JPS5922940A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:The titled composition, obtained by incorporating a specific rubberlike polymeric mixture with carbon black having specific properties and sulfur in relatively small amounts, capable of reducing the rolling resistance without deteriorating braking performance, etc. on wet road surfaces, and suitable for low-fuel consumption tires. CONSTITUTION:A rubber composition for tire treads, prepared by incorporating 100pts.wt. rubber consisting of (A) 20-50pts.wt. styrene-butadiene copolymeric rubber (SBR) with 15-30wt% content of combined styrene and 30-45% content of 1,2-bonds in the butadiene part, (B) 40-70pts.wt. SBR with 20-30wt% content of combined styrene and <=20% content of 1,2-bonds in the butadiene part and (C) 5-30pts.wt. natural rubber and/or polyisoprene rubber with 50-60pts.wt. carbon black having 60-100mg/g I2 adsorption and 100-130ml/100g dibutyl phthalate oil absorption and 1.5-1.8pts.wt. sulfur.

Description

DETAILED DESCRIPTION OF THE INVENTION More specifically, 1,2 bonds in the butanoene moiety are 1,
The rubber component is a normal styrene-ptanoene copolymer rubber with few 2 bonds, natural rubber and/or polyisoprene rubber, and by blending a relatively small amount of carbon black and sulfur with specific properties into the tire. The present invention relates to a comb composition for tire treads that can reduce rolling resistance without impairing various properties such as braking performance on wet road surfaces.

In recent years, from the viewpoint of energy conservation, fuel efficiency of automobiles has been desired, and accordingly, there has been a demand for reducing the rolling resistance of tires. The rolling resistance of a tire is primarily dependent on hysteresis losses in the materials that make up the tire.

Moreover, among the constituent materials, the cap tread, which has a large volume, makes the largest contribution. Therefore, using rubber with low hysteresis loss in the cap tread portion is effective in reducing rolling resistance.

However, these coils with low hysteresis loss have the disadvantage of reduced braking performance on wet road surfaces.
It is required to simultaneously satisfy two contradictory performances: transfer resistance and braking performance on wet road surfaces.

The rolling resistance of a tire is mostly due to hysteresis loss of the material caused by repeated deformation during rotation, and can be expressed as a rebound resilience of 60 to 70 DEG C. for a rubber material.

That is, a rubber material with high rebound resilience has less hysteresis loss and therefore has less rolling resistance.

On the other hand, braking performance on wet road surfaces is due to the frictional resistance caused by the deformation of the rubber material following the unevenness of the road surface when the tread rubber slides on the road surface. It is evaluated by the wet skid resistance value.

The wet skid resistance of a rubber material strongly depends on the molecular chain structure of the raw elastomer and the reinforcing carbon blank. That is, in the styrene-butanoene copolymer rubber commonly used for cap treads for passenger car tires, the wet skid resistance increases as the amount of 1°2 bonds in the butanoene moiety increases. In addition, by using carbon black with strong reinforcing properties or by increasing the blending amount of carbon black, it is possible to increase the tossing resistance. In either case, the impact resilience decreases, but the impact resilience is better when the amount of carbon black is increased than when using a styrene-butadiene copolymer with a high amount of 1,2-bond metal in the free diene part. The decline is steep. Therefore, using a styrene-butadiene copolymer rubber with a high content of 1,2-bond metal in the butatsuene moiety,
Although it is advantageous to satisfy both properties by reducing the amount of carbon black blended, the disadvantage in this case is that the wear resistance is significantly reduced.

The present inventors have conducted various studies regarding the use of styrene-butadiene copolymer rubber having a relatively large amount of 1,2-bond metal in the butanoene moiety. By using a styrene-butanoene copolymer coat with fewer 2-bonds, wet skid resistance can be improved while maintaining wear resistance, and carbon black and process oil can be blended to match this wet skid resistance. We have found that it is possible to reduce the amount. Therefore, as a result, it is possible to obtain a cap tread rubber that maintains wet skid resistance and has improved rebound resilience.

However, when the amounts of carbon black and process oil are reduced in this way, the physical properties at break of the rubber deteriorate. As a result, when an extremely severe turning test was performed on a tire using such tread rubber, a phenomenon was observed in which chunking occurred in a portion of the tire shoulder.

This severe turning test is conducted to simulate endurance driving on roads with continuous sharp curves such as mountain roads.
A portion of the shoulder is subjected to strong stress of 0.7 to 0.9 G in the lateral direction. At this time, the temperature in some parts of 7 Jorda reached over 95 degrees Celsius.

Therefore, a decrease in the breaking properties, especially at high temperatures, is undesirable because it reduces the durability against such severe turning tests. Furthermore, the decrease in physical properties at break at high temperatures also leads to the disadvantage that tread rubber is more likely to chip when the tire is removed from the mold after vulcanization.

Reducing the amount of carbon black and process oil blended causes problems in manufacturing as well as in the deterioration of fracture properties. That is,
If the amount of carbon black and process oil is reduced, the adhesion to other components will decrease. This may cause difficulty in molding work, or may cause malfunctions such as an air layer remaining at the interface with the adjacent rubber after vulcanization.

The present invention has been made to solve the various disadvantages or difficulties associated with tire cap tread rubber as described above. The purpose of the present invention is to provide a rubber composition for tire treads that does not impair other properties such as physical properties, and is suitably used as cap tread rubber for fuel-efficient tires.

As a result of intensive research in line with this objective, the present inventors found that a styrene-butanoene copolymer rubber with a relatively large number of 1.2 bonds in the butadiene moiety and a styrene-butadiene copolymer rubber with a relatively large number of 1.2 bonds in the butadiene moiety. A rubber composition containing polymer rubber and natural comb and/or polyisoprene rubber in a specific ratio, a relatively small amount of carbon black with specific properties, and sulfur in a specific range. It has been found that the above object can be achieved by the present invention.

That is, in the present invention, the amount of bound styrene is 15 to 30% by weight.
20 to 50 parts by weight of styrene-butadiene copolymer rubber (hereinafter referred to as SBR-A) in which the amount of 1.2 bonds in the butanoene moiety is 30 to 45 inches, and the amount of bound styrene is 20 to 30 parts by weight.
40 to 70 parts by weight of styrene-propylene copolymer rubber (hereinafter simply referred to as SDR) with a 1°2 bond content of butanoene moieties of 20% or less, natural rubber (NR) and/or polyisoprene rubber (IR). ) The amount of iodine adsorbed is 60 parts by weight per 100 parts by weight of the comb consisting of 5 to 30 parts by weight.
~100m9 I9-, Djibouti/l/7 Tallate (
DBP) 50-60 parts by weight of carbon black with an oil absorption of 100-13 Qmg/100y- and 1.0 parts by weight of sulfur.
A comb composition for a tire tread, characterized in that it contains 5 to 1.8 parts by weight.

5BR-A used in the present invention can be obtained by a normal solution polymerization method, but it is necessary that the amount of bound styrene is 15 to 30% by weight, and if it is less than 15% by weight, the effect of improving wet skid resistance is small; If it exceeds 30% by weight, it is not preferable because the impact resilience is greatly reduced. Furthermore, if the 1,2 bond in the butadiene moiety is less than 30%, the effect of improving wet skid resistance is small, and if it exceeds 4s%, the abrasion resistance is greatly reduced, which is preferable. The amount of 5BR-A used should be 20 to 50% by weight of the total rubber content, and if it is less than 20% by weight, the effect of improving wet skid resistance will be small.
If it exceeds 50% by weight, the abrasion resistance decreases, which is not preferable.

The SBR referred to in the present invention is used in ordinary rubber compositions, and is obtained by emulsion polymerization or solution polymerization and has a bound styrene content of 20 to 30% by weight.
, 5BR-A is contained in a total rubber content of 940 to 70% by weight in order to prevent deterioration in wear resistance and breakage properties due to the blending. If it is less than 40 parts by weight, there will be little improvement in abrasion resistance and rupture properties, and if it exceeds 70 parts by weight, impact resilience will decrease, which is undesirable.

Natural comb and/or polyisoprene rubber is blended in an amount of 5 to 30% by weight in the total rubber content in order to improve adhesion in an unvulcanized state and physical properties at break. If it is less than 5% by weight, no effect on adhesion can be expected, and if it exceeds 30% by weight, wet skid resistance will decrease, which is not preferable.

The carbon black used in the present invention contains iodine
) Adsorption amount is 60-1oomg/IF and dibutyl 7
L'-) (DBP) Oil absorption power loo~130m1/
100y-, and specific examples include carbon black N-330XN-339, N-347, and N-351. 2 adsorption amount 60 my/y-Ffi
6. If the oil absorption amount of DBP is less than 1 oomVlooy-, sufficient wear resistance and breaking characteristics cannot be obtained as a car or butt tread. If the adsorption amount exceeds 100m9/7 or the DBP oil absorption amount is 130mV100
? If it exceeds this value, the abrasion resistance and wet skid resistance are good, but the impact resilience is significantly lowered, which is undesirable. Carbine black having an I2 adsorption amount and a DBP oil absorption amount within the above range is 50 to 60 parts by weight per 100 parts by weight of rubber.
Parts by weight are added. If the amount of carbon black is less than 50 parts by weight, the abrasion resistance will be poor, and if it exceeds 60 parts by weight, the impact resilience will decrease, which is not preferable.

In the rubber composition of the present invention, it is desirable to incorporate a relatively small amount of sulfur as a vulcanizing agent, preferably 1.5 to 1.8 parts by weight per 100 parts by weight of rubber. If it is less than 1.5 parts by weight, sufficient crosslinking points will not be obtained and the abrasion resistance will deteriorate, and if it exceeds 1 or 8 parts by weight, the physical properties at break at high temperature will be greatly reduced, which is not preferable.

The rubber composition of the present invention contains compounding agents other than those mentioned above that are commonly used in the rubber industry, such as process oil, vulcanization accelerator,
Vulcanization aids, anti-aging agents, etc. can be added as appropriate.

The present invention will be specifically described below based on Examples and Comparative Examples. All formulations in the table are parts by weight.

Example J 5DR-A having the structure shown in Table 1, SDR and natural rubber as rubber components were mixed in a small closed mixer with the proportions of each rubber component changed as shown in Table 2 to form a rubber composition. Prepare things/ζ. The rubber composition thus obtained was
C. for 15 minutes to obtain a vulcanized rubber, and the impact resilience, wet skid resistance, and abrasion resistance of the vulcanized rubber were measured.
It is shown in Figure 3. These figures 1 to 3 are expressed as an index obtained by dividing the value of vulcanized rubber containing SDR alone as the rubber component by 100, and the impact resilience is determined by the Liebke impact resilience test at 60°C in accordance with JIS K6301, and the wet skid resistance is expressed by the Pretty Measurement was performed using a portable skid tester. The road surface was measured using a 3M Outdoor Tyzo B Safety Walk in an atmosphere of 25°C while shaking with distilled water. Abrasion resistance was measured using a pico abrasion tester according to ASTM D2228 at 60 rpm. The test was carried out under the condition of a load of 45 kg and expressed as the reciprocal of the wear loss.

Table 2 H: I2 adsorption t90m9/&, 120m17100g
, I2: N-(113-nomethylphthyl)-N/-phenyl-p-phenylenenoamine, I3: N-fuclohexyl-2-benzothiazolesulfenamide Figures 1 to 3, SBR exceeds 70 parts by weight In this case, the effect of improving rebound resilience is almost eliminated, and NR is 30
If the weight exceeds the weight limit, the wet skid resistance will decrease. Furthermore, if SBR is in the range of 40 to 70 parts by weight and NR is in the range of 5 to 30 parts by weight, and if 5BR-A exceeds 50 parts by weight, the wear resistance will be extremely reduced.

Examples 2 to 6 and Comparative Examples 1 to 5 After preparing rubber compositions in the same manner as in Example 1 using the formulations shown in Table 2 and changing the rubber content as shown in Table 3, Example 1
Vulcanization was carried out under the same conditions as above and the vulcanization characteristics were measured. In addition, only in Comparative Example 1, 60 parts by weight of carbon black (N339) and 20 parts by weight of aromatic gross oil were blended. Also,
Resilience, wet skid resistance, and abrasion resistance are as shown in Example 1.
It was measured in the same manner as above and expressed as an index with Comparative Example 2 set as 1oo.

Tensile strength, elongation, and JIS hardness were determined in accordance with JIS K 63 old, and adhesive strength was determined by PICFtliA TACK.
Using a II tack meter, the value of Comparative Example 2 was 2.
It is displayed as an index set to 00. The respective results are shown in Table 3.

As shown in Table 3, properties such as impact resilience change by changing the blending ratio of the ingredients.

Examples 2 to 6 all have improved impact resilience and wet skid resistance compared to Comparative Example 2, which was used as a standard, and the decrease in abrasion resistance is within an acceptable range.

Further, in Examples 2 to 6, when compared with Comparative Example 1, which is a general passenger car tread formulation, the impact resilience is significantly improved, while the wet skid resistance is less reduced. Furthermore, it can be seen that the adhesion is improved by blending NR.

Implementation/Example 5 and Comparative Examples 6 to 10 A comb composition was prepared in the same manner as in Example 1 using the formulation shown in Table 2 with the type and amount of carbon black changed as shown in Table 4. The vulcanization properties were measured under the following conditions. The measurement method was the same as in Example 2.

The results are shown in Table 4.

As shown in Table 4, by changing the carpin black, properties such as impact resilience change.

Example 5 using carbon black N-339 had satisfactory impact resilience, wet skid resistance, and abrasion resistance compared to Comparative Examples 6 to 8 using carbon black N-220XN-660 and N-326. I know it will happen.

Furthermore, it can be seen that Comparative Example 9, in which the blending amount of Carpin Black N339 was reduced, had a large decrease in wear resistance and elongation at break at high temperatures, and Comparative Example 10, in which the blending amount was increased, had a large decline in impact resilience.

Example 5 and Comparative Examples 11 to 12 Rubber compositions were prepared in the same manner as in Example 1 using the formulations shown in Table 2, with the specific amounts of sulfur shown in Table 5 being changed, and then under the same conditions as in Example 1. It was vulcanized and the vulcanization properties were measured. The measurement method was the same as in Example 2. The results are shown in Table 5.

Table 5 As shown in Table 5, properties such as impact resilience change by changing the blended amount of sulfur. In Comparative Example 11, which has a small amount of sulfur, and Comparative Example 12, which has a large amount of sulfur, wear resistance or elongation at break at high temperatures deteriorate.

As explained above, the rubber composition of the present invention is made by blending the three components SBRX5BR-A, NR and/or IR in a specific ratio to form a rubber component, and adding a small amount of carbon brane with specific properties to this. When used as a trend part of a tire, it significantly improves rolling resistance compared to conventional tires, and does not impair other properties such as braking performance on wet roads or wear resistance, and also eliminates manufacturing problems. Since this does not occur, it is preferably used as a fuel-efficient tire.

[Brief explanation of the drawing]

Figure 1 is a triangular diagram showing the relationship between the rubber content and impact resilience (60°C) in Example 1, and Figure 2 is a triangular diagram showing the relationship between the rubber content and impact resilience (60°C) in Example 1. A triangular diagram showing the relationship, and FIG. 3 are triangular diagrams showing the relationship between the blending ratio of the rubber component and the abrasion resistance in Example 1.
The values are expressed as an index, with the value of the vulcanized rubber containing only R blended as 100. Third! ! l

Claims (1)

[Claims] When the amount of bound styrene is 15 to 30% by weight, 1 of the butadiene moiety
, 20 to 50 parts by weight of styrene-butanoene copolymer rubber having a bond amount of 30 to 45, and a bond amount of 20 to 50 parts by weight.
40 to 70 parts by weight of styrene-butanoene copolymer rubber containing ~30% by weight and 20% or less of 1,2 bonds in the butadiene moiety, 5 to 3 parts by weight of natural rubber and/or polyinoprene rubber
50 to 60 parts by weight of carbon black with an iodine adsorption amount of 60 to 1.00 m9/I-, a dibutyl phthalate oil absorption amount of 100 to 130 ml/1007, and 1 sulfur to 100 parts by weight of rubber consisting of 0 parts by weight. .5~1.
A rubber composition for a tire tread, characterized in that it contains 8 parts by weight.