JPH0718124A - Rubber composition for tire - Google Patents

Abstract

PURPOSE:To obtain a rubber composition for tire composed of a rubber raw material containing a specific diene polymer, an unsaturated fatty acid containing a specific conjugated diene fatty acid, carbon black and a softening agent and having excellent workabillty without deteriorating the breakage characteristics. CONSTITUTION:This composition contains (A) 100 pts.wt. of a rubber raw material containing 5-100 pts.wt. of a diene polymer having a weight-average molecular weight of >=80mu10<4> and consisting of at least one of conjugated diene polymer and conjugated diene-vinylaromatic hydrocarbon copolymer, (B) 0.1-20 pts.wt. of an unsaturated fatty acid containing >=10wt.% (preferably >=25wt.%) of a conjugated diene fatty acid having at least one set of conjugated double bonds in the molecule, (C) preferably 25-80 pts.wt. of carbon black and (D) <=10 pts.wt. of a softening agent.

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 tires, and more specifically, it improves workability without impairing fracture characteristics and maintains a high balance between physical properties such as low loss property and workability. The present invention relates to a rubber composition for tires.

[0002]

2. Description of the Related Art In recent years, automobiles are required to have low fuel consumption and safety, so that a rubber composition used for a tread portion of a tire has low rolling friction resistance (loss property) and physical properties such as breaking properties. There is a demand for excellent rubber in.

Therefore, natural rubber, polyisoprene rubber, polybutadiene rubber or the like, which is known as a rubber material having a small loss, is used. It is also known to increase the molecular weight in order to significantly improve low loss.
This polymer becomes a polymer having very excellent physical properties,
It is used not only for low loss properties but also for physical properties excellent in fracture properties, especially at high temperatures, and has low rolling friction resistance, and thus is used in rubber compositions of fuel-efficient tires.

Further, in order to improve the physical properties such as breaking properties, the styrene-butadiene copolymer in the rubber composition is blended with polymers having different bound styrene contents or vinyl bond contents in the butadiene portion. (Japanese Patent Application Laid-Open No. 57-70137, etc.) and selection of the type and amount of compounding agent, such as a vulcanization accelerating aid, to be compounded with the rubber raw material (Japanese Patent Application Laid-Open No. 4-189850). There is.

[0005]

However, the improvement of the physical properties such as the breaking properties by the compounding agent is not sufficient in the desired physical properties such as low loss property. When the polymer has a high molecular weight in order to improve the low loss property, the viscosity of the rubber composition becomes very high, so that the dispersibility of the carbon black decreases, and there is a problem that buggy occurs during kneading. However, the workability is impaired, and at the same time, the breaking characteristics are significantly reduced. As a means for solving this, conventionally,
For the purpose of reducing the viscosity of the rubber composition, improving the dispersibility of carbon black and improving the workability, it is practiced to use a softening agent such as aroma oil and spindle oil, but the oil in the rubber composition is Since the amount was increased, the low loss property and the breaking property were impaired, and the workability and physical properties could not be balanced.

Accordingly, the present invention provides a rubber composition for a tire, which can improve workability without impairing the fracture property and can maintain a high balance between physical properties such as low loss property and workability. With the goal.

[0007]

The tire rubber composition according to claim 1 has a weight average molecular weight of 80 × 10 ⁴ or more,
100 parts by weight of a rubber raw material containing 5 to 100 parts by weight of a diene polymer composed of at least one of a conjugated diene polymer and a conjugated diene-vinyl aromatic hydrocarbon copolymer,
0.1 to 20 parts by weight of an unsaturated fatty acid containing 10% by weight or more of a conjugated diene fatty acid having at least one set of conjugated double bonds in the molecule with respect to 100 parts by weight of the rubber raw material, carbon black, and the rubber. It is characterized in that it contains 10 parts by weight or less of a softening agent with respect to 100 parts by weight of the raw material.

The rubber composition for a tire according to claim 2 is
In Claim 1, the unsaturated fatty acid is an unsaturated fatty acid containing 25% by weight or more of the conjugated diene fatty acid.

A rubber composition for a tire according to claim 3 is
In Claim 1 or 2, the carbon black is 25 to 80 parts by weight with respect to 100 parts by weight of the rubber raw material.

The present inventors have paid attention to the influence of the rubber raw material and the compounding agent, especially the reactive softening agent, on the physical properties of the rubber composition,
As a result of earnest studies, it was found that the above problems can be solved by using a high molecular weight polymer as a rubber raw material and incorporating the unsaturated fatty acid as a reactive softening agent. That is, since the unsaturated fatty acid first acts as a softening agent on the rubber raw material, it contributes to the improvement of workability like other softening agents, and when the obtained rubber composition is vulcanized. In addition, since the conjugated diene fatty acid contained in the unsaturated fatty acid has reactivity with the rubber raw material, the obtained vulcanized product maintains the desired physical properties. Therefore, the obtained rubber composition has improved workability without impairing the fracture characteristics, and can maintain a high balance between physical properties such as low loss property and workability, thus completing the present invention. It was

The present invention will be described in detail below. The rubber raw material contained in the rubber composition of the present invention contains 5 to 100 parts by weight of a diene polymer composed of at least one of a conjugated diene polymer and a conjugated diene-vinyl aromatic hydrocarbon copolymer, and other rubber components. 95 to 0 parts by weight are used.

Examples of the monomer serving as the conjugated diene unit of the polymer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-
Pentadiene, octadiene, etc. are mentioned, especially 1,3
-Butadiene is preferred. In addition, examples of the monomer serving as the vinyl aromatic hydrocarbon unit of the polymer include styrene, α-methylstyrene, p-methylstyrene, o
-Methylstyrene, p-butylstyrene, vinylnaphthalene, etc. are mentioned, and styrene is particularly preferable. The above monomers may be used alone or in combination of two or more.

As the rubber component, natural rubber, synthetic rubber such as polybutadiene, polyisoprene, butadiene-styrene copolymer and the like can be used alone or in admixture of two or more.

The diene polymer includes those having a weight average molecular weight of 80 × 10 ⁴ or more, preferably 100 × 10 ⁴ or more. When the weight average molecular weight is less than 80 × 10 ⁴ , the effects of breaking property and low loss property cannot be sufficiently obtained.

The unsaturated fatty acid used in the present invention is an unsaturated fatty acid containing 10% by weight or more, preferably 25% by weight or more, of a conjugated diene fatty acid having at least one set of conjugated double bonds in the molecule. This conjugated diene fatty acid is 1
If it is less than 0% by weight, the effect on the balance between physical properties and workability of the obtained rubber composition is not sufficient. Further, the conjugated diene fatty acid preferably has one pair of carbon-carbon double bonds in a conjugated relationship, but may have two or more pairs.

The unsaturated fatty acid is not particularly limited, but preferably has 10 to 22 carbon atoms, more preferably 12 carbon atoms.
It is preferable that the unsaturated fatty acid having 20 to 20 long chain hydrocarbon groups is contained in an amount of 75% by weight or more, and a carbon number and a content rate outside this range are not preferable from the viewpoint of the fracture characteristics of the obtained rubber composition. Further, the degree of unsaturation of all unsaturated fatty acids is preferably 130 or more in iodine value, and when the iodine value is 130 or less, the effect on the elastic modulus of rubber is not sufficient.

The unsaturated fatty acid is in the range of 0.1 to 20 parts by weight, preferably 0.3 to 15 parts by weight, more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the rubber raw material. Contained in. If it is less than 0.1 part by weight, the effect on workability cannot be sufficiently obtained, and if it exceeds 20 parts by weight, breaking property and low loss property cannot be maintained.

As the conjugated diene fatty acid, 2,4-
Pentadienoic acid, 2,4-hexadienoic acid, 2,4-decadienoic acid, 2,4-dodecadienoic acid, 9,11-octadecadienoic acid, 9,11,13,15-octadecatetraenoic acid, 9,11 , 13-octadecatrienoic acid and the like, and these may be used alone or in combination of two or more. Preferred examples of unsaturated fatty acids containing conjugated diene fatty acids include dehydrated castor oil fatty acids obtained by dehydrating castor oil, and the content of conjugated diene fatty acids can be changed by a dehydration method.
It is possible to obtain a product having a content of 60 parts by weight and 60 parts by weight.
Non-conjugated unsaturated fatty acids that can be used with the conjugated diene fatty acids include linoleic acid, linolenic acid, and the like.

Examples of the carbon black contained in the rubber composition of the present invention include HAF, ISAF and SAF, but the carbon black is not particularly limited. The amount of these carbon blacks added is not particularly limited, but the rubber raw material 1
It is preferably 25 to 80 parts by weight, more preferably 30 to 70 parts by weight, and most preferably 35 to 100 parts by weight.
It is contained in 60 parts by weight. If the content of carbon black is less than 25 parts by weight, the breaking property is 80%.
If it exceeds the weight part, both are not preferable from the viewpoint of low loss.

The softening agent used in the present invention is the rubber raw material 1
It is contained in an amount of 10 parts by weight or less, preferably 6 parts by weight or less with respect to 00 parts by weight, and when it exceeds 10 parts by weight, sufficient vulcanized physical properties cannot be obtained. Softeners used herein include process oils such as paraffin oil,
Examples thereof include naphthene oil and aroma oil.

In the present invention, in addition to these, vulcanizing agents such as sulfur which are usually used in the rubber industry, vulcanization accelerators such as thiazoles, fillers such as silica, zinc oxide, stearic acid, antioxidants. Compounding agents such as an ozone deterioration preventing agent and a foaming agent can be appropriately mixed.

The rubber composition of the present invention is obtained by kneading using a kneading machine such as a roll or an internal mixer. After molding, the rubber composition is vulcanized to obtain a tire tread, an undertread, a carcass and a side. It is used for tires such as walls and beads, and is particularly preferably used as rubber for tire treads.

[0023]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.

In the examples, parts and% mean parts by weight and% by weight unless otherwise specified.

Various measurements were made by the following methods. Mooney viscosity was used as an index of workability of the formulation. The Mooney viscosity (ML _{1+ 4} ) was measured according to JIS K6300 by using an L rotor and preheating at 130 ° C. for 1 minute to 4
The measurement was made after a lapse of minutes, and the result was expressed as an index with the value of Comparative Example 1 as 100. The smaller the index, the better the workability.

The fracture characteristics were evaluated by measuring elongation and tensile modulus (modulus) at 25 ° C. according to JIS K6301, and the results are shown in Comparative Example 1.
The value is shown as an index with the value of 100 as 100. The larger the index, the higher the value.

The low loss property was evaluated by measuring tan δ at 0 ° C. as rolling friction resistance and tan δ at 50 ° C. as wet skid resistance. The results are shown as an index with the value of Comparative Example 1 being 100, and the larger the index, the better the low loss property, that is, the smaller the rolling friction resistance and the wet skid resistance, which is preferable.

As the diene polymer, a polymer A having a weight average molecular weight of 120 × 10 ⁴ (styrene-butadiene copolymer, styrene content: 25%, vinyl amount: 35%) and a polymer B having a weight average molecular weight of 50 × 10 ⁴ are used. (Styrene-
Butadiene copolymer, styrene content; 25%, vinyl content; 35%) were used.

[Examples 1 to 4 and Comparative Examples 1 to 8] The compounds shown in Table 1 were kneaded in a Banbury mixer to obtain various rubber compositions, and workability, that is, Mooney viscosity was evaluated. After the evaluation, vulcanization was carried out under the condition of 145 ° C. for 30 minutes, and the vulcanizates obtained were evaluated for fracture properties, that is, elongation and tensile modulus (modulus) at 25 ° C., and low loss properties, that is, rolling friction resistance and wet skid resistance. did.

[0030]

[Table 1]

As shown in Table 1, with the rubber composition of the present invention, it was shown that workability was improved without impairing fracture characteristics, and a high balance between workability and low loss property was maintained. (Examples 1 to 4). Compared with the case where no softening agent is added (Comparative Example 1), when the softening agent having a commonly used composition is added (Comparative Example 2), the unsaturated fatty acid contained in the rubber composition is carbon- When one carbon double bond is contained (Comparative Example 3) and when a non-conjugated diene fatty acid is contained (Comparative Example 4), the workability is improved, but the breaking properties, particularly the modulus and the low loss property are maintained. In addition, when a diene-based polymer having a molecular weight of less than 80 × 10 ⁴ was used (Comparative Example 8), the breaking properties were considerably impaired and little effect was obtained even with low loss. Was done.

The effect of improving the workability and maintaining the breaking property is recognized when the unsaturated fatty acid containing the specific conjugated diene fatty acid is blended in a predetermined content (Examples 1 to 4). It was shown that when the content was outside the range (Comparative Examples 5 and 6), workability was not improved, or the fracture characteristics, particularly low loss property was significantly impaired.

Further, the above effect is similarly observed when the unsaturated fatty acid containing the conjugated diene fatty acid and the softening agent (aroma oil) are mixed in a predetermined ratio (Example 4), and the softening agent is added. When compounded in an amount outside the range (Comparative Example 7)
On the other hand, although the workability was improved, the modulus and rolling friction resistance were significantly decreased due to the increase in the amount of oil, indicating that the physical properties could not be maintained.

[0034]

EFFECTS OF THE INVENTION Since the present invention has the above-mentioned constitution, it is excellent in that workability can be improved without impairing the fracture characteristics, and a high balance between characteristics such as low loss property and workability can be maintained. Have an effect.

Claims (3)

[Claims] 1. A diene polymer ⁵ having a weight average molecular weight of 80 × 10 ⁴ or more and comprising at least one of a conjugated diene polymer and a conjugated diene-vinyl aromatic hydrocarbon copolymer.
100 parts by weight of a rubber raw material containing 100 to 100 parts by weight, and unsaturated fatty acid containing 10% by weight or more of a conjugated diene fatty acid having at least one set of conjugated double bonds in the molecule based on 100 parts by weight of the rubber raw material 0 1 to 20 parts by weight, carbon black, and 10 parts by weight or less of a softening agent with respect to 100 parts by weight of the rubber raw material, a rubber composition for a tire. 2. The rubber composition for a tire according to claim 1, wherein the unsaturated fatty acid is an unsaturated fatty acid containing 25% by weight or more of the conjugated diene fatty acid. 3. The rubber composition for a tire according to claim 1, wherein the carbon black is 25 to 80 parts by weight with respect to 100 parts by weight of the rubber raw material.