KR102227563B1 - Rubber compound for tire sidewall - Google Patents

Abstract

The present invention discloses a tire sidewall rubber.
Tire side wall rubber according to the present invention is a tire side wall rubber comprising a novel EPDM rubber mixed with natural rubber or synthetic rubber as a raw material rubber, wherein the EPDM rubber is represented by the following formula (1). In the meantime, it is possible to further improve the ozone resistance performance of the side wall rubber by using a novel EPDM instead of synthetic rubber in the mixture of natural rubber and synthetic rubber in addition to improving the crosslinking performance and ozone resistance of the tire sidewall rubber.

Description

Rubber compound for tire sidewall {Rubber compound for tire sidewall}

The present invention relates to a rubber composition for a tire sidewall, and more particularly, improves the ozone resistance and oxidation resistance of rubber for tire sidewalls, and uses a novel EPDM instead of butadiene rubber in a natural rubber and butadiene rubber mixture composition. It relates to a rubber composition for a tire sidewall capable of improving the covulcanization properties and ozone resistance performance of mixed rubber.

Tire Sidewall Rubber refers to the side of the tire, and when the tire is mounted on a car, it refers to the side where the tire standard size and pattern are visible from the consumer side.

The performance required for such a sidewall is largely three: first, maintaining a circular shape and appearance, second, having strong fatigue resistance due to flexion and expansion and contraction due to vehicle driving, and third, strong ozone resistance due to ozone in the air. .

To reinforce the ozone resistance of tires, chemical protective agents such as anti-aging agents and antioxidants are used, and the appearance of these additives is contaminated. This is the cause of the existing low molecular weight additives in the rubber reacting with ozone. Chemical structure is known to appear because the structure is deformed (Ozonization) and molecular weight is reduced by cutting the main chain, and these compounds are moved to the surface by diffusion in the rubber (called blooming), and such blooming is whitened. It is also said that it appears as a white turbidity phenomenon and a browning phenomenon in which the rubber side part turns brown.

In addition, when the antioxidant added to the rubber reaches its end of life, the aging of the rubber proceeds by ozone in the air and eventually appears as a rubber crack phenomenon. Although efforts were made to improve such performance by applying rubber materials with good properties, there were limitations.

Normally, natural rubber and BR belong to the unsaturated rubber, and have similar properties and are excellent in mutual compatibility. However, when natural rubber and EPDM are mixed and kneaded, EPDM is not well mixed as a saturated rubber with few double bond chains.

Due to this, non-uniform cross-linking occurs, resulting in a decrease in physical properties, so a design to increase the double bond chain content was devised to solve the cross-linking defect and rubber blending, which was cross-linked using diene, the side chain of EPDM. And increased branching performance.

Among rubbers, EPDM is a rubber with good aging resistance, weather resistance, and ozone resistance. EPDM (Ethylene Propylene Diene Monomers) rubber refers to ethylene propylene diene terpolymer rubber. It is used as a function, according to consumer preferences in the Middle East who prefer white, or to emphasize the tire brand name.

However, looking at the reason why EPDM is not widely used as a general tire sidewall material, there are the following problems in the application of rubber blends using EPDM.

When blending EPDM and general rubber, crosslinking failure occurs due to the difference in vulcanization rate when crosslinking reaction by sulfur between unsaturated rubber with double bonds in the molecular main chain and saturated rubber with almost no double bonds, resulting in poor crosslinking and is not similar in rubber properties. Due to poor compatibility, mechanical properties are deteriorated, and as a result, in order to solve poor crosslinking and rubber compounding, there is a limit to decrease in productivity while increasing the process steps, which has been limited in application.

In addition, as previously seen, natural rubber and BR belong to unsaturated rubbers, and have similar properties, so they have excellent blendability.However, when natural rubber and EPDM are mixed and kneaded, EPDM is well mixed into saturated rubbers with few double bond chains. In order to solve the problem of crosslinking defects and rubber mixing, it was devised to increase the content of double bond chains, and this was accomplished by crosslinking and branching by using EPDM's side chain diene. (Branch) ENB is used to increase the performance, but the mixing is limited in manufacturing with an ENB content of 8-10% by weight, and when the ENB content exceeds this, ENB monomers with double bonds are exposed to ozone, resulting in carck resistance. There was also a problem with this deterioration.

KR 0333412 B1 KR 0622999 B1 JP 2004-010863 A

Therefore, the technical problem to be solved by the present invention is to improve the ozone resistance and oxidation resistance of the tire sidewall rubber, and in addition, the ozone resistance of the sidewall rubber by using a novel EPDM instead of the synthetic rubber in the mixture of natural rubber and synthetic rubber. It is to provide tire sidewall rubber that can further improve performance and appearance performance.

In order to solve the above-described technical problem, the present invention relates to a tire sidewall rubber containing EPDM rubber used by mixing with natural rubber or synthetic rubber, which is a raw material rubber, wherein the EPDM rubber has a structure of the following formula (1) and has a viscosity of 36 It has ~46 (Moone unit, MU), and provides a rubber composition for a tire sidewall, characterized in that the glass transition temperature is -45 ~ -35 ℃.

<Formula 1>

(Here, n: 789 to 904, m: 608 to 493, x: 75 to 85)

According to an embodiment of the present invention, 30 to 60 parts by weight of EPDM rubber may be used based on 100 parts by weight of the raw rubber.

According to another embodiment of the present invention, the ENB content of the EPDM rubber may be 13 to 17% by weight.

According to another embodiment of the present invention, the EPDM rubber may have a linearity (Delta-delta) value ranging from 0.4 to 0.6.

According to the present invention, it is possible to further improve the ozone resistance performance of the side wall rubber by using EPDM instead of synthetic rubber in the mixture of natural rubber and synthetic rubber in addition to improving the crosslinking performance and ozone resistance of the tire sidewall rubber. have.

1 is a photograph showing the result of a peeling test according to a comparative example compared with an example of the present invention,
2 are photographs showing results of an ozone evaluation experiment according to a comparative example compared with an example of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, but detailed descriptions of known functions or configurations that may obscure the subject matter of the present invention may be omitted in the following description and the accompanying drawings.

The terms or words used in the present specification and claims described below should not be construed as being limited to their usual or dictionary meanings, and the inventors are appropriate as the concept of terms for describing their own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention on the basis of the principle that it can be defined.

Therefore, the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention, and do not represent all the technical ideas of the present invention, and thus various equivalents that can replace them at the time of filing It should be understood that there may be water and variations.

1 is a photograph showing the result of a peeling test according to a comparative example compared to an example of the present invention, and FIG. 2 is a photograph showing the result of an ozone evaluation test according to a comparative example compared to the example of the present invention. do.

In order to solve the above-described technical problem, the present invention relates to a tire sidewall rubber containing EPDM rubber used by mixing with natural rubber or synthetic rubber, which is a raw material rubber, wherein the EPDM rubber has a structure of the following formula (1) and has a viscosity of 36 It has ~46 (Moone unit, MU), and the glass transition temperature is characterized in that -45 ~ -35 ℃.

<Formula 1>

(Here, n: 789 to 904, m: 608 to 493, x: 75 to 85)

Here, the raw rubber is a raw material used for the tire sidewall rubber, and synthetic rubber such as butadiene rubber and stylene rubber may be used as raw rubber by mixing or mixing, as well as natural rubber.

On the other hand, it is possible to use 30 to 60 parts by weight of EPDM rubber based on 100 parts by weight of the raw rubber. If the EPDM rubber is less than 30 parts by weight, there may be a limitation in that the ozone resistance is not sufficiently expressed. Conversely, the EPDM rubber is 60 parts by weight. If it exceeds parts by weight, there is a problem in the rubber miscibility, which may result in poor mixing.

In the case of rubber miscibility, it is divided into a continuous phase and a dispersed phase.If EPDM rubber exceeds 60 parts by weight, it becomes a continuous phase, and NR becomes a dispersed phase, reducing the elasticity of the rubber, and natural rubber becomes a continuous phase, which can have the characteristics of general rubber compounding with excellent fatigue resistance. There may be limits to which there is no one.

In addition, the ethylene norbornene (ENB) content of the EPDM rubber may be 13 to 17% by weight, which decreases the unsaturation branch depending on the content of ENB, which is the third monomer, thereby slowing the crosslinking rate with the unsaturated rubber, and The miscibility may decrease, and other saturated rubbers (isoprene, isobutyrene rubbers, etc.) are additionally mixed to improve the miscibility. If it is less than 13% by weight, the dispersion of the saturated rubber is difficult and the interfacial adhesion decreases. There may be a problem, and on the contrary, if it exceeds 17% by weight, the crosslinking rate with the unsaturated rubber may be accelerated, so that there may be a scorch problem, and there is a limitation in the manufacturing method that cannot be synthesized more than this with the current metallocene polymerization catalyst system.

Here, the ENB (Ethyl, ethylene norbornene) is a monomer constituting a double bond, and the rubber according to the present invention has the characteristic of including EPDM with an increased ENB content, and the ENB content in EPDM of conventionally commercialized products Although it is difficult to exceed the maximum 10% by weight, the present invention provides a rubber containing EPDM that overcomes this, so that the ENB content can be manufactured to a maximum of 17% by weight while maintaining the existing ozone resistance. While maintaining, ozone resistance can be improved and crosslinking non-uniformity can be improved.

In addition, according to an embodiment of the present invention, the EPDM rubber may have an ethylene group (C2) content of 48 to 55% by weight, which is designed to be similar to the viscosity of butadiene, and thus ethylene is used to improve miscibility with natural rubber. Group is used, and if it is less than 48% by weight, the solvent does not volatilize well due to the low molecular weight composition ratio of ethylene group, which may cause a sticky appearance problem on the surface of the raw rubber. Conversely, if it exceeds 55% by weight, the crystal of the polymer Due to the increase in cristallinity, the gelataion and the glass transition temperature of the rubber are increased, and there may be a rubber heating problem.

In addition, the content of propylene (C3) in the EPDM rubber is preferably 30 to 37% by weight.

That is, in the present invention, the ENB content in the total weight of the raw material rubber and EPDM rubber is 13 to 17% by weight, the Mooney viscosity (125°C) is 36 to 46, the ethylene (C2) content is 48 to 55% by weight, and propylene ( The C3) content is 30 to 37% by weight, and the glass transition temperature is -45 to -35°C.

Meanwhile, the EPDM rubber has a linearity (Delta-delta) value ranging from 0.4 to 0.6. When the linearity value reaches an optimum value of 0.4 to 0.6, the EPDM rubber chain penetrates the surface of carbon black as a reinforcing agent. It is easy to form a bond by increasing the mutual attraction between the carbon black filler and the rubber matrix, and improves the rubber matrix and blendability, resulting in improved interfacial adhesion in the pad peeling test. However, if the linearity is less than 0.4, a structure similar to that of the conventional EPDM is obtained. There is a problem that the bond formation with the reinforcing agent (carbon black) is inferior due to the large amount of rubber branches of Jiyeo EPDM. On the contrary, when it exceeds 0.6, the rubber is mainly composed of amorphous regions due to high crystallinity due to the high linearity of the rubber chain. (Elastomer) and blending limitations may exist.

Particularly, preferably, ENB content is 15% by weight, Mooney viscosity (125°C) is 41, ethylene (C2) content is 55% by weight, glass transition temperature is -41.4°C, and EPDM rubber is preferable. It is shown in Table 1 below.

division Viscosity (ML1+4@125℃) C2 (WT%) ENB(WT%) Tg Comparative Example 2 60 60 8.0 -48.5 Example 1 41 55 15.0 -41.4

* C2: Ethylene

* ENB: Ethylene norbornene

* Tg: Glass transition temperature of rubber

division TanD@0.1Hz TanD@20.Hz Delta-delta Comparative Example 2 0.768 0.462 0.306 Example 1 0.817 0.402 0.412

* TanDat0.1Hz: The higher the chain is, the more rigid it is, the lower it is, the softer it is.

* Delta-delta: The higher the value, the higher the linearity of the polymer chain, and the lower the higher the branch degree is.

*The above measurement follows the RPA ASTM D6204 measurement method.

According to Table 2 above, according to the present invention, in order to improve compatibility (mixability, blendability) with natural rubber (NR), which is a raw material rubber, the viscosity is low, the ENB content is increased to 15% by weight, and the Tg is -41°C. It is a rubber with excellent NR and blendability by applying the new EPDM. In the end, it is possible to improve ozone resistance and improve the quality of rubber appearance without the use of anti-aging agents and waxes in existing rubber compositions for side walls.

Examples and Comparative Examples

Examples according to the present invention and comparative examples showing the prior art were prepared by blending the compositions shown in Table 2 below to prepare a tire sidewall rubber specimen, and the evaluation results of the physical properties are shown in Table 3 below.

division Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 NR 50 50 50 50 50 50 BR 50 EPDM 50 EPDM of the present invention 30 40 50 60 Reinforcement 50 50 50 50 50 50 Zinc oxide 3 3 3 3 3 3 Antioxidant 4 4 adhesive 3 3 3 3 3 3 Wax 2 2 Process oil 3 3 3 3 3 3 brimstone 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization accelerator 0.5 0.5 0.5 0.5 0.5 0.5

* Natural rubber NR

* Butadiene rubber BR

* KEP-350 with EPDM (manufactured by Kumho Polychem)

* EPDM according to Formula 1 of the present invention

division Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 Mooney viscosity (100℃) 54 57 59 61 70 72 Scorch Time (T5@125℃) 49.7 42.3 42.3 39.0 38.8 30.0 Hardness 55 61 60 61 66 66 300% modulus 71 84 85 95 98 99 The tensile strength 204 155 180 201 215 217 Elongation 628 514 530 549 559 569 Pad peeling test
(Mead load_Kgf) 39 14 25 39 40 30 Pad peeling test
(image) See figure 1 Ozone evaluation (O-ring)
(image) See figure 2

Referring to Table 4 above, as can be seen in Comparative Example 2, in the case of the existing EPDM, the tensile strength decreased and the blendability with the natural rubber NR had a disadvantage that it was easily separated when evaluating the pad peeling, but EPDM was applied according to the present invention. As shown in Examples 1, 2, 3, and 4, it can be seen that the hardness and modulus are improved due to the linearity of EPDM. In addition, the pad peeling test is a test that confirms the interfacial adhesion between rubbers. Compared to Example 2, it can be seen that the blendability, that is, compatibility with natural rubber, is improved, and the vulcanization uniformity is improved, so that the adhesion performance is dominant.

Embodiments of the present invention can manufacture sidewall rubber by replacing the existing NR/BR rubber for sidewall with EPDM, and a rubber composition for sidewall with improved aging resistance and ozone resistance without the use of antioxidants and waxes. Can provide.

Claims (4)

In the tire sidewall rubber containing EPDM rubber used by mixing with natural rubber or synthetic rubber, which is a raw material rubber,
The EPDM rubber has a structure represented by the following Formula 1, has a viscosity of 36 to 46 (Moone unit, MU), and a glass transition temperature of -45 to -35°C.
<Formula 1>

(Here, n: 789 to 904, m: 608 to 493, x: 75 to 85)
The method of claim 1,
A rubber composition for a tire sidewall, characterized in that 30 to 60 parts by weight of EPDM rubber is used based on 100 parts by weight of the raw rubber.
The method of claim 2,
The ENB content of the EPDM rubber is a rubber composition for a tire sidewall, characterized in that 13 to 17% by weight.
The method of claim 1,
The EPDM rubber has a linearity (Delta-delta) value ranging from 0.4 to 0.6.

Images