JPH05331316A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:To improve wet performance in high-speed driving. CONSTITUTION:The rubber composition comprises 100 pts.wt. rubber at least 70wt.% of which is a styrene/butadiene rubber (SBR) having a combined styrene content of 25-60%, at least 5 pts.wt. silica having a specific surface area determined by nitrogen adsorption (N2SA) of 130-280m<2>/g, and carbon black having an N2SA of 80m<2>/g or larger, the total amount of the silica and the carbon black being 80-180 pts.wt. It gives a vulcanizate having an extractable content determined with acetone/chloroform of 80 pts.wt. or higher.

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 tire tread, and more particularly to a rubber composition for a tire tread capable of exerting excellent braking performance and steering stability not only on general paved roads but also on wet road surfaces of circuits. The rubber composition of the present invention can also be used as a tread rubber for wet race tires as an application.

[0002]

2. Description of the Related Art With the recent increase in the speed of automobiles, the level of required characteristics for tires has increased. In order to improve various performance (wet performance) on wet road surface at high speed running, increase grip force to improve braking performance under wet condition, and steering stability under wet condition In order to improve, the block rigidity of the tread pattern is increased to improve the cornering property, and the drainage property is also improved.

Therefore, in the past, in order to enhance grip under wet conditions, high styrene SBR was used as the rubber component of the tire tread rubber, the filling amount and particle size of carbon black were appropriately set, and oil was used. The vulcanization density is lowered by increasing the addition amount or adjusting the vulcanization system.

[0004]

By the way, in order to improve the wet performance during high speed running, it is necessary to increase the grip force as described above.
In order to increase the hysteresis loss (increase Tan δ) in the minute strain range (for example, 0.1%) in the temperature range of -20 ° C and to secure the contact area by following the unevenness of the road surface, Reduce the elastic modulus (for example, lower E ')
It turned out to be important.

Further, in order to increase the block rigidity, it has been found that it is important to maintain or increase the modulus in the large deformation range as compared with the conventional one (for example, maintain or increase the modulus of 50% or more to the conventional level). It was
This is important for preventing fluctuations due to block deformation during cornering, and at the same time suppressing deformation of the groove portions so that the water flow becomes a laminar flow without turbulence and is smoothly drained.

However, the conventional method does not meet all of the above-mentioned needs, so that it is impossible to satisfy today's high-level required characteristics. Then, an object of the present invention is to provide a rubber composition for tire treads which can further improve wet performance at high speed running.

[0007]

In order to achieve the above object, the present invention has the following constitution. That is, the amount of bound styrene
Contain at least 70 parts by weight of styrene-butadiene rubber (SBR) of 25 to 60% and 100 parts by weight of rubber component, and 5 parts by weight or more of silica having a nitrogen adsorption specific surface area (N ₂ SA) of 130 to 280 m ² / g. , Carbon black with N ₂ SA of 80m ² / g or more (CB)
Is a rubber composition containing 80 to 180 parts by weight in total with silica, and the acetone / chloroform extract after vulcanization is at least 80 parts by weight. Moreover, it is preferable to contain 35 parts by weight or more of silica. Further, it is preferable that the silane coupling agent is contained in an amount of 3 to 20% by weight of silica.

It is specified that the rubber component used in the present invention contains at least 70 parts by weight of SBR having a bound styrene content of 25 to 60%, but other rubber components include SBR (within the range specified in the present invention. (Not required), butadiene rubber, isoprene rubber, natural rubber, halogenated butyl rubber, and the like, but are not particularly limited.

If the amount of SBR is less than 70 parts by weight,
It is inconvenient because a sufficient hysteresis loss cannot be obtained in the tire operating temperature range and a desired grip force cannot be obtained. Further, if the amount of bound styrene is less than 25%, the grip force is insufficient for the same reason as above. In contrast,
When the amount of bound styrene exceeds 60%, the elastic modulus (E ') in the temperature range and strain range becomes high, and sufficient wet performance in the tire use temperature range cannot be obtained, which is not preferable.

Further, in the present invention, N ₂ SA is 130 to 280 m ² / g.
It is specified that the above silica is contained in an amount of 5 parts by weight or more, more preferably 35 parts by weight or more, still more preferably 50 parts by weight or more. If it is less than 5 parts by weight, the hysteresis loss (Tan δ) in the temperature region and strain region is insufficient, and the elastic modulus cannot be lowered. At 35 parts by weight or more, 50 parts by weight or more,
It is more preferable for increasing the hysteresis loss in the temperature range and strain range and decreasing the elastic modulus, and in addition, the modulus in the large deformation range is improved. When N ₂ SA is less than 130 m ² / g, the reinforcing property is small and a modulus of 50% or more cannot be secured. If it exceeds 280 m ² / g, it is not preferable because the workability is deteriorated although the reinforcement cannot be expected to be improved.

In the present invention, it is specified that carbon black having N ₂ SA of 80 m ² / g or more is contained in a total amount of 80 to 180 parts by weight with silica. If the amount exceeds 180 parts by weight, the kneading workability deteriorates. If the N ₂ SA is less than 80 m ² / g, the wear resistance is significantly reduced, which is not preferable.

Further, in the present invention, the acetone / chloroform extract after vulcanization is specified to be at least 80 parts by weight, but if it is less than 80 parts by weight, the elastic modulus in the temperature range and strain range becomes too high, which is inconvenient. Is.

In addition, the present invention requires that the silane coupling agent be contained in an amount of 3 to 20% by weight of silica. The silane coupling agent has the action of strengthening the bond between silica and the rubber component (polymer), and can increase the modulus in the large deformation range. If it is less than 3% by weight, the effect of addition of the silane coupling agent does not appear, and if it exceeds 20% by weight, the cost is increased but the effect is not obtained, which is not preferable.

Silaneca which can be preferably used in the present invention
The formula is a general formula Y₃-Si-C _nH_2nA (Y in the formula
Is an alkyl group having 1 to 4 carbon atoms, an alkoxyl group or chlorine
The three Ys in an atom may be the same or different, and n is 1 to 6
Is an integer, and A is -S_mC _nH_2nSi-Y₃Groups, X groups and
-S_mA group selected from the group consisting of Z groups, where X is
Is a nitroso group, a mercapto group, an amino group, an epoxy group,
Vinyl group, chlorine atom or imide group, Z is chemical formula 1, chemical formula 2 or
Is a group represented by Chemical formula 3,

[0015]

[Chemical 1]

[0016]

[Chemical 2]

[0017]

[Chemical 3] m and n each represent an integer of 1 to 6, and Y is as described above. ), Specifically, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, Bis (2-trimethoxysilylethyl)
Tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane , 3-chloropropyltrimethoxysilane, 3
-Chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N, N -Dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzotinazole tetrasulfide, 3-tri Examples include ethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, and bis (3-triethoxysillypropyl) tetrasulfide. 3-trimethoxysilylpropyl benzothiazole tetrasulfide are preferable. Moreover, as an example in which three Y's are not the same, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-
Examples thereof include mercaptopropyldimethoxymethylsilane, 3-nitropropyldimethoxymethylsilane, 3-chloropropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide, and dimethoxymethylsilylpropylbenzothiazoletetrasulfide.

[0018]

EXAMPLES The present invention will be described below with reference to Examples 1 to 16 and Comparative Examples 1 to 1.
6 will be described. Tables 1 and 2 below show the compounding contents, physical property values, and actual vehicle performance of each example and each comparative example.

Comparative Examples 1 to 5 and Examples 1 to 15 used only high styrene SBR within the range specified in the present invention as a rubber component, and Comparative Examples 6 and 16 within the range specified in the present invention. High styrene SBR and chlorinated butyl rubber (Cl-IIR) were used together. Further, Comparative Examples 1 to 6 did not contain silica, and Comparative Example 6 and Example 16 used different vulcanization accelerators from the other examples. The acetone / chloroform extraction method conformed to JIS K 6350.

The internal loss (Tan δ) and the storage elastic modulus (E ') were measured by using a viscoelasticity spectrometer (for example, manufactured by Iwamoto Seisakusho) with an initial load of 160 g for a strip sample having a width of 4.7 mm, a thickness of 2 mm and a length of 20 mm. , Dynamic strain 0.1%, frequency 50Hz
It is a value of 0 ° C. when measured from −20 ° C. to 20 ° C. at a temperature rising rate of 3 ° C./min.

Then, for Tan δ and E ′, Comparative Example 2
Alternatively, the value of 6 was set as 100 and displayed as an index. For example,
(Tan δ value of Example 1 / Tan δ value of Comparative Example 2) × 100. The larger the Tan δ index and the smaller the E ′ index, the more preferable. The value of 300% modulus at 25 ℃ is JIS
The measurement was carried out according to K 6301, and the index was displayed with the value of Comparative Example 2 or 6 as 100. An example is (modulus of Example 1 / modulus of Comparative Example 2) × 100. The larger this value is, the more preferable.

The wet brake index is as follows: tires of various formulations (tire size: 215/635 R 18) are mounted on the drive wheels of a passenger car with a displacement of 2500cc, and a straight running condition of 60km / h is achieved on a wet road surface at an outside temperature of 25 ° C. Then, the distance from the start of braking to the complete stop was measured, and indexed with Comparative Examples 2 and 6 as a reference. To illustrate, (Comparative Example 2
Distance / distance in Example 1) × 100. The larger this value is, the more preferable.

The wet cornering index is shown by a broken line in FIG. 1 in which tires of each composition (tire size 215/635 R 18) are mounted (4 wheels) on a passenger car having a displacement of 2500 cc (4 wheels) and the road surface is wet at an outside air temperature of 25 ° C. V-shaped turning road (γ = 20
m, d = 10 m) was lapped 5 times at a possible limit speed, the total of lap times of 3 to 5 laps was measured, and indexed based on Comparative Example 2. An example is (total lap time of Comparative Example 2 / total lap time of Example 8) × 100. The larger this value is, the more preferable. The criteria of Examples 1 to 15 are Comparative Example 2 and the criteria of Example 16 are Comparative Example 6.

[0024]

[Table 1]

[0025]

[Table 2]

* 1 The product name Nipseal AQ manufactured by Nihon Silica Co., Ltd. is used. N ₂ SA is 200 m ² / g. * 2 Bis- (3-triethoxysilylpropyl) -tetrasulfide * 3 The extracted component contains wax, antioxidant, vulcanization accelerator, etc. in addition to the oil component. * 4 N-cyclohexyl-2-benzothiazol sulfenamide * 5 Tetramethylthiuram monosulfide * 6 Tetramethylthiuram disulfide

As described above, in each of the examples,
Since the Tan δ index is high and the E ′ index is low, it can be seen that the grip power can be improved. Further, in each of the examples, it can be seen that the block rigidity is secured because the modulus is increased by 300%. It can be seen that this results in good drainage.

Furthermore, since the wet brake index, which is the actual vehicle performance, is large in each of the examples, it was confirmed that the braking performance under wet conditions is improved. Also, since the wet cornering index, which is also the actual vehicle performance, is increased, it was confirmed that the steering stability under wet conditions is improved. In addition, according to the rubber composition of the present invention, the wet performance can be improved without being restricted by the pattern, but it is more effective when combined with the directional pattern in which the mounting direction of the tire is restricted. ..

[0029]

As described above, according to the present invention,
It is possible to provide a rubber composition for a tread rubber of a tire, which exhibits excellent wet performance when traveling at high speed not only on a general paved road but also on a wet road surface of a circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing an 8-shaped turning road.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C08L 21/00 KCX 8218-4J

Claims (3)

[Claims] 1. A rubber component 1 containing at least 70 parts by weight of a styrene-butadiene rubber (SBR) having a bound styrene content of 25 to 60%.
5 parts of silica having a nitrogen adsorption specific surface area (N ₂ SA) of 130 to 280 m ² / g is added to 00 parts by weight.
A rubber composition containing 80 to 180 parts by weight of carbon black having a total amount of at least 80 parts by weight of N ₂ SA and a total amount of silica of 80 m ² / g or more, and an acetone / chloroform extract content after vulcanization of at least 80 parts by weight.
A rubber composition for a tire tread, characterized in that it is parts by weight. 2. The rubber composition for a tire tread according to claim 1, which contains 35 parts by weight or more of silica. 3. A silane coupling agent comprising silica of 3 to 20.
The rubber composition for a tire tread according to claim 1 or 2, characterized in that the rubber composition contains the rubber composition in a weight percentage.