JPH08231772A - Pneumatic tire - Google Patents

Abstract

PURPOSE: To obtain at low cost a pneumatic tire having two-layer-structured sidewall with the outer layer consisting of a specific rubber composition, excellent in ozone resistance and weatherability, also excellent in adhesivity to other kinds of rubber, and free from the problem of the sidewall's debonding off the carcass. CONSTITUTION: This pneumatic tire is produced in such a way that the sidewall 2 covering and protecting the side of the carcass 1 is of two-layer structure made up of inner layer 3 adjacent to the carcass 1 and outer layer 4. The rubber component of a rubber composition constituting the outer layer 4 is a rubber containing an ethylene-propylene-diene rubber(EPDM) 24-36 in iodine value (e.g. a blend of 25-40wt.% of EPDM and other diene rubber). It is preferable that the ethylene/propylene ratio of EPDM is (55:45) to (80:20).

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 improved sidewall appearance and improved weather resistance. More specifically, the sidewalls for protecting the side surface of the carcass have different rubber compositions. The present invention relates to a pneumatic tire composed of inner and outer layers.

[0002]

2. Description of the Related Art Conventionally, a sidewall of a pneumatic tire has been made of a rubber composition containing a high unsaturated rubber such as natural rubber or isoprene rubber having a high content of double bonds in the main chain. The double bonds in these highly unsaturated rubber molecules have the property of reacting with ozone to depolymerize, so if the tire is left in a place with strong ultraviolet rays or in an atmosphere with a high ozone concentration in the air, , Cracks So-called ozone cracks occur. In order to prevent this, an amine anti-aging agent and an anti-ozone cracking agent such as wax have been blended in the sidewall rubber composition.

However, in a pneumatic tire having a sidewall composed of a rubber composition containing such an anti-ozone cracking agent, the anti-ozone cracking agent blooms on the surface of the sidewall during storage and it is as if dust were present. Has the appearance of being attached. Further, since the amine-based antiaging agent has a property of discoloring brown when exposed to air or sunlight, it migrates to the surface of the side wall by blooming and discolors the side wall, thereby lowering the commercial value. On the other hand, if the compounding amount of the anti-aging agent is reduced to improve discoloration, cracks will occur more quickly and the durability will decrease.

Therefore, in recent years, a low unsaturation degree rubber having a low content of unsaturated bonds is used to enhance the ozone resistance of the rubber component itself and reduce the content of the anti-ozone agent which causes bloom and discoloration. Rubber compositions are being investigated. For example, in Japanese Unexamined Patent Publication No. 1-297307, a pneumatic tire having a two-layer structure of an inner layer having a sidewall portion adjacent to a carcass and an outer layer disposed on the outer side of the inner layer has a structure of ethylene propylene diene rubber (EPDM) as a rubber component of the inner layer. ) 10
Using a rubber compounding 30 parts by weight and 90 to 70 parts by weight of a highly unsaturated rubber such as natural rubber, EP as the rubber component of the outer layer
DM 30 to 60 parts by weight and highly unsaturated rubber 70 such as natural rubber
A pneumatic tire using a rubber compounded with ˜40 parts by weight is disclosed.

[0005]

EPDM is excellent in weather resistance because the proportion of unsaturated bonds is much smaller than that of natural rubber or butadiene rubber, but it is more expensive than other diene rubbers. If this content rate becomes high, it will cause an increase in the price of the sidewall, and eventually the pneumatic tire itself. Further, since EPDM has a small proportion of unsaturated bonds, an increase in the EPDM content also causes a decrease in the adhesiveness with the rubber of other parts of the tire. The decrease in the adhesiveness of the sidewall also causes a problem of peeling from the carcass or the like.

The present invention has been made in view of such circumstances, and an object of the present invention is to construct a sidewall having a two-layer structure by forming an outer layer of a rubber composition containing a specific EPDM. Another object of the present invention is to provide a pneumatic tire that is inexpensive, has excellent weather resistance, and can solve the problem of separation from the carcass portion.

[0007]

[Means for Solving the Problems] Ethylene propylene diene rubber (EPDM) is a low unsaturated rubber obtained by copolymerizing a copolymer of ethylene and propylene with a diene as a third component in order to impart vulcanizability. Is. The present inventors have noticed that the adhesiveness of ethylene propylene diene rubber (EPDM) varies depending on the iodine value, and an EPDM capable of exhibiting the maximum adhesiveness while ensuring desired ozone resistance and weather resistance. Heading has led to the completion of the present invention.

That is, in the pneumatic tire of the present invention, as shown in FIG. 1, a sidewall 2 for covering and protecting the side surface of a carcass 1 has an inner layer 3 adjacent to the carcass 1 and an outer layer 4 provided outside thereof. In the pneumatic tire having the two-layer structure described above, the rubber composition forming the outer layer 4 contains ethylene propylene diene rubber having an iodine value of 24 to 36 as a rubber component.

The EPDM contained in the rubber composition constituting the outer layer 4 (hereinafter referred to as "outer layer rubber composition") is an EPDM having an iodine value of 24 to 36. Here, the iodine value is the number of grams of iodine that reacts with 100 g of the polymer, and is an index of the degree of unsaturation of the polymer. In the case of EPDM, it is proportional to the amount of the diene as the third component and is an index of the vulcanization rate. When the iodine value is small, the proportion of the diene component is small, and the covulcanizability with other diene rubbers is low. Is inferior,
As a result, it means a decrease in adhesive strength. Therefore, if the iodine value is less than 24, the adhesiveness with other diene rubbers such as the inner layer rubber is poor, and if the iodine value exceeds 36, the proportion of the diene component becomes too high and the desired ozone resistance is obtained. I can't. This is remarkable when the ethylene / propylene ratio of EPDM is in the range of 55/45 to 80/20.

In EPDM used in the rubber composition for the outer layer, it is desirable to use ethylidene norbornene, which has a high vulcanization rate, as the type of the diene as the third component excluding ethylene and propylene. The proportion of EPDM in the rubber component of the outer layer rubber composition is preferably 25 to 35% by weight. This is because if it is less than 25% by weight, the ozone resistance is remarkably lowered, and if it exceeds 35% by weight, the adhesion to the inner layer and the flex fatigue resistance are lowered.

As the balance of the rubber component of the rubber composition for the outer layer, a low unsaturation degree rubber having excellent weather resistance can be used in addition to general diene rubber having a high degree of unsaturation and EPDM. As the high unsaturated rubber, specifically, natural rubber,
Isoprene rubber, butadiene rubber, styrene-butadiene rubber (SBR), etc. can be used. As the low unsaturated rubber, for example, butyl rubber or halogenated butyl rubber can be used.

In addition to the above rubber components, the rubber composition for the outer layer may be appropriately blended with general rubber additives such as a vulcanizing agent and a reinforcing agent such as carbon black. The composition of the rubber composition (rubber composition for inner layer) forming the inner layer 3 of the sidewall 2 is not particularly limited. The rubber component may be composed of one or more natural rubbers or other highly unsaturated rubbers, or EP
It may be a rubber blended with low unsaturation rubber such as DM or halogenated rubber. However, it is unavoidable that the cost increases as the proportion of low unsaturation rubber increases in the inner layer. When using EPDM for the inner layer,
The type is not particularly limited. In addition to the above rubber components, the rubber composition of the inner layer may be appropriately added with a compounding agent for generally used rubber such as a vulcanizing agent and a reinforcing agent, if necessary.

A green tire is manufactured by a conventionally known method using the rubber sheet for a sidewall, which is obtained by stacking the rubber layer made of the rubber composition for the outer layer and the rubber layer made of the rubber composition for the inner layer as described above. When vulcanized and molded, the pneumatic tire according to the present invention is obtained. In the sidewall, the outer layer preferably has a thickness of about 0.4 to 0.8 mm, and the inner layer preferably has a thickness of about 2.0 to 4.0 mm.

The pneumatic tire of the present invention having the above constitution is excellent in ozone resistance and weather resistance even if a large amount of anti-ozone cracking agent such as an antioxidant is not mixed in the sidewall. . Therefore, even if it is used for a long time,
It is possible to prevent a change in appearance such as discoloration due to a bloom phenomenon of an antiaging agent or the like.

[0015]

EXAMPLES Hereinafter, the rubber composition for the outer layer and the rubber composition for the inner layer constituting the sidewall of the pneumatic tire of the present invention will be described based on Examples. [Rubber Composition for Outer Layer] As EPDM, three types of EPDM shown in Table 1 using ethylidene norbornene as a diene component were used. EPDM and EPDM
Is an EPDM according to the present invention, and the EPDM is an EPDM outside the scope of the present invention.

[0016]

[Table 1]

The rubber composition and various additives shown in Table 2 were blended to form the outer layer rubber composition No. 1 to 7 were prepared. EP
Rubber composition No. DM having DM outside the range of the present invention. 1 corresponds to the comparative example. In Table 2, N550 manufactured by Tokai Carbon Co., Ltd. as carbon black, Diana Process P32 manufactured by Idemitsu Kosan Co., Ltd. as process oil, Sunnock wax manufactured by Ouchi Chemical Co., Ltd. as wax, and refined as an antioxidant. Ozonon 6C manufactured by Kagaku,
As a vulcanization accelerator, Noxera-N manufactured by Ouchi Chemical Co., Ltd.
S and Noxera-DM were used. [Rubber composition for inner layer] Rubber composition No. 1 for inner layer having the composition shown in Table 2. 1 and 2 were prepared. No. No. 1 is a rubber composition in which the rubber component is composed only of a diene rubber having a high degree of unsaturation. 2 is a rubber composition containing EPDM.

As a reference example, the rubber compositions used for the conventional one-sided sidewalls are also shown in Table 2.
Shown in With respect to the rubber composition for the outer layer, the rubber composition for the inner layer, and the rubber composition of the reference example, which have been compounded according to the above composition, the following evaluation methods give adhesiveness, ozone resistance, and appearance,
The flex resistance was evaluated. Table 2 shows the evaluation results. [Evaluation Method] Adhesiveness: Rubber composition for outer layer No. 1 to No. Unvulcanized rubber sheet produced using No. 7 and the inner layer rubber composition No.
1 and the unvulcanized rubber sheet produced by using
A vulcanized rubber sheet obtained by vulcanizing this at 170 ° C. for 10 minutes was cut into a width of 2 cm to prepare an adhesive test piece.
The produced rubber test piece was peeled at a pulling speed of 10 mm / min, and the state of the peeling interface was visually observed.
The evaluation was made in three grades of ◯ (not peeled at the rubber / rubber interface, causing cohesive failure), Δ (partially peeled at the interface), and × (peeled at the interface).

Ozone resistance: Rubber composition for outer layer No. 1 to
No. A vulcanized rubber test piece was prepared using the rubber composition of Example 7 and the reference example, and the ozone deterioration test specified in JIS K6301 was performed using this. The test conditions are a temperature of 40 ° C., an ozone concentration of 50 pphm, and an elongation rate of 20%.
Left for hours. The cracked state of the test piece after leaving it
Evaluation was performed according to K6301.

"○" indicates that there were no cracks visible to the naked eye, and "A1" indicates that there were a small number of cracks that were invisible to the naked eye but could be confirmed with a magnifying glass.
“B3” indicates that there are many deep and relatively large cracks. Flex resistance; rubber composition for outer layer No. 1 to No. No. 7, inner layer rubber composition No. Vulcanized rubber test pieces were prepared using the rubber compositions of 1 and 2 and the reference example, and JIS K
The bending test specified in 6301 was performed. And
The vulcanized rubber test piece was evaluated by the crack growth length (mm) when it was repeatedly bent 100,000 times.

Appearance: Outer layer rubber composition No. 1 to No.
No. 7, inner layer rubber composition No. A vulcanized rubber test piece having a thickness of 4 mm was prepared using the rubber compositions of 1, 2 and Reference Example,
This test piece was exposed outdoors so that it would not be exposed to rainwater. Three
After 0 days of exposure, visually inspect the appearance, ○ (no discoloration)
And x (discoloration) were evaluated.

[0022]

[Table 2]

[Evaluation Result] As can be seen from Table 2, the rubber composition No. 1 containing EPDM as the rubber component was prepared. 1-8
It can be seen that each of them has an excellent appearance and has ozone resistance equal to or higher than that of the reference example. However, regarding ozone resistance, the content of EPDM in the rubber component is 25% by weight.
If it is less than 1, there is a tendency to decrease (rubber composition No. 4).
And No. 5).

However, even when the compounding amount of EPDM is the same, when compounding EPDM out of the range of the present invention (rubber composition No. 1) and when compounding amount of EPDM according to the present invention is large ( It can be seen that the rubber composition No. 7) is inferior in adhesiveness and flexibility. From the above, EPDM having an iodine value of 24 to 36, preferably 25 to 35% by weight
It can be seen that the rubber composition containing the rubber component contained therein can satisfy all of ozone resistance, adhesiveness, appearance and bending resistance.

Next, the rubber composition No. for the outer layer shown in Table 2 was obtained.
No. 3 outer layer having a thickness of 0.6 mm and the inner layer rubber composition No. 1 or No. A pneumatic tire (185 / 70R14) according to an example of the present invention in which an inner layer having a thickness of 3.0 mm was used to form a sidewall was manufactured (Example tire Nos. 1 and 2). Also, as a comparative example,
Using the rubber composition of the reference example shown in Table 2, a pneumatic tire having a single-layer sidewall was manufactured (comparative tire).

The tires of the examples and the comparative examples were tested at 2000c.
The vehicle was mounted on a rear-wheel drive (FR vehicle) type vehicle with a cross and driven for 2000 km. When the tire after running was observed, it was found that the tire No. No discoloration or cracks were observed in the sidewall portions 1 and 2.
On the other hand, although cracks were not observed in the sidewall portion of the tire of the comparative example, it was discolored to reddish brown (see Table 3).

[0027]

[Table 3]

[0028]

Industrial Applicability The pneumatic tire of the present invention is a pneumatic tire having a two-layered sidewall structure, in which the outer layer of the sidewall has a unique E value within a predetermined range.
Since it is composed of a rubber composition containing PDM, the outer layer of the sidewall can maximize its adhesiveness with other rubbers without deteriorating ozone resistance and weather resistance. In other words, since ozone resistance and weather resistance can be exhibited without lowering the adhesiveness with other rubbers, even if a rubber that does not contain expensive EPDM is used as the rubber that constitutes the inner layer, the sidewall is used. As a result, it is possible to guarantee the ozone resistance and the weather resistance required, and as a result, it is possible to reduce the cost of the sidewall portion of the pneumatic tire. To reduce the EPDM content of the inner rubber layer,
This means that the degree of unsaturation of the inner rubber layer is improved, and the adhesion between the inner layer and the carcass portion can be improved.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Carcass 2 Sidewall 3 Inner layer 4 Outer layer

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 20, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

However, in a pneumatic tire having a sidewall composed of a rubber composition containing such an anti-ozone cracking agent, the anti-ozone cracking agent blooms on the surface of the sidewall during storage and it is as if dust were present. Has the appearance of being attached. Further, since the amine-based antiaging agent has a property of discoloring brown when exposed to air or sunlight, it migrates to the surface of the side wall by blooming and discolors the side wall, thereby lowering the commercial value. On the other hand, if Genzure the amount of antioxidant in order to improve the discoloration, cracking becomes faster, the durability is lowered.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

The tires of the examples and the comparative examples were tested at 2000c.
mounted in crosswise on a vehicle wheel drive (FR vehicle) method after c, it was 2000 0 miles run. When the tire after running was observed, no discoloration or cracks were observed in the sidewall portion of the tire of this example. On the other hand, although cracks were not observed in the sidewall portion of the tire of the comparative example, it was discolored to reddish brown (see Table 3).

Claims (3)

[Claims] 1. A side wall (2) for covering and protecting a side surface of a carcass (1) has a two-layer structure of an inner layer (3) adjacent to the carcass (1) and an outer layer (4) arranged outside thereof. In a pneumatic tire, the rubber composition forming the outer layer (4) is used as a rubber component,
A pneumatic tire comprising ethylene propylene diene rubber having an iodine value of 24 to 36. 2. The rubber component in the rubber composition constituting the outer layer (4) is a mixture of ethylene propylene diene rubber and diene rubber, and the content of the ethylene propylene diene rubber in the rubber component is 25 to 40% by weight. %, The pneumatic tire according to claim 1. 3. The pneumatic tire according to claim 1 or 2, wherein the ethylene / propylene ratio of the ethylene propylene diene rubber is 55/45 to 80/20.