JP2003127617A - Pneumatic tire and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide pneumatic tire effectively improving the stiffness of block land portion formed on a tread portion, and having excellent steering stabilizing performance such as braking performance and turning performance not only on an ice and snow road surface but also on a dry road surface and a wet road surface. SOLUTION: This pneumatic tire according to a first invention structures a stead portion 2 by a rubber laminated element 13 composed of an outer rubber layer 11 forming a tread contacting with a road surface and consisting of comparatively soft rubber and an inner rubber layer 12 positioned in an inner peripheral side of the outer rubber layer 11 and consisting of comparatively hard rubber. The tread portion 2 is divided into plural block land portion 7 by arranging plural tread grooves 5, 6. In the same block land portion 7, the rubber thickness of the outer rubber layer 11 measured on at least either one of the cross-section of a longitudinal cross-section and a lateral cross-section is same as a cross-section center position or thinner than the cross-section center position in a cross-section side position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire having a tread portion in which a plurality of block land portions are defined by arranging a plurality of tread grooves, and in particular, an outer rubber layer made of a relatively soft rubber. TECHNICAL FIELD The present invention relates to a tire having a tread portion composed of two or more rubber laminates containing, for example, a winter tire such as a studless tire and a method for manufacturing the same, and more specifically to a block formed in the tread portion of the tire. The rigidity of the land area is effectively increased to improve steering stability performance such as braking performance and turning performance on dry or wet road surfaces.

[0002]

2. Description of the Related Art In conventional pneumatic tires, especially winter tires such as studless tires, in order to ensure performance on ice and on snow, the complex elastic modulus E'of the rubber constituting the tread portion is compared with that of general tires. When it is difficult to secure sufficient tire performance such as steering stability on general roads, because the rigidity of the tread portion during tire running tends to be insufficient accordingly. There is.

As a means for suppressing deterioration of tire performance on a general road surface of a pneumatic tire, an outer rubber layer made of a rubber having a relatively low complex elastic modulus E ′ is made of two layers of rubber constituting a tread portion. In general, a method is used in which the tread portion is constituted by a rubber laminate with an inner rubber layer made of rubber having a relatively high complex elastic modulus E ′, and a decrease in rigidity of the tread portion is suppressed.

A pneumatic tire, especially a winter tire, having a tread portion composed of the above rubber laminate is
Although the running performance on ice and snow has improved remarkably in recent years by optimizing the rubber that constitutes the outer rubber layer of the tread that contacts the road surface, braking performance and turning performance on dry and wet road surfaces It cannot be said that the maneuvering stability performance, etc. has reached a sufficient level, and further improvement is desired.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to effectively increase the rigidity of a land portion of a block formed on a tread portion, so that braking can be performed not only on ice and snowy road surfaces but also on dry and wet road surfaces. A pneumatic tire having excellent steering stability such as performance and turning performance, for example, a winter tire such as a studless tire, and a method for manufacturing the same.

[0006]

In order to achieve the above object, a first aspect of the present invention is to provide a tread portion, an outer rubber layer formed of a relatively soft rubber forming a tread surface in contact with a road surface, and an outer rubber layer of the outer rubber layer. It is composed of a rubber laminate having an inner rubber layer located on the inner peripheral side and made of relatively hard rubber, and the tread portion is divided into a plurality of block land portions by disposing a plurality of tread grooves. In a pneumatic tire, the rubber thickness of the outer rubber layer when measured in at least one of the longitudinal section and the lateral section in the same block land portion is equal to or more than the center position of the cross section at the lateral position of the cross section. It is also a pneumatic tire characterized by being thin.

In the pneumatic tire according to the first aspect of the invention, the rubber thickness of the outer rubber layer measured at the lateral position of the cross section of the block land portion is located adjacent to the block land portion and is the same. 20 to 70% of the groove depth of the tread groove having the groove width cross section within the tire cross section.

Further, a block having an outer rubber layer having the rubber thickness set by the relationship between the lateral position of the cross section and the central position of the cross section and / or the rubber thickness set by the relationship with the groove depth of the tread groove. It is preferable that the land portion occupies 50% or more of all block land portions arranged in the tread portion.

Furthermore, both the outer rubber layer and the inner rubber layer constituting the tread portion are made of foamed rubber, and have a ratio of 3 Shore A hardness of the inner rubber layer to Shore A hardness of the outer rubber layer. Is more preferably greater than 1.2.

According to a second aspect of the present invention, in the pneumatic tire manufacturing method of the first aspect, prior to vulcanization molding, a ribbon-shaped relatively hard rubber and a quadrilateral block land portion are provided on a green case. Of the four tread grooves to divide,
The rubber thickness of the inner rubber layer of the block land portion when spirally wound around two tread grooves extending in the same direction and measured in a tire cross section that traverses these two tread grooves in the width direction. Forms an inner rubber layer that is equal to or thicker than the cross-sectional center position at the cross-section lateral position, and then,
On the inner rubber layer, a ribbon-shaped relatively soft rubber is spirally wound so as to at least configure the entire tread surface of the block land portion, and the block land portion when measured in the tire cross section. A pneumatic tire characterized in that the outer rubber layer has an outer rubber layer having a rubber thickness equal to or thinner than the center position of the cross section at a lateral position of the cross section, thereby forming a tread rubber on the green case. Is a manufacturing method.

According to a third aspect of the present invention, in the pneumatic tire manufacturing method of the first aspect, prior to vulcanization molding, a rubber sheet for an inner rubber layer having a raised portion on an outer surface portion corresponding to an arrangement position of a tread groove is provided. , At the same time extruding an outer rubber layer rubber sheet having a recess in the inner surface portion corresponding to the raised portion, to form a tread portion by uniting and stacking these on a green case, and then on the raised portion position. A pneumatic tire manufacturing method comprising a step of forming a tread groove by scraping existing tread rubber inward in a tire radial direction.

A fourth aspect of the present invention provides the pneumatic tire manufacturing method according to the first aspect, wherein the green tire is provided at a blade portion of the vulcanization mold that faces the lateral position of the cross section of the block land portion during vulcanization molding. By applying a negative pressure from the slit-shaped air vent hole, the excess rubber part of the rubber that constitutes the outer rubber layer is sucked out, and the rubber of the outer rubber layer when measured at the cross section lateral position of the block land part A method for manufacturing a pneumatic tire, characterized in that the thickness is made equal to or thinner than the center position of the cross section.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the first invention will be described below with reference to the drawings. FIG. 1 shows a cross section in the width direction of a typical pneumatic tire according to the first aspect of the present invention, in which a part of the tread portion of the tire of FIG. 1 is a pneumatic tire, 2 is a tread portion, 3 is a sidewall portion, 4 is a bead portion, 5 is a circumferential groove, 6 is a lateral groove, 7 is a block land portion, and 11 is a block portion. An outer rubber layer, 12 is an inner rubber layer, and 13 is a rubber laminate.

The illustrated pneumatic tire 1 is a studless tire and has a tread portion 2, a pair of sidewall portions 3 and a pair of bead portions 4, and the tread portion 2 includes:
A plurality of tread grooves, in FIG. 1, two circumferential grooves 5 extending in the circumferential direction, and a plurality of lateral grooves 6 crossing the tread grooves are arranged to form a plurality of block land portions 7. Further, each block land portion 7 is provided with a plurality of sipes 8 as an edge component for ensuring the performance on the ice and snow road surface.

The term "tread groove" as used herein includes all of the grooves arranged in the tread portion 2, and, for example, in addition to the circumferential groove 5 and the lateral groove 6 described above, with respect to the tire circumferential direction 9. An inclined groove (not shown) that extends obliquely may be used.

The tread portion 2 forms a tread surface 10 that comes into contact with the road surface and is relatively soft (preferably a Shore A hardness of 35 to 5).
5) The outer rubber layer 11 made of rubber, and the inner rubber layer of the outer rubber layer 11 are relatively hard (preferably 50 Shore A hardness).
70 to 70), a rubber laminate having at least an inner rubber layer 12 made of rubber, and in FIG. 1, a rubber laminate 13 having two layers of an outer rubber layer 11 and an inner rubber layer 12.

A pneumatic tire having a tread portion constituted by the above rubber laminate 13, particularly a winter tire, has a running performance on ice and snow by optimizing the rubber constituting the outer rubber layer of the tread portion which comes into contact with the road surface. Although it has improved remarkably in recent years, it cannot be said that the driving stability performance such as braking performance and turning performance on dry road surface or wet road surface has necessarily reached a sufficient level, and further improvement is required. What is desired is as described above.

Therefore, in a pneumatic tire having a tread portion composed of the rubber laminate 13, a study for improving steering stability performance such as braking performance and turning performance on a dry road surface or a wet road surface has been made. As a result, the following findings were obtained.

That is, in the conventional tire having the tread portion made of the above rubber laminated body, when the block land portion is viewed in a longitudinal section or a transverse section, as shown in FIG.
The rubber thickness of the outer rubber layer 102 made of a relatively soft rubber that constitutes 1 is usually the cross-section lateral position 103 and the cross-section central position 104.
It was found that this is the main factor for reducing the rigidity of the block land portion 101.

Further, in the conventional tire, as shown in FIG. 7, the rubber thickness of the outer rubber layer 102 forming the block land portion 101 becomes thicker at the cross-section lateral position 103 than at the cross-section central position 104 as shown in FIG. As shown, during the vulcanization molding step, the tire tread portion 1 is formed to form the tread groove 105 such as the circumferential groove.
The land forming recess 108 of the vulcanization mold 107 is pressed against 06, and at this time, the cross-sectional lateral position 103 of the block land 101 is
The outer rubber layer 102 at, the pressing direction of the blade 108,
Specifically, it was also found that this was due to being dragged in the groove depth direction of the tread groove 105.

Therefore, the inventor should make the rubber thickness of the outer rubber layer 11 of the comparatively soft rubber forming the block land 7 equal to or smaller than the central position 15 of the cross section at the lateral position 14 of the cross section. , It is possible to effectively increase the rigidity of each block land portion 7, and by doing so, it is possible to improve the steering stability performance such as braking performance and turning performance not only on ice and snowy road surfaces but also on dry and wet road surfaces. As a result of repeated studies under the idea of, the present invention was successfully completed.

That is, the main characteristic feature of the pneumatic tire 1 according to the first aspect of the present invention is to optimize the rigidity within the same block land portion 7. More specifically, FIG. As described above, in the same block land portion 7, the rubber thickness of the outer rubber layer 11 when measured in at least one of the longitudinal section and the lateral section, that is, the lateral section in FIG.
14 is to make it equal to or thinner than the center position 15 of the cross section, and by adopting this configuration, the rigidity of each block land portion 7 can be effectively increased, and as a result, not only on the ice and snow road surface but also on the dry surface It is possible to improve steering stability performance such as braking performance and turning performance even on a wet road surface or a wet road surface.

In order to enhance the steering stability performance such as cornering performance and driving / braking performance in a well-balanced manner, in order to counteract any input to the block land portion 7 in any direction, the longitudinal section of the block land portion 7 and It is preferable that the rubber thickness of the outer rubber layer 11 when measured in both the cross sections is set to be equal to or thinner than the cross section central position 15 at the cross section lateral position 14. Further, when the rubber thickness of the outer rubber layer 11 constituting the block land portion 7 varies as shown in FIG. 3, the rubber thickness of the outer rubber layer 11 when measured at the cross-section center position 15 is When the land part 7 is divided into four equal parts, the outer rubber layer 1 is divided into two parts located inside.
The average value when the rubber thickness of 1 is measured shall be used instead.

The lateral position of the block land 7 on the cross section
The rubber thickness of the outer rubber layer 11 as measured at 14 is the tread groove located adjacent to the block land 7 and having a groove width cross section within the same tire cross section, the circumferential groove 5 in FIG. The groove depth is preferably 20 to 70%. If the rubber thickness is less than 20% of the groove depth of the tread groove, due to tread wear accompanying tire running, the upper rubber layer 11 disappears early and the inner rubber layer 12 is exposed,
This is because the performance on snowy roads may deteriorate.
Further, if it exceeds 70%, reinforcement by the inner rubber layer 12 may be insufficient, and sufficient block rigidity may not be ensured.

Further, the outer rubber layer 11 having the rubber thickness set by the relationship between the lateral position 14 of the cross section and the central position 15 of the cross section and / or the thickness of the rubber set by the groove depth of the tread groove is set. It is preferable from the viewpoint of tread reinforcement that the block land portion 7 having the above occupies 50% or more of all the block land portions arranged in the tread portion 2.

Further, both the outer rubber layer 11 and the inner rubber layer 12 constituting the tread portion 2 are preferably made of foamed rubber, and in addition, the inner rubber layer with respect to the Shore A hardness of the outer rubber layer 11 is added. It is more preferable to make the ratio of 3 Sure A hardness of No. 2 larger than 1.2 in order to obtain a sufficient reinforcing effect.

Next, the tire manufacturing method of the second invention will be described with reference to the drawings. 4 (a) and 4 (b) are views for explaining a method of forming a tread rubber on the green case 16, and FIG. 4 (a) is a state when the inner rubber layer 12 is formed, the same figure. (b) shows a state when the outer rubber layer 11 is formed.

In the tire manufacturing method of the second invention, as shown in FIG. 4 (a), a ribbon-shaped relatively hard rubber is formed on the green case 16 to partition the quadrilateral block land portion 4
Of the two tread grooves, two tread grooves extending in the same direction are spirally wound in the tire circumferential direction in a range centered between the two circumferential grooves 5 in FIG. The rubber thickness of the inner rubber layer 12 of the block land portion 7 when measured in the tire cross section that crosses the tread groove of the book in its width direction is equal to or thicker than the cross sectional center position 15 at the cross sectional lateral position 14. Preferably, the inner rubber layer 12 having a thickness of 30% or more is formed.

The inner rubber layer 12 shown in FIG. 4 (a) is formed in such a manner that a ribbon-shaped relatively hard rubber is spirally wound on the green case 16 to form a base portion of the inner rubber layer 12, as shown in FIG. In (a), a method is preferred in which a base layer 17) of one layer is formed and then spirally wound around the region 18 sandwiched by the tread groove (circumferential groove 5). The base portion 17 and the other portions of the rubber layer 12 can be made of different rubbers.

Next, as shown in FIG. 4 (b), a ribbon-like relatively soft rubber is spirally wound on the inner rubber layer 12 so as to form at least the entire tread surface of the block land portion 7. The outer rubber layer 11 of the block land portion 7 has a rubber thickness equal to or thinner than the central position 15 of the cross section at the lateral position 14 of the cross section when measured by turning the tire to form an outer rubber layer 11 of the same. Then, the pneumatic tire 1 can be manufactured by forming a tread rubber on the green case 16 and then performing vulcanization molding.

Next, a tire manufacturing method of the third invention will be described with reference to the drawings. FIGS. 5 (a) and 5 (b) are views for explaining another method for forming the tread rubber on the green case 16, and FIG. 5 (a) shows the inner rubbers from the respective rubber extruders 19 and 20. After the layer rubber sheet 21 and the outer rubber layer rubber sheet 22 are simultaneously extruded, a state in which the rubber laminate sheet 24 is formed by combining the rubber sheets 21 and 22 by passing through the inserter 23 is shown. FIG. 2B shows a cross section when a tread rubber is formed using the rubber laminate sheet 24 of FIG.

In the tire manufacturing method of the third invention, the rubber sheet 21 for the inner rubber layer having a raised portion (not shown) on the outer surface portion corresponding to the location of the tread groove, and the inner surface portion corresponding to the raised portion. A rubber sheet for the outer rubber layer that has a recess
22 and 22 are simultaneously extruded as shown in FIG. 5 (a), and these rubber sheets 21, 22 are passed by passing through the inserter 23.
The tread rubber is formed by stacking the rubber laminated sheet 24 formed by uniting the above on the green case 16.

Next, the tread rubber existing on the raised portion position 25 is scraped off inward in the tire radial direction,
By forming the tread groove 26 having the shape shown by the dotted line in FIG. 5B, the upper rubber layer 11 at the cross sectional lateral position 14 of the block land portion 7 can be set thin. And then
The pneumatic tire 1 can be manufactured by performing vulcanization molding.

Next, a tire manufacturing method of the fourth invention will be described with reference to the drawings. 6 (a) to 6 (c) are views for explaining the cross-sectional state of the tread portion 2 before and after vulcanization molding, and FIG. 6 (a) shows the vulcanization mold 2 before vulcanization molding.
7 immediately before the blade 28 is pressed against the tread portion 2, FIG. 7B shows the blade 28 being pushed into the tread portion 2, and FIG. 6 shows a state when negative pressure is applied from the air vent hole 29 of the blade 28.

In the tire manufacturing method according to the fourth aspect of the present invention, by laminating a general rubber sheet for the inner rubber layer and a general rubber sheet for the outer rubber layer on the green case 16, as shown in FIG. 6 (a), A tread rubber including an inner rubber layer 12 and an outer rubber layer 11 is formed to obtain a green tire.

Then, the blade 28 of the vulcanization mold 27 is pushed into the tread portion 2 of the green tire. At this time, the figure
As shown in 6 (b), the cross-sectional lateral position of the block land portion 7
The upper rubber layer 11 at 14 is thickened by being dragged in the pushing direction of the blade 28.

In the fourth invention, the blade 2 of the vulcanization mold 27 is used.
As the block 8, there is used a block land portion 7 having a slit-shaped air vent hole 29 in a blade portion facing the lateral position 14 of the cross section.

At the time of vulcanization molding, negative pressure is applied from the air vent hole 29 provided in the blade portion of the vulcanization mold, which is opposed to the lateral position 14 of the cross section of the block land portion 7, so that the outer rubber layer is formed. As shown in FIG. 6 (c), the outer rubber layer of the block land 7 is measured at the lateral position 14 of the cross section by sucking out the excess rubber part of the rubber constituting the 11
It is possible to manufacture the pneumatic tire 1 in which the rubber thickness 11 is equal to or thinner than the center position 15 of the cross section.

The above description merely shows one example of the embodiment of the present invention, and various modifications can be made within the scope of the claims.

[0040]

EXAMPLES Next, a studless tire according to the first invention was prototyped and its performance was evaluated, which will be described below. -Example 1 The tire of Example 1 is a radial studless tire for passenger cars having a tire size of 205 / 65R15, which has the configuration shown in Figs. 1 to 3, and is along the tire circumferential direction at the same block land portion. Of the outer rubber layer at the lateral position of the cross section and the rubber thickness at the central position of the cross section of the outer rubber layer measured in the longitudinal section when cut along the tire width direction and the cross section when cut along the tire width direction, respectively. The ratio B / A to A is 0.7 and 1.8
And the rubber thickness B is the groove depth (9.
5 mm), which is 34% of the block land area
The outer rubber layer and the inner rubber layer are made of foam rubber, and the Shore A hardnesses of the outer rubber layer and the inner rubber layer are 45% and
60. The other tire structures were substantially the same as those of a general pneumatic radial tire for passenger cars.

Example 2 The tire of Example 2 has a rubber thickness ratio B / A of the outer rubber layer measured in the longitudinal section and the transverse section, respectively.
However, the tire was constructed in the same manner as the tire of Example 1 except that the tires were 0.9 and 1.8.

Example 3 The tire of Example 3 has a ratio B / A of the rubber thickness of the outer rubber layer measured in the longitudinal section and the transverse section, respectively.
However, the tire was constructed in the same manner as the tire of Example 1 except that the tires were 0.7 and 0.8.

Conventional Example The tire of the conventional example has a ratio B / A of the rubber thickness of the outer rubber layer when measured in the longitudinal section and the transverse section, respectively.
The tire was constructed similarly to the tire of Example 1 except that both were 1.8.

(Test method) Each of the above-mentioned test tires is 6.5 J × 1
The tires and wheels obtained by assembling to 5 were mounted on a passenger car, and the vehicle was run on various road surfaces (dry road surface, wet road surface, icy road surface, snowy road surface), and braking performance and turning performance were evaluated. The tire internal pressure at this time is
Front and rear wheels are 210kPa, tire load is 4.12kN for each front tire and 3.43k for each rear tire
It was set to N.

The braking performance was evaluated by measuring the braking distance when full braking was performed on each road surface from 40 km / h, and evaluated from this measured value. The turning performance was evaluated by the driver's feeling of the grip force when turning while driving only each driver on each tire test course.

Table 1 shows the results of these evaluations. Table 1
The numerical values in the figure show the exponential ratio where the braking performance is 100 for the conventional example, and the exponential ratio where the turning performance is 5 for the conventional example. The larger the numerical value, the better.

[0047]

[Table 1]

From the evaluation results shown in Table 1, all of the tires of Examples 1 to 3 have the same level of braking performance and turning performance on an icy road surface or a snowy road surface as compared with the conventional example, but are dry. Excellent braking performance and turning performance on road surfaces and wet road surfaces.

[0049]

According to the present invention, the rigidity of the land portion of the block formed in the tread portion is effectively increased so that braking performance, turning performance, etc. can be obtained not only on ice and snowy road surfaces but also on dry and wet road surfaces. It is possible to provide a pneumatic tire having excellent steering stability performance, for example, a winter tire such as a studless tire.

[Brief description of drawings]

FIG. 1 is a widthwise sectional view of a pneumatic tire according to a first aspect of the invention.

FIG. 2 is a development view of a part of a tread portion of the tire shown in FIG.

FIG. 3 (a) is a cross-sectional view of the block land portion taken along line IIIa-IIIa, and (b) is a cross-sectional view of the block land portion taken along line IIIb-IIIb.

FIG. 4 is a view for explaining the method for manufacturing a tire according to the second invention, wherein (a) shows a state when an inner rubber layer is formed, and (b) shows a state when an outer rubber layer is formed. .

FIG. 5 is a view for explaining the method for manufacturing a tire according to the third invention, wherein (a) shows a rubber sheet for an inner rubber layer and a rubber sheet for an outer rubber layer which are simultaneously extruded from respective rubber extruders and then combined and laminated. The state of the above rubber laminate, (b) shows a cross section when a tread rubber is formed by the rubber laminate of (a).

FIG. 6 is a view for explaining the method for manufacturing a tire according to the fourth invention, wherein (a) is a state of the tread portion before vulcanization molding and immediately before pressing the blade of the vulcanization mold onto the tread portion, (b) shows a state in which the blade is pushed into the tread portion, and (c) shows a state during vulcanization molding and when negative pressure is applied from the air vent hole of the blade.

FIG. 7 is a sectional view of a block land portion of a conventional tire.

FIG. 8 is a diagram for explaining a conventional tire manufacturing method, in which (a) is a state of a tread rubber that constitutes a green tire before vulcanization molding, and (b) is a state of a tread rubber during vulcanization molding. Indicates.

[Explanation of symbols]

1 pneumatic tire 2 tread section 3 Side wall part 4 bead section 5 circumferential groove 6 lateral grooves 7 blocks land 8 sipes 9 tire circumferential direction 10 Tread tread 11 Outer rubber layer 12 Inner rubber layer 13 rubber laminate 14 Cross section lateral position of block land 15 Block land center position 16 green case 17 Base part of inner rubber layer 18 Area between tread grooves (or circumferential groove 5) 19,20 rubber extruder 21 Rubber sheet for inner rubber layer 22 Rubber sheet for outer rubber layer 23 Inserter 24 rubber laminated sheet 25 Inner rubber layer ridge position 26 tread groove 27 Vulcanizing mold 28 Vulcanization mold blade 29 Blade air bleed hole 30 carcass 31 bead core 32 belt

Claims (7)

[Claims] 1. An outer rubber layer made of a relatively soft rubber, which forms a tread surface in contact with a road surface, and an inner rubber layer made of a relatively hard rubber, which is located on the inner peripheral side of the outer rubber layer. In a pneumatic tire composed of a rubber laminated body having and a tread portion divided into a plurality of block land portions by disposing a plurality of tread grooves, the longitudinal cross section of the same block land portion And the rubber thickness of the outer rubber layer when measured in at least one of the cross sections is equal to or thinner than the center position of the cross section at the lateral position of the cross section. 2. The rubber thickness of the outer rubber layer when measured at the lateral position of the block land portion is equal to the groove width cross section in the tire cross section which is located adjacent to the block land portion and is the same as this. 20-70% of the groove depth of the tread groove which it has, The pneumatic tire of Claim 1 characterized by the above-mentioned. 3. The air, characterized in that the block land portion having the outer rubber layer set to the rubber thickness according to claim 1 or 2 occupies 50% or more of all the block land portions arranged in the tread portion. Included tires. 4. The outer rubber layer and the inner rubber layer forming the tread portion are both made of foamed rubber, and have a ratio of 3 Shore A hardness of the inner rubber layer to Shore A hardness of the outer rubber layer. The pneumatic tire according to any one of claims 1 to 3, which is larger than 1.2. 5. The method for manufacturing a pneumatic tire according to claim 1, wherein prior to vulcanization molding, a ribbon-shaped relatively hard rubber is provided on the green case.
A tire that spirally winds between two tread grooves that extend in the same direction among the four tread grooves that partition the quadrilateral block land portion and that crosses these two tread grooves in the width direction. The rubber thickness of the inner rubber layer of the block land portion when measured in the cross section forms an inner rubber layer that is equal to or thicker than the center position of the cross section at the lateral position of the cross section, and then on the inner rubber layer. The ribbon-shaped relatively soft rubber is spirally wound to form at least the entire tread surface of the block land portion, and the rubber thickness of the outer rubber layer of the block land portion when measured in the tire cross section. The method for producing a pneumatic tire is characterized in that an outer rubber layer is formed at a lateral position of the cross section, which is equal to or thinner than the central position of the cross section, thereby forming a tread rubber on the green case. . 6. The method of manufacturing a pneumatic tire according to claim 1, wherein the inner rubber having a raised portion on the outer surface portion corresponding to the position where the tread groove is arranged is formed before the vulcanization molding. A layer rubber sheet and an outer rubber layer rubber sheet having a recess in an inner surface portion corresponding to the raised portion are simultaneously extruded to form a tread rubber by uniting and laminating these on a green case, and then the above. The tread rubber that exists on the raised position,
A method for manufacturing a pneumatic tire, comprising a step of forming a tread groove by scraping inward in a tire radial direction. 7. The method for manufacturing a pneumatic tire according to claim 1, further comprising a vulcanization mold that opposes the cross-section lateral position of the block land portion during vulcanization molding of the green tire. By applying a negative pressure from the slit-shaped air vent hole provided in the blade part, sucking out the excess rubber part of the rubber that constitutes the outer rubber layer, when measuring at the cross section lateral position of the block land part A method for manufacturing a pneumatic tire, characterized in that the rubber thickness of the outer rubber layer is equal to or thinner than the center position of the cross section.