JPS5834834A - Rubber composition for white sidewall of tire - Google Patents

Abstract

PURPOSE:To provide the titled compsn. having improved modulus, adhesiveness and resistance to flex crack and ozone, by blending surface-treated clay with a component consisting of a diene rubber, an ethylene/propylene/diene terpolymer rubber and a halogenated butyl rubber. CONSTITUTION:55-85pts.wt. surface-treated clay is blended with 100pts.wt. rubber component consisting of 35-70pts.wt. diene rubber, 10-40pts.wt. ethylene/ propylene/diene terpolymer rubber and 10-40pts.wt. halogenated butyl rubber. Examples of surface-treating agents for clay are aminosilanes, mercaptosilanes and mixtures thereof. When the amount of the surface-treated clay is less than 55pts.wt. per 100pts.wt. rubber component, modulus is lowered. when the amount exceeds 85pts.wt., resistance to ozone and flex crack is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rubber composition for white sidewalls of tires, and more specifically to a rubber composition containing a diene rubber, an ethylene-propylene-diene terpolymer rubber, and a halogenated butyl rubber in a specific range. By blending surface-treated clay into the ingredients, the modulus after vulcanization is at the same level as the adjacent black rubber during tire molding, and the adhesion to the black rubber is good, as well as being flex crack resistant. The present invention relates to a rubber composition for white sidewalls of tires that has excellent properties and ozone resistance.

Conventionally, the modulus after vulcanization of a rubber composition for a white sidewall of a tire is 20 to 40 as 300 thimodules.
The modulus required for the sidewall is in the range of kg/cIIl, i.e. 50-80 as 300 thimodulus, 9/cr! It was significantly lower than that. Clays, calcium carbonate, white carbon, alumina, etc. are used as fillers in rubber compositions for white sidewalls, but because they do not chemically bond with polymers, the fillers have poor dispersion and carbon black This is because the reinforcing properties are significantly inferior to that of . Furthermore, even if the amount of these fillers is increased, the reinforcing effect is negligible, and on the contrary, the flex crack resistance is inferior.

On the other hand, in order to obtain an appropriate modulus for the side wall, it is necessary to increase the amount of Atteha and diene rubber in a white rubber composition containing diene rubber, ethylene-propylene-diene terpolymer rubber, and halogenated butyl rubber as rubber components. However, as a result, the blended amounts of ethylene-propylene-diene terpolymer rubber and halogenated butyl rubber are small, and the ozone resistance and flex crack resistance are poor.

In order to improve t-e, ozone resistance, and flex crack resistance, large amounts of ethylene-propylene-diene terpolymer rubber or halogenated butyl rubber are blended, but in this case, the rubber is mixed with other rubbers. - This results in a significant decrease in rubber adhesion, that is, adhesion to the adjacent black sidewall rubber.

As described above, at present, there has been no rubber composition for white sidewalls of tires that satisfies all of the requirements of appropriate modulus, flex crack resistance, ozone resistance, and adhesion to adjacent rubber.

The present invention provides a white tire sidewall rubber composition that improves modulus, which was considered extremely difficult to achieve with conventional white rubber compositions, and also improves ozone resistance, flex crack resistance, and adhesion to adjacent rubber. The purpose is to provide something.

As a result of extensive research, the present inventors have found that a rubber composition containing a diene comb, an ethylene-propylene-diene terpolymer rubber, and a halogenated butyl rubber as rubber components has been surface-treated with clay. The present invention has been achieved by discovering that the above object can be achieved by incorporating a limited amount of.

That is, the present invention includes 35 to 703i parts of diene rubber,
Ethylene-propylene-diene terpolymer rubber 10~
Rubber composition for white sidewalls of tires, characterized in that 55 to 85 parts by weight of surface-treated clay is blended to 10 parts by weight of a rubber component consisting of 1 part by weight of 4O and 10 to 40 parts by weight of halogenated butyl rubber. Open with something.

The rubber composition in the present invention is diene rubber, ethylene-
Contains a specific range of propylene-diene terpolymer rubber and halogenated butyl rubber as rubber components.

As the diene rubber, natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), or a mixture thereof is used, and the content thereof is 35 to 50% in the rubber component.
It is 75% by weight. If the content exceeds 75% by weight, the modulus will improve, but the ozone resistance and flex crack resistance will be poor. Moreover, if the content is less than 35 inches, the modulus decreases.

Ethylene-propylene-diene terpolymer rubber (EP
DM) Iti, usually monomer composition is ethylene 5°~80
The weight% is 20 to 50% by weight of propylene, the diene is ethylidene norbornene, dicyclo is ntadiene, and 1,4-hexadiene is used, and the content is 10 to 40% by weight in the rubber component. be. Content is 10
If it is less than 9.4% by weight, the ozone resistance and flex crack resistance will be poor, and if it exceeds 9.40% by weight, the adhesion to other rubbers will be poor.

Halogenated butyl rubber (HaAbIIR) is 1.0 to 2
．． It is preferable to contain 0% by weight of halogen, specifically chlorinated butyl rubber ((J-IIR) (chlorine content 1.0 to 1.5% by weight), brominated butyl rubber (Br-I
IR) (bromine content 1.8 to 2.0% by weight) or a mixture thereof can be used, and the content thereof is 10 to 40% by weight in the rubber component. If the content is less than 10% by weight, ozone resistance and flex crack resistance will be poor;
If it exceeds % by weight, the adhesion to other rubbers will be poor.

The surface-treated clay used in the present invention is called hard clay, and aminosilane, mercaptosilane, or a mixture thereof is used as a surface treatment agent. The blending amount is 55 to 85 parts by weight based on 100 parts by weight of the rubber component. If it is less than 55 parts by weight, the modulus will be low, and if it exceeds 85 parts by weight, the ozone resistance and flex crack resistance will be poor.

In the present invention, compounding agents such as titanium oxide, zinc oxide, process oil, anti-aging agent, sulfur, and vulcanization accelerator, which are commonly compounded in white rubber compositions in the rubber industry, are blended in appropriate amounts.

The present invention will be specifically described below based on Examples and Comparative Examples. Note that all formulations in Table 1 are parts by weight.

Examples 1 to 5 and Comparative Examples 1 to 6 Rubber compositions for roll sidewalls containing all rubber components were first prepared using the formulations shown in Table 1. This rubber composition
Press vulcanization was performed at 0° C. for 20 minutes to prepare a sample for modulus measurement, a sample for flex crack measurement by Deimateya test, and an ozone crack sample for dynamic ozone test. Using these samples, we tested 600 timodilous (according to JIS K 6!101), Frezuks crack resistance (50% at 40% stroke at room temperature).
Table 1 shows the measurement results of crack growth amount after 10,000 cycles (X) and dynamic ozone cracking property (50 pphm x 24°C x 72 hours). In addition, in the ozone crack property results in Table 1, the number of alphabet butterfly cracks (A
: Few, B: Many, C: Innumerable), numbers indicate the size of cracks, 1: Can be confirmed with a 10x magnification, 2: Can be confirmed with the naked eye, 3: Cracks less than 1%, 4: dP cracks 1~ 5%,
5 knee? fissure 3X or more) t shown respectively.

In addition, in order to evaluate the adhesion with other rubbers, a rubber composition for black sidewall rubber (2% sheet) and a reinforcing layer (
1% carcass + rubber composition for carcass cord) and the rubber composition for white sidewalls shown in Table 1 (2% sheet)
Ten reinforcing layers (1% carcass ten carcass cord rubber composition) were laminated together, co-vulcanized at 160°C for 20 minutes, and a tensile test was performed at 25°C using Autograph 15-2000 manufactured by Takasu Seisakusho. Bottom, tensile speed 200 iIm/
The adhesive strength (k5F/in) was measured at min. and the fracture state was evaluated, and the results are shown in Table 1. Table 2 shows the formulation and physical properties of the rubber composition for black sidewalls.

Comparative Example 1 in Table 2 is a formulation example of a conventional white rubber composition for sidewalls, and the modulus is extremely low. In order to improve this low modulus, in Comparative Example 2, a large amount of ordinary untreated hard clay was blended and, similarly to Comparative Example 1, a relatively large amount of diene rubber (natural rubber) was blended, and the modulus was improved to some extent. However, it has poor flex crack resistance and dynamic ozone crack resistance.

On the other hand, Examples 1 and 2 contain hard clay surface-treated with mercaptosilane.
The 0% modulus is increased to the same level as that of black sidewall rubber, and the flake crack resistance and dynamic ozone crack resistance are also improved.

Comparative Example 3 contains a large amount of diene rubber (natural rubber °) and contains relatively small amounts of ethylene-propylene-diene terpolymer rubber and halogenated butyl rubber. Despite using surface-treated hard clay, it has poor flex crack resistance and dynamic ozone crack resistance.

In Comparative Example 4, only a small amount of diene rubber (natural rubber) was blended, so the modulus was inferior to 300% even though Burr 1 clay whose surface had been treated with mercaptosilane was used. Furthermore, the adhesive force is low and the state of failure is interfacial failure.

Example 3 is an example in which natural rubber and polybutadiene rubber were used together as the diene rubber, and the flex crack resistance and dynamic ozone crack resistance were further improved compared to Examples 1 and 2.

In Example 4, the amount of hard clay surface-treated with mercaptosilane was further increased in the rubber composition of Example 3, but 300 Timodilous was further improved, and the flex crack resistance and dynamic ozone crack resistance were also favorable. in range.

In Comparative Example 5, the amount of surface-treated hard clay mixed with mercaptosilane was small, so the 300 timodine content was low. In addition, the adhesive force is low and the state of failure is interfacial failure.

Example 5 is an example in which hard clay surface-treated with aminosilane is blended, and the 300% modulus is within the desired range and other physical properties are also excellent.

Comparative Example 6 is an example in which a hard clay surface-treated with a large amount of aminosilane is further blended into the rubber composition of Example 5. Although the modulus is further improved, the flex crack resistance and dynamic ozone crack resistance are extremely poor. .

Example 6 and Comparative Example 7 The rubber compositions of Example 1 and Comparative Example 1 were vulcanized and placed as white sidewall rubber in part A of FIG. 1, which is a partial cross-sectional view of a tire (tire size 1858R14). Then, a scalpel cut growth test in an indoor drum test, which is one of the indicators of tire crack resistance, was conducted. The female cut growth drum test was conducted at an air pressure of 1.8 kg/cr+
t, 9 for load 650, @/hr for speed 80, mileage j
Under conditions of 000 Km, female karatora (4% tall x 1% deep) were placed in four locations on the circumference as shown in Figure 2, and the growth rate (A) was determined from the growth values before and after running. Moreover, the distortion (A) of the white part was calculated from the scalpel cut length at 0 load and 630 kg load.

The results are shown in Table 2. Also, white sidewall rubber (4
) and the adjacent black sidewall rubber (B).
The 0% modulus is also shown in Table 3.

Table 3 Example 6 shows the results of white sidewall rubber and black sidewall rubber! Since the 100% modulus is at the same level, the distortion in the white part is small compared to Comparative Example 7, which has a low 600 timidulus of white sidewall rubber.
Furthermore, the growth rate of female cuts will be significantly lower. As described above, since the stress applied to the sidewall portion of the tire of Example 6 can be dispersed over the entire tire, crack resistance is significantly improved, and peeling between the white sidewall rubber and the black sidewall rubber does not occur.

As explained above, the white rubber composition of the present invention improves the modulus after vulcanization to almost the same level as that of the adjacent black rubber during tire molding, and also has excellent flex crack resistance and ozone resistance. Moreover, since it has good adhesion to the adjacent black rubber, it is suitable as a white sidewall of a tire.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a tire (tire size 185 SR14), and FIG. 2 is a diagram showing a scalpel cut portion of the tire in a tire scalpel cut growth drum test. A: White sidewall, B: Black sidewall, 1
: carcass, 2: bead filler, 3: bead wire, R: rim. Patent Applicant: Yokohama Rubber Co., Ltd. Representative Patent Attorney Tatsuo Ito〃〃Tetsuya Ito Figure 1! Figure 2 3

Claims (1)

[Claims] Diene rubber weighs 35-70%! , 10 to 40 parts by weight of ethylene-propylene-diene terpolymer rubber, and 10 to 40 parts by weight of halogenated butyl rubber.
A rubber composition for a white sidewall of a tire, comprising 55 to 85 parts by weight of surface-treated clay.