JP3497030B2 - Pneumatic tire - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire excellent in high-speed durability and uniformity, and more specifically, a lightweight organic fiber even when a load on a belt portion is increased due to flattening of the tire. The present invention relates to a pneumatic tire that achieves excellent high-speed durability and uniformity with a cord-only reinforcing layer.

[0002]

2. Description of the Related Art In recent years, flattening of pneumatic tires for passenger cars has been progressing in order to further improve steering performance and high speed performance. Further, flattening of tires for trucks and buses has been promoted as a measure for increasing the loading capacity of vehicles by reducing the floor. When the flattening of the pneumatic tire progresses in this way, the load on the belt layer increases, especially in a pneumatic radial tire in which the belt layer is arranged in the tread portion, and the belt due to the phenomenon of the belt layer edge rising at high speed running. Separation of the edge portions of the layers and growth of the outer circumference of the tire are likely to occur, and the durability of the tire is significantly reduced.

As a measure against such a problem, the rigidity of the belt portion must be improved. In the case of pneumatic tires for passenger cars, it is common to provide a belt cover layer on the outside of the belt layer so that a nylon cord is continuously wound around substantially parallel to the tire circumferential direction. However, since the nylon cord has a small tensile elastic modulus, there is a limit in securing the tensile rigidity in the tire circumferential direction that corresponds to the increase in the load on the belt portion due to the recent ultra flattening.

For this reason, there is a proposal to use a steel cord having a large tensile elastic modulus, but the steel cord has a drawback that the weight of the tire is increased and that rust is generated due to external damage and durability is deteriorated. ing. In addition, since steel cords with a large tensile modulus are difficult to stretch, lifts during tire vulcanization (pushing the tread portion of a green tire toward the inner surface of the mold in the radial direction when the tire is circulated parallel to the tire circumferential direction). It becomes difficult to follow the operation), and it is practically impossible to obtain a vulcanized tire.

Therefore, it is conceivable to use a high elastic modulus organic fiber such as aramid fiber which is lightweight and has a high tensile elastic modulus. However, since aramid fiber also has a high elastic modulus like steel cord, the elongation is small and There is a problem that it cannot follow the lift during sulfurization. Therefore, even if it is lifted forcibly, the belt layer of the tire after vulcanization is unevenly disturbed, the tire uniformity is deteriorated, and it becomes impossible to obtain satisfactory durability.

As a method for solving the problem of such a high elastic modulus organic fiber, for example, Japanese Patent Laid-Open Nos. 1-247204 and 5-139112 disclose high elastic modulus organic fiber filament yarns and low elastic modulus organic fibers. A composite cord obtained by twisting a fiber filament yarn is used, and it is also disclosed in JP-A-7-1.
In JP49110, JP-A-7-149111, and JP-A-7-149112, a 1 + N structure in which organic fiber filament yarns having different elastic moduli are twisted together, 1 × N
It has been proposed to use a composite cord such as a structure for the belt cover layer.

These proposals are, as shown in FIG. 6, a lower twisted yarn Fa in which a bundle of high elastic modulus fiber filaments fh is twisted, and a lower twisted yarn in which a bundle of low elastic modulus fiber filaments fi is twisted. A composite cord 80 formed by adding a twist to Fb and further twisting it is used. However, with a composite cord having such a configuration, it is necessary to increase the elongation at low load so as to follow the lift during tire vulcanization. In addition, it is necessary to adjust the number of lower twists and the number of upper twists, and it is troublesome that the twist structure must be adjusted for each tire having a different lift ratio.

Further, since a yarn bundle of the high elastic modulus fiber filaments fh and a yarn bundle of the low elastic modulus fiber filaments fi are individually twisted and then twisted together, a large tensile tension is applied. However, there is a drawback that multi-stage yarn breakage easily occurs. Further, in the composite cord having such a configuration, when the tensile tension is applied, both the high elastic modulus fiber filament and the low elastic modulus fiber filament are integrally deformed, so that the tensile elastic modulus of the composite cord is equal to the elastic modulus of each fiber. It becomes the sum total average. That is, when trying to increase the elongation at low load in order to cope with a high lift rate during tire vulcanization, the volume fraction occupied by the low elastic modulus fiber filament in the composite cord is increased or the twist number of the composite cord is increased. Need to raise. As a result, the elastic modulus in the high load region decreases, so that it is difficult to sufficiently prevent the belt layer from rising when the tire runs at high speed, and the effect of improving the high-speed durability becomes insufficient.

On the other hand, if the ratio of the low elastic modulus fiber filaments to the composite cord is reduced and the ratio of the high elastic modulus fiber filaments is increased, or the twist number of the composite cord is reduced, then this time at low load. It becomes difficult to follow the lift during vulcanization because the elongation of the rubber becomes small.
As a result, the belt layer is deformed, the uniformity is deteriorated, and the effect of improving the high-speed durability is insufficient.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, to increase the weight of the tire, and to easily follow the lift during tire vulcanization. It is an object of the present invention to provide a pneumatic tire capable of exhibiting a high tensile elastic modulus in a tire after vulcanization and providing the tire belt portion with excellent uniformity and high-speed durability.

[0011]

A pneumatic tire of the present invention that achieves the above-mentioned object is provided on the outer peripheral side of a carcass layer with each other.
Of radial structure with belt layers crossing strong cords
In a pneumatic tire, a plurality of ply-twisted yarns A obtained by aligning and twisting a high elastic modulus organic fiber filament having a tensile elastic modulus of 300 g / d or more and a heat-shrinkable organic fiber filament are aligned and twisted. Composite cord formed by adding twist in the opposite direction and subjected to relaxation heat treatment ,
A reinforcing layer is formed on the tread side outside of the carcass layer by continuously orbiting substantially parallel to the tire circumferential direction,
Alternatively, cross reinforcing cords on the outer circumference of the carcass layer.
Pneumatic tire with radial structure that has a special belt layer
In, at least one undertwisted yarn A obtained by aligning and twisting a high elastic modulus organic fiber filament having a tensile elastic modulus of 300 g / d or more and a heat-shrinkable organic fiber filament, and a tensile elastic modulus of 300 g / d or more The high-modulus organic fiber filaments are aligned and at least one lower-twisted yarn B twisted in the same direction as the lower-twisted yarn A, and the upper-twisted yarn is added in the direction opposite to the twisting direction of these lower-twisted yarns A and B. Formed and subjected to relaxation heat treatment
The composite code, is characterized in that the formation of the reinforcing layer substantially parallel to continuously circulate in the tire circumferential direction on the tread surface side of the outer than the carcass layer.

Since the composite cord forming the reinforcing layer is formed based on the organic fiber cord as described above, the tire weight does not increase as in the case of using the steel cord, and the durability problem due to the rust occurs. Absent. Further, the composite cord is a ply-twisted yarn A obtained by aligning and twisting a high elastic modulus organic fiber filament and a heat-shrinkable organic fiber filament.
Since it is mainly used, when the relaxation heat treatment is applied, the high elastic modulus organic fiber filament can be integrally and morphologically contracted together with the heat-shrinkable organic fiber filament. Therefore, the composite cord having such a structure easily exhibits a high elongation in a low load region and can easily follow the lift during vulcanization, so that it does not disturb the belt layer and the tire uniformity. Can be improved. Furthermore, after this composite cord is morphologically stretched by the lift during vulcanization, the high tensile elastic modulus of the high elastic modulus fiber filament acts, so that the outer peripheral growth of the belt portion and the rise of the belt layer end portion do not occur. The suppression effect increases,
The high speed durability of the tire can be improved.

Further, since the above-mentioned composite cord develops the elongation property under a low load by the heat shrinkage of the heat-shrinkable organic fiber filament, a high twist is imparted to the high elastic modulus organic fiber filament like the above-mentioned conventional composite cord. No need to give. Therefore, the tensile elastic modulus of the high elastic modulus fiber filament can be utilized more effectively, and the effect of suppressing the outer peripheral growth of the belt portion and the rising of the belt layer end portion can be further increased.

Further, the heat-shrinkable organic fiber filament used in the composite cord does not obtain the elongation characteristics under a low load by utilizing the low elastic modulus unlike the low elastic modulus fiber in the conventional composite cord, and Since it is used only for the purpose of morphologically shrinking the high elastic modulus organic fiber filament by utilizing the heat shrinkability, the composite ratio is the minimum that can morphologically shrink the high elastic modulus organic fiber filament. You can combine them. Therefore, the composite ratio of the high elastic modulus organic fiber filaments can be increased as much as possible, and the tensile elastic modulus after tire vulcanization can be further increased.

Although it is conceivable to use the above-mentioned conventional composite cord after morphologically shrinking it by heat shrinkage, in the conventional composite cord, a low elastic modulus fiber filament yarn bundle and a high elastic modulus fiber filament yarn are used. Even if the low elastic modulus fiber filament has heat shrinkability, it is configured such that the bundle and the lower twisted yarn are individually twisted to form a lower twisted yarn, and then these lower twisted yarns are combined and upper twisted. , The composite cord does not shrink integrally when subjected to relaxation heat treatment, and the effect is that the lower twisted yarn of the high elastic modulus organic fiber filament is tightened in a vine shape. It just doesn't grow morphologically and shrink the whole code morphologically. Therefore, even if such a composite cord is used for the belt cover layer after being subjected to relaxation heat treatment, the effect of improving the high speed durability cannot be obtained.

[0016]

1 is a sectional view showing an example of a pneumatic tire of the present invention, and FIG. 2 is a developed plan view showing an internal structure of a tread portion of this tire. In FIG. 1, a pair of left and right bead portions 1 is connected to a pair of left and right side wall portions 2, and a tread portion 3 is formed so as to straddle the outer peripheral portions of the left and right side wall portions 2. Inside the tire, the carcass layer 4 has a cord angle between the left and right bead portions 1 with respect to the tire circumferential direction of 70 ° to 9 °.
Two belt layers 5 are mounted on the outer peripheral side of the carcass layer 4 in the tread portion 3 so as to cross the reinforcing cords 7 as shown in FIG. . This reinforcing cord 7 has a steel cord,
A cord having a high elastic modulus such as an aramid cord is used.

Further, 2 is provided on the tread portion 3 side of the belt layer 5.
A layer reinforcement layer 6 is arranged. This reinforcing layer 6 is shown in FIG.
As shown in FIG. 1, 1 to 10 of the aligned reinforcing cords 8 are continuously impregnated with rubber-impregnated strips at a cord angle of 0 °, preferably 0 ° to 10 ° with respect to the tire circumferential direction. It is formed endlessly around. A composite cord is used for the reinforcement cord 8 forming the reinforcement layer 6 from the configuration described later in detail.

The number of layers of the reinforcing layer 6 is not particularly limited, and may be two layers as shown in the figure, or one.
The number of layers may be three or more. Further, the reinforcing layer 6 may be provided so as to cover the entire width of the belt layer 5 as illustrated, or may be configured to cover only the end portion of the belt layer 5. Further, the reinforcing layer 6 is not particularly limited as long as it is arranged on the tread side of the carcass layer 4, and may be arranged on the outer peripheral side of the belt layer 5 as shown in the drawing, as well as the carcass layer 4 and the belt layer 5. May be arranged between the belt layers 5 and 5 or may be inserted in the middle of the plurality of belt layers 5.

The reinforcing cords forming the reinforcing layer 6 are composed of composite cords 8 as illustrated in FIG. The composite cord 8 is formed by aligning two or more ply-twisted yarns 8a and ply-twisting a plurality of the ply-twisted yarns 8a in a direction opposite to the ply-twisted direction. The number of lower twisted yarns 8a constituting the composite cord 8 is preferably two as shown in the figure from the viewpoint of productivity, but may be three or more as a matter of course.

As shown in FIG. 4 (a), the lower twisted yarn 8a constituting the composite cord 8 has a high elastic modulus organic fiber filament fh and a heat-shrinkable organic fiber filament fs.
Are formed into a single yarn bundle, and twisted (lower twist) is added to the single yarn bundle. The arrangement state of the high elastic modulus organic fiber filament fh and the heat-shrinkable organic fiber filament fs per one twisted yarn is 8a.
Each filament fh, f
s may be mixed in bundles, or
As in the case of the lower twisted yarn indicated by 8a 'in (c), the filament f
The individual filaments of h and filaments fs may be randomly mixed with each other to be in a mixed fiber state.

At least one of the plural twisted yarns constituting the composite cord 8 is always the above-mentioned twisted yarns 8a or 8
Like a ′, the high elastic modulus organic fiber filaments fh and the heat-shrinkable organic fiber filaments fs must be mixed, but the same lower twisted yarns 8a and 8a ′ can be used as the remaining lower twisted yarns. Well, or like the lower twisted yarn 8b shown in FIG. 4 (b), a high elastic modulus organic fiber filament f
A yarn bundle of only h may be twisted.

Therefore, the lower twisted yarns 8a and 8a 'in which the high elastic modulus organic fiber filaments fh and the heat-shrinkable organic fiber filaments fs are mixed are now classified as the lower twisted yarns A, and are composed only of the high elastic modulus organic fiber filaments fh. When the lower twisted yarn 8b is classified as the lower twisted yarn B, the composite cord 8 used in the pneumatic tire of the present invention has a plurality of the lower twisted yarns A.
The cords are made by aligning each other in one bundle and twisting them in the direction opposite to the twist direction, or at least one lower-twisted yarn A and at least one lower-twisted yarn B are aligned in one bundle. The cord is formed by twisting the lower twisted yarns A and B in the opposite direction to the lower twisted direction.

The composite cord having the above-described structure behaves such that when the relaxation treatment is applied to the composite cord, the high elastic modulus organic fiber filament fh uniformly shrinks together with the heat shrinkage of the heat-shrinkable organic fiber filament fs. I do. In order to smoothly perform such a uniform and uniform shrinkage behavior, as in the combination of the lower twisted yarns of FIGS. 4A and 4C, the high elastic modulus organic fiber filament fh and the heat-shrinkable organic fiber are used. Undertwisted yarns 8a and 8a containing both filaments fs
8a 'and 8a', or 8a and 8a
It is preferable that a'is combined with each other and twisted.

Composite cord 8 used in the reinforcing layer of the present invention
Uses the lower twisted yarn A in which the high elastic modulus organic fiber filament and the heat-shrinkable organic fiber filament are mixed as described above. Therefore, when the relaxation heat treatment is performed, the high elastic modulus organic fiber filament is combined with the heat-shrinkable organic fiber filament. Since it can be integrally and morphologically contracted, the behavior of elongation when a tensile load is applied to it is shown in FIG.
The curve E is shown in "Elongation curve".

That is, like the curve F in the conventional example composite cord having the structure shown in FIG. 6 and the curve G in the cord having only the aramid fiber (high elastic modulus organic fiber), both are almost straight from the low load to the high load region. However, the composite cord 8 of the present invention shows a high elongation in the low load region, and a high tensile modulus of the high elastic modulus fiber filaments exerts a low elongation in the high load region. become.

Therefore, the composite cord of the present invention can easily follow the lift at the time of vulcanization, thereby preventing the belt layer from being disturbed, thereby improving the uniformity of the tire. In addition, since the composite cord stretches less after being morphologically stretched by the lift during vulcanization, it suppresses the growth of the outer circumference of the belt and the rise of the belt layer end during high-speed running, and thus the high-speed durability of the tire. Improve sex.

On the other hand, in the case of the conventional composite cord of FIG. 6, in order to follow the lift during vulcanization, it is necessary to impart a high twist to the high elastic modulus organic fiber filament. However, the tensile elastic modulus of the high elastic modulus fiber filament cannot be effectively utilized, and the effect of suppressing the outer peripheral growth of the belt portion and the rising of the belt layer end portion must be reduced as compared with the composite cord of the present invention. I won't get it.

In the present invention which brings about the above-mentioned effects, the high elastic modulus organic fiber used in the composite cord has a tensile elastic modulus of 300 g / d or more. 300
When the organic fiber is less than g / d, the tensile rigidity of the composite cord in the tire circumferential direction is lowered, and the effect of improving the high speed durability of the tire becomes insufficient. Examples of the high elastic modulus fiber of 300 g / d or more include aramid fiber, polyarylate fiber, polyvinyl alcohol fiber, and poly-P-phenylenebenzbisoxazole fiber.

The heat-shrinkable organic fiber used in the composite cord is a fiber that exhibits shrinkage behavior by heat,
For example, polyester fiber, 6-nylon fiber, 66-nylon fiber, 46-nylon fiber and the like can be mentioned. Among these, polyester fiber is most suitable because it easily undergoes heat shrinkage. These heat-shrinkable organic fibers preferably have a heat shrinkage ratio at 150 ° C. of 5% or more, more preferably 8% or more. When the heat shrinkage rate is less than 5%, it is difficult to morphologically sufficiently shrink the composite cord even if the relaxation heat treatment is applied, and if the lift during vulcanization is large, the followability of the lift is reduced. . When it is 8% or more, it is possible to cope with a wide range of lift rates.

Here, "heat shrinkage at 150 ° C"
Is measured by free contraction according to the measurement method specified in JIS L1017. The composite ratio of the heat-shrinkable organic fiber filaments forming the composite cord is preferably such that the total denier number is 50% or less of the total denier number of the high elastic modulus organic fibers forming the composite cord.
It is more preferably 35% or less and 10% or more. When the composite ratio of the heat-shrinkable organic fiber filaments exceeds 50% of the total denier number of the high elastic modulus organic fibers, the tensile rigidity of the vulcanized tire of the composite cord subjected to the relaxation heat treatment as described above decreases, so that the tire The effect of suppressing outer peripheral growth and improving the durability of the belt portion is reduced. On the other hand, if it is less than 10%, the shrinkage effect of the composite cord due to the relaxation heat treatment is small, and it becomes difficult to follow the lift during vulcanization, so that the uniformity of the belt portion of the vulcanized tire decreases.

In the present invention, the twisting factor K represented by the following formula is 500 to 1900 for the twisted twist added to the composite cord.
It is preferable to set it so as to fall within the range. K = TD ^1/2 However, D: total denier of high elastic modulus fiber T: number of twists of composite cord (times / 10cm) When twist coefficient K is less than 500, convergence of cord is lowered and rubber The adhesiveness with Therefore, the effect of improving the durability of the tire belt portion is also reduced. On the other hand, 190
When it exceeds 0, the tensile rigidity of the composite cord in the vulcanized tire is reduced, so that the effect of improving the durability of the belt portion is reduced.

The number of twists of the lower twist added to each lower twist yarn is not particularly limited, but preferably 50% to 50% of the number of the upper twists.
From the viewpoint of productivity, it is preferable to set it within the range of 150%.
INDUSTRIAL APPLICABILITY The present invention described above is applicable to both passenger car tires and heavy load tires, and is particularly effective for tires having a small flatness. For example, it is very effective for passenger car tires having an oblateness of 60% or less and for heavy-duty tires having an oblateness of 70% or less.

[0033]

[Examples] Tire size, tire structure: carcass layer and belt layer, respectively, with the following specifications: tire size: 195 / 60R15 tire structure: Fig. 1 and Fig. 2 carcass layer: 1500d / 2 polyester fiber cord 1 layer belt layer: 2 + 2 (0.25) belt layers using steel cords are arranged so that the cords cross each other between layers. Reinforcing layer (belt cover layer): 8 reinforcement cords are driven into 1 cm width. The number of strips embedded in the rubber is continuously circulated substantially parallel to the tire circumferential direction so that the strip has two layers in common, and the reinforcement specified in the above reinforcement layer (belt cover layer) is common. Ten kinds of radial tires (invention tires 1 to 7, comparative example tires, conventional example tires) having different cords as follows are manufactured. Made

Tire 1 of the present invention: 1000d of aramid fiber and 1000d of polyester fiber having a heat shrinkage ratio (150 ° C) of 9.5%.
Twisted yarn in which and are added and twisted, and aramid fiber 10
Composite cord in which the upper twist is added together with the lower twist yarn prepared by adding the twist to 00d. Invention Tire 2: Aramid fiber 1000d and heat shrinkage (15
(0 ° C) A composite cord in which two lower twisted yarns, which are twisted by aligning 9.5% polyester fiber 500d, are added together and the upper twist is added.

Tire 3 of the present invention: A composite cord of the tire 2 of the present invention in which only the twist coefficient of the upper twist is different as shown in Table 1. Inventive tire 4: A composite cord of the inventive tire 2 in which only the twist coefficient of the upper twist is different as shown in Table 1. Inventive tire 5: In the composite cord of inventive tire 2, polyester fiber 250d is used instead of polyester fiber 500d, and the total denier of heat-shrinkable organic fibers is higher than the total denier of high elastic modulus organic fibers. 25% is a composite code.

Tire 6 of the present invention: In the composite cord of Tire 2 of the present invention, the heat-shrinkable organic fiber was added to the heat-shrinkage ratio (150
(° C) 4.5% composite cord. Inventive Tire 7: Aramid Fiber 1500d and Dry Heat Shrinkage 9.
A composite cord in which two lower twisted yarns, which are twisted by aligning 5% polyester fiber 500d, are added together and the upper twist is added.

Conventional tire: A composite cord in which a total of three twisted yarns, which are twisted aramid fiber 1000d and one twisted polyester fiber 1000d, are added together and twisted. Comparative tire: In the composite cord of the conventional tire,
A composite cord that has been subjected to relaxation heat treatment before being embedded in the tire. The ten types of radial tires thus obtained were evaluated for high speed durability and uniformity under the following test conditions, and the results shown in Table 1 were obtained.

(High-speed durability) A test tire was used with a rim size of 1
After running according to the JATMA high speed durability test using a rotating drum with a drum diameter of 1707 mm under the conditions of 5 × 6 JJ, air pressure of 260 kPa, and load of 4.6 kN, 10
The test was continued until the tire failed, increasing the speed by 10 km / hr each minute.

The test results are shown by an index with the measured value of the conventional tire being 100. The larger the index, the better the high-speed durability. (Uniformity-RFV) In accordance with JASO C607 "Uniformity test method for automobile tires",
The uniformity in the tire circumferential direction was measured. It is shown by an index with the measured value of the conventional tire being 100. The larger the index, the better the uniformity.

[0040]

[Table 1] As is clear from Table 1, the tires of the present invention show better high-speed durability than the tires of the conventional example, and at the same time, the uniformity of the tires is obviously improved.

[0041]

As described above, in the pneumatic tire of the present invention, a high elastic modulus organic fiber filament and a heat-shrinkable organic fiber filament are aligned as a reinforcing cord of a reinforcing layer arranged outside the carcass layer. By using a composite cord mainly composed of twisted ply-twisted yarn, it is possible to improve the uniformity of the belt portion at the time of high load because the elongation at low load that follows the lift can be obtained during tire vulcanization. Since high tensile elastic modulus is obtained, high-speed durability can be remarkably improved.

Further, since the composite cord is constructed based on the organic fiber cord, the tire weight is not increased unlike the steel cord, and the durability is not deteriorated due to the generation of rust.

[Brief description of drawings]

FIG. 1 is a meridian sectional view of a pneumatic tire according to an embodiment of the present invention.

FIG. 2 is a partial development view of a belt layer and a reinforcing layer in a tread portion of the tire shown in FIG.

FIG. 3 is a side view of a composite cord used for the reinforcing layer of the pneumatic tire of the present invention.

4 (a), (b) and (c) are cross-sectional views showing different aspects of the composite cord of FIG. 3, respectively.

FIG. 5 is a graph showing a load / elongation curve of a reinforcing cord.

6A and 6B are cross-sectional views showing a composite cord of a conventional example.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI D07B 1/02 D07B 1/02 (58) Fields investigated (Int.Cl. ⁷ , DB name) B60C 9/00 B60C 9/18 -9/22 D02G 3/48 D07B 1/02

Claims (6)

(57) [Claims] 1. Reinforcing cords on the outer peripheral side of the carcass layer
Radial structure with a belt layer that intersects
In the tire, a plurality of ply-twisted yarns A obtained by aligning and twisting a high elastic modulus organic fiber filament having a tensile elastic modulus of 300 g / d or more and a heat-shrinkable organic fiber filament are aligned and It is formed by adding twist in the opposite direction and is subjected to relaxation heat treatment.
The composite code management is performed, the carcass pneumatic tire substantially to form a reinforcing layer parallel to continuously circulate outside the tread side to the tire circumferential direction than the layer. 2. Reinforcing cords on the outer peripheral side of the carcass layer
Radial structure with a belt layer that intersects
In a tire, at least one undertwisted yarn A obtained by aligning and twisting a high elastic modulus organic fiber filament having a tensile elastic modulus of 300 g / d or more and a heat-shrinkable organic fiber filament, and a tensile elastic modulus of 300 g / d.
The above-mentioned high-modulus organic fiber filaments are aligned and at least one lower-twisted yarn B twisted in the same direction as the lower-twisted yarn A is aligned, and the upper-twisted yarns A and B are twisted in the direction opposite to the twisting direction. in addition it is formed, and a composite code relaxation heat treatment is performed, a pneumatic tire forming a reinforcing layer substantially parallel to continuously circulate in the tire circumferential direction on the tread surface side of the outer than the carcass layer. 3. The total denier number of all heat-shrinkable organic fiber filaments constituting the composite cord is 50% or less and 10% or more of the total denier number of all high elastic modulus organic fiber filaments constituting the composite cord. The pneumatic tire according to claim 1. 4. The twist coefficient K represented by the following formula for the twist of the composite cord is 500 to 1900.
The pneumatic tire according to any one of 1. K = TD ^1/2 where D: total denier of high elastic modulus organic fiber T: number of twists of composite cord (times / 10 cm) 5. One of the heat-shrinkable organic fiber filaments
The pneumatic tire according to any one of claims 1 to 4, which has a dry heat shrinkage ratio of 5% or more at 50 ° C. 6. The carcass layer, wherein at least two belt layers are arranged on the outer periphery of the carcass layer so that the reinforcing cords intersect each other, and the reinforcing layer made of the composite cord is arranged on the outermost side of the belt layer. The pneumatic tire according to any one of items 1 to 5.