JP2008285588A - Rubber composition for bead apex, and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a bead apex indicating excellent rigidity, especially excellent tensile strength and bending crack-resistance while sufficiently taking into consideration resource-saving and environment protection by further enhancing a content ratio of a material comprising a resource other than petroleum, and to provide a pneumatic tire provided with a bead apex comprising the rubber composition. <P>SOLUTION: The rubber composition for the bead apex contains 0.1-10 mass pts. of a zinc oxide particle having an average particle diameter of 200 nm or less relative to 100 mass pts. of a rubber component containing at least a natural rubber. The pneumatic tire is provided with the bead apex comprising the rubber composition. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition used for a tire, and more particularly to a rubber composition for a bead apex of a pneumatic tire. Moreover, this invention relates to a pneumatic tire provided with the bead apex which consists of the said rubber composition.

  In recent years, with the improvement of automobile performance, high maneuvering stability is also required for tires. In order to obtain a tire having high steering stability, it is necessary to improve the rigidity of the bead apex rubber. Conventionally, in order to improve the rigidity of the bead apex rubber, a rubber composition for the bead apex is used. It has been practiced to add a large amount of carbon black.

  However, by adding a large amount of carbon black, the bead apex can be stiffened, but it tends to generate heat while the tire is running, so the durability is lost due to the decrease in dynamic fatigue and the loss. There is a problem that the rolling resistance of the tire increases due to an increase in tangent (tan δ).

In recent years, environmental issues have become more important and CO ₂ emission regulations have been strengthened. However, there are limits to the use of raw materials made of petroleum resources such as carbon black in the future. In addition, since oil resources are limited and supply is decreasing year by year, oil prices are expected to rise in the future. Therefore, assuming that petroleum resources will be depleted in the future, it is necessary to replace raw materials made of petroleum resources such as carbon black with raw materials made of resources other than petroleum.

For example, Patent Document 1 discloses a rubber composition for bead apex that is reinforced by blending old paper such as old newspaper from the viewpoint of resource saving and environmental protection. However, the rubber composition described in Patent Document 1 uses a large amount of carbon black derived from petroleum resources as a reinforcing filler together with waste paper, and does not sufficiently consider resource saving and environmental protection. There wasn't. Patent Document 2 describes a rubber composition for clinch containing silica-containing carbon black and carbon black. However, the rubber composition for clinch having different required properties cannot be applied as it is to the rubber composition for bead apex, and the tensile strength and the bending crack resistance are not considered.
JP 2002-37929 A JP 2005-247984 A

  The present invention has been made in order to solve the above-mentioned problems, and the purpose of the present invention is to sufficiently consider resource saving and environmental protection by increasing the content ratio of materials made of resources other than petroleum. And providing a rubber composition for a bead apex exhibiting excellent rigidity, in particular, excellent tensile strength and resistance to flex cracking, and a pneumatic tire provided with a bead apex made of the rubber composition. .

  The rubber composition for bead apex of the present invention comprises a bead apex containing 0.1 to 10 parts by mass of zinc oxide particles having an average particle diameter of 200 nm or less with respect to 100 parts by mass of a rubber component containing at least natural rubber. Rubber composition for use. Here, it is preferable that the rubber component consists essentially of natural rubber.

  Moreover, it is preferable that the rubber composition for bead apex of this invention further contains 15-90 mass parts silica with respect to 100 mass parts of natural rubber.

  Furthermore, this invention provides a pneumatic tire provided with the bead apex which consists of the said rubber composition.

  According to the present invention, by increasing the content ratio of materials made from non-petroleum resources, consideration for resource saving and environmental protection is sufficient, and excellent rigidity, in particular, excellent tensile strength and resistance. Provided are a rubber composition for bead apex exhibiting bending crack performance, and a pneumatic tire provided with a bead apex made of the rubber composition.

  The rubber composition for bead apex of the present invention is a rubber composition for bead apex containing 0.1 to 10 parts by mass of zinc oxide particles having an average particle diameter of 200 nm or less with respect to 100 parts by mass of the rubber component. .

<Rubber component>
The rubber composition for bead apex of the present invention needs to contain at least natural rubber (NR) as a rubber component. The content of the natural rubber (NR) in the rubber component is preferably 50% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and 100% by mass, that is, natural rubber as the rubber component. It is particularly preferable to contain only. Use of natural rubber (NR) can provide high hardness, high durability, high fatigue resistance, and high rolling resistance. The higher the content of natural rubber (NR) in the rubber component, the higher the tensile strength. It is advantageous in that it can.

  As the natural rubber, those conventionally used in the rubber industry can be used, and examples thereof include natural rubber of grades such as RSS # 3 and TSR20.

  Moreover, the rubber composition for bead apex of this invention may contain rubber components other than natural rubber as a rubber component. Examples of rubber components other than natural rubber include epoxidized natural rubber (ENR), styrene butadiene rubber (SBR), butadiene rubber (BR), styrene isoprene copolymer rubber, isoprene rubber (IR), butyl rubber (IIR), Examples thereof include chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), halogenated butyl rubber (X-IIR), and a halide of a copolymer of isobutylene and p-methylstyrene. Among these, ENR, SBR, BR, and IR are preferable because of high hardness, high durability, high fatigue resistance, and high rolling resistance, and ENR is more preferable from the viewpoint of protecting petroleum resources.

  When the rubber composition for bead apex of the present invention contains a rubber component other than natural rubber, the content of the rubber component other than natural rubber in the rubber component is the preferable range described above for the content of natural rubber (NR). It is desirable to be

  As the epoxidized natural rubber (ENR), a commercially available product may be used, or an epoxidized natural rubber (NR) may be used. The method for epoxidizing NR is not particularly limited, and examples thereof include a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, and a peracid method. Examples of the peracid method include a method of reacting an organic peracid such as peracetic acid or formic acid with natural rubber.

  Here, the epoxidation rate of the epoxidized natural rubber (ENR) is preferably 5 mol% or more, and more preferably 10 mol% or more. When the epoxidation rate of ENR is less than 5 mol%, the glass transition temperature of ENR is low, and it tends to be difficult to obtain high hardness, high durability, high fatigue resistance and high rolling resistance. The epoxidation rate of the epoxidized natural rubber (ENR) is preferably 65 mol% or less, and more preferably 60 mol% or less. When the epoxidation ratio of ENR exceeds 65 mol%, the hardness tends to increase excessively and the bending fatigue resistance tends to decrease.

  When natural rubber (NR) and epoxidized natural rubber (ENR) are included as the rubber component, the content of NR and ENR in the rubber component is preferably 50% by mass or more, more preferably 80% by mass or more, and 90% by mass. % Or more is more preferable. If the content of NR and ENR in the rubber component is less than 50% by mass, sufficient hardness and durability, fatigue resistance and rolling resistance tend not to be obtained. Further, from the viewpoint of increasing the content ratio of non-petroleum resources, the content ratios of NR and ENR in the rubber component are particularly preferably 100% by mass.

<Zinc oxide>
The rubber composition for bead apex of the present invention contains zinc oxide particles having an average particle diameter of 200 nm or less as an essential component. Here, in this invention, the average particle diameter of a zinc oxide particle is measured with the laser diffraction type particle size distribution measuring apparatus.

  Zinc oxide is blended as a vulcanization acceleration aid, but by containing zinc oxide particles having an average particle size of 200 nm or less, it is possible to effectively prevent the occurrence of cracks due to zinc oxide, The bending crack resistance performance of the obtained bead apex rubber can be improved. Zinc oxide is a non-petroleum resource, and the bead apex rubber composition containing it can be said to be an earth-friendly rubber composition with sufficient consideration for resource saving and environmental protection.

  The average particle diameter of the zinc oxide particles to be blended needs to be 200 nm or less. When the average particle diameter of the zinc oxide particles exceeds 200 nm, it often becomes a base point of cracks, and the obtained bead apex rubber is inferior in bending crack resistance. In order to further improve the bending crack resistance, the average particle size of the zinc oxide particles is preferably 150 nm or less, and more preferably 100 nm or less. Moreover, the average particle diameter of the zinc oxide particles is preferably 1 nm or more, and more preferably 10 nm or more. When the average particle diameter of the zinc oxide particles is less than 1 nm, the dispersibility of zinc oxide in the rubber composition tends to be inferior.

  Content of a zinc oxide particle is 0.1 mass part or more with respect to 100 mass parts of rubber components, Preferably it is 1 mass part or more, More preferably, it is 3 mass parts or more. When the content of the zinc oxide particles is less than 0.1 parts by mass, the effect as a vulcanization acceleration aid by blending zinc oxide tends to be difficult to obtain. Further, the content of the zinc oxide particles is 10 parts by mass or less, preferably 8 parts by mass or less, with respect to 100 parts by mass of the rubber component. When the content of the zinc oxide particles exceeds 10 parts by mass, the bending crack resistance tends to be lowered. The most preferable range of the content of zinc oxide particles is in the range of 3 to 8 parts by mass with respect to 100 parts by mass of the rubber component. In this range, the bead apec is excellent in both tensile strength and flex crack resistance. A rubber can be obtained.

<Silica>
The rubber composition for bead apex of the present invention preferably further contains silica. Silica functions as a reinforcing filler, and the tensile strength of the resulting bead apex rubber can be improved by blending silica.

  Silica may be prepared by a wet method or may be prepared by a dry method.

The BET specific surface area of silica is preferably 70 m ² / g or more, and more preferably 80 m ² / g or more. If the BET specific surface area of silica is less than 70 m ² / g, sufficient hardness as a bead apex tends not to be obtained. Further, BET specific surface area of silica is preferably not more than 200 meters ² / g, more preferably at most 180 m ² / g. When the BET specific surface area of silica exceeds 200 m ² / g, the processability of rubber tends to be lowered.

  The content of silica is 15 parts by mass or more, preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. When the content of silica is less than 15 parts by mass, sufficient hardness as a bead apex tends to be not obtained, and particularly, sufficient tensile strength tends not to be obtained. The silica content is 90 parts by mass or less, preferably 80 parts by mass or less, with respect to 100 parts by mass of the rubber component. When the content of silica exceeds 90 parts by mass, the processability of the rubber tends to decrease and the heat generated by the rubber during running tends to increase.

<Silane coupling agent>
When silica is blended in the bead apex rubber composition of the present invention, it is preferable to blend a silane coupling agent together with silica. As the silane coupling agent, a conventionally known silane coupling agent can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4- Triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide, bis (3-triethoxy Silylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-trimethoxysilylethyl) ) Resulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3 -Trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-tri Ethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthio Sulfide systems such as rubamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-trimethoxysilylpropyl methacrylate monosulfide; 3-mercaptopropyltrimethoxysilane Mercapto series such as 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; Vinyl series such as vinyltriethoxysilane and vinyltrimethoxysilane; 3-aminopropyltriethoxysilane 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxy Amino systems such as silane; glycidoxy systems such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane Nitro compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltri Chloro-based compounds such as ethoxysilane; These silane coupling agents may be used alone or in combination of two or more.

  Of these, Si69 (bis (3-triethoxysilylpropyl) tetrasulfide), Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa are preferably used because of their good processability. It is done.

  2 mass parts or more are preferable with respect to 100 mass parts of silica, and, as for content of a silane coupling agent, 3 mass parts or more are more preferable. When the content is less than 2 parts by mass, the kneading and extrusion processability of rubber tends to be lowered, and the resistance to bending cracking tends to be lowered. Moreover, 20 mass parts or less are preferable with respect to 100 mass parts of silica, and, as for content of a silane coupling agent, 15 mass parts or less are more preferable. When the content exceeds 20 parts by mass, the effect of improving rubber kneading and extrusion processability is small, but the cost increases, which is not economical. Moreover, when content exceeds 20 mass parts, it exists in the tendency for a bending crack-proof performance to fall.

<Other ingredients>
In addition to the above-described components, the bead apex rubber composition of the present invention includes other additives conventionally used in the rubber industry, such as vulcanizing agents, stearic acid, vulcanization accelerators, oils, curing resins, You may contain a wax, various anti-aging agents, etc.

  As the vulcanizing agent, an organic peroxide or a sulfur-based vulcanizing agent can be used. Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide. , T-butyl cumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoyl) Peroxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 or 1,3-bis (t-butylperoxypropyl) benzene, di-t-butylperoxy- Diisopropylbenzene, t-butylperoxybenzene, 2,4-dichlorobenzoyl peroxide, 1,1-di t- butyl peroxy-3,3,5-trimethyl siloxane, and the like can be used n- butyl-4,4-di -t- butyl peroxy valerate. Of these, dicumyl peroxide, t-butylperoxybenzene and di-t-butylperoxy-diisopropylbenzene are preferred. Moreover, as a sulfur type vulcanizing agent, sulfur, morpholine disulfide, etc. can be used, for example. Of these, sulfur is preferred. These vulcanizing agents may be used alone or in combination of two or more.

  Vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Those containing at least one of them can be used. Examples of the sulfenamide system include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-tert-butyl-2-benzothiazylsulfenamide), N, N-dicyclohexyl-2- Sulfenamide compounds such as benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, and N, N-diisopropyl-2-benzothiazolesulfenamide can be used. Examples of the thiazole group include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), sodium salt of 2-mercaptobenzothiazole, zinc salt, copper salt, cyclohexylamine salt, 2- (2,4-dinitro). Thiazole compounds such as phenyl) mercaptobenzothiazole and 2- (2,6-diethyl-4-morpholinothio) benzothiazole can be used. Examples of thiurams include TMTD (tetramethyl thiuram disulfide), tetraethyl thiuram disulfide, tetramethyl thiuram monosulfide, dipentamethylene thiuram disulfide, dipentamethylene thiuram monosulfide, dipentamethylene thiuram tetrasulfide, dipentamethylene thiuram hexasulfide. Further, thiuram compounds such as tetrabutylthiuram disulfide and pentamethylenethiuram tetrasulfide can be used. As the thiourea series, for example, thiourea compounds such as thiacarbamide, diethylthiourea, dibutylthiourea, trimethylthiourea, diortolylthiourea and the like can be used. Examples of guanidine-based compounds include guanidine-based compounds such as diphenylguanidine, diortolylguanidine, triphenylguanidine, orthotolylbiguanide, and diphenylguanidine phthalate. Examples of dithiocarbamate include zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc diamyldithiocarbamate, zinc dipropyldithiocarbamate , Complex salt of zinc pentamethylenedithiocarbamate and piperidine, zinc hexadecyl (or octadecyl) isopropyldithiocarbamate, zinc dibenzyldithiocarbamate, sodium diethyldithiocarbamate, piperidine pentamethylenedithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, diamyl Di, such as cadmium dithiocarbamate And the like can be used Okarubamin acid compound. As the aldehyde-amine system or aldehyde-ammonia system, for example, an aldehyde-amine system or aldehyde-ammonia system compound such as acetaldehyde-aniline reaction product, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde-ammonia reaction product, etc. is used. can do. As the imidazoline-based compound, for example, an imidazoline-based compound such as 2-mercaptoimidazoline can be used. As the xanthate type, for example, a xanthate type compound such as zinc dibutylxanthate can be used. These vulcanization accelerators may be used alone or in combination of two or more.

  The rubber composition for bead apex of the present invention can further contain a cured resin. Specific examples of the cured resin include phenol-based cured resins and cresol-based cured resins. In the present invention, a phenolic cured resin is more preferable. Specific examples of the phenol-based cured resin include alkylphenol resins, oil-modified phenol resins, and cashew-modified phenol resins.

  The content of the cured resin is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component. When the content is less than 1 part by mass, there is a tendency that sufficient hardness as a bead apex cannot be obtained. On the other hand, when the content of the cured resin exceeds 20 parts by mass, the unvulcanized rubber becomes excessively hard and the processability tends to be lowered.

  The rubber composition for bead apex of the present invention may contain carbon black as a reinforcing filler, but from the viewpoint of resource saving and environmental protection, its content is preferably smaller, containing More preferably not.

  The pneumatic tire of the present invention is a pneumatic tire provided with a bead apex rubber made of the rubber composition for bead apex of the present invention. Hereinafter, the pneumatic tire of the present invention will be described with reference to FIG. FIG. 1 illustrates a pneumatic tire according to the present invention. The pneumatic tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 positioned at an inner end of each sidewall portion 3. A carcass 6 is bridged between the bead portions 4 and 4, and a belt layer 7 that reinforces the tread portion 2 with a tagging effect is disposed outside the carcass 6 and in the tread portion 2.

  The carcass 6 is formed of one or more carcass plies 6a in which the carcass cord is arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator CO. The carcass ply 6a extends from the tread portion 2 to the sidewall portion. 3, the periphery of the bead core 5 of the bead portion 4 is folded back and locked from the inner side to the outer side in the tire axial direction.

  The belt layer 7 is composed of two or more belt plies 7a in which the belt cord is arranged at an angle of, for example, 40 ° or less with respect to the tire equator CO. It is location. If necessary, a band layer (not shown) for preventing lifting at both ends of the belt layer 7 may be provided at least outside the belt layer 7. At this time, the band layer is formed of a low modulus organic fiber. The cord is formed of a continuous ply spirally wound substantially parallel to the tire equator CO.

  Further, a bead apex rubber 8 extending radially outward from the bead core 5 is disposed in the bead portion 4, and an inner liner rubber 9 forming a tire lumen surface is adjacent to the inside of the carcass 6. The outside of the carcass 6 is protected by the chafer rubber 4G and the side wall rubber 3G.

  The bead apex rubber composition of the present invention is used for the bead apex rubber 8.

  The pneumatic tire of the present invention is produced by a conventionally known method using the rubber composition for bead apex of the present invention. That is, a rubber composition for a bead apex containing the above-described essential components and other additives blended as necessary is kneaded and matched to the shape of the bead apex of the tire at an unvulcanized stage. An unvulcanized tire is formed by extruding and molding together with other members of the tire by a conventional method on a tire molding machine. The tire of the present invention can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

  The pneumatic tire according to the present invention has a higher content ratio of the material composed of non-petroleum resources to the bead apex rubber, has sufficient consideration for resource saving and environmental protection, and has excellent tensile strength and flex crack resistance. Since a rubber composition having performance is used, it is an “eco-tyre” friendly to the global environment and has high driving stability.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these.

<Examples 1-3 and Comparative Example 1>
In accordance with the formulation shown in Table 1, using a 1.7L Banbury mixer manufactured by Kobe Steel, the components other than sulfur and vulcanization accelerator were filled so that the filling rate would be 58%, and the rotational speed was 80 rpm. And kneading for 3 minutes until reaching 150 ° C. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded material in the amounts shown in Table 1, and then kneaded at 80 ° C. for 3 minutes using an open roll to obtain an unvulcanized rubber composition. . Next, the unvulcanized rubber composition was vulcanized at 160 ° C. for 20 minutes to prepare vulcanized rubbers of Examples 1 to 3 and Comparative Example 1.

The details of various blending components used in Examples and Comparative Examples are as follows.
(1) Natural rubber (NR): TSR20
(2) Silica: “Ultra Gil VN3” manufactured by Degussa (BET: 170 m ² / g)
(3) Silane coupling agent: “Si266” (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
(4) Cured resin: phenolic cured resin “Sumilite Resin PR12686” manufactured by Sumitomo Bakelite Co., Ltd.
(5) Stearic acid: “paulownia” made by NOF Corporation
(6) Zinc oxide (zinc oxide used in Comparative Example 1): Zinc oxide manufactured by Mitsui Kinzoku Mining Co., Ltd. (average particle size: 500 nm)
(7) Zinc oxide fine particles (zinc oxide used in Examples 1 to 3): “Zincox Super F-2” (average particle diameter: 65 nm) manufactured by Hakusui Tech Co., Ltd.
(8) Sulfur: Powdered sulfur produced by Tsurumi Chemical Industry Co., Ltd. (9) Vulcanization accelerator NS: “Noxeller NS” (N-tert-butyl-2-benzothiazoli produced by Ouchi Shinsei Chemical Co., Ltd.) Rusulfanamide)
(10) Vulcanization accelerator H: “Sunseller H” (hexamethylenetetramine) manufactured by Ogura Sandine Co., Ltd.
The vulcanized rubbers of Examples 1 to 3 and Comparative Example 1 were subjected to the following rubber strength test and dematcher flex crack growth test. The results are shown in Table 1.

(Rubber strength test)
A No. 3 dumbbell-shaped test piece was prepared from the vulcanized rubber sample, and a tensile test was carried out according to JIS-K6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”. The elongation at break (EB) was measured. The “rubber strength index” in Table 1 is a relative value when the rubber strength index of Comparative Example 1 is 100, and is calculated by the following formula. The larger the rubber strength index, the better the breaking strength of the rubber.
Rubber strength index = {(TB × EB) of each Example} / {(TB × EB) of Comparative Example 1} × 100
(Dematcher bending crack growth test)
According to JIS-K6260 “Dematcher bending crack growth test method for vulcanized rubber and thermoplastic rubber”, the number of times until the vulcanized rubber sample breaks 1 mm under the condition of room temperature 25 ° C. is obtained. The relative number when the number of times in Comparative Example 1 is 100 is shown. Note that 70% in Table 1 indicates the elongation percentage with respect to the length of the original vulcanized rubber sample.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic sectional drawing which shows an example of the pneumatic tire of this invention.

Explanation of symbols

  1 tire, 2 tread part, 3 sidewall part, 4 bead part, 5 bead core, 6 carcass, 7 belt layer, 8 bead apex rubber, 9 inner liner rubber.

Claims (4)

  A rubber composition for bead apex containing 0.1 to 10 parts by mass of zinc oxide particles having an average particle diameter of 200 nm or less with respect to 100 parts by mass of a rubber component containing at least natural rubber.   The rubber composition for a bead apex according to claim 1, wherein the rubber component consists essentially of natural rubber.   The bead apex rubber composition according to claim 1 or 2, further comprising 15 to 90 parts by mass of silica with respect to 100 parts by mass of natural rubber.   A pneumatic tire provided with the bead apex which consists of a rubber composition in any one of Claims 1-3.

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