JPH04224839A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:To provide the title compsn. which prevents the degradation of durability of a tire caused by heat buildup during high-speed running without detriment to the grip of the tire. CONSTITUTION:100 pts.wt. rubber component comprising at least one styrene- butadiene copolymer rubber having a combined styrene content of 30 % or higher, 70 pts.wt. or higher carbon black having an iodine adsorption capacity of 90 mg/g or higher, and 1-15 pts.wt. calcium oxide are compounded to give the title compsn., which has an improved heat resistance without detriment to the grip.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates primarily to rubber compositions used in the treads of pneumatic tires, such as tires for passenger cars, motorcycles, and racing tires.

0002

2. Description of the Related Art As the performance of vehicles improves, there is an increasing demand for tires with excellent high-speed performance not only for racing but also for general vehicles. Therefore, various improvements have been made regarding particularly important grip performance. For example, process oil is added to styrene-butadiene copolymer rubber with a high styrene content as a tire tread rubber composition.
A large amount of carbon black is blended to ensure grip performance.

However, in order to obtain high grip performance,
It is possible to improve the grip performance by increasing the styrene content of the styrene-butadiene copolymer rubber or by adding a large amount of process oil or carbon black, but on the other hand, this increases the heat generation of the rubber composition. That is, the compound system has a large loss coefficient, so-called tan δ value, which is an index of the calorific value of the rubber composition. When a tire with such a tread is worn and driven at high speeds, the tread becomes hot, causing foam to form inside the rubber, a phenomenon known as the blow phenomenon. In severe cases, the tread rubber can fly off and destroy the tire. bring. In order to withstand this heat generation, heat-resistant anti-aging agents have been added, but the reality is that the problem has not been solved.

[0004] JP-A No. 47-29471 describes the addition of calcium oxide to prevent thermal hydrolysis of polyester in polyester rubber laminates, but this relates to a tire reinforcing layer, and the balance between grip performance and heat resistance is described. It's not about the tread part issue, which is important. JP-A-57-195760 discloses that calcium oxide is added to butyl rubber used for inner liners or tubes for retaining air in pneumatic tires in order to suppress air bubbles and reduce air permeability during kneading or running. It is described that it is mixed. Also, JP-A-60-1
No. 90440 discloses an invention relating to a rubber filler containing calcium oxide, which also relates to general vulcanized physical properties of rubber.

[0005]

[Problems to be Solved by the Invention] When a vehicle runs, the temperature of the tread rubber repeatedly rises and falls rapidly, causing a blow phenomenon that can cause tire destruction.This invention eliminates the blow phenomenon while maintaining high grip performance. The object of the present invention is to provide a rubber composition with improved heat resistance in order to prevent this.

[0006]

[Means for Solving the Problems] In order to solve these conventional drawbacks, the inventors of the present invention have made intensive studies on the blending of rubber, fillers, etc. in tread rubber. As a result, the amount of iodine adsorbed (
It is characterized by blending 70 to 250 parts by weight of small-particle carbon black with IA) of 90 mg/g or more and 1 to 15 parts by weight of calcium oxide or calcium oxide treated with higher fatty acid or mixed fatty acid or process oil. The inventors have discovered that the rubber compositions described above are extremely effective, and have thus arrived at the present invention.

In order to obtain high grip performance, a styrene-butadiene copolymer rubber in which the total amount of bound styrene is 30% by weight or more of the total styrene-butadiene copolymer rubber and an iodine adsorption amount (IA) of 90 mg/ g or more of carbon black per 100 parts by weight of this diene rubber,
It is necessary to mix 70 or more. As a result, 70°C
The value of tan δ measured in can be increased, and a tread rubber with high grip performance can be obtained. The amount of carbon black was set to be 250 parts by weight or less since kneading becomes difficult if more than 250 parts by weight is blended.

[0008] Calcium oxide or calcium oxide treated with fatty acid or process oil is limited to 1 to 15 parts by weight because if it is less than 1 part by weight, no improvement in the exothermic foaming resistance of the rubber during running is observed. Further, if the amount is more than 15 parts by weight, a significant decrease in grip performance is observed in vehicle running tests compared to tires with conventional tread rubber.

[0009] Here, if calcium oxide is treated with higher fatty acids such as oleic acid and stearic acid, or mixed fatty acids thereof, or process oils such as naphthenic, paraffinic, and aromatic oils, the untreated oxidized Calcium oxide is easier to measure during blending than calcium, and calcium oxide has better dispersibility in rubber.

In the present invention, as the rubber, styrene-butadiene copolymer rubber can of course be used alone, but other rubber components such as natural rubber,
It can be used in combination with synthetic isoprene rubber, 1,4-butadiene rubber, various styrene-butadiene copolymer rubbers having different styrene contents, and the like. Furthermore, in addition to the above-mentioned compounding agents, the rubber composition of the present invention may also contain compounding agents commonly used in the rubber industry, especially in the compounding of tread rubber, such as fillers, softeners, anti-aging agents, vulcanizing agents, vulcanizing agents, etc. Sulfur accelerators, vulcanization accelerating aids, and the like can be added in suitable amounts by combining them as necessary.

The present invention will be explained below with reference to Examples. As the rubber, styrene-butadiene copolymer rubber with a styrene content of 40% was used, and carbon black with an iodine adsorption amount (IA) of 140 mg/g was used at 90 parts by weight based on 100 parts of the rubber. Table 1 for calcium oxide
Powdered product VESTA-PP (manufactured by Inoue Lime Co., Ltd.) was mixed in varying amounts as shown in FIG. Granular VESTA-BS was used as calcium oxide treated with fatty acid, and CML21 (manufactured by Ohmi Kagaku Co., Ltd.) in paste form was used as calcium oxide treated with process oil. This mixture, to which a vulcanizing agent, filler, etc. were added, was kneaded in a Banbury mixer according to a conventional method, passed through an extruder, molded, and vulcanized to form a tire.

[0012] After the rubber compositions having the formulations shown in Table 1 were vulcanized, they were evaluated by performing a dynamic viscoelasticity test, a heat blow phenomenon test, and a vehicle running test. Viscoelasticity test: Viscoelasticity was measured using a viscoelasticity measuring machine manufactured by Iwamoto Seisakusho at a dynamic strain of 5%.
, the tan δ was measured under the conditions of a frequency of 10 Hz and a temperature of 70°C. Heating blow phenomenon test: After leaving a 10 x 10 x 4 mm vulcanized rubber test piece in a hot air circulation oven set at various test temperatures for 30 minutes, observe the air bubbles on the cut section of the test piece. The blowout temperature was the temperature at which bubbles started to form. Therefore, the higher the blowout temperature, the better the heat resistance.

Vehicle running test: Size 380/600R1 motorcycle tires using tread rubber of various compositions
7 attached to the rear wheel of a motorcycle and run as fast as possible on the dry road surface of a circuit with one lap of 4.4km, at approximately 270km/h.
The tires were driven to achieve a maximum grip of m, and the feeling was scored, and the score when the grip level was the best for each tire was taken as the grip performance. Furthermore, if the vehicle continues to run at such high speeds, the grip performance will rapidly deteriorate due to blowouts during the run, but the distance traveled up to that point was defined as the blowout resistance. This grip performance and blowout resistance are expressed as an index compared to tires with conventional treads. The larger the value of both of these indexes, the better the performance.

[0014]

[Table 1]

As can be seen from the test results shown in Table 1, styrene-butadiene copolymer rubber with a high styrene content was used, and an appropriate amount of carbon black with a high iodine adsorption amount was used, and calcium oxide was added to the rubber by 1 to 15%. The tread rubber compounded in parts by weight does not impair grip performance, does not foam even when the temperature of the rubber rises to the point where conventional rubber compositions would foam, and can withstand higher temperatures. The so-called blowout resistance is improved. The amount of calcium oxide to be blended is more preferably around 5 to 10 parts by weight. Also,
It has been found that similar effects can be obtained by treating calcium oxide with fatty acids or process oil.

[0016]

[Effects of the Invention] As explained above, the rubber composition for tire tread of the present invention maintains grip performance, which is most important for a tire, and can provide a tire that has extremely good heat resistance during high-speed running. . As a result, as with conventional tires, the tread rubber generates heat during continuous driving, causing air bubbles to be generated inside the rubber, resulting in a reduction in grip performance and even the risk of serious accidents such as the tread being broken and flying off. can be prevented.

Claims (1)

[Claims] Claim 1: At least one compound in which the total amount of bound styrene is 30% by weight or more of the styrene-butadiene copolymer rubber.
70 parts by weight or more and 250 parts by weight or less of carbon black with an iodine adsorption amount of 90 mg or more per gram and calcium oxide alone or calcium oxide for 100 parts by weight of diene rubber containing styrene-butadiene copolymer rubber. A rubber composition for a tire tread, characterized in that it contains 1 part by weight or more and 15 parts by weight or less of calcium oxide treated with fatty acid or process oil.