shearing force generated in the kneaded product during mixing, it is preferable to use natural rubber alone or natural rubber in an amount of 50% by weight or more as the diene rubber.

  When the rubber composition is prepared using the short fiber masterbatch, the short fiber masterbatch is preferably added to the remaining diene rubber together with other compounding agents and mixed. The short fibers can be fibrillated.

  The rubber composition contains 20 to 70 parts by weight of a filler with respect to 100 parts by weight of the diene rubber. 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 unvulcanized rubber composition in which the fibrils obtained as described above are dispersed is formed into a sheet or tape using an extruder or a calender. At that time, the fibrils are oriented in the direction of travel of the rubber composition in the extruder or calendar. Then, the molded sheet is placed on the surface of the unvulcanized tread so that the fibrils are oriented perpendicularly to the tire circumferential direction, that is, the sheet running direction is perpendicular to the tire circumferential direction. Attach to the position of the main groove. Thereafter, 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 by vulcanization molding in a tire mold.

  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. Preparation of rubber composition constituting rubber film layer 22 100 parts by weight of natural rubber (RSS # 3) 25 parts by weight of vinylon short fibers (“Kuraron K-II SA” manufactured by Kuraray Co., Ltd.) fibrillated during mixing A short fiber master batch was prepared by mixing and mixing.

  Next, the short fiber masterbatch and SBR as a diene rubber were mixed by a Banbury mixer according to the formulation shown in Table 1 below to prepare rubber compositions of Formulations I to V. In addition, in the mixing | blending V, the vinylon short fiber which is not fibrillated was mix | blended instead of the said short fiber masterbatch. Each component in Table 1 is as follows.

SBR: Styrene-butadiene rubber “SBR1712” manufactured by JSR,
Vinylon short fibers: Vinylon short fibers that are not manufactured by the Kuraray solvent wet cooling gel spinning method and therefore do not fibrillate during mixing. Fineness = 2 dtex, fiber length = 4 mm,
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, 3 parts by weight of zinc oxide (“Zinc oxide type 3” manufactured by Mitsui Kinzoku Mining Co., Ltd.) and stearic acid (“LUNAC S” manufactured by Kao Co., Ltd.) per 100 parts by weight of diene rubber -25 ") 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 (" Soccinol CZ "manufactured by Sumitomo Chemical Co., Ltd.), sulfur (Sanshin Chemical Industry Co., Ltd.) 3 parts by weight of “Sanfel EX”) was blended.

2. Production and Evaluation of Pneumatic Tire According to the rubber film layer configuration shown in Table 2 below, a sheet (thickness 0.2 mm or 0.5 mm) made of the above rubber composition is oriented so that the fibrils are perpendicular to the tire circumferential direction. Further, the rubber is applied to the wall surface in the main groove 20 as shown in FIGS. 1 and 2 by being attached to the surface of the unvulcanized tread in accordance with the position of the main groove and vulcanized in a tire mold. A pneumatic radial tire (tire size: 215 / 60R16) including the membrane layer 22 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 3 according to the present invention are compared with Comparative Example 1 as a control, the grip performance is improved while suppressing deterioration in fuel economy as much as possible. In addition, the occurrence of cracks in the tread groove was suppressed without lowering the steering stability. On the other hand, in the comparative example 4 which mix | blended the short fiber which does not fibrillate with the rubber film layer 22, not only fuel-consumption property and steering stability deteriorated, but the crack had generate | occur | produced in the tread groove bottom part. From this, it is not possible to suppress the occurrence of cracks at the groove bottom even if the rigidity is increased by the reinforcement by the short fibers, and the dispersion of the fibrils is prevented from spreading at the bottom of the groove only by adding ordinary short fibers to the rubber film layer. It can be seen that this is effective for suppressing cracks.

  INDUSTRIAL APPLICABILITY Since the present invention can reduce the occurrence of cracks in the groove during long-term use without deteriorating fuel efficiency, grip performance, and steering stability, it can be used for various pneumatic tires including radial tires for passenger cars. Can do.

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 (1)

A method of manufacturing a pneumatic tire provided with main grooves extending in the tire circumferential direction on the tread surface, with respect to the diene rubber 100 parts by weight of short fibers to fibrillate during mixing is produced by a solvent wet cooling gel spinning 2 ~ 8 parts by weight and a sheet made of a rubber composition containing 20 to 70 parts by weight of a filler are attached to the surface of an unvulcanized tread so that the line direction is perpendicular to the tire circumferential direction and vulcanized. Thus, a method of manufacturing a pneumatic tire is characterized in that a rubber film layer in which fibrils generated during mixing are oriented perpendicularly to the tire circumferential direction is provided at the bottom of the main groove .

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