JPS6033134B2 - Rubber composition for tire tread - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rubber composition for a tire tread in order to simultaneously maintain high levels of tire rolling resistance, braking performance on wet road surfaces, and abrasion resistance.

Recently, from the viewpoint of energy saving, it is desired that automobiles have low fuel consumption, and along with this, there is a demand for reducing the rolling resistance of tires. It is known that the rolling resistance of a tire is most attributable to hysteresis loss in the tread.
P. R. Wmet) “Rubber Chemistry and Technology”
46, pp. 425-441" or in Tokusei No. 52-118705. Therefore, in order to reduce the rolling resistance of a tire, it is necessary to reduce the hysteresis loss of the tread rubber. The effect is the greatest.Also, with the spread of expressways, opportunities for high-speed driving are increasing, and from the viewpoint of tire durability, it is desirable to lower the heat generation of tread rubber.
Also from this point of view, tread rubber with small hysteresis loss is preferable. On the other hand, conventional elastomers for tread rubber, particularly for passenger car tires, have a relatively large hysteresis loss.

Styrene-butadiene-based synthetic rubbers have been mainly used. The main reason for this is the desire to improve braking performance on wet road surfaces and improve driving safety.
Naturally, the rolling resistance of tires using such conventional tread rubber is at a high level, and improvements are needed. As described above, when it comes to tread rubber, rolling resistance or heat generation and braking performance on wet road surfaces have been considered to be contradictory to each other.

The rolling resistance of a tire is due to the load that the tire receives at the contact point with the road surface when the car is running, and the hysteresis loss caused by the repeated deformation of the tire as it rotates.When testing rubber materials, it is generally determined by the impact resilience. This dynamic loss characteristic can be used as a guideline.

Furthermore, considering the driving conditions of the automobile, it is necessary to evaluate this rebound resilience at a temperature around 50 to 700 C, and the higher the rebound resilience in this temperature range, the lower the rolling resistance. On the other hand, the braking force on a wet road surface is due to the frictional resistance that occurs when the tread rubber deforms as it slides on the road surface, following the unevenness of the road surface. It can be evaluated by the wet skid resistance value.

The present inventors have determined the micromolecular structure of the styrene-butadiene copolymer rubber, that is, the amount of bound styrene, and the composition ratio of the trans-1,4-'cis-1,4- and 1,2-bond unit content of the butadiene moiety. We investigated this in detail and found that the amount of bound styrene and the content of 1,2-bond units in the butadiene moiety have a large effect on the impact modulus and wet skid resistance.

That is, the amount of bound styrene and the butadiene moiety 1,2
- As the bonding unit content increases, the wet skid resistance increases and the rebound modulus decreases. However, even when the same level of improvement in wet skid resistance is obtained, increasing the content of 1,2-bond units in the butadiene moiety results in a smaller decrease in the impact resilience modulus than increasing the amount of bound styrene. From this point of view, the present inventors created a rubber by blending a styrene-butadiene copolymer rubber with a relatively low amount of bound styrene and a high content of 1,2-bond units in the butadiene moiety, and other gen-based rubbers. Conventional styrene-butadiene copolymer rubber or styrene-butadiene copolymer rubber and PoI
They discovered a rubber composition for tire treads that balanced impact resilience and wet skid resistance at a higher level than the J-butadiene rubber blend system, and filed Japanese Patent Publication No. 56-185684. However, this patent application No. 56-85684
In the rubber composition for tire treads disclosed in the No. 1, a styrene-butadiene copolymer rubber with a low content of bound styrene and a high content of 1,2-bond units in the butadiene moiety, and a general-purpose styrene-butadiene copolymer rubber as a diene-based synthetic rubber are used. Rubber compositions blended with styrene copolymer rubber or polyisoprene rubber have favorable levels of impact resilience and wet skid resistance; Compared to the rubber composition used as the raw material rubber, the abrasion resistance, which is an important property required for tires from the viewpoint of energy conservation, was somewhat inferior, and further improvements were needed.

The purpose of the present invention is to obtain a rubber composition for tire treads that maintains the rebound modulus and wet skid resistance at a higher level than the conventional styrene-butadiene copolymer rubber and has excellent wear resistance. It is especially used in treads for low rolling resistance tires that have excellent braking performance and wear resistance on wet road surfaces.

As a result of intensive studies in accordance with the above object, the present inventors have determined that the diene rubber used in the rubber composition for tire treads disclosed in Tokukai No. 56-85694 is a general-purpose styrene-butadiene copolymer rubber or A combination of natural rubber and/or polyisoprene rubber and polybutadiene rubber, blended in a specific ratio, and the above-mentioned styrene-butadiene rubber with a low amount of bound styrene and a high content of 1,2-bond units in the butadiene moiety. The inventors have discovered that a rubber composition containing a specific amount of Jen copolymer rubber satisfies the above-mentioned objects, and have arrived at the present invention.

In the rubber composition of the present invention, 100 parts by weight of all the raw material rubber components have a '1-bonded styrene content of 10 to 2% by weight and a 1,2-bond unit content of the butadiene moiety of 40 to 70%. Styrene-butadiene copolymer rubber (hereinafter referred to as high 1,2-
(abbreviated as bonded SBR) 10 to 8 parts by weight; (1) the amount of bonded styrene is 15 to 25% by weight;
Styrene-butadiene copolymer rubber (hereinafter referred to as general-purpose SBR), or natural rubber (NR) and/or polyisoprene rubber (I
R) 10 to 85 parts by weight, 5 to 3 parts by weight of polybutadiene rubber (BR) having a 1,2-bond unit content of 20% or less, carbon black, a vulcanization accelerator,
A vulcanizable tire tread rubber composition containing a vulcanizing agent and other compounding agents.

As mentioned above, by using the raw rubber component [U, {2] and the glue in a specific ratio, the rebound modulus is lower than that of conventional tire tread rubber compositions that use normal SBR as the raw rubber component. , wet skid resistance, and abrasion resistance can be made to be equivalent or higher. The high 1,2-bond SBR'1}' used in the present invention is produced by a solution polymerization method, and the amount of bound styrene is 10 to 2% by weight according to infrared spectroscopy, which is commonly used for structural identification. , the 1,2-bond unit content of the butadiene moiety is 40-70
Must be %. If the amount of bound styrene is less than 1% by weight, the wet skid resistance will be insufficient, and if it exceeds 2% by weight, the abrasion resistance and rebound modulus will be insufficient, which is not preferable. The 1,2-bond unit content of the butadiene moiety is 4
If it is less than 0%, wet skid resistance is insufficient, and 70%
If it exceeds %, the abrasion resistance will be greatly reduced, which is not preferable.
The amount of high 1,2-bond SBR used is 10% of the total raw rubber component.
If the amount is less than 1% by weight, the effect of improving wet skid resistance will be small, and if it exceeds 8% by weight, the degree of improvement in wet skid resistance will be small, and the abrasion resistance will be greatly reduced, which is not preferable. The general-purpose SBR of the rubber component (2) used in the present invention is a styrene-butadiene copolymer rubber produced by the conventionally widely used solution polymerization method or emulsion polymerization method. , 2 bond unit content is less than 40%.

Polyisoprene rubber has a cis-1,4-bond unit content of 9
0% or more. The amount of general-purpose SBR or NR and/or IR used is 10 to 8 of the total raw rubber components.
If it is less than 1% by weight or more than 85% by weight, it will be difficult to maintain a balance between abrasion resistance and wet skid resistance. The BR legs used in the present invention are 1,2-
The content of bonding units is 20% or less, and if it exceeds 20%, wear resistance decreases, which is not preferable.

The amount of BR'3- used is 5 to 3 parts by weight; if it is less than 5 parts by weight, the abrasion resistance will be insufficient, and if it exceeds 3 parts by weight, the wet skid resistance will be greatly reduced, which is not preferable.
In the present invention, compounding agents such as zinc oxide, stearic acid, carbon black, anti-aging agent, wax, extensible powder, vulcanization accelerator, and sulfur, which are usually blended in rubber compositions for tire treads, are appropriately selected and used in appropriate amounts. It is blended.

The present invention will be specifically described below based on Examples and Comparative Examples.

In addition, all the formulations in Tables 1 to 3 are parts by weight. Examples 1 to 12 and Comparative Examples 1 to 17 100 parts by weight of raw rubber having the formulations shown in Tables 2 and 3 and the ingredients shown in Table 1 excluding sulfur and vulcanization accelerator were mixed in a volume of 1.8 ml in a sealed container. After mixing with a type mixer, sulfur and a vulcanization accelerator were further added and mixed using a 6-inch roll to prepare a rubber composition.

This rubber composition was press-cured at 160 q○ for 20 minutes to prepare a sample for measuring vulcanization characteristics. Vulcanization properties were evaluated using IJ Kupke impact modulus (value of 70qo based on JISK 6301), wet skid resistance (A
Measured by British Portable Skid Tester in accordance with STM E 303, the value of Comparative Example 1 was 1.
The index is set to 00, and the road surface is made of outdoor type B safety oak manufactured by Mushino Co., Ltd., and is moistened with distilled water to 25 qo.
(measured in atmosphere) and abrasion resistance (conducted by pico abrasion test according to ASTM D2228, the abrasion loss of Comparative Example 1 was 10
The measurement was performed using the reciprocal of the measured value (expressed as an index) with the value set as 0. The results are shown in Tables 2 and 3. Table 1 *1: ASTM designation, *2: N-isopro-N'-phenylene-p-phenylenediamine, *3: N-tertiarybutyl-penzothiadylene sulfenamide Table 1 Table 2 Astringent 4: Combined styrene content 150 weight*, butanene part 1,
2-bond content 48*, cis-1,4-bond content 21%,
Trans 1,4-bond content 31*×5: Nibol 15
02, manufactured by Nippon Zeon Co., Ltd., bound styrene content 23.5*
Weight Tsutomu, Fukujun part 1,2-bond content 17 omitted, trans 1,4-bond content 10*, trans 1,4-bond content 73%, astringent 6: Soen 35NF manufactured by Asahi Kasei Industries, Ltd., No. 2
The relationship between wet skid resistance (index) and rebound modulus of Comparative Examples 1 to 2, 4 to 10, and 16 in Table 3 and Examples 1 to 6 in Table 3 is shown in Figure 1 a, and wet skid resistance (
The relationship between the index) and the abrasion resistance (index) is shown in Figure 1b.

In Figures 1a and b, the dotted line separating the upper right part indicates a tire tread rubber composition (Comparative Example 1) whose wet skid resistance, rebound modulus, or abrasion resistance is made from conventionally used general-purpose SBR as a raw material rubber. indicates that it is at the same level as Therefore, the rubber composition in the upper right section delimited by the dotted line in FIGS. Figure 1 a and b are high 1
, 2-bond SBR/general-purpose SBR/BR-based rubber compositions were investigated.

In FIG. 1a, the high 1,2-bond SB of Examples 1 to 6
R/General-purpose SBR/BR-based rubber composition, Comparative Example 2 High 1,
Rubber compositions containing 2-bond SBR alone, high 1,2-bond SBR/general-purpose SBR rubber compositions of Comparative Examples 4 to 6, and high 1, 1,2-bond SBR rubber compositions containing a large amount of high 1,2-bond SBR of Comparative Example 9.
, 2-bond SBR/BR rubber composition has improved impact resilience and wet skid resistance compared to the rubber composition of Comparative Example 1. However, as shown in FIG. 1b, Comparative Example 2
, 4 to 6, and 9, the abrasion resistance of the rubber compositions of Comparative Example 1 is not as high as that of the rubber composition of Comparative Example 1. On the other hand, the rubber compositions of Examples 1 to 6 also have a preferable level of abrasion resistance. On the other hand, although the general-purpose SBR/BR rubber compositions of Comparative Examples 7 and 8 and the high 1,2-bond SBR/BR rubber composition of Comparative Example 10 have high impact modulus and abrasion resistance, Wet skid resistance is inferior to the rubber composition of Comparative Example 1.

In addition, Comparative Example 16 is a high 1,2-bond SBR/general-purpose SBR
Although it is a /BR-based rubber composition, it has poor wet skid resistance because it contains a large amount of BR. Figure 2 a and b are the same aircraft as Figure 1 a and b, and Comparative Examples 1 to 3 and 9 in Table 2
-15 and 17 and the relationship between wet skid resistance and impact modulus or abrasion resistance of Examples 7 to 12 in Table 3. We are mainly considering this.

In Fig. 2a, the heights 1 and 2 of Examples 7 to 12 are combined S
The BR/NR/BR rubber compositions, the high 1,2-bond SBR/NR rubber compositions of Comparative Examples 13 to 15, and the rubber compositions of Comparative Examples 2 and 9 described above have low impact modulus and wet skid resistance. It is equivalent to or better than the rubber composition of Comparative Example 1. However, as shown in Figure 2b, Comparative Examples 2 and 9
Rubber compositions Nos. 13 and 15 all have poor abrasion resistance. On the other hand, the rubber compositions of Examples 7 to 12 also have a preferable level of abrasion resistance. On the other hand, the impact resilience and abrasion resistance of the NR-only compounded rubber composition of Comparative Example 3, the NR/BR rubber compositions of Comparative Examples 11 and 12, and the rubber composition of Comparative Example 10 described above are at high levels. However, the wet skid resistance was inferior to that of the rubber composition of Comparative Example 1.

Although Comparative Example 17 is a high 1,2-bond SBR/NR/BR rubber composition, it has poor wet skid resistance because it contains a large amount of BR. As described above, the present invention
, 2-combined SBR/general purpose SBR or NR (and/
A rubber composition containing a specific amount of the three components (IR)/BR as a raw material rubber has a higher rebound modulus, wet skid resistance, and abrasion resistance than a conventional rubber composition using only SBR as a raw material rubber. All of the properties can be improved to the same or higher level, but in a rubber composition that uses two components, consisting of high 1,2-bond SBR and one type of gen-based rubber, as raw rubber, some of the properties may be impaired. I'll get lost.

Therefore, a tire using the rubber composition of the present invention as a tread has improved fuel efficiency, durability, and stability.

[Brief explanation of drawings]

Figure 1 shows the characteristics mainly of high 1,2-bond SBR/general-purpose SBR/BR rubber compositions, and Figure 2 shows the characteristics of high 1,2-bond SBR/general-purpose SBR/BR rubber compositions.
Characteristics mainly of the combined SBR/NR/BR rubber composition are shown. In addition, a in Figures 1 and 2 is the wet skid resistance (index).
is the rebound modulus (70℃), and b is the wet skid resistance (
It shows the relationship between index) and abrasion resistance (index). In each figure, 0 indicates an example, and Δ indicates a comparative example. Figure 1 (0) Figure 1 (b) Figure 2 (o)

Claims (1)

[Claims] 1 100 parts by weight of all the raw rubber components are (1) 10 to 80 parts by weight of a styrene-butadiene copolymer rubber having a bound styrene content of 10 to 20% by weight and a 1,2-bond unit content of the butadiene moiety of 40 to 70%; , (2) Amount of bound styrene 15-2
1,2-bond unit content of butadiene moiety at 5% by weight 40
10 to 85 parts by weight of styrene-butadiene copolymer rubber or natural rubber and/or polyisoprene rubber, and (3) 5 to 30 parts by weight of polybutadiene rubber with a 1,2 bond unit content of 20% or less. A rubber composition for tire tread, characterized by: