JPH09272306A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire of which appearance of the surface of a side wall part is excellent, and heat resistance, weatherproofing such as ozone resistance and ultraviolet resistance, and durability are excellent. SOLUTION: This tire is formed into double layer construction, and the outer layer is constituted out of a rubber composite. containing ethylenepropylenediene rubber and butyl rubber halide. When the total quantity of rubber content in the rubber composite is 100 weight part, the content of ethylenepropylenediene rubber is E weight part, and the content of butyl rubber halide is X weight part, the content of ethylenepropylenediene rubber and butyl rubber halide are shown as following formulas: 25<=E+0.5X<=33, and 15<=E<=25, and so that the iodine value of ethylenepropylenediene rubber is in the range 10-15, and the ratio of the number of ethylene monomer units to the number of propylene monomer units of the ethylenepropylenediene rubber is in the range of 65/35-85/15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having excellent side wall portion appearance, weather resistance, interlayer adhesion and durability.

[0002]

2. Description of the Related Art Conventionally, a rubber composition used for forming a sidewall portion of a pneumatic tire contains an antiaging agent for preventing deterioration due to ozone, ultraviolet rays and the like. However, if such an antioxidant is contained in the rubber composition of the sidewall portion,
This anti-aging agent migrates (blooms) to the surface of the sidewall of the pneumatic tire, causing the surface of the sidewall to be discolored, which reduces the commercial value of the pneumatic tire. Further, in order to prevent the discoloration as described above, if the compounding amount of the antioxidant is reduced, cracks are likely to occur in the sidewall portion, and the durability of the pneumatic tire is deteriorated. .

In order to solve such a problem, the amount of the antioxidant added to the rubber composition by increasing the ozone resistance and the ultraviolet resistance of the rubber component itself of the rubber composition of the sidewall portion. Are being studied.

Examples of such methods include rubber blends containing ethylene propylene diene rubber with a reduced content of antioxidants or rubber blends containing halogenated butyl rubber with a reduced content of antioxidants. The method used for the sidewall portion may be mentioned. However, according to these methods, the bending fatigue resistance of the sidewall portion is lowered, and cracks are likely to occur.

Further, in JP-A-59-14502, the tire side portion extending from the upper portion of the bead portion to the lower portion of the shoulder portion through the sidewall portion has a two-layer inner and outer structure.
This outer surface layer is composed of a rubber composition composed of chlorinated butyl rubber, ethylene propylene diene rubber and diene rubber, and a pneumatic tire composed of a rubber composition whose main layer is in contact with the outer surface layer is mainly a diene rubber. It is disclosed. In JP-A-59-20708, a sheet is arranged in the tire circumferential direction so as to cover the tire surface from the shoulder portion to the sidewall portion, and the sheet is made of natural rubber, polybutadiene rubber, halogenated butyl rubber and / or ethylene. A pneumatic tire composed of a rubber compound composed of propylene diene rubber is disclosed.
Further, JP-A-1-297307 discloses a two-layer structure in which a sidewall has an inner layer adjacent to a carcass and an outer layer disposed outside the carcass, and the inner layer comprises a halogenated butyl rubber and an ethylene propylene diene rubber. A rubber composition comprising at least one type of saturated rubber group and at least one type of highly unsaturated rubber group consisting of natural rubber, isoprene rubber, butadiene rubber and styrene-butadiene rubber, wherein the outer layer has the above-mentioned low content. A pneumatic tire composed of at least one kind of unsaturation rubber group and at least one kind of the high unsaturation rubber group is disclosed. However, these publications do not teach the polymer structure of the ethylene propylene diene rubber used.

Further, Japanese Patent Laid-Open No. 4-43106 discloses that
The outermost layer of the sidewall portion composed of a plurality of layers is composed of a rubber composition having a high iodine value and a high ethylene content of ethylene propylene diene rubber in an amount of 15% by weight or more of the rubber component and a reduced content of the antioxidant. A pneumatic tire is disclosed. However, according to a pneumatic tire using a rubber composition of this publication having a high iodine value and a high ethylene content ethylene propylene diene rubber in the sidewall portion, the sidewall portion is apt to cause poor adhesion, In addition, minute cracks are likely to exist in the sidewall portion. Therefore, when such a pneumatic tire is subjected to a drum durability test under severe conditions, for example, interlayer adhesion failure of the sidewall portion or cracking of the sidewall portion is likely to occur. That is, the pneumatic tire intended by the present invention cannot be obtained based on the knowledge of the rubber composition described in this publication.

[0007]

SUMMARY OF THE INVENTION The present invention is to improve the rubber composition forming the sidewall portion of a pneumatic tire to improve the appearance, weather resistance, and durability of the sidewall portion.
It is intended to improve interlayer adhesion and durability.

[0008]

The present invention has a two-layer structure in which a side wall portion for covering and protecting the side surface of a carcass has an inner layer adjacent to the carcass and an outer layer disposed outside the inner layer. The outer layer is composed of a rubber composition containing ethylene propylene diene rubber (hereinafter sometimes referred to as “EPDM”) and halogenated butyl rubber (hereinafter sometimes referred to as “X-IIR”). When the total amount of the rubber component is 100 parts by weight, the EPDM content is E parts by weight, and the X-IIR content is X parts by weight, the EPDM content and the X-
The content of IIR is represented by the formula: 25 ≦ E + 0.5X ≦ 35 and the formula: 15 ≦ E ≦ 25, and the iodine value of the EPDM is in the range of 10 to 15, and ethylene / propylene of the EPDM. The present invention relates to a pneumatic tire having a ratio (weight ratio) within the range of 65/35 to 85/15.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The pneumatic tire of the present invention has a sidewall portion for covering and protecting the side surface of a carcass. Further, the sidewall portion has a two-layer structure of an inner layer adjacent to the carcass and an outer layer disposed outside the inner layer. And, since the outer layer is formed of a specific rubber composition which does not require an antioxidant,
The pneumatic tire of the present invention is characterized in that the sidewall portion has excellent appearance, weather resistance, interlayer adhesion and durability.

Further, by forming the side wall portion into a two-layer structure, only the outer layer portion is formed of a specific rubber composition which does not require an antioxidant, and the inner layer portion is a conventionally known rubber for the side wall portion. It was made possible by the composition, which again does not require an antioxidant.

The rubber component of the rubber composition forming the outer layer contains a specific amount of EPDM, and X-II.
R is contained in a specific amount. By using such a rubber component, it is possible to obtain a rubber composition for the outer layer of the sidewall portion which is excellent in weather resistance without using an antioxidant. Further, by using such a rubber composition for the outer layer of the sidewall portion, it is possible to suppress the generation of microcracks in the outer layer of the sidewall portion, and to bond the outer layer of the sidewall portion and the portion in contact with this outer layer. The durability of the pneumatic tire will be improved because the durability is improved.

When the total amount of the rubber component in the rubber composition of the outer layer is 100 parts by weight, the specific EPDM content is E parts by weight, and the X-IIR content is X parts by weight,
The specific EPDM content and X-IIR content are
Formula: 25 ≦ E + 0.5X ≦ 35 and a range represented by the formula: 15 ≦ E ≦ 25, preferably 27.5 ≦ E + 0.5X ≦ 35 and a range represented by the formula: 17 ≦ E ≦ 25 is there. The value of E + 0.5X is 2
If it is smaller than 5, weather resistance such as ozone resistance and ultraviolet resistance of the outer layer of the side wall portion becomes poor, while 3
If it is larger than 5, the adhesion between the outer layer of the sidewall and the portion in contact with this outer layer becomes poor. Also, the above E
When the value of is less than 15, the weather resistance such as ozone resistance and ultraviolet resistance of the outer layer of the sidewall portion becomes poor, while when it is more than 25, the outer layer of the sidewall and the portion in contact with this outer layer are deteriorated. The adhesiveness of is poor.

When the value of E + 0.5X and the value of E are within the range represented by the above formula, good weather resistance such as ozone resistance and ultraviolet resistance can be obtained without adding an anti-aging agent, and adhesion can be improved. A good rubber composition for a sidewall can be obtained. Also, as mentioned above, a suitable amount of X
By blending -IIR, EPDM becomes easy to disperse in the rubber composition, and for this reason, the weather resistance such as ozone resistance and ultraviolet resistance of the sidewall portion using this rubber composition is improved. Moreover, it is considered that no microcracks can be seen in the outer layer of the sidewall portion.

The iodine value of the specific EPDM is 1
It is in the range of 0 to 15. When the iodine value of the specific EPDM is less than 10, the adhesion between the outer layer of the sidewall portion and the portion in contact with this outer layer becomes poor. On the other hand, when it is greater than 15, minute cracks are formed in the outer layer of the sidewall portion. Becomes easier to enter. EPDM having an iodine value of more than 15 is also disadvantageous in that it is expensive.

The ethylene / propylene ratio (molar ratio) of the specific EPDM is in the range of 65/35 to 85/15, preferably 70/30 to 82.5 / 17.5. When the number of moles of ethylene of the specific EPDM is less than the above range with respect to the number of moles of propylene, the adhesion between the outer layer of the sidewall portion and the portion in contact with this outer layer becomes poor, while it is more than the above range. In this case, EPDM tends to have high crystallinity and tend not to exhibit rubber elasticity, which is not preferable.

Examples of the X-IIR include chlorinated butyl rubber and brominated butyl rubber. Among them, chlorinated butyl rubber (hereinafter referred to as "Cl-IIR" is preferable in that it has good blendability with a diene rubber. It may be said that) is used.

In addition to the specific EPDM and X-IIR, a diene rubber is contained as a rubber component in the rubber composition forming the outer layer of the sidewall portion. As the diene rubber, any of those commonly used as a rubber component for the sidewall portion can be used. For example, one or two kinds of natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber and the like can be used. The above can be used.

A rubber composition for the outer layer of the side wall portion can be obtained by blending these rubber components with a conventional compounding agent excluding the antioxidant. Examples of the compounding agent to be compounded in the rubber composition include carbon black; process oil; mastication accelerators such as zinc white and mercaptan-based disulfide type; vulcanization accelerators such as stearic acid and zinc white; sulfur and insoluble sulfur. Vulcanizing agents such as; vulcanization accelerators such as sulfenamide-based and thiazole-based,
An appropriate amount is blended according to the required quality.

Further, the thickness of the outer layer of the sidewall portion is preferably in the range of about 0.4 to 0.8 mm from the viewpoint that the cost increases as the thickness increases and the reinforcing property decreases as the thickness decreases.

The inner layer of the side wall portion can be formed of a conventionally known rubber composition for the side wall portion (however, no antioxidant is required) as described above. The rubber component of such a rubber composition is, for example, one or two of diene rubbers such as natural rubber, isoprene rubber, styrene-butadiene rubber, and butadiene rubber.
There are more than one seed. Examples of compounding agents to be added to such rubber compositions include carbon black; process oils; mastication accelerators such as zinc white and mercaptan-based disulfides; vulcanization accelerators such as stearic acid and zinc white; Vulcanizing agents such as sulfur and insoluble sulfur; vulcanization accelerators such as sulfenamide type and thiazole type. The rubber composition of the inner layer of the sidewall portion,
The specific EPDM, other EPDM or XI
IR may be blended in an appropriate amount in order to improve the adhesiveness of the sidewall portion to the outer layer, but in that case, there is a tendency to increase the cost. In this way, the sidewall portion has a two-layer structure and the anti-aging agent is not mixed with the rubber composition of the inner layer, so that the anti-aging agent moves from the inner layer to the outer layer or from the carcass to the outer layer through the inner layer. Thus, it is possible to prevent the antioxidant from bleeding on the surface of the sidewall portion.

When the thickness of the inner layer of the side wall portion is thin, the reinforcing property is lowered, and when it is thick, rolling resistance is increased and cost is also increased, so that the thickness is about 2 to 4 mm, further 2.5 to 3 mm. It is preferably within the range of about 0.5 mm.

[0022]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

As the rubber and compounding agent of the rubber composition for the outer layer of the sidewall portion in the following Examples and Comparative Examples, EPDM: four types containing ethylidene norbornene as a diene component as shown in Table 1 (respectively, Type of E
They were PDM, EPDM, EPDM and EPDM. EPDM and EPDM are EPDs according to the present invention
M), Cl-IIR: Cl-IIR manufactured by Exxon Chemical Co., Ltd.
HT1066, Natural rubber: RSS1 Butadiene rubber: BR130B of Ube Industries Ltd. Carbon black: N550 made by Tokai Carbon Co., Ltd. Process oil: Diana Process PS32 made by Idemitsu Kosan Co., Ltd. Wax: Ouchi Shinko Chemical Co., Ltd. ) Sannock wax (used only in some comparative examples), Antiaging agent: Ozonone 6C manufactured by Seiko Chemical Co., Ltd. (used only in some comparative examples), Zinc Hua: Sakai Chemical Industry Co., Ltd. Zinc flower No. 1 Stearic acid: Tung stearate from NOF CORPORATION Sulfur: Sulfur from Tsurumi Chemical Co., Ltd. Vulcanization accelerator: Nocceller NS manufactured by Ouchi Shinko Chemical Co., Ltd. was used.

[0024]

[Table 1]

Further, the composition of the rubber composition for the inner layer of the sidewall portion in the following Examples and Comparative Examples is 45 parts by weight of natural rubber, 55 parts by weight of butadiene rubber, 60 parts by weight of carbon black, and 8 parts by weight of process oil. 2 parts by weight of zinc white, 3 parts by weight of stearic acid, 1.5 parts by weight of sulfur and 1 part by weight of vulcanization accelerator. The types of these rubbers and compounding agents (manufacturer, product number, etc.) are the same as those of the rubber composition for the outer layer of the sidewall portion.

Examples 1 and 2 and Comparative Examples 1 to 6 The unvulcanized rubber of the rubber composition was prepared by kneading and extruding the amounts of the rubbers and compounding agents shown in Table 2 shown in Table 2 by a conventional method. Sheets were prepared.

An unvulcanized rubber sheet of this rubber composition was pressed for 10 minutes at a temperature of 170 ° C. and a pressure of 80 kgf / cm ² to prepare a vulcanized rubber sheet having a thickness of 4 mm, and the following evaluation was made. It was submitted to the test.

<Evaluation of Vulcanized Rubber Sheet> (Evaluation of Appearance after Outdoor Exposure) This vulcanized rubber sheet was exposed outdoors for 30 days so as not to be exposed to rainwater. After the outdoor exposure, the appearance of the vulcanized rubber sheet was visually observed, and when no discoloration was observed, "○" was given, and when discoloration was observed, "x" was given. Table 1 shows the results.

(Ozone resistance test) The vulcanized rubber sheet is JIS
In accordance with the ozone deterioration test method (dynamic) prescribed in K6259, after leaving for 72 hours under the conditions of a temperature of 40 ° C., an ozone concentration of 50 ppm, and an elongation rate of 20%, 0 to 20.
%, The elongation was repeated and the state of crack generation was visually observed. And, "○" means that there are no cracks that can be recognized with the naked eye, "A2" means that there are a few cracks that are visible to the naked eye, and "B2" means that there are a few deep and relatively large cracks. "B3" means that there are many deep and relatively large cracks. In this test, the evaluation results of “◯” and “A2” are in the practical range. Table 2 shows the results.

Next, the amounts of the rubber and compounding agent of the rubber composition for the outer layer of the side wall portion shown in Table 2 were kneaded and extruded by a conventional method to form the outer layer of the side wall portion. I got an unvulcanized rubber sheet for. Also,
The rubber of the rubber composition for the inner layer of the sidewall portion and the compounding agent were kneaded by a usual method and extruded to prepare an unvulcanized rubber sheet for the inner layer of the sidewall portion. Air of 185 / 70R14 having a structure as shown in the schematic partial sectional view of FIG. 1 is formed by a conventional method except that the sidewall portion is formed by using the unvulcanized rubber sheet for the outer layer and the inner layer of the sidewall portion. A filled tire was produced. The outer layer of the sidewall portion had a thickness of 0.6 mm, and the inner layer had a thickness of 2.4 mm.

<Evaluation of pneumatic tire><Drum durability test (I)>
An endurance performance test was conducted in accordance with the conditions specified in SD4230. After the durability test, the evaluation of the interlayer adhesion between the outer layer and the inner layer of the sidewall portion of the pneumatic tire and the observation of the presence of microcracks in the outer layer were performed as follows.

(Interlayer adhesion between outer layer and inner layer) After the drum durability test, the sidewall portion (both inner layer and outer layer) was cut into a strip shape with a width of 1 cm so that a peeling test between the inner layer and the outer layer could be performed. A notch was made between the inner layer and the outer layer with a cutter. Then, the cut portion of the inner layer and the cut portion of the outer layer were respectively sandwiched by chucks and pulled at a chuck-to-chuck speed of 10 mm / min to perform a peeling test between the outer layer and the inner layer. When the side wall is cut out, there is already a part where interfacial peeling is present between the outer layer and the inner layer is marked as "x", and when the interface is broken by the peeling test as "△", the peeling test The one that was cohesively destroyed by the above was designated as "○". Table 2 shows the results.

(Observation of the presence of microcracks in the outer layer)
After the drum durability test, microcracks in the outer rubber layer of the sidewall portion were visually observed. The case where no microcracks were observed was marked with “◯”, the case where a small amount of microcracks was observed was marked with “Δ”, and the case where a large number of microcracks were observed was marked with “x”. Table 2 shows the results.

<Drum Durability Test (II)> JIS D42
The durability performance test of the pneumatic tire was conducted in the same manner as the drum durability test (I) except that the load condition specified in No. 30 was doubled, and the interlayer adhesion between the outer layer and the inner layer was evaluated by the same method. The presence of microcracks in the outer layer was also observed. Table 2 shows the results.

Comparative Example 7 The side wall rubber composition for the outer layer was replaced with the side wall rubber composition shown in Table 2 (a conventional side wall rubber composition containing an antioxidant and a wax). Except for this, the vulcanized rubber sheet was evaluated in the same manner as in Example 1. Table 2 shows the results.

[0036]

[Table 2]

From the evaluation results of the vulcanized rubber sheet in Table 2,
When a rubber composition containing EPDM is used for the outer layer of the side wall portion, a pneumatic tire having an excellent appearance and ozone resistance of the side wall portion can be obtained as compared with a rubber composition not using EPDM (Comparative Example 7). Can understand.

From the drum durability test (I), EPDM having a low iodine value and a small number of ethylene monomer units was obtained.
It can be seen that, when is used as the outer layer of the sidewall portion, the adhesiveness of the outer layer becomes poor, and when EPDM having a high iodine value or a high weight ratio of ethylene is used as the outer layer of the sidewall portion, the outer layer has good adhesiveness. .

Next, Examples 1 and 2 and Comparative Examples 1 to 6
The result of the drum endurance test (II) will be described with reference to FIG. In FIG. 2, Comparative Example 1 uses a rubber composition containing EPDM containing no Cl-IIR and a low ethylene weight ratio, and the presence of microcracks in the outer layer was "○", but the outer layer was The adhesiveness between the inner layer and the inner layer was “x”. By making the EPDM of Comparative Example 1 highly ethylene (instead of EPDM having a high ethylene weight ratio), the interlayer adhesion between the outer layer and the inner layer is improved as in Comparative Examples 2 and 3 (from "x" to " However, the state of existence of the microcracks in the outer layer becomes poor (from “◯” to “Δ”). Further, by making the EPDMs of Comparative Examples 2 and 3 highly iodinated (substituting EPDM having a high iodine value),
As in Comparative Example 4, the interlayer adhesion between the outer layer and the inner layer is further improved (from “Δ” to “◯”), but the presence of microcracks in the outer layer is further deteriorated (“Δ” to “x”).
become). Thus, by adding Cl-IIR to the rubber composition which cannot satisfy the interlayer adhesion between the outer layer and the inner layer and the state of existence of microcracks in the outer layer, the interlayer adhesion between the outer layer and the inner layer and / or The presence of microcracks in the outer layer can be improved. Above all, Comparative Example 2
By adding Cl-IIR to the rubber compositions according to (3) and (3) (by making the rubber compositions according to Examples 1 and 2), the interlayer adhesion between the outer layer and the inner layer was set to "○", and the fineness of the outer layer was reduced. The state of crack existence can be improved to "○". That is, the pneumatic tire using the rubber composition according to Example 1 or 2 as the outer layer of the sidewall portion has no problem in both performances regarding adhesiveness and microcracks,
It can be seen that satisfactory durability performance can be obtained.

Examples 3 to 12 and Comparative Examples 8 to 11 Table 3 shows the rubber components of the rubber composition for the outer layer of the sidewall portion.
A rubber composition (the compounding agent components were the same as in Example 1) was prepared in the same manner as in Example 1 except that the composition described in Example 1 was used, and the vulcanized rubber sheet was evaluated in the same manner as in Example 1. And the pneumatic tires were evaluated (however, the drum durability test (I) was not carried out in these Examples and Comparative Examples). Table 3 shows the results. In addition, in Table 3, the composition of the rubber composition of Example 2 already described in Table 2 and the evaluation results are also shown.

[0041]

[Table 3]

Table 3 shows EP having a large number of ethylene monomer units.
Using DM, this EPDM and Cl-I in the rubber component
It is a result of evaluating a vulcanized rubber sheet and a pneumatic tire prepared by using the rubber composition prepared by changing the IR (EPDM) component ratio.

According to Table 3, the value of "E + 0.5X" is 25.
It can be seen that the lower the ozone resistance, the lower the ozone resistance. Further, according to the drum durability test (II), it is found that when the value of “E + 0.5X] exceeds 35, the adhesion between the outer layer and the inner layer is deteriorated. Content of E, that is E, is calculated by the formula:
Within the range represented by 5 ≦ E ≦ 25, a pneumatic tire having a good balance of ozone resistance and adhesiveness of the outer layer of the sidewall portion can be obtained.

[0044]

EFFECTS OF THE INVENTION According to the present invention, good weather resistance such as ozone resistance and ultraviolet resistance is obtained without adding an antioxidant.
It is possible to obtain a rubber compound for the layer of the sidewall portion having good adhesiveness. By using a specific rubber compound that does not require such an antioxidant for the outer layer of the sidewall portion, the outer surface of the sidewall portion has an excellent appearance, and there are no microcracks in the outer layer of the sidewall portion. It is possible to obtain a pneumatic tire having excellent durability and excellent weather resistance such as ultraviolet resistance.

[Brief description of drawings]

FIG. 1 is a schematic partial cross-sectional view of a pneumatic tire of the present invention.

FIG. 2 is an explanatory diagram for explaining evaluation results of a drum durability test (II) in Examples 1 and 2 and Comparative Examples 1 to 6.

[Explanation of symbols]

 1 Carcass 2 Side wall part 3 Inner layer of side wall part 4 Outer layer of side wall part

Claims (1)

[Claims] 1. A side wall portion for covering and protecting a side surface of a carcass has a two-layer structure of an inner layer adjacent to the carcass and an outer layer disposed outside the inner layer, the outer layer being ethylene propylene diene rubber and a halogen. And a halogenated butyl rubber content of 100 parts by weight, the ethylene propylene diene rubber content is E parts by weight, and the halogenated butyl rubber content is X parts. In the case of parts by weight, the content of ethylene propylene diene rubber and the content of halogenated butyl rubber in the rubber composition are represented by the formula: 25 ≦ E + 0.5X ≦ 35 and the formula: 15 ≦ E ≦ 25. The iodine value of the ethylene propylene diene rubber is in the range of 10 to 15, and the ethylene / propylene ratio (heavy weight) of the ethylene propylene diene rubber is Ratio) is 65
A pneumatic tire in the range of / 35 to 85/15.