JPH06271706A - Tread rubber composition - Google Patents

Abstract

PURPOSE:To obtain a rubber composition for a tire tread which can give a vulcanizate having excellent wear resistance while retaining physical properties such as suitable hardness and modulus and needs to meet contradictory properties especially such as road surface grip, heat resistance and wear resistance. CONSTITUTION:This pneumatic tire is provided with a tread part which is made of a composition prepared by mixing 100 pts.wt. styrene/butadiene copolymer obtained by using at least an organolithium polyfunctional initiator and/or an orgaomonolithium initiator and a polyfunctional monomer, where the copolymer has a styrene binding content of 30-55wt.%, a glass transition temperature of -40 deg.C or above, a content of a component having a molecular weight (in terms of the molecular weight of polystyrene) of 1,000,000 or above of 40wt.% or above and a content of a component having a molecular weight (in terms of the molecular weight of polystyrene) of 250,000 or below of 12wt.% or below or a blend thereof containing 10 pts.wt. or above of the above-mentioned copolymer with 60-250 pts.wt. carbon black having a nitrogen absorption specific surface area (N2SA) of 105-250m<2>/g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition used for a tread rubber of a pneumatic tire which has stable high exercise performance (high grip performance) and is excellent in heat resistance and wear resistance.

[0002]

2. Description of the Related Art Recently, high dynamic performance has been required for pneumatic tires. In particular, grip performance is an important required characteristic, and a tire with higher acceleration and braking performance enables higher speed and more stable running. Conventionally, in order to obtain high exercise performance, especially high grip performance,
It is needless to say that the road surface gripping force (grip property) of the tread portion, which is one of the characteristics of high loss, needs to be high, and for this purpose, the tread member is being studied for improvement. As one of the methods, an approach by improving the tread pattern is used. That is, in this method, the groove of the pattern engraved on the tread
By making the tread deeper, the tread portion that comes into direct contact with the road surface can be easily deformed against the pressure received from the road surface, and the ability to convert the pressure from the road surface into heat energy inside the tread, that is, absorb the pressure from the road surface to some extent The ability is increased, and this improves the road grip of the tread.

However, in this method, on the other hand, since the rubber is easily deformed, the amount of abrasion of the tread portion is increased, and there is a problem that sufficient abrasion resistance cannot be obtained.

In order to obtain high kinetic performance, especially high grip performance, a styrene-butadiene copolymer rubber with a high styrene content is selected as the rubber component, that is, a polymer, or a softening agent and carbon black are highly filled. High exercise performance (high grip performance) was obtained by selecting a blending system, selecting a carbon black having a small particle size (having a large nitrogen specific surface area N ₂ SA), or a combination thereof. However, in general, a rubber composition containing a styrene-butadiene copolymer rubber having a high styrene content has a high grip property, but has a high glass transition temperature (Tg), so that the loss coefficient (tan δ) has a strong temperature dependence. When the air temperature and the road surface temperature are high, the high exercise performance is poor, and the wear resistance is poor.

On the other hand, it contains a styrene-butadiene copolymer rubber having a high styrene content and has a small particle size (nitrogen specific surface area).
In N large ₂ SA) highly filled formulation system of the carbon black, there is a problem that the heat resistance is deteriorated dynamics than blow chunk-out, etc. of the tread is significantly reduced by exothermic compounded rubber is increased significantly . In addition, in a system containing a high amount of a softening agent, there is a problem that the wear appearance of the tread is deteriorated due to the decrease in the strength of the compounded rubber, and the high exercise performance is significantly decreased.

Conventionally, in order to achieve both high exercise performance and heat resistance and wear resistance as described above, JP-A-4-277537 and Japanese Patent Application No.
-237008 discloses a method of using a copolymer having a polystyrene reduced weight average molecular weight of 1,000,000 or more. However, this method has been pointed out to have a problem in that even if the polystyrene-converted weight average molecular weight is used, it is not possible to achieve sufficient compatibility due to its molecular weight distribution.

[0007]

As described above, the rubber tread, the heat resistance, and the wear resistance of the tire tread, which are known so far, are said to be damaged if one of them is improved. Related, and it was extremely difficult to improve all performance at the same time. Therefore, the present invention has excellent heat resistance and wear resistance in a state where the vulcanizate has appropriate physical properties such as hardness and modulus, and is particularly contradictory to road graspability, heat resistance, and wear resistance. An object of the present invention is to provide a tread rubber composition that can be used for a pneumatic tire that requires various properties.

[0008]

To achieve the above object, the present invention provides a styrene-butadiene copolymerization obtained by using at least an organolithium polyfunctional initiator and / or an organomonolithium initiator and a polyfunctional monomer. A) a styrene bond content of 30 to 55% by weight b) a glass transition temperature of −40 ° C. or higher c) a polystyrene conversion molecular weight of 1,000,000 or higher
The nitrogen adsorption specific surface area (N ₂ SA) is 105 per 100 parts by weight of a rubber component containing a copolymer containing not less than 12% by weight and having a polystyrene-converted molecular weight of not less than 250,000 and not more than 12% by weight. ~
Add 60 to 250 parts by weight of 250 m ² / g of carbon black.

The present invention is particularly characterized in that a high molecular weight copolymer (A) having a specific microstructure and a specific molecular weight distribution, which is polymerized using a specific initiator, and a specific nitrogen specific surface area are used. By using in combination with the carbon black (B) having, for example, a rubber composition using an ordinary copolymer rubber and carbon black is used to improve the road surface gripping force as compared with a pneumatic tire used for a tread, and It is possible to achieve a marked improvement in heat resistance and wear resistance.

The styrene-butadiene copolymer used in the present invention is characterized in that it is copolymerized with an organolithium polyfunctional initiator, or is polymerized with at least an organomonolithium initiator and a polyfunctional monomer. Hold.

In anionic polymerization using an organolithium as an initiator, in order to obtain an ultra-high molecular weight copolymer, after completion of the polymerization, a compound having two or more halogen atoms is reacted with the active terminal to increase the molecular weight. You can jump.

Furthermore, when an organolithium polyfunctional initiator or an organomonolithium initiator and a polyfunctional monomer are used as in the present invention, the number of active terminals per polymer chain after the polymerization is increased, By the coupling reaction, the jump of the molecular weight is further increased and the molecular weight is increased. On the other hand, when the coupling agent is not used, a polymer having the same molecular weight as that at the end of the polymerization can be obtained.

Styrene-butadiene copolymerization is carried out by using an aliphatic hydrocarbon such as n-hexane or n-heptane, an aromatic hydrocarbon such as toluene or benzene, or cyclohexane as a solvent under a specific organolithium initiator. To do. Tetramethylene-
1,4-dilithium, hexamethylene-1,6-dilithium, 1,3-dilithiobenzene, 1,4-dilithiobenzene, octamethylene-1,8-dilithium, 1,4
-Organolithium polyfunctional initiators such as dilithiocyclohexane or these and organomonolithium initiators can be used in combination. N-butyl lithium, sec
It can also be obtained by using an organic monolithium initiator such as -butyllithium and adding a polyfunctional monomer such as divinylbenzene or diisopropenylbenzene before or during the polymerization. A polar compound such as a tertiary amine compound or an ether compound is preferably used as a styrene randomizer in the styrene-butazinine copolymer during polymerization.

After completion of the polymerization, a compound represented by the following general formula: SiR _p X _q (where X is a halogen atom which is a chlorine atom, a bromine atom or an iodine atom, R is an alkyl group, an alkenyl group or a cycloalkyl group) , A substituent selected from the group consisting of aryl groups, p is an integer of 0 to 2, q is an integer of 2 to 4, and p + q = 4.
Have a relationship. ) May be used for coupling, in which case a higher molecular weight component is obtained. The silane compound represented by the above general formula, tetrachlorosilane, tetrabromosilane, methyltrichlorosilane, butyltrichlorosilane, octyltrichlorosilane, dimethyldichlorosilane, dimethyldibromosilane, diethyldichlorosilane, dibutyldichlorosilane, dibutyldibromosilane, Dioctyldichlorosilane, diphenyldichlorosilane, diallyldichlorosilane, phenyltrichlorosilane, phenyltribromosilane and the like are used.

Styrene of the tread rubber composition of the present invention
The styrene bond content of the butadiene copolymer is 30 to 55% by weight, preferably 30 to 45% by weight. If the styrene bond content is less than 30% by weight, the hysteresis loss is small and the grip is poor, while if it exceeds 55% by weight, the blocky chain of styrene increases and the temperature dependence of the elastic modulus in the operating temperature range is large and stable. No exercise performance is obtained and wear resistance is poor.

The glass transition temperature of the styrene-butadiene copolymer is -40 ° C or higher. If it is less than -40 ° C, the hysteresis loss is small and the grip performance is poor, and the wet performance is poor.

Further, the ratio of the polystyrene reduced molecular weight of 1,000,000 or more of the styrene-butadiene copolymer is 40% by weight or more, preferably 50% or more, and the polystyrene reduced molecular weight of 250,000 or less is 12% by weight or less, preferably 6%. % Or less is required. Polystyrene equivalent molecular weight 1,00
If the proportion of 000 or more is less than 40% by weight, or the proportion of the polystyrene-converted molecular weight of 250,000 or less exceeds 12% by weight, the fracture properties are poor and the heat resistance and wear resistance are deteriorated. The molecular weight distribution of the copolymer of the present invention has a ratio of polystyrene-converted molecular weight of 1,000,000 or more within a manufacturable range, the higher the better, and the polystyrene-converted molecular weight is 250,000.
The following ratio, the lower the better, the workability at the time of copolymer production, and, considering the productivity, the ratio of polystyrene equivalent molecular weight of 1,000,000 or more is 40% by weight or more,
And the ratio of polystyrene-reduced molecular weight of 250,000 or less is 12
It is preferably less than or equal to weight%.

In the present invention, 60 parts of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 105 to 250 m ² / g is used per 100 parts by weight of a rubber component containing the above copolymer alone or 10 parts by weight or more.
Add 250 parts by weight. If the amount of the copolymer is less than 10 parts by weight, heat resistance and abrasion resistance are poor, which is not preferable. If the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is less than 105 m ² / g, the grip property is poor, and if it exceeds 250 m ² / g, the heat resistance is unfavorable.
On the other hand, if the blending number is less than 60 parts by weight, not only the reinforcing property is insufficient and the abrasion resistance is poor, but also the tan δ is not large and the grip property cannot be obtained. On the other hand, if it exceeds 250 parts by weight, the kneading workability is remarkably inferior and the abrasion resistance and the tensile strength are remarkably lowered.

30 to 150 parts by weight of the extender oil may be pre-extended with 100 parts by weight of the copolymer for obtaining the rubber composition of the tire tread of the present invention to further improve wear resistance. Can be achieved. If it exceeds 150 parts by weight, the processability during copolymer production cannot be obtained, and if it is less than 30 parts by weight, the effect of abrasion resistance is small. Aromatic oil is a typical extender oil, and naphthenic oil and paraffinic oil are also used.

The rubber composition of the present invention includes the above copolymer,
In addition to carbon black, compounding agents usually used in the rubber industry, for example, antioxidants, vulcanization accelerators, vulcanizing agents, extender oils and the like can be appropriately compounded.

[0021]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded. Copolymers A to L used in Examples and Comparative Examples were obtained by the following method, and the analysis results are shown in Table 1.

Sample A A 40 liter autoclave was charged with 18 liters of cyclohexane, 2.7 kg of butadiene and 1.3 kg of styrene, and after adding 200 g of tetrahydrofuran as a randomizer,
The polymerization temperature was adjusted to 70 ° C. so that the content of vinyl bond and the content of styrene having a predetermined glass transition temperature were adjusted, and 48 mmol of n-butyllithium was added to carry out polymerization. Then, 0.5 part by weight of di-tert-butyl-p-cresol and 60 parts by weight of aromatic oil were added to 100 parts by weight of the polymer, and the solvent was removed and dried by a conventional method.

Sample B Prepared in the same manner as Sample A except that 48 mmol of tetramethylene-1,4-dilithium was added instead of 48 mmol of n-butyllithium.

Sample C Prepared in the same manner as Sample A except that 36 mmol of tetramethylene-1,4-dilithium was added instead of 48 mmol of n-butyllithium.

Sample D was prepared in the same manner as in Sample B except that after the polymerization was completed, 24 mmol of dimethyldichlorosilane was used for coupling.

Sample E A sample C was prepared in the same manner as in sample C except that 24 mmol of dimethyldichlorosilane was coupled after completion of the polymerization.

Sample F was prepared in the same manner as Sample D except that 24 mmol of tetramethylene-1,4-dilithium was added instead of 48 mmol of tetramethylene-1,4-dilithium.

Samples G and H Samples G and H were prepared in the same manner as in Sample F except that the amount of styrene charged was changed so that the content of styrene bond became the value shown in Table 1.

Sample I After the polymerization was completed, a sample was prepared in the same manner as Sample C except that 25 parts by weight of aromatic oil was added.

Sample J A sample D was prepared in the same manner as in Sample D except that 54 mmol of tetramethylene-1,4-dilithium was added in place of 48 mmol of tetramethylene-1,4-dilitum.

Sample K was prepared in the same manner as Sample A except that after the polymerization was completed, 24 mmol of dimethyldichlorosilane was coupled.

Sample L n-Butyllithium 48 mmol, divinylbenzene 2.
It was prepared in the same manner as Sample A except that 7 g and 24 mmol of dimethylchlorosilane were used.

Table 1 shows the microstructure and molecular weight distribution of the polymer obtained. Using the carbon black shown in Table 2, a rubber composition was prepared with the compounding composition shown in Table 3 (the compounding amount is parts by weight). Further, tire sizes including a tread made using each rubber composition shown in Table 3, front 20
Tires of 5 / 515-13 and rear 225 / 515-13 were made and mounted respectively, and the difference in exercise performance and the difference in appearance due to heat and wear were measured by the following method, and the obtained results are also shown in Table 3.

Exercise performance A lap is a control tire (comparative example), in which the circuit is made up of 4.41 km per lap, and the circuit is made 20 laps at the maximum speed that can be safely driven, and the time difference between the first lap time and the lap time of the 20th lap is set. The time difference of (using the rubber composition of No. 1) is 100 and is displayed as an index. Greater than 100 means that there is no time difference and high exercise performance, and less than 100 means that there is a large time difference and poor athletic performance.

Appearance of tread The visual appearance of each of the tires after running on the circuit was set to 3 for the overall appearance of the tread of the control tire, and the larger the number between 1 and 5, the better the appearance.

In the present invention, various measurements are based on the following. The styrene content was measured from a calibration curve by infrared method based on the absorption of a phenyl group at 699 cm ^-1 . The glass transition temperature was measured at a temperature rising rate of 10 ° C / min using DSC200 manufactured by Seiko Instruments Inc. The molecular weight was measured by contacting two GMHX columns with HLC8020 (trade name) manufactured by Tosoh Corporation by GPC analysis, and determining the polystyrene-equivalent weight average molecular weight. Nitrogen adsorption specific surface area of carbon black
(N ₂ SA) was measured according to ASTM D3037.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

Here, Examples 1 to 6 use an organolithium polyfunctional initiator, and Example 7 uses an organomonolithium initiator and a polyfunctional monomer.

As a result, the pneumatic tire using the rubber composition according to the present invention as the tread rubber has high kinetic performance, and moreover, the change in tread appearance due to heat and abrasion is excellent as compared with the comparative example. I understood it.

[0042]

EFFECTS OF THE INVENTION By using the tread rubber composition of the present invention, it is possible to realize a pneumatic tire having an excellent effect that heat resistance and wear resistance are remarkably improved and stable and high exercise performance is obtained.

Claims (1)

[Claims] 1. A styrene-butadiene copolymer obtained by using at least an organolithium polyfunctional initiator and / or an organomonolithium initiator and a polyfunctional monomer, wherein a) the styrene bond content is 30 to 55% by weight. b) Glass transition temperature of -40 ° C or higher c) Ratio of polystyrene-equivalent molecular weight of 1,000,000 or higher is 40
The nitrogen adsorption specific surface area (N ₂ SA) is 105 per 100 parts by weight of a rubber component containing a copolymer containing not less than 12% by weight and having a polystyrene-converted molecular weight of not less than 250,000 and not more than 12% by weight. ~
A tread rubber composition comprising 60 to 250 parts by weight of 250 m ² / g of carbon black.