JP3054238B2 - Pneumatic tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, particularly a pneumatic tire having significantly improved driving, braking and maneuverability on icy and snowy roads without impairing the steering performance, durability and wear resistance in summer. Regarding tires.

[0002]

2. Description of the Related Art Conventional pneumatic tires often use spike tires in which spike pins are driven into a tread surface in order to ensure driving, braking, and maneuverability when traveling on icy and snowy road surfaces. However, such a tire generates dust due to wear of the spike pin itself or wear and tear of the road, and is a major social problem. In order to cope with this, regulations on the amount of spike pins projecting and the number of spike pins, materials of spike pins, and the like have been studied, but they have not been a fundamental solution to the social problem.

On the other hand, in recent years, studless tires having driving, braking, and maneuverability on icy and snowy road surfaces without using spikes or chains have been studied and are rapidly spreading, but still have sufficient snow and snow compared to spiked tires. It is difficult to say that the performance is excellent. Conventionally, for the tread rubber of studless tires, a compound using a polymer having a low glass transition point has been used in order to ensure rubber elasticity at low temperatures. However, depending on the hysteresis characteristics of such a polymer, there is a problem that even if a certain degree of performance is exhibited in an ice-snow temperature range, braking performance and maneuverability on wet or dry road surfaces are not sufficient.

Further, Japanese Patent Application Laid-Open Nos. 55-135149 and 58-199
No. 203, Japanese Unexamined Patent Publication No. 60-137945, etc., a method of similarly improving low-temperature characteristics by using a rubber composition in which a large amount of a softening agent or a plasticizer is blended with tread rubber is also known. However, these methods have many problems such as a decrease in wear resistance when running on a general road and occurrence of separation of tread rubber, although the performance on ice and snow is improved.

Further, in recent years, there has been a method in which a tread rubber is foamed by an appropriate method to generate closed cells (Japanese Patent Laid-Open No. Sho 63/63).
-89547). That is, since the ice surface of the tread rubber thus obtained is covered with a number of pores, a water removal effect on the ice surface and an edge effect of scraping ice accompanying micro-movement of the pores develop on ice. Develop high friction properties. In addition, there is a method in which various high-hardness materials are mixed into tread rubber, and the friction effect of the tread rubber on ice is increased by using a scratching effect on the ice surface in the high-hardness material (Japanese Patent Publication No. No. 31732, JP-A-51-147803
No., JP-B-56-52057). However, when foamed rubber is used for the tread, it cannot always be said that the tire durability such as abrasion resistance is at a satisfactory level.
In addition, when a high-hardness material having a high scratching effect is mixed into the matrix rubber of the tread, the effect of improving the performance on ice near 0 ° C with a large amount of water is small, and the high-hardness material is present as a foreign material having no affinity for the rubber. As a result, the friction resistance and fracture characteristics were significantly reduced.

As described above, in any of the conventional techniques, the performance on ice and snow in a relatively low temperature range of -5 ° C. or less (so-called dry-on-ice) and the wet state near 0 ° C. It has been extremely difficult to obtain a sufficient coefficient of friction and to improve driveability, braking performance and maneuverability in general while achieving compatibility with the performance on ice and snow in wet-on-ice.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned difficulties and to improve the driving performance, braking performance and maneuverability on icy and snowy roads without impairing the driving performance and durability in summer. It is an object of the present invention to provide a tire which has improved driving performance, braking performance and maneuverability on the icy and snowy road surface in a wet state as described above, without reducing wear resistance. .

[0008]

Means for Solving the Problems The present inventors preliminarily applied an internal cross-linking structure to a vinyl aromatic hydrocarbon conjugated diene-based thermoplastic elastomer and filled it into a predetermined foamed rubber tread rubber. At this time, this forms domains without melting and flowing, and improves the coefficient of friction of the tread foamed rubber on ice and snow, and also causes the thermoplastic elastomer to undergo a co-crosslinking reaction with the matrix foamed rubber. It was confirmed that the tread rubber composition maintained the same abrasion resistance irrespective of the presence or absence of the elastomer, and completed the present invention.

That is, the present invention relates to a vinyl aromatic hydrocarbon conjugated diene having an average particle diameter of 1 to 500 μm, which is internally cross-linked until the rate of increase in tensile stress at 100% elongation falls within the range of 10 to 1000%. 3 to 100 parts by weight of a block type thermoplastic elastomer per 100 parts by weight of rubber, and 3
This is a pneumatic tire in which a foamed rubber having closed cells having a foaming rate of about 35% is disposed in a tread.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The internally crosslinked aromatic hydrocarbon conjugated diene block type thermoplastic elastomer used in the present invention is the same as the conventional sulfur crosslinked type aromatic peroxide conjugated diene block type thermoplastic elastomer. Any of various crosslinking systems such as a product crosslinking system and a radiation crosslinking system may be applied, and the crosslinking method and the crosslinking structure are not particularly limited.

The aromatic hydrocarbon conjugated diene block type thermoplastic elastomer to be subjected to the crosslinking reaction is a non-rubber polymer block segment mainly composed of an aromatic hydrocarbon conjugated diene (hereinafter referred to as a polyaromatic hydrocarbon conjugated diene block). ), Preferably at least one, and at least one rubber-like polymer block segment (hereinafter referred to as a rubber block). Such an aromatic hydrocarbon conjugated diene-based thermoplastic elastomer has, for example, a molecular structure having a polystyrene block at both ends and a rubber block in the middle, a structure in which only one polystyrene block and the other are rubber blocks, It has a structure in which there are three or more polystyrene ends and these are connected by a rubber block, and a structure in which a polystyrene block and a rubber block are further introduced alternately in the above structure. The rubber block may be a polyolefin-based elastomer block such as a polybutadiene block or a polyisoprene block, and is not particularly limited. Among them, styrene-butadiene-styrene (S-B −
An S) type block copolymer elastomer or a styrene-butadiene (SB) type block copolymer elastomer is preferred.

Methods for producing these aromatic hydrocarbon conjugated diene-based thermoplastic elastomers are well known, and are described, for example, in JP-A-60-243109 and JP-B-48-24.
No. 23 discloses an SBS type block copolymer elastomer using an organic Li compound catalyst, and Japanese Patent Publication No. 36-19286 discloses an SB type and SBS type block copolymer using a similar catalyst. The preparation of polymeric elastomers is described.

The required degree of internal crosslinking of the aromatic hydrocarbon conjugated diene block thermoplastic elastomer is determined by ASTM D
It can be known from the fact that the rate of increase in tensile stress at 100% elongation measured according to 638 falls within the range of 10 to 1000%. By subjecting the internal crosslinked styrene-based thermoplastic elastomer to this degree or more, when filled in the tread rubber, it can be dispersed as particles having an average domain diameter of 1 μm or more in the matrix. If the average domain diameter of the particles is less than 1 μm, the performance of the tire on ice and snow is not sufficient. However, when the internal crosslinking reaction is excessively performed, the average domain diameter becomes 500
In this case, the wear resistance of the tread using the foamed rubber is deteriorated, which is not preferable.

[0014] The internally crosslinked aromatic hydrocarbon conjugated diene block thermoplastic elastomer is preferably blended in an amount of 3 to 100 parts by weight, more preferably 5 to 40 parts by weight, based on 100 parts by weight of the foamed rubber component. More preferred. If the amount is less than 3 parts by weight, the effect of improving the driving, braking and maneuverability on ice and snow roads is small, and if it exceeds 100 parts by weight, the kneading workability of the rubber composition is reduced.

The rubber component includes natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, styrene-isoprene-butadiene terpolymer rubber, styrene-isoprene copolymer rubber, and isoprene-butadiene copolymer. Although a polymer rubber etc. can be mentioned, it is not particularly limited. Further, in addition to the diene rubber and the internally cross-linked aromatic hydrocarbon conjugated diene block thermoplastic elastomer, the composition disposed in the tread, other rubbers and compounding agents usually used in tread rubbers, for example, fillers Agents, anti-aging agents, vulcanizing agents,
Vulcanization accelerators may be included, and the type and amount of these are within the range usually used for tread rubber, and are not particularly limited.

In the present invention, the tread rubber is 3 to 35%
It is necessary to increase the microscopic water absorption and drainage effect by the pores and to exhibit excellent ice and snow performance in a state where the ice surface near 0 ° C. has a lot of molten water in the vicinity of 0 ° C. This is because closed cells are indispensable.
Foaming may be carried out by a foaming agent or by high-pressure gas mixing. If the foaming ratio is less than 3%, the foaming effect is not sufficient, while if it exceeds 35%, the tread rigidity is insufficient. As a result, the wear resistance is reduced and the groove bottom cracks are greatly generated.

[0017] Here, the foaming rate V _s of the foamed rubber is expressed by the following equation _{V s = {(ρ o -ρ} g) / (ρ 1 -ρ g) -1} × 100
(%) (1) where ρ ₁ is the density of the foamed rubber (g / cm ³ ), ρ _o is the density of the solid phase portion of the foamed rubber (g / cm ³ ), and ρ _g is the foamed rubber. Is the density (g / cm ³ ) of the gas part in the bubbles. The foamed rubber is composed of a solid phase portion and a cavity (closed cell) formed by the solid phase portion, that is, a gas portion in the air bubble. Since the density ρ _{g of the} gas part is extremely small, almost close to zero, and extremely small with respect to the density ρ _{1 of the} solid phase part, the equation (1) becomes
Equation _{V s = {(ρ o -ρ} 1) -1} × 100 (%)
... It is almost equivalent to (2).

Incidentally, in the pneumatic tire of the present invention,
The foamed rubber containing the above-mentioned aromatic hydrocarbon conjugated diene-based thermoplastic elastomer may be provided only in the cap portion of the tread portion having the cap-base structure.

[0019]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. Tests of the properties of the tread rubber and tire performance using test tires described below were performed by the following methods. (1) Average domain diameter of internally crosslinked aromatic hydrocarbon conjugated diene block type thermoplastic elastomer in the tread rubber Select 10 lots of samples from the sample and select the internal crosslinked aromatic hydrocarbon conjugated diene system within the visual field of the optical microscope. The diameter (calculated by (longest diameter + shortest diameter) / 2) of 20 domains of the block type thermoplastic elastomer is measured, the average domain diameter is calculated for each lot, and the average of the average domain diameter of 10 lots is further calculated. Calculated. (2) Coefficient of friction on ice The coefficient of friction of rubber on ice, especially the coefficient of friction on ice in a wet state near 0 ° C, is measured on ice with a surface temperature of -0.5 ° C (sample size: length 10 mm, width 10 mm, thickness 5 mm). ) Was brought into contact with ice and measured using a dynamic / static friction coefficient meter manufactured by Kyowa Interface Science Co., Ltd. The measurement conditions were a load of 2 kg / cm ² ,
The sliding speed was 10 mm / sec, the ambient temperature was -2 ° C, and the surface condition was similar to a mirror surface. (3) Ice braking performance Test tires, radial tires for passenger cars PSR (165 SR 13) were made, and after 50 km normal running as normal running,
Tested. (The same applies to the following abrasion tests.) Four test tires were mounted on a passenger car with a displacement of 1500 cc, and the braking distance was measured on ice at an outside temperature of -5 ° C. The index of the tire of Comparative Example 1 was set to 100 and indicated as an index. The larger the value, the better the braking performance. (4) Abrasion test Two test tires were mounted on a drive shaft of a passenger car having a displacement of 1500 cc, and the test tires were driven at a predetermined speed on a concrete road surface of a test course. The amount of change in the groove depth was measured, and the index of the tire of Comparative Example 1 was set as 100. The larger the value, the better the wear resistance performance.

Examples 1 to 5 and Comparative Examples 1 to 4 The SB type aromatic hydrocarbon conjugated diene block thermoplastic elastomer was subjected to an internal crosslinking reaction at the blending content or radiation dose shown in Table 1 to obtain sulfur. A crosslinked or radiation crosslinked structure was formed. For A and B, pressurized at 145 ° C
Pre-crosslinking was performed for 30 minutes.

[0021]

[Table 1]

Samples A to D were prepared by kneading with the composition shown in Table 1 and then vulcanizing under pressure at 145 ° C. for 40 minutes to introduce sulfur crosslinking. A rubber composition containing the above-mentioned internally crosslinked aromatic hydrocarbon conjugated diene-based thermoplastic elastomer and a foamed rubber composition not containing the same were prepared according to the formulation shown in Table 2 for comparison. The coefficient, average domain diameter, and expansion ratio were measured. In addition, the braking performance on ice and the abrasion resistance of a tire in which these rubber compositions were disposed on a tread of foamed rubber were measured. Table 2 shows the results.

[0023]

[Table 2]

As is apparent from Table 2, by performing internal crosslinking, the average domain diameter of the aromatic hydrocarbon conjugated diene block thermoplastic elastomer in the rubber composition is in the range of 1 to 500 μm, and foaming is carried out. The compositions of Examples 1 and 2 in which the ratio was 3 to 35% had improved abrasion resistance as compared with the ordinary foamed rubber tread shown in Comparative Example 1, and all of them had significantly improved braking performance on ice. I have.

On the other hand, as shown in Comparative Examples 2 to 6, when the aromatic hydrocarbon conjugated diene block thermoplastic elastomer or the expansion ratio does not satisfy the requirements of the present invention, the tire is braked on ice. It can be seen that both performance and wear resistance cannot be improved simultaneously.

[0026]

As is clear from the examples and comparative examples,
An average of 100 parts by weight of a matrix rubber mainly composed of foamed rubber having closed cells having a foaming ratio of 3 to 35%, and an internal crosslink was performed until the rate of increase in tensile stress at 100% elongation became 10% to 1000. A block of a vinyl aromatic hydrocarbon conjugated diene-based thermoplastic elastomer having a particle size of 1 to 500 μm
A pneumatic tire in which a rubber composition containing up to 100 parts by weight is disposed on a tread has excellent drivability, braking performance and maneuverability on ice and snowy road surfaces in wet and dry conditions without reducing wear resistance. Can be significantly improved.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-89547 (JP, A) JP-A-1-297303 (JP, A) JP-A-1-118542 (JP, A) JP-A-59-1985 4634 (JP, A) JP-A-2-24334 (JP, A) JP-A-3-103454 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 11/00 B60C 1 / 00 B60C 11/14

Claims (2)

(57) [Claims] 1. The rate of increase in tensile stress at 100% elongation is
It contains 3 to 100 parts by weight of a vinyl aromatic hydrocarbon conjugated diene block type thermoplastic elastomer having an average particle diameter of 1 to 500 μm, which is internally cross-linked to a range of 10 to 1000%, based on 100 parts by weight of rubber. A pneumatic tire, wherein a foamed rubber having closed cells having a foaming ratio of 3 to 35% is provided in a tread. 2. A pneumatic tire, wherein the rubber composition according to claim 1 is provided on a cap portion of a tread portion having a cap-base structure.