JPH08319377A - Rubber composition for tread - Google Patents

Abstract

PURPOSE: To obtain a rubber composition for treads improved in road surface gripping properties and abrasion resistance while maintaining low heat buildup properties. CONSTITUTION: This rubber composition for treads is obtained by simultaneously blending an oil-extended rubber component A prepared by extending an SBR (rubber component A) having >=120 Mooney viscosity so as to provide 45-70 Mooney viscosity with a carbon masterbatch obtained by adding a carbon black having >=120g/kg amount of iodine adsorption to an SBR (rubber component B) having a higher Tg than that of the rubber component A so as to afford the Mooney viscosity of >=1.8 times that of the oil-extended rubber component A so that the amount of the rubber B component may be larger than that of the rubber component A and the sum total of the content of styrene and 1/2 of the content of 1,2-vinyl bond may be >=43wt.%.

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 which has improved road gripping properties and wear resistance while maintaining low heat buildup.

[0002]

2. Description of the Related Art Normally, the tread of a passenger car tire is
Styrene-butadiene rubber Rubber component 1 containing rubber as the main component
With respect to 00 parts by weight, N330, N339, N219,
A rubber composition containing 60 to 150 parts by weight of carbon black having an iodine adsorption amount of N220 or the like of 80 to 120 g / kg is used. By the way, recently, as interest in the environment or safety has increased, there has been a strong demand for improvement of road surface graspability and extension of wear life while maintaining low fuel consumption of tires. A rubber with a high glass transition point is used to improve road grip, and a large amount of carbon black and oil is used. To improve wear resistance, a rubber with a low glass transition point is used. Or blending carbon black with a small particle size. Generally, between the glass transition point of butadiene-based rubber and abrasion resistance, road surface graspability, for example, Rubber Chemistry and Technolo
As described in gy 44, page 996 (1971), as the glass transition point increases, the wear resistance decreases, and the skid resistance, so-called road graspability, increases. Also, if the particle size of carbon black is reduced, wear resistance improves, but when running at high speed for a long time, heat generation increases and separation easily occurs between tire constituent members, which in turn reduces tire life. It may shrink. As described above, the wear resistance, road surface gripping property, and high-speed durability are in a three-pronged relationship, and if one of them is improved, the other tends to be deteriorated.

It is well known that even if the rubber composition has the same composition, the physical properties differ if the state in which the carbon black is dispersed in the rubber is different. JP-A-1-272644
I is a combination of a styrene-butadiene rubber (hereinafter abbreviated as SBR) obtained by emulsion polymerization and a moat-type carbon masterbatch obtained by mixing carbon black into a latex of emulsion-polymerized SBR and drying the mixture, abrasion resistance, and road surface. Attempts have been made to improve comprehensibility, but have not yet been fully satisfied.

[0004]

DISCLOSURE OF THE INVENTION The present invention cuts off the three-way relationship between wear resistance, road surface graspability and high-speed durability to maintain wear resistance and road surface graspability while maintaining low heat generation. An object of the present invention is to provide a rubber composition for a tread that simultaneously improves

[0005]

When the glass transition point (hereinafter abbreviated as Tg) of SBR is lowered, the abrasion resistance of the rubber composition is increased, and when Tg is increased, the road surface is grasped better. Even if the SBR having a high Tg and the SBR having a low Tg are simply blended in an attempt to improve the performance at the same time, the both are compatible and become uniform, and the mixed carbon black is uniformly dispersed in the rubber component, and the Tg is Both S blended
The temperature is roughly the temperature obtained by arithmetically averaging the Tg of BR, and the physical properties are almost the same as those of the SBR having the averaged temperature Tg.

When carbon black having a large iodine adsorption amount is mixed with SBR, the rubber and the carbon black are physically and chemically bonded to form a bound rubber, and the bound rubber once generated is hard to be destroyed. The present invention was made based on the finding that carbon black may not be uniformly dispersed even if another rubber component is added.

The rubber composition of the present invention comprises an oil-extended styrene-butadiene rubber (A rubber component) having a high Mooney viscosity as a rubber component and a Tg formed into a carbon batch.
By blending with a high styrene-butadiene rubber (rubber B component), each rubber component is made independent in the rubber component to maintain the characteristics of each styrene-butadiene rubber.

That is, according to the present invention, the Mooney viscosity is 1
An oil-extended A rubber component obtained by oil-extending 20 or more styrene-butadiene rubber (A rubber component) so as to have a Mooney viscosity of 45 to 70, and a styrene-butadiene rubber (B rubber component) having a glass transition point higher than that of the A rubber component. Mooney viscosity is oil extension A
Iodine adsorption amount of more than 1.8 times of rubber component 120g
A carbon masterbatch in which carbon black of 1 kg / kg or more is mixed is made to have a large amount of B rubber component, and the amount of styrene contained in each of A rubber component and B rubber component (% by weight) and 1, 2 Vinyl bond amount (wt%)
Blend so that the total of 1/2 of the above is 43% by weight or more, and add commonly used compounding agents such as carbon black and sulfur, vulcanization accelerator, zinc white, stearic acid, antioxidant, softening agent, etc. A rubber composition for a tread obtained by mixing.

[0009]

[Function] Since the highly reinforcing carbon black used in the rubber composition for tread has a high adsorptivity, the particle size is usually 10 or less.
The primary aggregates of carbon black of ˜50 nm are further aggregated to form secondary aggregates. When carbon black is mixed with rubber in the mixer, the shearing force breaks the secondary agglomerates into primary agglomerates and disperses them in the rubber. Bound rubber is physicochemically combined with rubber. Bound rubber once made is hard to be destroyed, so
Even if another rubber and carbon black are added and mixed again, the bound rubber is hard to be completely destroyed, and while maintaining that state, it is dispersed in another rubber, and a small lump of bound rubber is surrounded by another rubber. The so-called sea-island structure is dispersed, and the added carbon black is distributed to both the sea-islands.

The characteristics of the rubber composition located on the exposed surface of the tread affect the wear, and the hysteresis of the entire rubber composition forming the tread affects the road gripping property. In the present invention, SBR having a high Mooney viscosity and a low glass transition point (A rubber component) is oil-extended to reduce the Mooney viscosity, and then SBR having a high glass transition point is used.
R (B rubber component) is used as a carbon masterbatch and blended into a product having a high Mooney viscosity. In the process of mixing the A rubber component, which has been oil-extended and whose viscosity has decreased, the B rubber component having bound rubber and carbon black, the B rubber component further takes in carbon black during stirring, and the Mooney viscosity increases and Then, it is dispersed as an island phase in the sea phase of the rubber component A that has been oil-extended and has a low Mooney viscosity. Thus, in the rubber composition, the A rubber component and the B rubber component exist independently of each other, and the SBR of each rubber component independently affects the physical properties affected by the glass transition point of the rubber component.
The element affected by the glass transition point of SBR remains, and the characteristics of each SBR are maintained. That is, since the rubber component A having a large Tg and a high molecular weight and a high Mooney viscosity and high abrasion resistance becomes the sea phase, the abrasion resistance of the tread rubber as a whole is improved. On the other hand, the road surface graspability is related to the hysteresis loss of the entire tread, so the total amount of styrene as the rubber component and 1/2 of the 1,2-vinyl bond amount (% by weight) should be 43% by weight or more. By increasing the amount of carbon black in SBR having a high Tg and the rubber component B having a large hysteresis loss as the island phase, the exothermic heat is not increased in the sea phase of the low heat-generating A rubber component having a low Tg. The graspability of the wet road surface and the dry road surface can be increased.

The Mooney viscosity is related to the molecular weight of rubber molecules, and the higher the molecular weight, the higher the Mooney viscosity. A
If the Mooney viscosity of the rubber component is lower than 120, the molecular weight becomes small and the wear resistance becomes insufficient. If the Tg is higher than that of the B rubber component, the wear resistance of the sea phase becomes low. When the Mooney viscosity of the carbon masterbatch of the B rubber component is smaller than 1.8 times that of the oil-extended A rubber component, the bound rubber is broken and homogeneously dispersed during mixing, so that the sea-island structure is not formed and abrasion resistance is improved. Road graspability is not improved at the same time. If the iodine adsorption amount of carbon black used in the B rubber component carbon masterbatch is less than 120 g / kg, the abrasion resistance of the island phase becomes too small even if the sea phase composed of the A rubber component is abrasion resistant. However, the wear resistance as a whole becomes small and the purpose cannot be achieved. Also, styrene and 1,2-vinyl bonds affect the hysteresis loss, and the road content graspability improves as the content of these increases. Since its influence is 1/2 of 1,2 vinyl bond to 1 of styrene, road graspability changes according to the sum of styrene amount and 1/2 of 1,2 vinyl bond amount (wt%). . The sum of the amount of styrene as the whole rubber component and 1/2 of the amount of 1,2 vinyl bonds (% by weight) is 43.
If it is less than weight%, improvement in road graspability cannot be expected. Also, when the B rubber component is less than the A rubber component,
We cannot hope to improve the road grip.

As a method for producing a carbon masterbatch, a method in which a rubber in a latex or solution state and a slurry in which carbon black is suspended in water are mixed, a so-called wet masterbatch method, and a method in which a rubber and a carbon black in a dry state are mixed are mixed. There is a so-called dry master batch system. Although both of them can be used in the present invention, the wet masterbatch method is preferable because the dispersion of carbon black is better. When blending the A rubber component and the B rubber component, the order of charging the rubber into the mixer is not particularly limited,
First, the A rubber component is charged and softened, then the carbon master batch is charged, and then the carbon black is charged to prevent the bound rubber of the B rubber component from being destroyed by the A rubber component to facilitate formation of a sea-island structure. Preferably.

[0013]

EXAMPLE To a latex of emulsion-polymerized SBR, water-suspended carbon black and emulsified oil were added in amounts as shown in Table 2 in terms of non-volatile content and stirred to disperse the carbon black. Hydrochloric acid was added to coagulate, washed with water and dried to obtain a carbon masterbatch of B rubber component. Next, the carbon master batch of B rubber component is shown in Table 1.
The oil-extended rubber of the A rubber component (solution-polymerized SBR) having the characteristics shown in Table 3 is weighed in the ratio by weight shown in Table 3 (the amount of the rubber component is shown in parentheses in the table), and the A component rubber is mixed in the mixer. , Then carbon masterbatch in that order, and a total of 10 rubber components
Carbon black and oil in the amounts shown in Table 3 with respect to 0 parts by weight (hereinafter, parts by weight will be simply referred to as parts), 3 parts by weight of zinc oxide,
2 parts of stearic acid, 1 part of anti-aging agent IPPD and 2 parts of wax are added, mixed and discharged. The discharged mixed rubber was molded into a sheet and cooled, and then 2 parts of sulfur and 1 part of vulcanization accelerator CBS were added and mixed again to obtain a rubber composition.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

The rubber composition obtained according to Table 3 above was used as J
Lambourn wear test according to IS K6264,
The results are shown in Table 3 as an index using Comparative Example 1 as a control. The larger the value, the better the wear resistance.

A tire of size 175R14 was formed using the rubber composition shown in Table 3 above as a tread rubber, and a road surface gripping test and a high speed durability test were conducted. As the road surface graspability test, a traction test on a wet road surface and a dry road surface was performed according to the asphalt road surface test conditions of the United States unified tire quality grade standard UTQGS.
It is shown as an index in Table 3 as 0. The larger the value, the better the road surface graspability. High-speed durability test is based on European Safety Regulation ECE
Drum test according to R30 high speed durability test,
Since it passed the three stages of the specified conditions, it was further extended for 20 minutes and the presence or absence of failure was examined. The results are shown in Table 3.

In each of the examples, the abrasion resistance, the wet road surface and the dry road surface traction are larger than those of Comparative Example 1 (control) of the conventional method in which carbon black is directly mixed without passing through the carbon masterbatch. . Comparative Example 2
Is the Tg of the A rubber component and the Tg of the B rubber component used in the examples.
This is an example in which only one type of SBR having a Tg about the same as the arithmetic average of is used, and wear is improved but traction (road surface graspability) is deteriorated. Comparative Example 3 is an example in which the use ratio of the carbon masterbatch is small, and Comparative Example 4 is an example in which the sum of the styrene content and the 1/2 vinyl bond content is less than 43, both of which are improved in wear. But the traction is getting worse. Comparative Example 5 is an example in which the difference in Mooney viscosity between the carbon master batches of the oil-extended A rubber component and the B rubber component is small, the effect of improving wear is small, and the traction on the dry road surface is slightly deteriorated. Comparative Example 6 is an example in which the carbon black used for the carbon masterbatch of the B rubber component has an iodine adsorption amount of less than 120 g / kg, and both wear and traction are poor. Comparative Example 7 is an example in which the sum of styrene content and 1/2 of 1,2 vinyl bond content is less than 43, and wear is improved but traction is poor.

[0021]

The rubber component of SBR (A rubber component) having a Mooney viscosity of 120 or more and the SBR (B rubber component) having a Tg higher than that of the A rubber component have an iodine adsorption amount of 1
It is composed of carbon masterbatch with 20 g / kg or more of carbon black, and the rubber is mixed in a sea-island structure in which the B rubber component is dispersed in the A rubber component to maintain low heat buildup. However, it is possible to improve wear resistance and road surface graspability at the same time.

Claims (2)

[Claims] 1. A rubber composition for a tread obtained by mixing carbon black with an A rubber component and a B rubber component having different glass transition points, wherein a Mooney viscosity of the A rubber component, which is a styrene-butadiene rubber, is 120 or more. Four
An oil-extended A rubber component that is oil-extended to 5 to 70
Carbon black having an iodine adsorption amount of 120 g / kg or more was mixed into the B rubber component, which is a styrene-butadiene rubber having a higher glass transition point than the A rubber component, so that the Mooney viscosity is 1.8 times or more that of the oil-extended A rubber component. A rubber composition for a tread, which comprises blending a carbon masterbatch prepared as described above so that the amount of the rubber component B is larger, and further additionally mixing carbon black and a compounding agent that is normally used. 2. The amount of styrene (% by weight) and the amount of 1,2 vinyl bonds (% by weight) contained in each of the rubber component A and the rubber component B in the rubber composition for a tread according to claim 1.
A rubber composition for a tread having a sum of / 2 of 43 or more.