KR20030042882A - Tread rubber composition for pneumatic tire - Google Patents

Abstract

PURPOSE: A rubber composition of pneumatic tire treads for heavy load, in particular, vehicles used in construction which has improved wear resistance, chipping/cutting resistance and heat generating resistance is provided. CONSTITUTION: The rubber composition for heavy load pneumatic tire treads comprises 100 parts by weight of a base rubber, 40 to 60 parts by weight of carbon black having a nitrogen adsorption specific surface of 125 to 135 m2/g and a tint coloring value of 120 to 130%, 5 to 10 parts by weight of silica, total 3.0-4.0 parts by weight of a vulcanization accelerator and sulfur wherein the weight ratio of the vulcanization accelerator to sulfur is between 0.4 and 0.7, and other conventional additives.

Description

Tread rubber composition for pneumatic tires for heavy loads

The present invention relates to a tread rubber composition of a heavy load pneumatic tire, and more particularly, to a tread rubber composition of a heavy load pneumatic tie which is very suitable for a construction vehicle by improving wear resistance and chipping / cutting resistance and improving heat resistance. will be.

Heavy-duty pneumatic tires used in construction vehicles such as dump trucks, loaders, and graders are heat-resistant with abrasion resistance, chipping and cutting resistance due to the severe use conditions by driving mainly heavy loads and unpaved roads. It is very important to be balanced at this high level.

As a method for improving the abrasion resistance and chipping / cutting resistance of tread rubber of tires used in these applications, it is common to use a carbon black as a reinforcing agent having a small particle size or a large structure with attention to the structural characteristics of the carbon aggregates. a method, a method which increased the amount of the carbon black to become weight for this enhanced interaction between the carbon black and the polymer and by the other hand to enhance the rubber reinforcement.

However, in general, the use of carbon black having a small particle diameter increases the reinforcement with rubber to improve wear resistance. However, it is generally known that the smaller the particle diameter, the lower the heat resistance. In the case of heavy duty tires, separation accidents caused by heat generation cause significant problems in performance of the product. In addition, even when the blending amount of carbon black is increased, the heat resistance resistance is unavoidable, and the unvulcanized viscosity due to the increase in the bonding phase of the carbon black and the polymer also increases, which leads to a decrease in processability.

On the other hand, particulate, chipping / cutting improve resistance Sikkim and at the same time a degree of Japanese Patent Laid-Open with a bar, one example which is known to improve the naebal recessive if the rubber composition suitably blended with silica using a tread rubber for a tire 11-209515 discloses a tire in which a rubber composition comprising 3 to 20 parts by weight of silica having a nitrogen adsorption specific surface area of 200 to 220 m 2 / g is used for tread rubber. However, even the technique using such a silica cannot be said to have sufficient heat resistance improvement.

On the other hand, it is generally thought to increase the blending ratio of silica to carbon black for the above purpose, but as the blending amount of silica increases, it is known that the wear resistance and the heat resistance are lowered due to the dispersibility of the silica, and the workability during tire production is also reduced. .

Japanese Patent Application Laid-Open No. 8-239515 discloses a rubber composition in which a certain amount of ABS (acrylonitrile butadiene styrene) resin having a heat deformation temperature of 70 to 180 ° C. is mixed to improve chipping / cutting resistance without deterioration of wear and heat resistance. This is because, after a certain period of use, the weak brittle ABS resin is cured, resulting in a sharp drop in cutting resistance.

In Japanese Patent Laid-Open No. 13-253974, a specific carbon black having a small particle size is mixed with a rubber base material using a specific butadiene rubber having a molecular weight distribution (ratio between the weight average molecular weight and the number average molecular weight) of 2.0 or more in natural rubber and a predetermined ratio. In addition, the present invention discloses a rubber composition in which the weight ratio of the vulcanization accelerator and sulfur is 0.35 to 1.3, and the total content of the vulcanization accelerator and sulfur is 2.5 to 3.0 parts by weight, although the wear resistance is improved due to the use of butadiene rubber. The problem that resistance falls is caused. On the other hand, when the weight ratio of the vulcanization accelerator and sulfur is around 0.8 to 1.3, it is usually classified as a semi-EV system. In the case of this vulcanization system, since the crosslinking structure has a large amount of thermally stable monosulfide or disulfide crosslinking structure, It is advantageous for thermal aging, but is disadvantageous for chipping resistance as modulus increase and elongation are reduced. In addition, since the total content of the vulcanization accelerator and sulfur may be low, the crosslinking density may be low. Generally, the higher the crosslinking density, the lower the hysteresis and the lower the exothermic temperature of the rubber. Therefore, due to the low crosslinking density, it is estimated that heat generation resistance is disadvantageous.

In recent years, tires for construction vehicles are becoming larger and larger, and thus heat generation performance is particularly important.

Accordingly, the present inventors blend a certain amount of specific carbon black with a small particle diameter in order to improve wear resistance and chipping / cutting resistance under the above circumstances, and adjust the vulcanizing agent to compensate for the deterioration of heat generation caused by the crosslinking density. To increase the heat resistance by increasing the vulcanizing agent content and increase the vulcanizing agent to reduce the elongation rate, so that the chipping resistance is not disadvantageous, the weight ratio of the vulcanization accelerator and sulfur is used at a constant ratio, and the content of silica is reduced to reduce the existing tread composition. As a result of improving heat resistance equal to or higher than in comparison, it has been found that the present invention is suitable as a heavy-load pneumatic tire tread rubber which is very suitable for construction vehicles.

Accordingly, it is an object of the present invention to provide a tread rubber composition of a pneumatic tire for heavy loads having improved wear resistance and chipping / cutting resistance and improved heat resistance.

The tread rubber composition of the pneumatic tire of the present invention for achieving the above object is carbon black having a nitrogen adsorption specific surface area of 125 to 135 m 2 / g and tint color value of 120 to 130% based on 100 parts by weight of the raw rubber. 40 to 60 parts by weight, 5 to 10 parts by weight of silica, 3.0 to 4.0 parts by weight of the vulcanization accelerator and sulfur (wherein the weight ratio of vulcanization accelerator and sulfur is 0.4 to 0.7) and the usual additives do.

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

In the tire tread rubber composition of the present invention, carbon black having a small particle size is mixed in an appropriate amount for the purpose of improving abrasion resistance and chipping / cutting resistance. The carbon black used herein has a nitrogen adsorption specific surface area of 125 to 135 m 2 / g. It is preferable that the tint coloring value is 120 to 130%, which is measured according to ASTM D4820, 3285.

The carbon black having such a small particle diameter is contained in an amount of 40 to 60 parts by weight based on 100 parts by weight of the raw material rubber. If the content is less than 40 parts by weight, it is difficult to expect an improvement in wear resistance and chipping / cutting resistance, and more than 60 parts by weight. Since the heat resistance fall is large, it is difficult to expect a complementary effect by adjusting the vulcanizing agent, and the workability is accompanied by a fall.

However, in the case of using carbon black having a small particle size as described above, heat resistance may be lowered, and a vulcanizing agent is adjusted to compensate for this.

Specifically, the weight ratio of the vulcanization accelerator and the sulfur is used in a certain ratio so as to increase the content of the vulcanizing agent for the purpose of improving the heat generation resistance through the increase of the crosslinking density, and the elongation rate is lowered so that the chipping resistance is not disadvantageous.

More specifically, the vulcanization accelerator and sulfur are used in total amounts of 3.0 to 4.0 parts by weight based on 100 parts by weight of the raw material rubber, and the weight ratio of the vulcanization accelerator and sulfur is used within the range of 0.4 to 0.7.

If the total amount of the vulcanization accelerator and sulfur is less than 3.0 parts by weight based on 100 parts by weight of raw material rubber, it is difficult to expect the effect of improving heat resistance due to the increase in the crosslinking density, and when it exceeds 4.0 parts by weight, the scorch time is shortened, resulting in deterioration of processability. This is undesirable.

In addition, when the weight ratio of the vulcanization accelerator and sulfur is less than 0.4, since the vulcanization density decreases because the vulcanization efficiency decreases, the chipping resistance decreases due to the increase in modulus and the elongation rate.

The vulcanization accelerator may be N-cyclohexyl benzothiazole-2-sulfenamide or N-t-butyl benzothiazole sulfenamide, which is a sulfenamide-based vulcanization accelerator, but is not limited thereto.

On the other hand, since the reinforcement is increased by using carbon black having a small particle size, the content of silica may be reduced as compared with a general rubber composition, thereby reducing the heat resistance. Preferable content of silica is 5-10 weight part with respect to 100 weight part of raw material rubbers. At this time, the silica is preferably a nitrogen adsorption specific surface area of 160 to 180 m 2 / g.

In the tire tread rubber composition of the present invention, as the raw material rubber, natural rubber may be used alone as in a conventional tire tread rubber composition, and styrene-butadiene rubber having favorable cutting resistance may be mixed with natural rubber. At the time of mixing, the styrene-butadiene rubber may be mixed up to 30 parts by weight. If the mixed amount of styrene-butadiene rubber is greater than the above range, the vulcanization time due to the increase of the synthetic rubber becomes longer, so the vulcanization time of the product must be extended and there may be a disadvantage in inhibiting crack growth.

In addition, the present invention, of course, includes additives such as vulcanizing agents and anti-aging agents that have been added in the general tire tread rubber composition.

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

Examples 1-3 and Comparative Example 1

Next, rubber specimens were prepared by conventional procedures using the additives shown in Table 1 at the composition ratios of Table 1.

With rubber specimens, wear resistance and chipping / cutting resistance were measured and the results are shown in Table 1 below.

Here, the measurement of wear resistance was evaluated by using a rambon abrasion tester, which is a method of relatively evaluating the wear resistance by measuring the weight difference before and after the test by rotating the specimen in the abrasive stone at a constant load and speed. The volume change obtained by dividing the loss weight of each specimen by the specific gravity is expressed as an index, and the higher this index value, the better the rubber wear resistance.

On the other hand, as a method of measuring chipping / cutting resistance, a guillotine cut test was carried out. This method is a method of measuring the depth of penetration into rubber by freely dropping a needle having a constant load at a specific height. The higher the value, the better the rubber's resistance to cutting or chipping by external sharp stones or objects, and the higher the index value, the shallower the depth of penetration, that is, the better the chipping / cutting resistance. In addition, the higher the hardness of the rubber, the better the resistance, and the hardness is measured according to KS M6518.

The heat resistance evaluation method of rubber is as follows.

Normally, the rubber is subjected to a certain load and deformation, and then the temperature change is measured to compare the heat resistance.However, when the temperature is directly measured, a test error often occurs, and only the surface temperature is measured, rather than the temperature inside the rubber. Since most testers are not able to express accurate heat resistance. Since the exothermic phenomenon is highly correlated with hysteresis due to the viscoelastic properties of rubber, in the present invention, the tan δ value is measured and compared with the heat generation resistance at the temperature generated during the actual tire running. The lower the tan δ value, the lower the hysteresis of the rubber, which means that the heat generation resistance is excellent, and the higher the index value is. The measurement condition of tan δ is 0.5 strain at 80 ° C. and 10 Hz.

Comparative Example 1 Example One 2 3 Natural rubber 80 80 80 100 Synthetic rubber 20 20 20 - Carbon black A 48 - - - Carbon black B - 48 50 48 Silica 15 10 5 5 Process oil 4 4 4 4 Zinc oxide 3 4 4 4 Stearic acid 3 3 3 3 Antioxidant A 2 2 2 2 Antioxidant B One One One One brimstone 1.8 2.2 2.4 2.2 NS 0.6 1.0 1.4 1.0 NS / sulfur weight ratio 0.33 0.45 0.58 0.45 NS + Sulfur Total Content 2.4 3.2 3.8 3.2 Scotch time 28 25 22 23 Hardness (Shore A) 63 67 69 66 Elongation (%) 530 550 500 530 Rambon Wear Index 100 107 110 108 Cutting performance index 100 112 115 110 Fever Resistance Index 100 103 105 102 Synthetic rubber: Styrene-butadiene copolymer carbon black A: Nitrogen adsorption specific surface area of 110 to 120 m 2 / g, tint coloring value of 110 to 120% carbon black B: Nitrogen adsorption specific surface area of 125 to 135 m 2 / g , Tint coloring value 120-130% Silica: Silica anti-aging agent A with nitrogen adsorption specific surface area of 160-180 m 2 / g A: N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylenediamine aging Inhibitor B: Poly- (2,2,4-trimethyl-1,2-dihydroquinoline) NS: Nt-butylbenzothiazole-2-sulfenamide

From the results of Table 1, in the case of Example 1 compared to the carbon black A used in Comparative Example 1 by the same amount of carbon black B having a smaller particle size and reduced the silica and other compounding agents were the same as the comparative example, The sulfur and vulcanization accelerators were increased, indicating that the abrasion resistance and the cutting resistance were increased compared to the comparative example. Also, the increase in the vulcanizing agent resulted in the decrease in the heat generation resistance due to the change of the carbon black having a small particle size due to the increase of the crosslinking density. It can be seen that.

In the case of Example 2, the carbon black B was increased in Example 1 and the silica content was decreased, and the vulcanization agent was also increased. The abrasion resistance and the cutting resistance were increased and the heat generation resistance was slightly improved as compared with the comparative example. Seemed.

In the case of Example 3, only natural rubber was used instead of 20 parts by weight of synthetic rubber in Example 1, but similarly, the wear resistance and the cut resistance were improved without degrading heat resistance.

As described in detail above, according to the present invention, a rubber composition having a certain amount of carbon black having a small particle diameter is added, the vulcanizing agent is increased, the weight ratio of the vulcanization accelerator and the sulfur is used at a constant ratio, and the silica content is reduced. It is useful as a tread rubber composition of heavy duty pneumatic tires, which is well suited for construction vehicles due to improved chipping / cutting resistance and improved heat resistance.

Claims (4)

Nitrogen adsorption specific surface area is 125-135 m2 / g with respect to 100 parts by weight of raw material rubber, 40-60 parts by weight of carbon black having a tint coloring value of 120-130%, silica 5-10 parts by weight, vulcanization accelerator and sulfur in total Tread rubber composition of a heavy-duty pneumatic tire containing 3.0 to 4.0 parts by weight (wherein the weight ratio of the vulcanization accelerator and sulfur is 0.4 to 0.7) and the usual additives. The tread rubber composition according to claim 1, wherein the silica has a nitrogen adsorption specific surface area of 160 to 180 m 2 / g. The tread rubber composition of a heavy-duty pneumatic tire according to claim 1, wherein the raw material rubber is natural rubber alone or a mixed rubber with less than 30 parts by weight of styrene-butadiene rubber. The tread rubber composition of a heavy-duty pneumatic tire according to claim 1, wherein the vulcanization accelerator is N-cyclohexylbenzothiazole-2-sulfenamide or N-t-butyl benzothiazole sulfenamide.