JP4587230B2 - Clinch rubber composition and pneumatic tire - Google Patents

Description

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

  When the tire is mounted on the rim, the tire clinch rubber located in the chafing portion with the rim has a function of transmitting driving force from the rim and maintaining a load of the tire when the tire travels, and is high. Hardness and heat aging characteristics are required, and further, wear resistance is required in order to reduce wear of the rubber due to rubbing with the rim due to repeated deformation during running of the tire. Further, the rigidity, hardness and strength of the clinch rubber have a great influence on the steering stability performance during running.

  Furthermore, the clinch rubber must also exhibit elongation at break (elongation characteristics) such that tire toe portion chipping often occurs at the time of tire replacement does not occur. Here, the clinch rubber refers to a rubber member disposed in a region in contact with the rim from the sidewall of the tire to the bead.

  Aiming to reduce fuel consumption and weight, the tire structure has been simplified, rubber gauges have been made thinner, and cords have been made lighter, and the performance required for each rubber compound has become even more stringent. There is a need for rubber compositions that exhibit a good balance of excellent handling stability and elongation characteristics over time.

  By the way, the tire currently marketed is comprised from the raw material which more than half of the total weight consists of petroleum resources. For example, a general passenger car tire contains about 20% of synthetic rubber, about 20% of carbon black, softener, synthetic fiber, etc. with respect to the total weight of the tire. Consists of raw materials.

In recent years, environmental issues have been emphasized and CO ₂ emission regulations have been strengthened. Oil resources are limited and the supply amount has been decreasing year by year. Therefore, it is desired to develop a rubber compounding for tires using raw materials of natural resources that satisfies the same or more required characteristics as those in the case where conventional petroleum-based materials are used as main raw materials.

  As described above, a high-hard rubber composition using a polybutadiene rubber containing 5% by weight or more of syndiotactic crystals has been proposed for clinch rubber that requires strict performance (Patent Document 1). Patent Document 2 discloses a chafer rubber composed of a composite rubber strip in which several kinds of rubbers having different blending and characteristics are joined. However, the multilayering of clinch rubber or chafer rubber is complicated and expensive.

Here, carbon black and silica are generally used as a reinforcing agent to be blended with the tire rubber composition. However, when carbon black is blended with the rubber composition alone, the elongation at break becomes low and silica alone is blended. When it mix | blends, there existed a problem that the steering stability performance in severe conditions was inferior. As a technique for making up for the drawbacks that occur when such carbon black and silica are blended alone, Patent Document 3 discloses that a low amount of rolling can be achieved by blending a specific amount of silica-containing carbon black material in the tire tread portion. A tire tread rubber composition having both resistance and wear resistance is disclosed. However, even if this technique is applied to a clinch rubber that is required to have high rigidity and high hardness, it is impossible to improve steering stability and stretch physical properties in a balanced manner. Patent Document 4 describes a rubber composition for clinch containing silica-containing carbon black and carbon black. However, there was room for improvement in terms of tensile strength and wear resistance.
Japanese Patent Laid-Open No. 7-118444 Japanese Patent Laid-Open No. 7-81335 JP 2000-198883 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. At the same time, it is to provide a rubber composition for clinch that exhibits characteristics suitable for clinch rubber, in particular, excellent tensile strength and wear resistance, and a pneumatic tire provided with clinch made of the rubber composition.

  The rubber composition for clinches of the present invention contains 0 to 50 nm of zinc oxide particles having an average particle size of 200 nm or less with respect to 100 parts by mass of a rubber component containing 30 to 90% by mass of natural rubber and 10 to 70% by mass of epoxidized natural rubber. A rubber composition for clinch containing 1 to 10 parts by mass.

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

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

  According to the present invention, by increasing the content ratio of materials consisting of non-petroleum resources, consideration for resource saving and environmental protection is sufficient, and for clinch that exhibits excellent tensile strength and wear resistance. A rubber composition and a pneumatic tire provided with a clinch made of the rubber composition are provided.

  The rubber composition for clinch of the present invention is a rubber composition for clinch 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 clinch of the present invention contains at least natural rubber (NR) and epoxidized natural rubber as rubber components.

  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.

  The content of natural rubber (NR) in the rubber component is 30% by mass or more, preferably 40% by mass or more. When the content of NR is less than 30% by mass, the rubber strength is not sufficient. Moreover, the content rate of the natural rubber (NR) in a rubber component is 90 mass% or less, Preferably it is 80 mass% or less. When the content ratio of NR exceeds 90% by mass, the improvement of wear resistance is not sufficient.

  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 rate of ENR exceeds 65 mol%, the rubber strength tends to be insufficient.

  The content of epoxidized natural rubber (ENR) in the rubber component is 10% by mass or more, preferably 20% by mass or more. When the ENR content is less than 10% by mass, the improvement in wear resistance is not sufficient. The content of epoxidized natural rubber (ENR) in the rubber component is 70% by mass or less, preferably 50% by mass or less. When the ENR content exceeds 70% by mass, the rubber strength is not sufficient.

  The rubber composition for clinch of the present invention may contain a rubber component other than natural rubber and epoxidized natural rubber as a rubber component. Examples of rubber components other than natural rubber and epoxidized natural rubber include styrene butadiene rubber (SBR), butadiene rubber (BR), styrene isoprene copolymer rubber, isoprene rubber (IR), butyl rubber (IIR), chloroprene rubber ( CR), acrylonitrile butadiene rubber (NBR), halogenated butyl rubber (X-IIR), a halide of a copolymer of isobutylene and p-methylstyrene, and the like. Among these, SBR, BR, and IR are preferable because they can provide high hardness, high durability, high fatigue resistance, and high rolling resistance.

  When the rubber composition for clinch of the present invention contains a rubber component other than natural rubber and epoxidized natural rubber, the content of the rubber component other than natural rubber and epoxidized natural rubber in the rubber component is 20% by mass or less. It is preferable. In view of saving resources and protecting the environment, it is more preferable not to include rubber components other than natural rubber and epoxidized natural rubber from the viewpoint of increasing the content of non-petroleum resources.

<Zinc oxide>
The rubber composition for clinch of the present invention contains zinc oxide particles having an average particle diameter of 200 nm or less. 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 strength and wear resistance of the resulting clinch rubber can be improved and the flex crack resistance can be improved. Zinc oxide is a non-petroleum resource, and the rubber composition for clinch 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 is 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 clinch rubber is inferior in flex crack resistance, and the strength and wear resistance of the clinch rubber are not sufficiently improved. 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 tensile strength, the wear resistance and the flex crack resistance are improved. Excellent clinch rubber can be obtained.

<Silica>
The rubber composition for clinch of the present invention preferably further contains silica. Silica functions as a reinforcing filler, and the tensile strength of the resulting clinch 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. When the BET specific surface area of silica is less than 70 m ² / g, there is a tendency that sufficient hardness as clinch rubber cannot 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 strength as clinch rubber tends not to be obtained, and particularly sufficient tensile strength tends to be not 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 rubber composition for clinch 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-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxy 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. If the content is less than 2 parts by mass, the rubber strength tends to decrease. 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, 18 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 rubber | gum strength to fall.

<Other ingredients>
The rubber composition for clinch of the present invention includes, in addition to the above-described components, other additives conventionally used in the rubber industry, such as vulcanizing agents, stearic acid, vulcanization accelerators, oils, cured resins, waxes, Various anti-aging agents may be contained.

  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, 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 (tetramethylthiuram disulfide), tetraethylthiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram monosulfide, dipentamethylenethiuram tetrasulfide, dipentamethylenethiuram 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.

  As the anti-aging agent, amine-based, phenol-based, imidazole-based, carbamic acid metal salts, and the like can be appropriately selected and used.

  In addition, the rubber composition for clinch of the present invention may contain carbon black as a reinforcing filler, but from the viewpoint of resource saving and environmental protection, the content is preferably smaller and not contained. Is more preferable.

  The pneumatic tire of the present invention is a pneumatic tire provided with clinch rubber made of the rubber composition for clinch 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 clinch rubber 4G and sidewall rubber 3G.

The rubber composition for clinch of the present invention is used for the clinch rubber 4G.
The pneumatic tire of the present invention is manufactured by a conventionally known method using the rubber composition for clinch of the present invention. That is, the rubber composition for clinch containing the above-described essential components and other additives blended as necessary is kneaded, and extruded according to the shape of the tire clinch at the unvulcanized stage, An unvulcanized tire is formed by molding in a normal manner on a tire molding machine together with other members of the tire. The tire of the present invention can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

  Such a pneumatic tire according to the present invention has a higher content ratio of materials composed of non-petroleum resources to clinch rubber, and sufficient consideration is given to resource saving and environmental protection, as well as excellent tensile strength, wear resistance, and resistance to abrasion. Since a rubber composition having a bending crack performance is used, it is an “eco-tyre” friendly to the global environment and has high steering 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 140 ° 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 5 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) Epoxidized natural rubber (ENR): “ENR25” (epoxidation rate: 25 mol%) manufactured by Kumpoulang Guthrie
(3) Silica: “Ultra Gil VN3” manufactured by Degussa (BET: 170 m ² / g)
(4) Silane coupling agent: “Si266” (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
(5) Wax: “OZOACE-0355” made by Nippon Seiwa
(6) Anti-aging agent: “6C” (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
(7) Stearic acid: “Kiri” manufactured by Nippon Oil & Fats Co., Ltd.
(8) Zinc oxide (zinc oxide used in Comparative Example 1): Zinc oxide (average particle size: 500 nm) manufactured by Mitsui Metal Mining Co., Ltd.
(9) Zinc oxide fine particles (zinc oxide used in Examples 1 to 3): “Zincox Super F-2” (average particle size: 65 nm) manufactured by Hakusui Tech Co., Ltd.
(10) Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Co., Ltd. (11) Vulcanization accelerator NS: “Noxeller NS” (N-tert-butyl-2-benzothiazoli manufactured by Ouchi Shinsei Chemical Co., Ltd.) Rusulfanamide)
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”. And elongation at break (EB) were 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 (pico abrasion test)
In accordance with JIS-K6264 “vulcanized rubber and thermoplastic rubber rubber—how to determine wear resistance”, surface rotation speed 60 rpm, load load 4 kg, test time 1 minute using a pico abrasion tester manufactured by Ueshima Seisakusho Co., Ltd. The weight change before and after the test of each vulcanized rubber specimen was measured. The “pico wear index” in Table 1 is a relative value when the pico wear index of Comparative Example 1 is 100, and is calculated by the following formula. Higher pico wear index indicates higher severe wear resistance.
Pico wear index = {weight change of each example} / {weight change of comparative example 1} × 100
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 portion, 3 sidewall portion, 4 bead portion, 5 bead core, 6 carcass, 7 belt layer, 8 bead apex rubber, 9 inner liner rubber, 4G clinch rubber.

Claims (5)

Carbon black- free material containing 3 to 10 parts by mass of zinc oxide particles having an average particle size of 200 nm or less with respect to 100 parts by mass of a rubber component containing 30 to 90% by mass of natural rubber and 10 to 70% by mass of epoxidized natural rubber. Containing rubber composition for clinch.   The rubber composition for clinch of Claim 1 which further contains 15-90 mass parts silica with respect to 100 mass parts of rubber components. The silica has a BET specific surface area of 70 to 200 m. ² The rubber composition for clinch according to claim 2, which is / g. The rubber composition for clinch according to claim 2 or 3, further comprising 2 to 20 parts by mass of a silane coupling agent with respect to 100 parts by mass of the silica. A pneumatic tire provided with the clinch rubber which consists of a rubber composition in any one of Claims 1-4.

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