JPS624732A - Tire tread rubber composition - Google Patents

Abstract

PURPOSE:To obtain a tire tread rubber composition having an increased frictional performance on a frozen road surface without a marked decrease in a frictional performance on a wet road surface and hardness, by forming a rubber composition prepared by mixing an elastomer such as natural rubber or polyisoprene rubber with carbon black, a liquid softener and factice at a specified ratio. CONSTITUTION:A tire tread rubber composition having the following composition. Namely, 100pts.wt. at least one elastomer component selected from among natural rubber, polyisoprene rubber and polybutadiene rubber of a 1,2-bond unit content >=20% is mixed with 40-90pts.wt. carbon black 5-60pts.wt. process oil and/or low-temperature plasticizer (liquid softener) and 5-30pts.wt. nonflowable substance (factice) obtained by reacting an animal or vegetable oil or fat of an iodine value >=70with a sulfur-containing substance (e.g., sulfur or sulfur chloride).

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a rubber composition, and particularly to a rubber composition for a tire tread that has increased frictional resistance on icy roads and wet roads without significantly reducing hardness.

<Prior Art> Icy road surfaces are the most slippery and dangerous among the road surfaces on which automobiles travel. Therefore, in cold regions where vehicles frequently drive on icy roads, automobile tires with metal spikes driven into their treads or chains are widely used.

However, even in cold regions, roads are rarely frozen all the time during the winter, and in fact, the roads are often free of ice for most of the winter.

With the development of automobile transportation, in cold regions, cars equipped with tires with spikes or chains are frequently traveling on roads that are not covered with ice. Social problems such as damaging roads and inducing dust pollution, and requiring large amounts of money to repair damaged roads, have become apparent. To address these problems, there is a need for the development of tires that can be driven safely on icy roads without the use of spikes or chains.

One way to obtain such tires is to develop rubber materials for treads that have high frictional resistance on icy roads.

As a means of increasing the frictional resistance of rubber materials on icy road surfaces, a compound that maintains softness even at low temperatures is generally used. In order to obtain a rubber material that remains soft even at low temperatures, the selection of polymer is most important, and tread rubber for winter tires usually uses relatively large amounts of polybutadiene rubber or natural rubber, which have a low glass transition temperature. ing.

As a method to further enhance the excellent frictional performance of these polymers on icy roads, we have developed process oils with low viscosity specific gravity constants (Japanese Patent Publication No. 58-7662) and low-temperature plasticizers (Japanese Patent Publication No. 58-7662).
9-126443) as a liquid softener. It is also known that in order to effectively utilize these liquid softeners, it is better to use them in relatively large amounts within a specific range (Japanese Patent Application No. 58-2).
No. 17839), but using liquid softeners such as those mentioned above can significantly reduce frictional resistance on wet road surfaces.
In addition, if a large amount of liquid softener is used, the hardness will decrease excessively, which will reduce the rigidity of the rubber blocks in the tread, impairing the responsiveness of the vehicle when steering, and causing the liquid softener to leak from the tread to adjacent tires. The problem is that the frictional performance of the tread deteriorates over time, and the bending resistance and strength of members adjacent to the tread deteriorate, resulting in a decrease in the durability of the tire.

<Objective of the Invention> The present invention is particularly useful as a tread rubber material for winter tires and all-season tires that run on icy roads, without significantly reducing wet road friction performance or hardness.
An object of the present invention is to provide a rubber composition for a tire tread that has excellent friction performance on icy road surfaces.

<Structure of the Invention> The present invention provides (a) one or more elastomers selected from natural rubber, polyisoprene rubber, and polybutadiene rubber having a 1.2-bond unit content of 20% or less; (b) 40 to 90 parts by weight of carbon black based on 100 parts by weight of the components.

(C) Process oil and/or low temperature plasticizer 5-60
(d) 5 to 30 parts by weight of a non-flowable substance obtained by reacting an animal or vegetable oil or fat having an iodine value of 70 or more with a sulfur-containing substance. be.

The present invention also includes (a) one or more elastomers selected from natural rubber, polyimprevin rubber, and polybutadiene rubber having a 1.2-bond unit content of 20% or less, and styrene.・An elastomer component containing 50% by weight or less of one or more elastomers selected from butadiene copolymer rubber, polybutadiene rubber with a 1.2-bond content of more than 20%, and halogenated butyl rubber. 10
0 parts by weight, (b) 40 to 90 parts by weight of carbon black, (c) 5 to 60 parts by weight of process oil and/or low-temperature plasticizer, and (d) animal and vegetable oils and fats with an iodine value of 70 or more. A rubber composition for a tire tread, comprising 5 to 30 parts by weight of a non-flowable substance obtained by reacting with a sulfur.

Here, the rubber composition for a tire tread is preferably such that the polybutadiene rubber having a 1.2-bond unit content of 20% or less accounts for 50% by weight or less of the elastomer component.

The configuration of the present invention will be explained in detail below.

The elastomer component used in the rubber composition for tire treads of the present invention includes one or more elastomers selected from natural rubber, polyisoprene rubber, and polybutadiene rubber having a 1,2-bond content of 20% or less. Select and use. These elastomers have a low glass transition temperature and are suitable for treads of tires running on snowy and icy roads. 20% 1.2-bond content of polybutadiene
1.2- The glass transition temperature of the elastomer increases as the content of bonding units increases.
This is because in order to maintain flexibility at low temperatures, the content of 1,2-bond units must be kept at 20% or less. Elastomers with low glass transition temperatures generally reduce frictional resistance on wet road surfaces, but in particular, polybutadiene rubber with a 1.2-bond content of 20% or less significantly reduces frictional resistance on wet road surfaces. Therefore, when using this elastomer, it is preferable that the amount used is 50% by weight or less of the total elastomer components.

This is to keep the reduction in frictional resistance on wet road surfaces within an acceptable range.

Further, in order to further increase the frictional resistance of the rubber composition for tire treads of the present invention on wet road surfaces.

Less than 50% by weight of the above elastomer is made of styrene-butadiene copolymer rubber, with a 1,2-bond content of 20% by weight.
% or more, such as polybutadiene rubber or halogenated butyl rubber, may be used by replacing the elastomer with a large frictional resistance on a wet road surface.
The reason for setting the content to be 0% by weight or less is that while these replacing elastomers increase the frictional resistance on wet road surfaces, they reduce the frictional resistance on icy road surfaces, so the frictional resistance on icy road surfaces should be kept within an allowable range. be.

In the rubber composition for a tire tread of the present invention, 40 to 90 parts by weight of carbon black is used per 100 parts by weight of the elastomer component.

If the amount of carbon black is less than 40 parts by weight, the reinforcing effect will be insufficient, and if it exceeds 90 parts by weight, the heat generated during running of the tire will increase, causing durability problems, and the rubber will harden and deteriorate. The type of carbon black, which is undesirable because it significantly reduces frictional performance on icy road surfaces, is not particularly limited as long as it is used for treads.

In the tire tread rubber composition of the present invention, 5 to 60 parts by weight of a process oil and/or a low-temperature plasticizer are used as a liquid softener based on 100 parts by weight of the elastomer component. Process oil is a plasticizer consisting of components originally found in petroleum, and is composed of saturated or inert unsaturated hydrocarbons. Low-temperature plasticizers include mineral oils other than process oils and synthetic plasticizers such as DO3, DOA, and DIOA.

Liquid softeners such as process oils and low-temperature plasticizers are used to improve workability when processing rubber compositions, and at the same time to suppress increases in hardness at low temperatures when used as tire treads. As a process oil,
V, G, C: Value (viscosity specific gravity constant) is 0.8 to 0.9
A plasticizer for low temperature use preferably has a solubility parameter of 8.0 to 9.0, and a particularly preferable range of solubility parameter is 8.2 to 8.7. The amount of these liquid softeners used is 10% of the elastomer component.
If the amount is less than 5 parts by weight, the effect of suppressing the increase in hardness at low temperatures will be small, and if it exceeds 60 parts by weight, the hardness will be significantly reduced, resulting in poor wear resistance and vehicle maneuverability. This is not preferable because it lowers the

The rubber composition for tire tread of the present invention has an iodine value of 70
It contains 5 to 30 parts by weight of a non-flowable substance (factice) obtained by reacting the above animal and vegetable oils and fats with sulfur or a sulfur-containing substance such as sulfur chloride under heating. Compared to liquid softeners, factice has the same or higher effect of increasing frictional resistance on icy roads, but on the other hand, it reduces the hardness of the rubber composition to a lesser extent, so it does not impair responsiveness during vehicle steering. Suitable for increasing frictional resistance on icy roads.

Furthermore, factice has the effect of increasing the frictional resistance on wet roads, which was conventionally considered to be in a contradictory relationship to the frictional resistance on icy roads.

The amount of factice used in the rubber composition for tire tread of the present invention is 5 parts by weight per 100 parts by weight of the elastomer component.
~30 parts by weight. If the factice is less than 5 parts by weight,
The effect of increasing frictional resistance on icy roads and wet roads is small, and if it exceeds 30 parts by weight, wear resistance and strength decrease, which is not preferable.

Factice, also called sub, has a specific gravity of 1.03 to 1.0.
It is a hardened oil of No. 5 and is an elastic body similar to rubber. It is mainly made by reacting rapeseed oil, cottonseed oil, soybean oil, etc. with sulfur chloride.

There is white sub, which is white or pale yellow, with a sulfur content of 6 to 8%, and black sub, which is a dark brown elastic material made by adding sulfur to oxidized vegetable oil and heating it to a high temperature, and has a sulfur content of 15 to 20%. In addition, there are special factices made from different animal and vegetable oils and fats, and transparent factices called Amesub made solely from the action of sulfur chloride.

Factice has traditionally been used as a rubber compounding agent as a softener and plasticizer to improve processability. It is mainly used,
It has never been considered as a component of a rubber composition for tire treads that requires high hardness.

The present invention contains a predetermined amount of factice and appropriately adjusts other rubber components to increase the frictional resistance on icy roads, especially on icy roads near the melting point of ice, and at the same time to increase the frictional resistance on wet roads. Furthermore, a rubber composition for tire treads is obtained which reduces the degree of decrease in the hardness of the rubber composition.

<Example> Examples and Comparative Examples Among the rubber compositions shown in Table 1, elastomers and compounding agents other than sulfur, vulcanization accelerator, and factice were kneaded in an internal mixer, and then sulfur was mixed with an oven roll. After adding and kneading a vulcanization accelerator and factice, a sample for a friction test was prepared under vulcanization conditions of 160° C. for 15 minutes.

The friction test was carried out using a British portable fist skid tester and a dry Safety Walk (outdoor 3M
), a wet safety walk with the surface submerged in water to a depth of approximately 1 mm, using ice plates at -2°C and -8°C as the road surface.
Dry friction resistance, wet friction resistance, and ice friction resistance (-2°C, -8°C) were measured, respectively. Furthermore, the JIS hardness at 25° C. of the sample subjected to the friction test was measured.

Table 3 shows the composition of each sample and the measurement results. Shown below.

Notes: 1) RSS #3゜2) N1pol BR1441, Nippon Zeon Co., Ltd., Sisho IJ 7”) Six 7 (1,2-content 0.4%
) 100 for highly aromatic process oil 3765
Contains parts by weight.

3) N1pol 1502. Manufactured by Nippon Zeon.

4) N-1,3-dimethylbutyl-N'-phenyl-
Phenyldiamine 5) ASTM designation N339.

6) Golden, manufactured by Tenba Sub Kako Co., Ltd., pale yellow factice.

7) Pure black sub, made by Tenba Sub Kako Co., brown factice (
black sub).

8) Neo-N, manufactured by Tenba Sub Kako Co., Ltd., special factis.

9) Amesub, manufactured by Tenba Sub Kako Co., Ltd. 10) N-oxydiethylene-2-benzothiazyl-
Sulfenamide.

11) Frictional performance was expressed as a comparative value with the frictional resistance of Comparative Example 1 as 100.

Comparative Examples 1 to 3 are examples in which only a liquid softener such as a process oil or a low-temperature plasticizer was used as a softener in a blend system of natural rubber and polybutadiene rubber. Comparative Example 2, which added 10 parts by weight of process oil to Comparative Example 1,
In Comparative Example 3, in which 10 parts by weight of dioctyl sebacate, which is a low-temperature plasticizer, was added, the frictional resistance on icy road surfaces was improved, but the hardness was significantly reduced. Furthermore, in Comparative Example 3, which has a large effect of improving frictional resistance on icy roads, a decrease in frictional resistance on wet road surfaces is also observed.

On the other hand, inventive examples 4 to 7, in which 10 parts by weight of various factices were added in place of liquid softeners such as process oil and low-temperature plasticizer, compared to comparative example 1, the friction on icy and wet road surfaces was improved. Not only is the resistance improved at the same time, but the hardness decreases less than when using a liquid softener.

Inventive Examples 10 to 12 are examples in which different types of factice were mixed in varying amounts, and it can be seen that as the amount of factice increases, the frictional resistance on wet road surfaces and ice plates (-2°C) improves. .

Further, Example 9 of the present invention, which contains a styrene-butadiene copolymer rubber in the elastomer component, has particularly high frictional resistance on wet roads and improved frictional resistance on icy roads.

As described above, it is clear that there are many advantages to using factice, but the most noteworthy one is that the frictional resistance on the high temperature side (-2° C.) is significantly improved. Frictional resistance on frozen roads is greatly affected by the temperature of the ice; the closer it is to the melting point of the ice, the smaller the frictional resistance.
Differences between different rubber compositions also tend to become smaller, and until now no rubber composition has been known that has large frictional resistance near the melting point. The rubber composition of the present invention containing factice brings about a remarkable improvement effect in the temperature range where such improvement is difficult.

<Effect of the invention> As explained above, the rubber composition of the present invention.

It has the advantage of being able to significantly increase the frictional resistance on frozen roads and simultaneously increase the frictional resistance on wet roads without causing a significant decrease in hardness, especially increasing the frictional resistance near the melting point of ice. It has an effect not found in other rubber compositions.

The rubber composition of the present invention is suitable for application to fields where it is necessary to improve the friction performance on snowy and icy road surfaces, such as the tread portion of winter tires.

Sad sadness:-

Claims (4)

[Claims] (1) (a) natural rubber, polyisoprene rubber and 1,
2-For 100 parts by weight of one or more elastomer components selected from polybutadiene rubbers having a bonding unit content of 20% or less, (b) carbon black 4
0 to 90 parts by weight, (c) 5 to 60 parts by weight of process oil and/or low-temperature plasticizer, and (d) a non-flowable substance obtained by reacting an animal or vegetable oil or fat with an iodine value of 70 or more with a sulfur-containing substance. 5 to 30 parts by weight of a rubber composition for a tire tread. (2) The polybutadiene rubber having a 1,2-bond unit content of 20% or less is 50% by weight of the elastomer component.
A rubber composition for a tire tread according to claim 1, which is as follows. (3) (a) natural rubber, polyisoprene rubber and 1,
2-One or more elastomers selected from polybutadiene rubbers with a bond unit content of 20% or less, styrene-butadiene copolymer rubber, and polybutadiene with a 1,2-bond content of more than 20%. Elastomer component 10 containing 50% by weight or less of one or more elastomers selected from rubber and halogenated butyl rubber
0 parts by weight, (b) 40 to 90 parts by weight of carbon black, (c) 5 to 60 parts by weight of process oil and/or low-temperature plasticizer, and (d) animal and vegetable oils and fats with an iodine value of 70 or more. A rubber composition for a tire tread, comprising 5 to 30 parts by weight of a non-flowable substance obtained by reacting with a sulfur. (4) The polybutadiene rubber having a 1,2-bond unit content of 20% or less is 50% by weight of the elastomer component.
A rubber composition for a tire tread according to claim 3, which is as follows.