JP3483673B2 - Tread rubber composition for studless tires - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a tread rubber composition for a studless tire.

[0002]

2. Description of the Related Art In order to prevent dust pollution caused by spiked tires, the prohibition of spiked tires has been legalized, and studless tires have been used instead of spiked tires in cold regions. As a result of improvements, studless tires have been developed that have grip properties on snow similar to those of spiked tires, but on frozen roads, the grip properties may be inferior to those of spiked tires.

On a road surface having a very small friction coefficient, such as a frozen road surface, factors that affect the grip of a studless tire include the adhesive frictional force between the tread rubber and the road surface and the excavated frictional force. In order to increase the adhesive frictional force, the rubber itself affects the adhesive frictional force. Therefore, for example, softening the rubber to increase the contact area between the tire and the road surface is also an effective method.
In order to soften the rubber quality, it has been practiced to reduce the amount of filler, to use a rubber such as butadiene rubber or isoprene rubber which is hard to be hardened at a low temperature, or to add a softening agent. However, from the viewpoint of steering stability and wear resistance on a frozen road surface, the rubber material cannot be made extremely soft. That is, only softening the rubber is not sufficient from the viewpoint of balance between steering stability and wear resistance.

The surface morphology of the tread pattern and tread rubber is important for increasing the excavation frictional force. Spike tires have a large digging frictional force, but even in studless tires, foam rubber is used to increase the digging frictional force and unevenness on the tread surface is made by mixing organic fibers, which is also effective on frozen road surfaces. Furthermore, the unevenness of the tread surface eliminates the water film generated between the tread surface and the frozen road surface, and thus has the effect of indirectly increasing the adhesive friction force. However, in the method of increasing the unevenness of the tread surface, there is a limit in expanding the actual contact area, and there is also a limit in increasing the adhesive friction force.

As described above, the current studless tires have a performance comparable to that of spiked tires in terms of snow performance including gripping characteristics, but on frozen roads, they have better gripability than spiked tires. In some cases, it is inferior, and improvement is required. As an example of such an improvement, the present applicant has previously proposed a rubber composition for a tread containing a silylating agent in Japanese Patent Application Laid-Open No. 7-118452, and the effect of improving the grip performance is obtained by the present invention. Therefore, it is desired to further improve the grip performance during braking.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a tread rubber composition used for a studless tire which exhibits excellent grip properties even on a frozen road surface.

[0007]

Means for Solving the Problems The inventors of the present application have made earnest studies on the combined use of a silylating agent and other components in order to further improve the grip performance during braking on a frozen road surface. The present invention has been arrived at from the finding that the compounding amount is important and the finding that the balance between grip property and reinforcing property is also important when determining the types and compounding amounts of other components.

That is, the tread rubber composition for studless tires of the present invention comprises a diene rubber composed of at least one of natural rubber and diene synthetic rubber, calcium carbonate, and a silylating agent. 5 to 40 parts by weight of the calcium carbonate and 0.05 to 8 parts of the silylating agent with respect to 100 parts by weight of the diene rubber.
It is part by weight.

The average particle diameter of the calcium carbonate is 1 μm
The following is preferable. The calcium carbonate is preferably surface-treated with a fatty acid and / or a surfactant. The silylating agent is preferably an alkoxysilane compound. The alkoxysilane compound is preferably at least one of phenyltriethoxysilane and vinyltris (β-methoxyethoxy) silane.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The tread rubber composition for a studless tire of the present invention contains a diene rubber, calcium carbonate, and a silylating agent. The diene rubber is made of at least one of natural rubber and diene synthetic rubber. Specific examples of the diene synthetic rubber include styrene-butadiene rubber (SBR) and butadiene rubber (B
R), isoprene rubber (IR), and other diene-based synthetic rubbers. These diene rubbers may be used alone or in combination of two or more as required.

Calcium carbonate is usually used for increasing the volume of rubber, plastic products, etc., for the purpose of cost reduction, and for imparting appropriate plasticity to rubber which is not vulcanized, and for improving the processability, so that the amount of calcium carbonate can be increased inexpensively. It is used as an agent.
However, in the present invention, calcium carbonate is used together with a silylating agent to improve water repellency and grip on frozen road surfaces. This can be understood from the fact that the rubber composition containing calcium carbonate has higher water repellency and grip on a frozen road surface than the rubber composition containing only carbon black.

The average particle diameter of calcium carbonate is not particularly limited, but from the viewpoint of not impairing the reinforcing effect of carbon black, the average particle diameter is preferably 1 μm or less, more preferably 0.001 to 0. .5
μm, most preferably 0.01 to 0.1 μm. If the average particle size is larger than this, the reinforcing property may be deteriorated. Furthermore, when calcium carbonate is surface-treated with a fatty acid and / or a surfactant, the dispersibility of calcium carbonate in the rubber composition is improved, and calcium carbonate is preferably dispersed uniformly in the tread rubber composition. .

The fatty acid used for surface treatment of calcium carbonate is not particularly limited. Specific examples of the fatty acid include stearic acid, oleic acid and palmitic acid. These fatty acids may be used alone or in combination of two or more as required. Among them, stearic acid is preferable as the fatty acid. The surfactant used for the surface treatment of calcium carbonate is not particularly limited. Specific examples of the surfactant include inorganic salts and organic salts of fatty acids such as stearic acid, oleic acid and palmitic acid. These surfactants may be used alone or in combination of two or more as required.

The compounding amount of calcium carbonate in the tread rubber composition is 5 to 40 parts by weight of calcium carbonate based on 100 parts by weight of diene rubber. The compounding amount of calcium carbonate is preferably 7 to 35 parts by weight of calcium carbonate, and more preferably 8 to 25 parts by weight of calcium carbonate with respect to 100 parts by weight of diene rubber. If the blending amount of calcium carbonate is out of this range, the water repellency and the grip performance on a frozen road surface will be low.

The silylating agent is used together with calcium carbonate to improve the water repellency by converting the hydrophilic portion having active hydrogen such as hydroxyl group, amino group and carboxyl group in the rubber composition into the hydrophobic portion, The grip performance on a frozen road surface is improved. The silylating agent is not particularly limited, and examples thereof include an alkoxysilane compound, a chlorosilane compound and a silazane compound. Above all, it is preferable that the silylating agent is an alkoxysilane compound, because the water repellency is further improved and a more excellent grip property is exhibited even on a frozen road surface.

Specific examples of the alkoxysilane compound include phenyltriethoxysilane and vinyltris (β-
Methoxyethoxy) silane, γ-aminopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane and the like can be mentioned. These alkoxysilane compounds may be used alone or in combination of two or more if necessary. Among them, alkoxysilane compounds include phenyltriethoxysilane and vinyltris (β-
It is preferable that it is at least one kind of (methoxyethoxy) silane because the water repellency is most improved and the grip performance is further improved even on a frozen road surface.

The amount of the silylating agent in the tread rubber composition is 0.05 to 8 parts by weight based on 100 parts by weight of the diene rubber. The amount of the silylating agent blended is preferably 0.1 to 6 parts by weight of the silylating agent, more preferably 10 parts by weight of the diene rubber based on 100 parts by weight of the diene rubber.
0.5 to 5 parts by weight, and most preferably 1 to 4 parts by weight of the silylating agent relative to 0 part by weight. If the amount of the silylating agent is too small, the effect of improving the water repellency and the grip performance on a frozen road surface cannot be expected due to the addition. If the amount of the silylating agent is too large, the amount of unreacted silylating agent that does not react with active hydrogen such as hydroxyl group, amino group and carboxyl group in the rubber composition increases, the rubber hardness decreases, and the cost decreases. Get higher

The tread rubber composition for studless tires of the present invention contains calcium carbonate and a silylating agent as essential components. Therefore, the water repellency and the grip performance on the frozen road surface are significantly improved. The tread rubber composition for a studless tire of the present invention has a sufficient hardness when used for a studless tire,
It may contain carbon black.

The blending amount of carbon black in the tread rubber composition is not particularly limited, and is preferably 30 to 80 parts by weight of carbon black with respect to 100 parts by weight of diene rubber. The blending amount of carbon black is more preferably 40-60 with respect to 100 parts by weight of the diene rubber.
Parts by weight, most preferably 40 to 50 parts by weight. If the blending amount of carbon black is too small, the abrasion resistance and crack resistance tend to be poor. If the blending amount of carbon black is too large, the obtained tire tends to generate heat during use and the rubber tends to cure.

In the tread rubber composition for studless tires of the present invention, if necessary, specifically, a softening agent such as naphthenic process oil; a vulcanization aid such as zinc oxide or stearic acid; a mercaptobenzothiazole. (MBT),
Benzothiazyl disulfide (MBTS), N-ter
Vulcanization accelerator consisting of thiazole accelerator such as t-butyl-2-benzothiazolyl sulfenamide (TBBS) and N-cyclohexyl-2-benzothiazyl sulfenamide (CBS); sulfur; organic fiber; foaming Agents; antioxidants; additives such as waxes can be added.
The compounding amount of these additives in the tread rubber composition is not particularly limited and can be appropriately used.

As a method for producing the tread rubber composition for studless tires of the present invention, known methods can be applied. It can be obtained by kneading the above-mentioned components by a conventional method and conditions using a kneading machine such as a Banbury mixer. The kneading temperature is 120 to 18
It is preferably 0 ° C. The studless tire is obtained by molding and vulcanizing the tread rubber composition for a studless tire described above.

[0022]

EXAMPLES Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples. (Examples 1 to 9 and Comparative Examples 1 to 4) 150 using a Banbury mixer with the formulations shown in Tables 1 and 2 below.
A tread rubber composition was prepared by kneading at 5 ° C for 5 minutes. The performance of the rubber sample obtained by vulcanizing the obtained tread rubber composition at 170 ° C. for 10 minutes was evaluated by the following evaluation methods. The results are shown in Tables 1 and 2.

<Evaluation Method> 1. Rubber hardness The rubber hardness Hs (JIS-A) at 0 ° C. was measured according to the method specified in JIS K6301. 2. Contact angle The contact angle means the angle (θ) at which the boundary between the rubber 1 and the water droplet 2 is in contact with the water droplet 2 on the surface of the rubber 1 as shown in FIG. Means The obtuse contact angle indicates that it is hard to get wet,
The water repellency of rubber is excellent.

Using the measuring apparatus shown in FIG. 2, the advancing contact angle and the receding contact angle were measured, and the contact angle was calculated according to the following formula. The values for the examples and examples are displayed. Therefore, the larger the value, the larger the contact angle. cos θ = 1/2 × (cos θ _a + cos θ _r ) θ: contact angle θ _a : advancing contact angle θ _r : receding contact angle The water repellency is quantitatively measured by measuring the contact angle between water and the rubber composition. The larger the contact angle, the more water repellent it means. The contact angle is measured by the number of samples and the number of measurements so that the difference of unit value 1 of the average value can be detected at the 5% significance level.

3. Braking stop distance on ice A studless tire was manufactured using a tread rubber composition (185 / 70R14). These tires were mounted on a front-wheel drive (FF vehicle) type domestic vehicle having a displacement of 2000 cc, and the stopping distance on ice required to stop the vehicle was measured by suddenly stopping the vehicle at a speed of 30 km / h. With the stop distance of Comparative Example 1 set to 100, the values of other Comparative Examples and Examples were displayed. The larger the value, the better the braking resistance.

Test location: Skating rink Air temperature: 2 ° C. 4. Abrasion resistance Using a Lambourn abrasion tester manufactured by Iwamoto Seisakusho, load 2.
The wear of the test piece was measured under the conditions of 5 kg, slip ratio of 20% and 40%. The average value at both slip ratios was calculated, and the value of Comparative Example 1 was set to 100, and the values of other Comparative Examples and Examples were displayed as the wear index. The larger the wear index, the better the wear resistance.

[0027]

[Table 1]

[0028]

[Table 2]

Carbon black: N220 calcium carbonate (1) manufactured by Tokai Carbon Co., Ltd .: Shiroishi Calcium CC calcium carbonate of Shiraishi Calcium Co., Ltd. whose particle size is 0.04 μm and whose surface is treated with fatty acid (mainly stearic acid). (2): Neolite S silylating agent manufactured by Takehara Chemical Co., Ltd. having a particle diameter of 0.04 μm and a surface treated with fatty acid (mainly stearic acid) (1): KBE-103 manufactured by Shin-Etsu Chemical Co., Ltd.
(Phenyltriethoxysilane) Silylating agent (2): Shin-Etsu Chemical Co., Ltd. KBC-100
3 (Vinyltris (β-methoxyethoxy) silane) Process oil: Diana Process PS32 manufactured by Idemitsu Kosan Co., Ltd. Wax: Sunnock wax anti-aging agent manufactured by Ouchi Shinko Chemical Co., Ltd .: Ozonon 6C manufactured by Seiko Chemical Co., Ltd. Sulfurization accelerator: Noxera-NS manufactured by Ouchi Shinko Chemical Co., Ltd. <Evaluation results> From the comparison between Example 3 and Comparative Examples 2 and 3, it was found that water repellency and performance on ice were improved when calcium carbonate and a silylating agent were combined. It turns out that it improves significantly.

From the comparison between Examples 1 to 4 and Comparative Example 4, the contact angle increases as the amount of calcium carbonate added increases,
Although the on-ice performance is improved, it can be seen that when the addition amount is more than 40 parts (Comparative Example 4), the wear resistance performance is significantly reduced. From Example 3 and Examples 7 to 9, it can be seen that the contact angle increases and the performance on ice improves as the amount of the silylating agent added increases.

From Example 3 and Examples 5 to 6, it can be seen that equivalent performance can be obtained even if the types of the silylating agent and calcium carbonate are changed. As described above, it can be seen that in the example, the water repellency and the performance on ice are improved while the deterioration of the reinforcing property is suppressed to the minimum.

[0032]

INDUSTRIAL APPLICABILITY The tread rubber composition for studless tires of the present invention can provide a studless tire exhibiting excellent grip even on a frozen road surface. When the average particle size of calcium carbonate is 1 μm or less, the reinforcing property is less likely to decrease. A tread rubber composition containing calcium carbonate surface-treated with a fatty acid and / or a surfactant improves the dispersibility of calcium carbonate in the rubber composition, and the calcium carbonate is uniformly dispersed in the tread rubber composition. be able to.

When the silylating agent is an alkoxy compound, water repellency is further improved, and more excellent grip performance can be exhibited even on a frozen road surface. When the alkoxy compound is at least one of phenyltriethoxysilane and vinyltris (β-methoxyethoxy) silane, the water repellency is most improved, and even more excellent grip performance can be exhibited even on a frozen road surface. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the definition of a contact angle.

FIG. 2 is a block diagram of a contact angle measuring device.

[Explanation of symbols]

1 rubber 2 water drops

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08L ^7/ 00-21/02

Claims (5)

(57) [Claims] 1. A diene rubber comprising at least one of natural rubber and a diene synthetic rubber, calcium carbonate, and a silylating agent, and the mixing ratio of the three is 100 parts by weight of the diene rubber. Against said calcium carbonate 5
-40 parts by weight and the silylating agent 0.05 to 8 parts by weight, the tread rubber composition for studless tires. 2. The average particle diameter of the calcium carbonate is 1 μm.
The tread rubber composition for a studless tire according to claim 1, which is: 3. The method according to claim 1 or 2, wherein the calcium carbonate is surface-treated with a fatty acid and / or a surfactant.
The tread rubber composition for a studless tire according to 1. 4. The tread rubber composition for a studless tire according to claim 1, wherein the silylating agent is an alkoxysilane compound. 5. The tread rubber composition for a studless tire according to claim 4, wherein the alkoxysilane compound is at least one of phenyltriethoxysilane and vinyltris (β-methoxyethoxy) silane.