JP2003292674A - Rubber composition for studless tire and studless tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for studless tires which can improve performances on ice while maintaining high level performances of abrasion resistance and steering stability and also to provide the studless tire having all the performances, which uses the rubber composition in the tread portion. <P>SOLUTION: The rubber composition for studless tires comprises at least one kind of a rubber component selected from the group consisting of a natural rubber and a diene based synthetic rubber, which includes 0.2-0.9 pt.wt. of sulfur and 0.2-5 pts.wt. of a specific thiazole vulcanization accelerator based on 100 pts.wt. of the rubber component. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rubber composition for a studless tire capable of improving on-ice performance without deteriorating wear resistance and steering stability, and excellent on-ice performance using the same for a tread portion. Regarding studless tires.

[0002]

2. Description of the Related Art In recent years, a studless tire has been used as a tire to be mounted on an automobile running on a snowy and snowy road surface. For the tread of this studless tire, a rubber composition having an adhesive friction and a digging-up frictional force is used in order to increase the frictional force with the road surface on ice.

To improve the adhesive friction, for example, a large amount of a polymer having a low glass transition temperature (Tg) such as natural rubber or butadiene rubber is used as compared with the tread of a general summer tire, and softening of process oil or the like. It is practiced to add a large amount of the agent to keep the rubber hardness at low temperature low. That is, the increase of the dynamic elastic modulus (E ′) is suppressed by preventing the rubber composition from being cured at a low temperature, and the low temperature range (0 to −10).
It maintains the elasticity of the rubber at around (° C.) And secures the contact area between the road surface on ice and the rubber to obtain an adhesive friction force so that it can follow the unevenness of the road surface. Further, there has been conventionally performed a technique of removing a water film between an icy road surface and rubber by using a fine foamed rubber made of a foaming agent in a tread surface layer portion.

Further, in order to improve the digging-up frictional force, various techniques have been studied and put to practical use, which exhibit a scratching effect by adding a granular material composed of short fibers or an organic or inorganic hard material as a filler and a micro-spike effect by foamed rubber. Has been done.

However, there is a limit to the improvement of the polymer itself for improving the performance on ice by the above low Tg polymer, and although the performance on ice is improved to some extent by blending a large amount of a softening agent or the use of foamed rubber, the block rigidity of the tread is increased. Therefore, there is a problem in that the steering stability is reduced and the braking performance is deteriorated on a general road and a wet road surface due to the decrease of the vehicle. Further, low hardness rubber, foamed rubber or a rubber composition to which a large amount of filler is added deteriorates the wear resistance, and there is a problem that the tire life is significantly shortened due to premature wear or uneven wear particularly when used on a dry road surface.

Further, in the study of vulcanization type compounding agents, when a large amount of sulfur is mixed, the steering stability is maintained well, but the change over time is large, and vulcanization type accelerators such as sulfenamide type vulcanization accelerators are used. Even if a variable amount is used, there is a limit in lowering the low temperature side E ′ of the rubber composition.

There is a limit to lowering the low temperature side E'of a rubber composition using conventional polymers and compounding agents, and the performance on ice and wear resistance of studless tires can be improved by the use of foamed rubber and the technology of adding fillers. It was difficult to maintain high level of both stability and steering stability.

[0008]

The object of the present invention has been made in view of the above problems of the prior art, and uses the sulfur compounding amount of a rubber composition and an appropriate amount of a specific vulcanization accelerator. By lowering the low temperature side E ′ of the rubber composition, the adhesion friction between the ice surface and the rubber composition is improved, the performance on ice is improved, and the modulus of the rubber is kept good and the wear resistance and steering stability are improved. To provide a rubber composition for a studless tire that maintains a high level of performance, and a studless tire that uses the rubber composition for a tread portion and has both on-ice performance, abrasion resistance, and steering stability.

[0009]

The invention according to claim 1 is a rubber composition for a studless tire, which comprises at least one selected from the group consisting of natural rubber and diene-based synthetic rubber as a rubber component. Studless, characterized by containing 0.2 to 0.9 parts by weight of sulfur and 0.2 to 5 parts by weight of a specific thiazole vulcanization accelerator with respect to 100 parts by weight of the rubber component. A rubber composition for a tire.

According to the rubber composition for a studless tire of the present invention, sulfur is added to 100 parts by weight of a rubber component composed of at least one kind of rubber selected from the group consisting of natural rubber and diene synthetic rubber. By containing 2 to 0.9 parts by weight and 0.2 to 5 parts by weight of the thiazole vulcanization accelerator, the rubber modulus is kept good and abrasion resistance and steering stability are maintained at a high level. Then, it is possible to suppress the curing of the rubber composition at a low temperature and lower the low temperature side E ′ as compared with the case of using another vulcanization accelerator such as a sulfenamide type, and to improve the on-ice performance of the rubber composition. You can

As described in claim 2, the benzothiazole compound vulcanization accelerator according to claim 1 is 2-mercaptobenzothiazole, dibenzothiazyl disulfide, zinc salt of 2-mercaptobenzothiazole, 2 −
Cyclohexylamine salt of mercaptobenzothiazole, sodium salt of 2-mercaptobenzothiazole,
2- (4'-morpholinodithio) benzothiazole, 2
It is preferably at least one selected from the group consisting of-(N, N-diethylthiocarbamoylthio) benzothiazole.

When the specific thiazole vulcanization accelerator is at least one of the above, a synergistic effect with the action of the low content of sulfur is exhibited, and the low temperature side E'of the rubber composition is surely lowered. It is possible to develop excellent performance on ice.

In the rubber composition for a studless tire according to claim 3, 1 to 20 short fibers or vegetable granules are added to 100 parts by weight of the rubber component.
It may contain parts by weight.

As a result, in addition to the adhesive friction performance, the rubber composition for a studless tire can be imparted with the effect of scratching the road surface on ice, and the performance on ice can be further improved.

The invention according to claim 4 is characterized in that the rubber composition for a studless tire according to any one of claims 1 to 3 is used for at least a part of a tread ground contact portion. Is.

According to the studless tire of the present invention,
Achieves good balance between on-ice performance on ice and snow roads, wear resistance and handling stability, and wear resistance on dry road surfaces.
A studless tire capable of maintaining steering stability can be provided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber component used in the present invention is
It comprises at least one rubber selected from the group consisting of natural rubber and diene-based synthetic rubber. That is, a rubber selected from natural rubber (NR) and diene-based synthetic rubber may be used alone, or two or more of them may be used in a blend. Examples of the diene-based synthetic rubber include isoprene rubber (IR) and polybutadiene rubber (B
R), styrene-butadiene rubber (SBR), butyl rubber (IIR) and the like.

NR has a glass transition temperature of -70 to -80 ° C.
It is suitable as a rubber component of a rubber composition for studless tires because it is near and has good low temperature characteristics. When blended with other rubber, NR is blended in an amount of 5 parts by weight or more, and further 10 parts by weight or more. Is preferred,
The rubber component used together with NR is preferably a diene-based synthetic rubber having a glass transition temperature of −70 ° C. or lower.

Therefore, in the present invention, among these rubber components, a polymer such as NR having a low glass transition temperature, or a blend of NR / BR, a blend of NR / SBR, a blend of NR / SBR / BR, etc., may be used. It is preferably used in terms of producing effects.

In the present invention, 0.2 to 0.9 parts by weight of sulfur is contained with respect to 100 parts by weight of the rubber component. If the sulfur content is less than 0.2 parts by weight, the rubber composition will not have sufficient rubber characteristics such as strength and modulus necessary for the tire tread, and the abrasion resistance and steering stability will be insufficient, and 0.9 If it exceeds the weight part, it causes a change with time such as increase in rubber hardness and the performance on ice deteriorates during use, and if the amount of sulfur is further increased, the rubber elasticity decreases and it becomes difficult to obtain the initial performance on ice.

The thiazole vulcanization accelerator used in the present invention is 2-mercaptobenzothiazole (M), dibenzothiazyl disulfide (DM), zinc salt of 2-mercaptobenzothiazole (MZ), 2-mercaptobenzo. Cyclohexylamine salt of thiazole, sodium salt of 2-mercaptobenzothiazole, 2- (4′-morpholinodithio) benzothiazole, 2- (N, N-diethylthiocarbamoylthio) benzothiazole (MDB)
Are preferred, and these can be used alone or in combination of two or more.

The content of the thiazole vulcanization accelerator is
It is 0.2 to 5 parts by weight with respect to 100 parts by weight of the rubber component, and if the content is less than 0.2 parts by weight, the effect of lowering the low temperature side E ′ of the rubber composition cannot be obtained, and it exceeds 5 parts by weight. And E'becomes too large, abrasion resistance and steering stability are deteriorated, and scorch property, bloom property, etc. are deteriorated and workability in the process and vulcanization stability are deteriorated, which is not preferable.

Further, in addition to the above thiazole type vulcanization accelerator as a vulcanization accelerator, N-cyclohexyl-2-benzothiazolylsulfenamide (CZ), N-tert.
-Butyl-2-benzothiazolylsulfenamide (N
S), N-oxydiethylene-2-benzothiazolylsulfenamide (OBS) and other sulfenamide vulcanization accelerators, tetrabutylthiuram disulfide (TB
T), a thiuram-based vulcanization accelerator such as tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N),
Other vulcanization accelerators such as guanidine-based vulcanization accelerators such as 1,3-diphenylguanidine (D) and di-O-tolylguanidine (DT) may be appropriately used in combination.

In the present invention having the above-mentioned constitution, by containing a low sulfur content and a specific amount of a specific thiazole type vulcanization accelerator, the rubber modulus of the rubber composition is maintained and abrasion resistance and steering stability are maintained. However, the performance on ice can be improved by lowering the low temperature side E ′.

That is, although the above thiazole vulcanization accelerator has already been used as a vulcanization accelerator for rubber as a known substance, at least one selected from the group consisting of natural rubber and diene synthetic rubber. When used in a rubber composition containing a rubber component at a low sulfur content within a predetermined range, its synergistic effect is exhibited, and other sulfenamide vulcanization accelerators, thiuram vulcanization accelerators, and guanidine vulcanization agents are used. The present inventors have discovered a new effect that could not be found with accelerators, etc., and realized excellent on-ice performance of a rubber composition at low cost, and realized compatibility with abrasion resistance and steering stability. To do.

Further, in the present invention, 1 to 20 parts by weight of short fibers or vegetable granules can be contained per 100 parts by weight of the rubber component, and the rubber composition for a studless tire has an adhesive friction performance. In addition, a scratching effect with the road surface on ice can be imparted to improve the coefficient of friction and further improve the performance on ice.

As the short fibers, polyester, polyamide, polyvinyl alcohol fibers or the like having a length of 10 mm or less,
A monofilament having a diameter of 0.01 to 0.01 mm is desirable. If the length and the diameter of the short fibers are too small, the scratching effect is not sufficient, and if the length and the diameter are more than that, the mixing property with rubber and workability are deteriorated, and the abrasion resistance is deteriorated. On the other hand, if the content is less than 1 part by weight, the improvement of the performance on ice is insufficient.
If it exceeds 20 parts by weight, workability such as mixing and extruding properties of rubber is significantly reduced, which is not preferable.

Examples of the vegetable granules include granules of fruits such as walnuts and camellias, nut shells, and cores of fruits such as peaches and plums, and the average particle diameter thereof is about 0.01 to 5 mm. Preferably, if the particle size is too small, the scratching effect is insufficient,
On the other hand, if it is too large, the mixing property with rubber and workability are deteriorated, the abrasion resistance is deteriorated, and the rubber surface is liable to fall off, which is not preferable. If the content is less than 1 part by weight, the performance on ice is insufficiently improved, and if it exceeds 20 parts by weight, the mixing property of the rubber is significantly lowered, which is not preferable.

The rubber composition for a studless tire according to the present invention may be blended with carbon black usually used as a reinforcing filler, or silica may be used in combination with carbon black.

The carbon black is not particularly limited, but from the viewpoint of rubber strength, abrasion resistance, heat generation, etc.
For example, HAF, SAF, ISAF, and FEF grade carbon black is preferable, and the compounding amount thereof is 30 to 100 parts by weight with respect to 100 parts by weight of the rubber component, and when the amount of carbon black is too small, abrasion resistance deteriorates, If the amount is too large, workability and heat generation are deteriorated, which is not preferable.

In the rubber composition for a studless tire according to the present invention, various process oils, zinc white, stearic acid, which are used in ordinary rubber compounding, are added to the above rubber component together with sulfur, a vulcanization accelerator and carbon black. Various softening agents, waxes, anti-aging agents, and other various compounding agents generally compounded for rubber compositions can be appropriately compounded, and the compounding amount thereof can be used within a range that does not impair the effects of the present invention. it can.

The rubber composition for a studless tire of the present invention can be prepared by mixing it with a mixer such as a Banbury mixer, a kneader or a roll generally used in the rubber industry.

In the studless tire according to the present invention, an unvulcanized tire tread is produced by using the above rubber composition for a studless tire using a molding machine such as a rubber extruder generally used in the rubber industry. However, it can be applied to a tread portion of a passenger car, a light truck, and a truck / bus studless tire having a normal internal structure to manufacture a studless tire through a vulcanization process.

Further, the studless tire uses the rubber composition for a studless tire in at least a part of the ground contact portion of the tire tread, and the tread may be a tire composed of one kind of tread rubber. It can be used only for the tread side tread of a multi-layered tire such as a cap / base structure, and is also used for the grounding part only inside or outside in the radial direction on the tire circumference. is not.

(Examples) The present invention is described below with reference to examples, but the present invention is not limited to the following examples.

Examples 1 to 3 and Comparative Examples 1 to 5 were prepared by adding the sulfur and the vulcanization accelerator shown in Table 2 (parts by weight) to the composition common to Examples and Comparative Examples shown in Table 1. The rubber composition for a studless tire of Example 1 was prepared and mixed according to a conventional method using a closed Banbury mixer having a capacity of 20 liters to prepare a rubber composition for a studless tire of each Example and Comparative Example.

The rubber components and various compounding agents used in the examples and comparative examples are as follows.

-Natural rubber (NR): RSS # 3-Butadiene rubber (BR): JSR Corporation BR01-Carbon black (CB): Showa Cabot Corporation Showblack N330-Process oil: Aromatic process oil- Zinc flower: Mitsui Mining & Smelting Co., Ltd. No. 3 Zinc flower-Stearic acid: Industrial stearic acid-Anti-aging agent (6C): Flexis Co., Ltd. Santoflex 13-Wax: Paraffin wax-Sulfur: 5% oil-treated sulfur- Vulcanization accelerator DM: Nouchira DM, Ouchi Shinko Chemical Industry Co., Ltd.-Vulcanization accelerator CZ: Noxceller CZ, Ouchi Shinko Chemical Industry Co., Ltd.-Vulcanization accelerator D: Noxeller D, Ouchi Shinko Chemical Industry Co., Ltd.・ Vulcanization accelerator TOT-N: Nouchira TOT-N, Ouchi Shinko Chemical Industry Co., Ltd.

[Table 1]

The Mooney scorch time (t5) of each of the obtained rubber compositions for studless tires was measured according to the following measuring method. The results are shown in Table 2.

An unvulcanized cap tread was extruded from each of the above-mentioned rubber compositions for studless tires using an ordinary rubber extruder, and a test having a general cap / base structure and a size of 185 / 65R14 was conducted. It was applied to a cap tread of a studless tire for automobiles, an unvulcanized tire was molded and vulcanized in a conventional manner to produce a studless tire, and the on-ice performance, abrasion resistance and steering stability were evaluated by the following test methods. The results are shown in Table 2.

[Moonie Scorch Time (t5)] J
The Mooney viscosity was measured according to the Mooney Scorch test described in IS K 6300 (test temperature 125 ° C.),
A Mooney viscosity-time curve was created. After closing the die, measure the time required for the Mooney viscosity reading to rise by 5 points from the minimum Mooney viscosity value Vm. T
Set to 5 (minutes). t5 is represented by an index with Comparative Example 1 being 100, and the larger the value, the better the vulcanization stability.

[Performance on ice] Four studless tires for each test were mounted on a specified rim, the air pressure was adjusted to 180 KPa, and the engine was mounted on a domestic passenger car with a displacement of 2000 cc. Braking was performed at a speed of 40 km / h, and the performance on ice was evaluated from the braking distance on ice. Indicated by an index with the braking distance of Comparative Example 1 as 100,
The higher the value, the better.

[Abrasion resistance] Two test studless tires of Comparative Example 1 and two other test studless tires were assembled to a specified rim, the air pressure was adjusted to 180 KPa, and the engine was mounted on a domestic passenger car with a displacement of 2000 cc. , Rotate the dry general road surface every 5,000km, 20,000
The wear resistance was evaluated by determining the tread wear amount from the tread residual groove depth after running for 0 km. It is shown by an index with Comparative Example 1 as 100, and the larger the value, the better.

[Steering Stability] Four studless tires for each test were mounted on a specified rim, the air pressure was adjusted to 180 KPa, the displacement was 2000 cc, and the vehicle was mounted on a domestic passenger car. Sensory evaluation of straight running performance, lane change performance, cornering performance, and slalom running performance was performed by a plurality of test drivers, and the average value was evaluated. Based on Comparative Example 1, the steering stability is equivalent to Comparative Example 1, "○", excellent is "◎",
The inferiority was represented by "△".

[0045]

[Table 2]

As shown in the evaluation results of Table 2, Examples 1 to 1
In the present invention No. 3, it can be seen that the scorch time is stable, the wear resistance and the steering stability are improved in a well-balanced manner, and the performance on ice is excellent. On the other hand, in a compounding system with a large amount of sulfur, the performance on ice was not improved even if the amount of the thiazole-based accelerator was appropriate (Comparative Examples 2 and 5), and with a small amount of sulfur, wear resistance deteriorated (comparative Example 4) Also, when the amount of the thiazole-based accelerator is too much, the scorch stability and the steering stability are deteriorated (Comparative Example 3), and in each Comparative Example outside the scope of the present invention, one of the characteristics cannot be satisfied and the balance is good. No improvement in performance can be obtained.

[0047]

According to the present invention, the amount of sulfur compounded in the rubber composition for studless tires is 0.2 to 0.9 parts by weight, and the proper amount of the specific thiazole vulcanization accelerator is used. By lowering the low temperature side E ′ of the rubber composition, the adhesive friction between the ice surface and the rubber composition is improved to improve the performance on ice, and the rubber modulus is kept good to improve wear resistance and steering stability. Can be maintained at a high level. Therefore,
The studless tire using the rubber composition for a studless tire of the present invention in the tread ground contact portion can improve both the wear resistance and the steering stability in a well-balanced manner while also improving the performance on ice.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 9/00 C08L 9/00 F term (reference) 4J002 AC011 AC021 AC031 AC061 AC081 AH002 BB181 BE022 CF002 CL002 DA046 EV327 FA042 FA082 FD010 FD146 FD157 GN01

Claims (4)

[Claims] 1. A rubber composition for a studless tire, which comprises at least one selected from the group consisting of natural rubber and diene-based synthetic rubber as a rubber component, wherein sulfur is 0 based on 100 parts by weight of the rubber component. 2 to 0.9 parts by weight, and 0.2 to 5 parts by weight of a specific thiazole-based vulcanization accelerator, a rubber composition for studless tires. 2. The thiazole vulcanization accelerator comprises 2-mercaptobenzothiazole, dibenzothiazyl disulfide, zinc salt of 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and 2-mercaptobenzothiazole. It is at least 1 sort (s) selected from the group which consists of sodium salt, 2- (4'-morpholinodithio) benzothiazole, and 2- (N, N-diethylthiocarbamoylthio) benzothiazole, It is characterized by the above-mentioned. The rubber composition for a studless tire described. 3. The rubber composition for a studless tire according to claim 1, wherein 1 to 20 parts by weight of short fibers or vegetable granules are contained with respect to 100 parts by weight of the rubber component. object. 4. A studless tire, wherein the rubber composition for a studless tire according to any one of claims 1 to 3 is used for at least a part of a tire tread ground contact portion.