JP2000025425A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide new sidewall parts. SOLUTION: The pneumatic tire has carcass each of which extends from a tread part 2 to a bead core 5 of a head part 4 through a sidewall part 3, and a belt layer 7. A sidewall rubber 9 arranged in the area of the sidewall part 3 is formed of a three-layer structure comprising an inner layer rubber 10 on the side of the carcass 6, an outer layer rubber 12 forming the surface of the sidewall part, and an intermediate layer rubber 11 arranged between the inner and outer layer rubbers. The inner layer rubber 10 and the outer layer rubber 12 are integrated with each other without interposing the intermediate layer rubber in at least the outer end part of the area in the radial direction of the tire. Further, a belt-cushion layer 15 obtained by extending the outer end part 10a of the inner layer rubber 10 in the tire-radial direction between the belt layer 7 and the carcass 6 is formed between the belt layer 7 and the carcass 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pneumatic tire having improved sidewall rubber.

[0002]

2. Description of the Related Art In addition to cut resistance for protecting a side portion of a tire from external force, weather resistance, and discoloration resistance, a sidewall rubber of a pneumatic tire is used for attaching to an outer surface of a carcass in a tire manufacturing process. (Hereinafter, these properties may be collectively referred to as "basic properties").

FIG. 5 is a cross-sectional view of a conventional sidewall rubber a before a tire is formed, and has a one-layer structure made of a rubber composition having the above-described basic characteristics.
The side wall rubber a has a clinch rubber b which comes into contact with the flange surface of the rim on the tire radial inner side, and a cushion extending between the belt layer and the carcass on the tire radial outer side. Each of the rubbers c may be attached.

[0004]

In recent years, there have been many demands for tires from the market. Among them, as for the sidewall portion, for example, the rigidity of the sidewall portion for improving handle response is required. (Hysteresis loss reduction in sidewalls to improve fuel economy, improve vibration absorption performance to ensure ride comfort and stability at high speeds, and improve tire vulcanization speed.) Hereinafter, these performances may be collectively referred to as “high value-added characteristics.”).

However, with respect to rubber, the basic characteristics and the high value-added characteristics generally have a trade-off relationship in many cases. Therefore, in order to satisfy the high value-added characteristics while maintaining the basic characteristics in the sidewall portion, it is necessary to form the sidewall rubber into a multilayer structure composed of two or more rubbers.
-30563, JP-A-1-278805,
It has been proposed in Japanese Patent Application Laid-Open No. 2-102805.

The present invention proposes a novel multi-layered side wall rubber, which is different from the conventionally proposed various side wall rubbers. In particular, the present invention provides the basic characteristics and the high value-added characteristics. It is an object of the present invention to provide a pneumatic tire that is useful for achieving both compatibility and that can reduce the load on equipment such as an extruder and improve productivity while having a multilayer structure.

[0007]

The first object of the present invention is as follows.
The invention described is a pneumatic tire having a carcass extending from a tread portion to a bead core of a bead portion via a sidewall portion, and a belt layer disposed radially outward of the tire and inward of the tread portion, wherein the sidewall The side wall rubber disposed in the region of the portion is formed of a three-layer structure of the inner layer rubber on the carcass side, the outer layer rubber forming the surface of the side wall portion, and the intermediate layer rubber disposed therebetween. The inner rubber and the outer rubber are integrated without the intermediate rubber at least at the outer end in the tire radial direction of the region, and between the belt layer and the carcass, the inner rubber in the tire radial direction is formed. The present invention is characterized in that a belt cushion layer is formed by extending an outer end portion between the belt layer and the carcass.

In the invention according to claim 2, the belt cushion layer has a tire axial length CW of 10 mm or more, and the inner rubber and the outer rubber are formed of a rubber composition mainly composed of natural rubber. The pneumatic tire according to claim 1, wherein the intermediate layer rubber is formed of a rubber composition having a polymer ratio or a carbon ratio different from the inner layer rubber and the outer layer rubber by 1% or more. is there.

According to a third aspect of the present invention, the sidewall rubber disposed in the region of the sidewall portion is formed of a structure having at least two or more layers including an inner layer rubber on the carcass side and an outer layer rubber on the tire outer side. And the outer rubber layer has a bead base line B at its radial inner end.
In addition to terminating at a position P1 on the tire outer surface at a distance of 5 mm or more from L in the tire radial direction, the inner rubber layer is exposed to the tire outer surface from the position P1 to approximately the bead base line BL, thereby reducing the rim of the rim. A pneumatic tire characterized by forming a clinch that comes into contact with a flange surface directly or via a reinforcing layer.

According to a fourth aspect of the present invention, in the three-layer structure, the sidewall rubber includes an inner rubber layer on the carcass side, an outer rubber layer on the outer surface of the tire, and an intermediate rubber layer disposed therebetween. And the inner layer rubber and the outer layer rubber are radially inner ends of the sidewall portion region in the tire radial direction,
While being integrated without the intermediate rubber layer at the outer end, the intermediate rubber was formed from a rubber composition having a polymer ratio or a carbon ratio different from the inner rubber or the outer rubber by 1% or more. 4. The method according to claim 3, wherein
It is a pneumatic tire of the statement.

According to a fifth aspect of the present invention, a belt cushion layer is formed between the belt layer and the carcass by extending an outer end of the outer rubber layer in the tire radial direction. 5. The pneumatic tire according to 3 or 4.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An example of the first embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the tread portion 2 reaches the bead core 5 of the bead portion 4 via the side wall portion 3, and in this example, the bead core 5
1 shows a radial tire for a passenger car having a carcass 6 that is folded back around the carcass 6 and a belt layer 7 disposed radially outside the carcass 6 and inside the tread portion 2.

The carcass 6 comprises, for example, one or more plies 6A in which carcass cords are arranged at an angle of about 75 ° to 90 ° with respect to the tire equator C.
As the carcass cord, an organic fiber cord such as polyester, nylon or rayon is preferably employed, but a steel cord may be employed if necessary. In the present embodiment, at least two belt plies 7A in which steel cords are arranged at a small angle of 15 to 40 ° with respect to the tire equator, in this embodiment, two inner and outer belt plies 7A,
7B illustrates an example in which the cords are overlapped in a direction in which the cords cross each other.

As is clear from FIG. 1 and FIG. 2 showing the state before the tire is molded, the side wall rubber 9 disposed in the region of the side wall portion 3 has an inner layer rubber 10 on the carcass 6 side, This figure shows a three-layer structure including an outer rubber layer 12 forming a surface of a sidewall portion and an intermediate rubber layer 11 disposed therebetween. In addition, an example in which a clinch rubber 14 that is in contact with a flange of a rim is continuously provided on the inner end side in the tire radial direction of the sidewall rubber 9 is illustrated.

The inner rubber layer 10 and the outer rubber layer 12 are formed at least in the tire radial outer end portion of the sidewall region, in the present embodiment, at the tire radial outer end portion o, and at the inner end portion i, the intermediate rubber portion 11 is formed. 1 illustrates an example integrated without any intermediary. Such integration is preferable in that the bonding between the rubbers of the inner rubber layer 10, the intermediate rubber layer 11, and the outer rubber layer 12 is strengthened, and delamination of the rubber can be effectively prevented.

Further, between the belt layer 7 and the carcass 6, a belt cushion layer 15 is formed by extending a tire radially outer end portion 10a of the inner rubber layer 10 between the belt layer 7 and the carcass 6. Is formed. In this example, as shown in FIG. 2, such a belt cushion layer 15 is formed integrally with a sidewall rubber portion by changing a die of an extruder that extrudes the inner rubber 10. ing.

As described above, the outer end portion 10a of the inner rubber layer 10 in the tire radial direction is integrally formed and used as the belt cushion layer 15, so that the belt cushion rubber is separately extruded and the sidewall rubber 9 in the tire radial direction is formed. Since the step or equipment connected to the outer end can be omitted, the productivity of the tire can be improved. Belt cushion layer 1
Since the rubber composition 5 and the inner rubber layer 11 of the side wall rubber 10 are made of the same rubber composition, the number of types of rubber used for the tire can be reduced, and the cost can be reduced.

Here, the belt cushion layer 15 preferably has, for example, a tire axial length CW of 10 mm or more. When the length CW of the belt cushion layer 15 in the tire axial direction is less than 10 mm, the strain relieving ability of the belt layer 7 tends to decrease, and the durability tends to decrease. From this viewpoint, the width CW of the belt cushion layer 15 in the tire axial direction is 1
It is desirable to set it to 0 to 25 mm, more preferably 10 to 20 mm.

In the present embodiment, the inner rubber 10
The outer layer rubber 12 is formed of a rubber composition mainly composed of natural rubber having excellent adhesiveness and cut resistance. Therefore, the inner rubber 10 can improve the adhesion to the carcass 6, and the outer rubber 12 can improve the cut resistance, so that the basic characteristics of the sidewall rubber can be satisfied.

Among them, the rubber composition used for the outer layer rubber 12 is, for example, a rubber base material in which a natural rubber (NR) and a polybutadiene rubber (BR) having excellent weather resistance and friction resistance are blended. A compound containing HAF carbon black or FEF carbon black having a thickness of about 30 nm is preferable. Similarly, as the rubber composition used for the inner rubber layer 10, for example, natural rubber is used so that the strain relaxation ability of the belt cushion layer 15 becomes a suitable performance.
Polybutadiene rubber or styrene-butadiene rubber (S
It is preferable to mix the HAF carbon black with the rubber base compounded with BR). However, the HAF carbon black may be mixed so as to accelerate vulcanization, or may be foamed.

In the present embodiment, the intermediate layer rubber 11 is formed of a rubber composition having a polymer ratio or a carbon ratio different from the inner layer rubber 10 and the outer layer rubber 12 by 1% or more. I have. In other words, for the intermediate layer rubber 11, it is possible to adopt a rubber that can exhibit the high value-added characteristics without being bound by the basic characteristics required for the sidewall rubber. This can be useful for achieving compatibility.

The intermediate rubber 11 and the inner rubber 10
Alternatively, the difference in rubber composition between the outer rubber layer 12 and the outer rubber layer 12 is made different by 1% or more in the polymer ratio or the carbon ratio because the difference in rubber composition between the inner rubber layer 11 and the inner and outer rubber layers 10 and 12 exceeds the rubber analysis accuracy. Is sufficient, but it is preferable that there is a difference of 2% or more. In other words, in the present specification, those having a difference between the polymer ratio and the carbon ratio of less than 1% are handled as the same rubber in the compounding.

Although rubber analysis can be performed by various methods,
For example, JIS K6227 “Quantitative / thermal decomposition method and chemical decomposition method of rubber-carbon black” (or JIS K62
31 "Rubber-Measurement by Pyrolysis Gas Chromatography").

As the intermediate layer rubber 11, for example, a rubber capable of increasing the rigidity of the side wall portion, a rubber having a good rolling resistance or a good damping performance can be used.
This is preferable in that high value-added characteristics are given to the tire.

For example, to improve the damping performance including the safety and the noise performance at the time of high-speed running, it is effective to suppress the rebound resilience of the side wall rubber 9 and to have a shock absorbing function. In such a case, the intermediate layer rubber 11 is made of butyl rubber (I) having low rebound characteristics as a rubber base material.
IR) is preferable, for example, natural rubber 50
It is desirable to mix 40 to 60 parts by weight, preferably 45 to 60 parts by weight of SAF carbon with 100 parts by weight of the rubber base material of 70 to 70 parts by weight and 50 to 30 parts by weight of butyl rubber. In addition, such a rubber composition has a loss tangent tan δ,
It is preferred to be in the range of 0.15 to 0.35.

The “loss tangent tan δ” of the rubber is 4 mm
A strip sample having a width of 30 mm, a length of 1.5 mm and a thickness of 1.5 mm was cut out, and measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho under the conditions of a temperature of 70 ° C., a frequency of 10 Hz and a dynamic strain of ± 2%. Value.

Another rubber composition for the intermediate rubber layer 11 which can improve the damping performance has a specific gravity of 0.6 to 0.1.
About 9 foamed rubbers are preferred. For example, without using butyl rubber, 100 parts by weight of a rubber base material in which NR, BR, and SBR are substantially uniformly blended, for example, carbon (ISA)
It is also preferable to mix 45 to 60 parts by weight of F, HAF, GPF, etc.) and 4 parts by weight or less, for example, about 2 parts by weight of a foaming agent. This rubber is preferable in that the rolling resistance can be reduced at the same time.

Further, as an effective means for reducing the cost of the tire, the intermediate layer rubber 11 can be composed of an inexpensive rubber. For example, a rubber base in which NR is reduced and BR and SBR are blended is used. , And about 50 parts by weight of GPF carbon and calcium carbonate, respectively.

The inner rubber 10 and the outer rubber 12 may be composed of the same natural rubber composition or the same rubber composition mainly composed of natural rubber and polybutadiene rubber. In this case, the sidewall rubber 9 can be configured as a three-layer structure while suppressing the rubber composition to two types, that is, a rubber composition of the inner and outer rubbers 10 and 11 and a rubber composition of the intermediate rubber 12. Is preferred in that it can reduce

The thickness of each rubber layer is variously adjusted depending on the required tire performance and rubber compounding. The thickness of the intermediate rubber layer is, for example, 0.5 to 1.5 mm. 6
mm is illustrated.

(Second Embodiment) Next, an example of a second embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 3, the pneumatic tire of this embodiment has a carcass 6 and a belt layer 7 having the same configuration as those of the first embodiment.

Also in this embodiment, the side wall rubber 20 disposed in the region of the side wall portion 3 includes an inner layer rubber 21 on the carcass 6 side and an outer layer rubber 23 on the tire outer side.
And a three-layer structure including an intermediate layer rubber 22 disposed therebetween. The intermediate rubber layer 22 may be omitted, and a two-layer structure including the inner rubber layer 21 and the outer rubber layer 23 may be used.

The inner rubber layer 21 and the outer rubber layer 23 are provided at the radially inner ends i in the side wall portion region in the tire radial direction.
The outer end o is integrated without the intermediate rubber layer 22 therebetween. Thereby, the inner layer rubber 10,
The bonding between the rubbers of the intermediate layer rubber 11 and the outer layer rubber 12 is strengthened, and delamination of the rubber can be effectively prevented as in the above-described embodiment.

In the present embodiment, the outer rubber 2
3 terminates the tire radial inner end 23a at a position P1 on the tire outer surface that is separated from the bead base line BL by 5 mm or more in the tire radial direction, and the inner rubber 21 is substantially bead base line from the position P1. BL
Until the rim is exposed to the outside of the tire
The clinch 24 which is in contact with the flange surface Jf directly or via a reinforcing layer is formed.

In this embodiment, such a clinch 24 is shown in FIG.
As shown in the figure, an extruder extruding the inner layer rubber 21 is formed integrally with the sidewall rubber portion by changing a die.

As described above, the inner end 21a of the inner rubber 21 in the tire radial direction is integrally formed and used as the clinch 24, so that the clinch is separately extruded to be attached to the outer end of the sidewall rubber 9 in the tire radial direction. Since it is possible to omit the steps or facilities to be connected, the productivity of the tire can be improved. In addition, since the clinch 24 and the inner rubber 21 of the sidewall rubber 20 are made of the same rubber composition, the number of types of rubber used for the tire can be reduced, and the cost can be reduced.

The inner rubber 20 forming the clinch 24 is in contact with, for example, a rim flange directly or via a reinforcing layer, so that the inner rubber 20 is more resistant to friction than the outer rubber.
It is preferable to use a rubber having excellent abrasion resistance, for example, a rubber composition containing 50 to 70 parts by weight of carbon black ISAF to FEF class in a rubber base material having an NR of 30 to 100 parts by weight and a BR of 0 to 70 parts by weight. Things can be used.

The inner end 21a of the inner rubber layer 21 in the radial direction of the tire substantially extends to the bead base line BL. Accordingly, the length of the clinch 24 in the tire radial direction can be adjusted by regulating the terminal position of the inner end of the outer rubber layer 23 in the tire radial direction. For example, the clinch 2 appearing on the outer surface of the tire
It is preferable that the length L in the radial direction of 4 is 5 mm or more and 40 mm or less, more preferably 5 to 30 mm. The length L is 5
If it is less than mm, the number of clinch 24 is reduced, and problems such as rim detachment and rim misalignment are likely to occur.

Further, in this embodiment, the outer end 23b of the outer rubber layer in the tire radial direction is extended between the belt layer 7 and the carcass 6 between the belt layer 7 and the carcass 6. A belt cushion layer 25 is formed as an example. Such a belt cushion layer 25
In this example, as shown in FIG. 4, an extruder that extrudes the outer rubber 23 is formed integrally with the side wall rubber portion by changing a die of the extruder.

As described above, by using the outer end 23b of the outer layer rubber 23 in the tire radial direction integrally formed as the belt cushion layer 25, the belt cushion rubber is separately extruded and the side wall rubber 9 is extruded in the tire radial direction. Since the steps or equipment connected to the outer end can be omitted, the productivity of the tire can be further improved. Further, since the belt cushion layer 25 and the inner rubber layer 11 of the side wall rubber 10 are made of the same rubber composition, the number of types of rubber used for the tire can be reduced, and the cost can be reduced.

The inner rubber 21 and the outer rubber 23 of the present embodiment
In this case, the rubber composition described in the first embodiment can be suitably used. However, in this example, the outer rubber 23 is required to have a cushioning function for alleviating the distortion at the end of the belt layer 7, while the inner rubber 21 is required to have abrasion resistance or friction when contacting the rim. Therefore, it is particularly preferable to form a rubber composition having a polymer ratio or a carbon ratio different by 1% or more when compared with each other.

In the intermediate rubber layer 22, various rubber compositions exhibiting the high value-added characteristics described in the first embodiment can be suitably used, and the inner rubber layer 21 and the outer rubber layer 23 are made of a polymer. It is the same as described above that it can be formed by a rubber composition having a different ratio or carbon ratio by 1% or more.

[0043]

EXAMPLES (First Embodiment) Table 1 shows the compounding of the outer layer rubber and the results of rubber analysis.

[0044]

[Table 1]

Next, the intermediate layer rubber and the inner layer rubber are blended as shown in Table 2 (in Examples 1 and 2, the blending is different from that of the outer layer rubber), and the pneumatic tire for passenger cars having a tire size of 195 / 65R15 is used. Tires were prototyped and evaluated for durability, damping, and cost. In addition, a conventional tire (conventional example 1) having one layer of sidewall rubber was also prototyped and the performance was compared. Example 1
With emphasis on damping performance, Example 2 used a rubber compound that emphasized cost.

The durability performance was evaluated by a drum durability test. The damping performance was evaluated based on the driver's sensuality. Further, the cost is represented by an index with Conventional Example 1 being 100. The larger the index, the better. Table 2 shows the test results.

[0047]

[Table 2]

(Second Embodiment) The compounding of the outer layer rubber is shown in Table 1 above, and the compound of the intermediate layer rubber and the inner layer rubber is shown in Table 3 (the inner layer and the intermediate layer rubber of Example 3 are the same as the outer layer rubber). The composition is different, and the composition focuses on cost reduction.)
A prototype of a pneumatic tire for passenger cars having a tire size of 195 / 65R15 was evaluated for durability, damping performance, steering wheel responsiveness, and cost.
In addition, the conventional tires (conventional examples 1 and 2) each having one layer of the sidewall rubber were also prototyped, and the performance was compared.

The durability performance was evaluated by a drum durability test. The damping performance and handle response were evaluated by the driver's sensuality. The cost is represented by an index with Conventional Example 1 being 100. The larger the index, the better. Table 3 shows the test results.

[0050]

[Table 3]

As a result of the test, it was confirmed that the durability and the diping property were improved in the examples, and that the costs were significantly reduced in the examples 2 and 3. Conventional example 2
It was also confirmed that when the cost was reduced by forming the sidewall portion as a single layer, the durability was greatly reduced.

[0052]

As described above, in the first aspect of the present invention, the belt cushion rubber is separately extruded by using the outer end of the inner rubber layer of the sidewall rubber in the tire radial direction as the belt cushion layer. Since the step or equipment for connecting the sidewall rubber to the radially outer end portion of the sidewall rubber can be omitted, the productivity of the tire can be improved.
Further, since the belt cushion layer and the inner rubber layer of the side wall rubber are made of the same rubber composition, it is possible to reduce the number of types of rubber used for the tire and to reduce the cost. In addition, by integrating the inner rubber and the outer rubber at least at the outer end in the tire radial direction in the region of the sidewall portion, the mutual bonding of the rubbers of the inner rubber, the intermediate rubber and the outer rubber is strengthened, and delamination and the like are caused. Can be effectively prevented.

According to the second aspect of the present invention, the inner rubber that is attached to the carcass and the outer rubber that forms the tire outer surface of the sidewall portion are made of a rubber composition mainly composed of natural rubber. The inner rubber can improve the adhesion to the carcass, and the outer rubber can improve cut resistance. Therefore, as the intermediate layer rubber, various rubber compositions for giving the above-mentioned high added value to the tire can be suitably employed without considering the basic characteristics of the sidewall rubber. In addition, by limiting the length of the belt cushion layer in the tire axial direction, the effect of alleviating the distortion of the belt layer end is enhanced.

According to the third aspect of the present invention, the inner end of the inner layer rubber in the tire radial direction is integrally formed as a clinch and used, so that the clinch is separately extruded and the outer end of the sidewall rubber in the tire radial direction is formed. Since the step or equipment connected to the tire can be omitted, the productivity of the tire can be improved. In addition, since the clinch and the inner layer rubber of the sidewall rubber are made of the same rubber composition, the number of types of rubber used for the tire can be reduced, and the cost can be reduced.

Further, in the invention according to claim 4, the sidewall rubber has a three-layer structure including an inner rubber layer on the carcass side, an outer rubber layer on the outer surface of the tire, and an intermediate rubber layer disposed therebetween. And the inner rubber and the outer rubber are integrated without interposing the intermediate rubber layer at the inner end and the outer end of the sidewall region in the tire radial direction. In addition, the mutual bonding of the rubbers of the outer layer rubber becomes strong, and delamination and the like can be effectively prevented. As the intermediate layer rubber, various rubber compositions for giving high added value to the tire without considering the basic characteristics of the sidewall rubber can be suitably employed.

According to the fifth aspect of the present invention, not only the clinch, but also a belt cushion layer formed by extending the outer end of the outer rubber layer in the tire radial direction is formed between the belt layer and the carcass. Since the step or equipment for extruding the belt cushion rubber separately from the side wall rubber at the radially outer end of the sidewall rubber can be omitted, the productivity of the tire can be further improved. Further, since the belt cushion layer and the inner rubber layer of the side wall rubber are made of the same rubber composition, it is possible to reduce the number of types of rubber used for the tire and to reduce the cost.

[Brief description of the drawings]

FIG. 1 is a right half sectional view of a tire showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of sidewall rubber before tire molding.

FIG. 3 is a right half sectional view of a tire showing another embodiment of the present invention.

FIG. 4 is a cross-sectional view showing an example of sidewall rubber before tire molding.

FIG. 5 is a sectional view of a conventional sidewall rubber before tire molding.

[Explanation of symbols]

 Reference Signs List 2 tread portion 3 side wall portion 4 bead portion 5 bead core 6 carcass 7 belt layer 9 side wall rubber 10 inner layer rubber 11 intermediate layer rubber 12 outer layer rubber 15 belt cushion layer 20 side wall rubber 21 inner layer rubber 22 intermediate layer rubber 24 outer layer rubber 24 Clinch 25 Belt cushion layer

Claims (5)

[Claims] 1. A pneumatic tire having a carcass extending from a tread portion to a bead core of a bead portion via a sidewall portion, and a belt layer disposed radially outward of the tire and inward of the tread portion. The side wall rubber disposed in the region of the portion comprises a three-layer structure of the inner layer rubber on the carcass side, the outer layer rubber forming the surface of the side wall portion, and the intermediate layer rubber disposed therebetween. The inner layer rubber and the outer layer rubber are integrated without interposing the intermediate layer rubber at least at the outer end in the tire radial direction of the region, and between the belt layer and the carcass, the inner layer rubber in the tire radial direction A pneumatic tire comprising a belt cushion layer having an outer end extending between the belt layer and the carcass. 2. The belt cushion layer has a tire axial length CW of 10 mm or more, and the inner rubber layer and the outer rubber layer are formed of a rubber composition mainly composed of natural rubber. 2. The pneumatic tire according to claim 1, wherein the rubber is formed of a rubber composition having a polymer ratio or a carbon ratio different from the inner layer rubber and the outer layer rubber by 1% or more. 3. The sidewall rubber disposed in the region of the sidewall portion has a structure of at least two layers including an inner layer rubber on the carcass side and an outer layer rubber on the tire outer surface side, and the outer layer rubber is The tire radially inner end is terminated at a position P1 on the tire outer surface separated from the bead base line BL by a distance of 5 mm or more in the tire radial direction, and the inner rubber layer extends from the position P1 to substantially the bead base line BL. A pneumatic tire characterized by forming a clinch that is in contact with the flange surface of the rim directly or via a reinforcing layer by being exposed to the outer surface of the tire between the two. 4. The sidewall rubber comprises a three-layer structure including an inner rubber layer on the carcass side, an outer rubber layer on the outer surface of the tire, and an intermediate rubber layer disposed therebetween. The outer rubber is integrated with the inner end portion of the sidewall portion region in the tire radial direction without the intermediate rubber layer at the outer end portion, and the intermediate rubber is the inner rubber and the outer rubber. 4. The pneumatic tire according to claim 3, wherein the pneumatic tire is formed of a rubber composition having a polymer ratio or a carbon ratio different by 1% or more. 5. The pneumatic pneumatic pump according to claim 3, wherein a belt cushion layer is formed between the belt layer and the carcass by extending a radially outer end of the outer rubber layer in the tire radial direction. tire.