JPH0368899B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to tire tread rubber compositions, and particularly to tread rubber compositions for spikeless tires having excellent high friction properties on ice. Generally, the rubber composition constituting the tire tread portion hardens at low temperatures and loses its original flexibility, resulting in a decrease in road grip. In other words, the vehicle cannot grip the road surface on snow or ice, resulting in slipping. Also, the brakes do not work and the vehicle cannot be controlled using the steering wheel. Snow tires with spikes are used to compensate for this problem, but in recent years, snow tires with spikes have caused damage to the road surface and the resulting dust generation, floating, and even noise, which has become a social problem. There is an increasing demand for spikeless snow tires that have sufficient low-temperature characteristics. Conventionally, in order to prevent curing at low temperatures, (1) the use of polymers with low glass transition temperatures (Tg), (2) the use of large amounts of aromatic oils and naphthenic oils, (3) di-(2- Low-temperature plasticizers such as ethylhexyl) adipate (DOA), di-(2-ethylhexyl) phthalate (DOP), di-(2-ethylhexyl) azelate (DOZ), and di-(2-ethylhexyl) sebacate (DOS) are added to the rubber. It is known to add it to compositions. In order to prevent hardening at low temperatures and greatly improve the coefficient of friction on ice, the inventors filed a patent application No. 58-206699.
(Japanese Patent Application Laid-open No. 60-99145) proposed the use of α-olefin oligomers as low-temperature plasticizers. This treaded rubber composition exhibited a higher coefficient of friction on ice at -20°C than those using other plasticizers, oils, and softeners. By the way, when we talk about icy road surfaces, the icy temperature generally varies, and it is particularly important to note that the coefficient of friction of rubber on ice varies considerably depending on the difference in icy temperature. For example, when comparing BR (high-cis 1,4-polybutadiene rubber), which is the same diene-based synthetic rubber, and E-SBR (emulsion polymerized styrene-butadiene copolymer rubber containing 23.5% styrene), at freezing temperatures around -5°C, −
Although SBR has a larger coefficient of friction on ice, the relationship in magnitude between the coefficients of friction on ice is reversed around -12℃, and as the temperature decreases further, the coefficient of friction on ice of BR increases (E-SBR's coefficient of friction on ice increases). It is generally known that the coefficient of friction decreases. In this case, even if BR and E-SBR are used as a blend, no special combination effect can be obtained, and when BR and E-SBR are used alone at each temperature,
It is inferior to the higher ice friction coefficient. Additionally, the aforementioned methods of using large amounts of oil and conventional low-temperature plasticizers are somewhat effective in improving the coefficient of friction on ice at ice temperatures below around -20°C;
Almost no improvement effect was observed on the coefficient of friction on ice at around -5°C. The above-mentioned α-olefin oligomers are also natural rubber (NR), which is usually used in snow tire treads.
When used with BR and E-SBR, the coefficient of friction on ice at around -5°C was not high enough. In this way, when measuring the coefficient of friction on ice of various rubber compositions, the value of the coefficient of friction on ice changes as the ice temperature changes, and it is difficult to obtain a rubber composition with a high coefficient of friction on ice over a wide range of ice temperatures. It was extremely difficult. However, the actual ice temperature of frozen roads varies over a considerable range depending on the season and region. Therefore, there has been a strong desire to develop a tire tread rubber composition that has a high coefficient of friction on ice over the entire freezing temperature range in which spikeless tires are used. As a result of intensive research aimed at developing a treaded rubber composition that satisfies these demands, the present inventors discovered a solution-polymerized styrene-butadiene copolymer (S
-SBR) and α-olefin oligomer, it was discovered that a rubber composition that exhibits a high coefficient of friction on ice over the freezing temperature range from -5°C to -25°C, where spikeless tires are normally used, was discovered, and the present invention Reached. That is, the present invention has a glass transition temperature (Tg) of -
50 parts by weight or more of carbon black per 100 parts by weight of a rubber component containing at least 70% of solution polymerized styrene-butadiene copolymer at 60°C or less;
The present invention relates to a tire tread rubber composition containing 3 parts by weight or more of an α-olefin oligomer. In the present invention, the rubber component has a Tg of -60°C.
It is necessary to contain at least 70% of the following solution polymerized styrene-butadiene polymer (S-SBR). When Tg is higher than -60°C, hardening at low temperatures is large, and the coefficient of friction on ice at around -25°C decreases significantly. In addition, the amount of S-SBR in the rubber component is 70
If it is less than %, the effect of the combined use with the α-olefin oligomer will be reduced, and Iceμ will tend to decrease in the freezing temperature range of -5°C to -25°C. S-
As the SBR component, a single S-SBR may be used, or two or more types of S-SBR with Tg of -60℃ or less may be used.
A blend of SBR may also be used. As the rubber component other than the solution polymerized styrene-butadiene copolymer used in the present invention, one or more of natural rubber (NR) and/or synthetic rubber is used. Examples of synthetic rubber include polyisoprene rubber (IR), polybutadiene rubber (BR), emulsion polymerized styrene-butadiene rubber (E-SBR), isoprene-isobutylene rubber (IIR), modified products thereof, blends thereof, etc. Either can be used. In the present invention, carbon black is used in an amount of 50 parts or more based on 100 parts (by weight, hereinafter the same) of the rubber component.
Preferably it is 55 to 120 parts. If it is less than 50 parts, the abrasion resistance of the vulcanized rubber will be extremely poor, and if it exceeds 120 parts, the vulcanized rubber will generate a lot of heat, which is likely to cause separation. It is preferable to use carbon black with a large specific surface area, especially
It is preferable to use carbon black having a specific surface area (N ₂ SA) of 90 m ² /g or more as determined by the nitrogen adsorption method according to ASTMD3037 because it can improve the wear resistance of the tire surface. The α-olefin oligomer used in the present invention preferably has a pour point of -45 to -80°C, and has the chemical structure shown below.
Particularly preferred is a trimer of 1-decene. In the present invention, it is preferable to use 3 parts or more of the α-olefin oligomer, and if it is less than 3 parts, the effect of increasing the coefficient of friction on ice is small. The present invention is characterized in that the above-mentioned S-SBR and α-olefin oligomer are used simultaneously rather than separately. A method of using a conventional type of plasticizer in this polymer component, or a method of using a conventional type of polymer with this α-
It is also possible to increase Iceμ to a certain extent by changing the method of blending olefin oligomers.
However, by combining the polymer component of the present invention and the α-olefin oligomer, the temperature can be lowered from -5°C to -25°C compared to when they are used individually or when they are used separately, or when compared to the conventional case where both are not used. It has become possible to obtain a rubber composition for tires that exhibits high Iceμ over a range and exhibits excellent performance as a spikeless tire tread. Generally, in order to exhibit a high Ice μ at low temperatures, a rubber composition must be sufficiently soft even at low temperatures, and for this purpose it is necessary to lower the hardness at room temperature, but if the hardness at room temperature is too low, Abrasion properties tend to deteriorate. On the other hand, it is known that the coefficient of friction on a wet road surface (Wetμ) is correlated with rebound resilience at room temperature.
If the impact resilience at room temperature is too high, the Wet μ will decrease, causing a practical problem as a tire tread rubber composition. Therefore, the hardness of the rubber composition of the present invention is preferably in the range of JIS hardness at 23°C of 50 to 66, and furthermore, the rebound resilience (%) at 23°C is preferably in the range of 55 or less. It has particularly excellent road grip, wet grip, and abrasion resistance. The rubber composition of the present invention can be obtained by kneading the above components using conventional processing equipment such as rolls, banburys, mixers, kneaders, etc. In addition to the above components, known vulcanizing agents, vulcanization accelerators, vulcanization accelerators, vulcanization retarders, organic peroxides, reinforcing agents, fillers, anti-aging agents, tackifiers, colorants, etc. Of course, it is possible to add. This will be explained in detail below using Examples and Comparative Examples. Note that parts simply indicate parts by weight. JIS hardness is according to JIS K6301, Pico wear index is
It was evaluated using a Pico abrasion tester in accordance with ASTM D2228, and expressed as an index with Comparative Example 14 set as 100. The larger the number, the better. Repulsion resilience (%) was measured using the JIS K6301 impact resilience test method. The coefficient of friction on ice was measured using a friction coefficient measurement tester manufactured by Iwamoto Seisakusho, with a load pressure of 2.7 Kg/cm ² and a sliding speed of 0.1.
Measured in cm/sec. The value of Comparative Example 14 was set as 100 and expressed as an index. The larger the number, the better. Regarding tire performance, we created treads for each formulation and used the treads to determine the tire size.
A 185/70 SR14 tire was manufactured and its wet grip property (Wetμ) was measured. Measurement is based on US UTQGS (Tire Quality Grading Standard)
According to the method specified in , the tires were mounted on a test trailer using 5J x 14 rims, and the tires were run on a wet asphalt dense-grained road surface under the conditions of a filling air pressure of 1.8 kg/cm ² and a load of 336 kg. We measured the frictional resistance when the rotation of the tire was locked, and compared Comparative Example 14.
Comparisons are made using an index set to 100, and the larger the value, the better. Examples and Comparative Examples Rubber components, carbon black, α-olefin oligomer, oil, and plasticizer in the proportions listed in Tables 1 and 2, 3 parts of zinc white, and 3 parts of stearic acid.
part, anti-aging agent (paraphenylenediamine type) 3
1.5 parts of a vulcanization accelerator (thiazole) and 2 parts of sulfur were uniformly kneaded using a Banbury mixer to obtain a rubber composition. The physical properties and tire properties of each rubber composition are also shown in Tables 1 and 2. The rubber compositions listed in Tables 1 and 2 will be specifically explained using the compound No. 25 (Comparative Example 14), which is an example of a typical spikeless snow tire tread compound, as a control. . In Examples 1 to 11, compared to the control formulation, the Pico wear index is almost the same or higher, the Wet μ is also almost the same, and the resistance at -5℃ and -25℃
Iceμ is very good. Examples 1 to 3 are S- with Tg of -60°C or less.
Although it is a combination of SBR and α-olefin oligomer, both exhibit high Ice μ at both temperatures of −5° C. and −25° C., and the pico wear coefficient and Wet μ are maintained at sufficient levels. However, in Comparative Example 1 using S-SBR with Tg higher than -60°C, curing is large at low temperatures, and Iceμ at -5°C and -25°C is low. Even if a blend of S-SBR and BR with a Tg higher than -60°C is used to prevent curing at low temperatures (Comparative Example 4), the Ice μ is significantly inferior to that of the Examples. Thus, the Tg of S-SBR needs to be -60°C or lower. Furthermore, even if the S-SBRs of the present invention are used as a blend as in Example 4,
Iceμ is good. Comparative Examples 2 and 3, in which the amount of S-SBR in the rubber component is less than 70°C, have lower temperatures at -5°C and -25°C, compared to Examples 5 and 6, in which the amount of S-SBR is 70% or more.
Ice μ is low. -5°C and -25°C, which are the objects of the present invention.
In order to show high Iceμ at both temperatures, S-
The amount of SBR is required to be 70% or more. The feature of the present invention is that S-SBR having a Tg of -60°C or lower is used in combination with α-olefin oligomer. Comparative Example 5, which used α-olefin oligomer in a control formulation that did not use S-SBR, showed a large improvement in Ice μ at -25°C, but
Iceμ has hardly been improved. Comparative Example 6, in which no α-olefin oligomer was used, had a very low Ice μ at −25°C compared to Examples 5, 7, and 8, in which α-olefin oligomer was used in combination. Also, α−
When DOS (Comparative Example 7) or DOA (Comparative Example 8), which are ordinary low-temperature plasticizers, are used instead of olefin oligomers, Iceμ at -25°C is slightly improved, but lower than in Example 7. , -5°C tends to decrease rather than Comparative Example 6. On the other hand, in Example 7 in which α-olefin oligomer was used in combination, the Iceμ at -5°C did not decrease, but the Iceμ at -25°C was greatly improved. Thus, in the present invention, the α-olefin oligomer is preferably used in combination with S-SBR having a Tg of -60°C or lower, and the amount thereof is preferably 3 parts or more. As in Comparative Example 9, the filling amount of carbon black is
When the N ₂ SA of the carbon black used is less than 90 m ² /g, as in Comparative Example 10, the abrasion resistance is extremely poor. The amount of carbon black used in this way must be at least 50 parts, and the _N2SA must be
It is desirable that it is 90m ² /g or more. Comparative example 11 with rebound resilience greater than 55 at 23°C
has a low Wet μ and poor braking performance on wet road surfaces, making it undesirable for practical use. Those with a hardness of less than 50 at 23°C, such as Comparative Example 12, have significantly inferior wear resistance. Moreover, if the hardness at 23° C. is greater than 66 as in Comparative Example 13, the hardness at low temperatures will also be high and the Iceμ will be inferior. As described above, the tire tread rubber composition of the present invention has high wear resistance and wet road braking force over the temperature range of -5°C to -25°C without deteriorating the wear resistance and wet road braking force.
It exhibits Iceμ and has properties that are extremely suitable as a tread rubber composition for spikeless snow tires. In addition, in the table (1) S-SBR-A styrene content 10wt%, butadiene moiety microstructure (%); cis 35, trans 52, vinyl 13; Tg = -85℃ (2) S-SBR-B Tuffden 1534 ( (manufactured by Asahi Kasei); Tg=-76℃ (3) S-SBR-C Tuffden 2000R (manufactured by Asahi Kasei);
Tg=-71℃ (4) S-SBR-D Solprene 1204 (manufactured by Asahi Kasei); Tg=-51℃ (5) 1-decene triplex PAO (manufactured by Kyodo Oil);
Incidentally, Tg was measured using DSC-2 model manufactured by Perkin Elmer.

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Claims (1)

[Claims] 1. 50 parts by weight or more of carbon black per 100 parts by weight of a rubber component containing at least 70% or more of a solution-polymerized styrene-butadiene copolymer having a glass transition temperature (Tg) of -60°C or less; A tire tread rubber composition having a high coefficient of friction on ice, characterized by containing 3 parts by weight or more of an α-olefin oligomer. 2. The tire tread rubber composition according to claim 1, wherein the vulcanized tread rubber composition has an impact resilience (%) of 55 or less at 23°C and a JIS hardness of 50 to 66 at 23°C.