JP2678658B2 - Rubber composition for tire tread - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a rubber composition for a tread which enables the production of a tire exhibiting good steering stability, particularly not only in summer but also in winter. Regarding

[Prior Art] There is a strong demand for tires having excellent steering stability for passenger cars, which have been advanced in power by the development of motorization in recent years.

If the hardness of the rubber composition at room temperature is at the same level, the steering stability is improved because the higher the tan δ, the greater the frictional force and the greater the tire gripping force (road gripping force). In order to increase the frictional force of such a rubber composition for tread, it is common to increase the glass transition point (Tg) of the rubber composition or decrease the particle size of carbon black in the rubber composition. Is.

Specific examples of the former include a styrene-butadiene copolymer rubber (hereinafter, abbreviated as SBR) having a high Tg of -40 ° C or more as a rubber component and a high vinyl content SBR having a high vinyl bond content. There is. However, these T
When SBR with a high g is compounded, the temperature dependence of the rubber hardness of the rubber composition increases, and the tire operating temperature range (20 to 100 ° C)
Since the change in the rubber hardness at 1 is too large, for example, if tan δ is set to be maximum at room temperature, there is a problem that steering stability is deteriorated due to temperature increase of the tire in winter or during running.

In the latter case, if the particle size of carbon black is reduced, the rubber hardness of the rubber composition increases more than necessary, so that the steering stability of the tire is not improved. In this case, it is possible to prevent the rubber hardness from increasing by increasing the blending amount of the process oil. However, when the blending amount of the process oil increases, the physical properties of the rubber composition deteriorate.

[Problems to be solved by the invention]

An object of the present invention is to provide a rubber composition which has a large tan δ, exhibits a high gripping force, and is useful as a tread for a tire having a small temperature dependency of rubber hardness.

[Means for solving the problem]

Such an object of the present invention is that the glass transition point (Tg) is −
110-140m per 100 parts by weight of rubber component consisting of one or more SBRs below 40 ° C and diene rubbers other than this SBR
² / nitrogen specific surface area of _{g (N 2 SA), 24M4} DBP of 85～95Ml / 100 g
Oil absorption, full width at half maximum (ΔDst) of aggregate distribution measured by centrifugal sedimentation method of 55 mμ or less, 0.43 or less [ΔDst / N ₂ SA]
It can be achieved by a rubber composition for a tire tread in which a carbon black having a ratio is compounded in an amount of 30 to 100 parts by weight.

The characteristics of the rubber component and carbon black constituting the rubber composition of the present invention and the compounding ratio of these rubber component and carbon black will be described in detail below.

(1) Rubber component: Consists of one or more SBR having a glass transition point (Tg) of less than -40 ° C and a diene rubber other than this SBR.

The compounding ratio in this rubber composition is not particularly limited, but it is preferable to compound the diene rubber other than SBR in the range of 0 to 80 wt% with respect to 100 to 20 wt% of SBR. Diene rubbers other than SBR include natural rubber (N
R), polyisoprene rubber, SBR having a glass transition point Tg of −40 ° C. or higher, polybutadiene rubber, butyl rubber (IIR), halogenated butyl rubber and the like can be exemplified.

The present invention has a large temperature dependence of rubber hardness and a high Tg.
By using SBR having Tg of less than −40 ° C. as a rubber component instead of SBR, the temperature dependency of hardness of the rubber composition is reduced and the tire operating temperature range (−20 to 100 ° C.)
Strength characteristics such as rigidity, tensile strength, wear resistance, etc.
It is possible to prevent a decrease in tan δ at 60 ° C.

(2) Carbon black: Nitrogen specific surface area (N ₂ SA) is 11
0-140m ² / g, 24M4 DBP oil absorption 85-95ml / 100g, full width at half maximum (ΔDst) of aggregate distribution measured by centrifugal sedimentation method is 5
It should be 5 mμ or less. That is, by using such carbon black, it becomes possible to use SBR having a glass transition point Tg of less than -40 ° C as described above.

However, when the nitrogen specific surface area (N ₂ SA) is less than 110 m ² / g, the tan δ of the rubber composition at 60 ° C. is not more than a desired level, and the grip force is reduced to improve the steering stability. I can't. On the other hand, when N ₂ SA exceeds 140 m ² / g, the tan δ of the rubber composition increases and the grip strength is improved, but the hardness at low temperature increases and the steering stability in winter decreases.

Further, if the 24M4 DBP oil absorption is less than 85 ml / 100 g, the wear resistance of the rubber composition decreases, and the practical performance as a rubber composition for tire tread cannot be satisfied. On the other hand, if it exceeds 95 ml / 100 g, the tensile strength is greatly reduced, and it cannot be put to practical use.

Further, when the full width at half maximum (ΔDst) of the aggregate distribution measured by the centrifugal sedimentation method exceeds 55 mμ, the above-mentioned tan δ at 0 ° C. and 60 ° C. does not reach the desired level, and a rubber composition having good steering stability is obtained. I can't.

Here, the centrifugal sedimentation method is a method of measuring an aggregate distribution using a disc centrifuge manufactured by Joyce Label Co., Ltd. By utilizing the fact that particles having a larger Stokes diameter (Dst) diffuse and settle faster. This is a method of determining the size of the sedimented particles.

The full width at half maximum (ΔDst) of the aggregate distribution is a parameter indicating the size distribution and properties of the aggregate in which the carbon black particles are firmly fused and bonded. Therefore, it is closely related to the production conditions such as the reaction temperature and the degree of disturbance of the combustion gas in the production process of carbon black. Therefore, the full width at half maximum (ΔDst) of the aggregate distribution has a correlation with the nitrogen specific surface area (N ₂ SA) of carbon black, and as this N ₂ SA increases, ΔDst decreases and [ΔDst / N ₂ SA ] The ratio tends to be small.

Tan δ at 0 ° C. and 60 ° C. of the rubber composition of the present invention
In order to increase the
It is necessary to set the [ΔDst / N ₂ SA] ratio of st to 0.43 or less. If this value exceeds 0.43, tan δ at 0 ° C. and 60 ° C. will not reach the desired level when using carbon black in the range of N ₂ SA 110 to 140 m ² / g, which is not preferable.

(3) Blending ratio: The blending amount of the carbon black should be 30 to 100 parts by weight with respect to 100 parts by weight of the rubber component.

If the blending amount of carbon black is less than 30 parts by weight, the wear resistance for tread rubber will be insufficient, and, on the other hand,
If it exceeds 100 parts by weight, it becomes difficult to uniformly disperse the carbon black particles in the rubber, and a good rubber composition cannot be obtained.

Furthermore, the rubber composition used in the present invention has a difference ΔHs of 12 between the rubber hardness at −10 ° C. and the rubber hardness at 20 ° C.
It is desirable that it is below, preferably below 10.

The rubber composition of the present invention, if necessary, in addition to the carbon black, for example, a vulcanizing agent such as sulfur, a vulcanization accelerator,
It may contain a vulcanization accelerator, an antioxidant, a tackifier, a softener, a filler and the like.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples.

The nitrogen specific surface area (N ₂ SA) of carbon black, 24M4 DBP oil absorption amount, and half-width of aggregate distribution (Δ
Dst), tan δ, and glass transition point (Tg) are values measured by the following measuring methods.

Nitrogen Specific Surface Area (N ₂ SA): ASTM-D3037-78 “Standard Methods of Treating Carbon Black-Surfac
e Area by Nitrogen Adsorption "Method C.

24M4 DBP oil absorption: According to ASTM D-3494.

Full width at half maximum (ΔDst) of aggregate distribution: Measured by the following method using Disc Centrifuge (manufactured by Joice Loebl, UK). That is, a carbon black is precisely weighed, an aqueous 20% by volume ethanol solution and a surfactant are added, and ultrasonically dispersed so that the carbon black concentration becomes 5 mg / 100 cc to prepare a sample solution. Next, after setting the rotation speed of the disc centrifuge to 8000 rpm and adding 10 ml of spin liquid (distilled water) to the disc centrifuge,
Inject 0.5 ml of buffer solution (20% by volume ethanol aqueous solution). Then, 0.5 to 1.0 ml of the sample solution is added to the mixture by a syringe, centrifugal sedimentation is started, and an aggregate distribution curve converted into Stokes diameter by a light sedimentation method is created. The half value width (ΔDst) is defined as the distribution value of the aggregate when the maximum frequency (maximum absorbance) is 1/2 in the histogram.

tanδ: Temperature 0 ° C and 60 ° C, strain rate 10 ± 2%, frequency 20Hz using a viscoelasticity spectrometer (manufactured by Iwamoto Seisakusho Co., Ltd.)
It is the value measured in. Tan δ at 0 ° C is a measure of grip on wet roads and tan δ at 60 ° C is a measure of grip on dry roads. In any case, the larger the value of tan δ, the greater the tire grip force.

Glass transition point (Tg): Measured according to JIS K 6301.

Twelve kinds of rubber compositions having the compounding composition (parts by weight) shown in Table 3 were prepared by using the four kinds of carbon black shown in Table 1 and the four kinds of SBR shown in Table 2.

The vulcanizates obtained by vulcanizing each of these rubber compositions at 160 ° C. for 30 minutes were -10 ° C. and 20 ° C. JIS
Hardness, ΔHs, tan δ at 0 ℃ and 60 ℃,
The results are shown in Table 3.

As shown in Table 3, in Examples 1 and 2 in which CB-1 and CB-2 satisfying the physical property values specified in the present invention were blended, CB-N220 which did not satisfy the physical property values specified in the present invention was blended. The rubber hardness at −10 ° C. and 20 ° C. is the same as that of Comparative Example 1 which is different only. However, tan δ at 0 ℃ and 60 ℃
It is understood that the rubber compositions are all large, have a large gripping force on the wet road and the dry road, and have excellent steering stability. In addition, the physical property values specified in the present invention are not satisfied.
Comparative Example 2, which differs only in the addition of CB-N110, has a smaller tan δ at 0 ° C. and 60 ° C. and a larger rubber hardness than Examples 1 and 2.

In addition, when only the type of carbon black was changed for each of the four types of rubber compositions in which the type and blending amount of the rubber component were changed in Example 1, Example 3 and Comparative Example 3, Example 4 and Comparative Example 4, As shown in Example 5 and Comparative Example 5 and Example 6 and Comparative Example 6, those containing carbon black satisfying the physical property values stipulated in the present invention have large tan δ and are stable in handling for tread rubber. It can be seen that the rubber composition has good properties. Also, Tg is -40
Comparative Example 7 in which SBR-2 having a temperature of 21 ° C or higher is blended is -10 ° C.
It can be seen that JIS hardness in No. 2 increases, ΔHs increases, and winter performance deteriorates.

Next, Example 1, Comparative Example 1, Example 5 and Comparative Example 5
4 types of rubber compositions were used as tread rubbers, and four types of tires of the present invention tires I and II and comparative tires I and II were prepared. With respect to these four types of tires, dry and snow steering stability and wet braking performance were evaluated, and the results shown in Table 4 were obtained.

The size of each of these tires is 195 / 60R14.

Steering stability and wet braking performance are values evaluated by the following methods.

Steering stability: Based on feeling evaluation. The evaluation results of the comparative tires I and II were set to 100, and the evaluation results of the tires I and II of the present invention were shown as indexes. The larger the index value, the better the steering stability.

Wet braking performance: The braking distance on a wet road surface having a water depth of 1 to 3 mm was measured, and the braking distance of the tires I and II for comparison was set to 100,
The braking distances of the tires I and II of the present invention corresponding thereto are shown by indexes. The larger this index value, the better the braking performance.

As is clear from Table 4, the tire I of the present invention using the rubber composition of Example 1 containing CB-1 as the tread rubber has the rubber composition of Comparative Example 1 containing CB-N220. It can be seen that compared with the comparative tire I used for the tread rubber, the steering stability on snow does not change, but the wet braking performance is excellent and the dry steering stability is significantly improved.

Further, a tire II of the present invention using the rubber composition of Example 5 containing CB-1 as a tread rubber, and a comparative tire II using the rubber composition of Comparative Example 5 containing CB-N110 as a tread rubber. Comparing these, it is understood that the tire II of the present invention is excellent in dry steering stability, and is significantly improved in wet braking performance and snow steering stability.

〔The invention's effect〕

As described above, according to the present invention, one or two or more SBs having a glass transition point of less than −40 ° C. as a rubber component are used.
By using R and blending the above-mentioned specific carbon black into this SBR,
Both tan δ are high, and it is possible to maintain a high grip force regardless of whether the temperature is high or low. Therefore, not only in summer, but also in winter, the steering stability of the tire is excellent, and not only the dry steering stability, but also the steering stability on snow, and the rubber composition for a tread having good wet braking performance. can do.

Claims (1)

(57) [Claims] 1. A rubber component consisting of one or more styrene-butadiene copolymer rubbers having a glass transition temperature of less than -40 ° C. and a diene rubber other than the rubber, relative to 100 parts by weight of a rubber component,
Nitrogen specific surface area (N ₂ SA) is 110-140m ² / g, 24M4 DBP oil absorption is 85-95ml / 100g, full width at half maximum (ΔDst) of aggregate distribution measured by centrifugal sedimentation method is 55mμ or less and ΔDst / N _{2 A} rubber composition for a tire tread, which comprises 30 to 100 parts by weight of carbon black having an SA ratio of 0.43 or less.