JPH0551485A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To prevent the lowering of abrasion resistance caused by swelling with oil without deteriorating various properties necessary for a tire. CONSTITUTION:The rubber composition to be used in the subject tire has a weight change of <=35% when immersed in JIS No. 1 spindle oil at 24 deg.C for 60hr and is produced by compounding 100 pts.wt. of a diene rubber with 10-70 pts.wt. of carbon black having a nitrogen-adsorption specific surface area of >=140m<2>/g, 10-30pts.wt. of silica having a purity of >=80% (the sum of carbon black and silica is 40-80 pts.wt.) and 5-20% silane-coupling agent based on the amount of compounded silica. The rubber composition is used as the tread of the subject pneumatic tire.

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 for automobiles having improved oil swelling resistance without impairing initial wear resistance, steering stability and the like. It is about.

[0002]

2. Description of the Related Art Improving wear resistance is an important point in the performance required for automobile tires, and many studies and improvements have been made in the past. For example, when limiting the rubber physical properties of the tire tread part, effective methods include controlling and optimizing the particle size of carbon black, colloidal physical properties such as structure, and the filling amount of carbon black itself other than abrasion resistance. The wear resistance has been improved by strengthening and optimizing the rubber reinforcement phase by increasing the amount while balancing with other performance. In addition, the raw rubber, natural rubber (N
R), styrene butadiene rubber (SBR) and butadiene rubber (BR) are appropriately blended to reduce rolling friction resistance and improve dispersibility of carbon black, thereby improving abrasion resistance. I have been trying.

[0003]

However, under the conditions of use in which oil can permeate the tread surface from the road surface, in practice, such as Egypt and the Middle East where the paved road surface contains a relatively large amount of low-molecular oil components, the oil content is low. The problem arises that swelling significantly reduces the wear resistance. To reduce wear resistance due to oil swelling, it is sufficient to strengthen the reinforcing phase with carbon black, which has been conventionally used to improve wear resistance, and to improve the dispersibility of carbon black with a polymer blend. It couldn't be a countermeasure.

[0004] Generally, as a rubber composition formulation example for improving oil resistance, its polarity is greatly different from that of paraffin-based, aroma-based, and spindle-based oils such as nitrile rubber, so that it is resistant to dissolution in oil components. A method of blending a rubber having a high viscosity as a raw material polymer has been considered and implemented. However, even if such a method is adopted as a tread portion of a pneumatic tire, in addition to oil swelling resistance, performance required for the tire, for example, initial wear resistance, steering stability, etc. can be balanced. It is not possible and it is difficult to apply it to the actual situation.

Therefore, an object of the present invention is to improve oil content swelling resistance without deteriorating various tire performances such as initial wear resistance and steering stability.

[0006]

Means for Solving the Problems The inventors of the present invention have made earnest studies on a method for suppressing a decrease in abrasion resistance caused by oil swelling without deteriorating various performances of an automobile tire. It has been found that the decrease in abrasion resistance is mainly due to the morphological change of the carbon black reinforcing phase of the rubber composition constituting the tread portion, particularly the phase in which the interaction between the raw material polymer molecular chain and carbon black is dense. .. Therefore, by introducing a method to prevent the morphological change of the interaction phase of the polymer and carbon black due to such oil intrusion, the wear resistance deterioration due to oil swelling can be significantly reduced while maintaining the basic performance required for the tire. The present invention has been completed based on the finding that it can be improved.

That is, the pneumatic tire of the present invention has a nitrogen adsorption specific surface area (N _{2 of} 100 parts by weight of diene rubber).
10 to 70 parts by weight of carbon black having a SA) of 140 m ² / g or more, 10 to 30 parts by weight of silica having a purity of 80% or more, and 5 to 20% of the silica compounding amount of the silane coupling agent are mixed with the carbon black. A rubber composition with a total silica content of 40-80 parts by weight, and a weight change of 35% when immersed in JIS No. 1 spindle oil for 60 hours in a 24 ° C atmosphere.
A tread has the following rubber composition.

Examples of the diene rubber used in the present invention include natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, and the like containing a conjugated diene as a monomer.

The N ₂ SA used in the present invention is 140 m ²
Examples of carbon black having a content of at least / g include N 110 (SA
F) is used. Further, carbon black for color having a higher N ₂ SA or a similar one may be used.
Here, N ₂ SA is measured by the ASTM D3037-88 method.

The above-mentioned silane coupling agent generally has a chemical structure of RSiX ₃ and has an organic functional group R having a substituent in the same molecule which binds to a rubber component, and a hydrolyzable group which reacts with silica. Have X. R is a glycidoxy group, a mercapto group, a vinyl group, a methacryl group, an amino group or the like, and X is mainly an alkoxy group and a halogen group such as chlorine. Of these, those shown in Table 1 below can be preferably used.

[0011]

[Table 1]

Commercially available products of γ-glycidoxypropyltrimethoxysilane shown in Table 1 include A-187 (Nippon Unicar, UCC (US)), KBM 403 (Shin-Etsu Chemical), Toray Silicone SH 6040 Silane (Toray).・ Silicone, Do
w Corning (US)), FinishGF 81 (Wacker-Chemie (West Germany)), and commercial products of mercaptopropyltrimethoxysilane include Toray Silicone SH 6062 Silane (Toray Silicone, Dow Corning (US)). ,
A commercially available product of γ-mercaptopropyltrimethoxysilane is 189 (Nihon Unicar, UCC (US)).

It is needless to say that the rubber composition according to the present invention can be appropriately blended with a commonly used compounding agent, for example, sulfur, a vulcanization accelerator, a softening agent, an antiaging agent and the like. ..

[0014]

[Function] Due to the oil permeation into the rubber composition, the morphology of the interaction phase, which the polymer molecular chains physically adsorb to the carbon black and surrounds, changes, and the reinforcing effect of the carbon black on the polymer is significantly reduced. .. Carbon black having a large specific surface area, specifically N ₂ SA
It is effective to use 40 m ² / g or more and to expand the volume of the reinforcing phase.

However, the improvement by only filling carbon black having N ₂ SA of 140 m ² / g or more is not sufficient because it causes a large local swelling of the oil content, and the expansion of the specific surface area of carbon black only. If it is attempted to maintain or improve the oil content swelling resistance only by increasing the oil content or the filling amount, it becomes difficult to maintain the dispersibility of the carbon black in the rubber composition, and conversely, the wear resistance decreases and It causes difficulties. Therefore, in the present invention, N ₂ SA provides a reinforcing phase composed of silica and a silane coupling agent having a reinforcing property by a chemical bond different from carbon black.
By using an appropriate amount of each in combination with carbon black of 140 m ² / g or more, it is intended to solve such a problem. The appropriate amount referred to herein is an amount determined in relation to the prevention of deterioration of wear resistance due to other than oil permeation in addition to the prevention of deterioration of wear resistance during oil permeation. In particular,
To 100 parts by weight of the rubber component, 10 to 30 parts by weight of silica (SiO ₂ ) is added to 10 to 70 parts by weight of carbon black having N ₂ SA of 140 m ² / g or more, and the total amount of these is 40 to The amount in the area shown in FIG. 1 is 80 parts by weight. At this time, it is necessary to separately mix 5 to 20% of the SiO ₂ content of the silane compound.

Referring to FIG. 1, in the area A,
Not only the oil swelling resistance but also the abrasion resistance usually required is sufficient. On the other hand, in the region B, the tire performance which is usually required is satisfied, but a sufficient improvement effect cannot be obtained in terms of oil content swelling resistance. On the contrary, in the range of C, the oil swelling resistance can be greatly improved, but the abrasion resistance usually required is slightly inferior. In the area D, the reinforcing particles are excessively filled, so that not only various performances required for the tire, such as steering stability, cannot be maintained, but also carbon black and silica in the rubber compound are uniformly dispersed. Is difficult to manufacture.

The combination system of carbon black, silicone and silane coupling agent defined as described above prevents the oil content from swelling, that is, the oil content from permeating into the tread, without deteriorating other performances of the tire. It becomes possible to improve against the resulting reduction in wear resistance.

However, even with such a blending system, the morphological change of the interaction phase between the polymer and carbon black cannot be completely stopped, and the improvement effect cannot be guaranteed when the oil content continues for a long period of time. Is possible. Therefore, the present inventors have further earnestly examined what level of wear resistance becomes a problem with the amount of oil that permeates during the life of the tire. As a result, in a 24 ° C atmosphere, JIS
From a simulation test of immersing the rubber compound sample after vulcanization in No. 1 spindle oil, if the weight increment of the sample is 35% or less 60 hours after immersion, the normal ratio is
The carbon black-polymer interaction phase morphology change rate that causes a decrease in wear resistance of 10% or more is less than the rate at which the tread part is completely worn under normal use conditions. Found that he never saw any problems.

Compounds other than the above-mentioned compounding system of carbon black, silica and silane coupling agent are not particularly specified, but even if the carbon black, silica and silane coupling agent are within the above-specified ranges, For example, if the amount of sulfur is insufficient and a sufficient mesh design is not formed, the required oil swelling resistance may not be achieved. Also in this sense, in the present invention, the carbon black, silica, and silane coupling agent satisfy the above requirements, and then JIS 1
35% change in weight when immersed in No. Spindle oil for 60 hours
It must meet the following requirements:

As described above, in order to suppress the above-mentioned weight change, in addition to the above-mentioned carbon black, silica, and silane coupling agent, a vulcanization accelerator is added in an amount larger than the amount of sulfur.
For example, it is preferable to use a (vulcanization accelerator / sulfur) ratio of more than 1.0 and 2.5 or less. This is because if the vulcanization accelerator is used in an amount greater than the amount of sulfur, the amount of monosulfide in the sulfur cross-linking form will increase, and the rubber cross-linking network will become solid. Further, the heat deterioration resistance of the rubber composition is also improved, so that the oil content swelling resistance is maintained even when the tire is used for a long period of time, and the oil content swelling resistance under high temperature use conditions is also improved. On the other hand, if the above ratio exceeds 2.5, the crack growth resistance decreases, and it becomes difficult to further improve the oil content swelling resistance due to cracks or the like.

[0021]

EXAMPLES Next, the present invention will be explained with reference to Examples and Comparative Examples. Carbon black with N ₂ SA of 145 m ² / g (using carbon black with N ₂ SA of 121 m ² / g as a comparative example)
The following formula, a silane coupling agent represented by [(C ₂ H ₅ O) ₃ SiC ₃ H ₆ ] ₂ S ₄ (manufactured by Degussa, West Germany,
Various test rubber compositions were prepared by compounding with a rubber component in a compounding ratio (parts by weight) shown in Table 2 below together with a trade name: Si 69).

For these test rubber compositions, the following weight change after oil immersion, initial Lambourn abrasion index, and Lambourn abrasion index after oil immersion were measured. (A) Weight change after oil immersion : The rubber composition sample after vulcanization was immersed in JIS No. 1 spindle oil in an atmosphere of 24 ° C., and the weight change rate of the sample after 60 hours was measured. (B) Initial Lambourn abrasion index : The compounding ingredients in Table 2 were mixed and the Lambourn abrasion index was measured immediately after vulcanization. The larger the number, the better the result. (C) Lambourn abrasion index after immersion in oil : The Lambourn abrasion index was measured after mixing the compounding agents shown in Table 2 and immersing in spindle oil under the same conditions as the above-mentioned weight change after immersion in oil (A). .. The larger the number, the better the result. Each measurement result is also shown in Table 2.

[0023]

[Table 2]

From the measurement results shown in Table 2, the following was confirmed. Comparative Example 1 is N ₂ S that satisfies the requirements of the present invention.
A conventional rubber composition (control) using a carbon black having no A value is shown. Silica, which is an essential component of the present invention, was excessively added to this rubber composition to reduce the amount of carbon black added. (Comparative Example 2), one in which the amount of silica added was too small (Comparative Example 3), one in which the total amount of carbon black and silica was too small relative to the rubber (Comparative Example 4), and one in which it was too large (Comparative Example). No. 5) had problems in oil swelling resistance, initial abrasion resistance and workability. The carbon black having no N ₂ SA value satisfying the requirements of the present invention (Comparative Example 6) had a problem in abrasion resistance in the initial stage. There was a problem in wear resistance also in the case where the silane content was too low (Comparative Example 7) and the sulfur content was too low (Comparative Example 8). On the other hand, in the rubber composition in which carbon black having a N ₂ SA value of 140 m ² / g or more, which satisfies the requirements of the present invention, a silane coupling agent and silica are used in combination, the NR type, NR-SBR type and In all of the NR-SBR-BR systems, and in all of those in which the blending ratios of carbon black and silica were varied within the range satisfying the requirements of the present invention, a remarkable oil resistance was obtained as compared with the rubber compositions of Comparative Examples. The effect of improving the partial swelling property was recognized, and the initial wear resistance was not impaired.

[0025]

As described above, the rubber composition of the present invention can prevent deterioration of wear resistance due to oil penetration without impairing various performances required for a tire such as steering stability. The effect is obtained. Therefore, even when the rubber composition of the present invention is applied under the condition that the oil content may permeate from the road surface to the tread surface, it is possible to prevent the abrasion resistance from lowering.

[Brief description of drawings]

FIG. 1 is a graph showing a satisfactory range of a blending ratio of silica and carbon black in a tire rubber composition of the present invention.

Claims (1)

[Claims] 1. 100 to 100 parts by weight of a diene rubber, 10 to 70 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 140 m ² / g or more, and 10 to 70 parts by weight of silica having a purity of 80% or more. 30
The weight part and the silane coupling agent are 5 to 5 of the silica compounding amount.
A rubber composition containing 20% of carbon black and silica in a total amount of 40 to 80 parts by weight, and the weight change when immersed in JIS No. 1 spindle oil for 60 hours in a 24 ° C atmosphere. A pneumatic tire having a tread with a rubber composition of 35% or less.