JP2008018912A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire enabling improvement of both of wet driveability and dry driveability, in the tire blended with low PCA (Polycyclic Aromatics) oil in rubber composition of a tread part. <P>SOLUTION: In this tire, oil containing less than 3 wt.% dimethylsulfoxide (DMSO) extract materials by IP346/92 method is blended by 10-50 pts.wt. with rubber 100 pts.wt. in the rubber composition of the tread part 1, and tread patterns designated with inside and outside mounting positions on a vehicle are provided. The tread part 1 is constituted of inside and outside two layer structures. Rubber hardness conformed to JIS K6253 type A of the outside layer 4 is made a range of 70-78, and rubber hardness of the inside layer 5 is made smaller than that of the outside layer 4. Thickness of the outside layer 4 is made different so that thickness may be increased in a vehicle outside region and reduced in a vehicle inside region when mounting the tread part 1 on the vehicle. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire in which both dry / wet handling stability is improved in a tire in which low PCA oil is blended as a process oil for a rubber composition in a tread portion.

  In a rubber composition used for a pneumatic tire, a process oil is used as a softening agent in order to soften the rubber or improve processability. In general, an aroma oil containing polycyclic aromatic hydrocarbons (hereinafter abbreviated as “PCA”) in which three or more benzene rings are connected is often used as the process oil. However, in recent years, the recognition that PCA has an adverse effect on human health has been increased mainly in Europe, and oil with a low PCA content (hereinafter referred to as “low PCA oil”) is substituted for an aromatic oil with a high PCA content. Research is underway to use.

  However, when low PCA oil is blended in the rubber composition of the tread portion of a pneumatic tire, the softening point and viscosity of the oil itself are lowered, so that the viscoelastic properties of the rubber composition change and the embrittlement temperature decreases. For this reason, there is a problem that the wet steering stability is lowered particularly when the frictional force against the wet road surface is lowered.

As a countermeasure, it has been proposed to blend a resin component into the rubber composition (see, for example, Patent Document 1). However, this proposal is not sufficient to obtain the same tire performance as that of the conventional aroma oil because there is a problem that the modulus is lowered or the wear resistance is lowered unless a specific resin is used. There was a problem.
Japanese Patent Laid-Open No. 11-130909

  An object of the present invention is to provide a pneumatic tire in which wet steering stability is improved together with dry steering stability in a tire in which a low PCA oil is blended with a rubber composition in a tread portion.

  In the pneumatic tire of the present invention that achieves the above object, the rubber composition of the tread portion is 10 to 50 wt.% Of oil whose dimethyl sulfoxide (DMSO) extractant is less than 3 wt. In a pneumatic tire having a tread pattern in which the inner and outer mounting positions of the vehicle are specified, the tread portion has an inner and outer two-layer structure, and the outer layer has a rubber hardness of 70 to 78 according to JIS K6253 type A. In addition, the inner layer is made smaller than the rubber hardness of the outer layer, and the thickness of the outer layer is made different in such a way that it is larger in the vehicle outer region when mounted on the vehicle and smaller in the inner region. Features.

  In the pneumatic tire of the present invention, the tread portion has an inner / outer two-layer structure, and the outer layer is made of a rubber composition having a rubber hardness of 70 to 78 to secure rigidity necessary for steering stability, and the inner layer is Since the rubber hardness is softer than that of the outer layer, the insertion of the soft inner layer can increase the wet frictional force in the vehicle inner region and improve the wet handling stability, and the thickness of the outer layer By increasing the value in the vehicle outer region, the rigidity of the outer region can be increased and the dry steering stability can be improved.

  A rubber composition comprising 10 to 50 parts by weight of a low PCA oil containing less than 3% by weight of a dimethyl sulfoxide (DMSO) extract by IP346 / 92 method based on 100 parts by weight of rubber in the tread part of the pneumatic tire of the present invention. Things are being used. By using the low PCA oil and limiting its blending amount to a certain range, the processability of the rubber composition can be maintained well while eliminating the adverse effects of the PCA on the human body. On the other hand, the problem of reduced wet steering stability caused by using low PCA oil in the tread portion is improved as follows.

  In the pneumatic tire of the present invention illustrated in FIG. 1, the pneumatic tire is composed of a tread portion 1, a sidewall portion 2, and a bead portion 3, and the mounting positions inside and outside the vehicle are designated as shown in the figure. A carcass layer 7 is mounted between a pair of left and right bead cores 6 embedded in the bead portion 3, and both end portions thereof are folded around the bead core 6 from the tire inner side to the outer side. A plurality of belt layers 8 are arranged over the circumference of the tire on the outer periphery side of the carcass layer 7, and a tread portion 1 is further arranged on the outer side. The tread portion 1 has an inner and outer two-layer structure including an outer layer 4 and an inner layer 5. It is configured. The land portion 10 in the tread portion is provided with a plurality of narrow grooves 9a to 9e such as sipes.

  As described above, the tread portion 1 is composed of a rubber composition in which 10 to 50 parts by weight of low PCA oil is blended with 100 parts by weight of rubber, and the outer layer 4 has a rubber hardness (hereinafter referred to as JIS K6253 type A). It is simply abbreviated as “rubber hardness”.) 70 to 78, and the thickness is different in such a manner that the thickness is large in the vehicle outer region and smaller in the inner region when the vehicle is mounted. Further, the inner layer 5 of the tread portion 1 has a rubber hardness smaller than that of the outer layer 4, and the thickness is different from the outer layer thickness so as to be larger in the vehicle inner region and smaller in the outer region. Is formed. In the present invention, the rubber hardness is a value measured at a temperature of 25 ° C. with a durometer in accordance with JIS K6253 Type A.

  As described above, when the tread portion 1 is composed of a rubber composition containing a low PCA oil, the viscoelastic characteristics of the rubber composition change and the embrittlement temperature decreases as compared with the case of a conventional aroma oil. Moreover, the frictional force on the wet road surface is reduced as it is. In the tire of the present invention, the tread portion 1 has an inner and outer two-layer structure, and a soft inner layer 5 is disposed inside the outer layer 4 so as to increase the thickness particularly in the vehicle inner region that contributes to wet steering stability. By inserting into the tread, it is possible to increase the contact area of the tread when it comes in contact and increase the wet frictional force, thereby improving wet steering stability. At the same time, by increasing the thickness of the outer layer 4 having a high rubber hardness in the vehicle outer region, the rigidity of the tread portion 1 can be secured, and the dry steering stability at cornering or when switching lanes at high speed can be improved. .

  The thickness ratio of the outer layer 4 / inner layer 5 is preferably 1/4 to 1 / 1.5 in the vehicle inner region and 1.5 / 1 to 4/1 in the vehicle outer region. By making the ratio of the thickness of the outer layer 4 / inner layer 5 within this range, the effect of improving the wet steering stability by the inner layer in the vehicle inner region and the improvement of the dry steering stability by the outer layer in the vehicle outer region are achieved. Each effect can be made remarkable. The change in the thickness of the outer layer 4 may be gradually increased from the vehicle inner region toward the outer region, or may be increased stepwise. Similarly, the thickness of the inner layer 5 may be gradually increased from the vehicle outer region toward the inner region, or may be increased stepwise. In either case, the effects of the outer layer 4 and the inner layer 5 can be exhibited. Further, the outer layer 4 and the inner layer 5 may be divided into a plurality of land portions 10 in the tire width direction by a circumferential main groove or the like of the tread pattern, and the respective effects of the outer layer 4 and the inner layer 5 are as follows. Not lost.

  The outer layer 4 has a rubber hardness of 70 to 78, preferably 72 to 76. If the rubber hardness of the outer layer 4 is less than 70, sufficient dry steering stability cannot be obtained, and if it exceeds 78, wet steering stability deteriorates.

  The rubber hardness of the inner layer 5 is preferably 65 or more, and the rubber hardness difference with the outer layer 4 is 10 or less. By setting the rubber hardness of the inner layer 5 in such a range, both dry / wet handling stability can be improved. Further, if the rubber hardness difference exceeds 10, the dry steering stability may be lowered.

  Further, a plurality of land portions 10 constituting the tread pattern may be provided with narrow grooves to adjust the rigidity of the tread portion. Although this narrow groove may have the same groove depth, as shown in FIG. 1, the groove depths of the narrow grooves 9a to 9e are made deeper in order from the vehicle inner region to the vehicle outer region when the vehicle is mounted. It is good to form. By deepening the narrow grooves 9d and 9e in the land portion close to the vehicle outer region in this way, even when the tire is worn, the rigidity of the land portion in the vehicle outer region is appropriately made flexible. It can be maintained effectively.

  In the present invention, as shown in FIG. 2, a thin layer 11 is disposed adjacent to the outer layer 4 on the non-ground surface of the tread portion outside the vehicle when the vehicle is mounted, and the rubber hardness of the thin layer 11 is 65 or more. It is more preferable that the outer layer 4 has a rubber hardness smaller than that of the outer layer 4. The non-ground surface on the outside of the vehicle does not contribute to steering stability during normal traveling, but the thin layer 11 on the non-ground surface on the outside of the vehicle contacts the ground when the traveling limit is exceeded during cornering of wet traveling. Thus, wet steering stability can be improved. The thin layer 11 may use the same rubber composition as the inner layer 5.

  The present invention can exert a great effect particularly when applied to a super flat tire having a tire flatness ratio of 50% or less. In super flat tires with a tire flatness ratio of 50% or less, the contact length becomes shorter than the contact width on the contact surface. Therefore, when the tread portion is made of a rubber composition containing low PCA oil, wet handling stability is improved. This is because the decrease in the resistance becomes remarkable.

  The low PCA oil blended in the rubber composition used in the present invention is not particularly limited as long as the dimethyl sulfoxide (DMSO) extractable material by the IP346 / 92 method is less than 3% by weight, and any commercially available oil should be used. Can do. The rubber composition constituting the outer layer and the inner layer of the tread portion may be blended with 10 to 50 parts by weight, preferably 10 to 45 parts by weight, of low PCA oil with respect to 100 parts by weight of rubber. If the amount is too small, the processability deteriorates, which is not preferable. On the other hand, if the amount is too large, the processability deteriorates or migrates to an adjacent compound, which is not preferable.

  The rubber used in the rubber composition may be any rubber that can be used for tires, such as natural rubber (NR), various butadiene rubbers (BR), various styrene-butadiene copolymer rubbers (SBR), polyisoprene rubber (IR ), Diene rubbers such as butyl rubber (IIR), and the like, and these can be used alone or as any blend depending on the application. The rubber includes an oil-extended rubber obtained by adding a low PCA oil to the rubber in advance, and the DMSO extract may be less than 3% by weight for the low PCA oil. Moreover, the low PCA oil previously contained in rubber | gum as extending oil shall also be handled as the low PCA oil content contained in a rubber composition.

  For rubber compositions, other reinforcing agents (fillers) such as carbon black and silica, vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, various oils, antioxidants, plasticizers, etc. In addition, various additives generally blended in other rubber compositions can be blended, and these additives are kneaded by a general method into a composition and used for vulcanization or crosslinking. Can do. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  As the rubber composition constituting the tread, three types of rubber compositions (rubber A to rubber C) having the composition shown in Table 1 were prepared. Using these rubber compositions, the tire size was 275 / 45R19, Six types of pneumatic tires (Examples 1 to 4 and Comparative Examples 1 and 2) were manufactured in which the configuration of the tread portion of the tire in which the internal and external mounting positions to the vehicle were specified as shown in Table 2 was manufactured.

  In the first and second embodiments, the inner / outer two-layer structure of the tread portion has an outer layer / inner layer thickness ratio of 1 / 2.5 in the inner region when the vehicle is mounted, and 2.5 / 1 in the outer region. In this pneumatic tire, the groove depth of the narrow groove provided in the land portion of the tread portion is 8.9 mm in the center region of the tire width and 6.2 mm in both the inner and outer regions when the vehicle is mounted. Example 3 is a pneumatic tire formed so that the groove depth of the narrow groove of Example 1 is increased by 1 mm from the inner region to the outer region when the vehicle is mounted, and Example 4 is the pneumatic tire of Example 1. This is a pneumatic tire in which a thin layer made of rubber B is disposed on the non-ground surface on the outside when the tire is mounted on the vehicle. Further, Comparative Example 1 is a pneumatic tire having a tread portion with a single layer structure of only rubber A, and Comparative Example 2 is an air having a left and right structure between the vehicle outer side and the vehicle inner side when the vehicle is mounted with respect to the tread center. This is a tire.

  The six types of pneumatic tires obtained were mounted on a rim with a rim size of 21 × 10 J, filled with air pressure of 250 kPa, mounted on a four-wheel drive vehicle, and sensory evaluation of dry / wet handling stability by five test drivers. Went. The sensory evaluation was carried out with an average value of 5 persons, and the results are shown in Table 2 as indices with Comparative Example 1 as 100. The higher the index value, the better.

  In Table 1, the rubber hardness is a value measured at 25 ° C. according to JIS K-6253 Type A by vulcanizing each rubber composition at 160 ° C. for 20 minutes to produce a vulcanized rubber sheet. The types of raw materials used are shown below.

SBR: composed of rubber and low PCA oil. The rubber is emulsion polymerization (styrene 42.6 parts by weight, 1,3-butadiene 57.5 parts by weight, molecular weight modifier (t-dodecyl mercaptan) 0.16 by weight. Styrene-butadiene copolymer synthesized with 0.1 parts by weight of a polymerization initiator (diisopropylbenzene hydroperoxide), 2 parts by weight of an emulsifier (sodium rosin acid, polymerization temperature 8 ° C.), and low PCA oil is IP346 / The DMSO extract material according to Method 92 was 2.5% by weight.

BR: BR1220 manufactured by Nippon Zeon
Silica: ULTRASIL VN-3 manufactured by Degussa
Carbon black: Cabot Japan Show Black N234
ZnO: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Beads manufactured by Nippon Oil & Fats Co., Ltd. Anti-aging agent for stearic acid: SANTOFLEX 6PPD manufactured by Flexis
Silane coupling agent: Si69 manufactured by Degussa
Sulfur: Fine powder sulfur vulcanization accelerator with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd. CZ: Noxeller CZ manufactured by Ouchi Shinsei Chemical
Vulcanization accelerator DPG: PERKACITDPG manufactured by Flexis

  From the results in Table 2, in Comparative Example 2, when the tread is divided into two on the vehicle inner side and the outer side when the vehicle is mounted, and a soft rubber B is disposed on the vehicle inner side and a hard rubber A is disposed on the vehicle outer side, wet steering stability is improved. Although improved, the dry handling stability is reduced. On the other hand, in Example 1, it turns out that wet maneuvering stability can be improved with dry maneuvering stability by making tread part 1 into inner and outer two-layer structure.

It is meridian direction sectional drawing which shows an example of the pneumatic tire of this invention. It is meridian direction sectional drawing which shows the other example of the pneumatic tire of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 4 Outer layer 5 Inner layer 9a, 9b, 9c, 9d, 9e Narrow groove 10 Land part 11 Thin layer

Claims (5)

The rubber composition of the tread part contains 10 to 50 parts by weight of an oil whose dimethyl sulfoxide (DMSO) extract material is less than 3% by weight based on IP346 / 92 method with respect to 100 parts by weight of the rubber, and the mounting position inside and outside the vehicle is designated. In a pneumatic tire having a tread pattern,
The tread portion has an inner and outer two-layer structure, the outer layer has a rubber hardness in accordance with JIS K6253 Type A in the range of 70 to 78, the inner layer is made smaller than the outer layer, and the outer layer. Pneumatic tires with different thicknesses so that they are larger in the vehicle outer area and smaller in the inner area when the vehicle is mounted.   The pneumatic tire according to claim 1, wherein the inner layer of the tread portion has a rubber hardness in accordance with JIS K6253 type A of 65 or more and a difference in rubber hardness with the outer layer of 10 or less.   The pneumatic tire according to claim 1 or 2, wherein narrow grooves are provided in a plurality of land portions constituting the tread pattern, and the depth of the narrow grooves is increased in order from the vehicle inner side to the outer side when the vehicle is mounted.   The pneumatic tire according to any one of claims 1 to 3, wherein a tire flatness ratio is 50% or less.   5. A thin layer having a rubber hardness of 65 or more conforming to JIS K6253 type A and having a rubber hardness smaller than that of the outer layer is disposed on the non-ground surface of the tread portion on the vehicle outer side when the vehicle is mounted. The pneumatic tire according to any one of the above.

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