JP4917348B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire provided with a tread rubber having a cap / base structure to improve braking performance.

  In general, in a pneumatic tire, the improvement of the braking performance, that is, the reduction of the braking distance, has a large effect mainly by improving the hysteresis loss of the cap rubber. However, this method improves the braking performance, but causes a trade-off problem that rolling resistance increases and fuel efficiency is impaired. Therefore, a method for improving the braking performance with a configuration other than the cap rubber layer is required.

  Patent Document 1 below proposes that the ratio η of the circumferential modulus to the width direction modulus in the base rubber layer is made larger at the tire equator portion than at the tread shoulder portion, so that both riding comfort and braking performance can be achieved. ing. More specifically, the higher the circumferential shear rigidity of the tread, the better the braking performance, and the greater the contribution of the equator, and the better the riding comfort, the flexural rigidity of the tread is better. In particular, since the contribution of the shoulder portion is high, it has been proposed to set the circumferential modulus low at the tread shoulder portion of the base rubber layer.

The following Patent Document 2 discloses a structure in which a tread rubber base rubber layer is provided by partitioning a tread shoulder portion and a tread center portion, and the tread center portion has a higher modulus than the tread shoulder portion. The use of rubber is disclosed.
JP-A-8-175108 Japanese Patent Laid-Open No. 60-15203

  Contrary to the above proposal of Patent Document 1, according to the analysis by the present inventors, when the circumferential modulus of the tread shoulder portion, which is subjected to a large load during braking, is reduced, the ground pressure is deteriorated and the braking performance is improved. It turned out that it was not possible to plan.

  Patent Document 2 is intended to improve the tread-belt separation resistance and the cut / chipping resistance without impairing the heat generation, and is not intended to improve the braking performance. Also, the tread shoulder portion uses rubber having a lower modulus in terms of configuration, which is different from the present invention.

  An object of the present invention is to provide a pneumatic tire in which braking performance is improved by increasing a circumferential modulus of a tread shoulder portion in a base rubber layer of a tread rubber.

  As a result of diligent examination of the braking performance, the present inventor has applied a braking load by adopting a configuration opposite to the above-described conventional configuration in which only the circumferential rigidity (modulus) of the tread shoulder portion of the base rubber layer is increased. It is found that the change of the contact shape at the time of the control can be controlled and the contact pressure deterioration of the shoulder portion can be suppressed, and the contact width can be increased, thereby reducing the braking distance. It came to be completed.

That is, the pneumatic tire according to the present invention is a pneumatic tire for a passenger car in which a tread rubber is provided at a crown portion of the carcass, and the tread rubber includes a cap rubber layer on the ground surface side and a base rubber layer on the carcass side. The tread shoulder portion of the base rubber layer is formed of an anisotropic rubber having a high circumferential modulus relative to the width modulus , and the anisotropic rubber is made of rubber blended with short fibers. orientation direction are arranged such that the tire circumferential direction Rutotomoni, wherein the base rubber forming the tread center portion of the rubber layer not short fiber is compounded, the circumferential modulus of the base of the anisotropic rubber those that have been set higher than the circumferential modulus of the rubber forming the tread center portion of the rubber layer.

  According to the present invention, by increasing the circumferential modulus of the tread shoulder portion in the base rubber layer, it is possible to increase the extension of the contact width at the time of a braking load and to improve the braking performance.

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

  FIG. 1 is a half cross-sectional view in the tread width direction of a pneumatic tire according to an embodiment. The tire includes a pair of left and right bead cores 12, a toroidal carcass 14 that is locked at both ends so as to straddle between the pair of bead cores 12, and a belt layer provided on a radially outer side of a crown portion of the carcass 14. 16 and a tread rubber 18 provided outside the belt layer 16 in the radial direction.

  The tread rubber 18 is composed of two layers of a cap rubber layer 20 on the ground surface side and a base rubber layer 22 on the carcass 14 side. The base rubber layer 22 includes a tread center portion 24 including the tire equator line CL, and a tread shoulder portion 26 disposed adjacent to the outer side in the tire width direction. The tread center portion 24 and the tread shoulder portion 26 are formed of different blended rubber compositions so that only the modulus is high.

  Here, the ratio between the tread center portion 24 and the tread shoulder portion 26 is preferably set as follows in order to exhibit the effect of the present invention. That is, the distance from the tire equator line CL to the tread ground contact E (the outer end of the tread rubber 18 that contacts the road surface when a standard load (75% of the maximum load specified by JATMA) is applied to the tire) is x. The boundary line F between the tread center portion 24 and the tread shoulder portion 26 is preferably set within a range of y = 0.2x to 0.8x from the tire equator line CL, more preferably 0.4x to 0.0. Is set within a range of 7x.

  The shoulder rubber that forms the tread shoulder portion 26 is substantially the same as the center rubber that forms the tread center portion 24 in terms of the width direction modulus, but the circumferential modulus is formed of a rubber that is higher than the center rubber. ing. More specifically, as the center rubber, an isotropic rubber having substantially the same circumferential modulus and width direction modulus is used, while the shoulder rubber has a higher circumferential modulus than the width direction modulus. Anisotropic rubber is used.

  Here, the circumferential modulus is a modulus in the direction along the tire circumferential direction, and the width direction modulus is a modulus in the direction along the tire width direction. The modulus is a 100% modulus measured according to JIS K6251.

  The anisotropic rubber that forms the tread shoulder portion 26 is not particularly limited, but a configuration in which rubber blended with short fibers is arranged so that the orientation direction of the short fibers is in the tire circumferential direction is suitable.

  Examples of such short fibers include organic fibers such as polyvinyl alcohol (PVA) fibers, aramid fibers, polyester fibers and nylon fibers, inorganic fibers such as glass fibers, carbon fibers and metal fibers, polymer whiskers, metals and ceramics. A whisker is mentioned. PVA short fibers are preferred, and those obtained by treating PVA short fibers with resorcin / formalin / latex liquid (RFL liquid) are particularly preferably used. Here, the RFL liquid is prepared by mixing an initial condensate of resorcin and formalin (reaction of resorcin and formalin in a basic catalyst) with latex, and immersing PVA short fibers in this RFL liquid ( What is processed by dipping) is used.

  The fineness and the fiber length of the short fibers are not particularly limited, but for example, those having a fineness of 0.5 to 5 dtex and a fiber length of about 1 to 10 mm are preferable. Moreover, the compounding quantity of a short fiber is not specifically limited, However About 2-8 weight part is suitable with respect to 100 weight part of rubber components.

  The rubber composition blend used as a base for blending the short fibers can be a normal base rubber blend. That is, the rubber component includes diene rubbers such as natural rubber, isoprene rubber, butadiene rubber, and styrene butadiene rubber. Used as additives are sulfur, vulcanization accelerator, zinc white, stearic acid, reinforcing fillers such as carbon black and silica, softeners, anti-aging agents and the like.

  When rubber blended with such short fibers is extruded using an extruder, the short fibers are oriented in the transport direction, that is, the row direction. Therefore, if this extrudate is arranged on the belt layer 16 so that the longitudinal direction (line direction) is the tire circumferential direction, the short fibers can be oriented in the tire circumferential direction. Thereby, the modulus in the tire circumferential direction is high, and the modulus in the tire width direction and the tire radial direction (thickness direction of the base rubber layer 22) orthogonal to the circumferential direction can be set low.

  As described above, by increasing only the circumferential modulus of the tread shoulder portion 26 of the base rubber layer 22, in the shoulder portion to which a large load is applied at the time of braking, the change in the contact shape when the braking load is applied from the normal contact time. It is possible to control and suppress the contact pressure deterioration of the shoulder portion. Further, at the time of braking, in the tread shoulder portion 26, the extension of the contact length is suppressed by a high circumferential modulus, and the modulus is set low in the width direction. Can be increased. Therefore, the braking distance is shortened and the braking performance can be improved. In other words, in order to improve braking performance, the extension of the contact length at the center part during braking is not suppressed, but the extension of the contact length at the shoulder part is suppressed and the contact width at the shoulder part is increased. It is considered that it is effective to increase the amount of only the circumferential modulus of the tread shoulder portion 26 as described above, and this effect can be advantageously achieved.

  Further, according to the present embodiment, the braking performance is improved by the configuration of the base rubber layer 22, and the cap rubber layer 20 can adopt the same configuration as the conventional one. It is possible to avoid impairing the tire performance.

  It is preferable from the point of the said effect that the circumferential direction modulus of the anisotropic rubber which forms the said tread shoulder part 26 is 1.5 times or more of the width direction modulus, More preferably, it is 2 times or more. In addition, although an upper limit is not specifically limited, Usually, it is 4 times or less. Further, the circumferential modulus of the anisotropic rubber is preferably 1.5 times or more of the circumferential modulus of the rubber forming the tread center portion 24 from the viewpoint of the above-described effect, and more preferably 2 times or more. It is. In addition, although an upper limit is not specifically limited, Usually, it is 4 times or less.

(Rubber preparation and physical property measurement)
According to the formulations shown in Table 1 below, rubber compositions of Formulations A to C were prepared. The details of each component in Table 1 are as follows.

SBR: styrene butadiene rubber (trade name “SBR1502”) manufactured by JSR,
・ Natural rubber: RSS # 3,
Short fiber 1: Kuraray Co., Ltd. RFL-treated vinylon short fiber (trade name “FW-R”),
Short fiber 2: Aramid short fiber (trade name “Tauron 1091”) manufactured by Teijin Limited,
-FEF: Tokai Carbon Co., Ltd. carbon black (trade name "Seast SO"),
Aroma oil: Aroma-based process oil (trade name “JOMO process X-140”) manufactured by Japan Energy Co., Ltd.

  In each rubber composition, 1.5 parts by weight of an anti-aging agent (manufactured by Flexis, trade name “Sant Flex 6PPD”), stearic acid (manufactured by Kao Soap, product) with respect to 100 parts by weight of the rubber component as a common compound Name "Lunac S20") 2.0 parts by weight, Zinc Hana (Mitsui Metal Mining Co., Ltd., trade name "Zinc Hana 1") 2.0 parts by weight, Vulcanization accelerator CZ (Ouchi Shinsei Chemical Industries, Ltd.) , 1.5 parts by weight of a trade name “Noxeller CZ-G” and 2.0 parts by weight of sulfur (made by Hosoi Chemical Co., Ltd., trade name “powder sulfur 150 mesh”).

For each rubber composition, an unvulcanized rubber sheet having a thickness of 2 mm was prepared using a 12-inch roll, molded into a length of 120 mm × width of 130 mm × thickness of 2 mm, and press vulcanized at 160 ° C. for 20 minutes to obtain a sample. Produced. And about this sample, 100% modulus was measured by the method based on JISK6251 about two directions of a process direction (extrusion direction) and a direction orthogonal to the process direction, respectively. The results are shown in Table 1. In addition, () in Table 1 is an index display in which 100% modulus in the line direction of Formulation A is 100.

(Production and evaluation of tires)
As the tires of Examples 1 and 2 and Comparative Examples 1 to 3, pneumatic radial tires for passenger cars having the cross-sectional structure shown in FIG. 1 were produced with a tire size of 215 / 65R16. The rubber composition of the base rubber layer 22 in each tire is as shown in Table 2 below. Except for the rubber composition, Examples 1 and 2 and Comparative Examples 1 to 3 have the same structure. Comparative Example 1 is a tire in which the base rubber layer is not divided into a tread shoulder portion and a tread center portion as a control. In each tire, the base rubber layer 22 had a thickness of 2.0 mm, and the cap rubber layer 20 had a thickness of 8.0 mm. The distance y from the tire equator line CL to the boundary line F between the tread center portion 24 and the tread shoulder portion 26 was set to y = 0.6x (x = 83 mm, y = 50 mm).

  For each tire of Examples 1 and 2 and Comparative Examples 1 to 3, the contact width elongation, the contact length elongation at the shoulder portion, and the maximum contact pressure at the time of braking were measured, and the braking performance was evaluated and measured. Each measuring method is as follows.

・ Elongation of contact width, contact length, maximum contact pressure: rim used: 16 × 6.5JJ, air pressure: 230kPa, load applied to the tire is 640kg during normal operation and 830kg during braking, and the contact width from normal to braking And the change in contact length at the shoulder were measured and displayed as an index with Comparative Example 1 taken as 100. Moreover, the maximum contact pressure at the time of a braking load was displayed as an index with Comparative Example 1 as 100.

-Braking performance (braking distance shortening rate): rim used: 16 x 6.5 JJ, air pressure: 230 kPa, each tire was mounted on a 2500 cc passenger car, and the stopping distance from a speed of 100 km / h was measured. The shortening rate of the braking distance as a reference was obtained.

  As shown in Table 2, in Examples 1 and 2 according to the present invention, compared to Comparative Example 1, the extension of the contact length at the shoulder portion during braking is suppressed, and the extension of the contact width is increased. Maximum ground pressure was reduced. As a result, the braking distance was shortened compared to Comparative Example 1, and the braking performance was improved.

  On the other hand, the tread center part 24 and the tread shoulder part 26 are both treads using Comparative Example 2 using the anisotropic rubber of the above-mentioned blend B or the above-mentioned blended B anisotropic rubber only for the tread center part 24. In Comparative Example 3 in which only the circumferential modulus of the center portion 24 was increased, the effect of improving the braking performance was not recognized.

  As described above, according to the present invention, the braking performance can be improved, so that the present invention is suitably used for various pneumatic tires.

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

Explanation of symbols

  DESCRIPTION OF SYMBOLS 12 ... Bead core, 14 ... Carcass, 16 ... Belt layer, 18 ... Tread rubber, 20 ... Cap rubber layer, 22 ... Base rubber layer, 24 ... Tread center part, 26 ... Tread shoulder part

Claims (2)

In a pneumatic tire for a passenger car in which a tread rubber is provided in a crown portion of a carcass, and the tread rubber includes a cap rubber layer on a ground surface side and a base rubber layer on a carcass side.
The tread shoulder portion of the base rubber layer is formed of an anisotropic rubber having a high circumferential modulus relative to the width direction modulus , and the anisotropic rubber is made of rubber blended with short fibers, and the orientation direction of the short fibers There Rutotomoni arranged such that the tire circumferential direction, wherein the base rubber forming the tread center portion of the rubber layer not short fiber is compounded, the circumferential modulus of the base rubber layer of the anisotropic rubber the circumferential higher set pneumatic tire for passenger cars than the modulus of the rubber forming the tread center portion of. The circumferential modulus of the anisotropic rubber forming the tread shoulder portion is 1.5 times or more of the width direction modulus and 1.5 times or more of the circumferential modulus of the rubber forming the tread center portion. The pneumatic tire for passenger cars according to claim 1.

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