JP2009120739A - Chafer rubber composition and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chafer rubber composition for tires having improved workability in rim assembling while maintaining basic properties such as rim slippage resistance, creep resistance, and toe chipping resistance, and to provide a pneumatic tire using the chafer rubber composition. <P>SOLUTION: The chafer rubber composition for tires includes 100 pts.mass of a diene rubber component and 2-12 pts.mass of a higher fatty acid metal salt. Here, the higher fatty acid metal salt is zinc stearate, magnesium stearate, calcium stearate, zinc oleate, magnesium oleate, calcium oleate, zinc laurate, magnesium laurate, or calcium laurate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a chafer rubber composition and a pneumatic tire provided with the chafer rubber composition.

  The tire chafer rubber is disposed on the side that comes into contact with the rim in the region from the toe (tip) of the tire bead to the vicinity of the upper end of the rim flange through the heel. The tire reinforcement is prevented from being exposed due to abrasion of the bead portion region where the tire engages and contacts the rim, and the engagement between the tire and the rim is firmly held. Furthermore, in tubeless tires, the filling air pressure is kept constant to ensure driving safety. In particular, chafer rubbers for heavy duty pneumatic tires that are subjected to severe repeated deformation and high heat generation conditions under high internal pressure and high load are required to have stricter performance. Here, the following characteristics are required as the chafer rubber.

  Rim assembly workability: The ease of work when mounting a tire on a rim. The tire is rim-assembled by an automatic mounter. At this time, the bead portion is required to have a certain degree of flexibility and a slipperiness in the rubber of the bead portion that contacts the rim.

  Rim slip resistance: The tire bead portion is repeatedly deformed when the tire is running. At this time, the chafer rubber formed in the tire bead portion is damaged by friction between the abutting bead base and the rim flange. Particularly, heavy tires for heavy vehicles are subject to wear resistance because of heavy load and high temperature.

  Creep resistance: Tires are susceptible to creep distortion due to high compressive force in the contact area between the bead base and rim flange and chafer rubber under high internal pressure and high load conditions. Such creep strain causes stress strain of the reinforcing material in the bead portion, and breaks the bead portion. Therefore, a creep resistant rubber composition is required.

  Toe chip resistance: When a heavy load pneumatic tire, particularly a tubeless tire is assembled and removed from the rim, the toe portion of the chafer rubber may be locally deformed and the toe portion may be lost. If the toe part is damaged, the tie, durability, and internal pressure holding performance of the tubeless tire are significantly impaired. Usually, the rubber composition having improved creep resistance tends to have a small elongation at break, and generally the toe chip resistance is lowered.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 7-118444) discloses a technique of blending a filler and sulfur with a polybutadiene rubber containing a syndio crystal component, for a high-hardness rubber composition used for an industrial trash tire. Yes. This technique does not relate to the chafer rubber composition of a pneumatic tire and does not satisfy all the required characteristics.

Patent Document 2 (Japanese Patent Laid-Open No. 2005-272508) discloses 100 parts by mass of a rubber component containing 5 to 100% by mass of an epoxidized natural rubber in order to improve the wear resistance and heat resistance of the rubber composition for a tire tread. In contrast, 5 to 150 parts by mass of silica having a nitrogen adsorption specific surface area of 100 to 300 m ² / g, 1 to 10 parts by mass of metal stearate, and a specific silane coupling agent are disclosed. Yes.
Japanese Patent Laid-Open No. 7-118444 JP 2005-272508 A

  The present invention uses a chafer rubber composition for tires, particularly the chafer rubber composition, which has improved rim assembly workability while maintaining basic characteristics such as rim slip resistance, creep resistance and toe chip resistance. Provide pneumatic tires.

  The present invention relates to a tire chafer rubber composition containing 2 to 12 parts by mass of a higher fatty acid metal salt with respect to 100 parts by mass of a diene rubber component. Here, the higher fatty acid metal salt is preferably zinc stearate, magnesium stearate, calcium stearate, zinc oleate, magnesium oleate, calcium oleate, zinc laurate, magnesium laurate, or calcium laurate. These higher fatty acid metal salts are preferably contained in an amount of 5 to 10 parts by mass with respect to 100 parts by mass of the diene rubber component.

  In the present invention, carbon black is preferably contained in an amount of 20 to 100 parts by mass with respect to 100 parts by mass of the diene rubber component, and the diene rubber preferably contains either natural rubber or polybutadiene rubber. The present invention relates to a pneumatic tire provided with a chafer rubber made of the chafer rubber composition.

  In the present invention, since a specific higher fatty acid metal salt is blended in the chafer rubber composition, an appropriate amount of the higher fatty acid metal salt that precipitates on the surface of the chafer rubber enhances slippage with the rim when the tire is mounted on the rim. Therefore, the rim assembly work can be easily performed.

  The present invention is a tire chafer rubber composition containing 2 to 30 parts by mass of a higher fatty acid metal salt with respect to 100 parts by mass of a diene rubber component.

<Diene rubber component>
In the chafer rubber composition of the present invention, as the diene rubber, natural rubber (NR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), polyisoprene rubber (IR), ethylene-propylene-diene rubber (EPDM) ), Chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), and the like. These rubbers may be used alone or in combination of two or more.

  In the present invention, among 100 parts by mass of the diene rubber component, it is composed of a mixture containing 40 to 80 parts by mass of natural rubber, further 50 to 70 parts by mass, 60 to 20 parts by mass of polybutadiene rubber, and further 50 to 30 parts by mass. It is preferred that

  Chafer rubber is subject to severe repetitive deformation under high internal pressure and high load, and its temperature tends to rise due to friction with the rim. Therefore, it is necessary to maintain the toe chip resistance and rim slip resistance by suppressing the heat generation and increasing the tensile strength and elongation. Therefore, it is preferable to mix 40 parts by mass or more of natural rubber. However, when it exceeds 80 parts by mass, the hardness of the chafer rubber tends to decrease. It is also possible to use polyisoprene rubber instead of natural rubber.

  As the polybutadiene rubber, a high cis polybutadiene rubber having a cis content of 60% by mass or more, a low cis polybutadiene rubber having a cis content of less than 60% by mass, and a vinyl polybutadiene rubber having a vinyl content of 20% by mass or more can be used. In particular, the hardness can be increased by using a polybutadiene rubber containing 5% by mass or more of syndiotactic 1,2 polybutadiene crystals (hereinafter referred to as “syndio crystals”). If the amount of polybutadiene rubber is less than 20 parts by mass, the rubber hardness is low and the rim displacement resistance is deteriorated. Get higher.

<Higher fatty acid metal salt>
The higher fatty acid metal salt includes an alkali metal salt, an alkaline earth metal salt, a zinc salt, a nickel salt, and a molybdenum salt of a fatty acid having 6 or more carbon atoms, preferably 10 or more carbon atoms. The fatty acid may be a saturated fatty acid or an unsaturated fatty acid. Specific examples of higher fatty acids include saturated fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid, and unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid.

  Examples of the alkali metal include potassium and sodium. Examples of the alkaline earth metal include magnesium, calcium, strontium, and barium. These higher fatty acid metal salts may be used alone or in combination of two or more.

  Specific examples of the higher fatty acid metal salt include magnesium stearate, magnesium 12-hydroxystearate, calcium stearate, calcium 12-hydroxystearate, barium stearate, barium 12-hydroxystearate, stearic acid. Examples thereof include zinc and zinc 12-hydroxystearate.

  In particular, higher fatty acid metal salts include zinc stearate, magnesium stearate, calcium stearate, zinc oleate, and oleic acid, in order to increase rim slip resistance and improve rim assembly and workability. Magnesium, calcium oleate, zinc laurate, magnesium laurate and calcium laurate are preferred.

  The content of the higher fatty acid metal salt is 2 parts by mass or more, preferably 5 parts by mass or more with respect to 100 parts by mass of the diene rubber component. When the content of the higher fatty acid metal salt is less than 2 parts by mass, the higher fatty acid metal salt does not appropriately precipitate on the surface of the chafer rubber, and the slipperiness with the rim cannot be improved. The content of the higher fatty acid metal salt is 12 parts by mass or less, preferably 10 parts by mass or less. If the content of the higher fatty acid metal salt exceeds 12 parts by mass, the adhesion to other tire components will be reduced when a tire is molded using the unvulcanized rubber composition, and the hardness and modulus of the vulcanized rubber will be reduced. Decreases and wear resistance decreases.

<Carbon black>
Carbon black is preferably added to the chafer rubber composition of the present invention. Carbon black has a nitrogen adsorption specific surface area of 40 to 120 m ² / g. When the nitrogen adsorption specific surface area is less than 40 m ² / g, the reinforcing effect is not sufficient, and the strength, hardness and rigidity of the rubber composition cannot be obtained. On the other hand, when it exceeds 120 m ² / g, the heat generation of the rubber composition is increased and the resistance to rim displacement is lowered. Here, the nitrogen adsorption specific surface area is measured by the BET method according to ASTM D3037-81. And the compounding quantity of carbon black is 20-100 mass parts with respect to 100 mass parts of rubber components, Preferably it is 40-75 mass parts. If the amount is less than 20 parts by mass, the reinforcing effect is insufficient, and the hardness and rigidity are low. On the other hand, if the amount exceeds 100 parts by mass, the exothermic property increases and the elongation at break decreases, resulting in poor toe chip resistance.

<Filler>
The chafer rubber composition may contain a filler such as silica, clay, calcium carbonate, aluminum hydroxide. Silica produced by a wet method or a dry method can be used as the silica. For example, silica having a nitrogen adsorption specific surface area (N ₂ SA) of 100 m ² / g or more and 300 m ² / g or less is used. This is to balance the reinforcing effect, dispersibility, and heat build-up of the rubber composition. In addition, when mix | blending a silica, it is preferable to contain a silane coupling agent.

  These fillers are blended in an amount of 5 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the diene rubber component to enhance the reinforcing effect of the rubber composition and reduce the deterioration of workability and workability. There is a need.

<Sulfur / Vulcanization accelerator>
Next, in the present invention, it is desirable that the ratio S / A of the blending amount S of sulfur and the blending amount A of the vulcanization accelerator is in the range of 1.2 to 1.7. In general, a vulcanized rubber based on a sulfur vulcanization system composed of sulfur and a vulcanization accelerator is inferior in thermal stability because it mainly comprises polysulfide bonds. Therefore, in the present invention, it is desirable to reduce the amount of sulfur as compared with the amount of vulcanization accelerator so as to reduce the number of sulfur per unit cross-linking so that the formation of polysulfide bonds is reduced. On the other hand, when the polysulfide bond is reduced, the flexibility of the rubber composition is impaired. Therefore, it is preferable to form an appropriate polysulfide bond. In the present invention, when the ratio S / A of the blending amount of both is less than 1.2, the crosslinking density becomes small and the strength and hardness are not sufficient, while when it exceeds 1.7, the thermal stability tends to be lowered. The sulfur content is preferably 1.0 to 2.0 parts by mass with respect to 100 parts by mass of the diene rubber component. If the amount is less than 1.0 part by mass, the crosslinking density becomes too low, and if it exceeds 2.0 parts by mass, the vulcanized rubber becomes too hard.

  As the vulcanization accelerator, vulcanization accelerators such as thiourea, guanidine, thiazole, sulfenamide, thiuram, and dithiocarbamate can be used. For example, mercaptobenzothiazole, dibenzothiazyl disulfide, N-cyclohexylbenzothiazylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide can be used. Although the compounding quantity of a vulcanization accelerator is based also on the compounding quantity of sulfur, it is 0.7-1.4 mass parts per 100 mass parts of diene rubber components.

<Other ingredients>
The chafer rubber composition of the present invention is used in a normal rubber industry such as a softening agent such as oil, an anti-aging agent, a vulcanizing agent such as sulfur, a vulcanization accelerator, and a vulcanization acceleration aid as necessary. The compounding agent used can be blended as appropriate.

<Pneumatic tire>
FIG. 1 shows a right half of a cross-sectional view of a pneumatic tire provided with a chafer rubber composition. In FIG. 1, a tire 1 includes a tread portion 7, a pair of sidewall portions 8 extending inward in the tire radial direction from both ends thereof, and a bead portion 3 positioned at an inner end of each sidewall portion 8. . A carcass 10 is formed in a toroidal shape between the bead portions 3 on both sides, and a belt layer 9 that reinforces the tread portion 7 with a tagging effect on the outside of the carcass 10 and on the inside of the tread portion 7. Arranged. The carcass 10 is formed of one or more carcass plies in which a carcass cord is arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator, and the carcass ply extends from the tread portion 7 to the sidewall portion 8. Around the bead core 11 of the bead portion 3 is folded back from the inner side in the tire axial direction to be locked. The belt layer 9 includes two or more belt plies in which belt cords are arranged at an angle of, for example, 30 ° or less with respect to the tire equator, and the belt cords 9 are stacked in different directions so that the belt cords cross each other. .

  If necessary, a band layer 5 for preventing lifting of the belt layer 9 may be provided outside the belt layer 9, and at this time, the band layer has an organic fiber cord having a low modulus substantially equal to the tire equator. Formed with continuous plies spirally wound in parallel. The bead portion 3 is provided with a bead apex 6 extending radially outward from the bead core 11, and an inner liner rubber (not shown) forming a tire lumen surface can be formed inside the carcass 10. .

  A chafer rubber 2 is disposed in a region that contacts the bead base and the rim flange from the tire lumen surface of the bead portion 3 to the tire outer surface. The chafer rubber 2 is formed by sticking a sheet-like rubber along the contour shape of the tire bead portion, and is reinforced with a clinch rubber 4 in the vicinity of the upper end of the rim flange. In the present invention, the chafer rubber and the clinch rubber can be integrated into the chafer rubber composition of the present invention. The shape of the chafer rubber of the present invention can be appropriately changed according to the category, size, and required characteristics of the applied tire.

Examples 1-3, Comparative Example 1
A compounding agent obtained by removing sulfur and a vulcanization accelerator from the basic compounding shown in Table 1 was kneaded with a Banbury mixer at 150 ° C. for 3 minutes. Thereafter, sulfur and a vulcanization accelerator were added to the obtained rubber composition and kneaded with an open roll at 140 ° C. for 5 minutes.

  Each chafer rubber composition was vulcanized under conditions of 196 N at 150 ° C. for 30 minutes to produce a 255 / 35R18 repair tire. The details of the ingredients used in Table 1 are as follows.

(Note 1) Natural rubber: “RSS # 3 grade” was used.
(Note 2) Polybutadiene: “BR150B” manufactured by Ube Industries, Ltd. was used.
(Note 3) Carbon black: “N550” manufactured by Showa Cabot Corporation was used (nitrogen adsorption specific surface area of 42 m ² / g).
(Note 4) Process oil: “Diana Process AH-24” manufactured by Idemitsu Kosan Co., Ltd. was used.
(Note 5) Wax: “Sannokk Wax” from Ouchi Shinsei Chemical was used.
(Note 6) Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd. was used.
(Note 7) Stearic acid: “Kashiwa” manufactured by NOF Corporation was used.
(Note 8) Zinc oxide: Mitsui Metal Mining Co., Ltd. product was used.
(Note 9) Sulfur: Powdered sulfur produced by Karuizawa Sulfur Co., Ltd. was used.
(Note 10) Vulcanization accelerator: “Noxeller CZ” manufactured by Ouchi Shinsei Chemical Co., Ltd. was used.
(Note 11) Higher fatty acid metal salt: “Structol WB16” (mixture of higher fatty acid calcium salt and saturated fatty acid amide) manufactured by Schill-Seilacher was used.

  The chafer rubber composition of the present invention and the tire performance evaluation method using the same are as follows.

<Loss tangent (viscoelasticity test)>
A test piece was prepared from the chafer rubber composition of a new tire, and the loss tangent (tan δ) at 60 ° C. was measured with a viscoelastic spectrometer manufactured by Iwamoto Seisakusho under the conditions of a frequency of 10 Hz and a dynamic strain of 1.0%. . The smaller the numerical value, the lower the tan δ, and the lower the heat generation and the better the performance.

<Hardness (JIS-A)>
The hardness of a new chafer rubber composition was measured at 25 ° C. with a JIS-A hardness meter. A hardness value in the range of 50-60 is suitable.

<Tensile test>
A No. 3 dumbbell was produced from the chafer rubber composition in accordance with JIS-K6251 and a tensile test was conducted to measure the strength at break (TB) and the elongation at break (EB). The breaking strength indicates a value of MPa, and the elongation at break (EB) is indicated by%.

<Rim assembly workability>
Rim assembly work was performed using an automatic mounter machine using a tire for repair of a prototype tire (size: 255 / 35R18). Three tests were conducted for each of the examples and comparative examples, and the following evaluations were made.

A: All three tires were not damaged in the chafer.
B: The chafer was damaged in one or two tires.

C: All three tires were damaged in the chafer.
<Evaluation results>
Table 1 shows the evaluation results. It is recognized that Examples 1 to 3 have excellent basic characteristics as a chafer rubber and improved rim assembly workability. In Example 1, the amount of the higher fatty acid metal salt was as small as 3 parts by mass, and the rim assembly workability was slightly inferior to Examples 2 and 3.

  The chafer rubber composition of the present invention is applied to the categories of passenger car tires, truck bus tires, light truck tires and motorcycle tires, and a pneumatic tire having the chafer rubber composition has excellent rim assembly workability. Have

The right half of sectional drawing of the pneumatic tire of this invention is shown.

Explanation of symbols

  1 tire, 2 chafer rubber, 3 bead parts, 4 clinch rubber.

Claims (6)

  A chafer rubber composition comprising 2 to 12 parts by mass of a higher fatty acid metal salt with respect to 100 parts by mass of a diene rubber component.   The higher fatty acid metal salt includes at least one selected from the group of zinc stearate, magnesium stearate, calcium stearate, zinc oleate, magnesium oleate, calcium oleate, zinc laurate, magnesium laurate and calcium laurate The chafer rubber composition according to claim 1.   The chafer rubber composition according to claim 1, comprising 5 to 10 parts by mass of a higher fatty acid metal salt with respect to 100 parts by mass of the diene rubber component.   The chafer rubber composition according to claim 1, comprising 20 to 100 parts by mass of carbon black with respect to 100 parts by mass of the diene rubber component.   The chafer rubber composition according to claim 1, wherein the diene rubber component includes any of natural rubber and polybutadiene rubber.   A pneumatic tire provided with a chafer rubber comprising the chafer rubber composition according to claim 1.

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