JP5529623B2 - Pneumatic tire - Google Patents

Description

The present invention relates to a pneumatic tire.

A side surface (side) portion of a general pneumatic tire is divided into a portion where the tire bends (side wall portion) and a portion which contacts the rim. The clinch rubber located at the portion in contact with the rim is required to have good chafing performance (rubber wear resistance when the tire and the rim are rubbed). Therefore, conventionally, a large amount of carbon black having a specific surface area of a certain level or more has been blended in the clinch rubber in order to blend natural rubber with a butadiene rubber having good wear resistance and further improve the wear resistance. . Thus, conventionally, a large amount of butadiene rubber and carbon black, which are raw materials derived from petroleum resources, have been used for clinch rubber in order to obtain good chafing performance.

However, in recent years, environmental issues have become more important and regulations on carbon dioxide emissions have been strengthened. In addition, since oil reserves are limited, the use of raw materials derived from petroleum resources is limited. This environment-oriented orientation is no exception in the tire field, and there is an increasing demand to replace some or all of the petroleum-derived raw materials currently used with raw materials derived from non-oil resources. There is an increasing demand for rubber compositions.

Eco tires using silica or the like as an alternative raw material for carbon black have been developed (for example, Patent Document 1). However, in a rubber composition for clinching, if a large amount of natural rubber is blended instead of butadiene rubber, which is a synthetic rubber, or if a white filler such as silica is blended instead of carbon black, it can be used in a heavy-duty passenger car. Under traveling conditions with high severity such as when used, chafing may occur, resulting in rim displacement or deterioration in durability. In order to solve such a problem, a method of improving the wear resistance by adding a large amount of silica as a reinforcing filler can be considered. However, when a large amount of silica is blended, the rubber hardness becomes very high, and there is a problem that it is difficult to assemble the rim. There is also room for improvement in the chafing performance. Thus, when a part or all of raw materials derived from petroleum resources of clinch rubber are replaced with raw materials derived from resources other than petroleum, the present situation is that good chafing performance is not obtained.

JP 2007-169431 A

The present invention solves the above-mentioned problem and provides a pneumatic tire that can obtain good chafing performance even when a part or all of raw materials derived from petroleum resources of clinch rubber are replaced with raw materials derived from resources other than petroleum. The purpose is to provide.

The present invention includes a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, a bead apex rubber extending radially outward from the bead core, and a bead apex rubber disposed on the outer side in the tire axial direction of the bead apex rubber. A pneumatic tire having a clinch rubber forming an outer surface of a portion, wherein the clinch rubber has a surface layer forming an outer surface of the bead portion, and an inner layer disposed on the inner side in the tire axial direction of the surface layer. The average thickness of the surface layer is 0.3 to 2.5 mm, the hardness of the surface layer is 75 or more, the hardness of the inner layer is 75 or less, and the difference in hardness between the surface layer and the inner layer is 5 Thus, the surface layer and the inner layer have a total content of natural rubber and modified natural rubber in 100% by mass of the rubber component of 70% by mass or more, and the reinforcing filler 100 quality. The content of silica in% is a pneumatic tire which is manufactured by using the rubber composition for clinch is at least 50 mass%.

The clinch rubber is preferably composed of the surface layer and the inner layer.

It is preferable that the silica has a nitrogen adsorption specific surface area of 50 to 300 m ² / g.

In the rubber composition for clinch, the silica content is preferably 25 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are specified in a 5% internal pressure state in which the tire is assembled on a regular rim and filled with air so as to be 5% of the regular internal pressure. Value. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, JATMA is a standard rim, TRA is “DESIGN Rim”, If it is ETRTO, it means “MEASURING Rim”. The “regular internal pressure” is the air pressure defined by the tire for each tire. The maximum air pressure for JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFRATION PRESURES” for TRA. In the case of ETRTO, it means “INFLATION PRESURE”, but in the case of a passenger car tire, it is 180 kPa.

The clinching rubber used in the present invention is a clinching rubber composition in which the total content of natural rubber and modified natural rubber is a specific amount or more and the silica content in the reinforcing filler is a predetermined amount or more. A part or all of raw materials derived from petroleum resources of clinch rubber have been replaced with raw materials derived from resources other than petroleum. Therefore, it is possible to reduce the ratio of raw materials derived from petroleum resources, to prepare for the depletion of raw materials derived from petroleum resources, and to consider the environment. Further, even when such a clinch rubber is used, the clinch rubber has a surface layer forming the outer surface of the bead portion and an inner layer disposed on the inner side in the tire axial direction of the surface layer. Good chafing performance can be obtained when the average thickness is in a specific range, the hardness of the surface layer is a specific value or more, the hardness of the internal layer is a specific value or less, and the difference in hardness between the surface layer and the internal layer is a specific value or more. It is done. Further, since the hardness of the clinch rubber as a whole is lowered, rim assembly performance can be secured.
This is because the inner layer (soft clinching layer) is easily deformed with respect to the load by adopting the above configuration, and accordingly, the surface layer (hard clinching layer) forming the outer surface of the bead portion is also deformed. The rim assembling performance can be ensured, and further, the area of the portion in contact with the rim is increased due to deformation, and local wear is less likely to occur. Therefore, it is presumed that good chafing performance can be obtained. In addition, in rubber compositions mainly composed of natural rubber and silica, the wear resistance of the rubber itself is insufficient. Therefore, by setting the hardness of the surface layer (hard clinch layer) to a specific value or more, an even better chain It is estimated that fing performance can be obtained.

1 is a cross-sectional view illustrating a part of a pneumatic tire according to an embodiment of the present invention.

First, the rubber composition for clinch for producing the clinch rubber used for the pneumatic tire of this invention is demonstrated.

(Rubber composition for clinch)
The rubber composition for clinch is a total content of natural rubber, which is a raw material derived from non-petroleum resources, and a modified natural rubber, and a content of silica, which is a raw material derived from non-petroleum resources, in a reinforcing filler. Is greater than or equal to a predetermined amount. That is, the rubber composition for clinch is a rubber composition in which a part or all of raw materials derived from petroleum resources are replaced with raw materials derived from resources other than petroleum (the ratio of raw materials derived from petroleum resources is reduced). Therefore, by using the rubber composition, it is possible to prepare for the exhaustion of raw materials derived from petroleum resources and to consider the environment.

The total content of natural rubber (NR) and modified natural rubber in 100% by mass of the rubber component of the rubber composition for clinch is 70% by mass or more, preferably 85% by mass or more, and more preferably 100% by mass. If it is less than 70% by mass, the ratio of raw materials derived from petroleum resources cannot be sufficiently reduced, and the environment tends not to be considered sufficiently. NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (HPNR). Modified natural rubber includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafting. Examples include natural rubber. Moreover, as NR, what is common in tire industry, such as SIR20, RSS # 3, TSR20, can be used, for example.

In addition to NR and modified natural rubber, rubber components that can be used in the rubber composition for clinch include butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), isoprene rubber (IR), ethylene propylene. Examples include diene-based synthetic rubbers such as diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). A diene type synthetic rubber may be used independently and may use 2 or more types together.

When the rubber composition for clinch contains a diene synthetic rubber, the content of the diene synthetic rubber in 100% by mass of the rubber component is 30% by mass or less. If it exceeds 30% by mass, the ratio of raw materials derived from petroleum resources cannot be sufficiently reduced, and the environment tends not to be considered sufficiently.

The rubber composition for clinch contains silica which is a raw material derived from resources other than petroleum. Silica functions as a reinforcing filler. By blending silica, the ratio of raw materials derived from petroleum resources can be reduced, and fuel efficiency and wear resistance can be improved.

The content of silica in 100% by mass of the reinforcing filler contained in the rubber composition for clinch is 50% by mass or more, preferably 70% by mass or more, more preferably 85% by mass or more, and further preferably 100% by mass. . If it is less than 50% by mass, the ratio of raw materials derived from petroleum resources cannot be sufficiently reduced, and there is a tendency that the environment cannot be fully considered.

Examples of the silica include, but are not limited to, dry method silica (anhydrous silicic acid), wet method silica (anhydrous silicic acid), and the like, and wet method silica is preferable because it has many silanol groups. Silica may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 50 m ² / g or more, more preferably 100 m ² / g or more. If it is less than 50 m < ² > / g, there exists a tendency for it to be inferior to abrasion resistance. Further, N ₂ SA of silica is preferably 300 m ² / g or less, more preferably 250 m ² / g or less, and further preferably 200 m ² / g or less. When it exceeds 300 m ² / g, the dispersibility tends to be inferior or the fuel efficiency tends to be inferior.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica in the rubber composition for clinch used for the surface layer is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, still more preferably 40 parts by mass or more, particularly 100 parts by mass of the rubber component. Preferably it is 60 mass parts or more. If the amount is less than 25 parts by mass, sufficient wear resistance may not be obtained. The content of the silica is preferably 100 parts by mass or less, more preferably 80 parts by mass or less. When it exceeds 100 parts by mass, the rubber viscosity becomes high, and the process passability (processability and productivity) tends to be inferior, or the fuel efficiency tends to deteriorate.

The content of silica in the rubber composition for clinch used for the inner layer is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and further preferably 40 parts by mass or more with respect to 100 parts by mass of the rubber component. . If the amount is less than 25 parts by mass, sufficient wear resistance may not be obtained. Content of this silica becomes like this. Preferably it is 100 mass parts or less, More preferably, it is 80 mass parts or less, More preferably, it is 60 mass parts or less. When it exceeds 100 parts by mass, the rubber viscosity becomes high, and the process passability (processability and productivity) tends to be inferior, or the fuel efficiency tends to deteriorate.

The rubber composition for clinching preferably contains a silane coupling agent together with silica. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry, and examples thereof include sulfide systems such as bis (3-triethoxysilylpropyl) disulfide, 3- Mercapto type such as mercaptopropyltrimethoxysilane, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltrimethoxy Examples thereof include nitro compounds such as silane and chloro compounds such as 3-chloropropyltrimethoxysilane. Among these, sulfide type is preferable, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferable.

The content of the silane coupling agent is preferably 4 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 4 parts by mass, the rubber strength tends to decrease. Further, the content of the silane coupling agent is preferably 15 parts by mass or less, more preferably 12 parts by mass or less. When it exceeds 15 parts by mass, the wear resistance tends to be inferior.

The rubber composition for clinch may contain carbon black as a reinforcing filler other than silica. By containing carbon black, rubber reinforcement and wear resistance can be improved. However, from the viewpoint of resource saving and environmental protection, it is preferable that carbon black derived from petroleum / coal is not substantially contained (0% by mass).

In addition to the above components, the rubber composition for clinching includes compounding agents generally used in the production of rubber compositions, such as zinc oxide, stearic acid, various anti-aging agents, antioxidants, ozone deterioration inhibitors, oils A softener such as wax, a vulcanizing agent such as wax and sulfur, a vulcanization accelerator, and the like can be appropriately blended.

As the vulcanizing agent, an organic peroxide or a sulfur-based vulcanizing agent can be used. As the organic peroxide, for example, dicumyl peroxide, t-butylperoxybenzene, di-t-butylperoxy-diisopropylbenzene can be preferably used. Moreover, as a sulfur type vulcanizing agent, sulfur, morpholine disulfide, etc. can be used, for example, and sulfur can be used conveniently.

Examples of vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, and xanthate vulcanization accelerators. It is done.

The rubber composition for clinch is manufactured by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The pneumatic tire of the present invention is produced by a normal method using the rubber composition for clinch. That is, the rubber composition for clinch containing the above components is extruded in accordance with the shape of clinch (surface layer, inner layer) at an unvulcanized stage, and usually on a tire molding machine together with other tire members. By molding by this method, an unvulcanized tire is formed. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a pneumatic tire.

In the present invention, even when a clinching rubber produced by using the clinching rubber composition obtained by substituting a part or all of a raw material derived from petroleum resources with a raw material derived from non-petroleum resources is used, By making the structure a specific structure, good chafing performance can be obtained.

Hereinafter, an example of a preferred embodiment of the pneumatic tire of the present invention will be described with reference to the drawings as appropriate.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention. In FIG. 1, the vertical direction is the tire radial direction, and the horizontal direction is the axial direction.

As shown in FIG. 1, a pneumatic tire 1 includes a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and a bead apex rubber 8 extending radially outward from the bead core 5. And a clinch rubber 9 disposed on the outer side in the tire axial direction of the bead apex rubber 8 and forming the outer surface of the bead portion 4. The tread portion 2 is provided with a tough belt layer 7 extending radially outward of the carcass 6 in the tire circumferential direction. An inner liner 15 forming a tire lumen surface is disposed on the radially inner side of the carcass 6.

The belt layer 7 is formed of two or more belt plies 7A and 7B in which high strength belt cords such as steel cords are arranged at an angle of, for example, 10 to 40 ° with respect to the tire circumferential direction. The belt cords cross each other between the plies, thereby increasing the belt rigidity, and substantially reinforcing the entire width of the tread portion 2 with a tagging effect. Further, on the outer side of the belt layer 7 in the radial direction, a band layer in which a band cord of an organic fiber such as nylon is spirally wound at an angle of 5 degrees or less with respect to the circumferential direction for the purpose of improving high-speed durability. 10 can be provided. As the band layer 10, a pair of left and right edge band plies that covers only the outer end portion of the belt layer 7 in the tire axial direction and a full band ply that covers substantially the entire width of the belt layer 7 can be used as appropriate. A band ply and a single full band ply may be used in combination.

Next, the carcass 6 is formed from two carcass plies 6A and 6B in the radial direction in which carcass cords are arranged at an angle of, for example, 70 to 90 ° with respect to the tire circumferential direction. As the carcass cord, a well-known organic fiber cord such as nylon, polyester, rayon or the like is preferably used.

The inner carcass ply 6A includes a main body portion 11 straddling the bead cores 5 and 5 and a winding portion that is connected to the main body portion 11 and is wound around the bead core 5 from the inner side to the outer side in the tire axial direction. 12, and a hard bead apex rubber 8 extending radially outward from the bead core 5 is disposed between the main body 11 and the hoisting part 12.

The outer carcass ply 6B extends along the outer surface of the main body portion 11 of the inner carcass ply 6A, the main body portion 13 straddling the bead cores 5 and 5, and the main body portion 13 and the circumference of the bead core 5. It is formed as a so-called rolled-up carcass ply having a wound-up portion 14 that is wound up and locked from the inner side in the tire axial direction. The radially outer end of the winding part 14 is sandwiched between the winding part 12 of the carcass ply 6 </ b> A and the bead apex rubber 8 and is interrupted.

The bead apex rubber 8 has a substantially triangular cross section extending from the bead core 5 radially outward. The bead apex rubber 8 is made of a highly hard crosslinked rubber.

The clinch rubber 9 extends radially outward from the radial outer end of the chafer rubber 16 located at the radially inner end of the bead portion 4 and extends outward in the tire axial direction of the clinch rubber 9. The side surface is exposed and forms the outer surface of the bead portion 4. On the other hand, the inner side surface of the clinch rubber 9 on the inner side in the tire axial direction is in contact with the winding portion 12 of the carcass ply 6A.

The clinch rubber 9 is composed of two layers: a surface layer 9A that forms the outer surface of the bead portion 4, and an inner layer 9B that is disposed on the inner side in the tire axial direction of the surface layer 9A. The clinch rubber 9 is composed of only two layers.

The average thickness ts of the surface layer 9A is 0.3 mm or more, preferably 0.7 mm or more, more preferably 1.0 mm or more. If the thickness is less than 0.3 mm, the thickness of the surface layer is small, so that the inner layer is likely to be exposed due to wear of the surface layer, and sufficient chafing performance may not be obtained. The average thickness ts of the surface layer 9A is 2.5 mm or less, preferably 2.3 mm or less, more preferably 2.0 mm or less. If it exceeds 2.5 mm, the thickness of the inner layer is reduced by the increase in the thickness of the surface layer, the effect of deformation of the inner layer is reduced, and sufficient chafing performance may not be obtained.
In the present specification, the thickness of the surface layer 9A means a thickness in the normal direction from the outer surface of the surface layer 9A on the outer side in the tire axial direction. Further, the average thickness ts of the surface layer 9A is an average value obtained by measuring the thickness at each point on the outer surface on the outer side in the tire axial direction of the surface layer 9A every 5 mm from the radially inner end toward the radially outer side. It is.

The ratio (ts / ti) of the average thickness ts of the surface layer 9A and the average thickness ti of the inner layer 9B is preferably 0.08 or more, more preferably 0.12 or more, and still more preferably 0.5 or more. If it is less than 0.08, the effect obtained by the surface layer 9A may be reduced. ts / ti is preferably 2.0 or less, more preferably 1.5 or less, and still more preferably 1.3 or less. If it exceeds 2.0, the effect obtained by the inner layer 9B may be reduced.
In the present specification, the thickness of the inner layer 9B means the thickness in the normal direction from the outer surface of the inner layer 9B on the outer side in the tire axial direction. The average thickness ti of the inner layer 9B is an average value obtained by measuring the thickness at each point on the outer surface of the inner layer 9B on the outer side in the tire axial direction every 5 mm from the radially inner end toward the radially outer side. It is.

The hardness Hs1 of the surface layer 9A is 75 or higher, preferably 77 or higher, more preferably 80 or higher. If it is less than 75, the wear resistance of the surface layer 9A itself becomes insufficient, and there is a possibility that sufficient chafing performance cannot be obtained. For example, by setting the content of silica in the above range, the hardness Hs1 of the surface layer 9A can be adjusted in the above range. In addition, in this specification, hardness is a value measured by the method as described in the below-mentioned Example.

The hardness Hs2 of the inner layer 9B is 75 or less, preferably 74 or less, more preferably 73 or less. If it exceeds 75, the inner layer 9B (soft clinching layer) becomes difficult to deform with respect to the load, and accordingly, the surface layer 9A (hard clinching layer) that forms the outer surface of the bead portion also becomes difficult to deform. Assembly performance cannot be secured, and there is a possibility that sufficient chafing performance cannot be obtained. For example, by setting the content of silica in the above range, the hardness Hs2 of the inner layer 9B can be adjusted in the above range.

The difference (Hs1-Hs2) between the hardness Hs1 of the surface layer 9A and the hardness Hs2 of the inner layer 9B is 5 or more, preferably 6 or more, more preferably 7 or more. If it is less than 5, the function of improving the wear resistance of the surface layer 9A and the function of softening the inner layer 9B are insufficient, so that sufficient chafing performance may not be obtained.

In the present embodiment, the case where the clinch rubber 9 is composed of two layers of the surface layer 9A and the inner layer 9B has been described, but in the present invention, the clinch rubber includes a surface layer that forms the outer surface of the bead portion, As long as it has an inner layer arranged on the inner side in the tire axial direction of the surface layer, another layer may be further included.

As mentioned above, although an example of preferable embodiment of the pneumatic tire of this invention was demonstrated, this invention is not limited to the said embodiment, It can deform | transform and implement in a various aspect.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: SIR20
BR: BR150B manufactured by Ube Industries, Ltd.
Carbon black: Dia Black I (N220) manufactured by Mitsubishi Chemical Corporation
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Silica: Ultrazil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Anti-aging agent: Antigen 6C (N- (1,3-dimethyl-butyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd. DPG: Noxeller D (diphenylguanidine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator TBBS: NOXERA-NS (TBBS) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-4 and Comparative Examples 1-9
(Preparation of rubber composition for clinch)
According to the blending contents shown in Table 1, using a 1.7 L Banbury mixer, among the blended materials, materials other than sulfur and a vulcanization accelerator were kneaded for 3 minutes at 150 ° C. to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the kneaded material obtained, and kneaded for 5 minutes under the condition of 80 ° C. using an open roll to obtain an unvulcanized rubber composition. Further, the obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 20 minutes to obtain a vulcanized rubber composition (clinch rubber (surface layer, inner layer)).
(Production of test pneumatic tire)
The obtained unvulcanized rubber composition was extruded in accordance with the shape of the clinched portion, and bonded to other members to form an unvulcanized tire so as to have the basic structure shown in FIG. Vulcanization was carried out for 20 minutes under the condition of ° C. to produce a test pneumatic tire (size: 195 / 65R15 91H). Table 1 shows the average thickness ts of the surface layer, the average thickness ti of the inner layer, and the average thickness (average thickness of the clinch rubber) when the clinch rubber has a one-layer structure. The average thickness of the clinch rubber is an average value obtained by measuring the thickness at each point on the outer surface on the outer side in the tire axial direction of the clinch rubber every 5 mm from the radially inner end toward the radially outer side.

The following evaluation was performed using the obtained vulcanized rubber composition (clinch rubber (surface layer, inner layer)) and a test pneumatic tire. Each test result is shown in Table 1.

(hardness)
Based on JIS K6253, the hardness of the obtained vulcanized rubber composition (clinch rubber) was measured using a hardness meter at a temperature of 25 ° C. (Shore-A measurement).

(Measurement of rim chaefing in durability test)
Using a test pneumatic tire, after performing a 30000 km drum running durability test under conditions of an internal pressure of 200 KPa, a load of 7 km, and a speed of 80 km / h, the tire was removed from the rim, and the thickness of the rim contact portion (clinch portion) Was compared with the thickness at the start of the test, and the amount of shaving (chafing amount) was measured. The smaller the amount of chafing, the better the chafing performance.

In the case of using a clinching rubber produced using a clinching rubber composition in which the total content of natural rubber and modified natural rubber is a specific amount or more, and the silica content in the reinforcing filler is a predetermined amount or more. Even if there is, the clinch rubber has a surface layer forming the outer surface of the bead portion and an inner layer disposed on the inner side in the tire axial direction of the surface layer, the average thickness of the surface layer is a specific range, the hardness of the surface layer is The example in which the hardness of the inner layer was not less than a predetermined value and the hardness difference between the surface layer and the inner layer was not less than a certain value had good chafing performance. Compared to Example 2, the hardness of the surface layer is high, the hardness of the internal layer is low, and the difference in hardness between the surface layer and the internal layer is large. Example 1 has better chafing performance than Example 2. It was. Moreover, compared with Example 2, Example 4 with a large average thickness of the surface layer had better chafing performance than Example 2. A large amount of butadiene rubber or carbon black, which is a petroleum resource-derived material (the total content of natural rubber and modified natural rubber is less than a specific amount, and / or the content of silica in the reinforcing filler is a predetermined amount. Comparative Examples 1 and 2 below) had good chafing performance even when the clinch rubber had a single layer structure. However, since petroleum resource-derived materials are used, it is impossible to prepare for the depletion of petroleum resource-derived raw materials or to consider the environment. Also, a clinching rubber produced using a clinching rubber composition in which the total content of natural rubber and modified natural rubber is a specific amount or more and the silica content in the reinforcing filler is a predetermined amount or more is used. Comparative Examples 3 and 4 in which the clinch rubber has a single layer structure, Comparative Examples 5 and 6 in which the average thickness of the surface layer is outside a specific range, Comparative Example 7 in which the difference in hardness between the surface layer and the internal layer is less than a certain value, Surface layer Comparative Example 8 in which the hardness of the inner layer is less than a specific value, and Comparative Example 9 in which the hardness of the inner layer exceeds a predetermined value and the difference in hardness between the surface layer and the inner layer is less than a certain value is compared with the embodiment. Was inferior.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass ply 6B in carcass 6A Outer carcass ply 7 Belt layer 8 Bead apex rubber 9 Clinch rubber 9A Surface layer 9B Inner layer 10 Band layer 11 Main body part 12 Winding part 13 Body part 14 Winding part 15 Inner liner 16 Chafer

Claims (6)

A carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, a bead apex rubber extending radially outward from the bead core, and an outer surface of the bead portion disposed on the outer side in the tire axial direction of the bead apex rubber A pneumatic tire having clinch rubber
The clinch rubber has a surface layer that forms the outer surface of the bead portion, and an inner layer that is disposed on the inner side in the tire axial direction of the surface layer,
The surface layer has an average thickness of 0.3 to 2.5 mm;
The hardness of the surface layer is 75 or more, the hardness of the inner layer is 75 or less, the difference in hardness between the surface layer and the inner layer is 5 or more,
In the surface layer and the inner layer, the total content of natural rubber and modified natural rubber in 100% by mass of the rubber component is 70% by mass or more, and the content of silica in 100% by mass of the reinforcing filler is A pneumatic tire manufactured using a rubber composition for clinch that is 50% by mass or more. The pneumatic tire according to claim 1, wherein the clinch rubber is composed of the surface layer and the inner layer. The pneumatic tire according to claim 1 or 2, wherein the silica has a nitrogen adsorption specific surface area of 50 to 300 m ² / g. The pneumatic tire according to any one of claims 1 to 3, wherein in the rubber composition for clinch, the silica content is 25 to 100 parts by mass with respect to 100 parts by mass of the rubber component. The ratio of the average thickness of the surface layer to the average thickness of the inner layer (average thickness of the surface layer / average thickness of the inner layer) is 0.08 to 2.0. Pneumatic tires. The pneumatic tire according to any one of claims 1 to 5, wherein the rubber composition for clinching includes a silane coupling agent.

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