JPH0333187B2 - - 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 hardens at low temperatures and loses its inherent 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, methods for improving the low-temperature properties of rubber and increasing the coefficient of friction on ice include (1) the use of polymers with a high coefficient of friction on ice, (2) the use of large amounts of aromatic oils and naphthenic oils, and (3) the use of (2-ethylhexyl) adipate (DOA), di-(2-ethylhexyl) phthalate (DOP), di-(2-ethylhexyl) azelate (DOZ), di-(2-ethylhexyl) azelate (DOZ),
It is known to add low temperature plasticizers such as ethylhexyl) sebacate (DOS) to rubber compositions. 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, BR (polybutadiene rubber), which is the same diene-based synthetic rubber.
Comparing SBR (styrene-butadiene copolymer rubber) and SBR, even though SBR has a larger coefficient of friction on ice at an ice temperature of around -5°C, the relationship in magnitude between the coefficients of friction on ice is reversed at around -12°C. However, it is generally known that the coefficient of friction on ice of BR increases as the temperature decreases (the coefficient of friction of SBR decreases). in this case,
Blends of BR and SBR do not provide any special combination effect and are inferior to the higher ice friction coefficients obtained when BR and SBR are used alone at each temperature. In addition, the method of using a large amount of oil or using a low-temperature plasticizer as described above is effective in improving the coefficient of friction on ice at ice temperatures lower than around -20°C, but the coefficient of friction on ice at around -5°C is effective. No significant improvement effect was observed. 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 considerably 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 inventor has developed a rubber composition with improved low-temperature properties using a low-temperature plasticizer with a freezing point of -40°C or lower. It has been shown that when alumina with a specific particle size range is used in combination, the combined effect of the two appears, and a rubber composition that exhibits a high coefficient of friction on ice over the entire temperature range from -5°C to -35°C can be obtained. Heading, we arrived at the present invention. That is, the present invention uses 10 to 80 parts by weight of a low-temperature plasticizer whose freezing point is -40°C or lower and an average particle size of 100 parts by weight of natural rubber and/or diene-based synthetic rubber.
The present invention relates to a tire tread rubber composition which is combined with 5 to 45 parts by weight of alumina having a diameter of 0.01 to 0.5 mm. The low-temperature plasticizer with a freezing point of -40°C or lower used in the present invention is di-(2-ethylhexyl).
Adipate (DOA, freezing point -70℃), di(2-
ethylhexyl) phthalate (DOP, freezing point -
55℃), di-(2-ethylhexyl) azelate (DOZ, freezing point -65℃), di-(2-ethylhexyl) sebacate (DOS, freezing point -65℃), α-olefin oligomer (PAO, freezing point -65℃) ) etc. The blending amount is 10 to 80 parts by weight.If it is less than 10 parts by weight, the coefficient of friction on ice at low temperatures will not increase, and if it is blended in excess of 80 parts by weight, the coefficient of friction on ice will decrease at around -5℃. This is not preferable because it tends to reduce the wear resistance and has poor wear resistance. The alumina used in the present invention has an average particle size of 0.01~
It is 0.5 mm, more preferably 0.05 to 0.3 mm.
If it is less than 0.01 mm, no improvement in the coefficient of friction on ice can be expected, and if it exceeds 0.5 mm, it is undesirable because it tends to damage the road surface and the abrasion resistance decreases significantly. The amount of alumina blended in the present invention is 100%
15 to 45 parts by weight, more preferably 10 parts by weight
~30 parts by weight. If it is less than 5 parts by weight, a sufficient improvement in the coefficient of friction on ice cannot be expected, and if it exceeds 45 parts by weight, the abrasion resistance will be markedly lowered, which is not preferable. The rubber component in the present invention is natural rubber (NR)
and/or diene-based synthetic rubber. Suitable diene-based synthetic rubbers include, for example, polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), and blends thereof. The rubber composition of the present invention can be obtained by kneading the above components using conventional processing equipment such as rolls, Banbury mixers, kneaders, etc. In addition to the above components, known vulcanizing agents, vulcanization accelerators, vulcanization accelerators, vulcanization retarders, organic peroxides, reinforcing agents,
Fillers, oils, softeners, plasticizers, anti-aging agents,
Of course, tackifiers, colorants, etc. can be added. Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples. The evaluation method is as follows. ● JIS hardness: Measured according to JIS K6301. ● Pico friction index: Evaluated using a Pico abrasion tester according to ASTM D2228, control formulation
It is expressed as an index with No. 1 as 100. The larger the number, the better. ● Ice μ (friction coefficient on ice): Measured using a friction coefficient measurement tester made by Iwamoto Seisakusho at a load pressure of 2.7 Kg/cm ² and a sliding speed of 0.1 cm/sec. Control formulation No.
The value of 1 was set as 100 and expressed as an index. The larger the number, the better. ● Tire wet μ: Create a tread for each formulation and use that tread to adjust the tire size to 185/70.
An SR14 tire was manufactured and its wet grip property (wetμ) was measured. The measurement was carried out in accordance with the method specified by the US UTQGS (tire quality grading standard).The tire was mounted on a test trailer using a 5J x 14 rim, and the air pressure was adjusted.
The frictional resistance was measured when the tire was running on a wet asphalt dense-grained road surface under conditions of 1.8 kg/cm ² and a load of 336 kg, and the rotation of the tire was locked. The friction coefficient of control formulation No. 1 was set as 100 and expressed as an index. The larger the number, the better. ● Road surface damage level: Using a friction coefficient measurement tester made by Iwamoto Seisakusho, the vehicle was operated on an asphalt road surface at 30°C with a load pressure of 2.7 Kg/cm ² and a sliding speed of 0.1 cm/sec, and the road plate was rotated 50 times. The degree of damage to the asphalt road surface was observed and evaluated. Evaluation is based on the degree of road surface damage (no damage) due to control formulation No. 1
A 5-grade evaluation was performed, with 1 being the degree of road damage measured by driving spike pins into control formulation No. 1 and 5 being the degree of road surface damage. The smaller the number, the better. Examples and Comparative Examples Various rubber compositions shown in Table 1 were kneaded and then vulcanized. Each physical property of these rubber compositions was evaluated and the results are shown in Table 1. In addition to the ingredients listed in Table 1, each formulation contains zinc white (3 parts), stearic acid (3 parts), anti-aging agent (paraphenylenediamine type, 3 parts), and vulcanization accelerator (thiazole). 1.5 parts) and sulfur (2 parts).

【table】

【table】

【table】

[Table] Regarding the evaluation of the rubber compositions listed in Table 1, composition No. 1, which is an example of a typical spikeless snow tire tread composition, is specifically shown as a control. Blend No. 2, 3, 5, 6, 15, corresponding to Examples
16, 17, and 18 all have pico friction index and wet μ at almost the same level as control formulation No. 1,
It can be seen that Iceμ is very good over the entire temperature range from -5°C to -35°C. Blend No. 4 is a comparative example in which only a low-temperature plasticizer is blended and no alumina is blended. Compared to control formulation No. 1, Iceμ at -35°C is excellent, but Iceμ at -5°C is hardly improved. Blend No. 14 is a comparative example in which only alumina is blended and no low temperature plasticizer is blended. Compared to control formulation No. 1, Iceμ at -5°C is excellent, but Iceμ at -35°C is hardly improved. Blend No. 8 is a comparative example in which alumina with an average particle size of less than 0.01 mm and a low-temperature plasticizer are combined. Compared to formulation No. 7, there is no improvement in Ice μ near -5°C. Blend No. 9 is a comparative example in which alumina with an average particle size exceeding 0.5 mm and a low temperature plasticizer are combined. This is not preferable because it significantly reduces the pico wear index and tends to damage the road surface. Blend No. 10 is a comparative example in which the amount of alumina blended is less than 5 parts by weight. Control formulation No.
Ice μ at −5° C. is hardly improved compared to No. 1. Blend No. 11 is a comparative example in which the blended amount of alumina exceeds 45 parts by weight. A significant decrease in pico wear index is undesirable. Formulation No. 12 is a comparative example in which more than 80 parts by weight of a low-temperature plasticizer and alumina are combined. Compared to Blend No. 6, the Iceμ at -5°C is inferior, and the pico wear index is also lower, which is not preferable. Blend No. 13 is a comparative example in which the amount of low temperature plasticizer blended is less than 10 parts by weight. Iceμ at −35℃
No improvement is seen. From the above, the treaded rubber composition of the present invention has excellent braking power on ice over all temperatures from -5°C to -35°C without deteriorating wear resistance, wet road braking power, or road damage resistance. It can be seen that it has properties that are extremely suitable as a tread rubber composition for spikeless snow tires that do not cause pollution like spiked tires.

Claims (1)

[Claims] 1. 10 to 80 parts by weight of low-temperature plasticity with a freezing point of -40°C or lower and 5 to 45 parts by weight of alumina with an average particle size of 0.01 to 0.5 mm per 100 parts by weight of natural rubber and/or diene synthetic rubber. A tire tread rubber composition comprising a combination of the following.