JPS60173031A - Tiretread rubber composition - Google Patents

Abstract

PURPOSE:The titled rubber composition which can provide tires capable of retaining a braking performance of frozen road surfaces over a long period of time, prepared by adding a process oil to a specified stock rubber containing an ethylene/propylene/diene terpolymer. CONSTITUTION:100pts.wt. stock rubber comprising a mixture of at least 30pts.wt. ethylene/propylene/diene terpolymer (ethylene content of 55-75wt%) containing ethylidenenorbornene of an iodine value of 8-20 as the diene and at most 70pts.wt. other rubbers (e.g., natural rubber, polybutadiene rubber, or styrene/ butadiene copolymer) is mixed with 50-150pts.wt. process oil of an aromatic carbon content <=30wt% and other additives (e.g., zinc oxide, carbon black, vulcanizing agent or antioxidant).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rubber composition for a tire tread that has excellent braking performance on icy road surfaces and can maintain its excellent properties over a long period of time.

Conventionally, oil-extended natural rubber and polybutadiene rubber have been reported as rubbers with excellent braking performance on icy roads, that is, excellent frictional resistance. In order to improve frictional resistance on icy road surfaces, it is preferable to blend rubber with a low glass transition temperature (Tg).

By the way, Tie A7 generates heat during normal driving, so the temperature inside the tread can reach over 60°C, and the tread surface in particular can reach a high temperature of over 100°C during normal driving due to friction against the road surface during acceleration and deceleration. It is estimated that It is known that Tires 1 to 12 react with oxygen in the air and deteriorate in such a high-temperature atmosphere, and this deterioration reaction changes the quality of the tread and reduces the frictional resistance on icy road surfaces over time.

The present invention has been made in order to solve the above problems, and provides a rubber composition for tire treads that has excellent frictional resistance on icy road surfaces, maintains its performance for a long time, and can be used particularly well in low-temperature conditions. With the goal.

The present inventors believe that frictional resistance on icy road surfaces mainly depends on the contact area between the tread and snow or ice, so in order to improve braking performance, carbon black and a process oil that has a low viscosity even at low temperatures should be added to They discovered that it is sufficient to add a large amount of ethylene to the rubber composition that is the raw material for Red, and in order for this rubber composition to maintain good braking performance on snow and ice, the ethylene content must be 55 to 15% by weight. 3 ingredients are 8~
Ethylidene norbornene (E
At least 30 m of ethylene-propylene-diene terpolymer rubber (EPDM), which is NB), is added to the raw material rubber.
The inventors have discovered that if the content is m% or more, it is possible to prevent the deterioration of braking performance on frozen roads due to the deterioration reaction of the vulcanized product, and have thus arrived at the present invention.

That is, in the present invention, the ethylene content is between 55 and 15% by weight.
, the third component is ethylidene having an iodine value of 8 to 20.
50 to 1 part of process oil is added to 100 parts by weight of raw material rubber containing at least 30 parts by weight of ethylene propylene diene terpolymer rubber, which is norbornene.
50 parts by weight of the process oil, and the aroma carbon content of the process oil is 30% by weight or less of the process oil.

In the raw material rubber for the rubber composition of the present invention, the ethylene-propylene-diene terpolymer rubber (EPDM) used as the main rubber must have an ethylene content in the range of 55 to 75% by weight. . If the ethylene content is less than 55% by weight or more than 75% by weight, the ice skid resistance will decrease, which is undesirable. Furthermore, by using ethylidene norbornene (ENB) as the diene component, which is the third component of EPDM, compared to the case where dicyclopentadiene (DCPD) and 1,4-hexadiene are used as the third component, , it is possible to reduce the decrease in ice skid resistance due to heat aging. This third
The iodine value of ENB, which is a component, must be in the range of 8 to 20. If the iodine value exceeds 20, the ice skid resistance due to heat aging will significantly decrease, which is undesirable.
Further, if the iodine value is less than 8, the vulcanization rate will be delayed. In addition,
The ice skid resistance referred to here is the Pretty Portable Skid Tester (3tanley L on
don ;portable 5kid Re5iSt
an(ie Te5ter.

D S I R Road Research Lab
The skid number is the skid number of a rubber composition on an ice surface during vulcanization or after aging when the temperature of the ice and rubber test piece is -15℃, and if the ice skid resistance is increased, the skid number is Tire braking performance can be improved.

This EPDM used in the present invention needs to be contained at least 30 parts by weight in 100 parts by weight of raw rubber,
If it is less than 30 parts by weight, the ice skid resistance will drop significantly due to heat aging.

In the present invention, the raw rubber to be blended with the EP and DM is not particularly limited and may be any rubber commonly used for tire treads, such as natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber ( BR),
Diene rubbers such as styrene-butadiene copolymer rubbers are exemplified.

In the present invention, raw rubber 100! ! ! 50 to 150 parts by weight of process oil is added to part ffi. Further, it is necessary that the aroma carbon content of this process oil is 30% by weight or less of the process oil. If the proportion of process oil is less than 50 parts by weight, ice skid resistance cannot be improved, and if it exceeds 150 parts by weight, it becomes excessively soft and cornering performance and wear resistance are significantly reduced. If a process oil containing aroma carbon content exceeds 30% by weight, ice skid resistance cannot be improved. Note that the aroma carbon content in the present invention refers to the content of aroma components relative to the sum of the aroma components, naphthene components, and paraffin components in the process oil, and is contained in all the process oils blended into the rubber composition. Refers to the content of aroma carbon components.

In the present invention, in addition to the process oil, compounding agents such as zinc oxide, stearic acid, anti-aging agents, carbon black, sulfur, and vulcanization accelerators, which are usually blended in tire treads, are blended in appropriate amounts.

Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. In Table 1, all the numerical values of the formulation contents are parts by weight.

, '1 to 4 and Comparative Examples 1 to 3 Rubber compositions were prepared by kneading and mixing raw rubber and various compounding agents according to the formulations shown in Table 1. In addition, E in Table 1
Properties of PDM-1 to 3 (third component, ethylene content m1 iodine value, oil extension period, aroma carbon content of process oil)
are shown in Table 2.

This rubber composition was vulcanized at 160° C. for 15 minutes to obtain a vulcanized rubber. The JIS hardness, tensile strength, elongation, and ice skid resistance of this vulcanized rubber were measured, and the results are shown in Table 1. In addition, JISN width, tensile strength and elongation are JISN
Measured according to SK6301. Furthermore, the ice skid resistance was measured using the British Portable Skid Tester described above.

Further, the vulcanized rubber was heat treated in an oven at 150° C. for 8 hours, and the JIS hardness and ice skid resistance after heat aging were measured.

The results are shown in Table 1. The ice skid resistance values before aging and after aging were expressed as an index with the ice skid resistance value of Comparative Example 1 before aging as 100.

Table 2 (P, E, We+), Vol, 33, p, 21
5 (1961)", the propylene content m is determined, and the remaining 0 is the ethylene content.

1:12: Based on JIS KOO70 iodine value measurement method.

*13: Denseness of process oil per 100fi parts of rubber.

In Table 1, Comparative Example 1 is a rubber composition in which natural rubber and SR are used as raw rubbers, and aromatic and paraffinic oils are used in combination as process oils.

Comparative Example 2 is a rubber composition that uses EPDM with a high iodine value as a raw material rubber and contains a relatively large amount of paraffin-based process oil with a low aroma carbon content.
Similar to Comparative Example 1, the ice skid resistance after aging is low.

Also, the tensile strength is poor.

Example 1 is a rubber composition using EPDM with a relatively low iodine value as a raw material rubber, but compared to Comparative Example 1, the ice skid resistance after aging is at a higher level and the vulcanization properties are also favorable.

Example 2 is a rubber composition in which EPDM, which has a relatively low iodine value, is used as a raw material rubber and paraffinic process oil is contained therein, and almost the same results as in Example 1 were obtained.

Example 3 is a rubber composition in which raw rubber is prepared by mixing EPDM with a relatively low iodine value and natural rubber, and contains paraffin-based process oil, but the ice skid resistance before and after aging is the highest. It shows a high value, and the vulcanization properties are also within a preferable range.

Comparative Example 3 is EPDM with a relatively low iodine value and oil-extended SBR.
This rubber composition is made by mixing raw material rubber and containing paraffinic process oil, but since the content of process oil is small, the ice skid resistance before and after aging is low.

It also has low elongation.

Example 4 uses EPDM with a relatively low iodine value and natural rubber,
This is a rubber composition in which BR is mixed as a raw material rubber, and this is combined with an aromatic process oil and a paraffinic process oil, but the ice skid resistance after aging is higher than that of Comparative Example 1. shows.

As explained above, the raw rubber contains at least 30% by weight of EPDM, which is ENB having an ethylene content of 55 to 75% by weight and a third component having an iodine value of 8 to 20, and aromatic carbon. The rubber composition of the present invention containing a specific amount of process oil with a low content can maintain ice skid resistance at a high level after heat aging. For this reason, the rubber composition of the present invention can be suitably used as a tread material for snow tires and studless ties.

Patent applicant: Yokohama Rubber Co., Ltd. Agent: Patent Attorney Tatsuo Ito Agent: Patent Attorney Tetsuya Ito

Claims (1)

[Claims] Ethylene content is 55-75% by weight, third component is 8-2
Containing 50 to 150 parts by weight of process oil for 100 parts by weight of raw rubber containing at least 30 parts by weight of ethylene-propylene-diene terpolymer rubber, which is edilidene norbornene having an iodine value of 0,
A rubber composition for reding a tire 1, characterized in that the aroma carbon content of the process oil is 30% by weight or less of the process oil.