JPH0469183B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to an improved radial tire, particularly a radial tire for heavy vehicles with improved uneven wear resistance and rib tear resistance. Conventional technology Traditionally, natural rubber compounds have been used as tread rubber for radial tires for heavy vehicles due to their low heat build-up, fracture strength, and rib tear resistance, but as they become more popular for high-speed long-distance running. As a result, railway wear, that is, uneven wear such as abnormal wear occurring at the rib edges along both sides of the circumferential zigzag main groove, has become noticeable at the tread contact area, and a solution to this problem has been strongly desired. Regarding this, it was reported in Japanese Patent Laid-Open No. 58-117 that the railway wear can be significantly improved when a rubber made of a blend of natural rubber (NR) and styrene-butadiene rubber (SBR) is used as the tread rubber.
Publication No. 161605 shows. However, when the above-mentioned NR/SBR blend rubber is simply used instead of the natural rubber compounded natural rubber, rib tear resistance, which is another property required for the tread contact area of radial tires, especially radial tires for heavy vehicles, is reduced. It could not be put to practical use at all because the properties and other characteristics were significantly impaired. This is NR・
The SBR blend system consists of a micro NR phase and an SBR phase, and the distribution ratio of sulfur to both phases is high in the NR phase under processing conditions such as kneading and vulcanization, so the crosslinking density of both phases is reduced. This is also thought to be due to the fact that it cannot be optimized. On the other hand, JP-A-57-170939 discloses that the heat aging resistance and flex cracking resistance of vulcanized rubber can be improved by using a polysulfide polymer alone or in combination with sulfur. , did not disclose anything about the use of this vulcanizing agent for blended rubber, and even in the examples showing its use in combination with sulfur, the amount of sulfur (S _P ) and amount of sulfur (S _E ) contained in the polysulfide polymer was not disclosed. Since it is only shown that the sum of 11.6 and the ratio of S _P to S _E is 0.08 per 100 parts by weight of the rubber component, this vulcanization system can be used for contacting the ground at the tread part of radial tires, especially radial tires for heavy vehicles. It is absolutely impossible to relate this to improving both the uneven wear resistance of the part and the rib tear resistance. DISCLOSURE OF THE INVENTION The inventors have conducted intensive research to improve the uneven wear resistance of the ground contact area of the tread of radial tires, especially radial tires for heavy vehicles, while maintaining other necessary properties, especially the necessary rib tear resistance. Surprisingly, the present invention was achieved by confirming that the above object can be achieved only when polysulfide polymer and sulfur are blended within a specific range into a blended rubber of natural rubber and styrene-butadiene rubber. That is, the present invention includes a tread portion, a pair of side portions that are connected to the tread portion at both shoulders of the tread portion, and a pair of bead portions formed on the inner periphery of the side portions, so that the tread portion substantially extends in the tire circumferential direction.
In a radial tire reinforced with a carcass having cords arranged at 90 degrees and a belt surrounding the carcass, the cord direction forming a relatively small angle with respect to the tire circumferential direction, and having more than one cord layer intersecting with each other, The grounding part of the tread part is made of polyisoprene structural rubber (A) and styrene-butadiene rubber (B) selected from the group consisting of natural rubber, isoprene rubber, and blended rubbers of both, and the weight ratio of A to B is For the rubber component whose ratio is within the range of 80/20 to 50/50, the formula [-(CH ₂ CH ₂ -O)- _n CH ₂ CH ₂ -S _x ]- _o (x in the formula is 3 to 6 , n is 10 to 300, m is 1 to
The sum of the amount of sulfur contained in the polysulfide polymer (S _P ) and the amount of sulfur (S _E ) contained in the polysulfide polymer is 0.5 per 100 parts by weight of ingredients
~3.5 parts by weight, and the ratio of S _P to S _E is within the range of
An improved radial tire constructed from a rubber composition formulated within the range of 0.4 to 2.5. In this invention, isoprene rubber (IR) of the polyisoprene structural rubber (A) refers to a rubber-like synthetic polymer of isoprene, which is almost similar to natural rubber in terms of molecular structure, processability, vulcanizability, physical properties, etc. be. The styrene-butadiene rubber (B) may be a rubber commonly used for tire tread rubber. It is necessary that the weight ratio A/B of polyisoprene structural rubber (A) to styrene butadiene rubber (B) is 80/20 to 50/50, and if this ratio is greater than 80/20, uneven wear resistance will be reduced. If the ratio becomes worse and becomes smaller than 50/50, the rib tear resistance becomes poor and the object of the present invention cannot be achieved. Furthermore, if the above ratio is smaller than 50/50, the heat generation property of the tire will also deteriorate. The polysulfide polymer used in this invention is a substance represented by the above formula. This polysulfide polymer can be prepared, for example, by reacting a dithiol having a suitable polyether bond with sulfur chloride as described in JP-A-57-170939, but it is not particularly limited to this production method. .
The polysulfide polymers of this invention are typically oily and can be easily mixed with rubber.
As a polysulfide polymer, m=2, n=10~
100, x=3 to 6 is particularly preferred in terms of processability and physical properties of the vulcanized rubber, particularly in achieving rib tear resistance and uneven abrasion resistance, which are the objectives of this invention. The sum of the amount of sulfur contained in the polysulfide polymer (S _P ) and the amount of sulfur added as sulfur itself (S _E ) in combination with this S _P +S _E is the rubber component A+
The amount is within the range of 0.5 to 3.5 parts by weight based on 100 parts by weight of B. If it is less than 0.5 parts by weight, sufficient vulcanization cannot be achieved, and if it exceeds 3.5 parts by weight, rib tear resistance will deteriorate. Furthermore, if the S _P /S _E ratio is smaller than 0.4, the rib tear resistance will be poor, and if it is larger than 2.5, the wear resistance will be poor. As mentioned above, the distribution ratio of sulfur (S _E ) in the blend system of polyisoprene structural rubber (A) and styrene-butadiene rubber (B) is high in the A phase. It was confirmed that, on the contrary, the distribution ratio of S _P becomes higher in the B phase. Therefore, by using polysulfide polymer and sulfur together within the range of S _P + S _E and S _P /S _E ratio, the distribution ratio of the vulcanizing agent in the A and B phases can be controlled, and the crosslinking density of both phases can be controlled. It can be optimized to meet the purpose of this invention. While polysulfide polymers have the advantage of forming flexible crosslinks containing ether bonds,
When it is used alone, it has the disadvantage of low crosslinking density and low modulus, but by using it in combination with sulfur, the modulus can be made higher than when sulfur is used alone with the same amount of sulfur. In addition, since the polysulfide polymer of this invention is in the form of an oil, it also has the effect of lowering the viscosity of the rubber compound during processing and improving processability. In the present invention, the rubber composition constituting the ground contact part of the tread part contains the above-mentioned combination vulcanizing agent in the rubber component consisting of A and B as described above, as well as carbon black used in the ground contact part of a normal radial tire tread. It goes without saying that rubber chemicals are blended, for example, various vulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, diphenylguanidine, etc., various accelerators such as zinc white, stearic acid, etc. Auxiliary agents and various anti-aging agents such as amine-based anti-aging agents are used. The carbon black is usually blended in 30 to 90 parts by weight per 100 parts by weight of rubber, and has a nitrogen adsorption specific surface area of 65 m ² /g or more according to ASTM D-3037.
From the viewpoint of wear resistance, it is preferable that the DBP value shown in JISK6221 is in the range of 80 ml/100 g or more. Although there is no particular upper limit to the nitrogen adsorption specific surface area and DBP value, the limits are usually about 150 m ² /g and 125 ml/100 g, respectively, and these ranges are preferably used. Examples of such preferred carbon blacks include ISAF,
Examples include N110 (SAF), N220 (ISAF-HM), and N339. Note that N110, N220, and N339 are ASTM type names. The present invention also includes cases where the entire tread portion of the radial tire is made of the same rubber composition as the tread contact portion of the present invention. EXAMPLES OF THE INVENTION Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 to 6, Comparative Examples 1 to 9 Tire size 10.00R20, 14-ply, three-groove tread pattern running in the circumferential direction of a truck/bus radial tire.Only the formulation of the ground contact area of the tread, that is, the cap tread, was as shown in Table 1. Fifteen types of tires were manufactured with the changes shown in Table 2, and tire performance was evaluated. The test tire is (3+9+15)×0.175mm+1×
It has a one-ply carcass structure with 0.15mm steel cords arranged in a radial arrangement at a driving density of 8 cords/25mm.The crown of this carcass is surrounded by a total of 4 layers of belts, each layer having 3× 0.20mm
+9 x 0.38mm steel cord in the first layer
A driving density of 14 lines/25mm is applied to the second, third and fourth layers, and the first layer is 50 degrees upward to the right in the circumferential direction of the tire, and each of the second, third and fourth layers is In each case, the chord arrangement was set at 20 degrees with stone up, left up, and left up, respectively. In the tire performance evaluation test, the test tire was run-in for 3 hours at 85% of the rated load at a speed of 60 km/h at standard air pressure, and then the load was increased to the rated load and the following conditions were applied: I conducted a test. Wear resistance evaluation: The vehicle was driven for 50,000 km on a road consisting of 60% ordinary roads and 40% highways. After running, the remaining grooves of the tire in areas where uneven wear did not occur were measured, and the wear resistance was evaluated using an index, with the tire of Comparative Example 10 set as 100. Therefore, the larger this value is, the better the wear resistance is. Uneven wear resistance: After running the tires as described above, the degree of railway wear on the tread contact surface was measured and evaluated. The degree of occurrence of railway wear is determined by the degree of wear with a step between the main groove 1 and the tread surface 2, where no railway wear occurs, as shown in Fig. 1 in the radial cross section of the tire, i.e., the step (h) in the figure. It is evaluated based on the railway wear width (w) and can be expressed as an index using the following formula. h×w/h _p ×w _p ×100 h _p , w _p : Step difference and railway wear width of Comparative Example 10 tire, respectively h, w : Step difference and railway wear width of test tire, respectively For the index, 80 or less is A, greater than 0 and less than 90 is B, greater than 0 and less than 110 is C,
Those larger than 110 are shown as D in Tables 1 and 2. The smaller the index, that is, the better the uneven wear resistance in the order of D, C, B, and A. Rib tear resistance: The occurrence of cracks at the bottom of the rib grooves of the test tires was observed. Rib tear is a term used to define the tendency of the portion of the tread to tear away from the main body of the tread when the tire is struck by a sharp object such as a cement pavement edge stone. . The tendency of treads to cause rib tearing is especially severe in heavily loaded truck tires. To determine the resistance of various treads to rib tearing, a test was used in which a heavily loaded truck, equipped with test tires on dual rear wheels, was driven repeatedly back and forth over a cement heel at a small angle. there was. The results are shown in Tables 1 and 2.

【table】

【table】

【table】

[Table] From Tables 1 and 2, A/B80/20~50/50,
Improving uneven wear resistance while keeping rib tear resistance within a satisfactory range only within the range of S _P + S _E 0.5 to 3.5 parts by weight and S _P /S _E ratio of 0.4 to 2.5 (Examples 1 to 6). The above two characteristics can be achieved by A/B being larger than the above ratio (Comparative Example 2), smaller than the above ratio (Comparative Example 3), or A or B alone (Comparative Examples 10, 1, 4). It can be seen that the above two properties cannot be achieved at the same time, and also when the S _P /S _E ratio is smaller than the above range (Comparative Example 6) or when sulfur is used alone (Comparative Example 5). When the S _P /S _E ratio is larger than the above range (Comparative Example 8) or when polysulfide polymer is used alone (Comparative Example 9), the above two properties are good, but the wear resistance is significantly deteriorated. Moreover, when S _P +S _E exceeds 3.5 parts by weight (Comparative Example 7), the above two properties are not compatible. Effects of the Invention As explained above in the Examples and Comparative Examples, the present invention provides a radial tire in which the ground contact portion of the tread is made of polyisoprene structural rubber (A) and styrene-butadiene rubber (B), and the A/B ratio is A polysulfide polymer having a polyether bond represented by the formula and sulfur are added to the rubber component in a weight ratio of 80/20 to 50/50 such that the S _P + S _E and S _P /S _E ratios are within a specific range. By constructing a compounded rubber composition, it was the first time that we succeeded in improving the uneven wear resistance of radial tires, especially radial tires for heavy vehicles, without sacrificing rib tear resistance, which had not been solved for a long time. Other necessary properties, such as tire wear resistance, are not impaired.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main groove in the tire radial direction. 1...Main groove, 2...Tread surface that does not cause railway wear.

Claims (1)

[Scope of Claims] 1. A tread portion, a pair of side portions connected to the tread portion at both shoulders of the tread portion, and a pair of bead portions each formed on the inner periphery of the side portion,
A carcass consisting of cords arranged substantially at 90 degrees to the tire circumferential direction, and two or more cord layers surrounding the carcass, the cord directions making a relatively small angle to the tire circumferential direction, and intersecting each other. In a radial tire reinforced with a belt, the ground contact part of the tread part is made of polyisoprene structural rubber (A) selected from the group consisting of natural rubber, isoprene rubber, and blended rubbers of both, and styrene-butadiene rubber (B). and the weight ratio of A to B is within the range of 80/20 to 50/50, the formula [-(CH ₂ CH ₂ -O)- _n CH ₂ CH ₂ -S _x ]- _o ( In the formula, x is 3 to 6, n is 10 to 300, and m is 1 to
The sum of the amount of sulfur contained in the polysulfide polymer (S _P ) and the amount of sulfur (S _E ) contained in the polysulfide polymer is 0.5 per 100 parts by weight of ingredients
~3.5 parts by weight, and the ratio of S _P to S _E is within the range of
An improved radial tire comprising a rubber composition blended within the range of 0.4 to 2.5.