JPH10195249A - Side wall rubber composition for radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a side wall rubber composition for a radial tire capable of providing abrasion resistance, a low heat build-up and destruction resistance required for side wall rubber in a good valance. SOLUTION: This side wall rubber composition of a radial tire is obtained by formulating 100 pts.wt. rubber component comprising substantially a compound of a natural rubber and/or a polyisoprene and a polybutadiene in which the weight ratio thereof [(natural rubber and/or polyisoprene)/polybutadiene] is (60/40) to 30/70), with 1-30 pts.wt. polyethylene having >=120 deg.C melting point and <=20 melt flow rate and 20-50 pts.wt. carbon black having a grade not more than ISAF.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a side rubber composition for a radial tire.

[0002]

2. Description of the Related Art Among the required properties of tire side rubbers,
Abrasion resistance, low heat build-up, and anti-destructive properties have become increasingly important in recent years. C to meet the diversifying needs of tires
Side rubber with improved curb resistance has been developed for ITYBUS tires, low heat-generating side rubber for fuel-efficient tires, and side rubber with excellent anti-destructive properties for off-road tires.

In order to improve abrasion resistance, increasing the amount of polybutadiene, upgrading of carbon black, increasing the amount of carbon black, increasing the amount of sulfur, and the like are effective methods. Deteriorates.

[0004] When dicyclopentadiene, ABS resin or the like is blended, the anti-destructive property can be improved, but the low heat build-up and abrasion resistance are deteriorated.
It is very difficult to achieve both low heat build-up and anti-destructive properties.

[0005] US Pat. No. 4,675,349 discloses a rubber composition containing polyethylene, which has a softening point of 1;
US Pat. No. 5,341,863 discloses a composition in which polyethylene having a temperature of 35 ° C. or higher is blended at a temperature lower than its softening point. A composition is disclosed.

[0006]

SUMMARY OF THE INVENTION U.S. Pat.
The composition described in the specification of JP-A No. 49 needs to incorporate fine polyethylene, and there is a problem that the polyethylene particles may be re-aggregated to cause deterioration in physical properties.

The composition described in US Pat. No. 5,341,863 has a remarkable change in physical properties due to blending at a high temperature.
There is a problem in using it as a rubber composition for tires. The present invention is abrasion resistance required as side rubber, low heat generation,
It is an object of the present invention to provide a radial rubber side rubber composition capable of imparting a good balance of anti-destructive properties.

[0008]

The side rubber composition for radial tires of the present invention is substantially a blend of natural rubber and / or polyisoprene and polybutadiene, and their weight ratio [(natural rubber and / or Polyisoprene) /
[Polybutadiene] is a polyethylene component having a melting point of 120 ° C. or higher and a melt flow rate of 20 or lower, based on 100 parts by weight of a rubber component having a 60/40 to 30/70 ratio.
0 to 100 parts by weight and 20 to 50 parts by weight of carbon black of ISAF or lower grade. The rubber component used in the present invention is substantially a blend of natural rubber and / or polyisoprene and polybutadiene, and their weight ratio [(natural rubber and / or polyisoprene) / polybutadiene] is 60/40 to 30. / 7
Must be 0. If the polybutadiene is less than the lower limit, the flexibility and abrasion resistance decrease, and if the polybutadiene exceeds the upper limit, the anti-fracture property decreases.

[0009] In the composition of the present invention, polyethylene is dispersed in rubber and adsorbs with rubber, thereby increasing the reinforcing property of rubber. It is necessary that the blending amount of polyethylene is 1 to 30 parts by weight with respect to 100 parts by weight of the rubber component, and if the blending amount is less than the lower limit, a significant effect cannot be obtained, and the upper limit is exceeded. In this case, the flexibility is significantly reduced. The amount of the polyethylene is preferably 5 to 20 parts by weight based on 100 parts by weight of the rubber component.

[0010] Polyethylene must have a melting point of 120 ° C or higher and a melt flow rate of 20 or lower.
If the melting point of the polyethylene is less than 120 ° C., the modulus of elasticity is reduced and the loss component is increased due to melting of the polyethylene crystal in the tire operating temperature range, which has a negative effect on low heat build-up. The melting point of polyethylene is preferably 12
5 ° C. or higher. If the melt flow rate of the polyethylene exceeds 20, sufficient dispersibility during kneading cannot be obtained,
Decreases anti-destructive properties. The melt flow rate of the polyethylene is preferably 1 to 15.

The composition of the present invention contains 20 to 50 parts by weight of carbon black having a grade of ISAF or less based on 100 parts by weight of the rubber component. Grades below ISAF include, for example, ISAF, HAF, FEF, GPF,
FF, HMF, SRF, FT, MT, CF, EPC, M
PC, HPC, CC and acetylene black, preferably HAF and FEF. When a grade higher than ISAF, for example, SAF, is used, the low heat buildup deteriorates. I
The amount of the carbon black of the SAF or lower grade is
If the amount is less than the lower limit, the abrasion resistance is inferior. Further, the nitrogen adsorption specific surface area of the carbon black is preferably 125 m ² / g or less from the viewpoint of improving the heat buildup.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a preferred embodiment of the present invention will be described below. An example of a preferred embodiment of the composition of the present invention has a melting point of 12 with respect to 100 parts by weight of the rubber component.
5 to 20 parts by weight of polyethylene having a melt flow rate of 20 or less at 0 ° C. or more, and a grade of HAF or FE
F is a blend of 20 to 50 parts by weight of carbon black.

When the rubber composition is prepared and kneaded in a plurality of stages, the kneaded material is compounded in at least one stage such that the temperature of the kneaded material is higher than the melting point of the compounded polyethylene by 10 ° C. or more. Is preferred. By doing so, it is possible to prevent the viscosity of the polyethylene from being increased and to improve the dispersibility of the polyethylene and the affinity with the matrix rubber, thereby preventing a decrease in the anti-destructive property of the compound.

In the composition of the present invention, in addition to the above components, fillers such as silica and clay, softeners such as oil, tackifiers, antioxidants, vulcanization accelerators, vulcanization accelerators, A sulfuric acid or the like can be appropriately compounded.

[0015]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to these Examples. (Examples 1-4 and Comparative Examples 1-6) Table 1 shows the formulation of the side rubber composition.

[0016]

[Table 1]

The methods for measuring the properties of polyethylene, the kneading method, the method for measuring the temperature of the compound, and the methods for evaluating abrasion resistance, heat build-up and anti-destructive properties are as follows.

(Method of Measuring Characteristics of Polyethylene) (1) Measurement of Melting Point The melting point was measured by a differential thermal analyzer (D) manufactured by Seiko Electronics Industry Co., Ltd.
SC200) at 10 ° C. with a nitrogen flow rate of 20 ml / min.
/ Min at 20-180 ° C. The melting point was the temperature at which the endothermic peak converged. (2) Measurement of melt flow rate This was based on JIS K6760.

(Kneading method) The kneading method was carried out by dividing into two stages. In the first stage, the chemicals and rubber, polyethylene, carbon black, etc. are added, excluding vulcanizing agents, vulcanization accelerators, vulcanization accelerating aids, etc., which do not greatly affect the crosslinking of the rubber matrix at high temperatures. 10 from the melting point of
It was kneaded at a high temperature of at least ℃. In the second stage, chemicals and the like not added in the first stage were added and kneaded, but at this time, the temperature of the rubber compound clearly did not reach the melting point of polyethylene.

(Method of Measuring Compound Temperature) The surface temperature of the compounded rubber at the end of the first stage of kneading was measured to obtain the compound temperature.

(Evaluation method) (1) Abrasion resistance (pico wear) In accordance with JIS K6264. (2) Exothermicity (Tanδ) Initial strain 4-5% Amplitude 2% Frequency 52Hz Measurement temperature 25 ° C Testing machine Mechanical spectrometer manufactured by Rheometrics

(3) Anti-fracture property (high temperature elongation) Measured at 100 ° C. in accordance with JIS K6301. Table 2 shows the components of the above-mentioned compositions whose amounts were changed and the evaluation results.

[0023]

[Table 2]

An index is shown based on Comparative Example 1. With respect to abrasion resistance and heat generation, the smaller the numerical value, the better the direction, and the larger the anti-fracture property as an index, the better. Comparative Example 2 is a composition in which carbon black (HAF) was increased by 5 parts by weight. Although the abrasion resistance is improved as compared with Comparative Example 1, the low heat build-up and the anti-destructive properties tend to be inferior.

Example 1 in which 5 parts by weight of polyethylene was added to Comparative Example 1 had at least the same abrasion resistance and low heat build-up as Comparative Example 2, and the anti-fracture property was greatly improved. Also,
When the amount of polyethylene was increased as in Examples 2 and 3,
Improves anti-destructive properties without compromising wear resistance and low heat build-up. When the grade of carbon black is increased as in Comparative Example 6, the wear resistance and the anti-fracture property can be improved, but the low heat build-up is remarkably inferior. As compared with Comparative Example 6, Example 3 is slightly inferior in abrasion resistance, but is excellent in anti-destructive property and has greatly improved low heat buildup.

In Comparative Example 5, the low heat buildup was improved by lowering the grade of carbon black, but both the abrasion resistance and the anti-destructive properties were inferior. On the other hand, as in Example 4, by adding 5 parts by weight of carbon black (FEF) and adding 10 parts by weight of polyethylene, low heat build-up can be maintained and abrasion resistance and anti-fracture property can be simultaneously improved. .

Further, by increasing the amount of sulfur and the amount of polybutadiene (Comparative Examples 3 and 4), the abrasion resistance and the low heat buildup are improved, but the anti-destructive property is reduced. With the combination of general-purpose materials as in the comparative example, the three elements, wear resistance, low heat build-up, and anti-destructive property, contradict each other, and there is a limit to improvement. On the other hand, by blending a predetermined amount of polyethylene, abrasion resistance, low heat generation,
A balance of physical properties of anti-destructive property can be achieved at a higher level.

[0028]

According to the present invention, it is possible to provide a radial rubber side rubber composition capable of imparting a good balance of abrasion resistance, low heat build-up and anti-destructive properties required as a side rubber.

Claims (3)

[Claims] 1. A blend of substantially natural rubber and / or polyisoprene and polybutadiene having a weight ratio [(natural rubber and / or polyisoprene) / polybutadiene] of 60/40 to 30/70. A certain rubber component 10
Side rubber composition for radial tires containing 1 to 30 parts by weight of polyethylene having a melting point of 120 ° C. or more and a melt flow rate of 20 or less, and 20 to 50 parts by weight of carbon black of ISAF or less, based on 0 part by weight. Stuff. 2. The side rubber composition for a radial tire according to claim 1, wherein the nitrogen adsorption specific surface area of the carbon black is 125 m ² / g or less. 3. When the side rubber composition for a radial tire is kneaded in a plurality of stages, the temperature of the kneaded material is at least 10 ° C. higher than the melting point of the blended polyethylene in at least one stage. The side rubber composition for a radial tire according to claim 1, which is blended as follows.