JPH07102115A - Rubber composition - Google Patents

Abstract

PURPOSE:To obtain a composition, good in operating efficiency and having both low heat buildup and fracture resistance and capable of providing a belt coating rubber by blending a rubber component containing natural rubber, etc., with specific silica, carbon black and a silane coupling agent. CONSTITUTION:This rubber composition is obtained by blending 100 pts.wt. rubber component containing natural rubber or polyisoprene rubber with 30-70 pts.wt. total amount of silica and carbon black in which the amount of the silica is 10-50wt.%. based on the total amount and a silane coupling agent in an amount of 10-30wt.% based on the silica. The carbon black has 80-160m<2>/g specific surface area (N2SA value) measured by the nitrogen adsorption method and 70-100ml/100g dibutyl phthalate oil absorption volume (DBP value). An organic unsaturated fatty acid containing >=10wt.% conjugated dienoic acid containing at least one set of two double bonds between carbon atoms in a conjugated relationship in the molecule and >=2 double bonds between carbon atoms in the molecule in an amount of 0.5 pts.wt. may be blended therewith. A belt coating rubber has g 40 fracture index and >=63% resilience at 25'C and provides a large-sized pneumatic radial tire for construction.

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 coating a tire belt, and more particularly to a rubber composition suitable for a large pneumatic radial tire for construction which has improved fracture resistance and low heat buildup. It is a thing. Generally, in a tire for a large vehicle, since the rubber layer constituting the tire is thick, heat generation inside the tire becomes a problem, and it is easy to cause a tire failure due to separation of the belt portion due to extreme use. Are known. Therefore, the belt coating rubber used is required to have a low heat generation property and a good fracture resistance.
In order to achieve both low exothermicity and fracture resistance, conventionally, a method of using low exothermicity of low exothermic carbon black, or a method of replacing a part of carbon black with low exothermic silica is used. It was

However, the method using low heat-generating carbon black is still inadequate in terms of compatibility with fracture resistance, especially for large pneumatic radial tires for construction. In addition, in the method of using carbon black and silica together, although a tentative compatibility effect can be obtained, on the other hand, the fracture resistance after aging is inferior, and further, silica cures the compounded rubber to improve workability in production. There was also a drawback that it worsened.

It is a first object of the present invention to provide a rubber composition for coating a tire belt, which has both low heat buildup and fracture resistance. The second object of the present invention is to
An object of the present invention is to provide a rubber composition having improved low heat buildup and fracture resistance without deteriorating workability.

The present invention has been earnestly developed as a solution to the above drawbacks, and as a result, a silane coupling agent was further added to a silica-containing constant rubber composition, and in view of workability, a specific organic fatty acid was used. The present invention has been completed based on the finding that it is effective to blend the above. That is, the first invention by the present inventor is that the total amount of silica and carbon black is 30 to 70 with respect to 100 parts by weight of a rubber component mainly composed of natural rubber or polyisoprene rubber.
In a rubber composition in which 10 to 50% by weight of silica is blended, the carbon black has a nitrogen adsorption specific surface area (N ₂ SA value) of 80 to 120.
m ² / g and dibutyl phthalate oil absorption (DBP value)
Is 70 to 100 mg / 100 g, and a silane coupling agent is further compounded with 10 to 30% by weight of silica.

In the second invention, the total amount of silica and carbon black is 30 to 70 with respect to 100 parts by weight of a rubber component mainly composed of natural rubber or polyisoprene rubber.
In parts by weight, silica is 10 to 50% by weight of the total amount, and the silane coupling agent is 5% by weight of silica.
In the range of 30 to 30% by weight, and in the molecule containing 10% by weight or more of a conjugated dienoic acid containing at least one pair of two carbon-carbon double bonds in a conjugated relationship in the molecule. A rubber composition for tire belt coating, comprising 0.5 to 10 parts by weight of an organic unsaturated fatty acid containing 2 or more of Hereinafter, the present invention will be described in detail.

The total amount of silica and carbon black is 30 to 70 parts by weight based on 100 parts by weight of the rubber component. Three
If it is less than 0 parts by weight, the fracture resistance is poor due to insufficient reinforcement of rubber, and if it exceeds 70 parts by weight, heat generation is poor. Further, the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is 80 to
120 m ² / g and dibutyl phthalate oil absorption (DB
P) is preferably 70 to 100 mg / 100 g. N ₂ S
When A is less than 80 m ² / g, the fracture resistance of the rubber is insufficient and 12
When it exceeds 0 m ² / g, the exothermicity is poor, and the DBP is 7
If the amount is less than 0 mg / 100 g, the heat build-up of the rubber is poor and 100 m
If it exceeds g / 100g, the fracture resistance becomes insufficient. The amount of silica is 10 with respect to the total amount of carbon black.
˜50 wt%, but preferably 20-40 wt%. If it is less than 10% by weight, the effect of exothermicity is not obtained, and if it is 50% by weight or more, the reinforcing property of rubber becomes insufficient.

The silane coupling agent is contained in an amount of 5 to 30% by weight, preferably 10 to 2%, based on silica, from the viewpoint of heat generation effect.
It is in the range of 0% by weight. Examples of the silane coupling agent include bis- (3-triethoxysilylpropyl) -tetrasulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazoletetrasulfide. Examples thereof include sulfide.

On the other hand, when carbon black is used in combination with silica and a silane coupling agent, it is effective in achieving both breakage resistance and low heat build-up, but on the other hand, compounded unvulcanized rubber tends to cure. Therefore, improvement in workability such as mastication and mixing during tire production is also desired. To improve workability, a process oil such as an aromatic process oil is usually added, but on the other hand, an amount sufficient to obtain satisfactory workability is added because it reduces fracture resistance and low heat buildup. I can't.

In the present invention, it is preferable to add the specific organic unsaturated fatty acid described below in order to obtain the effects of both breaking resistance and low heat buildup without deteriorating workability. That is, the organic unsaturated fatty acid used in the rubber composition of the present invention contains 10% or more of conjugated dienoic acid containing at least one pair of two carbon-carbon double bonds having a conjugated relationship in the molecule. It is an organic unsaturated fatty acid containing two or more carbon-carbon double bonds.

The conjugated dienoic acid is an organic unsaturated monocarboxylic acid containing at least one set of two carbon-carbon double bonds having an intramolecular conjugation relationship, and two conjugated carbonic acid double bonds having an intramolecular conjugation relationship. Is preferably one set. Further, the organic unsaturated fatty acid contains the conjugated dienoic acid, but the other organic unsaturated fatty acids contain two or more carbon-carbon double bonds in the molecule, but they are unsaturated in a non-conjugated relationship with each other. It is a fatty acid. The content of the conjugated dienoic acid in the total organic unsaturated fatty acids is required to be 10% by weight or more, preferably 20% by weight or more in order to improve workability.

Specific examples of the conjugated dienoic acid include 2,4-
Pentadienoic acid, 2,4-hexadienoic acid, 2,4-decadienoic acid, 2,4-dodecadienoic acid, 9,11-octadecadienoic acid, 9,11,13,15-octadecatetraene, eleostearic acid (9, 11, 13, 15
-Octadecatrienoic acid), pseudoeleostearic acid (10,12,14-octadecatrienoic acid), dehydrated linoleic acid (trans 10, trans 12, octadecadienoic acid), and the like, alone or as a mixture. Alternatively, it is used as contained in the organic unsaturated fatty acid.

A preferred example of unsaturated fatty acid containing conjugated dienoic acid is dehydrated castor oil fatty acid obtained by dehydrating castor oil containing about 90% of ricinoleic acid. Depending on the dehydration method, conjugated dienoic acid is used. The content of can be varied, for example 35% by weight, 60% by weight can be obtained. In this case, the conjugated dienoic acid is 9, 1
The main component is 1-octadecadienoic acid. The content of the organic unsaturated fatty acid in the rubber composition is 0.5 to 10 parts by weight, preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the rubber component.
The amount is 5.0 parts by weight, and more preferably 1.0 to 3.0 parts by weight. If it is less than 0.5 parts by weight, the workability cannot be improved, and if it exceeds 10 parts by weight, the adhesive strength to the steel cord, which is the belt reinforcing material, is greatly reduced. The rubber component used in the present invention is a natural rubber or a polyisoprene rubber alone or a rubber containing these as a main component.

When the rubber composition according to the present invention is used as a belt coating rubber for a large pneumatic radial tire for construction, the physical properties of the vulcanized rubber have a fracture index after aging of 400 or more, preferably 400 to 500. ,and,
It is desired that the resilience at 25 ° C be 63% or more. Hereinafter, the present invention will be described with reference to Examples and Comparative Examples. The rubber compositions obtained in Examples and Comparative Examples were evaluated by the following tests.

Fracture index after aging A vulcanized rubber test piece (thickness: 2 mm) was accelerated at 100 ° C. for 24 hours and then subjected to a tensile test in accordance with JIS K6301 to obtain an elongation (%) at break and a tension at that time ( The product of Kg / cm @ 2) was calculated and divided by 2. This value was taken as the fracture index. The larger the value, the better.

A value (%) at 25 ° C. was obtained by a resilience test according to resilience JIS K6301. The larger the value, the better.

Mooney viscosity 1 at 130 ° C. according to JIS K 6300-1974
The value (L1 + 4) after 4 minutes of rotor rotation after minute preheating was determined. The smaller the value, the better the workability.

The heat generation durability was evaluated according to JIS standard (D-4230: Durability Drum Test), and the running distance at that time was obtained and displayed as an index. The larger the value, the better.

The carbon black characteristic N ₂ SA value is in accordance with ASTM D 3037 and the DBP
Values were measured according to ASTM D3493.

(Examples 1 to 9), (Comparative Examples 1 to 10) Table 1 shows the basic composition of the rubber used in Examples and Comparative Examples. The carbon black, silica, and silane coupling agent were variable, and the amounts thereof are shown in Tables 2 to 4 together with the evaluation results. In addition, Comparative Examples 2 and 3 are those in which the total amount of silica and carbon black is out of the range specified in the present invention. In Comparative Examples 4 to 5, the compounding ratio of silica is outside the range specified in the present invention. Further, in Comparative Example 6, silica is compounded but no silane coupling agent is compounded, and in Comparative Example 7, the compounding ratio of the silane coupling agent is out of the range specified by the present invention. Further, in Comparative Examples 8 to 10, the characteristic value of carbon black is out of the range of the present invention.

From the above results, it is clear that only the examples according to the present invention have improved both low heat buildup and fracture resistance after aging, and further, those containing a dehydrated castor oil fatty acid at the same time. It can be seen that workability has also been significantly improved. Further, by using the rubber composition of the same table as the belt coating rubber, various tires (size ORR 1800R2
5) was prototyped and the heat resistance was evaluated by a drum test. The results are shown in Tables 2 to 4, but it is clear that the durability of the tire according to the present invention is extremely good.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

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Claims (3)

[Claims] 1. A total amount of silica and carbon black is 30 to 70 parts by weight based on 100 parts by weight of a rubber component mainly composed of natural rubber or polyisoprene rubber, and silica is 10 to 50 parts by weight of the total amount. %, And further, a silane coupling agent is blended with 10 to 30% by weight of silica, and the carbon black has a specific surface area (N ₂ SA value) measured by a nitrogen adsorption method of 80 to 160 m.
² / g and the oil absorption of dibutyl phthalate (DB
Rubber composition for tire belt coating, characterized in that P value) is 70 to 100 ml / 100 g 2. The total amount of silica and carbon black is 30 to 70 parts by weight with respect to 100 parts by weight of a rubber component mainly composed of natural rubber or polyisoprene rubber, and silica is 10 to 50 parts by weight of the total amount. %, And the silane coupling agent in the range of 5 to 30% by weight of silica,
And an organic unsaturation containing two or more carbon-carbon double bonds in the molecule containing 10% by weight or more of a conjugated dienoic acid containing at least one pair of two carbon-carbon double bonds in a conjugated relationship in the molecule A rubber composition for coating a tire belt, characterized by containing 0.5 to 10 parts by weight of a fatty acid. 3. The belt coating rubber has a fracture index of 40.
A large pneumatic radial tire for construction, characterized in that it has a resilience of 0% or more and a resilience at 25 ° C of 63% or more.