JPH1017715A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the rubber composition for tire treads capable of maintaining initial performances for long periods and little in the increases of hardness in the ends of the using periods. SOLUTION: This rubber composition for tire treads comprises a rubber component comprising 2-17.5wt.% of a copolymer having isobutylene monomer units and para-methylstyrene monomer units wherein at least one part of the para-methylstyrene monomer units are halogenated, and 72.5-98wt.% of a dienic polymer, and a vulcanizing agent of the formula (R<1> and R<2> are each an alkyl wherein R<1> and R<2> are same or different each other).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a rubber composition for a tire tread.

[0002]

2. Description of the Related Art Formulations have been developed to improve various performances of tires. However, since performance deteriorates with the aging of rubber, it is difficult to maintain the performance until the end of tire use. In particular, tires for heavy-duty vehicles have severe use conditions (high load, internal pressure and heat generation, and are used for a long period of time).
Particularly, the increase in hardness is remarkable.

[0003] With respect to dump tires used on rough roads, chipping resistance is deteriorated as hardness is increased and physical properties are reduced, so that not only the appearance is remarkably deteriorated, but also the wear life is inevitably shortened, and cut burst and It also triggers damage such as water permeation to the steel cord. In order to solve these problems, depending on the purpose of use, an EV vulcanized rubber composition (a compound that reduces sulfur content and forms a monosulfide bridge), a rubber composition containing various vulcanizing agents, and the like Has been proposed.

[0004]

However, the conventional E
In some categories, V-vulcanized rubber compositions alone are not sufficient to maintain initial performance. Therefore, an object of the present invention is to provide a rubber composition for a tire tread, which can maintain initial performance for a long period of time and has a small increase in hardness at the end of use.

[0005]

The rubber composition for a tire tread according to the present invention has an isobutylene monomer unit and a paramethylstyrene monomer unit, and at least a part of the paramethylstyrene monomer unit. 2 to 17.5% by weight of a halogenated copolymer and a diene polymer 8
A rubber component consisting of 2.5 to 98% by weight, and the following formula (1):

[0006]

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(Wherein R ¹ and R ² represent an alkyl group, and R ¹ and R ² may be the same or different from each other). The compounding ratio of the vulcanizing agent is 0.5 to 2.0 with respect to 100 parts by weight of the rubber component.
It is preferred that the amount be parts by weight.

[0008] Sulfur is further contained, and the compounding ratio of the sulfur is 0.5 to 1.2 with respect to 100 parts by weight of the rubber component.
It is preferred that the amount be parts by weight. It is preferable that the composition further contains a vulcanization accelerator, and the compounding ratio of the vulcanization accelerator is 1.0 to 2.4 parts by weight based on 100 parts by weight of the rubber component. The weight ratio of the sulfur to the vulcanization accelerator (sulfur / vulcanization accelerator) is preferably 0.5 or less.

The rubber composition for a tire tread of the present invention comprises:
It is preferably used for a tire tread of a heavy-duty vehicle.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber composition for a tire tread according to the present invention contains a rubber component and a vulcanizing agent represented by the formula (1) as essential components. Hereinafter, the rubber composition for a tire tread of the present invention will be described in detail. [Rubber component] The rubber component has a copolymer unit having an isobutylene monomer unit and a paramethylstyrene monomer unit, and at least a part of the paramethylstyrene monomer unit is halogenated. And the diene-based polymer.

The copolymer A is blended for the purpose of preventing the rubber from being deteriorated due to long-term use, and particularly suppressing the increase in hardness. Since the copolymer A has no double bond in its main chain, polymerization reaction and oxidation reaction caused by the double bond do not occur, so that the copolymer A is excellent in heat resistance and oxidation resistance. The halogenation is not particularly limited, and examples thereof include fluorination, chlorination, bromination, and iodination. Among them, bromination is preferred because of high reactivity during vulcanization.

The halogenation rate of the copolymer A is not particularly limited, but is preferably about 1 to about 10% by weight, and about 1 to about 5% by weight. More preferred. When the halogenation rate is low, there is a problem that the reactivity is low. If the halogenation ratio is high, there is a problem that the cost increases. The halogenation of at least a portion of the paramethylstyrene monomer unit is performed on a methyl group in the monomer unit. That is, at least a portion of methyl groups contained in the para methylstyrene monomer units represented by the following formula _{(2): -CH 3-n} X n (2) ( wherein, n an integer of 1 to 3, X is Halogen atom).

Regarding the degree of halogenation of the methyl group,
Although not particularly limited, in the above formula (2), usually, n =
It is one. There is no particular limitation on the halogen atom,
Examples of X in the above formula (2) include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
The weight ratio of the isobutylene monomer unit to the paramethylstyrene monomer unit (isobutylene monomer unit: paramethylstyrene monomer unit) in the copolymer A is not particularly limited. The ratio is preferably from 2 to 85:15, and more preferably from 97: 3 to 88:12. If the ratio of the paramethylstyrene monomer unit is too low, there is a problem that the improvement effect is reduced. If the ratio of the paramethylstyrene monomer units is too high, the copolymer A
However, there is a problem that the viscosity increases and the processability decreases.

The method for producing the copolymer A is not particularly limited, but includes, for example, a copolymerization step of copolymerizing isobutylene and paramethylstyrene to obtain a copolymer;
And a halogenation step of reacting the obtained copolymer with halogen. This production method is preferable because a halide can be efficiently produced.

The rubber component used in the present invention contains a diene polymer as a component other than the copolymer A. There is no particular limitation on the diene-based polymer, for example, natural rubber, each single system of diene-based synthetic rubber, or,
Any of these combined systems may be used, but when the rubber composition of the present invention is used for a tire tread of a heavy-duty vehicle, the diene-based polymer preferably contains at least natural rubber. The diene-based synthetic rubber is not particularly limited, but includes, for example, natural rubber, butadiene rubber, styrene-butadiene rubber, and the like, and one or more kinds can be used.

The mixing ratio of the copolymer A and the diene-based polymer in the rubber component is 2 to 17.5% by weight of the copolymer A and 82.5 to 98% by weight of the diene-based polymer, assuming that the entire rubber component is 100% by weight. %, Preferably 5 to 12.5% by weight of copolymer A and diene polymer 87.
5 to 95% by weight, more preferably copolymer A7 to
10% by weight and 90 to 93% by weight of a diene polymer. When the blending ratio of the copolymer A is less than 2% by weight,
There is a problem that the effect of preventing an increase in curing does not appear. When the blending ratio of the copolymer A exceeds 17.5% by weight, abrasion resistance, tensile strength and tear strength are extremely reduced. [Vulcanizing agent] The vulcanizing agent represented by the formula (1) is a component for co-vulcanizing the copolymer A and the diene-based polymer. By using this vulcanizing agent, the number of monosulfide bonds having high heat resistance increases, and the number of polysulfide bonds, which often occur in a general vulcanizing system and are easily broken by heat, are reduced. In addition, in the case of a new product immediately after vulcanization, the vulcanization becomes strong, so that the hysteresis loss is reduced and LRR (fuel efficiency is reduced).

The amount of the vulcanizing agent represented by the above formula (1) is 0.5 to 2.0 parts by weight, preferably 0.75 to 1.50 parts by weight, per 100 parts by weight of the rubber component. Parts by weight, more preferably 0.8 to 1.2 parts by weight. If the amount is less than 0.5 part by weight, there is a problem that the reactivity is low and a large number of monosulfide bonds are not formed. If the amount exceeds 2 parts by weight, there is a problem that scorch becomes short and cost increases.

In the above formula (1), R ¹ and R ² are not particularly limited as long as they are alkyl groups. Specific examples thereof include a tert-butyl group, a tert-octyl group and a te-octyl group.
rt-amyl group and the like. Specific examples of the vulcanizing agent represented by the formula (1) are not particularly limited, and include, for example, Valtac 3, Valtac 4, Valtac 5,
Bartac 7, Bartac 10 (both made by Atochem)
And the like. [Other Components Constituting Rubber Composition for Tire Tread] The rubber composition for tire tread according to the present invention preferably further contains sulfur and / or a vulcanization accelerator as other components constituting the rubber composition.

When sulfur is contained, its amount is not particularly limited, but is preferably 0.5 to 1.2 parts by weight, more preferably 0.1 to 100 parts by weight, per 100 parts by weight of the rubber component.
6 to 1.0 part by weight. If it is less than 0.5 parts by weight,
There is a problem of poor mechanical fatigue resistance. If it exceeds 1.2 parts by weight, there is a problem that many polysulfide bonds weak in heat fatigue resistance are generated.

When a vulcanization accelerator is included, the amount thereof is not particularly limited, but is preferably 1.0 to 2.4 parts by weight, more preferably 1.2 parts by weight, per 100 parts by weight of the rubber component. ２．０2.0 parts by weight. If the amount is less than 1.0 part by weight, there is a problem that heat fatigue resistance is poor. If the amount exceeds 2.4 parts by weight, there is a problem that mechanical fatigue resistance is weakened.

The vulcanization accelerator that can be used is not particularly limited, and examples thereof include sulfenamide-based N-cyclohexyl-2-benzothiazylsulfenamide,
In addition to N-oxydiethylene-2-benzothiazylsulfenamide, thiazole-based 2-mercaptobenzothiazole, dibenzothiazyldisulfide and the like can be mentioned. These may be used alone or in combination of two or more.

When both sulfur and the vulcanization accelerator are contained,
It is preferable that their weight ratio (sulfur / vulcanization accelerator) is 0.5 or less. If this weight ratio exceeds 0.5, there is a problem that a large amount of monosulfide bonds are generated and the thermal fatigue resistance is poor. The rubber composition of the present invention may contain, if necessary, fillers such as carbon black, silica, clay, and calcium carbonate, and an antioxidant, a vulcanizing agent, a vulcanizing aid, an adhesive, and an additive such as a plasticizer. One or more kinds may be included.

The method for producing the rubber composition of the present invention is not particularly limited, and a known method can be applied. Specifically, using a kneading machine such as a Banbury mixer, base chemicals such as a filler, an antioxidant, a vulcanization aid, and a plasticizer are kneaded with the rubber component at 100 to 160 ° C for 4 to 6 minutes. After discharging, a final chemical such as sulfur or a vulcanization accelerator is added, and the mixture is kneaded again at 80 to 100 ° C. for 2 to 3 minutes.

[0024]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. However, the present invention is not limited to the following Examples. (Examples 1 to 7 and Comparative Examples 1 to 3) Rubber compositions for tire treads having the formulations shown in Tables 1 and 2 below were produced by the following methods. That is, fillers, antioxidants, vulcanization aids, base chemicals such as plasticizers are kneaded with the rubber component at 150 ° C. for 4 minutes, and after discharging, sulfur, final chemicals such as a vulcanization accelerator are added. The mixture was kneaded again at 90 ° C. for 2 minutes to produce a rubber composition for a tire tread.

The obtained rubber composition for a tire tread is
The composition was vulcanized at 150 ° C. for 40 minutes under the condition of 80 kgf to evaluate the performance.

[0026]

[Table 1]

[0027]

[Table 2]

Copolymer A: Exxpro 90-10, manufactured by Exxon Chemical Company. Carbon black: Diamond Black I, manufactured by Mitsubishi Chemical Corporation. Wax: Sunnock wax, manufactured by Ouchi Shinko Chemical Co., Ltd. Anti-aging agent: Ozonone 6C, manufactured by Seiko Chemical Co., Ltd. Stearic acid: manufactured by NOF Corporation.

Zinc flower: manufactured by Mitsui Kinzoku Co., Ltd. Sulfur: manufactured by Tsurumi Chemical Company. Vulcanization accelerator: Noxeller NS, manufactured by Ouchi Shinko Chemical Co., Ltd. Vulcanizing agent: Baltac 5, manufactured by Sumitomo Chemical Co., Ltd. Various physical properties of a tire tread obtained by vulcanizing each of the rubber compositions of the above Examples and Comparative Examples were measured by the following methods.

Hardness change: After aging in an oven at 100 ° C. for 72 hours, the hardness was measured by a method according to JIS-A. Original tan δ index: Viscoelastic spectrum meter manufactured by Iwamoto Seisakusho Co., Ltd., 70 ° C, 10Hz, strain 0.2%
Was measured. Here, assuming that Comparative Example 1 is 100, the smaller the number, the better the lower the hysteresis.

Tensile test index: Measured according to JIS K-6251. Lambourn abrasion index: The abrasion of the test piece was measured using a Lambourn abrasion tester manufactured by Iwamoto Seisakusho under the conditions of a load of 5 kg and a slip ratio of 60%. With Comparative Example 1 set to 100, the larger the number, the better the performance. Compared with the rubber composition of Comparative Example 1, it was confirmed that the rubber composition of the example was able to suppress the increase in hardness, reduce tan δ, and minimize the reduction in tensile properties and wear index. . In addition, comparing Example and Comparative Examples 2 and 3, the amount of copolymer A was 20% by weight in the rubber component.
Above, there is an effect of suppressing an increase in hardness, but wear and tensile properties are greatly reduced.

[0032]

The rubber composition for a tire tread of the present invention can maintain initial performance for a long period of time, and in particular, hardly increases in hardness at the end of use. In addition, the rubber composition for a tire tread of the present invention has low hysteresis loss and can achieve low fuel consumption.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08L 23:22)

Claims (6)

[Claims] 1. A copolymer having an isobutylene monomer unit and a paramethylstyrene monomer unit, wherein at least a part of the paramethylstyrene monomer unit is halogenated, from 2 to 17.5% by weight. And a diene polymer 82.5-9
A rubber component consisting of 8% by weight, and the following formula (1): (In the formula, R ¹ and R ² represents an alkyl group, R ¹ and R
² may be the same or different from each other. ), And a vulcanizing agent represented by the formula (1): 2. The compounding ratio of said vulcanizing agent is 10% of said rubber component.
The amount is 0.5 to 2.0 parts by weight per 0 parts by weight.
The rubber composition for a tire tread according to the above. 3. The composition further contains sulfur, and the compounding ratio of the sulfur is 0.5 to 1.2 with respect to 100 parts by weight of the rubber component.
The rubber composition for a tire tread according to claim 2, which is a part by weight. 4. A rubber composition further comprising a vulcanization accelerator, wherein the compounding ratio of the vulcanization accelerator is 1.0 to 100 parts by weight of the rubber component.
The rubber composition for a tire tread according to claim 2 or 3, wherein the amount is from 2.4 to 2.4 parts by weight. 5. The rubber composition for a tire tread according to claim 4, wherein the weight ratio of the sulfur to the vulcanization accelerator (sulfur / vulcanization accelerator) is 0.5 or less. 6. The rubber composition for a tire tread according to claim 1, which is used for a tire tread of a vehicle for heavy load.