JP2012030737A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire improving durable performance, while being reduced in weight.SOLUTION: In this pneumatic radial tire, a composite cord composed by bundling at least two aramid lower twisting yarns made by adding lower twisting to an aramid fiber bundle, and a polyester lower twisting yarn made by adding lower twisting to a polyester fiber bundle, and adding upper twisting is used as a reinforcing cord of a carcass layer. The composite cord has total fineness of 2,500-6,000 dtex and an upper twisting coefficient K shown by the following numerical formula (1) of 1,200-2,500. Fineness of the polyester fiber bundle is 20-50% in relation to total fineness of the composite cord. In (1): K=T×(D/ρ+D/ρ), T is the number of upper twisting (times/10 cm) of the composite cord, Dis the total fineness (dtex) of the aramid fiber bundle, ρis specific gravity of the aramid fiber bundle, Dis fineness (dtex) of the polyester fiber bundle, and ρis specific gravity of the polyester fiber bundle.

Description

  The present invention relates to a pneumatic radial tire using a composite cord formed by bundling two aramid lower twisted yarns and one polyester lower twisted yarn and applying an upper twist as a reinforcing cord for a carcass layer. The present invention relates to a pneumatic radial tire with improved durability.

  In recent years, aramid fibers have been used as reinforcing cords for carcass layers in order to reduce the weight of pneumatic radial tires. However, when an aramid fiber alone is used as a reinforcing cord for a carcass layer, there is a problem that durability is lowered. Therefore, a composite fiber cord in which aramid fibers and low-elasticity fibers such as nylon fibers are twisted together is used as the reinforcing cord of the carcass layer (see Patent Documents 1 and 2).

  Patent Document 1 discloses a pneumatic radial tire in which a composite fiber cord in which one 46 nylon fiber yarn and two aramid fiber yarns subjected to under twist are twisted in opposite directions is used for a carcass layer. Is disclosed.

  Patent Document 2 discloses a pneumatic tire using a composite cord of an aramid fiber and a polyester fiber as a carcass cord. In this Patent Document 2, the carcass cord is composed of a composite cord in which a first strand made of an aramid fiber and a second strand made of a polyester fiber are twisted together by an upper twist, and the first strand is a lower twist. Two filament bundles of aramid fibers are formed by twisting each other by intermediate twist, and the second strand is composed of one filament bundle of polyester fibers twisted.

JP 2009-132324 A International Publication No. 2009/063913

  As described above, in order to reduce the weight of a pneumatic radial tire, a flat spot phenomenon occurs when a composite fiber cord in which an aramid fiber and a low-elasticity fiber such as nylon fiber are twisted as in Patent Document 1 is used. There is a problem that it is easy.

  In Patent Document 2, a composite cord of an aramid fiber and a polyester fiber is used. However, the composite cord of Patent Document 2 has a first strand formed by twisting two strands of aramid fiber filaments twisted together with an intermediate twist and a second strand made of polyester fiber. Are twisted together. The aramid fiber is more twisted and the amount of the first strand made of the aramid fiber bundle is increased, so that a sufficient weight reduction of the tire cannot be obtained. Further, there is a problem that the flatness of the cord is lost and handling at the time of processing becomes difficult.

  An object of the present invention is to provide a pneumatic radial tire that solves the problems based on the above-described conventional technology and that has improved durability while reducing weight.

In order to achieve the above object, the present invention has a carcass layer provided with a reinforcing cord, which is mounted between a pair of left and right bead portions, and the carcass layer is obtained by adding a lower twist to an aramid fiber bundle. At least two aramid lower twisted yarns and a polyester fiber bundle are bundled with one polyester lower twisted yarn obtained by adding a lower twist in the same direction as the aramid lower twisted yarn, and an upper twist in a direction opposite to the lower twist is added. A composite cord is used as the reinforcing cord, the composite cord has a total fineness of 2500 to 6000 dtex, and an upper twist coefficient K expressed by the following formula (1) is 1200 to 2500, and the polyester fiber bundle This provides a pneumatic radial tire characterized in that the fineness is 20 to 50% of the total fineness of the composite cord.
K = T · (D _a / ρ _a + D _p / ρ _p ) ^1/2 (1)
Where T is the number of twists of the composite cord (times / 10 cm), D _a is the total fineness (dtex) of the aramid fiber bundle, ρ _a is the specific gravity of the aramid fiber bundle, and D _p is the fineness of the polyester fiber bundle. (Dtex), ρ _p is the specific gravity of the polyester fiber bundle

In this case, the composite cord has a lower twist number of the polyester lower twist yarn than the lower twist number of the aramid lower twist yarn, and the lower twist number of the polyester lower twist yarn is equal to the lower twist number of the aramid lower twist yarn. It is preferable that it is 15 to 90%.
The carcass layer preferably has a single layer configuration.

  According to the pneumatic radial tire of the present invention, it is possible to improve the fatigue resistance of the cord while reducing the weight, and to improve the durability performance such as a longer travel distance.

It is sectional drawing which shows the cross-sectional shape of the pneumatic radial tire which concerns on embodiment of this invention. It is sectional drawing which shows an example of the composite cord used for the carcass layer of the pneumatic radial tire of embodiment of this invention.

Hereinafter, a pneumatic radial tire of the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.
FIG. 1 is a cross-sectional view showing a cross-sectional shape of a pneumatic radial tire according to an embodiment of the present invention.

A pneumatic radial tire (hereinafter simply referred to as a tire) 10 shown in FIG. 1 includes a tread portion 12, a shoulder portion 14, a sidewall portion 16, and a bead portion 18 as main components.
In the following description, as indicated by arrows in FIG. 1, the tire width direction refers to a direction parallel to a tire rotation axis (not shown), and the tire radial direction is orthogonal to the rotation axis. The direction. Further, the tire circumferential direction refers to the direction of rotation with the rotation axis as the axis serving as the center of rotation. Further, the tire inner side means the lower side of the tire in FIG. 1 in the tire radial direction, that is, the tire inner side facing the cavity region R that applies a predetermined internal pressure to the tire, and the tire outer side means the upper side of the tire in FIG. That is, it means the tire outer surface side that is visible to the user, on the side opposite to the tire inner peripheral surface.

  The tire 10 includes a carcass layer 20, a belt layer 22, a belt auxiliary reinforcing layer 24, a side reinforcing layer 26, a bead core 28, a bead filler 30, a tread rubber layer 32, a sidewall rubber layer 34, a rim. It mainly includes a cushion rubber layer 36 and an inner liner rubber 38 layer.

  The tread portion 12 is provided with a land portion 12b constituting a tread surface 12a outside the tire and a tread groove 12c formed in the tread surface 12a. The land portion 12b is partitioned by the tread groove 12c. The tread groove 12c has a main groove formed continuously in the tire circumferential direction and a plurality of lug grooves (not shown) extending in the tire width direction. A tread pattern is formed on the tread surface 12a by the tread groove 12c and the land portion 12b.

The carcass layer 20 extends in the tire width direction from a portion corresponding to the tread portion 12 to a bead portion 18 through a portion corresponding to the shoulder portion 14 and the sidewall portion 16 to form a tire skeleton.
The carcass layer 20 has a configuration in which reinforcing cords composed of composite cords, which will be described later, are arranged in one direction at regular intervals, for example, in the tire width direction, and covered with cord coating rubber. The carcass layer 20 is folded back from the tire inner side to the tire outer side by a pair of left and right bead cores 28, which will be described later, and forms an end A in the region of the side wall part 16. 20b. That is, in the present embodiment, the carcass layer 20 is mounted between one pair of left and right bead portions 18.

As the cord coating rubber of the carcass layer 20, one or more kinds of rubbers selected from natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene rubber (IR) are preferably used. . In addition, these rubbers are end-modified with functional groups containing elements such as nitrogen, oxygen, fluorine, chlorine, silicon, phosphorus, or sulfur, such as amine, amide, hydroxyl, ester, ketone, siloxy, or alkylsilyl. Or those end-modified with epoxy can be used.
The carbon black to be blended into these rubbers, for example, an iodine adsorption amount 20~100 (g / kg), preferably 20~50 (g / kg), DBP absorption amount is 50~135 ^(cm 3 / 100g ), preferably 50~100 ^(cm 3 / 100g), and CTAB adsorption specific surface area of 30 to 90 ^(m 2 / g), preferably those which are 30~45 ^(m 2 / g) is used.
Moreover, the quantity of sulfur to be used is 1.5-4.0 mass parts with respect to 100 mass parts of rubber | gum, for example, Preferably it is 2.0-3.0 mass parts.
The carcass layer 20 will be described in detail later.

The belt layer 22 is a reinforcing layer that is attached in the tire circumferential direction to reinforce the carcass layer 20. The belt layer 22 is provided in a portion corresponding to the tread portion 12, and includes an inner belt layer 22a and an outer belt layer 22b.
In the present embodiment, the inner belt layer 22a and the outer belt layer 22b include a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect each other between the layers. The inner belt layer 22a and the outer belt layer 22b are configured such that a reinforcing cord is a steel cord, for example, and is covered with a cord coating rubber.
In the inner belt layer 22a and the outer belt layer 22b, the cord angle of the reinforcing cord with respect to the tire circumferential direction is, for example, 24 to 35 °, and preferably 27 to 33 °. Thereby, high-speed durability can be improved.

  The inner belt layer 22a and the outer belt layer 22b of the belt layer 22 are not limited to the steel cord being the reinforcing cord, and the steel belt may be applied to only one of them, or at least one of them. May be a conventionally known reinforcing cord made of an organic fiber cord made of polyester, nylon, aromatic polyamide or the like.

In the tire 10, a belt auxiliary reinforcing layer 24 that reinforces the belt layer 22 is disposed on the outer side belt layer 22 b that is the uppermost layer of the belt layer 22 in the tire circumferential direction.
In the belt auxiliary reinforcing layer 24, for example, organic fiber cords are spirally arranged in the tire circumferential direction as reinforcing cords, and these organic fiber cords are covered with a cord coating rubber.

  As shown in FIG. 1, the belt auxiliary reinforcing layer 24 is provided so as to cover only the end portion β of the belt layer 22, for example. The belt auxiliary reinforcing layer 24 in the illustrated example is a so-called edge cover.

  The belt auxiliary reinforcing layer 24 is not limited to that shown in FIG. For example, a configuration that covers the belt layer 22 from end to end in the tire width direction, a so-called full cover may be used. Furthermore, the belt auxiliary reinforcing layer 24 may have a configuration in which a plurality of full covers are stacked, or may have a configuration in which an edge shoulder and a full cover are combined.

  In the belt auxiliary reinforcing layer 24, as an organic fiber cord, for example, nylon 66 (polyhexamethylene adipamide) fiber, aramid fiber, composite fiber composed of aramid fiber and nylon 66 fiber (aramid / nylon 66 hybrid cord), PEN Fibers, POK (aliphatic polyketone) fibers, heat-resistant PET fibers, rayon fibers, and the like are used.

The bead portion 18 is provided with a bead core 28 that functions to fold the carcass layer 20 and fix the tire 10 to the wheel, and a bead filler 30 so as to contact the bead core 28. Therefore, the bead core 28 and the bead filler 30 are sandwiched between the main body portion 20a and the folded portion 20b of the carcass layer 20.
Further, a side reinforcing layer 26 including a reinforcing cord that is inclined with respect to the tire circumferential direction is embedded in the bead portion 18.

In the present embodiment, the side reinforcing layer 26 includes the bead portion 18 between the main body portion 20a of the carcass layer 20 and the bead filler 30, and the side wall portion 16 includes the main body portion 20a and the folded portion 20b of the carcass layer 20. And extends from the bead core 28 to the end B on the shoulder 14 side along the tire radial direction from the end A of the folded portion 20b.
The other end portion C of the side reinforcing layer 26 exists in the vicinity of the bead core 28 between the main body portion 20 a of the carcass layer 20 and the bead filler 6. The side reinforcing layer 26 is provided between the folded portion 20b of the carcass layer 20 and the bead core 28 and / or the bead filler 30 in the bead portion 18, and between the main body portion 20a and the folded portion 20b in the sidewall portion 16. The bead portion 18 may be disposed outside the folded portion 20b in the tire width direction, and the sidewall portion 16 may be disposed outside the main body portion 20a. Furthermore, these may be arranged in combination.

  The side reinforcing layer 26 is configured by arranging reinforcing cords made of steel cords in a direction inclined with respect to the tire circumferential direction at regular intervals and covering them with cord coating rubber. As the reinforcing cord of the side reinforcing layer 26, for example, an organic fiber cord made of polyester, nylon, aromatic polyamide or the like is used in addition to the steel cord.

If the side reinforcing layer 26 can reinforce the side (side surface) of the tire 10, that is, the bead portion 18 and / or the sidewall portion 16, only the whole or a part of the bead portion 18 and / or the sidewall portion 16 may be used. The position of the end portion is not limited. For example, the end portion of the side reinforcing layer 26 may be extended to a region in contact with the belt layer 22 of the shoulder portion 14 and may be provided for all of the bead portion 18 and the sidewall portion 16, or only the bead portion 18. Alternatively, it may be provided only for the side wall part 16, or may be provided by being divided into a plurality of parts, for example, divided into a bead part 18 and a side wall part 16.
Furthermore, you may change the area | region which provides the side reinforcement layer 26 according to the kind of reinforcement cord. For example, when a conventionally known steel cord is used as the reinforcing cord of the side reinforcing layer 26, the side reinforcing layer 26 is preferably disposed between the bead filler 30 and the folded portion 20b of the carcass layer 20, and the organic fiber When the cord is used, it is preferable to arrange the side reinforcing layer 26 so as to wrap the bead core 28 and the bead filler 30.

  In addition to this, the tire 10 is provided as a rubber material on a tread rubber layer 32 that constitutes the tread portion 12, a sidewall rubber layer 34 that constitutes the sidewall portion 16, a rim cushion rubber layer 36, and an inner peripheral surface of the tire. An inner liner rubber layer 38 is provided.

Next, the carcass layer 20 will be described in detail.
In the present embodiment, the carcass layer 20 uses a composite cord 40 having the configuration shown in FIG. 2 as a reinforcing cord. The composite cord 40 is composed of, for example, two aramid lower twist yarns 42 and one polyester lower twist yarn 44.
In the composite cord 40, the number of the aramid under-twisted threads 42 is two in the illustrated example, but at least two may be sufficient, and three or more may be used.

Aramid twist yarn 42, the aramid fiber bundle, leaving those formed by adding a twist to the twist direction t _1.
The polyester lower twist yarn 44 is formed by adding a lower twist to the polyester fiber bundle in the lower twist direction t ₁ in the same direction as the aramid lower twist yarn 42.
Composite cord 40 includes aramid twist yarn 42 of these two, a bundle of polyester twist yarn 44 of one, and the direction t ₁ twist was added to the aramid fiber bundle and polyester fiber bundle, is opposite the direction and it is formed by adding a twist on the upper twisting direction t _2.
For example, an aromatic polyamide fiber is used as the aramid fiber. For example, polyethylene terephthalate (PET) fiber or polyethylene naphthalate (PEN) fiber is used as the polyester fiber.

A fineness in the composite code 40 is that the total fineness D, defined as the sum of the fineness D _p of the polyester fiber bundle (polyester twist yarn 44), and the total fineness D _a aramid fiber bundle (aramid twist yarn 42).
In the composite cord 40, only one polyester lower twist yarn 44 (polyester fiber bundle) is used. Therefore, the fineness of polyester twist yarn 44 (polyester fiber bundle) is simply a fineness D _p.
On the other hand, the number of aramid under-twisted yarns 42 (aramid fiber bundles) is two in the illustrated example, but at least two are used. Therefore, fineness of aramid twist yarn 42 (aramid fiber bundle) is a total fineness D _a which is the sum of the fineness of the aramid first twist yarn 42 (aramid fiber bundle).

  The composite cord 40 has a total fineness D of 2500 to 6000 dtex, and an upper twist coefficient K represented by the following mathematical formula (1) of 1200 to 2500.

K = T · (D _a / ρ _a + D _p / ρ _p ) ^1/2 (1)
However, T is the number of first twists (times / 10 cm) of the composite cord, D _a is the total fineness (dtex) of the aramid fiber bundle (aramid lower twisted yarn 42), and ρ _a is the specific gravity of the aramid fiber bundle, D _p is the polyester twist yarn 44 fineness (polyester fiber bundle) (dtex), ρ _p is the specific gravity of the polyester fiber bundle.

In the composite cord 40, when the total fineness D is less than 2500 dtex, the strength of the composite cord is lowered, and thus the damage resistance is lowered.
On the other hand, in the composite cord 40, when the total fineness D exceeds 6000 dtex, the cord diameter of the composite cord increases, which inhibits weight reduction of the tire.

Further, in the composite cord 40, if the upper twist coefficient K is less than 1200, the fatigue resistance deteriorates and the durability of the tire decreases.
On the other hand, in the composite cord 40, when the upper twist coefficient K exceeds 2500, ply breaks are likely to occur in the carcass layer 20, and the strength of the tire is significantly reduced.

In the hybrid cord 40, the fineness _{D p} of the polyester fiber bundle, 20 to 50% relative to the total fineness D of the composite code 40. That is, 0.2D ≦ D _p ≦ 0.5D.

Fineness _{D p} of the polyester fiber bundle is less than 20% of the total fineness D of the composite code 40, _i.e., the D p <0.2D, the amount of aramid fibers is relatively large, complex code The tensile elastic modulus of the composite cord becomes high, and the fatigue resistance of the composite cord deteriorates.
On the other hand, the fineness _{D p} of the polyester fiber bundle is more than 50% relative to the total fineness D of the composite code 40, i.e., the 0.5 D _{<D p,} the amount of aramid fibers is relatively small, complex The strength of the cord decreases.

The composite code 40 is twist number T _p of the polyester twist yarn 44 is smaller than the twist number T _a aramid twist yarn 42, and twist number T _p of the polyester twist yarn 44, aramid first twist yarn 42 it is preferred that 15 to 90 percent of the twist number _{T a.} That is, the lower the twist _{T p} of the polyester twist yarn 44 _is preferably _{0.15T a <T p <0.9T a} (0.15 <T p / T a <0.9).

Twist number T _p of the polyester twist yarn 44 is greater than the twist number T _a aramid twist yarn 42, i.e., if a T a _{<T p,} is possible to sufficiently improve the fatigue resistance of the composite cord It is not possible to improve tire durability performance.
Further, the polyester constituting twist number _{T p} of the polyester twist yarn 44, is less than 15% of the twist number _{T a} aramid twist yarn 42, i.e. the _T p <0.15 T _a, the polyester twist yarn 44 The fiber bundle is easily broken. So-called filament breakage is likely to occur. For this reason, the workability of the composite cord 40 is deteriorated.
Meanwhile, twist number _{T p} of the polyester twist yarn 44, if more than 90% of the number of _{T a} twists of aramid twist yarn 42, i.e., the 0.90T _{a <T p,} the fatigue resistance of the composite cord sufficiently Cannot be improved.

  In the tire 10 of the present embodiment, the carcass layer 20 is preferably a one-layer structure (one ply) from the viewpoint of weight reduction because the effect of weight reduction is small when two or more layers are used.

  In the present embodiment, two aramid lower twisted yarns 42 formed by adding a lower twist to an aramid fiber bundle, and a polyester lower twisted yarn 44 formed by applying a lower twist in the same direction as the aramid lower twisted yarn 42 to a polyester fiber bundle. Is used as a reinforcing cord of the carcass layer 20 by using a composite cord formed by adding an upper twist in the opposite direction to the lower twist added to the aramid fiber bundle and the polyester fiber bundle. Fatigue resistance can be improved. Moreover, by using this composite cord, sufficient strength and fatigue resistance can be ensured even if the carcass layer 20 has a single-layer structure. Thereby, a tire can be reduced in weight. As described above, by using the composite cord 40 of the present embodiment for the carcass layer 20, it is possible to improve the durability performance such as improving the fatigue resistance of the composite cord and increasing the travel distance while reducing the weight of the tire. it can.

  The present invention is basically configured as described above. As mentioned above, although the pneumatic radial tire of this invention was demonstrated in detail, this invention is not limited to the said embodiment, Of course, in the range which does not deviate from the main point of this invention, a various improvement or change may be made. It is.

Examples of the pneumatic radial tire of the present invention will be specifically described below.
In this example, tires of Examples 1 to 4 and Comparative Examples 1 to 5 having the configurations shown in Tables 1 and 2 below are manufactured, and durability of each tire is evaluated and tire mass is measured. did. The results of durability performance and tire mass are shown in Tables 1 and 2 below. The tire size of each tire is 275 / 45R19.

The “code material” column in Tables 1 and 2 below shows the material of the composite cord of the carcass layer.
In the column of “Cord Structure” in Tables 1 and 2 below, “1670 dtex × 2 + 1100 dtex × 1” means that two lower aramid twisted yarns made of an aramid fiber bundle having a fineness of 1670 dtex and a polyester fiber bundle made of a polyester fiber bundle having a fineness of 1100 dtex Indicates that one twisted yarn is bundled. “1840 dtex / 3” indicates that three rayon yarns having a fineness of 1840 dtex are twisted. “1670 dtex / 3” indicates that three 1670 dtex aramid fiber yarns are twisted.

In this example, the durability performance is measured as follows.
First, each tire of Examples 1 to 4 and Comparative Examples 1 to 5 is incorporated into a rim having a rim size of 19 × 9 JJ, and inflated at a test internal pressure of 120 kPa. Then, for each tire, a drum tester having a steel surface with a smooth drum surface and a diameter of 1707 mm was used, the ambient temperature was controlled to 38 ± 3 ° C., a load of 9.6 kN was applied to each tire, and a speed of 80 km / h The running test was conducted under the conditions described above, and the drum running was continued until the tire broke down.
In addition, the numerical value of the column of "endurance performance" shown in following Table 1, 2 is shown by the index | exponent which sets the comparative example 1 to 100, and it shows that durability performance is excellent, so that this figure is large.

  Moreover, about the tire mass, the mass of each tire of Examples 1 to 4 and Comparative Examples 1 to 5 was measured using a scale. In addition, the numerical value of the column of "tire mass" shown in the following Tables 1 and 2 is shown by the index which sets the comparative example 1 to 100, and it shows that it is so lightweight that this numerical value is small.

As shown in Table 1 above, in Example 1, although T _p / _Ta was not within the preferred range, the composite cord had high fatigue resistance and excellent durability. Moreover, compared with Comparative Example 1, the tire mass was small and the weight could be reduced.
In Example 2, T _p / T _a was also in a preferable range, the fatigue resistance of the composite cord was further higher, and the durability was superior to that of Example 1. Moreover, compared with Comparative Example 1, the tire mass was small and the weight could be reduced.
In Example 3, T _p / T _a was also in a preferable range, the fatigue resistance of the composite cord was further higher, and the durability was superior to that of Example 1. Moreover, compared with Comparative Example 1, the tire mass was small and the weight could be reduced.
In Example 4, T _p / T _a was also in a preferable range, the fatigue resistance of the composite cord was further higher, and the durability was superior to that of Example 1. Moreover, compared with Comparative Example 1, the tire mass was small and the weight could be reduced.

On the other hand, Comparative Example 1 is used as a reference for evaluation, and the carcass layer has a two-layer structure, and rayon is used as a reinforcing cord. Comparative Example 1 has lower durability than any of Examples 1 to 4, and the tire mass is large and the tire is heavy.
Comparative Example 2 uses a reinforcing cord made of only aramid fibers in the carcass layer. Although the tire mass of Comparative Example 2 is about the same as that of Examples 1 and 2, since the reinforcing cord is only an aramid fiber, the durability is remarkably worse than that of Examples 1 to 4.

In Comparative Example 3, although the tire mass is approximately the same as in Examples 1 and 2, the upper twist coefficient K is small and out of the scope of the present invention, and the fatigue resistance of the composite cord is reduced, and the durability is improved. Remarkably worse than Examples 1-4.
In Comparative Example 4, although the tire mass is approximately the same as in Examples 1 and 2, the upper twist coefficient K is large and is out of the scope of the present invention, the ply break is likely to occur, and the tire strength is greatly increased. It falls and durability is bad compared with Examples 1-4.
In Comparative Example 5, although the tire mass is approximately the same as in Examples 1 and 2, the amount of polyester fiber is outside the scope of the present invention. For this reason, in Comparative Example 5, the amount of aramid fibers is small, the strength of the composite cord is lowered, and the durability is poor as compared with Examples 1 to 4.

10 Pneumatic radial tire (tire)
12 Tread portion 14 Shoulder portion 16 Side wall portion 18 Bead portion 20 Carcass layer 22 Belt layer 22a Inner belt layer 22b Outer belt layer 24 Belt auxiliary reinforcing layer 26 Side reinforcing layer 28 Bead core 30 Bead filler 32 Tread rubber layer 34 Side wall rubber layer 36 Rim cushion rubber layer 38 Inner liner rubber layer 40 Composite cord 42 Aramid lower twist yarn 44 Polyester lower twist yarn

Claims (3)

Having a carcass layer with a reinforcing cord mounted between a pair of left and right bead portions;
The carcass layer bundles at least two aramid lower twisted yarns obtained by adding a lower twist to an aramid fiber bundle and one polyester lower twisted yarn obtained by adding a lower twist in the same direction as the aramid lower twisted yarn to a polyester fiber bundle. A composite cord formed by adding an upper twist in the direction opposite to the lower twist is used as the reinforcing cord,
The composite cord has a total fineness of 2500 to 6000 dtex, and an upper twist coefficient K represented by the following formula (1) is 1200 to 2500,
The pneumatic radial tire according to claim 1, wherein the fineness of the polyester fiber bundle is 20 to 50% with respect to the total fineness of the composite cord.
K = T · (D _a / ρ _a + D _p / ρ _p ) ^1/2 (1)
Where T is the number of twists of the composite cord (times / 10 cm), D _a is the total fineness (dtex) of the aramid fiber bundle, ρ _a is the specific gravity of the aramid fiber bundle, and D _p is the fineness of the polyester fiber bundle. (Dtex), ρ _p is the specific gravity of the polyester fiber bundle   The composite cord has a lower twist number of the polyester lower twist yarn than the lower twist number of the aramid lower twist yarn, and the lower twist number of the polyester lower twist yarn is 15 to 90 of the lower twist number of the aramid lower twist yarn. The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is%.   The pneumatic radial tire according to claim 1 or 2, wherein the carcass layer has a single-layer configuration.

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