JPH03119042A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:To obtain a rubber composition suitable for tire tread parts with high responsiveness by blending a raw material rubber composed of specific styrene-butadiene copolymer rubber, natural rubber and high-cis polybutadiene rubber with specific carbon black and a petroleum-based softener. CONSTITUTION:A composition, obtained by blending 100 pts.wt. raw material rubber composed of (A) 30-80 pts.wt. amorphous styrene-butadiene copolymer rubber, containing 3-30wt.% combined styrene and having >=70wt.% 1,2-vinyl content in the butadiene part, (B) 10-50 pts.wt. natural rubber and (C) 10-40 pts.wt. polybutadiene rubber containing >=95wt.% cis-1,4-bonds with (D) 80-130 pts.wt. carbon black having >=100m<2>/g nitrogen specific surface area and a small particle diameter and (E) 20-90 pts.wt. petroleum-based softener with 0.90-0.98 viscosity specific gravity constant and having <=500MPa shearing storage elastic modulus at -30 deg.C and <=15 difference in hardness between 60 deg.C and -10 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rubber composition for a tire tread that has stable maneuverability over a wide temperature range and also has excellent grip on snowy and icy road surfaces.

[Conventional technology]

Traditionally, the performance requirements for automobile tires include safety, economy, ride comfort, etc. In particular, with the development of expressway networks, cornering characteristics during high-speed driving of vehicles,
There is a desire for tires with improved maneuverability and safety such as braking performance, but in recent years there has also been a demand for tires that have excellent responsiveness, so to speak, that accurately follow the driver's intentions.

As a measure to improve tire motion performance, particularly grip performance, it is important to increase the frictional force with the road surface by increasing the hysteresis loss of the tread rubber. That is, the tread surface that is in friction with the road surface is deformed at high speed due to minute irregularities on the road surface, and the greater the energy dissipation due to hysteresis loss that occurs during this periodic deformation process, the greater the frictional force becomes. Moreover, since the deformation on the friction surface is extremely fast, Williams
It is known that the temperature-time conversion side of the Landelferie depends on hysteresis losses measured at temperatures lower than the temperature at which the tire is used. In fact, there is a good correlation between tanδ (tj! lapse coefficient), which is a measure of hysteresis loss, and the coefficient of friction of a tire, but it is measured at a temperature 30 to 40 degrees Celsius lower than the temperature at which the tire is used. tanδ is involved. Conventionally, in order to increase the hysteresis loss of a rubber composition, a method of compounding a rubber with a high glass transition temperature (Tg) such as a high styrene-containing styrene-butadiene copolymer rubber (SBR) has been used. . This is because the tan δ of rubber has a peak near Tg, so by bringing the tan δ peak closer to the temperature range that is involved in friction performance (equivalent to 0°C if the tire running temperature is 30°C). This is intended to utilize a high tan δ.

Figure 1 shows emulsion polymerized styrene with different styrene contents.
This figure shows the tan δ temperature dependence of butadiene copolymer rubber. When the styrene content increases, the tan δ peak temperature moves to the high temperature side, and the jan δ value increases near 0° C., which is the base of the tan δ peak. However, at the same time, the temperature dependence of tan δ also increases around 0° C., and therefore the grip performance of the tire also changes greatly depending on the environmental temperature. Furthermore, the elastic modulus also changes rapidly corresponding to the tan δ peak.

In other words, as the temperature decreases, the elastic modulus increases rapidly, making it impossible for the rubber to follow the unevenness of the road surface, or in the case of waterways, etc., the rubber cannot deform at all.
There was a problem in that maneuverability and braking performance deteriorated.

On the other hand, if a polymer with a low Tg, such as high-cis butadiene rubber (BR), is used, the grip performance at low temperatures will improve, but on the other hand, the tan δ around 0°C will decrease, and the grip performance will improve at high temperatures. This creates a contradiction in terms of lack of ability. Therefore, attempts have been made to harmonize the above-mentioned antinomy by blending different types of polymers called SBR/BR or by incorporating a large amount of small particle size carbon (Il, p1Moore''T
he Fr1ction of Pneumatic
Tyres', Elasevier Scientific
ic Publishing Company 197
5+ U, S.

Patent No. 4.748.168. Unexamined Japanese Patent Publication 1986
-12932 etc.).

Furthermore, JP-A-62-260843, JP-A-62
Publication No. 190238 utilizes the compatibility of these blended polymers and delicate control of Tg to successfully exhibit all-weather resistance from high to low temperatures.

However, since such rubber exhibits properties intermediate to those of the blended polymers, it cannot take full advantage of the inherent strengths of the constituent polymers, and has the disadvantage that neither high-temperature nor low-temperature grips are completely satisfactory. In addition, incorporating a large amount of small particle size carbon has problems in processability and increases heat generation.

As a measure to deal with this trade-off,
-66733 and JP-A-62-62840 disclose a technique of adding a low-temperature plasticizer to these blended polymers, but although the low-temperature grip is certainly improved, the rubber elastic modulus decreases at high temperatures. The decline is significant,
The handling stability at high temperatures is not always satisfactory.

The goal of these technologies is to improve the all-weather performance of tires, and tread rubber is suitable for all-weather, high-performance tires that pursue the ultimate performance. However, in recent years, the performance required of tires is not only high grip for handling performance.
There is a need for tires that accurately respond to the driver's intentions. In other words, the requirements for automobile tires must match social demands for automobiles, but recent advances in ergonomics and electronics engineering have made it possible for automobiles to not only have excellent acceleration and cornering performance, but also to improve human performance. Does not cause discomfort to the sensibilities of
There is a demand for cars that, like well-made shoes, do not make you feel that there are tires on them. This requires tires that respond to the intentions of the driver of the vehicle without any phase delay.

If we were to call these tires high-responsive tires, they would generate lateral force without any time delay when the driver of the vehicle turns the steering wheel, that is, they would have excellent responsiveness to slight steering. is necessary.

That is, in addition to the conventional all-weather performance, the high-responsive tire needs to have excellent responsiveness even when the steering angle is small. From this perspective, we investigated the factors that delay the response at small steering angles, and found that in addition to the tire structure, the phase lag of the tread rubber and tread blocks also has an effect.

As an index of phase lag, hardness at 60°C and -10
It can be expressed as the difference in hardness in °C. In other words, the greater the difference in hardness of the rubber, the faster the stress relaxation (as a result, stress attenuation occurs easily in response to minute deformations in the tread, making it impossible to maintain a predetermined stress, resulting in poorer slight steering response. A conclusion has been reached.

As shown in Figure 1, the difference between the hardness at 60°C and the hardness at -10°C (hereinafter referred to as coefficient M) is greater for emulsion-polymerized styrene-butadiene copolymer rubber with a higher Tg and high styrene content. big. That is, if a styrene-butadiene copolymer rubber with a high Tg is used to improve grip performance, the coefficient M also increases, resulting in poor responsiveness.

After careful consideration to resolve these contradictions, we found that
The tread rubber composition of the present invention has been achieved. in this way,
There is no known example in which a tread rubber composition has been studied from the viewpoint of tire responsiveness, and therefore the technology of the present invention is completely new.

[Problem to be solved by the invention]

The present invention provides an all-season type high-responsive (small coefficient M) rubber composition for trend tires that has stable maneuverability over a wide temperature range and also has excellent grip on snowy and icy road surfaces. The purpose is to

[Means to solve the problem]

The present inventors have conducted intensive studies on rubber compositions that increase the absolute value of tan δ and lower the coefficient M in the temperature range involved in friction in styrene-butadiene copolymer rubber, and as a result, the results have been determined to be limited to a specific range. The above objectives were achieved in a system in which an essentially amorphous styrene-butadiene copolymer rubber having a styrene content and a vinyl content in the butadiene portion was blended with specific ranges of natural rubber and polybutadiene rubber. The inventors have discovered that it is possible to do so and have arrived at the present invention.

Therefore, the rubber composition for tire tread of the present invention is
30 to 80M essentially amorphous styrene-butadiene copolymer rubber containing 3 to 30% by weight of bound styrene and having a 1,2-vinyl content of the butadiene moiety of 70% by weight or more
M parts, 10 to 50 parts by weight of natural rubber, and cis 1,4
- 10 to 40 parts by weight of polybutadiene rubber containing 95% by weight or more of bonds constitutes a raw material rubber with a total rubber amount of 100ii1 part, and the nitrogen specific surface area is 100rrf/g or more with respect to 100 parts by weight of this raw material rubber. 80 to 130 parts by weight of certain carbon black and viscosity specific gravity constant 0.90
It is made by blending 20 to 90 parts by weight of a petroleum-based softener with a temperature of ~0°98, and has a shear storage modulus of 500M at -30°C.
Pa or less, and the difference between the hardness at 60°C and the hardness at -10°C is 15 or less.

This means will be explained in detail below.

(11 raw rubber.

Consisting of 30 to 80 parts by weight of styrene-butadiene copolymer rubber, 10 to 50 parts by weight of natural rubber, and 10 to 40 parts by weight of polybutadiene rubber, with a total rubber amount of 100 parts by weight.
Parts by weight.

(al　Styrene-butadiene copolymer rubber.

High vinyl SB containing 3 to 30% by weight of bound styrene and having a 1,2-vinyl content in the butadiene moiety of 70% by weight or more
R, which is essentially amorphous.

The amount of bound styrene must be 3-30% by weight. This is because when the amount of bound styrene is less than 3% by weight, the strength of the polymer is insufficient, and when it exceeds 30% by weight, the coefficient M
This is because the tire becomes large, which adversely affects the responsiveness of the tire. Furthermore, the 1,2-vinyl content of the butadiene moiety must be 70% by weight or more. If it is less than 70% by weight, the Tg of the styrene-butadiene copolymer rubber is too low and 0.
This is because the tan δ at °C decreases, resulting in poor grip performance. Although a higher 1,2-vinyl content is desirable, the upper limit is about 95% by weight for manufacturing reasons. The appropriate amount of the styrene-butadiene copolymer rubber is 30 to 80 parts by weight. If it is less than 30 parts by weight, the properties of the styrene-butadiene copolymer rubber will not be exhibited, and if it exceeds 80 parts by weight, the rubber strength will not be sufficient and it will be unsuitable for use as a tire tread rubber.

As a method for producing such a block copolymer,
For example, by adjusting the amount of styrene and the amount of 1.3-butadiene to a predetermined ratio, using a polar compound such as ether as a dispersant in a hydrocarbon solvent, and polymerizing styrene and butadiene in the presence of a lithium-based polymerization initiator, Ratio, amount of preparation,
Copolymerization may be carried out while controlling the polymerization initiator and the like.

This method may be a batch method or a continuous polymerization method. Furthermore, it is also desirable to apply known techniques for modifying copolymers, such as terminal modification or coupling, as long as it does not adversely affect the temperature dependence improvement of coefficient M and viscoelasticity, which is the goal of the present invention. It is.

(bl natural rubber.

Blending natural rubber with styrene-butadiene copolymer rubber is important from a practical standpoint. This is because automobile tires are often used not only on paved roads but also on rough and uneven roads, and in such cases, blending natural rubber can prevent chipping and
This is because trend damage caused by sudden external force such as cutting can be reduced. For this purpose, a blending amount of 10 parts by weight or more is required. On the other hand, if the amount of natural rubber blended is too large, the essential properties of the styrene-butadiene copolymer rubber will be diluted and the grip performance will deteriorate, so it is necessary to keep the amount blended to 50 parts by weight or less. There is.

(C) Polybutadiene rubber.

High cis B containing 95% by weight or more of cis 1,4-bonds
It is R. Formulated to improve low temperature performance and wear resistance. The amount required is 10 to 40 parts by weight; if it is less than 10 parts by weight, no improvement in low temperature performance and wear resistance can be expected;
Grip performance is poor when the weight exceeds the weight range.

(2) Carbon black.

Furthermore, in order to be put to practical use as a tread for automobile tires, it must have sufficient performance in terms of wear resistance and handling stability. In order to improve steering stability to a level suitable for high-performance tires, the nitrogen specific surface area must be 100r.
It is necessary to mix 80 parts by weight or more of small particle diameter carbon blanks of rr/g or more with respect to 100 parts by weight of the raw material rubber. However, if it exceeds 130 parts by weight, the abrasion resistance and heat generation properties will be extremely poor, so the content must be 130 parts by weight or less.

(3) Petroleum-based softener (extension oil).

Other characteristics of tires include ride comfort, noise, and braking performance, and in order to improve these performances, it is also necessary to add extender oil to improve processability during tire manufacturing. If the viscosity specific gravity constant of the extender oil is less than 0.90, no improvement in braking performance will be observed, and if it exceeds 0.98, the softening effect will not work and workability will not be improved. For this reason, 0.90~
The range is 0.98. Note that it is desirable to use an aromatic extender oil of about 0.98. It is necessary to adjust the tread rubber modulus by appropriately increasing or decreasing the blending amount of extender oil depending on the blending amount of carbon black. However, if it is less than 20 parts by weight per 100 parts by weight of the raw material rubber, the compounded rubber will not elongate, resulting in poor chipping and cutting properties.
It is also difficult to process, so it is not preferred. On the other hand, if the amount exceeds 90 parts by weight, the strength decreases and the wear resistance becomes extremely poor, making it difficult to put it into practical use.

(4) The rubber composition obtained by blending carbon blank and petroleum softener with the raw rubber in this way can be heated to -30°C.
The shear storage modulus at 500 MPa or less is required. Generally, a rubber-like substance is in a glass state at a temperature of 7 g or less, and its elastic modulus is more than 100 times that at room temperature, making it brittle and breaking at the slightest strain. The temperature at this time is called the low-temperature embrittlement temperature, and is known as an indicator of the low-temperature performance of rubber materials. However, when the elastic modulus changes slowly with temperature as in the rubber composition according to the present invention, the embrittlement temperature cannot be simply estimated from Tg. Figure 2 plots the low-temperature embrittlement temperature and shear storage modulus (G'') at that temperature for various rubber compositions.From this, it can be seen that the G' value at the embrittlement temperature for all samples is It can be seen that the pressure exceeds 500 MPa.

Therefore, if it is 500 MPa or less, it can be said that the embrittlement temperature is not exceeded. Furthermore, the reason why the shear storage modulus is set at -30°C is that tires are not normally used at temperatures lower than -30°C.

In addition, this shear modulus was determined using a dynamic torsion tester.
It is measured at a distortion of 0.5% and a frequency of 20 Hz.

Furthermore, in order to improve the responsiveness at the time of a small steering angle, it is better that the difference (coefficient M) between the hardness at 60° C. and the hardness at -10° C. is small. If this difference is 16 or more, even if the tire has tread rubber with good grip performance, the evaluation of responsiveness will be poor, and as a result, the overall steering stability evaluation of the tire will be poor. . 1
If it is 5 or less, it has sufficient performance as a highly responsive tire, but it is more preferably 13 or less.

The hardness at this time is measured according to JIS K 6301.

For reference, a rubber composition in which such a high vinyl content styrene-butadiene copolymer rubber is blended with a diene rubber such as natural rubber or polybutadiene rubber is disclosed in JP-A-56-110753. Although this technology is well-known in the official gazette, the emphasis is on achieving both low drying resistance and wet grip, so changes in hardness due to temperature are not taken into consideration.Also, since the amount of carbon black blended is small, Not suitable as a responsive high-performance tire.

Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded.

Example 1 A styrene-butadiene copolymer rubber having the components shown in Table 1 was produced. Furthermore, these copolymer rubbers and emulsion polymerized SBR for comparison were vulcanized in the formulations shown in Table 2. Numbers in the table are parts by weight unless otherwise specified. The conditions for vulcanization are 16
0 x 20 minutes, and a 2 m thick rubber sheet was obtained. The physical properties of this sheet were measured. In addition, the measurements in the examples were performed by the following method.

The amount of vinyl bonds in the butadiene moiety was determined by the Morello method. The styrene content was determined by the Hampton method using an infrared spectrometer.

- Shear modulus G' at 30°C (-30°C) and 0
tan δ at °C is RHEOMETRIC
The measurement was performed using a dynamic viscoelasticity measuring device manufactured by S Company at a frequency of 20 Hz and a shear strain of 0.5%. )Is is JIS K 630
The hardness is based on 1.

(Margins below this page) As can be seen from Table 2, Comparative Example 4.5 is emulsion polymerized SBR.
This is an example. The formulation of Comparative Example 5 has good low temperature performance, but low tan δ (0°C) and poor grip performance. On the contrary, in Comparative Example 4, the tan δ (0° C.) is high, but the low temperature performance is poor. Comparative Example 1 is an example in which a styrene-butadiene copolymer rubber whose 1,2-vinyl content is out of the range of the present invention is blended with natural rubber and polybutadiene rubber, but the coefficient M is small and good. Of things, 0
The tan δ at °C is low and the grip performance is poor. Comparative Example 2 is a blend of emulsion polymerized SBR with a bound styrene content of 35% by weight, but has a low tan δ at 0°C and a low coefficient M.
is also large, so it is expected that the responsiveness will be poor. Comparative Example 6 is an example in which 50 parts by weight of polybutadiene rubber having a cis-1,4-bond content of 98% by weight was blended.
nδ is low and grip performance is poor. Compared to these, Examples 1 to 3, which satisfy the scope of the present invention, have well-balanced performance.

Example 2 Trend rubber was prepared using the formulations of Example 1 and Comparative Example 2.4 in Table 2, tires were prepared, and a handling stability test was conducted. The evaluation was divided into steering response and limit performance, and testers evaluated the feeling of each. The results are shown in Table 3. As can be seen from Table 3, although the tire with the rubber composition of Example 1 in its tread was inferior to Comparative Example 4 in marginal performance, it was proven to have excellent fine steering response and excellent overall evaluation. Ta.

Note) (Domestic 5-seater sedan, tire size 195/65R15)
The evaluation score is out of 10, the higher the better.

〔Effect of the invention〕

As explained above, the rubber composition of the present invention has more stable grip performance and fine steering response over a wide temperature range than conventional technologies, and also has excellent grip on snowy and icy road surfaces. The present invention can be suitably used in a pneumatic tire tread section, particularly in an all-season type tire trend section with high responsiveness.

[Brief explanation of drawings]

Figure 1 shows the ta of emulsion polymerized SBR that differs only in styrene content.
An explanatory diagram showing that the nδ-temperature curve shows that the peak temperature is higher when the styrene content is high. Figure 2 is an explanatory diagram showing the relationship between the low-temperature embrittlement temperature and shear modulus of a rubber compound. .

Claims (1)

[Claims] 30 to 80 parts by weight of an essentially amorphous styrene-butadiene copolymer rubber containing 3 to 30% by weight of bound styrene and having a 1,2-vinyl content of the butadiene moiety of 70% by weight or more, and 10 parts by weight of natural rubber. ~50 parts by weight, and cis 1,4
- A raw material rubber with a total rubber amount of 100 parts by weight is composed of 10 to 40 parts by weight of polybutadiene rubber containing 95% by weight or more of bonds, and a nitrogen specific surface area of 100 m^2/g or more with respect to 100 parts by weight of this raw material rubber. 80 to 130 parts by weight of carbon black, and a viscosity specific gravity constant of 0.90 to 130 parts by weight.
Contains 20 to 90 parts by weight of a petroleum softener with a shear storage modulus of 500 MP at -30°C.
A rubber composition for a tire tread, characterized in that the difference between the hardness at 60°C and the hardness at -10°C is 15 or less.