JPH04277537A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To provide a pneumatic tire having a tire tread which in the form of a vulcanizate, has physical properties such as suitable hardness and modulus and excels in abrasion resistance and road surface grip. CONSTITUTION:100 pts.wt. blend rubber comprising a styrene/butadiene copolymer rubber (A) obtained by using at least an organolithium polyfunctional initiator or an organolithium initiator and a polyfunctional monomer and having a weight-average molecular weight (in terms of polystyrene) of 1000000 or above and a low-molecular weight styrene/butadiene copolymer rubber (B) obtained by using an organolithium initiator and having a weight-average molecular weight (in terms of polystyrene) of 2000-50000, having a weight ratio of the copolymer rubber (A) to the copolymer rubber (B) of 100/(20-100) and further containing 100 pts.wt. or 10 pts.wt. copolymer (A) is mixed with 60-250 pts.wt. carbon black of a nitrogen absorption specific surface area of 90-250m<2>/g.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides stable and high exercise performance (
The present invention relates to a pneumatic tire that has high grip performance and excellent wear resistance.

0002

2. Description of the Related Art Recently, pneumatic tires have been required to have high maneuverability. In particular, grip performance is an important required characteristic, and tires with higher acceleration and braking performance enable faster and more stable driving. Conventionally, in order to obtain high exercise performance, especially high grip performance,
It is necessary for the tread portion to have high road surface grip (grip), which is one characteristic of high loss, and it goes without saying that improvements to tread members are being studied to achieve this. One approach is to improve the tread pattern. In other words, in this method, by deepening the grooves in the pattern carved into the tread, the tread portion that directly touches the road surface is easily deformed in response to the pressure received from the tread surface. This increases the ability of the tread to convert it into thermal energy internally, that is, the ability to absorb some amount of pressure from the road surface, thereby improving the tread's ability to grip the road surface.

However, this method has the problem that, on the other hand, it facilitates the deformation of the rubber, which increases the amount of wear on the tread portion, making it impossible to obtain sufficient wear resistance. Conventionally, in order to obtain high athletic performance, especially high grip performance, a styrene-butadiene copolymer rubber with a high styrene content was selected as the rubber component, i.e., a polymer, or a compound system with a high content of softener and carbon black was selected. Or the particle size is small (nitrogen specific surface area N2 SA
High maneuverability (high grip performance) was obtained by selecting carbon black (with a large size) or by combining them. However, they generally include high styrene content styrene-butadiene copolymer rubbers. Although rubber compositions provide high grip properties, their loss coefficients (tan δ) are highly temperature dependent due to their high glass transition temperatures (Tg), and their high maneuverability is poor when air and road temperatures are high. , and has poor abrasion resistance. On the other hand, in systems in which the softener and carbon black are highly filled, there is a problem in that the strength of the compounded rubber is reduced, which deteriorates the worn appearance of the tread and significantly reduces high performance.

0004

[Problems to be Solved by the Invention] As described above, even if conventional rubber materials are used to improve tire tread grip on the road surface and wear resistance, if one is improved, the other is impaired. There is a trade-off between the two, and it was considered extremely difficult to improve both. The present invention has been made against the background of the problems of the prior art, and the vulcanized product has excellent wear resistance while maintaining appropriate physical properties such as hardness and modulus, and has particularly good road grip. An object of the present invention is to provide a pneumatic tire having a tire tread that requires the antinomic property of wear resistance.

[0005]

[Means for Solving the Problems] The above object is to provide a pneumatic tire having a tread portion, a sidewall portion, and a bead portion, using at least an organolithium polyfunctional initiator or an organomonolithium initiator and a polyfunctional monomer. The weight average molecular weight obtained in terms of polystyrene is 1,00
0,000 or more styrene-butadiene copolymer rubber (
A) and a low molecular weight styrene-butadiene copolymer rubber (B) having a polystyrene equivalent weight average molecular weight within the range of 2,000 to 50,000 obtained using an organolithium initiator, and the copolymer rubber (A) and The ratio of the copolymer (B) is 20 to 120 parts by weight to 100 parts by weight of the copolymer rubber (A), and
60 to 250 parts by weight of carbon black having a nitrogen adsorption specific surface area (N SA) of 90 to 250 m2/g is blended to 100 parts by weight of copolymer (A) or 100 parts by weight of a blend rubber containing 10 parts by weight or more, This can be achieved by a pneumatic tire with high maneuverability characterized by being constructed by applying a rubber composition obtained by vulcanization to tread rubber.

A particular feature of the present invention is that the ultra-high molecular weight copolymer (A) is polymerized using a specific initiator.
), a specific low molecular weight copolymer (B), and carbon black with a specific nitrogen adsorption specific surface area. Compared to the pneumatic tires used, it is possible to improve road surface grip and achieve a significant improvement in wear resistance.

The styrene-butadiene copolymer (A) used in the present invention is copolymerized using an organolithium polyfunctional initiator, or at least an organomonolithium initiator and a polyfunctional monomer. The copolymer (B) can be obtained by copolymerization using an organic monolithium initiator. In anionic polymerization using organolithium as an initiator, after the polymerization is completed, the active end is reacted with a compound having two or more halogen atoms, thereby causing a jump in molecular weight. Furthermore, as in the present invention, organolithium polyfunctional initiators or organic-
When a polyfunctional monomer is used as a monolithium initiator, the number of active terminals per single chain of polymer increases after polymerization, and the molecular weight jump further increases due to the coupling reaction, resulting in higher molecular weight. . On the other hand, if no coupling agent is used, only a polymer having the same molecular weight as at the end of polymerization can be obtained.

Copolymerization of the copolymer (A) is carried out using a specific organolithium initiator using an aliphatic hydrocarbon such as n-hexane or n-heptane, an aromatic hydrocarbon such as toluene or benzene, or a cyclohexane as a solvent. Do it at the bottom. As an organolithium initiator, tetramethylene-1,4-
Dilithium, hexamethylene-1,6-dilithium, 1
, 3-dilithiobenzene, 1,4-dilithiobenzene,
Organolithium polyfunctional initiators such as octamethylene-1,8-dilithium and 1,4-dilithiocyclohexane, or a combination of these and an organomonolithium initiator can be used. It can also be obtained by a method in which an organic monolithium initiator such as n-butyllithium or sec-butyllithium is used and a polyfunctional monomer such as divinylbenzene or diisopropenylbenzene is added before or during polymerization. In the styrene-butadiene copolymer, it is preferable to use a polar compound such as a tertiary amine compound or an ether compound as a randomizing agent for styrene during polymerization. For copolymer (B), the same solvent is used and an organic monolithium initiator is used. As the organic monolithium initiator, n-butyllithium, sec-
Butyllithium and the like can be used. Further, the same styrene randomizing agent as described above can be suitably used.

Regarding the copolymer (A), after the polymerization is completed, a compound represented by the following general formula, SiRp
(wherein, Integer, q is an integer from 2 to 4, p+q=4
There is a relationship between ) may be used for coupling, in which case a higher molecular weight component can be obtained and more preferable wear resistance can be obtained. Examples of the silane compound represented by the above general formula include tetrachlorosilane, tetrabromosilane, methyltrichlorosilane, butyltrichlorosilane, octyltrichlorosilane, dimethyldichlorosilane, dimethyldibromosilane, diethyldichlorosilane,
Dibutyldichlorosilane, dibutyldibromosilane, dioctyldichlorosilane, diphenyldichlorosilane,
diallyldichlorosilane, phenyltrichlorosilane,
Phenyltribromosilane and the like are used.

The weight average molecular weight of the styrene-butadiene copolymer (A) used in the tread of the pneumatic tire of the present invention in terms of polystyrene must be 1,000,000 or more, preferably 1,200,000 or more. If the weight average molecular weight in terms of polystyrene is less than 1,000,000, desired wear resistance cannot be obtained. In addition, the molecular weight of the copolymer of the present invention is preferably higher as long as it is within the range that can be manufactured, and there should be no particular upper limit, but when considering workability and productivity during the production of the copolymer, the weight average molecular weight in terms of polystyrene is is preferably 5,000,000 or less.

The weight average molecular weight of the styrene-butadiene copolymer (B) used in the present invention in terms of polystyrene is 2.
Within the range of 000 to 50,000, preferably 5,00
0 to 30,000. If it is less than 2,000, the desired effect of improving abrasion resistance and grip is small, and if it exceeds 50,000, it has excellent abrasion resistance but poor grip properties.Tread rubber containing a copolymer (B) with a molecular weight within these limits. Only the compositions satisfy both the desired abrasion resistance and grip properties.

In the present invention, the ratio of the copolymer rubber (A) to the copolymer rubber (B) is 20 to 120 parts by weight of the copolymer (B) to 100 parts by weight of the copolymer rubber (A). Part is necessary. At the end of polymerization, copolymers (A) and (B) are preferably blended in a solution state, dried in a conventional manner, and taken out. If the amount of copolymer (B) is less than 20 parts by weight per 100 parts by weight of copolymer rubber (A), the improvement effect on abrasion resistance and grip properties will be small, while if it exceeds 120 parts by weight, the grip properties will be large. However, the wear resistance is poor, and at the same time, the workability is significantly reduced, making it difficult to manufacture tires.

In the present invention, the nitrogen adsorption specific surface area (N2 SA
) of 90 to 250 m2 /g of carbon black 60
~250 parts by weight is blended. If the nitrogen adsorption specific surface area (N2 SA) of carbon black is less than 90 m2/g, the grip property will be poor, and if it exceeds 250 m2/g, the heat resistance will be unfavorable. If the number of parts is less than 60 parts by weight, not only will the reinforcing properties be insufficient and the abrasion resistance will be poor, but the tan δ will also not be large and the grip will not be good. On the other hand, if it exceeds 250 parts by weight, the kneading workability will be extremely poor and the abrasion resistance and tensile strength will also be significantly reduced.

[0014] The tire of the present invention comprises the above copolymer (A),
(B) is characterized in that a rubber composition containing a predetermined amount of carbon black is used in the tread rubber;
In addition to the copolymers (A) and (B) and carbon black, the rubber composition contains compounding agents commonly used in the rubber industry, such as anti-aging agents, vulcanization accelerators, and vulcanizing agents. They can be blended as appropriate.

[0015]

EXAMPLES The present invention will be explained below with reference to Examples and Comparative Examples, but the present invention is not limited by these Examples unless the gist thereof is exceeded. Polymers (A) and (B) used in Examples and Comparative Examples were obtained by the following method. Table 1 shows the analysis results for polymer (A).

Production of copolymer rubber (A) (a) Production of copolymer rubber (A-1) A 40-liter autoclave was charged with 16 liters of cyclohexane, 2.7 kg of butadiene, and 1.3 kg of styrene, and 200 g of tetrahydrofuran was added. The polymerization temperature was adjusted to 70° C. so as to have predetermined vinyl bond content and bound styrene content, and 48 mmol of tetramethylene-1,4-dilithium was added to perform polymerization. After the polymerization was completed, coupling was performed with 24 mmol of dimethyldichlorosilane to obtain a polymer. Next, 0.5 parts by weight of di-tert-butyl-p-cresol was added to 100 parts by weight of the polymer. (b) Production of copolymer rubber (A-2) Same as A-1 except that 24 mmol of tetramethylene-1,4-dilithium was added. (c) Production of copolymer rubber (A-3) Same as A-2 except that coupling with dimethyldichlorotin is performed after completion of polymerization. (d) Production of copolymer rubber (A-4) Table 1 shows the characteristic values of these copolymers, which were the same as A-2 except that the amounts of styrene and tetrahydrofuran were changed.

[Table 1]

Production of copolymer rubber (B) Using a reactor with a capacity of 40 liters, polymerization was carried out in a solvent of 16 liters of cyclohexane with varying amounts of styrene, 1,3-butadiene, and n-butyllithium to obtain various molecular weights and A copolymer with bound styrene content was obtained. Table 2 shows the characteristic values of these copolymers.
Shown below.

[Table 2]

[0018] After mixing the solution of copolymer rubber (A) (A-1 to A-4) and copolymer (B) (B-1 to B-5) in the predetermined amounts shown in Table 3, The solvent was dried to obtain various copolymers (C-1 to C-9). Using the carbon black shown in Table 4 as the obtained polymer, a rubber composition was made with the compounding composition shown in Table 5 (the amount is in parts by weight). Furthermore, the tire sizes with treads made using each rubber composition shown in Table 5 are: front 205/515-13, rear 22.
5/515-13 tires were made, each was installed, and the driving performance and wear appearance were measured using the following methods. Table 5 shows the results.
Shown below.

[Table 3]

[Table 4]

[Table 5]

Maneuverability: Run 20 laps around a circuit consisting of 4.41 km per lap, and calculate the time difference between the first lap time and the 20th lap time as the time of the control tire (using the rubber composition of Comparative Example 2). Expressed as an index with the difference as 100. 100
A value larger than 100 means that there is no time difference and high athletic performance, and a value smaller than 100 means that there is a large time difference and poor athletic performance.

[0020] A 5-point tread wear appearance system is used, and the tread wear appearance of the control tire is set as 3, with higher numbers being better and 5 being best, higher numbers being better and 5 being best, and smaller numbers being better. is inferior to 1
was considered defective.

[0021] In the present invention, various measurements were made in accordance with the following. The cyclostructure (vinyl content) of the butadiene moiety was determined by an infrared method (Morello method). The styrene content is
Measured from a calibration curve using an infrared method based on the absorption of phenyl groups at 699 cm-1. The molecular weight was determined by GPC analysis using HLC8020 (trade name) manufactured by Tosoh Corporation.
The weight average molecular weight in terms of polystyrene was determined by measuring by connecting two columns. The nitrogen adsorption specific surface area (N2 SA) of carbon black was measured in accordance with ASTM D3037.

[0022]

Effects of the Invention As shown in the Examples and Comparative Examples above, the pneumatic tire with high maneuverability of the present invention comprises an ultra-high molecular weight copolymer having a specific molecular weight polymerized with a specific initiator, As is clear from Table 5, by using a rubber composition consisting of a low molecular weight polymer having a specific molecular weight and carbon black having a specific nitrogen adsorption specific surface area as the tread rubber, the wear appearance is significantly improved and a stable high The excellent effect of having athletic performance can be obtained.

Claims (2)

[Claims] Claim 1: A pneumatic tire having a tread portion, which has a polystyrene equivalent weight average molecular weight of 1,000,00 obtained using at least an organolithium polyfunctional initiator or an organomonolithium initiator and a polyfunctional monomer.
0 or more styrene-butadiene copolymer rubber (A) and a low molecular weight styrene-butadiene copolymer rubber (B) having a polystyrene equivalent weight average molecular weight within the range of 2,000 to 50,000, obtained using an organolithium initiator. and the ratio of the copolymer rubber (A) to the copolymer (B) is 20 to 120 parts by weight of the copolymer (B) per 100 parts by weight of the copolymer rubber (A), and , Nitrogen adsorption specific surface area (N2
A pneumatic tire characterized in that a rubber composition containing 60 to 250 parts by weight of carbon black having an SA) of 90 to 250 m2/g is applied to the tread rubber. 2. The copolymer rubber (A) is a compound of the following general formula: SiRp 2. The copolymer anion is coupled by a substituent selected from the group, p is an integer of 0 to 2, q is an integer of 2 to 4, and p+q=4. pneumatic tires.