JPH06248114A - Rubber composition for tire tread - Google Patents

Abstract

PURPOSE:To reduce the viscosity and improve the processibility of the subject compsn. before vulcanization and to inhibit a increase in rolling resistance and improve the abrasion resistance after vulcanization by compounding a specific diene rubber with a specific process aid. CONSTITUTION:This rubber compsn. is obtd. by compounding 100 pts.wt. diene rubber contg. at least 70 pts.wt. styrene-butadiene copolymer rubber which is obtd. by soln. polymn. and has a wt.-average mol.wt. of 350,000 or higher, a styrene unit content of 15-30wt.%, and a vinyl group content in the butadiene parts of 9-60wt.% with 1-10 pts.wt. zinc salt of a fatty acid as a process aid. The compsn., unlike the conventional one having a high viscosity and being difficult to process, has a suitably lowered viscosity and a good processibility before vulcanization and gives a vulcanizate which has an improved abrasion resistance and a rolling resistance capable of being kept low one of the important characteristics of a low-fuel-consumption tire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire tread, and in particular, it has improved processing characteristics of solution-polymerized styrene-butadiene copolymer rubber such as unvulcanized rubber and rolling resistance of vulcanized rubber. And a rubber composition for a fuel efficient tire tread.

[0002]

2. Description of the Related Art As a social demand for energy saving, low fuel consumption tires are being developed, and one of the countermeasures is to reduce the weight of tires and increase the life of tires, and further, to improve the rolling resistance of tires, that is, rubber. There are developments such as reduction of composition hysteresis loss and low heat generation. However, in the former case, there is a problem of deterioration in wear resistance due to the thinning of the tire tread portion, and in the latter case, problems caused by the tire shape structure and the rubber chemical structure composition have been pointed out.

By the way, a solution-polymerized styrene-butadiene copolymer rubber (hereinafter abbreviated as S-SBR) has recently attracted attention as a rubber for reducing rolling resistance. This S-SBR
Since it is relatively easy to control the microstructure in increasing the molecular weight, a high vinyl S-SBR that has a relatively low styrene bond content suitable for the above performance and at the same time has a high vinyl bond content in the butadiene part. In many cases, the ends of the molecular chains are modified with tin compounds or polar organic compounds.

However, since these S-SBR are originally used in the non-oil-extended state, the viscosity of unvulcanized rubber is high and there is a problem that the processability of the rubber is difficult. Generally, various attempts have been made to adjust the viscosity of unvulcanized rubber to improve workability. For example, addition of an ordinary plasticizer generally used for imparting plasticity to a diene rubber is not suitable because the physical properties of the vulcanized rubber cannot be reduced even if the processability of the unvulcanized rubber is improved. It was For example, an increase in rolling resistance, a decrease in wear resistance and the like. However, addition of various plasticizers and softeners has been attempted in order to improve these conventional defects.

One of them is liquid low molecular weight polyisoprene (JP-A-54-7450) or a zinc salt of a reaction product of liquid polyisoprene and maleic anhydride (JP-A-57-6).
3338), and further polyhydric alcohol unsaturated fatty acid ester (JP-A-57-100150) and the like are added and blended. On the other hand, on the other hand, an ester compound additive containing a polyhydric alcohol and higher fatty acids and dicarboxylic acids as constituent components (JP-A-59-193937), and a polyhydric alcohol and higher fatty acids, lower fatty acids and dicarboxylic acids are further constituted. Attempts have also been made to blend an ester compound as a component (Japanese Patent Laid-Open No. 61-81444).
However, all of these additives are intended for general diene rubbers, and although the reduction in viscosity of unvulcanized rubber has been improved, the rolling resistance of vulcanized rubber as a fuel-efficient tire increases. The current situation is that the control and improvement of wear resistance have not yet been achieved.

[0006]

In view of the above-mentioned circumstances, the inventors of the present invention balance the dynamic characteristics of low fuel consumption tires, especially vulcanized rubber, with the processability of unvulcanized rubber. Therefore, we first selected S-SBR as the rubber for the tread, and as a result of extensive studies on the chemical structural relationship between the fatty acid metal salt and the processing aid, we found that the amount of bound styrene and butadiene within a certain range A specific fatty acid derivative reduces the viscosity of unvulcanized rubber and improves the processability of S-SBR having a partial amount of bonded vinyl, while at the same time controlling the increase in rolling resistance of vulcanized rubber and at the same time abrasion resistance. The present invention has been completed based on the finding that it is also effective for maintaining and improving.

Based on the above findings, the present invention reduces the viscosity of unvulcanized rubber by adding a metal salt of a specific fatty acid to S-SBR having a specific chemical composition as a processing aid. The object is to improve both the rolling resistance and wear resistance of the vulcanized rubber as a tire tread at the same time as improving the workability.

[0008]

According to the present invention which meets the above object, however, the weight average molecular weight is 350,000 or more, the styrene bond content is 15 to 30% by weight, and the vinyl bond content of the butadiene portion is 15 to 30% by weight. 1 to 10 parts by weight of a processing aid composed of a zinc salt of fatty acid is added to 100 parts by weight of a diene rubber containing at least 70 parts by weight of a solution-polymerized styrene-butadiene copolymer rubber having a content of 9 to 60% by weight, A rubber composition for a tire tread having improved processability and physical properties after vulcanization.

The base rubber that constitutes the rubber composition of the present invention must be S-SBR, and even S-SBR must have a weight average molecular weight of 350,000 or more. If the molecular weight is less than 350,000, no processing aid is required and the physical properties are not sufficient for a tire tread.
If the amount of S-SBR as the base rubber is less than 70 parts by weight, the characteristics of S-SBR will not be fully exerted and it will be insufficient as a fuel-efficient tire. Further, if the styrene bond content is less than 15% by weight, wet grip performance in the case of the tread rubber of the tire is insufficient, and if it exceeds 30% by weight, rolling resistance becomes high and it is not suitable as a fuel-efficient tire. Further, if the vinyl bond content of the butadiene portion is less than 9% by weight, wet grip performance is similarly insufficient, and 6
If it exceeds 0% by weight, rolling resistance becomes high and it is also unsuitable.

The fatty acid which is the main constituent of the processing aid compounded in the rubber composition of the present invention is not particularly limited, but as the fatty acid, zinc salts of saturated fatty acid and unsaturated fatty acid may be used alone or in combination. .

Specifically, as the saturated fatty acid, palmitic acid, stearic acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, arachidic acid, behenic acid, cerotic acid, montanic acid, melissic acid and the like are preferable. The unsaturated fatty acids include zomarinic acid, petroselinic acid, oleic acid, erucic acid, whale oil acid, linoleic acid, eleostearic acid, moloctic acid, valinaric acid, siwacic acid, hiragashicholic acid, nisinic acid, ricinoleic acid, and laurolein. Acids, elaidic acid, erucic acid, linoelaidic acid, linolenic acid, arachidonic acid and the like are preferable.
Then, these fatty acids become fatty acid zinc salts by addition of zinc salts. A usual method is applied to the production method, and for example, it can be obtained by directly heating a fatty acid and an oxide of zinc.

Next, the addition amount of the processing aid constituting a part of the rubber composition of the present invention is at least 70% of S-SBR.
1 to 10 parts by weight is necessary for 100 parts by weight of the diene rubber including parts by weight. In this case, if it is less than 1 part by weight, the effect of lowering the viscosity of the rubber is insufficient, and if it exceeds 10 parts by weight, rolling resistance becomes high, which is not preferable. Therefore, the optimum range is 2 to 7 parts by weight.

Further, as described above, when a mixture of a saturated fatty acid zinc salt and an unsaturated fatty acid zinc salt is used as a constituent of the fatty acid zinc, further processability and physical properties of the vulcanized rubber, especially an effect of suppressing an increase in rolling resistance, are suppressed. Is obtained, which is preferable. In this case, the mixing ratio of the saturated fatty acid zinc salt and the unsaturated fatty acid zinc salt should be at least 70% of S-SBR in total.
1 to 1 to 100 parts by weight of diene rubber including parts by weight
0 parts by weight. As a method of using both, a mixture of both may be mixed in the rubber in advance, or may be mixed in the rubber separately. The combination ratio of the two is appropriately determined according to the purpose.

The diene rubber constituting the rubber composition of the present invention means natural rubber (NR), styrene-butadiene copolymer rubber (SBR), polyisoprene rubber (IR), polybutadiene rubber (BR), polychloroprene rubber. (C
R), isoprene-isobutylene copolymer rubber (II
R), acrylonitrile-butadiene copolymer rubber (NB
R) and ethylene-propylene copolymer rubber (EPD
M) and the like, which may be used alone or in admixture, but the blending ratio thereof is blended as another diene rubber when S-SBR is contained at least 70 parts by weight. Therefore, 100 parts by weight of S-SBR, that is, S-SBR alone is also suitable.

In the rubber composition of the present invention, in addition to the processing aid, as a compounding agent which is widely used in the rubber industry,
For example, vulcanizing agent, vulcanization accelerator, reinforcing agent, softening agent, filler,
An antiaging agent or the like can be appropriately added and used.

[0016]

The rubber composition for tire tread thus obtained has a plasticizing effect when not vulcanized and therefore has improved rubber processability, and in the vulcanized rubber, fatty acid zinc salt is vulcanized.
Since it exerts a synergistic effect with S-SBR, it is thought that its physical properties are to well control the increase in rolling resistance and improve wear resistance. And, in particular, the zinc salt of saturated fatty acid contributes to the improvement of the wear resistance with respect to S-SBR used in the present invention, while the zinc salt of unsaturated fatty acid causes the vulcanization reaction at the double bond part in the molecule. Therefore, it is presumed that it will be added to the rubber molecular chain to suppress the increase in the rolling resistance of the rubber and control it well. Therefore, it is presumed that the combined use of both fatty acid salts exerts a function of making the balance between wear resistance and rolling resistance as dynamic properties of the tire vulcanized rubber good.

Therefore, the present invention has the operational effect of making it possible to improve both the processability of rubber as a tire tread and the physical properties of a fuel-efficient tire.

[0018]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

First, the compounding ratios of the compounding ingredients shown in the following Table 1 are used as the basic composition of the rubber, and 8 kinds of processing aids (A to
H) was used to prepare a total of 29 rubber compositions as shown in Tables 3 to 5 and evaluated by the following test methods. The results are shown in Tables 3-5.

[0020]

[Table 1]

[0021]

[Table 2]

Test method (1) Workability (plasticity) (Moonie viscosity) (M
L _{1 + 4} ); the unvulcanized rubber was measured according to JIS K 6300. The smaller the number, the better. (2) Abrasion resistance; using the processing aids shown in Table 2,
Using the rubber composition obtained in the formulation shown in 5, a tread-formed tire (175/70 R13) was mounted on an actual vehicle,
After traveling 5000 km on a fixed road, the residual groove of the tire tread pattern was measured, and the compound No. 10 was set as 100 and indexed and displayed. Exponentially better. (3) Rolling resistance: The same tire as used in (2) above was tested by the Society of Automotive Engineers of America (Society of Aut.
(Omotive Engineers) standard SAE J 1269 was measured, and as in (2) above, compound No. 1 and No. 10 were set as 100 and indexed and displayed. The smaller the index, the better.

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

[Table 5]

First, Table 3 shows processing aids G and H, which are one of the constituents of the rubber composition of the present invention, and other processing aids (A to A) for comparison.
This is the result of comparison with F). Formulation Nos. 8 and 9 are examples, and rolling resistance does not change compared to other comparative examples,
It shows that ML _{1 + 4} was reduced and the workability of unvulcanized rubber was improved.

Next, Table 4 shows the results of comparative examples similarly carried out for various S-SBRs constituting the rubber composition of the present invention, the processing aids (G, H) and the aroma oil (B) for comparison. In addition, Table 5 shows Examples showing formulation Nos. 23 to 29, which are excellent in workability as well as in rolling resistance, and have good wear resistance as compared with other Comparative Examples. That is, No.23, N
Addition of o.24 unsaturated fatty acid zinc salt has the effect of suppressing the increase in rolling resistance with ML _{1 + 4,} and No. 25, No.
The addition of 26 saturated fatty acid zinc salt improved the wear resistance with ML _{1 + 4,} and even when both No. 29 fatty acid salts were used in combination, the Mooney viscosity (ML _{1+ 4} ) as well as the control of rolling resistance and resistance to abrasion were improved. It can be seen that there is an excellent effect in improving the wear property.

[0028]

As described above, the rubber composition for a tire tread of the present invention has a specific molecular weight as its base rubber, and has a styrene bond content and a vinyl bond content of the butadiene portion as its chemical structure composition. A fatty acid zinc salt, which is a characteristic processing aid of the rubber composition of the present invention, is added to a diene rubber containing S-SBR in a specific amount and at least 70 parts by weight of S-SBR. By compounding it, it has been difficult to process it as an unvulcanized rubber because it has a high viscosity in the past, but it reduces the viscosity appropriately to make it easier to process, and further, the physical properties of the vulcanized rubber, especially wear resistance as a tire tread. And it has the effect of suppressing the increase in rolling resistance, which is one of the characteristics of low fuel consumption tires, and controlling it well. Moreover, the rolling resistance of the vulcanized rubber is more remarkably increased by appropriately selecting and combining the fatty acid, which is the base component of the fatty acid zinc salt as a processing aid, with a saturated fatty acid and an unsaturated fatty acid, and forming each zinc salt. It is possible to provide the two major characteristics of controlling the wear resistance and improving wear resistance. As a result, both the properties of unvulcanized rubber and vulcanized rubber are improved, and the tire tread rubber made of the rubber composition of the present invention has an economical effect that it is possible to reduce the cost as a fuel-efficient tire. is there.

Claims (2)

[Claims] 1. A weight average molecular weight of 350,000 or more,
At least 70 solution-polymerized styrene-butadiene copolymer rubbers having a styrene bond content of 15 to 30% by weight and a vinyl bond content of the butadiene portion of 9 to 60% by weight.
1 to 10 parts by weight of a processing aid consisting of a fatty acid zinc salt is mixed with 100 parts by weight of a diene rubber containing 100 parts by weight,
A rubber composition for a tire tread, which has improved processability and physical properties after vulcanization. 2. The rubber composition for a tire tread according to claim 1, wherein the fatty acid zinc salt is a mixture of a saturated fatty acid zinc salt and an unsaturated fatty acid zinc salt.