JPH0621191B2 - Vulcanized rubber composition for tire tread - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vulcanized rubber composition for a tire tread having improved performance at low temperatures, and more specifically, it has excellent braking performance on snow and ice and on wet road surfaces. The present invention relates to a vulcanized rubber composition for a tire tread, which has good braking performance and dynamic performance required for a tire.

<Prior art> Conventionally, in order to secure the exercise performance of the tire on ice and snow in cold regions, spiked tires with spikes in the tread and snow tires with a special compound in the tread have been used. There is. Since the performance required for these tires used at low temperatures is significantly different from the performance of general-purpose tires used at room temperature, it is common that the rubber used in the compound used for the tread is also of a different type. Target. As a result, until now, it was necessary to prepare both general-use tires and winter tires, and to use them properly as needed.

However, recently, with the development of highways, the range of action of automobiles has become wider, and snow removal in winter has become more frequent, making it difficult to use two types of tires properly.
As a result, many cars equipped with general-purpose tires were put into cold regions in the winter, and conversely, cars equipped with spiked tires and snow tires were driven on highways and snow-cleared roads.

<Problems to be Solved by the Invention> Tires for general use are mainly composed of a styrene-butadiene copolymer having a relatively high glass transition point in the tread in order to give importance to braking performance on wet road surfaces and operability. It is common to use a rubber composition, so the rubber becomes brittle at low temperatures, and the braking performance (ice / skid resistance) on ice and snow is inferior, so it is dangerous to use it in cold regions in winter. is there.

On the other hand, when running on a normal road surface with spiked tires, damage to the paved road surface due to spikes and the generation of dust due to it, and noise have become a social problem, and when running on a general road surface with snow tires, Not only the braking performance (wet and skid resistance) on a wet road surface is inferior, but also there is a problem such as severe abrasion of the ledge, which is not suitable.

Attempts to improve such problems have been made, for example, in JP-B-58-7662, JP-B-58-46257, and JP-A-56-122845, but the effect is not always sufficient. Not all of the above, but in addition to the performance of ordinary tires, we are looking for the emergence of all-weather tires with improved low-temperature performance that can be used throughout the year, and spikeless tires that have good braking performance without spikes in winter. It was rare.

<Means and Actions for Solving Problems> Under the circumstances, the present inventors have improved the performance at low temperatures, have good braking performance on snow or ice, and have improved braking performance on wet road surfaces. As a result of further intensive studies to obtain a vulcanized rubber composition for tire tread having excellent wear resistance, a styrene-butadiene copolymer having a specific structure is contained as a raw material rubber component, and a more limited type and The inventors have found that the above object can be achieved by using a vulcanized rubber composition having a specific hardness by using an amount of a rubber extender oil, a limited type and an amount of carbon black, and arrived at the present invention.

That is, the present invention contains raw rubber, carbon black, extender oil for rubber, vulcanizing agent, and other compounding chemicals for rubber,
A vulcanized rubber composition obtained by vulcanization, wherein 30 to 100% by weight of [I] raw material rubber is obtained by copolymerizing styrene and butadiene with (a) a lithium-based catalyst, b) Styrene content is 5 to 30% by weight, (c) Vinyl bond content of the microstructure of the butadiene part is 16
%, (D) Mooney viscosity (ML _{1 + 4} , 100 ° C.) is 60 to 15
0, (e) Relaxation time of 10 measured by Mooney viscometer
Is a branched styrene-butadiene copolymer, wherein [II] the other raw material rubber is natural rubber, polyisoprene rubber,
It is one or more selected from emulsion-polymerized styrene-butadiene copolymer rubbers, and [III] has a viscosity specific gravity of 0.82 as an extending oil for rubber.
-0.92, the naphthene carbon content by Kurz analysis is 35% or more, containing 20 to 40 parts by weight per 100 parts by weight of the raw rubber, extender oil for naphthenic rubber, [IV] as a carbon black, 80 mg of iodine adsorption
/ G or more, dibutyl phthalate oil absorption is 100 ml / 10
A carbon black of 0 g or more is contained in an amount of 50 to 95 parts by weight per 100 parts by weight of the raw rubber, and [V] the difference between the weight of the carbon black and the weight of the extending oil for rubber is 25 to 35 parts by weight. VI Vulcanized product A vulcanized rubber composition for tire tread having a JIS hardness of 65 or less measured at -10 ° C.

Hereinafter, the present invention will be described in detail.

30 of the raw rubber used in the rubber composition for tires of the present invention
-100% by weight is a specific styrene-butadiene copolymer. This styrene-butadiene copolymer having a specific structure is obtained by copolymerizing styrene and butadiene with a lithium catalyst. The bound styrene content of the copolymer is 5 to 30% by weight. The amount of bound styrene is 5
If it is less than wt%, the tensile strength of the vulcanizate will be low, and the wet skid resistance will be insufficient. On the other hand, if the amount of bound styrene exceeds 30 wt%, the impact resilience will be poor and the low-temperature performance will be poor. The vinyl bond content of the microstructure of the butadiene part of the styrene-butadiene copolymer is 16%.
Is less than. If the vinyl bond content exceeds 16%, the abrasion resistance is lowered at the same styrene content. Furthermore, the Mooney viscosity of styrene-butadiene copolymer (ML _{1 + 4} ,
100 degreeC) is 60-150. When the Mooney viscosity of the copolymer is less than 60, the abrasion resistance is poor, while when the Mooney viscosity exceeds 150, the processability at the time of compounding and kneading and molding is poor, and it is not preferable because the characteristics of high molecular weight cannot be utilized. The Mooney viscosity of the copolymer is 80 to 130.
Is preferred. Furthermore, the styrene-butadiene copolymer is a branched polymer having a specific branch. Such a branched styrene-butadiene copolymer is obtained by using a batch polymerization method or a continuous polymerization method to obtain an active polymer having a lithium active terminal obtained by copolymerizing styrene and butadiene with a lithium catalyst. It is obtained by reacting with a polyfunctional compound capable of reacting with the active end and coupling. Examples of such polyfunctional compounds include silicon tetrachloride, tin tetrachloride, silicon tetrabromide, active halogen compounds of methyl silicon trichloride, polyepoxy compounds, polyisocyanates, polyfunctional esters and the like. The branched styrene-butadiene copolymer has a temperature of 100 ° C.
It can also be obtained by polymerizing for a relatively long time at the above-mentioned high temperature while maintaining a state in which gel is unlikely to occur. The degree of branching of such a branched styrene-butadiene copolymer can be judged by using a Mooney viscometer and measuring the relaxation time after applying a shearing force. The relaxation time of the styrene-butadiene copolymer measured with a Mooney viscometer is required to be in the range of 10 to 150 seconds in order to balance the vulcanized physical properties and processability.

Here, the relaxation time measured using a Mooney viscometer is measured by the following method. That is, ASTM-D-
The Mooney viscometer of 1646 uses a Mooney viscometer with a clutch attached between the drive unit and the worm gear of the torque detection unit. FIG. 1 shows an example of a block diagram of this apparatus.
In FIG. 1, 1 is a drive unit, 1 is a gear for shifting gears,
3 is a clutch, 4 is a worm gear, 5 is a dial gauge for detecting torque, 6 is a die, 7 is a rotor, 8 is an air cylinder, 9 is a heater, 10 is a temperature measuring element, and 11 is a temperature controller. The dimensions and the like are in accordance with ASTM-D-1646. The gear and worm gear are designed so that the rotor will be 2 rpm.

The sample is shown above and below the rotor, i.e. in the die,
The die temperature is set to 100 ° C.

A pressure of 1.2 tons is applied to the air cylinder, preheated by a usual measuring method for 1 minute, then the rotor is rotated for 4 minutes, and the Mooney viscosity is measured from the reading of the dial gauge. After rotating for 4 minutes, the clutch is removed (electromagnetic clutch is desirable), and the time until the gauge reading reaches 20% of the Mooney viscosity just before the clutch is removed is defined as relaxation time (seconds).

The relaxation time according to the above-mentioned measurement method shows the viscosity of the entanglement between polymer molecules.
Good entanglement between molecules.

By using such a branched styrene-butadiene copolymer rubber, the workability in a Banbury mixer and the workability with a mixing roll are higher than those of a conventional unbranched styrene-butadiene copolymer with a lithium catalyst. The width is improved, and the cold flow (low-temperature flow of rubber when stored at room temperature) is improved, which is effective in improving the process of compounding a rubber composition, simplifying the packaging form in rubber packaging, and the like.

Furthermore, the molecular weight distribution (weight average molecular weight (▲ ▼) and number average molecular weight (▲ ▼) measured by GPC (gel permeation chromatography) of the copolymer of branched styrene-butadiene used in the present invention. ) With (▲
▼ / ▲ ▼)) is preferably 1.5 to 4.0,
In order to maintain a good balance between processability and physical properties of vulcanized products, the molecular weight distribution is particularly preferably 2.0 to 3.0.

Further, the content of block styrene of the branched styrene-butadiene copolymer used in the composition of the present invention is preferably less than 5% by weight in order to maintain the dynamic characteristics, and 3% by weight is preferable.
The following is more preferable.

In the present invention, the specific branched styrene-butadiene copolymer as the raw material rubber is 30 to 10 of the raw material rubber.
0% by weight is used. When the amount used is less than 30% by weight, the effect of improving the balance between the wet skid characteristics and the ice skid characteristics is small.

The other rubber used as the raw material rubber of the present invention together with the branched styrene-butadiene copolymer is one or more selected from natural rubber, polyisoprene rubber, polybutadiene rubber, and emulsion-polymerized styrene-butadiene rubber. The glass transition temperature of these rubbers measured by DSC is
In order to maintain the low temperature performance of the vulcanized rubber, it is preferably -50 ° C or lower.

The extender oil for rubber used in the present invention is a extender oil for naphthenic rubber having a viscosity specific gravity constant of 0.82 to 0.92 and a naphthene carbon content of 35% or more by the Kurtz analysis method. 20 to 60 parts by weight are used per part by weight.

In the case of using an extender oil having a viscosity specific gravity constant of less than 0.82 and a rubber extender oil having a naphthene carbon content of less than 35% by the Kurz analysis method even when the viscosity specific gravity constant is 0.82 or more, Although the vulcanized rubber composition has good low-temperature performance (ice / skid property), it has poor wet / skid property and poor balance between both skid properties, and mechanical strength such as tensile strength and tear strength of the vulcanized product. Is inferior. On the other hand, when a so-called aroma-based extending oil having a viscosity specific gravity constant of more than 0.92 is used, the composition is inferior in ice skid characteristics, and the object of the present invention cannot be achieved.

In the present invention, the rubber extender oil is preferably contained in advance in the raw rubber as a master batch, but in order to improve the dispersibility of carbon black during kneading, a small amount of process oil for the rubber is used. It is also possible to add extender oils. It is also possible to use a small amount of oil other than the above as a process oil, but those oil components are not limited to types and amounts within a range that does not impair the performance of the extender oil for naphthenic rubber of the present invention. I won't. When the amount of the naphthenic rubber extending oil is less than 20 parts by weight per 100 parts by weight of the raw rubber,
Ice skid characteristics are not always sufficient, while 6
If it exceeds 0 parts by weight, the strength and dynamic properties are significantly deteriorated.

In the present invention, as the carbon black, 50 to 95 parts by weight of a reinforcing carbon black having an iodine adsorption amount of 80 mg / g or more and a dibutyl phthalate oil absorption amount of 100 ml / 100 g or more is used per 100 parts by weight of the raw rubber. .

As the carbon having an iodine adsorption amount and a dibutyl phthalate oil absorption amount within the above ranges, among the carbon blacks having various particle sizes and structures, the ISAF grade, IISAF grade, and HAF grade carbon blacks are applicable. When a carbon black other than the above-mentioned one is used, the reinforcing effect and the abrasion resistance improving effect of the vulcanized rubber composition are poor.

When the amount of carbon black used is less than 50 parts by weight, tear strength and the like are reduced, while when it exceeds 95 parts by weight,
Poor low temperature performance and dynamic properties.

The JIS hardness (A) of the vulcanized rubber composition of the present invention measured at −10 ° C. is required to be 65 or less in order to impart good ice skid characteristics.

The above, in order to obtain a vulcanized rubber composition having JIS hardness at low temperature, in the present invention, it is necessary to limit the raw material rubber, the extension oil for rubber, further, the amount of carbon black, and the extension for rubber It is necessary that the difference from the amount of oil is 25 to 35 parts by weight. If this difference is less than 25, the tensile strength will be insufficient, while if the difference exceeds 35, the ice skid properties will be poor.

The vulcanizing agent used in the present invention mainly contains sulfur, and peroxides and sulfur-donating substances can also be used.

In addition, as a rubber compound used in the composition, there are vulcanization aids typified by stearic acid, vulcanization accelerators of various systems, zinc white, antioxidants, and other compounding agents. Any of them can be used in the composition of the present invention unless they prevent the achievement of the object of the present invention.

The composition of the present invention is used as a kneading machine for rubber, mixed and kneaded by an internal mixer, an open roll or the like, molded, and then vulcanized at a temperature of 130 to 200 ° C. to obtain a desired molded product. Become.

Examples and comparative examples will be shown below. These are illustrative of the invention and are not limiting in scope. Various measurements in Examples and Comparative Examples were measured by the following methods.

Hardness (-10 ° C): Using JIS hardness tester (A type),
Measured after leaving the test piece in a room at -10 ° C for 2 hours Tensile strength: Measured according to JIS-K-6301 JIS impact resilience: According to JIS-K-6301, a sample of 60
Measured by heating to ℃ Abrasion resistance: Measured using a pico abrasion tester. Comparative Example 1
Displayed as an index with the composition of SBR1502 of -6 as 100.

Wet skid resistance: Measured in a room at 23 ° C using a Britishu portable skid tester and a safety walk (3M) as the road surface.
Displayed as an index with the measured value of the composition of Comparative Example 1-6 being 100.

Ice skid resistance: Uses the same measuring machine as the wet skid resistance. Measured inside a room set at -10 ° C with a surface temperature of -10 ° C as the road surface. Displayed as an index with the measured value of Comparative Example 1-6 being 100.

Further, as the raw material rubber, the extending oil and the carbon black, those shown below were used.

Naphthene-based extender oil: K-Petroleum, R-200, viscosity specific gravity constant = 0.836, naphthene carbon content = 38% (Kurz method) Aroma-based extender oil: Joint petroleum X-140, viscosity specific gravity constant = 0 .965, naphthene carbon content = 25% (Kurz method) Paraffin type extender oil: Fuji Kosan P-200, viscosity specific gravity constant = 0.813, naphthene carbon content = 29% (Kurz method) Diene 35R: Asahi Kasei Made, solution-polymerized polybutadiene rubber, Mooney viscosity 35 SBR1502: made by Nippon Zeon, emulsion-polymerized styrene-butadiene copolymer rubber, styrene content 23.5%, Mooney viscosity 52 natural rubber: RSS No. 1 carbon black N339: iodine adsorption amount = 90 mg / g dibutyl phthalate oil absorption = 120 ml / 100 g Carbon black N285 Iodine adsorption = 102 mg / g dibutyl phthalate Rate oil absorption = 124 ml / 100 g Carbon black N550 Iodine adsorption = 43 mg / g Dibutyl phthalate oil absorption = 121 ml / 100 g <Example> [Preparation of sample] A reactor equipped with a stirrer and a jacket with an internal volume of 10 and purified butadiene 24.6 g / min, purified styrene 5.4 g / min, purified cyclohexane 130 g / min, n
-Butyllithium was added in an amount of 0.
At a rate of 065 parts by weight, each was continuously fed by a pump from the bottom of the reactor, the reactor internal temperature was maintained at 100 ° C., and the reactor internal pressure was maintained at 8 kg / cm ² , from the reactor top, The solution containing the active polymer in which the polymerization reaction was completed was continuously withdrawn. After the Mooney viscosity of the obtained styrene-butadiene copolymer became stable, the polymer solution extracted from the reactor was continuously supplied to the second reaction group, while the active lithium contained in the polymer solution was supplied. Against
A silicon tetrachloride equivalent to 0.6 equivalent is continuously supplied,
A coupling reaction was performed to obtain a branched polymer. To the solution containing this branched polymer, after adding BHT as a stabilizer,
The solvent was removed to obtain the desired branched styrene-butadiene copolymer (referred to as sample-A). The analytical values of Sample A are shown in Table 1. In addition, the amount of block styrene by the Korsov's O _S O ₄ decomposition method of sample A is 1.1%, the glass transition temperature by the DSC method is −79 ° C., and the molecular weight distribution measured by GPC using a polystyrene calibration curve ( ▲ w ▼ / ▲
▼) was 2.45.

The relaxation time measurement using a Mooney viscometer was performed according to the method described in the text.

Sample-B, sample-F, sample-G, sample-listed in Table 1.
J and sample-K are the same amount of styrene and n-butyllithium supplied by the same method as that for obtaining sample-A.
By changing the amount of coupling agent, different styrene contents,
The Mooney viscosity and the degree of branching (relaxation time) were used as samples. For sample-J, a small amount of tetrahydrofuran was added to the polymerization system in order to adjust the amount of vinyl in the butadiene portion.

For Samples-C and E, the batch polymerization method was used.
After initially charging a predetermined amount of styrene and 70% of butadiene and adding n-butyllithium to start polymerization,
Add the remaining amount of butadiene to the polymerization system in the latter half of the polymerization reaction,
After completion of the polymerization reaction, a predetermined coupling agent was added to obtain the compound. Sample-H was obtained by the method described above without adding the coupling agent.

The analysis results are shown in Table 1 for all the samples.

Sample-H, which is an unbranched polymer, had a large cold flow when it was left at room temperature, but no cold flow was a practical problem with other prepared samples.

Example 1 and Comparative Example 1 With the composition shown in Table 2, kneading was carried out using a B type Banbury mixer to obtain an unvulcanized rubber compound, and then the compound was molded into a predetermined shape and then vulcanized. It was vulcanized at 160 ° C. using a press to obtain a test piece.

Table 2 shows the measurement results of the obtained physical properties of vulcanized products.

From the results in Table 2, it is clear that in the composition of the present invention, the limitation of the extender oil for rubber, the limitation of the amount of carbon black, and the limitation of the type of rubber are necessary to achieve the effects of the present invention. is there.

Example 2 and Comparative Example 2 In the same manner as in Example 1, compositions within the scope of the present invention shown in Table 3 and compositions for comparison were obtained, and vulcanized physical properties were measured. The results are shown in Table 3.

From the results of Table 3, in the composition of the present invention, styrene-
It is clear that the styrene content of the butadiene copolymer, the vinyl bond content of the butadiene portion, the Mooney viscosity, the relaxation time, and the hardness of the vulcanizate are required to achieve the effects of the present invention.

Example 3 and Comparative Example 3 In the same manner as in Example 1, a composition having the composition shown in Table 4 was obtained.
The physical properties of the vulcanized product were measured.

As is clear from the results in Table 4, Examples 3-1 to 3-4 in which the specific styrene-butadiene copolymer was used within the scope of the present invention even when blended with other raw rubbers
The composition of will be a balance of each physical property,
The composition of Comparative Example 3-1 is poor in the balance between the wet skid resistance and the ice skid resistance because the specific styrene-butadiene copolymer is small.

Further, the composition of Comparative Example 3-2 using the carbon black whose iodine adsorption amount and dibutyl phthalate oil absorption amount of the carbon black are outside the scope of the present invention is a composition using the carbon black within the limits of the present invention. The tensile strength and wear resistance are inferior to those of the products.

<Effect> The vulcanized rubber composition of the present invention attaches particular importance to low temperature characteristics,
It is suitable for all-weather tires or studless tires, but can also be used for other applications by taking advantage of its characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a Mooney viscometer for measuring the relaxation time of polybutadiene rubber used in the composition of the present invention. 1 ... Driving part, 2 ... gear for gear shifting, 3 ... clutch, 4 ... worm gear, 5 ... dial gauge for torque detection, 6 ... die, 7 ... rotor, 8 ... air Cylinder, 9 ... Heater, 10 ... Temperature measuring element, 1
1 ... Temperature controller

Claims (1)

[Claims] 1. A vulcanized rubber composition obtained by vulcanizing a raw material rubber, a carbon black, an extender oil for rubber, a vulcanizing agent, and other compounding chemicals for rubber, the raw material being [I] a raw material. 30 to 100% by weight of rubber is obtained by (a) copolymerizing styrene and butadiene with a lithium-based catalyst, (b) styrene content of 5 to 30% by weight, and (c) butadiene part microstructure. The vinyl bond amount of the structure is 16
%, (D) Mooney viscosity (ML _{1 + 4} , 100 ° C.) is 60 to 15
0, (e) Relaxation time of 10 measured by Mooney viscometer
Is a branched styrene-butadiene copolymer, wherein [II] the other raw material rubber is natural rubber, polyisoprene rubber,
One or more selected from polybutadiene rubber and emulsion-polymerized styrene-butadiene copolymer rubber, and [III] as a extending oil for rubber, a viscosity specific gravity constant of 0.82.
˜0.92, containing 20 to 60 parts by weight per 100 parts by weight of raw rubber, an extender oil for naphthenic rubber having a naphthene carbon content of 35% or more by the Kurtz analysis method, and as [IV] carbon black, 80 mg of iodine adsorption
/ G or more, dibutyl phthalate oil absorption is 100 ml / 10
A carbon black of 0 g or more is contained in an amount of 50 to 95 parts by weight per 100 parts by weight of the raw material rubber, [V] the difference between the weight of the carbon black and the weight of the extending oil for rubber is 25 to 35 parts by weight, VI] Vulcanized rubber composition for tire tread having a JIS hardness of 65 or less measured at −10 ° C.