JP7131052B2 - RUBBER COMPOSITION FOR RIM CUSHION AND HEAVY-LOAD PNEUMATIC TIRE USING SAME - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rim cushion rubber composition that exhibits excellent durability when the rim is attached and detached, and a heavy-duty pneumatic tire using the same.

A bead portion of a pneumatic tire is provided with a rim cushion as an outer layer so as to be in close contact with the rim when the tire is mounted on the rim. This rim cushion must be in close contact with the rim flange to prevent the rim from slipping from the rim and to maintain air sealing performance. However, the rim cushion suffers from the problem of reduced durability due to the occurrence of cracks due to the compression force and heat generated from the rim, and the occurrence of fatigue due to repeated deformation.

Heavy-duty tires mounted on trucks, buses, and construction vehicles are used as retread tires for multiple uses by retreading when the tread is worn. As for the durability of a heavy-duty tire, the belt portion and the bead portion that come into contact with the rim, which constitute the tire, are important. A rim cushion with high rubber hardness is used in the bead portion to suppress deformation, and as described above, this rim cushion rubber may deteriorate due to heat and fatigue from the rim, and the breaking elongation may decrease. As a result, chipping may occur when attaching and detaching from the rim, and even if retreading is performed, the tire cannot be used as a retreaded tire. In addition, if there is a failure such as a crack in the bead portion, there is concern that the safety of the tire will be impaired.

Patent Document 1 discloses a rubber composition containing 40 to 60 parts by mass of carbon black having a nitrogen adsorption specific surface area of 90 m ² /g or more per 100 parts by mass of a rubber component and a sulfenamide-based vulcanization accelerator. It is proposed to improve the crack resistance by using However, considering the use as a retreaded tire, it is required to further improve the durability when the rim is attached and detached.

JP 2005-171016 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a rubber composition for a rim cushion which has excellent aging resistance and has improved durability when the tire is attached to and removed from the rim, and a heavy-duty pneumatic tire using the same.

The rubber composition for a rim cushion of the present invention, which achieves the above objects, comprises 100 parts by mass of a diene rubber containing 10 to 30 mass % of natural rubber or isoprene rubber and 70 to 90 mass % of butadiene rubber, and having a nitrogen adsorption specific surface area. 50 to 80 parts by mass of carbon black of 75 to 130 [×10 ³ m ² /kg], A parts by mass of a sulfenamide-based vulcanization accelerator, and S parts by mass of sulfur are blended, and the sulfenamide-based vulcanization is performed. The ratio A/S of the blending amount A of the accelerator and the blending amount S of sulfur is 3.0 or more and 3.2 or less, and the tensile elongation at break at 20° C. is 300% or more .
Further, the pneumatic tire of the present invention is characterized by having a rim cushion made of a rubber composition for a rim cushion.

Since the rubber composition for a rim cushion of the present invention has the structure described above, it is excellent in aging resistance, and can improve the durability at the time of attaching and detaching to the rim beyond the conventional level. In addition, it has the rubber hardness required for a rim cushion of a heavy-duty pneumatic tire, reduces heat generation, makes it difficult to reach a high temperature, and suppresses thermal aging.
In the heavy-duty pneumatic tire of the present invention, the rim cushion is made of a rubber composition for a rim cushion that is excellent in aging resistance and durability. is useful as

The rim cushion rubber composition preferably has a tensile elongation at break of 250% or more after being heated at 100° C. for 48 hours. Further, it is preferable that the tensile elongation at break at 20°C is 300% or more. This makes it possible to improve aging resistance and durability when attaching/detaching the rim.
Moreover, the pneumatic tire of the present invention is preferably a retreaded tire having a nominal tire diameter of 19 inches or more.

FIG. 2 is a cross-sectional view illustrating the configuration of a bead portion of a heavy-duty pneumatic tire;

The rim cushion rubber composition of the present invention is suitable for heavy-duty pneumatic tires for trucks, buses, construction vehicles, and the like. It is particularly suitable for constructing a portion of the bead portion of a heavy-duty pneumatic tire that contacts the rim, that is, a rim cushion.

FIG. 1 is an explanatory diagram illustrating a cross-sectional configuration of a bead portion of a heavy-duty pneumatic tire mounted on a truck or bus. A rim R on which a heavy-duty pneumatic tire is mounted is indicated by a dashed line. In FIG. 1, 1 indicates a bead portion and 2 indicates a sidewall portion. A carcass layer 5 formed by arranging a plurality of steel cords is mounted between the right and left bead portions 1 of a pneumatic tire for trucks and buses. The carcass layer 5 is wound up from the inside of the tire to the outside around a pair of left and right bead cores 3 embedded in the bead portion 1 . A fiber reinforcing layer 8 formed by arranging a plurality of steel cords is arranged along the carcass layer 5 in the bead portion 1 . A lower bead filler 4a is arranged outside the bead core 3 in the tire radial direction, and an upper bead filler 4b is arranged adjacent to the lower bead filler 4a. Also, a gum finishing 7 is arranged on the inner surface of the bead portion 1 in the tire radial direction, and a rim cushion 6 is arranged on the outer surface of the bead portion 1 in the tire width direction. It is configured to be in close contact with the rim R when the tire is mounted on the rim.

In this specification, the terms rim cushion and gum finishing are not limited to members with such names, but other names for the portion of the bead that contacts the rim, as illustrated in FIG. shall also include members of The rim cushion and gum finishing can be constructed independently as illustrated above. Also, the rim cushion and the gum finishing can be constructed integrally. The name of the integrally constructed member of the rim cushion and gum finishing may be rim cushion, gum finishing or other names. The rubber composition for rim cushions of the present invention is suitably used for rim cushions and/or gum finishing.

In the rubber composition for a rim cushion, the diene rubber comprises natural rubber or isoprene rubber and butadiene rubber as essential components. The content of the butadiene rubber is 60 to 90% by mass, preferably 70 to 88% by mass, based on 100% by mass of the diene rubber. If the butadiene rubber content is less than 60% by mass, the tensile elongation at break after heat aging cannot be sufficiently improved. Also, if the butadiene rubber content exceeds 90% by mass, when retreading a tire that has been running for a long time, there is a risk that the bead portion may be chipped or cracked when the tire is attached to or detached from the rim. As the butadiene rubber, a butadiene rubber commonly used in rubber compositions for tires can be used.

The content of natural rubber and isoprene rubber is 10 to 40% by mass, preferably 12 to 30% by mass, based on 100% by mass of the diene rubber. If the content of natural rubber and isoprene rubber is less than 10% by mass, the bead portion may be chipped or cracked when retreading a tire that has been running for a long period of time. Moreover, if the natural rubber and isoprene rubber exceed 40% by mass, the tensile elongation at break after heat aging cannot be sufficiently improved. As natural rubber and isoprene rubber, natural rubber and isoprene rubber that are commonly used in rubber compositions for tires can be used.

The carbon black compounded in the rim cushion rubber composition has a nitrogen adsorption specific surface area of 75 to 130 [×10 ³ m ² /kg], preferably 90 to 120 [×10 ³ m ² /kg]. If the nitrogen adsorption specific surface area is less than 75 [×10 ³ m ² /kg], the rubber hardness is insufficient, the breaking elongation after heat aging is lowered, and the durability of the bead portion cannot be sufficiently improved. On the other hand, when the nitrogen adsorption specific surface area exceeds 130 [×10 ³ m ² /kg], the tensile elongation at break after heat aging cannot be sufficiently improved due to the increase in heat build-up. The nitrogen adsorption specific surface area can be measured according to JIS K6217-2. Such carbon black can be appropriately selected from HAF grade, ISAF grade, and SAF grade carbon black and used.

The amount of carbon black compounded is 50 to 90 parts by mass, preferably 60 to 80 parts by mass, per 100 parts by mass of the diene rubber. If the carbon black is less than 50 parts by mass,
The lack of rubber hardness reduces the breaking elongation after heat aging, and when retreading a tire that has been running for a long time, there is a risk that the bead part may be chipped or cracked when it is attached to or removed from the rim. On the other hand, if the carbon black exceeds 90 parts by mass, the heat generation becomes high, the temperature tends to be high, and the elongation at break after heat aging decreases, and when retreading a tire that has been running for a long time, the bead when detaching from the rim. There is a risk that parts may be chipped or cracked.

The rim cushion rubber composition may contain a reinforcing filler other than carbon black. Examples of reinforcing fillers include silica, clay, calcium carbonate, talc and mica. In particular, it is preferable to blend silica. By blending silica, the heat build-up of the rubber composition can be further reduced, heat aging can be suppressed, and the rolling resistance when made into a tire can be further reduced.

A rim cushion rubber composition contains a sulfenamide-based vulcanization accelerator and sulfur. When the compounding amount of the sulfenamide vulcanization accelerator is A parts by mass and the compounding amount of sulfur is S parts by mass, the ratio A/S of the compounding amounts of the sulfenamide vulcanization accelerator and sulfur is 2. It is more than 0 and 3.2 or less, preferably 2.1 to 3.1, more preferably 2.2 to 3.0. If the compounding amount ratio A/S is 2.0 or less, the elongation at break after heat aging decreases, and when retreading a tire that has been running for a long time, the bead portion may be chipped or cracked when it is attached to or removed from the rim. There is a risk of Even if the ratio A/S exceeds 3.2, the elongation at break after heat aging is reduced, and when retreading a tire that has been running for a long time, the bead may be chipped or cracked when it is attached to or removed from the rim. There is

Sulfenamide-based vulcanization accelerators include, for example, N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide (DZ), N-cyclohexyl-2-benzothiazolesulfenamide (CZ), N -oxydiethylene-2-benzothiazolesulfenamide (OBS), N-(tert-butyl)benzothiazole-2-sulfenamide (NS). These sulfenamide-based vulcanization accelerators can be blended singly or in combination. Among them, N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide (DZ) and/or N-(tert-butyl)benzothiazole-2-sulfenamide (NS) are preferred.

Various additives commonly used in tire rubber compositions, such as vulcanizing or cross-linking agents, vulcanization accelerators, various oils, anti-aging agents, and plasticizers, may be added to the rim cushion rubber composition. and such additives can be compounded by conventional methods into rubber compositions and used to vulcanize or crosslink. The blending amount of these additives can be a conventional general blending amount as long as it does not contradict the object of the present invention. The rubber composition for a rim cushion of the present invention can be produced by mixing the above components using a conventional rubber kneading machine such as a Banbury mixer, a kneader, and a roll.

The rim cushion rubber composition preferably has a tensile elongation at break of 300% or more, more preferably 350 to 500% at 20°C. When the tensile elongation at break at 20°C is 300% or more, it is possible to suppress tire failure during rim assembly. As used herein, the tensile elongation at break is the tensile elongation at break when a tensile test is performed in accordance with JIS K6251 using a JIS No. 3 dumbbell-shaped test piece at a temperature of 20 ° C. and a test speed of 500 mm / min. .

The rubber composition for a rim cushion preferably has a tensile elongation at break of 250% or more, more preferably 300 to 450% at 20°C when a tensile test piece heated at 100°C for 48 hours is used. When the tensile elongation at break after heat aging at 100°C for 48 hours is 250% or more, when retreading a tire whose tread has worn out due to long-term use, tire failure during rim assembly can be suppressed. In the tensile test after heat aging treatment, the condition adjustment described in JIS K6251 is performed after heat aging treatment, and the tensile elongation at break at 20°C is measured by the above method.

The retention of the tensile elongation at break after heat treatment at 100° C. for 48 hours relative to the tensile elongation at break before heat treatment is preferably 80% or more, more preferably 85 to 100%. By setting the retention rate of the tensile elongation at break after heat treatment to 80% or more, it is possible to improve the rim assembly performance when retreading a tire that has been running for a long time beyond the conventional level.

The rubber composition for a rim cushion of the present invention is suitably used for the portion of the bead portion of a pneumatic tire that contacts the rim, that is, the rim cushion. A pneumatic tire having a rim cushion made of the rubber composition for a rim cushion of the present invention is made of a rubber composition having excellent aging resistance and durability. , useful as a retread tire. In addition, the pneumatic tire of the present invention can be used as a heavy-duty tire mounted on trucks, buses, and construction vehicles having a tire nominal diameter of 19 inches or more. It is expensive, and the retread tire can be manufactured multiple times.
EXAMPLES The present invention will be further described with reference to examples below, but the scope of the present invention is not limited to these examples.

In preparing 10 types of rubber compositions (Examples 1 to 3, Comparative Examples 1 to 7) having the formulations shown in Table 1, each component except sulfur and vulcanization accelerator was weighed, and 1.7 L closed type After kneading in a Banbury mixer for 5 minutes, the masterbatch was discharged and allowed to cool to room temperature. This masterbatch was supplied to a 1.7 L internal Banbury mixer, sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition. The ratio A/S of the blending amount A of the sulfenamide vulcanization accelerator and the blending amount S of sulfur is shown in the column "ratio A/S of blending amount" in the middle of the table.

The rubber composition obtained above was press-vulcanized at 150° C. for 30 minutes using a mold of a predetermined shape to prepare a test piece. Using the obtained test pieces, rubber hardness, heat build-up, tensile elongation at break, and tensile elongation at break after heat aging were evaluated by the following test methods. In addition, the following method was used to evaluate the rim assembly performance when retreading a tire that had been vulcanized and had a worn tread after running for a long period of time.

Rubber Hardness The rubber hardness of the test piece obtained above was measured at a temperature of 20° C. using a durometer type A according to JIS K6253. The obtained results are shown in the "rubber hardness" column of Table 1 as an index with the value of Comparative Example 1 set to 100. A higher index means higher rubber hardness and higher tire durability.

Exothermicity (tan δ at 60°C)
The dynamic viscoelasticity of the test piece obtained above was measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. at an initial strain of 10%, an amplitude of ±2%, and a frequency of 20 Hz, and tan δ at a temperature of 60 ° C. was calculated. did. The obtained results are shown in the column of "Pyrogenicity" in Table 1 as indices with the value of Comparative Example 1 being 100. A smaller index means a smaller tan δ at 60° C. and a lower heat build-up.

Tensile elongation at break (20°C)
Using the test piece obtained above, a JIS No. 3 dumbbell-shaped test piece was cut out according to JIS K6251. The tensile elongation at break was measured under the conditions of a temperature of 20° C. and a tensile speed of 500 mm/min. The obtained results are described in the column of "elongation at break (20°C)" in Table 1. It means that the higher the tensile elongation at break at 20°C, the more excellent the durability of the rim assembly.

Tensile elongation at break after heat aging Using the test piece obtained above, a JIS No. 3 dumbbell-shaped test piece was cut out according to JIS K6251. These dumbbell-shaped specimens were placed in a gear oven at 100° C. in air for 48 hours for heat aging treatment. After the heat-aged test piece was conditioned according to JIS K6251, the tensile elongation at break at 20°C was measured by the method described above. The obtained results are shown in Table 1, "Breaking elongation after heat aging". It means that the higher the tensile elongation at break after heat aging, the better the aging resistance, and the better the durability of the rim assembly even after long-term use.

Retention Rate of Tensile Elongation at Break after Heat Aging The retention rate of the tensile elongation at break of the test piece subjected to heat aging was calculated relative to the tensile elongation at break of the test piece obtained above without heat aging. The obtained results are shown in the column of "retention rate of elongation at break" in Table 1. A higher retention rate of elongation at break means better aging resistance and better durability of the rim assembly even after long-term use.

Rim Assemblability During Retreading A heavy-duty pneumatic tire (size 11R22.5) using the obtained rubber composition for a rim cushion was vulcanized and molded. The obtained pneumatic tire for heavy loads was mounted on a rim specified by JATMA, mounted on a truck with a load capacity of 4 tons, and run for two years. After the running test, the heavy-duty pneumatic tire was removed from the rim, and the state of the rim cushion was visually observed when the rim was reassembled, and a score was given based on the following criteria.
3: No damage to the rim cushion is observed.
2: A crack was observed in a part of the rim cushion.
1: Part of the rim cushion was peeled off and missing.

The types of raw materials used in Table 1 are shown below.
・NR: natural rubber, STR-20
・ BR: butadiene rubber, Nipol BR 1220 manufactured by Nippon Zeon Co., Ltd.
Carbon black-1: ISAF grade carbon black, Niteron #300 manufactured by Shin Nikka Carbon Co., Ltd., nitrogen adsorption specific surface area of 110 m ² /g
・Carbon black-2: FEF grade carbon black, Niteron #10N manufactured by Shin Nikka Carbon Co., Ltd., nitrogen adsorption specific surface area of 42 m ² /g
・Aroma oil: Extract No. 4 S manufactured by Showa Shell Sekiyu K.K.
・ Zinc white: 3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. ・ Stearic acid: YR stearate manufactured by NOF Corporation
・Sulfur: Karuizawa Smelting & Refining Co., Ltd. Oil refining sulfur ・Vulcanization accelerator: N-cyclohexyl-2-benzothiazolylsulfenamide, Ouchi Shinko Kagaku Co., Ltd. Noxcellar CZ-G (CZ)

As is clear from Table 1, the rubber compositions for rim cushions of Examples 1 to 3 have rubber hardness, low heat build-up, initial tensile elongation at break, tensile elongation at break after heat aging treatment, and tensile break after heat aging treatment. It was confirmed that the elongation retention rate is excellent, and the rim assembly durability during retreading of heavy-duty tires is also excellent.

In the rim cushion rubber composition of Comparative Example 2, the ratio A/S of the compounding amounts of the sulfenamide vulcanization accelerator and sulfur was less than 2.0, so the tensile elongation at break after heat aging and its retention rate were is inferior. In addition, the rim assembly durability during retreading of the heavy-duty tire is inferior.
In the rim cushion rubber composition of Comparative Example 3, the ratio A/S of the compounded amounts of the sulfenamide vulcanization accelerator and sulfur exceeded 3.2, so the tensile elongation at break after heat aging and its retention rate were as follows: Inferior. In addition, the rim assembly durability during retreading of the heavy-duty tire is inferior.
The rubber composition for a rim cushion of Comparative Example 4 contains less than 10 parts by mass of natural rubber and more than 90 parts by mass of butadiene rubber, and therefore has poor rim assembly durability during retreading of a heavy-duty tire.
Since the rubber composition for a rim cushion of Comparative Example 5 contained less than 50 parts by mass of carbon black, the rubber hardness was low, and the tensile elongation at break after heat aging and its retention rate were poor. In addition, the rim assembly durability during retreading of the heavy-duty tire is inferior.
Since the rubber composition for a rim cushion of Comparative Example 6 contains more than 90 parts by mass of carbon black, it has high heat build-up, and is inferior in tensile elongation at break after heat aging and retention thereof. In addition, the rim assembly durability during retreading of the heavy-duty tire is inferior.
In the rim cushion rubber composition of Comparative Example 7, the carbon black-2 has a nitrogen adsorption specific surface area of less than 75 [×10 ³ m ² /kg], so that it has a high heat build-up, a tensile elongation at break after heat aging and a Poor retention. In addition, the rim assembly durability during retreading of the heavy-duty tire is inferior.

Claims (4)

Carbon black having a nitrogen adsorption specific surface area of 75 to 130 [×10 ³ m ² /kg] is added to 100 parts by mass of diene rubber containing 10 to 30% by mass of natural rubber or isoprene rubber and 70 to 90% by mass of butadiene rubber. 50 to 80 parts by mass, A parts by mass of a sulfenamide vulcanization accelerator, and S parts by mass of sulfur are blended, and the ratio of the amount A of the sulfenamide vulcanization accelerator to the amount S of sulfur is A/ A rubber composition for a rim cushion, wherein S is 3.0 or more and 3.2 or less, and the tensile elongation at break at 20°C is 300% or more . The rubber composition for a rim cushion according to claim 1, which has a tensile elongation at break of 250% or more after being heated at 100°C for 48 hours. A heavy duty pneumatic tire having a rim cushion made of the rubber composition for a rim cushion according to claim 1 or 2 . The heavy-duty pneumatic tire according to claim 3 , which is a retreaded tire having a tire nominal diameter of 19 inches or more.

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