JPH03210344A - Rubber composition for tire sidewall - Google Patents

Abstract

PURPOSE:To obtain the title compsn. excellent in the crack growth resistance and failure characteristics by using, as the principal component, an isoprene- butadiene copolymer rubber having a trans-1,4 bond content, isoprene content, and Mooney viscosity each in a specified range. CONSTITUTION:The title compsn. contains, as the principal component, an isoprene-butadiene copolymer rubber having a trans-1,4 bond content in the isoprene part of 90% or higher, an isoprene content of 10-95wt.%, and a Mooney viscosity (ML1+4, 100 deg.C) of 30-100. A trans-1,4 bond content lower than 90% gives an inferior crack growth resistance. A Mooney viscosity lower than 30 also gives an inferior crack growth resistance, and one higher than 100, a poor processability. An isoprene content lower than 10% degrades the failure characteristics and one higher than 95%, the crack growth resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rubber composition for tire sidewalls that has excellent crack growth resistance.

[Prior art] Passenger car tires have been rapidly becoming flatter in recent years, and as a result, the load placed on the sidewalls has increased and distortion is increasing, so it is desired to improve crack growth resistance. .

As a method for improving crack growth properties, polybutadiene rubber, which has excellent crack growth properties, is generally used. However, if polybutadiene is used in large amounts or singly, the fracture properties will be extremely low and there will be problems in terms of durability.

For the reasons mentioned above, polybutadiene rubber is often used in blends with natural rubber, which has excellent fracture properties, but natural rubber does not have very good crack growth resistance, and there is no way to satisfy this problem. isn't it.

[Problems to be Solved by the Invention] An object of the present invention is to provide a rubber composition for tire sidewalls that has excellent crack growth resistance and fracture properties.

[Means for Solving the Problems] The present invention provides transformers 1 and 4 of the microstructure of the isoprene portion.
- bond content of 90% or more and isoprene content of 10
~95% by weight and Mooney viscosity (ML, 10
The present invention is a rubber composition for a tire sidewall, which contains as a main component a 1+4 isoprene-butadiene copolymer rubber having a temperature of 30 to 100 (0°C), and thereby solves the above-mentioned problems.

The trans-1,4-bond content of the isoprene-butadiene copolymer rubber used in the present invention is 90% or more, preferably 92 to 99%; if it is less than 90%, the crack growth resistance, which is the object of the present invention, is poor. .

The Mooney viscosity (ML, 100cm + 4℃) of the copolymer rubber is 30 to 100, preferably 40 to 90, more preferably 45 to 75. If it is less than 30, the crack growth resistance will be poor, and if it exceeds 100, it will be difficult to process. Sexuality becomes worse.

The isoprene content of the copolymer rubber is 10 to 95% by weight, preferably 20 to 90%, and more preferably 50 to 90% by weight. If it is less than 10%, the fracture properties will be poor, and if it exceeds 95%, the crack growth resistance will be poor. Become.

The copolymer rubber of the present invention is obtained by solution polymerizing isoprene and butadiene simultaneously or sequentially in an inert organic solution in the presence of a catalyst system consisting of a Ti compound supported on an Mg compound and an organoaluminum compound, for example. It is suitably manufactured by this method.

The rubber composition of the present invention can be obtained by kneading it using conventional processing equipment such as rolls, Banbury mixers, kneaders, etc.

In addition, commonly used compounding agents such as reinforcing agents such as carbon black, vulcanization accelerators, anti-aging agents, sulfur, etc. can also be used as appropriate.

The preferred amount of the reinforcing agent is 30 to 150 parts by weight, more preferably 40 to 100 parts by weight, based on 100 parts by weight of the raw rubber.
Parts by weight. If it is too large, the crack growth resistance tends to be poor, and if it is too small, the fracture properties are reduced.

The composition of the present invention uses the isoprene-butadiene copolymer rubber of the present invention as a main component as a rubber component.
Other rubbers (for example, polybutadiene rubber, natural rubber, polyisoprene rubber, etc.) can be blended and used within a range of less than % by weight.

[Examples] Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. All compounding figures for the rubber compositions in the table are parts by weight, and the properties of the rubber were evaluated by the following test methods.

Test method> (1) Tensile strength: According to JIS K6301.

(2) Crack growth resistance: JIS K6301 No. 3 dumbbell with a length of 0.7 length and a width of 0 in the center of the dumbbell in the direction perpendicular to the dumbbell.
．． 1 degree scratch, vibration frequency 600 cycles/min, strain 30
%, and the number of times it takes to break is expressed as an index, with Comparative Example 3 set as 100.

(3) Microstructure analysis method and determination of isoprene/butadiene composition ratio: Polybutadiene and polyisoprene were obtained in advance under the same conditions as in the example. Each of these polymers was dissolved in 0-dichlorobenzene and formed into a film by a casting method. Each film was analyzed by infrared absorption analysis, and for polybutadiene, method CD, Morer et al.
o ; Chemie 1rad,.

41, 758 (1959)). For polyisoprene, P, C1alpell
Methods such as i [Macromol, Cheap,
61.250 (1983)) was used.

In this way, polybutadiene and polyisoprene, whose microstructures had been clarified in advance, were mixed in an arbitrary ratio to form a film. D138 by infrared absorption spectrometry
5/D967 and isoprene/butadiene ratio or D13
A calibration curve of 85/D911 and the isoprene/butadiene ratio was created to determine the isoprene/butadiene ratio composition in the copolymer. Furthermore, the microstructure of the copolymer was confirmed by the above method since it was no different from that of a homopolymer mixed film.

Moreover, the isoprene-butadiene copolymer rubber used in the examples was manufactured by the following method.

Preparation of catalyst 1.5 g of palladium carbon powder (palladium content 5%) was placed in a 500 ml flask purged with nitrogen.

300 ml of dried 1,2-dichloroethane and 11 ml of titanium tetrachloride were charged, and 43 ml of n-dibutyl ether was added dropwise while stirring. Keep the flask at 25°C.
While stirring, add 0.0% hydrogen. Bubbling was carried out at a rate of 21/ml for 15 hours to produce a yellow-black solution. The solution was filtered under nitrogen and the powdered palladium carbon was removed from door to door.

The P solution was a uniform yellow-black solution. When this homogeneous solution was analyzed by redox titration, the reduction rate of titanium tetrachloride was approximately 100%, indicating that it was a homogeneous solution of titanium trichloride. 1,2-dichloroethane was added to this solution to bring the concentration of titanium trichloride to 0. It was adjusted to 2 mol/1.

Next, 25 g (0°262 mol) of anhydrous powdered magnesium chloride was placed in 12 flasks that had been thoroughly dried and purged with nitrogen.
and di(2-ethylhexyloxy)(2-ethylhexyl)phosphine oxide 360ml (0,78
7 mol) was added and dissolved under stirring. Add n-hexane to this and make a total volume of 524ml (0.0ml with MgC12).
The amount was set at 50 mol/j.

200 ml of the above homogeneous solution containing magnesium chloride (0.1 mol of MgC12) was placed in a No. 32 flask, and then 150 ml of the above titanium dioxide solution (30 mmol) was added.
added. Furthermore, add 1500ml of n-hexane,
A green homogeneous solution was obtained.

When 80 ml of titanium tetrachloride as a precipitating agent was slowly added dropwise to the homogeneous solution thus produced while stirring, a dark green fine powder solid was produced. After stirring for 1 hour, fine powder was precipitated. The supernatant was a black homogeneous solution. P the supernatant
Separately remove the finely powdered solid in 2000ml of fresh n-hexane.
Washed with 1. This operation was repeated three times. 2,000 ml of n-hexane was added to this finely powdered solid, and 2,000 ml of a hexane solution containing 30 mmol of diisobutylaluminum monochloride was added. After stirring at 30°C for 1 hour, the mixture was allowed to stand, the supernatant was removed separately from P, and the remaining fine The powdered solid was washed by adding fresh 2000 ml of n,-hexane. This operation was repeated six times. N-hexane was added to bring the total volume to 2000 ml to obtain an n-hexane suspension of a slightly yellow-green fine powder solid. The Ti concentration was determined by colorimetric analysis and was 0.003 mol/A.

Polymerization 52 1590 g of n-hexane, 425 g of isoprene, 75 g of butadiene, and 15.3 moles of diisobutylaluminum were placed in an autoclave and stirred. The content temperature was 23°C. Next, after adding the solid catalyst suspension prepared above (1.53 mmol based on Ti atoms), polymerization was carried out at 50° C. for 3.5 hours, and post-treatment was carried out according to a conventional method. After vacuum drying, 183 g of polymer was obtained (Document IBR-I). The butadiene portion of the resulting polymer had a composition of 98% trans-1,4-bonds, and the isoprene portion had a composition of 97% trans-1,4-bonds. The Mooney viscosity ML (100°C) of the polymer was 60. The 1+4 isoprene content in the polymer was 58% by weight. Samples I BR-II to IBR-m shown in Table 1 were polymerized in the same manner.

Examples 1 to 3, Comparative Examples 1 to 4 Table 2 shows the formulation and the test results of the vulcanizate cured at 145°C.

As seen in Examples 1 to 3 below, the rubber composition of the present invention has excellent crack growth resistance and has a good balance with fracture properties, which are also indicators of durability. It is suitable as a composition. On the other hand, comparative example 2
．． 4 has excellent fracture properties but significantly poor crack growth resistance;
Comparative Examples 1.3 are not suitable as rubber compositions for tire sidewalls because they are inferior in both crack growth resistance and fracture properties.

[Effects of the Invention] As shown in the above Examples and Comparative Examples, the isoprene-butadiene copolymer rubber composition of the present invention significantly improves the crack growth resistance required for tire sidewalls and also improves the fracture properties. This rubber composition is extremely preferable and useful for tire sidewalls.

Claims (1)

[Claims] (1) The trans-1,4-bond content of the microstructure of the isoprene part is 90% or more, and the isoprene content is 10 to 9
5% by weight, and Mooney viscosity (ML_1_+_4, 1
A rubber composition for tire sidewalls, which contains as a main component an isoprene-butadiene copolymer rubber having a temperature of 30 to 100 (00C).