JP2020114707A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire in which a bead filler has a two-layer structure constituted of an upper bead filler and a lower bead filler, which has low rolling resistance and has a bead part being excellent in durability.SOLUTION: A pneumatic tire has a bead filler 6 having a two-layer structure constituted of an upper bead filler 6A and a lower bead filler 6B. The upper bead filler 6A is constituted of a rubber composition obtained by compounding 15 pts.mass-60 pts.mass of carbon black, in which a nitrogen adsorption specific surface area N2 SA is 70 m2/g-100 m2/g, into 100 pts.mass of a rubber component containing 50 pts.mass or more of natural rubber and 15 pts.mass or more of terminal-modified butadiene rubber, where hardness of the rubber composition constituting the upper bead filler 6A is set to 65 or less and is set to be lower than hardness of the rubber composition constituting the lower bead filler 6B.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pneumatic tire having a two-layer structure in which a bead filler is composed of an upper bead filler and a lower bead filler.

Pneumatic tires are required to have improved fuel efficiency during running in order to reduce environmental load. Therefore, heat generation of the rubber composition forming each part of the pneumatic tire is suppressed. In recent years, in order to further improve fuel efficiency, for example, it is required to suppress heat generation in a rubber composition that constitutes a bead filler arranged in a bead portion of a pneumatic tire.

As an index of exothermicity of the rubber composition, tan δ at 60° C. (hereinafter, referred to as “tan δ (60° C.)”) measured by dynamic viscoelasticity is generally used, and tan δ (60° C.) of the rubber composition is small. The lower the exothermicity, the less. Then, as a method of reducing tan δ (60° C.) of the rubber composition, for example, a compounding amount of a filler such as carbon black may be reduced or a particle size of carbon black may be increased. Alternatively, it has been proposed to blend silica (see, for example, Patent Document 1). However, these methods do not always provide sufficient rubber hardness and fatigue resistance, and there is a concern that their durability will be affected when used in tires (particularly when used as bead fillers). Therefore, in a rubber composition for a tire intended to be used as a bead filler, there is a demand for further measures for improving low rolling properties while maintaining good load durability when the tire is used.

JP, 2015-059181, A

An object of the present invention is to provide a pneumatic tire having a two-layer structure in which a bead filler is composed of an upper bead filler and a lower bead filler, which has low rolling resistance and excellent durability of a bead portion. To do.

The pneumatic tire of the present invention which achieves the above object, a tread portion which extends in the tire circumferential direction and forms an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and tires of these sidewall portions. In a pneumatic tire comprising a pair of bead portions arranged on the inner side in the radial direction, a bead core provided on each of the pair of bead portions, and a bead filler arranged on the tire radial outside of the bead core. , The bead filler has a two-layer structure consisting of a lower bead filler adjacent to the bead core and an upper bead filler located on the tire radial outer end side of the bead filler, the upper bead filler being per 100 parts by mass of the rubber component containing a natural rubber 50% by mass or more and terminal-modified butadiene rubber 15 wt% or more, the carbon black specific surface area by nitrogen adsorption N ₂ SA is 70m ² / g~100m ² / g is 15 1 to 60 parts by mass of the rubber composition, the hardness of the rubber composition constituting the upper bead filler is 65 or less, and lower than that of the rubber composition constituting the lower bead filler. It is characterized by hardness.

The pneumatic tire of the present invention uses the above-mentioned specific rubber composition as the rubber composition that constitutes the upper bead filler set to a hardness lower than that of the lower bead filler, so while reducing the rolling resistance, The durability of the bead portion can be improved. In particular, since the rubber composition constituting the upper bead filler uses the carbon black having a specific particle diameter and the terminal-modified butadiene rubber in combination, it is possible to appropriately increase the rubber hardness without deteriorating the heat generation property. This makes it possible to improve the above-mentioned performance in a well-balanced manner.

In the present invention, the "hardness" is the hardness of the rubber composition measured by a durometer type A at a temperature of 20°C according to JIS K6253. Further, the "nitrogen adsorption specific surface area N ₂ SA of carbon black" is measured in accordance with JIS 6217-2.

In the present invention, the molecular weight distribution (Mw/Mn) determined from the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the terminal-modified butadiene rubber compounded in the rubber composition constituting the upper bead filler is 2.0. The following is preferable. By narrowing the molecular weight distribution in this manner, the rubber physical properties become better, which is advantageous for improving the durability while reducing the rolling resistance. The "weight average molecular weight Mw" and the "number average molecular weight Mn" are measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

In the present invention, the terminal functional group of the terminal-modified butadiene rubber compounded in the rubber composition constituting the upper bead filler is selected from the group consisting of a hydroxyl group, an amino group, an amide group, an alkoxyl group, an epoxy group, and a siloxane bonding group. It is preferable that it is at least one kind. This increases the affinity with carbon black and further improves the dispersibility of carbon black, so it is possible to more effectively increase rubber hardness and load durability while maintaining low exothermicity. It is advantageous to achieve a good balance.

In the present invention, the hardness difference ΔHs between the hardness of the rubber composition forming the upper bead filler and the hardness of the rubber composition forming the lower bead filler is preferably in the range of 20 to 30. As a result, the hardness of the bead filler as a whole gradually decreases from the bead core side toward the tire radial outside, so that the strain of the bead portion can be dispersed and the durability of the bead portion can be increased. ..

It is a meridian half cross section of the pneumatic tire which consists of embodiment of this invention.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, a pneumatic tire of the present invention includes a tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a sidewall portion 2 which is arranged inside a tire radial direction. And a pair of bead portions 3. In FIG. 1, reference symbol CL indicates the tire equator. Although not shown because FIG. 1 is a meridional cross-sectional view, the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction to form an annular shape. The toroidal basic structure of is constructed. Hereinafter, although the description with reference to FIG. 1 is basically based on the meridian cross-sectional shape shown in the drawing, each tire constituent member extends in the tire circumferential direction to form an annular shape.

A carcass layer 4 is mounted between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded around the bead core 5 arranged in each bead portion 3 from the tire width direction inner side to the tire width direction outer side. A bead filler 6 is arranged on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4.

The bead filler 6 of the present invention has a two-layer structure of an upper bead filler 6A and a lower bead filler 6B. The lower bead filler 6B is arranged at a position adjacent to the outer side of the bead core 5 in the tire radial direction. The upper bead filler 6A is adjacent to the lower bead filler 6B, and is arranged on the radially outer end side of the bead filler 6. In particular, in the illustrated example, the upper bead filler 6A is arranged on the tire width direction outer side and the tire radial direction outer side of the lower bead filler 6B, and the end portion of the folded portion of the carcass layer 4 is the tire of the upper bead filler 6A. It touches the outside in the width direction. The upper bead filler 6A is configured to have a lower hardness than the lower bead filler 6B, whereby the hardness of the bead filler 6 as a whole gradually decreases from the bead core 5 side toward the tire radial direction outer side. Therefore, the strain of the bead portion 3 can be dispersed and the durability of the bead portion 3 can be enhanced.

A plurality of layers (four layers in the illustrated example) of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction. The reinforcing cords are arranged between layers so that the reinforcing cords intersect each other. In these belt layers 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in the range of, for example, 10° to 60°. Although only the belt layer 7 is provided in the illustrated example, a belt reinforcing layer (not shown) may be further provided on the outer peripheral side of the belt layer 7.

A tread rubber layer 11 is arranged on the outer peripheral side of the carcass layer 4 in the tread portion 1, a side rubber layer 12 is arranged on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and in the bead portion 3 A rim cushion rubber layer 13 is arranged on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4. The tread rubber layer 11 in the illustrated example has a two-layer structure including a cap tread 11A exposed on the surface of the tread portion 1 and an undertread 11B embedded inside the cap tread 11A in the radial direction.

In the present invention, since the upper bead filler 6A is basically composed of a specific rubber composition described below, the air having a two-layer structure in which the bead filler 6 is composed of the upper bead filler 6A and the lower bead filler 6B. The sectional structure of the filled tire is not limited to the illustrated example. Examples of the pneumatic tire having a two-layer structure include heavy duty tires such as truck and bus tires.

In the rubber composition for tires that constitutes the upper bead filler 6A (hereinafter sometimes referred to as "rubber composition part for tires of the present invention"), the rubber component is a diene rubber, and natural rubber and terminal-modified butadiene rubber are used. Be sure to include.

As the natural rubber, a rubber usually used in a rubber composition for tires can be used. By blending natural rubber, it is possible to obtain sufficient rubber strength as a rubber composition for tires. When the total amount of the rubber component (diene rubber) is 100% by mass, the content of the natural rubber is 50% by mass or more, preferably 50% by mass to 80% by mass, more preferably 65% by mass to 80% by mass. If the compounding amount of the natural rubber is less than 50% by mass, the rubber strength will decrease.

The terminal-modified butadiene rubber is a butadiene rubber modified with an organic compound having a functional group at one end or both ends of the molecular chain. By blending such a terminal-modified butadiene rubber, the affinity with the carbon black described later is increased and the dispersibility is improved, so that the action and effect of the carbon black is further improved while keeping the exothermicity low. The rubber hardness can be increased. Examples of the functional group that modifies the terminal of the molecular chain include an alkoxysilyl group, a hydroxyl group (hydroxyl group), an aldehyde group, a carboxyl group, an amino group, an amide group, an imino group, an alkoxyl group, an epoxy group, an amide group, a thiol group, Examples thereof include ether groups and siloxane bonding groups. Among them, at least one selected from a hydroxyl group (hydroxyl group), an amino group, an amide group, an alkoxyl group, an epoxy group, and a siloxane bonding group is preferable. Here, the siloxane bonding group is a functional group having a -O-Si-O- structure.

When the total amount of the rubber component (diene rubber) is 100% by mass, the amount of the terminal-modified butadiene rubber is 15% by mass or more, preferably 15% by mass to 50% by mass, preferably 20% by mass to 35% by mass. is there. If the compounding amount of the terminal-modified butadiene rubber is less than 15% by mass, fuel economy is deteriorated. If the compounding amount of the terminal-modified butadiene rubber exceeds 50% by mass, the rubber strength will decrease.

The terminal-modified butadiene rubber used in the present invention has a vinyl content of preferably 0.1% by mass to 20% by mass, more preferably 0.1% by mass to 15% by mass. When the vinyl content of the terminal-modified butadiene rubber is less than 0.1% by mass, the affinity with carbon black is insufficient and it becomes difficult to sufficiently reduce heat generation. When the vinyl content of the terminal-modified butadiene rubber exceeds 20% by mass, the glass transition temperature Tg of the rubber composition increases, and rolling resistance and abrasion resistance cannot be sufficiently improved. The vinyl unit content of the terminal-modified butadiene rubber is measured by infrared spectroscopic analysis (Hampton method). The increase/decrease in vinyl unit content in the terminal-modified butadiene rubber can be appropriately adjusted by a usual method such as a catalyst.

The glass transition temperature Tg of the terminal-modified butadiene rubber used in the present invention is preferably -85°C or lower, and more preferably -90°C to -100°C. By setting the glass transition temperature Tg in this way, heat generation can be effectively reduced. If the glass transition temperature Tg exceeds −85° C., the effect of reducing heat generation cannot be sufficiently obtained. The glass transition temperature Tg of natural rubber is not particularly limited, but can be set to, for example, −70° C. to −80° C.

The molecular weight distribution (Mw/Mn) obtained from the weight average molecular weight (Mw) and number average molecular weight (Mn) of the terminal-modified butadiene rubber is preferably 2.0 or less, more preferably 1.1 to 1.6. As described above, by using a terminal-modified butadiene rubber having a narrow molecular weight distribution, the rubber physical properties become better, and the rolling resistance can be reduced while effectively improving the durability of the tire. .. When the molecular weight distribution (Mw/Mn) of the terminal-modified butadiene rubber exceeds 2.0, the hysteresis loss becomes large, the heat generation property of the rubber becomes large, and the compression set resistance decreases.

The tire rubber composition of the present invention may contain a diene rubber other than natural rubber and terminal-modified butadiene rubber. Other diene rubbers include, for example, butadiene rubber without terminal modification, styrene butadiene rubber, isoprene rubber, acrylonitrile-butadiene rubber and the like. These diene rubbers can be used alone or as an arbitrary blend.

The rubber composition for a tire of the present invention always contains carbon black as a filler. By blending carbon black, the strength of the rubber composition can be increased. In particular, carbon black used in the present invention, the nitrogen adsorption specific surface area N ₂ SA is 70m ² / g~100m ² / g. By thus combining carbon black having a specific particle size with the above-mentioned terminal-modified butadiene rubber, it is possible to effectively increase the rubber hardness while maintaining low exothermicity. When the nitrogen adsorption specific surface area N ₂ SA of carbon black is less than 70 m ² /g, the durability of the tire is deteriorated. When the nitrogen adsorption specific surface area N ₂ SA of carbon black exceeds 100 m ² /g, the exothermic property deteriorates.

The blending amount of carbon black is 15 parts by mass to 60 parts by mass, preferably 30 parts by mass to 60 parts by mass, and more preferably 40 parts by mass to 50 parts by mass with respect to 100 parts by mass of the rubber component. When the blending amount of carbon black is less than 15 parts by mass, the hardness is lowered and the durability of the tire is lowered. If the blending amount of carbon black exceeds 60 parts by mass, the exothermic property deteriorates.

The rubber composition of the present invention may contain an inorganic filler other than carbon black. Examples of other inorganic fillers include silica, clay, talc, calcium carbonate, mica, aluminum hydroxide and the like.

Compounding agents other than the above may be added to the rubber composition for a tire of the present invention. Examples of other compounding agents include various compounding agents generally used for pneumatic tires, such as vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, liquid polymers, thermosetting resins, and thermoplastic resins. can do. The compounding amount of these compounding agents can be a conventional general compounding amount as long as the object of the present invention is not impaired. As the kneading machine, a usual kneading machine for rubber, for example, Banbury mixer, kneader, roll or the like can be used.

The hardness of the tire rubber composition of the present invention having such a composition is 65 or less, preferably 45 to 65, more preferably 55 to 65. The tan δ at 60° C. of the rubber composition for a tire of the present invention is preferably 0.06 to 0.10, more preferably 0.06 to 0.08. Since the rubber composition of the present invention has such physical properties, it is possible to improve the durability when used as a tire while reducing rolling resistance. In particular, the hardness is 65 or less, and the bead filler 6 having the two-layer structure has an appropriate hardness as the upper bead filler 6A, which is advantageous for improving the durability of the bead portion 3. If the hardness exceeds 65, the hardness of the upper bead filler 6A is too high, and the durability of the bead portion 3 cannot be improved. Moreover, it becomes difficult to sufficiently reduce the rolling resistance. If tan δ at 60° C. exceeds 0.10, heat generation is deteriorated and rolling resistance cannot be reduced. Incidentally, these hardness and tan δ are not determined only by the above-mentioned blending, but are physical properties that can be adjusted by, for example, kneading conditions and kneading methods.

The rubber composition for a tire of the present invention can improve the durability when made into a tire while reducing rolling resistance due to the above-mentioned composition and physical properties. In particular, since the carbon black having a specific particle size and the terminal-modified butadiene rubber are used in combination, it is possible to appropriately increase the rubber hardness without deteriorating heat generation and improve the above-mentioned performance in a well-balanced manner. be able to. Therefore, the rubber composition for a tire of the present invention is preferably used for the upper bead filler 6A of the bead filler 6 having the above-mentioned two-layer structure, and the pneumatic tire using the rubber composition for a tire for the upper bead filler 6A. Can improve fuel efficiency and durability of the bead portion.

As described above, in the bead filler 6 having a two-layer structure, the upper bead filler 6A to which the rubber composition for a tire of the present invention is applied has a lower hardness than the lower bead filler 6B. At that time, the hardness difference ΔHs between the hardness of the rubber composition constituting the upper bead filler 6A (rubber composition part for tire of the present invention) and the hardness of the rubber composition constituting the lower bead filler 6B is preferably 20 to 30. , And more preferably in the range of 22 to 27. By setting the hardness difference ΔHs in this manner, the bead filler 6 as a whole has a structure in which the hardness gradually decreases from the bead core 5 side toward the tire radial direction outer side, so that the strain of the bead portion 3 is dispersed. Thus, the durability of the bead portion 3 can be improved. When the hardness difference ΔHs is less than 20, there is substantially no difference from the bead filler 6 composed of a single rubber composition, and the effect of forming the bead filler 6 into a two-layer structure cannot be sufficiently obtained. When the hardness difference ΔHs exceeds 30, the upper bead filler 6A becomes relatively soft, and it becomes difficult to sufficiently secure the durability of the bead portion 3. The hardness of the rubber composition constituting the lower bead filler 6B is not particularly limited, but it is preferably set in the range of 75 to 95, more preferably 80 to 90. When the hardness of the rubber composition constituting the lower bead filler 6B is less than 75, the hardness difference from the upper bead filler 6A becomes small, and the effect of forming the bead filler 6 into a two-layer structure cannot be sufficiently obtained. When the hardness of the rubber composition forming the lower bead filler 6B exceeds 95, the hardness of the bead portion 3 becomes excessive, and cracks occur between the bead fillers.

Hereinafter, the present invention will be further described with reference to examples, but the scope of the present invention is not limited to these examples.

17 types of rubber compositions having the formulations shown in Tables 1 and 2 (Standard Example 1, Comparative Examples 1 to 4 and Examples 1 to 10) were weighed for the compounding components except the vulcanization accelerator and sulfur, and 1 The mixture was kneaded for 5 minutes with an 8 L closed Banbury mixer, the master batch was discharged at a temperature of 150° C., and the mixture was cooled to room temperature. Then, this masterbatch was subjected to a 1.8 L closed Banbury mixer, and a vulcanization accelerator and sulfur were added and mixed for 2 minutes to prepare a rubber composition.

The obtained rubber composition was press-vulcanized in a predetermined mold for 20 minutes to prepare a vulcanized rubber test piece, and the rubber hardness and tan δ at 60° C. were measured and shown in Tables 1 and 2. In Tables 1 and 2, the hardness of the rubber composition was measured at a temperature of 20° C. by a durometer type A according to JIS K6253. In addition, tan δ at 60° C. was measured in accordance with JIS K6394 using a viscoelasticity spectrometer under the conditions of 10%±2% elongation deformation strain, 20 Hz frequency, and 60° C. temperature.

Further, a pneumatic tire (tire size 11R22.5) using the obtained rubber composition as the upper bead filler was produced. Each pneumatic tire has the basic structure shown in FIG. 1, and the items shown in Tables 1 and 2 are different. Incidentally, in these pneumatic tires, any of the lower bead fillers A, B and C shown in Table 3 was used as the rubber composition constituting the lower bead filler.

With respect to the obtained pneumatic tires, the fuel efficiency performance and the bead portion durability were evaluated by the methods described below.

Low fuel consumption performance Each pneumatic tire was assembled to a standard rim (rim size 22.5 x 7.50), and an indoor drum tester (drum diameter: 1707.6 mm) was used, in accordance with ISO28580, air pressure 210 kPa, load. The rolling resistance was measured under the conditions of 4.82 kN and speed of 80 km/h. The evaluation result is shown by an index with the value of Standard Example 1 being 100, using the reciprocal of the measured value. The smaller the index value, the lower the rolling resistance and the better the fuel efficiency.

Bead Durability Each pneumatic tire is mounted on a standard rim (rim size 22.5×7.50), and an indoor drum tester (drum diameter: 1707 mm) is used to comply with JIS D-4230 and JATMA 2018. After the end of the annual version specified load durability test, the load was increased by 20% every 5 hours, and the running distance until failure in the bead portion was measured. The evaluation results are shown by an index with the measured value of Standard Example 1 being 100. The larger this index value, the better the durability of the bead portion.

The types of raw materials used in Tables 1 and 2 are shown below.
-NR: Natural rubber, TSR20 (glass transition temperature Tg = -65°C)
SBR: Styrene butadiene rubber, Nipol 1502 (glass transition temperature Tg=-60°C) manufactured by Nippon Zeon Co., Ltd.
-Modified S-SBR: Terminal-modified solution-polymerized styrene-butadiene rubber, Nipol NS612 manufactured by Zeon Corporation (non-oil-extended product, glass transition temperature Tg=-60°C)
BR: butadiene rubber, Nipol BR1220 manufactured by Zeon Corporation (glass transition temperature Tg=-105°C)
Modified BR1: terminal modified butadiene rubber, BR54 manufactured by JSR (glass transition temperature Tg: −107° C., functional group: silanol group, molecular weight distribution Mw/Mn=2.5)
-Modified BR2: terminal-modified butadiene rubber synthesized by the following method (glass transition temperature Tg: -93°C, functional group: polyorganosiloxane group, refer to the following for molecular weight distribution)
-Modified BR3: Terminal-modified butadiene rubber, Nipol BR1250H manufactured by Nippon Zeon Co., Ltd. (glass transition temperature Tg: -96°C, functional group: N-methylpyrrolidone group, molecular weight distribution Mw/Mn = 1.1).
CB1: carbon black, seashore N manufactured by Tokai Carbon Co., Ltd. (nitrogen adsorption specific surface area N ₂ SA: 70 m ² /g)
CB2: carbon black, Tokai Carbon Seast F (nitrogen adsorption specific surface area N ₂ SA: 45 m ² /g)
・Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Co., Ltd. ・Anti-aging agent: Santoflex 6PPD manufactured by Flexis
・Stearic acid: Shin-Rika's stearic acid 50S
・Sulfur: Miklon OT-20 (Sulfur content: 80% by mass) manufactured by Shikoku Chemicals
・Vulcanization accelerator: Nocceller CZ manufactured by Ouchi Shinko Chemical Co., Ltd.

Method for synthesizing modified BR2 After charging cyclohexane 5670 g, 1,3-butadiene 700 g and tetramethylethylenediamine 0.17 mmol in a nitrogen atmosphere in an autoclave equipped with a stirrer, the polymerization contained in cyclohexane and 1,3-butadiene is inhibited. The amount of n-butyllithium necessary for neutralizing the impurities was added, and further, 8.33 mmol of n-butyllithium for the polymerization reaction was added, and the polymerization was started at 50°C. After 20 minutes from the start of the polymerization, 300 g of 1,3-butadiene was continuously added over 30 minutes. The maximum temperature during the polymerization reaction was 80°C. After the continuous addition was completed, the polymerization reaction was continued for another 15 minutes, and after confirming that the polymerization conversion rate was in the range of 95% to 100%, a small amount of the polymerization solution was sampled. A small amount of the sampled polymerization solution was quenched by adding excess methanol and then air-dried to obtain a polymer, which was used as a sample for gel permeation chromatography (GPC) analysis. Using the sample, the peak top molecular weight and the molecular weight distribution of the polymer (corresponding to a conjugated diene-based polymer chain having an active end) were measured and found to be "230,000" and "1.04", respectively.

Immediately after sampling the aforementioned small amount of the polymerization solution, 40% by weight of 0.288 mmol of 1,6-bis(trichlorosilyl)hexane (corresponding to 0.0345 times mol of n-butyllithium used for the polymerization) was added to the polymerization solution. It was added in the state of a cyclohexane solution and reacted for 30 minutes. Further, after that, 0.0382 mmol of polyorganosiloxane A (corresponding to 0.00459 times mol of n-butyllithium used for polymerization) was added in the state of a 20 wt% xylene solution, and the reaction was carried out for 30 minutes. Then, as a polymerization terminator, methanol was added in an amount corresponding to twice the mol of n-butyllithium used. As a result, a solution containing the modified butadiene rubber was obtained. To this solution, after adding 0.2 parts of 2,4-bis(n-octylthiomethyl)-6-methylphenol as an antioxidant per 100 parts of rubber component, the solvent was removed by steam stripping, It was vacuum dried at 24° C. for 24 hours to obtain a solid modified butadiene rubber (modified BR2). With respect to this modified butadiene rubber (modified BR2), the weight average molecular weight, molecular weight distribution, coupling rate, vinyl bond content, and Mooney viscosity were measured to be "510,000", "1.46", and "28", respectively. %", "11 mass%" and "46".

The types of raw materials used in Table 3 are shown below.
-NR: Natural rubber, TSR20 (glass transition temperature Tg = -65°C)
SBR: Styrene butadiene rubber, Nipol 1502 (glass transition temperature Tg=-60°C) manufactured by Nippon Zeon Co., Ltd.
CB: carbon black, Tokai Carbon Co., Ltd., Nest, a specific surface area N ₂ SA: 70 m ² /g
・Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Co., Ltd. ・Anti-aging agent: Santoflex 6PPD manufactured by Flexis
・Stearic acid: Shin-Rika's stearic acid 50S
・Sulfur: Miklon OT-20 (Sulfur content: 80% by mass) manufactured by Shikoku Chemicals
・Vulcanization accelerator: Nouchira NS-P manufactured by Ouchi Shinko Chemical Co., Ltd.

As is clear from Tables 1 and 2, the pneumatic tires of Examples 1 to 10 improved the fuel economy performance and load durability in a well-balanced manner as compared with Standard Example 1.

On the other hand, in the pneumatic tire of Comparative Example 1, the rubber composition constituting the upper bead filler contained styrene-butadiene rubber instead of the terminal-modified butadiene rubber, so that the fuel economy performance and the bead portion durability were deteriorated. In the pneumatic tire of Comparative Example 2, the rubber composition constituting the upper bead filler contained the end-modified solution-polymerized styrene-butadiene rubber in place of the end-modified butadiene rubber, and thus the fuel economy performance and the bead portion durability were deteriorated. In the pneumatic tire of Comparative Example 3, the compounding amount of the terminal-modified butadiene rubber in the rubber composition constituting the upper bead filler was small, and therefore the effect of improving the fuel economy performance and the bead portion durability could not be obtained. In the pneumatic tire of Comparative Example 4, the nitrogen adsorption specific surface area of the carbon black blended in the rubber composition constituting the upper bead filler was too small, so the fuel economy performance and the bead portion durability were deteriorated.

1 tread part 2 sidewall part 3 bead part 4 carcass layer 5 bead core 6 bead filler 6A upper bead filler 6B lower bead filler 7 belt layer 11 tread rubber layer 12 side rubber layer 13 rim cushion rubber layer CL tire equator

Claims (4)

An annular tread portion extending in the tire circumferential direction, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged on the tire radial inner side of these sidewall portions. In a pneumatic tire having a bead core provided in each of the pair of bead parts, and a bead filler arranged on the tire radial direction outer side than the bead core,
The bead filler has a two-layer structure composed of a lower bead filler adjacent to the bead core and an upper bead filler located on the tire radial direction outer end side of the bead filler,
Said upper bead filler, per 100 parts by weight of the rubber component containing a natural rubber 50% by mass or more and terminal-modified butadiene rubber 15 wt% or more, a nitrogen adsorption specific surface area N ₂ SA is 70m ² / g~100m ² / g Is composed of a rubber composition containing 15 to 60 parts by mass of carbon black, and the hardness of the rubber composition constituting the upper bead filler is 65 or less, and the lower bead filler is constituted. A pneumatic tire having a hardness lower than that of a rubber composition. The molecular weight distribution (Mw/Mn) obtained from the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the terminal-modified butadiene rubber blended in the rubber composition constituting the upper bead filler is 2.0 or less. The pneumatic tire according to claim 1, wherein: The terminal functional group of the terminal-modified butadiene rubber compounded in the rubber composition constituting the upper bead filler is at least one selected from the group consisting of a hydroxyl group, an amino group, an amide group, an alkoxyl group, an epoxy group, and a siloxane bonding group. The pneumatic tire according to claim 1 or 2, which is a seed. The hardness difference ΔHs between the hardness of the rubber composition that constitutes the upper bead filler and the hardness of the rubber composition that constitutes the lower bead filler is in the range of 20 to 30. The pneumatic tire according to any one of the above.

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