KR20020094120A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE: A rubber composition for the tread of a tire is provided, to improve the gasoline mileage, the abrasion resistance and the braking performance on a wet road by using a fused silica having a specific property and a rubber having a specific glass transition temperature. CONSTITUTION: The rubber composition comprises 100 parts by weight of a source rubber; 30-100 parts by weight of a styrene-butadiene rubber with a glass transition temperature of -50 to -10 deg.C; 10-120 parts by weight of silica with a OH-group density (Sears number) of 20 ml/5 g or less as a reinforcement; and at least one additive selected from the group consisting of a curing agent, a curing activator, a softening agent, a process promoter, a curing promoter and a coupling agent. Preferably the silica has a BET specific area of 400 m2/g or less and a CTAB (cetyltrimethylammonium bromide) specific area of 400 m2/g or less.

Description

Rubber composition for tire treads

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for tire treads. More specifically, (i) Sheath number is 20 ml / 5 g or less, nitrogen adsorption (BET) specific surface area is 400 m 2 / g or less, and cetyltrimethylammonium bromide (CTAB) The rubber composition for tire treads having a low fuel efficiency, abrasion resistance and wear resistance on wet roads by simultaneously containing silica having a specific surface area of 400 m 2 / g or less and (ii) styrene-butadiene rubber having a glass transition temperature of -50 to -10 ° C. It is about.

As the tire industry develops, we are expanding our technology to produce low fuel consumption, low rolling resistance and environmentally friendly products. The first concern was to improve the interaction between carbon black and polymers, the most widely used reinforcing agent.

However, due to the characteristics of carbon black, there is a problem in that the heat generation of the rubber while driving the vehicle not only decreases the durability of the tire, but also generates high heat during processing, thereby lowering the adhesiveness of the rubber and lowering the physical properties.

As a solution to this, silica has been proposed.Since silica has a high polarity, it is not easily miscible with a nonpolar rubber, so that a coupling agent (coupling agent), which is sometimes referred to as a silane coupler, is introduced. Since the working force was improved, tire technology using silica began to develop rapidly.

On the other hand, in the prior art, in the case of a tread rubber composition used in a low fuel efficiency tire, it was very difficult to simultaneously improve the wear resistance and braking performance on the wet road surface with low fuel efficiency.

That is, in order to solve the problem of low wear resistance, carbon black is increased or butadiene rubber is used. When carbon black is used, low fuel efficiency is reduced, but butadiene rubber is used, and damping performance is reduced. There was a problem.

In addition, in order to solve the problem of low braking performance on wet roads, there is a problem in that low fuel consumption performance is reduced by increasing the amount of carbon black or using rubber having a high glass transition temperature.

Accordingly, the present invention comprises a rubber composition for tire treads that improves low fuel consumption performance, wear resistance and braking performance on wet roads by containing precipitated silica having specific properties and rubber having a specific glass transition temperature in order to solve the conventional problems. It aims to provide.

In the present invention, in order to achieve the above object (i) as precipitated silica having specific properties, the Sears number is 20 ml / 5 g or less, the nitrogen adsorption (BET) specific surface area is 400 m 2 / g or less, and cetyltrimethylammonium bromide ( CTAB) Silica having a specific surface area of 400 m 2 / g or less (ii) As a rubber having a specific glass transition temperature, for tire treads, a styrene-butadiene rubber having a glass transition temperature of -50 to -10 ° C is used. Provide a rubber composition.

Hereinafter, the present invention will be described in detail.

The rubber composition for tire tread of the present invention is a raw material rubber and a reinforcing agent including styrene-butadiene rubber having a glass transition temperature of -50 to -10 ° C, and has a hydroxyl group density (OH-group density; Sears number) of 20 ml / 5g or less. 10 to 120 parts by weight of silica having a BET specific surface area of 400 m 2 / g or less and cetyltrimethylammonium bromide (CTAB) specific surface area of 400 m 2 / g or less of the raw material rubber; Typical additives include sulfur as a vulcanizing agent, zinc oxide as a vulcanizing agent, aromatic oil as a softener, Structol A60 as a processing aid, CZ as a vulcanization accelerator, 1,3-diphenylguanidine and sulfide compounds as coupling agents.

Styrene-butadiene rubber having a glass transition temperature of -50 to -10 ° C, which is a rubber added to the rubber composition for tire tread of the present invention, serves to increase braking performance on wet road surfaces.

The styrene-butadiene rubber having a glass transition temperature of -50 to -10 ° C is used in an amount of 30 to 100% by weight based on the raw material rubber, and the glass transition temperature of -50 to -10 ° C is 30% by weight of a styrene-butadiene rubber. If it is used above, braking performance on wet road surface is increased.

On the other hand, it will be described in more detail with respect to the silica used in the present invention.

Silica added to the rubber composition for tire tread of the present invention

First, the hydroxyl group density (OH-Group-Density) is preferably 20ml / 5g or less.

In this case, the hydroxy group density represents a Sears number, which is a criterion of the degree to which silica is dispersed in rubber. That is, since the hydroxyl group is hydrophilic, the larger the hydroxy group density of the silica, the more difficult it is to disperse in the hydrophobic rubber, and the smaller the silica, the better the silica is dispersed in the rubber.

However, if the hydroxy group density is less than 10ml / 5g, the absolute value of chemical bonding with the rubber may become small, and if the hydroxy group density is greater than 20ml / 5g, the hydrophilic silica becomes difficult to disperse in hydrophobic rubber. It is more preferable that the hydroxyl group density of the silica becomes a value of 10 to 20 ml / 5 g.

The hydroxy group density is determined by titrating the hydroxy group distributed on the silica surface with Sears reagent.Even if the silica has any form such as powder, granule or micro pearl, it should be carried out after pretreatment to a certain form. do.

Secondly, the nitrogen adsorption specific surface area is preferably 400 m 2 / g or less.

Nitrogen adsorption specific surface area is the specific surface area of precipitated silica measured by Brunauer, Emmett and Teller method (BET method) using nitrogen as adsorbent (hereinafter referred to as "BET specific surface area"). Abbreviated).

When the BET specific surface area of the silica used in the present invention is smaller than 100 m 2 / g, there is a problem in that reinforcing performance such as abrasion performance is lowered. More preferably, the BET specific surface area is from 100 to 400 m 2 / g.

Third, the cetyltrimethylammonium bromide specific surface area is preferably 400 m 2 / g or less.

The cetyltrimethylammonium bromide specific surface area refers to the value of the specific surface area of precipitated silica (hereinafter abbreviated as "CTAB specific surface area") measured using a standard Cetyltrimethylammonium bromide solution.

When the CTAB specific surface area of the silica used in the present invention is smaller than 100 m 2 / g, there is a problem in that reinforcing performance such as abrasion performance is deteriorated. More preferably, the CTAB specific surface area is from 100 to 400 m 2 / g.

In addition, the coupling agent included in the rubber composition of the present invention has two functional groups, and serves to improve the reinforcement of the silica to facilitate the mixing of the polar silica and the non-polar rubber.

Coupling agents used in rubber treads for tire treads typically contain sulfur in the areas where they can bind with rubber, where the reaction with rubber is monosulfide, disulfide, and poly It is classified as a case of polysulfide.

Examples of the use of sulfur-containing coupling agents include U.S. Pat. .

Hereinafter, the present invention will be described in more detail based on Examples. However, this invention is not limited by the following Example.

Example 1

Including silica D having the properties shown in Table 1, as shown in Table 2, KBR31 and s-SBR, Si-69 as a coupling agent, A # 2 Oil as a softener, zinc oxide, stearic acid, a processing aid Structol A60, sulfur, vulcanization accelerator CZ and 1,3-diphenylguanidine were added to mix in a half-barrier mixer was released at 155 ℃ to prepare a rubber composition.

Detailed description of the process step by step, first, to the raw material rubber is added 2/3 silica, 2/3 Si-69, 2/3 A # 2 Oil, zinc oxide and stearic acid for the amounts shown in Table 2 below. After mixing in a half-barrier mixer was released at 155 ℃. Then, to the obtained compound rubber, 1/3 of silica, 1/3 of Si-69, 1/3 of A # 2 Oil and processing aids were added to the used amounts shown in Table 2, followed by mixing in a half-barrier mixer. It was released at ℃. Finally, sulfur and zinc oxide were added thereto, mixed in a half-barrier mixer, and then released after 1 minute and 30 seconds.

Example 2

A rubber composition was prepared in the same manner as in Example 1, except that 80 parts by weight of silica E having the properties shown in Table 1 was used.

Example 3

A rubber composition was prepared in the same manner as in Example 1, except that 80 parts by weight of silica F having the properties shown in Table 1 was used.

Comparative Example 1

A rubber composition was prepared in the same manner as in Example 1, except that 80 parts by weight of silica A having the properties shown in Table 1 was used.

Comparative Example 2

A rubber composition was prepared in the same manner as in Example 1, except that 85 parts by weight of silica A having the properties shown in Table 1 was used.

Comparative Example 3

A rubber composition was prepared in the same manner as in Example 1, except that 80 parts by weight of silica B having the properties shown in Table 1 was used.

Comparative Example 4

A rubber composition was prepared in the same manner as in Example 1, except that 80 parts by weight of silica C having the properties shown in Table 1 was used.

TABLE 1

Sears Water (ml / 5g) BET specific surface area (㎡ / g) CTAB specific surface area (㎡ / g) Silica A 24.7 176 153 Silica B 21.9 153 154 Silica C 23.2 179 161 Silica D 18.9 152 154 Silica E 19.4 146 148 Silica F 15.5 177 161

TABLE 2

Comparative example Example One 2 3 4 One 2 3 Raw material rubber KBR31 33 33 33 33 33 33 33 s-SBR 76 76 76 76 76 76 76 Silica A 80 85 - - - - - B - - 80 - - - - C - - - 80 - - - D - - - - 80 - - E - - - - - 80 - F - - - - - - 80 Coupling Agent (Si-69) 6.4 6.4 6.4 6.4 6.4 6.4 6.4 Softener (A # 2 Oil) 31 31 31 31 31 31 31 Zinc oxide 3 3 3 3 3 3 3 Stearic acid 2 2 2 2 2 2 2 Processing aid 1.5 1.5 1.5 1.5 1.5 1.5 1.5 brimstone 1.4 1.4 1.4 1.4 1.4 1.4 1.4 CZ 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1,3-diphenylguanidine 2 2 2 2 2 2 2 1) Unit: parts by weight 2) KBR31: A # 2 Oil 37.5 phr extended butadiene rubber 3) s-SBR: solution polymerization styrene-butadiene rubber with glass transition temperature -20 ℃

Experimental Example

In the 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.

TABLE 3

Comparative example Example One 2 3 4 One 2 3 300% modulus (MPa) 117 131 137 114 131 131 110 Elongation (%) 344 310 422 417 403 401 448 Wear (g) 0.393 0.371 0.365 0.366 0.344 0.327 0.345 tanδ 0 ℃ 0.202 0.212 0.207 0.199 0.197 0.194 0.192 60 ℃ 0.122 0.133 0.132 0.121 0.114 0.116 0.112

In this case, the degree of wear refers to a Lambon abrasion, which represents the loss of rubber worn by rotating at a sliding ratio of 25% and a load of 1.5 kg at room temperature. The smaller the value, the better the wear performance.

In addition, tanδ at 0 ° C. indicates braking characteristics, and the higher the value, the better the braking performance, and tanδ at 60 ° C. indicates the rotational resistance, and the lower the value, the better the rotation resistance.

From the results of Table 3, in Examples 1 to 3, by using silica having a Sears number of 20 ml / 5g or less, the braking performance was similar but the rotational resistance and the abrasion performance were comparable to those of Comparative Examples 1 to 4, which were not. It can be seen that the improvement.

As described above, the rubber composition for tire treads according to the present invention has a Sears number of 20 ml / 5 g or less, a BET specific surface area of 400 m 2 / g or less, a CTAB specific surface area of 400 m 2 / g or less, and a glass transition. By containing styrene-butadiene rubber having a temperature of -50 to -10 ° C, rotational resistance and abrasion performance can be improved while maintaining braking performance, thereby lowering fuel economy.

In other words, the rubber composition for tire treads according to the present invention has the effect of simultaneously improving low fuel efficiency, wear resistance and braking performance on wet road surfaces.

Claims (2)

Styrene-butadiene rubber having a glass transition temperature of -50 to -10 ° C is contained in an amount of 30 to 100 wt% based on the raw material rubber, and a silica having a hydroxyl group density (OH-group-density; Sears number) of 20 ml / 5 g or less 10 to 120 parts by weight based on 100 parts by weight of the raw material rubber, and for a tire tread comprising at least one additive selected from the group consisting of vulcanizing agents, vulcanizing agents, softeners, processing aids, vulcanization accelerators and coupling agents. Rubber composition. The method of claim 1, The silica has a nitrogen adsorption (BET) specific surface area of 400 m 2 / g or less, cetyltrimethylammonium bromide (CTAB) specific surface area of 400 m 2 / g or less rubber composition for the tire tread.