JPH11245619A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance anti-chucking properties while enhancing steering stability at the time of off-road travel. SOLUTION: A tread portion 2 is comprised of a cap rubber body 7 forming a tread surface 2a and a base rubber body 9 disposed inside the cap rubber body 7 at a tire radial direction. In the cap rubber body 7, a sum blended amount (α+β) of a blended amount α of silica and a blended amount β of carbon black is 70 to 120 parts by weight based on 100 parts by weight of a rubber component, and a ratio γ (=α/(α+β)) of a blended amount α of silica occupied in the sum blended amount of silica and carbon black is 20 to 80%. A silane coupling agent is contained in the cap rubber body 7 at an amount of 5 to 10% of the blended amount α of silica. Further, in the base rubber body 9, a dynamic storage elasticity modulus (E') after vulcanization is 9.5 (MPa) or more and a JISA hardness is 77 deg. or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having improved handling stability on rough terrain and improved chunking resistance.

[0002]

2. Description of the Related Art When traveling on rough terrain such as sand, rocky terrain, rubble, etc., cracks are generated in the tread portion of the tire, for example, at the base of the block, which grows and the block grows during traveling. Damage called splashing chunking may occur. When such chunking occurs, the life of the tire is shortened, and the running performance is greatly affected, such as a sudden loss of road grip.

Hitherto, in order to prevent such chunking, improvements have been made in the direction of hardening the rubber by increasing the amount of carbon black in the tread rubber or reducing the oil content. .

[0004] However, when the tread rubber is reinforced in this way, although the chunking performance can be expected to be improved to some extent, the grip performance of the tire is greatly reduced, and the road surface can be effectively gripped particularly on uneven terrain. However, there was a problem that the steering stability performance was greatly reduced.

The present invention has been devised in view of the above-described problems, and comprises a tread portion including a cap rubber member forming a tread surface and a base rubber member disposed radially inward of the cap rubber member. On the basis of specifying the compounding and physical properties of these rubbers, pneumatic tires that can improve chunking resistance without lowering steering stability performance,
In particular, it is an object of the present invention to provide a pneumatic tire that frequently travels on uneven terrain.

[0006]

According to a first aspect of the present invention, there is provided a pneumatic tire having a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion. A cap rubber body forming a tread surface which is an outer surface of the tread portion, and a base rubber body disposed radially inward of the cap rubber body in a tire radial direction, wherein the cap rubber body is a rubber component of the cap rubber body. The total blended amount of the blended amount α of silica and the blended amount β of carbon black with respect to 100 parts by weight (α + β)
Is 70 to 120 parts by weight, and the ratio γ (= α / (α + β)) of the amount α of silica in the total amount (α + β) of silica and carbon black is 20 to 80%.
In addition, the base rubber body contains a dynamic storage elastic modulus (E ') after vulcanization of 9.5 (MP
a) and the JISA hardness is 77 ° or more.

According to a second aspect of the present invention, the tread portion is provided with a tread groove and a plurality of blocks defined by the tread groove, and the base rubber body is substantially formed on a bottom surface of the tread groove. The pneumatic tire according to claim 1, further comprising a layered portion extending along the layered portion and a thickened portion connected to the layered portion and increasing the thickness in the block.

In this specification, the dynamic storage elastic modulus (E ') is obtained by cutting a strip sample of 4 mm width × 30 mm length × 22.0 mm thickness and using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. Using a meter, initial distortion 10%, frequency 10
Hz, an amplitude of 2%, and a measurement temperature of 70 ° C. The JISA hardness is measured based on a JIS K6253 durometer hardness test (type A).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 2 and a sidewall portion 3.
And a carcass 6 composed of a carcass ply that is folded back around the bead core 5 of the bead portion 4 and locked.

The pneumatic tire of this embodiment has a tread width, which is the distance between the edges E of the tread portion 2 in the axial direction of the tire, and forms the tire's maximum width. 1 illustrates a pneumatic tire for a motorcycle.

The carcass 6 is made of, for example, an organic fiber cord and a carcass ply having a bias structure of a plurality of layers in which the cord is arranged at an angle of, for example, 30 to 65 ° with respect to the tire equator C.

The tread portion 2 has a deeply formed tread groove T and a plurality of blocks B defined by the tread groove T in the present embodiment, and is configured to be able to transmit a driving force on uneven terrain. Is done. And this tread part 2
Is a two-layer structure including a cap rubber body 7 forming a tread surface 2a which is an outer surface of the tread portion 2 and a base rubber body 9 disposed radially inward of the cap rubber body in the tire radial direction. I have.

In order to improve the grip performance of the cap rubber body 9 during running on uneven terrain, the inventors of the present invention have determined that the mixing amount α of silica and carbon Black content β
Is a total amount (α + β) of 70 to 120 parts by weight, and a ratio γ (= α) of the amount α of silica in the total amount (α + β) of silica and carbon black.
/ (Α + β)) is 20 to 80%, and it is found that it is preferable to include a silane coupling agent in an amount of 5 to 10% of the blending amount α of the silica.

First, if the total amount (α + β) of the silica blending amount α and the carbon black blending amount β is less than 70 parts by weight with respect to 100 parts by weight of the rubber component of the cap rubber body 7, While sufficient reinforcement cannot be obtained when running on uneven terrain, durability decreases,
If the total compounding amount (α + β) exceeds 120 parts by weight, the heat generated by the rubber increases, and the temperature of the cap rubber body 9 increases due to the history due to the periodic distortion caused by the uneven terrain running, which tends to cause thermal destruction.

At this time, if the ratio γ (= α / (α + β)) of the amount α of silica in the total amount (α + β) of silica and carbon black is less than 20%, the conventional reinforcing method using carbon black is used. Although the road surface grip force is reduced and the steering stability performance is not expected to be improved by silica, if the ratio γ exceeds 80%, there is a problem that the destruction characteristics at high temperatures are significantly reduced.

That is, it is difficult to improve the dispersion of silica in rubber as compared with carbon black. In particular, it is extremely difficult to improve dispersion when the ratio γ of silica is increased. , Reduced fracture properties,
Especially when the rubber is heated to a high temperature, the breaking characteristics are greatly reduced.

The grip improving effect of silica is as follows.
Sufficient bonding with the polymer is required,
It is necessary to incorporate a silane coupling agent. The compounding amount of the silane cup agent is determined according to the compounding amount α of silica. In the present invention, the compounding amount needs to be 5 to 10% of the compounding amount α of silica.

If the compounding amount of the silane coupling agent is less than 5% of the compounding amount α of silica, the bond between the silica and the polymer is weak, and the grip cannot be effectively improved or the reinforcing property cannot be exhibited effectively. If the amount exceeds the above range, the elastic modulus of the rubber will be significantly increased, and the durability will be greatly reduced.

As the rubber component, various diene rubbers and the like can be suitably used. For example, natural rubber (NR), butadiene rubber (BR), so-called emulsion-polymerized styrene-butadiene rubber (E-SBR), Styrene butadiene rubber (S-SBR) of solution polymerization, synthetic polyisoprene rubber (IR), nitrile rubber (NBR) which is a copolymer of butadiene and acrylonitrile, chloroprene rubber (CR) which is a polymer of chloroprene, and the like. It is preferable to use a rubber obtained by blending one or more of these.

The silica has a nitrogen adsorption specific surface area (BET) of 100 to 250 m ² / g and an oil absorption of dibutyl phthalate (DBP) of 150 ml / 100.
Those having a colloidal property of not less than g are preferable in terms of rubber reinforcing effect, rubber processability, and the like. Note that silica having improved dispersibility can also be suitably used.

Various carbon blacks commercially available for tire production can be used as the carbon black. Further, as the silane coupling agent, for example, bis (triethoxysilylpropyl) tetrasulfide and α-mercaptopropyltrimethoxysilane are preferable.

It is necessary for the base rubber member 9 disposed radially inward of the cap rubber member 7 to particularly improve the chunking resistance. It was found that it was necessary that the dynamic storage elastic modulus (E ') of the JIS needs to be 9.5 (MPa) or more and the JISA hardness was 77 ° or more.

When the dynamic storage modulus (E ') of the base rubber body 9 is less than 9.5 (MPa) or when the JISA hardness is less than 77 °, the anti-chunking performance is improved. Becomes difficult. The base rubber body 9
Preferably has a dynamic storage modulus (E ') of 9.5 to 12.
It is desirable that the hardness is in the range of 0 and the JISA hardness is in the range of 77 to 88.

It is preferable that the dynamic storage elastic modulus (E ') and the JISA hardness of the cap rubber body 7 are smaller than those of the base rubber body in order to increase the grip force on the road surface.

In this embodiment, the base rubber body 9
As shown in an enlarged view in FIG. 2, a layered portion 9a extending substantially along a groove bottom surface 10 of the tread groove T, and a layered portion 9a
And a thickened portion 9b which increases the thickness in the tire radial direction in the block B.
As a result, the inside of the block B has a JISA hardness of 77 ° while utilizing the excellent road grip force of the cap rubber body 7.
By being particularly effectively reinforced by the thickened portion 9b of the base rubber body 9 having the above hardness, it is possible to further improve the steering stability and the anti-chunking performance when running on uneven terrain.

At the position of the groove bottom surface 10 of the tread groove T, the thickness ratio tc: tb of the cap rubber member 7 and the base rubber member 9 is preferably, for example, about 30:70 to 70:30.

[0027]

EXAMPLES Tables 1 and 2 show the composition of the rubber used for the cap rubber body and the base rubber body.

[0028]

[Table 1]

[0029]

[Table 2]

Next, by combining the cap rubber body and the base rubber body, a pneumatic tire for a motorcycle for running on uneven terrain having a tire size of 110 / 90-19 and as shown in FIG. Then, the steering stability, durability and chunking resistance were tested. Pneumatic tires for motorcycles for running on uneven terrain that are not included in the present invention were also prototyped (Comparative Examples 1 to 8) and their performances were compared. In Comparative Example 1, the tread rubber had a one-layer structure. The test method is as follows.

<Steering stability> 250 cc of test tires
The motorcycle is mounted on the rear wheel of a motorcycle for motocross, and runs for about 2 hours on a motocross course at Hiro Park, Green Park in Hiroshima Prefecture. Comprehensive evaluation of driveability, braking performance, controllability, etc. Was evaluated with an index of 100. The higher the value, the better.

<Durability of Cap Rubber> Observation of the tire block after the steering stability test shows that the edge of the block is round and worn as shown in FIG. 3, and the reduction a of the edge is measured and compared. The evaluation was made by using an index with the value of Example 1 being 100. The higher the value, the better.

<Chunking resistance> Observation of the tire blocks after the steering stability test was performed, and the number of blocks that were cut off from the root due to the chunking was examined as a ratio to the total number of blocks. Was evaluated.
The higher the value, the better. Table 3 shows test results
Shown in

[0034]

[Table 3]

* 1 to * 11 in the table are as follows. * 1 Sumitomo Chemical 1502 * 2 Mitsubishi Chemical Diamond Black 1 * 3 Degussa Ultrasil VN3 * 4 Degussa Si69 * 5 Flexis Santoflex 13 * 6 Ouchi Shinko Sannox N * 7 Nippon Oil & Fat Stearic Acid Tung * 8 Zinc oxide made by Mitsui Metals * 9 Sulfur powder made by Karuizawa Sulfur * 10 Noxera-CZ made by Ouchi Shinko * 11 Diana Process Oil made by Idemitsu Kosan

As a result of the test, it was confirmed that the tires of the examples improved the chunking resistance while improving the steering stability during running on uneven terrain.

[0037]

As described above, according to the first aspect of the present invention, the chunking resistance can be improved while improving the steering stability when traveling on uneven terrain.

According to the second aspect of the present invention, the inside of the block is preferably formed by the thickened portion of the base rubber body having a JISA hardness of 77 ° or more while utilizing the excellent road grip force of the cap rubber body. By being reinforced, the chunking resistance can be further improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a pneumatic tire showing one embodiment of the present invention.

FIG. 2 is an enlarged view of the vicinity of the tread groove.

FIG. 3 is a sectional view showing a worn state of a block.

[Explanation of symbols]

 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Cap rubber body 9 Base rubber body 9a Layered part 9b Thickened part T Tread groove B block

Claims (2)

[Claims] 1. A pneumatic tire having a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion, wherein the tread portion has a cap rubber body forming a tread surface which is an outer surface of the tread portion. A base rubber body disposed radially inward of the cap rubber body in the tire radial direction, wherein the cap rubber body is composed of 100 parts by weight of a rubber component of the cap rubber body and a compounding amount of silica α and a compounding amount of carbon black. The total blending amount (α + β) with the amount β is 70 to 12
0 parts by weight, and the total blending amount of this silica and carbon black (α +
β) ratio of silica blending amount α in γ (= α / (α
+ Β)) is 20 to 80%, and further contains 5 to 10% of the silane coupling agent of the compounding amount α of the silica, and the base rubber body has a dynamic storage modulus (E ′) after vulcanization. )
A pneumatic tire having a hardness of 9.5 (MPa) or more and a JISA hardness of 77 ° or more. 2. The tread portion is provided with a tread groove and a plurality of blocks defined by the tread groove, and the base rubber body extends substantially along a groove bottom surface of the tread groove; 2. A thickening portion connected to the layered portion and increasing a thickness in the block.
The pneumatic tire as described.