JPS5821435A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:To obtain a tread for a tire having low rolling resistance, high braking performance on wet road surface, and excellent abrasion resistance, by adding a specific amount of a styrene-butadiene copolymer having low content of bonded styrene, and high content of 1,2-bonded unit in the butadiene segment. CONSTITUTION:The objective rubber composition (100pts.wt.) is composed of (A) 10-80pts.wt. of a styrene-butadiene copolymer rubber having a bonded styrene content of 10-20wt% and a 1,2-bonded unit content in the butadiene segment of 40-70wt%, (B) 10-80pts.wt. of a styrene-butadiene copolymer rubber, natural rubber, and/or polybutadiene rubber having a bonded styrene content of 15-25wt% and a 1,2-bonded unit content in the butadiene segment of <40wt%, and (C) 5-30pts.wt. of a polybutadiene rubber having a 1,2-bonded unit content of <=20wt%. The abrasion resistance can be improved while maintaining the impact resilience and the wet skid resistance at high levels.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rubber composition for a tire tread that simultaneously maintains a tire's low rolling resistance, braking performance on wet road surfaces, and abrasion resistance at a high level.

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, Wi 1let) ``Rubber Chemistry and Technology (Rubber Cherni)
stryand TechnolOg)' ) J 4th
Volume 6, No. 425-441 Hard-Zo”.

Alternatively, it is disclosed in Japanese Patent Application Laid-Open No. 118705/1983.

Therefore, reducing the hysteresis loss of the tread rubber has the greatest effect in reducing the rolling resistance of the tire. In addition, with the spread of expressways, opportunities for high-speed driving are increasing, and from the perspective of tire durability, it is desirable to reduce the heat generation of tread rubber, and from this perspective, tread rubber with low hysteresis loss is desirable. preferable.

On the other hand, styrene-buta-citric synthetic rubber, which has a relatively large hysteresis loss, has conventionally been mainly used as a nidistomer for tread rubber, especially for passenger car tires. The main reason for this is the desire to improve braking performance on wet roads and improve safety during driving. 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 caused by tire rotation. This dynamic loss characteristic can be used as a guideline. Furthermore, this rebound resilience is also 5 when considering the driving condition of the car.
It is necessary to evaluate at a temperature around 0 to 70°C, and the higher the rebound modulus in this temperature range, the lower the transfer resistance.

On the other hand, the braking force on a wet road surface can be evaluated by the wet skid resistance value using a portable skid tester due to the frictional resistance generated by the deformation of the tread rubber as it follows the unevenness of the road surface as it slides on the road surface.

The present inventors investigated the micromolecular structure of the styrene-butadiene copolymer rubber, that is, the amount of bound styrene, and the butadiene moiety's trans 1.4-, cis 1,4-, and 1,2
- We investigated in detail the composition ratio of the bond unit content and found that the amount of bonded styrene and the content of 1,2-bond units in the butadiene moiety have a large effect on the impact resilience and wet skid resistance. That is, as the amount of bound styrene and the content of 1,2-bond units in the butadiene moiety increase, 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 have found that the amount of bound styrene is relatively small, and the butadiene moiety 1,
2-By blending styrene-butadiene copolymer rubber with a high content of bonding units and other diene-based rubbers, conventional styrene-butadiene copolymer rubber or styrene-
They discovered a rubber composition for tire treads that has a higher balance of rebound modulus and wet skid resistance than blends of sitadiene copolymer rubber, polybuta, and diene rubber, and filed Japanese Patent Application No. 85,684/1984.

However, the rubber composition for tire treads disclosed in Japanese Patent Application No. 56-85684 also uses 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 diene-based rubber composition. Rubber compositions that are blended with general-purpose styrene-butadiene copolymer rubber or polyisoprene rubber as synthetic rubbers have favorable levels of impact resilience and wet skid resistance. - Compared to rubber compositions using butadiene copolymer rubber as a raw material rubber, abrasion resistance, which is an important property required of tires from the viewpoint of energy saving, is somewhat inferior, and further improvements have been required.

The object of the present invention is to obtain a tire tread comb composition that maintains the impact modulus and wet skid resistance at a higher level than 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.

The present inventors investigated the amount of iron in accordance with the above objective, and found that the diene rubber used in the rubber composition for tire treads disclosed in Japanese Patent Application No. 56-85694 was selected from general-purpose styrene-buta-diene 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 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 copolymer rubber satisfies the above object, and have thus arrived at the present invention.

In the rubber composition of the present invention, 100 parts by weight of the total raw rubber component contains (1) styrene 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%; - Butadiene copolymer (hereinafter abbreviated as high 1.2-bond SBR) content ± 10 to 80 parts by weight, (2) the amount of bound styrene is 15 to 25% by weight, and 1 of the butadiene part
．． 2-Styrene- having a bonding unit content of less than 40
butadiene co-ft composite rubber (hereinafter referred to as general-purpose SBR),
or 10 to 85 parts by weight of natural rubber (NR) and/or polyurethane rubber (IR), (3) polybutadiene rubber (BR) with a 1,2-bond unit content of 20 units or less
This is a vulcanizable rubber composition for tire treads, comprising 5 to 30 parts by weight of carden black, a vulcanization accelerator, a vulcanizing agent, and other compounding agents.

As mentioned above, raw rubber components (1), (2) and (3)
By using SBR in a specific ratio, compared to conventional tire tread rubber compositions that use normal SBR as the raw rubber component, the three properties of rebound modulus, wet skid resistance, and abrasion resistance are the same or higher. can do.

The high 1,2-bond 5BR (1,) used in the present invention is obtained by solution polymerization, and the amount of bound styrene is 10 to 20% by weight as determined by infrared spectroscopy, which is commonly used for structural identification. The 1,2-bond unit content of the butadiene moiety must be 40-70%.

If the amount of bound styrene is less than 10% by weight, the wet skid resistance will be insufficient, and if it exceeds 20% by weight, the abrasion resistance and rebound modulus will be insufficient, which is not preferable. If the content of 1,2-bond units in the butanoene moiety is less than 40%, the wet skid resistance will be insufficient, and if it exceeds 70%, the abrasion resistance will be greatly reduced, which is undesirable. High 1,2-bond SBH
The amount used is 10 to 80% by weight of the total raw rubber components,
If it is less than 10% by weight, the effect of improving wet skid resistance will be small, and if it exceeds 80% 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, and has a bound styrene content of 15 to 25% by weight and a butadiene moiety. The 1,2-bond unit content is less than 40 units. The polyethylene rubber has a cis-1,4-bond unit content of 90% or more. General-purpose SBR1 or NR and/or IR(2
) is used in an amount of 10 to 85% by weight of the total raw material comb components, and if it is less than 10% by weight or more than 85% by weight, it becomes difficult to maintain a balance between abrasion resistance and wet skid resistance.

The BR(3) used in the present invention has a 1,2-bond unit content of 20 inches or less, and if it exceeds 20 inches, the wear resistance decreases, which is not preferable. The amount of B R(3) used is 5-3
If the amount is less than 5 parts by weight, the abrasion resistance will be insufficient, and if it exceeds 30 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 agents, wax, extender oil, vulcanization accelerator, and sulfur, which are usually blended in rubber compositions for tire treads, may be used as appropriate. Selected and blended in appropriate amounts.

The present invention will be specifically described below based on Examples and Comparative Examples. The formulations in Tables 1 to 3 are all 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 placed in a sealed container with a volume of 1.81. After mixing using 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 heated to 160"C,
A sample for measuring vulcanization characteristics was prepared by press vulcanization for 20 minutes. Evaluation of vulcanization properties is based on the Ryuzoke impact modulus (JIS
K 6301), wet skid resistance (measured with a British Data Pull skid tester in accordance with ASTM E303),
Comparison f: Index display with l11 value as 100, road surface is 3
Measured using an outdoor type Safety Walk made by Company M, moistened with distilled water, and measured in an atmosphere of 25℃) and abrasion resistance (
A pico abrasion test was conducted according to ASTM D 2228, and the abrasion loss of Comparative Example 1 was set as 100, and the index was expressed as the reciprocal of the measured value. The results are shown in Tables 2 and 3.

Table 1 *1: ASTM indication, *2: N-isozoro-N
'-fur-p-phenylenediamine, *3: N-Tasha! J-7'Thylbenzothiaderusulfenamide Comparative Examples 1 to 2.4 to 1o and 16 in Table 2 and Examples 1 to 6 in Table 3 The relationship between wet skid resistance (index) and rebound modulus Figure 1 (,) shows the relationship between wet skid resistance (index) and abrasion resistance (index).
Shown in b). In Figures 1(,) and (b), the dotted line separating the upper right part indicates the wet skid resistance, rebound modulus, or abrasion resistance of a rubber composition for tire tread made from conventionally used general-purpose SBR as raw material rubber ( Comparative example 1
) indicates that it is at the same level as Therefore, Fig. 1 (
The rubber composition in the upper right section separated by the dotted line in a) and (b) shows that wet skid resistance, rebound modulus, and abrasion resistance are all superior to Comparative Example 1.

Figures 1 (,) and (b) are studies focusing on high 1,2-bond SBR/general-purpose SBR/BR rubber compositions. In FIG. 1(a), height 1 of Examples 1 to 6
．． 2-bond SBR/general-purpose SBR/BR system 1 rubber composition, rubber composition containing only high 1,2-bond SBR of Comparative Example 2, high 1,2-bond SBR of Comparative Examples 4 to 6/general-purpose S.B.
R-based rubber composition and high 1,2-bond SBR of Comparative Example 9
The high 1,2-bonded SBR/BR rubber composition containing a large amount of
This is an improvement over other rubber compositions. However, in Figure 1 (b
), the rubber compositions of Comparative Examples 2.4 to 6 and 9 all have abrasion resistance that does not reach the level 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, the general-purpose SBR/BR rubber compositions of Comparative Examples 7 and 8,
Although the high 1,2-bond SBR/BR rubber composition of Comparative Example 10 has high impact resilience and abrasion resistance, it is inferior to the rubber composition of Comparative Example 1 in wet skid resistance. Although Comparative Example 16 is a high 1.2-bond SBR/general-purpose SBR/BR rubber composition, it is inferior in wet skid resistance because it contains a large amount of BR.

Figure 2 (,) and (b) are the same as Figure 1 (a-) and (g)), Comparative Examples 1 to 3.9 to 15 and 17 in Table 2 and Example 7 in Table 3. This figure illustrates the relationship between wet skid resistance and rebound modulus or abrasion resistance of 12 to 12, and focuses on high 1,2-bond SBR/NR/BR rubber compositions. In FIG. 2(a), the high 1,2-bond SBR/NR/BR rubber compositions of Examples 7 to 12 and the high 1,2-bond SBR/N of Comparative Examples 13 to 15 are shown.
The R-based rubber composition and the rubber composition of Comparative Example 2.9 described above have impact resilience and wet skid resistance that are equal to or higher than those of the rubber composition of Comparative Example 1.

However, as shown in FIG. 2(b), the rubber compositions of Comparative Examples 2.9 and 13 to 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 NR single compounded rubber composition of Comparative Example 3, Comparative Example 11
~12 NR/BR rubber compositions and the aforementioned Comparative Example 1
Although the rubber composition of No. 0 has a high impact modulus and abrasion resistance, its wet skid resistance is 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 high 1,2-bond SBR/general purpose SBR of the present invention
A rubber composition containing a specific amount of the three components BR or NR (and/or IR)/BR as a raw material rubber has a higher rebound modulus and wet skid resistance than a conventional rubber composition using only SBR as a raw material rubber. It is possible to improve all three properties of wear resistance and abrasion resistance to the same or higher level, but in a rubber composition using two components as raw rubber consisting of high 1,2-bond SBR and one type of diene rubber, Some of the characteristics will be 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 the drawing]

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 are shown mainly for bonded SBR/NR/BR rubber compositions. In addition, (a) of FIGS. 1 and 2 shows the relationship between wet skid resistance (index) and rebound modulus (70° C.), and (b) shows the relationship between wet skid resistance (index) and abrasion resistance (index). In each figure, ◯ indicates an example, and Δ indicates a comparative example. Patent applicant Yokohama Rubber Co., Ltd.

Claims (1)

[Claims] 100 parts by weight of the total raw material rubber component includes (1) 10 to 80 parts by weight of a styrene-butanoene 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 inches; (2) 10 to 85 parts by weight of styrene-butanoene copolymer rubber or natural rubber and/or polyisoprene rubber having a bound styrene content of 15 to 25% by weight and a content of 1,2-bond units in the butadiene moiety of less than 40 units, and (3) A rubber composition for a tire tread, comprising 5 to 30 parts by weight of polybutanoene rubber having a 1.2-bond unit content of 20 inches or less.