JPH1076809A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire which exerts excellent maneuvering stability and comfortableness with vibrations while the car is running on a wet road surface till the final period of the tire lifetime. SOLUTION: A pneumatic tire concerned includes a cap rubber layer installed outside in the radial direction and a base rubber layer installed inside the radial direction consisting of different rubber compounds and is formed from tread rubber consisting of the two layers, wherein the top of the base rubber layer lies at a level ranging 40-80% from the groove bottom of block to its surface and the base rubber contains 0.5-5.0 parts by wt. vulcanization accelerating agent expressed by the given formula relative to 100 parts by wt. rubber component. In the formula, R<1> and R<2> independently represent hydrogen atom, alkyl radical, and aryl radical, excluding the case that R<1> and R<2> may be hydrogen atoms simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire, which has improved handling stability on wet road surfaces (hereinafter referred to as "WET") and vibration riding comfort (hereinafter referred to as "shocking") until the end of use. The present invention relates to a pneumatic tire having a structure in which a tread is hardly lowered and a tread includes a cap rubber layer and a base rubber layer.

[0002]

2. Description of the Related Art Hitherto, in order to improve the wettability of a pneumatic tire, a rubber having a high styrene content such as SBR or silica has been used for a rubber of a tread portion which comes into contact with a road surface. For this purpose, a method of softening the rubber of the tread portion is used. According to these techniques, it is possible to surely improve the wettability and the shocking property when the tire is new, but there is a problem that the performance of each tire decreases from the middle to the end of use of the tire.

As a countermeasure against this, for example, Japanese Unexamined Patent Publication No.
No. 205 discloses a method in which different rubbers are used for the cap rubber layer and the base rubber layer of the tread, and the base rubber layer is exposed with wear to maintain the performance. However, since this base rubber layer is exposed to heat and strain internally until it appears on the tread surface, when it is exposed on the tread surface after abrasion, it is already aged and the intended performance is not attained. was there.

Japanese Patent Application Laid-Open No. 58-87138 is known for the purpose of suppressing the aging of tread rubber and side rubber on the surface and improving the appearance of tires at the end of running. The effect on the base rubber used is unknown, and there is no description or prediction about the wettability and the shaking property.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned facts, and an object of the present invention is to provide a pneumatic tire having stable WET performance and oscillating performance from the middle stage to the end of tire running. Is to provide.

[0006]

Means for Solving the Problems The present inventors have analyzed the aging phenomenon of the base rubber layer inside the tread in detail, and unlike the cap rubber layer exposed on the surface, the main factor of the aging is oil. Is not a volatilization or oxidation by oxygen or ozone in the air, but a change in the cross-linking state due to further cross-linking by sulfur remaining in the base rubber. Based on the new finding that the present invention has been made, it has been found that the problem can be solved by the following means, and the present invention has been completed.

That is, (1) In the pneumatic tire of the present invention, the cap rubber layer disposed on the radially outer side and the base rubber layer disposed on the radially inner side have different rubber compositions from each other. A pneumatic tire formed by a tread rubber layer comprising: a base rubber layer having an upper end at a height in the range of 40 to 80% from a block groove bottom to a block surface, and The rubber contains 0.5 to 5.0 parts by weight of a vulcanization accelerator represented by the following general formula based on 100 parts by weight of the rubber component of the base rubber.

[0008]

Embedded image

(Wherein R ¹ and R ² are each independently
Represents a hydrogen atom, an alkyl group or an aryl group. Where R
Except when ¹ and R ² are simultaneously hydrogen atoms. (2) In the pneumatic tire of the present invention, in the above item (1), R ¹ and R ² of the vulcanization accelerator represented by the general formula each independently represent a hydrogen atom, a methyl group, an ethyl group or Phenyl group). (However, this excludes the case where R ¹ and R ² are both hydrogen atoms at the same time.) (3) In the pneumatic tire of the present invention, in the above (1), the vulcanization accelerator may be bis (4-methylbenzoic acid). Thiazolyl-2) -disulfide, bis (5-methylbenzothiazolyl-2) -disulfide, mercapto-4-
At least one selected from the group consisting of methylbenzothiazole and mercapto-5-methylbenzothiazole
It is a seed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the upper end of the base rubber layer may be at a height h within a range of 40 to 80% of the distance t from the groove bottom of the block 10 to the block surface as shown in FIG. is necessary. That is, (h / t) × 100 = 40-
It is necessary to satisfy the relationship of the expression (80) (%). This is because the base rubber 12 having excellent wettability and oscillating properties is exposed on the surface during the middle and late stages of running, and complements the wettability that has decreased due to the decrease in groove volume and the oscillating ability that has decreased due to an increase in block rigidity. This is to make it possible. Here, when h / t is less than 40%, the use time until reaching the slip mark is short, and it is insufficient as a period for improving the wettability and the shaking performance. On the other hand, when h / t is more than 80%, the period for which the performance of the original cap rubber 14 is exhibited is insufficient.

Further, the base rubber contains a vulcanization accelerator represented by the above general formula in an amount of 0.5 to 5.
It is necessary to include 0 parts by weight. If the amount is less than 0.5 part by weight, the aging of the base rubber during the period in which it is present in the tread rubber cannot be suppressed. Therefore, increasing the amount further is not effective.

In the above general formula of the vulcanization accelerator used in the present invention, each of R ¹ and R ² independently represents a hydrogen atom, an alkyl group or an aryl group, unless R ¹ and R ² are simultaneously a hydrogen atom. Preferably, a hydrogen atom and a carbon atom number of 1 to 6
And an aryl group having 6 to 10 carbon atoms, and more preferably a hydrogen atom, a methyl group, an ethyl group or a phenyl group, respectively.

These vulcanization accelerators include, for example, 2
-Mercapto-4-methylbenzothiazole, 2-mercapto-4-ethylbenzothiazole, 2-mercapto-5-methylbenzothiazole, 2-mercapto-5
Ethyl benzothiazole, 2-mercapto-6-methylbenzothiazole, 2-mercapto-6-ethylbenzothiazole, 2-mercapto-4,5-dimethylbenzothiazole, 2-mercapto-4,5-diethylbenzothiazole, 2- Mercapto-4-phenylbenzothiazole, 2-mercapto-5-phenylbenzothiazole, 2-mercapto-6-phenylbenzothiazole,
Bis (4-methylbenzothiazolyl-2) -disulfide, bis (4-ethylbenzothiazolyl-2) -disulfide, bis (5-methylbenzothiazolyl-2)
-Disulfide, bis (5-ethylbenzothiazolyl-2) -disulfide, bis (6-methylbenzothiazolyl-2) -disulfide, bis (6-ethylbenzothiazolyl-2) -disulfide Sulfide, bis (4,5-
Dimethylbenzothiazolyl-2) -disulfide, bis (4,5-diethylbenzothiazolyl-2) -disulfide, bis (4-phenylbenzothiazolyl-2)
-Disulfide, bis (5-phenylbenzothiazolyl-2) -disulfide, bis (6-phenylbenzothiazolyl-2) -disulfide and the like. Among them, bis (4-methylbenzothiazolyl-2) -disulfide, bis (5-methylbenzothiazolyl-2)-
Disulfide, mercapto-4-methylbenzothiazole and mercapto-5-methylbenzothiazole are preferred. These vulcanization accelerators can be used alone or in a mixture of two or more.

The method for producing these vulcanization accelerators is not particularly limited, but they can be easily produced by using, for example, JP-A-49-93361.

Considering the effect of the present invention that the wet property and the shaking property are maintained from the middle stage to the end stage of use of the tire, it is necessary to use a base rubber having a compound excellent in both properties as compared with the cap rubber. When the storage elastic modulus (E 'value) of the cap rubber measured at room temperature, 50 Hz and dynamic strain 1% is 100, the E' value of the base rubber shows an index of 95 to 80. Assuming that the tan δ value of the cap rubber measured at a strain of 1% is 100, the loss tangent (tan δ) value of the base rubber preferably shows an index of 105 or more.

The cap rubber and the base rubber of the present invention include natural rubber, synthetic rubber such as isoprene rubber, butadiene rubber,
The components such as butyl rubber (including halogenated butyl rubber), ethylene-propylene rubber, carbon black, silica, zinc oxide, stearic acid, antioxidant, WAX, silane coupling agent, oil, vulcanizing agent, etc. It can be appropriately blended within a range that does not impair the effect.

Examples of the vulcanizing agent include sulfur and the like. The amount of the sulfur is 0.1 to 5 parts by weight, preferably 0.5 to 2 parts by weight based on 100 parts by weight of the rubber component. . If the amount is less than 0.1 part by weight, the breaking strength and abrasion resistance of the vulcanized rubber decrease, and if it exceeds 5 parts by weight, the rubber elasticity is lost.

The rubber composition according to the present invention can be obtained by kneading using a kneading machine such as a roll, an internal mixer, a Banbury mixer, etc., and after molding, vulcanizing to be used for a tire tread or the like. To form the pneumatic tire of the present invention.

Further, as the block height decreases due to wear, the block rigidity sharply increases, and this contributes to a decrease in the oscillating property and the wet property (particularly, the controllability of the limit area). For the purpose of complementing this, the present invention is superior to the inside of the tread after abrasion, and has excellent shaking properties and WET properties.
The feature is that the base rubber, which is difficult to age, is exposed. However, even after the base rubber is exposed, as the wear progresses, the block rigidity also increases. Therefore, as shown in FIG. 2, the cap rubber 14, the base rubber 1
2. Composed of 3 layers of base rubber 16, more wettability,
By using a rubber composition excellent in oscillating property and resistant to aging in the inner layer, that is, the base rubber 1
By making the physical properties of the base rubber 16 better than those of the base rubber 12 in the second embodiment, it is possible to further maintain the performance in the middle to end stages of wear. Further, a multilayer structure may be used, but considering processing costs, three or four layers are considered to be the limit.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention.

Various measurements were made according to the following methods. (1) WET performance The initial WET performance is evaluated by a test driver on a wet road test course by driving test, braking performance, steering wheel responsiveness, road surface grip performance during steering, and controllability after exceeding the slip limit. , And 80k
Judgment was made comprehensively based on the stopping distance from m / h. Further, when the vehicle was driven on a domestic road and the block height was worn to 50% (50% wear), the same WET evaluation was performed again.
Larger numbers are better.

(2) Shaking performance Various road surfaces such as asphalt, concrete, and Belgian roads having different roughnesses were run on a test course, and comprehensive evaluation was made by feeling of a test driver. This was also evaluated for tires at the initial stage and at the time of 50% wear. Larger numbers are better.

The evaluation results are shown as indices in Examples 1 and 2, with the initial performance of Comparative Example 1 being 100, and in Examples 3, 4, and 5, with the initial performance of Comparative Example 2 being 100. Also,
When the difference between the indices of both the WET property and the shaking property is ± 1 to 5, the test driver can judge the difference, and when the difference exceeds ± 5, the level can be judged by the general user.

(3) E ′ and tan δ E ′ and tan δ were measured using a viscoelasticity measuring device (manufactured by Toyo Seiki), E ′ was room temperature, frequency was 50 Hz, dynamic strain was 1%.
Tan δ is 0 ° C., frequency 50 Hz, dynamic strain 1
%. The E ′ / tan δ of the base rubber was expressed as an index with the E ′ / tan δ of the cap rubber A being 100/100. [Examples 1 to 5, Comparative Examples 1 and 2] Kneading and blending were performed according to the blending recipes shown in Table 1 below to obtain rubber compositions A to G. These various rubber compositions were combined as a cap rubber and a base rubber according to Table 2 to obtain a size 225 / 50R16 using a two-layer tread as shown in FIG.
No. 1 tire was prototyped, and the actual vehicle performance was evaluated using an 8J-16 rim. The results are shown in Table 2. The upper end of the base rubber layer of this prototype tire had a block height of 70 mm.
%.

[0025]

[Table 1]

[0026]

[Table 2]

As shown in Table 2, it can be seen that the pneumatic tire of the present invention has stable WET properties and oscillating properties until the end of tire running. In the tire using silica as the base rubber, significant improvement in wettability and oscillating property is recognized.

There is no significant difference in the initial performance since the same cap rubber is used in both the embodiment and the comparative example.

In each of Comparative Examples 1 and 2, since the vulcanization accelerator of the present invention was not used in the base rubber,
Both the wettability and the oscillating property at the time of% abrasion are deteriorated as compared with the embodiment.

[0030]

The pneumatic tire of the present invention has the above-described structure, and thus has an excellent effect of having a high level of stable WET property and oscillating property until the end of tire running.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of one of tread portions of a pneumatic tire of the present invention.

FIG. 2 is another schematic sectional view of a tread portion of the pneumatic tire of the present invention.

[Explanation of symbols]

 10 Block 12 Base rubber 14 Cap rubber 16 Base rubber t Distance from groove bottom to block surface h Distance from groove bottom to base rubber upper end

Claims (3)

[Claims] 1. A pneumatic tire formed of a tread rubber comprising a rubber composition in which a cap rubber layer disposed radially outward and a base rubber layer disposed radially inward have different rubber compositions. Wherein the upper end of the base rubber layer has a height in the range of 40 to 80% from the bottom of the block groove to the surface of the block, and the base rubber has a vulcanization acceleration represented by the following general formula: 0.5 to 5.0 with respect to 100 parts by weight of the rubber component of the base rubber.
A pneumatic tire comprising a weight part. Embedded image (In the formula, R ¹ and R ² each independently represent a hydrogen atom, an alkyl group or an aryl group, provided that R ¹ and R ² are not simultaneously a hydrogen atom.) 2. The vulcanization accelerator represented by the general formula, wherein R ¹ and R ² each independently represent a hydrogen atom, a methyl group, an ethyl group or a phenyl group. Pneumatic tires. (However, this excludes the case where R ¹ and R ² are simultaneously hydrogen atoms.) 3. The vulcanization accelerator comprises bis (4-methylbenzothiazolyl-2) -disulfide, bis (5-methylbenzothiazolyl-2) -disulfide, mercapto-4-methylbenzo. Thiazole and mercapto-5
The pneumatic tire according to claim 1, wherein the pneumatic tire is at least one member selected from the group consisting of -methylbenzothiazole.