KR100479159B1 - Rubber composition of tire for side wall - Google Patents

Abstract

The present invention relates to a rubber composition for the side wall of a pneumatic tire, comprising 70 to 100 parts by weight of natural rubber, butadiene rubber, styrene butadiene rubber or a mixture thereof and a rubber component of 30 parts by weight of ethylene-propylene-diene terpolymer The rubber composition consisting of 1 to 4 parts by weight of an anti-aging agent composed of 10% by weight of mono-cumylated diphenylamine and 90% by weight of di-cumylated diphenylamine based on 100 parts by weight of tensile strength, phosphorus It has excellent physical properties such as heat strength and fatigue resistance and ozone resistance, and does not cause discoloration even when ozone aging, so that no appearance contamination occurs.

Description

Rubber composition for sidewalls of pneumatic tires {Rubber composition of tire for side wall}

The present invention relates to a rubber composition for sidewalls of pneumatic tires, and more particularly, by adding a diphenylamine anti-aging agent to a rubber component composed of natural rubber and ethylene-propylene-diene terpolymer, The present invention relates to a rubber composition capable of improving tear strength, fatigue resistance and dynamic ozone resistance, and improving appearance contamination by surface discoloration of a tire sidewall.

The sidewall of the tire is a place where weather resistance, ozone resistance, and heat resistance are required. As a commonly used material, a rubber composition in which a large amount of an amine antioxidant or wax is added to a diene rubber component is widely used.

However, such an amine antioxidant has a disadvantage of discoloring the rubber due to precipitation on the surface of the rubber over time, in particular from the black cover strip rubber covering the white sidewall and the white sidewall of the sidewall to the amine antioxidant Discoloration due to this is noticeable.

Therefore, there is a method of adding a very small amount of an antioxidant to the rubber component to prevent such discoloration of the appearance, or adding a large amount of wax instead of such an antioxidant. Thus, in the case of the rubber composition using a large amount of wax, it was possible to prevent the appearance deterioration caused by the amine antioxidant to some extent while maintaining the ozone resistance in the static state.

However, it was not possible to solve the problem that the other properties required for the sidewall rubber, such as heat resistance, dynamic ozone resistance and weather resistance, were deteriorated, and the wax turned white as the wax precipitated on the black cover strip surface, causing another unexpected appearance deterioration. Resulted in

 Ultimately, amine antioxidants or waxes should not be used to solve these problems, but if the amine antioxidants or waxes are not mixed, the weather resistance, ozone resistance, and heat resistance, which are the main required properties of the sidewall rubber, are greatly reduced. Problems arise.

In order to satisfy these required properties, rubber compositions composed of ethylene-propylene-diene terpolymers, halogenated butyl rubbers and diene-based rubbers are used for the white sidewalls and the black cover strips, and the use of natural rubber is reduced and ethylene-propylene- The amount of diene terpolymer or halogenated butyl rubber should be greatly increased. However, in this case, there is a problem that the durability, such as fatigue resistance, tensile strength, tear strength before aging is significantly lowered.

Therefore, in order to satisfy the required physical properties of the tire sidewall, the amount of natural rubber is increased, and the amount of ethylene-propylene-diene terpolymer or halogenated butyl rubber is reduced to increase fatigue resistance, tensile strength and tear strength before aging, There is a need to improve ozone resistance by using an anti-aging agent that does not cause external contamination.

The present inventors are trying to find a rubber composition for the sidewall of the pneumatic tire with excellent ozone resistance without causing contamination on the appearance, while increasing the content of natural rubber without using a halogenated butyl rubber The tensile strength, tear strength, static and dynamic before and after aging of diphenylamine anti-aging agents composed of mono-cutylated diphenylamine and di-cumylated diphenylamine were added to the sidewall rubber composition. The present invention has been completed by recognizing that the ozone resistance is excellent and the appearance contamination due to the surface discoloration of the tire sidewall generated when the amine antioxidant is combined is improved.

Accordingly, an object of the present invention is to provide a rubber composition for sidewall parts of pneumatic tires which is excellent in tensile strength, tear strength, static and dynamic ozone resistance before and after aging, and does not cause appearance contamination due to surface discoloration of the tire sidewall parts. There is.

Rubber composition for the side wall of the pneumatic tire of the present invention for achieving the above object is 70 to 100 parts by weight of natural rubber, butadiene rubber, styrene butadiene rubber or mixtures thereof, 30 parts by weight of ethylene-propylene-diene terpolymer It is characterized in that the rubber composition consisting of 1 to 4 parts by weight of an antioxidant consisting of 10% of mono-cumylated diphenylamine and 90% of di-cumylated diphenylamine based on 100 parts by weight of the rubber component.

The present invention will be described in more detail as follows.

The present invention relates to a rubber composition for a sidewall of a pneumatic tire in which a diamine-based antioxidant is added to a rubber selected from natural rubber, butadiene rubber, styrene butadiene rubber and mixtures thereof and an ethylene-propylene-diene terpolymer.

The anti-aging agent used in the present invention is composed of 10% by weight of mono-cumylated diphenylamine of Formula 1 and 90% by weight of di-cumylated diphenylamine of Formula 2.

These antioxidants are added in an amount of 1 to 4 parts by weight with respect to 100 parts by weight of rubber. If the content is less than 1 part by weight, the anti-aging effect is significantly reduced, so that the aging of the rubber is not sufficiently suppressed, and more than 4 parts by weight. In this case, the increase in the anti-aging effect is insignificant and there is a disadvantage in economic efficiency.

The rubber composition used in the present invention is a natural rubber, butadiene rubber, styrene butadiene rubber or a mixture of 70 to 100 parts by weight and ethylene-propylene-diene terpolymers are added to within 30 parts by weight.

If 100 parts by weight of other diene rubber is used without using the ethylene-propylene-diene terpolymer, the tensile strength, tear strength, and fatigue resistance before aging are higher than those of adding the ethylene-propylene-diene terpolymer rubber. It is excellent, but physical properties and ozone resistance after aging is disadvantageous, but when the anti-aging agent is added, it exhibits sufficient ozone resistance at the level required for sidewall rubber.

However, ethylene-propylene-diene rubber is dispersed and present as particles or regions on other diene rubbers, and when the crack tip of ozone cracks generated in other diene rubbers meets the ethylene-propylene-diene rubber region, growth is delayed and ozone resistance It is preferable to mix | blend the above rubber | gum, since it can improve further.

On the other hand, when the content of the ethylene-propylene-diene rubber in the rubber containing the anti-aging agent exceeds 30 parts by weight, it is preferable to use within 30 parts by weight because the improvement in ozone resistance is insufficient.

In addition, of course, the rubber composition of this invention can use the additive used for the rubber composition for normal pneumatic sidewall parts.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1

As shown in Table 1 below, a rubber composition was prepared by blending the rubber sheet composition before vulcanization according to a conventional method.

Comparative Examples 1 to 4

Comparative Example 1 is an example in which the composition of the present invention and the rubber deviates, and the content of natural rubber is different and shows an example using a conventional halogenated butyl rubber, and Comparative Examples 2 and 3 do not use an anti-aging agent in the composition of the present invention. Comparative Example 4 is the same method as in Example 1 except for the use of conventional N-phenyl-N'-1,3-dimethylbutyl-P-phenylenediamine as an antioxidant in the composition of the present invention Rubber was prepared.

Furtherance Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Natural rubber 80 50 80 100 80 EPDM ⁽¹⁾ 20 30 20 - 20 Halogenated Butyl Rubber - 20 - - - White filler 45 45 45 45 45 Zinc oxide 4 4 4 4 4 Stearic acid 2 2 2 2 2 Wax 2.5 2.5 2.5 2.5 2.5 brimstone 1.3 1.3 1.3 1.3 1.3 Accelerators ⁽²⁾ 1.0 1.0 1.0 1.0 1.0 Antioxidant 1 ⁽³⁾ - - - - 3 Antioxidant 2 ⁽⁴⁾ 3 - - - - (1) Ethylene-propylene-diene terpolymer (2) Nt-butyl-2-benzodiazyl sulfenamide (3) N-phenyl-N'-1,3-dimethylbutyl-P-phenylene Diamine (4) Mixed antioxidant of 10% mono cumylated diphenylamine and 90% dicumylated diphenylamine

In addition, the rubber specimens prepared in Examples and Comparative Examples were vulcanized at 170 ° C. for 20 minutes and then physical properties were measured as follows. The results are shown in Table 2 below.

(Measurement method)

(1) tensile strength

It refers to the amount of force measured at break by tensioning vulcanized rubber specimens.

(2) tear strength

It refers to the magnitude of the force measured at break when the vulcanized rubber specimen (JIS test tear test type B) is tensioned.

(3) static strain fatigue

After the vulcanized rubber specimen is stretched to 120% of its original length at room temperature, the cycle is repeated until the specimen breaks by repeatedly removing the tensile force and recovering the original length.

(4) Crack resistance

Crack resistance was measured by applying a 2mm crack tip to the center of the vulcanized rubber specimen in accordance with JIS K6301 test method, and repeatedly performing a bending deformation test to measure the rate of crack growth in the specimen.

(5) ozone resistance

Static ozone resistance was measured by fixing the vulcanized rubber specimen to 120% of its original length, and then leaving it on an ozone aging tester that maintains a concentration of 50 ppm ozone at 40 ° C to evaluate the elapsed time until cracking and color change of the rubber surface. will be.

The dynamic ozone resistance was measured in the same rubber specimen under repeated fatigue test under the same conditions as the static strain fatigue in the ozone aging tester.

Properties Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile Strength (Kg / cm ² ) Before aging 49 40 50 54 51 After aging ⁽¹⁾ 30 31 23 22 32 Tear strength (Kg / cm ² ) Before aging 35 31 35 36 34 After aging 28 28 24 20 28 Positive strain fatigue (Kcycle) Before aging 69 64 67 69 67 After aging 42 40 35 33 43 Crack Growth Rate (㎛.cycle) Before aging 0.08 0.14 0.10 0.08 0.07 After aging 0.15 0.15 0.19 0.20 0.14 Ozone Resistance (day) ⁽²⁾ Dynamic (discoloration) 30 or more (NC) 30 or more (C) 5 (NC) 5 (NC) 30 or more (C) Static (discoloration) 100 or more (NC) 100 or more (NC) 10 (NC) 8 (NC) 100 or more (NC) (1) Physical properties after aging indicate physical properties after aging of the rubber specimens prepared in Examples and Comparative Examples for 24 hours in an oven at 100 ° C. (2) In the result of ozone resistance, C is the color change Indicates brown, and NC indicates no change in color.

From the results of Table 2, it can be seen that in the case of Comparative Example 1 using the reduced content of natural rubber and halogenated butyl rubber, tensile strength, tear strength and fatigue resistance before aging are greatly reduced. In addition, in Comparative Examples 2 and 3, in which the amount of natural rubber is increased and no anti-aging agent is used, tensile strength, tear strength, and fatigue resistance before aging are improved, but physical properties after aging are lowered, and aging increases as the amount of natural rubber is increased. Later physical properties are further lowered. On the other hand, in the case of Comparative Example 4 using an increase in the amount of natural rubber and using a conventional anti-aging agent, both before and after aging properties are improved, but the rubber surface is discolored to brown in dynamic ozone resistance.

However, in Example 1 using the anti-aging agent of the present invention it can be seen that the tensile strength, tear strength and fatigue resistance before and after aging is excellent, and the discoloration of the rubber surface does not appear at all in static and dynamic ozone resistance.

As described in detail above, as a result of using a diphenylamine compound as an anti-aging agent in the rubber composition for sidewalls of a pneumatic tire according to the present invention, physical properties such as tensile strength, tear strength and fatigue resistance before and after aging It has excellent ozone resistance and no discoloration during ozone aging, so no external contamination occurs.

Claims (1)

Mono-cumilated to the rubber component consisting of 70 to 100 parts by weight of the rubber selected from natural rubber, butadiene rubber, styrene butadiene rubber and mixtures thereof and within 30 parts by weight of ethylene-propylene-diene terpolymer An pneumatic tire comprising 1 to 4 parts by weight of an anti-aging agent comprising 10% by weight of diphenylamine and 90% by weight of di-cumylated diphenylamine represented by the formula (2) based on 100 parts by weight of the rubber component. Rubber composition for sidewall parts. Formula 1 Formula 2