JP2001288296A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for tire tread which has excellent abrasion resistance and excellent heat resistance, and furthermore reduces lower ing in performance with traveling distance, particularly lowering in grip, and especially a tread rubber composition for studless tire suited in traveling on the frozen road surface and the snow road surface. SOLUTION: The rubber composition for tire tread comprises 100 pts.wt. rubber component comprising >=80 wt.% at least one kind of a natural rubber, a synthetic polyisoprene rubber and a polybutadiene rubber and 0.05-0.21 pts.wt. sulfur and, in addition, an organic peroxide in an amount so that its active oxygen content (Y) comes to not less than 8 wt.% of the compounding amount (X) of the sulfur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a high-performance tire, in which the grip performance at the beginning of running of the tire is improved while the wear resistance is maintained, and the decrease in grip performance with the running distance is reduced. The present invention relates to a rubber composition for a studless tire suitable for running on an icy road surface and a snowy road surface.

[0002]

2. Description of the Related Art Hitherto, in a tread rubber composition for a high performance tire, a styrene-butadiene rubber having a high styrene content has been used in order to obtain a high grip property, or a large amount of fine carbon and a softener have been blended to obtain a high hardness. It has been attempted to increase the hysteresis loss at a predetermined temperature by preparing a low rubber composition. In such a rubber composition, when the tire travels over a long distance under high-speed conditions, internal heat is generated, and the grip properties tend to decrease with the traveling distance. This is because the reaction of the rubber composition proceeds due to the heat, and the rubber deteriorates. In order to maintain the grip at a constant level over a long period of time, it is necessary to increase the thermal stability of the rubber composition. Such thermal stability is affected by the crosslinked form of the vulcanized rubber.

[0003] The most common vulcanized rubber composition based on a sulfur vulcanization system composed of sulfur and a vulcanization accelerator generally has a polysulfide bond as a main component, and therefore has excellent abrasion resistance but low thermal stability. There is a problem of inferiority. That is, the cross-linked form of the polysulfide bond changes to the cross-linked form of monosulfide due to internal heat generation during running of the tire, so that the grip property is lowered.

On the other hand, EV vulcanization systems have long been known for the purpose of improving the thermal stability of sulfur vulcanization rubber compositions. The EV vulcanization system is a vulcanization method that minimizes the amount of sulfur as a vulcanizing agent and reduces the number of sulfur per unit crosslink as much as possible.
Low wear resistance, short fatigue life, poor adhesion to metals and the like.

On the other hand, organic peroxides that do not use sulfur form cross-links due to heat-resistant carbon-carbon bonds, and the change in the cross-linking structure of the rubber composition with the running distance is small, so that the deterioration of rubber physical properties such as grip properties Reduction can be reduced. However, since the crosslinked structure is strengthened and the degree of freedom inside the rubber molecule is restricted, the loss tangent (tan δ) of the vulcanized rubber composition itself is reduced, and the grip at the beginning of running is reduced.

[0006]

SUMMARY OF THE INVENTION The present invention has excellent abrasion resistance in a sulfur vulcanization system and excellent thermal stability in an organic peroxide vulcanization system, and further has a performance decrease with mileage. Provided is a rubber composition for a tire, which has a reduced grip property, particularly a tread rubber composition for a studless tire suitable for running on an icy road surface or a snowy road surface.

[0007]

According to the present invention, 0.05 to 0.21 sulfur is added to 100 parts by weight of a rubber component containing at least one of natural rubber, synthetic polyisoprene rubber and polybutadiene rubber in an amount of 80% by weight or more. A tread rubber composition for a tire, wherein the organic peroxide is compounded so that the amount of active oxygen (Y) is at least 8% by weight of the compounding amount (X) of the sulfur. It is.

It is preferable that the active oxygen content (Y) and the sulfur content (X) satisfy the following formula (1).

Y ≧ −85X + 25 (1) Further, 5 to 20 parts by weight of an aromatic oil and 4 to 15 parts by weight of an adhesive resin having a softening point of 60 ° C. or more are mixed with 100 parts by weight of the rubber component. preferable.

The rubber component used in the present invention is natural rubber,
It contains at least one kind of synthetic polyisoprene rubber or polybutadiene rubber by 80% by weight or more. For example, a mixture of natural rubber and polybutadiene rubber, and a mixture of synthetic polyisoprene and polybutadiene can be used in addition to using the above rubber component alone. Emulsion-polymerized styrene-butadiene rubber, solution-polymerized styrene-
Those generally used for tires, such as butadiene rubber, EPDM, and butyl rubber, can be mixed in a range of less than 20% by weight.

In the rubber composition of the present invention, a sulfur vulcanizing system and a crosslinking system with an organic peroxide are used in combination as a vulcanizing agent. The sulfur vulcanization system refers to a combination of sulfur and a vulcanization accelerator. The amount of sulfur is 0.05 to 100 parts by weight of the rubber component.
0.21 parts by weight. If the amount is less than 0.05 part by weight, the vulcanization density due to sulfur becomes small, and the tensile properties and abrasion resistance of the rubber composition, which are excellent properties due to sulfur crosslinking, are not sufficient. , The thermal stability is reduced, and the performance is deteriorated with the tire running distance.

As the vulcanization accelerator, general vulcanization accelerators can be used, for example, mercaptobenzothiazole, dibenzothiazyldisulfide, N-cyclohexylbenzothiazylsulfenamide, N-tert-butyl-
2-benzothiazolylsulfenamide may be used.
The compounding amount of the vulcanization accelerator is generally 0.1 to 2.0 parts by weight per 100 parts by weight of the rubber component.

The organic peroxides used in the present invention are those used for ordinary rubber vulcanization, such as dicumyl peroxide, 2,2-bis (tert-butylperoxy) octane, 2,5-dimethyl-2. , 5-di (tert-butylperoxy) hexane, α, α'-bis (tert-butylperoxy) diisopropylbenzene, 1,3-bis (tert-butylperoxyisopropyl) benzene and the like.

The amount of the organic peroxide is such that the amount of active oxygen (Y) is at least 8% by weight based on the amount of sulfur (X). Active oxygen refers to free radicals generated from the organic peroxide. If the amount of active oxygen is less than 8% by weight with respect to the amount of sulfur (X), crosslinking between rubber molecules by free radicals cannot be formed at a sufficient density.

The theoretical active oxygen ratio (Aw) is a value obtained by dividing the product of the atomic weight (N) of active oxygen in the organic peroxide and the atomic weight (16) of active oxygen by the molecular weight (W) of the organic peroxide. Is represented by The amount of active oxygen (Y) to be blended is defined as the product of the value and the blended amount of organic peroxide (P) with respect to 100 parts by weight of the diene rubber. That is, Aw = (16 N / W) Y = Aw × P.

Next, the present invention preferably comprises an active oxygen content (Y).
And the blending amount (X) of sulfur satisfy the following relationship.

Y ≧ −85X + 25 FIG. 1 shows the relationship between the amount of active oxygen (Y) and the amount of sulfur (X). Even when the amount of active oxygen (Y) is 8% by weight or more, Y
In the range of <-85X + 25, the content of sulfur (X) is small, and the density of the crosslinked form by sulfur becomes smaller than the density of the crosslinked form by peroxide. From the viewpoint of the overall balance of the physical properties of the rubber composition. Is disadvantageous.

Next, in the present invention, 5 to 20 parts by weight of a softening agent is added to 100 parts by weight of the rubber component so that the Shore A hardness of the rubber composition at a temperature of 0 ° C. becomes 55 degrees or less. Here, the softener is a petroleum softener, for example, process oil, extender oil, paraffin, liquid paraffin, petrolatum or petroleum resin, coal tar softener,
For example, coal tar, fatty oil-based softeners, for example, fatty acids, fatty acid salts, fatty oils or waxes, as well as synthetic resin softeners and liquid rubbers can be used.

When the amount of the softener is less than 5 parts by weight, the hardness of the rubber composition cannot be reduced. On the other hand, if it exceeds 20 parts by weight, the abrasion resistance and tensile properties are undesirably reduced.

Next, in the present invention, the softener has a softening point of 60.
It is desirable to use an adhesive resin having a temperature of at least ℃. Here, the adhesive resin is used as a tackifier, for example, a terpene resin such as coumarone-indene resin, a terpene resin or a terpene-phenol resin, a rosin derivative, a hydrogenated rosin derivative, an alkylphenol-based resin, or a petroleum resin. Can be used.

The following products are commercially available as the tacky resin having a softening point of 60 ° C. or higher. Examples of the coumarone-indene resin include Coumarone resin NG4 (softening point: 81 to 100 ° C.) manufactured by Nippon Steel Chemical Co., Ltd., and Process Resin AC5 (softening point: 75 ° C.) manufactured by Kobe Oil Chemical Industry Co., Ltd. As terpene phenolic resins, Hitachil Chemical Co., Ltd., Hitachil 1501 (softening point 80-100 ° C), Arakawa Forestry Co., Ltd. Tamanol 510 (softening point 75-95 ° C), Sumitomo Chemical Co., Ltd. Tucky Roll 101 (softening point 75-95
℃), tacky roll 160 (softening point 85-110 ℃)
And tacky roll EP30 (softening point 90-110)
C), Sumitomo Durez Co., Ltd. Sumilite Resin PR19
There are 900. Alcon P90 (softening point 90 ° C) and Ester Gum H (softening point 68 ° C) from Arakawa Hayashi Co., Ltd., Petroresin 80 from Mitsui Petrochemical Co., Ltd.
(Softening point 80 ° C), Heylets G100X (softening point 10
0 ° C), Maruzetsu of Maruzen Oil Co., Ltd. (softening point approx.
2 ° C). As a rosin derivative, there is Nicanol A70 (softening point: 70 to 90 ° C.) of Mitsubishi Gas Chemical Company, Ltd.

By blending an adhesive resin having a softening point of 60 ° C. or higher, flexibility is imparted without impairing basic properties such as tensile strength and abrasion resistance of the rubber composition, and the rubber composition can be used on iced and snow-covered road surfaces. Grip properties can be improved. From such a viewpoint, the softening point of the adhesive resin is 80 ° C to 11 ° C.
A range of 0 ° C. is more preferred.

The rubber composition of the present invention may further contain, if necessary, fillers such as carbon black and silica, additives, antioxidants and the like. The rubber composition for a tire of the present invention can be used for general tires, and is particularly suitably used for treads for studless tires.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

A rubber composition having the compounding composition shown in Table 1 was prepared, and this was used for a tread rubber to obtain a tire size T.
An L195 / 65R15 passenger car tire was manufactured. Table 2 shows the evaluation results. The contents of the ingredients in Table 2 are as follows.

[0026]

[Table 1]

[0027]

[Table 2]

Note 1) BR is trade name BR15 of JSR Corporation.
Was used. The mixing ratio of NR / BR is 50/50.

Note 2) SBR: solution-polymerized styrene-butadiene rubber having a styrene content of 23.5% by weight.

Note 3) Marcarez (softening point 102 ° C)
(Maruzen Petrochemical Co., Ltd.) Note 4) Aromax No. 5 (Fujikosan Co., Ltd.) Note 5) Perbutyl P (Nippon Oil & Fats Co., Ltd.): 95% peroxide content, 0.0897 theoretical active oxygen ratio vulcanization The physical properties of the rubber composition and the tire were evaluated by the following methods.

(1) Rubber Hardness (Shore A Hardness) The rubber hardness of a new tire measured at a temperature of 0 ° C. is defined as the initial rubber hardness.
After heat aging at 7 ° C. for 7 days, it was allowed to cool, and the rubber hardness measured at 0 ° C. was evaluated as the rubber hardness after thermal deterioration. The difference in rubber hardness before and after aging was used as an index of rubber deterioration.

The measurement conditions were based on JIS K6257. (2) Wear Resistance Evaluated by a pico abrasion test, the value of Comparative Example 1 was set to 100, and the relative value was indicated as an index. The higher the value, the better.

The measurement conditions were based on JIS K6264. (3) Grip performance on ice and snow We measured the distance to the ice on the test course and the sudden braking on the snowy road surface to stop. The numerical value of the initial ice / snow grip performance of Comparative Example 1 was expressed as an index with 100 being set. The larger the value, the better the grip. Here, the value at the time of a new article was defined as the initial grip performance on ice and snow, and the value after the tire was thermally aged at 70 ° C. for 7 days in an oven was defined as the grip performance on ice and snow after thermal aging.

In Examples 1 and 2, even after heat aging, the change in rubber hardness is smaller than that of a new rubber, while the grip on ice and snow is almost constant. Further, the abrasion resistance is almost the same level as Comparative Example 1.

In Example 3, the amount of the adhesive resin was small,
Since the blending amount of the aromatic oil is relatively large, the heat aging resistance due to the migration of the aromatic oil is slightly inferior to those of Examples 1 and 2, but it can be satisfied by comprehensively evaluating the abrasion resistance and the like.

In Comparative Example 2, since the amount of the styrene-butadiene rubber was as large as 30 parts by weight, the initial rubber hardness at a temperature of 0 ° C. was high, and the grip performance on ice and snow was inferior.

In Comparative Example 3, since the amount of sulfur was as large as 0.4 part by weight, the change in hardness after heat aging was large.

In Comparative Example 4, since the amount of the organic peroxide was too small, the amount of active oxygen was insufficient, and the rubber had low strength and poor abrasion resistance.

The embodiment disclosed this time is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0040]

As described above, the present invention provides a rubber containing natural rubber, IR or polybutadiene rubber as a main component,
Since the organic peroxide is compounded in a predetermined range, and the aromatic oil and the adhesive resin having a softening point of 60 ° C. or more are compounded in a predetermined amount, the tire has excellent heat aging resistance without deteriorating abrasion resistance. In addition, tires having excellent grip on ice and snow even after long running of the tires, particularly studless tires, can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of sulfur and the amount of active oxygen in a peroxide.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // (C08L 7/00 (C08L 7/00 91:00) 91:00) (C08L 7/00 (C08L 7/00) 101: 00) 101: 00)

Claims (3)

[Claims] 1. The method of claim 1, wherein at least one of natural rubber, synthetic polyisoprene rubber and polybutadiene rubber is 80% by weight.
With respect to 100 parts by weight of the rubber component containing the above, 0.0
5 to 0.21 parts by weight of the organic peroxide and the active oxygen content (Y) of the organic peroxide is 8% of the sulfur content (X).
A tread rubber composition for a tire, which is blended so as to be at least 10% by weight. 2. The tread rubber composition for a tire according to claim 1, wherein the active oxygen content (Y) and the sulfur content (X) satisfy the following formula (1). Y ≧ −85X + 25 (1) 3. The rubber composition according to claim 1, wherein 5 to 20 parts by weight of an aromatic oil and 4 to 15 parts by weight of an adhesive resin having a softening point of 60 ° C. or more are mixed with 100 parts by weight of the rubber component. Or the tread rubber composition for a tire according to 2.