JP5148374B2 - Rubber composition for chafer pad and pneumatic radial tire - Google Patents

Description

  The present invention relates to a rubber composition used for a chafer pad provided in a bead portion of a pneumatic radial tire, and a pneumatic radial tire using the rubber composition.

  Generally, in a pneumatic radial tire, both end portions of a carcass are wound around a bead core and locked at a bead portion. In order to protect the carcass winding portion, a chafer formed by coating an organic fiber material such as nylon, a steel cord, or the like with rubber may be provided in the bead portion (for example, see Patent Document 1 below).

  Such a failure of the bead portion having a chafer is caused by a rubber portion called a chafer pad interposed between the chafer and the rim strip on the outer side in the tire axial direction of the bead filler. . That is, when the chafer pad is greatly deformed, the rubber is sagged, which may cause separation at the interface between the chafer edge and the coating rubber or in the rubber near the chafer (for example, bead filler). . Further, there is a problem that heat is accumulated due to compression deformation of the chafer pad to promote deterioration of rubber, or ozone cracks are generated near the rim line in the rim strip. Therefore, in the chafer pad, rigidity and low exothermic property (being difficult to generate heat) must be considered.

  As for the rigidity of the chafer pad, if it becomes harder than the bead filler in the vicinity thereof, stress is concentrated on the chafer pad, which may cause separation at the chafer end. Moreover, if it is too soft for the bead filler, ozone cracks may occur due to heat generated by bending. Therefore, for the chafer pad, the balance of rigidity with the bead filler is important.

  On the other hand, as a method for improving the low heat generation property of the chafer pad, there is a method of blending a large amount of natural rubber. However, the chafer pad has a thin gauge at the time of extrusion at the time of production, and therefore, when a large amount of natural rubber is blended, there is a problem in processability such as edge breakage and bad rubber skin. Although it is conceivable to use a processing aid to improve the workability, when a general processing aid is added, the workability is improved, but there is a problem that the low heat build-up deteriorates, and the low heat generation It is required to satisfy both properties and workability at the same time.

In addition, in Patent Documents 2 to 4 below, in order to improve the durability of the bead portion, a proposal for a rubber composition constituting the rubber member in the bead portion has been made. The use of processing aids is not disclosed.
JP 2008-69207 A JP 2007-23070 A JP-A-2005-219606 Japanese Patent Laid-Open No. 2001-261887

  The present invention has been made in view of the above points, and provides a rubber composition for a chafer pad that can satisfy low heat buildup and workability at the same time and can improve the durability of a bead portion. The purpose is to do.

  The present invention provides a bead core embedded in a bead portion, a carcass wound around and locked around the bead core, a bead filler provided on a radially outer side of the bead core, and the carcass around the bead core. A pneumatic radial tire comprising: a chafer disposed so as to wrap the tire from the inner side in the tire radial direction; and a rim strip constituting a bead portion outer surface portion including a portion in contact with the wheel rim. In a rubber composition for a chafer pad used for a chafer pad interposed between an outer portion in the tire axial direction of the chafer and the rim strip arranged along a side surface, at least 80 parts by weight of natural rubber Carbon black and silica for 100 parts by weight of diene rubber component It is related with the rubber composition for chafer pads which mix | blended 50-70 weight part which consists of at least one of these, and 0.5-3.0 weight part of processing aids of the fatty acid metal salt containing the peptizer. .

  The present invention also relates to a pneumatic radial tire provided with a chafer pad using the rubber composition, and the chafer pad is measured at 23 ° C. according to JIS K6253 (durometer type A). The rubber hardness is preferably in the range of +2 to −7 with respect to the rubber hardness of the bead filler.

  According to the present invention, in the rubber applied to the chafer pad, by using a specific processing aid having an effect of promoting mastication together with the specific diene rubber component and filler, low heat build-up and processability are achieved. Can be improved at the same time.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the rubber composition for a chafer pad of the present invention, 100 parts by weight of a diene rubber component containing at least 80 parts by weight of natural rubber (NR) is used as the rubber component. That is, the rubber component consists of natural rubber alone or a blend of 80 parts by weight or more of natural rubber and 20 parts by weight or less of other diene rubbers. Thus, by using natural rubber as a main component, low heat build-up can be improved and ozone crack resistance can be improved.

  Examples of other diene rubber blended with natural rubber include isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), chloroprene rubber (CR), and nitrile rubber (NBR). In particular, butadiene rubber is preferable.

  The rubber composition of the present invention is blended with a filler composed of carbon black and / or silica. As the carbon black, for example, SAF, ISAF, HAF, FEF grade carbon black can be used. Examples of the silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), and surface-treated silica. Preferably, carbon black alone or a mixture of carbon black and silica is used.

  The filler is blended in an amount of 50 to 70 parts by weight with respect to 100 parts by weight of the diene rubber component. If the blending amount of the filler exceeds 70 parts by weight, processability and low exothermicity are deteriorated, and the chafer pad becomes too harder than the bead filler, which may cause separation at the chafer end. On the other hand, if the amount is less than 50 parts by weight, the chafer pad is too soft, the ozone crack resistance is impaired due to heat generated by bending, and the chafer edge is separated.

  In the rubber composition of the present invention, a processing aid of a fatty acid metal salt containing a peptizer is blended. By using a processing aid having such an effect of promoting mastication, the low heat build-up and processability can be improved at the same time as shown in the examples described later. That is, when a processing aid for a simple fatty acid metal salt was used, the processability was improved, but the tendency to deteriorate the low heat build-up was seen. However, by containing a peptizer, the rubber component polymer As a result of appropriately cutting the molecular chain, the uniformity of the rubber composition can be improved and a low heat generation effect can be exhibited.

  The amount of the processing aid is 0.5 to 3.0 parts by weight with respect to 100 parts by weight of the diene rubber component. When the blending amount is less than 0.5 parts by weight, the effects of the present invention are hardly obtained. Conversely, when it exceeds 3.0 parts by weight, the processability is excellent, but the molecular chain scission of the rubber component polymer is large. As a result, the modulus decreases and the low heat build-up deteriorates.

  The fatty acid of the fatty acid metal salt is a saturated or unsaturated fatty acid having 6 to 28 carbon atoms, such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, behenic acid. And nervonic acid. These may be used alone or in combination of two or more. Preferably, a saturated fatty acid having 14 to 20 carbon atoms is used. Examples of the metal forming the salt of these fatty acids include alkali metals such as potassium and sodium, alkaline earth metals such as magnesium, calcium and barium, zinc, nickel and molybdenum, and zinc is particularly preferable. These fatty acid metal salts may be used alone or in combination of two or more.

  The peptizer can be used as long as it can react with the molecular chain radical of the cut rubber component polymer to suppress recombination. For example, 2,2′-dibenzamide diphenyl disulfide (DBD) , Zinc salt of 2-benzamidothiophenol, xylyl mercaptan, β-naphthyl mercaptan and the like, and DBD is particularly preferable.

  The processing aid preferably contains 5 to 10% by weight of a peptizer. If the content of the peptizer is less than 5% by weight, the uniformity of the rubber composition is insufficient and it is difficult to exert a low exothermic effect, and if it exceeds 10% by weight, the molecular chain breakage of the rubber component polymer This is disadvantageous in terms of low exothermicity.

  As a processing aid for the fatty acid zinc salt containing 5 to 10% by weight of DBD, “Actiplast MS” manufactured by Rhein Chemie is exemplified as a suitable one.

  In addition to the above components, the rubber composition of the present invention contains various additives such as zinc white, stearic acid, anti-aging agent, softener such as oil, vulcanizing agent such as sulfur, and vulcanization accelerator. can do. The rubber composition is prepared by kneading according to a conventional method using a rubber kneader such as a normal Banbury mixer or kneader.

  The rubber composition comprising the above is used for a chafer pad provided in a bead portion of a pneumatic radial tire. FIG. 1 is an enlarged cross-sectional view showing the periphery of a bead portion of a pneumatic radial tire according to an embodiment of the present invention. Hereinafter, the tire of the embodiment will be described with reference to this drawing.

  An annular bead core (2) formed by winding a bead wire in the tire circumferential direction is embedded in the pair of left and right bead portions (1). A carcass (3) extending between the pair of bead portions (1) is provided, and the carcass (3) is formed by arranging fiber cords such as nylon cords and steel cords in the tire radial direction and covering with a coating rubber. The both end portions of the bead portion (1) are locked by being wound around the bead core (2) from the inner side in the tire axial direction to the outer side.

  A bead filler (4) is provided outside the bead core (2) in the tire radial direction. The bead filler (4) is a rubber member that tapers outward in the tire radial direction along the tire axial direction outer surface of the main body (3A) of the carcass (3). In this example, the bead filler (4) includes a first rubber portion (4A) extending outward in the tire radial direction between the main body portion (3A) and the winding portion (3B) of the carcass (3), and the carcass winding portion. The second rubber portion disposed in contact with the outer surface in the tire axial direction of (3B) and disposed in contact with the outer surface in the tire axial direction of the carcass main body portion (3A) on the outer side in the tire radial direction of the first rubber portion (4A). (4B).

  A chafer (5) is disposed around the bead core (2) so as to wrap the carcass (3) from the inside in the tire radial direction. The chafer (5) is a sheet-like reinforcing member formed by rubber coating on both surfaces of a fiber material made of nylon, polyester, aramid, steel, or the like. In this example, the inner portion (5A) disposed along the inner side surface in the tire axial direction of the carcass main body portion (3A) and the outer side surface in the tire axial direction of the second rubber portion (4B) of the bead filler (4). And an outer portion (5B) extending outward in the radial direction of the tire.

  The bead portion (1) includes a rim strip (6) as a rubber portion constituting an outer surface portion of a portion that contacts the wheel rim (R). The rim strip (6) is provided so as to cover the inner surface in the tire radial direction of the chafer (5) at a portion in contact with the wheel rim (R), and extends outward in the tire radial direction therefrom. The outer side surface in the tire axial direction of the bead portion (1) is formed and terminated after the rim line (6A) is formed. Reference numeral (7) denotes a sidewall rubber.

  A chafer pad (8) made of a relatively thin rubber layer is interposed between the outer portion (5B) of the chafer (5) and the rim strip (6). 8) is formed using the rubber composition. In this example, the chafer pad (8) covers the entire outer surface in the tire axial direction of the outer portion (5B), and further, the second rubber portion (4) of the bead filler (4) at the outer end in the tire radial direction. 4B) is provided so as to cover a part of the outer surface in the tire axial direction. Further, the chafer pad (8) is covered with the side worm rubber (7) together with the rim strip (6) on the outer side in the tire axial direction. Accordingly, the chafer pad (8) is more specifically composed of the outer portion (5B) of the chafer (5) and the second rubber portion (4B) of the bead filler (4), the rim strip (6) and the side worm rubber. (7) is interposed.

  The chafer pad (8) has a rubber hardness measured at 23 ° C. according to JIS K6253 (durometer type A) within a range of +2 to −7 with respect to the rubber hardness of the bead filler (4). preferable. If the hardness of the chafer pad (8) exceeds the hardness of the bead filler (4) by more than 2 points, stress concentrates on the chafer pad (8) and separates at the end of the chafer (5). May cause. On the other hand, if the hardness of the chafer pad (8) is lower than the hardness of the bead filler (4) by more than 7 points, ozone cracks may occur in the rim strip (6) due to heat generated by bending, or the chafer (5 ) May cause separation at the edges. The rubber hardness of the bead filler (4) is not particularly limited, but is preferably A65 to A75. The rubber hardness of the chafer pad (8) is not particularly limited, but is preferably A60 to A70.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, a chafer pad rubber composition was prepared according to the formulation shown in Table 1 below. The details of each formulation in Table 1 are as follows.

・ Natural rubber: RSS # 3,
・ Butadiene rubber: “BR150B” manufactured by Ube Industries, Ltd.
Carbon black: N326, “Seast 300” manufactured by Tokai Carbon Co., Ltd.
・ Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.
・ Zinc flower: “Zinc flower 3” manufactured by Mitsui Mining & Smelting Co., Ltd.
・ Stearic acid: “Lunac S20” manufactured by Kao Corporation
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
Processing aid 1: Fatty acid zinc salt containing 5 to 10% by weight of DBD as a peptizer (constituent fatty acid is a saturated fatty acid having 18 carbon atoms as a main component), “Actiplast MS” manufactured by Rhein Chemie,
・ Processing aid 2: Saturated fatty acid zinc salt, “Actinplast PP” manufactured by Rhein Chemie,
・ Oil: “JOMO Process NC-140” manufactured by Japan Energy Co., Ltd.
・ Sulfur: “Powder sulfur” manufactured by Tsurumi Chemical Co., Ltd.
・ Vulcanization accelerator: “SOC SEAL CZ” manufactured by Sumitomo Chemical Co., Ltd.

  About each rubber composition, while evaluating the workability in an unvulcanized state, the rubber hardness and low exothermic property were evaluated using the test piece of the predetermined shape vulcanized at 150 degreeC x 30 minutes. In addition, pneumatic radial tires (tire size: 11R22.5 14PR) having a bead portion cross-sectional structure shown in FIG. 1 in which each rubber composition is used for a chafer pad are produced, and ozone crack resistance and separation resistance ( The presence or absence of separation at the chafer edge) was evaluated. A rubber composition having a rubber hardness of A70 was used as the bead filler. Each evaluation method is as follows.

Rubber hardness: measured at room temperature (23 ° C.) according to JIS K6253 (durometer type A).

Processability: The Mooney viscosity at 100 ° C. was measured according to JIS K6300, and displayed as an index with the value of Comparative Example 1 being 100. Smaller values indicate lower Mooney viscosity and better processability.

Low heat generation: Using a spectrometer manufactured by Toyo Seiki, the loss factor tan δ was measured at a temperature of 60 ° C., a frequency of 50 Hz, an initial strain of 10%, and a dynamic strain of 2%. did. Smaller values indicate less heat generation and better low heat build-up.

・ Ozone crack resistance: The tires are assembled on a rim and mounted on a large vehicle. After running in June, the vehicle is collected and evaluated for ozone cracks on the rim strip in three stages based on Comparative Example 1. did. If it was the same as Comparative Example 1, “Δ” was displayed, “◯” was displayed if it was better, and “X” was displayed if it was inferior.

Separation resistance: The tire after running 70,000 km was disassembled in a drum test, and it was confirmed whether cracks occurred at the chafer edge. The case where there was no crack was indicated as “◯”, the case where the crack was 0.1 mm or more and less than 1 mm was indicated as “Δ”, and the case where the crack was 1 mm or more was indicated as “x”.

  The results are as shown in Table 1. Compared to Comparative Example 1 as a control, in Comparative Example 2, the processability was improved by adding the processing aid 2 comprising a fatty acid metal salt, but the low exothermic property was It was damaged.

  On the other hand, when it is Examples 1-4 which mix | blended the processing aid 1 of the fatty-acid metal salt containing a peptizer, processability is improved with respect to the comparative example 1, and low exothermic property is also improved. It was. Moreover, it was excellent in ozone crack resistance and separation resistance.

  On the other hand, in Comparative Example 3 in which the amount of carbon black is too large, the workability and low heat build-up are deteriorated, the chafer pad is too harder than the bead filler, and the separation resistance is deteriorated. The ozone crack resistance was also worse than that of Example 1 due to the poor low heat build-up. In Comparative Example 4 in which the amount of carbon black was too small, the chafer pad was too soft than the bead filler and the separation resistance was deteriorated.

  Moreover, in comparative example 5, since there were too many compounding quantities of the said processing aid 1, the low exothermic property was impaired with respect to Example 1, and the ozone crack resistance was getting worse. Moreover, in the comparative example 6, since the ratio of the natural rubber in a rubber component was low, it was inferior to low heat generation property, and the ozone crack resistance was getting worse.

  The rubber composition for a chafer pad of the present invention can be used for various pneumatic radial tires such as passenger cars, trucks and buses.

It is sectional drawing which shows the bead part of the pneumatic radial tire which concerns on embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Bead part, 2 ... Bead core, 3 ... Carcass, 4 ... Bead filler, 5 ... Chafer, 5B ... Outer part of chafer, 6 ... Rim strip, 8 ... Chafer pad

Claims (3)

A bead core embedded in the bead portion, a carcass wound around and locked around the bead core, a bead filler provided on the outer side in the tire radial direction of the bead core, and the carcass around the bead core in the tire radial direction A pneumatic radial tire comprising a chafer disposed so as to wrap from the inside and a rim strip constituting a bead portion outer surface portion including a portion in contact with a wheel rim, along a tire axial direction outer surface of the bead filler. A rubber composition for a chafer pad used for a chafer pad interposed between an outer portion in the tire axial direction of the chafer disposed and the rim strip,
A processing aid for fatty acid metal salts containing 50 to 70 parts by weight of a filler composed of at least one of carbon black and silica and 100 parts by weight of a diene rubber component containing at least 80 parts by weight of natural rubber and a peptizer. A rubber composition for a chafer pad, characterized by containing 0.5 to 3.0 parts by weight.   The rubber composition for chafer pads according to claim 1, wherein the peptizer is 2,2'-dibenzamide diphenyl disulfide, and the processing aid contains 5 to 10% by weight of the peptizer. . A pneumatic radial tire provided with a chafer pad using the rubber composition according to claim 1 or 2,
The chafer pad is characterized in that the rubber hardness measured at 23 ° C. according to JIS K6253 (durometer type A) is in the range of +2 to −7 with respect to the rubber hardness of the bead filler. Entering radial tire.

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