JPH08104779A - Rubber composition for studless tire - Google Patents

Abstract

PURPOSE: To improve both of the braking characteristics on the ice and the abrasion resistance of a rubber composition for a studless tire. CONSTITUTION: This composition is obtained by mixing 100 pts.wt. rubber oil- extended so as to provide a Mooney viscosity of 27 to 43 and containing at least 50% styrene-butadiene rubber which is made by solution polymerization and has a weight-average molecular weight of at least 250,000 and a glass transition temperature of -70 deg.C or lower with 3-40 pts.wt. insoluble gelatin having a mean particle diameter of 5-300μm.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rubber composition used for a tread of a studless tire.

[0002]

2. Description of the Related Art Conventionally, so-called spike tires in which a large number of hard alloy studs are planted in a tread have been generally used for vehicles often traveling on ice and snow roads. However, the studs of spiked tires dig up the road surface, and the resulting dust and damage to the road surface increase with the increase of vehicles and become a social problem.Therefore, there is a demand for tires that can run safely on ice and snow roads without studs. A studless tire using a special rubber composition for the tread is provided.

In order to improve friction performance on ice and to improve braking performance on ice and snow roads, a method is used in which foamed rubber is used for the tread to form fine irregularities on the surface to increase friction (for example, Japanese Patent Laid-Open No. 63-63). No. 89547), a method of forming a tread from a rubber composition containing a granular material such as alumina or walnut shells, and protruding these granular materials on the surface (for example, JP-A-60-13956), gelatin. A method of forming a tread with a rubber composition containing a granular material of a hydrophilic substance (eg, JP-A-2-228342) has been proposed. However, when foamed rubber is used, there is a problem in wear resistance, and when a rubber composition containing a granular material such as alumina is used, these particles have a large hardness difference with the rubber, so they fall off the tread surface. When used with a rubber composition containing gelatin, gelatin does not adhere well to rubber and is easy to separate, and wear resistance and improved braking performance on ice are improved. There was a problem that the action of was small. As described above, in the current state of the art, a rubber composition for a studless tire that satisfies both braking performance on a snowy road and wear resistance has not been developed.

[0004]

It is an object of the invention to provide a rubber composition for a studless tire having improved braking performance on an icy road surface without impairing general properties required for the tire such as abrasion resistance. To do.

[0005]

A blend rubber of natural rubber and butadiene rubber or styrene-butadiene rubber is widely used in a rubber composition for a tread. Styrene-butadiene rubber that is commonly used is obtained by polymerizing styrene and butadiene using an organolithium compound as a polymerization initiator in a non-polar solvent such as cyclohexane, and coupling such as tin chloride when the polymerization reaction is almost completed. Solution-polymerized styrene-butadiene rubber produced by increasing the molecular weight with an agent and emulsion-polymerized styrene-butadiene rubber obtained by polymerizing styrene and butadiene by using an organic peroxide as a polymerization initiator in water containing a surfactant. Compared to the latter, the former is easier to control the bonding mode of the butadiene moiety, that is, the ratio of cis, trans, and vinyl bonds, has a molecular weight distribution that is sharp and easy to adjust, and can increase the molecular weight. Therefore, there is an advantage that desired characteristics can be easily obtained.
The present invention is made by taking advantage of the characteristics of solution-polymerized styrene-butadiene rubber and the slip resistance on the icing surface of gelatin.

That is, a styrene-butadiene rubber having a weight average molecular weight of 250,000 or more and a glass transition temperature of -70 ° C. or less obtained by solution polymerization has a Mooney viscosity of 27-.
To styrene-butadiene rubber oil-extended so as to be 43, 100 parts by weight of a rubber component containing at least 50% by weight of insoluble gelatin having an average particle size of 5 to 300 μm.
It is a rubber composition for studless tires, containing 40 parts by weight, preferably 5 to 25 parts by weight.

The insoluble gelatin used in the present invention is obtained by contacting and insolubilizing ordinary gelatin with a compound having an aldehyde group such as formalin and glutaraldehyde, a compound having an epoxy group such as epoxide, or alum as a crosslinking agent. Is. In the present invention, the insolubilization degree is 1
0% or more, preferably 80% or more is used.

[0008]

[Function] A blended rubber of natural rubber and butadiene rubber has excellent low-temperature characteristics and is suitable as a rubber component of a rubber composition for a studless tire, but has poor wear resistance. Therefore, a solution-polymerized styrene-butadiene rubber is used in the present invention. To be done.
The solution-polymerized oil-extended styrene-butadiene rubber (hereinafter abbreviated as soln-SBR) used in the present invention has a rubber component having a weight average molecular weight (hereinafter abbreviated as MW) of 250,000 or more and a glass transition temperature (hereinafter abbreviated as Tg). Is below -70 ° C,
The Mooney viscosity in the oil-extended state is preferably 27 to 43. If the MW is less than 250,000, the wear resistance is poor and the Tg is -7.
If the temperature is higher than 0 ° C, the low-temperature property is poor and the performance on ice is not improved. If the Mooney viscosity is less than 27, the polyethylene softens while being stacked and stored in a package packed in polyethylene film,
So-called cold flow occurs and the polyethylene film packaging is liable to break and flow out, so that the storage stability is poor, and when it is 43 or more, the dispersion of the filler such as carbon black is deteriorated in the mixing step, and the abrasion resistance and heat generation characteristics are deteriorated.

In the present invention, natural rubber and other diene rubbers are used within a range not exceeding 50% of the above soln-SBR for the purpose of improving workability or rolling resistance unless the object of the invention is impaired. Can be replaced. In addition, reinforcing agents such as carbon black and silica and commonly used compounding agents such as zinc white, stearic acid, sulfur, vulcanization accelerators and antioxidants are compounded in usual amounts. Reinforcing agents such as carbon black and silica are mixed in an amount of 30 to 100 parts with respect to 100 parts by weight of the rubber component (hereinafter simply referred to as "part"). If it is less than 30 parts, the abrasion resistance is inferior, and if it is more than 100 parts, the hardness becomes high and it becomes difficult to deform, so that the area actually contacting the road surface becomes small and the braking performance on ice deteriorates. The amount of insoluble gelatin blended is in the range of 3 to 40 parts, preferably 5 to 25 parts per 100 parts of the rubber component. If it is less than 3 parts, the blending amount is insufficient and the braking property on ice is small, and if it is more than 40 parts, there is no effect of improving the braking property on ice corresponding to the blending amount, and only the cost increases, which is not preferable. By reacting with the cross-linking agent to make it insoluble, the surface becomes hydrophobic, the affinity with rubber increases, the adhesiveness increases, and the dispersion in the rubber improves and the adhesiveness improves. In addition, the effect of improving the adhesiveness of the cross-linking agent prevents it from falling off during use, and it is one of the causes of slipperiness on ice, which absorbs water that forms a thin layer on ice. Since the gelatin is absorbed and the tread comes into direct contact with the ice, the braking property on ice and the wear resistance are improved.

Gelatin having a different degree of insolubility of gelatin is used.
The relationship with the friction coefficient on the ice surface of the rubber composition blended with 5 parts is shown in FIG. The friction coefficient increases as the degree of insolubilization increases, and the rate of increase increases as the degree of insolubilization increases. From the figure, the degree of insolubilization of gelatin is preferably 10% or more, and further 8
It is shown that 0% or more is a more preferable range. If it is less than 10%, it is not insolubilized, but there is not much difference from the friction coefficient, and the effect of improving the braking performance on ice by insolubilization is small.

[0011]

Example 1 The low temperature characteristics, the braking property on ice and the abrasion resistance of the rubber composition for a studless tire obtained by the composition shown in Table 1 were measured and shown in Table 1. The SBR-1 in the table is styrene content 10%, MW 310,000, Tg-86 ° C soln-SB
R aroma oil 50 parts Oil-extended rubber with Mooney viscosity 30
And SBR-2 has a styrene content of 10% and a MW of 24
10,000, Tg-86 ℃ soln-SBR aroma oil 3
7.5 parts oil-extended rubber with Mooney viscosity 31 and SBR-
3 has a styrene content of 15%, a MW of 300,000 and a Tg of -68 ° C.
It has a Mooney viscosity of 55 for soln-SBR 20 parts aroma oil oil extended rubber. The rubber component of the oil-extended rubber was 100 and the amount of oil was the sum of the oil of the oil-extended rubber and the additional naphthenic oil. Insoluble gelatin has an insolubility of 9
5, having an average particle diameter of 100 μm.

The characteristics were measured as follows. The low temperature characteristics showed a hardness of -5 ° C according to JIS K6301. On-ice braking is Rubber Chemistry and Technology
38, 840 (1965)
The skid resistance on the ice surface at a temperature of −10 ° C. was measured and indicated by an index with the compounding number 5 as 100 (the larger the value, the better). The abrasion resistance was measured according to ASTM D2228, and was shown as an index with the compounding number 5 as 100 (the larger the value, the better).

[0013]

[Table 1]

Formulation No. 5 is a blend rubber of butadiene rubber and natural rubber as a rubber component and does not use gelatin. Formulation No. 6 is an example using soln-SBR having a high Tg and is inferior in low temperature characteristics and on-ice braking property. Formulation number 7 is an example using soln-SBR having a small MW and is inferior in wear resistance.

[0015]

[Example 2] Except for insoluble gelatin, the gelatin shown in Table 2 was blended under the same conditions as in Formulation No. 1 of Example 1 to measure the braking property on ice and abrasion resistance, and the result was subjected to crosslinking treatment. The index is shown in Table 2 with the compounding number I in which gelatin which is not added is compounded as 100. It is understood from Formulation Nos. A to E that the smaller the particle size is, the better the braking performance on ice is, and from the Formulation Numbers B, G and H, the larger the blending amount is, the better the braking performance on ice is, but the wear resistance is decreased. To be understood.

[0016]

[Table 2]

[0017]

The rubber composition for a studless tire has a weight average molecular weight of 250,000 or more and a glass transition temperature of -70 ° C.
A rubber composition is prepared by mixing 3 to 40 parts by weight of insoluble gelatin having an average particle diameter of 5 to 300 μm with 100 parts by weight of a rubber component containing at least 50% or more of oil-extended styrene-butadiene rubber obtained by solution polymerization. This improves braking performance on ice and wear resistance.

[0018]

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the degree of insolubilization of insoluble gelatin and the friction coefficient on ice of a rubber composition containing it.

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[Procedure amendment]

[Submission date] April 7, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

The rubber composition for a studless tire has a weight average molecular weight of 250,000 or more and a glass transition temperature of -70 °.
3-40 parts of insoluble gelatin having an average particle size of 5-300 μm is added to 100 parts by weight of a rubber component containing at least 50% or more of a solution-polymerized styrene-butadiene rubber of C or less.
By being formed of a rubber composition blended in parts by weight, the braking property on ice is improved without lowering the wear resistance.

Claims (2)

[Claims] 1. A solution-polymerized polymer having a weight average molecular weight of 250,000 or more and containing at least 50% of an oil-extended styrene-butadiene rubber, and having an average particle diameter of 5 to 300 μm with respect to 100 parts by weight of a rubber component. Insoluble gelatin 3
A rubber composition for a studless tire, which is blended in an amount of -40 parts by weight. 2. The oil-extended styrene-butadiene rubber according to claim 1, which is a rubber obtained by oil-extending a styrene-butadiene rubber having a glass transition temperature of −70 ° C. or less so that the Mooney viscosity becomes 27 to 43. Rubber composition for studless tires.