JP2013067676A - Heavy-duty pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heavy-duty pneumatic tire whose cost is prevented from increasing while the surface of a sidewall is prevented from being microcracked.SOLUTION: This invention relates to the heavy-duty pneumatic tire, configured such that: the outerlayer of the sidewall comprises a rubber composition, the rubber component of which contains 10 mass% or more of ethylene-propylene rubber and a 20 mass% or more of butyl rubber, wherein the outerlayer has a thickness of 0.5 mm or larger; and the innerlayer of the sidewall comprises a rubber composition, the rubber component of which contains 60 mass% or more of natural rubber.

Description

The present invention relates to a heavy-duty pneumatic tire having two sidewalls, an outer layer and an inner layer.

Since the sidewall that supports the load of the tire is distorted by being bent, minute cracks are likely to occur on the sidewall surface. These minute cracks on the surface are likely to occur at the buttress portion and the bead portion having a large strain, and when the minute cracks occur, they grow by running. In the case of a heavy-duty tire, it is necessary to suppress the occurrence of minute cracks particularly in the sidewall in order to carry out retreading (rehabilitation) by attaching a tread again after the tire wear ends.

As a method for preventing the occurrence of microcracks, a tire is known in which the sidewall portion of the tire is covered with a thin layer made of ethylene propylene rubber or halogenated butyl rubber (Patent Document 1). However, there is a problem that these rubbers are expensive and lead to cost increase.

Further, as a rubber composition for a sidewall, a method is known in which the ratio of natural rubber to butadiene rubber in the rubber component is increased from 60/40 to increase the ratio of butadiene rubber having good bending fatigue performance to 50/50. . However, there is a problem that the destructive energy is lowered and the cut-resistant performance is lowered as a heavy load tire.

On the other hand, thinning the sidewall gauge is effective for cost reduction, but there is a problem that it is difficult to implement because the cut resistance is lowered.

JP-A-2-45202

An object of the present invention is to provide a heavy duty pneumatic tire that suppresses the cost while preventing the occurrence of microcracks on the sidewall surface.

The present invention is a heavy duty pneumatic tire having a sidewall composed of two layers, an outer layer and an inner layer, wherein the outer layer contains 10% by mass or more of ethylene propylene rubber and 20% by mass or more of butyl rubber in a rubber component. It consists of a rubber composition and has an average thickness of 0.5 mm or more, and the inner layer relates to a heavy duty pneumatic tire made of a rubber composition containing 60% by mass or more of natural rubber in a rubber component.

The outer layer is preferably made of a rubber composition containing 10 to 20% by mass of ethylene propylene rubber and 20 to 40% by mass of butyl rubber in the rubber component.

The thickness of the outer layer is preferably 0.5 to 1.5 mm.

The inner layer is preferably made of a rubber composition in which the content of the antioxidant is 2.0 parts by mass or less with respect to 100 parts by weight of the rubber component.

The thickness at the thinnest portion of the sidewall is preferably 4.5 to 5.5 mm.

The heavy-duty pneumatic tire preferably has a carcass ply or breaker made of a steel cord.

According to the present invention, two layers of an outer layer made of a rubber composition containing a specific amount of ethylene propylene rubber and butyl rubber and having an average thickness of 0.5 mm or more and an inner layer made of a rubber composition containing a specific amount of natural rubber Since it is a heavy-duty pneumatic tire having a sidewall, it is possible to provide a heavy-duty pneumatic tire with reduced costs while preventing the occurrence of microcracks on the sidewall surface.

(A) is sectional drawing of the side wall part of the pneumatic tire for heavy loads in this invention, (b) is the figure which expanded the area | region X. FIG.

The heavy-duty pneumatic tire of the present invention has a sidewall composed of two layers, an outer layer and an inner layer, and the outer layer contains a rubber component containing 10% by mass or more of ethylene propylene rubber and 20% by mass or more of butyl rubber. It consists of a composition, and an average thickness is 0.5 mm or more, and this inner layer consists of a rubber composition which contains 60 mass% or more of natural rubber in a rubber component. Here, as shown in the cross-sectional view of the tire in FIG. 1, the outer layer and the inner layer of the sidewall are 1, and 2 is the sidewall inner layer.

The outer layer of the sidewall is made of a rubber composition containing 10% by mass or more of ethylene propylene rubber and 20% by mass or more of butyl rubber in 100% by mass of the rubber component. 10-20 mass% is preferable and, as for content of ethylene propylene rubber, 12-18 mass% is more preferable. If it exceeds 20% by mass, the cost increases, and if it is less than 10% by mass, the occurrence of microcracks on the sidewall surface tends to increase. Moreover, 20-40 mass% is preferable and, as for content of butyl rubber, 25-37 mass% is more preferable. When it exceeds 40% by mass, the processability of the sidewall is deteriorated, and when it is less than 20% by mass, the occurrence of micro cracks on the sidewall surface tends to increase. Here, ethylene propylene rubber includes ethylene propylene diene rubber, and butyl rubber includes halogenated butyl rubber.

As the rubber component of the outer layer, in addition to ethylene propylene rubber and butyl rubber, other rubber components can be blended. Other rubber components include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile butadiene rubber ( A diene rubber such as NBR) can be preferably used. Among these, it is preferable to use natural rubber and butadiene rubber in combination.

In the rubber composition used for the outer layer, the content of the natural rubber in 100% by mass of the rubber component is preferably 20 to 40% by mass, and more preferably 22 to 35% by mass. If it exceeds 40% by mass, the occurrence of microcracks on the sidewall surface increases, and if it is less than 20% by mass, the cut resistance of the sidewall tends to deteriorate. The content of butadiene rubber in 100% by mass of the rubber component is preferably 20 to 30% by mass, and more preferably 22 to 27% by mass. If it exceeds 30% by mass, the cut-off performance of the sidewall is deteriorated, and if it is less than 20% by mass, the occurrence of micro cracks on the sidewall surface tends to increase.

In addition to rubber components such as ethylene propylene rubber and butyl rubber, a filler such as carbon black or silica, or a silane coupling agent may be blended in the rubber composition used for the outer layer. The filler content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, sufficient reinforcing properties tend not to be obtained. Further, the filler content is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, and still more preferably 20 parts by mass or less with respect to 100 parts by mass of the rubber component. If it exceeds 100 parts by mass, the fuel efficiency tends to deteriorate.

Further, in the outer layer, in addition to the rubber component, filler component, and coupling agent, compounding agents generally used in the production of rubber compositions, for example, oils such as zinc oxide, stearic acid, various anti-aging agents, and aroma oil Further, vulcanizing agents such as wax and sulfur, vulcanization accelerators and the like can be appropriately blended.

The average thickness of the outer layer is preferably 0.5 mm or more, more preferably 0.5 to 1.5 mm, and even more preferably 0.8 to 1.2 mm. If it is less than 0.5 mm, the rubber is sucked up by the air vent hole (Max.φ1.5 mm) in the sidewall portion at the time of manufacturing the tire, and the sidewall of the inner layer comes out on the tire surface, so that it becomes a base point of surface cracks. On the other hand, if it exceeds 1.5 mm, it is a special rubber and is more expensive than a normal side wall composition, so that the cost tends to increase. Moreover, since generation | occurrence | production of the micro crack on the side wall surface can be prevented by outer layer rubber, it becomes possible to reduce the compounding quantity of the anti-aging agent mix | blended with inner layer rubber, and can suppress cost.

The rubber composition used for the inner layer of the sidewall contains 60% by mass or more of natural rubber in 100% by mass of the rubber component. The content of natural rubber is preferably 63% by mass or more. The upper limit is not particularly limited, but is preferably less than 80% by mass. By setting the content of the natural rubber to 60% by mass or more, the destruction energy can be increased and the cut resistance can be improved.

In the present invention, in particular, one of the major features of the present invention is that the content of natural rubber in the rubber component used in the inner layer is 60% by mass or more. In general, when the ratio of natural rubber is decreased and the ratio of other rubber components such as butadiene rubber is increased, the occurrence of minute cracks on the sidewall surface is reduced and the weather resistance is improved. Therefore, in a general passenger car tire, the blending amount of natural rubber is as low as 40% by mass. However, in the case of a heavy-duty tire, an extremely large load is applied as compared with a passenger car tire, it is easily cut by an external force, and cannot be used if the ratio of natural rubber remains low. For example, in the composition of natural rubber and butadiene rubber, assuming that the fracture energy when the content of natural rubber is 50% by mass is 100, the content of natural rubber is 87 when the content of natural rubber is 40% by mass. When the content is 60% by mass, 118 is obtained. When the content of natural rubber is 40% by mass, the fracture energy is very low, and it can be understood that it is very severe for heavy duty tires. Here, the breaking energy was determined by performing a tensile test using a No. 3 dumbbell-shaped specimen of vulcanized rubber according to JIS K 6251 “Tensile test method for vulcanized rubber” and determining the tensile strength (TB) and elongation at break ( The fracture energy can be calculated from the formula (EB) to TBXEB / 2.

Therefore, in the present invention, for the inner layer, a rubber composition in which the blending amount of natural rubber is intentionally increased is used, and minute cracks generated on the side wall surface caused by increasing the blending amount of natural rubber are removed from the outer layer. It is improved by using a rubber composition with good weather resistance, and the cutting performance by the external force of the sidewall is improved.

As the rubber component of the inner layer, other rubber components can be blended in addition to natural rubber. Other rubber components include isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), etc. Rubber can be preferably used. Among these, it is preferable to use butadiene rubber in combination.

In the rubber composition used for the inner layer, the content of butadiene rubber in 100% by mass of the rubber component is preferably 20 to 40% by mass, and more preferably 25 to 35% by mass. When it exceeds 40% by mass, the fracture energy decreases, and when it is less than 20% by mass, the bending performance of rubber tends to decrease.

In the rubber composition used for the inner layer, the content of the anti-aging agent is preferably 2.0 parts by mass or less and more preferably 1.0 part by mass or less with respect to 100 parts by mass of the rubber component. Although it does not specifically limit about a minimum, 0.5 mass part or more is preferable and 1.0 mass part or more is more preferable. If the blending amount of the anti-aging agent exceeds 2.0 parts by mass, the cost tends to increase, and if it is less than 0.5 parts by mass, the anti-aging performance of the rubber tends to decrease.

In addition to the rubber component and the antioxidant, the rubber composition used for the inner layer may contain a filler such as carbon black or silica, or a silane coupling agent. 40-60 mass parts is preferable with respect to 100 mass parts of rubber components, and, as for content of a filler, 45-55 mass parts is more preferable. If the amount is less than 40 parts by mass, sufficient reinforcing properties tend not to be obtained. Moreover, when it exceeds 60 mass parts, there exists a tendency for the bending performance of rubber | gum to become small.

In the inner layer, in addition to the above components, compounding agents generally used in the production of rubber compositions, such as zinc oxide, stearic acid, various anti-aging agents, oils such as aroma oil, vulcanizing agents such as wax and sulfur, A vulcanization accelerator or the like can be appropriately blended.

In the heavy duty pneumatic tire of the present invention, the thickness of the thinnest portion of the sidewall is preferably 4.5 to 5.5 mm, more preferably 4.5 to 5.0 mm. When it is less than 4.5 mm, the cutting performance of the sidewall is lowered, and when it exceeds 5.5 mm, the cost tends to increase. Here, the thickness at the thinnest portion of the sidewall refers to the total thickness of the inner layer and the outer layer at the thinnest portion of the two-layer sidewall.

In the heavy duty pneumatic tire of the present invention, it is preferable to have a carcass ply or breaker made of a steel cord in order to use the tread again after the tire has been worn.

The rubber composition for the outer layer and inner layer of the side wall described above is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing. Next, the obtained rubber composition is extruded in accordance with the shape of the tire sidewall and the like at an unvulcanized stage, molded by a normal method on a tire molding machine, and together with other tire members Bonding to form an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

The pneumatic tire of the present invention is suitably used as a heavy duty pneumatic tire for buses, trucks, etc., because a special rubber excellent in weather resistance is disposed on the sidewall outer layer to prevent the occurrence of micro cracks on the sidewall surface. Can be used.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Natural rubber: TSR20
Butadiene rubber: Ubepol BR150B manufactured by Ube Industries, Ltd.
Butyl rubber: Exon Chlorobutyl 1066 manufactured by ExxonMobil Co., Ltd.
EPDM: ESPRENE 502 manufactured by Sumitomo Chemical Co., Ltd. (copolymer of 56% by mass of ethylene, 40% by mass of propylene, and 4% by mass of 5-ethylidene-2-norbornene)
Carbon black 1: N660 made by Tokai Carbon Co., Ltd.
Carbon black 2: N330 manufactured by Tokai Carbon Corporation
Process oil: Diana Process P32 made by Idemitsu Kosan Co., Ltd.
Wax: Sannoc Wax anti-aging agent manufactured by Ouchi Chemical Co., Ltd .: Ozonon 6C manufactured by Seiko Chemical Co., Ltd.
Zinc oxide: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Beads Tsubaki stearate manufactured by NOF Corporation: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Ouchi Chemical Co., Ltd. Noxeller DM made

Examples 1-7, Comparative Examples 1-5 and Reference Example 1
According to the composition shown in Tables 1 and 2, using a 1.7 L Banbury mixer, among the blended materials, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. to obtain a kneaded product. . Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 3 minutes at 80 ° C. using a biaxial open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition is molded into the shape of the sidewall outer layer and the inner layer, bonded together with other tire members on a tire molding machine, and vulcanized at 150 ° C. for 30 minutes, thereby testing a heavy duty tire. (Size: 11R22.5) was manufactured.

The following evaluation was performed using the obtained test tire, and the results are shown in Table 2.

(Crack test)
After running the tire under the following conditions, the presence or absence of cracks was visually observed.
Tire running condition load: Standard maximum load internal pressure: Standard maximum internal pressure -100 kPa
Speed: 40km / h
Ozone concentration: 50 pphm
Traveling time: 600 hours Evaluation criteria 1: No cracking 2: Cracks are visible when the tire is rubbed 3: Cracks are visible 4: Cracks are conspicuous but not connected to the vicinity 5: At the time of retreading in the market, the claim becomes retread Impossible level

(Sidewall cut index)
The number of cuts generated on both side portions of the sidewall of the tire after running the road test 100,000 km was counted, and the number of cuts per tire was indexed with the number of cuts of the tire of Comparative Example 1 being 100. The smaller the numerical value, the smaller the number of cuts and the better.

(cost)
The costs of the rubber composition of the outer layer and the inner layer of Example 1 were set to 100, and the cost of the rubber composition of the outer layer and the inner layer of each compounding was indexed.
(Overall cost index) =
(Cost index of outer layer) × (ratio of SW outer layer thickness to total SW thickness) + (cost index of inner layer) × (ratio of SW inner layer thickness to total SW thickness)

As can be seen from Table 2, when the sidewall is composed of one layer, cracks are often generated and the cut property is poor. Even when the sidewall is composed of two layers, when the content of the natural rubber in the rubber composition used for the inner layer is small, cracks are frequently generated and the cut property is also inferior. Even when the blending amount of natural rubber is 60% by mass or more, cracks increase when the ratio of the butadiene rubber as the rubber component in the rubber composition used for the outer layer is small or when the outer layer is thin. .

On the other hand, in the tire of the present invention in which the outer layer and the inner layer have a specific composition and the outer layer has a specific thickness, as in Examples 1 to 7, the generation of cracks was small and the cut property was excellent. The cost was also good.

1 2 layer sidewall outer layer 2 2 layer sidewall inner layer 3 carcass ply T ₁ 2 layer sidewall inner layer thickness T ₂ 2 layer sidewall outer layer thickness

Claims (6)

A heavy-duty pneumatic tire having a sidewall composed of two layers, an outer layer and an inner layer,
The outer layer is made of a rubber composition containing 10% by mass or more of ethylene propylene rubber and 20% by mass or more of butyl rubber in the rubber component, and has an average thickness of 0.5 mm or more.
The inner layer is a heavy duty pneumatic tire made of a rubber composition containing 60% by mass or more of natural rubber in a rubber component. The heavy-duty pneumatic tire according to claim 1, wherein the outer layer comprises a rubber composition containing 10 to 20% by mass of ethylene propylene rubber and 20 to 40% by mass of butyl rubber in a rubber component. The heavy-duty pneumatic tire according to claim 1 or 2, wherein the outer layer has a thickness of 0.5 to 1.5 mm. The heavy-duty pneumatic tire according to any one of claims 1 to 3, wherein the inner layer is made of a rubber composition having an antioxidant content of 2.0 parts by mass or less with respect to 100 parts by weight of the rubber component. The heavy-duty pneumatic tire according to any one of claims 1 to 4, wherein the thinnest portion of the sidewall has a thickness of 4.5 to 5.5 mm. The heavy duty pneumatic tire according to any one of claims 1 to 5, comprising a carcass ply or a breaker made of a steel cord.

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