JPS6234340B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pneumatic tire that exhibits excellent maneuverability and good wear resistance, and more specifically, a styrene-butadiene copolymer that has a large amount of bound styrene and the binding mode of the butadiene moiety within a specific range. The present invention relates to a pneumatic tire using a rubber composition containing rubber in the cap tread. In recent years, along with the development of fuel-efficient tires (tires aimed at reducing vehicle fuel consumption by reducing the tire's rolling resistance), which aim to conserve resources, safety (humidity) Tires are being developed that use a rubber composition in the cap tread portion that is similar to the cap tread rubber composition of competition tires, which has improved driving performance on road surfaces and dry road surfaces. Rubber compositions for the cap treads of such pneumatic tires are
Styrene-butadiene copolymer rubber with a large amount of bound styrene (30 to 50% of bound styrene) as shown in No. 14581 (hereinafter referred to as high styrene SBR)
is the most common use. However, when high styrene SBR was used, there was a drawback in that the wear resistance was significantly reduced. As described above, a tire that has improved maneuverability on wet and dry road surfaces and also has good wear resistance has not yet been obtained. An object of the present invention is to provide a pneumatic tire that has excellent wear resistance and maneuverability on wet and dry road surfaces, as well as good workability. Conventionally, the use of high styrene SBR as mentioned above has been proposed as a means of improving the dynamic performance of tires.
Rubber compositions that use SBR as the rubber component generally have reduced abrasion resistance, so it is difficult to use them in the cap treads of general tires other than competition tires, or even if they are used, There was a problem that the tires had to have a short running life. The present inventors have developed high styrene in line with the above objective.
As a result of a more detailed study of SBR,
The amount of bound styrene is 30 to 50% by weight, the bonding mode of the butadiene part is 1,2 vinyl bond 20% or more, cis 1,
The above object is achieved by using a rubber composition containing a specific ratio of high styrene SBR having 15% or more of 4-bonded styrene and SBR having 22 to 25% by weight of bound styrene as the rubber component for the cap tread of a tire. We have discovered that this is the case, and have arrived at the present invention. That is, the tire of the present invention has a cap tread containing 30 to 50% by weight of bound styrene, and a microstructure of the butadiene portion having 20% or more of 1,2 vinyl bonds and 15% or more of cis 1,4 bonds. High styrene SBR (hereinafter referred to as specific SBR)
10-50% by weight and bound styrene amount 22-25% by weight
It is characterized by using a rubber composition containing 75 parts by weight or more of carbon black per 100 parts by weight of rubber consisting of 90 to 50% by weight of SBR (hereinafter generally referred to as SBR). In the rubber composition used for the cap tread of the tire of the present invention, the specific SBR is contained in the rubber component.
It is contained in an amount of 10 to 50% by weight, preferably 20 to 40% by weight. If it is less than 10% by weight, the dynamic performance of the tire, that is, the braking performance on dry and wet roads, will be poor.
If the amount exceeds 50% by weight, the abrasion resistance deteriorates, and adhesion to rolls occurs during the mixing and extrusion steps, resulting in a decrease in processing workability. If the styrene content of this specific SBR exceeds 50% by weight, the wear resistance will be poor, and if it is less than 30% by weight, the maneuverability will be poor. Also,
If the 1,2-vinyl bond is less than 20%, the tire will not be able to exhibit sufficient driving performance, and if the cis-1,4 bond is less than 15%, the tire will have low wear resistance. This specific SBR may be oil-extended or used as a wet carbon masterbatch, which is preferable from the viewpoint of processability. SBR usually includes oil-extended SBR, and may be used alone or in combination of two or more. In the present invention, carbon black is a rubber component.
The carbon black should be blended in an amount of 75 parts by weight or more per 100 parts by weight, and the carbon black should have high reinforcing properties, and therefore have an iodine adsorption amount of 80 mg/g or more.
It is best to use a DBP with an oil absorption capacity of 100ml/100g or more. If the amount of carbon black added is less than 75 parts by weight, the effects of using the specific SBR, including braking performance and wear resistance, will not appear. The rubber composition used in the cap tread of the tire of the present invention contains compounding agents that are usually added to rubber, such as anti-aging agents, zinc oxide, stearic acid, wax, oils, resins, vulcanization accelerators, and sulfur. A suitable amount is added as appropriate. The present invention will be specifically described below based on Examples and Comparative Examples. Examples 1 to 6 and Comparative Examples 1 to 6 Rubber compositions were prepared by mixing each SBR and high styrene resin having the properties shown in Table 1 and compounding agents in the proportions shown in Table 2. This rubber composition was heated at 160°C.
The vulcanization properties were evaluated by press vulcanization for 20 minutes. Furthermore, the obtained vulcanized rubber was placed on the cap tread of a 185/70HR13 size tire, and its braking performance on dry and wet road surfaces was evaluated. These evaluation methods were performed as follows. In evaluating vulcanized physical properties, tensile strength, elongation,
300% tensile stress and JIS hardness were determined in accordance with JIS K6301, and wear resistance was determined by Pico abrasion test in Comparative Example 1.
It is expressed as an index with the reciprocal of the abrasion loss as 100, and the larger the value, the less the abrasion loss and the better the wear resistance. Braking performance on dry and wet road surfaces was measured on the Japan Automobile Research Institute General Test Road (Yatabe-cho, Tsukuba-gun, Ibaraki Prefecture)
Measure the braking distance from 60Km/hr under the same conditions, divide the value of Comparative Example 1 by each measured value, and calculate this by 100
It is expressed as a multiplied index, and the higher the number, the better the exercise performance is. The respective measurement results are shown in Table 2 and Figures 1 to 3. In addition, as a comprehensive evaluation value that combines driving performance and wear resistance, the value of √Wet road braking distance index (A) x Dry road braking distance index (B) x Wear resistance index (C) x 1/100 is combined. second
It is listed in the table.

【table】

【table】

[Table] In Table 2, Comparative Example 1 is normal SBR
(SBRA) as the rubber component, and on the other hand, Comparative Examples 2 to 3 and Example 1 are ordinary rubber compositions.
A portion of SBR is converted into high styrene SBR with a styrene content of 40% by weight, namely SBR B, SBR C, and SBR D.
This is a rubber composition that has been replaced. Comparative Example 2 has poor wear resistance because the amount of cis-1,4 bonds in the butadiene moiety of SBR B, which contains 20% by weight in the rubber content, is small. Similarly, in Comparative Example 3, the amount of cis-1,4 bonds in the butadiene moiety of SBR C, which is contained at 20% by weight in the rubber content, is somewhat small, so it not only has somewhat inferior wear resistance, but also has a slightly lower abrasion resistance.
Since the amount of 1,2 vinyl bonds is also small, the braking performance on wet road surfaces is not as improved as in Comparative Example 2. On the other hand, in Example 1, SBR containing 20% by weight in the rubber content
Since the butadiene moiety of D has a large amount of 1,2 vinyl bonds and a large amount of cis-1,4 bonds, the braking performance on dry and wet road surfaces is improved compared to Comparative Example 1, and the wear resistance is hardly impaired. . This comparative example 2~
Figure 1 shows the relationship between the amount of 1,2-vinyl bonds in the butadiene moiety and braking performance on dry and wet road surfaces in Example 3 and Example 1, and the relationship between the amount of cis-1,4 bonds in the butadiene moiety and abrasion resistance. are shown in Figure 2. In Examples 1 to 5 and Comparative Examples 4 to 5, the rubber content was
As shown in Figure 3, the braking performance on dry and wet road surfaces improves as the amount of SBR D increases, while the wear resistance decreases. gradually decreases. Comprehensive evaluation value considering both characteristics [√(A)×(B)×(C)×1/10
0], the content of SBR D is preferably 10 to 50% by weight in the rubber. Although Comparative Example 5 has a relatively preferable comprehensive evaluation value, it is not preferable because its wear resistance is too low, resulting in poor balance with braking performance, and its roll workability is also poor. Example 6 is obtained by reducing the amount of carbon black and oil from the formulation of Example 1, and although its braking performance on wet and dry road surfaces is somewhat inferior to that of Example 1, it is within a relatively preferable range. However, it is not preferable to reduce the amount of carbon black more than this because the braking performance on wet and dry road surfaces will deteriorate. Comparative Example 6 is a rubber composition containing a high styrene resin instead of SBR D in Example 2, but the braking performance is not as improved as in Example 2, and the wear resistance is significantly inferior. As explained above, in high styrene SBR, the bonding mode of the butadiene moiety is 20% of the 1,2 vinyl bond.
or more, high styrene with 15% or more of cis-1,4 bonds
Tires with a cap tread containing a rubber composition containing 10 to 50% by weight of SBR, with the remainder usually SBR, can improve maneuverability without sacrificing wear resistance. It also has good workability.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of 1,2 vinyl bonds in the butadiene moiety of high styrene SBR contained in Comparative Examples 2 to 3 and Example 1 and the braking distance index on dry and wet road surfaces. Figure 2 is a graph showing the relationship between the total amount of cis 1,4 and the wear resistance index, and Figure 3 is a graph showing the relationship between the total amount of cis-1,4 and the wear resistance index, and Figure 3 is a graph showing the relationship between the total amount of cis-1,4 and the wear resistance index, and Figure 3 is a graph showing the relationship between the total amount of cis-1,4 and the wear resistance index, and Figure 3 is a graph showing the relationship between the total amount of cis-1,4 and the wear resistance index, and Figure 3 shows the graph of Examples 1 to 5 and Comparative Example 4.
Graph showing the relationship between SBR D content of ~5, wear resistance index, and braking distance index on dry and wet road surfaces.

Claims (1)

[Claims] 1 Combined with 10-50% by weight of a styrene-butadiene copolymer rubber in which the amount of bound styrene is 30 to 50% by weight or more, and the bonding mode of the butadiene moiety is 20% or more of 1,2 vinyl bonds and 15% or more of cis-1,4 bonds. The amount of styrene
22-25% by weight styrene-butadiene copolymer rubber
1. A pneumatic tire characterized in that a rubber composition in which 75 parts by weight or more of carbon black is blended with 100 parts by weight of rubber consisting of 90 to 50% by weight is used in the cap tread part.