KR20030049660A - Rubber composition for tire sidewall - Google Patents

Abstract

PURPOSE: A rubber composition for tire side walls having excellent tensile strength and extension as well as improved durability, anti-fatigue property and processing capability is provided. CONSTITUTION: The rubber composition for tire side walls comprises a base rubber consisting of 30 to 70 parts by weight of a natural rubber and 30 to 70 parts by weight of a butadiene rubber as raw materials, and 35 to 90 parts by weight of carbon black having heterogeneity index of 1.7 to 2.5 based on 100 parts by weight of the base rubber. The carbon black has CTAB specific surface area of 45 to 75 m2/g, IA adsorption of 90 mg/g, DBP oil absorption of 80 to 120 ml/100g, CDBP oil absorption of 60 to 100 ml/100g, STSA specific surface area of 40 to 75 m2/g, N2SA specific surface area of 50 to 80 m2/g, a mean diameter of primary particle determined by transmission electron microscopy of 30 to 40 nm, and a weight mean diameter of primary particle of 50 to 80 nm.

Description

Rubber composition for tire sidewall

The present invention relates to a rubber composition for tire sidewalls, and more particularly, to a rubber composition for tire sidewalls to which new carbon black is added so as to improve not only fatigue resistance but also processing performance.

Rubber compositions suitable for tire sidewalls must exhibit a certain degree of strength and elongation, especially at high temperatures, as well as reduced exothermicity, low permanent set, and good adhesion to adjacent parts of the cured tire. In addition, good flex fatigue resistance and ozone and ultraviolet resistance are all other conditions required for sidewall rubber compositions.

The use of blends of polymers has led to the ability to meet such complex and balanced performance demanded by modern tires. For example, all the polymers used in the formulations described by J. Walker et al. Have a high degree of unsaturation, and such formulations are readily vulcanized by using an accelerated sulfur curing agent system.

In the past, vulcanization of ethylene-propylene-diene monomers (EPDM) and highly unsaturated rubbers together generally showed poor strength when cured with conventional accelerated sulfur vulcanization systems. Accordingly, several different attempts have been made to find a way to achieve the desired covulcanization of rubbers with varying degrees of saturation, particularly those of high unsaturated rubbers and EPDM.

One of the most frequently employed attempts is to halogenate highly saturated rubber (usually EPDM) to give a combination of such halogen-modified rubber and sulfur-curable unsaturated rubber. That is, Choen et al. Disclose a sulfur-curable blend of halogenated EPDM and unsaturated rubber in US Pat. No. 3,936,430. Likewise, Hopper et al. Disclose a sulfur curable blend of N-chlorothiocarboxy amide or imide with unsaturated rubber in US Pat. No. 4,017,468. In contrast, Kresge et al. Disclose a sulfur-cured co-vulcanizate of brominated EPDM and highly unsaturated rubbers in US Pat. No. 3,524,826. In the same vein, Landy et al. Disclosed sulfur-curable blends of halogenated EPDM and diene rubber in US Pat. No. 3,956,247, and Hopper et al. In N-chlorothiosulfenamide-modified EPDM in US Pat. No. 3,915,907. Sulfur curable formulations of and diene rubbers are disclosed.

To some extent similar to the sulfur curable formulations described above, Son et al. Disclose a combination of EPDM and highly unsaturated rubbers having -SH or -SN bonds grafted in US Pat. No. 3,897,405. Is sulfur-curable.

In general, the sidewall of the tire is mainly made of natural rubber and polybutadiene rubber, and since the working conditions are always subjected to bending fatigue, the internal and external performance performance against oxygen bending, cracking, cracks, etc. Since it is exposed to ozone, light, etc., it is a part that requires much weather resistance.

Therefore, reducing the thickness of the sidewall portion in order to reduce tire weight and reduce fuel consumption causes problems in trauma resistance, bending fatigue resistance and workability, and reducing the amount of filler such as carbon black degrades the rubber-filler interaction, resulting in problems in reinforcement. There are limits and risks.

In addition, there is a way to improve the rubber reinforcement in order to reduce the thickness of the side wall portion, it is a conventional method to use a more reinforcing filler or to increase the blending amount. However, even in such a case, performances such as hardness, modulus of elasticity, durability, etc. are improved, but workability aspects such as mixing property and extrudability and heat generation are disadvantageous.

Therefore, there is a need for a method of improving rubber reinforcement by methods other than reinforcement by conventional fillers. As part of this, Korean Laid-Open Patent No. 2000-73985 adds a high performance rubber-resin composite vinyl cis rubber (VCR) to a composite of natural rubber and polybutadiene rubber, or replaces polybutadiene with natural rubber. Flexural fatigue resistance, trauma resistance, heat aging resistance, low heat generation, processability, etc. when reducing the thickness of the sidewall for weight reduction and low fuel consumption of the tire by using a composite and at the same time using carbon black less than the usual addition amount Disclosed is a rubber composition for sidewall parts of a tire that is not damaged and has improved performance.

However, the current technology has a problem that the production cost burden is very high.

Thus, the present inventors have completed the present invention by discovering that the new carbon black is applied in place of the carbon black generally used in the sidewall portion, thereby improving durability and fatigue resistance and improving workability.

Accordingly, it is an object of the present invention to provide a rubber composition for sidewalls having excellent tensile strength and elongation as well as improved fatigue resistance and improved workability.

The rubber composition for the side wall of the present invention for achieving the above object comprises 30 to 70 parts by weight of natural rubber and 30 to 70 parts by weight of butadiene rubber as a raw material rubber, HI (Heterogenietty Index, WM / M) value of 1.7 as a reinforcing agent It characterized in that it comprises 35 to 90 parts by weight of carbon black of 2.5 to 100 parts by weight of the raw material rubber.

The present invention will be described in more detail as follows.

In the rubber composition for tire sidewall of the present invention, carbon black having a specific property different from that of carbon black usually added is used. Specifically, the CTAB specific surface area is 45 to 75 m 2 / g, and the IA adsorption amount is 70 to 90 mg /. g, DBP oil absorption of 80 to 120 ml / 100 g, CDBP oil absorption of 60 to 100 ml / 100 g, STSA specific surface area of 40 to 75 m 2 / g, N2SA specific surface area of 50 to 80 m 2 / g, and TEM (Transmission Electron Microscopy) Mean Diameter of Primary Particle (M) is 30 to 40nm, Weight Mean Diameter of Primary Particle (WM) is 50 to 80nm, and HI (Heterogeneity Index = WM / M) Use a value of 1.7 to 2.5.

In more detail, carbon blacks commonly used in tire sidewalls are N330 (HAF), N550 (FEF), N660 (GPF), and the like. These are used individually or in mixture according to the required characteristic of a side wall part. When N330 is used alone, its high modulus improves handling performance, but suffers from fatigue resistance and processing characteristics. In addition, when N550 or N660 is used alone, fatigue resistance and processing characteristics are improved, while tensile strength and elongation are deteriorated.

In some cases, a combination of the N330 and N550 (or N660) is used to compensate for this. In this case, physical properties such as elongation may be improved, but improvement of fatigue resistance is known to be difficult. When two carbon blacks having very different carbon black particle characteristics are mixed, it is presumed that the effect of carbon black having a large particle diameter is greater than that of carbon black having a small particle diameter.

On the contrary, firstly, the carbon black used in the present invention exhibits moderate characteristics of particle diameters so as to simultaneously exhibit the characteristics of N330 and N550.

Commonly known carbon black particle characteristic factors CTAB, DBP, CDBP, TINT, STSA, N2SA all have properties between N330 and N550. The reason why the production of such carbon black is necessary is that, as described above, the improvement of reinforcing performance which cannot be obtained by mixing two carbon blacks having different characteristics can be obtained.

Second, although the basic particle size (M) and the weighted average particle size (WM) by the basic particle size analysis by the TEM photograph have a value between N330 and N550, HI (WM / M) value defined as the ratio of two values It should have this particular value. The meaning of HI indicates the size distribution of the base particles. It is an essential characteristic for improving the fatigue resistance and improvement of processing characteristics obtained by using single carbon black. That is, it is characterized by having a larger value than HI that N330 or N660 has. It is preferable that the characteristic range is 1.7-2.5. If the HI of the carbon black is less than 1.7, the processing characteristics may be lowered, and if it exceeds 2.5, the fatigue resistance may be reduced.

In addition to the carbon black having the above characteristics, the rubber composition for the side wall of the present invention includes 30 to 70 parts by weight of natural rubber and 30 to 70 parts by weight of butadiene rubber as a raw material rubber, and is contained in the rubber composition for sidewalls. Process oils, zinc oxide, stearic acid, antioxidants, waxes, tackifiers, accelerators and sulfur.

It is preferable that the addition amount of carbon black is 35-90 weight part with respect to 100 weight part of raw material rubbers.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

Example 1

As shown in Table 2 below, 50 parts by weight of natural rubber (NR), 50 parts by weight of butadiene rubber (BR), and 75 parts by weight of carbon black are used, and the process oil, zinc oxide, stearic acid, An anti-aging agent, wax, pressure-sensitive adhesive, accelerator, and sulfur were combined to prepare a sidewall rubber composition.

However, in Example 1, those having the properties described as new carbon in Table 1 below were used as carbon black.

Comparative Example 1

Except that 75 parts by weight of N550 in Table 1 was used as the carbon black, a sidewall rubber composition was prepared in the same composition as in Example 1.

Comparative Example 2

Except that 75 parts by weight of N330 in Table 1 was used as the carbon black, a sidewall rubber composition was prepared in the same composition as in Example 1.

Comparative Example 3

As carbon black, 34 parts by weight of N330 and 34 parts by weight of N550 in Table 1 were used, and the other compositions were combined as in Table 2 to prepare a sidewall rubber composition.

Comparative Example 4

45 parts by weight of N330 in Table 1 and 23 parts by weight of N550 in Table 1 were used as the carbon black, and the other compositions were combined as in Table 2 to prepare a sidewall rubber composition.

Comparative Example 5

23 parts by weight of N330 in Table 1 and 45 parts by weight of N550 in Table 1 were used as the carbon black, and the other compositions were combined as in Table 2 below to prepare a sidewall rubber composition.

Comparative Example 6

As carbon black, 37.5 parts by weight of N330 and 37.5 parts by weight of N550 in Table 1 were used, and the other compositions were combined as in Table 2 to prepare a sidewall rubber composition.

new carbon N330 (HAF) N550 (FEF) CTAB (ASTM D3765-99), ㎡ / g 58 82 42 IA (ASTM D1510-99), mg / g 84 82 43 DBP (ASTM D 2414-99), ml / 100g 101 102 121 CDBP (ASTM D3493-99), ml / 100g 82 88 88 TINT (ASTM D 3265-99a),% 76 103 59 STSA (ASTM D 5816-99), ㎡ / g 56 76 39 N2SA (ASTM D 4820-99), ㎡ / g 69 79 41 M, nm 32.8 29.7 50.1 WM, nm 63.2 46.5 85.2 HI, exponent 1.93 1.57 1.70 M: Mean Diameter of Primary Particle WM: Weight Mean Diameter of Primary Particle HI: Heterogeneity Index = WM / Mnew carbon: Columbia Chemicals Company

(Unit: parts by weight) Example 1 Comparative Example One 2 3 4 5 6 Rubber NR 50 50 50 50 50 50 50 BR 50 50 50 50 50 50 50 Carbon black N330 - - 75 34 45 23 37.5 N550 - 75 - 34 23 45 37.5 new carbon 75 - - - - - - Process oil 7 Zinc oxide 3 Stearic acid 2 Anti-aging 3 Wax 1.5 adhesive 3 Accelerator (TBBS) 0.7 brimstone 1.8

Experimental Example

The physical properties of the rubber products obtained according to the above Examples and Comparative Examples were measured, and the results are shown in Table 3 below.

Example 1 Comparative Example One 2 3 4 5 6 Mooney Viscosity (ML _{1 + 4} ) 32.2 33.6 38.2 - - - 35.4 300% modulus (MPa) 9.8 12.0 12.2 9.8 9.5 9.6 12.2 Tensile Strength (MPa) 16.1 16.3 19.3 16.9 17.9 16.0 17.8 Elongation (%) 520 470 470 530 540 520 470 % Dispersion 98.4 97.9 86.6 90.6 90.2 86.0 95.9 Fatigue Resistance (Kcycle) 818 798 220 393 - 285 -

As described in detail above, according to the present invention, the CTAB specific surface area is 45 to 75 m 2 / g, IA adsorption amount is 70 to 90 mg / g, DBP oil absorption is 80 to 120ml / 100g, CDBP oil absorption is 60 to 100ml / 100g , STSA specific surface area is 40 to 75 m 2 / g, N2SA specific surface area is 50 to 80 m 2 / g, and the Mean Diameter of Primary Particle (M) measured by Transmission Electron Microscopy (TEM) is 30 to 40 nm. , Weight Mean Diameter of Primary Particle (WM) is 50 to 80nm, especially rubber composition for sidewall containing carbon black with HI (Heterogeneity Index = WM / M) value of 1.7 to 2.5 lowers modulus and elongation It is possible to improve the processing performance at the same time, that is, to improve not only the fatigue resistance but also the processing performance at the same time.In the end, when such carbon black is used, the carbon black can be increased. Cost savings can be achieved without compromising performance.

Claims (3)

30 to 70 parts by weight of natural rubber and 30 to 70 parts by weight of butadiene rubber as raw materials, and as a reinforcing agent, HI (Heterogenietty Index) value of 1.7 to 2.5 ring carbon black containing 35 to 90 parts by weight based on 100 parts by weight of raw rubber Rubber composition for tire sidewalls. The carbon black has a CTAB specific surface area of 45 to 75 m 2 / g, IA adsorption amount of 70 to 90 mg / g, DBP oil absorption of 80 to 120 ml / 100 g, CDBP oil absorption of 60 to 100 ml / 100 g, STSA The specific surface area is 40 to 75 m 2 / g, the N2SA specific surface area is 50 to 80 m 2 / g, and the Mean Diameter of Primary Particle (M) measured by Transmission Electron Microscopy (TEM) is 30 to 40 nm and weighted. Rubber composition for a tire sidewall, characterized in that the average particle diameter (WM, Weight Mean Diameter of Primary Particle) is 50 to 80nm. The rubber composition for a tire sidewall according to claim 1, wherein the composition further comprises at least one additive selected from the group consisting of process oil, zinc oxide, stearic acid, anti-aging agent, wax, pressure-sensitive adhesive, and sulfur.